Variable shaped electron beam exposure system and method of writing a pattern by a variable shaped electron beam

An aperture member in a variable shaped electron beam exposure system to be used in combination with a counterpart aperture member is provided for a variable shaped electron beam exposure. The counterpart aperture member has a first aperture and the aperture member has a second aperture for shaping an electron beam, wherein the aperture member further has at least one aperture mask pattern having a shape different from a shape of the second aperture and the at least one aperture mask pattern has a smaller size than the first aperture so that the electron beam is shaped in accordance with the shape of the at least one aperture mask pattern except when the electron beam is shaped by a combination of the first and second apertures for the variable shaped electron beam exposure.

BACKGROUND OF THE INVENTION
 The present invention relates to a variable shaped electron beam exposure
 system, and a method of writing a pattern on a resist with a variable
 shaped electron beam exposure as well as a storage medium having stored a
 computer program for execution of a variable shaped electron beam exposure
 to write any patterns on the resist, and more particularly to a variable
 shaped electron beam exposure system suitable for forming application
 specific integrated circuits (ASICs) with less regularly repeated patterns
 or for logic devices of microcomputers, and a method of writing a pattern
 on a resist with a variable shaped electron beam exposure for forming the
 same as well as a storage medium having stored a computer program for
 execution of a variable shaped electron beam exposure to write any
 patterns on the resist.
 The electron beam exposure methods are classified into two typical types.
 The first one is one-shot electron beam exposure in projection mode using
 a mask. The second one is a variable shaped electron beam exposure without
 use of any mask.
 The one-shot electron beam exposure systems operable in projection mode
 using the mask are disclosed in Japanese laid-open patent publications
 Nos. 6-140305 and 7-56318. An electron beam is emitted from an electron
 gun for projecting a pattern image of a mask through a projection system
 onto a resist over a wafer. This method is suitable for writing regularly
 repeated patterns on the resist over the wafer, for example, in order to
 form dynamic random access memory devices and static random access memory
 devices.
 In the meantime, the variable shaped electron beam exposure method is
 suitable for random patterns with less regularly repeated patterns, for
 example, in order to form the application specific integrated circuits
 (ASIC) and the logic devices of the microcomputer.
 FIG. 1A is a view illustrative of first and second aperture plates with
 first and second apertures used in a conventional variable shaped electron
 beam exposure system. The conventional variable shaped electron beam
 exposure system has a first aperture plate 31 with a first aperture 30
 which is rectangular-shaped and a second aperture plate 33 with a second
 aperture 32 which is also rectangular-shaped, so that the electron beam
 emitted from the electron gun is firstly defined by the first aperture 30
 and then deflected by a deflector not illustrated for subsequent second
 definition of the electron beam by the second aperture 33. The electron
 beam shaped by the first and second apertures 30 and 32 are transmitted to
 the resist over the wafer. By controlling or adjusting the deflection of
 the electron beam by the deflector, the shape of the electron beam having
 penetrated through the first and second apertures 30 and 32 are varied.
 FIG. 1B is a plane view illustrative of first and second apertures of the
 conventional variable shaped electron beam exposure system. The first and
 second aperture plates 31 and 33 are placed to have a distance in a
 direction along which the electron beam is transmitted. The first and
 second aperture plates 31 and 33 are also placed to be relatively
 displaced from each other on a plane vertical to the direction along which
 the electron beam is transmitted, so that, in the plane view, the fist and
 second apertures 30 and 32 are partially overlapped to have a
 rectangular-shaped overlap area 34 through which the electron beam is
 transmitted. Namely, the electron beam having penetrated through both the
 first and second apertures 30 and 32 are defined to have the same shape as
 the rectangular-shaped overlap area 34. As a result, the resist over the
 wafer is exposed to the rectangular-shaped electron beam having been
 shaped by the first and second apertures 30 and 32.
 FIG. 1C is a plane view illustrative of completely overlapping first and
 second apertures of the conventional variable shaped electron beam
 exposure system. The first and second apertures completely overlap to have
 a maximum overlap area 35 with the same shape as the first and second
 apertures 30 and 32. The maximum overlap area 35 may be considered to be a
 maximum electron beam exposure area which means the maximum area of a
 single time variable shaped electron beam exposure. This means it
 necessary to divide each of the required patterns with optional shapes
 into plural rectangular-shaped unit patterns which are, however, smaller
 in size than the maximum electron beam exposure area so that the variable
 shaped electron beam exposures are sequentially conducted to sequentially
 write the divided rectangular shaped unit patterns. FIG. 2 is a plane view
 illustrative of one of required patterns, each of which is divided into
 unit patterns by separation lines 36. Six required patterns with different
 shapes are individually divided by the separation lines 36 into thirty
 three rectangular-shaped unit patterns which are smaller in size than the
 maximum electron beam exposure area. The electron beam is variably shaped
 by adjusting the overlapping area of the first and second apertures 30 and
 32 so that the electron beam has the same shape as the rectangular shaped
 unit pattern.
