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United States Patent
6118129
Oae , ; et al.
September 12, 2000
Title
Method and system for exposing an exposure pattern on an object by a charged particle beam which is shaped into a plurality of beam elements
Abstract
A method for exposing an exposure pattern on an object by a charged particle beam, including the steps of: shaping a charged particle beam into a plurality of charged particle beam elements in response to first bitmap data indicative of an exposure pattern, such that the plurality of charged particle beam elements are selectively turned off in response to the first bitmap data; focusing the charged particle beam elements upon a surface of an object; and scanning the surface of the object by the charged particle beam elements; the step of shaping including the steps of: expanding pattern data of said exposure pattern into second bitmap data having a resolution of n times (n.gtoreq.2) as large as, and m times (m.gtoreq.1) as large as, a corresponding resolution of the first bitmap data, respectively in X- and Y-directions; dividing the second bitmap data into cells each having a size of 2n bits in the X-direction and 2m bits in said Y-direction; and creating the first bitmap data from the second bitmap data by selecting four data bits from each of the cells, such that a selection of the data bits is made in each of the cells with a regularity in the X- and Y-directions and such that the number of rows in the X-direction and the number of columns in the Y-direction are both equal to 3 or more.
Inventors:
Oae; Yoshihisa
(Kawasaki,
JP
)
, Abe; Tomohiko
(Kawasaki,
JP
)
, Arai; Soichiro
(Kawasaki,
JP
)
, Maruyama; Shigeru
(Kawasaki,
JP
)
, Yasuda; Hiroshi
(Kawasaki,
JP
)
, Miyazawa; Kenichi
(Kawasaki,
JP
)
, Kai; Junichi
(Kawasaki,
JP
)
, Satoh; Takamasa
(Kawasaki,
JP
)
, Betsui; Keiichi
(Kawasaki,
JP
)
, Nasuno; Hideki
(Kasugai,
JP
)
Assignee:
Fujitsu Limited
(Kawasaki,
JP
)
Appl. No.:
283974
Filed:
April 1, 1999
Foreign Application Priority Data
Mar 15, 1994 [JP] 6-044468
Mar 17, 1994 [JP] 6-047521
Mar 17, 1994 [JP] 6-047522
Mar 17, 1994 [JP] 6-047523
Mar 18, 1994 [JP] 6-049491
Mar 18, 1994 [JP] 6-049496
Mar 29, 1994 [JP] 6-059301
Apr 26, 1994 [JP] 6-088753
Jun 03, 1994 [JP] 6-122436
Nov 28, 1994 [JP] 6-292762
Current U.S. Class:
250/492.22
250/398
Current International Class:
H01J 37/30 (20060101)
Field of Search:
250/492.22,398
U.S. Patent Documents
4433384
February 1984
Berrian et al.
4511980
April 1985
Watanabe
4541115
September 1985
Werth
4641252
February 1987
Tokita
4661709
April 1987
Walker et al.
5041764
August 1991
Midland et al.
5262341
November 1993
Fueki et al.
5369282
November 1994
Arai et al.
5391886
February 1995
Yamada et al.
5430304
July 1995
Yasuda et al.
5444257
August 1995
Satoh et al.
5448075
September 1995
Fueki et al.
5500930
March 1996
Fueki
5866300
February 1999
Satoh et al.
Foreign Patent Documents
2-1111
Jan., 1990
JP
64-20619
Jan., 1989
JP
Primary Examiner:
Anderson; Bruce C.
Attorney, Agent or Firm:
Armstrong, Westerman, Hattori, McLeland & Naughton
Parent Case Text
This application is a division of prior application Ser. No. 09/022,881 filed Feb. 12, 1998 now U.S. Pat. No. 5,920,077, which is a division of Ser. No. 08/745,632 filed Nov. 8, 1996, U.S. Pat. No. 5,997,548 and a con of Ser. No. 08/404,830, Mar. 15, 1995, U.S. Pat. No. 5,528,048.
Claims
What is claimed is:
1. A method for exposing an exposure pattern on an object by a charged particle beam, comprising the steps of:
shaping a charged particle beam into a plurality of charged particle beam elements in response to first bitmap data indicative of an exposure pattern, such that said plurality of charged particle beam elements are selectively turned off in response to said first bitmap data;
focusing said charged particle beam elements upon a surface of an object; and
scanning said surface of said object by said charged particle beam elements;
said step of shaping including the steps of:
expanding pattern data of said exposure pattern into second bitmap data having a resolution of n times (n.gtoreq.2) as large as, and m times (m.gtoreq.1) as large as, a corresponding resolution of said first bitmap data, respectively in X- and Y-directions;
dividing said second bitmap data into cells each having a size of 2n bits in said X-direction and 2m bits in said Y-direction; and
creating said first bitmap data from said second bitmap data by selecting four data bits from each of said cells, such that a selection of said data bits is made in each of said cells with a regularity in said X- and Y-directions and such that the number of rows in said X-direction and the number of columns in said Y-direction are both equal to 3 or more.
2. A method as claimed in claim 1, wherein said selection of said data bits is achieved identically in each of said cells.
3. A method as claimed in claim 1, wherein said number of rows in said X-direction and including said selected data bits, and said number of columns in said Y-direction and including said selected data bits, are both four, and wherein said rows are separated from each other by a distance that is identical to a distance between said columns.
4. A method as claimed in claim 2, wherein said X- and Y-directions intersect perpendicularly with each other, said resolution is set such that m=n=2, and
wherein said step of selecting said four bit of data bit is conducted by selecting a data bit on a first row and a first column, a data bit on a second row and a third column, a data bit on a third row and a second column, and a data bit of a fourth row and a fourth column.
5. A method as claimed in claim 1, wherein said step of dividing said second bit map data into cells is conducted such that a plurality of cells form a cluster and such that a plurality of clusters are repeated regularly in said X- and Y-directions, wherein said step of dividing said second bit map data into cells is conducted identically in each of said plurality of clusters.
6. A method as claimed in claim 5, wherein said rows extending in said X-directions are separated from each other by a distance identical with a distance between said columns extending in said Y-direction in each of said clusters.
7. A method as claimed in claim 1, wherein said step of creating said first bitmap data is conducted by selecting a single data bit from a region defined on said second bitmap and including n data bits in said X-direction and m data bits in said Y-direction, said region being included in a band extending in said Y-direction and having a width of n bits, wherein said step of selection of said single data bit is conducted with a regularity in said Y-direction, and wherein said selected data bits form a plurality of columns each extending in said Y-direction.
8. A method for expanding exposure bitmap data from pattern data indicative of a geometrical pattern, said exposure bit map data being used for controlling turning on and turning off of beams to be emitted upon an object in accordance with said geometrical pattern, comprising the steps of:
expanding pattern data into first bitmap data having a resolution of n times (n.gtoreq.2) as large as, and m times (m.gtoreq.1) as large as, a corresponding resolution of said exposure bitmap data, respectively in X- and Y-directions;
dividing said first bitmap data into cells each having a size of 2n bits in said X-direction and 2m bits in said Y-direction; and
creating said exposure bitmap data from said first bitmap data by selecting four data bits from each of said cells, such that a selection of said data bits is made in each of said cells with a regularity in said X- and Y-directions and such that the number of rows in said X-direction and the number of columns in said Y-direction are both equal to 3 or more.
9. A charged particle beam exposure system for exposing a pattern on an object by a charged particle beam, comprising:
beam source means for producing a charged particle beam;
beam shaping means for shaping said charged particle beam to produce a plurality of charged particle beam elements in accordance with exposure bitmap data indicative of a dot pattern to be exposed on said object;
focusing means for focusing said charged particle beam elements upon a surface of said object; and
deflection means for deflecting said charged particle beam elements over said surface of said object;
said beam shaping means comprising:
a first data expansion unit supplied with exposure data indicative of a pattern to be exposed on said object, for expanding said exposure data into first bitmap data such that said first bitmap data has a resolution that is n times (n.gtoreq.2) as large as, and simultaneously m times (m.gtoreq.1) as large as, a resolution of said exposure bitmap data, respectively in X- and Y-directions; and
a second data expansion unit for creating said exposure bitmap data from said first bitmap data, said second data expansion unit dividing said first bitmap data into cells each having a size of 2n bits in said X-direction and 2m bits in said Y-direction; and creating said exposure bitmap data from said first bitmap data by selecting four data bits from each of said cells, such that a selection of said data bits is made in each of said cells with a regularity in said X- and Y-directions and such that the number of rows in said X-direction and the number of columns in said Y-direction are both equal to 3 or more.
10. A charged particle beam exposure system as claimed in claim 5, wherein said second data expansion unit carries out a selection of a single data bit from a region defined on said second bitmap and including n data bits in said X-direction and m data bits in said Y-direction, said region being included in a band extending in said Y-direction and having a width of n bits, wherein said second data expansion unit carries out said selection of said single data bit with a regularity in said Y-direction, and such that said selected data bits form a plurality of columns each extending in said Y-direction.
11. A charged particle beam exposure system as claimed in claim 9, wherein said beam shaping means includes a beam shaping mask carrying thereon a plurality of apertures aligned in said X- and Y-directions for producing said plurality of charged particle beam elements as a result of shaping of said charged particle beam, each of said apertures carrying a deflector for causing a deflection of said charged particle beam elements shaped by said aperture.
12. A charged particle beam exposure system for exposing a pattern on an object, comprising:
a base body for accommodating an object to be exposed;
a plurality of electron optical systems provided commonly on said base body, each of said electron optical systems including:
beam source means for producing a charged particle beam, said beam source means emitting said charged particle beam toward an object on which a pattern is to be exposed, along an optical axis;
beam shaping means for shaping said charged particle beam to produce a plurality of charged particle beam elements in accordance with exposure data indicative of a dot pattern to be exposed on said object, said beam shaping means comprising a beam shaping mask carrying thereon a plurality of apertures for producing a charged particle beam element by shaping said charged particle beam;
focusing means for focusing said charged particle beam elements upon a surface of said object;
deflection means for deflecting said charged particle beam elements over said surface of said object; and
a column for accommodating said beam source means, said beam shaping means, said focusing means, and said deflection means;
said electron optical system thereby exposing said charged particle beam element upon said object held in said base body;
exposure control system supplied with exposure data indicative of a pattern to be exposed on said object and expanding said exposure data into dot pattern data corresponding to a dot pattern to be exposed on said object, said exposure control system being provided commonly to said plurality of electron optical systems and including memory means for holding said dot pattern data;
said exposure control system supplying said dot pattern data to each of said plurality of electron optical systems simultaneously, such that said pattern is exposed on said object by said plurality of electron optical systems simultaneously.
13. A charged particle beam exposure system as claimed in claim 12, wherein said exposure control system includes delay means for synchronizing the timing of exposure caused by said plurality of electron optical systems.
14. A charged particle beam exposure system as claimed in claim 12, wherein said base body carries a plurality of said electron optical systems which are movable with respect to a reference electron optical system.
15. A charged particle beam exposure system as claimed in claim 14, wherein said plurality of electron optical systems are provided movable in a two-dimensional plane perpendicular to respective optical axes of said electron optical systems, except for said reference electron optical system.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to charged particle beam exposure systems and methods and, more particularly, to a charged particle beam exposure system and method for exposing a desired pattern on a surface of an object as a result of raster scanning of charged particle beams, while controlling each of the plurality of charged particle beams such that the charged particle beams as a whole form a beam bundle having the desired exposure pattern.
2. Description of the Related Art
The present invention uses some of the teachings of the U.S. Pat. No. 5,369,282 and the U.S. patent application Ser. No. 08/241,409 filed May 11, 1994, which are herein incorporated by reference.
With the advancement in the art of fine lithographic patterning, recent integrated circuits are formed with such a high integration density that they are now used commonly and widely in industries including computers, telecommunications, system control, and the like. Looking back at the history of dynamic random access memories, for example, it will be noted that the dynamic random memories have increased the integration density as represented in terms of storage capacity of information, from
1 Mbits to 4 Mbits, from 4 Mbits to 16 Mbits and from 16 Mbits to 64 Mbits. Currently, dynamic random access memories having a storage capacity of 256 Mbits or 1 Gbits are studied intensively. In correspondence to such an increase in the integration density, extensive studies are in progress for developing the art of so-called charged particle beam exposure that uses a charged particle beam such as an electron beam for exposing fine patterns on an object. By using such a charged particle beam, it is possible to expose a pattern having a size of 0.05 .mu.m or less, with an alignment error of 0.02 .mu.m or less.
On the other hand, conventional charged particle beam exposure systems have suffered from the problem of low throughput of exposure, and there has been a pessimistic atmosphere prevailing among those skilled in the art about the production of integrated circuits by means of such a charged particle beam exposure system. It should be noted that the conventional charged-particle-beam exposure systems have used a single charged particle beam for the exposure and it has been necessary to draw a desired pattern on the object such as a substrate by a single stroke of the charged particle beam.
On the other hand, most of such pessimistic observations addressing negative predictions about the future of charged-beam-exposure system and method, are not well founded, as is typically demonstrated by the inventors of the present invention who have succeeded in constructing a block exposure system and a BAA (blanking aperture array) exposure system that provide a throughput of as much an 1 cm.sup.2 /sec. With the high throughput of 1 cm.sup.2 /sec thus achieved, the main disadvantage of the charged-particle-beam exposure system and method is substantially eliminated. Now, it is thought that the charged-particle-beam exposure system and process are superior to any other conventional exposure systems in terms of high resolution, small alignment error, quick turn around time, and reliability.
As already noted, it in particularly essential for a charged-particle-beam exposure system to have a high exposure throughput, and block exposure process or BAA process has been developed for clearing the requirement of high exposure throughput. Hereinafter, a BAA exposure system proposed previously by the inventors of the present invention will be described briefly. For the sake of simplicity, the description hereinafter will be made for an electron beam exposure system, while the present invention is by no means limited to an electron beam exposure system but is applicable to any other charged particle beam exposure systems such as an ionic beam exposure system that uses a focused ionic beam.
In a BAA exposure system, a plurality of electron beams are produced such that the plurality of electron beams as a whole form a desired electron beam bundle with a shape corresponding to a pattern to be exposed on an object. Thereby, each of the plurality of electron beams is turned on and off individually according to the desired pattern to be exposed. Thus, each time the exposure pattern is changed, different set of electron beams are turned on. While being exposed by the electron beams on the object, which may be a substrate, the object is moved, together with a stage on which the object is supported while deflecting the electron beams back and forth by activating a deflector.
In order to produce the foregoing plurality of electron beams, the BAA exposure system employs a BAA mask that is a plate formed with a number of rectangular apertures arranged in rows and columns for shaping a single electron beam incident thereto. Each of the apertures carries a pair of electrodes on opposing edges, wherein one of the electrodes is set to a ground potential level while the other of the electrodes is supplied with a control signal that changes the level between the ground level and a predetermined energization level. In response to the energization of the electrodes on the BAA mask, the path of the electron beam through the aperture is deflected and the arrival of the electron beam upon the object is controlled accordingly. In other words, the electron beams are turned-on and off on the object in response to the control signal applied to the electrodes of the apertures on the BAA mask. It should be noted that the control signals applied to the apertures on the BAA mask represent a pattern of the electron beams produced by the BAA mask, and the control signals are changed in synchronization with a raster scanning of the surface of the object by the electron beam bundle. As a result of the raster scanning, the object is exposed along a band or zone.
In such conventional BAA exposure systems and methods, there are still various problems to be overcome, such as further improvement of the exposure throughput including improvement of data transfer rate and data compression, improvement in the precision of the exposed patterns including optimization of exposure dose and improvement of resolution when expanding exposure data into bit map data, uniform distribution of the electron beam intensity throughout the substrate, improved data processing such as expansion and transfer of the exposure dot data, positive on-off control of the electron beam, easy maintenance of the BAA mask, exposure of large diameter wafers, improvement of electron optical systems, and easy switching between a BAA exposure mode and a block exposure mode, and the like.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel and useful charged-particle-beam exposure system and method wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a charged-particle-beam exposure method and system for exposing versatile patterns on an object by means of a charged particle beam that forms an exposure dot pattern, in which the creation of-dot pattern data representing the exposure dot pattern and the exposure of the object by means of the charged particle beam can be achieved separately.
Another object of the present invention is to provide a charged-particle-beam exposure method and system that is capable of holding a large amount of dot pattern data representing the exposure dot pattern and that can control a blanking aperture array based upon the dot pattern data at a high speed for producing a charged particle beam bundle including a number of charged particle beams in correspondence to each dot of the exposure dot pattern.
Another object of the present invention is to provide a method for exposing a pattern on an object by means of a charged particle beam, comprising the steps of:
shaping a charged particle beam into a plurality of charged particle beam elements forming collectively a charged particle beam bundle having a desired pattern in response to exposure data;
calculating a beam correction to be applied upon said charged particle beam elements for compensating for a beam distortion when exposing said desired pattern on said object, as a function of said exposure data, said step of calculation being conducted in response to a correction clock; and
exposing said desired pattern upon said substrate by radiating said charged particle beam bundle upon said object in response to an exposure clock;
said step of exposing comprising the steps of:
setting a frequency of said exposure clock based upon a sensitivity of a resist provided on said object and a current density of said charged particle beam elements; and
emitting said charged particle beam elements forming said charged particle beam bundle upon said object in response to said exposure clock, with said beam correction applied to said charged beam elements;
wherein said correction clock is synchronized to said exposure clock and held at a substantially constant, predetermined frequency when changing the frequency of said exposure clock in said step of setting the frequency of said exposure clock.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a desired pattern on an object, comprising:
a charged particle beam source for producing a charged particle beam and emitting the same along a predetermined optical axis;
beam shaping means provided on said optical axis so as to interrupt said charged particle beam, said beam shaping means carrying thereon a plurality of apertures for shaping said charged particle beam into a
plurality of charged particle beam elements collectively forming a charged particle bundle, each of said apertures carrying switching means for selectively turning off said charged particle beam element in response to exposure data;
beam focusing means for focusing each of said charged particle beam elements forming said charged particle beam bundle upon said object;
deflection means for deflecting said charged particle beam elements collectively over a surface of said object in response to a deflection control signal supplied thereto;
deflection control means supplied with deflection data for producing said deflection control signal;
beam correction means for calculating a beam correction to be applied to said electron beam element as a function of said exposure data for compensating for a beam distortion, said beam correction calculation means carrying out said calculation in response to a correction clock;
exposure control means for conducting an exposure of said charged particle elements in response to an exposure clock; and
clock control means supplied with control data indicative of a current density of said charged particle beam elements and a sensitivity of said electron beam resist, for producing said exposure clock and said correction clock, such that said exposure clock has a clock speed determined as a function of said control data, said clock control means further holding said correction clock substantially constant at a predetermined frequency irrespective of the frequency of said exposure clock.
According to the present invention, it is, possible to conduct the development of exposure data into exposure dot data and the exposure of the pattern on the object at respective timings. Thereby, the exposure throughput is no longer limited by the data expansion of the exposure data to the exposure dot data and a high exposure throughput can be achieved. Further, it is possible to hold or save a large amount of exposure dot data in the primary storage device that may be a hard disk device. By using a non-volatile storage device such as a hard disk for the primary storage device, it is possible to examine the exposure data in the form of exposure dot data. Further, such exposure dot data can be used repeatedly in the production of a semiconductor device. Although the primary storage device may have a limited access speed, it should be noted that the exposure dot data is supplied to the beam shaping means, which is a blanking aperture array, at high speed from the secondary storage device.
In a preferred embodiment of the present invention, two or more high speed memory devices are used for the secondary storage device each having a storage capacity smaller than the primary storage device.
Another object of the present invention is to provide a charged particle beam exposure system and method wherein a high precision exposure in guaranteed even when the setting for the current density of the electron beam or the sensitivity of the electron beam resist is changed.
Another object of the present invention is to provide a method for exposing a pattern on an object by means of a charged particle beam, comprising the steps of:
shaping a charged particle beam into a plurality of charged particle beam elements forming collectively a charged particle beam bundle having a desired pattern in response to exposure data;
calculating a focusing error correction and an aberration correction to be applied upon said charged particle beam elements when exposing said desired pattern on said object, as a function of said exposure data, said step of calculation being conducted in response to a correction clock; and
exposing said desired pattern upon said object by radiating said charged particle beam bundle upon said object;
said step of exposing comprising the steps of:
setting an exposure clock speed based upon a sensitivity of an electron beam resist provided on said object and a current density of said charged particle beam elements; and
emitting said charged particle beam elements forming said charged particle beam bundle upon said object in response to said exposure clock, with said focusing error correction and said aberration correction;
wherein said correction clock is held in the vicinity of a predetermined clock speed when changing a clock speed of said exposure clock in said step of setting the exposure clock speed.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a desired pattern on an object, comprising:
a charged particle beam source for producing a charged particle beam and emitting the same along a predetermined optical axis;
beam shaping means provided on said optical axis so as to interrupt said charged particle beam, said beam shaping means carrying thereon a plurality of apertures for shaping said charged particle beam into a plurality of charged particle beam elements collectively forming a charged particle bundle, each of said apertures carrying switching means for selectively turning off said charged particle beam element in response to exposure data;
beam focusing means for focusing each of said charged particle beam elements forming said charged particle beam bundle upon said object;
deflection means for deflecting said charged particle beam elements collectively over a surface of said object in response to a deflection control signal supplied thereto;
deflection control means supplied with deflection data for producing said deflection control signal;
beam correction means for calculating a correction to be applied to said electron beam element as a function of said exposure data, said beam correction calculation means carrying out the calculation in response to a correction clock;
exposure control means for conducting an exposure of said charged particle elements in response to an exposure clock; and
clock control means supplied with control data indicative of a current density of said charged particle beam elements and a sensitivity of said electron beam resist, for producing said exposure clock and said correction clock, such that said exposure clock has a clock speed determined as a function of said control data, said clock control means further holding said correction clock substantially constant irrespective of said exposure clock.
