U.S. patent application number 09/402052 was filed with the patent office on 2001-05-24 for surface inspecting device and surface inspecting method.
Invention is credited to HAGA, KAZUMI, ISHIGURO, YOSHIHIRO, SAKAI, MOTOSHI.
Application Number | 20010001573 09/402052 |
Document ID | / |
Family ID | 13649164 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001573 |
Kind Code |
A1 |
HAGA, KAZUMI ; et
al. |
May 24, 2001 |
SURFACE INSPECTING DEVICE AND SURFACE INSPECTING METHOD
Abstract
The present invention enables measurement of the configuration
of a pattern with irregularity in a wide surface region with a high
accuracy and in a single operation by using an apparatus having
relatively simple construction. The surface inspecting method for
inspecting a surface condition a measurement objective region to be
measured, which comprises a periodic irregular pattern with a
period, by irradiating the measurement objective region with an
illuminating light of an approximately parallel beam, comprising: a
first step of irradiating a measurement objective region with an
illuminating light in an oblique direction thereto; a second step
of forming an image of reflected light from the measurement
objective region by one system selected from the group consisting
of an object-side telecentric optical system and an
image-object-side telecentric optical system, which has an optical
axis coinciding with an incident direction of the illuminating
light to the measurement objective region, the formed image of
reflected light having points with luminance corresponding to the
incident angle of the illuminating light at respective points on
the measurement objective region; a third step of picking up the
formed image to collect luminance data of respective points in the
measurement objective region; a fourth step of analyzing spatial
frequencies of the luminance data with respect to positions in a
desired direction to make a plurality
Inventors: |
HAGA, KAZUMI; (TOKYO,
JP) ; SAKAI, MOTOSHI; (TOKYO, JP) ; ISHIGURO,
YOSHIHIRO; (TOKYO, JP) |
Correspondence
Address: |
EVENSON MCKEOWN EDWARDS & LENAHAN
1200 G STREET NW
SUITE 700
WASHINGTON
DC
20005
|
Family ID: |
13649164 |
Appl. No.: |
09/402052 |
Filed: |
January 18, 2000 |
PCT Filed: |
March 19, 1998 |
PCT NO: |
PCT/JP98/01170 |
Current U.S.
Class: |
356/237.2 |
Current CPC
Class: |
G01B 11/306
20130101 |
Class at
Publication: |
356/237.2 |
International
Class: |
G01N 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 1997 |
JP |
9/077985 |
Claims
1. A surface inspecting method for inspecting a surface condition a
measurement objective region to be measured, which comprises a
periodic irregular pattern with a period, by irradiating the
measurement objective region with an illuminating light of an
approximately parallel beam, comprising: a first step of
irradiating a measurement objective region with an illuminating
light in an oblique direction thereto; a second step of forming an
image of reflected light from the measurement objective region by
one system selected from the group consisting of an object-side
telecentric optical system and an image-object-side telecentric
optical system, which has an optical axis coinciding with an
incident direction of the illuminating light to the measurement
objective region, the formed image of reflected light having points
with luminance corresponding to the incident angle of the
illuminating light at respective points on the measurement
objective region; a third step of picking up the formed image to
collect luminance data of respective points in the measurement
objective region; a fourth step of analyzing spatial frequencies of
the luminance data in a desired direction to make a plurality of
spatial frequency data; and a fifth step of extracting a desired
frequency component from the plurality of spatial frequency data,
to synthesize.
2. A surface inspecting apparatus for inspecting a surface
condition which comprises a periodic irregular pattern with a
predetermined period of a measurement objective region to be
measured by irradiating the measurement objective region with an
illuminating light of a parallel beam, comprising: a light
irradiation part for irradiating an measurement objective region
with an illuminating light in an oblique direction of the
measurement objective region; a system selected from the group
consisting of an object-side telecentric optical system and an
image-object-side telecentric optical system, for forming an image
of reflected light from the measurement objective region, which has
an optical axis coinciding with an incident direction of the
illuminating light to the measurement objective region, the formed
image of reflected light having points with luminance corresponding
to the incident angle of the illuminating light at respective
points on the measurement objective region; an image pickup part
for picking up the formed image to collect luminance data of
respective points in the measurement objective region; a first data
changing part for analyzing spatial frequencies of the luminance
data in a desired direction to make a plurality of spatial
frequency data; and a second data changing part for extracting a
desired frequency component from the plurality of spatial frequency
data, to synthesize.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a surface inspecting method and an
apparatus for carrying out the inspecting method, for measuring the
shape or the state of surfaces of measurement objective regions,
more particularly, to a surface inspecting method and a surface
inspecting apparatus, suitable for inspection of surface
characteristics of specific measurement objective regions, which
comprises a periodic irregular pattern formed thereon.
BACKGROUND OF THE INVENTION
[0002] Measurement of the shape or the state of a surface of an
object is carried out for an instrumentation of the object's
characters, a decision whether the quality of the object is good or
not as a product, and the like. In particular, measurement of the
shape or the state of the surface of the object is often used for
measuring the irregularity of a surface of an object having an
approximate plate-like shape.
[0003] FIG. 9 shows a typical example of a measuring apparatus for
measuring the irregularity of the surface of the object having an
approximate plate-like shape. As shown in FIG. 9, the measuring
apparatus is provided with (a) a light source 910 for generating
substantially parallel light beams, (b) a half mirror 920 for
accepting the light beams output from the light source 910 and for
outputting these light beams toward a specific measurement
objective region on the object 990 to be measured, (c) an optical
image formation system 930 for receiving the reflected light from
the measurement objective region of the object 990 to be measured
and for forming an optical image thereof, (d) an image pickup part
940 having a light receiving surface 941 at the image formation
surface of the optical image formation system 930, and (e) an image
information processor 950 for collecting the luminance data output
from the image pickup part 940 and for image processing the
collected data.
[0004] By using the above-described measuring apparatus,
measurement of the shape or the like of the measurement objective
region is carried out as follows. A substantially parallel light
beam outputs from the light source 910 are irradiated through the
half mirror 920 onto measurement objective regions of the object
990 to be measured. Light beams reflected from the measurement
objective region forms an image through the image formation system
930, and the formed image is picked up by the image pickup part
940. The picked up image results are output from the image pickup
part 940 and are collected by the image information processor 950.
The processor 950 reconstructs the image of the measurement
objective region by processing the collected luminance data. By
inspection of the obtained image of the measured objective region,
the presence or absence of irregularity or the position of the
irregularity is measured through fading or blurry portions in the
image.
[0005] Conventionally, since an object shape measurement has been
carried out as described above, an approximate shape of the
irregular portion could be recognized. However, when the
irregularity is formed as a periodic pattern, for example, a
circuit pattern is formed on a surface of a wafer, a precise
measurement for the shape of the irregular pattern could not be
performed.
[0006] Accordingly, in order to precisely measure the shape of the
irregular pattern, use of a large scale, complicated and expensive
apparatus such as a scanning confocal electron microscope has been
required.
[0007] The present invention was developed in view of the
above-described problems. An object of the present invention is to
provide an improved surface inspecting method which enables
measurement of the configuration of a pattern with irregularity in
a wide surface region with a high accuracy and in a single
operation by using an apparatus having relatively simple
construction. Another object of the present invention is to provide
an improved surface inspecting apparatus having a simple
construction for suitably carrying out the surface inspecting
method according to the invention.
SUMMARY OF THE INVENTION
[0008] The improved surface inspecting method of the invention
according to the claim 1 is one for inspecting a surface condition
a measurement objective region to be measured, which comprises a
periodic irregular pattern with a period, by irradiating the
measurement objective region with an illuminating light of an
approximately parallel beam, comprising: a first step of
irradiating a measurement objective region with an illuminating
light in an oblique direction thereto; a second step of forming an
image of reflected light from the measurement objective region by
one system selected from the group consisting of an object-side
telecentric optical system and an image-object-side telecentric
optical system, which has an optical axis coinciding with an
incident direction of the illuminating light to the measurement
objective region, the formed image of reflected light having points
with luminance corresponding to the incident angle of the
illuminating light at respective points on the measurement
objective region; a third step of picking up the formed image to
collect luminance data of respective points in the measurement
objective region; a fourth step of analyzing spatial frequencies of
the luminance data with respect to positions in a desired direction
to make a plurality of spatial frequency data; and a fifth step of
extracting a desired frequency component from the plurality of
spatial frequency data, to synthesize. In this specification, the
term "parallel beam" or "parallel light flux" includes not only a
perfect parallel beam or light flux but an approximately parallel
beam or light flux which is formed by a pseudo-point light
source.
[0009] The improved surface inspecting apparatus of the invention
according to the claim 2 is one for inspecting a surface condition
which comprises a periodic irregular pattern with a predetermined
period of a measurement objective region to be measured by
irradiating the measurement objective region with an illuminating
light of a parallel beam, comprising: a light irradiation part for
irradiating an measurement objective region with an illuminating
light in an oblique direction of the measurement objective region;
a system selected from the group consisting of an object-side
telecentric optical system and an image-object-side telecentric
optical system, for forming an image of reflected light from the
measurement objective region, which has an optical axis coinciding
with an incident direction of the illuminating light to the
measurement objective region, the formed image of reflected light
having points with luminance corresponding to the incident angle of
the illuminating light at respective points on the measurement
objective region; an image pickup part for picking up the formed
image to collect luminance data of respective points in the
measurement objective region; a first data changing part for
analyzing spatial frequencies of the luminance data with respect to
positions in a desired direction to make a plurality of spatial
frequency data; and a second data changing part for extracting a
desired frequency component from the plurality of spatial frequency
data, to synthesize.
[0010] According to the present invention, the spatial frequency of
periodic luminance data with respect to positions are analyzed in a
predetermined direction to determine a plurality of spatial
frequency data, and then a desired frequency component is extracted
from the spatial frequency data, to synthesize, so that it is
possible to detect a desired irregular state.
[0011] For example, it is possible to detect just an irregular
state of a particular pattern of an integrated circuit formed on a
semiconductor wafer with an eliminated irregular state of a base
itself, or just the irregular state of the base itself with an
eliminated irregular state of the particular pattern of the
integrated circuit. It is extremely useful for the latter steps of
the semiconductor device production (i.e., steps for producing the
integrated circuit). The reason for this is that it is possible to
inspect a warp of the semiconductor wafer by an influence of heat,
a warp of the semiconductor wafer by formation of a passivation
film or the like, a formation condition of a particular pattern of
wiring, in each step.
[0012] In the present invention, before analyzing spatial
frequencies of the luminance data with respect to positions, for
example, it is possible to determine an inclination distribution in
the measurement objective region by primary differentiating a
distribution of a luminance data, to determine an integral data of
the luminance data, and to determine a regression curve from the
integral data. Further, it is possible to frequency-analyze the
integral data, or to frequency-analyze the irregular data in the
measurement objective region, which are determined on the basis of
the difference between the regression curve and the integral
data.
[0013] The light from the light source can be irradiated to the
measurement objective region through a band pass filter, or the
reflected light from the measurement objective region can be picked
up to form an image, through a band pass filter. Accordingly, it is
possible to remove the adverse effect caused by the diffracted
light from the measurement objective region. In particular, this is
effective when there are a large number of fine irregularities
having a small pitch in the measurement objective region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a view showing the construction of a surface
inspecting apparatus according to the first embodiment of the
present invention.
[0015] FIG. 2 are explanation views of image forming operation of
the surface inspecting apparatus according to the present
invention.
[0016] FIG. 3 are explanation views of image forming operation of
the surface inspecting apparatus according to the present
invention.
[0017] FIG. 4 are explanation views of image forming operation of
the surface inspecting apparatus according to the present
invention.
[0018] FIG. 5 is an explanation view of image forming operation of
the surface inspecting apparatus according to the present
invention.
[0019] FIG. 6 are explanation views of image forming operation of
the surface inspecting apparatus according to the present
invention.
[0020] FIG. 7 is a view showing the construction of a surface
inspecting apparatus according to the second embodiment of the
present invention.
[0021] FIG. 8 is a view showing the construction of a surface
inspecting apparatus according to the third embodiment of the
present invention.
[0022] FIG. 9 is a view showing the construction of a conventional
surface inspecting apparatus.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
[0023] Hereinafter, the surface inspecting method and the surface
inspecting apparatus according to embodiments of the present
invention will be explained with reference to the attached figures.
In the figures explaining a plurality of embodiments, the same
structural members, elements or the like are designated with the
same reference numerals, and
[0024] FIG. 1 shows a construction of a surface inspection
apparatus according to the first embodiment of the present
invention. As shown in this figure, this apparatus is provided
with: a light irradiation section 110 for irradiating an
measurement objective region with an illuminating light of a
parallel light beam; an angle setting member 200 which enables
inclination of the measurement objective region so as to irradiate
the measurement objective region with an illuminating light from an
oblique direction with respect to the surface of the measurement
objective region; an object-side telecentric optical system 300
having an optical axis coinciding with the incident direction of
the illuminating light onto the measurement objective region and
having a predetermined object-side angular aperture with respect to
a point on the measurement objective region so as to form an image
of reflected light issued from the measurement objective region; an
image pickup part 400 for picking up the formed image to collect
luminance data of respective pixels (respective points on
measurement objective region); a data transform part (first and
second data transform parts) 520 for frequency-analyzing the
luminance data in a predetermined direction by Fourier transform to
determine a plurality of frequency data, or for extracting the
predetermined frequency component from the plurality of frequency
data and carrying out the inverse Fourier transform; and a
processing part 510 for determining an integral data of the
luminance or the like and for determining the surface the inverse
Fourier transform; and a processing part 510 for determining an
integral data of the luminance or the like and for determining the
surface characteristics of the measurement objective region.
[0025] In this construction, the light irradiating section 110
comprises a light source 111, an aperture 112, a half mirror 113
and a collimating lens 114. The collimating lens 114 constitutes
also a part of the image formation system. Further the object-side
telecentric optical system 300 is provided with (1) an image
formation lens system 320 including the collimating lens 114, (2) a
light limiting member 310 such as an aperture stop, an aperture or
the like, located at the position of a stop of the object-side
telecentric optical system 300, and (3) an angular aperture
changing member 330 for changing the aperture diameter of the light
limiting member 310 to change the object-side angular aperture of
the object-side telecentric optical system 300.
[0026] According to the first embodiment, the surface inspecting
apparatus uses the fact that the reflected light of the irradiated
illuminating light, issued from the measurement objective region
forms an image with a luminance which depends on the incident angle
(average of the incident angle) of the illuminating light at
respective points in the measurement objective region.
[0027] The reason why the luminance at each point of the image
corresponds to the incident angle at the each corresponding point
in the measurement objective region is as follows.
[0028] Generally, in order to generate a parallel light beam
through the collimating lens 114, a point light source is produced
by using a light source 111 and an aperture or an aperture stop
112. However, since the aperture or the aperture stop 112 has a
certain degree of size, a perfect point source cannot be obtained.
Accordingly, since the light beams collimated through the
collimating lens 114 are not perfect parallel light beams, light
beams having various angle components corresponding to the angular
aperture of the aperture or the aperture stop 112 illuminate
respective points of the measurement objective region. In other
words, the illuminating light is irradiated on the measurement
objective region with a certain illumination angular aperture. As a
result, even when the measurement objective region has an even
surface, reflecting lights which are diverged with a certain angle
scope is generated at the each point under the Reflection Law.
Assuming now a case where the object-side angular aperture .theta.
is set such that the whole reflecting light beams from a surface
parallel to a plane (a reference plane) perpendicular to the
incident direction (an average incident direction) of the
illuminating light enter just into the aperture stop 310 (that is,
in the case of the irradiating angular aperture being equal to the
object-side angular aperture .theta.), the incident illuminating
light with a certain irradiating angular aperture shown in FIG.
2(a) is reflected on the measurement object region, while the
reflected light is diffused in the full scope of .theta., as shown
in the FIG. 2(b). In this case, the whole reflecting light are
taken into the aperture of the aperture stop 310 to reach the image
pick up part 400, so that a bright image with a luminance of 100%
is obtained on the surface of this part 400.
[0029] On the other hand, in the case of a surface inclined to the
reference plane, the incident illuminating lights shown in FIG. 3
or FIG. 4 are reflected on the surface of the measurement objective
region, and the whole or a part of the reflected light are not
taken into the aperture of the aperture stop 310 (shown in FIG. 3
or FIG. 4), so that the obtained image becomes a dark one with a
luminance of 0% or one with a luminance corresponding to the
quantity of light passing through the aperture of the aperture stop
310. Next, it is assumed that a conical concave is found in the
measurement objective region (substantially flat surface) of the
object 900 to be measured, and that there is a relationship of
d=(L/2) tan (.theta.'/2) among the inclination angle .theta.'/2 of
the sloping surface of the concave, the diameter L thereof, and the
depth d thereof.
[0030] In cases where the object-side angular angle .theta. is set
so that the whole reflected light beams from a plane parallel to
the reference plane enter just the aperture of the aperture stop
310, and the illuminating light is irradiated in the normal
direction with respect to measurement objective region, as shown in
FIG. 5, when the inclination angle of the slope (.theta.'/2) of the
concave is larger than (.theta./2), the reflecting lights from the
slope do not pass at all through the aperture of the aperture stop
310, so that the obtained image of the concave has a luminance of
0%, while the other portions (even portion) have a luminance of
100%.
[0031] When the measurement objective region is inclined at an
angle of .theta." (=.theta./4) from the state shown in FIG. 5, the
inclination of one side slope (surface A) of the concave with
respect to the reference plane is now ((.theta.'/2)-(.theta./4)),
and the inclination of the other side slope (surface B) with
respect to the reference plane is ((.theta.'/2)+(.theta./4)). In
this case, when the inclination of the slope (.theta.'/2) is equal
to (.theta./4), because the one side slope (surface A) becomes
parallel to the reference plane, the whole reflected light from the
slope does enter the aperture of the aperture stop 310. As a
result, the image of the portion has a luminance of 100%. On the
contrary, because the other side slope (surface B) has an
inclination of (.theta./2) with respect to the reference plane, the
whole reflected light from the slope does not enter at all the
aperture of the aperture stop 310. As a result, the image of the
slope (surface B) has a luminance of 0%. In this case, because the
even portion has an inclination of (.theta./4) with respect to the
reference plane, only a half of the reflected light from the even
portion enter the aperture of the aperture stop 310, the image of
the portion has a luminance of about 50%, as shown in FIGS. 6(a)
and 6(b).
[0032] On the other hand, in cases where the object-side angular
aperture .theta. is set to be twice the spread (divergence) angle
of the reflected lights from the even portion in the measurement
objective region (in cases where twice the illumination angle is
equal to the object-side angular aperture .theta.), when the
measurement objective region is inclined at an angle of .theta."
(=.theta./4) from the state shown in FIG. 5, the image of the even
portion has a luminance of about 50%, the image of one slope
(surface C) in the concave having a inclination angle (.theta.'/2)
which is (.theta./4) has a luminance of about 100%, and the image
of the other slope (surface D) has a luminance of about 0%.
[0033] In the surface inspecting apparatus according to the
above-described embodiments, although images are formed with a
luminance corresponding to the incident angle for the measurement
objective region, it is clearly possible to freely adjust the
sensitivity for inspecting the concave by changing the diffusion
(divergence) angle of the reflected lights from the even portion in
the measurement objective region, that is, the irradiation angular
aperture, or by changing the object-side angular aperture .theta..
Therefore, in this embodiment, an angular aperture changing member
330 for changing the angular aperture of the aperture stop 310 is
provided to freely change the object-side angular aperture .theta..
If an aperture diameter changing member 125 for changing the
aperture diameter of the aperture stop 112 is also provided to move
with each other, it is possible to very easily adjust the
sensitivity.
[0034] In the surface inspecting apparatus according to the
embodiments, although the image pickup part 400 picks up images
which was formed by the object-side telecentric optical system 300,
while the processing part 510 collects the luminance data for every
pixel (for each point in the measurement objective region), the
luminance data with respect to positions thereof are collected for
example with 256 gradations.
[0035] In the case, it is desirable to collect both luminance data
obtained in the case of an inclination of the measurement objective
region in one direction (X direction) and luminance data obtained
in the case of an inclination of the measurement objective region
in the other direction (Y direction) crossing with the X
direction.
[0036] In general, when a measurement objective region is inclined
with respect to the reference plane, luminances of respective
points are changed corresponding to the inclination thereof with
respect to the reference plane. The surface inspecting apparatus
according to this embodiment enables determination of the presence
or absence and the shape of the irregular portions by using the
variation of luminances. In this case, however, it may occur some
cases wherein the irregular portions (such as undulation or slip)
having a crest and a valley extending along a single axis can not
be exactly inspected only by inclining the measurement objective
region with respect to the single axis.
[0037] In order to solve the problem, the measurement objective
region is preferably inclined with respect to X and Y axes crossing
with each other in the reference plane (preferably, with the same
inclination angle), and the luminance data are collected in the
respective inclined position.
[0038] The processing part 510 determines a distribution of
inclination in the measurement objective region by
primary-differentiating a distribution of the luminance data,
determines an integral data of the luminance data, or determines a
regression curve from the integral data. Further, the processing
part 510 indicates a predetermined direction and informs each kind
of data, to a data transform part (Fourier transform part) 520.
[0039] According to the Fourier transform part 520, it is possible
to suitably adopt a fast Fourier transform apparatus (FFT).
Further, it is also possible to adopt an apparatus which enables
spatial-frequency-analy- sis of the luminance data other than an
FFT. For example, it is possible to use a discrete cosine transform
apparatus (DCT), or the like. Further, it is also possible to use
an apparatus for frequency dividing by the maximal entropy
method.
[0040] In general, the luminance data has a high-spatial frequency
component with respect to length according to a periodic irregular
pattern formed in the measurement objective region and a low
spatial-frequency component with respect to length according to
flexure, distortion and the like, as a whole the measurement
objective region, in a mixed state. For example, in a semiconductor
wafer having circuits formed to arrange periodically thereon, the
high spatial-frequency component is caused by a component according
to the periodic formed circuit pattern and the low frequency
component is caused by a component according to a flexure and a
distortion arisen by heat treatment or the like on the
semiconductor wafer.
[0041] The data transform part 520 performs a Fourier
transformation of the luminance data in a predetermined direction
indicated by the processing part 510, to produce Fourier
transformed images. The Fourier transformed images are sent back to
the processing part 510. As the predetermined direction, one or
more directions are selected, according to the state of the
periodicity of the irregular pattern formed in the measurement
objective region. That is, if the periodicity of the irregular
pattern is one-dimensional, it is suitable to select a direction
corresponding to the periodicity. If the periodicity of the
irregular pattern is two-dimensional, it is suitable to select one
direction corresponding to a periodicity and a second direction
perpendicular to the one direction. In the case when directions not
less than two are selected, a Fourier transformation is preferably
carried out to the data in each of the directions. Then, low
spatial-frequency components are removed from the fundamental
frequency data analyzed by the Fourier transformation to extract a
high spatial-frequency component; or high spatial-frequency
components are removed from the fundamental frequency data analyzed
by the Fourier transformation to extract a low spatial-frequency
component. In the other hand, the processing part 510 indicates a
predetermined direction to the data transform part 520; and the
data transform part 520 transforms the data of the high
spatial-frequency component in the predetermined direction
indicated by the processing part 510, by inverse Fourier
transformation and sends the inverse-Fourier transformed data to
the processing part 510.
[0042] The data sent from the data transform part 520 to the
processing part 510 may form an image having just an irregular
pattern only formed periodically by removing low spatial-frequency
components from the image picked up by an image pickup part 400 or
form an image having just an irregular pattern only formed
periodically by removing high spatial-frequency components from the
image picked up by the image pickup part 400. For example, in an
inspection of the surface of a wafer which has a circuit pattern
formed thereon, the data may form an image having the irregularity
of the circuit pattern formed periodically on the wafer by removing
the irregular components having a large period, e.g., a period near
the whole length of the wafer; or the data may form an image having
the irregularity having a large period, e.g., a period near the
whole length of the wafer by removing the irregular components of
the circuit pattern formed periodically on the wafer.
[0043] Thus, it is possible to suitably inspect an irregular
pattern having a desired period which is formed in the measurement
objective region.
[0044] (Second Embodiment)
[0045] FIG. 7 shows a construction of a surface inspecting
apparatus according to the second embodiment of the present
invention. As shown in the figure, the apparatus according to the
second embodiment is different from the first embodiment in that a
light irradiation section 110B further comprises a band pass filter
115 which can selectively passes through a light having a
wavelength in a predetermined range.
[0046] In the surface inspection of the present invention, when a
surface having a periodic irregular pattern thereon is irradiated
with an illuminating light, the periodic irregular pattern may
function as a diffraction grating. Accordingly, if the illuminating
light has wavelengths in a wide range, not only a 0-order
diffracted light by a reflection but also a n-order (n.noteq.0)
diffracted light may be created.
[0047] A wavelength .lambda.n of the diffracted light can be
represented by the following equation: 1 n = ( d sin ( n ) ) / n (
1 )
[0048] where .theta.n is the outgoing angle and d is the period of
the irregular pattern. The wavelength .lambda.n is dependent on
also the quality of the film on the semiconductor wafer.
[0049] The diffracted lights form individual observed images
independently which do not match up to each other, so that the
observed images are out of focus. Therefore, it is possible to
precisely inspect a surface by generating only a predetermined
order of a diffracted light.
[0050] According to the present embodiment, the surface inspecting
apparatus operates like the first embodiment except that the
wavelength range of the illuminating light for illuminating the
measurement objective region is limited.
[0051] According to the present embodiment, the apparatus inspects
a surface without an image by an unnecessary order of a diffracted
light which degrades the accuracy of the inspection. Therefore, the
inspecting apparatus enables more precise inspection of a surface
than the first embodiment.
[0052] A wavelength range to be selected by the band pass filter
115 is changed by the wavelength range of the light from the light
source 11 and by the period of the irregular pattern in the
measurement objective region. Therefore, it is preferable that the
band pass filter 115 can be exchanged. In particular, it is
preferable that a band pass filter having a plurality of
transmissive wavelength ranges is prepared and the transmissive
wavelength range is selected by the instruction of the processing
part 510.
[0053] (Third Embodiment)
[0054] FIG. 8 shows a construction of a surface inspecting
apparatus according to the third embodiment of the present
invention. As shown in this figure, the apparatus according to the
third embodiment is different from the first embodiment in that the
apparatus further comprises a band pass filter 350 for interrupting
a diffracted light having a wavelength other than a predetermined
order of diffracted light caused by a predetermined periodic
irregular pattern, and the band pass filter 350 is disposed in the
course of the optical path from the measurement objective region to
the image pick up part 400.
[0055] According to the second embodiment, the surface inspecting
apparatus prevents a diffracted light having a wavelength other
than a predetermined order of diffracted light from arriving at the
image pick up part 400 in the generation stage of the illuminating
light. On the contrary, according to the third embodiment, the
surface inspecting apparatus limits the light having a wavelength
which can arrive at the image pick up part 400, from the whole
lights reflected from the measurement objective region.
[0056] That is, the surface inspecting apparatus of the present
embodiment removes an unnecessary order of a diffracted light which
degrades the accuracy of the inspection, by the band pass filter
350 before the light from the measurement objective region arrives
at the image pickup part 400. Except this point, the surface
inspecting apparatus of the present embodiment operates like that
of the first embodiment.
[0057] According to the present embodiment, the apparatus inspects
a surface without an image by an unnecessary diffracted light which
degrades the accuracy of the inspection, like the second
embodiment. Therefore, the inspecting apparatus enables more
precise inspection of a surface than the first embodiment.
[0058] A wavelength range to be selected by the band pass filter
350 is changed by the wavelength range of the light from the light
source 111 and by the period of the irregular pattern in the
measurement objective region. Therefore, it is preferable that the
band pass filter 350 can be exchanged. In particular, it is
preferable that a band pass filter having a plurality of
transmissive wavelength ranges is prepared and the transmissive
wavelength range is selected by the instruction of the processing
part 510.
[0059] The present invention is not limited to the embodiment as
described above and various changes maybe made. For example,
according to the embodiment as described above, an operation of
Fourier transform or inverse Fourier transform is carried out to
data obtained after picking up an image. However, it is also
possible to carry out the operation of Fourier transform or inverse
Fourier transform in a optical system.
[0060] In the above-described embodiment, only a direct surface
inspection for the surface of a semiconductor wafer on which a
circuit pattern is formed periodically has been explained for
example. However, the surface inspection of the present invention
can be applied to a back surface of the semiconductor wafer which
has a lot of fine irregularities or to a cut surface of a wafer or
the like by a wire saw having periodic steps.
[0061] Industrial Applicability
[0062] Typical effects according to the present invention will be
explained as follows. According to the present invention, because
the spatial frequency of the luminance data in a predetermined
direction is analyzed to make a plurality of frequency data and a
predetermined spatial frequency component is extracted the made
frequency data, it is possible to detect the state of desired
irregularity. of spatial frequency data; and a fifth step of
extracting a desired frequency component from the plurality of
spatial frequency data, to synthesize.
* * * * *