 In recent years, it has been required to shorten the necessary time for the
 electron beam lithography process as the variation of the logic devices
 has been increased and the production in a small scale has been required.
 However, the required patterns with different shapes are individually
 divided into many rectangular-shaped unit patterns which are smaller in
 size than the maximum electron beam exposure area for sequential exposures
 for every the rectangular-shaped unit patterns. This means it difficult to
 shorten the necessary time for the electron beam lithography process,
 resulting in a drop of the throughput.
 If further the required pattern has a complicated shape, then such the
 pattern is divided into may fine rectangular shaped unit patterns. This
 may raise an issue of increased variation in size of the required pattern,
 whereby the accuracy in writing the pattern is dropped.
 In the above circumstances, it had been required to develop a novel
 variable shaped electron beam exposure system and a method of writing a
 pattern on a resist with a variable shaped electron beam exposure free
 from the above problems and disadvantages, as well as a storage medium
 having stored a computer program for execution of a variable shaped
 electron beam exposure to write any patterns on the resist.
 SUMMARY OF THE INVENTION
 Accordingly, it is an object of the present invention to provide a novel
 variable shaped electron beam exposure system free from the above
 problems.
 It is a further object of the present invention to provide a novel variable
 shaped electron beam exposure system which allows shortening the necessary
 time for an electron beam lithography process.
 It is a still further object of the present invention to provide a novel
 variable shaped electron beam exposure system which allows obtaining a
 high throughput.
 It is yet a further object of the present invention to provide a novel
 variable shaped electron beam exposure system capable of writing any
 complicatedly shaped patterns with a minimum variation in size.
 It is a further more object of the present invention to provide a novel
 variable shaped electron beam exposure system capable of writing any
 complicatedly shaped patterns with a high accuracy in size.
 It is still more object of the present invention to provide a novel method
 of writing a pattern on a resist with a variable shaped electron beam
 exposure free from the above problems.
 It is moreover object of the present invention to provide a novel method of
 writing a pattern on a resist with a variable shaped electron beam
 exposure, which allows shortening the necessary time for an electron beam
 lithography process.
 It is another object of the present invention to provide a novel method of
 writing a pattern on a resist with a variable shaped electron beam
 exposure, which allows obtaining a high throughput.
 It is still another object of the present invention to provide a novel
 method of writing a pattern on a resist with a variable shaped electron
 beam exposure for writing any complicatedly shaped patterns with a minimum
 variation in size.
 It is yet another object of the present invention to provide a novel method
 of writing a pattern on a resist with a variable shaped electron beam
 exposure for writing any complicatedly shaped patterns with a high
 accuracy in size.
 It is further another object of the present invention to provide a storage
 medium having stored a computer program for execution of a variable shaped
 electron beam exposure to write any patterns on the resist free from the
 above problems.
 It is an additional object of the present invention to provide a storage
 medium having stored a computer program for execution of a variable shaped
 electron beam exposure to write any patterns on the resist for shortening
 the necessary time for an electron beam lithography process.
 It is a still additional object of the present invention to provide a
 storage medium having stored a computer program for execution of a
 variable shaped electron beam exposure to write any patterns on the resist
 for obtaining a high throughput.
 It is yet an additional object of the present invention to provide a
 storage medium having stored a computer program for execution of a
 variable shaped electron beam exposure to write any patterns on the resist
 for writing any complicatedly shaped patterns with a minimum variation in
 size.
 It is a further additional object of the present invention to provide a
 storage medium having stored a computer program for execution of a
 variable shaped electron beam exposure to write any patterns on the resist
 for writing any complicatedly shaped patterns with a high accuracy in
 size.
 The present invention provides an aperture member in a variable shaped
 electron beam exposure system. The aperture member is to be used in
 combination with a counterpart aperture member for a variable shaped
 electron beam exposure. The counterpart aperture member has a first
 aperture and the aperture member has a second aperture for shaping an
 electron beam, wherein the aperture member further has at least one
 aperture mask pattern having a shape different from a shape of the second
 aperture and the at least one aperture mask pattern has a smaller size
 than the first aperture so that the electron beam is shaped in accordance
 with the shape of the at least one aperture mask pattern except when the
 electron beam is shaped by a combination of the first and second apertures
 for the variable shaped electron beam exposure.
