U.S. patent application number 11/187997 was filed with the patent office on 2006-01-26 for photo mask, focus measuring method using the mask, and method of manufacturing semiconductor device.
Invention is credited to Hiroshi Nomura.
Application Number | 20060019180 11/187997 |
Document ID | / |
Family ID | 34937898 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060019180 |
Kind Code |
A1 |
Nomura; Hiroshi |
January 26, 2006 |
Photo mask, focus measuring method using the mask, and method of
manufacturing semiconductor device
Abstract
A photo mask includes an asymmetrical diffraction grating
pattern in which diffraction efficiencies of plus primary
diffracted light and minus primary diffracted light are different,
the asymmetrical diffraction grating pattern including a shielding
portion which shields light, a first transmitting portion which
transmits light, and a second transmitting portion which transmits
light, a ratio of widths of the shielding portion, the first
transmitting portion, and the second transmitting portion being n11
where n is a positive real number except 2, the asymmetrical
diffraction grating pattern approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion, and a reference pattern
for obtaining an image as a reference for measuring a shift of an
image of the asymmetrical diffraction grating pattern.
Inventors: |
Nomura; Hiroshi;
(Kawasaki-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
34937898 |
Appl. No.: |
11/187997 |
Filed: |
July 25, 2005 |
Current U.S.
Class: |
430/5 ; 430/22;
430/30; 430/322; 430/323; 430/324 |
Current CPC
Class: |
G03F 7/70641 20130101;
G03F 7/706 20130101; G03F 1/44 20130101 |
Class at
Publication: |
430/005 ;
430/022; 430/030; 430/322; 430/323; 430/324 |
International
Class: |
G03C 5/00 20060101
G03C005/00; G03F 9/00 20060101 G03F009/00; G03F 1/00 20060101
G03F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2004 |
JP |
2004-217874 |
Claims
1. A photo mask comprising: an asymmetrical diffraction grating
pattern in which diffraction efficiencies of plus primary
diffracted light and minus primary diffracted light are different,
the asymmetrical diffraction grating pattern including a shielding
portion which shields light; a first transmitting portion which
transmits light; and a second transmitting portion which transmits
light, a ratio of widths of the shielding portion, the first
transmitting portion, and the second transmitting portion being
n:1:1 where n is a positive real number except 2, the asymmetrical
diffraction grating pattern approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; and a reference pattern
configured to obtain an image as a reference for measuring a shift
of an image of the asymmetrical diffraction grating pattern.
2. The photo mask according to claim 1, wherein the reference
pattern is an asymmetrical diffraction grating pattern symmetrical
to the asymmetrical diffraction grating pattern.
3. The photo mask according to claim 1, wherein the reference
pattern includes first and second reference patterns, and the
asymmetrical diffraction grating pattern is disposed between the
first and second reference patterns.
4. The photo mask according to claim 1, wherein the asymmetrical
diffraction grating pattern includes first and second asymmetrical
diffraction grating patterns, and the reference pattern is disposed
between the first and second asymmetrical diffraction grating
patterns.
5. The photo mask according to claim 1, wherein the asymmetrical
diffraction grating pattern includes first and second asymmetrical
diffraction grating patterns, the reference pattern includes first
and second reference patterns, the first asymmetrical diffraction
grating pattern and the first reference pattern are arranged in
parallel on a first line, and the second asymmetrical diffraction
grating pattern and the second reference pattern are arranged in
parallel on a second line vertical to the first line.
6. The photo mask according to claim 1, wherein the asymmetrical
diffraction grating pattern includes a plurality of asymmetrical
diffraction grating patterns, the reference pattern includes a
plurality of reference patterns, and the plurality of asymmetrical
diffraction grating patterns and the plurality of reference
patterns are arranged in parallel on a line, and alternately
arranged.
7. The photo mask according to claim 1, wherein the .theta. and the
n approximately satisfy 360.degree./(n+2)+.theta.=180.degree..
8. The photo mask according to claim 1, wherein the .theta. is
approximately 36.degree., and the n is approximately 0.5.
9. The photo mask according to claim 1, wherein the .theta. is
approximately 60.degree., and the n is approximately 1.
10. The photo mask according to claim 1, wherein the .theta. is
approximately 108.degree., and the n is approximately 3.
11. The photo mask according to claim 1, further comprising: a
device pattern.
12. The photo mask according to claim 2, further comprising: a
device pattern.
