U.S. patent application number 12/852015 was filed with the patent office on 2010-12-23 for surface inspecting apparatus and surface inspecting method.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Kazuhiko FUKAZAWA.
Application Number | 20100321677 12/852015 |
Document ID | / |
Family ID | 40952215 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100321677 |
Kind Code |
A1 |
FUKAZAWA; Kazuhiko |
December 23, 2010 |
SURFACE INSPECTING APPARATUS AND SURFACE INSPECTING METHOD
Abstract
There is provided a surface inspecting apparatus capable of
performing inspection at higher speed and with higher accuracy. A
surface inspecting apparatus (1) is provided with an illumination
optical system (30) for irradiating linearly polarized light to a
surface of a wafer (10) under a plurality of inspection conditions;
an imaging optical system (40) for capturing an image of the wafer
(10) formed by polarization components having an oscillation
direction that is different from that of the linearly polarized
light as part of reflected light from the surface of the wafer (10)
irradiated by the linearly polarized light under the plurality of
inspection conditions; and an image-processing apparatus (50) for
extracting for individual pixels an image having the smallest
signal intensity from among images of the wafer (10) captured under
the plurality of inspection conditions by the imaging optical
system (40), and for inspecting for the presence of defects in a
repeated pattern of the wafer (10) on the basis of an inspection
image of the wafer (10) generated by connecting each of the
extracted pixels.
Inventors: |
FUKAZAWA; Kazuhiko;
(Kamakura-shi, JP) |
Correspondence
Address: |
MILES & STOCKBRIDGE PC
1751 PINNACLE DRIVE, SUITE 500
MCLEAN
VA
22102-3833
US
|
Assignee: |
NIKON CORPORATION
|
Family ID: |
40952215 |
Appl. No.: |
12/852015 |
Filed: |
August 6, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2009/051962 |
Feb 5, 2009 |
|
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12852015 |
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Current U.S.
Class: |
356/237.2 |
Current CPC
Class: |
H01L 2924/0002 20130101;
G01N 21/956 20130101; H01L 2924/0002 20130101; H01L 22/20 20130101;
G01N 2021/9513 20130101; H01L 2924/00 20130101; H01L 22/12
20130101 |
Class at
Publication: |
356/237.2 |
International
Class: |
G01N 21/00 20060101
G01N021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 6, 2008 |
JP |
2008-026759 |
Claims
1. A surface inspection apparatus comprising: an illumination unit
for irradiating linearly polarized light onto a surface of an
inspected substrate having a predetermined repeating pattern; an
imaging unit for capturing an image of the inspected substrate
formed by polarization components having an oscillation direction
that is different from that of the linearly polarized light as part
of the reflected light from the surface of the inspected substrate
irradiated by the linearly polarized light; a setting unit for
setting a plurality of conditions in at least one of an
illumination condition in the illumination unit and an imaging
condition in the imaging unit; and an information processing unit
for calculating a signal intensity for each portion of each of a
plurality of images of the inspected substrate photographed by the
imaging unit under the plurality of inspection conditions,
comparing the signal intensity of the same portions in the
plurality of images of the inspected substrate, and generating
inspection information of the inspected substrate from information
of the portions having the smallest signal intensity.
2. The surface inspection apparatus according to claim 1, wherein
the signal intensity is a signal intensity standardized according
to the signal intensity from a normal repeating pattern.
3. The surface inspection apparatus according to claim 1,
comprising a display unit for generating an inspection image on the
basis of the inspection information generated by the information
processing unit and visibly displaying the inspection image.
4. The surface inspection apparatus according to claim 1,
comprising an inspection unit for inspecting for the presence of a
defect in the repeating pattern; wherein the inspection unit is
configured so as to inspect for the presence of a defect in the
repeating pattern by comparing the inspection information and
predetermined reference information; the illumination unit
irradiates linearly polarized light onto a surface of a reference
substrate as a reference for the inspection under the plurality of
inspection conditions, and the imaging unit captures an image of
the reference substrate formed by polarization components having an
oscillation direction that is different from that of the linearly
polarized light as part of the reflected light from the surface of
the reference substrate irradiated by the linearly polarized light;
and the information processing unit calculates a signal intensity
for each portion of each of the plurality of images of the
reference substrate photographed by the imaging unit under the
plurality of inspection conditions, compares the signal intensity
of the same portions in the plurality of images of the reference
substrate, extracts a portion having the smallest signal intensity
for each of the portions, and generates the reference information
from information of the extracted portion.
5. The surface inspection apparatus according to claim 1, wherein
the inspection condition set by the setting unit is an angle formed
by the oscillation direction of the linearly polarized light and
the oscillation direction of the polarization components.
6. The surface inspection apparatus according to claim 1, wherein
the inspection condition set by the setting unit is an angle formed
by the repetition direction of the repeating pattern and the
oscillation direction of the linearly polarized light on the
surface of the inspected substrate.
7. The surface inspection apparatus according to claim 1, wherein
the inspection condition set by the setting unit is the wavelength
of the linearly polarized light.
8. A surface inspection method comprising: a first step of setting
an inspection condition; a second step of irradiating linearly
polarized light to a surface of an inspected substrate having a
predetermined repeating pattern; a third step of capturing an image
of the inspected substrate formed by polarization components having
an oscillation direction that is different from that of the
linearly polarized light as part of the reflected light from the
surface of the inspected substrate irradiated by the linearly
polarized light; and a fourth step of calculating a signal
intensity for each portion of each of a plurality of images of the
inspected substrate photographed under the plurality of inspection
conditions in the third step, comparing the signal intensity of the
same portions in the plurality of images of the inspected
substrate, and generating inspection information of the inspected
substrate from information of the portions having the smallest
signal intensity.
9. The surface inspection method according to claim 8, comprising a
fifth step of generating an inspection image on the basis of the
inspection information generated in the fourth step and visibly
displaying the inspection image.
