U.S. patent application number 15/191209 was filed with the patent office on 2017-08-24 for methods of defect inspection for photomasks.
The applicant listed for this patent is SK hynix Inc.. Invention is credited to Goo Min JEONG, Mun Sik KIM.
Application Number | 20170241917 15/191209 |
Document ID | / |
Family ID | 59581457 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170241917 |
Kind Code |
A1 |
JEONG; Goo Min ; et
al. |
August 24, 2017 |
METHODS OF DEFECT INSPECTION FOR PHOTOMASKS
Abstract
A method of defect inspection for a photomask is provided.
According to the method, a light transmittance correction is
performed to reduce a light transmittance of a calibration key
pattern region of a photomask including a field region and the
calibration key pattern region to the light transmittance of the
field region. Light calibration is performed using the calibration
key pattern region having corrected light transmittance. Defect
inspection for the field region is performed by applying a result
of the light calibration.
Inventors: |
JEONG; Goo Min;
(Chungcheongbuk-do, KR) ; KIM; Mun Sik;
(Chungcheongbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SK hynix Inc. |
Gyeonggi-do |
|
KR |
|
|
Family ID: |
59581457 |
Appl. No.: |
15/191209 |
Filed: |
June 23, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/95676
20130101; G01N 21/956 20130101; G01N 21/95607 20130101; G01N
2021/95615 20130101; G01N 21/93 20130101 |
International
Class: |
G01N 21/956 20060101
G01N021/956 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 22, 2016 |
KR |
10-2016-0020499 |
Claims
1. A method of defect inspection for a photomask, the method
comprising: obtaining registration errors existing in a field
region of the photomask, wherein the photomask includes the field
region and a calibration key pattern region; obtaining a first
light transmittance of the field region; performing registration
correction by irradiating a first laser beam onto the field region;
obtaining a first transmittance reduction in the field region by
the registration correction; obtaining a second light transmittance
in the field region by using the first transmittance reduction;
performing light transmittance correction to the calibration key
pattern region so that the calibration key pattern region has light
transmittance substantially equal to the second light
transmittance; performing light calibration using the corrected
calibration key pattern region to obtain a light calibration
result; and performing defect inspection to the field region by
using the light calibration result.
2. The method of claim 1, wherein the first laser beam forms local
first deformation elements in the field region to compensate for
the registration errors.
3. The method of claim 2, wherein the first deformation elements
change the first light transmittance of the field region to the
second light transmittance.
4. The method of claim 1, wherein the performing of the light
transmittance correction includes forming second deformation
elements in the calibration key pattern region.
5. The method of claim 4, wherein the second deformation elements
are formed by irradiating a second laser beam onto the calibration
key pattern region.
6. The method of claim 4, wherein the performing of the light
transmittance correction comprises: obtaining a third light
transmittance of the calibration key pattern region before the
light transmittance correction; calculating a second transmittance
reduction using a difference between the second light transmittance
and third light transmittance; and irradiating a second laser beam
so that the second deformation elements are formed to reduce the
third light transmittance of the calibration key pattern region to
a fourth transmittance.
7. A method of defect inspection for a photomask, the method
comprising: performing registration correction by irradiating a
first laser beam onto a field region of the photomask to form a
registration corrected field region, wherein the photomask includes
the field region and a calibration key pattern region; performing
light transmittance correction to reduce light transmittance of the
calibration key pattern region; performing light calibration using
the reduced light transmittance of the calibration key pattern
region to obtain a result of the light calibration; and performing
defect inspection to the registration corrected field region by
applying the result of the light calibration.
8. The method of claim 7, wherein the first laser beam forms local
deformation elements to the photomask.
9. The method of claim 8, wherein the first deformation elements
reduce light transmittance of the field region.
10. The method of claim 7, wherein the performing of the light
transmittance correction includes forming second deformation
elements in the calibration key pattern region.
11. The method of claim 10, wherein the second deformation elements
are formed by irradiating a second laser beam onto the calibration
key pattern region to make the reduced light transmittance of the
calibration key pattern region substantially equal to light
transmittance of the registration corrected field region.