13. A focus measuring method comprising: preparing a focus test
mask, the focus test mask comprising: an asymmetrical diffraction
grating pattern in which diffraction efficiencies of plus primary
diffracted light and minus primary diffracted light are different,
the asymmetrical diffraction grating pattern including a shielding
portion which shields light, a first transmitting portion which
transmits light, and a second transmitting portion which transmits
light, a ratio of widths of the shielding portion, the first
transmitting portion, and the second transmitting portion being
n:1:1 where n is a positive real number except 2, the asymmetrical
diffraction grating pattern approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; and a reference pattern
configured to obtain an image as a reference for measuring a shift
of an image of the asymmetrical diffraction grating pattern;
applying a photosensitive agent on the substrate; exposing images
of the asymmetrical diffraction grating pattern and the reference
pattern in the photo mask at the same time onto the substrate;
developing a pattern transferred on the substrate; and measuring a
relative distance between the images of the asymmetrical
diffraction grating pattern and the reference pattern formed on the
substrate.
14. The focus measuring method according to claim 13, wherein the
reference pattern is an asymmetrical diffraction grating pattern
symmetrical to the asymmetrical diffraction grating pattern.
15. The focus measuring method according to claim 13, wherein the
reference pattern includes first and second reference patterns, and
the asymmetrical diffraction grating pattern is disposed between
the first and second reference patterns.
16. The focus measuring method according to claim 13, wherein the
asymmetrical diffraction grating pattern includes first and second
asymmetrical diffraction grating patterns, and the reference
pattern is disposed between the first and second asymmetrical
diffraction grating patterns.
17. The focus measuring method according to claim 13, wherein the
asymmetrical diffraction grating pattern includes first and second
asymmetrical diffraction grating patterns, the reference pattern
includes first and second reference patterns, the first
asymmetrical diffraction grating pattern and the first reference
pattern are arranged in parallel on a first line, and the second
asymmetrical diffraction grating pattern and the second reference
pattern are arranged in parallel on a second line vertical to the
first line.
18. The focus measuring method according to claim 13, wherein the
asymmetrical diffraction grating pattern includes a plurality of
asymmetrical diffraction grating patterns, the reference pattern
includes a plurality of reference patterns, and the plurality of
asymmetrical diffraction grating pattern and plurality of the
reference pattern are arranged in parallel on a line, and
alternately arranged.
19. The focus measuring method according to claim 13, wherein the
.theta. and the n approximately satisfy
360.degree./(n+2)+.theta.=180.degree..
20. A method of manufacturing a semiconductor device comprising:
preparing an exposure mask, the exposure mask comprising an
asymmetrical diffraction grating pattern in which diffraction
efficiencies of plus primary diffracted light and minus primary
diffracted light are different, the asymmetrical diffraction
grating pattern including a shielding portion which shields light,
a first transmitting portion which transmits light, and a second
transmitting portion which transmits light, a ratio of widths of
the shielding portion, the first transmitting portion, and the
second transmitting portion being n:1:1 where n is a positive real
number except 2, the asymmetrical diffraction grating pattern
approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; a reference pattern
configured to obtain an image which is a reference in measuring a
shift of an image of the asymmetrical diffraction grating pattern;
and a device pattern; applying a photosensitive agent on the
substrate; exposing images of the asymmetrical diffraction grating
pattern, the reference pattern, and the device pattern in the photo
mask at the same time onto the substrate; developing a pattern
transferred on the substrate; inspecting the device pattern formed
on the substrate; and measuring a relative distance between the
images of the asymmetrical diffraction grating pattern and the
reference pattern in a case where a defect is detected in the
device pattern in the inspecting the device pattern formed on the
substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2004-217874,
filed Jul. 26, 2004, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a photo mask for use in a
semiconductor field, a focus measuring method using the mask, and a
method of manufacturing a semiconductor device.
[0004] 2. Description of the Related Art
[0005] A tolerance of focus permitted in lithography has been
narrowed as a design rule of a semiconductor device to be
manufactured is miniaturized. When the tolerance of the focus is
narrowed, flatness of a wafer and specifications with respect to
curvature of field of an exposure apparatus has been strict.
Moreover, a high-precision measuring method of the focus, curvature
of field and the like using a resist pattern transferred onto the
wafer has become important.
[0006] A focus test mask comprising an asymmetrical diffraction
grating pattern and a reference pattern, and a focus measuring
method using the focus test mask and utilizing a phenomenon in
which an image of the asymmetrical diffraction grating pattern
shifts in proportion to a focus value have been known (Jpn. Pat.
No. 3297423). Since the focus measuring method has a high
measurement precision having a measurement error of 5 nm or less,
and the measuring is simple, the method can be said to be one of
most promising techniques at present.
[0007] The asymmetrical diffraction grating pattern comprises a
shielding portion, a transmitting portion, and 90.degree. phase
grooved portion. A line width ratio of the shielding portion,
transmitting portion, and 90.degree. phase grooved portion is
ideally 2:1:1. On the other hand, an alternating type phase shift
exposure mask including a pattern (device pattern) for
manufacturing an actual semiconductor product comprises a
180.degree. phase grooved portion.
[0008] A method of manufacturing an exposure mask comprising the
asymmetrical diffraction grating pattern and the device pattern
includes a step of forming the 90.degree. phase grooved portion,
and a step of forming the 180.degree. phase grooved portion. When
these two steps are performed, a manufacturing process is
complicated, and manufacturing costs remarkably rise. This respect
will be further described hereinafter.
[0009] The step of forming the 180.degree. phase grooved portion
includes a step of forming a trench vertically in the surface of a
quartz glass substrate by a dry process (e.g., a vertical etching
process such as an RIE process); and a step of expanding the trench
by predetermined amounts in a lateral direction and a vertical
direction by a wet process (isotropic etching process). A sum of
grooved amounts by the dry and wet processes is a grooved amount by
which a phase of transmitted light delays by 180.degree. as
compared with a case where there is not any grooved portion.
[0010] To obtain a high-precision alternating type phase shift
exposure mask, the groove has to be made vertically, and further
expanded in the lateral direction. However, an etching process to
expand the groove only in the lateral direction does not exist.
Therefore, as described above, combined use of the dry and wet
processes is required. Since an amount to be expanded in the
lateral direction needs to be controlled with a high precision, the
grooved amount in the dry process is a depth obtained by
subtracting the amount to be expanded in the lateral direction from
the amount corresponding to 180.degree.. On the other hand, to
obtain a high-precision focus test mask, a grooved portion
corresponding to 90.degree. has to be formed only by the dry
process.
[0011] Therefore, in a conventional technique, the above-described
etching processes have to be separately performed in order to
realize the high-precision alternating type phase shift exposure
mask and the high-precision focus test mask in one exposure mask,
and a mask manufacturing cost rises by at least 30% or more as
compared with the conventional alternating type phase shift
exposure mask.
BRIEF SUMMARY OF THE INVENTION
[0012] According to an aspect of the present invention, there is
provided a photo mask comprising: an asymmetrical diffraction
grating pattern in which diffraction efficiencies of plus primary
diffracted light and minus primary diffracted light are different,
the asymmetrical diffraction grating pattern including a shielding
portion which shields light; a first transmitting portion which
transmits light; and a second transmitting portion which transmits
light, a ratio of widths of the shielding portion, the first
transmitting portion, and the second transmitting portion being
n:1:1 where n is a positive real number except 2, the asymmetrical
diffraction grating pattern approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; and a reference pattern
configured to obtain an image as a reference for measuring a shift
of an image of the asymmetrical diffraction grating pattern.
[0013] According to an aspect of the present invention, there is
provided a focus measuring method comprising: preparing a focus
test mask, the focus test mask comprising: an asymmetrical
diffraction grating pattern in which diffraction efficiencies of
plus primary diffracted light and minus primary diffracted light
are different, the asymmetrical diffraction grating pattern
including a shielding portion which shields light, a first
transmitting portion which transmits light, and a second
transmitting portion which transmits light, a ratio of widths of
the shielding portion, the first transmitting portion, and the
second transmitting portion being n:1:1 where n is a positive real
number except 2, the asymmetrical diffraction grating pattern
approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; and a reference pattern
configured to obtain an image as a reference for measuring a shift
of an image of the asymmetrical diffraction grating pattern;
applying a photosensitive agent on the substrate; exposing images
of the asymmetrical diffraction grating pattern and the reference
pattern in the photo mask at the same time onto the substrate;
developing a pattern transferred on the substrate; and measuring a
relative distance between the images of the asymmetrical
diffraction grating pattern and the reference pattern formed on the
substrate.
[0014] According to an aspect of the present invention, there is
provided a method of manufacturing a semiconductor device
comprising: preparing an exposure mask, the exposure mask
comprising an asymmetrical diffraction grating pattern in which
diffraction efficiencies of plus primary diffracted light and minus
primary diffracted light are different, the asymmetrical
diffraction grating pattern including a shielding portion which
shields light, a first transmitting portion which transmits light,
and a second transmitting portion which transmits light, a ratio of
widths of the shielding portion, the first transmitting portion,
and the second transmitting portion being n:1:1 where n is a
positive real number except 2, the asymmetrical diffraction grating
pattern approximately satisfying
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
where .theta. (.noteq.90.degree.) indicates an absolute value of a
difference between a phase of the light transmitted through the
first transmitting portion and that of the light transmitted
through the second transmitting portion; a reference pattern
configured to obtain an image which is a reference in measuring a
shift of an image of the asymmetrical diffraction grating pattern;
and a device pattern; applying a photosensitive agent on the
substrate; exposing images of the asymmetrical diffraction grating
pattern, the reference pattern, and the device pattern in the photo
mask at the same time onto the substrate; developing a pattern
transferred on the substrate; inspecting the device pattern formed
on the substrate; and measuring a relative distance between the
images of the asymmetrical diffraction grating pattern and the
reference pattern in a case where a defect is detected in the
device pattern in the inspecting the device pattern formed on the
substrate.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0015] FIG. 1 is a plan view schematically showing a photo mask
(focus test mask) of an embodiment;
[0016] FIG. 2 is a plan view schematically showing another photo
mask (exposure mask) of the embodiment;
[0017] FIG. 3 is a plan view showing details of a test mask of the
embodiment;
[0018] FIG. 4 is a sectional view along arrows A-A' of FIG. 3;
[0019] FIGS. 5A to 5H are sectional views showing a method of
manufacturing the exposure mask of the embodiment;
[0020] FIG. 6 is a sectional view showing the exposure mask of the
embodiment;
[0021] FIG. 7 is a diagram showing a relation between n and
.theta.;
[0022] FIGS. 8A to 8F are sectional views of PSG patterns
corresponding to n=0.5, 1.0, 1.5, 2.0, 2.5, 3.0;
[0023] FIGS. 9A to 9C are plan views showing test marks including
typical reference patterns;
[0024] FIGS. 10A to 10C are plan views showing test marks capable
of eliminating measurement errors attributed to a measuring
apparatus;
[0025] FIGS. 11A to 11C are plan views showing another test marks
capable of eliminating the measurement errors attributed to the
measuring apparatus;
[0026] FIG. 12 is a plan view showing a test mark capable of
measuring focus and astigmatism;
[0027] FIGS. 13A to 13D are plan views showing test marks
corresponding to automatic measurements by an alignment shift
inspection apparatus;
[0028] FIGS. 14A and 14B are sectional views along A-A' and B-B' of
FIG. 13D;
[0029] FIGS. 15A and 15B are plan views of test marks capable of
linearizing a relation between a focus value and a positional
shift;
[0030] FIG. 16 is a plan view showing an exposure mask including
the test mark of FIG. 15;
[0031] FIG. 17 is an explanatory view of a double exposure method
using the exposure mask of FIG. 16; and
[0032] FIG. 18 shows a test mark for measuring a focus based on a
profile of reflected light.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings.
[0034] FIGS. 1 and 2 are plan views schematically showing a photo
mask of the embodiment. Concretely, FIG. 1 shows an example of a
focus test mask PM1, and FIG. 2 shows an example of an exposure
mask PM2.
[0035] The focus test mask PM1 comprises a quartz glass substrate
1, and a test mark TM for focus measurement, provided on the quartz
glass substrate 1.
[0036] The exposure mask PM2 comprises the quartz glass substrate
1, the test mark TM provided on the quartz glass substrate 1, and
an alternating type phase shift mask PSM provided on the quartz
glass substrate 1 and including a pattern (device pattern) for
manufacturing an actual semiconductor product. The phase shift mask
PSM comprises a shielding portion, and first and second
transmitting portions (phase grooved portions). An absolute value
of a difference between phases of lights transmitted through the
first and second transmitting portions is 180.degree..
[0037] Each of the test marks TM in the focus test masks PM1, PM2
comprises an asymmetrical diffraction grating pattern (hereinafter
referred to as the PSG pattern) 2 including a periodic pattern
which differs in diffraction efficiency with plus and minus primary
diffracted lights, and a reference pattern 3.
[0038] FIG. 3 is a plan view showing details of the PSG pattern 2.
FIG. 4 is a sectional view along arrows A-A' of FIG. 3.
[0039] The PSG pattern 2 comprises shielding portions 4 which are
provided on the glass substrate 1 and shield the light; the first
transmitting portions 5 which are provided on the glass substrate 1
and transmit the light; and the second transmitting portions 6
(phase grooved portions) which are provided on the glass substrate
1 and transmit the light.
[0040] The shielding portion 4, the first transmitting portion 5,
and the second transmitting portion 6 satisfy the following two
equations ([1], [2]). W1:W2:W3=n:1:1 [Equation 1]
163.degree..ltoreq.360.degree./(n+2)+.theta..ltoreq.197.degree.
[Equation 2]
[0041] W1 . . . width of the shielding portion 4
[0042] W2 . . . width of the first transmitting portion 5
[0043] W3 . . . width of the second transmitting portion 6
[0044] n . . . positive real number other than 2
[0045] .theta. . . . absolute value of the difference between the
phase of the light transmitted through the first transmitting
portion 5 and that of the light transmitted through the second
transmitting portion 6. Additionally, 90.degree. is excluded.
[0046] FIGS. 5A to 5H are sectional views showing a method of
manufacturing the exposure mask PM2. A left side of a one-dot chain
line shows a region (PSG region) occupied by the PSG pattern 2 in
the mask, and a right side of the one-dot chain line shows a region
(alternating PSM region) occupied by the phase shift mask PSM in
the mask.
[0047] First, as shown in FIG. 5A, a chromium film (shielding film)
4 to be processed into the shielding portion is formed on the
quartz glass substrate 1.
[0048] Next, as shown in FIG. 5B, a resist film is formed on the
chromium film 4, and thereafter exposing and developing are
performed with respect to the resist film to form a resist pattern
11. The resist pattern 11 forms shielding portions in a PSG region
and alternating PSM region. The resist film is exposed, for
example, by EB drawing.
[0049] Next, as shown in FIG. 5C, the chromium film 4 is etched
using the resist pattern 11 a mask. As a result, the shielding
portions 4 comprising chromium are formed in the PSG region and
alternating PSM region. Thereafter, the resist pattern 11 is
removed.
[0050] In the present embodiment, a step of forming the resist
pattern for forming the shielding portion 4 in the PSG region, and
a step of forming the resist pattern for forming the shielding
portion in the alternating PSM region are simultaneously performed
in the step of FIG. 5B. Furthermore, an etching step for forming
the shielding portion 4 in the PSG region, and an etching step for
forming the shielding portion in the alternating PSM region are
simultaneously performed in the step of FIG. 5C. Therefore, a
manufacturing process of the exposure mask PM2 of the present
embodiment is not changed as compared with the manufacturing
process of a phase shift mask of a conventional alternating
type.
[0051] It is to be noted that the step of forming the resist
pattern for forming the shielding portion 4 in the PSG region, and
the step of forming the resist pattern for forming the shielding
portion in the alternating PSM region may be performed in separate
steps, and the etching step for forming the shielding portion 4 in
the PSG region and the etching step for forming the shielding
portion in the alternating PSM region may be performed in separate
steps.
[0052] In this case, the process of forming the shielding portion 4
in the PSG region, and the process of forming the shielding portion
in the alternating PSM region can be easily optimized. For example,
the step of forming the resist pattern for forming the shielding
portion 4 in the PSG region may be performed using a photo repeater
which is a apparatus having a higher alignment precision as
compared with an EB exposure apparatus.
[0053] Next, as shown in FIG. 5D, a resist pattern 12 is formed on
the shielding portions 4 and quartz glass substrate 1. The resist
pattern 12 forms the first and second transmitting portions (phase
grooved portions) in the PSG and alternating PSM regions.
[0054] Next, as shown in FIG. 5E, the surface of the quartz glass
substrate 1 is etched by an RIE process (dry process) using the
resist pattern 12 as a mask. As a result, a plurality of grooved
portions (trenches) are formed in the surface of the quartz glass
substrate 1. These grooved portions have substantially vertical
side walls. FIG. 5E shows seven grooved portions. Thereafter, the
resist pattern 12 is removed.
[0055] Among the plurality of grooved portions, the grooved
portions in the PSG region form the second transmitting portions 6.
Among the plurality of grooved portions, the grooved portions in
the alternating PSM region form the second transmitting portions
through a wet process of FIG. 5G.
[0056] Moreover, portions in which any shielding portion 4 is not
formed and any grooved portion is not formed form the first
transmitting portions 5 in the PSG region and the alternating PSM
region.
[0057] Next, as shown in FIG. 5F, a resist pattern 13 is formed on
the shielding portions 4 and the quartz glass substrate 1. The
resist pattern 13 forms second transmitting portions (phase grooved
portions) in the alternating PSM region. The PSG region is masked
by the resist pattern 13. The alternating PSM region excluding the
grooved portions is masked by the resist pattern 13.
[0058] Next, as shown in FIG. 5G, the surface of the quartz glass
substrate 1 is etched by the wet process using the resist pattern
13 as a mask, and the grooved portions in the alternating PSM
region are expanded in the lateral and vertical directions. The
grooved portions expanded in the lateral and vertical directions
form second transmitting portions 6' in the alternating PSM
region.
[0059] Thereafter, as shown in FIG. 5H, the resist pattern 13 is
removed, and the exposure mask PM2 is obtained.
[0060] FIG. 6 shows a sectional view of the exposure mask PM2 to
which concrete dimensional values are attached.
[0061] A depth of the grooved portion of the second transmitting
portion 6' is strictly controlled in such a manner that the
absolute value of the difference between the phase of the light
transmitted through the first transmitting portion 5 in the
alternating PSM region and that of the light transmitted through
the second transmitting portion 6' is 180.degree..
[0062] The depth of the grooved portion of the second transmitting
portion 6' having a depth corresponding to 180.degree. described
above can be formed only by the RIE process without using any wet
process. However, the grooved portion of the second transmitting
portion 6' is formed using the RIE and wet processes for the
following reasons.
[0063] Reaction products generated in the RIE process of FIG. 5E
adhere to the side walls of the grooved portions. When the reaction
products adhere to the side walls of the grooved portions, light
transmission intensity of the grooved portion is reduced as
compared with a non-grooved opening (surface portion of the quartz
glass substrate 1 coated with the resist pattern 12). The reduction
of the light transmission intensity of the grooved portion causes a
dimensional error of the resist pattern formed on the wafer.
[0064] Then, after the RIE process, by performing the wet process,
the reaction products adhering to the side walls of the grooved
portions is removed and the grooved portion of the second
transmitting portion 6' having the depth corresponding to
180.degree. described above is formed.
[0065] A total etching amount in the RIE and wet processes needs to
be set to an amount corresponding to 180.degree. described
above.
[0066] In this case, distribution of the etching amounts in a depth
direction (vertical direction) in the RIE process and in a depth
direction (vertical direction) in the wet process is determined in
consideration of a side etching amount (etching amount in the
lateral direction, required for removing the reaction products)
required in the wet process.
[0067] Generally, an etching amount corresponding to 75.degree. is
selected in the RIE process of FIG. 5E, and an etching amount
corresponding to 105.degree. is selected in the wet process of FIG.
5E. In this case, the depth of the grooved portion of the second
transmitting portion 6' in the PSG region is a depth corresponding
to 75.degree..
[0068] In the case of W1:W2:W3=n:1:1, the condition that one of
plus primary diffracted light and minus primary diffracted light
turns to be vanished is represented by the following equation.
360.degree./(n+2)+.theta.=180.degree. [Equation 3]
[0069] When .theta.=75.degree. is substituted into [Equation 3],
n=1.4286. A line width ratio (W1:W2:W3) of the PSG pattern is
designed beforehand at 1.43:1:1.
[0070] That is, the line width ratio of the PSG pattern is selected
in such a manner that the etching of the quartz glass substrate 1
for forming the PSG pattern is performed only by the RIE process
without using any wet process. Therefore, a test mark having a high
dimensional precision is manufactured.
[0071] Furthermore, the method of manufacturing the exposure mask
PM2 of the present embodiment is the same as the conventional
method of manufacturing an exposure mask except the pattern layout
(shape and dimension of the pattern) on the quartz glass substrate
1.
[0072] Therefore, according to the present embodiment, it is
possible to easily realize the exposure mask including the device
pattern and the test mark having the high precision without
incurring any increase of the manufacturing cost.
[0073] Moreover, when the device pattern is omitted from the
exposure mask, it is possible to easily realize a focus test mark
including high precision test mark without incurring any increase
of manufacturing cost.
[0074] FIG. 7 shows a relation between n and .theta. in the case of
W1:W2:W3=n:1:1.
[0075] In FIG. 7, c denotes a ratio (light intensity ratio) of an
intensity of the plus primary diffracted light to that of the minus
primary diffracted light. The primary diffracted light having a
higher intensity is selected for a denominator of the light
intensity ratio.
[0076] A thick solid line shows .epsilon.=0. A curve of .epsilon.=0
shows a relation between n and .theta. in a case where one primary
diffracted light completely vanishes .epsilon.=0.01 (ideal
condition).
[0077] On the other hand, two thin solid lines show .epsilon.=0.01.
A curve of .epsilon.=0.01 shows a relation between n and .theta. in
a case where one primary diffracted light has an intensity of about
1% of that of the other diffracted light.
[0078] Moreover, two dotted lines show .epsilon.=0.02. A curve of
.epsilon.=0.02 shows a relation between n and .theta. in a case
where one primary diffracted light has an intensity of about 2% of
that of the other diffracted light. In a region held between these
two dotted lines, focus measuring is sufficiently correctly
performed. This region is represented by [Equation 2] described
above.
[0079] Here, Table 1 shows a relation between n and .theta. (ideal
value, effective range) in the case of .epsilon.=0.02.
TABLE-US-00001 TABLE 1 .theta. Ideal Effective n value range 0.5
36.degree. 19 to 53.degree. 1.0 60.degree. 43 to 77.degree. 1.5
77.143.degree. 60 to 94.degree. 2.0 90.degree. 73 to 107.degree.
2.5 100.degree. 83 to 117.degree. 3.0 108.degree. 91 to
125.degree.
[0080] As .theta. is closer to the ideal value, needless to say, a
focus measurement precision becomes higher. However, when ease of
designing of the mask is considered, n is preferably a definite
number (round number). FIGS. 8A to 8F show sectional views of PSG
patterns corresponding to n=0.5 (.theta.=36.degree.), 1.0
(.theta.=60.degree.), 1.5 (.theta.=77.143.degree.), 2.0
(.theta.=90.degree.), 2.5 (.theta.=100.degree.), 3.0
(.theta.=108.degree.). Especially, the mask of FIG. 8D is a mask
comprising a structure described as one example in Jpn. Pat. No.
3297423. Masks having realistic .theta. and n are the masks shown
in FIGS. 8A, 8B, and 8F.
[0081] The focus test mask PM1 of the present embodiment will be
described further. As described above, the focus test mask PM1 of
the present embodiment comprises the test mark TM and the reference
pattern 3.
[0082] As the reference pattern 3, mainly there are three types
shown in FIGS. 9A to 9C. That is, there are a large isolated
pattern 3a shown in FIG. 9A, a diffraction grating pattern 3b shown
in FIG. 9B, and an asymmetrical diffraction grating 3c whose
direction is opposite to that of the PSG pattern 2 as shown in FIG.
9C.
[0083] Since the large isolated pattern 3a has a broad DOF, the
measuring having a broad focus range is possible. Since an
influence of coma aberration of the diffraction grating pattern 3b
is equivalent to that of an asymmetrical diffraction grating, the
measuring which is not influenced by the coma aberration is
possible. Moreover, since a relative shift amount of the opposite
directed asymmetrical diffraction grating 3c is double, the
measuring having twice sensitivity is possible.
[0084] Moreover, to remove the measurement error attributed to the
measuring apparatus, as shown in FIGS. 10A to 10C and 11A to 11C,
it is preferable to use the test mark TM having a structure in
which one PSG pattern 2 is put between two reference patterns (two
large isolated patterns 3a, two diffraction grating patterns 3b, or
two asymmetrical diffraction gratings 3c). Conversely, even when
using a structure in which one reference pattern is put between two
PSG patterns, similarly the measurement error attributed to the
measuring apparatus can be removed. It is to be noted that in FIG.
10 and subsequent figures, patterns are not necessarily denoted
with reference numerals for simplicity, and the same hatching shows
the same portion.
[0085] Furthermore, when astigmatism exists in a projection lens,
as shown in FIG. 12, by the use of the test mark TM having a
structure in which PSG patterns 2 in two directions crossing each
other at right angles are disposed in the vicinity of each other,
not only the focus but also the astigmatism can be measured.
[0086] FIG. 13 show plan views showing test marks corresponding to
automatic measurements by an alignment shift inspection apparatus.
FIG. 14 show sectional views along arrows A-A' and B-B' of FIG.
13D.
[0087] A test mark TM shown in FIG. 13A includes two asymmetrical
diffraction grating patterns 2 (the first and second asymmetrical
diffraction grating patterns), and two reference patterns (the
first and second reference patterns) 3a.
[0088] In a test mark TM shown in FIG. 13B, reference patterns 3a
in the test mark TM shown in FIG. 13A is replaced with reference
patterns 3b.
[0089] In a test mark TM shown in FIG. 13C, reference patterns 3a
in the test mark TM shown in FIG. 13A is replaced with reference
patterns 3c.
[0090] A test mark TM shown in FIG. 13D comprises a rectangular
test mark TM1, and a rectangular test mark TM2 provided in such a
manner as to surround the test mark TM1. The test marks TM1, TM2
are test marks obtained by changing a linear test mark obtained by
vertically extending the test mark of one of FIGS. 13A to 13C into
a rectangular shape.
[0091] That is, the test mark TM shown in FIG. 13D includes the
first and second asymmetrical diffraction grating patterns and the
first and second reference patterns, the first asymmetrical
diffraction grating pattern and the first reference pattern are
disposed in parallel on the first line, and the second asymmetrical
diffraction grating pattern and the second reference pattern are
disposed in parallel on the second line vertical to the first
line.
[0092] In the test marks of FIGS. 13A to 13D, a relation between a
focus value and a positional shift is not linear.
[0093] Examples of a test mark which improve the situation include
test marks shown in FIGS. 15A and 15B. Exposure is performed using
a test mark TMa shown in FIG. 15A, and thereafter the exposure is
performed using a test mark TMb shown in FIG. 15B. Measurement
patterns formed by these exposures have advantages that a relation
between the focus value and the positional shift is substantially
linear.
[0094] FIG. 16 is a plan view showing an exposure mask including
the test marks TMa, TMb. The test marks TMa, TMb are arranged in a
peripheral portion of an exposure region of an exposure mask.
[0095] FIG. 17 is an explanatory view of a double exposure method
using the exposure mask of FIG. 16. In this method, the double
exposure is performed utilizing an overlap region 24 of exposure
regions 22, 23 adjacent to each other on a wafer 21.
[0096] That is, two exposure steps for two adjacent exposure
regions 22, 23 are performed in such a manner that the pattern of
the test mark TMa transferred in the exposure region 22 and the
pattern of the test mark TMb transferred in the exposure region 23
overlap each other in a predetermined manner in the overlapped
region 24. Accordingly, two exposure steps for performing the
double exposure of the test marks do not have to be separately
added.