10. The surface inspection method according to claim 8, comprising:
a sixth step of inspecting for the presence of a defect in the
repeating pattern on the basis of the inspection information
generated in the fourth step, the sixth step comprising inspecting
for the presence of a defect in the repeating pattern by comparing
the inspection information and predetermined reference information;
a seventh step of irradiating linearly polarized light onto a
surface of a reference substrate as a reference for the inspection
under the plurality of inspection conditions; an eighth step of
capturing an image of the reference substrate formed by
polarization components having an oscillation direction that is
different from that of the linearly polarized light as part of the
reflected light from the surface of the reference substrate
irradiated by the linearly polarized light under the plurality of
inspection conditions; and a ninth step of calculating a signal
intensity for each portion of each of the plurality of images of
the reference substrate photographed under the plurality of
inspection conditions in the eighth step, comparing the signal
intensity of the same portions in the plurality of images of the
reference substrate to extract the portions having the smallest
signal intensity for each of the portions, and generating the
reference information from information of the extracted
portions.
11. The surface inspection method according to claim 8, wherein the
inspection condition set in the first step is an angle formed by
the oscillation direction of the linearly polarized light and the
oscillation direction of the polarization components.
12. The surface inspection method according to claim 8, wherein the
inspection condition set in the first step is an angle formed by
the repetition direction of the repeating pattern and the
oscillation direction of the linearly polarized light on the
surface of the inspected substrate.
13. The surface inspection method according to claim 8, wherein the
inspection condition set in the first step is the wavelength of the
linearly polarized light.
Description
[0001] This is a continuation of PCT International Application No.
PCT/JP2009/051962, filed on Feb. 5, 2009, which is hereby
incorporated by reference. This application also claims the benefit
of Japanese Patent Application No. 2008-026759, filed in Japan on
Feb. 6, 2008, which is hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a surface inspecting
apparatus and surface inspecting method for inspecting the surface
of a semiconductor wafer, liquid crystal substrate, or the
like.
TECHNICAL BACKGROUND
[0003] In the process of manufacturing a semiconductor circuit
element or liquid crystal display element, repeated patterns
(wiring patterns and other line-and-space patterns) formed on the
surface of the semiconductor wafer or liquid crystal substrate
(hereinafter referred to generically as "the substrate") are
inspected for defects. In an automated surface inspecting
apparatus, the substrate is placed on a tiltable stage,
illuminating light (non-polarized light) for used in performing an
inspection is irradiated onto the surface of the substrate, an
image of the substrate is acquired based on diffracted light (e.g.,
1.sup.st-order diffracted light) generated from the repeated
pattern on the substrate, and the locations of defects in the
repeated pattern are identified based on the differences between
lightness and darkness (contrast) in the image (see, e.g., Patent
Document 1). In such a surface inspecting apparatus, adjusting the
tilt of the stage makes it possible to inspect for defects in a
repeated pattern having a different repetition pitch on the
substrate.
[0004] Techniques for inspecting a repeated pattern formed on the
surface of a substrate include inspection using diffracted light
such as described above (referred to hereinafter as diffraction
inspection), using direct reflection light, utilizing changes in
polarization state due to structural birefringence of the pattern
(hereinafter referred to as PER inspection), and other techniques.
These inspection methods enable resist application defects, line
width defects based on defocusing or dose shift of an exposure
apparatus, and other defects to be detected at high speed with high
accuracy.
[0005] As the line width of the repeated pattern decreases, the
wavelength of the illumination used for diffraction inspection must
be shortened, and in repeated patterns having a line width of 45 nm
or less, there is no illumination light source that is optimal for
diffraction inspection, and the inspection is performed by PER
inspection. In repeated patterns having a line width of 45 nm or
less, changes in the shape of the pattern on the order of 1 nm must
be detected, and high sensitivity is required to detect changes in
the shape of the pattern.
Patent Document 1: Japanese Laid-open Patent Publication No.
H10-232122
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0006] Although three types of parameters such as the illumination
wavelength, for example, are known as conditions that enhance the
sensitivity of detection in PER inspection, it is difficult to
derive the optimum inspection conditions by combining these three
types of parameters, and there is also no method of determining the
appropriateness of inspection conditions. Performing all
inspections under a plurality of inspection conditions with varying
parameters is also problematic because of the long time required,
and false positives occur in defect detection.
[0007] The present invention was developed in view of such
problems, and an object of the present invention is to provide a
surface inspection apparatus and surface inspection method capable
of inspection at high speed with high accuracy.
Means to Solve the Problems
[0008] The surface inspection apparatus of the present invention
for achieving the abovementioned objects comprises an illumination
unit for irradiating linearly polarized light onto a surface of an
inspected substrate having a predetermined repeating pattern; an
imaging unit for capturing an image of the inspected substrate
formed by polarization components having an oscillation direction
that is different from that of the linearly polarized light as part
of the reflected light from the surface of the inspected substrate
irradiated by the linearly polarized light; a setting unit for
setting a plurality of conditions in at least one of an
illumination condition in the illumination unit and an imaging
condition in the imaging unit; and an information processing unit
for calculating a signal intensity for each portion of each of a
plurality of images of the inspected substrate photographed by the
imaging unit under the plurality of inspection conditions,
comparing the signal intensity of the same portions in the
plurality of images of the inspected substrate, and generating
inspection information of the inspected substrate from information
of the portions having the smallest signal intensity.
[0009] In the surface inspection apparatus described above, the
signal intensity is preferably a signal intensity standardized
according to the signal intensity from a normal repeating
pattern.
[0010] The surface inspection apparatus described above preferably
comprises a display unit for generating an inspection image on the
basis of the inspection information generated by the information
processing unit and visibly displaying the inspection image.
[0011] The surface inspection apparatus described above preferably
comprises an inspection unit for inspecting for the presence of a
defect in the repeating pattern; wherein the inspection unit is
configured so as to inspect for the presence of a defect in the
repeating pattern by comparing the inspection information and
predetermined reference information; the illumination unit
irradiates linearly polarized light to a surface of a reference
substrate as a reference for the inspection under the plurality of
inspection conditions, and the imaging unit captures an image of
the reference substrate formed by polarization components having an
oscillation direction that is different from that of the linearly
polarized light as part of the reflected light from the surface of
the reference substrate irradiated by the linearly polarized light;
and the information processing unit calculates a signal intensity
for each portion of each of the plurality of images of the
reference substrate photographed by the imaging unit under the
plurality of inspection conditions, compares the signal intensity
of the same portions in the plurality of images of the reference
substrate, extracts a portion having the smallest signal intensity
for each of the portions, and generates the reference information
from information of the extracted portion.
[0012] In the surface inspection apparatus described above, the
inspection condition set by the setting unit is preferably an angle
formed by the oscillation direction of the linearly polarized light
and the oscillation direction of the polarization components.
[0013] In the surface inspection apparatus described above, the
inspection condition set by the setting unit is preferably an angle
formed by the repetition direction of the repeating pattern and the
oscillation direction of the linearly polarized light on the
surface of the inspected substrate.
[0014] In the surface inspection apparatus described above, the
inspection condition set by the setting unit is preferably the
wavelength of the linearly polarized light.
[0015] The surface inspection method of the present invention
comprises a first step of setting an inspection condition; a second
step of irradiating linearly polarized light onto a surface of an
inspected substrate having a predetermined repeating pattern; a
third step of capturing an image of the inspected substrate formed
by polarization components having an oscillation direction that is
different from that of the linearly polarized light as part of the
reflected light from the surface of the inspected substrate
irradiated by the linearly polarized light; and a fourth step of
calculating a signal intensity for each portion of each of a
plurality of images of the inspected substrate photographed under
the plurality of inspection conditions in the third step, comparing
the signal intensity of the same portions in the plurality of
images of the inspected substrate, and generating inspection
information of the inspected substrate from information of the
portions having the smallest signal intensity.
[0016] The surface inspection method described above preferably
comprises a fifth step of generating an inspection image on the
basis of the inspection information generated in the fourth step
and visibly displaying the inspection image.
[0017] The surface inspection method described above preferably
comprises a sixth step of inspecting for the presence of a defect
in the repeating pattern on the basis of the inspection information
generated in the fourth step, the sixth step comprising inspecting
for the presence of a defect in the repeating pattern by comparing
the inspection information and predetermined reference information;
a seventh step of irradiating linearly polarized light onto a
surface of a reference substrate as a reference for the inspection
under the plurality of inspection conditions; an eighth step of
capturing an image of the reference substrate formed by
polarization components having an oscillation direction that is
different from that of the linearly polarized light as part of the
reflected light from the surface of the reference substrate
irradiated by the linearly polarized light under the plurality of
inspection conditions; and a ninth step of calculating a signal
intensity for each portion of each of the plurality of images of
the reference substrate photographed under the plurality of
inspection conditions in the eighth step, comparing the signal
intensity of the same portions in the plurality of images of the
reference substrate to extract the portions having the smallest
signal intensity for each of the portions, and generating the
reference information from information of the extracted
portions.
[0018] In the surface inspection method described above, the
inspection condition set in the first step is preferably an angle
formed by the oscillation direction of the linearly polarized light
and the oscillation direction of the polarization components.
[0019] In the surface inspection method described above, the
inspection condition set in the first step is preferabl.sub.y an
angle formed by the repetition direction of the repeating pattern
and the oscillation direction of the linearly polarized light on
the surface of the inspected substrate.
[0020] In the surface inspection method described above, the
inspection condition set in the first step is preferably the
wavelength of the linearly polarized light.
ADVANTAGEOUS EFFECTS OF THE INVENTION
[0021] The present invention enables inspection at higher speed and
accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a view showing the overall structure of the
surface inspection apparatus according to the present
invention;
[0023] FIG. 2 is a view showing the appearance of the surface of
the semiconductor wafer;
[0024] FIG. 3 is a perspective view showing the irregular structure
of the repeating pattern;
[0025] FIG. 4 is a view showing the state of inclination between
the plane of incidence of the linearly polarized light and the
repetition direction of the repeating pattern;
[0026] FIG. 5 is a schematic view showing the illumination
apparatus;
[0027] FIG. 6 is a first flowchart showing the surface inspection
method according to the present invention;
[0028] FIG. 7 is a second flowchart showing the surface inspection
method according to the present invention; and
[0029] FIG. 8 is a view showing a modification of the surface
inspection apparatus.
EXPLANATION OF NUMERALS AND CHARACTERS
[0030] 1: surface inspection apparatus [0031] 10: wafer (inspected
substrate) [0032] 12: repeated pattern [0033] 30: illumination
optical system (illumination unit) [0034] 40: imaging optical
system (imaging unit) [0035] 50: image-processing apparatus (image
processing unit, display unit, and inspection unit) [0036] 55:
control apparatus (setting unit) [0037] L: linearly polarized
light
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Preferred embodiments of the present invention will be
described with reference to the drawings. As shown in FIG. 1, the
surface inspection apparatus 1 according to the present embodiment
is composed primarily of a stage 20 for supporting a semiconductor
wafer 10 (hereinafter abbreviated as wafer 10) as the substrate
under inspection, an illumination optical system 30, an imaging
optical system 40, an image-processing apparatus 50, and a control
apparatus 55. The surface inspection apparatus 1 is an apparatus
for automatically inspecting a surface of the wafer 10 in the
process of manufacturing a semiconductor circuit element. The wafer
10 is transported from a wafer set or development apparatus (not
shown in the drawing) by a conveyance system (not shown in the
drawing) after exposure/development of a resist film forming the
topmost layer, and the wafer 10 is retained on the stage 20 by
suction.
[0039] On the surface of the wafer 10, a plurality of chip regions
11 is arranged in the X and Y directions, and a predetermined
repeating pattern 12 is formed in each of the chip regions, as
shown in FIG. 2. As shown in FIG. 3, the repeating pattern 12 is,
e.g., a resist pattern (e.g., wiring pattern), in which a plurality
of line portions 2A is arranged at a constant pitch P in the
minor-axis direction (X direction) thereof. Space portions 2B occur
between adjacent line portions 2A. The arrangement direction (X
direction) of the line portions 2A is referred to as the
"repetition direction of the repeating pattern 12."
[0040] Here, the line width D.sub.A of the line portions 2A in the
repeating pattern 12 is set to a value 1/2 the pitch P.
Specifically, the repeating pattern 12 has an irregular shape in
which line portions 2A and space portions 2B are alternately
arranged in the X direction, and when exposed at the proper
exposure focus, the pattern edges are sharply formed. In the case
of such an ideal shape, the luminance (signal intensity) of the
polarization components detected by the imaging optical system 40
described hereinafter is maximized. However, when the exposure
focus is not at the proper value, pattern breakdown occurs, and the
luminance of the polarization components at this time is reduced
relative to the ideal case.
[0041] The surface inspection apparatus 1 of the present embodiment
performs defect inspection (PER inspection) of the repeating
pattern 12 by utilizing luminance variations (variations in signal
intensity) in the repeating pattern 12 such as described above,
i.e., variations in the polarization state due to structural
birefringence of the pattern. As described above, luminance
variations are caused by a discrepancy of the exposure focus from
the proper state, and occur in each shot region of the wafer
10.
[0042] In the present embodiment, the pitch P of the repeating
pattern 12 is set adequately small in relation to the wavelength of
the illuminating light (linearly polarized light described
hereinafter) directed to the repeating pattern 12. Diffracted light
from the repeating pattern 12 is therefore not created, and cannot
be used to inspect the repeating pattern 12 for defects.
[0043] The stage 20 of the surface inspection apparatus 1 supports
the wafer 10 on the top surface thereof, and fixes the wafer 10 in
place, e.g., by vacuum suction. The stage 20 is also capable of
rotating about a normal A1 as a rotational axis in the center of
the top surface of the stage. This rotation mechanism enables the
repetition direction (X direction in FIGS. 2 and 3) of the
repeating pattern 12 in the wafer 10 to be rotated on the surface
of the wafer 10.
[0044] In the present embodiment, in order to maximize the
reflectance of defect inspection for the repeating pattern 12, the
repetition direction of the repeating pattern 12 in the wafer 10 is
set to an angle of 45.degree. with respect to the oscillation
direction of the illuminating light (linearly polarized light L) on
the surface of the wafer 10. This angle is not limited to
45.degree., and may be set to 22.5.degree., 67.5.degree., or any
other angle direction.
[0045] As shown in FIG. 1, the illumination optical system 30 is
composed of an illumination apparatus 60 for emitting light at a
specific wavelength, a first polarizing plate 32, and a first lens
33. As shown in FIG. 5, the illumination apparatus 60 is composed
of three illuminators 61a, 61b, 61c for emitting light having
mutually different wavelengths, and a collecting optical system 63
for directing the light emitted from each of the illuminators 61a,
61b, 61c to the wafer 10. The first illuminator 61a is not shown in
detail in the drawings, but is composed of a xenon lamp, mercury
lamp, or other light source; an interference filter (band-pass
filter) for extracting a desired wavelength component (bright-line
spectrum) from the light from the light source, and other
components, and the first illuminator 61a is configured so as to
emit light having a wavelength of 546 nm (e-line).
[0046] The second illuminator 61b has the same structure as the
first illuminator 61a, but is configured so as to emit light having
a wavelength of 436 nm (g-line). The third illuminator 61c also has
the same structure as the first illuminator 61a, but is configured
so as to emit light having a wavelength of 405 nm (h-line). The
three illuminators 61a, 61b, 61c each actually emit light in
wavelength regions .+-.10 nm to .+-.30 nm from the aforementioned
wavelengths.
[0047] The collecting optical system 63 is composed of three
collective lenses 64a, 64b, 64c, three neutral density filters 65a,
65b, 65c, and three mirrors 66, 67, 68. The first collective lens
64a collects the light emitted from the first illuminator 61a and
directs the light to the first neutral density filter 65a. The
second and third collective lenses 64b, 64c collect the light
emitted from the second and third illuminators 61b, 61c,
respectively, and direct the light to the second and third neutral
density filters 65b, 65c, in the same manner as the first
collective lens 64a.
[0048] The first neutral density filter 65a is formed having a disk
shape in which the transmittance continuously varies in the
circumferential direction, and the light from the first collective
lens 64a is transmitted by the first neutral density filter 65a to
the first mirror 66. The first neutral density filter 65a is
configured so as to be rotatable in the circumferential direction
by a rotary drive apparatus not shown in the drawing, and the
quantity of light emitted from the first illuminator 61a is
adjusted in accordance with the rotation angle of the first neutral
density filter 65a. The second and third neutral density filters
65b, 65c also have the same structure as the first neutral density
filter 65a, and the light from the second and third collective
lenses 64b, 64c is transmitted by the second and third neutral
density filters 65b, 65c, respectively, to the second and third
mirror 67, 68. The quantity of light emitted from the second and
third illuminators 61b, 61c is also adjusted in accordance with the
rotation angle of the second and third neutral density filters 65b,
65c, respectively.
[0049] A first shutter 69a is provided between the first neutral
density filter 65a and the first mirror 66 so as to be insertable
into and removable from the optical path, and is configured so that
illumination by the first illuminator 61a can be switched on and
off. A second shutter 69b is provided between the second neutral
density filter 65b and the second mirror 67 so as to be insertable
into and removable from the optical path, and is configured so that
illumination by the second illuminator 61b can be switched on and
off. A third shutter 69c is provided between the third neutral
density filter 65c and the third mirror 68 so as to be insertable
into and removable from the optical path, and is configured so that
illumination by the third illuminator 61c can be switched on and
off.
[0050] The third mirror 68 is a normal reflective mirror. The light
from the third neutral density filter 65c is reflected toward the
second mirror 67 by the third mirror 68. The second mirror 67 is a
so-called dichroic mirror. The light from the second neutral
density filter 65b is reflected toward the first mirror 66 by the
second mirror 67, and the light from the third neutral density
filter 65c is transmitted by the second mirror 67 toward the first
mirror 66.
[0051] The first mirror 66 is also a so-called dichroic mirror. The
light from the first neutral density filter 65a is transmitted by
the first mirror 66 toward the surface of the wafer 10, and the
light from the second mirror 67 is reflected by the first mirror 66
toward the surface of the wafer 10. Through this configuration, by
opening any one of the first through third shutters 69a through
69c, any one of the beams from the first through third illuminators
61a through 61c (i.e., light having a wavelength of 546 nm
(e-line), 436 nm (g-line) or 405 nm (h-line)) can be selectively
emitted toward the wafer 10. By opening a plurality of shutters,
the light from (any of) the first through third illuminators 61a
through 61c can be synthesized and emitted to the wafer 10.
[0052] The first polarizing plate 32 is disposed on the optical
path between the illumination apparatus 60 and the first lens 33,
and converts the light emitted from the illumination apparatus 60
into linearly polarized light L (see FIG. 4) in accordance with the
orientation of the transmission axis thereof. The first lens 33
converts the illumination light from the first polarizing plate 32
to a parallel luminous flux which is irradiated to the wafer 10
that is the inspected substrate. Specifically, the illumination
optical system 30 is a telecentric optical system with respect to
the wafer 10 side. The optical axis O1 of the illumination optical
system 30 is at an angle .theta. with respect to the normal A1 to
the stage 20.
[0053] In the illumination optical system 30 described above, the
light from the illumination apparatus 60 is converted to
p-polarized linearly polarized light L via the first polarizing
plate 32 and the first lens 33, and is incident as illumination
light on the entire surface of the wafer 10. Since the propagation
direction (direction of the principal ray of the linearly polarized
light L reaching any point on the surface of the wafer 10) of the
linearly polarized light at this time is substantially parallel to
the optical axis O1, the incident angle of the linearly polarized
light L is the same at each point of the wafer 10, since the light
is a parallel luminous flux, and the incident angle corresponds to
the angle .theta. between the optical axis O1 and the normal
A1.
[0054] In the present embodiment, since the linearly polarized
light L incident on the wafer 10 is p-polarized light, in a case in
which the repetition direction of the repeating pattern 12 is set
to an angle of 45.degree. with respect to the incident plane
(propagation direction of the linearly polarized light L at the
surface of the wafer 10) of the linearly polarized light L as shown
in FIG. 4, for example, the angle formed by the repetition
direction of the repeating pattern 12 and the oscillation direction
of the linearly polarized light L at the surface of the wafer 10 is
also set to 45.degree.. In other words, the linearly polarized
light L is incident on the repeating pattern 12 so as to traverse
the repeating pattern 12 at an angle in a state in which the
oscillation direction of the linearly polarized light L at the
surface of the wafer 10 is at a 45.degree. angle to the repetition
direction of the repeating pattern 12.
[0055] As shown in FIG. 1, the imaging optical system 40 is
composed of a second lens 41, a second polarizing plate 42, and an
imaging apparatus 45, and is disposed so that the optical axis O2
thereof is at an angle .theta. with respect to the normal A1
through the center of the stage 20. Consequently, direct reflection
light directly reflected by the surface (repeating pattern 12) of
the wafer 10 propagates along the optical axis O2 of the imaging
optical system 40. The second lens 41 collects the direct
reflection light toward the imaging apparatus 45, the direct
reflection light having been directly reflected by the surface of
the wafer 10. The direct reflection light from the wafer 10 thereby
reaches the imaging surface of the imaging apparatus 45 via the
second lens 41 and the second polarizing plate 42, and an image of
the wafer 10 is formed.
[0056] The second polarizing plate 42 is disposed on the optical
path between a second lens 41 and the imaging apparatus 45, the
azimuth of the transmission axis thereof (the polarization
direction) can be rotated about the optical axis of the imaging
optical system 40 by using a rotary drive apparatus 43, and the
azimuth of the transmission axis of the second polarizing plate 42
is set so as to be tilted at an angle about 90.degree. from the
transmission axis of the first polarizing plate 32. Consequently,
(substantially right-angled) polarization components having an
oscillation direction that is different from that of the linearly
polarized light L as part of the direct reflection light from the
wafer 10 (repeating pattern 12) can be extracted by the second
polarizing plate 42 and directed to the imaging apparatus 45. As a
result, a reflection image of the wafer 10 formed by (substantially
right-angled) polarization components having an oscillation
direction that is different from that of the linearly polarized
light L as part of the direct reflection light from the wafer 10 is
formed on the imaging surface of the imaging apparatus 45.
[0057] The imaging apparatus 45 is composed of a CCD picture device
or the like, for example, which photoelectrically converts the
reflection image of the wafer 10 formed on the imaging surface and
outputs an image signal to the image-processing apparatus 50. The
brightness or darkness of the reflection image of the wafer 10 is
substantially proportional to the signal intensity (luminance) of
the polarization components detected by the imaging apparatus 45,
and varies in accordance with the shape of the repeating pattern
12. The reflection image of the wafer 10 is brightest in a case in
which the repeating pattern 12 is ideally shaped.
[0058] The image-processing apparatus 50 acquires the reflection
image of the wafer 10 on the basis of the image signal outputted
from the imaging apparatus 45. A reflection image of a good wafer
is stored in advance in the image-processing apparatus 50 for
comparison. A good wafer is one in which the repeating pattern 12
is ideally formed or considered to be of ideal shape on the entire
surface of the wafer. The luminance information (signal intensity)
of the reflection image of a good wafer is therefore considered to
exhibit the highest luminance value.
[0059] Consequently, when the image-processing apparatus 50
acquires the reflection image of the wafer 10 functioning as the
inspected substrate, the image-processing apparatus 50 compares the
luminance information (signal intensity) thereof with the luminance
information (signal intensity) of the reflection image of the good
wafer. A defect in the repeating pattern 12 is detected on the
basis of the amount by which the luminance value of a dark location
is reduced in the reflection image of the wafer 10. For example, a
determination of "defective" is made when the luminance variation
is greater than a predetermined threshold value (allowable value),
and a determination of "normal" is made when the luminance
variation is smaller than the threshold value. The result of
comparing the luminance information (signal intensity) by the
image-processing apparatus 50 and the reflection image of the wafer
10 at that time are visibly displayed by a monitor unit of the
image-processing apparatus 50. The control apparatus 55 controls
operations in general for the stage 20, the illumination apparatus
60, the rotary drive apparatus 43 of the second polarizing plate
42, the image-processing apparatus 50, and other components.
[0060] The image-processing apparatus 50 may be configured so as to
store a reflection image of a good wafer in advance, as described
above, or may be configured so as to store a luminance threshold
value and arrangement data for a shot region of the wafer 10. In
this case, the position of each shot region in the acquired
reflection image of the wafer 10 is known based on the arrangement
data of the shot regions, and the luminance value of each shot
region can therefore be calculated. Defects in the pattern are then
detected by comparing the luminance value with the stored threshold
value. A shot region in which the luminance value is smaller than
the threshold value triggers a determination of "defective."
[0061] A surface inspection method using the surface inspection
apparatus 1 configured as described above will be described with
reference to the flowcharts shown in FIGS. 6 and 7. The step of
generating a reference image of a good wafer (not shown) performed
at the time of recipe creation will first be described using the
flowchart shown in FIG. 6. First, in step S101, a good wafer is
conveyed onto the stage 20 and positioned with respect to the
repeating pattern on the good wafer. The control apparatus 55 at
this time controls driving of the stage 20 so that the azimuth
angle (angle formed by the oscillation direction of the linearly
polarized light L on the surface of the wafer and the repetition
direction of the repeating pattern) of the pattern with respect to
the oscillation direction of the linearly polarized light L matches
the predetermined azimuth angle (of the initial setting). The
control apparatus 55 also controls driving of the rotary drive
apparatus 43 at this time so that the bearing of the transmission
axis of the second polarizing plate 42 with respect to the
transmission axis of the first polarizing plate 32 is at the
predetermined angle of inclination (of the initial setting). Also
at this time, the control apparatus 55 controls the operation of
the first through third shutters 69a through 69c so that the
wavelength of the light emitted from the illumination apparatus 60
is a prescribed wavelength (of the initial setting).
[0062] When the inspection conditions have thus been set, the
linearly polarized light L is irradiated onto the surface of the
good wafer, and an image of the good wafer is captured in the next
step S102, the image being formed by polarization components having
an oscillation direction at substantially a right angle to the
linearly polarized light L as part of the direct reflection light
from the surface of the good wafer. At this time, the light emitted
from the illumination apparatus 60 is converted to p-polarized
linearly polarized light L by the first polarizing plate 32,
converted to a parallel luminous flux by the first lens 33, and
irradiated onto the surface of the good wafer. The direct
reflection light reflected by the surface of the good wafer is
collected by the second lens 41, and polarization components having
an oscillation direction at a substantially right angle to the
linearly polarized light L as part of the direct reflection light
are extracted by the second polarizing plate 42 and directed onto
the imaging surface of the imaging apparatus 45. The imaging
apparatus 45 then photoelectrically converts the reflection image
of the good wafer formed by the polarization components having an
oscillation direction at substantially a right angle to the
linearly polarized light L as part of the direct reflection light,
and outputs an image signal to the image-processing apparatus
50.
[0063] When the image signal is outputted to the image-processing
apparatus 50 from the imaging apparatus 45, in the next step S103,
the image-processing apparatus 50 acquires the reflection image of
the good wafer on the basis of the image signal outputted from the
imaging apparatus 45 and stores image data of the good wafer in an
internal memory (not shown) of the image-processing apparatus
50.
[0064] In the next step S104, a determination is made as to whether
the good wafer was photographed under all the necessary inspection
conditions. In a case in which the determination is "No," after
step S105 is performed, steps S102 and S103 are repeated under the
inspection conditions in which an image had not yet been captured.
In a case in which the determination is "Yes," the process proceeds
to step S106.
[0065] The inspection conditions determined in step S104 are the
three parameters of the azimuth angle of the pattern, the angle of
inclination of the second polarizing plate 42, and the illumination
wavelength. Specifically, an image of the good wafer is captured
for each set of inspection conditions made up of combinations of
the three parameters. Therefore, processing takes place in step
S105 whereby the control apparatus 55 changes the setting of at
least one of the three types of parameters in the inspection
conditions. At this time, any azimuth angle selected from, e.g.,
45.degree., 67.5.degree., and 22.5.degree. is set as the azimuth
angle of the pattern. This is because the condition (azimuth angle)
under which the detection sensitivity increases with respect to
defocusing varies according to the type of pattern (e.g., memory
circuit pattern or logic circuit pattern). Azimuth angles of
135.degree., 157.5.degree., and 112.5.degree. may be further
added.
[0066] The inclination angle of the second polarizing plate 42 is
set at a 0.5.degree. pitch in a range of 90.degree. (crossed Nicols
state).+-.4.degree.. This is because in defect inspection (PER
inspection) of the type performed in the present embodiment,
although the detection sensitivity with respect to defocusing has
been found to increase when the inclination angle of the second
polarizing plate 42 is slightly offset from 90.degree. (crossed
Nicols state), the condition for increasing the detection
sensitivity varies according to the semiconductor process. The
illumination wavelength is set to any of 546 nm (e-line), 436 nm
(g-line) and 405 nm (h-line). This is also for the reason that the
condition for increasing the detection sensitivity varies according
to the semiconductor process. However, since unevenness due to
interference with the base of the pattern can occur at some
illumination wavelengths, such illumination wavelength conditions
are excluded from the inspection conditions in advance. Since
unevenness due to interference with the base of the pattern also
sometimes occurs under some conditions irrespective of the
illumination wavelength, conditions that produce such anomalies are
also excluded.
[0067] The quantity of illumination light is also adjusted by the
first through third neutral density filters 65a through 65c in each
inspection condition so that the luminance value (signal intensity)
of the portion used as a reference in the image of the good wafer
captured in step S102 is constant. At this time, the control
apparatus 55 controls driving of the rotary drive apparatuses (not
shown) of the first through third neutral density filters 65a
through 65c so that the luminance value (signal intensity) of the
portion used as a reference in the image of the good wafer is
constant, or in other words, so that standardization is obtained
according to the luminance value (signal intensity) of the portion
(repeating pattern) used as a reference in the image of the good
wafer. The gain in the image-processing apparatus 50 may also be
adjusted instead of adjusting the quantity of light through the use
of the first through third neutral density filters 65a through
65c.
[0068] In step S106, the good wafer which has been photographed
under a plurality of inspection conditions is unloaded and
recovered from the stage 20, and in the next step S107, the
image-processing apparatus 50 compares pixels in the same pixel
position in the images of the good wafer photographed under a
plurality of conditions, extracts each of the pixels (of the
inspection conditions) having the smallest luminance value (signal
intensity), and sets the current luminance value (signal intensity)
as the luminance value (true value) for the corresponding pixel
position.
[0069] In the next step S108, the image-processing apparatus 50
generates a single reference image by connecting the pixels having
the smallest luminance values (signal intensities) on the basis of
the luminance value (signal intensity) of each pixel set in step
S107. A reference image of the time of wafer inspection is thereby
generated as an image of the good wafer, and the reference image of
the good wafer is stored in the internal memory of the
image-processing apparatus 50. In step S108, in a case in which the
process is changed, such as when the material of the resist film
changes in the same type of pattern, the same processing as in
steps S101 through S107 is performed for a good wafer
exposed/developed by the new process, and additional study can be
performed for replacing pixels whose luminance values (true values)
have become relatively brighter by comparison with the reference
image of the good wafer stored in the internal memory.
[0070] The flowchart shown in FIG. 7 will next be used to describe
the process for inspecting the wafer 10. First, in step S201, the
wafer 10 as the inspected substrate is conveyed onto the stage 20
and positioned with respect to the repeating pattern 12 on the
wafer 10. The control apparatus 55 at this time controls driving of
the stage 20 so that the azimuth angle of the pattern matches the
predetermined azimuth angle (of the initial setting), under the
same conditions as in the case of generating the reference image of
the good wafer. The control apparatus 55 also controls driving of
the rotary drive apparatus 43 so that the inclination angle of the
second polarizing plate 42 is at the predetermined inclination
angle (of the initial setting), and the control apparatus 55
controls the operation of the first through third shutters 69a
through 69c so that the illumination wavelength is the
predetermined wavelength (of the initial setting).
[0071] When the inspection conditions have thus been set, the
linearly polarized light L is irradiated onto the surface of the
wafer 10, and an image of the wafer 10 is captured in the next step
S202, the image being formed by polarization components having an
oscillation direction at substantially a right angle to the
linearly polarized light L as part of the direct reflection light
from the surface of the wafer 10. At this time, the light emitted
from the illumination apparatus 60 is converted to p-polarized
linearly polarized light L by the first polarizing plate 32,
converted to a parallel luminous flux by the first lens 33, and
irradiated onto the surface of the wafer 10. The direct reflection
light reflected by the surface of the wafer 10 is collected by the
second lens 41, and polarization components having an oscillation
direction at a substantially right angle to the linearly polarized
light L as part of the direct reflection light are extracted by the
second polarizing plate 42 and directed onto the imaging surface of
the imaging apparatus 45. The imaging apparatus 45 then
photoelectrically converts the reflection image of the wafer 10
formed by the polarization components having an oscillation
direction at substantially a right angle to the linearly polarized
light L as part of the direct reflection light, and outputs an
image signal to the image-processing apparatus 50.
[0072] When the image signal is outputted to the image-processing
apparatus 50 from the imaging apparatus 45, in the next step S203,
the image-processing apparatus 50 acquires the reflection image of
the wafer 10 on the basis of the image signal outputted from the
imaging apparatus 45 and stores image data of the wafer 10 in an
internal memory (not shown) of the image-processing apparatus
50.
[0073] In the next step S204, a determination is made as to whether
the wafer 10 was photographed under all the necessary inspection
conditions. In a case in which the determination is "No," after
step S205 is performed, steps S202 and S203 are repeated under the
inspection conditions in which an image had not yet been captured.
In a case in which the determination is "Yes," the process proceeds
to step S206.
[0074] The inspection conditions determined in step S204 are the
same as those under which the reference image of the good wafer was
generated. Specifically, as many images of the wafer 10 are
captured as the number of inspection conditions that are the same
as those of the case in which the reference image of the good wafer
was generated. Therefore, processing takes place in step S205
whereby the control apparatus 55 changes the setting of at least
one of the three types of parameters (azimuth angle of the pattern,
inclination angle of the second polarizing plate 42, and
illumination wavelength) in the inspection conditions. The quantity
of illumination light is also adjusted by the first through third
neutral density filters 65a through 65c under the same conditions
as when the reference image of the good wafer was generated.
[0075] In step S206, the wafer 10 which has been photographed under
a plurality of inspection conditions is unloaded and recovered from
the stage 20, and in the next step S207, the image-processing
apparatus 50 compares pixels in the same pixel position in the
images of the wafer 10 photographed under a plurality of
conditions, extracts each pixel (of the inspection conditions)
having the smallest luminance value (signal intensity), and sets
the current luminance value (signal intensity) as the luminance
value (true value) for the corresponding pixel position.
[0076] In the next step S208, the image-processing apparatus 50
generates a single inspection image by connecting the pixels having
the smallest luminance values (signal intensities) on the basis of
the luminance value (signal intensity) of each pixel set in step
S207. An inspection image of the wafer 10 is thereby generated, and
the inspection image of the wafer 10 is stored in the internal
memory of the image-processing apparatus 50.
[0077] In the next step S209, the image-processing apparatus 50
compares the luminance information (i.e., inspection information)
of the inspection image of the wafer 10 generated in step S208 with
the luminance information (i.e., reference information) of the
reference image of the good wafer generated previously in step
S108, and determines that a defect is present when the luminance
variation exceeds a pre-set threshold value. At this time, the
result of comparing the luminance information (signal intensity) by
the image-processing apparatus 50 and the reflection image
(inspection image) of the wafer 10 at that time are visibly
displayed by a monitor unit of the image-processing apparatus 50,
and visual inspection is also made possible.
[0078] As a result, through the surface inspection apparatus 1 and
surface inspection method of the present embodiment, since the
luminance information (signal intensity) of the image of the good
wafer is considered to exhibit the highest luminance value in
defect inspection (PER inspection) such as that of the present
embodiment, highly accurate inspection at high speed and high
detection sensitivity is made possible by performing inspection on
the basis of an inspection image of the wafer 10 generated by
extracting for each pixel of the image having the smallest
luminance value (signal intensity) among the images of the wafer 10
photographed under a plurality of inspection conditions and
connecting the pixels having the smallest luminance value (signal
intensity), rather than conducting inspections under all inspection
conditions. The luminance value in the reflection image of the
wafer 10 decreases as well in cases in which exposure was not
performed at the correct dose amount, but the optimum conditions
for detecting dose amount defects vary according to whether the
dose amount is excessive or inadequate. Thus, even for defects of
the same type, the optimum conditions for detecting defects vary
according to the severity of the defect. Through the present
embodiment, however, since the wafer 10 is inspected based on an
inspection image of the wafer 10 generated by connecting pixels
having the smallest luminance value (signal intensity) among the
images of the wafer 10 photographed under a plurality of inspection
conditions, defects of different types or defects of the same type
with different severity can all be easily recognized from a single
inspection image, and inspection can be performed with high
detection sensitivity and high accuracy. Inspecting a wafer on the
basis of a single inspection image in this manner also shortens the
image processing time for detecting defects for each shot, thus
enabling high-speed inspection.
[0079] By generating the reference image of the good wafer by the
same procedure as the inspection image of the wafer 10 is
generated, erroneous detection of defects can be prevented, and a
more highly accurate inspection can be obtained. Since the resist
film of the wafer 10 decreases in thickness from the center of the
wafer 10 outward, the dose amount sometimes varies according to the
thickness of the resist film. In such cases, the line width or the
like is sometimes increased in order to prevent the pattern from
collapsing at the outside of the wafer 10 where the resist film is
relatively thin, and the luminance value used as a reference in the
good wafer then varies for each shot. However, by generating the
reference image of the good wafer by the same procedure as the
inspection image of the wafer 10, since a reference image of the
good wafer is generated in which the luminance value varies for
each shot, erroneous detection of defects can be prevented, and a
more highly accurate inspection can be obtained.
[0080] In the embodiment described above, three types of parameters
including the azimuth angle of the pattern, the inclination angle
of the second polarizing plate 42, and the illumination wavelength
are varied in the inspection conditions in photographing the wafer,
but this configuration is not limiting; a configuration may be
adopted in which the setting of only one (or two) of the three
types of parameters is varied (specifically, inspection conditions
may be used in which the setting of any one (or two) of the
parameters including the azimuth angle of the pattern, the
inclination angle of the second polarizing plate 42, and the
illumination wavelength is varied).
[0081] In the embodiment described above, the second polarizing
plate 42 is configured so that the bearing of the transmission axis
can be rotated about the optical axis O2 of the imaging optical
system 40 by using the rotary drive apparatus 43, but this
configuration is not limiting. For example, a configuration may be
adopted in which a 1/2 .lamda. plate 47 is provided between the
second lens 41 and the second polarizing plate 42, and the bearing
of the slow axis of the 1/2 .lamda. plate 47 is rotated about the
optical axis O2 by using a rotary drive apparatus 48, as shown in
FIG. 8.
[0082] In the embodiment described above, 546 nm (e-line), 436 nm
(g-line), and 405 nm (h-line) are used as the illumination
wavelengths, but this configuration is not limiting; other
wavelengths may also be used, such as 365 nm (i-line) and 313 nm
(j-line).
[0083] In the embodiment described above, the image-processing
apparatus 50 generates the inspection image of the wafer 10 and
inspects for the presence of defects in the repeating pattern 12 on
the basis of the generated inspection image of the wafer 10, but
this configuration is not limiting; each of an image processing
unit for generating an inspection image of the wafer 10, and an
inspection unit for inspecting for the presence of defects in the
repeating pattern 12 may be separately provided.
* * * * *