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United States Patent6534242
Sugita , ; et al.March 18, 2003
Title
Multiple exposure device formation
Abstract
An exposure method for transferring a device pattern to a resist, wherein the device pattern includes a first element and a second element having a linewidth narrower than the first element. The method includes a first exposure step for exposing the resist by use of an interference fringe, produced by interference of two light beams, through an exposure amount substantially not greater than a threshold of the resist, and a second exposure step for exposing the resist with a light pattern related to the first and second elements. A light component, of the light pattern, related to the first element bears an exposure amount greater than the threshold, a light component, of the light pattern, related to the second element bears an exposure amount not greater than the threshold and is to be combined with light in a portion of the interference fringe, and a sum of the exposure amount of the light component related to the second element and an exposure amount provided by the light in the portion of the interference fringe is greater than the threshold.
Inventors:Sugita; Mitsuro (Utsunomiya, JP), Suzuki; Akiyoshi  (Tokyo, JP), Kawashima; Miyoko  (Tochigi-ken, JP), Saitoh; Kenji  (Utsunomiya, JP), Iwasaki; Yuichi  (Utsunomiya, JP)
Assignee:Canon Kabushiki Kaisha (Tokyo, JP)
Appl. No.:783600
Filed:February 15, 2001
Foreign Application Priority Data
Nov 06, 1997 [JP] 9-304232
Feb 26, 1998 [JP] 10-045415
May 02, 1998 [JP] 10-137473
May 02, 1998 [JP] 10-137474
Jul 21, 1998 [JP] 10-221097
Sep 09, 1998 [JP] 10-255143
Current U.S. Class:430/312 430/328 430/394 430/30 
Field of Search:430/30,296,311,312,327,328,394,942,945 250/492.1
U.S. Patent Documents
4456371June 1984Lin
4644170February 1987Komatsu
4680084July 1987Heimann et al.
4869999September 1989Fukuda et al.
4902899February 1990Lin et al.
4947413August 1990Jewell et al.
5415835May 1995Brueck et al.
5532090July 1996Borodovsky
5563012October 1996Neisser
5595843January 1997Dao
5702868December 1997Kellam et al.
5705321January 1998Brueck et al.
5726739March 1998Hayata
5851703December 1998Hasegawa et al.
5851707December 1998Shibuya et al.
6087074July 2000Hasegawa et al.
6128068October 2000Suzuki et al.
Foreign Patent Documents
0 366 367May., 1990EP
0 534 463Mar., 1993EP
2636700Apr., 1997JP
2650962May., 1997JP
6-333795Dec., 1994JP
7-253649Oct., 1995JP
9-199390Jul., 1997JP
WO 94/24610Oct., 1994WO
WO 96/26468Aug., 1996WO
Other References
IBM Technical Disclosure Bulletin, vol. 32, No. 3A, Aug. 1989, p. 431..~
Primary Examiner: Young; Christopher G.
Attorney, Agent or Firm:Fitzpatrick, Cella, Harper & Scinto
Parent Case Text


This application is a continuation-in-part of application Ser. No. 09/184,958, filed Nov. 3, 1998 now abandoned, and application Ser. No. 09/255,330, filed Feb. 23, 1999 now abandoned. Application Ser. No. 09/255,330, in turn, is a continuation-in-part of application Ser. No. 09/244,844, filed Feb. 4, 1999.
Claims

We claim:
1. An exposure method for transferring a device pattern to a resist, wherein the device pattern includes a first element and a second element having a linewidth narrower than the first element, said method comprising: a first exposure step for exposing the resist by use of an interference fringe, produced by interference of two light beams, through an exposure amount substantially not greater than a threshold of the resist; and a second exposure step for exposing the resist with a light pattern related to the first and second elements, wherein a light component, of the light pattern, related to the first element bears an exposure amount greater than the threshold, a light component, of the light pattern, related to the second element bears an exposure amount not greater than the threshold and is to be combined with light in a portion of the interference fringe, and a sum of the exposure amount of the light component related to the second element and an exposure amount provided by the light in the portion of the interference fringe is greater than the threshold.

2. A method according to claim 1, further comprising applying a multiplex exposure amount distribution in the second exposure step.

3. A method according to claim 2, further comprising performing the second exposure step by use of plural masks having different patterns.

4. A method according to claim 2, further comprising performing the second exposure step by use of a mask with plural transparent regions having different transmissivities.

5. A method according to claim 1, further comprising performing the first exposure step by use of a pattern of a phase shift mask and a projection exposure apparatus.

6. A method according to claim 1, further comprising performing the first exposure step by use of an interferometer.

7. A method according to claim 1, further comprising performing the first and second exposure steps by use of a projection exposure apparatus.

8. A method according to claim 7, further comprising performing the first exposure step by use of a phase shift mask.

9. A method according to claim 1, further comprising applying a multiplex exposure amount distribution in the first exposure step.

10. A device manufacturing method including a step of transferring a device pattern onto a workpiece by use of an exposure method as recited in any one of claims 1-9.

11. An exposure method for exposing a resist so that, with a development process, a first fine pattern and a second fine pattern having a linewidth larger than that of the first fine pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first fine pattern, with an interference fringe provided by interference of plural light beams, through an exposure amount with which the first fine pattern cannot be formed with the development process; and a second exposure step for exposing, with light, a portion of the resist in relation to the second fine pattern through an exposure amount with which the second fine pattern can be formed with the development process, and for exposing, with light, another portion of the resist in relation to the first fine pattern through an exposure amount with which the first fine pattern cannot be formed with the development process, such that the first fine pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

12. A method according to claim 11, wherein the first and second fine patterns are contiguous.

13. A method according to claim 11, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

14. A method according to claim 12, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

15. An exposure method for exposing a resist so that, with a development process, a first fine pattern and a second fine pattern having a linewidth larger than that of the first fine pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first fine pattern through an exposure amount with which the first fine pattern cannot be formed with the development process; and a second exposure step for exposing, with light, the resist in relation to the second fine pattern through an exposure amount with which the second fine pattern can be formed with the development process, and for exposing, with light, the resist in relation to the first fine pattern through an exposure amount with which the first fine pattern cannot be formed with the development process, such that the first fine pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

16. A method according to claim 15, wherein the first and second fine patterns are contiguous.

17. A method according to claim 15, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

18. A method according to claim 16, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

19. An exposure method for exposing a resist so that, with a development process, a first pattern and a second pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first pattern, with an interference fringe provided by interference of plural light beams through an exposure amount with which the first pattern cannot be formed with the development process; and a second exposure step for exposing, with light, a portion of the resist in relation to the second pattern through an exposure amount with which the second pattern can be formed with the development process, and for exposing, with light, another portion of the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process, such that the first pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

20. A method according to claim 19, wherein the first and second patterns are contiguous.

21. A method according to claim 19, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

22. A method according to claim 20, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

23. An exposure method for exposing a resist so that, with a development process, a first pattern and a second pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process; and a second exposure step for exposing, with light, the resist in relation to the second pattern through an exposure amount with which the second pattern can be formed with the development process, and for exposing, with light, the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process, such that the first pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

24. A method according to claim 23, wherein the first and second patterns are contiguous.

25. A method according to claim 23, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

26. A method according to claim 24, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

27. An exposure method for exposing a resist so that, with a development process, a first pattern and a second pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first pattern, with an interference fringe provided by interference of plural light beams through an exposure amount with which the first pattern cannot be formed with the development process; and a second exposure step for exposing, with light, a portion of the resist in relation to the second pattern through an exposure amount with which the second pattern can be formed with the development process, and for exposing, with light, another portion of the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process, such that the first pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

28. A method according to claim 27, wherein the first and second patterns are contiguous.

29. A method according to claim 27, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

30. A method according to claim 28, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

31. An exposure method for exposing a resist so that, with a development process, a first pattern and a second pattern are formed on the resist, said method comprising: a first exposure step for exposing the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process; and a second exposure step for exposing, with light, the resist in relation to the second pattern through an exposure amount with which the second pattern can be formed with the development process, and for exposing, with light, the resist in relation to the first pattern through an exposure amount with which the first pattern cannot be formed with the development process, such that the first pattern can be formed as a result of accumulation of the exposure amounts provided by said first and second exposure steps.

32. A method according to claim 31, wherein the first and second patterns are contiguous.

33. A method according to claim 31, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

34. A method according to claim 32, wherein said first and second exposure steps are performed sequentially in the named order, sequentially in an order opposite to the named order, or simultaneously.

35. A device manufacturing method including a step of transferring a device pattern onto a workpiece by use of an exposure method as recited in any one of claims 11 through 34.

36. An exposure method for performing exposure of a resist in relation to a pattern, said method comprising: a step of applying a first exposure amount distribution on the basis of a dual-beam interference exposure; and a step of applying a second exposure amount distribution including a first portion having a smaller exposure amount, not being zero, and a second portion having a larger exposure amount; performing the exposure of a first region of the pattern by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution; and performing the exposure of a second region of the pattern through the second portion of the second exposure amount distribution as superposed with another portion of the first exposure amount distribution.

37. A method according to claim 36, further comprising performing the dual-beam interference exposure by illuminating a mask having an array of at least one of a phase shifter and a light blocking portion.

38. A method according to claim 36, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

39. A method according to claim 37, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

40. A method according to claim 36, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

41. A method according to claim 37, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

42. A method according to claim 36, wherein the first region of the pattern is a portion of the pattern wherein a smallest linewidth is included.

43. A method according to claim 37, wherein the first region of the pattern is a portion of the pattern wherein a smallest line width is included.

44. A method according to claim 36, wherein the pattern comprises a circuit pattern.

45. A method according to claim 37, wherein the pattern comprises a circuit pattern.

46. An exposure method for performing exposure of a resist in relation to a pattern, said method comprising: a step of applying a first exposure amount distribution having an exposure amount not greater than an exposure threshold value of the resist, on the basis of a dual-beam interference exposure using a first mask having an array of at least one of a phase shifter and a light blocking portion; a step of applying a second exposure amount distribution including a first portion having an exposure amount not being zero but being not greater than the exposure threshold value of the resist, and a second portion having an exposure amount not less than the exposure threshold value; performing the exposure of a first region of the pattern by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution; and performing the exposure of a second region of the pattern through the second portion of the second exposure amount distribution as superposed with another portion of the first exposure amount distribution.

47. A method according to claim 46, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

48. A method according to claim 46, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

49. A method according to claim 46, wherein the first region of the pattern is a portion of the pattern wherein a smallest linewidth is included.

50. A method according to claim 46, wherein the first mask comprises one or two masks, and wherein the second mask comprises one or two masks.

51. A method according to claim 46, wherein the pattern comprises a circuit pattern.

52. A mask for producing the first exposure amount distribution in the exposure method as recited in any one of claims 36-51.

53. A mask for producing the second exposure amount distribution in the exposure method as recited in any one of claims 36-51.

54. An exposure apparatus for performing the exposure method as recited in any one of claims 36-51.

55. A pattern forming method including a process for exposing a resist and a process for developing the resist, said method comprising: a step of applying a first exposure amount distribution on the basis of a dual-beam interference exposure; a step of applying a second exposure amount distribution including a first portion having a smaller exposure amount, not being zero, and a second portion having a larger exposure amount; forming a first region of a pattern through a portion of the first exposure amount distribution as superposed with the first portion of the second exposure amount distribution; and forming a second region of the pattern through the second portion of the second exposure amount distribution as superposed with another portion of the first exposure amount distribution.

56. A method according to claim 55, further comprising performing the dual-beam interference exposure by illuminating a mask having an array of at least one of a phase shifter and a light blocking portion.

57. A method according to claim 55, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

58. A method according to claim 56, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

59. A method according to claim 55, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

60. A method according to claim 56, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

61. A method according to claim 55, wherein the first region of the pattern is a portion of the pattern wherein a smallest linewidth is included.

62. A method according to claim 56, wherein the first region of the pattern is a portion of the pattern wherein a smallest linewidth is included.

63. A method according to claim 55, wherein the pattern comprises a circuit pattern.

64. A method according to claim 56, wherein the pattern comprises a circuit pattern.

65. A pattern forming method including a process for exposing a resist and a process for developing the resist, said method comprising: a step of applying a first exposure amount distribution having an exposure amount not greater than an exposure threshold value of the resist, on the basis of a dual-beam interference exposure using a first mask having an array of at least one of a phase shifter and a light blocking portion; a step of applying a second exposure amount distribution including a first portion having an exposure amount not being zero but being not greater than the exposure threshold value of the resist, and a second portion having an exposure amount not less than the exposure threshold value; forming a first region of the pattern through a portion of the first exposure amount distribution as superposed with the first portion of the second exposure amount distribution; and forming a second region of the pattern through the second portion of the second exposure amount distribution as superposed with another portion of the first exposure amount distribution.

66. A method according to claim 65, wherein the step of applying the first exposure amount distribution is performed before the step of applying the second exposure amount distribution.

67. A method according to claim 65, wherein the step of applying the first exposure amount distribution is performed after the step of applying the second exposure amount distribution.

68. A method according to claim 65, wherein the first region of the pattern is a portion of the pattern wherein a smallest linewidth is included.

69. A method according to claim 65, wherein the first mask comprises one or two masks, and the second mask comprises one or two masks.

70. A method according to claim 65, wherein the pattern comprises a circuit pattern.

71. A device manufacturing method including a process for producing a device by use of the pattern forming method as recited in any one of claims 55-70.

72. An exposure method for printing a particular pattern on a resist, said method comprising: a first step for applying a first exposure amount distribution with an exposure amount not greater than an exposure threshold value of the resist, through a dual-beam interference exposure process using a first mask having an array of at least one of a phase shifter and a light blocking portion; and a second step for applying a second exposure amount distribution, including a first portion with an exposure amount not being equal to zero but being not greater than the exposure threshold value of the resist and a second portion with an exposure amount not less than the exposure threshold value of the resist, through an exposure process using a second mask having a pattern being analogous to the particular pattern to be printed on the resist, wherein (i) the printing of a certain portion of the particular pattern to be printed on the resist is accomplished by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution, being not equal to zero but being not greater than the exposure threshold value, and (ii) the printing of another portion of the particular pattern is accomplished by use of the second portion of the second exposure amount distribution, being not less than the exposure threshold value and being superposed on another portion of the first exposure amount distribution.

73. An exposure method for exposing a resist in relation to a pattern, comprising: a first step for applying a first exposure amount distribution to the resist on the basis of dual-beam interference exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with a small exposure amount not being equal to zero and a second portion with a large exposure amount, by use of a mask having a pattern analogous to the pattern, wherein exposure in relation to a portion of the pattern is performed by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution, and wherein exposure in relation to another portion of the pattern is performed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion, of the first exposure amount distribution.

74. An exposure method for exposing a resist in relation to a pattern, comprising: a first step for applying, to the resist and by use of a first mask having at least one of a phase shifter and a light blocking portion, a first exposure amount distribution with an exposure amount not greater than an exposure threshold value of the resist, on the basis of dual-beam interference exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with an exposure amount not being equal to zero but being not greater than the exposure threshold value and a second portion with an exposure amount not less than the exposure threshold value, by use of a mask having a pattern analogous to the pattern, wherein exposure in relation to a portion of the pattern is performed by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution, and wherein exposure in relation to another portion of the pattern is performed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

75. An exposure method for exposing a resist in relation to a pattern, comprising: a first step for applying a first exposure amount distribution to the resist on the basis of periodic pattern exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with a small exposure amount not being equal to zero and a second portion with a large exposure amount, by use of a mask having a pattern analogous to the pattern, wherein exposure in relation to a portion of the pattern is performed by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution, and wherein exposure in relation to another portion of the pattern is performed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

76. An exposure method for exposing a resist in relation to a pattern, comprising: a first step for applying, to the resist and by use of a first mask having at least one of a phase shifter and a light blocking portion, a first exposure amount distribution with an exposure amount not greater than the exposure threshold value of the resist, on the basis of periodic pattern exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with an exposure amount not being equal to zero but being not greater than the exposure threshold value and a second portion with an exposure amount not less than the exposure threshold value, by use of a mask having a pattern analogous to the pattern, wherein exposure in relation to a portion of the pattern is performed by superposing a portion of the first exposure amount distribution and the first portion of the second exposure amount distribution, and wherein exposure in relation to another portion of the pattern is performed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

77. A method according to any one of claims 73-76, wherein the first and second steps are carried out in the named order, in the reverse order or simultaneously.

78. A method according to any one of claims 73-76, wherein the portion of the pattern is a portion having a smallest linewidth.

79. A method according to any one of claims 73-76, wherein the pattern is a circuit pattern.

80. A mask to be used in an exposure method as recited in any one of claims 73-76, for producing the first exposure amount distribution.

81. A mask to be used in an exposure method as recited in any one of claims 73-79, for producing the second exposure amount distribution.

82. An exposure apparatus for performing an exposure method as recited in any one of claims 73-76.

83. A pattern forming method including exposure of a resist and development of the same, said method comprising: a first step for applying a first exposure amount distribution to the resist on the basis of dual-beam interference exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with a small exposure amount not being equal to zero and a second portion with a large exposure amount, by use of a mask having a pattern analogous to the pattern, wherein a portion of the pattern is formed on the basis of a portion of the first exposure amount distribution to be superposed with the first portion of the second exposure amount distribution, and wherein another portion of the pattern is formed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

84. A pattern forming method including exposure of a resist and development of the same, said method comprising: a first step for applying, to the resist and by use of a first mask having at least one of a phase shifter and a light blocking portion, a first exposure amount distribution with an exposure amount not greater than an exposure threshold value of the resist, on the basis of dual-beam interference exposure: and a second step for applying, to the resist, a second exposure amount distribution including a first portion with an exposure amount not being equal to zero but being not greater than the exposure threshold value and a second portion with an exposure amount not less than the exposure threshold value by use of a mask having a pattern analogous to the pattern, wherein a portion of the pattern is formed on the basis of a portion of the first exposure amount distribution to be superposed with the first portion of the second exposure amount distribution, and wherein another portion of the pattern is formed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

85. A pattern forming method including exposure of a resist and development of the same, said method comprising: a first step for applying a first exposure amount distribution to the resist on the basis of periodic pattern exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with a small exposure amount not being equal to zero and a second portion with a large exposure amount, by use of a mask having a pattern analogous to the pattern, wherein a portion of the pattern is formed on the basis of a portion of the first exposure amount distribution to be superposed with the first portion of the second exposure amount distribution, and wherein another portion of the pattern is formed on the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

86. A pattern forming method including exposure of a resist and development of the same, said method comprising: a first step for applying, to the resist and by use of a first mask having at least one of a phase shifter and a light blocking portion, a first exposure amount distribution with an exposure amount not greater than an exposure threshold value of the resist, on the basis of periodic pattern exposure; and a second step for applying, to the resist, a second exposure amount distribution including a first portion with an exposure amount not being equal to zero but being not greater than the exposure threshold value and a second portion with an exposure amount not less than the exposure threshold value, by use of a mask having a pattern analogous to the pattern, wherein a portion of the pattern is formed on the basis of a portion of the first exposure amount distribution to be superposed with the first portion of the second exposure amount distribution, and wherein another portion of the pattern is formed an the basis of the second portion of the second exposure amount distribution to be superposed with another portion of the first exposure amount distribution.

87. A method according to any one of claims 83-86, wherein the first and second steps are carried out in the named order, in the reverse order or simultaneously.

88. A method according to any one of claims 83-86, wherein the portion of the pattern is a portion having a smallest linewidth.

89. A method according to any one of claims 83-86, wherein the pattern is a circuit pattern.

90. A mask to be used in an exposure method as recited in any one of claims 83-86, for producing the first exposure amount distribution.