 It is preferable that the counterpart aperture member is used as a first
 aperture member and the aperture member is used as a second aperture
 member so that the electron beam has been transmitted through the
 counterpart aperture member before the electron beam is subsequently
 transmitted through the aperture member. Each of write-required patterns
 is divided into a plurality of unit patterns in order to collate the unit
 patterns with the shape of the at least one aperture mask pattern so as to
 confirm any correspondence between the unit patterns and the shape of the
 at least one aperture mask pattern, so that if the correspondence between
 the unit patterns and the shape of the at least one aperture mask pattern
 is confirmed, then a deflection of the electron beam by a deflector is
 controlled to allow the electron beam to be transmitted toward the at
 least one aperture mask pattern of the aperture member whereby the
 electron beam is shaped in accordance with the shape of the at least one
 aperture mask pattern, and so that if, however, no correspondence between
 the unit patterns and the shape of the at least one aperture mask pattern
 is confirmed, then the deflection is controlled to allow the electron beam
 to be transmitted toward the second aperture whereby the electron beam is
 shaped by a combination of the first and second apertures for the variable
 shaped electron beam exposure.
 It is preferable that the aperture member has a set of plural aperture mask
 patterns differing in shape from each other. The unit patterns are
 collated with the shapes of the plural aperture mask patterns to confirm
 any correspondence between the unit patterns and the shapes of the plural
 aperture mask patterns, so that if any correspondence between the unit
 patterns and any of the shapes of the plural aperture mask patterns is
 confirmed, then the deflection is controlled to allow the electron beam to
 be transmitted toward a corresponding one of the plural aperture mask
 patterns of the second aperture member whereby the electron beam is shaped
 in accordance with the shape of the corresponding one of the plural
 aperture mask patterns, and so that if no correspondence between the unit
 patterns and any of the shapes of the plural aperture mask patterns is
 confirmed, then the deflection is controlled to allow the electron beam to
 be transmitted toward the second aperture whereby the electron beam is
 shaped by a combination of the first and second apertures for the variable
 shaped electron beam exposure.
 It is preferable that the second aperture is positioned at a center of the
 aperture member and the plural aperture mask patterns are positioned
 around the second aperture.
 It is preferable that the aperture member is used as a first aperture
 member and the counterpart aperture member is used as a second aperture
 member so that the electron beam has been transmitted through the aperture
 member before the electron beam is subsequently transmitted through the
 counterpart aperture member. Each of write-required patterns is divided
 into a plurality of unit patterns in order to collate the unit patterns
 with the shape of the at least one aperture mask pattern to confirm any
 correspondence between the unit patterns and the shape of the at least one
 aperture mask pattern, so that if the correspondence between the unit
 patterns and the shape of the at least one aperture mask pattern is
 confirmed, then a deflection of the electron beam by a deflector is
 controlled to allow that the electron beam penetrated through and shaped
 by the at least one aperture mask pattern is passed through the second
 aperture whereby the electron beam is shaped in accordance with the shape
 of the at least one aperture mask pattern, and so that if no
 correspondence between the unit patterns and the shape of the at least one
 aperture mask pattern is confirmed, then the deflection is controlled to
 allow that the electron beam penetrated through and shaped by the first
 aperture is transmitted toward the second aperture whereby the electron
 beam is shaped by a combination of the first and second apertures for the
 variable shaped electron beam exposure.
 It is preferable that the aperture member has a set of plural aperture mask
 patterns differing in shape from each other. The unit patterns are
 collated with the shapes of the plural aperture mask patterns to confirm
 any correspondence between the unit patterns and the shapes of the plural
 aperture mask patterns, so that if any correspondence between the unit
 patterns and any of the shapes of the plural aperture mask patterns is
 confirmed, then the deflection is controlled to allow that the electron
 beam penetrated through and shaped by a corresponding one of the plural
 aperture mask patterns is passed through the second aperture whereby the
 electron beam is shaped in accordance with the shape of the corresponding
 one of the plural aperture mask patterns, and so that if no correspondence
 between the unit patterns and any of the shapes of the plural aperture
 mask patterns is confirmed, then the deflection is controlled to allow
 that the electron beam penetrated through and shaped by the first aperture
 is passed through the second aperture whereby the electron beam is shaped
 by a combination of the first and second apertures for the variable shaped
 electron beam exposure.
 It is preferable that the second aperture is positioned at a center of the
 aperture member and the plural aperture mask patterns are positioned
 around the second aperture.
 In accordance with the above present invention, any of the plural aperture
 mask patterns is optionally and effectively used for the variable shaped
 electron beam exposure. For this reason, a total number of the unit
 patterns divided from the write-required patterns is remarkably reduced as
 compared to the prior art. This remarkable reduction in the total number
 of the unit patterns results in a remarkable reduction in the number of
 the processes of the electron beam lithography. The remarkable reduction
 in the number of the processes of the electron beam lithography further
 results in a remarkable improvement in throughput. Further, the remarkable
 reduction in the number of the processes of the electron beam lithography
 also results in a remarkable reduction in the necessary time for the
 electron beam lithography. In addition, the remarkable reduction in the
 total number of the unit patterns results in a reduction in error of sizes
 of the final patterns written by the above novel variable shaped electron
 beam exposure. This means that an accuracy in size of the final patterns
 written by the above novel variable shaped electron beam exposure is
 remarkably improved.
 The above and other objects, features and advantages of the present
 invention will be apparent from the following descriptions.