U.S. patent application number 10/657098 was filed with the patent office on 2004-03-11 for visual inspection apparatus and method.
This patent application is currently assigned to Tokyo Seimitsu Co., Ltd.. Invention is credited to Kuwabara, Masayuki.
Application Number | 20040047501 10/657098 |
Document ID | / |
Family ID | 15393586 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040047501 |
Kind Code |
A1 |
Kuwabara, Masayuki |
March 11, 2004 |
Visual inspection apparatus and method
Abstract
A plurality of chips arranged in the same scanning row of a
wafer is divided into groups, which include a predetermined number
of chips. The images of the chips in each group are compared with
each other in the double detection. If one group includes the
first, the second and the third chips; the first chip and the
second chip are compared, then the first chip and the third chip
are compared, and at last, the second chip and the third chip are
compared while the images are captured. It is therefore possible to
detect the defects in the double detection for all the chips
including peripheral chips by comparing the images for the same
number of comparison times as the number of chips.
Inventors: |
Kuwabara, Masayuki;
(Mitaka-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Tokyo Seimitsu Co., Ltd.
Mitaka-shi
JP
|
Family ID: |
15393586 |
Appl. No.: |
10/657098 |
Filed: |
September 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10657098 |
Sep 9, 2003 |
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09315136 |
May 20, 1999 |
|
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|
6643394 |
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Current U.S.
Class: |
382/149 |
Current CPC
Class: |
G01N 21/95607 20130101;
H01L 21/67288 20130101 |
Class at
Publication: |
382/149 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 1998 |
JP |
10-145806 |
Claims
What is claimed is:
1. A visual inspection apparatus, comprising: imaging means for
capturing images of at least three areas arranged in a line on an
object; image comparison means for dividing the areas into at least
one group, each group including at least consecutive three of the
areas; for designating one of the areas as a subject area and other
two of the areas as comparison areas for the subject area, the
comparison areas being in the same group with the subject area and
within a predetermined distance from the subject area; and for
comparing the image of the subject area with the images of the
comparison areas; and defect detection means for detecting a defect
in the object in accordance with the comparison between the images
of the areas by the image comparison means, wherein the image
comparison means is configured to number the areas in each group
along the line and to select the comparison areas as follows: when
the subject area is odd-numbered and is not one of ends of
odd-numbered areas in the group, the comparison areas are two
odd-numbered areas closest to the subject area; when the subject
area is one of the ends of the odd-numbered areas in the group, the
comparison areas are one odd-numbered area and one even-numbered
area closest to the subject area; when the subject area is
even-numbered and is not one of ends of even-numbered areas in the
group, the comparison areas are two even-numbered areas closest to
the subject area; and when the subject area is one of the ends of
even-numbered areas in the group, the comparison areas are one
even-numbered area and one odd-numbered area closest to the subject
area.
2. The visual inspection apparatus as defined in claim 1, wherein
the areas are arranged in a row on the object.
3. The visual inspection apparatus as defined in claim 1, wherein
the imaging means relatively scans the object along the line to
sequentially capture the images of the areas.
4. The visual inspection apparatus as defined in claim 1, wherein
the imaging means relatively scans the object along the line by one
of a CCD line sensor and a TDI sensor to sequentially capture the
images of the areas.
5. A visual inspection method, comprising the steps of: capturing
images of at least three areas arranged in a line on an object;
dividing the areas into at least one group, each group including at
least consecutive three of the areas; designating one of the areas
as a subject area and other two of the areas as comparison areas
for the subject area, the comparison areas being in the same group
with the subject area and within a predetermined distance from the
subject area; and comparing the image of the subject area with the
images of the comparison areas to determine whether the subject
area is defective, wherein the designating step comprises the steps
of numbering the areas in each group along the line and selecting
the comparison areas as follows: when the subject area is
odd-numbered and is not one of ends of odd-numbered areas in the
group, the comparison areas are two odd-numbered areas closest to
the subject area; when the subject area is one of the ends of the
odd-numbered areas in the group, the comparison areas are one
odd-numbered area and one even-numbered area closest to the subject
area; when the subject area is even-numbered and is not one of ends
of even-numbered areas in the group, the comparison areas are two
even-numbered areas closest to the subject area; and when the
subject area is one of the ends of even-numbered areas in the
group, the comparison areas are one even-numbered area and one
odd-numbered area closest to the subject area.
6. The visual inspection method as defined in claim 5, wherein the
areas are arranged in a row on the object.
7. The visual inspection method as defined in claim 5, wherein the
capturing step comprises the step of relatively scanning the object
along the line to sequentially capture the images of the areas.
8. The visual inspection method as defined in claim 5, wherein the
capturing step comprises the step of relatively scanning the object
along the line by one of a CCD line sensor and a TDI sensor to
sequentially capture the images of the areas.
Description
[0001] This is a continuation of application Ser. No. 09/315,136
filed May 20, 1999. The entire disclosure of the prior application
is hereby incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a visual
inspection apparatus and method, and more particularly to a visual
inspection apparatus and method applied to find defects in patterns
on a semiconductor wafer, a photo mask, a liquid crystal display,
or the like.
[0004] 2. Description of Related Art
[0005] Conventionally, two adjacent chips are compared to each
other in order to inspect patterns on a semiconductor wafer, a
photo mask, a liquid crystal display, or the like. In order to
inspect the patterns, an image obtaining part, which is composed of
an optical microscope and an imaging device such as a time delay
and integration (TDI) sensor, obtains images of the patterns
represented with multiple values while continuously scanning the
object along the X-axis. The obtained images are stored in an image
data storage part such as a memory. When two images in the
corresponding areas on the adjacent first and second chips are
obtained, sub-pixel alignment is performed for these two images at
regular frame intervals, and the two images are compared with each
other on a pixel-by-pixel basis. In this comparison, a pair of a
pixel of the first image and the corresponding pixel of the second
image that has a gray level difference in excess of a preset
threshold is recognized as having a possibility of being defective.
At this point in such single detection, it is not clear which chip
of the first and second chips has a possibility of being defective,
and thus, a differential image of the first and second images is
temporarily stored in a defect detecting part as two values. The
above-mentioned comparison is performed between the second chip and
the third chip to obtain another differential image, which is
collated with the differential image of the first and second chips.
It is therefore possible to determine which chip of the first and
second chips has a possibility of being defective. In this
detecting method (double detection), it is possible to determine
defective parts on the chips and improve the reliability of the
results since the same chip is subjected to the comparison
twice.
[0006] In the conventional method, however, the chips except end
chips (peripheral chips) in the same row or column are compared
with the adjacent two chips in the same scanning to thereby
accurately detect the defects. Since there are no chips outside the
peripheral chips, only the single detection can be performed for
the peripheral chips. Thus, the unreliable inspection is performed,
or the peripheral chips are not inspected at all.
[0007] There is a conventional image comparison method, which
comprises the steps of rescanning only the peripheral chips, which
have been detected as having a possibility of being defective in
the single detection, and comparing those peripheral chips with the
second chips to the inside from those peripheral chips in order to
find whether the peripheral chips have a possibility of being
defective. This method, however, is inefficient since it is
necessary to rescan the peripheral chips. In order to eliminate the
need for rescanning the peripheral chips, the images of the
peripheral chips and the second chips to the inside from the
peripheral chips are stored in an image storage part such as a
memory, and the images of these chips are read from the image
storage part on completion of the scanning to compare the images.
This is also inefficient since the third chip must be compared
three times with the first, second and fourth chips. An ordinary
comparison unit has only the minimum capacity for processing the
captured images within a set amount of time, and therefore, the
extra comparison lowers the inspection speed. To solve this
problem, only the image of the first chip may be stored in the
memory until the completion of one scanning, and the images of the
peripheral chips stored in the previous scanning are compared with
one another while the image of the first chip is captured in the
next scanning, thereby performing the double detection for all the
chips. If the distance between the peripheral chips becomes longer
with the increase in the diameters of the wafers, a slight
variation in a manufacturing process will cause noise problems such
as odd color. This deteriorates the inspection sensitivity. It is
therefore desirable to compare the closest chips available.
[0008] Alternatively, in a scanning method of Japanese Patent
Provisional Publication No. 2-210249, the last chip in each
scanning row or column is compared with the first chip in the next
scanning row or column to perform the double detection even for the
peripheral chips. Since, however, the straightness in the scanning
direction (the X-axis) is higher than the absolute position
accuracy along the Y-axis, the difference of the images along the
Y-axis is greater than that of the images of chips in the same
scanning rows. To correct the difference of the images, the images
are normally shifted by less than a pixel and laid upon one another
(a sub-pixel alignment). In this case, however, there is always
such a possibility that there is a difference of 0.5 pixel at the
maximum. The more the difference is corrected in the sub-pixel
alignment, the lower the defect defecting sensitivity becomes due
to the deterioration of the captured images. Moreover, this method
cannot be applied to the inspection for only one row or column.
SUMMARY OF THE INVENTION
[0009] In view of the foregoing, it is an object of the present
invention to provide a visual inspection apparatus, which is
capable of detecting defects efficiently and accurately for all the
chips including peripheral chips in double detection by comparing
images a minimum amount of times.
[0010] To achieve the above-mentioned object, the present invention
is directed to a visual inspection apparatus, comprising: an
imaging means for capturing images of at least three areas arranged
in a line on an object; an image comparison means for dividing the
areas into at least one group, each group including at least
consecutive three of the areas; for designating one of the areas as
a subject area and other two of the areas as comparison areas for
the subject area, the comparison areas being in the same group with
the subject area and within a predetermined distance from the
subject area; and for comparing the image of the subject area with
the images of the comparison areas; and a defect detection means
for detecting a defect in the object in accordance with the
comparison between the images of the areas by the image comparison
means.
[0011] The visual inspection apparatus is preferably characterized
in that: the image comparison means numbers the areas in each group
along the line; if the subject area is odd-numbered and is not one
of ends of odd-numbered areas in the group, the comparison areas
are two odd-numbered areas closest to the subject area; if the
subject area is one of the ends of the odd-numbered areas in the
group, the comparison areas are one odd-numbered area and one
even-numbered area closest to the subject area; if the subject area
is even-numbered and is not one of ends of even-numbered areas in
the group, the comparison areas are two even-numbered areas closest
to the subject area; and if the subject area is one of the ends of
even-numbered areas in the group, the comparison areas are one
even-numbered area and one odd-numbered area closest to the subject
area. Preferably, the imaging means relatively scans the object
along the line by one of a line sensor and a TDI sensor to
sequentially capture the images of the areas.
[0012] The visual inspection apparatus of the present invention
scans the object along the X-axis to sequentially capture the
images of the areas with the same pattern, which are arranged along
the X-axis. Then, the areas arranged along the X-axis are divided
into a predetermined number of groups. In each group, two areas in
a predetermined interval are respectively combined with one another
so that each area can be combined with other two areas. The image
of each area, which is captured by the imaging means, is compared
with the images of the other two areas. It is therefore possible to
compare the images of all the areas including both ends (the
peripheral chips) in the double detection in the minimum amount of
comparison times (the same as the number of areas arranged along
the X-axis). In addition, the image of each area is compared to the
images of the close areas, and thus, the defects can be detected
accurately.
[0013] To achieve the above-mentioned object, the present invention
is directed to a visual inspection method, comprising the steps of:
capturing images of at least three areas arranged in a line on an
object; dividing the areas into at least one group, each group
including at least consecutive three of the areas; designating one
of the areas as a subject area and other two of the areas as
comparison areas for the subject area, the comparison areas being
in the same group with the subject area and within a predetermined
distance from the subject area; and comparing the image of the
subject area with the images of the comparison areas to determine
whether the subject area is defective.
[0014] The visual inspection method is preferably characterized in
that: the designating step comprises the step of numbering the
areas in each group along the line; if the subject area is
odd-numbered and is not one of ends of odd-numbered areas in the
group, the comparison areas are two odd-numbered areas closest to
the subject area; if the subject area is one of the ends of the
odd-numbered areas in the group, the comparison areas are one
odd-numbered area and one even-numbered area closest to the subject
area; if the subject area is even-numbered and is not one of ends
of even-numbered areas in the group, the comparison areas are two
even-numbered areas closest to the subject area; and if the subject
area is one of the ends of even-numbered areas in the group, the
comparison areas are one even-numbered area and one odd-numbered
area closest to the subject area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The nature of this invention, as well as other objects and
advantages thereof, will be explained in the following with
reference to the accompanying drawings, in which like reference
characters designate the same or similar parts throughout the
figures and wherein:
[0016] FIG. 1 is a view showing the entire structure of an
embodiment of a visual inspection apparatus according to the
present invention;
[0017] FIG. 2 is a view showing an example of a scanning track of a
TDI sensor on a wafer;
[0018] FIG. 3 is a block diagram showing an embodiment of a defect
detecting part;
[0019] FIG. 4 is a view showing an example of the arrangement of
chips on the wafer;
[0020] FIG. 5 is a view showing the areas in each chip, which are
denoted by reference numerals;
[0021] FIG. 6 is a view showing a relationship in time between the
capture of images and the comparison of images; and
[0022] FIGS. 7(A) and 7(B) are views showing examples of
combinations of chips subject to comparison.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] This invention will be described in further detail by way of
example with reference to the accompanying drawings.
[0024] FIG. 1 is a view showing the entire structure of a preferred
embodiment of a visual inspection apparatus, which determines
whether each chip on a wafer contains a defective part or not. As
shown in FIG. 1, the visual inspection apparatus comprises: a
control part 12, which performs a variety of processing; an XY
stage 14, which moves along X and Y axes horizontally under the
control of the control part 12; a sample table 16 provided on the
XY stage 14; a microscope 18 arranged above the sample table 16;
and a TDI sensor 20 attached at the focusing position of the
microscope 18.
[0025] A wafer W as an object is placed on the sample table 16. An
image of the surface of the wafer W is enlarged and formed on an
imaging surface of the TDI sensor 20 by the microscope 18.
[0026] As is well known, the TDI sensor 20 is a multistage sensor
composed of one-dimensional line sensors such as charge-coupled
device (CCD) line sensors. Signal electric charges accumulated in
CCD elements of the line sensor at each stage are sequentially
transferred to CCD elements of the line sensor at the next stage in
synchronism with a scanning speed. Consequently, a plurality of CCD
elements overlaps the signal electric charges at one point subject
for imaging. Therefore, even if the electric charges are
accumulated in each CCD element only for a short period, the signal
electric charges at each point subject for imaging are amplified to
make up for the shortage in the quantity of light. Thus, the TDI
sensor 20 is able to scan the object at a higher speed than the
ordinary single-stage CCD line sensor.
[0027] In the visual inspection apparatus of the embodiment, the
TDI sensor 20 scans the surface of the wafer W along the X-axis.
The TDI sensor 20 scans the surface image of the wafer W, which is
moved by the XY stage 14 along the X-axis. In this embodiment, the
TDI sensor 20 is used as the imaging means, but it is possible to
use the ordinary one-dimensional sensor such as the CCD line sensor
or a two-dimensional sensor.
[0028] The control part 12 controls the XY stage 14 to move the
wafer W along the X and Y-axes. The control part 12 controls the
TDI sensor 20, which relatively scans the wafer W, and obtains the
surface image of the wafer W from the TDI sensor 20. FIG. 2 shows
an example of a scanning track of the TDI sensor 20 on the wafer W
under the control of the control part 12. As shown in FIG. 2, a
number of chips C are regularly arranged along the X and Y-axes on
the wafer W, and the chips have the same patterns. As indicated by
a dashed and dotted line in FIG. 2, the TDI sensor 20 starts
scanning the wafer W along the X-axis from the upper left corner of
a chip C.sub.s on the highest row, and reciprocally scans the wafer
W until it reaches a chip C.sub.e on the lowest row. The TDI sensor
20 shifts the scanning line along the Y-axis downward little by
little (by the image reading width (scanning width) in a direction
along the Y-axis perpendicular to the scanning direction along the
X-axis) to complete the scanning for all the chips C arranged on
the wafer W. The scanning is not necessarily performed on the
scanning track in FIG. 2, but the scanning may also be performed in
any other scanning tracks.
[0029] Then, the control part 12 sends the obtained surface image
of the wafer W to a defect detecting part, which is a component of
the control part 12. The defect detecting part detects a defective
part in each chip on the wafer W.
[0030] FIG. 3 is a block diagram showing an embodiment of the
defect detecting part in the control part 12. As shown in FIG. 3,
the defect detecting part comprises a signal processing part 50, an
image storage part 52, an image comparison part 54, a defect
storage part 55 and a CPU 56.
[0031] The signal processing part 50 receives image signals
sequentially from the TDI sensor 20, and converts the image signals
into digital image data. The signal processing part 50 outputs the
image data to the image storage part 52.
[0032] The image storage part 52 is composed of a memory such as a
RAM. The image data, which is outputted from the signal processing
part 50, is sequentially stored in the image storage part 52.
[0033] The image comparison part 54 reads the image data
sequentially from the image storage part 52, and compares the image
data of two chips to determine whether the two chips have a
possibility of being defective. The image comparison part 54 sends
the results to the defect storage part 55.
[0034] The CPU 56 reads the two results for each chip and finds
defective chips and their coordinates, and outputs the results to a
monitor, etc.
[0035] A description will now be given of the operation of the
defect detecting part. For example, five chips C1-C5 are arranged
in the first row and seven chips C1-C7 are arranged in the second
row of the wafer W as shown in FIG. 4. In this case, the TDI sensor
20 reciprocally scans the chips in a predetermined scanning width
as indicated by an arrow in FIG. 4, and the images of the chips are
sequentially captured into the image storage part 52 in accordance
with the scanning track. In FIG. 5, the chips in the first and
second rows in FIG. 4 are divided along the Y-axis at intervals of
the scanning width, and the divided areas are denoted by reference
numerals. "m" in the reference numeral "Sm-n" (m, n=1, 2, . . . )
indicates an order in which the TDI sensor 20 scans each area of
each chip, and "n" indicates a row number of each chip (a chip
number). "Sm" will be referred to as a scanning number. To
reciprocally scan the wafer W as shown in FIG. 4, the TDI sensor 20
sequentially scans the areas S1-1, S1-2, S1-3, S1-4 and S1-5 of the
chips C1-C5 arranged in the first row. After scanning the area
S1-5, the XY stage is shifted along the Y-axis by the scanning
width so that the TDI sensor 20 can continuously scan the areas
S2-5, S2-4, S2-3, S2-2 and S2-1. This scanning is continued to
capture the images of the wafer W as a whole into the image storage
part 52.
[0036] While the TDI sensor 20 is capturing the images of the
chips, the image comparison part 54 reads the images of the chips
from the image storage part 52 in a predetermined order and
compares the images of two areas. Referring to FIG. 6, while the
TDI sensor 20 is capturing the image of the area S1-1 in the chip
C1 on the first row, there is no image of another chip subject to
comparison, and hence, the image comparison part 54 does not
compare any images. When the TDI sensor 20 starts capturing the
image of the area S1-2 in the corresponding parts of the image of
the area S1-1, which is read from the image storage part 52. If a
difference between the parts of the images exceeds a predetermined
threshold, the parts are determined as having a possibility of
being defective, and the data relating to those images are
temporarily stored in the defect storage part 55. For example, each
of the images of the areas S1-1, S1-2, . . . , is divided into a
predetermined number of frames, and the frames are read from the
image storage part 52. The image comparison part 54 compares the
images on a frame-by-frame basis.
[0037] When the TDI sensor 20 starts capturing the image of the
area S1-3 of the chip C3, the image comparison part 54 compares the
image of the area S1-3 with the image of the area S1-1, which is
read from the image storage part 52. Since the image of the area
S1-1 has been compared with the two areas S1-2 and S1-3 of the two
different chips C2 and C3 (i.e., the double detection has been
performed), the already-compared parts of the image of the area
S1-1 are sequentially erased from the image storage part 52. If the
same position in the area S1-1 is detected as having a possibility
of being defective in both comparisons with the areas S1-2 and
S1-3, the CPU 56 determines the area S1-1 as being defective.
[0038] When the TDI sensor 20 starts capturing the image of the
area S1-4 of the chip C4, the image comparison part 54 compares the
image of the area S1-4 with the image of the area S1-2, which is
read from the image storage part 52. Since the image of the area
S1-2 has been compared with the two different chips in the double
detection, the already-compared parts of the image are sequentially
erased from the image storage part 52. Then, the CPU 56 determines
the presence of a defect in the area S1-2 as is the case with the
area S1-1.
[0039] Likewise, when the TDI sensor 20 starts capturing the image
of the area S1-5 of the chip C5, the image comparison part 54
compares the image of the area S1-5 with the image of the area
S1-3. When the capturing of the image of the area S1-5 is
completed, the TDI sensor 20 starts the next scanning S2. Since the
double detection has not been performed for the areas S1-4 and S1-5
in the previous scanning S1, the image comparison part 54 compares
the images of the areas S1-4 and S1-5 while the TDI sensor is
scanning the area S2-5 in the scanning S2. Consequently, the double
detection is performed for all the areas in the scanning S1. Since
the areas S1-4 and S1-5 are compared while the image of the area
S2-5 is captured in the scanning S2, at the corresponding time to
the time when the image of the area S1-1 is captured and no
comparison is performed, the scanning will not be delayed by the
last comparison in the scanning S1.
[0040] In the above-described manner, the defects are detected by
comparing the images sequentially in the scanning S1, S2, and S3.
When the scanning S3 is completed, the double detection has not
been performed for the areas S3-4 and S3-5. The double detection
for the areas S3-4 and S3-5 is completed while the TDI sensor 20
scans the area S1-7 in the scanning for the chips C1-C7 on the
second row.
[0041] More specifically, when each scanning is completed, the
double detection is always incomplete for the last two chips in
each scanning row. This, however, does not effect the inspection
time since the double detection is performed for the last two chips
in each scanning row while the TDI sensor 20 is capturing the first
image in the next scanning row. On completion of the scanning for
the entire wafer W, the double detection is incomplete for the last
two chips in the last scanning row. This does not effect the
inspection time since the double detection can be completed for the
last two chips in the last scanning row within a negligible time,
which is about the same as the time required for scanning one
chip.
[0042] In the above explanation, there are five chips in one
scanning row. If the number of the chips in one scanning row is any
other, the processing is performed in a manner described below. The
order in which the images are read from the image storage part 52
can be classified into the following three cases according to the
number of chips in one scanning row: case 1 wherein the number of
chips in one scanning row is 3n+3; case 2 wherein the number of
chips in one scanning row is 3n+4; and case 3 wherein the number of
chips in one scanning row is 3n+5 (n=0, 1, 2, 3, . . . ).
[0043] More specifically, the chips are made in groups of three
from the top of the scanning row, and the chips in each group are
referred to as the first chip, the second chip and the third chip.
In each group, the first chip and the second chip are compared
first, then the first chip and the third chip are compared, and at
last, the second chip and the third chip are compared. Thus, the
double detection is performed in each group. The comparison is
completed for 3n chips in the above equation even if n is any
natural number.
[0044] Considering the remaining chips for which the double
detection is incomplete, in the case 1, there are three chips
remaining, and these three chips can be read in the above-mentioned
manner.
[0045] The case 2 is, for example, the case where the seven chips
C1-C7 are arranged in the second row in FIG. 4. As for the
remaining four chips, the first chip and the second chip are
compared first, then the first chip and the third chip are
compared, and the second chip and the fourth chip are compared, and
at last, the third chip and the fourth chip are compared. In the
case of the arrangement on the second row in FIG. 4, the remaining
four chips are equivalent to the chips C4-C1 in the scanning S1 on
the second row in FIG. 6.
[0046] The case 3 is, for example, the case where the five chips
C1-C5 are arranged in the first row in FIG. 4. As for the remaining
five chips, the first chip and the second chip are compared first,
then the first chip and the third chip are compared, the second
chip and the fourth chip are compared, the third chip and the fifth
chip are compared, and at last, the fourth chip and the fifth chip
are compared.
[0047] Comparing the images of the chips in the same scanning row
in the above-mentioned manner detects the presence of defects for
all the chips in the minimum comparison times, which are equal to
the number of the chips.
[0048] In the above-mentioned comparison method, the images are
compared between two chips that are close to one another by a twice
as long as an interval between the adjacent chips or less, and
therefore, the defects can be accurately detected.
[0049] In the above-mentioned comparison method, the chips in the
same scanning row are compared with one another, and thus, this
method may be applied to detect the defects in the chips in only
one row.
[0050] In the above explanation, three chips make one group. If
three or more chips are in one group, each chip can be compared
twice. Thus, any number larger than two (three or more) of chips
may make one group.
[0051] A description will now be given of a preferred method for
combining each of any number of chips with other two chips. If 2N
(N=2, 3, 4, . . . ) chips from the first chip to the 2N-th chip are
sequentially arranged as shown in FIG. 7(A), the 2N chips are
divided into even-numbered chips and odd-numbered chips. As
indicated by a solid line in FIG. 7(B), each chip is connected to
the adjacent chips, and the chips are arranged like a closed loop.
The images of the adjacent chips are compared in this arrangement.
More specifically, each even-numbered chip is compared with two
closest even-numbered chips, and each odd-numbered chip is compared
with two closest odd-numbered chips. In this case, however, the
odd-numbered chips at both ends (the first chip and the (2N-1)-th
chip) and the even-numbered chips at both ends (the second chip and
the 2N-th chip) are compared with adjacent chips among them.
Consequently, each chip is compared with the close chips, which are
next to the chip or the next chip but one. When the capturing of
the image in one chip is completed, the image data subject to the
next comparison is captured into the image storage part 52. Thus,
the images can be compared with one another while the chips are
scanned continuously. As shown by dotted lines in FIG. 7(B), if
there are odd number (2N+1) of chips, the (2N-1)-th chip and the
(2N+1)-th chip are compared with one another, and the 2N-th chip
and the (2N+1)-th chip are compared with one another in stead of
comparing the (2N-1-th chip and the 2N-th chip.
[0052] In each group (the number of the chips is 3, 4 or 5) in the
above-described cases 1, 2 and 3, the combinations of the chips
subject to comparison are determined in the method shown in FIG.
7(B). Likewise, if the number of chips in one group is determined
arbitrarily, the combinations of the chips subject to comparison
can be determined in the method shown in FIG. 7(B). That makes it
possible to perform the double detection by properly combining
every chip with other two chips in the same scanning row without
grouping the chips in the same scanning row.
[0053] The combinations of the chips are not necessarily determined
in the method in FIG. 7(B). Two chips at a predetermined interval
may be combined in each group, and each chip may be combined with
other two chips. In other words, the closed loop of chips as shown
in FIG. 7(B) is not necessarily arranged in the above-mentioned
manner. If the distance between the first chip and the 2N-th chip
is allowable in view of the image comparison accuracy in the case
that the first to 2N-th chips are arranged as shown in FIG. 7(A), a
closed loop is formed by arranging the first chip next to the 2N-th
chip with the positional relationship between the first chip to the
2N-th chip being unchanged. The adjacent chips are combined in this
arrangement. This method can be used if each group has a small
number of chips.
[0054] In the above-described embodiment, the present invention is
applied to the visual inspection apparatus that detects the
presence of defects in the chips with the same pattern, which are
arranged on the wafer. The present invention, however, may also be
applied to a visual inspection apparatus, which inspects other
object such as a photo-mask and a liquid crystal display.
[0055] As set forth hereinabove, the visual inspection apparatus of
the present invention scans the object along the X-axis to
sequentially capture the images of the areas with the same pattern,
which are arranged along the X-axis. Then, the areas arranged along
the X-axis are divided into a predetermined number of groups. In
each group, two areas in a predetermined interval are respectively
combined with one another so that each area can be combined with
other two areas. The image of each area, which is captured by the
imaging means, is compared with the images of the other two areas.
It is therefore possible to compare the images of all the areas
including both ends (the peripheral chips) in the double detection
in the minimum amount of comparison times (the same as the number
of areas arranged along the X-axis). Moreover, the images can be
compared almost at the same time as the capture of the images. This
improves the inspection efficiency and speed in the visual
inspection. In addition, the image of each area is compared to the
images of the close areas, and thus, the defects can be detected
accurately.
[0056] It should be understood, however, that there is no intention
to limit the invention to the specific forms disclosed, but on the
contrary, the invention is to cover all modifications, alternate
constructions and equivalents falling within the spirit and scope
of the invention as expressed in the appended claims.
* * * * *