12. A method of defect inspection for a photomask, the method
comprising: performing light transmittance correction to reduce
light transmittance of a calibration key pattern region of the
photomask to a corrected light transmittance, wherein the corrected
light transmittance is substantially equal to light transmittance
of a field region, wherein the photomask includes the field region
and the calibration key pattern region; performing light
calibration using the calibration key pattern region having the
corrected light transmittance to obtain a result of the light
calibration; and performing defect inspection to the field region
by applying the result of the light calibration.
13. The method of claim 12, wherein the performing of the light
transmittance correction includes forming deformation elements in
the calibration key pattern region.
14. The method of claim 13, wherein the deformation elements are
formed by irradiating a laser beam onto the calibration key pattern
region.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority under 35 U.S.C
119(a) to Korean Application No. 10-2016-0020499, filed on Feb. 22,
2016, which is herein incorporated by reference in its entirety as
set forth in full.
BACKGROUND
[0002] 1. Technical Field
[0003] Various embodiments of the present disclosure relate to
lithography technologies and, more particularly, to methods of
defect inspection for a photomask.
[0004] 2. Related Art
[0005] As semiconductor devices become more highly integrated, a
wavelength of light generated from a light source used in
photolithography processes has been continuously shorter and
shorter to transfer finer patterns onto a wafer. In order to
transfer finer patterns, mask patterns which are transferred onto
the wafer need to have a small line width or a small line pitch. In
case that pattern errors occur, such as overlay errors, after
performing the photolithography processes using the photomask, a
photomask correction process to correct or to improve such pattern
errors may be performed. The photomask correction process may
change light transmittance of a field region of the photomask, in
which the mask patterns are located, thus inspection noise may be
generated during the defect inspection process of the
photomask.
SUMMARY
[0006] According to one embodiment, there is provided a method of
defect inspection for a photomask. The method includes obtaining
registration errors existing in a field region of the photomask,
wherein the photomask includes the field region and a calibration
key pattern region, obtaining a first light transmittance of the
field region, performing registration correction by irradiating a
first laser beam onto the field region, obtaining a first
transmittance reduction in the field region by the registration
correction, obtaining a second light transmittance in the field
region using the first transmittance reduction, performing light
transmittance correction to the calibration key pattern region so
that the calibration key pattern region has light transmittance
substantially equal to the second light transmittance, performing
light calibration using the corrected calibration key pattern
region to obtain a light calibration result, and performing defect
inspection to the field region by using the light calibration
result.
[0007] According to one embodiment, there is provided a method of
defect inspection for a photomask. The method includes performing
registration correction by irradiating a first laser beam onto a
field region of the photomask to form a registration corrected
field region, wherein the photomask includes the field region and a
calibration key pattern region, performing light transmittance
correction to reduce light transmittance of the calibration key
pattern region, performing light calibration using the reduced
light transmittance of the calibration key pattern region to obtain
a result of the light calibration, and performing defect inspection
to the registration corrected field region by applying the result
of the light calibration.
[0008] According to one embodiment, there is provided a method of
defect inspection for a photomask. The method includes performing
light transmittance correction to reduce light transmittance of a
calibration key pattern region of the photomask to a corrected
light transmittance, wherein the corrected light transmittance is
substantially equal to light transmittance of a field region,
wherein the photomask includes the field region and the calibration
key pattern region; performing light calibration using the
calibration key pattern region having the corrected light
transmittance to obtain a result of the light calibration, and
performing defect inspection to the field region by applying the
result of the light calibration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Various embodiments of an inventive concept will become more
apparent in view of the attached drawings and accompanying detailed
description, in which:
[0010] FIGS. 1 to 3 are schematic views illustrating a photomask
according to an embodiment;
[0011] FIG. 4 is a schematic view illustrating a registration error
map according to an embodiment;
[0012] FIG. 5 is a schematic view illustrating a registration
correction system according to an embodiment;
[0013] FIG. 6 is a cross-sectional view illustrating a registration
correction process according to an embodiment;
[0014] FIG. 7 is a cross-sectional view illustrating a process of
reducing light transmittance of a calibration key pattern region of
a photomask according to an embodiment; and
[0015] FIG. 8 is a process flow chart illustrating a method of
defect inspection of a photomask according to an embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0016] The terms used herein may correspond to words selected in
consideration of their functions in the embodiments, and the
meanings of the terms may be construed to be different according to
ordinary skill in the art to which the embodiments belong. If
defined in detail, the terms may be construed according to the
definitions. Unless otherwise defined, the terms used herein have
the same meaning as commonly understood by one of ordinary skill in
the art to which the embodiments belong.
[0017] It will be understood that although terms first, second,
third etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another element. Thus, a first
element in some embodiments could be termed a second element in
other embodiments without departing from the teachings of the
inventive concept.
[0018] It will also be understood that when an element or layer is
referred to as being "on," "over," "below," "under," or "outside"
another element or layer, the element or layer may be in direct
contact with the other element or layer, or Intervening elements or
layers may be present. Other words used to describe the
relationship between elements or layers should be interpreted in a
like fashion for example, "between" versus "directly between" or
"adjacent" versus "directly adjacent".
[0019] The terminology "pattern" used herein may indicate a mask
pattern such as a light blocking pattern or a phase shift pattern
that is formed on a photomask to realize an element of an
electronic circuit or an integrated circuit of a semiconductor
device. The semiconductor device may correspond to a memory device
or a logic device. The memory device may be a dynamic random access
memory (DRAM) device, a static random access memory (SRAM) device,
a flash memory device, a magnetic random access memory (MRAM)
device, a resistive random access memory (ReRAM) device, a
ferroelectric random access memory (FeRAM) device, or a phase
change random access memory (PcRAM) device. The semiconductor
device may be employed in communication systems such as mobile
phones, electronic systems associated with biotechnology or health
care, or wearable electronic systems.
[0020] Same reference numerals refer to same elements throughout
the specification. Thus, even though a reference numeral is not
mentioned or described with reference to a drawing, the reference
numeral may be mentioned or described with reference to another
drawing. In addition, even though a reference numeral is not shown
in a drawing, it may be mentioned or described with reference to
another drawing.
[0021] FIG. 1 schematically illustrates a cross-sectional feature
of a transmissive photomask 100. FIG. 2 schematically illustrates a
planar feature of the photomask 100. FIG. 3 schematically
illustrates a planar feature of a calibration key pattern 170.
[0022] Referring to FIGS. 1 and 2, a transmissive photomask 100 may
be prepared as a photolithography mask used in a photolithography
process. The photomask 100 includes a substantially transparent
substrate 110. The transparent substrate 110 includes a front side
or a first surface 120 and a back side or a second surface 130
opposite to the first surface 120. The substrate 110 may be formed
of a transparent material, for example, quartz. The transparent
material may be a material capable of transmitting a deep ultra
violet (DUV) light, for example, light with approximately a 193 nm
wave length band, which may be used as an exposure light 200.
[0023] Mask patterns 160 providing features to be transferred onto
a wafer may be disposed on the first surface 120 of the photomask
100. The features provided by the mask patterns 160 may be
transferred onto the wafer by an exposure process. A region where
the mask patterns 160 providing the features to be transferred onto
the wafer are located is an active region and may be set as a field
region 140 located in the photomask 100. An outer region of the
field region 140 is an inactive region and may be set as a frame
region 150.
[0024] The mask pattern 160 may include a layer of a light blocking
material such as chrome (Cr), or may include a phase shift layer
such as molybdenum silicon (MoSi) layer. The frame region 150 may
include a frame layer 180 substantially including a light blocking
layer 181, or a double-layer of the light blocking layer 181 and a
phase shift layer 186. The exposure light 200 may not pass through
the frame region 150, thus the features in the frame region 150
cannot be transferred onto the wafer.
[0025] A pellicle 190 to protect the mask patterns 160 may be
attached over the field region 140. A pellicle supporting portion
195 supporting the pellicle 190 may be attached on the frame layer
180. The pellicle 190 can prevent the mask patterns 160 from being
exposed to an external environment.
[0026] After manufacturing the photomask 100, a process of
inspecting the photomask 100 is performed to determine whether
defects are generated on the photomask 100. For example, during
performing an exposure process using the photomask 100, defects
known as haze may be generated on the photomask 100, and a process
for inspecting the defects may be performed. To improve inspection
accuracy of the defect inspection process, sensitivity to detect
the defects may be set by performing light calibration, and then, a
defect inspection for the field region 140 may be performed.
Calibration key patterns 170 for the light calibration may be
disposed in an outer region of the field region 140 or in the frame
region 150.
[0027] A plurality of the calibration key patterns 170 may be
disposed in a plurality of locations in the frame region 150
outside the field region 140, as illustrated in FIG. 2. The
calibration key pattern 170 may be formed by patterning the frame
layer 180 in a predetermined feature.
[0028] As illustrated in FIG. 3, each of the calibration key
patterns 170 may include a dark pattern 175 and a clear pattern
171. The clear pattern 171 may be defined by the dark pattern 175
and be formed in a cross shape. The dark pattern 175 may be set by
a portion of the frame layer 180. The clear pattern 171 may be a
quartz portion of the substrate 110, which is exposed by the frame
layer 180. The clear pattern 171 may be a substantially transparent
feature region.
[0029] The clear pattern 171 may be used as a clear level that can
be a reference to determine the upper limit of transmittance that
can be detected in the defect inspection. The dark pattern 175 may
be used as a dark level that can be a reference of light blocked by
the light blocking layer 181 forming the frame layer 180, for
example, a reference used to determine the lower limit of the
transmittance that can be detected in the defect inspection.
[0030] By performing light calibration using the calibration key
patterns 170, data of a detection light detected by irradiating an
inspection light onto the field region 140 of the photomask 100,
for example, light transmittance may be calibrated between the
clear level and the dark level. The light calibration may be
performed to improve the reliability of defect inspection results
by adjusting the inspection sensitivity of the photomask 100.
[0031] Referring to FIG. 1, the photomask 100 may allow an exposure
wavelength of an extreme ultra violet (EUV) wavelength range, for
example, approximately 13.5 nm to pass through. The EUV mask
structure may include a multi-layered mirror structure for
reflection of the EUV.
[0032] Referring to FIG. 1 again, wafer patterns such as resist
patterns (not illustrated) may be formed by transferring images of
the mask patterns 160 on the wafer (not illustrated) using the
photomask 100. The formed resist patterns may not exactly
correspond to a predetermined structure as originally intended.
This type of errors can be referred to as registration errors. Such
registration errors may generally be exemplified in a
two-dimensional (2D) map 230. See arrows in FIG. 4.
[0033] FIG. 4 illustrates an example of the registration error map
230. The direction of the arrow of the registration error map 230
represents a direction that the pattern components are shifted from
an intended pattern location, and the length of the arrow
represents the amount of shift. The registration error can be
caused by many factors included in the photolithography process,
but a registration correction process for the photomask 100 can be
carried out to correct the factors due to the photomask 100.
[0034] The registration correction process may include a step of
measuring the registration errors shown in the registration error
map 230 of FIG. 4, and performing a correction process for the
photomask 100 using a laser to compensate for the registration
errors. The registration correction process using a laser, as
illustrated in FIG. 5, may be performed using a registration
correction (RegC) system 300.
[0035] Referring to FIG. 5, the registration correction system 300
includes a chuck 350 on which the photomask 100 is seated. In an
embodiment, the chuck 350 may be movable in three dimensions. The
registration correction system 300 includes a pulsed laser source
310 generating a pulsed beam, an optical pulsed beam or a laser
beam 320.
[0036] The laser source 310 may generate optical pulses. Although
the registration correction system 300 is exemplified to include
only one laser source 310 in this embodiment, the registration
correction system 300 may include one or more laser sources
generating a laser beam of different wavelength bands or the same
wavelength band.
[0037] A steering mirror 330 and a focus objective lens 340 may be
arranged between the laser source 310 and photomask 100. The
steering mirror 330 directs the pulse laser beam 320 emitted from
the laser source 310 to the focus objective lens 340. The pulse
laser beam 320 is focused on the photomask 100 through the focus
objective lens 340. In an embodiment, the focus objective lens 340
may be arranged to be movable in three dimensions. The registration
correction process may be performed by irradiating a laser beam
onto the photomask 100 through the registration correction system
300. As the laser beam is irradiated onto the photomask 100, local
errors of the photomask 100 can be corrected.
[0038] FIG. 6 illustrates the registration correction process
according to an embodiment. Referring to FIG. 6, a first laser beam
301 for registration correction is irradiated onto the substrate
110 of the photomask 100 using the registration correction system
300 of FIG. 5. A beam spot of the first laser beam 301 may be
irradiated to the field region 140 of the substrate 110. The first
laser beam 301 may be scanned to the substrate 110 to be irradiated
to a plurality of local regions of the substrate 110.
[0039] As illustrated in the registration error map 230 of FIG. 4,
the errors located in the field region 140 may have different sizes
and different directions. To correct the errors illustrated in the
registration error map 230 of FIG. 4, the first laser beam 301 may
be irradiated with different beam spot densities or different
energies to the local regions corresponding to the field region 140
of the substrate 110.
[0040] The first laser beam 301 irradiated onto the substrate 110
of the photomask 100 may be incident through the second surface 130
to the substrate 110. The first laser beam 301 may cause first
deformation elements 360 in the quartz material constituting the
substrate 110. The first deformation element 360 may have a three
dimensional volume and may have a morphological organization of
atoms. That is, the deformation element 360 is relatively less
dense in packing structure or has a lower density than the quartz
material therearound. The acting direction or size of the first
deformation elements 360 may vary depending on pulse energy, pulse
length, a repetition rate, or the number of repeated scans of the
first laser beam 301. The registration errors generated differently
with respect to the local regions can be corrected by inducing the
first deformation elements 360.
[0041] The first deformation elements 360 applied to correct the
registration errors may change a light transmittance of the field
region 140. The light transmittance of the local regions in the
field region 140 may be dropped in different amounts depending on
density of the first deformation elements 360. This may cause an
overall drop of the light transmittance in the field region 140.
The overall drop of the light transmittance of the field region 140
may be evaluated as an average value of drops in the light
transmittance of the local areas.
[0042] The average drop of the light transmittance in the field
region 140 of the photomask 100 caused by the registration
correction process may cause unexpected difficulties to the defect
correction for the photomask 100. The average light transmittance
of the field region 140 of the photomask 100 after the registration
correction can be relatively decreased compared with the average
light transmittance in the field region 140 of the photomask 100
before the registration correction.
[0043] Furthermore, the light transmittance of the calibration key
pattern region 170 after the registration correction may not be
varied or may be relatively slightly varied. Accordingly, the
difference between the light transmittance of the calibration key
pattern region 170 and the average light transmittance of the field
region 140 of the photomask 100 after registration correction can
be quite large.
[0044] When performing light calibration based on the calibration
key pattern region 170 having relatively high light transmittance,
defect inspection sensitivity for the field region 140, which has
relatively low light transmittance, may increase. Accordingly, an
error may occur of misrecognizing a normal pattern as a defect.
Erroneous correction to the normal pattern may be cause.
[0045] Despite the fact that critical dimension uniformity is not
substantially changed by the registration correction, inspection
result data containing a large number of defects may be obtained.
The detection sensitivity, which is overly high, erroneously
determines a non-defect to be a defect. As a result, a noise due to
such erroneous detection may increase significantly. For example,
sub-resolution assist features (SRAFs) may be detected as a defect
that is a noise in the result data. The increase of noise in the
defect inspection result data may not only make defect inspection
itself erroneous but also acts as a constraint when applying the
registration correction process.
[0046] Scan of the first laser beam 301 to correct the registration
errors may affect the light transmittance or luminance of the
calibration key pattern region 170. The first deformation elements
360 caused to the field region 140 by the first laser beam 301 may
cause a local and irregular expansion of the photomask 100.
Accordingly, the light transmittance or luminance of the
calibration key pattern region 170 may vary differently depending
on the location of the calibration key patterns 170.
[0047] When the calibration key patterns regions 170 have different
light transmittances from each other, the accuracy and
effectiveness of the light calibration may be degraded. The
reliability of the light calibration is degraded and the defect
inspection result may include a large number of noises, thus the
reliability of the defect inspection may be degraded. The light
transmittance difference between the field region 140 subjected to
registration correction and calibration key pattern region 170 can
be compensated for by reducing the light transmittance of the
calibration key pattern region 170.
[0048] FIG. 7 illustrates a process of reducing the light
transmittance in the calibration region including the calibration
key patterns 170 of the photomask 100. Referring to FIG. 7, a
second laser beam 307 for reducing light transmittance is
irradiated onto the calibration key pattern region 170 of the
photomask 100 using the registration correction system 300 of FIG.
5. A beam spot of the second laser beam 307 is irradiated onto the
calibration key pattern region 170 and may cause second deformation
elements 370. The second deformation elements 370 may have a three
dimensional volume and may have a morphological organization of
atoms having a relatively less dense packing structure and a lower
density than the quartz material therearound.
[0049] The light transmittance of the calibration key pattern
region 170 may be reduced by the second deformation elements 370.
The second deformation elements 370 may reduce the light
transmittance of the calibration key pattern region 170 so that the
light transmittance of the calibration key pattern region 170 is
similar to or substantially equal to the light transmittance of the
registration corrected field region 140.
[0050] Since a degree of reduction of light transmittance can be
varied by the density or size of the second deformation elements
370, desired light transmittance reduction can be obtained by
adjusting the energy of the second laser beam 307 or the density of
a beam spot of the second laser beam 307 causing the second
deformation elements 370.
[0051] For example, as illustrated in FIG. 6, the average initial
value of a first light transmittance for the field region 140 can
be obtained before irradiating the first laser beam 301 of FIG. 6
for registration correction. Then, an amount of the first light
transmittance reduction caused by the process of irradiating the
first laser beam 301 of FIG. 6 for registration correction to the
field region 140 can be obtained from a correlation between the
average initial value of the first light transmittance for the
field region 140 and the light transmittance reduction after the
irradiation of the first laser beam 301.
[0052] The average second light transmittance for the field region
140 after the registration correction can be obtained from an
amount of the detected first transmittance reduction. After
obtaining the initial value of a third light transmittance for the
calibration key pattern region 170 prior to the registration
correction, a difference between the third light transmittance for
the calibration key pattern region 170 before the registration
correction and the average second light transmittance for the field
region 140 after the registration correction can be obtained as the
amount of a second transmittance reduction.
[0053] Parameters for the second laser beam 307 to obtain the
amount of the second transmittance reduction may be set from the
correlation between light transmittances according to irradiation
of the second laser beam 307. The second laser beam 307 may be
irradiated onto the calibration key pattern region 170 by applying
the obtained parameters for irradiation of the second laser beam
307, for example, the type of the second laser beam 307, the energy
or density of the beam spot, and so on. Accordingly, the
calibration key pattern region 170 may be induced to have a fourth
light transmittance that is substantially equal to or similar to
the average second light transmittance for the field region 140
after the registration correction.
[0054] Since the corrected fourth light transmittance of the
calibration key pattern region 170 has a reduced value compared to
the third light transmittance, the calibration key pattern region
170 whose light transmittance is corrected may provide a new
reference of light calibration. By performing light calibration
using the corrected calibration key pattern region 170 having
reduced light transmittance, references such as the sensitivity of
defect inspection may be reset or updated and defect inspection may
be performed for the field region 140 on which the registration
correction is performed.
[0055] Result data of defect inspection may be calibrated to values
between the clear level and dark level which are reset or updated
by the light calibration using the calibration key pattern region
170 having the reduced light transmittance after irradiation of the
second laser beam 307. Since the light transmittance of the
corrected calibration key pattern region 170 is reduced, light
calibration using the corrected calibration key pattern region 170
may function to reset the inspection sensitivity for the field
region 140 to meet the reduced light transmittance of the field
region 140. Accordingly, a noise which is caused by erroneously
correcting a non-defective pattern may be avoided.
[0056] The light calibration using the corrected calibration key
pattern region 170 can eliminate noises and improve the reliability
of the defect inspection result by re-adjusting the inspection
sensitivity for the photomask 100. By excluding noises, it is
possible to overcome a burden for the defect inspection and to
overcome the limitations of applying the registration correction
process.
[0057] The light transmittance correction using the second laser
beam 307 may be performed to the calibration key pattern regions
170 which are located in different locations from each other. As a
result, the calibration key pattern regions 170 may have
substantially the same fourth light transmittance. Accordingly, the
phenomenon that the calibration key pattern regions 170 located in
different locations from each other have different light
transmittances can be compensated for. Since the calibration key
pattern regions 170 located in different locations from each other
can have substantially the same fourth light transmittance by the
light transmittance correction using the second laser beam 307, the
reliability of the light calibration process based on the
calibration key pattern regions 170 can be improved and the
reliability of the defect inspection can be improved.
[0058] FIG. 8 is a flow chart illustrating a method of defect
inspection for a photomask according to an embodiment. Referring to
FIG. 8, defect inspection for the photomask according to an
embodiment may be performed by fabricating the photomask 100 as
illustrated in FIG. 1, and measuring registration error data for
the field region 140 and obtaining the registration error map 230
as illustrated in FIG. 4 (S801). An initial value of the first
light transmittance for the field region 140 may be measured
(S802). The third light transmittance for the calibration key
pattern region 170 may be measured (S803). The registration
correction process may be performed by irradiating the first laser
beam 301 onto the field region 140 of the photomask 100 of FIG. 1,
as illustrated in FIG. 6, using the registration correction system
500 of FIG. 5 illustrated in FIG. 5 (S804).
[0059] The first transmittance reduction associated with the
registration correction for the field region 140 of FIG. 1 may be
calculated (S805). The second light transmittance for the field
region 140 of FIG. 1 after the registration correction may be
calculated from the first light transmittance and the first
transmittance reduction (S806). As illustrated in FIG. 7, the
second laser beam 307 may be irradiated onto the calibration key
pattern region 170 to reduce a difference between the light
transmittance of the calibration key pattern region 170 and the
light transmittance of the field region using the second
transmittance reduction (S808).
[0060] The light calibration may be performed using the corrected
light transmittance of the calibration key pattern region 170
(S809). Then, defect inspection for the field region 140 may be
performed by applying the light calibration result (S810). Defects
detected in the defect inspection may be foreign substances such as
haze or particles, which may be attached to or created by the
photomask 100 by the exposure light source.
[0061] In the method of defect inspection for the photomask, as
described with reference to FIG. 6, registration correction may be
performed by irradiating the first laser beam 301 onto the field
region 140 of the photomask 100 of FIG. 1, and, as illustrated in
FIG. 7, the light transmittance correction to reduce the light
transmittance of the calibration key pattern region 170 of the
photomask 100 may be performed.
[0062] In the method of defect inspection for the photomask, as
illustrated in FIG. 1, the photomask 100 includes the field region
140 and the calibration key pattern region 170. When a difference
between the light transmittances of the field region 140 and the
calibration key pattern region 170 is great, the light
transmittance correction process may be performed to reduce the
light transmittance of the calibration key pattern region 170 to be
substantially equal to the light transmittance value of the field
region 140, as illustrated in FIG. 7.
[0063] The methods according to the aforementioned embodiments and
structures formed thereby may be used in photolithography processes
for fabricating integrated circuit (IC) chips. The IC chips may be
supplied to users in a raw wafer form, in a bare die form or in a
package form. The IC chips may also be supplied in a single package
form or in a multi-chip package form. The IC chips may be
integrated in intermediate products such as mother boards or end
products to constitute signal processing devices. The end products
may include toys, low end application products, or high end
application products such as computers. For example, the end
products may include display units, keyboards, or central
processing units (CPUs).
[0064] The embodiments of the inventive concept have been disclosed
above for illustrative purposes. Those of ordinary skill in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the inventive concept as disclosed in the accompanying
claims.
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