91. An exposure method for performing, to a workpiece to be exposed, a dual exposure having a first exposure based an a periodic pattern and a second exposure based on a pattern different from the periodic pattern, wherein: a mask to be used in the second exposure has a pattern with a portion including a pair of lines having the same linewidth and being disposed with a spacing similar to the linewidth of the paired lines, wherein I.sub.0 is a largest value in one period of a light intensity distribution upon the workpiece in the first exposure, I.sub.1 is a smallest value of the same, b is an intensity value, at positions corresponding to the paired lines, of a light intensity distribution on the workpiece in the second exposure, c is an intensity value at a position corresponding to a region between the paired lines, Is is a light intensity, at a region other than the pattern, of the light intensity distribution on the workpiece in the second exposure, and Ic is a sensitization threshold value of a resist on the workpiece, the light quantity ratio between the first and second exposures is 1:k, and relations I.sub.0 <Ic, I.sub.1 <Ic, k.times.c<Ic, and k.times.b<Ic are satisfied, when the resist is a negative type, the mask to be used for the second exposure has its pattern defined by a light transmitting portion, and the positions corresponding to the paired lines, in the light intensity distribution in the second exposure, are superposed with positions of adjacent largest values of the light intensity distribution in the first exposure, and additionally, relations k.times.b+I.sub.0 >Ic, k.times.c+I.sub.1 <Ic, and k.times.Is+I.sub.0 <Ic are satisfied, and when the resist is a positive type, the mask to be used for the second exposure has its pattern defined by a light blocking portion, and the positions corresponding to the paired lines, in the light intensity distribution in the second exposure, are superposed with positions of adjacent smallest values of the light intensity distribution in the first exposure, and additionally, relations k.times.b+I.sub.1 <Ic, k.times.c+I.sub.0 >Ic, and k.times.Is+I.sub.1 >Ic are satisfied.

92. An exposure method for performing, to a workpiece to be exposed, a dual exposure having a first exposure based on a periodic pattern and a second exposure based on a pattern different from the periodic pattern, wherein: a mask to be used in the second exposure has a pattern including a first portion with a pair of lines having the same linewidth and being disposed with a spacing similar to the linewidth of the paired lines, and a second portion having a linewidth larger than the linewidth of the paired lines, the second portion of the pattern of the mask to be used for the second exposure is printed on the workpiece so as to stretch over more than one pattern of the periodic pattern in the first exposure, wherein I.sub.0 is a largest value in one period of a light intensity distribution upon the workpiece in the first exposure, I.sub.1 is a smallest value of the same, "a" is an intensity value at a position corresponding to the second portion, of a light intensity distribution on the workpiece in the second exposure, b is an intensity value, at positions corresponding to the paired lines, of a light intensity distribution upon the workpiece in the second exposure, c is an intensity value at a position corresponding to a region between the paired lines, Is is a light intensity, at a region other than the pattern, of the light intensity distribution on the workpiece in the second exposure, and Ic is a sensitization threshold value of a resist on the workpiece, and when the light quantity ratio between the first and second exposures is 1:k, (i) when the resist is a negative type, the mask to be used for the second exposure has its pattern defined by a light transmitting portion, and the positions corresponding to the paired lines, in the light intensity distribution in the second exposure, are superposed with positions of adjacent largest values of the light intensity distribution in the first exposure, and additionally, relations I.sub.0 <Ic, I.sub.1 <Ic, k.times.c<Ic, k.times.b<Ic, and k.times.a>Ic as well as relations k.times.b+I.sub.0 >Ic, k.times.c+I.sub.1 <Ic, k.times.a+I.sub.0 >Ic, k.times.a+I.sub.1 >Ic and k.times.Is+I.sub.0 <Ic are satisfied, and (ii) when the resist is a positive type, the mask to be used for the second exposure has its pattern defined by a light blocking portion, and the positions corresponding to the paired lines, in the light intensity distribution in the second exposure, are superposed with positions of adjacent smallest values of the light intensity distribution in the first exposure, and additionally, relations I.sub.0 <Ic, I.sub.1 <Ic, k.times.a<Ic, k.times.b<Ic, and k.times.a<Ic as well as relations k.times.b+I.sub.1 <Ic, k.times.c+I.sub.0 >Ic, k.times.a+I.sub.0 <Ic, k.times.a+I.sub.0 <Ic and k.times.Is+I.sub.1 >Ic are satisfied.

93. A method according to claim 91 or 92, wherein the first and second exposures are performed under different illumination modes.

94. A method according to claim 93, wherein, in the first exposure, sigma is not greater than 0.3.

95. A method according to claim 93, wherein, in the second exposure, sigma is not less than 0.6.

96. A method according to claim 93, wherein the second exposure is performed with ring-like illumination having an illuminance distribution being lower at an inside portion than at an outside portion thereof.

97. A method according to claim 91 or 92, wherein, in each exposure, the exposure amount is changed so that the light quantity ratio between the first and second exposures is kept at 1:k.

98. A method according to claim 97, wherein the second exposure is performed with an exposure amount approximately twice the exposure amount in the first exposure.

99. A method according to claim 97, wherein, when the first exposure is performed with a sigma of 0.3 and the second exposure is performed with a sigma of 0.8 or less, the exposure amount in the second exposure is made not greater than twice that of the first exposure.
100. A method according to claim 97, wherein, when the first exposure is performed with a sigma of 0.3 and the second exposure is performed with a ring-like illumination and with a small ring width, the exposure amount in the second exposure is made not less than twice that of the first exposure.
101. A method according to claim 97, wherein, when the first exposure is performed with a sigma of 0.3 or less, the exposure amount in the second exposure is made not less than twice that of the first exposure.
102. A method according to claim 91 or 92, wherein, in the first exposure, a rotational position of the mask is adjusted so that patterns of the periodic pattern become parallel to a direction of a fine pattern to be printed by the second exposure.
103. An exposure apparatus for transferring a pattern onto a photosensitive substrate by use of an exposure method as recited in claim 91 or 92.
104. A device manufacturing method, comprising the steps of: exposing a wafer to a circuit pattern in accordance with an exposure method as recited in claim 91 or 92; and developing the exposed wafer.
Description
FIELD OF THE INVENTION AND RELATED ART

This invention relates to an exposure method, an exposure apparatus and a device manufacturing method. In one preferred embodiment, the invention is concerned with a dual or multiple exposure method for printing a fine circuit pattern on a photosensitive substrate, and an exposure apparatus and a device manufacturing method based on the dual (multiple) exposure method. The exposure method and apparatus of the present invention are suitably usable in the manufacture of microdevices such as semiconductor chips (e.g., IC or LSI), display devices (e.g., a liquid crystal panel), detecting devices (e.g., a magnetic head), or image pickup devices (e.g., a CCD), for example.

In the manufacture of devices such as IC, LSI, or liquid crystal panels, for example, on the basis of photolithography, generally, a projection exposure method and a projection exposure apparatus are used, in which a circuit pattern of a photomask or reticle (hereinafter "mask") is projected by a projection optical system onto a photosensitive substrate (hereinafter "wafer") such as a silicon wafer or glass plate having a photoresist coating applied thereto, for example, whereby the pattern is transferred or printed on the substrate.

In order to meet further increases in the density of integration of such devices, further miniaturization of a pattern to be transferred to a wafer (that is, further improvement of resolution) as well as a further increase of the area of a single chip are required. In projection exposure methods and projection exposure apparatuses which are the primary types of microfabrication technology, attempts have been made to improve the resolution and the exposure area that an image of a size (linewidth) of 0.5 micron or less can be formed in a wide range.

FIG. 19 is a schematic view of a projection exposure apparatus of a known type. Denoted in FIG. 19 at 191 is an excimer laser which is a light source for deep ultraviolet light exposure. Denoted at 192 is an illumination optical system, and denoted at 193 is illumination light. Denoted at 194 is a mask, and denoted at 195 is object-side exposure light which, after being emitted from the mask 194, enters an optical system 196. The optical system 196 comprises a reduction projection optical system. Denoted at 197 is image-side exposure light which, after being emitted from the optical system 196, impinges on a photosensitive substrate 198. The substrate 198 comprises a wafer. Denoted at 199 is a substrate stage for holding the photosensitive substrate 198.

Laser light emitted by the excimer laser 191 is directed by a guiding (or directing) optical system to the illumination optical system 192. By means of the projection optical system 192, the light is adjusted or transformed into illumination light 193 having a predetermined light intensity distribution, an orientation distribution, and an opening angle (numerical aperture NA), for example. The illumination light 193 illuminates the mask 194. The mask 194 has a fine pattern of chromium, for example, formed on a quartz substrate. The pattern has a size corresponding to an inverse (e.g., 2.times., 4.times., or 5.times.) of the projection magnification of the projection optical system 192. The illumination light 193 is transmissively diffracted by the fine pattern of the mask 194, whereby object-side exposure light 195 is provided. The projection optical system 196 serves to transform the object-side exposure light 195 into image-side exposure light 197 with which the fine pattern of the mask 194 is imaged upon the wafer 198, at the above-described projection magnification and with sufficiently small aberration. As illustrated in an enlarged view at the bottom of FIG. 19, the image-side exposure light 197 is converged upon the wafer 198 with a predetermined numerical aperture (NA=sin .theta.), whereby an image of the fine pattern is formed on the wafer 198. For sequentially printing the fine pattern on different regions (shot regions, each being a region for the production of one or plural chips), the substrate stage 199 moves stepwise along an image plane of the projection optical system to change the position of the wafer 198 with respect to the projection optical system 196.

Practically, however, with current projection exposure apparatuses having an excimer laser as a light source, it is difficult to form a pattern of 0.15 micron or less.

In the projection optical system 196, there is a limitation in resolution due to a tradeoff between optical resolution and depth of focus which is attributable to the wavelength of exposure light (hereinafter "exposure wavelength"). The relation between resolution R and depth of focus DOF of a projection exposure apparatus can be expressed in accordance with Rayleigh's equation, such as equations (1) and (2) below:

R=k.sub.1 (.lambda./NA) (1)

where .lambda. is the exposure wavelength, NA is the image-side numerical aperture that represents brightness of the projection optical system 196, and k.sub.1 and k.sub.2 are constants which are usually about 0.5-0.7. It is seen from equations (1) and (2) that, in order to provide higher resolution with a smaller resolution value R, the numerical aperture NA may be enlarged (enlargement of NA). However, in a practical exposure process, the depth of focus DOF of the projection optical system
196 should be not less than a certain value and, therefore, enlargement of the numerical aperture NA beyond a certain level is not practicable. Thus, for higher resolution, it is necessary to make the exposure wavelength .lambda. shorter (shortening of wavelength).

However, shortening of the wavelength raises a serious problem. That is, there is no lens glass material available for the projection optical system 196. Almost all glass materials have about a zero transmissivity to the deep ultraviolet region. While there is a fused silica which can be produced as a glass material in an exposure apparatus with an exposure wavelength about 248 nm in accordance with a special manufacturing method, the transmissivity of even such fused silica decreases drastically to an exposure wavelength not longer than 193 nm. Thus, it may be very difficult to develop a practical glass material having a sufficiently high transmission factor in a region not longer than an exposure wavelength of 150 nm, corresponding to a fine pattern of 0.15 micron or less. Further, the glass material to be used in the deep ultraviolet region should, to some extent, satisfy several other conditions such as durability, uniformness of birefringence or refraction factor, optical distortion, and workability or machining characteristic, for example. For these reasons, development of a practical glass material for use in an exposure wavelength region not longer than 150 nm will not easily be accomplished.

In conventional projection exposure methods and projection exposure apparatuses, such as described, for the formation of a pattern of 0.15 micron or less upon a wafer 198, the exposure wavelength should be shortened to about 150 nm or less. Nevertheless, since there is no practical glass material available for such a wavelength region, practically, it is very difficult to form a pattern of 0.15 micron or less on the wafer 198.

U.S. Pat. No. 5,415,835 shows a process of forming a fine pattern by use of dual-beam interference exposure (also known as "double-beam interference exposure"). This exposure process involves the use of two mutually coherent light beams that interfere with each other to produce an interference fringe. With this dual-beam interference exposure process, a pattern of 0.15 micron or less may be formed on a wafer.

Referring to FIG. 15, the principle of dual-beam interference exposure will be explained. In accordance with dual-beam interference exposure, laser light from a laser 151 which comprises parallel light having coherency is divided by a half mirror 152 into two light beams. These light beams are then reflected by flat mirrors 153, such that the two laser light beams (coherent parallel light beams) intersect with each other at an angle not less than zero deg. and not greater than 90 deg., whereby an interference fringe is produced at the intersection. A wafer 154 is exposed and sensitized by use of this interference fringe (i.e., the light intensity distribution of it), by which a fine periodic pattern corresponding to the intensity distribution of the interference fringe is formed on the wafer.

When the two light beams intersect at the wafer surface in a state wherein they are inclined with respect to a normal to the wafer surface oppositely by the same angle, the resolution R attainable with this dual-beam interference exposure process can be expressed by equation (3) below:

R=.lambda./(4 sin .theta.)

where R represents widths of line and space, respectively, that is, widths of bright and dark portions of the interference fringe, respectively, and .theta. denotes an incidence angle (absolute value) of the two light beams with respect to the image plane. (AS noted above, NA=sin .theta..)

Comparing equation (1) for resolution according to an ordinary projection exposure process with equation (3) for resolution according to a dual-beam interference exposure process, since resolution R in the dual-beam interference exposure corresponds to that in a case where k.sub.1 =0.25 in equation (1), it is seen that with the dual-beam interference exposure, a resolution two or more times higher than that of an ordinary projection exposure process (k.sub.1 =0.5 to 0.7) can be provided. Although it is not discussed in the aforementioned U.S. patent, if .lambda.=0.248 nm (KrF excimer laser) and NA=0.6, a resolution R=0.10 micron may be attainable.

In accordance with the dual-beam interference exposure process just described, however, basically only a simple fringe pattern corresponding to the light intensity distribution of an interference fringe (i.e., exposure amount distribution) is attainable. It is not possible to produce a complicated pattern of a desired shape, such as a circuit pattern, on a wafer using this exposure process.

The aforementioned U.S. Pat. No. 5,415,835 proposes a procedure in which, after a simple (periodic) exposure amount distribution is applied to a resist of a wafer through an interference fringe by using a dual-beam interference exposure apparatus, a separate exposure apparatus is used so that a portion of the resist corresponding to the bright portion of the interference fringe is exposed to an image of an opening of a mask by which a certain exposure amount is applied to that portion (dual exposure). By this, the exposure amounts only at particular line portions of plural bright portions of the interference fringe are enlarged uniformly, beyond the threshold of the resist. Consequently, after development, isolated lines (resist pattern) are produced.

With this dual exposure method proposed in U.S. Pat. No. 5,415,835, however, what is attainable is only a circuit pattern of a simple shape which comprises a portion of stripe patterns that can be formed by double-beam interference exposure. On the other hand, an ordinary circuit pattern comprises a combination of many types of patterns having various linewidths and various orientations. It is, therefore, not attainable to produce a complicated pattern such as a circuit pattern.

Further, while the aforementioned U.S. Pat. No. 5,415,835 discusses a combined use of a dual-beam interference exposure process and an ordinary exposure process, it does not mention the structure of an exposure apparatus suitable for this combination.

Japanese Laid-Open Patent Application, Laid-Open No. 253649/1995 shows a dual exposure method with which a fine isolated pattern similar to that of the aforementioned U.S. Pat. No. 5,415,835 may be formed. In accordance with this dual exposure method, an ordinary projection exposure apparatus is used to perform both a double-beam interference exposure based on a phase shift pattern and an exposure based on an image of a fine opening pattern (which are not resolvable with this exposure apparatus), to the same region on a resist of a wafer. The exposure wavelengths used in these exposures differ from each other by 50 nm or more.

Further, in the dual exposure method shown in Japanese Laid-Open Patent Application, Laid-Open No. 253649/1995, the pattern of the mask is formed by use of a material having a wavelength selectivity such that the double-beam interference exposure and the ordinary exposure are performed by using one and the same mask (pattern). The pattern (of the mask) in the ordinary exposure comprises one or more isolated patterns, and also, the circuit pattern (exposure amount distribution or surface step distribution after development) produced as a result of dual exposure comprises one or more isolated patterns, only.

Therefore, even with the dual exposure method shown in Japanese Laid-Open Patent Application, Laid Open No. 253649/1995, like the aforementioned U.S. Pat. No. 5,415,835, it is not attainable to produce a pattern of a complicated shape such as a circuit pattern.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exposure method and/or an exposure apparatus by which a circuit pattern of a complicated shape can be produced through multiple exposure. Here, the words "multiple exposure" refer to a process wherein exposures are made to the same location on a resist without intervention of a development process between these exposures. The exposures may be double or triple or more.

It is another object of the present invention to provide a device manufacturing method and/or an exposure apparatus that uses a dual or multiple exposure method.

In accordance with an aspect of the present invention, there is provided an exposure method for dual or multiple exposure, comprising the steps of: performing a first exposure process by use of an interference fringe produced by interference of two light beams; and performing a second exposure process by use of a light pattern different from the interference fringe; wherein, in at least one of the first and second exposure processes, a multiplex exposure amount distribution is provided.

In one preferred form of this aspect of the present invention, in the second exposure process, a multiplex exposure amount distribution may be applied.

In one preferred form of this aspect of the present invention, the second exposure process may be performed by use of plural masks having different patterns.

In one preferred form of this aspect of the present invention, the second exposure process may be performed by use of a mask with plural transparent regions having different transmissivities.

In one preferred form of this aspect of the present invention, the first exposure process may be performed by use of a pattern of a phase shift mask and a projection exposure apparatus.

In one preferred form of this aspect of the present invention, the first exposure process may be performed by use of an interferometer.

In one preferred form of this aspect of the present invention, the first and second exposure processes may be performed by use of a projection exposure apparatus.

In one preferred form of this aspect of the present invention, the first exposure process may be performed by use of a phase shift mask.

In one preferred form of this aspect of the present invention, in the first exposure process, a multiplex exposure amount distribution may be applied.

In accordance with another aspect of the present invention, there is provided a device manufacturing method including a step for transferring a device pattern onto a workpiece by use of an exposure method as recited above.

In accordance with a further aspect of the present invention, there is provided a projection exposure apparatus for performing an exposure method as recited above.

The first and second exposure processes may be performed sequentially or at the same time. When they are performed sequentially, basically, either may be performed first.

Here, the word "multiplex" referred to above in relation to the phrase "multiplex exposure amount distribution" means that, unlike a binary exposure amount (two levels including a zero level exposure amount) to be applied to a photosensitive substrate, more than a binary exposure amount (three or more levels including a zero level exposure amount) is given. Further, the words "ordinary exposure (process)" are used to refer to an exposure process which is to be done with a resolution lower than that attainable with dual-beam interference exposure and to be done with a pattern different from that used in the dual-beam interference exposure. A typical example of such an ordinary exposure process is projection exposure for projecting a mask pattern through a projection exposure apparatus such as shown in FIG. 19.

Each of the dual-beam interference exposure process and ordinary exposure process to be performed in the present invention may comprise a single exposure step or plural exposure steps. In the latter case, in each step, a different exposure amount may be applied to a photosensitive substrate.

In an exposure method and exposure apparatus according to the present invention, if the second exposure process is to be performed through projection exposure, the first and second exposure processes may use exposure wavelengths not greater than
400 nm, preferably not greater than 250 nm. Exposure light of a wavelength not greater than 250 mm may be available from a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 nm).

An exposure apparatus according to the present invention may comprise a projection optical system for projecting a pattern of a mask onto a wafer, and a mask illumination system for selectively providing partially coherent illumination and coherent illumination. An ordinary exposure process may be performed with partially coherent illumination, while dual-beam interference illumination may be performed with coherent illumination. Here, the words "partially coherent illumination" are used to refer to an illumination mode with .sigma. (="numerical aperture of the illumination optical system" divided by "numerical aperture of the projection optical system") which is larger than zero and smaller than one. The words "coherent illumination" are used to refer to an illumination mode with .sigma. which is equal to or close to zero, it being very small as compared with the a value of the partially coherent illumination.

The exposure apparatus described just above may use an exposure wavelength not greater than 400 nm, preferably not greater than 250 nm. Exposure light of a wavelength not greater than 250 mm may be available from a KrF excimer laser (about 248
nm) or an ArF excimer laser (about 193 nm).

One preferred embodiment of the present invention, to be described later, includes an optical system for a mask illumination optical system that enables interchanging between partially coherent illumination and coherent illumination.

An exposure system according to another preferred embodiment of the present invention may comprise a combination of a dual-beam interference exposure apparatus and an ordinary (projection) exposure apparatus, and a movement stage for holding a workpiece (photosensitive substrate) and being used in both of these apparatuses. This exposure system may use an exposure wavelength not greater than 400 nm, preferably not greater than 250 nm. Exposure light of a wavelength not greater than 250 mm may be available from a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 nm).

In accordance with another aspect of the present invention, there is provided an exposure method and exposure apparatus for exposing a resist with a mask having pattern portions being different with respect to contrast of image, wherein the position where an image of a pattern portion, of the mask, having lowest contrast of image is formed is exposed with an image of contrast higher than the lowest contrast image, whereby contrast of an exposure amount distribution related to the pattern portion of lowest contrast is improved.

In accordance with still another aspect of the present invention, there is provided an exposure method and apparatus for exposing a resist with a mask having pattern portions being different with respect to linewidth, wherein the position where an image of a pattern portion, of the mask, having a smallest linewidth is formed is exposed with an image of contrast higher than the image of the smallest linewidth pattern portion, whereby contrast of an exposure amount distribution related to the pattern of lower contrast is improved.

In accordance with a further aspect of the present invention, there is provided an exposure method and exposure apparatus for exposing a resist with a mask having plural pattern portions being different with respect to contrast of image, wherein multiple exposure to be performed with the method or apparatus includes a first exposure in which an exposure amount by an image of a pattern portion, of the pattern portions of the mask, of lowest contrast does not exceed an exposure threshold of the resist while an exposure amount by an image of another pattern portion exceeds the exposure threshold, and a second exposure in which the position where the image of lowest contrast is formed is exposed with an image of contrast higher than the image of lowest contrast.

In accordance with a still further aspect of the present invention, there is provided an exposure method and exposure apparatus for exposing a resist with a mask having plural pattern portions being different with respect to linewidth, wherein multiple exposure to be performed with the method or apparatus includes a first exposure in which an exposure amount by an image of a pattern portion, of the pattern portions of the mask, of smallest linewidth does not exceed an exposure threshold of the resist while an exposure amount by an image of another pattern portion exceeds the exposure threshold, and a second exposure in which the position where the image of smallest linewidth is formed is exposed with an image of a contrast higher than the image of lowest contrast.

In one preferred form of these aspects of the present invention, the resist may be exposed with images of patterns of the mask by use of radiation such as ultraviolet rays, X-rays, or an electron beam, for example, and with the use of or without use of a projection optical system.

The image of high or higher contrast may be formed by use of radiation of the same wavelength as the aforementioned radiation.

The resist may be exposed with the higher contrast image and the image of the pattern simultaneously. The resist may be exposed with the higher contrast image and, thereafter, it may be imaged with the image of the pattern. The resist may be exposed with the image of the pattern and, thereafter, it may be exposed with the higher contrast image.

The image of higher contrast may be formed by projecting a mask of a phase shift type. The phase shift type mask may comprise a Levenson-type phase shift mask. The phase shift type mask may include a phase shifter portion for applying a mutual phase shift of 180 deg. to radiation beams passing through two regions, respectively, without passing a light blocking portion. The phase shift type mask may include an isolated pattern provided by the phase shifter portion. The phase shift type mask may include a repetition pattern having arrayed phase shifter portions.

The image of higher contrast may be formed by projecting two parallel lights, resulting from division of laser light, onto the resist in different directions, to cause interference of them on the resist. The image of higher contrast may be formed by using a probe of light or electrons. The image of higher contrast may be formed by illuminating a repetition pattern of the mask along an oblique direction and by projecting it.

The first-mentioned mask may comprise a phase shift mask. The first-mentioned mask may comprise a phase shift mask of one of halftone type, rim type and chromium-less shifter light blocking type, with a result of a good-contrast exposure amount distribution.

The pattern of the first-mentioned mask may be illuminated along an oblique direction and may be projected by a projection optical system. The image of higher contrast may be formed in a state where a is not greater than 0.3 and by imaging a pattern of a phase shift mask, wherein the phase shift mask may comprise a Levenson-type phase shift mask.

In one preferred form of an exposure method and exposure apparatus of the present invention, the center position of the intensity distribution of an image of the pattern of the mask should be registered with the center position of the intensity distribution of the image of higher contrast. However, from the relation with contrast of an exposure amount distribution to be finally formed upon the resist, deviation within a certain range is allowed to the center positions of the intensity distributions of these images.

There is no limitation to exposure wavelength, in the present invention. However, the present invention is particularly suitably usable with an exposure wavelength of 250 nm or shorter. An exposure wavelength not longer than 250 nm may be provided by use of a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 nm).

The present invention may be embodied, for example, by use of a projection exposure apparatus comprising a projection optical system for projecting a pattern of a mask to a wafer, and a mask illumination optical system which can perform (large .sigma.) partial coherent illumination wherein .sigma. (sigma) is relatively large, and (small .sigma.) partial coherent illumination wherein .sigma. is relatively small or coherent illumination. For example, projection exposure of the mask pattern (circuit pattern) may be performed through the large .sigma. partial coherent illumination, while a phase shift type mask may be illuminated through coherent illumination or small .sigma. partial coherent illumination. With such double-beam interference illumination, exposure of a higher contrast image by an interference image can be made.

The words "partial coherent illumination" refer to illumination wherein the value of .sigma. (="mask side numerical aperture of the illumination optical system"/"mask side numerical aperture of the projection optical system") is larger than zero and smaller than 1. The words "coherent illumination" refer to one in which the value of g is zero or close to zero, and it is very small as compared with .sigma. of partial illumination. A large .sigma. refers to .sigma. not smaller than 0.6, while a small .sigma. refers to .sigma. not larger than 0.3.

The exposure apparatus may include an optical system for the mask illumination optical system, wherein partial coherent illumination, coherent illumination, and partial coherent illumination of a relatively small .sigma. can be interchanged.

The present invention may be embodied by an exposure system which includes a double-beam interference exposure apparatus such as shown in FIG. 15, a projection exposure apparatus such as shown in FIG. 19, and a movement stage used in both of these exposure apparatuses for holding a wafer (photosensitive substrate). An exposure wavelength to be used may be not longer than 400 nm as described and, particularly, not longer than 250 nm. Light of an exposure wavelength not longer than 250 nm may be provided by use of a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 nm).

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of an exposure method according to an embodiment of the present invention.

FIGS. 2A and 2B are schematic views, respectively, for explaining an exposure pattern through a dual-beam interference exposure process.

FIGS. 3A and 3B are graphs, respectively, for explaining an exposure sensitivity characteristic of resist materials.

FIG. 4 is a schematic view for explaining pattern formation with a development process.

FIG. 5 is a schematic view for explaining an exposure pattern through an ordinary dual-beam interference exposure process.

FIG. 6 is a schematic view for explaining an exposure pattern through a dual-beam interference exposure according to the present invention.

FIGS. 7A and 7B are schematic views, respectively, for explaining an example of an exposure pattern (lithographic pattern) to be produced in a first embodiment of the present invention.

FIGS. 8A and 8B are schematic views, respectively, for explaining another example of an exposure pattern (lithographic pattern) to be produced in the first embodiment of the present invention.

FIGS. 9A and 9B are schematic views, respectively, for explaining another example of an exposure pattern (lithographic pattern) to be produced in the first embodiment of the present invention.

FIG. 10 is a schematic view for explaining a gate pattern.

FIGS. 11A, 11B, 11C and 11D are schematic views, respectively, for explaining a second embodiment of the present invention.

FIG. 12 is a schematic view for explaining a dual-beam interference exposure pattern in a third embodiment of the present invention.

FIG. 13 is a schematic view for explaining a pattern formed with two-dimensional blocks, in the third embodiment of the present invention.

FIG. 14 is a schematic view for explaining an example of an exposure pattern to be formed in accordance with the third embodiment of the present invention.

FIG. 15 is a schematic view of a main portion of an example of a dual-beam interference exposure apparatus.

FIG. 16 is a schematic view of a main portion of an example of a projection exposure apparatus for performing dual-beam interference exposure.

FIG. 17 is a schematic view for explaining an example of a mask and illumination method which can be used in the apparatus of FIG. 16.

FIG. 18 is a schematic view for explaining another example of a mask and illumination method which can be used in the apparatus of FIG. 16.

FIG. 19 is a schematic view of a projection exposure apparatus of a known type.

FIG. 20 is a schematic view of an example of a dual-beam interference exposure apparatus according to the present invention.

FIG. 21 is a schematic view of an example of a high-resolution exposure apparatus according to the present invention.

FIG. 22 is a schematic view of another example of a high-resolution exposure apparatus according to the present invention.

FIG. 23 is a flow chart for explaining an exposure method according to another embodiment of the present invention.

FIGS. 24A and 24B are schematic views, respectively, for explaining a periodic pattern (exposure pattern) which can be produced by double-beam interference exposure.

FIGS. 25A and 25B are graphs for explaining an exposure sensitivity characteristic of a resist.

FIG. 26 is a schematic view for explaining pattern formation with development.

FIG. 27 is a schematic view for explaining a periodic pattern (exposure pattern) which can be produced by double-beam interference exposure.

FIG. 28 is a schematic view for explaining a periodic pattern (exposure pattern) which can be produced by double-beam interference exposure according to an embodiment of the present invention.

FIGS. 29A and 29B are schematic views, respectively, for explaining an example of an exposure pattern (lithography pattern) which can be produced in a first embodiment of the present invention.

FIGS. 30A and 30B are schematic views, respectively, for explaining another example of an exposure pattern (lithography pattern) which can be produced in the first embodiment of the present invention.

FIGS. 31A and 31B are schematic views, respectively, for explaining a further example of an exposure pattern (lithography pattern) which can be produced in the first embodiment of the present invention.

FIG. 32 is a schematic view for explaining a gate pattern which can be produced in a second embodiment of the present invention.

FIG. 33 is a schematic view for explaining a dual exposure process in the second embodiment of the present invention.

FIG. 34 is an enlarged view of a gate pattern.

FIG. 35 is a schematic view for explaining a pattern forming process.

FIG. 36 is a schematic view for explaining an example of a projection exposure apparatus for performing periodic pattern exposure based on double-beam interference.

FIG. 37 is a schematic view for explaining an example of a mask and an illumination method therefor, to be used in a projection exposure apparatus of the present invention.

FIG. 38 is a schematic view for explaining another example of a mask and an illumination method therefor, to be used in a projection exposure apparatus of the present invention.

FIG. 39 is a schematic view for explaining an example of a double-beam interference exposure apparatus according to the present invention.

FIG. 40 is a schematic view for explaining an example of a high resolution exposure apparatus according to the present invention.

FIG. 41 is a schematic view for explaining another example of a high resolution exposure apparatus according to the present invention.

FIG. 42 is a flow chart for explaining an exposure method according to a third embodiment of the present invention.

FIGS. 43A-43G are schematic views, respectively, for explaining an exposure pattern to be produced by pattern exposure.

FIGS. 44A-44G are schematic views, respectively, for explaining an example of an exposure pattern (lithography pattern) to be produced by an embodiment of the present invention.

FIGS. 45A-45H are schematic views, respectively, for explaining examples of a phase shift mask for producing various patterns, as well as exposure amount distributions on wafer surfaces.

FIGS. 46A-46H are schematic views, respectively, for explaining another example of an exposure pattern (lithography pattern) to be produced by an embodiment of the present invention.

FIGS. 47A-47F are schematic views, respectively, for explaining a ground mask for gate pattern exposure and an ordinary mask, as well as an exposure distribution on the mask surface.

FIGS. 48A-48C are schematic views, respectively, for explaining an exposure amount distribution and a resist image, provided by dual exposure for gate pattern production.

FIG. 49 is a schematic view for two-dimensionally explaining an embodiment of the present invention.

FIGS. 50A-50F are schematic views, respectively, for explaining another example of forming a gate pattern by using a black ground.

FIGS. 51A-51C are schematic views, respectively, for explaining an exposure amount distribution and a resist pattern, to be provided by dual exposure.

FIG. 52 is a schematic view for two-dimensionally explaining the pattern forming procedure.

FIGS. 53A and 53B are schematic views, respectively, for explaining another example of a mask pattern for producing a circuit pattern.

FIGS. 54A-54F are schematic views, respectively, for explaining an exposure amount distribution in relation to a circuit pattern.

FIGS. 55A-55E are schematic views, respectively, for explaining the circuit pattern forming procedure.

FIGS. 56A-56C are schematic views, respectively, for explaining dual exposure with a high-contrast periodic pattern and a low-contrast pattern with a single to three bars.

FIG. 57 consists of three schematic views for explaining intensity distributions (exposure amount distributions) to be produced on a resist by exposure with a three-bar pattern (image), exposure with a periodic pattern (image) and dual exposure with a three-bar pattern (image) and periodic pattern (image), respectively.

FIG. 58 is a schematic view for explaining intensity distributions to be produced by dual exposure using patterns (images) with single to three bars and a periodic pattern (image).

FIG. 59 is a schematic view for explaining intensity distributions resulting from exposures using patterns (images) with single to three bars, being made by use of a phase shift mask and while changing illumination condition (.sigma.).

FIG. 60 shows graphs for explaining the relation between defocus and contrast, when exposures of patterns with single to three bars are made by use of a phase shift mask and under .sigma.=0.5.

FIG. 61 shows graphs for explaining the relation between defocus and contrast, when dual exposure by a pattern with single to three bars and a periodic pattern is made in accordance with ordinary illumination of .sigma.=0.2 for the periodic pattern and with ring-like illumination of .sigma.=0.8 for the bar pattern.

FIG. 62 shows graphs for explaining a linewidth linearity error, when exposures by patterns (images) of single to three bars are made in accordance with ring-like illumination of .sigma.=0.53-0.8.

FIG. 63 shows graphs for explaining linewidth linearity error, when dual exposures by patterns (images) of single to three bars and a periodic pattern (image) are made in accordance with ordinary illumination of .sigma.=0.2 for the periodic pattern and with ring-like illumination of .sigma.=0.53-0.8 for bar patterns.

FIG. 64 is a schematic view for explaining dual exposure with a periodic pattern and a three-bar pattern having a large linewidth ratio.

FIG. 65 is a schematic view for explaining dual exposure with a periodic pattern and a bar pattern having different linewidth bars.

FIG. 66 is a schematic view for explaining a difference in two-dimensional image by single exposure with a single bar pattern and dual exposure combined with a periodic pattern.

FIG. 67 is a schematic view for explaining intensity distributions resulting from exposure with a zero-contrast pattern (image), exposure with a high-contrast periodic pattern (image) and dual exposure based on these exposures.

FIG. 68 is a schematic view for explaining intensity distributions resulting from exposure with a zero-contrast pattern (image), exposure with a high-contrast periodic pattern (image) and dual exposure based on these exposures.

FIG. 69 is a schematic view of a reticle having an ordinary chromium pattern.

FIG. 70 is a schematic view of a reticle having a halftone phase shift pattern.

FIG. 71 is a schematic view of a reticle having a rim type phase shift pattern.

FIG. 72 is a schematic view of a reticle having a chromium-less shifter light blocking type phase shift pattern.

FIG. 73 is a schematic view of an example of an exposure apparatus for double-beam interference, according to the present invention.

FIG. 74 is a schematic view for explaining a mask and an illumination method which are usable in the exposure apparatus of FIG. 73.

FIG. 75 is a schematic view for explaining another example of a mask and an illumination method, usable in the exposure apparatus of FIG. 73.

FIG. 76 is a schematic view of a mask according to the present invention.

FIG. 77 is a schematic view of another mask according to the present invention.

FIG. 78 is a schematic view for explaining an effective light source in an illumination system of the FIG. 73 apparatus.

FIG. 79 is a schematic view for explaining light intensity distribution upon a pupil plane in the FIG. 73 apparatus.

FIG. 80 is a schematic view for explaining another example of an effective light source in the illumination optical system of the FIG. 73 apparatus.

FIG. 81 is a schematic view for explaining another example of a light intensity distribution upon a pupil plane in the FIG. 73 apparatus.

FIG. 82 is a schematic view for explaining a further example of a light intensity distribution upon a pupil plane in the FIG. 73 apparatus.

FIG. 83 is a schematic view for explaining another example of an effective light source in the illumination optical system of the FIG. 73 apparatus.

FIG. 84 is a schematic view for explaining another example of a light intensity distribution upon a pupil plane in the FIG. 73 apparatus.

FIG. 85 is a schematic view for explaining a further example of a light intensity distribution upon a pupil plane in the FIG. 73 apparatus.

FIG. 86 is a schematic view for explaining a double-beam interference pattern according to the present invention.

FIG. 87 is a schematic view for explaining a double-beam interference pattern and an ordinary pattern, according to the present invention.

FIG. 88 is a schematic view for explaining a check pattern according to the present invention.

FIG. 89 is a schematic view for explaining a desired pattern according to the present invention.

FIG. 90 is a schematic view of a main portion of an exposure apparatus according to an embodiment of the present invention.

FIG. 91 is a schematic view of a mask usable in the FIG. 90 embodiment.

FIG. 92 is a schematic view for explaining the principle of double-beam interference in the present invention.

FIG. 93 is a schematic view for explaining a mask and an illumination method in the double-beam interference, according to the present invention.

FIG. 94 is a schematic view of an effective light source, in FIG. 92.

FIG. 95 is a schematic view for explaining a light intensity distribution on a pupil plane, in FIG. 92.

FIG. 96 is a schematic view for explaining a mask and a check pattern image, in FIG. 92.

FIG. 97 is a schematic view of a main portion of an exposure apparatus according to another embodiment of the present invention.

FIG. 98 is a schematic view of an effective light source in an illumination system according to the present invention.

FIG. 99 is a schematic view for explaining intensity distribution at a pupil, in an exposure apparatus according to the present invention.

FIG. 100 is a schematic view for explaining another example of an intensity distribution at a pupil, in an exposure apparatus according to the present invention.

FIG. 101 is a schematic view of a light pattern upon a photosensitive substrate, in an embodiment of the present invention.

FIG. 102 is a schematic view for explaining multiple exposure based on double-beam interference and ordinary exposure, according to the present invention.

FIG. 103 is a schematic view of an example of a circuit pattern which can be produced in accordance with the present invention.

FIG. 104 is a schematic view of another example of a circuit pattern which can be produced in accordance with the present invention.

FIG. 105 is a schematic view for explaining pupil filters usable in the present invention.

FIG. 106 is a schematic view for explaining a light intensity distribution upon a pupil plane, in the present invention.

FIG. 107 is a schematic view of a light pattern on a photosensitive substrate, provided by four-beam interference in accordance with the present invention.

FIG. 108 is a schematic view for explaining multiple exposure based on four-beam interference and ordinary exposure, in accordance with the present invention.

FIG. 109 is a schematic view of an example of a pattern, which can be produced by the four-beam interference and ordinary exposure in the present invention.

FIG. 110 is a schematic view for explaining exposure amount setting in a multiple exposure process according to the present invention.

FIGS. 111A and 111B are schematic views, respectively, for explaining defocus characteristics of a pattern produced in accordance with the multiple exposure process of the present invention.

FIGS. 112A and 112B are schematic views, respectively, similarly for explaining defocus characteristics a pattern produced in accordance with the multiple exposure process of the present invention.

FIG. 113 is a flow chart of device manufacturing processes according to an embodiment of the present invention.

FIG. 114 is a flow chart of a wafer process, in the procedure of FIG. 113.

FIG. 115 is a schematic view for explaining another example of exposure amount setting for a positive type resist, in a multiple exposure method according to a further embodiment of the present invention.

FIGS. 116A-116D are schematic views, respectively, for explaining a pattern defocus characteristic in the multiple exposure process, according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-9, an exposure method according to an embodiment of the present invention will be described.

FIG. 1 is a flow chart showing the exposure method in this embodiment of the present invention. FIG. 1 illustrates a dual-beam interference exposure step, a projection exposure step (ordinary exposure step), and a developing step, in respective blocks of the flow chart. The order of the dual-beam interference exposure step and the projection exposure step may be reversed from that shown in FIG. 1. If any one of these steps comprises plural exposures, these steps may be made alternately. Between these exposure steps, a step for a fine alignment operation may be included, while not shown in the drawings.

In an exposure operation according to the flow chart of FIG. 1, first a wafer (photosensitive substrate) is exposed with a periodic pattern (interference fringe) such as shown in FIG. 2A through the dual-beam interference exposure. The numerals in FIG. 2A denote the amount of exposure. Those regions with hatching in FIG. 2A correspond to portions with exposure amount 1 (actually, arbitrary), while the blank regions correspond to portions with a zero exposure amount.

For development of such a periodic pattern after exposure, usually the exposure threshold E.sub.th for the resist of the photosensitive substrate is set between exposure amounts 0 and 1, as illustrated at the bottom of FIG. 2B. The upper portion of FIG. 2B illustrates a lithographic pattern (pattern with concaved and protruded portions) to be produced finally.

FIGS. 3A and 3B illustrate an exposure amount dependency of film thickness after development and exposure threshold, with regard to the resist of the photosensitive substrate, in this case, the graphs being plotted in relation to a positive type resist and negative type resist. The film thickness after development becomes zero, with a level higher than the exposure threshold in the case of a positive type resist, and with a level lower than the exposure threshold in the case of a negative type resist.

FIG. 4 is a schematic view for explaining, in relation to the positive and negative type resists, the formation of a lithographic pattern after a development process and an etching process after the exposure process is performed as described above.

In this embodiment, as compared with a usual exposure sensitivity setting described above, as shown in FIG. 5 (the same as FIG. 2A) and FIG. 6, the exposure threshold E.sub.th for the resist of the photosensitive substrate is set to be larger than 1 where the largest exposure amount with the dual-beam interference exposure is taken as 1. In this photosensitive substrate, if the exposure pattern (exposure amount distribution) provided only by the dual-beam interference exposure (FIG. 2) is developed, because of an insufficient exposure amount, there is no portion produced wherein the film thickness becomes zero with the development, although there is a small thickness variation. Thus, no lithographic pattern is formed through the etching. This can be regarded as being a disappearance of a dual-light interference exposure pattern. (Here, while the invention is described with reference to a case where a negative type resist is used, the invention is applicable also to a case where a positive type resist is used.) In FIG. 6, the upper portion illustrates a lithographic pattern (no pattern is formed). The graph at the bottom of the drawing illustrates the relation between the exposure amount distribution and the exposure threshold value. Reference character E.sub.1 at the bottom denotes the exposure amount in the dual-beam interference exposure, and reference character E.sub.2 denotes the exposure amount in the ordinary projection exposure.

In this embodiment, an exposure pattern of a high resolution which may otherwise disappear only through dual-beam interference exposure is mixed with an exposure pattern through ordinary projection exposure, to assure that only a desired region is selectively exposed by an amount greater than the exposure threshold for a resist, such that a desired lithographic pattern is finally produced.

FIG. 7A illustrates an exposure pattern through ordinary projection exposure. In this embodiment, the resolution of this ordinary projection exposure is about a half of that of the dual-beam interference exposure. Thus, the linewidth of the exposure pattern with the projection exposure is illustrated as being about twice that of the linewidth of the exposure pattern through the dual-beam interference exposure.

When the projection exposure process for defining the exposure pattern of FIG. 7A is performed, after the dual-beam interference exposure process of FIG. 5 without a development process, superposedly to the same region of the same resist, the total exposure amount distribution of this resist is such as shown in the graph at the bottom of FIG. 7B. Here, since the ratio between the exposure amount E.sub.1 of the dual-beam interference exposure and the exposure amount E.sub.2 of the projection exposure is 1:1 and the exposure threshold E.sub.th for the resist is set to be between exposure amount E.sub.1 (=1) and the sum (=2) of the exposure amount E.sub.1 and exposure amount E.sub.2, a lithographic pattern such as shown in the upper portion of FIG. 7B can be produced. The isolated line pattern shown in the upper portion of FIG. 7B has a resolution determined by the dual-beam interference exposure and, additionally, it is not a simple periodic pattern. Thus, it is seen that a pattern of high resolution, greater than the resolution attainable with ordinary projection exposure, is produced.

If it is assumed that a projection exposure process that can produce an exposure pattern of FIG. 8 (i.e., projection exposure of a linewidth twice the exposure pattern of FIG. 5 and with an exposure amount higher than the exposure threshold (here, an exposure amount twice higher than the threshold)) is performed, after the dual-beam interference exposure process of FIG. 5 and without a development process, superposedly to the same region of the same resist, then the total exposure amount distribution on the resist will be such as illustrated in FIG. 8B. Thus, the exposure pattern through the dual-beam interference exposure disappears, and finally only a lithographic pattern through projection exposure is produced.

The same concept applies also to a case where a linewidth three times larger than the exposure pattern of FIG. 5 is to be produced, as illustrated in FIGS. 9A and 9B. For an exposure pattern of a linewidth four times larger or more, basically from the combination of an exposure pattern with a double linewidth and an exposure pattern with a triple linewidth, the linewidth of the finally produced lithographic pattern is apparent. Any lithographic pattern that can be accomplished through projection exposure can be produced in this embodiment.

By adjusting the exposure amount distribution (absolute value and distribution) through the dual-beam interference exposure and projection exposure described above as well as by adjusting the threshold level for a resist of a photosensitive substrate, a circuit pattern which comprises one of various combinations of patterns such as illustrated in FIGS. 6, 7B, 8B and 9B and which has a minimum linewidth corresponding to the resolution of dual-beam interference exposure (i.e., the pattern of FIG. 7B), can be produced.

The principle of the exposure method in this embodiment of the present invention may be summarized as follows: (1) A pattern region not exposed by projection exposure, that is, a dual-beam interference exposure pattern less than an exposure threshold of a resist, disappears with a developing process. (2) As regards a pattern region of projection exposure made with an exposure amount not larger than the exposure threshold of the resist, an exposure pattern having a resolution of dual-beam interference exposure as determined by the combination of the projection exposure and dual-beam interference exposure, is produced. (3) As regards a pattern region of the projection exposure made with an exposure amount not less than the exposure threshold, a desired pattern (corresponding to a mask) is produced, like the projection exposure.

It is an additional advantage of the exposure method that, in the portion of highest resolution dual-beam interference exposure, a depth of focus which is remarkably larger than that with ordinary exposure is attainable.

In the foregoing description, as regards the order of dual-beam interference exposure and projection exposure, the dual-beam interference exposure is made first. However, the order is not limited to this.

Next, another embodiment will be described.

This embodiment concerns a circuit pattern (lithography pattern) comprising what can be called a gate-like pattern, such as shown in FIG. 10, to be produced through the exposure process.

The gate pattern shown in FIG. 10 has a minimum linewidth of 0.1 micron in a lateral direction, i.e., along a line A--A in the drawing, while it is 0.2 micron or more in a longitudinal direction. In accordance with this embodiment of the present invention, for a two-dimensional pattern in which high resolution is required only with respect to a one-dimensional direction, dual-beam interference exposure may be performed only with respect to the one-dimensional direction for which high resolution is required.

Referring to FIGS. 11A-11D, examples of a combination of dual-beam interference exposure only in a one-dimensional direction with ordinary projection exposure according to this embodiment, will be described.

FIG. 11A shows a periodic exposure pattern made through dual-beam interference exposure only with respect to a one-dimensional direction. This exposure pattern has a period of 0.2 micron, and this exposure pattern corresponds to a line-and-space pattern of a linewidth 0.1 micron. Numerals in the lower portion of FIG. 11A denote exposure amount.

An exposure apparatus that accomplishes such dual-beam interference exposure described above, may be one as shown in FIG. 15 that includes a wave dividing and combining optical system having a laser 151, a half mirror 152 and a flat mirror 153. Alternatively, it may be a projection exposure apparatus such as shown in FIG. 16 with its mask and illumination method being arranged such as shown in FIG. 17 or 18.

The exposure apparatus of FIG. 15 will be described in detail.

In the exposure apparatus of FIG. 15, two light beams to be combined with each other as described are obliquely incident on a wafer 154 at an angle .theta.. The linewidth of an interference fringe pattern (exposure pattern) formed on the wafer
154 can be expressed by equation (3) set forth above. The relation between the angle .theta. and the numerical aperture NA at the image plane side of the wave dividing and combining optical system is NA=sin .theta.. The angle .theta. can be adjusted and set as desired by changing the angles of a pair of flat mirrors 153, respectively. If the angle .theta. of the paired flat mirrors is set large, the linewidth of fringes of the interference fringe pattern becomes smaller. For example, if the two light beams have a wavelength 248 nm (KrF excimer laser), even with .theta.=38 deg., an interference fringe pattern of a fringe linewidth of about 0.1 micron can be produced. Here, in this case, NA=sin .theta.=0.62. As a matter of course, if the angle .theta. is made larger than 38 deg., a higher resolution is attainable.

Next, an exposure apparatus shown in FIGS. 16-18 will be described.

The exposure apparatus of FIG. 16 is a projection exposure apparatus having an ordinary reduction projection optical system which comprises a number of lenses. Currently, an apparatus of NA=0.6 or more with respect to an exposure wavelength 248
nm is available.

Denoted in FIG. 16 at 161 is a mask, and denoted at 162 is exposure light on the object side which is emitted from the mask 161 and enters an optical system 163. The optical system 163 comprises a projection optical system. Denoted at 164 is an aperture stop, and denoted at 165 is exposure light on the image side which is emitted from the projection optical system 163 and impinges on a wafer 166. The wafer 166 comprises a photosensitive substrate. Reference numeral 167 denotes the position of light, in a pair of dots, upon a pupil plane corresponding to the circular opening of the stop 164. FIG. 16 is a schematic view which shows the state in which dual-beam interference exposure is being performed. Each of exposure light 162 on the object side and exposure light 165 on the image side comprises two parallel light beams, as compared with ordinary projection exposure shown in FIG. 19.

In order to perform dual-beam interference exposure with the use of an ordinary projection exposure apparatus such as shown in FIG. 16, its mask and its illumination method may be set as shown in FIG. 17 or 18. Three examples will be described below.

FIG. 17 at the upper right shows a Levensen type phase shift mask which comprises a mask having light blocking portions 171 of chromium, with a pitch P.sub.0 which is 0 as can be expressed by equation (4) below, as well as phase shifters 172 of pitch P.sub.0S as can be expressed by equation (5) below:

where M is the projection magnification of the projection optical system 163, .lambda. is the exposure wavelength, and NA is the numerical aperture of the projection optical system 163 on the image side.

On the other hand, a mask shown in FIG. 17 at the lower right is a shifter edge type phase shift mask, and it is arranged like the Levensen type to provide phase shifters 181 of pitch P.sub.0S that satisfy equation (5) above.

In order to use the phase shift masks of FIG. 17 to perform dual-beam interference exposure, the mask may be illuminated with coherent illumination wherein .sigma.=0 or a value close to 0. More specifically, parallel light is projected to the mask in a direction perpendicular to the mask surface (in a direction parallel to the optical axis).

With this illumination, as regards zero-th order transmissively diffractive light from the mask in the aforementioned perpendicular direction, since phase differences of adjacent transmissive light rays provided by phase shifters are n and canceled with each other, there is no such light produced. As regards positive and negative first order diffractive light, two parallel light beams are produced from the mask symmetrically with respect to the optical axis of the projection optical system 163, and they provide two exposure lights on the object side, shown in FIG. 16. As regards diffractive light rays of second order or higher, they do not enter the aperture of the aperture stop 164 of the projection optical system 163. Thus, they do not contribute to imaging.

A mask shown in FIG. 18 comprises a mask having light blocking portions 171 of chromium, with a pitch P.sub.0 which can be expressed by equation (6) similar to equation (4).

where M is the projection magnification of the projection optical system 163, .lambda. is the exposure wavelength, and NA is the numerical aperture of the projection optical system 163.

For the mask of FIG. 18 having no phase shifter, oblique illumination with one or two parallel light beams is performed. The incidence angle .theta..sub.0 of the parallel light upon the mask is set to satisfy equation (7) below. When two parallel light beams are used, the mask is illuminated with parallel lights oppositely inclined with each other by an angle .theta..sub.0 with reference to the optical axis.

where M is the projection magnification of the projection optical system 163, and NA is the numerical aperture of the projection optical system 163.

When the mask of FIG. 18 without a phase shifter is illuminated by oblique illumination with the use of parallel light satisfying equation (7), there are produced two light beams from the mask to provide two object-side exposure lights 162 (FIG.
16): that is, zero-th order transmissively diffractive light which advances at an angle .theta..sub.0 with respect to the optical axis, and negative first order transmissively diffractive light which advances along a light path symmetrical with the path of zero-th order transmissively diffractive light with respect to the optical axis of the projection optical system. These two light beams enter the aperture of the aperture stop 164 of the projection optical system 163, by which imaging is performed.

In the present invention, oblique illumination with the use of one or two parallel light beams as described above, is regarded as one of "coherent illumination".

A dual-beam interference exposure process using an ordinary projection exposure apparatus is such as described above. Since the illumination optical system of the ordinary projection exposure apparatus such as shown in FIG. 19 is arranged to perform partially coherent illumination, in this projection exposure apparatus, the coherent illumination can be substantially effected, for example, by replacing an aperture stop (not shown) corresponding to 0<.sigma.<1 of the illumination optical system of FIG. 19 by a peculiar aperture stop corresponding to .sigma..apprxeq.0.

Referring back to FIGS. 10 and 11, the embodiment shown in these drawings will be described in greater detail.

In this embodiment, through the ordinary projection exposure (e.g., by partially coherent illumination to a mask with the apparatus of FIG. 19) subsequent to the dual-beam interference exposure described hereinbefore, an H-shaped pattern exposure shown in FIG. 11B may be performed. An upper half of FIG. 11B shows a relative positional relationship with the exposure pattern through the dual-beam interference exposure as well as an exposure amount at five regions of the exposure pattern defined through the ordinary projection exposure. The lower half of FIG. 11B illustrates a map of an exposure amount to a resist of the wafer through the ordinary projection exposure, depicted at a resolution of 0.1 micron pitch laterally and longitudinally.

The linewidth of an exposure pattern resulting from this projection exposure is 0.2 micron, which is twice that in dual-beam interference exposure. A projection exposure process which produces a multiplex exposure amount distribution (different exposure amounts in different regions) such as described above, may use a particular mask having plural stages of transmissivities: that is, for example, a transmissivity T % at apertures of the mask corresponding to the regions depicted with numeral 1
in the drawing, and a transmissivity 2T % at apertures of the mask corresponding to the regions depicted with numeral 2 in the drawing. According to this method, the projection exposure can be accomplished through a single exposure. As regards the exposure amount ratio upon the wafer (photosensitive substrate) in these exposure processes when the above-described particular mask is used, there is a relation "dual-beam interference exposure":"projection exposure at apertures with transmissivity T":"projection exposure with transmissivity 2T"=1:1:2.

Another method for accomplishing projection exposure with different exposure amounts at different regions may be a method wherein two types of masks effective to produce exposure patterns such as shown in the upper half and lower half of FIG. 11D are used to perform exposures sequentially. On that occasion, since the exposure amount with each mask may be a single stage (level), the transmissivity of apertures of the mask may also be a single stage. As regards the exposure amount ratio upon the wafer (photosensitive substrate) in this case, there is a relation "dual-beam interference exposure":"first projection exposure":"second projection exposure"=1:1:1.

Next, the manner of formation of a fine circuit pattern (FIG. 10) through a combination of dual-beam interference exposure and ordinary projection exposure, as described above, will be explained. In this embodiment, there is no development process between the dual-beam interference exposure and ordinary projection exposure. Thus, within the region wherein exposure patterns through these exposure processes are superposed one upon another, the exposure amounts are accumulated, and the exposure amount (distribution) after accumulation defines a fresh exposure pattern.

The upper half of FIG. 11C shows an exposure amount distribution (exposure pattern) resulting from accumulation or superposition of an exposure pattern of FIG. 11A and an exposure pattern of FIG. 11B, in this embodiment. The lower half of FIG.
11C shows a pattern which can be defined as a result of a development process made to this exposure pattern. This embodiment uses a wafer resist having an exposure threshold larger than 1 and smaller than 2. For this reason, only the portion with an exposure amount larger than 1 appears as a pattern as a result of a development process. The shape and size of the pattern shown in the lower half of FIG. 11C correspond to the shape and size of the gate pattern of FIG. 10, respectively. It is seen, therefore, that, in accordance with the exposure method of this embodiment of the present invention, a circuit pattern with a fine linewidth such as 0.1 micron, for example, can be produced by a projection exposure apparatus having an illumination optical system with which partially coherent illumination and coherent illumination can be performed selectively.

Referring to FIGS. 12-14, another embodiment of the present invention will be described. In this embodiment, an exposure pattern of a multiplex exposure amount distribution (with four exposure amounts of 0, 1, 2 and 3) is produced by superposing an interference fringe pattern of longitudinal fringes and an interference fringe pattern of lateral fringes, by performing dual-beam interference exposure twice.

FIG. 12 shows a map of an exposure amount distribution of an exposure pattern as a longitudinal interference fringe pattern and a lateral interference fringe pattern are superposed one upon another through twice dual-beam interference exposures. Here, in order to expand the variation of an exposure pattern (lithography pattern) to be finally obtainable from superposition of dual-beam interference exposure and ordinary exposure, the exposure amount (numeral 2) at bright portions of the longitudinal interference fringe pattern is set to be twice that of the exposure amount (numeral 1) at the bright portions of the lateral interference fringe pattern. However, the types of exposure amounts at the bright portions are not limited to two, as disclosed.

In the exposure pattern of FIG. 12, as a result of twice dual-beam interference exposures, the exposure amount comprises four stages, from 0 to 3. The number of stages of exposure amount through projection exposure, which is sufficiently effective in regard to such dual-beam interference exposure, is not less than 5. In this case, the exposure threshold for a resist of a wafer (photosensitive substrate) may be set to be larger than 3 (largest exposure amount in dual-beam interference exposure) and smaller than 4 (largest level of exposure amounts 0, 1, 2, 3 and 4) of projection exposure.

FIG. 13 illustrates exposure amounts of exposure patterns which can be provided as a result of projection exposure with five-stage exposure amounts (0, 1, 2, 3, 4). Portions with hatching in FIG. 13 correspond to regions above the exposure threshold. These portions finally provide exposure patterns. The illustration in FIG. 13 is made in terms of resolution of projection exposure of a half of that in dual-beam interference exposure, and in the unit of a block having a side with a length twice that of FIG. 12.

FIG. 14 illustrates an example of an exposure pattern (lithography pattern) formed in a wider area, by changing the exposure amount of projection exposure in the unit of a block. It is seen from FIG. 14 that, in accordance with this embodiment, a circuit pattern having a resolution of dual-beam interference exposure and including a wide variety of patterns other than a periodic pattern, can be produced.

In this embodiment, an ordinary exposure process is performed in the unit of a block which is twice the linewidth of dual-beam interference exposure. However, the invention is not limited to this. Projection exposure may be performed to an arbitrary exposure pattern within the range of resolution of the projection exposure.

Further, in the embodiment described above, the exposure pattern linewidth through dual-beam interference exposure is the same both for longitudinal fringes and lateral fringes. However, they may have different linewidths. Also, desired angles may be chosen for these two types of fringes.

FIG. 20 is a schematic view of an example of an exposure apparatus for dual-beam interference exposure. Denoted in FIG. 20 at 201 is a light interference exposure optical system having a basic structure similar to that of the optical system of FIG. 15. Denoted at 202 is a KrF or an ArF excimer laser, and denoted at 203 is a half mirror. Denoted at 204 is a flat mirror, and denoted at 205 is an off-axis type alignment optical system with which the positional relation with the optical system
201 is fixed or it can be detected appropriately as a base line (amount). The alignment optical syste