U.S. patent application number 09/732931 was filed with the patent office on 2002-06-13 for manufacturing method of mask for electron beam proximity exposure and mask.
Invention is credited to Shimazu, Nobuo, Utsumi, Takao.
Application Number | 20020071994 09/732931 |
Document ID | / |
Family ID | 24945498 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020071994 |
Kind Code |
A1 |
Shimazu, Nobuo ; et
al. |
June 13, 2002 |
Manufacturing method of mask for electron beam proximity exposure
and mask
Abstract
A method for manufacturing a mask which is used in an electron
beam proximity exposure apparatus comprising an electron beam
source which emits a collimated electron beam, the mask having an
aperture which is arranged on a path of the electron beam, and a
stage which holds and moves an object, wherein the mask is arranged
in proximity to a surface of the object and a pattern corresponding
to the aperture of the mask is exposed on the surface of the object
with the electron beam having passed through the aperture, the
method comprises the steps of: dividing the mask into a plurality
of partial areas, and forming a plurality of partial masks which
have apertures with patterns identical with the plurality of
partial areas, respectively; and manufacturing the mask by exposing
the patterns of the plurality of partial masks on corresponding
positions of a mask substrate in an electron beam proximity
exposure method. Thus, the method of manufacturing the masks for
the electron beam proximity exposure at reduced costs is
accomplished.
Inventors: |
Shimazu, Nobuo; (Tokyo,
JP) ; Utsumi, Takao; (Watchung, NJ) |
Correspondence
Address: |
NIXON PEABODY, LLP
8180 GREENSBORO DRIVE
SUITE 800
MCLEAN
VA
22102
US
|
Family ID: |
24945498 |
Appl. No.: |
09/732931 |
Filed: |
December 11, 2000 |
Current U.S.
Class: |
430/5 ; 430/296;
430/942 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01J 37/3174 20130101; Y10S 430/143 20130101; B82Y 40/00 20130101;
G03F 1/20 20130101 |
Class at
Publication: |
430/5 ; 430/296;
430/942 |
International
Class: |
G03F 009/00 |
Claims
What is claimed is:
1. A method for manufacturing a mask which is used in an electron
beam proximity exposure apparatus comprising an electron beam
source which emits a collimated electron beam, the mask having an
aperture which is arranged on a path of the electron beam, and a
stage which holds and moves an object, wherein the mask is arranged
in proximity to a surface of the object and a pattern corresponding
to the aperture of the mask is exposed on the surface of the object
with the electron beam having passed through the aperture, the
method comprising the steps of: dividing the mask into a plurality
of partial areas, and forming a plurality of partial masks which
have apertures with patterns identical with the plurality of
partial areas, respectively; and manufacturing the mask by exposing
the patterns of the plurality of partial masks on corresponding
positions of a mask substrate in an electron beam proximity
exposure method.
2. The method as defined in claim 1, wherein each of the plurality
of partial masks has a positioning mark.
3. The method as defined in claim 1, wherein: distortion of the
plurality of partial masks with respect to desired patterns is
determined after the forming thereof; and when each of the patterns
of the plurality of partial masks is exposed, an application
direction of the electron beam is changed so as to correct the
determined distortion.
4. The method as defined in claim 1, wherein the step of forming
the plurality of partial masks comprises: a first step of forming
the plurality of partial masks separately from each other on a
single partial mask substrate; a second step of inspecting each of
the plurality of partial masks concerning defect; a third step of
correcting a correctable defect of each of the plurality of partial
masks; a fourth step of forming, on a subsidiary partial mask
substrate, a partial mask having a pattern which a partial mask
having an, uncorrectable defect among the plurality of partial
masks should have had; a fifth step of inspecting the partial mask
formed on the subsidiary partial mask substrate concerning defect;
and a sixth step of correcting a correctable defect of each partial
mask formed on the subsidiary partial mask substrate, wherein if
the plurality of partial masks without defect are obtained
corresponding to all of the plurality of partial areas of the mask
in the third step, the step of forming the plurality of partial
masks is terminated, wherein if the plurality of partial masks
without defect are not obtained corresponding to all of the
plurality of partial areas of the mask in the third step, the
fourth step through the sixth step are repeated until the plurality
of partial masks without defect are obtained corresponding to all
of the plurality of partial areas of the mask.
5. The method as defined in claim 4, wherein in the first step, the
plurality of partial masks are formed on the partial mask substrate
corresponding to all of the plurality of partial areas of the mask,
and at least one partial mask is further formed on the partial mask
substrate corresponding to at least one of the plurality of partial
areas of the mask.
6. The method as defined in claim 4, wherein in the fourth step,
partial masks concerning the uncorrectable defect are formed as
many as possible on the subsidiary partial mask substrate.
7. A mask manufactured in accordance with the method of claim
1.
8. A mask manufactured in accordance with the method of claim
2.
9. A mask manufactured in accordance with the method of claim
3.
10. A mask manufactured in accordance with the method of claim
4.
11. A mask manufactured in accordance with the method of claim
5.
12. A mask manufactured in accordance with the method of claim 6.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a manufacturing method of a
mask for an exposure apparatus used to expose fine patterns in a
manufacturing process of semiconductor integrated circuits, etc.,
and more particularly to a manufacturing method of a mask used in
an electron beam proximity exposure apparatus in which the mask
having apertures corresponding to a pattern to be exposed is
disposed in proximity to a surface of an object such as a
semiconductor wafer, the mask is irradiated with an electron beam,
and exposure of the pattern with the electron beam having passed
through the apertures is thereby performed.
[0003] 2. Description of the Related Art
[0004] Attempts are being made to enhance integration degrees of
semiconductor integrated circuits and finer circuit patterns are
desired. Presently, a limit of the finer circuit patterns is
defined mainly by exposure apparatuses, and a stepper, which is an
optical exposure apparatus, takes various measures such as a light
source that emits rays having shorter wavelengths, a larger NA
(numerical aperture) and a phase shift method. However, much finer
circuit patterns involve various kinds of problems such as a rapid
increase of production costs. New types of exposure apparatus such
as an electron beam direct lithography apparatus and an X-ray
exposure apparatus have been therefore developed, but there still
remain many problems in terms of stability, productivity, cost,
etc.
[0005] An electron beam proximity exposure system is conventionally
under research and development, since the exposure principle
thereof is simple, as "High Throughput Submicron Lithography with
Electron Beam Proximity Printing" (H. Bohlen et al., Solid State
Technology, September 1984, pp. 210-217) (hereinafter referred to
as literature 1) exemplifies. However, it was thought that it was
of no practical use since it was difficult to eliminate the
proximity effect peculiar to the electron beam.
[0006] U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent
No. 2951947) and "Low energy electron-beam proximity projection
lithography: Discovery of missing link" (Takao Utsumi, J. Vac. Sci.
Technol. B 17(6), Nov/Dec 1999, pp. 2897-2902) disclose an electron
beam proximity exposure apparatus that overcomes the
above-mentioned problems and is usable for processing with very
fine resolution at a mass production level.
[0007] FIG. 1 is a view showing a fundamental configuration to
realize the electron beam proximity exposure apparatus disclosed in
U.S. Pat. No. 5,831,272. Referring to this drawing, the electron
beam proximity exposure apparatus disclosed in U.S. Pat. No.
5,831,272 will be briefly described. As shown in FIG. 1, in a
column 10 are disposed an electron gun 12, which includes an
electron beam source 14 emitting an electron beam 15, a shaping
aperture 16, and a condenser lens 18 collimating the electron beam
15; scanning means 20, which includes a pair of main deflecting
devices 22 and 24 and scans with the electron beam parallel to the
optical axis; an object mask (hereinafter simply referred to as a
mask) 30, which has apertures corresponding to an exposed pattern;
and an object (a semiconductor wafer) 40, of which surface is
coated with a resist layer. The mask 30 has a film 32 with the
apertures formed at the center within a thick rim 34, and the
object 40 is disposed so that the surface thereof is in proximity
to the mask 30. In this state, when the electron beam is vertically
applied to the mask, the electron beam passing through the mask's
apertures is applied to the resist layer 42 on the surface of the
object 40. The entire surface of the film 32 on the mask 30 is
scanned by deflecting the electron beam 15 (A, B, and C in FIG. 1
denote the deflected beam toward three points) with the scanning
means 20, so that all aperture patterns of the mask 30 are exposed.
The scanning means 20 has subsidiary deflecting devices 51 and 52,
which slightly lean the electron beam, and is used to position the
mask 30 and the object 40 and to correct a difference between the
exposure positions due to distortion of the mask and distortion of
the object.
[0008] The mask for an electron beam proximity exposure apparatus
must not have any defect. Accordingly, prior to be used, a
manufactured mask is inspected whether it has no defect. Although a
correction device corrects defects if any, some of the defects are
uncorrectable. If the mask has the uncorrectable defects, it is
required to dispose of the mask and to form a new mask without
defect.
[0009] Variety kinds of factors cause defects of the mask, and the
major one of the factors is contamination with dust (particles). On
the same manufacturing conditions, an incidence of the defect
caused by dust is in proportion to the area of the mask. Therefore,
manufacture of bigger masks involves a higher incidence of the
defect.
[0010] The mask for the electron beam proximity exposure is
manufactured by exposing the pattern by a conventional electron
beam exposure apparatus that can expose desired patterns. Such an
apparatus takes an extremely long time for exposing patterns with
high quality, and the costs of the masks are thereby increased. As
described above, if the mask has the uncorrectable defects, it is
required to dispose of the mask and to expose a new mask for a long
time until a defectless mask is obtained. It produces a problem in
that the production costs of masks are even increased.
SUMMARY OF THE INVENTION
[0011] The present invention has been developed in view of the
above-described circumstances, and has as its object the provision
of a method for manufacturing masks for the electron beam proximity
exposure at reduced costs.
[0012] The inventors of the present invention have directed their
attention to the features that the electron beam proximity exposure
apparatus is an actual-size exposure apparatus, an exposed pattern
is identical with a pattern of the mask, and the electron beam
proximity exposure apparatus can be used to copy the masks.
[0013] The method for manufacturing a mask for the electron beam
proximity exposure according to the present invention is
characterized in method for manufacturing a mask which is used in
an electron beam proximity exposure apparatus comprising an
electron beam source which emits a collimated electron beam, the
mask having an aperture which is arranged on a path of the electron
beam, and a stage which holds and moves an object, wherein the mask
is arranged in proximity to a surface of the object and a pattern
corresponding to the aperture of the mask is exposed on the surface
of the object with the electron beam having passed through the
aperture, the method comprising the steps of: dividing the mask
into a plurality of partial areas, and forming a plurality of
partial masks which have apertures with patterns identical with the
plurality of partial areas, respectively; and manufacturing the
mask by exposing the patterns of the plurality of partial masks on
corresponding positions of a mask substrate in an electron beam
proximity exposure method.
[0014] The patterns of the partial masks should be exposed at
predetermined positions with respect to each other, and it is
preferable that each of the plurality of partial masks has a
positioning mark.
[0015] As described in the above, the mask for the electron beam
proximity exposure is a very thin film, which is required to have
an excellent flatness. Then, it is necessary to form a thin film on
the surface of the film to apply a force in the direction of it
shrinking so that a stress to tense the thin film portion is
applied from the thick portion around the mask. However, the film
for stressing causes a very small distortion on the aperture
pattern, which results in a difference between the actual aperture
pattern and a desired pattern.
[0016] As disclosed in U.S. Pat. No. 5,831,272, etc., the electron
beam proximity exposure apparatus can correct a small distortion of
the mask by adjusting a direction of the electron beam applied to
the mask. Then, after the manufacturing of the partial mask, it is
preferable to measure an amount of distortion of the pattern
thereof, and to perform the exposure of the mask while correcting
the amount of the distortion.
[0017] Since the partial masks are masks of areas into which a mask
of size of one chip is divided, they are smaller than the mask of
size of one chip. Accordingly, if a substrate on which the mask of
size of one chip can be formed or a bigger substrate is used as a
partial mask substrate, a plurality of partial masks can be formed
separately from each other. For example, the partial mask substrate
big enough to arrange all partial masks separately from each other
is used, so that all partial masks are separately formed on a
single partial mask substrate. If no uncorrectable defect is
detected in all partial masks on inspection, a pattern of one mask
is exposed by using only the partial mask substrate when a moving
mechanism for the partial mask substrate is provided on the
electron beam proximity exposure apparatus. In this case, it is
unnecessary to take the partial mask substrate out the apparatus to
replace it while exposing the pattern of one mask, so that it can
reduce a time for performing the exposure.
[0018] If one or more of the partial masks has an uncorrectable
defect, partial masks concerning the uncorrectable defect are
formed as many as possible on the second partial mask substrate.
For example, when the partial mask substrates on each of which
sixteen partial masks can be formed are used, and if there are four
pieces of the partial mask with uncorrectable detects on the first
partial mask substrate, four pieces of the partial mask each
corresponding to each of the partial masks with the uncorrectable
defects can be formed on the second partial mask substrate. On
account of a low incidence of uncorrectable defects on all the four
partial masks, all patterns of the mask are generally exposed by
using the two pieces of the partial mask substrates.
[0019] The use of the partial mask substrate that can have more
partial masks so as to form a plurality of pieces of each the
partial mask on a single partial mask substrate improves a chance
of providing a complete set of defectless partial masks on the
single partial mask substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The nature of this invention, as well as other objects and
advantages thereof, will be explained in the following with
reference to the accompanying drawings, in which like reference
characters designate the same or similar parts throughout the
figures and wherein:
[0021] FIG. 1 is a view showing a fundamental configuration of an
electron beam proximity exposure apparatus;
[0022] FIG. 2 is a diagram illustrating a fundamental concept
according to the present invention;
[0023] FIG. 3(A) is a view showing an arrangement of partial masks
on a partial mask substrate in addition to each shape of partial
masks according to a first embodiment of the present invention, and
FIG. 3(B) is a sectional view taken along line 3(B)-3(B) in FIG.
3(A);
[0024] FIG. 4 is a view showing partial masks formed on the second
partial mask substrate when the partial masks formed on the first
partial mask substrate have defects according to the first
embodiment;
[0025] FIG. 5 is a view showing an arrangement of partial masks on
a partial mask substrate according to the second embodiment of the
present invention;
[0026] FIG. 6 is a view showing another example of dividing a mask
into partial mask areas;
[0027] FIG. 7 is a view showing an example of a customized
semiconductor chip;
[0028] FIG. 8 is a diagram illustrating mask groups provided in the
third embodiment of the present invention;
[0029] FIG. 9 is a diagram illustrating an exposure of the mask
according to the third embodiment;
[0030] FIG. 10 is a view showing a configuration of the electron
beam proximity exposure apparatus used in the embodiments of the
present invention;
[0031] FIG. 11 is a view illustrating a method of exposing while
correcting a distortion of the partial mask in the electron beam
proximity exposure apparatus; and
[0032] FIG. 12 is a diagram illustrating a correction of distortion
produced on the partial mask.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] FIG. 2 is a diagram illustrating a fundamental concept
according to the present invention.
[0034] As described in FIG. 2, a mask 30 over an entire surface of
one chip (die), which is required after all, is divided into a
plurality of partial areas A-P. Then, each of the partial areas A-P
is exposed by using a conventional electron beam exposure apparatus
101 that can expose desired patterns, and partial masks 111
respectively corresponding to the partial areas A-P are formed.
Each of the formed partial masks 111 is inspected. If a correctable
defect is detected, it is then corrected. If an uncorrectable
defect is detected, only the partial mask that has the
uncorrectable defect is re-formed. Thus, the partial masks 111 that
have no defect and respectively correspond to all the partial areas
A-P are formed. For instance, when the partial areas are sixteen
parts identical in size, and when only one of them has an
uncorrectable defect, a time for exposing the one partial mask
again is estimated to be substantially {fraction (1/16)} (a real
exposure time is determined with substantial patterns) of a time
for exposing the whole mask 30 or all the partial areas A-P.
[0035] Next, the defectless partial masks 111 corresponding to the
partial areas A-P are exposed at corresponding positions,
respectively, by an electron beam proximity exposure apparatus 102
having a configuration similar to the configuration disclosed in
U.S. Pat. No. 5,831,272, so that the mask 30 is formed. A time for
exposing all the partial masks 111 corresponding to the partial
areas A-P is between thousandths and {fraction (1/10000)} of a time
for exposing the whole mask 30 by the conventional electron beam
exposure apparatus 101.
[0036] The thus formed mask 30 is inspected. If an uncorrectable
defect is detected, the partial masks 111 corresponding to the
partial areas A-P are exposed at corresponding positions,
respectively, by the electron beam proximity exposure apparatus 102
so that the mask 30 is re-formed. This procedure is repeated until
the mask 30 without defect is obtained. In this case, an incidence
of the defect caused by dust may not be different between such case
that the conventional electron beam exposure apparatus 101 is used
for the exposure of the whole mask 30 and such case that the
electron beam proximity exposure apparatus 102 is used for the
exposure of the plurality of partial masks 111. However, since the
time for the exposure by the electron beam proximity exposure
apparatus 102 is far shorter, the time for processing that is
repeated until the defectless mask 30 is obtained is far shortened.
The production costs of the masks are thus significantly
reduced.
[0037] According to the first embodiment of the present invention,
a pattern of one mask is divided into sixteen partial areas A-P as
shown in FIG. 2, and the sixteen partial masks respectively having
the patterns of the partial areas A-P are formed. According to the
first embodiment, a partial mask substrate is used on which the
sixteen partial masks can be formed to have some distances away
from each other. FIG. 3(A) is a view showing an example of an
arrangement of the sixteen partial masks 111 on the partial mask
substrate 121, and FIG. 3(B) is a sectional view taken along line
3(B)-3(B) in FIG. 3(A); where the partial masks corresponding to
the partial areas A-P are denoted with A-P. The partial mask
substrate 121 is, for example, a thin plate (wafer) with a
thickness of a few millimeters. In each of the partial masks 111, a
portion denoted with a reference number 132 is processed in the
thickness of a few micrometers or submicrometers, in which an
aperture pattern is formed at a portion denoted with a reference
number 133. A reference number 135 denotes a mark for determining
the position of the mask. When the partial mask substrate is
processed, the patterns of the partial masks A-P are exposed to
have some distances away from each other as illustrated, by the
conventional electron beam exposure apparatus 101 on a resist layer
formed on a side of the partial mask substrate 121. Then, the
resist layer is developed and the side of the partial mask
substrate 121 is etched to form holes at aperture parts of the
pattern. The holes are made deeper than a thickness of the portion
denoted with the reference number 132. At this point, holes
corresponding to a pattern of the marks 135 are also formed.
[0038] Next, a resist layer is formed on the other side of the
partial mask substrate 121, and the resist layer at the portions
denoted with the reference number 132 of the masks is removed by
lithography. That is, the resist layer is formed except for the
portions denoted with the reference number 132. Then, the other
side of the partial mask substrate 121 is etched so as to process
to the thickness of a few micrometers. Thereby, the holes formed on
the side are perforated, so that the aperture pattern is formed.
The sixteen partial masks are thus formed on the partial mask
substrate 121. Each of the partial masks on the partial mask
substrate 121 is inspected, correctable defects are then corrected,
and useable partial masks are selected. For example, as shown in
FIG. 3(A), C, F and G of the sixteen partial masks have
uncorrectable defects.
[0039] Next, as illustrated in FIG. 4, partial masks of C, F and G
are formed on the second partial mask substrate 122. Since sixteen
partial masks can be formed on the second partial mask substrate
122 as the first partial mask substrate 121 in FIG. 3, six pieces
of the partial mask C, five pieces of the partial mask F and five
pieces of the partial mask G are formed. The partial masks C, F,
and G on the second partial mask substrate 122 are inspected to
select useable partial masks. At least one useable mask is
sufficient for each of the partial masks C, F and G. If one of the
partial masks C, F, and G does not have any useable mask yet, only
partial masks corresponding to the one partial mask are formed on
another partial mask substrate. For instance, when each of the
partial masks C and G has the useable partial mask and all of five
pieces of the partial mask F have uncorrectable defects, sixteen
pieces of the partial mask F are formed on another partial mask
substrate. Thus, the above-described process is repeated until at
least one partial mask without defect is obtained as for each of
the partial masks A-P.
[0040] At this point, since six pieces of the partial mask C are
formed on the partial mask substrate 122, a possibility that all of
the six pieces of the partial masks C have uncorrectable defects is
lowered. This applies to also the partial masks F and G.
[0041] The patterns of the partial masks A-P are exposed at the
corresponding positions on the substrate 31 of the mask 30 by using
the defectless partial masks A-P, which are formed as described
above, in the electron beam proximity exposure apparatus 102, so
that the mask 30 is formed in the same method as described above.
This exposure is accomplished in a short time, since it is
performed by merely scanning the partial masks A-P to expose with
the electron beam after positioning them with respect to the
substrate 31 of the mask 30. In a case where the first partial mask
substrate 121 has an unusable partial mask and partial masks are
also formed on the second partial mask substrate, after the
exposure of the normal partial masks on the first partial mask
substrate 121 is completed, the second partial mask substrate is
mounted and the exposure of the remaining partial mask is
performed. At this point, the second partial mask substrate may be
set after the first partial mask substrate is taken out of the
electron beam proximity exposure apparatus 102; however, it is
preferable that a moving mechanism for the partial mask substrate
is provided within the electron beam proximity exposure apparatus
so that the partial mask substrates to use can be changed.
[0042] The thus formed mask 30 is inspected. If an uncorrectable
defect is detected, the mask 30 is formed again. This procedure is
repeated until the mask 30 without defect is obtained. Since each
exposure time is short, the total exposure time does not become
long, even though the procedure is repeated until the mask 30 is
obtained.
[0043] The conventional electron beam exposure apparatus is
extremely expensive, and the production costs of masks mainly
depends on a time for using it. According to the present invention,
a time for using the extremely expensive and conventional electron
beam exposure apparatus is significantly shortened, and the
production costs of masks are thus reduced. Moreover, the electron
beam proximity exposure apparatus is far less complicated and less
expensive than the conventional electron beam exposure apparatus.
Therefore, since the costs of use of the electron beam proximity
exposure apparatus are small and the using time is short, such
amount of the costs do not augment the production costs.
[0044] The mask for the electron beam proximity exposure comprises
an extremely thin film with its thickness of a few micrometers or
submicrometers, and the film is required to have an excellent
flatness. Then, a stressing film is formed on the surface of the
film of the mask to apply a stress to tense the film portion from a
thick portion around the mask, and the excellent flatness is thus
achieved. However, the film has apertures of which pattern is
partially different, so that the contracting force of the stressing
film is partially varied and it causes distortion on the film of
the mask. The above-described literature 1 and U.S. Pat. No.
5,831,272 disclose a technique in the electron beam proximity
exposure apparatus to correct the distortion on the mask by
changing a direction of the electron beam applied to the mask. In
the first embodiment, this technique is utilized to reduce the
distortion as described below when the pattern of the partial mask
is exposed.
[0045] FIG. 10 is a view showing a configuration of an electron
beam proximity exposure apparatus 102 used in the embodiment of the
present invention. Since the fundamental configuration is similar
to the one shown in FIG. 1 and the one disclosed in the above
literature 1, the same function parts with FIG. 1 are denoted with
the same reference numbers.
[0046] As shown in FIG. 10, in an electron optical column 10 are
disposed an electron gun 14, which emits electron beam 15, a
condenser lens 18, which collimates the electron beam 15, a main
deflecting device 20 and a subsidiary deflecting device 50.
Although shown as a single deflecting device in FIG. 10, each of
the main deflecting device 20 and the subsidiary deflecting device
50 is actually configured in two stages as shown in FIG. 1. In a
vacuum object chamber 8 are disposed a mask stage 36, which holds
and moves a mask (the partial mask substrate 121 (or 122) in the
present embodiment), and a stage 131, which holds and moves an
object (the substrate 31 of the mask 30 in the present
embodiment).
[0047] In FIG. 10, a state is shown where an applied position of
the electron beam 15 on the partial mask substrate 121 is changed
by the main deflecting device 20. As illustrated, even when the
main deflecting device 20 changes the applied position, the
electron beam 15 is substantially vertically applied to the partial
mask substrate 121.
[0048] In contrast, as shown in FIG. 11, when the subsidiary
deflecting device 50 changes an incident angle of the electron beam
15 onto the partial mask substrate 121, the electron beam 15 falls
on the same position on the partial mask substrate 121 while the
incident angle is changed. As the incident angle is changed, the
applied position on the substrate 31 of the mask 30 is changed in
spite of the electron beam having passed through the same position
of the mask. The changing amount is a product of the incident angle
and the distance between the partial mask substrate 121 and the
substrate 31 of the mask 30. Hence, the distortion amount of the
partial mask is determined in advance, the incident angle is set so
that the changing amount of the applied position according to the
incident angle is equivalent and in the compensating direction to
the distortion amount, and the distortion of the partial mask can
be thus corrected.
[0049] The smaller electron beam scanning the partial mask can
theoretically correct any distortion; however, it is preferable
that the electron beam has a certain size to satisfy the
throughput, and in such a case, a rather large distortion cannot be
corrected. Also, although the distortion can be corrected even if
it is non-linear, an example is described where the correction is
performed while approximating the distortion to be linear as shown
in FIG. 12 in order to simplify the control of the subsidiary
deflecting device.
[0050] As illustrated in FIG. 12, points P1-P4 are respectively
exposed at desired positions while the partial mask is exposed.
However, as a result of forming of holes corresponding to the
apertures and processing of the film portion, suppose that the
points P1, P2, P3 and P4 have been formed at the points P1', P2',
P3' and P4', respectively, in the partial mask that has been
actually manufactured. This is considered as the original ideal XY
coordinates are linear-transformed into actually distorted xy
coordinates. In order to correct the distorted xy coordinates to
the original ideal XY coordinates, a linear transformation is
performed by the following transformational functions:
X=a.sub.1+a.sub.2.multidot.x+a.sub.3.multidot.y+a.sub.4.multidot.xy
; and
Y=b.sub.1+b.sub.2.multidot.x+b.sub.3.multidot.y+b.sub.4.multidot.xy,
where a.sub.1-a.sub.4 and b.sub.1-b.sub.4 are correction factors
for the partial mask's distortion.
[0051] The correction factors a.sub.1-a.sub.4 and b.sub.1-b.sub.4
are obtained by substituting the coordinates of P1'-P4' and the
coordinates of P1-P4 into the above transformational functions.
[0052] The incident angle is determined according to the correction
amount at each point on the mask that is calculated from the above
transformational functions, the deflecting amount of the subsidiary
deflector is determined, and the exposure is then performed, so
that the pattern without distortion can be exposed on the substrate
31 of the mask 30 even if the partial mask has been distorted.
[0053] The first embodiment is an example where sixteen partial
masks into which one mask is divided are formed on a partial mask
substrate; however, it is possible to use the partial mask
substrate that can have more partial masks. FIG. 5 is a view
showing a configuration of a partial mask substrate according to
the second embodiment of the present invention. In the second
embodiment, the mask 30 is divided into sixteen partial areas A-P
in the same way as the first embodiment. As shown in FIG. 5,
forty-nine partial masks 113 are formed on the partial mask
substrate 123 according to the second embodiment. Four pieces of
the partial mask A and three pieces of each of the other partial
masks B-P are formed. In this case, although the exposure time is
increased, one set of the defectless partial masks A-P can be
obtained on one partial mask substrate in most cases, since an
incidence of uncorrectable defects on all four pieces or all three
pieces of the same partial mask is low. This embodiment is suitable
for a case when there is a high incidence of defect.
[0054] A partial mask substrate can have sixteen partial masks in
the first embodiment and forty-nine partial masks in the second
embodiment; however, a partial mask substrate can have less number
of partial masks. A partial mask substrate may have a single
partial mask. In this case, although the partial mask substrates
have to be changed every exposure time for each of the partial
masks, the period of time using an expensive and conventional
electron beam exposure apparatus is shortened, and the production
costs of the masks are hence reduced.
[0055] Furthermore, although the mask is divided into a number of
partial areas that have almost identical shapes in the first and
second embodiments, the partial areas can have any shape. For
example, the mask can be divided into areas A-Q as shown in FIG. 6.
At each boundary of the areas, the areas are divided in accordance
with the patterns so as to be easily connected with each other.
[0056] Conventionally, a plurality of general semiconductor chips
are assembled to make a circuit device having a desired function.
In contrast, in order to make a circuit apparatus compact in size
and saving electricity, customization is advanced so that one
semiconductor chip includes variety kinds of functional circuits.
FIG. 7 shows an example of a customized semiconductor chip 200,
into which a CPU 201, a DSP 202, a cash memory 203, a display
controller 204, an image processing unit 205 and a DRAM 206 are
integrated. By such configuration, the device can be compact in
size and save electricity. However, a production amount of such
customized device is generally a little. When one kind of chips are
manufactured, the larger the production amount of the chips, the
less the cost of the mask per chip. Then, a small production amount
of customized semiconductor chips causes a serious problem of the
mask's cost. In the third embodiment, an example is given about the
method of manufacturing the mask that is suitable for such
customized semiconductor chips.
[0057] To generally design the customized semiconductor chip,
fundamental circuits that are suitable for an objective circuit
device are selected from a library that contains design data for
fundamental circuit groups classified by functions such as the CPU,
the DSP, the DRAM, the SRAM, the flush memory, the image processing
circuit, the display controller, and the analog circuit. Then, the
selected fundamental circuits are integrated. According to the
third embodiment of the present invention, the masks are provided
in advance according to the design data for the fundamental circuit
groups classified by their functions. For example, as shown in FIG.
8, a CPU mask group 211, a DSP mask group 212, a DRAM mask group
216, an SRAM mask group 217, an image processing mask group 215,
and a display controller mask group 214 are provided. Then, as
shown in FIG. 9, according to the circuits to be integrated, a mask
set 230, which includes the CPU 231, the DSP 232, the memory 234
and the display 235, is selected from the provided mask groups.
Further, a connection pattern 240 that is required for connecting
the patterns of the masks in the mask set 230 is separately
provided. Then, these patterns are unitedly exposed so that a
pattern for the objective circuit device is exposed, and the mask
250 is thus formed. In view of the above method, the connection
pattern 240 is only required to be newly formed, which extremely
shorten a lead time of manufacturing the mask 250.
[0058] In this case, since the electron beam proximity exposure
apparatus is also used for exposing the patterns of the masks in
the mask set 230 and the connection pattern 240, a period of time
for exposure can be extremely shortened compared to a period of
time for exposing all patterns of the mask 250 by the conventional
electron beam exposure apparatus.
[0059] When the connection pattern 240 is not many, the patterns of
the masks in the mask set 230 are exposed by the electron beam
proximity exposure apparatus, and the connection pattern 240 can be
exposed by the conventional electron beam exposure apparatus. Even
in such a case, since the patterns for great portions are exposed
by the electron beam proximity exposure apparatus, the period of
time for exposing is extremely shortened compared to the case that
all patterns are exposed by the conventional electron beam exposure
apparatus.
[0060] As described in the above, according to the present
invention, the masks to be used in the electron beam proximity
exposure apparatus can be manufactured by reduced costs and a short
lead time.
[0061] It should be understood, however, that there is no intention
to limit the invention to the specific forms disclosed, but on the
contrary, the invention is to cover all modifications, alternate
constructions and equivalents falling within the spirit and scope
of the invention as expressed in the appended claims.
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