According to the invention of the present embodiment, one can guarantee a necessary exposure dose by changing the exposure clock as a function of the resist sensitivity and the current density. On the other hand, the analog signal supplied to the deflection means, which includes a main deflector and a sub-deflector, changes generally linearly with time, and the problem of the exposure beam failing to hit the desired point on the substrate is effectively eliminated.
Another object of the present invention is to provide a charged particle beam exposure system and method that is capable of exposing an object by charged particle beams produced by a BAA mask with a uniform electron beam intensity irrespective of the location of the apertures on the BAA mask that are used for shaping the electron beams.
Another object of the present invention is to provide a method for exposing a pattern on an object, comprising the steps of:
shaping a charged particle beam into a plurality of charged particle beam elements forming collectively a charged particle beam bundle having a desired pattern in response to exposure data;
exposing a desired pattern upon said object by radiating said charged particle beam bundle upon said object;
said step of beam shaping comprising the steps of:
activating a plurality of apertures provided on a beam shaping mask for shaping said charged particle beam, such that a predetermined number of said apertures are activated each time as a unit, each of said apertures including a deflector for deflecting a charged particle beam element passing therethrough in response to an activation of said aperture, said predetermined number of apertures thereby producing a plurality of charged particle beam elements equal in number to said predetermined number; and
detecting the intensity of said predetermined number of charged particle beam elements on said object;
said step of activating said plurality of apertures being conducted such that the intensity of said charged beam elements, produced as a unit, is equal to the intensity of said charged particle beam elements of other units, by optimizing an energization of said deflectors on said predetermined number of apertures.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object, comprising:
a charged particle beam source for producing a charged particle beam and emitting the same along a predetermined optical axis;
beam shaping means provided on said optical axis so as to interrupt said charged particle beam, said beam shaping means carrying thereon a plurality of apertures for shaping said charged particle beam into a plurality of charged particle beam elements collectively forming a charged particle bundle;
switching means for selectively turning off said charged particle beam element in response to a control signal;
driving means for driving said switching means on said beam shaping means by supplying thereto said control signal in response to exposure data;
beam focusing means for focusing each of said charged particle beam elements forming said charged particle beam bundle upon said object;
detection means for detecting the intensity of said charged particle beam elements on said object;
correction means for controlling said driving means such that said driving means supplies said control signal to said switching means with an offset added thereto, said correction means evaluating said offset in response to the intensity of said charged particle beam elements detected by said detection means, such that a group of charged particle beam elements including a predetermined number of charged particle beam elements therein has an intensity that is substantially identical to the intensity of other charged particle beam elements forming other groups, each of said other groups including said charged particle beam elements in number identical to said predetermined number.
According to the present invention as set forth above, the intensity of the charged particle beam elements is detected for each unit or group including a predetermined number of charged particle beam elements, wherein the intensity of the charged particle beam elements in adjusted for each unit in response to the detected beam intensity on the object, by adjusting the energization of the switching means or deflectors cooperating with each of the apertures, such that the beam intensity is substantially uniform over the entire surface of the object. Thereby, the problem of the exposure dots shaped by the apertures on the marginal area of the BAA mask is substantially eliminated, and a high precision exposure becomes possible.
Another object of the present invention is to provide a charged particle beam exposure system and method that improves the data transfer rate and hence the exposure throughput by compressing the dot pattern data during the process of data transfer.
Another object of the present invention is to provide a method for exposing a pattern on an object by means of a charged particle beam, comprising the steps of:
producing a plurality of charged particle beam elements in the form of dot pattern data, said plurality of charged particle beam elements being produced simultaneously as a result of shaping of a single charged particle beam by a mask, said mask carrying a plurality of beam shaping apertures arranged in rows and columns on a mask area;
focusing said plurality of charged particle beam elements upon an object; and
scanning a surface of said object by means of said plurality of charged particle beam elements in a first direction;
said step of producing the plurality of charged particle beam elements includes the steps of:
dividing said dot pattern data into a plurality of data blocks each corresponding to a rectangular area on said beam shaping mask, said rectangular area having a size in a second direction perpendicular to said first direction such that said size is smaller than a size of said mask area in said second direction;
providing identification codes to said data blocks for discriminating said data blocks from each other, such that identical data blocks have an identical identification code;
storing said data blocks respectively in corresponding dot memories, together with said discrimination codes corresponding to said data blocks;
reading out said data blocks from said dot memories consecutively by specifying said identification codes consecutively; and
shaping said single charged particle beam by said beam shaping mask into said plurality of beam shaping beam elements in response to said data blocks read out from said dot memories.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object, comprising:
beam source means for producing a charged particle beam and for emitting the same along an optical axis in the form of a charged particle beam toward an object;
beam shaping means disposed on said optical axis so as to interrupt said primary charged particle beam, said beam shaping means carrying on a mask area thereof a plurality of apertures each supplied with exposure dot data representing a dot pattern to be exposed on said object, said apertures thereby shaping said charged particle beam into a plurality of charged particle beam elements in response to said exposure dot data, said plurality of charged particle beam elements as a whole forming a charged particle beam bundle;
focusing means for focusing each of said charged particle beam elements in said charged particle beam bundle upon said object with a demagnification;
scanning means for scanning a surface of said object by said charged particle beam elements in a first direction;
a dot memory for storing dot pattern data for data blocks each corresponding to a group of exposure dots to be formed on a rectangular area on said object, said rectangular area having a size on said object, in a second direction perpendicular to said first direction, to be equal to or smaller than a size of said mask area projected upon said object and measured in said second direction;
a code memory for storing codes each specifying one of said data blocks;
block addressing means for addressing, based upon said codes read out from said code memory, said dot memories consecutively from a first address to a last address of a data block specified by said code; and
code memory control means for reading said codes from said code memory consecutively in the order of exposure,
According to the present invention set forth above, the same exposure data is used repeatedly by specifying the codes. It should be noted that the same data block has the same code. Thereby, the amount of the dot pattern data is substantially reduced. It should be noted that such a reduction in the amount of data decreases the duration of data transfer, and the throughput of exposure is improved substantially.
Another object of the present invention is to provide a charged particle beam exposure method and system that are capable of exposing a pattern on an object at a high speed, without requiring particular data processing with respect to pattern width or contour of the exposed pattern when conducting a minute adjustment of the exposed pattern.
Another object of the present invention is to provide a method and system for exposing an exposure pattern on an object by a charged particle beam, comprising the steps of:
shaping a charged particle beam into a plurality of charged particle beam elements in response to first bitmap data indicative of an exposure pattern, such that said plurality of charged particle beam elements are
selectively turned off in response to said first bitmap data;
focusing said charged particle beam elements upon a surface of an object; and
scanning said surface of said object by said charged particle beam elements;
said step of shaping including the steps of:
expanding pattern data of said exposure pattern into second bitmap data having a resolution of n times (n.gtoreq.2) as large as, and m times (m.gtoreq.1) as large as, a corresponding resolution of said first bitmap data, respectively in X- and Y- directions;
dividing said second bitmap data into cells each having a size of 2n bits in said X-direction and 2m bits in said Y-direction; and
creating said first bitmap data from said second bitmap data by selecting four data bits from each of said cells, such that a selection of said data bits is made in each of said cells with a regularity in said X- and Y-directions and such that the number of rows in said X-direction and the number of columns in said Y-direction are both equal to 3 or more.
According to the present invention, it becomes possible to achieve a fine adjustment of the exposure pattern by using the first bitmap data without considering the effect of pattern width or conducting a processing along the contour of the pattern boundary. Thereby, the processing speed and hence the exposure throughput increases substantially.
Another object of the present invention is to provide a BAA exposure system having a BAA mask wherein the deflection of the electron beam elements is made in the same direction throughout the BAA mask.
Another object of the present invention is wherein the resistance and capacitance of wiring used for carrying drive signals to the electrostatic deflectors provided on the BAA mask, are optimized with respect to the timing of turning on and turning off the apertures of the BAA mask.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object, comprising:
beam source means for producing a charged particle beam;
beam shaping means for shaping said charged particle beam to produce a plurality of charged particle beam elements in accordance with exposure data indicative of a dot pattern to be exposed on said object;
focusing means for focusing said charged particle beam elements upon a surface of said object; and
deflection means for deflecting said charged particle beam elements over said surface of said object;
said beam shaping means comprising:
a substrate formed with a plurality of apertures for shaping said charged particle beam into said plurality of charged particle beam elements;
a plurality of common electrodes provided on said substrate respectively in correspondence to said plurality of apertures, each of said plurality of common electrodes being provided in a first side of a corresponding aperture; and
a plurality of blanking electrodes provided on said substrate respectively in correspondence to said plurality of apertures, each of said plurality of blanking electrodes being provided in a second, opposite side of a corresponding aperture on said substrate.
Another object of the present invention is to provide a beam shaping mask for shaping a charged particle beam into a plurality of charged particle beam elements, comprising:
a substrate formed with a plurality of apertures for shaping said charged particle beam into said plurality of charged particle beam elements;
a plurality of common electrodes provided on said substrate respectively in correspondence to said plurality of apertures, each of said plurality of common electrodes being provided in a first side of a corresponding aperture; and
a plurality of blanking electrodes provided on said substrate respectively in correspondence to said plurality of apertures, each of said plurality of blanking electrodes being provided in a second, opposite side of a corresponding aperture on said substrate.
Another object of the present invention is to provide a process for fabricating a beam shaping mask for shaping a charged particle beam into a plurality of charged particle beam elements, comprising the steps of:
providing a plurality of conductor patterns on a surface of a substrate with respective thicknesses such that at least one of said conductor patterns has a thickness that is different from the thickness of another conductor pattern; and
providing a ground electrode and a blanking electrode on said substrate respectively in electrical contact with said conductor patterns, said ground electrode and said blanking electrode forming a deflector for deflecting said charged particle beam elements.
According to the present embodiment set forth above, the beam shaping mask causes a uniform deflection when turning off the charged particle beam, over entire area of the mask, and the problem of leakage of the deflected charged particle beam elements upon the reversal deflection upon the blanking of the charged particle beam is successfully eliminated. Further, by optimizing the thickness and hence the resistance of the conductor patterns on the beam shaping mask, it is possible to adjust the timing of activation of the individual electrostatic deflectors formed on the beam shaping means for selectively turning off the charged particle beam elements.
Another object of the present invention is to provide a BAA exposure system in which maintenance of the BAA mask is substantially facilitated.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object by a charged particle beam, comprising:
beam source means for producing a charged particle beam, said beam source means emitting said charged particle beam toward an object on which a pattern is to be exposed, along an optical axis;
beam shaping means for shaping said charged particle beam to produce a plurality of charged particle beam elements in accordance with exposure data indicative of a dot pattern to be exposed on said object;
focusing means for focusing said charged particle beam elements upon a surface of said object; and
deflection means for deflecting said charged particle beam elements over said surface of said object;
said beam shaping means comprising:
a beam shaping mask carrying thereon a plurality of apertures for producing a charged particle beam element by shaping said charged particle beam and a plurality of deflectors each provided in correspondence to one of said plurality of apertures, said beam shaping means further including a plurality of electrode pads each connected to a corresponding deflector on said beam shaping means;
a mask holder provided on a body of said charged particle beam exposure system for holding said beam shaping mask detachably thereon, said mask holder comprising: a stationary part fixed upon said body of said charged particle beam exposure system; a movable part provided movably upon said stationary part such that said movable part moves in a first direction generally parallel to said optical axis and further in a second direction generally perpendicular to said optical axis, said movable part carrying said beam shaping mask detachably; a drive mechanism for moving said movable part in said first and second directions; and
a contact structure provided on said body of said charged particle beam exposure system for contacting with said electrode pads on said beam shaping mask, said contact structure including a base body and a plurality of electrode pins extending from said base, said of said electrode pins having a first end connected to said base body of said contact structure and a second, free end adapted for engagement with said electrode pads on said beam shaping mask.
According to the construction of the present embodiment, particularly the construction of the beam shaping mask held on the mask holder and the construction of the cooperating contact structure, it is possible to dismount the BAA mask easily, without breaking the vacuum inside the electron beam column. Thus, the time needed for maintenance of the BAA mask is substantially reduced, and the throughput of exposure increases substantially, Further, the BAA exposure system of the present embodiment is advantageous in the point that one can use various beam shaping masks by simply dismounting an old mask and replacing with a new mask. Thereby, the charged particle beam exposure system of the present invention is not only useful in the BAA exposure system but also in the block exposure system.
Another object of the present invention is to provide a BAA exposure system capable of exposing a pattern on a large diameter substrate without increasing the size of the control system excessively.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object, comprising:
a base body for accommodating an object to be exposed;
a plurality of electron optical systems provided commonly on said base body, each of said electron optical systems including:
beam source means for producing a charged particle beam, said beam source means emitting said charged particle beam toward an object on which a pattern is to be exposed, along an optical axis;
beam shaping means for shaping said charged particle beam to produce a plurality of charged particle beam elements in accordance with exposure data indicative of a dot pattern to be exposed on said object, said beam shaping means comprising a beam shaping mask carrying thereon a plurality of apertures for producing a charged particle beam element by shaping said charged particle beam;
focusing means for focusing said charged particle beam elements upon a surface of said object;
deflection means for deflecting said charged particle beam elements over said surface of said object; and
a column for accommodating said beam source means, said beam shaping means, said focusing means, and said deflection means;
said electron optical system thereby exposing said charged particle beam element upon said object held in said base body;
exposure control system supplied with exposure data indicative of a pattern to be exposed on said object and expanding said exposure data into dot pattern data corresponding to a dot pattern to be exposed on said object, said exposure control system being provided commonly to said plurality of electron optical systems and including memory means for holding said dot pattern data;
said exposure control system supplying said dot pattern data to each of said plurality of electron optical systems simultaneously, such that said pattern is exposed on said object by said plurality of electron optical systems simultaneously.
According to the foregoing embodiment of the present invention, the size of the BAA exposure system is substantially reduced, even when exposing a large diameter wafer by using a plurality of electron optical systems simultaneously.
Another object of the present invention is to provide a charged particle beam exposure system that uses an immersion electron lens, wherein the compensation of beam offset caused by the eddy current is successfully achieved with a simple construction of the electron optical system.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object by a charged particle beam, comprising:
a stage for holding an object movably;
beam source means for producing a charged particle beam and emitting said charged particle beam toward said object held on said stage along an optical axis; and
a lens system for focusing said charged particle beam upon said object held on said stage;
said lens system including an immersion lens system comprising: a first electron lens disposed at a first side of said object closer to said beam source means, a second electron lens disposed at a second, opposite side of said object, said first and second electron lenses creating together an axially distributed magnetic field penetrating through said object from said first side to said second side; and a shield plate of a magnetically permeable conductive material disposed between said object and said first electron lens, said shield plate having a circular central opening in correspondence to said optical axis of said charged particle beam.
According to the present embodiment as set forth above, the electric field inducted as a result of the eddy current is successfully captured by the magnetic shield plate and guided therealong while avoiding the region in which the electron beam passes through. Thereby, adversary effects upon the electron beam by the eddy current is effectively eliminated.
Another object of the present invention is to provide a charged beam exposure process capable of exposing both a BAA exposure process and a block exposure process on a common substrate.
Another object of the present invention is to provide a charged particle beam exposure system for exposing a pattern on an object, comprising:
a stage for holding an object thereon;
beam source means for producing a charged particle beam such that said charged particle beam is emitted toward said object on said stage along a predetermined optical axis;
a blanking aperture array provided in the vicinity of said optical axis for shaping an electron beam incident thereto, said blanking aperture array including a mask substrate, a plurality of apertures of identical size and shape disposed in rows and columns on said mask substrate and a plurality of deflectors each provided in correspondence to an aperture on said mask substrate;
a block mask provided in the vicinity of said optical axis, said block mask carrying thereon a plurality of beam shaping apertures of different shapes for shaping an electron beam incident thereto;
selection means for selectively deflecting said electron beam from said beam source means to one of said blanking aperture array and said block mask;
focusing means for focusing an electron beam shaped by any of said blanking aperture array and said block mask upon said object on said stage.
According to the construction of the present embodiment set forth above, it is possible to switch the BAA exposure and block exposure by using the single electron exposure system. Thereby, the addressing deflector, used in the block exposure process for selecting an aperture on the block mask, is used also as the selection beams for selecting the BAA exposure process and the block exposure process. Thereby, no extraneous fixture is needed for implementing the selection of the exposure mode.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the scanning employed in a BAA exposure system;
FIG. 2 is a diagram showing a part of FIG. 1 in an enlarged scale;
FIG. 3 is a diagram showing the overall construction of a conventional BAA exposure system;
FIG. 4 is a diagram showing an example of a BAA mask used in the exposure system of FIG. 3;
FIG. 5 is a diagram showing another example of the BAA mask;
FIG. 6 is a block diagram showing the construction of the BAA exposure system according to a first embodiment of the present invention;
FIG. 7 is a block diagram showing a part of the circuit of FIG. 6;
FIGS. 8A-8G are diagrams showing the timing chart for explanation of the operation of the BAA exposure system of the first embodiment;
FIGS. 9A-9C show another timing charts for explaining the operation of the BAA exposure system of the first embodiment;
FIG. 10 is a diagram showing the construction of a clock generator used in a conventional BAA exposure system of FIG. 3;
FIGS. 11A-11E are diagrams showing the clocks used in the conventional BAA exposure system of FIG. 3;
FIGS. 12A and 12B are diagrams showing the deflector output of the conventional BAA exposure system of FIG. 3:
FIG. 13 is a block diagram showing the overall construction of the BAA exposure system according to a second embodiment of the present invention;
FIG. 14 is a block diagram showing the construction of a clock generator used in the BAA exposure system of FIG. 13;
FIGS. 15A-15E are diagrams showing various clocks including the exposure clock and correction clock used in the BAA exposure system of FIG. 13;
FIG. 16 is a diagram showing the deflector output of the BAA exposure system of FIG. 13;
FIG. 17 is a diagram showing the overall construction of the BAA exposure system according to a third embodiment of the present invention;
FIG. 18 is a diagram showing the construction of a D/A converter used in the BAA exposure system of FIG. 17;
FIG. 19 is a diagram showing the principle of the third embodiment;
FIG. 20 is a block diagram showing the process of setting voltage offset in the BAA exposure system of FIG. 17;
FIG. 21 is a diagram showing the relationship the detected current and the offset voltage used in the BAA exposure system of FIG. 17;
FIGS. 22A-22E are diagrams showing the operation of the BAA exposure system of FIG. 17;
FIG. 23 is a diagram showing the construction of a D/A converter used in the BAA exposure system of FIG. 17;
FIG. 24 is a block diagram showing the construction of a BAA exposure system according to a fourth embodiment of the present invention;
FIG. 25 is a block diagram showing the construction of a BAA mask used in the BAA exposure system of FIG. 24 together with a BAA control circuit cooperating with the BAA mask;
FIG. 26 is a block diagram showing the construction of the BAA control circuit of FIG. 25 in detail;
FIG. 27 is a block diagram showing the construction of a read/write control circuit in the circuit of FIG. 25;
FIG. 28 is a diagram showing the scanning scheme used in the BAA exposure system of FIG. 24;
FIGS. 29A and 29B are diagrams showing the main deflection and stage movement employed in the BAA exposure system of FIG. 24 as a function of time;
FIG. 30 is a diagram showing an example of a pattern to be exposed on a substrate in the BAA exposure system of FIG. 24;
FIG. 31 is a diagram showing the construction of a BAA control circuit used in a first modification of the fourth embodiment of the present invention;
FIGS. 32A and 32B are diagrams respectively showing the construction of a BAA control circuit and exposure dot data used in the BAA exposure system of FIG. 24 as a second modification of the fourth embodiment;
FIG. 33 is a block diagram showing a part of the BAA control circuit used in the BAA exposure system of FIG. 24 as a third modification of the fourth embodiment;
FIG. 34 is a diagram showing another example of the scanning of the substrate by an electron beam used in the fourth embodiment of the present invention;
FIG. 35 is a map showing the relationship between a bit data acquisition point and a corresponding beam spot point according to a fifth embodiment of the present invention;
FIG. 36 is a map showing a part of FIG. 35 in an enlarged scale;
FIGS. 37A-37D are diagrams showing the relationship between the movement of a pattern boundary and the bit data acquisition points;
FIG. 38 is a block diagram showing the construction of the circuit used for implementing the fifth embodiment of the present invention;
FIGS. 39A-39C are diagrams showing the construction and principle of the circuit of FIG. 38;
FIG. 40 is a map showing the relationship between a bit data acquisition point and a corresponding beam spot point according to a first modification of the fifth embodiment;
FIGS. 41A and 41B are diagrams showing the relationship between a movement of a pattern boundary and the bit data acquisition point in a cluster of FIG. 40 according to the first modification;
FIGS. 42A and 42B are diagrams showing other examples of the relationship between a movement of a pattern boundary and the bit data acquisition point in a cluster of FIG. 40;
FIGS. 43A, 44A, 45A and 43B, 44B, 45B are diagrams showing various examples of modification of the rectangular pattern data and corresponding rectangular exposure patterns;
FIGS. 46A, 47A, 48A and 46B, 47B, 48B are diagrams showing various examples of modification of the triangular pattern data and corresponding triangular exposure patterns;
FIGS. 49A-49C are diagrams showing the construction and principle of the circuit of FIG. 38 according to the first modification of the fifth embodiment;
FIG. 50 is a map showing the relationship between a bit data acquisition point and a corresponding beam spot point according to a second modification of the fifth embodiment;
FIGS. 51A and 51B are diagrams showing the relationship between a movement of a pattern boundary and the bit data acquisition point in a cluster of FIG. 50 according to the first modification;
FIGS. 52A and 52B are diagrams showing other examples of the relationship between a movement of a pattern boundary and the bit data acquisition point in a cluster of FIG. 50;
FIG. 53 is a diagram showing the construction of a BAA mask and a problem thereof addressed in a sixth embodiment of the present invention;
FIG. 54 is a diagram showing the problem caused in a BAA exposure system when the BAA mask of FIG. 53 is used;
FIG. 55 is a diagram showing the principle of a sixth embodiment of the present invention;
FIG. 56 is a diagram showing the construction of the BAA mask of the sixth embodiment of the present invention in a cross sectional view;
FIG. 57 is a diagram showing the construction of a BAA mask of FIG. 56;
FIGS. 58A-58C are diagrams showing the measurement of the pattern resistance on the BAA mask;
FIGS. 59A and 59B are diagrams showing the construction of wiring patterns provided on the BAA mask of the present embodiment;
FIGS. 60A-60H are diagrams showing the fabrication process of the BAA mask of the sixth embodiment;
FIGS. 61A-61D are diagrams showing the fabrication process of the conductor patterns on the BAA mask of the sixth embodiment with optimization of the pattern thickness;
FIGS. 62A-62C are diagrams showing the process for changing the thickness of the conductor pattern partially;
FIGS. 63A-63C are diagrams showing other processes for forming the conductor patterns with respective different thicknesses;
FIG. 64 is a diagram showing the construction of a BAA exposure system that uses the BAA mask of the sixth embodiment;
FIG. 65 is a diagram showing a conventional construction for detachably mounting a BAA mask on a BAA exposure system;
FIG. 66 is a diagram showing the overall construction of the BAA exposure system according to a seventh embodiment of the present invention;
FIGS. 67 and 68 are diagrams showing the detachable mounting of the BAA mask employed in the BAA exposure system of FIG. 66;
FIGS. 69-72 are diagrams showing the construction of a mask holder mechanism for holding the BAA mask movably and detachably in the BAA exposure system of FIG. 66;
FIG. 73 is a diagram showing an example of the BAA mask used in the BAA exposure system of FIG. 66;
FIG. 74 is an example of a beam shaping mask that can be used in the exposure system of FIG. 66;
FIGS. 75A-75D show various patterns that can be exposed on a substrate by using the mask of FIG. 74;
FIG. 76 is a diagram showing another beam shaping mask;
FIG. 77 is a diagram showing the construction of a charged particle beam exposure system that uses the beam shaping mask of FIG. 76 as a modification of the seventh embodiment;
FIG. 78 is a diagram showing the construction of a beam blanking unit used in the charged particle beam exposure system of FIG. 77;
FIG. 79 is a diagram showing the deflection of the charged particle beam caused by the beam blanking unit of FIG. 78;
FIG. 80 is a diagram showing a conventional BAA exposure system for exposing a large diameter wafer;
FIG. 81 is a diagram showing the overall construction of the BAA exposure system according to an eighth embodiment of the present invention;
FIG. 82 is a diagram showing a part of the BAA exposure system in detail;
FIG. 83 is a diagram showing the BAA exposure system of FIG. 81 in more detail;
FIG. 84 is a diagram showing the adjustment employed in the BAA exposure system of FIG. 81;
FIG. 85 is a diagram showing the correction of the position of the electron optical system associated with the adjustment of FIG. 84;
FIG. 86 is a diagram showing the construction of an immersion lens and the problem occurring in an electron beam exposure system associated with the use of such an immersion lens;
FIG. 87 is a diagram showing the construction used conventionally for eliminating the problem of beam offset in the electron beam exposure system that uses an immersion lens;
FIG. 88 is a diagram showing the problem occurring in the conventional system of FIG. 87;
FIG. 89 is a diagram showing an electron beam exposure system according to an eighth embodiment of the present invention;
FIG. 90 is a diagram showing the essential part of the electron beam exposure system of FIG. 89;
FIG. 91 is a diagram showing the axial distribution of the electric field strength of the immersion lens system of FIG. 90;
FIG. 92 is a diagram explaining the function of a shield plate used in the immersion lens system of the present embodiment;
FIG. 93 is another diagram explaining the function of the magnetic shield plate;
FIG. 94 is a diagram showing the lateral distribution of the electric field strength of the immersion lens system of FIG. 90;
FIG. 95 is a diagram showing the reflection of electrons occurrent in the electron beam exposure system of FIG. 90;
FIG. 96 is a diagram showing the determination of optimum size of the shield plate of the present embodiment;
FIGS. 97A and 97B are diagrams showing the optimization of the opening provided in the shield plate of the present embodiment;
FIG. 98 is a diagram showing the principle of a tenth embodiment of the present invention;
FIG. 99 is a diagram showing the overall construction of the electron beam exposure system of the tenth embodiment;
FIG. 100 is a diagram showing the essential part of the electron beam exposure system of FIG. 99;
FIG. 101 is a diagram showing the construction of the beam shaping mask used in the electron beam exposure system of FIG. 99;
FIG. 102 is a diagram showing the construction of the exposure controller used in the electron beam exposure system of FIG. 99;
FIGS. 103A-103C are diagrams showing the scanning of the substrate by the electron beam;
FIGS. 104A and 104B are diagrams showing an example of exposing a sub-field;
FIG. 105 is a flowchart showing the operation of the electron beam exposure system of FIG. 99; and
FIGS. 106A-106C are diagrams showing various modifications of the exposure sequence of the electron beam exposure system of FIG. 99.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[first embodiment]
Hereinafter, the scanning of electron beam employed conventionally as well as in a first embodiment of the present embodiment, will be described with reference to FIG. 1, wherein FIG. 1 shows a scanning of a single wafer 10 by means of electron beams forming together an electron beam bundle. The wafer 10 corresponds to the foregoing object and includes a plurality of regions corresponding to the chips to be formed. It should be noted, however, that the scanning scheme of the BAA exposure system is not limited to the one described in FIG. 1 but other scanning schemes are also possible. Some of the embodiments of the present invention described later uses a different scanning scheme.
Referring to FIG. 1, the wafer 10 is moved continuously in a Y-direction while exposing the surface of the wafer 10 by electron beams shaped by a BAA mask and forming an electron beam bundle.
In such an exposure process, the scanning of the electron beam bundle to be described is achieved in each cell defined on the wafer 10, wherein an example of such a cell is shown in FIG. 1 by a reference numeral 14. In the illustrated example, the cell 14 has a size of 2 mm in the X-direction that corresponds to the coverage area of a main deflector used in the electron beam exposure system. On the other hand, the cell 14 has a size smaller than the chip area 12 in the Y-direction. Thereby, the electron beam bundle formed of the plurality of electron beams is deflected in the Y-direction to scan the surface of the wafer 10 while the wafer 10 is transported continuously in the Y-direction. Further, the scanning of the electron beam bundle is repeated while deflecting the same in the X-direction.
As the stage carrying the wafer 10 moves in the Y-direction continuously, it is not necessary, in principle, to limit the size of the cell 14 in the Y-direction. However, it is desired to suitably limit the site of the cell in the Y-direction in view of necessity of various processings for beam compensation as well as other necessary data processings of the exposure data. Typically, the size of the cell in the Y-direction is set equal to the chip size in the maximum. When it is desired to carry out more accurate beam compensation, on the other hand, one may reduce the cell size in the i-direction.
Here, the concept of cell stripe will be defined. A cell stripe is a region of the substrate 10 that can be exposed by a maximum deflection of the electron beams by a sub-deflector of the electron beam exposure system. Typically, the sub-deflector is formed of an electrostatic deflector and can cover an area of about 100 .mu.m. In the case the sub-deflector can cover the area of about 100 .mu.m by way of beam deflection, the cell stripe has a size of 100 .mu.m in the Y-direction. Further, when the width of the electron beam bundle in the X-direction is set to 10 .mu.m, the cell strips has a size of 10 .mu.m in the X-direction.
FIG. 2 shows the black-painted region of FIG. 1 in an enlarged scale.
Referring to FIG. 2, it will be noted that there are formed a number of cell stripes 16 each extending in the Y-direction and repeated a number of times in the X-direction, wherein the electron beam bundle is deflected in each cell stripe 16 in the Y-direction by the sub-deflector such that the substrate is scanned by the electron beams forming the electron beam bundle. In the case each of the cell stripes 16 has a size of 10 .mu.m in the X-direction and 100 .mu.m in the Y-direction, a region including ten cell stripes 16 disposed in parallel may be scanned by the sub-deflector without energizing the main deflector or moving the stage. Thereby, the sub-deflector scans the area having a size of 10 .mu.m.times.100 .mu.m, and it should be noted that a plurality of such sub-deflector areas form the cell region 14. As already noted, the cell region 14 has a size of about 2 mm in the X-direction in correspondence to the coverage area of
the main deflector.
The cell stripe 16 may have a size smaller than the foregoing size of 10 .mu.m.times.100 .mu.m. Such a reduction in the cell stripe 16 is achieved easily by turning off the electron beams from the edge region of the BAA mask. In order to reduce the size of the cell stripe in the i-direction, one may reduce the stroke of scanning in the Y-direction or turn off the beams from the part of the BAA mask corresponding to the edge part of the cell stripe. It in advantageous to set the length of the cell stripe coincident to the pitch of repetition for the exposure pattern when the exposure pattern includes a repetition.
Next, the general construction of a conventional electron beam exposure system used for the BAA exposure will be described with reference to FIG. 3 together with problems thereof.
Referring to FIG. 3, the electron beam exposure system comprises generally an electron optical system 100 that produces a focused electron beam and a control system 200 for controlling the electron optical system 100. The electron optical system
100 includes an electron gun 101 as an electron beam source, and the electron gun 101 emits the electron beam as a divergent electron beam along a predetermined optical axis O.
The electron beam thus produced by the electron gun 101 is shaped by an aperture 102a provided on an aperture plate 102, wherein the aperture 102a shapes the electron beam upon passage therethrough. The aperture 102a is in alignment with the optical axis O, and shapes the incident electron beam to have a rectangular cross section.
The shaped electron beam thus formed is focused on a BAA mask 110 by an electron lens 103, wherein the BAA mask carries thereon a blanking aperture array. Thus, the electron lens 103 projects the image of the aforementioned rectangular aperture
102a on the BAA mask 110. On the mask 110, there are formed a plurality of small apertures corresponding to the exposure dots to be exposed on a semiconductor substrate, and an electrostatic deflector is provided on the BAA mask 110 in correspondence to each of the apertures. The electrostatic deflector is controlled by a driving signal E to pass the electron beam directly in a non-activated state, or to deflect the passing electron beam in an activated state, so that the direction of the passing electron beam deviates from the optical axis O. As a result, and as will be described below, an exposure dot pattern corresponding to the non-activated apertures on the BAA mask 110 is formed on the semiconductor substrate.
The electron beam passed through the BAA mask 110 is focuses at a focal point f.sub.1 on the optical axis O after passing through the electron lenses 104 and 105 that form a demagnifying optical system, and the image of the selected apertures is projected at the focal point f.sub.1. The focused electron beam is further focused on a semiconductor substrate 115 held on a movable stage 114 by electron lenses 106 and 107 that form another demagnifying optical system, after passing through a round aperture 113a provided on a blanking plate 113. Thus, an image of the BAA mask 110 is projected on the substrate 115. Here, the electron lens 107 acts as an objective lens and includes therein various correction coils 108 and 109 for correcting focal point and aberrations as well as deflectors 111 and 112 for moving the focused electron beam over the surface of the substrate 115.
Further, there is provided an electrostatic deflector 116 between the lens 104 and lens 105, wherein the path of the electron beam is deviated from the optical axis O, which is set to pass through the round aperture 113a on the plate 113, upon activation of the electrostatic deflector 116. As a result, it becomes possible to switch the electron beam on/off at a high speed on the semiconductor substrate 115. Furthermore, the electron beams, which have been deflected by the electrostatic deflectors on the apertures on the BAA mask 110 described above, deviate also from the round aperture 113a. Therefore, the electron beams thus deflected do not reach the semiconductor substrate and it becomes possible to control the exposure dot pattern on the substrate 115.
The electron-beam exposure system of FIG. 3 uses a control system 200 for controlling such exposure operations. The control system 200 includes an external storage device 201, such as a magnetic disk drive or a magnetic tape drive for storing data relating to the patterns of the semiconductor device to be exposed.
The data stored in the storage device 201 is read out by a CPU 202, and the data compression thereof is removed by a data expansion unit 203. Thereby, the data is converted to the exposure dot data which switches the individual apertures on the BAA mask 110 on/off according to the desired exposure pattern. In order to enable a delicate correction of the exposure pattern, the electron-beam exposure system of FIG. 3 carries out a multiple exposure of exposure dots on the substrate 115, wherein N independent exposure patterns are superposed. Accordingly, the data expansion unit 203 includes N circuits 203.sub.1 to 203.sub.N, wherein the circuits 203.sub.1 to 203.sub.N generate N sets of mutually independent exposure dot pattern data used for carrying out the foregoing multiple exposures superposed N times, based upon the exposure data provided from the external storage 201.
Each of the circuits 203.sub.1 to 203.sub.N is composed of a buffer memory 203a for holding exposure data supplied from the external storage 201, a data expansion section 203b which generates the dot pattern data representing the exposure dot pattern based upon the exposure data held in the buffer memory 203a, and a canvas memory 203c for holding the dot pattern data expanded by the data expansion section 203b, wherein the data expansion unit 203 supplies the dot pattern data held in the canvas memory 203c to a corresponding shoot memory 204. More specifically, the output shoot memory 204 includes N memory circuits 204.sub.1 -204.sub.N corresponding to the N data expansion circuits 203.sub.1 to 203.sub.N, and each of the memory circuits, e.g, the circuit 204.sub.1, includes 128 memory circuits each formed of a dynamic random access memory, in correspondence to the total of 128 apertures aligned in the X-direction on the BAA mask 110. Thus, each of the 128 memory circuits is supplied with one-bit data that switches the aperture on the BAA mask 110 on/off, from said canvas memory 203c. The memory circuits 204.sub.1 to 204.sub.N, in turn, supply the one-bit data held therein to the BAA mask 110 after converting the same into analog signals by means of corresponding D/A converters 205.sub.1 to 205.sub.N. As a result, the electrostatic deflectors aligned in the Y-direction on said BAA mask 110 in correspondence to the apertures are activated sequentially.
Furthermore, the electron-beam exposure system of FIG. 3 includes an exposure control unit 206 which is supplied with a control signal from the CPU 202 based upon the control program stored in the external storage device 201, wherein the exposure control unit 206 controls the operation of the data expansion circuit 203 and the shoot memory 204, the transfer of data from the data expansion circuit 203 to the shoot memory 204, and the activation of the BAA mask 110 by means of the D/A converter
205. Furthermore, the exposure control unit 206 controls the main deflector 111 and the sub-deflector 112 via a main deflector control circuit 207 and a sub-deflector control circuit 208, such that the electron beam scans over the surface of the substrate 115.
The system of FIG. 3 further includes correction circuits 207a and 208a for compensation of beam distortion respectively caused by the main deflector and the sub-deflector, wherein the correction circuit 208a is supplied with correction coefficients GX and GY for gain, RX and RY for pattern rotation, OX and OY for pattern offset and HX and HY for trapezoidal pattern deformation, from a deflection correction memory 211, wherein the memory 211 stores the foregoing correction coefficients at respective addresses that correspond to the main deflection data supplied from the main deflector control circuit 207. Thus, in response to the main deflection data from the main deflector control circuit 207, the memory 211 supplies the foregoing correction coefficients GX and GY, RX and RY, OX and OY and HX and HY to the correction circuit 208a for correction of the sub-deflection data supplied from the sub-deflector control circuit 208. The sub-deflection data thus corrected is then supplied to the sub-deflector 112. Similarly, the memory 211 stores correction coefficients DX and DY for pattern distortion at respective addresses corresponding to the main deflection data and supplies the same to the correction circuit 207a in response to the main deflection data from the main deflector control circuit 207. Thereby, deflection data supplied from the main deflector control circuit 207 to the correction circuit 207a is corrected, and the deflection data thus corrected is supplied further to the main deflector 111.
Further, the memory 211 stores correction data SX and SY for dynamic astigmatic correction as well as correction data F for dynamic focusing correction at respective addresses corresponding to the main deflector data. Thereby, the dynamic astigmatic compensation is in response to the main deflection data achieved by way of the correction circuit 208a similarly as before. Further, the dynamic focusing control is achieved in response to the main deflection data by the memory 211 that drives the compensation coil 108.
The electron beam exposure system of FIG. 3 further includes a refocus control circuit 203e and a refocus data memory 203f for compensating for the divergence of electron beam caused by the Coulomb repulsion of electrons forming the focused electron beam. The refocus control circuit 203e thereby produces a drive signal of a refocus compensation coil 118 in response to the exposure pattern.
Next, the construction of the BAA mask 110 will be described briefly.
Referring to FIG. 4 showing a part of the BAA mask 110 in a plan view, the BAA mask 110 is formed of a thin silicon substrate or metal plate and carries a number or apertures 120 arranged in rows and columns, wherein each of the apertures 120
includes a drive electrode 121 and a ground electrode 122 at respective, mutually opposing edges of the aperture. In the illustrated example, eight of such apertures 120 are aligned in the Y-direction to form a column, and such aperture columns extending in the Y-direction are repeated 128 times in the X-direction. As a result, there are formed eight aperture rows A-H each extending in the X-direction, wherein each aperture row in fact is formed of two aperture rows. For example, the aperture row A is formed of an aperture row A.sub.1 and an aperture row A.sub.2, the aperture row B is formed of an aperture row B.sub.1 and an aperture row B.sub.2, . . . . Thereby, it will be noted that there is formed a pattern of apertures arranged in a row and column formation in a staggered relationship on the BAA mask 110. In all, 1024 apertures are formed on the BAA mask 110, each in fact including two apertures.
Upon illumination of the BAA mask 110 of FIG. 4 by an electron beam produced by the electron gun 101 and shaped by the aperture 102a, it will be noted that a bundle of electron beam including a row and column formation of electron beam elements is produced as a result of beam shaping at the apertures on the BAA mask 110. The electron beam elements thus produced are then focused upon the substrate 115 after demagnification by the electron lenses 104 and 105 as well as the electron lenses 106
and 107, and an exposure dot pattern including 1024 exposure dots in maximum, each having a site of 0.08 .mu.m.times.0.08 .mu.m, is exposed on the substrate 115. In such an exposure, all the exposure dots on the substrate 115 are exposed simultaneously.
It should be noted that the electron beam elements forming the-electron beam bundle scans the surface of the substrate 115 in the Y-direction as a result of energization of the deflector 112, and each point on the substrate 115 experiences a multiple exposure of the exposure dots in correspondence to the foregoing apertures forming the aperture rows A-H, wherein such a multiple exposure is repeated eight times in the maximum.
More specifically, a row of exposure dots corresponding to the aperture row A1 are exposed on the substrate 115, followed by an exposure of the exposure dots corresponding to the aperture row B1, such that the exposure dots corresponding to the aperture row B1 are superposed upon the exposure dots corresponding to the aperture row A1. Further, the exposure dots corresponding to the aperture rows C1, D1, . . . are superposed thereon. A similar situation holds also in the exposure of dots by using the aperture rows A2, B2, C2, . . . . As the apertures in the row A1 and the apertures in the row A2 are formed with a staggered relationship as already noted, the exposure dots formed by the aperture rows A2 fill the gap between the exposure dots formed by the aperture rows A1, and there is formed a single exposure line extending in the X-direction as a result of such a multiple exposure of the exposure dots. By forming the apertures on the BAA mask with a staggered relationship as indicated in FIG. 4, it is possible to reduce the Coulomb repulsion between the electron beam elements by avoiding excessive approaching of the electron beam elements. When such a Coulomb repulsion occurs in the electron beam elements, the effective focal length of the electron lens increases.
In the simplest case of exposure, the same exposure data is supplied consecutively from the aperture row A1 to the aperture rows B1, C1, D1, E1, F1, G1 and H1, or from the aperture row A2 to the aperture rows B2, C2, D2, E2, F2, G2 and H2, and there occurs a multiple exposure of the exposure dots with a desired dose. Further, it should be noted that it is possible to achieve an extremely delicate control of the exposure pattern by changing the exposure data in each aperture group such as a group K1, K2, K3 and K4, wherein, in the illustrated example, the aperture group K1 includes the aperture rows A and B, the aperture group K2 includes the aperture rows C and D, the aperture group K3 includes the aperture rows E and F, and the aperture group K4 includes the aperture rows G and H. As a result of such a multiple exposure process, it should be noted that different patterns are superposed. Such a multiple exposure process is extremely useful for compensating for the proximity effect that is an unwanted exposure caused by the electrons backscattered from the substrate. By using the foregoing multiple exposure process, it is possible to compensate for the proximity effect efficiently by a single scanning of the electron beam bundle.
FIG. 5 shows another conventional example of the BAA mask 110, wherein it will be noted that the apertures forming the groups K1-K4 are formed with a positional offset with respect to the apertures of other groups. For example, the aperture a of the group K1 is offset with respect to the corresponding aperture c of the group K2 in the X-direction with a quarter of the pitch of the apertures on the BAA mask 110. Similarly, the aperture a' of the group K3 is offset with respect to the corresponding aperture a of the group K1 in the Y direction by a quarter pitch. Generally, by providing the apertures on the BAA mask 110 with a mutual offset of M/N pitch (M<N) in one or both of the X- and Y-directions, it is possible to achieve the desired modification of the exposure pattern with increased precision. More detailed description of the M/N pitch shift of the BAA mask is given in the U.S. Pat. No. 5,369,282, which is incorporated herein as reference.
In such a conventional BAA exposure system, it will be noted that the data transfer rate of the dot pattern data to the BAA exposure system is a critical factor, wherein such a data transfer of the dot pattern data includes decompression or expansion of pattern data in the data expansion unit 203b to form dot pattern data and storage of the dot pattern data thus expanded in the canvas memory 203c. In order to achieve a fast data transfer, conventional BAA exposure system has to use a very large memory for the shoot memories 204.sub.1 -204.sub.N, while it is difficult, at least at the present juncture, to have a shoot memory that can store the dot pattern data of whole chip or several chips.
Thus, in the conventional BAA exposure system, it has been practiced to interrupt the exposure after exposing the dot pattern data held in the canvas memory 203c for carrying out a data expansion of next pattern data. After the data expansion of the next pattern data, the exposure is resumed based upon the newly expanded data in the canvas memory 203c. In order to facilitate the exposure process, it is also practiced to carry out exposure while expanding the pattern data in the data expansion unit 203b.
It should be noted, however, that the exposure throughput is limited in
such a conventional exposure process by the capacity of the shoot memory 204 and the rate of data expansion in the unit 203b. Further, such a conventional exposure process that overwrites the exposure data in the canvas memory by the next data, is disadvantageous in the point that it is not possible to inspect the exposure dot data in the event there occurred anomaly or defect in the result of exposure. Further, currently available dynamic random access memories suitable for canvas memory are volatile in nature and cannot save the expanded dot pattern for repeated use.
In addition, the conventional BAA exposure system has a drawback in that the throughput for exposing a whole area on the substrate 115 decreases substantially as compared with the conventional variable-shaped beam exposure process, unless the transfer of the dot pattern to the exposure system is achieved at very high speed.
In the BAA exposure system described above, it should further be noted that the aperture b in FIG. 4 is separated from the aperture a in the Y-direction by a distance corresponding to six apertures. Thus, the aperture b is given with the exposure data identical to the data supplied to the aperture a with a delay of six clocks. In such a construction, the number of channels for supplying the dot pattern data to each of the apertures aligned on the BAA mask 110 in the Y-direction is reduced to one half as compared with the case of supplying independent exposure dot data to the apertures a and b. Further, independent-activation of the aperture groups K1-K4 increases the number of channels by four. Similarly, respective dot pattern data are supplied to the aperture e, which is separated on the BAA mask 110 from the aperture a in the Y-direction by a distance of three apertures, with a delay of three clocks. Thereby, the timing of exposure has to be set extremely stringently in order to achieve exact alignment of the exposure dot formed by the aperture a and the exposure dot formed by the aperture e on the BAA mask 110.
Conventionally, such a stringent timing control of the dot pattern data has been achieved in each channel by controlling the timing of reading the data based upon the predicted delay of the channel, while such a timing control, requiring a precision of within several nanoseconds, has been extremely difficult. It is also proposed to provide an offset to the exposure data so as to compensate for the delay caused in the dot pattern data, while such a modification of the original exposure data has to be changed depending upon the exposed pattern and such a process increases the complexity of preparing the exposure pattern.
Thus, the present embodiment has an object to provide a charged particle exposure system and method for exposing versatile patterns on an object by means of a charged particle beam that forms an exposure dot pattern, in which the creation of dot pattern data representing the exposure dot pattern and the exposure of the object by means of the charged particle beam can be achieved separately.
Further, the present embodiment provides a charged-particle-bean exposure method and system that is capable of holding a large amount of dot pattern data representing the exposure dot pattern and that can control a blanking aperture array based upon the dot pattern data at a high speed for producing a charged particle beam bundle including a number of charged particle beams in correspondence to each dot of the exposure dot pattern.
Hereinafter, the construction of the BAA exposure system according to a first embodiment of the present invention will be described.
FIG. 6 is a block diagram showing a part of the charged particle beam exposure system according to a first embodiment of the present invention.
Referring to FIG. 6, there is provided a hard disk device 301 corresponding to the external storage device 201 of FIG. 3 for storing pattern data to be exposed. The pattern data in the hard disk device 301 in read out therefrom under control of a central controller 302 corresponding to the CPU 202, wherein the exposure data thus read out is stored in a buffer memory 303 corresponding to the buffer memory 203a of FIG. 2. The exposure data in the buffer memory 303 is then transferred under control of a data transfer controller 304 to a data expansion unit 305 corresponding to the expansion unit 203b and a canvas memory 203c, wherein the exposure data is expanded in the expansion unit 305 to bitmap data or dot pattern data that represents the exposure pattern on the substrate 115 in the form of exposure dots. Hereinafter, the expansion unit 305 will be referred to as a canvas memory.
The dot pattern data thus obtained in the canvas memory 305 is then supplied, by means of a data transfer unit 306, to a number of hard disk drives 309a-309j under control of the foregoing transfer control circuit 304, wherein the transfer of the dot pattern data is achieved via transfer channels 307a-307j and transfer controllers 308a-308j respectively cooperating with the hard disk drives 309a-309j.
In the exposure system that uses the BAA mask 110 of FIG. 4, which includes 1024 apertures (=128.times.8), it should be noted that one has to provide 512 channels (=1024.div.2) for driving the BAA mask 110 when the same dot pattern data is supplied to the aperture a and further to the aperture b with a delay of six clocks for the aperture b. In the event the accuracy of exposure is negotiable, one may supply the dot pattern data of the aperture a of the group K1 to the corresponding aperture c of the group K2 after a delay of three exposure clocks, further to the corresponding aperture of the group K3 after a delay of additional three clocks, and further to the corresponding aperture of the group K4 after a delay of additional three clocks. In this case, one can reduce the independent channels to 256 (=1024.div.4).
When exposing an eight-inch wafer with a throughput of 20 wafers per hour, it is necessary to expose one wafer with a duration of 180 seconds. Defining a frame on the wafer as a stripe region having a width of 2 mm and extending in the Y-direction for a length covered by the movement of the stage 114 an indicated in FIG. 1, exposure of ten such frames is required in order to complete the exposure of one chip having a size of 20 mm for each edge. In each chip, the frame forms a limited strip or single chip fame" having a limited size of 2.times.20 mm, while exposure of such a single chip frame requires exposure dot data of 25 Gbits, assuming that four channels are used in the exposure
As there are 10 chip frames in one chip, it is necessary to transfer the dot pattern data for one chip frame in 18 seconds for achieving the foregoing exposure of a single chip, while this means that a data transfer rate of 174 Mbyte/sec (=25
Gbit/18 sec) is required for transferring the exposure dot data to the BAA exposure system. Here, it should be noted that the same exposure dot data is used in the BAA exposure system for exposing the same chips on the wafer. Such a data transfer rate is achieved by arranging 10 hard disk drives 309a-309j each having a data transfer rate of 20 Mbyte/sec in parallel, such that the data transfer occurs in parallel in these hard disk drives.
As there are 512 independent channels for the apertures on the BAA mask 110, each of the hard disk drives 309a-309j store dot pattern data for about 52 channels.
Meanwhile, it should be noted that the exposure control system of FIG. 6 achieves a refocus control such that the amount of refocus compensation increases with increasing number of the apertures that are turned on the BAA mask 110, in order to avoid the divergence of the electron beams as a result of the Coulomb interaction of the electrons in the beams. In order to achieve such a refocus control, the canvas memory 305 creates refocus data when expanding the dot pattern data, based upon the number of bite forming the dot pattern data, wherein such refocus data is transferred from the data transfer unit 306 to another separate hard disk drive 312 via a transfer channel 320 and a transfer control circuit 312. Thereby, the hard disk drive 322
constitutes the refocus data memory 203f.
It should be noted that the foregoing dot data pattern is expanded and transferred to the hard disk drives 309a-309j for each of the cell stripes shown in FIG. 2. In such a data transfer of the refocus data, the number of the turned-on apertures in an exposure cycle in evaluated, and the refocus data is produced for each cell region 14 called also "band," based upon the same. The refocus data thus produced is then transferred to the disk drive 312. Thereby, the disk drives 309a-309j and the disk drive 312 store the dot pattern data for one chip as well as the refocus data.
In the construction of FIG. 6, each of the disk drives such as the disk drive 309a cooperates with a number of high speed shoot memories such as 310A.sub.1a, 310B.sub.1a, . . . 310A.sub.52a, 301B.sub.52a, wherein the shoot memories 310A correspond to the shoot memory 204 of FIG. 3. There are in all 104 such shoot memories (=52 channels.times.2) connected to each of the disk drives via the foregoing transfer controller such as the controller 308a. Each of the shoot memories 310 may be formed of a high speed bitmap memory such as a dynamic random access memory. Thereby, it should be noted that the shoot memories are arranged to form memory pairs such that the memories 310A.sub.1a and 310B.sub.1a form a pair, . . . the memories
310A.sub.52a and 310B.sub.52a form a pair, wherein the memories forming a memory pair such as the memories 310A.sub.1a and 310B.sub.1a are connected to a corresponding selector such as a selector 311.sub.1a. Thereby, the selector 311.sub.1a selects the output of one of the cooperating memories 310A.sub.1a and 310A.sub.1b and transfers the same to a corresponding parallel-to-serial converter 312.sub.ij. A similar construction exists also for other hard disk drives such as the hard disk drive 309j or
322. Thereby, it will be noted that the hard disk drives 309a-309j are disposed between the canvas memory 305 corresponding to the canvas memory 203c and the shoot memories 310A.sub.1a, 310B.sub.1a -310A.sub.52j, 310B.sub.52j. Further, there are provided also high speed shoot memories 323A and 323B cooperating with the hard disk drive 322 for storing the refocus data transferred thereto via the transfer controller 321, wherein the memories 323A and 323B form a part of the refocus data memory
203f. The memories 323A and 323B are thereby connected to an output circuit 325 via a selector 324.
In order to control the foregoing various elements, there is provided an exposure controller 330 corresponding to the exposure controller 206 of FIG. 3, wherein the exposure controller 330 controls the data transfer of the dot pattern data for one chip frame from all of the hard disk drives 308a-308i to the respective memory pairs by way of a transfer controller 322, such that the dot pattern data is stored, in each memory pair, in one of the memories such as the memories 310A.sub.1j -310A.sub.52j or the memories 310B.sub.1j -310B.sub.52j. Further, the exposure controller 330 controls the transfer controller 332 such that the refocus data in the hard disk drive 322 is transferred to one of the memories 323A and 323B that holds the refocus data.
In order to guarantee the synchronization of data transfer, each of the transfer controllers 308a-308j and 321 issues a completion signal indicative of completion of data transfer to the exposure controller 330 via the transfer controller 332, such that any delay in data transfer caused for example by defects in the hard disk medium is compensated for.
Upon reception of the completion signal, the exposure controller 330 carries out reading of the dot pattern data as well as the refocus data from the memories 310A.sub.1j -310A.sub.52j or from the memories 310B.sub.1j -310B.sub.52j, wherein the transfer controller 332 reads out the dot pattern data, under control of the exposure controller 330, from the memories 310A.sub.1a -310A.sub.52a or from the memories 310B.sub.1a -310B.sub.52a substantially simultaneously and transfers the same to the parallel-to-serial converters 312.sub.1a -312.sub.52a, . . . 312.sub.1j -312.sub.52j. Further, the refocus data is read out from one of the memories 323A and 323B and is transferred to the output circuit 325 via the selector 324.
After the foregoing data transfer is completed, the exposure controller 330 activates a similar data transfer from the other memories such as the memories 310B.sub.1a -310B.sub.52a, . . . 310B.sub.1j -310B.sub.52j as well as from the other memory 323B, assuming that the data transfer has been made in the previous step from the memories 310A.sub.1a -310A.sub.52a, . . . 310A.sub.1j -310A.sub.52j and from the other memory 323A.
It will be noted that the system of FIG. 6 further includes a SEM/MD controller 335, while thin controller 335 is used for controlling the SEM operation or marker detection of the electron beam exposure system. As the controller 335 is outside the scope of the present invention, further description thereof will be omitted.
According to the exposure system of FIG. 6, it will be noted that the expansion of the dot pattern data can be achieved separately to the exposure operation. This in turn means that the throughput of exposure is not influenced by the rate of the data expansion. By using such pre-expanded dot pattern data stored in the hard disk drives, it is possible to expose the pattern of integrated circuits repeatedly on or more waters by merely reading out the dot pattern data from the hard disk drives. As such hard disk drives are not volatile in nature, it is possible to examine the dot pattern data held in the hard disk drive in the event there occurred an anomaly in the exposed pattern for any defects, As the actual exposure is achieved by transferring the dot pattern data from each of the hard disk drives to a number of high speed memories cooperating with each of the hard disk drives in parallel, it is possible to read out and transfer the dot pattern data from such high speed memories, and a high exposure throughput can be attained as a result. As the reading of the dot pattern data is achieved from the memories 310A.sub.1a -310B.sub.52j in synchronization under control of an exposure clock, the exposure dots are formed on the substrate 115 with exact alignment. One may use high speed volatile memories such as a dynamic random access memory or static random access memory for the memories 310A.sub.1a -310B.sub.52j as well as for the memories 323A or 323B.
In the construction of FIG. 6, it should be noted that the exposure controller 330 controls the transfer of the dot pattern data such that the reading of the dot pattern data is carried out from the first memory set that includes the memories
310A.sub.1a, . . . 310A.sub.52a, . . . 310A.sub.1j, . . . 310A.sub.52j, while simultaneously writing the dot pattern data into the second memory set that includes the memories 310B.sub.1a, . . . 310B.sub.52a, . . . 310B.sub.1j, . . . 310B.sub.52j, or vice versa. Thereby, it is possible to eliminate the interruption of the exposure that may occur while rewriting the memories by next dot pattern data or refocus data.
FIG. 7 shows the construction of the parallel-to-serial converter such as the converter 312.sub.1a in a block diagram.
Referring to FIG. 7, the parallel dot pattern data of 64 bits read out form a corresponding high speed memory such as the memory 310A.sub.1a and is supplied, via a corresponding selector such as the selector 311.sub.1a, to a parallel-to-serial conversion unit 350 that includes a register. Thereby, the register holds the parallel dot pattern data supplied thereto and outputs the same as serial dot pattern data with a clock speed of 400 MHz.
The serial dot pattern data thus obtained is then supplied from the conversion unit 350 to an inversion switching circuit 352 for causing a selective data inversion, wherein the inversion switching circuit 352 supplies the serial dot pattern data to a delay circuit 353 that causes a delay in the serial data supplied thereto, with an inversion in the polarity of the serial dot data in response to a control signal from the central controller 302. By providing the inversion switching circuit 352, it is possible to select the positive exposure and negative exposure of the exposure dot on the substrate 150 simply under control of the central controller 302, while such a negative/positive control of the exposure dot pattern is extremely effective for compensating for the proximity effect.
The serial dot pattern data thus delayed in the delay circuit 353 is then supplied to next delay circuits 354 and 355 in parallel for delaying, wherein the serial dot pattern data thus delayed in the circuits 354 and 355 are supplied further to phase correction circuits 356 and 357, respectively for timing correction. Thereby, the serial dot pattern that has experienced timing correction in the phase correction circuit 356 is supplied to the drive electrode 121 on the BAA mask 110 via a selector 358
and the D/A converter 205 described in FIG. 3, wherein the selector 358 selects either the serial dot pattern data or the SEM/MD data in response to a SEM/MD control signal supplied from the control circuit 335. Similarly, the serial dot pattern processed by the phase correction circuit 357 is supplied to the BAA mask 110 after passing through a selector 359 similar to the selector 358 and after a D/A conversion in the D/A converter 205.
Here it should be noted that the delay circuit 353 provides a delay to the serial dot pattern data based upon a control signal from the central controller 302, wherein the amount of delay of the delay circuit 353 is changed with respect to the delay of other channels. For example, the delay circuit 353 or a parallel-to-serial conversion circuit 312 that is included in one of the circuits 312.sub.1a -312.sub.52j and controls the apertures a and b on the BAA mask 110 of FIG. 4 or FIG. 5, provides a delay of three clocks to the serial dot pattern data, wherein the delay circuits 354 and 355 provide respectively a zero clock delay and 6 clock delay. Similarly, the parallel-to-serial conversion circuit 312 for the apertures c and d causes a delay of 12 clocks. Here, the clocks have a frequency of 400 MHz and are used as the data transfer clock as will be described below. In each of the parallel-to-serial conversion circuits 312, it should be noted that the delay circuits 354 and 355 are set, by the central controller 302, to have a predetermined delay correspondence to the distance between the apertures exposed consecutively by the same dot pattern data. For example, the delay circuit 355 for the aperture b provides a delay of 6 clocks with respect to the delay circuit 354 in correspondence to the separation from the aperture a of 6 clocks.
As a result of the setting of the delay as set forth above, the dot pattern data shown in FIG. 8B is supplied to the aperture a in synchronization to the data transfer clock of FIG. 3A. Further, the same dot pattern data as the one shown in FIG.
8B is supplied to the aperture b after a delay of 6 clocks as indicated in FIG. 8C. Further, the next dot pattern data different from the one shown in FIG. 8B is supplied to the aperture e as indicated in FIG. 8D with a delay of three clocks from the data of FIG. 8B, and the same dot pattern data as indicated in FIG. 8D is supplied to the aperture f as indicated in FIG. 8E with a delay of 6 clocks. Similarly, the next dot pattern data different from any of the foregoing dot pattern data is supplied to the aperture c with a delay of 12 clocks with respect to the data of FIG. 8B as indicated in FIG. 8F, and the same dot pattern data as the data of FIG. 8F is supplied to the aperture d with a delay of 6 clocks from the data of FIG. 8F, as indicated in FIG. 8G.
It should be noted that the phase correction circuits 356 and 357 are used to correct the timing of the data and provides a minute delay to the serial dot pattern data supplied thereto under control of the central controller 302, wherein the timing correction is made with a division of 1/10 the interval of the data transfer clock shown in FIG. 8A.
In the exposure system described above, the delay of the dot pattern data is made in each of the channels. Thus, there is no need to adjust the timing of the dot pattern data when transferring the dot pattern data, and the control of the data transfer to the BAA mask is substantially simplified. Thereby, it should be noted that the relative timing between the channels is determined by the delay circuit 353 while the relative timing within the channel is determined by the delay circuits 354
and 355. As the timing of the dot pattern data is further adjusted by means of the phase correction circuits 356 and 357, it is possible to align the exposed dots exactly on the substrate 115.
As already noted, the selectors 358 and 359 are supplied with one bit data indicative of the SEM/MD data as well as a selection control signal from the SEM/MD controller 335. Thus, the selectors 358 and 359 selectively outputs the SEM/MD data in response to the selection control signal when operating the electron beam exposure system in the SEM/MD mode, while in the normal exposure mode, the selectors 358 and 359 selectively supply the serial dot pattern data from the phase correction circuits
356 and 357 to the BAA mask 110.
It should be noted that the output circuit 325 of FIG. 6 supplies the refocus data supplied thereto via the selector 324 to the electron lens 109 in synchronization to the dot data from the output circuits 312.sub.1a -312.sub.52a, . . . ,
312.sub.1j -312.sub.52.sub.j for controlling the intensity of the electron lens 109.
Next, the operation of the exposure controller 330 will be described with reference to FIGS. 9A-9C.
Referring to FIG. 9A, the exposure controller 330 reads the dot pattern A shown in FIG. 9B from a memory such as the memory 310A.sub.1a, . . . by issuing a read control signal CW1 shown in FIG. 9A and transfers the dot pattern data A thus read out to the parallel-to-serial conversion unit 350 of a corresponding parallel-to-serial converter such as 312.sub.1a by issuing a transfer control signal CR.sub.1 shown in FIG. 9C. Similarly, the dot pattern data B shown in FIG. 9B is subsequently read out from a different memory such as the memory 310B.sub.1a in response to the read control signal CW.sub.2 shown in FIG. 9A, wherein the exposure controller 330 causes a transfer of the data B thus read out to the parallel-to-serial conversion unit 350
of the corresponding parallel-to-serial converter by issuing a transfer control signal CR.sub.2.
In the event the same dot pattern data B is used repeatedly in the exposure, it should be noted that the exposure controller 330 issues the transfer control signals CR.sub.2 -CR.sub.4 without issuing the read control signal. Thereby, the same dot pattern data held in the memory 310B.sub.2a, . . . are repeatedly transferred to the corresponding parallel-to-serial converts 312.sub.1a, . . . . As the same dot pattern data is used for such a repetitive exposure of dot patterns already held in the memories 310A or 310B, it should be noted the stop for expanding the data in the hard disk drive such as the hard disk 309a for each exposure can be omitted. Here, the memories 310A and 310B includes the foregoing memories 310.sub.1a -310A.sub.52j and 310B.sub.1a -310B.sub.52j.
[second embodiment]
Next, a second embodiment of the present invention will be described.
In the conventional electron beam exposure systems that carry out variable beam shaping or block exposure, an example of which is described in the U.S. Pat. Nos. 5,173,582 or 5,194,741, the exposure and deflection of the electron beam are generally conducted repeatedly and alternately.
More specifically, the electron beam is deflected to a desired position on the substrate prior to the exposure or "shot," and various corrections such as beam position correction, focusing correction, aberration correction, and the like, are carried out for exposing a sharply defined patt