U.S. patent application number 14/208757 was filed with the patent office on 2015-10-01 for inspection method.
This patent application is currently assigned to NuFlare Technology, Inc.. The applicant listed for this patent is NuFlare Technology, Inc.. Invention is credited to Hiroteru AKIYAMA, Takafumi INOUE, Manabu ISOBE, Nobutaka KIKUIRI, Hideo TSUCHIYA, Makoto YABE.
Application Number | 20150279024 14/208757 |
Document ID | / |
Family ID | 51520017 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150279024 |
Kind Code |
A1 |
TSUCHIYA; Hideo ; et
al. |
October 1, 2015 |
INSPECTION METHOD
Abstract
An inspection method comprising, virtually dividing a sample, in
which a plurality of chip patterns are formed, into a plurality of
strip-shaped stripes along a predetermined direction to acquire an
optical image of the chip pattern in each of the stripes,
performing filtering based on design data of the chip pattern to
produce a reference image corresponding to the optical image,
comparing the chip pattern using a die-to-database method and
comparing a repetitive pattern portion in the chip pattern using a
cell method, obtaining at least one of a dimension difference and a
dimension ratio between a pattern of the optical image and a
pattern of the reference image compared to the pattern of the
optical image by the die-to-database method; and obtaining a
dimension distribution of the plurality of chip patterns from at
least one of the dimension difference and the dimension ratio.
Inventors: |
TSUCHIYA; Hideo; (Tokyo,
JP) ; ISOBE; Manabu; (Kanagawa, JP) ; AKIYAMA;
Hiroteru; (Kanagawa, JP) ; YABE; Makoto;
(Kanagawa, JP) ; INOUE; Takafumi; (Kanagawa,
JP) ; KIKUIRI; Nobutaka; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NuFlare Technology, Inc. |
Yokohama |
|
JP |
|
|
Assignee: |
NuFlare Technology, Inc.
Yokohama
JP
|
Family ID: |
51520017 |
Appl. No.: |
14/208757 |
Filed: |
March 13, 2014 |
Current U.S.
Class: |
382/144 |
Current CPC
Class: |
G06T 2207/30148
20130101; G06T 2207/30168 20130101; G06T 7/0006 20130101; G01N
21/95607 20130101; G06T 2207/30108 20130101; G01N 2021/95615
20130101; G06T 7/001 20130101; G03F 1/84 20130101; G06T 7/74
20170101; G06K 9/6215 20130101; G03F 7/7065 20130101; G06T 2200/24
20130101; G06T 7/0008 20130101 |
International
Class: |
G06T 7/00 20060101
G06T007/00; G06K 9/62 20060101 G06K009/62 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2013 |
JP |
2013-055500 |
Claims
1. An inspection method comprising: virtually dividing a sample, in
which a plurality of chip patterns are formed, into a plurality of
strip-shaped stripes along a predetermined direction to acquire an
optical image of the chip pattern in each of the stripes;
performing filtering based on design data of the chip pattern to
produce a reference image corresponding to the optical image;
comparing the chip pattern using a die-to-database method and
comparing a repetitive pattern portion in the chip pattern using a
cell method; obtaining at least one of a dimension difference and a
dimension ratio between a pattern of the optical image and a
pattern of the reference image compared to the pattern of the
optical image by the die-to-database method; and obtaining a
dimension distribution of the plurality of chip patterns from at
least one of the dimension difference and the dimension ratio,
wherein, with respect to a position determined to be a defect by
the comparison of the die-to-database method, a result of the
die-to-database method is stored when a dimension distribution from
the position to a preceding position where at least one of the
dimension difference and the dimension ratio is obtained falls
within a predetermined range by comparing the dimension
distribution to a dimension distribution in the stripe including
the position determined to be the defect, or a dimension
distribution of the chip pattern assumed from the stripe in which
the dimension difference is acquired in advance of the stripe
concerned, and a result of the cell method is stored instead of the
result of the die-to-database method when the dimension
distribution from the position determined to be the defect to the
preceding position where at least one of the dimension difference
and the dimension ratio is obtained exceeds the predetermined range
by comparing the dimension distribution to the dimension
distribution in the stripe including the position determined to be
the defect, or the dimension distribution of the chip pattern
assumed from the stripe in which the dimension difference is
acquired in advance of the stripe concerned.
2. The inspection method according to claim 1, wherein the result
of the die-to-database method is stored irrespective of the
dimension distribution from the position determined to be the
defect to the preceding position, where at least one of the
dimension difference and the dimension ratio is obtained, when the
result of the cell comparison does not exist because the repetitive
pattern portion does not exist in the position determined to be the
defect by the comparison of the die-to-database method.
3. The inspection method according to claim 1, wherein the
dimension difference is a difference in line width between the
pattern of the optical image and the pattern of the reference image
or a difference of a distance between the patterns of the optical
image and a distance between the patterns of the reference
image.
4. The inspection method according to claim 1, wherein the
dimension ratio is a line width ratio of the pattern of the optical
image and the pattern of the reference image, or a ratio of a
distance between the patterns of the optical image and a distance
between the patterns of the reference image.
5. An inspection method comprising: acquiring an optical image of a
sample in which a plurality of chip patterns are formed; performing
filtering based on design data of the chip pattern to produce a
reference image corresponding to the optical image; comparing the
chip pattern by a die-to-database method and comparing a repetitive
pattern portion in the chip pattern by a cell method; obtaining at
least one of a dimension difference and a dimension ratio between a
pattern of the optical image, and a pattern of the reference image
compared to the pattern of the optical image by the die-to-database
method; and obtaining a dimension distribution of the plurality of
chip patterns from at least one of the dimension difference and the
dimension ratio, wherein, with respect to a position determined to
be a defect by the comparison of the die-to-database method, a
result of the die-to-database method is stored when a dimension
distribution from the position to a preceding position where at
least one of the dimension difference and the dimension ratio is
obtained falls within a predetermined range by comparing the
dimension distribution to a dimension distribution in a chip or a
dimension distribution among chips, and a result of the cell method
is stored instead of the result of the die-to-database method when
the dimension distribution from the position determined to be the
defect to the preceding position, where at least one of the
dimension difference and the dimension ratio is obtained, exceeds
the predetermined range by comparing the dimension distribution to
the dimension distribution in the chip or the dimension
distribution among the chips.
6. The inspection method according to claim 5, wherein the result
of the die-to-database method is stored irrespective of the
dimension distribution from the position determined to be the
defect to the preceding position, where at least one of the
dimension difference and the dimension ratio is obtained, when the
result of the cell comparison does not exist because the repetitive
pattern portion does not exist in the position determined to be the
defect by the comparison of the die-to-database method.
7. The inspection method according to claim 5, wherein the
dimension difference is a difference in line width between the
pattern of the optical image and the pattern of the reference image
or a difference of a distance between the patterns of the optical
image and a distance between the patterns of the reference
image.
8. The inspection method according to claim 5, wherein the
dimension ratio is a line width ratio of the pattern of the optical
image and the pattern of the reference image, or a ratio of a
distance between the patterns of the optical image and a distance
between the patterns of the reference image.
9. An inspection method comprising: virtually dividing a sample in
which a plurality of chip patterns are formed into a plurality of
strip-shaped stripes along a predetermined direction to acquire an
optical image of the chip pattern in each of the stripes; comparing
the chip pattern by a die-to-die method and comparing a repetitive
pattern portion in the chip pattern by a cell method; obtaining at
least one of a dimension difference and a dimension ratio between a
pattern of the optical image and a pattern of the reference image
compared to the pattern of the optical image by the die-to-die
method; and obtaining a dimension distribution of the plurality of
chip patterns from at least one of the dimension difference and the
dimension ratio, wherein, with respect to a position determined to
be a defect by the comparison of the die-to-die method, a result of
the die-to-die method is stored when a dimension distribution from
the position to a preceding position where at least one of the
dimension difference and the dimension ratio is obtained falls
within a predetermined range by comparing the dimension
distribution to a dimension distribution in the stripe including
the position determined to be the defect, or a dimension
distribution of the chip pattern assumed from the stripe in which
the dimension difference is acquired in advance of the stripe
concerned, and a result of the cell method is stored instead of the
result of the die-to-die method when the dimension distribution
from the position determined to be the defect to the preceding
position where at least one of the dimension difference and the
dimension ratio is obtained exceeds the predetermined range by
comparing the dimension distribution to the dimension distribution
in the stripe including the position determined to be the defect or
the dimension distribution of the chip pattern assumed from the
stripe in which the dimension difference is acquired in advance of
the stripe concerned.
10. The inspection method according to claim 9, wherein the result
of the die-to-die method is stored irrespective of the dimension
distribution from the position determined to be the defect to the
preceding position where at least one of the dimension difference
and the dimension ratio is obtained, when the result of the cell
method does not exist because the repetitive pattern portion does
not exist in the position determined to be the defect by the
comparison of the die-to-die method.
11. The inspection method according to claim 9, wherein the
dimension difference is a difference in line width between the
patterns of the optical images or a difference in distance between
the patterns of the optical images.
12. The inspection method according to claim 9, wherein the
dimension ratio is a line width ratio of the patterns of the
optical images or a ratio of a distance between the patterns of the
optical image.
Description
CROSS-REFERENCE TO THE RELATED APPLICATION
[0001] The entire disclosure of the Japanese Patent Application No.
2013-055500, filed on Mar. 18, 2013 including specification,
claims, drawings, and summary, on which the Convention priority of
the present application is based, are incorporated herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an Inspection Method.
BACKGROUND
[0003] With high integration and large capacity of a Large Scale
Integration (LSI), a circuit dimension required for a semiconductor
element becomes increasingly narrowed. For example, a pattern
having a line width of several tens of nanometers is required to be
formed in the latest typical logic device.
[0004] It is necessary to improve a production yield of the
expensive LSI in a production process. In the semiconductor
element, during a production process, an original design pattern
(that is, a mask or a reticle, hereinafter collectively referred to
as a mask) in which a circuit pattern is formed is exposed and
transferred onto a wafer by a reduction projection exposure
apparatus called a stepper or a scanner. A shape defect of a mask
pattern can be cited as a large factor that reduces a production
yield of the semiconductor element.
[0005] The finer the dimensions of an LSI pattern formed on the
wafer becomes, the smaller the shape defect of the mask pattern
becomes. As fluctuations of various process conditions are absorbed
by enhancing dimensional accuracy of the mask, it is necessary to
defect the defect of the extremely small pattern in a mask
inspection. At this point, it is also necessary to determine the
defect in consideration of the fluctuation in line width dimension
or position shift amount of the pattern in a mask surface. For
example, Japanese Patent No. 4236825 discloses an inspection
apparatus that can detect the fine defect in the mask.
[0006] Examples of defect detection techniques include a
die-to-database comparison method and a die-to-die comparison
method. In the die-to-database comparison method, a reference image
generated from design pattern data used in mask production and an
optical image of the actual pattern in the mask are compared to
each other. In the die-to-die comparison method, in the case that
multiple chips having identical pattern configuration are disposed
in a part or the whole of the identical mask, the optical images
having the identical pattern in chips of the different masks are
compared to each other.
[0007] A cell comparison method can also be cited as another defect
detection technique. The cell comparison method is effectively used
in the case that a repetitive pattern called a cell exists in the
mask. In the die-to-die comparison method, the chips repetitively
formed in the mask are compared to each other. On the other hand,
in the cell comparison method, the repetitive patterns such as
memory mats, namely, the cells are compared to each other in one
chip. For example, the defect is inspected by the cell comparison
method in a memory cell group of a DRAM (Dynamic Random Access
Memory) element in which the repetitive pattern is formed. On the
other hand, a logic element in which the repetitive pattern does
not exist is inspected by the die-to-die comparison method in which
the pattern of the logic element is compared to the pattern of a
dummy logic element in an inspection dummy pattern provided at a
predetermined position in the mask. Nowadays, with increasing
demand for an embedded memory in logic, sometimes both the
die-to-die comparison method and the cell comparison method are
performed in a one-time inspection process (for example, see
Japanese Patent No. 4564768).
[0008] The conventional mask inspection is aimed at the detection
of the shape defect of the pattern, and a defect determination
algorithm suitable for the detection of the shape defect of the
pattern and a defect recording method are devised. In the mask
inspection apparatus, a function of detecting the defect caused by
the fluctuation in line width of the pattern is improved in order
to meet a challenge of a lack of an LSI production margin caused by
the fluctuation in line width. However, in a contemporary mask
pattern, the shape defect or the dimension of the defect determined
to be the cause of the fluctuation in line width becomes
substantially equal to the fluctuation in line width (line width
distribution) in the whole surface of the mask. Therefore, the
number of detected defects becomes large.
[0009] In a process of generating the reference image in the
die-to-database comparison method, filtering the optical image of a
typical pattern position in the mask, namely, the learning process
of a filter coefficient is performed to the design pattern data,
whereby the reference image becomes the pattern image having a line
width tendency imitating the pattern line width of a region where
the learning process is performed. Therefore, the line width
dimension has a distribution in the mask even in the
die-to-database comparison method, and the optical image and the
reference image are compared to each other with a line width bias
(deviation) of the pattern in inspecting the region having the
pattern line width different from the pattern line width of the
region where the learning process is performed. As a result, the
shape defect to be detected or the fluctuation in line width cannot
be detected, or the shape and line width that do not need the
detection is detected as the defect.
[0010] Additionally, in the die-to-die comparison method, the
patterns having the line width bias (deviation) are compared to
each other when the chips in the regions having the different line
widths are compared to each other. Accordingly, the defect to be
detected cannot be detected, or the shape and line width that do
not need the detection is detected as the defect.
[0011] An object of the invention is to provide an inspection
method, able to reduce the detection of the unnecessary defect
while detecting the defect to be detected.
[0012] Other challenges and advantages of the present invention are
apparent from the following description.
SUMMARY OF THE INVENTION
[0013] According to one aspect of the present invention, an
inspection method comprising, virtually dividing a sample, in which
a plurality of chip patterns are formed, into a plurality of
strip-shaped stripes along a predetermined direction to acquire an
optical image of the chip pattern in each of the stripes,
performing filtering based on design data of the chip pattern to
produce a reference image corresponding to the optical image,
comparing the chip pattern using a die-to-database method and
comparing a repetitive pattern portion in the chip pattern using a
cell method, obtaining at least one of a dimension difference and a
dimension ratio between a pattern of the optical image and a
pattern of the reference image compared to the pattern of the
optical image by the die-to-database method, and obtaining a
dimension distribution of the plurality of chip patterns from at
least one of the dimension difference and the dimension ratio,
wherein, with respect to a position determined to be a defect by
the comparison of the die-to-database method, a result of the
die-to-database method is stored when a dimension distribution from
the position to a preceding position where at least one of the
dimension difference and the dimension ratio is obtained falls
within a predetermined range by comparing the dimension
distribution to a dimension distribution in the stripe including
the position determined to be the defect, or a dimension
distribution of the chip pattern assumed from the stripe in which
the dimension difference is acquired in advance of the stripe
concerned, and a result of the cell method is stored instead of the
result of the die-to-database method when the dimension
distribution from the position determined to be the defect to the
preceding position where at least one of the dimension difference
and the dimension ratio is obtained exceeds the predetermined range
by comparing the dimension distribution to the dimension
distribution in the stripe including the position determined to be
the defect, or the dimension distribution of the chip pattern
assumed from the stripe in which the dimension difference is
acquired in advance of the stripe concerned.
[0014] Further to this aspect of the present invention, an
inspection method, wherein the result of the die-to-database method
is stored irrespective of the dimension distribution from the
position determined to be the defect to the preceding position,
where at least one of the dimension difference and the dimension
ratio is obtained, when the result of the cell comparison does not
exist because the repetitive pattern portion does not exist in the
position determined to be the defect by the comparison of the
die-to-database method.
[0015] Further to this aspect of the present invention, an
inspection method, wherein the dimension difference is a difference
in line width between the pattern of the optical image and the
pattern of the reference image or a difference of a distance
between the patterns of the optical image and a distance between
the patterns of the reference image.
[0016] Further to this aspect of the present invention, an
inspection method, wherein the dimension ratio is a line width
ratio of the pattern of the optical image and the pattern of the
reference image, or a ratio of a distance between the patterns of
the optical image and a distance between the patterns of the
reference image.
[0017] In another aspect of the present invention, an inspection
method comprising, acquiring an optical image of a sample in which
a plurality of chip patterns are formed, performing filtering based
on design data of the chip pattern to produce a reference image
corresponding to the optical image, comparing the chip pattern by a
die-to-database method and comparing a repetitive pattern portion
in the chip pattern by a cell method, obtaining at least one of a
dimension difference and a dimension ratio between a pattern of the
optical image, and a pattern of the reference image compared to the
pattern of the optical image by the die-to-database method, and
obtaining a dimension distribution of the plurality of chip
patterns from at least one of the dimension difference and the
dimension ratio, wherein, with respect to a position determined to
be a defect by the comparison of the die-to-database method, a
result of the die-to-database method is stored when a dimension
distribution from the position to a preceding position where at
least one of the dimension difference and the dimension ratio is
obtained falls within a predetermined range by comparing the
dimension distribution to a dimension distribution in a chip or a
dimension distribution among chips, and a result of the cell method
is stored instead of the result of the die-to-database method when
the dimension distribution from the position determined to be the
defect to the preceding position, where at least one of the
dimension difference and the dimension ratio is obtained, exceeds
the predetermined range by comparing the dimension distribution to
the dimension distribution in the chip or the dimension
distribution among the chips.
[0018] Further to this aspect of the present invention, an
inspection method, wherein the result of the die-to-database method
is stored irrespective of the dimension distribution from the
position determined to be the defect to the preceding position,
where at least one of the dimension difference and the dimension
ratio is obtained, when the result of the cell comparison does not
exist because the repetitive pattern portion does not exist in the
position determined to be the defect by the comparison of the
die-to-database method.
[0019] Further to this aspect of the present invention, an
inspection method, wherein the dimension difference is a difference
in line width between the pattern of the optical image and the
pattern of the reference image or a difference of a distance
between the patterns of the optical image and a distance between
the patterns of the reference image.
[0020] Further to this aspect of the present invention, an
inspection method, wherein the dimension ratio is a line width
ratio of the pattern of the optical image and the pattern of the
reference image, or a ratio of a distance between the patterns of
the optical image and a distance between the patterns of the
reference image.
[0021] In another aspect of the present invention, an inspection
method comprising, virtually dividing a sample in which a plurality
of chip patterns are formed into a plurality of strip-shaped
stripes along a predetermined direction to acquire an optical image
of the chip pattern in each of the stripes, comparing the chip
pattern by a die-to-die method and comparing a repetitive pattern
portion in the chip pattern by a cell method, obtaining at least
one of a dimension difference and a dimension ratio between a
pattern of the optical image and a pattern of the reference image
compared to the pattern of the optical image by the die-to-die
method, and obtaining a dimension distribution of the plurality of
chip patterns from at least one of the dimension difference and the
dimension ratio, wherein, with respect to a position determined to
be a defect by the comparison of the die-to-die method, a result of
the die-to-die method is stored when a dimension distribution from
the position to a preceding position where at least one of the
dimension difference and the dimension ratio is obtained falls
within a predetermined range by comparing the dimension
distribution to a dimension distribution in the stripe including
the position determined to be the defect, or a dimension
distribution of the chip pattern assumed from the stripe in which
the dimension difference is acquired in advance of the stripe
concerned, and a result of the cell method is stored instead of the
result of the die-to-die method when the dimension distribution
from the position determined to be the defect to the preceding
position where at least one of the dimension difference and the
dimension ratio is obtained exceeds the predetermined range by
comparing the dimension distribution to the dimension distribution
in the stripe including the position determined to be the defect or
the dimension distribution of the chip pattern assumed from the
stripe in which the dimension difference is acquired in advance of
the stripe concerned.
[0022] Further to this aspect of the present invention, an
inspection method, wherein the result of the die-to-die method is
stored irrespective of the dimension distribution from the position
determined to be the defect to the preceding position whereat least
one of the dimension difference and the dimension ratio is
obtained, when the result of the cell method does not exist because
the repetitive pattern portion does not exist in the position
determined to be the defect by the comparison of the die-to-die
method.
[0023] Further to this aspect of the present invention, an
inspection method, wherein the dimension difference is a difference
in line width between the patterns of the optical images or a
difference in distance between the patterns of the optical
images.
[0024] Further to this aspect of the present invention, an
inspection method, wherein the dimension ratio is a line width
ratio of the patterns of the optical images or a ratio of a
distance between the patterns of the optical image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic configuration diagram of an inspection
apparatus according to a first embodiment and a second
embodiment.
[0026] FIG. 2 is a view illustrating a data flow in the inspection
apparatus of FIG. 1.
[0027] FIG. 3 is a view illustrating a procedure for acquiring an
optical image for the detection of the defect of the pattern formed
in the mask.
[0028] FIG. 4 is a flowchart illustrating an example of the
inspection method according to the first embodiment.
[0029] FIG. 5 is a flowchart illustrating an example of the
inspection method according to the second embodiment.
[0030] FIG. 6 illustrates an example of the dimension difference
map of the mask.
[0031] FIG. 7 illustrates the dimension distribution corresponding
to the map in FIG. 6.
[0032] FIG. 8 illustrates the dimension distribution of the pattern
measured by the dimension measuring circuit.
[0033] FIG. 9 illustrates the dimension difference from the
reference value of the line width in the measured portion after the
influence of the dimension distribution is removed.
[0034] FIG. 10 is an example of a schematic diagram of a chip
pattern of a mask.
[0035] FIG. 11 is another example of a schematic diagram of a chip
pattern of a mask.
[0036] FIG. 12 is a view explaining a method for measuring a line
width, and illustrates a schematic diagram of an optical image of a
pattern formed in a mask and a luminance value of each pixel along
a broken line.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Embodiment 1
[0037] FIG. 1 is a schematic configuration diagram of an inspection
apparatus according to a first embodiment. FIG. 2 is a view
illustrating a data flow in the inspection apparatus of FIG. 1. In
FIGS. 1 and 2, a configuration unit necessary in the first
embodiment is illustrated. However, another well-known
configuration unit necessary for an inspection may be used. As used
herein, a "unit" or "circuit" can be configured by a program
operating on a computer. Alternatively, the "unit" or "circuit" may
be constructed by not only the program that is software, but also a
combination of software, hardware, or firmware. In the case that
the "unit" or "circuit" may be constructed by the program, the
program can be recorded in a recording device such as a magnetic
disk drive.
[0038] In the first embodiment, a mask used in photolithography is
used as an inspection target. Alternatively, as another example, a
wafer may be used as the inspection target.
[0039] As illustrated in FIG. 1, an inspection apparatus 100
includes a configuration unit A that constitutes an optical image
acquisition unit and a configuration unit B that performs
processing necessary for an inspection using an optical image
acquired by the configuration unit A.
[0040] The configuration unit A includes a light source 103, an
XY.theta.-table 102 that is movable in a horizontal direction
(X-direction and Y-direction) and a rotation direction
(.theta.-direction), an illumination optical system 170 that
constitutes a transmission illumination system, a magnifying
optical system 104, a photodiode array 105, a sensor circuit 106, a
laser length measuring system 122, and an auto-loader 130.
[0041] In the configuration unit A, the optical image 204 of a mask
101 that becomes an inspection target is acquired. The optical
image data 204 is an image of a mask in which a figure pattern is
written based on graphic data included in design pattern data of
the mask 101. For example, the optical image data 204 is 8-bit data
with no code, and expresses a gradation of brightness of each
pixel.
[0042] Multiple chip patterns are formed in the mask 101. FIG. 10
is a partially enlarged schematic diagram illustrating the chip
pattern. As illustrated in FIG. 10, 2n chip patterns are formed in
a region in the mask 101, and cells A and B each of which is formed
by a repetitive pattern are formed in each chip pattern.
[0043] The auto-loader 130 locates the mask 101 on the
XY.theta.-table 102. An auto-loader control circuit 113 drives the
auto-loader 130 under the control of a control computer 110. When
the mask 101 is positioned on the XY.theta.-table 102, the patterns
formed in the mask 101 are irradiated with light from the light
source 103 disposed above the XY.theta.-table 102. More
particularly, the mask 101 is irradiated with a light emitted from
the light source 103 through the illumination optical system 170.
The magnifying optical system 104, the photodiode array 105, and
the sensor circuit 106 are disposed below the mask 101. The light
transmitted through the mask 101 forms the optical image on the
photodiode array 105 through the magnifying optical system 104.
[0044] The magnifying optical system 104 may be configured such
that a focal point is automatically adjusted by an automatic
focusing mechanism (not illustrated). Although not illustrated, the
inspection apparatus 100 may irradiate the mask 101 with the light
from below and guide the reflected light to the photodiode array
through the magnifying optical system. In this case, the optical
image formed by the transmitted light and reflected light can
simultaneously be acquired.
[0045] The photodiode array 105 performs photoelectric conversion
to the pattern image of the mask 101 formed on the photodiode array
105, and the sensor circuit 106 performs A/D (analog-digital)
conversion to the pattern image. A plurality of sensor pixels (not
illustrated) is disposed in the photodiode array 105. A TDI (Time
Delay Integration) sensor can be cited as an example of the sensor.
In this case, the TDI sensor captures the image of the pattern in
the mask 101 while the XY.theta.-table 102 moves continuously. At
this point, the light source 103, the enlarging optical system 104,
the photodiode array 105, and the sensor circuit 106 constitute a
high-magnification inspection optical system.
[0046] In the configuration unit B, the control computer 110, that
is, the controller controlling the whole of the inspection
apparatus 100 is connected to a position measuring circuit 107, a
comparison circuit 108 that includes a first comparator 108a and a
second comparator 108b, a reference image generating circuit 112
that is an example of the reference image producing unit, an
pattern generating circuit 111, a dimension measuring circuit 125
that is an example of the dimension difference/dimension ratio
acquisition unit, a map producing circuit 126 that is an example of
the dimension distribution acquisition unit, an auto-loader
controller 113, a table control circuit 114, a magnetic disk drive
109 that is an example of the storage device, a magnetic tape
device 115, a flexible disk drive 116, a CRT 117, a pattern monitor
118, and a printer 119 through a bus 120 that constitutes a data
transmission line. The XY.theta.-table 102 is driven by an X-axis
motor, a Y-axis motor, and a .theta.-axis motor under the control
of the table control circuit 114. For example, an air slider, a
linear motor, and a step motor can be used as these driving
mechanisms and can further be used in any combination with each
other.
[0047] As described above, the "unit" or "circuit" in FIG. 1 can be
configured as a program operating on the computer. Alternatively,
the "unit" or "circuit" may be constructed by not only the program
that is software, but also a combination of software, hardware, or
firmware. In the case that the "unit" or "circuit" may be
constructed by the program, the program can be recorded in the
magnetic disk drive 109. For example, each of the auto-loader
control circuit 113, the table control circuit 114, the comparison
circuit 108, and the position measuring circuit 107 may be
constructed by an electric circuit, the software that can be
processed by the control computer 110, or the combination of the
electric circuit and the software.
[0048] The control computer 110 controls the table control circuit
114 to drive the XY.theta.-table 102. A moving position of the
XY.theta.-table 102 is measured by the laser length measuring
system 122, and transmitted to the position measuring circuit
107.
[0049] The control computer 110 controls the auto-loader control
circuit 113 to drive the auto-loader 130. The auto-loader 130
automatically conveys the mask 101, notifies an operator of an end
of the inspection, reviews a defect as needed, and automatically
discharges the mask 101.
[0050] The design pattern data that becomes reference data of the
die-to-database method is stored in the magnetic disk drive 109. In
the progress of the inspection, the design pattern data is read and
transmitted to the pattern generating circuit 111. The design
pattern data will be described with reference to FIG. 2.
[0051] As illustrated in FIG. 2, CAD data 201 produced by a
designer (user) is converted into design intermediate data 202
having a hierarchical format such as OASIS. The design pattern
data, which is produced in each layer and formed in the mask, is
stored in the design intermediate data 202. At this point,
generally the inspection apparatus is configured not to directly
read OASIS data. That is, independent format data is used by each
manufacturer of an inspection apparatus. For this reason, the OASIS
data is input to the inspection apparatus 100 after conversion into
format data 203 unique to the inspection apparatus in each layer.
In this case, the format data 203 can be set to a data format that
is unique to the inspection apparatus 100 or to the data format
that is compatible with a drawing apparatus.
[0052] The format data 203 is input to the magnetic disk drive 109
in FIG. 1. That is, the design pattern data used during the
formation of the pattern in the mask 101 is stored in the magnetic
disk drive 109.
[0053] The figure patterns included in the design pattern may be a
rectangle or a triangle as a basic graphic pattern. For example,
Graphic data in which the shape, size, and position of each figure
pattern is stored in the magnetic disk drive 109. For example, the
graphic data is information such as a coordinate (x, y) from the
original position of the graphic pattern, a side length, and a
figure code that becomes an identifier identifying a figure pattern
type such as a rectangle and a triangle.
[0054] A set of graphic patterns existing within a range of several
tens of micrometers is generally called a cluster or a cell, and
the data is layered using the cluster or cell. In the cluster or
cell, a disposition coordinate and a repetitive amount are defined
in the case that various graphic patterns are separately disposed
or repetitively disposed with a certain distance. The cluster or
cell data is disposed in a strip-shaped region called a stripe. The
strip-shaped region has a width of several hundred micrometers and
a length of about 100 mm that corresponds to a total length in an
X-direction or a Y-direction of the mask 101.
[0055] The pattern generating circuit 111 reads the input design
pattern data from the magnetic disk drive 109 through the control
computer 110.
[0056] In the pattern generating circuit 111, the design pattern
data is converted into image data (bit pattern data). That is, the
pattern generating circuit 111 extracts the design pattern data to
individual data of each graphic pattern, and interprets the figure
pattern code and figure pattern dimension, which indicate the
figure pattern shape of the design pattern data. The design pattern
data is extracted to binary or multi-level image data as the
pattern disposed in a square having a unit of a grid of a
predetermined quantization dimension. Then an occupancy rate of the
graphic pattern in the design pattern is calculated in each region
(square) corresponding to a sensor pixel, and the occupancy rate of
the graphic pattern in each pixel becomes a pixel value.
[0057] The image data converted by the pattern generating circuit
111 is transmitted to the reference image generating circuit 112,
that is, the reference image producing unit, and used to produce a
reference image (also referred to as reference data).
[0058] The optical image data 204 output from the sensor circuit
106 is transmitted to the comparison circuit 108 together with data
indicating a position of the mask 101 on the XY.theta.-table 102.
The data is output from the position measuring circuit 107. The
reference image is also transmitted to the comparison circuit
108.
[0059] In the comparison circuit 108, the optical image data 204
and the reference data are compared to each other using a proper
comparison determination algorithm. In the configuration of FIG. 1,
transmission images are compared to each other. In a configuration
in which a reflection optical system is used, reflection images are
compared to each other, or a comparison determination algorithm in
which transmission and reflection are combined is used. As a result
of the comparison, in the case that a difference between the two
exceeds a predetermined threshold, the position is determined to be
the defect.
[0060] For example, the determination threshold registered as a
line width defect is assigned by a line width dimension difference
(nm) between the optical image data 204 and the reference data and
a dimension ratio (%). For example, the determination thresholds of
the line width dimension difference of 16 nm and the dimension
ratio of 8% are assigned in two ways. When the dimension difference
with the reference data is 20 nm while the pattern of the optical
image data 204 has the line width of 200 nm, because the pattern is
larger than both the thresholds of the dimension difference and
dimension ratio, the pattern is registered as the defect.
[0061] In the case that the line width is larger than that of the
reference data and the case that the line width is smaller than
that of the reference data, the threshold of the defect
determination may separately be assigned. The threshold may be
assigned in both the case that not the line width but the
inter-pattern distance is larger than that of the reference data
and the case that the inter-pattern distance is smaller than that
of the reference data. The thresholds of a hole diameter or a
diameter dimension ratio may be assigned for the pattern having a
hole shape. In this case, the threshold may be assigned for
sections in the X-direction and Y-direction of the hole.
[0062] In the comparison circuit 108, the reference image
corresponding to the (stripe-shaped) optical image data 204 is
divided into small rectangular regions of several tens of
micrometers called inspection frames. A sensor frame image
extracted from the optical image data 204 and a reference frame
image extracted from the reference image are input to a comparison
unit. The comparison unit compares the sensor frame image and the
reference frame image to each other to detect the defect. Several
tens of comparison units are included in the comparison circuit 108
so as to concurrently process multiple inspection frames. Each
comparison unit captures the unprocessed frame image when ending
the processing of one inspection frame. Therefore, many inspection
frames are sequentially processed.
[0063] The processing of the comparison unit is specifically
performed as follows. The sensor frame image and the reference
frame image are aligned with each other. At this point, in order to
align edge positions of the pattern or luminance peak positions,
the sensor frame image or the reference frame image is shifted in
parallel in units of sensor pixels, and the sensor frame image and
the reference frame image are aligned up to the sensor pixel or
less by prorating luminance values of neighboring pixels. After the
alignment, a level difference between the sensor frame image and
the reference frame image is evaluated in each pixel, and
derivative values of the pixels in a pattern edge direction are
compared to each other, whereby the defect is detected according to
the proper comparison algorithm. Hereinafter, occasionally the
comparison of the sensor frame image and the reference frame image
is simply referred to as comparison of the optical image and the
reference image. The sensor frame images are compared to each other
in the comparison by the die-to-die method. However, in this case,
sometimes the comparison of the sensor frame images is simply
referred to as the comparison of the optical images.
[0064] At the same time, in the comparison circuit 108, the
repetitive pattern in the optical image data 204 is searched for
and extracted within a proper dimensional range, and the cells are
compared to each other. The repetitive pattern is searched for by a
method for extracting a pattern feature from a repetitive
disposition command of the graphic pattern or cell included in the
layer structure of the design data and the acquired optical image
data 204. For example, a subframe that becomes one unit of a
predetermined repetitive pattern is defined in the inspection frame
of the optical image. The subframes are compared to each other in
one inspection frame, and the repetitive pattern is determined to
have the defect when the difference exists between the patterns of
the subframes.
[0065] In the first embodiment, the optical image data 204 is also
transmitted to the dimension measuring circuit 125. In the
dimension measuring circuit 125, for example, the line width of the
line pattern written in the mask 101 is measured from the optical
image data 204. The reference image generating circuit 112
transmits the reference data to the dimension measuring circuit
125, and the position measuring circuit 107 transmits the data
indicating the position of the mask 101 on the XY.theta.-table 102
to the dimension measuring circuit 125. In the dimension measuring
circuit 125, the line width of the pattern corresponding to the
line pattern is measured from the reference data. The dimension
difference or dimension ratio between the pattern line width of the
optical image and the pattern line width of the reference image is
obtained based on the measured value.
[0066] The pattern dimension measurement in the dimension measuring
circuit 125 is performed concurrently with the acquisition of the
optical image of the mask 101. Alternatively, for example, the
pattern dimension measurement in the dimension measuring circuit
125 may be performed concurrently with the inspection performed by
the comparison circuit 108.
[0067] The dimension measuring circuit 125 is an example of the
dimension difference/dimension ratio acquisition unit of the
invention. In the embodiment, the space width between the line
patterns, namely, the inter-line distance is measured instead of
the line width, and the difference or ratio between the inter-line
distances may be obtained. Both the dimension difference and the
dimension ratio between the line widths or the inter-line distances
may be obtained.
[0068] In the dimension difference or the dimension ratio, for
example, the pattern in the mask 101 is divided to form multiple
inspection regions, and the line width of each pixel is obtained
for the optical image of each inspection region. Then, a frequency
of the obtained line width is compiled, and an average value of the
line widths is calculated from the compiled result of the frequency
distribution. The dimension difference or dimension ratio of the
line width is obtained from the average value and the line width
obtained from the reference image. Specifically, the method
disclosed in Japanese patent No. 3824542 can be applied.
[0069] The data of the dimension difference or dimension ratio,
which is obtained by the dimension measuring circuit 125, is
transmitted to the map producing circuit 126, that is, the
dimension distribution acquisition unit. In the map producing
circuit 126, for example, a map of the dimension difference or
dimension ratio of the pattern line width in the surface on the
mask 101 is produced based on the transmitted data. The produced
map is stored in the magnetic disk drive 109. The inspection
apparatus 100 does not necessarily include the map producing
circuit 126, but the dimension measuring circuit 125 may have the
map producing function, or the map may be produced by an external
computer. Alternatively, a defect determination may be made by the
data of the dimension difference or dimension ratio, which is
obtained by the dimension measuring circuit 125, without producing
the map.
[0070] When the comparison circuit 108 determines that the pattern
has a defect, the coordinate of the defect and the optical image
and reference image, which are the basis of the defect
determination, are stored as a mask inspection result 205 in the
magnetic disk drive 109. The mask inspection result 205 is
transmitted to a review tool 500 as illustrated in FIG. 2. A review
process is an operation in which the operator determines whether
the detected defect will become a practical problem. For example,
the operator visually determines whether the defect needs to be
corrected by comparing the reference image that is the basis of the
defect determination to the optical image including the defect.
[0071] The defect information determined through the review process
is also stored in the magnetic disk drive 109 of FIG. 1. As
illustrated in FIG. 2, when the defect to be corrected is confirmed
by the review tool 500, the mask 101 is transmitted to a repair
apparatus 600, that is, the external device of the inspection
apparatus 100 together with a defect information list 207. Because
a correction method depends on whether the defect is projected or
recessed, a defect type including the distinction between the
projection and the recess and the defect coordinate are added to
the defect information list 207.
[0072] An example of a method for inspecting the mask 101 with the
inspection apparatus 100 in FIG. 1 will be described below.
[0073] FIG. 4 is a flowchart illustrating an example of the
inspection method of the first embodiment. As illustrated in FIG.
4, an inspection process includes a process of acquiring the
optical image of the mask 101 (optical image acquisition process;
S1), a process of storing the design pattern data of the pattern
formed in the mask 101 (Store the Design Pattern data; S2), an
pattern generating process (S3) and a filtering process (S4), that
is, an example of the process of generating the reference image
(S3), a process of comparing the optical image to the image that
becomes a reference (comparison process; S5 and S6), a process of
measuring the pattern dimension difference from the optical image
and the reference image (dimension measuring process; S7), a
process of producing the dimension difference map in the surface of
the mask 101 based on the measured dimension difference (map
producing process; S8), a process of comparing the dimension
distribution in the neighborhood of the defect detection position
to the dimension distribution in another region (S9), and a process
of determining whether the dimension distribution in the
neighborhood of the defect detection position falls within a
predetermined range (S10).
(Optical Image Acquisition Process)
[0074] The mask 101 is positioned on the XY.theta.-table 102. In
order to obtain the correct inspection result, it is necessary to
locate the mask 101 at a predetermined position of the
XY.theta.-table 102. Therefore, an alignment mark is usually formed
in the mask 101, and the mask 101 is aligned on the XY.theta.-table
102 using the alignment mark.
[0075] The alignment of the mask 101 (plate alignment) will be
described with reference to FIG. 11. In the example of FIG. 11,
cross mask alignment marks MA are formed at four corners of the
mask 101. Multiple chip patterns (C1, C2, C3, . . . ) are formed in
the mask 101, and chip alignment marks CA are also formed in each
chip. The mask 101 is positioned on the XY.theta.-table 102, and it
is assumed that the XY.theta.-table 102 includes an XY-stage moving
in a horizontal direction and a .theta.-stage that is disposed on
the XY-stage to move in a rotational direction.
[0076] Specifically, in the alignment process, an X-axis and a
Y-axis of the pattern, that is, the inspection target are aligned
with running axes of the XY-stage while the mask 101 is positioned
on the XY.theta.-table 102.
[0077] In the mask alignment marks MA provided in the four
positions, the images of the two mask alignment marks MA having the
smaller values of the Y-coordinates are captured, the .theta.-stage
is rotated such that the two mask alignment marks MA correctly
become the equal Y-coordinate, thereby finely adjusting the
rotation direction of the mask 101. At this point, the distance
between the mask alignment marks MA is correctly measured. Then the
images of the two mask alignment marks MA having the larger values
of the Y-coordinates are captured. Therefore, the coordinates of
the mask alignment marks MA at four positions are correctly
measured.
[0078] It is discovered from the above measurement that the two
mask alignment marks MA having the larger values of the
Y-coordinates are located at vertices of a trapezoid having the two
mask alignment marks MA having the smaller values of the
Y-coordinates at both ends of a base. At this point, because the
mask 101 originally has the rectangular shape, the two mask
alignment marks MA having the larger values of the Y-coordinates
are supposed to be located at the vertices of the rectangle.
However, the measurement result shows that the two mask alignment
marks MA having the larger values of the Y-coordinates are located
at the vertices of the trapezoid. In consideration of these facts,
it is discovered the shape of the mask 101 is deformed.
Accordingly, it is assumed that the region of the pattern that
becomes the inspection target has the trapezoidal deformation
similar to the trapezoid and expansion and contraction of the
distance between the mask alignment marks MA, and compensation is
performed on the assumption of the trapezoidal deformation and the
expansion and contraction of the distance when the reference image
generating circuit 112 generates the reference data.
[0079] The mask alignment mark MA is not necessarily provided in
the mask 101. In this case, the alignment is performed using the
vertex of the corner or the side of the edge pattern, which is
close to an outer periphery of the mask 101 and equal to the
coordinates of the XY-coordinate, in the pattern that becomes the
inspection target.
[0080] In the optical image acquisition process of the first
embodiment, the configuration unit A in FIG. 1 acquires the optical
image of the mask 101. FIG. 3 is a view illustrating an optical
image acquiring procedure for the purpose of the detection of the
defect of the pattern formed in the mask 101. As described above,
the optical image corresponds to the optical image data 204 in FIG.
2.
[0081] In FIG. 3, it is assumed that the mask 101 is positioned on
the XY.theta.-table 102 in FIG. 1. The inspection region in the
mask 101 is virtually divided into the strip-shaped multiple
inspection regions, namely, stripes 20.sub.1, 20.sub.2, 20.sub.3,
20.sub.4, . . . as illustrated in FIG. 3. For example, each stripe
is a region having the width of several hundred micrometers and the
length of about 100 mm corresponding to the total length in the
X-direction or Y-direction of the mask 101.
[0082] The optical image is acquired in each stripe. That is, in
acquiring the optical image in FIG. 3, the operation of the
XY.theta.-table 102 is controlled such that the each stripe
20.sub.1, 20.sub.2, 20.sub.3, 20.sub.4, . . . is continuously
scanned. Specifically, the optical image of the mask 101 is
acquired while the XY.theta.-table 102 moved in the -X-direction of
FIG. 3. The image having a scan width W in FIG. 3 is continuously
input to the photodiode array 105 in FIG. 1. That is, the image of
the second stripe 20.sub.2 is acquired after the image of the first
stripe 20.sub.1 is acquired. In this case, after the
XY.theta.-table 102 moves in the -Y-direction in a stepwise manner,
the optical image is acquired while the XY.theta.-table 102 moves
in the direction (X-direction) opposite to the direction
(-X-direction) in which the image of the first stripe 20.sub.1 is
acquired, and the image having the scan width W is continuously
input to the photodiode array 105. In the case that the image of
the third stripe 20.sub.3 is acquired, after moving in the
-Y-direction in the stepwise manner, the XY.theta.-table 102 moves
in the direction opposite to the direction (X-direction) in which
the image of the second stripe 20.sub.2 is acquired, namely, the
direction (-X-direction) in which the image of the first stripe
20.sub.1 is acquired. An arrow in FIG. 3 indicates the optical
image acquiring direction and sequence, and a hatched portion
indicates the region where the optical image is already
acquired.
[0083] FIG. 10 illustrates a state in which the optical image is
being acquired. In FIG. 10, 2n chip patterns are formed in a
predetermined region in the mask 101, and a cell A and a cell B
each of which includes the repetitive pattern are formed in each
chip pattern. The sensor captures the image of the pattern along
the stripe in the order of the first chip, the second chip, the
third chip, . . . , and n-th chip.
[0084] The photodiode array 105 performs the photoelectric
conversion to the pattern image formed on the photodiode array 105
in FIG. 1, and the sensor circuit 106 performs the A/D
(analog-digital) conversion to the pattern image. Then the optical
image is transmitted from the sensor circuit 106 to the comparison
circuit 108 in FIG. 1.
[0085] The A/D-converted sensor data is input to a digital
amplifier (not illustrated) that can adjust an offset and a gain in
each pixel. The gain for each pixel of the digital amplifier is
fixed in a calibration process. For example, in the calibration
process for transmitted light, a black level is fixed while the
image of a light-shielding region in the mask 101, sufficiently
wide with respect to an area in which the image is captured by the
sensor, is captured. Then a white level is fixed while the image of
a transmitted light region in the mask 101, sufficiently wide with
respect to an area in which the image is captured by the sensor, is
captured. At this point, in consideration of a fluctuation in light
quantity during the inspection, the offset and the gain are
adjusted in each pixel such that amplitudes of the white level and
black level are distributed in a range of 10 to 240 corresponding
to about 4 to about 94% of 8-bit gradation data.
(Storage Process)
[0086] In the case of inspection by the die-to-database comparison
method, the reference image generated from the design pattern data
becomes a reference of the defect determination. In the inspection
apparatus 100, the design pattern data used to form the pattern in
the mask 101 is stored in the magnetic disk drive 109.
(Pattern Generating Process)
[0087] In the pattern generating process, the pattern generating
circuit 111 in FIG. 1 reads the design pattern data from the
magnetic disk drive 109 through the control computer 110, and
converts the read design pattern data of the mask 101 into the
binary or multi-value image data (design image data). The image
data is transmitted to the reference image generating circuit
112.
(Filtering Process)
[0088] In the filtering process, the reference image generating
circuit 112 in FIG. 1 performs the proper filtering to the design
pattern data, that is, the graphic image data. The reason is as
follows.
[0089] In the production process because roundness of the corner
and a finished dimension of the line width is adjusted, the pattern
in the mask 101 is not strictly matched with the design pattern.
The optical image data 204, that is, the optical image obtained
from the sensor circuit 106 in FIG. 1 is faint due to a resolution
characteristic of the magnifying optical system 104 or an aperture
effect of the photodiode array 105, in other words, the state in
which a spatial lowpass filter functions.
[0090] Therefore, the mask that becomes the inspection target is
observed in advance of the inspection, a filter coefficient
imitating the production process or a change of an optical system
of the inspection apparatus is determined to subject the design
pattern data to a two-dimensional digital filter. Thus, the
processing of imitating the optical image is performed to the
reference image.
[0091] The learning process of the filter coefficient may be
performed using the pattern of the mask that becomes the reference
fixed in the production process or a part of the pattern of the
mask (in the first embodiment, mask 101) that becomes the
inspection target. In the latter case, the filter coefficient is
acquired in consideration of the pattern line width of the region
used in the learning process or a finished degree of the roundness
of the corner, and reflected in a defect determination criterion of
the whole mask.
[0092] In the case that the mask that becomes the inspection target
is used, advantageously the learning process of the filter
coefficient can be performed without removing influences such as a
variation of production lot and a fluctuation in condition of the
inspection apparatus. However, when the dimension fluctuates in the
surface of the mask, the filter coefficient becomes optimum with
respect to the position used in the learning process, but the
filter coefficient does not necessarily become optimum with respect
to other positions, which results in a pseudo defect. Therefore,
preferably the learning process is performed around the center of
surface of the mask that is hardly influenced by the fluctuation in
dimension. Alternatively, the learning process is performed at
multiple positions in the surface of the mask, and the average
value of the obtained multiple filter coefficients may be used.
(Dimension Measuring Process)
[0093] In the dimension measuring process, the pattern dimension
difference is measured from the optical image and the reference
image. In the inspection apparatus 100 in FIG. 1, the dimension
measuring circuit 125 measures the dimension difference of the
pattern line width between the optical image and the reference
image using the optical image data 204 output from the sensor
circuit 106 and the reference data output from the reference image
generating circuit 112. The dimension ratio of the pattern line
width may be measured instead of or in addition to the dimension
difference of the pattern line width, or the inter-pattern distance
difference or the inter-pattern distance ratio may be obtained
instead of or in addition to the pattern line width.
[0094] For example, a frequency at which the dimension measuring
circuit 125 measures the dimension difference during the inspection
can be set to the proper number of sampling times (about 1000
points) in the length direction (X-direction) of the stripe
(20.sub.1, 20.sub.2, 20.sub.3, 20.sub.4, . . . ) in FIG. 3, and set
to almost the same number of sampling times in the width direction
(Y-direction) of the stripe. A proper line pattern in which a
distance of an edge pair can be measured is used in the
neighborhood of a potential point where the dimension difference is
measured. In this case, the one edge pair may be used. However,
preferably the dimension difference is measured using the edge
pairs of multiple positions, the frequency of the obtained value is
compiled, and the highest frequency value (mode) of the compiled
result of the frequency distribution is used as a representative
value. In the case that the edge pair is not found in the
neighborhood of the potential point, or in the case of a small
number of edge pairs, the dimension difference does not need to be
measured, or the mode may be obtained from the limited number of
samples.
(Map Producing Process)
[0095] In the inspection apparatus 100, at the same time as the
optical image of the mask 101 is acquired, the dimension measuring
circuit 125 measures the pattern dimension difference between the
optical image and the reference image, and the obtained data of the
dimension difference is transmitted to the map producing circuit
126. In the map producing circuit 126, the map expressing the
dimension distribution in the surface of the mask is produced from
the accumulated data of the dimension difference. The dimension
distribution in the currently inspected stripe or the dimension
distribution of the stripe in which the inspection is already
performed in the same mask can be recognized from the map.
(Die-to-Database Comparison Process and Cell Comparison
Process)
[0096] As illustrated in FIG. 2, the optical image data 204
acquired in the optical image acquisition process is transmitted to
the comparison circuit 108. The reference image generating circuit
112 transmits the reference data to the comparison circuit 108. The
comparison circuit 108 includes the first comparator 108a and the
second comparator 108b, and the first comparator 108a compares the
optical image data 204 to the reference data by the die-to-database
method. Concurrently with the processing performed by the
die-to-database comparison method, the second comparator 108b
searches the repetitive pattern in the optical image data 204, and
extracts the repetitive pattern in a proper dimension range to
perform the cell comparison. However, in the case that the cell
that becomes the reference does not exist because the repetitive
pattern does not exist near the cell that becomes the inspection
target, the processing is performed only by the die-to-database
comparison method.
[0097] In both methods, the data that becomes the inspection target
and the data that becomes the reference of the defect determination
are compared to each other using the proper comparison
determination algorithm. The data that becomes the inspection
target is determined to be the defect in the case that the
difference between the two exceeds the predetermined threshold.
[0098] For example, it is assumed that the chip patterns are matrix
aligned in the mask 101. In the die-to-database comparison method,
when the n-th chip is considered as the inspection target, the n-th
chip is determined to be the defect in the case that the pattern
difference between the optical image and reference image of the
n-th chip exceeds the predetermined threshold. On the other hand,
in the cell comparison method, the patterns that are separated from
each other by a pitch of the repetitive pattern (cell) such as the
memory mat portion in the one chip are compared to each other, and
the pattern is determined to be the defect in the case that the
difference between the two exceeds the predetermined threshold. In
this case, when the specific cell in the n-th chip is the
inspection target, the optical image preceding the specific cell
becomes the reference image to be compared. For example, assuming
that the second cell is the inspection target in the cell A of FIG.
10, the optical image of the first cell becomes the reference
image.
[0099] More specifically the defect determination can be made by
the following two methods. One of the methods is the method for
determining that the inspection target is the defect in the case
that the difference exceeding a predetermined threshold is
recognized between the position of a contour in the reference image
and the position of a contour in the optical image. The other
method is the method for determining that the inspection target is
the defect in the case that the ratio of the pattern line width in
the reference image and the pattern line width in the optical image
exceeds a predetermined threshold. In this method, the ratio of the
inter-pattern distance in the reference image and the inter-pattern
distance in the optical image may be used.
[0100] (Process of Determining Whether Dimension Distribution in
the Neighborhood of the Defect Detection Position Falls within
Predetermined Range by Comparing Dimension Distribution in
Neighborhood of Defect Detection Position to Dimension Distribution
of Another Region)
[0101] In the case that the dimension measuring circuit 125
measures the pattern dimension concurrently with the acquisition of
the optical image of the mask 101, the latest data is referred to
in the dimension difference data measured by the dimension
measuring circuit 125 when the defect is detected by the
die-to-database comparison method. When the dimension distribution
from the position where the defect is detected to the preceding
position where the dimension difference is obtained falls within
the predetermined range by comparing the dimension distribution to
the dimension distribution in the chip and the dimension
distribution among the chips, the result of the die-to-database
comparison method, namely, the defect coordinate and the optical
image and reference image, which are the basis of the defect
determination are stored as the mask inspection result 205 in the
magnetic disk drive 109.
[0102] In the case that the dimension measuring circuit 125
measures the pattern dimension concurrently with the inspection of
the comparison circuit 108, at a time point when the defect is
detected by the die-to-database comparison method, the dimension of
the pattern in which the comparison is already performed is
measured, however the dimension of the pattern in which the
comparison is not performed is not measured. Therefore, in this
case, the latest data is referred to from the dimension difference
data measured by the dimension measuring circuit 125.
[0103] On the other hand, the defect is detected by the
die-to-database comparison method, and the dimension distribution
from the position where the defect is detected to the preceding
position where the dimension difference is obtained exceeds the
predetermined range by comparing the dimension distribution to the
dimension distribution in the chip and the dimension distribution
among the chips. In this case, the result of the die-to-database
comparison method is not adopted with respect to the position, but
the result of the cell comparison method performed concurrently is
adopted. At this point, whether the defect is detected as a result
of the cell comparison method not a problem. That is, even the
position determined to be the defect by the die-to-database
comparison method is not registered as the defect unless the
position is determined to be the defect by the cell comparison
method.
[0104] However, in the case that the cell that becomes the
reference does not exist because the repetitive pattern does not
exist near the cell that becomes the inspection target, the
processing is performed only by the die-to-database comparison
method. In this case, even if the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained exceeds the
predetermined range by comparing the dimension distribution to the
dimension distribution in the chip and the dimension distribution
among the chips, preferably the result of the die-to-database
comparison method is adopted. That is, the coordinate of the defect
detected by the die-to-database comparison method and the optical
image and reference image, which are the basis of the defect
determination, are stored as the mask inspection result 205 in the
magnetic disk drive 109.
[0105] By way of example, the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained is compared to the
dimension distribution in the chip and the dimension distribution
among the chips. Alternatively, the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained may be compared to the
dimension distribution of the region separated by the chip
pitch.
[0106] For example, when the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained falls within the
predetermined range by comparing the dimension distribution to (1)
the dimension distribution in the stripe including the position
determined to be the defect or (2) the dimension distribution of
the chip pattern assumed from the stripe in which the dimension
difference is acquired in advance of the stripe including the
position determined to be the defect, the defect coordinate and the
optical image and reference image, which are the basis of the
defect determination may be stored in the magnetic disk drive 109.
At this point, (1) the dimension distribution and (2) the dimension
distribution are derived from the map produced by the map producing
circuit 126. (1) The dimension distribution and (2) the dimension
distribution can also directly be derived from the dimension
difference data obtained by the dimension measuring circuit
125.
[0107] In the above modification, the defect is detected by the
die-to-database comparison method, and the dimension distribution
from the position where the defect is detected to the preceding
position where the dimension difference is obtained is compared to
(1) the dimension distribution and (2) the dimension distribution.
When the dimension distribution from the position where the defect
is detected to the preceding position where the dimension
difference is obtained deviates from the predetermined range, the
result of the die-to-database comparison method is not adopted with
respect to the position, but the result of the cell comparison
method performed in parallel is adopted. In this case, whether the
defect is detected as a result of the cell comparison method is not
a problem. That is, even the position determined to be the defect
by the die-to-database comparison method is not registered as the
defect unless the position is determined to be the defect by the
cell comparison method.
[0108] However, in the case that the cell that becomes the
reference does not exist because the repetitive pattern does not
exist near the cell that becomes the inspection target, the
processing is performed only by the die-to-database comparison
method. In this case, even if the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained deviates from the
predetermined range by comparing the dimension distribution to (1)
the dimension distribution and (2) the dimension distribution, the
result of the die-to-database comparison method is adopted. That
is, the coordinate of the defect detected by the die-to-database
comparison method and the optical image and reference image, which
are the basis of the defect determination, are stored as the mask
inspection result 205 in the magnetic disk drive 109.
[0109] In the case that the defect is detected by the
die-to-database comparison method, the excess of the dimension
distribution from the position where the defect is detected to the
preceding position where the dimension difference is obtained over
the predetermined range by comparing the dimension distribution in
the chip and the dimension distribution among the chips means that
the tendency of the line width in the region where the learning
process of the two-dimensional digital filter is performed differs
from the tendency of the line width in the position where the
defect is detected during the generation of the reference data. The
same holds true for the case that the dimension distribution from
the position where the defect is detected to the preceding position
where the dimension difference is obtained exceeds the
predetermined range by comparing the dimension distribution to (1)
the dimension distribution in the stripe including the position
determined to be the defect or (2) the dimension distribution of
the chip pattern assumed from the stripe in which the dimension
difference is acquired in advance including the position determined
to be the defect.
[0110] Therefore, in the first embodiment, whether the reference
data is suitable for the reference of the defect determination by
comparing the tendency of the dimension difference in the chip, the
tendency of the dimension among the chips, the tendency of the
dimension difference in the same chip, or the tendency of the
dimension difference in the surface on the mask to the tendency of
the dimension distribution from the position where the defect is
detected to the preceding position where the dimension difference
is obtained, can be determined. The determination can be made by
the control computer 110 in FIG. 1. The control computer 110
determines whether the result of the cell comparison method exists,
and the control computer 110 sets the result of the die-to-database
comparison method to the mask inspection result 205 irrespective of
the comparison result in the case that not the result of the cell
comparison method but only the result of the die-to-database
comparison method exists.
[0111] In the case that the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained exceeds the
predetermined range as a result of the comparison, because the
dimension fluctuates in the surface of the mask, the filter
coefficient of the defect detection position is not the optimum
value, and the reference data is determined not to be suitable for
the reference of the defect determination. The result of the cell
comparison method is adopted. When the position is also determined
to be the defect by the cell comparison method, the position is
registered as the defect. For example, the control computer 110
stores the defect coordinate and the optical image and reference
image, which are the basis of the defect determination, as the mask
inspection result 205 in the magnetic disk drive 109. Unless the
position is determined to be the defect by the cell comparison
method, it is assumed that the defect detected by the
die-to-database comparison method fails within an acceptable range,
but the position is not registered as the defect. However, the
result of the die-to-database comparison method may be stored.
[0112] When the dimension difference obtained by the dimension
measuring circuit 125 is large, the position can be registered as
the defect even if the position is not determined to be the defect
in the comparison circuit 108. Therefore, in first embodiment, the
defect determination can be made as follows.
[0113] For example, it is assumed that the threshold by which the
comparison circuit 108 determines the line width defect is set to
the line width dimension difference of 16 nm and the dimension
ratio of 8%. The threshold of the defect determination for the
measurement result of the dimension measuring circuit 125 is
slightly relaxed compared with the threshold by which the
comparison circuit 108 determines the line width defect, the line
width dimension difference is set to 20 nm, and the dimension ratio
is set to 10%. As to the predetermined range that becomes the
criterion to which one of the result of the die-to-database
comparison method and the result of the cell comparison method is
adopted, the line width dimension difference is set to 12 nm or
more, and the dimension ratio is set to 6% or more.
[0114] The result of the die-to-database comparison method is
adopted, when the dimension difference obtained by the dimension
measuring circuit 125 is less than 12 nm while the dimension ratio
is less than 6%. On the other hand, the result of the cell
comparison method is adopted, when the dimension difference
obtained by the dimension measuring circuit 125 is greater than or
equal to 12 nm and less than 20 nm while the dimension ratio is
greater than or equal to 6% and less than 10%. The position is
registered as the defect, when the dimension difference obtained by
the dimension measuring circuit 125 is greater than or equal to 20
nm while the dimension ratio is greater than or equal to 10%.
[0115] The predetermined range that becomes the criterion to which
one of the result of the die-to-database comparison method and the
result of the cell comparison method is adopted is set in each mask
that becomes the inspection target. At this point, the
predetermined range is set to the range that does not exceed the
threshold in the case that the position is determined to be the
defect from the measured value of the dimension measuring circuit
125. The setting method is similar to the threshold setting method
in the comparison circuit 108. That is, the predetermined range can
individually be assigned for the case that the line width is larger
than the reference data and the case that the line width is smaller
than the reference data, and the predetermined range may be
assigned for the case that not the line width but the inter-pattern
distance is larger than the reference data and the case that the
inter-pattern distance is smaller than the reference data.
Additionally, the predetermined range of the hole diameter or the
dimension ratio of the diameters can be assigned for the pattern
having the hole shape. In this case, the predetermined range can be
assigned for both the sections in the X-direction and Y-direction
of the hole.
[0116] In the conventional inspection method, all the information
on the defect detected by the die-to-database comparison method is
registered. Therefore, sometimes the defect information that
originally is not required to be detected is registered. On the
other hand, in the first embodiment, the result of the
die-to-database comparison method is replaced with the result of
the cell comparison method in some cases in order to remove the
influence of the line width distribution in the surface of the mask
from the acquired data. Therefore, because the defect that
originally needs not to be detected is removed from the mask
inspection result, the number of defects that is reviewed by the
operator decreases thus shortening the inspection time. Because the
number of defects described in the defect information list is also
decreased, the production yield of the mask can be improved.
Additionally, the shape defect and the defect caused by the
fluctuation in local line width can be detected by removing the
influence of the line width distribution in the surface of the
mask.
[0117] The map produced by the map producing circuit 126 of the
first embodiment can be used to transfer the pattern of the mask
101 to the wafer. For example, when the exposure apparatus that
transfers the pattern of the mask 101 to the wafer can input
irradiation energy (dose) as a map, the map produced by the map
producing circuit 126 is input to the exposure apparatus, and
converted into the map of the irradiation energy, which allows the
line width to be homogeneously transferred to the wafer. For
example, in the position where the dimension difference becomes
negative in the mask 101, namely, the position where the line width
is thinned, the irradiation energy is adjusted such that the
pattern transferred to the wafer is thickened. On the other hand,
in the position where the dimension difference becomes positive in
the mask 101, namely, the position where the line width is
thickened, the irradiation energy is adjusted such that the pattern
transferred to the wafer is thinned. Therefore, the line width of
the pattern transferred to the wafer is homogenized evenly in the
mask in which the pattern has the dimension distribution.
Second Embodiment
[0118] The inspection method in which the die-to-database
comparison method and the cell comparison method are combined is
described in the first embodiment. In a second embodiment, the
inspection can be performed by the combination of the die-to-die
comparison method and the cell comparison method. In this case, the
inspection apparatus 100 in FIG. 1 may be used.
[0119] The die-to-die comparison method is the method for comparing
the optical images of the same pattern in the chips of the
different masks to each other in the case that the multiple chips
partially or wholly having the pattern configuration are disposed
in the same mask. That is, the chips repetitively formed in the
mask are compared to each other in the die-to-die comparison
method, and the repetitive patterns such as the memory mat portions
in the one chip, namely, the cells are compared to each other in
the cell comparison method. In the example of FIG. 10, the first
chip and the second chip are compared to each other in the
die-to-die comparison method. On the other hand, the first cell and
second cell of the cell A are compared to each other in the cell
comparison method.
[0120] The die-to-die comparison method and the cell comparison
method will be described in detail with reference to FIG. 11. As
illustrated in FIG. 11, the sensor captures the image of the
pattern along the stripe 20 in the order of the chip C1, the chip
C2, and the chip C3. In the comparison circuit 108, the captured
image of the stripe data is divided in units of inspection frames,
and an inspection frame 1 extracted from the chip C1 is compared to
an inspection frame 2 extracted from the chip C2. The comparison is
performed by the comparison unit, which is provided in the
comparison circuit 108, to perform processing for each unit of the
inspection frame.
[0121] Several tens of comparison units are provided so as to be
able to concurrently process the multiple inspection frames, and
each comparison unit captures the unprocessed frame image when
ending the processing of one inspection frame. Specifically, the
comparison unit aligns the image of the inspection frame 1 with the
image of the inspection frame 2. At this point, in order to align
the edge positions of the pattern or the luminance peak positions,
the image of the inspection frame 1 or the image of the inspection
frame 2 is shifted in parallel in units of sensor pixels. The image
of the inspection frame 1 and the image of the inspection frame 2
are aligned up to the sensor pixel or less by prorating the
luminance values of neighboring pixels. Then the first comparator
108a performs the die-to-die comparison to the image of the
inspection frame 1 and the image of the inspection frame 2.
Similarly, the die-to-die comparison is performed to the image of
the inspection frame 2 and the image of the inspection frame 3.
[0122] As illustrated in FIG. 11, the subframe that becomes one
unit of the repetitive pattern is defined in each inspection frame.
For example, the second comparator 108b performs the cell
comparison to the image of a subframe 1 and the image of a subframe
2 in the inspection frame 1.
[0123] In both the die-to-die comparison method and the cell
comparison method, the level difference between the two images to
be compared is evaluated in each pixel, and the derivative values
of the pixels in the pattern edge direction are compared to each
other, whereby the defect is detected according to the proper
comparison algorithm.
[0124] FIG. 5 is a flowchart illustrating an example of the
inspection method of the second embodiment. That is, FIG. 5
illustrates the inspection method in which the die-to-die
comparison method and the cell comparison method are combined.
[0125] As illustrated in FIG. 5, the inspection process includes a
process of acquiring the optical image of the mask 101 (optical
image acquisition process; S11), a process of comparing the optical
image that becomes the inspection target to the optical image (also
referred to as a reference image) that becomes the reference
(comparison process; S12 and S13), a process of measuring the
pattern dimension difference from the optical image and the
reference image (dimension measuring process; S14), a process of
producing the dimension difference map in the surface of the mask
101 based on the measured dimension difference (map producing
process; S15), a process of comparing the dimension distribution in
the neighborhood of the defect detection position to the dimension
distribution in another region (S16), and a process of determining
whether the dimension distribution in the neighborhood of the
defect detection position falls within a predetermined range
(S17).
(Optical Image Acquisition Process)
[0126] Because the optical image acquisition process (S11) in FIG.
5 is already described in FIGS. 1 to 4 of the first embodiment, a
description will be omitted.
(Dimension Measuring Process)
[0127] In the inspection apparatus 100, the dimension measuring
circuit 125 measures the pattern dimension difference between the
optical images in parallel with the acquisition of the optical
image of the mask 101. In the dimension measuring process (S14),
the pattern dimension difference between the optical image that
becomes the inspection target and the optical image that becomes
the reference is measured by the die-to-die comparison method. In
the inspection apparatus 100 in FIG. 1, the dimension measuring
circuit 125 measures the dimension difference of the pattern line
width between the optical images using the optical image data
output from the sensor circuit 106.
[0128] A specific example of the line width measuring method will
be described with reference to FIG. 12. FIG. 12 is a view
schematically illustrating the optical image of the pattern formed
in the mask 101 and a luminance value of each pixel along a broken
line. For example, when the line and space pattern is inspected as
illustrated in FIG. 12, the threshold in the middle of the white
and black amplitude of the optical image is set to the threshold of
the line width determination, and the position of the pattern edge
is obtained from the pixel position where the luminance value of
the optical image intersects the threshold. Then the positions of
the pattern edges are converted into the distance of the edge pair
to obtain the line width.
[0129] In the dimension measuring process, the positional
information of the mask 101 on the XY.theta.-table 102 is added to
the optical image data from the sensor circuit 106. The positional
information is transmitted from the position measuring circuit 107.
The dimension ratio of the pattern line width may be measured
instead of or in addition to the dimension difference of the
pattern line width, or the inter-pattern distance difference or the
inter-pattern distance ratio may be obtained instead of or in
addition to the pattern line width.
[0130] For example, the frequency at which the dimension measuring
circuit 125 measures the dimension difference during the inspection
can be set to the proper number of sampling times (about 1000
points) in the length direction (X-direction) of the stripe
(20.sub.1, 20.sub.2, 20.sub.3, 20.sub.4, . . . ) in FIG. 3, and set
to approximately the same number of sampling times in the width
direction (Y-direction) of the stripe. The proper line pattern in
which the distance of the edge pair can be measured is used in the
neighborhood of the potential point where the dimension difference
is measured. In this case, the one edge pair may be used. However,
preferably the dimension difference is measured using the edge
pairs of multiple positions, the frequency of the obtained value is
added, and the highest frequency value (mode) of the compiled
result of the frequency distribution is used as a representative
value. In the case that the edge pair is not found in the
neighborhood of the potential point, or in the case of a small
number of edge pairs, the dimension difference needs not to be
measured, or the mode may be obtained from the limited number of
samples.
(Map Producing Process)
[0131] The data of the dimension difference acquired by the
dimension measuring circuit 125 is transmitted to the map producing
circuit 126. In the map producing circuit 126, the map expressing
the dimension distribution in the surface of the mask is produced
from the accumulated data of the dimension difference (map
producing process; S15). The dimension distribution in the
currently inspected stripe or the dimension distribution of the
stripe in which the inspection is already performed in the same
mask can be recognized from the map.
(Die-to-Die Comparison Process and Cell Comparison Process)
[0132] The optical image data 204 acquired in the optical image
acquisition process is transmitted to the comparison circuit 108 in
FIG. 1. The comparison circuit 108 includes the first comparator
108a and the second comparator 108b. In the second embodiment, the
first comparator 108a compares the optical image data to each other
by the die-to-die method (die-to-die comparison process; S12) In
parallel with the comparison performed by the die-to-die comparison
method, the second comparator 108b searches the repetitive pattern
in the optical image data 204, and extracts the repetitive pattern
in the proper dimension range to perform the cell comparison (cell
comparison process; S13). However, in the case that the cell that
becomes the reference does not exist because the repetitive pattern
does not exist near the cell that becomes the inspection target,
the processing is performed only by the die-to-die comparison
method.
[0133] In both the methods, the data that becomes the inspection
target and the data that becomes the reference of the defect
determination are compared to each other using the proper
comparison determination algorithm. The data that becomes the
inspection target is determined to be the defect in the case that
the difference between the two exceeds the predetermined
threshold.
[0134] For example, it is assumed that the lattice-shaped the chip
patterns are matrix aligned in the mask 101. In the die-to-die
comparison method, when the n-th chip is considered as the
inspection target, the n-th chip is determined to be the defect in
the case that the pattern difference between the optical image of
the n-th chip and the optical image of the (n-1)-th chip exceeds
the predetermined threshold. On the other hand, in the cell
comparison method, the patterns that are separated from each other
by the pitch of the repetitive pattern (cell) such as the memory
mat portion in the one chip are compared to each other, and the
pattern is determined to be the defect in the case that the
difference between the two exceeds the predetermined threshold. In
this case, when the specific cell in the n-th chip is the
inspection target, the optical image preceding the specific cell
becomes the reference image to be compared. For example, assuming
that the second cell is the inspection target in the cell A of FIG.
10, the optical image of the first cell becomes the reference
image.
[0135] For example, the determination threshold registered as the
line width defect is assigned in units of line width dimension
differences (nm) and units of dimension ratios (%). For example,
the determination thresholds of the line width dimension difference
of 16 nm and the dimension ratio of 8% are assigned in two ways.
When the dimension difference with the reference data is 20 nm
while the pattern of the optical image data 204 that becomes the
inspection target has the line width of 200 nm, because the pattern
is larger than both the thresholds of the dimension difference and
dimension ratio, the pattern is registered as the defect.
[0136] The threshold of the defect determination may separately be
assigned for the case that the line width is larger than that of
the reference data and the case that the line width is smaller than
that of the reference data. The threshold may be assigned in both
the case that not the line width but the inter-pattern distance is
larger than that of the reference data and the case that the
inter-pattern distance is smaller than that of the reference data.
The thresholds of the hole diameter and diameter dimension ratio
may be assigned for the pattern having the hole shape. In this
case, the threshold may be assigned for the sections in the
X-direction and Y-direction of the hole.
[0137] When compared with the cell comparison method, basically the
whole chips is set to the inspection range in the die-to-die
comparison method, and the inspection can be performed irrespective
of the portion in which the repetitive pattern exists. However,
because the separation of the dies are larger than the distance
between the cells that are compared to each other, the die-to-die
comparison method is easily influenced by the dimension
distribution in the surface of the mask. That is, when the chips in
the regions having the different dimensions are compared to each
other, the patterns having dimension biases (deviations) are
compared to each other, which results in a problem in that the
defect to be detected cannot be detected or the shape or line width
which needs not to be detected is detected as the defect.
Therefore, the result of the die-to-die comparison method is
replaced with the result of the cell comparison method in some
cases in order to remove the influence of the dimension
distribution in the surface of the mask from the acquired data. A
specific technique will be described below.
[0138] (Process of Determining Whether Dimension Distribution in
the Surrounding Area of Defect Detection Position Falls within
Predetermined Range by Comparing Dimension Distribution in
Neighborhood of Defect Detection Position to Dimension Distribution
of Another Region)
[0139] FIG. 6 illustrates an example of the dimension difference
map of the mask. In the example of FIG. 6, the line width is larger
than the reference value in regions A and C. On the other hand, the
line width is smaller than the reference value in regions B and D.
FIGS. 7 to 9 are views illustrating the dimension distribution
corresponding to the section along a line X-X' in FIG. 6. In FIGS.
7 to 9, a horizontal axis has the same scale, and an origin is
positioned at the same position.
[0140] FIG. 7 illustrates the dimension distribution corresponding
to the map in FIG. 6. FIG. 8 illustrates the dimension distribution
of the pattern measured by the dimension measuring circuit. In FIG.
8, an absolute value of the dimension difference in the portion
surrounded by the broken line is smaller than absolute values of
the dimension differences at the remaining four points.
Accordingly, the point in the broken line seems not to be the
defect at a glance. On the other hand, the absolute values of the
dimension differences in the portion surrounded by an alternate
long and short dash line is larger than the absolute value of the
dimension difference at the remaining two points. Accordingly, the
points in the alternate long and short dash line seem to be the
defect.
[0141] However, as can be seen from FIG. 7, the surrounding of the
portion surrounded by the broken line (P2) is the region where the
dimension difference becomes negative. That is, the line width in
the surrounding area is smaller than the reference value. On the
other hand, because the dimension difference in the portion
surrounded by the broken line becomes the positive value, the
portion surrounded by the broken line has the line width that is
larger than the surrounding area. FIG. 9 illustrates the dimension
difference from the reference value of the line width in the
measured portion after the influence of the dimension distribution
is removed. As can be seen from FIG. 9, the dimension difference in
the portion surrounded by the broken line (P2) becomes positive,
the portion surrounded by the broken line is unusually large
compared with the surrounding area from the value of the positive
dimension difference, and the portion surrounded by the broken line
should therefore be detected as the defect.
[0142] On the other hand, as can be seen from FIG. 7, the
surrounding area of the portion surrounded by the dot dash line
(P1) in FIG. 8 is the region where the dimension difference becomes
positive. Accordingly, in FIG. 8, the dimension difference of the
portion indicates the large positive value as a result of the
addition of the tendency of the line width distribution in the
region. In FIG. 9, although the dimension difference of the portion
surrounded by the dot dash line (P1) has the positive value, the
dimension difference falls within the acceptable range, and the
point should not be detected as the defect.
[0143] In the die-to-die comparison method, the chips in the
regions A and B in FIG. 6 are compared to each other. The regions A
and B have the contradictory tendencies of the line widths as
illustrated in FIG. 7. Therefore, when the defect determination is
made from the result of the dimension distribution in FIG. 8, there
is a possibility that the defect to be detected cannot be detected,
or the defect that need not to be detected is detected as the
defect.
[0144] In the region A where the line width is increased as a
whole, the dimension difference of the position where the line
width is further increased indicates the large value even if the
dimension difference of the position is practically acceptable. On
the other hand, in the region B where the line width is decreased
as a whole, the dimension difference of the position where the line
width is increased indicates the small value even if the dimension
difference of the position is practically unacceptable. Therefore,
when the regions A and B are compared to each other, the region A
indicating the large dimension difference is determined to be the
defect and the region B indicating the small dimension difference
is determined not to be the defect.
[0145] In such cases, the regions A and B are not compared to each
other, however the cells in the region A are compared to each
other, or the cells in the region B are compared to each other.
That is, the cell comparison method is adopted instead of the
die-to-die comparison method. In the cell comparison method,
because the regions having the same tendency of the line width are
compared to each other, the comparison can be performed in the
state of FIG. 9 after the influence of the dimension distribution
is removed. Because the defect that needs not to be detected is
removed from the mask inspection result, the number of defects
reviewed by the operator is decreased to shorten the inspection
time. Because the number of defects described in the defect
information list is also decreased, the production yield of the
mask can be improved. Additionally, the defect that is hardly
detected due to the influence of the dimension distribution can be
detected.
[0146] As to which one of the result of the die-to-die comparison
method and the result of the cell comparison method is adopted is
determined according to the flowchart in FIG. 5.
[0147] In the case that the dimension measuring circuit 125
measures the pattern dimension in parallel with the acquisition of
the optical image of the mask 101, the latest data is referred to
in the dimension difference data measured by the dimension
measuring circuit 125 when the defect is detected by the die-to-die
comparison method. The dimension distribution from the position
where the defect is detected to the preceding position where the
dimension difference is obtained is compared to the dimension
distribution in the chip and the dimension distribution among the
chips (S16). As a result of the comparison, when the dimension
distribution from the position where the defect is detected to the
preceding position where the dimension difference is obtained is
determined to fall within the predetermined range in S17 of FIG. 5,
the result of the die-to-die comparison method, namely, the defect
coordinate and the optical image and reference image, which are the
basis of the defect determination, are stored as the mask
inspection result 205 in the magnetic disk drive 109.
[0148] In the case that the dimension measuring circuit 125
measures the pattern dimension in parallel with the inspection of
the comparison circuit 108, at the time when the defect is detected
by the die-to-die comparison method, the dimension of the pattern
in which the comparison is already performed is measured, but the
dimension of the pattern in which the comparison is not performed
is not measured. Therefore, in this case, the latest data is
referred to from the dimension difference data measured by the
dimension measuring circuit 125.
[0149] On the other hand, the defect may be detected by the
die-to-die comparison method, and the dimension distribution from
the position where the defect is detected to the preceding position
where the dimension difference is obtained exceeds the
predetermined range by comparing the dimension distribution to the
dimension distribution in the chip and the dimension distribution
among the chips. In this case, the result of the die-to-die
comparison method is not adopted with respect to the position, but
the result of the cell comparison method performed in parallel is
adopted. At this point, whether the defect is detected as a result
of the cell comparison method is not a problem. That is, the
position determined to be the defect by the die-to-die comparison
method is not registered as the defect unless the position is also
determined to be the defect by the cell comparison method.
[0150] However, in the case that a cell having a repetitive pattern
that could be used as a reference does not exist near the cell that
becomes the inspection target, the processing is performed only by
the die-to-die comparison method. In this case, even if the
dimension distribution from the position where the defect is
detected to the preceding position where the dimension difference
is obtained exceeds the predetermined range by comparing the
dimension distribution to the dimension distribution in the chip
and the dimension distribution among the chips, preferably the
result of the die-to-die comparison method is adopted. That is, the
coordinate of the defect detected and the optical image and
reference image, which are the basis of the defect determination,
are stored as the mask inspection result 205 in the magnetic disk
drive 109.
[0151] By way of example, the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained is compared to the
dimension distribution in the chip and the dimension distribution
among the chips. Alternatively, the dimension distribution from the
position where the defect is detected to the preceding position
where the dimension difference is obtained may be compared to the
dimension distribution of the region separated by the chip
pitch.
[0152] For example, the dimension distribution from the position
where the defect is detected to the preceding position where the
dimension difference is obtained may be compared to (1) the
dimension distribution in the stripe including the position
determined to be the defect or (2) the dimension distribution of
the chip pattern assumed from the stripe in which the dimension
difference is acquired in advance of the stripe including the
position determined to be the defect. Whether the dimension
distribution acquired from the dimension difference measured by the
dimension measuring circuit 125 falls within the predetermined
range by comparing the dimension distribution to (1) the dimension
distribution or (2) the dimension distribution is determined. When
the dimension distribution falls within the predetermined range,
the coordinate of the defect detected by the die-to-die comparison
method and the optical image and reference image, which are the
basis of the defect determination may be stored as the mask
inspection result 205 in the magnetic disk drive 109. At this
point, (1) the dimension distribution and (2) the dimension
distribution are derived from the map produced by the map producing
circuit 126. (1) The dimension distribution and (2) the dimension
distribution can also directly be derived from the dimension
difference data obtained by the dimension measuring circuit
125.
[0153] In the above modification, the defect is detected by the
die-to-die comparison method, and the dimension distribution from
the position where the defect is detected to the preceding position
where the dimension difference is obtained is compared to (1) the
dimension distribution and (2) the dimension distribution. When the
dimension distribution from the position where the defect is
detected to the preceding position where the dimension difference
is obtained deviates from the predetermined range, the result of
the die-to-die comparison method is not adopted with respect to the
position, but the result of the cell comparison method performed in
parallel is adopted. In this case, whether the defect is detected
as a result of the cell comparison method is not a problem. That
is, even the position determined to be the defect by the die-to-die
comparison method is not registered as the defect unless the
position is determined to be the defect by the cell comparison
method. Alternatively, whether the result of the die-to-die
comparison method is stored may be determined.
[0154] In the case that the cell that becomes the reference does
not exist because the repetitive pattern does not exist near the
cell that becomes the inspection target, the processing is
performed only by the die-to-die comparison method. In this case,
even if the dimension distribution from the position where the
defect is detected to the preceding position where the dimension
difference is obtained deviates from the predetermined range by
comparing the dimension distribution to (1) the dimension
distribution or (2) the dimension distribution, the result of the
die-to-die comparison method is adopted. When the mask is seen as a
whole, the addition of the defect that needs not to be detected to
the mask inspection result is reduced, and the defect that is
hardly detected due to the influence of the dimension distribution
can be detected.
[0155] In the second embodiment, the control computer 110 in FIG. 1
can determine whether the result of the die-to-die method is
suitably adopted by comparing the dimension distribution in the
chip and the dimension distribution among the chips to the
dimension distribution from the position where the defect is
detected to the preceding position where the dimension difference
is obtained. Alternatively, the control computer 110 may determine
whether the result of the die-to-die method is suitably adopted by
comparing the dimension distribution from the position where the
defect is detected to the preceding position where the dimension
difference is obtained to (1) the dimension distribution or (2) the
dimension distribution. The control computer 110 can determine
whether the result of the cell comparison method exists. In the
case that not the result of the cell comparison method but only the
result of the die-to-die comparison method exists, the result of
the die-to-die comparison method is stored as the mask inspection
result 205 in the magnetic disk drive 109 irrespective of the
comparison result.
[0156] When the dimension difference obtained by the dimension
measuring circuit 125 has the large degree, the position can be
registered as the defect even if the position is not determined to
be the defect in the comparison circuit 108. Therefore, in second
embodiment, the defect determination can be made as follows.
[0157] For example, it is assumed that the threshold by which the
comparison circuit 108 determines the line width defect is set to
the line width dimension difference of 16 nm and the dimension
ratio of 8%. The threshold of the defect determination for the
measurement result of the dimension measuring circuit 125 is
slightly relaxed compared with the threshold by which the
comparison circuit 108 determines the line width defect, the line
width dimension difference is set to 20 nm, and the dimension ratio
is set to 10%. As to the predetermined range that becomes the
criterion to which one of the result of the die-to-die comparison
method and the result of the cell comparison method is adopted, the
line width dimension difference is set to 12 nm or more, and the
dimension ratio is set to 6% or more.
[0158] The result of the die-to-die comparison method is adopted,
when the dimension difference obtained by the dimension measuring
circuit 125 is less than 12 nm while the dimension ratio is less
than 6%. On the other hand, the result of the cell comparison
method is adopted, when the dimension difference obtained by the
dimension measuring circuit 125 is greater than or equal to 12 nm
and less than 20 nm while the dimension ratio is greater than or
equal to 6% and less than 10%. The position is registered as the
defect, when the dimension difference obtained by the dimension
measuring circuit 125 is greater than or equal to 20 nm while the
dimension ratio is greater than or equal to 10%.
[0159] The predetermined range that becomes the criterion to which
one of the result of the die-to-die comparison method and the
result of the cell comparison method is adopted is set in each mask
that becomes the inspection target. At this point, the
predetermined range is set to the range that does not exceed the
threshold in the case that the position is determined to be the
defect from the measured value of the dimension measuring circuit
125. The setting method is similar to the threshold setting method
in the comparison circuit 108. That is, the predetermined range can
individually be assigned for the case that the line width is larger
than the reference data and the case that the line width is smaller
than the reference data, and the predetermined range may be
assigned for the case that not the line width but the inter-pattern
distance is larger than the reference data and the case that the
inter-pattern distance is smaller than the reference data.
Additionally, the predetermined range of the hole diameter or the
dimension ratio of the diameters can be assigned for the pattern
having the hole shape. In this case, the predetermined range can be
assigned for both the sections in the X-direction and Y-direction
of the hole.
[0160] In the second embodiment, the map produced by the map
producing circuit 126 can be used to transfer the pattern in the
mask 101 to the wafer. For example, when the exposure apparatus
that transfers the pattern in the mask 101 to the wafer can input
the irradiation energy (dose) as the map, the map produced by the
map producing circuit 126 is input to the exposure apparatus, and
converted into the map of the irradiation energy, which allows the
line width to be homogeneously transferred to the wafer. For
example, in the position where the dimension difference becomes
negative in the mask 101, namely, the position where the line width
is thinned, the irradiation energy is adjusted such that the
pattern transferred to the wafer is thickened. On the other hand,
in the position where the dimension difference becomes positive in
the mask 101, namely, the position where the line width is
thickened, the irradiation energy is adjusted such that the pattern
transferred to the wafer is thinned. Therefore, the line width of
the pattern transferred to the wafer is homogenized even in the
mask in which the pattern has the dimension distribution.
[0161] According to the present invention, an inspection apparatus
comprises, an optical image acquisition unit that virtually divides
a sample into a plurality of strip-shaped stripes along a
predetermined direction to acquire an optical image of the sample
in each of the stripes, a reference image producing unit that
performs filtering based on design data of the chip pattern which
is formed on the sample to produce a reference image corresponding
to the optical image, a first comparator that compares the chip
pattern of the optical image output from the optical image
acquisition unit to the chip pattern of the reference image output
from the reference image producing unit by a die-to-database
method, a second comparator that compares repetitive pattern
portions in the chip pattern of the optical image output from the
optical image acquisition unit using a cell method, a dimension
difference/dimension ratio acquisition unit that obtains at least
one of a dimension difference and a dimension ratio between a
pattern of the optical image and a pattern of the reference image
compared to the pattern of the optical image by the die-to-database
method, a dimension distribution acquisition unit that obtains a
dimension distribution of the plurality of chip patterns from at
least one of the dimension difference and the dimension ratio,
which are output from the dimension difference/dimension ratio
acquisition unit, and a controller that stores a result of the
first comparator when, with respect to a place determined to be a
defect by the comparison of the first comparator, a dimension
distribution from the place to a preceding place where at least one
of the dimension difference and the dimension ratio is obtained by
the dimension difference/dimension ratio acquisition unit falls
within a predetermined range by comparing the dimension
distribution to a dimension distribution in the stripe including
the place determined to be the defect or a dimension distribution
of the chip pattern guessed from the stripe in which the dimension
difference is acquired in advance of the stripe concerned, and
stores a result of the second comparator instead of the result of
the first comparator when the dimension distribution from the place
determined to be the defect to the preceding place where at least
one of the dimension difference and the dimension ratio is obtained
by the dimension difference/dimension ratio acquisition unit
exceeds the predetermined range by comparing the dimension
distribution to the dimension distribution in the stripe including
the place determined to be the defect or the dimension distribution
of the chip pattern guessed from the stripe in which the dimension
difference is acquired in advance of the stripe concerned.
[0162] The controller stores the result of the first comparator
irrespective of the dimension distribution from the place
determined to be the defect to the preceding place where at least
one of the dimension difference and the dimension ratio is obtained
by the dimension difference/dimension ratio acquisition unit, when
the result of the second comparator does not exist because the
repetitive pattern portion does not exist in the place determined
to be the defect by the comparison of the first comparator.
[0163] Further, according to the present invention, an inspection
apparatus comprises, an optical image acquisition unit that
virtually divides a sample into a plurality of strip-shaped stripes
along a predetermined direction to acquire an optical image of the
sample in each of the stripes, a first comparator that compares the
chip patterns of the optical image output from the optical image
acquisition unit by a die-to-die method, a second comparator that
compares repetitive pattern portions in the chip pattern of the
optical image output from the optical image acquisition unit by a
cell method, a dimension difference/dimension ratio acquisition
unit that obtains at least one of a dimension difference and a
dimension ratio between a pattern of the optical image and a
pattern of the reference image compared to the pattern of the
optical image by the die-to-die method, a dimension distribution
acquisition unit that obtains a dimension distribution of the
plurality of chip patterns from at least one of the dimension
difference and the dimension ratio, which are output from the
dimension difference/dimension ratio acquisition unit, and a
controller that stores a result of the first comparator when, with
respect to a place determined to be a defect by the comparison of
the first comparator, a dimension distribution from the place to a
preceding place where at least one of the dimension difference and
the dimension ratio is obtained by the dimension
difference/dimension ratio acquisition unit falls within a
predetermined range by comparing the dimension distribution to a
dimension distribution in the stripe including the place determined
to be the defect or a dimension distribution of the chip pattern
guessed from the stripe in which the dimension difference is
acquired in advance of the stripe concerned, and stores a result of
the second comparator instead of the result of the first comparator
when the dimension distribution from the place determined to be the
defect to the preceding place where at least one of the dimension
difference and the dimension ratio is obtained by the dimension
difference/dimension ratio acquisition unit exceeds the
predetermined range by comparing the dimension distribution to the
dimension distribution in the stripe including the place determined
to be the defect or the dimension distribution of the chip pattern
guessed from the stripe in which the dimension difference is
acquired in advance of the stripe concerned.
[0164] The controller stores the result of the first comparator
irrespective of the dimension distribution from the place
determined to be the defect to the preceding place where at least
one of the dimension difference and the dimension ratio is obtained
by the dimension difference/dimension ratio acquisition unit, when
the result of the second comparator does not exist because the
repetitive pattern portion does not exist in the place determined
to be the defect by the comparison of the first comparator.
[0165] The present invention is not limited to the embodiments
described and can be implemented in various ways without departing
from the spirit of the invention.
[0166] The above description of the present embodiment has not
specified apparatus constructions, control methods, etc., which are
not essential to the description of the invention, since any
suitable apparatus construction, control methods, etc. can be
employed to implement the invention. Further, the scope of this
invention encompasses all support apparatuses employing the
elements of the invention and variations thereof, which can be
designed by those skilled in the art.
* * * * *