[0097] FIG. 18 shows a plan view of the test mark for measuring a
focus based on a profile of reflected light.
[0098] The test mark of FIG. 18 includes a plurality of
asymmetrical diffraction grating patterns 2 and a plurality of
reference patterns 3. The asymmetrical diffraction grating patterns
2 and the reference patterns 3 are arranged in parallel on a line,
and shifted in a lateral direction by a certain amount, while the
asymmetrical diffraction grating patterns 2 and the reference
patterns 3 are alternately arranged in a vertical direction.
[0099] In the configuration, since the patterns alternately shift
in a vertical direction by the focus, the profile of the reflected
light changes by interference by the shift. A focus value can be
measured from the change of the profile. The profile of the
reflected light can be acquired, for example, using a device
referred to as a scatterometoroy. When the test mark of FIG. 18 is
used, there is an advantage that the double exposure is not
required.
[0100] A focus measuring method of the present embodiment is as
follows.
[0101] In the focus measuring method of the present embodiment, a
projection exposure apparatus is used which projects an image of a
mask pattern formed on a photo mask onto a substrate via an optical
projection system. The image of the test mark formed on the photo
mask (focus test mask) of the present embodiment is projected onto
the substrate using the projection exposure apparatus, and a
defocus amount on the surface of the substrate is acquired using
the image.
[0102] In further detail, at first, a photosensitive agent is
applied on the substrate.
[0103] Next, images of the diffraction grating pattern and
reference pattern in the test mark in the photo mask are exposed at
the same time on the substrate.
[0104] Next, the pattern transferred onto the substrate is
developed.
[0105] Next, a relative distance between the images of the
diffraction grating pattern and the reference pattern formed on the
substrate is measured, and the defocus amount is acquired based on
the measured distance.
[0106] A method of manufacturing a semiconductor device of the
present embodiment is as follows.
[0107] In the method of manufacturing the semiconductor device of
the present embodiment, the projection exposure apparatus which
projects the image of the mask pattern formed on the exposure mask
onto the substrate via the optical projection system is used. The
images of the device pattern and the test mark formed on the photo
mask (exposure mask) of the embodiment are projected onto the
substrate using the projection exposure apparatus, an actual
semiconductor product is manufactured using the images, and the
defocus amount of the surface of the substrate is acquired. Various
combinations of the phase shift mask PSM of the exposure mask of
the embodiment and the test mark TM are considered, and any
combination may be used.
[0108] In further detail, at first, a photosensitive agent is
applied on the substrate.
[0109] Next, the images of the asymmetrical diffraction grating
pattern, reference pattern, and device pattern in the photo mask
are exposed on the substrate at the same time.
[0110] Next, the pattern transferred on the substrate is
developed.
[0111] Next, the device pattern formed on the substrate is
inspected.
[0112] Next, when a defect is detected in the device pattern formed
on the substrate in a step of inspecting the device pattern, the
relative distance between the images of the diffraction grating
pattern and the reference pattern is measured, and the defocus
amount is acquired based on the measured distance.
[0113] Next, the device pattern in which the defect is detected,
and the defocus amount are recorded in a memory device. A type of
the memory device is not especially limited.
[0114] Next, the photo mask related to the device pattern in which
the defect is detected is corrected.
[0115] Here, a case where the defocus amount is acquired when the
defect is detected has been described, but the defocus amount may
be acquired irrespective of presence of detection of the
defect.
[0116] By constructing a database of a wafer history including the
device pattern and the defocus amount, a cause for an inadvertently
generated yield reduction can be easily investigated, and the
reduction of the yield can be prevented beforehand.
[0117] Examples of the semiconductor device include a liquid
crystal display (LCD) and devices using LCD (e.g., a cellular
phone, liquid crystal television, personal computer, PDA) in
addition to a DRAM, logic LSI, and system LSI (DRAM embedded
LSI).
[0118] As described above, the photo mask in which the line width
ratio of the shielding portion, transmitting portion, and phase
grooved portion is 2:1:1 and a phase difference between the lights
transmitted through the transmitting portion and the phase grooved
portion is 90.degree. is a most ideal photo mask for focus
measuring. However, even by the use of the photo mask of the
embodiment in which the phase difference and the line width ratio
satisfy [Equation 2] instead of the above-described ideal photo
mask, the high precision focus measuring substantially similar to
that by the ideal photo mask is possible. Accordingly, for example,
even when the asymmetrical diffraction grating is formed on a usual
alternating type phase shift mask, a grooved amount can be set with
respect to the phase difference having few loads on the mask
manufacturing, and a high precision focus measuring technique
equivalent to a conventional technique can be realized even in
various exposure masks.
[0119] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *