U.S. patent application number 09/783618 was filed with the patent office on 2002-04-18 for manufacturing process for semiconductor device, photomask, and manufacturing apparatus for semiconductor device.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Aoyama, Satoshi, Hosono, Kunihiro.
Application Number | 20020043725 09/783618 |
Document ID | / |
Family ID | 18745831 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020043725 |
Kind Code |
A1 |
Hosono, Kunihiro ; et
al. |
April 18, 2002 |
MANUFACTURING PROCESS FOR SEMICONDUCTOR DEVICE, PHOTOMASK, AND
MANUFACTURING APPARATUS FOR SEMICONDUCTOR DEVICE
Abstract
Provided are a manufacturing process for a semiconductor device
capable of transferring a pattern corrected with respect of optical
distortion of an exposure apparatus, a mask, and a manufacturing
apparatus for a semiconductor device. The manufacturing process,
regarding optical distortion of said exposure apparatus as a
variation in reduction rate of a transferred pattern in each of
regions, includes: a first step transferring a fundamental pattern
formed on a reference photomask for measuring the optical
distortion to measure a size of a transferred pattern in a
corresponding one of regions; and a second step of, based on a
result obtained in said first step, forming a corrected photomask
having a pattern corrected in said corresponding one of regions
with respect to said optical distortion.
Inventors: |
Hosono, Kunihiro; (Hyogo,
JP) ; Aoyama, Satoshi; (Hyogo, JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha
|
Family ID: |
18745831 |
Appl. No.: |
09/783618 |
Filed: |
February 15, 2001 |
Current U.S.
Class: |
257/776 |
Current CPC
Class: |
G03F 7/70433 20130101;
Y10S 430/15 20130101; G03F 7/706 20130101 |
Class at
Publication: |
257/776 |
International
Class: |
H01L 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2000 |
JP |
2000-257364 |
Claims
What is claimed is:
1. A manufacturing process for a semiconductor device including a
step of transferring a pattern on a photomask onto a semiconductor
wafer by means of an exposure apparatus, regarding optical
distortion of said exposure apparatus as a variation in reduction
rate of a transferred pattern in each of regions of a photomask,
including: a first step of transferring a fundamental pattern
formed on a reference photomask for measuring the optical
distortion to measure a size of said transferred pattern in a
corresponding one of regions; and a second step of, based on a
result obtained in said first step, forming a corrected photomask
having a pattern corrected in said corresponding one of regions
with respect to said optical distortion.
2. The manufacturing process for a semiconductor device according
to claim 1, wherein a fundamental pattern on said reference
photomask is a plurality of unit patterns of the same shape
arranged on the reference photomask.
3. The manufacturing process for a semiconductor device according
to claim 1, wherein a fundamental pattern on said reference mask is
a non-periodical pattern with no periodicity formed on the
reference photomask.
4. The manufacturing process for a semiconductor device according
to claim 1, wherein said first step includes: a step of obtaining a
reduction rate which is a rate between a size of said transferred
fundamental pattern and a size of said fundamental pattern on said
reference photomask in each of regions of said reference
photomask.
5. The manufacturing process for a semiconductor device according
to claim 4, wherein, in said second step, a size of a pattern in
each of said regions of said corrected photomask is formed such
that a corrected reduction rate which is a rate between a size of a
corrected, transferred pattern that is a transferred pattern of a
pattern of said corrected photomask and a size of a pattern on said
photomask prior to the correction in each of the regions is the
same throughout all said regions regardless of each locality
6. The manufacturing process for a semiconductor device according
to claim 5, wherein, in said second step, a size of a pattern in
each of said regions of said corrected photomask is formed such
that a product of a pattern correction rate which is a rate between
a size of a pattern in a region on said corrected photomask and a
size of a pattern in a corresponding region of said photomask prior
to the correction, and a reduction rate in said region is the same
regardless of which of all said regions said region belongs to.
7. The manufacturing process for a semiconductor device according
to claim 4, wherein, in said second step, a pattern of a prescribed
portion of said semiconductor device is arranged in each of said
regions of said corrected photomask in a similar way, and a size of
a pattern in each of said regions of said prescribed portion of
said semiconductor device is determined such that a product of a
size of a pattern of said prescribed portion of said semiconductor
device in a region on the corrected photomask and a reduction rate
in said region is the same all over said regions regardless of
which of all said regions said region belongs to.
8. The manufacturing process for a semiconductor device according
to claim 1, wherein said second step includes: a photomask
manufacturing process and a pattern of said corrected photomask is
corrected in terms of size by adjusting at least one of a writing
beam diameter and a writing dose with respect to a position of said
corrected photomask in a resist writing step of the photomask
manufacturing process.
9. The manufacturing process for a semiconductor device according
to claim 1, wherein said second step includes: a photomask
manufacturing process and a pattern on said corrected photomask is
corrected in terms of a size by adjusting a way of supply of a
developer in a resist developing step of the photomask
manufacturing process.
10. The manufacturing process for a semiconductor device according
to claim 1, wherein said second step includes a photomask
manufacturing process and a pattern on said corrected photomask is
corrected in terms of size by adjusting a way of supply of an
etching liquid in a wet etching step for a Cr film in the photomask
manufacturing process.
11. The manufacturing process for a semiconductor device according
to claim 1, wherein said second step includes: a photomask
manufacturing process and a pattern of said corrected photomask is
corrected in terms of size by adjusting a strength of a magnetic
field in a dry etching step for a Cr film of the photomask
manufacturing process.
12. The manufacturing process for a semiconductor device according
to claim 11, wherein said magnetic field in a dry etching step for
said Cr film is a rotating magnetic field formed such that a
combination of two orthogonal magnetic fields are applied in
synchronism with each other in parallel to a surface of said
corrected photomask and adjustment of a strength of said magnetic
field is effected by controlling said two magnetic fields
independently of each other.
13. The manufacturing process for a semiconductor device according
to claim 1, wherein said second step includes: a photomask
manufacturing process and a pattern on said corrected photomask is
corrected in terms of size by combining factors for a change in
size of a pattern in at least two steps among a resist writing
step, a resist developing step and a Cr film etching step of the
photomask manufacturing process.
14. A photomask is a photomask having a pattern thereon, employed
in transfer of said pattern onto a semiconductor wafer by means of
an exposure apparatus, wherein, correction of a size of a pattern
on said photomask is performed such that correction is effected on
a variation in reduction rate of a transferred pattern in each of
regions caused by optical distortion of said exposure
apparatus.
15. A photomask according to claim 14, wherein said reduction rate
is one as measured in each of said regions of a transferred pattern
from a fundamental pattern formed on a reference photomask
exclusively used in measurement of optical distortion of an
exposure apparatus.
16. A manufacturing apparatus for a semiconductor device to
transfer a pattern arranged on a photomask onto a semiconductor
wafer to perform exposure, wherein a photomask according to claim
14 is disposed between a light source for said exposure and said
semiconductor wafer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a manufacturing process for
a semiconductor device by means of which improvements are achieved
on accuracy and uniformity of a size of a transferred pattern in a
pattern transfer step of the manufacturing process for a
semiconductor device by suppressing optical distortion of an
exposure apparatus, a photomask and a manufacturing apparatus for a
semiconductor device.
[0003] 2. Description of the Background Art
[0004] In an exposure apparatus used in manufacturing a
semiconductor device, light radiated from a light source is
transmitted through patterns on a photomask to be projected on a
wafer surface to make an image. In FIGS. 28 and 29, shown are prior
art photomasks formed by means of a prior art method. In FIG. 28,
arranged are rectangular patterns 113a of the same shape having a
side a in length in a uniform distribution on a photomask 103.
Furthermore, in FIG. 29, formed is a single pattern 113b having a
constant width L along a bending shape in photomask 103. A
photoactive positive or negative photo resist is applied on a
semiconductor wafer in advance. When a positive photoresist is
employed, a part of the photoresist on which light through a
photomask is irradiated is removed in a following developing step,
while a non-irradiated part of the photoresist on which the light
doesn't irradiate remains in the following developing step. With
such a process adopted, a pattern on the photomask is transferred
on the wafer as a pattern of photo resist. By using the pattern of
the photoresist, etching and impurity implantation are performed to
manufacture a semiconductor device.
[0005] A photomask is manufactured such that as shown in FIG. 28,
patterns of the same size are arranged in a repeated arrangement
periodical arrangement) and the same patterns are distributed in a
uniform manner with respect to a size in each of regions all over
the surface of the mask regardless of locality of a region to
increase uniformity in terms of size of devices. Moreover, there is
also included a step in which a non-repeated pattern
(non-periodical pattern) as shown in FIG. 29 is transferred. The
pattern with no repetition is also transferred by means of a
transfer apparatus such that no variation in size occurs. Hence,
each optical systems such as lenses of exposure apparatuses are
designed and manufactured such that a pattern is transferred with
uniformity.
[0006] Distortion in an optical system of an exposure apparatus is,
however, difficult to be perfectly eliminated and in addition,
characteristics of the distortion are different in each exposure
apparatus. For this reason, a pattern on a photomask is not
necessarily transferred in a faithful manner. As a result, a
transferred resist pattern is affected by optical distortion
specific to each exposure apparatus, resulting in a variation in
performance of a semiconductor device.
[0007] In order to solve such a problem, a proposal has been made
on a photomask to correct optical distortion in an exposure
apparatus (see Japanese Patent Laying-Open No. 60-167328 and
Japanese Patent Laying-Open No. 8-95229). By use of such a
photomask corrected with respect to optical distortion, a variation
in performance of a semiconductor device is alleviated. Correction
methods for optical distortion disclosed in the above described
publications are, however, to correct positional displacements of
points on a photomask, wherein objects for the correction are a
direction of a displacement and a distance thereof. Therefore,
there has remained a problem in that the correction of optical
distortion is complex and that no recognizable improvement can be
achieved without the correction with very high accuracy. Since in a
manufacturing process of a semiconductor device, a tremendous
number of photomasks are employed, even only photomasks used in
manufacturing steps which affect characteristics of the
semiconductor device are difficult to be corrected in advance when
depending on too complex a correction method. Hence, in company
with progress in microfabrication of a semiconductor device, there
has been built up a demand for a manufacturing process for a
semiconductor device capable of obtaining an exposure-transferred
pattern with high accuracy in a simple and convenient manner.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a
manufacturing process for a semiconductor device capable of
correcting optical distortion of an exposure apparatus in simple
and convenient manner, a mask for use in the manufacturing process,
and a manufacturing apparatus provided with the mask for a
semiconductor device.
[0009] A manufacturing process for a semiconductor device of the
present invention is a manufacturing process for a semiconductor
device including a step of transferring a pattern on a photomask
onto a semiconductor wafer by means of an exposure apparatus. The
manufacturing process regards optical distortion of an exposure
apparatus as a variation in reduction rate of a transferred pattern
in each of regions of a photomask and includes: a first step of
transferring a fundamental pattern formed on a reference photomask
for measuring the optical distortion to measure a size of the
transferred pattern in a corresponding one of regions; and a second
step of, based on a result obtained in the first step, forming a
corrected photomask having a pattern corrected in the corresponding
one of regions with respect to the optical distortion.
[0010] According to such a constitution, an optical distortion can
be obtained as a size of a pattern in each region on a photomask,
or a rate of a size of a transferred pattern in a corresponding
region and a size of a pattern on the photomask. The size and size
rate can be obtained with ease, and furthermore, a corrected
photomask can be fabricated based on the size or size rate in a
simple and convenient manner. For this reason, a tremendous number
of photomasks for use in manufacturing steps to affect
characteristics of a semiconductor device can be replaced with
respective corrected photomasks in a simple and convenient manner.
Consequently, not only can a variation in a transferred pattern in
each of exposure apparatuses can be restricted, but a dimensional
variation in each of portions in a semiconductor device caused by
optical distortion, which differs between exposure apparatuses, can
be suppressed, such that sizes of portions in a semiconductor
device formed through a different exposure apparatus can be all
uniform. As a result, miniaturized semiconductor devices with high
reliability can be provided with a high manufacturing yield. Note
that optical distortion appears as a variation in a magnification
rate or reduction rate in each region; therefore, the above
described fundamental patterns are desirably provided across all
regions of a reference photomask.
[0011] In the manufacturing process for a semiconductor device of
the present invention, a fundamental pattern on the reference
photomask is, for example, a plurality of unit patterns of the same
shape arranged on the reference photomask.
[0012] By providing a reference photomask having unit patterns
arranged thereon as described above, the area of a photomask is
divided into regions including each unit pattern and a
magnification rate or reduction rate can be obtained in each
region. In a corrected photomask, a pattern size is corrected in
each region based on a magnification rate or reduction rate for the
region. This correction is performed such that a product of a
magnification rate or reduction rate in each region and a pattern
size in a corresponding region of a corrected photomask is the same
as each other in any of all the regions regardless of particularity
of a region. By use of the corrected photomask, when patterns of
the same shape are intended to be disposed, for example, in a
repeated arrangement (periodical arrangement) in a transferred
pattern, the same patterns can be obtained in the respective
regions as intended, in the transferred pattern.
[0013] In the manufacturing process of a semiconductor device of
the present invention, a fundamental pattern on the reference
photomask may be, for example, a non-periodical pattern with no
periodicity formed on the reference photomask.
[0014] In manufacture of a semiconductor device, there are many
cases where a single pattern with no periodicity is transferred and
such a non-periodical pattern is necessary to be corrected with
respect to a variation in size due to optical distortion. In a case
of the non-periodical pattern as well, correction of a variation in
size is effected by correcting a variation in reduction rate of
each region similar to the case of a periodical pattern. As a
result, a size accuracy in a pattern is improved and a variation in
size between semiconductor devices processed by respective
different exposure apparatuses can be restricted.
[0015] In the manufacturing process for a semiconductor device of
the present invention, the first step desirably includes: for
example, a step of obtaining a reduction rate which is a rate
between a size of the transferred fundamental pattern and a size of
the fundamental pattern on the reference photomask in each of
regions of the reference photomask.
[0016] By obtaining a reduction rate in each of the regions, a
corrected photomask can be manufactured with simplicity and
convenience. When it is intended that the same patterns are
provided in respective regions in a transferred pattern, patterns
on a corrected photomask have only to be formed such that a size of
each of the respected patterns on the corrected photomask is in
inverse proportion to a reduction rate of a corresponding
region.
[0017] In the manufacturing process for a semiconductor device of
the present invention, it is desirable that in the second step, for
example, a size of a pattern in each of the regions of the
corrected photomask is desirably formed such that a corrected
reduction rate which is a rate between a size of a corrected,
transferred pattern that is a transferred pattern of a pattern of
the corrected photomask and a size of a pattern on the photomask
prior to the correction in each of the regions is the same
throughout all the regions regardless of each locality.
[0018] According to the above described constitution, optical
distortion of an exposure apparatus is eliminated and a transferred
pattern as intended can be obtained. For this reason, even when a
transfer step is performed in a different exposure apparatus,
photoresist patterns of the same size or the like are formed on a
semiconductor substrate; and etching, impurity implantation and
others can be performed based on the photoresist patterns of the
same size. As a result, semiconductor devices with a high
manufacturing yield, high reliability and high performance can be
provided with simplicity and convenience.
[0019] In the manufacturing process for a semiconductor device, in
the second step, for example, a size of a pattern in each of the
regions of the corrected photomask is desirably formed such that a
product of a pattern correction rate which is a rate between a size
of a pattern in a region on the corrected photomask and a size of a
pattern in a corresponding region of the photomask prior to the
correction and a reduction rate in the region is the same
regardless of which of all the regions the region belongs to.
[0020] The photomask prior to the correction is a photomask in a
case where it is assumed that no optical distortion is present in
an exposure apparatus and may be either existent or imaginary. By
forming a pattern on a corrected photomask as described above, when
the corrected photomask is used in the exposure apparatus, the
optical distortion can be eliminated in terms of size. As a result,
patterns which have been transferred in different ways in
respective different exposure apparatuses can be transferred in a
similar way as each other regardless of an exposure apparatus;
therefore, high reliability semiconductor devices can be
manufactured with a high manufacturing yield. Note that the above
described pattern may be either a pattern set constituted of the
same pattern repeatedly arranged in each of regions in a similar
way or a pattern with no periodicity (non-periodical pattern)
arranged across regions.
[0021] In the manufacturing process for a semiconductor device of
the present invention, it is desirable that in the second step, for
example, a pattern of a prescribed portion of the semiconductor
device are arranged in each of the regions of the corrected
photomask in a similar way, and a size of a pattern in each of the
regions of the prescribed portion of the semiconductor device is
determined such that a product of a size of a pattern of the
prescribed portion of the semiconductor device in a region on the
corrected photomask and a reduction rate in the region is the same
all over the regions regardless of which of all the regions the
region belongs to.
[0022] In a case where a pattern set is constituted of patterns of
the same shape arranged in respective regions, a photomask prior to
correction is not necessary to be referred to but a corrected
photomask can be manufactured according to the above described
constitution. By using the corrected photomask in the exposure
apparatus, optical distortion can be eliminated in terms of size,
thereby enabling manufacturing a high reliability semiconductor
device with a high yield.
[0023] In the manufacturing method for a semiconductor device of
the present invention, it is allowed that the second step includes
a photomask manufacturing process and a pattern of the corrected
photomask may be corrected in terms of size by adjusting at least
one of a writing beam diameter and a writing dose with respect to a
position of the corrected photomask in a resist writing step of the
photomask manufacturing process.
[0024] In a case where a positive resist is used, a resist-lacking
section occurs covering a large area if a writing beam diameter and
a writing dose is large. That is, since an area of a resist-lacking
section is in proportion to a writing beam diameter or a writing
dose, a size of a pattern in each region can be adjusted by
controlling such factors. The adjustment of a size in this case is
not so large as to produce a change in shape of a pattern, but only
at a subtle level of the order to be perceptible by an expertise,
which is achieved by controlling at least one of a writing beam
diameter or a writing dose as described above. Hence, by
controlling the factors in a proper manner, an appropriate
correction can be effected in a simple and convenient manner with
good efficiency.
[0025] In the manufacturing process for a semiconductor device of
the present invention, it is allowed that the second step includes
a photomask manufacturing process and a pattern on the corrected
photomask is corrected in terms of-a size by adjusting a way of
supply of a developer in a resist developing step of the photomask
manufacturing process.
[0026] The adjustment can also be performed in a resist developing
step. A developing reaction is accelerated at a writing site
supplied with a fresh, unused developer and thereby, resist removal
progresses ahead of the other sites to a larger extent there. For
this reason, by adjusting a position and a direction of a nozzle; a
residence time at each site of a nozzle, if movable; in addition, a
discharge amount of a developer; and others, formation of a
corrected pattern with a desired pattern size distribution is
effected. Since the optical distortion, in many cases, differs at a
degree thereof in each of regions partitioned concentrically,
formation of a pattern in each of the regions may be sufficiently
controlled, in many cases, if the photomask is separated into
central and peripheral regions and an intermediate region
therebetween. Note that correction of an area of a resist-lacking
section can also be effected on an area of a writing site of the
same magnitude.
[0027] In the manufacturing process of a semiconductor device of
the present invention, it is also allowed that the second step
includes a photomask manufacturing process and a pattern on the
corrected photomask is corrected in terms of size by adjusting a
way of supply of an etching liquid in a wet etching step for a Cr
film in the photomask manufacturing process.
[0028] The way of supply of a developer applies to a way of supply
of the etching liquid in the wet etching of a Cr film without any
change therein. Hence, a size of a Cr film-lacking section can be
corrected even when an area of a resist-lacking section is the
same.
[0029] In the manufacturing process of a semiconductor device of
the present invention, it is also allowed that the second step
includes a photomask manufacturing process and a pattern of the
corrected photomask is corrected in terms of size by adjusting a
strength of a magnetic field in a dry etching step for a Cr film of
the photomask manufacturing process.
[0030] By adjusting a strength of a magnetic field, a flow of a
plasma gas, which is constituted of an etching gas, can be
controlled. As a result, a desired, corrected photomask can be
obtained by adjusting an etching rate in each of central and
peripheral regions and an intermediate region therebetween.
[0031] In the manufacturing process for a semiconductor device of
the present invention, it is desirable that the magnetic field in a
dry etching step for the Cr film is a rotating magnetic field
formed such that a combination of two orthogonal magnetic fields
are applied in synchronism with each other in parallel to a surface
of the corrected photomask and adjustment of a strength of the
magnetic field is effected by controlling the two magnetic fields
independently of each other.
[0032] By adjusting the two magnetic fields independently of each
other, the center of the rotating magnetic field can be migrated
along a surface of the photomask. Hence, when optical distortion
occurs in one side portion of the photomask or in the like case,
the above described constitution is preferable in correcting such a
kind of optical distortion. Moreover, this can applies to
cancellation of optical distortion whose degree changes along a
concentric circle.
[0033] In the manufacturing process of a semiconductor device of
the present invention, it is also allowed that the second step
includes a photomask manufacturing process and a pattern on the
corrected photomask is corrected in terms of size by combining
factors for a change in size of a pattern in at least two steps
among a resist writing step, a resist developing step and a Cr film
etching step of the photomask manufacturing process.
[0034] As described above, a size of a pattern in each of regions
can increase or decease with a larger adjustment width by combining
at least two steps. Hence, as high degree an optical distortion as
not to be adjustable in a single step of an exposure apparatus can
be adjusted with simplicity and convenience.
[0035] A photomask of the present invention is a photomask having a
pattern thereon, employed in transfer of the pattern onto a
semiconductor wafer by means of an exposure apparatus. Correction
of a size of a pattern on the photomask is performed such that
correction is effected on a variation in reduction rate of a
transferred pattern in each of regions caused by optical distortion
of the exposure apparatus.
[0036] This photomask is a corrected one described above and the
photomask can be fabricated with simplicity and convenience. Since
optical distortion on a pattern on the photomask is corrected in
terms of size, a transferred pattern with an as-intended size can
be obtained in each of regions thereof.
[0037] In the photomask of the present invention, a reduction rate
can be regarded to be one as measured in each of the regions of a
transferred pattern from a fundamental pattern formed on a
reference photomask exclusively used in measurement of optical
distortion of an exposure apparatus.
[0038] Since optical distortion is measured as a size of each of
regions, the optical distortion can be evaluated with much of
simplicity and convenience and a method for reflecting the measured
optical distortion on fabrication of a corrected photomask is also
very simple and convenient. Therefore, a tremendous number of
photomasks required in a manufacturing process for a semiconductor
device can be replaced only with a necessary number of corrected
ones in a simple and convenient manner. As a result, for example, a
semiconductor device having a memory capacity larger than a
currently available one by one rank can be manufactured using
currently existing facilities with none of an additional large
investment thereon.
[0039] A manufacturing apparatus for a semiconductor device
provided with a photomask of the present invention is a
manufacturing apparatus for a semiconductor apparatus to transfer a
pattern arranged on a photomask onto a semiconductor wafer to
perform exposure. In the manufacturing apparatus for a
semiconductor device, the photomask is disposed between a light
source for exposure and the semiconductor wafer.
[0040] By employing the above described manufacturing apparatus for
a semiconductor device, a high reliability semiconductor device can
be provided with a high yield.
[0041] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a diagram representing an exposure step in a
manufacturing process for a semiconductor device of a first
embodiment of the present invention;
[0043] FIG. 2 is a plan view representing an example pattern on a
photomask in a manufacturing process for a semiconductor device of
the first embodiment;
[0044] FIG. 3 is a plan view representing another example pattern
on a photomask in a manufacturing process of a semiconductor device
of the first embodiment;
[0045] FIG. 4 is a plan view representing an example unit pattern
as a kind of fundamental pattern on a reference photomask for
measurement of optical distortion of an exposure apparatus;
[0046] FIG. 5 is a plan view representing a state where the unit
patterns on the reference photomask shown in FIG. 4 are transferred
onto a semiconductor wafer by a stepper;
[0047] FIG. 6 is a diagram representing a distribution of a
reduction rate shown in Table 1;
[0048] FIG. 7 is a sectional view representing a state of a
photomask having a synthetic quartz substrate on which a Cr film is
vapor deposited and then coated with a photoresist in a
manufacturing process flow for a photomask in a second embodiment
of the present invention;
[0049] FIG. 8 is a sectional view representing a state of a
photomask, over a resist on which EB irradiation has been performed
following the stage of FIG. 1, and in the resist on which a writing
section is formed;
[0050] FIG. 9 is a sectional view representing a state of the
photomask, from the resist on which the writing section has been
removed following the stage of FIG. 8;
[0051] FIG. 10 is a sectional view representing a state of the
photomask, a Cr film on which has been etched off with the resist
as a mask following the stage of FIG. 9;
[0052] FIG. 11 is a sectional view representing a state of the
photomask, the resist on which is removed following the stage of
FIG. 10;
[0053] FIG. 12 is a view describing a step in which a dose has a
distribution in EB writing in the second embodiment of the present
invention;
[0054] FIG. 13 is a sectional view of a state of the photomask
completed through a developing step and an etching step, following
the state of FIG. 12;
[0055] FIG. 14 is a view describing a step in which an exposure
process is performed using the photomask shown in FIG. 13;
[0056] FIG. 15 is a view describing a step in which a beam diameter
has a distribution in EB writing in a third embodiment of the
present invention;
[0057] FIG. 16 is a sectional view of a state of the photomask
completed through a developing step and an etching step, following
the stage of FIG. 15;
[0058] FIG. 17A is a view of a step of supplying a developer, FIG.
17B is a view of a step in stoppage of supply of the developer to
allow a developing reaction to proceed, FIG. 17C is a step of
supplying a rinse liquid and FIG. 17D is a step in stoppage of
supply of the rinse liquid, all being included in the fourth
embodiment of the present invention;
[0059] FIG. 18 is a sectional view describing a state of a
photomask after EB writing is over in the fourth embodiment of the
present invention;
[0060] FIG. 19 is a view describing a state in which a developer is
supplied from a movable nozzle located in the central region of a
photomask;
[0061] FIG. 20 is a view describing a state in which a developer is
supplied from a movable nozzle located in the peripheral region of
the photomask;
[0062] FIG. 21 is a view describing a state in which a etching
liquid is supplied from a movable nozzle located in the central
region of a photomask in a fifth embodiment of the present
invention;
[0063] FIG. 22 is a view describing a state in which a etching
liquid is supplied from a movable nozzle located in the peripheral
region of the photomask in the fifth embodiment;
[0064] FIG. 23 is a view describing a state of etching in a case
where a magnetic field strength is low in magnetic-enhanced dry
etching of a sixth embodiment of the present invention;
[0065] FIG. 24 is a view describing a state of etching in a case
where a magnetic field strength is higher than that of FIG. 23 in
magnetic-enhanced dry etching of the sixth embodiment;
[0066] FIG. 25 is a view describing a state of etching in a case
where a magnetic field strength is higher than that of FIG. 24 in
magnetic-enhanced dry etching of the sixth embodiment;
[0067] FIG. 26 is a plan view describing dry etching applied with a
plurality of magnetic fields of a seventh embodiment of the present
invention;
[0068] FIG. 27 is a front view representing a configuration in the
dry etching of FIG. 26;
[0069] FIG. 28 is a plan view representing an example photomask
having a prior art uncorrected pattern; and
[0070] FIG. 29 is a plan view representing another example
photomask having a prior art uncorrected pattern.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Below, description will be given of embodiments of the
present invention using the accompanying drawings.
[0072] [First Embodiment]
[0073] In a manufacturing process for a semiconductor device of the
first embodiment of the present invention, description will be
given including a correcting process for optical distortion of an
exposure apparatus. Referring to FIG. 1, in an exposure apparatus
5, light rays radiated from a light source 5a are transmitted
through a photomask 3 on which a pattern is formed and projected
onto a surface of a semiconductor wafer to make an image. A
photoactive photoresist 2 is applied on the wafer 1 in advance of
exposure. When a positive photoresist is employed, part of the
photoresist 2 irradiated with light transmitted through a light
transparent region of a pattern 3 is removed in a developing step
coming later, while part of the photoresist 2 not irradiated with
the light is remained. Thereby, a pattern on the photomask is
transferred on the wafer as a resist pattern. The above described
step is an exposure/transfer step in a manufacturing process for a
semiconductor device. Note that a light source for exposure may be
of any type with which writing can be effected on the resist: for
example laser light or an electron beam.
[0074] FIG. 2 is a plan view representing an example corrected
photomask 3 in the first embodiment of the present invention. The
mask is a mask obtained by correcting a pattern 113a of no
correction on the photomask 103 shown in FIG. 28. Moreover, FIG. 3
is a plan view representing another example corrected photomask 3
in the first embodiment of the present invention. The example of
FIG. 3 is a mask obtained by correcting a pattern 113b of no
correction on the photomask 103 shown in FIG. 29. In the present
invention, objects include not only a pattern set 13a composed of
similar patterns in a repeated arrangement as shown in FIG. 2, but
also a pattern 13b with no repetition of pattern as shown in FIG.
3.
[0075] Next, description will be given of a manufacturing process
for the patterns on corrected photomasks shown in respective FIGS.
2 and 3.
[0076] First of all, in order to measure optical distortion of an
exposure apparatus in terms of size, for example, a reference
photomask 23 as shown in FIG. 4 is prepared on which 9 cross
patterns 24, which are unit patterns (fundamental pattern) for use
in size evaluation for an element, are arranged. Positions of the
unit patterns each correspond to a point in the vicinity of the
center of each of regions of the reference photomask 23. The 9 unit
patterns 24 are all formed so as to be of the same size as each
other. Then, as shown in FIG. 5, the unit patterns are projected
onto a surface of a wafer and such a projection is repeated by a
stepper to transfer images of the unit pattern set onto all the
surface of the wafer. An issue to be processed with respect to
optical distortion of the exposure apparatus is a variation in size
of the unit patterns P1 to P9 in a one exposure step. That is, the
issue points out a variation in size of the unit patterns P1 to P9
in a one step field of a transfer pattern set 30 in FIG. 5. By
measuring an element size on the photomask and an element size on
the semiconductor wafer, the optical distortion of the exposure
apparatus can be determined. Results of the measurement are shown
in Table 1.
1TABLE 1 Regions P1 P2 P3 P4 P5 P6 P7 P8 P9 Pattern 1.52 1.53 1.56
1.52 1.53 1.54 1.57 1.56 1.53 size on mask (M) Trans- 0.32 0.31
0.33 0.31 0.30 0.31 0.33 0.32 0.33 ferred pattern size (U) Re-
0.211 0.203 0.212 0.204 0.196 0.201 0.210 0.205 0.216 duction rate
(U/M) unit (.mu.m)
[0077] When an exposure apparatus has no optical distortion, a
pattern on the photomask is to be transferred onto a surface of the
wafer at a 1/5.times.reduction rate. Due to optical distortion of
the exposure apparatus, however, a reduction rate is not the same
all over the surface of the photomask; reduction rates are
different between in the central region and in the peripheral
region. According to the results of Table 1, it is seen that the
patterns in the peripheral region are transferred onto the wafer
with a size larger than that in the central region. That is, the
exposure apparatus has a characteristic that patterns in the
peripheral region of a mask are transferred onto a wafer with a
size larger or at a reduction rate larger than that in the central
region.
[0078] In FIG. 6, shown is a result of plotting of the reduction
rate of Table 1 in regions. While optical distortion occurs at the
same level along a concentric circle with an optical axis of the
mask as a center, changing radially; in FIG. 6 as well, the same
values of a reduction rate are located along a concentric circle
and optical distortion changes radially while keeping values equal
to each other along a concentric circle.
[0079] Corrected photomasks shown in FIGS. 2 and 3 can be obtained
in the following way: Note that for convenience of description,
regions in which the unit patterns P1 to P9, respectively, are
located are indicated by symbols P1 to P9 of the respective unit
patterns P1 to P9.
[0080] Describing of the corrected photomask of FIG. 2, the
patterns a of the same size of FIG. 28 are rewritten in proportion
to a reciprocal of a reduction rate shown in FIG. 6. That is, a
smaller pattern size al is adopted in the peripheral regions P1,
P3, P7 and P9 in which a pattern is harder to be shrunk in transfer
when compared with the other regions, while contrary to this, a
larger pattern size a.sub.3 is adopted in the central region P5 in
which a pattern is shrunk at a degree larger than in the other
regions. A pattern size a.sub.2 is adopted in the intermediate
regions P2, P4, P6 and P8. With such a procedure, pattern
correction rates a.sub.3/a (for the central region), a.sub.1/a (for
the peripheral region) and a.sub.2/a (for the intermediate region)
can be obtained in the respective regions of FIG. 2.
[0081] A corrected photomask shown in FIG. 3 is that obtained by
rewriting the pattern shown in FIG. 29 such that a size L in each
region of FIG. 29 is changed in proportion to a reciprocal of a
corresponding reduction rate. That is, a size L.sub.1 of the
peripheral region is set smaller than that of the other regions, a
size L.sub.3 of the peripheral region is set larger than that of
the other regions and a size L.sub.2 of the intermediate region is
set as an intermediate value therebetween.
[0082] By use of the corrected photomasks of FIGS. 2 and 3 obtained
by correcting with respect to optical distortion in transferring
patterns onto a wafer, corrected transferred patterns are obtained
and in turn, patterns with as-intended sizes specific to respective
regions can be transferred. As a result, a corrected reduction
rate, that is a rate in size between a corrected transferred
pattern and a pattern on a photomask prior to the correction,
assumes the same values, regardless of a region, throughout all the
regions.
[0083] In the above description, description is given of the case
where a pattern is transferred larger as the pattern is located
closer to the peripheral region. However, there is no specific
limitation to this tendency with respect to optical distortion of
an exposure apparatus, but a pattern is transferred larger either
in the central region or in a specific side of the peripheral
region; an optical distortion characteristic alters in various ways
according to an exposure apparatus. The present invention makes it
possible that a pattern image of a uniform size can be, in any
case, transferred onto a wafer by use of a photomask corrected
according to the characteristic of optical distortion of a
particular exposure apparatus.
[0084] In the mean time, a measuring method for optical distortion
is described above with patterns on a photomask arranged such that
one cross pattern is located in each region which is one of 9
regions obtained by dividing a photomask into 9 pieces for
convenience of description. It is naturally needless to say that
there is no specific limitation to this way to divide the photomask
into the 9 regions. By dividing the photomask into more regions
each with a smaller area, accuracy of correction can be
enhanced.
[0085] When optical distortion of an exposure apparatus, that is a
distribution of a reduction rate of a cross pattern, is measured
and a pattern is formed on a photomask such that a size thereof is
inverse proportion to a reduction rate, then a transferred pattern
set each with a uniform size as intended can be obtained. As a
result, microfabrication of a semiconductor device can be realized
in a simple and convenient manner without installing facilities of
a immensely great cost.
[0086] [Second Embodiment]
[0087] In the second embodiment of the present invention,
description will be given of a manufacturing process for a
photomask corrected with respect to optical distortion, for use in
the above described manufacturing process for a semiconductor
device.
[0088] First of all, description is directed to a manufacturing
process for a photomask used in a manufacturing process for a
semiconductor device. As shown in FIG. 7, in a first stage, a Cr
film 32 is vapor deposited onto a synthetic quartz substrate 31 as
a base of a photomask and then, an EB resist 33, for example a
positive resist ZEP-7000 (a registered trade mark) made by Nihon
Zeon K.K., is spin-coated thereon to a desired thickness of about
400 nm. Thereafter, the photoresist coat is baked at 190.degree. C.
for one min. Following the baking step, writing is performed by an
EB (Electron Beam) writing apparatus (not shown) to form a writing
section 33q, which is a portion irradiated with EB. Thereafter,
when a pattern image in the photoresist 33 is developed by a
developer, the writing section 33q is selectively removed to form
resist-lacking sections 33c and 33e as shown in FIG. 9. The Cr film
32 is partially etched off based on the resist pattern to complete
a photomask. When wet etching is adopted in the etching step, the
etching liquid is sprayed. On the other hand, when dry etching is
adopted in the etching step, the Cr film is partially etched off
using a magnetic-enhanced dry etching apparatus as an example. By
the etching step, Cr film-lacking sections 32c and 32e are formed
as shown in FIG. 10. Thereafter, the resist is removed as shown in
FIG. 11 to complete a photomask 3 composed of the synthetic quartz
substrate 31 and the Cr film 32 with the film-lacking sections.
[0089] A photomask having a pattern size distribution to correct
optical distortion of an exposure apparatus as shown in the first
embodiment is fabricated by means of the following process in the
second embodiment.
[0090] When writing on a mask is performed by means of an EB
writing apparatus, a size of a writing site alters according to a
dose, which is an irradiation amount of an electron beam. When a
positive resist is employed, a size of the writing section 33q
increases in proportion to a dose and over-processing occurs with
an excessive dose irradiated.
[0091] FIG. 12 is a view representing a manufacturing process for a
photomask to be corrected with respect to optical distortion having
a characteristic that a transfer size is smaller in the central
region but larger in the peripheral region as shown in Table 1. In
FIG. 12, a dose of EB is more in the central region of a photomask
but less in the peripheral region. As a result, a writing section
33q is larger in the central region, but smaller in the peripheral
region. When the manufacturing process for a photomask as shown in
FIGS. 7 to 12 is applied to a resist 33 having such a writing
section distribution, then a photomask 3 having a pattern shown in
FIG. 13 can be obtained. In the photomask of FIG. 13, a diameter
a.sub.3 of a Cr-lacking section 32c in the central region is larger
than a diameter a.sub.1 of a Cr-lacking section 32e in the
peripheral region.
[0092] When thus corrected photomask is used in an exposure
apparatus having the measurement result of Table 1 to form a
transferred pattern, then, for example, gate patterns with a
uniform size a.sub.0 as intended or the like can be obtained in a
photoresist 42 on a semiconductor substrate 41 as shown in FIG.
14.
[0093] [Third Embodiment]
[0094] The third embodiment of the present invention is a process
for performing correction of a pattern on a photomask in a writing
step similar to the second embodiment. A process shown in FIG. 15
is a process in which in EB writing, a beam diameter of EB with
which a resist is irradiated is adjusted, for example, such that a
beam diameter is larger in the central region and smaller in the
peripheral region. A large sized writing section 33q is formed in
an irradiated portion where a beam diameter is larger and contrary
to this, a smaller writing section 33q is formed in an irradiated
portion where a beam diameter is smaller. Thereafter, by applying
the manufacturing process for a photomask shown in FIGS. 7 to 11, a
photomask 3 shown in FIG. 16 can be obtained.
[0095] In FIG. 16, a diameter as of a Cr-lacking section 32c in the
central region where an EB beam diameter is larger is larger than a
diameter a.sub.1 of a Cr-lacking 32e in the peripheral region. As a
result, when the photomask shown in FIG. 16 is used in an exposure
apparatus having optical distortion as shown in Table 1, then a
transferred pattern having a uniform distribution as intended can
be obtained as shown in FIG. 14.
[0096] [Fourth Embodiment]
[0097] In the fourth embodiment of the present invention,
description will be given of a manufacturing process for a
photomask which is corrected in a developing step with respect to
optical distortion of an exposure apparatus. Detailed description
will be first given of a developing step. FIG. 17A is a figure
showing a substep in which a developer 35 is supplied while
rotating a photoresist having a writing section 33q about its
center and FIG. 17B is a figure showing a substep in which supply
of the developer is temporarily ceased to progress a developing
chemical reaction for t1 second. The substeps of FIGS. 17A and 17B
are major substeps. Moreover, FIG. 17C is a figure showing a
substep in which a rinse liquid 36 to remove the developer is
applied and FIG. 17D is a figure showing a substep in which supply
of the rinse liquid is ceased for t2 second. In the developing
step, a series of the substeps shown in FIGS. 17A to 17D are
repeated several times.
[0098] FIG. 18 is a photomask having a resist including writing
sections 33q in a stage after EB writing is over. For convenience
of description, it is assumed that areas of the writing sections
33q are uniform regardless of respective locations on a resist.
When in development of the photomask in the state of FIG. 18, a
developer nozzle 37 is positioned in the central region or is
directed toward the central region, then an unused, fresh developer
is first supplied in the central region. Although the photomask is
developed while rotating, a fresh developer is supplied more in the
central region than in the peripheral region; therefore, a
developing reaction progresses faster in the central region than in
the peripheral region. As a result, as shown in FIG. 19, a diameter
of a resist-lacking section 33c in the central region is larger
than a diameter of a resist-lacking section 33e in the peripheral
region.
[0099] To the contrary, as shown in FIG. 20, when the developer
nozzle 37 is positioned in the peripheral region or directed toward
the peripheral region, an unused, fresh developer is first supplied
in the peripheral region. Since the photomask is rotated during the
developing step, the fresh developer is supplied not only in part
of the peripheral region, but all over the peripheral region of the
photomask. As a result, as shown in FIG. 20, a diameter of the
resist-lacking section 33e in the peripheral region of the
photomask is larger than that of the resist-lacking section 33C in
the central region. While FIGS. 19 and 20 described above are for
the case where a movable nozzle is employed, a nozzle position is
unnecessary to be fixed through all the step of development. The
positions thereof shown in FIGS. 19 and 20 are alternately selected
with a prescribed period at one position to obtain a desired
pattern.
[0100] Moreover, it is easy to attain an idea from the above
description that when a plurality of nozzles are used in the
development, a supply amount of a developer is adjusted according
to regions: the central region and the peripheral region and
thereby, a size distribution of a resist-lacking section is
provided across the photomask.
[0101] When the photomask having a diameter distribution of a
resist-lacking section is subjected to the following manufacturing
steps, the photomask can be obtained in a completed form having a
desired size distribution of a Cr-lacking section.
[0102] [Fifth Embodiment]
[0103] In the fifth embodiment of the present invention,
description will be given of a manufacturing process for a
photomask having a desired size distribution in a wet etching step.
That is, in the wet etching, a size distribution can be achieved on
a photomask by altering a discharge direction of and a discharge
method for the etching liquid.
[0104] A case is considered of, for example, etching of a photomask
on which uniformly sized resist-lacking sections are distributed
for convenience of description. As shown in FIG. 21, even when
uniformly sized resist-lacking sections are distributed, a size of
a Cr film-lacking section 32c in the central region is larger than
that of a Cr film-lacking section 32e in the peripheral region when
an etching liquid nozzle 47 is positioned in the central region or
directed toward the central region.
[0105] To the contrary, as shown in FIG. 22, when the etching
liquid nozzle 47 is positioned in the peripheral region or directed
toward the peripheral region, an unused, fresh developer is first
supplied in the peripheral region. Since the photomask is rotated
during the developing site, the fresh developer is supplied not
only in part of the peripheral region, but also all over the
peripheral region of the photomask. As a result, as shown in FIG.
22, a diameter of a Cr film-lacking section 32e in the peripheral
region of the photomask is larger than that of a Cr film-lacking
section 32c in the central region.
[0106] Similar to the developing step, there is no need to fixedly
keep a nozzle position through all the step of the etching. The
positions thereof shown in FIGS. 21 and 22 are alternately selected
with a prescribed period at one position to obtain a desired
pattern.
[0107] Moreover, it is easy to attain an idea from the above
description that when a plurality of nozzles are used in the
etching, a supply amount of an etching liquid is adjusted according
to regions: the central region and the peripheral region and
thereby, a desired size distribution of a Cr film-lacking section
is provided across the photomask.
[0108] When the photomask having a size distribution of a Cr
film-lacking section is employed, a transferred pattern having a
desired size distribution including that of uniform sizes can be
obtained on a semiconductor wafer.
[0109] [Sixth Embodiment]
[0110] In the sixth embodiment of the present invention, a
photomask having a desired size distribution can be obtained by
control of a plasma by a magnetic field in dry etching.
[0111] It is assumed that resist-lacking sections have a
distribution of uniform sizes for the sake of convenience of
description. When a magnetic-enhanced dry etching is applied and a
magnetic flux density B is low as shown in FIG. 23, that is when a
magnetic field strength is weak, then a plasma flow constituted of
a etching gas is supplied more in the peripheral region and a Cr
film-lacking section 32e in the peripheral region is larger
compared with a Cr film-lacking section 32c in the central region.
As a magnetic field strength increases, sizes of Cr film-lacking
sections in the central region and peripheral region are almost
equal to each other as shown in FIG. 24. As a magnetic field
strength increases further, a size distribution can be obtained in
which a Cr-lacking section in the peripheral region is larger
compared with that in the central region.
[0112] As described above, even when resist-lacking sections have a
size distribution of uniform sizes, a photomask on which a desired
size distribution of a Cr-lacking section is formed can be obtained
by adjusting a strength of an applied magnetic field in plasma gas
dry etching.
[0113] [Seventh Embodiment]
[0114] In the seventh embodiment of the present invention, a
plurality of magnetic fields are applied in parallel to a photomask
surface to control a plasma gas flow in dry etching. In FIGS. 26
and 27, coils 51x and 52x are arranged such that magnetic fields
which have equal strengths to each other in X directions with
opposed senses are applied on the photomask, acting from both sides
thereof and furthermore, coils 51y and 52y are arranged such that
magnetic fields work on the photomask in Y direction similar to the
case of X direction. There is established a relation of Bx=B.sub.1
sin .theta.and By-B.sub.2 cos .theta., and Bx and By generate a
rotating magnetic field with a direction of rotation 57 on the
photomask in synchronism between Bx and By, between the X direction
magnetic field and the Y direction magnetic field. While a center
55 of the composite magnetic field is located at the center of the
photomask when B.sub.1 and B.sub.2 are equal in magnitude, by
altering magnitudes of B.sub.1 and B.sub.2 relatively, the center
can be shifted, for example, along a direction 56. As a result,
when optical distortion does not exist at the same level along a
concentric circle and an optical distortion alters with a gradient
in a prescribed direction, a size distribution of a Cr film-lacking
section which can correct such optical distortion can be provided
with simplicity and convenience. As a result, by altering magnetic
field strengths on a pattern independently using respective
magnetic field generators, a photomask can be obtained which
corrects any type of optical distortion.
[0115] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *