U.S. patent number RE33,991 [Application Number 07/360,971] was granted by the patent office on 1992-07-14 for foreign particle detecting method and apparatus.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Mitsuyoshi Koizumi, Masataka Shiba, Sachio Uto.
United States Patent |
RE33,991 |
Shiba , et al. |
July 14, 1992 |
Foreign particle detecting method and apparatus
Abstract
The foreign particle detecting method and apparatus are
disclosed wherein a polarized laser beam emitted by a laser beam
irradiating system from a direction inclined with respect to the
direction perpendicular to the surface of a substrate is used by a
scanning means to linearly scan the substrate surface from a
direction approximately 90.degree. with respect to the laser light
irradiating direction; and the laser light reflected from a foreign
particle on the substrate surface is detected by a polarized light
analyzer and a photoelectric conversion device from a direction set
approximately equal to said scanning direction and inclined with
respect to the direction perpendicular to the substrate
surface.
Inventors: |
Shiba; Masataka (Yokohama,
JP), Uto; Sachio (Yokohama, JP), Koizumi;
Mitsuyoshi (Yokohama, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
27458440 |
Appl.
No.: |
07/360,971 |
Filed: |
June 2, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
548516 |
Nov 3, 1983 |
04669875 |
Jun 2, 1987 |
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Foreign Application Priority Data
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Nov 4, 1982 [JP] |
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57-192461 |
Nov 4, 1982 [JP] |
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57-192462 |
Feb 21, 1983 [JP] |
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58-26156 |
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Current U.S.
Class: |
356/237.3;
250/559.09; 250/559.41 |
Current CPC
Class: |
G01N
21/94 (20130101); G01N 2015/0238 (20130101); G01N
2021/4792 (20130101); G01N 2201/1053 (20130101) |
Current International
Class: |
G01N
21/94 (20060101); G01N 21/88 (20060101); G01N
15/02 (20060101); G01N 021/32 () |
Field of
Search: |
;356/237,339,343,338
;250/572,578 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bowers, Jr.; Charles L.
Assistant Examiner: Doody; Patrick A.
Attorney, Agent or Firm: Antonelli, Terry Stout &
Kraus
Claims
What is claimed is:
1. A foreign particle detecting method comprising the steps of:
irradiating two halves of a substrate having a frame with a
pellicle mounted thereon with a respective laser beam emitted by a
laser beam irradiating means in a direction inclined with respect
to the substrate surface and polarized thereafter so as to scan
respective halves of the substrate surface in a predetermined
direction while linearly moving said substrate in a direction
crossing at substantially right angles to the light scanning
direction;
positioning, at least prior to the step of irradiating, a
respective polarized-light analyzer in said scanning direction
inclined with respect to said substrate surface for analyzing the
scattered light from a foreign particle on respective halves of the
substrate; and
detecting said scattered light by a photo-electric conversion
means;
whereby the entirety of the substrate is enabled to be inspected
for detection of foreign particles irrespective of the frame and
pellicle mounted on the substrate.
2. A foreign particle detecting method comprising the steps of:
irradiating two halves of a substrate, through a preventive means
mounted on the substrate by a frame for preventing adherence of
foreign particles to the substrate, with a respective laser beam
emitted by a laser beam irradiating means in a direction inclined
with respect to the substrate surface so as to scan respective
halves the substrate surface which is covered with said preventive
means in a predetermined direction while linearly moving said
substrate in a direction substantially 90.degree. with respect to
the laser beam crossing at substantially right angles to the light
scanning direction;
positioning, at least prior to the step of irradiating, a
respective polarized-light analyzer in said scanning direction
inclined with respect to said substrate surface for analyzing the
scattered light from a foreign particle on respective halves of the
substrate; and
detecting said scattered light by a photoelectric conversion means;
wherein the entirety of the substrate is enabled to be inspected
for detection of foreign particles irrespective of the frame and
preventive means mounted on the substrate.
3. A foreign particle detecting apparatus comprising:
irradiating means for irradiating a respective polarized laser beam
spot linearly scanning on respective halves of two halves of a
substrate in a direction inclined with respect to the direction
perpendicular to the surface of the substrate placed on a
horizontal plane and having a frame with a pellicle mounted
thereon, said irradiating means including a laser beam oscillator
and a polarizer; scattered light detecting means for detecting
scattered light from a foreign particle in the laser beam spot on
respective halves of the surface of the substrate, said scattered
light detecting means being positioned along an extended direction
of said scanning line and being inclined with respect to the
direction perpendicular to the surface of the substrate, said
scattered light detecting means including a polarized light
analyzer, condenser lens, and photoelectric converter, whereby the
entirety of the substrate is enabled to be inspected for detection
of foreign particles irrespective of the frame and pellicle mounted
on the substrate.
4. A foreign particle detecting apparatus according to claim 3,
comprising a light blocking means disposed between said condenser
lens and photoelectric converter of said scattered light detecting
means.
5. A foreign particle detecting apparatus according to claim 3
wherein the inclination angle of at least one of said optical axis
of the irradiating means and scattered light detecting means is
22.5.degree..+-.15.degree..
6. A foreign particle detecting apparatus according to claim 3
wherein said optical axes of the irradiating means and the
scattered light detecting means intersect each other at angle of
90.degree..+-.10.degree. on said surface of the substrate.
7. A foreign particle detecting apparatus comprising:
frame position detecting means for detecting a position of a frame
of a pellicle mounted on a substrate; and
detection means for detecting a foreign particle existing in the
inspection area enclosed with said frame according to the frame
mounting position detected by said frame position detecting
means.
8. A foreign particle detecting apparatus comprising:
laser beam irradiating means for irradiating two halves of a
substrate having a frame with a pellicle mounted thereon with a
respective polarized laser beam spot, each of said laser beam spots
being scanned over one half of the substrate in a direction
inclined with respect to a direction perpendicular to the surface
of the substrate; and
a pair of light detecting means positioned in the direction along
which said scanning line is extended for detecting scattered light
from a foreign particle on respective halves of the substrate, for
analyzing the scattered light by a polarized light analyzer, for
condensing the scattered light by a condenser lens, and for
detecting the image formation obtained from said condenser lens by
a photoelectric converting means, wherein blocking means for
blocking the light scattered from other than the surface of said
substrate is disposed between said condenser lens and said
photoelectric converting means;
whereby the entirety of the substrate is enabled to be inspected
for detection of foreign particles irrespective of the frame and
pellicle mounted on the substrate.
9. A foreign particle detecting apparatus according to claim 8
wherein said blocking means of said scattered light detecting means
is disposed along a direction inclined with respect to the optical
axis of said condenser lens.
10. A foreign particle detecting apparatus according to claim 9
wherein the magnification of said condenser lens of said scattered
light detecting means is equal to or less than one.
11. A foreign particle detecting apparatus according to claim 9
wherein said blocking means is formed by a slit.
12. A foreign particle detecting apparatus according to claim 11
wherein the width of said slit of said blocking means changes in
the longitudinal direction.
13. A foreign particle detecting apparatus according to claim 8
wherein at least a pair of said irradiating means are disposed
opposing to each other with respect to said substrate, at least a
pair of aid light detecting means is disposed opposing to each
other with respect to said substrate.
14. A foreign particle detecting apparatus comprising:
projecting means including;
a laser source;
a rotating mirror for performing scanning by use of a laser beam
projected from said laser source in a predetermined direction;
a changeover mirror for changing over the direction of the laser
beam by reflecting said laser beam outputted from said rotating
mirror;
a pair of projecting optical systems, each of said projecting
optical systems being arranged for projecting said laser beam
changed over by said changeover mirror as a laser spot from a
direction inclined with respect to a substrate having a frame with
a pellicle mounted thereon so that said laser beam projected by one
of said projecting optical systems is projected in a direction
opposite to the direction of projecting of said laser beam by the
other of said projecting systems for scanning different halve of
said substrate; and
at least a pair of detecting means disposed opposing to each other
with respect to said substrate, which detects from an inclined
direction with respect to said substrate, scattered light from a
foreign particle existing in the laser spot on the different halves
of said substrate projected by said projecting optical systems
through a polarized-light analyzer and a condenser lens and for
providing output electric signals by photoelectric converting means
disposed along each axis of said pair of detecting means;
whereby the entirety of the substrate is enabled to be inspected
for detection of foreign particles irrespective of the frame and
pellicle mounted on the substrate.
15. A foreign particle detecting apparatus comprising:
projecting means including;
a laser source;
a rotating mirror for performing scanning by use of a laser beam
projected from said laser source in a predetermined direction;
a changeover mirror for changing over the direction of the laser
beam by reflecting said laser beam outputted from said rotating
mirror;
a pair of projecting optical systems, each of said projecting
optical systems being arranged for projecting said laser beam
changed over by said changeover mirror as a laser spot from a
direction inclined with respect to a substrate so that said laser
beam projected by one of said projecting optical systems is
projected in a direction opposite to the direction of projection of
aid laser beam by the other of said projecting optical systems;
at least a pair of detecting means disposed opposing to each other
with respect to said substrate, which detects from an inclined
direction with respect to said substrate, scattered light from a
foreign particle, existing in the laser spot on said substrate
projected by said projecting optical systems through a
polarized-light analyzer and a condenser lens and for providing
output electric signals by photoelectric converting means disposed
along each axis of said pair of detecting means; and
frame detecting means for detecting a position of a frame for
supporting means for preventing adherence of foreign particles on
said substrate.
16. A foreign particle detecting method comprising the steps
of:
actuating one of a set of scanners to scan one half of a substrate
to be inspected, the substrate having a frame with a pellicle
mounted thereon, each scanner being positioned in a direction
capable of scanning an opposite one half of the substrate to be
inspected;
actuating the other of the set of scanners to scan the opposite one
half of the substrate to be detected; and
inspecting, during the actuation of each of the scanners, a
respective one half of the substrate to be inspected using a
respective one of a set of detectors positioned substantially at a
right angle to the scanning direction, when viewed from above the
substrate;
whereby the entirety of the substrate is enabled to be inspected
for detection of foreign particles irrespective of the frame and
pellicle mounted on the substrate.
17. A foreign particle detecting method according to claim 16,
wherein each of the scanners has an optical axis arranged at an
inclination angle of 22.5.degree..+-.15.degree. with respect to the
substrate.
18. A foreign particle detecting method according to claim 16,
wherein each of the detectors has an optical axis arranged at an
inclination angle of 22.5.degree..+-.5.degree. with respect to the
substrate.
19. A foreign particle detecting apparatus comprising:
a pair of light directing means disposed opposing to each other
with respect to a substrate for directing a pair of light beams to
the substrate in a direction inclined with respect to the substrate
so as to enable light to be scattered from a particle on the
substrate, the light directing means including;
a laser beam source,
a rotating mirror for performing scanning of a laser beam produced
from said laser beam source in a predetermined direction,
a changeover mirror for changing over the direction of the laser
beam reflected from the rotating mirror,
table driving means for driving a table carrying the substrate so
as to enable two-dimensional scanning of a part of the substrate
with the scanning by the rotating mirror, and
lens and mirrors set in a path of said laser beam from said laser
beam source for polarizing and focusing the laser beam onto the
substrate in the direction inclined with respect to the
substrate,
a pair of scattered light detecting means for detecting scattered
light from the substrate and disposed opposing to each other and
substantially at right angles with respect to said pair of light
beams, each of said pair of light detecting means including;
a polarized light analyzer,
a condenser lens,
slit means for blocking light scattered from other than the surface
of the substrate, and
photoelectric converting means arranged along said scanning
direction and inclined with respect to the substrate,
set-up means for setting up at least four different foreign
particle inspecting areas on the substrate including;
sensor means for detecting a metallic attachment for the substrate
and for producing signals indicative of the detection result,
and
specifying means for specifying the presence or absence and the
position of a foreign particle in the inspection area including
determining means for determining position signals representing the
position of the foreign particle when output signals of said sensor
means are greater than a predetermined varying standard.
20. A foreign particle detecting apparatus according to claim 19,
wherein the metallic attachment is a frame of a pellicle mounted on
the substrate and which encloses the different inspection areas.
.Iadd.
21. An apparatus for detecting a foreign particle on a surface of a
substrate having a circuit pattern comprising:
irradiating means for irradiating a polarized laser beam spot
linearly scanning on the substrate in a direction inclined with
respect to a direction perpendicular to the surface of the
substrate, the irradiating means including a polarized laser
source; and
detecting means for detecting scattered light generated from the
foreign particle in the polarized laser beam spot on the surface of
the substrate, the detecting means being positioned along an
extended direction of the scanning line and being inclined with
respect to the direction perpendicular to the surface of the
substrate, the scattered light detecting means including a
polarized light analyzer, condenser lens and photoelectric
converter for enabling detection of foreign particles on the
surface of the substrate without detecting edge scattered light
generated from an edge of the circuit pattern of the substrate, the
polarized light analyzer enabling discrimination of the foreign
particle scattered light generated from the foreign particle from
the edge scattered light generated from the edge of the circuit
pattern so as to enable detection of the foreign particle on the
surface of the substrate. .Iaddend. .Iadd.
22. An apparatus according to claim 21, wherein the irradiating
means includes a focus lens for focusing a laser beam projected
from the polarized laser source as the polarized laser beam spot on
the substrate, and a scanning means for linearly scanning the
polarized laser beam spot on the substrate. .Iaddend. .Iadd.23. An
apparatus according to claim 22, wherein the focus lens includes a
f.multidot..theta. lens. .Iaddend. .Iadd.24. An apparatus according
to claim 22, wherein the scanning means includes a rotating mirror.
.Iaddend. .Iadd.25. An apparatus according to claim 21, wherein the
detecting means includes light blocking means disposed between the
condenser lens and the photoelectric converter. .Iaddend. .Iadd.26.
An apparatus according to claim 22, wherein the detecting means
includes light blocking means disposed between the condenser lens
and the photoelectric converter. .Iaddend. .Iadd.27. An apparatus
according to claim 21, wherein the irradiating means and the
scattered light detecting means have respective optical axes
intersecting one another at an angle of 90.degree..+-.10.degree.
projected on the surface of the substrate. .Iaddend. .Iadd.28. An
apparatus according to claim 25, wherein the light blocking means
includes a slit plate for enabling detection of the foreign
particle scattered light generated from the foreign particle along
the scanning line. .Iaddend. .Iadd.29. An apparatus according to
claim 28, wherein the slit plate is inclinedly disposed on an image
focusing plane of the condenser lens. .Iaddend. .Iadd.30. An
apparatus for detecting a foreign particle on a surface of a
substrate having a circuit pattern comprising:
irradiating means for irradiating a polarized laser beam spot
linearly scanning on the substrate in a direction inclined with
respect to a direction perpendicular to the surface of the
substrate, the irradiating means including a polarized laser source
for generating a polarized laser beam, a focus lens for focusing
the polarized laser beam on the substrate as the polarized laser
beam spot, and scanning means for linearly scanning the polarized
laser beam spot on the substrate; and
detecting means for detecting scattered light generated from the
foreign particle in the polarized laser beam spot on the surface of
the substrate, the detecting means being positioned along an
extended direction of the scanning line and being inclined with
respect to the direction perpendicular to the surface of the
substrate, the detecting means including a polarized light
analyzer, condenser lens and photoelectric converter for enabling
detection of foreign particles o the surface of the substrate
without detecting edge scattered light generated from an edge of
the circuit pattern of the substrate, the polarized light analyzer
enabling discrimination of the foreign particle scattered light
generated from the foreign particle from the edge scattered light
generated from the edge of the circuit pattern, thereby enabling
the photoelectric converter to provide a signal indicative of the
foreign particle on the surface of the substrate. .Iaddend.
.Iadd.31. An apparatus according to claim 30, wherein the scanning
means includes a rotating mirror. .Iaddend. .Iadd.32. An apparatus
according to claim 30, wherein the focus lens enables scanning of
the polarized laser beam spot at a constant speed on the surface of
the substrate. .Iaddend. .Iadd.33. An apparatus according to claim
32, wherein the focus lens includes a f.multidot..theta. lens.
.Iaddend. .Iadd.34. An apparatus according to claim 30, wherein the
detecting means includes light blocking means disposed between the
condenser lens and the photoelectric converter. .Iaddend. .Iadd.35.
An apparatus according to claim 31, wherein the detecting means
includes light blocking means disposed between the condenser lens
and the photoelectric converter. .Iaddend. .Iadd.36. An apparatus
according to claim 30, wherein the irradiating means and the
scattered light detecting means have respective optical axes
intersecting one another at an angle of 90.degree..+-.10.degree.
projected on the surface of the substrate. .Iaddend. .Iadd.37. An
apparatus according to claim 30, wherein the light blocking means
includes a slit plate for enabling detecting of the scattered light
from the foreign particle along the scanning line. .Iaddend.
.Iadd.38. An apparatus according to claim 37, wherein the slit
plate is inclinedly disposed on a image focusing plane of the
condenser lens. .Iaddend. .Iadd.39. A method for detecting a
foreign particle on a surface of a substrate having a circuit
pattern, comprising the steps of:
irradiating, by irradiating means including a polarized laser
source, a polarized laser beam spot linearly scanning on the
substrate in a direction inclined with respect to a direction
perpendicular to the surface of the substrate; and
detecting, by detecting means positioned along an extended
direction of the scanning line and inclined with respect to the
direction perpendicular to the surface of the substrate, scattered
light generated from the foreign particle in the polarized laser
beam spot on the surface of the substrate, the scattered light
detecting means including a polarized light analyzer, condenser
lens and photoelectric converter for enabling detection of the
foreign particle on the surface of the substrate without detecting
edge scattered light generated from an edge of the circuit pattern
of the substrate, and discriminating the foreign particle scattered
light generated from the foreign particle from the edge scattered
light generated from the edge of the circuit pattern by the
polarized light analyzer so as to detect the foreign particle on
the surface of the substrate. .Iaddend. .Iadd.40. A method
according to claim 39, wherein the step of detecting further
includes blocking scattered light other than scattered light
generated from an extremely fine portion of the polarized laser
beam spot projected on the surface of the substrate. .Iaddend.
.Iadd.41. A method for detecting a foreign particle on a surface of
a substrate having a circuit pattern, comprising the steps of:
irradiating, by irradiating means, a polarized laser beam spot
linearly scanning on the substrate in a direction inclined with
respect to a direction perpendicular to the surface of the
substrate, the irradiating means including a polarized laser source
for generating a polarized laser beam, a focus lens for focusing
the polarized laser beam on the substrate as a polarized laser beam
spot, and scanning means for linearly scanning the polarized laser
beam spot on the substrate; and
detecting, by detecting means positioned along an extended
direction of the scanning line and inclined with respect to the
direction perpendicular to the surface of the substrate, scattered
light generated from the foreign particle in the polarized laser
beam spot on the surface of the substrate, the detecting means
including a polarized light analyzer, condenser lens and
photoelectric converter for enabling detection of the foreign
particle on the surface of the substrate without detecting edge
scattered light generated from an edge of the circuit pattern of
the substrate, and discriminating the foreign particle scattered
light generated from the foreign particle from the edge scattered
light generated from the edge of the circuit pattern by the
polarized light analyzer so as that the photoelectric converter
provides a signal indicative of the foreign
particle on the surface of the substrate. .Iaddend. .Iadd.42. A
method according to claim 41, wherein the step of detecting
includes blocking scattered light other than scattered light
generated from an extremely fine portion of the polarized laser
beam spot projected on the surface of the substrate. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for
detecting foreign particles existing on the surface of a
substrate.
2. Description of the Prior Art
The conventional foreign particle detecting apparatus is
constructed, as disclosed in the U.S. Pat. No. 4,342,515, in a
manner shown in FIG. 1. In this Figure, s-polarized laser beams 5,
6 from linearly polarized laser oscillators 3, 4 are irradiated to
a foreign particle 2 on a wafer 1 widewards along two directions,
and a random polarized laser light 7 is scattered from the foreign
particle 2. After, the random polarized light 7 is focused by a
condenser lens 8, only the s-polarized light of the condensed laser
light is blocked by an analyzer 9; then, only a p-polarized light
10 is passed through a slit 11 for limiting the detection field and
is detected by a photoelectric conversion device 12. On the other
hand, the s-polarized light is scattered from an edge of a circuit
pattern. Therefore, the presence of a foreign particle is
recognized according to the output of the photoelectric conversion
device 12.
In the conventional foreign particle detecting apparatus however, a
wafer 1 being rotated must be fed along an axial direction of said
wafer surface; hence, the foreign particle detecting speed is
disadvantageously reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and
apparatus for correctly detecting foreign particles existing on the
substrate surface at a high speed by use of a simple construction
whereby the abovementioned disadvantage of the conventional
apparatus is removed.
To achieve the object of the present invention, linearly polarized
laser beam irradiated from a laser light irradiating means to a
substrate from a direction inclined by 7.5.degree. to 37.5.degree.
with respect to the surface of the substrate is linearly scanned on
the substrate surface along the direction substantially 90.degree.
(90.degree..+-.10.degree.) relative to said irradiating direction
by a scanning means comprising a rotating or swinging
galvanomirror, polygonal mirror, prism, or the like. The scattered
light from a foreign particle on the substrate is detected by a
light analyzing means and a photoelectric converter in a direction
substantially equal to the scanning direction and inclined by
approximately 7.5.degree. to 37.5.degree. relative to the substrate
surface.
On the other hand, if foreign particles exist on a reticle or
photomask for a semiconductor exposure system, such as an automatic
reduction projection mask aligner, when a pattern on the reticle or
photomask is exposed onto a semiconductor wafer by a
step-and-repeat way or the like, the latent images of the foreign
particles are also exposed onto the wafer together with the circuit
pattern and consequently all of the exposed portion (chip) on the
completed wafer are rejected in some cases. As a
counter-measurement to prevent adhesion of foreign particles, it
has been considered to mount a so-called pellicle which comprises a
pellicle thin film of nitrocellulose, etc. fixed to a frame formed
of a metal or the like on a substrate, such as a reticle and
photomask after the substrate is washed. The present invention
enables to rapidly detect foreign particles on the substrate
surface with high reliability without being affected by the frame
of the pellicle even after the pellicle is mounted on the
substrate; furthermore, the present invention enables to simplify
the optical system for detecting the scattered light. Therefore,
the foreign particle detecting apparatus according to the present
invention comprises a light irradiating means for irradiating a
light spot linearly scanning on the substrate from the direction
inclined with respect to the direction perpendicular to the
substrate surface so that an inclined linearly polarized light
spot, such as a linearly polarized laser beam is irradiated
alternately from two directions, and a scattered light detecting
means for detecting a scattered light scattered on a foreign
particle on the substrate surface in a direction substantially
equal to an extended direction of said scanning line and inclined
with respect to the direction perpendicular to the substrate
surface, said scattered light detecting means being disposed at two
symmetrical positions, said scattered light detecting means
including a polarized light analyzer and a condenser lens for
analyzing and condensing the scattered light of the foreign
particles and a light receiving device for detecting the analyzed
and condensed light. The present invention is characterized also by
a pinhole- or a slit-shaped light blocking means disposed in the
scattered light detecting system for preventing a malfunction to
recognize the presence of a foreign matter on the substrate surface
by receiving scattered light from the frame of the pellicle, the
edge (step) of a circuit pattern of substrate, a foreign particle
on the pellicle, or the like. Specifically, the present invention
is characterized in that said foreign particle detecting apparatus
includes said pinhole or slit provided at a position inclined
relative to an optical axis of condenser lens so that in image
formation by the condenser lens the scattered light obtained from
other that the substrate surface is blocked.
Further, the present invention has the following characteristic:
The positional relationship between the frame of the pellicle and
the pellicled substrate is measured before inspection, thereby
allowing to automatically set the effective inspection area.
Since the frame of pellicle is formed of a metal such as aluminum,
the position of the frame can be measured by use of light
reflection, light scattering, a mechanical contact sensor, or an
electrostatic or magnetic noncontact sensor. This characteristic is
advantageously utilized in the present invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of a conventional foreign particle
detecting apparatus.
FIG. 2 is the exploded view of an embodiment of the present
invention.
FIG. 3 is a diagram showing the fundamental construction according
to the present invention.
FIG. 4 is a schematic cross-sectional diagram illustrating the
influence of a pellicle frame.
FIGS. 5a and 5b are cross-sectional diagrams showing the
relationship between irradiated light and inspection area and that
between the foreign particle detecting direction and the inspection
area.
FIG. 6 is a schematic diagram illustrating the inspection area on a
substrate.
FIG. 7 shows the electric circuit according to the present
invention.
FIG. 8 is a signal waveform diagram obtain by the circuit shown in
FIG. 7.
FIG. 9 is a schematic diagram illustrating the construction of an
apparatus for inspecting the upper and lower surfaces of a
substrate.
FIG. 10(A) is a diagram of the fundamental construction according
to the present invention, wherein a pinhole-shaped light blocking
means is added to the construction depicted in FIG. 3.
FIG. 10(B) is a magnified diagram of the portion of the diagram
shown in FIG. 10(A) viewed from the direction A10.
FIG 11(A) is a schematic diagram of a foreign particle detecting
apparatus in which a slit-shaped light blocking means is
disposed.
FIG. 11(B) is a magnified diagram of a portion of FIG. 10(A) viewed
from the direction A11.
FIGS. 12(A) and 12(B) are diagrams depicting characteristics of the
present invention.
FIG. 13 is a perspective side view of a pellicled substrate
according to the present invention.
FIG. 14 is a front view of a substrate.
FIGS. 15 and 16 are side views of a substrate, respectively.
FIG. 17 is a representation of output signals corresponding to
respective portions of a substrate.
FIG. 18 is a diagram showing a circuit for discriminating a frame
position.
FIG. 19 is a side view of an embodiment of the pellicle frame
position detecting means according to the present invention.
FIG. 20 is a front view of still another embodiment of a pellicle
frame position detecting means according to the present
invention.
FIG. 21 is a side view of another embodiment of the pellicle frame
position detecting means according to the present invention.
FIG. 22 is a diagram illustrating locations of abnormal scattered
light viewed from the direction A shown in FIG. 23.
FIG. 23 is a view showing another embodiment of the foreign
particle detecting apparatus according to the present
invention.
FIG. 24 is a schematic diagram illustrating the method for blocking
abnormally scattered light according to the present invention.
FIG. 25 is a view for explaining the principle of the slit action
in conjunction with the light passing therethrough.
FIGS. 26, 27, and 28 are view showing the shapes of the slit viewed
from the direction B shown in FIG. 23.
FIG. 29 is a diagram of the optical system employed as the
scattered light detecting system of the present invention viewed
from the direction C shown in FIG. 23.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be concretely described according to the
embodiments in conjunction with the accompanying drawing. FIG. 2
shows an embodiment of an apparatus for detecting foreign particles
on a substrate wherein a pellicle is mounted on a substrate of a
photomask, reticle, or the like according to the present invention.
A laser beam 30 emitted from a laser oscillator 27 is polarized by
a polarizer 29 to be a linearly polarized wave having a
predetermined polarization angle on a substrate (for example to be
an s-polarized laser) and is totally reflected on a galvanomirror
28 linked with a motor 34 which swings, then it is delivered to a
mirror 32 through a f.multidot..theta. lens 31. The laser beam
further passes through mirrors 35a and 36a or mirrors 35b and 36b
and is irradiated having a s-polarized light element (polarization
vector is parallel to the substrate) on the surface of a substrate
21 from an inclined direction having an angle .alpha. with respect
to the surface of a substrate 21. The galvanomirror 28 swings with
a saw-wave-shaped rotation, while the lens 31 is an
f.multidot..theta. lens which can scan the surface of the substrate
21 at a constant speed by use of a laser spot.
A scattered light 25 from a foreign particle 24 existing on the
surface of the substrate 21 shown in FIG. 3 becomes a random
polarized light. Along a direction approximately parallel
(0.degree..+-.10.degree.) to the laser scanning direction and
inclined by 7.5.degree. to 37.5.degree. with respect to the surface
of the substrate 21, the scattered light from a pattern (formed
substantially in the 45.degree. direction from the scanning
direction) edge becomes a p-polarized light depending on the shape
of a pattern edge or the like.
To detect the scattered light 25 (only s-polarized light) from the
foreign particle 24 existing on the surface of the substrate 21 as
shown in FIG. 2 two light detecting systems 37a and 37b are
disposed at two positions symmetrical with respect to the y
direction of the reticle substrate 21, each position being in a
direction perpendicular to the respective laser light 30a or 30b
(FIG. 2) and inclined upward by an angle .beta. with respect to the
horizontal surface of the substrate 21. The scattered light
detecting systems 37a and 37b comprise s-polarized light analyzers
41a and 41b by which p-polarized light from the pattern edge is
blocked, condenser lenses 40a and 40b, slit-shaped light blocking
means 39a and 39b, and photoelectric conversion device 38a and 38b,
respectively. The s-polarized light analyzers (41a) and (41b)
extract linearly polarized waves having a predetermined
polarization vector out of the scattered light 25 (FIG. 23) from
the foreign particle 24. The light extracted through the
s-polarized light analyzer is condensed by the condenser lenses 40a
or 40b (FIG.2) and reaches the photoelectric conversion device 38a
or 38b through the split-shaped light blocking means 39a or 39b.
The photoelectric conversion device 38, such as a photoelectric
multiplier having high sensitivity produces an electric signal
proportional to the magnitude of a received light.
A pair of light irradiating means 35a, 36a and 35b, 36b; and a pair
of light detecting systems 37a and 37b are provideed in the means
shown in FIG. 2 because of the following reasons.
FIGS. 5 and 6 illustrate irradiating directions of the laser beams
30a, 30b and detecting directions of a scattered light 25. To
prevent the laser beams 30a and 30b and the scattered light 25 from
the foreign particle 24 from being blocked by a pellicle frame
(22), the substrate is subdivided into two parts as shown in FIG. 5
so that the laser beams 30a and 30b are always being irradiated
from the opposite sides and the scattered light from the
foreign-particle 24 is detected from the opposite sides of the area
in which the foreign particle 24 exists. That is, assuming that the
inspection area on the substrate 21 is subdivided into four parts
as illustrated in FIG. 6, the laser beam 30a is irradiated to
inspection areas A and C, whereas the laser beam 30b is irradiated
to inspection areas B and D. In this case, the laser beams 30a and
30b are alternately projected by turning the mirror 32 (FIG. 2) by
90.degree. by a motor 33. The scattered light detecting systems 37a
is actuated when the laser spot resides in the area A or B on the
surface of the substrate 21, while the light detecting means 37b is
actuated when the laser spot resides in the area C or D on the
surface of the substrate 21. This means that the scattered light
detection signal of the photoelectric conversion device 38a or 38b
such as a photoelectric multiplier is turned on or off in
synchronism with the rotation angle of the galvanomirror 28. Since
the detecting sensibility for the scattered light 25 from a foreign
particle 24 varies between the case where the foreign particle
resides in the vicinity of the center of the substrate 21 (FIG. 2)
and the case where it resides in a peripheral location thereof, the
electrical threshold value (slice level) for detecting a foreign
particle can be changed, in synchronism with the position of the
laser spot residing on the surface of the substrate 21 in the
present foreign particle detecting apparatus.
FIG. 7 outlines the scattered light detecting circuit
configuration. Analog signals output from the photoelectric
conversion devices 38a and 38b are inputted to a multiplexer 43
through voltage amplifiers 42a and 42b, respectively. The
multiplexer 43 is switched by a change-over pulse 50c (shown as (d)
in FIG. 8) in synchronism with a timing pulse 50b (depicted as (c)
in FIG. 8) to be generated by a driving signal 50a (illustrated as
(a) in FIG. 8) output from a galvanomirror driving circuit 44 in
proportion to the rotation angle. For the areas A and B, the
photoelectric conversion device 37a (signal 38a) is selected as
indicated by a signal 51a (shown as (e) in FIG. 8); whereas for the
areas C and D, the photoelectric conversion device 37b (signal 38b)
is selected as indicated by a signal 51b (depicted as (f) in FIG.
8). In a comparator 47 (for handling the threshold value), an
analog signal 52 shown as (h) in FIG. 8 is compared with a variable
threshold value signal 53 (shown as (g) in FIG. 9) generated by a
threshold value generator circuit 46 for varying voltage
synchronized with an electric signal output from the galvanomirror
driving circuit 44. As a result, a signal 54 shown as (i) in FIG. 8
is obtained. If the value of the detection signal 52 exceeds the
threshold value 53 in this case, the peak value of the detection
signal 51 is stored in a particle data storage 48 by use of an A/D
converter 49; and at the same time, a clock pulse signal (shown as
(b) in FIG. 8) which generates a driving signal of the
galvanomirror driving circuit 44 is converted into the y coordinate
of a point on the substrate 21 and an electric signal of an x
coordinate detecting sensor obtained from a table driving circuit
45 or a signal obtained by accumulating signals 50b (shown as (c)
in FIG. 8) is converted into the x coordinate of the point on the
substrate 21. Consequently, the coordinate (x, y) of the position
at which the foreign particle exists is obtained, thus the
dimensions and the shape of the foreign particle can be observed by
a means, such as a microscope, after the foreign particle is
detected.
The explanation above applies to a detecting unit 90 for detecting
foreign particles on the upper surface of the substrate 21. To
detect foreign particles on the lower surface of the substrate 21,
a detecting unit 91 for detecting foreign particles on the lower
surfaces need only be disposed below the substrate 21. In this
case, the construction and electric circuit configuration are
completely the same.
Since foreign particles having their sizes from 5 .mu.m to 10 .mu.m
must be detected on the upper surface of a reticle and those having
sizes from 2 .mu.m to 5 .mu.m must be detected on the lower pattern
surface for a reticle of a reduction projection type mask aligner,
the threshold values of the detecting units 90 and 91 for the upper
and lower surfaces must be set to the levels for detecting said
foreign particles, respectively.
According to the present invention as explained above, to prevent
influence of a pellicle frame 22 (for example, thickness: 2 mm,
height: 4 mm or 6.3 mm) or a 107 mm pellicle mounted on the surface
of a substrate, the irradiating optics 27 and 29, 31 are disposed
at positions (.alpha.(FIGS. 2 and 3)=22.5.degree..+-.15.degree.)
which allow the irradiating means 27 and 29, 31 to irradiate light
on the substrate surface without being affected by the pellicle
frame, and a scattered light detecting systems 37 is disposed along
a line which is drawn substantially perpendicular
(90.degree..+-.10.degree.) to the line along which the irradiating
means 27 and 29 are placed and which is inclined upward
(.beta.(FIGS. 2 and 3)=22.5.degree..+-.15.degree.) with respect to
the substrate surface, thereby enabling to detect foreign particles
on the surface of the substrate 21. However, as shown in FIG. 4
since the laser beam is irradiated on the substrate 21 along an
inclined direction, a scattered light 26a from the upper surface of
the pellicle frame 22, a scattered light 26b from a reticle pattern
surface, or a scattered light 26c from a foreign particle 58 on a
pellicle 23 is erroneously detected as a foreign particle 24 on the
surface of the substrate 21.
In the present invention, the erroneous detection is prevented by
adding pinhole-shaped light blocking means 57 illustrated in FIG.
10 and the slit-shaped light blocking means 39 depicted in FIG. 11
to the foreign particle detecting apparatus. To detect foreign
particles on the substrate surface by use of the foreign particle
detecting apparatus to which the pinhole-shaped light blocking
means 57 shown in FIG. 10 is added, the substrate 21 must be
scanned in two directions (2-dimensional scanning) by mounting the
substrate on a table (not shown) which travels along a direction
while moving to the x-axis or y-axis direction or rotating. To
detect foreign particles on the substrate surface by using the
foreign particle detecting apparatus to which the slit-shaped light
blocking means 39 is added, the laser beam scanning is performed
along a direction (y-axis direction) by a scanning means
(comprising the galvanomirror 28, f.multidot..theta. lens 31, etc.)
while the substrate mounted on an x-direction table (not shown) is
being moved to the direction (x-axis direction) perpendicular to
the laser beam scanning direction. Adoption of the pinhole-shaped
or shaped or slit-shaped light blocking means shown in FIGS. 10 and
11, respectively as explained above allows to detect foreign
particles on the substrate surface with high sensibility without
being affected by the scattered light, for example, from the
pellicle frame shown in FIG. 12.
FIG. 13 illustrates a pellicle mounted on the substrate for
preventing foreign particles from adhering to the substrate 21. The
pellicle comprises the pellicle thin film 23 and the frame 22. The
frame 22 is adhered to the substrate 21 by use of adhesive,
double-sided adhesive tape, or the like.
To detect foreign particles on the substrate 21 enclosed with the
pellicle frame 22, an effective inspection area 55 in the area
enclosed with the frame 22 must be specified as shown in FIG. 14.
Reference numeral 56 relative mounting position of the frame 22 on
the substrate 21 is not exact in general, the interference between
the effective inspection area 55 and the frame 22 must be
prevented.
For this purpose, an s-polarized laser beam 30, which is oscillated
from the laser oscillator 27 and polarized by the s-polarizer,
through the f.multidot..theta. lens 31 as shown in FIG. 3 is
irradiated on the substrate 21 to form the laser spot from a
direction inclined by an angle of incidence
.alpha.=22.5.degree..+-.15.degree.). Scattered lights from the
pattern and foreign particles are detected by a detecting system 37
disposed approximately perpendicularly (90.degree..+-.20+) to the
line along which the s-polarized laser light 10 is irradiated. In
this case, the light scattered only from the foreign particles can
be extracted by using the analyzer 41 which passes only the
s-polarized light. The condenser lens 40 and slit 39 block the
scattered light from other than the scanning line of the spot 24.
The scattered light detecting system 37 is disposed along an
inclined line with an angle .beta. equal to
22.5.degree..+-.15.degree. to prevent the interference from the
pellicle frame 22. The interference from the frame 22 can be
prevented also when the pellicle 23 is mounted on the substrate 21
by disposing the scattered light detecting systems 37a and 37b as
shown in FIG. 2 and by alternating the laser beams 30a and 30b and
the scattered light detecting systems 37a and 37b,
respectively.
Next, an embodiment of the present invention will be explained in
which the position of the pellicle frame is obtained by the
scattered light detecting function of the foreign particle
detecting apparatus.
FIG. 15 illustrates the optical system viewed from the Y direction.
The laser spot 94 is formed on the substrate 21 through the
f.multidot..theta. lens 31a or 31b. The spot 94 is formed on the
pellicle surface 23 by moving the substrate 21 in the Z direction
as depicted in FIG. 16. If the laser spot 94 scanning is performed
in the X and Y directions under this condition, a photoelectric
multiplier output 60 indicated as (B) corresponding to the diagram
indicated as (A) in FIG. 17 is obtained according to light
scattered on the frame 22 when the spot 94 comes to the frame 22.
In the diagram depicted as (B) in FIG. 17, the reference numerals
53, 61, and 62 indicate a threshold value, the peak value caused by
the frame 22, and the peak value caused by a foreign particle 63,
respectively.
FIG. 18 depicts an electric circuit for discriminating the peak
value 61 caused by the frame 22 from the peak value 62 caused by
the foreign particle 63. The time period in which the signal 54
indicating that the level of the photoelectric multiplier exceeds
the threshold value 53 in FIG. 8 is on is measured by a counter 65
counting the clock signal 58. When the level becomes equal to or
less than the threshold value 53 and the signal 54 turns off, the
falling edge of the signal 54 is detected by a Schmitt-trigger
circuit 66 to produce a reset signal, which resets a comparator 69
and the counter output counted so far is compared with a preset
value w by the comparator 69 to generate a signal 70. Then, the
counter 65 is reset by the reset signal through a timer 67. If the
preset value (clock count) w is less than the value of the counter
65, the detected light is assumed to be scattered from the frame;
otherwise, it is assumed to be scattered from a foreign particle.
This operation is performed along reticle central lines 71 and 72
shown in FIG. 14 to determine the frame positions with respect to x
and y axes, then the effective inspection area 55 is determined in
the frame with a space disposed between each side of the effective
inspection area 55 and the corresponding side of the frame 22.
Next, an embodiment of the present invention will be explained in
conjunction with FIG. 19, wherein the frame mounting position is
measured by use of the magnitude of the reflected light. A laser
beam 74 from a laser tube 73 or the like is irradiated on the
pellicle 23 along a line drawn upward relative to the pellicle, and
the reflected light is received by a light receiving device 76
through a slit 75. If the laser beam 74 is projected on the
pellicle 23 which has not the frame 22 thereunder, the light is
passed through the pellicle, hence the light reception level is
low; if the frame is disposed under the pellicle, the regular
reflection therefrom is received by the light receiving device 76,
hence the light reception level increases and the frame mounting
position is detected. A sensor operating as explained above is
disposed in a portion of the foreign particle detecting
apparatus.
FIG. 20 shows another embodiment of the present invention in which
a mechanical contact sensor is utilized. A pin 78 is pressed
against the frame 22 and the amount of pin movement is measured by
a position detecting sensor 77, thereby calculating the frame
position.
FIG. 21 depicts still another embodiment of the present invention
in which the pellicle frame 22 is formed with a magnetic material
and a noncontact electromagnetic sensor 79 is used to detect the
frame position.
If the foreign particle detection must be performed on the upper
and lower surfaces of a substrate, the frame position detecting
means need not only be disposed on each surface.
According to the present embodiment, since the effective inspection
area of foreign particles on the substrate on which the pellicle is
mounted can be set automatically, operational procedures become
simple even if there is fluctuation in the position for mounting
the pellicle. Moreover, the frame can be discriminated from foreign
particles, thus the foreign particle detecting performance is
remarkably improved.
FIGS. 22(a) to 22(d) show a diagram of light scattering position
viewed from the y direction, illustrating the locations of
abnormally scattered light that can be detected by the foreign
particle detecting system.
When the laser beam 30 is irradiated to the point D on the foreign
particle detecting surface along a line inclined by .alpha. degree
(7.5.degree. to 37.5.degree.), the refracted light reaches the
lower surface E because the substrate 21 is transparent. If the
pattern 21a ((a) in FIG. 22) or a foreign particle 80 ((b) in FIG.
22) exists at the position where the refracted light reaches, the
scattered light therefrom can be detected. With a pellicle mounted
on the substrate, if a large foreign particle 26c exists at the
position F where the laser beam 30 passes through the pellicle 23
on the substrate 21 ((c) in FIG. 22) or if the light reflected on
the surface of the substrate 21 hits the position G on the edge of
the metal frame 22 of the pellicle ((d) in FIG. 22), the scattered
light can be detected. Consequently, hindrances on the lower
surface of the substrate, pellicle, or the like may cause erroneous
foreign particle detection in procedures explained above.
To overcome this difficulty according to the present invention, the
slit 39 is disposed between the condenser lens 40 and photoelectric
multiplier 38 to block the scattered light from other than the
detecting surface of the substrate, thereby enabling to detect only
foreign particles existing on the substrate. Details will be
explained as follows. FIG. 24 is the diagram of the location of
abnormally scattered light shown in FIG. 23 viewed from the upper
surface of the substrate. As illustrated in FIG. 24, the laser beam
30 may be scattered at points D, E, F, and G. When a portion of the
scattered light is focused by the condenser lens 40, the
corresponding spots D', E', F', and G' are imaged on the image
focusing plane 82. If the slit 39 is disposed to block only the
abnormally scattered light corresponding to the points E', F', and
G', only the scattered light from the point D' to be inspected can
be received by the photoelectric multiplier 38. The optical axis of
the condenser lens 40 exists on the plane where the extended
portion of the scanning line 80 of the laser beam 30 is found.
On the other hand, FIG. 25 shows a diagram corresponding to that
depicted in FIG. 23 viewed from the direction C. The optical axis
81 of the condenser lens 40 is inclined by .beta. degrees with
respect to the laser beam scanning line 80. The scattered light
emitted from the positions I, O, and J on the scanning line 80 is
imaged as the points I', O', and J' on the image focusing plane 82.
Therefore, a slit-shaped light blocking plate 39 (FIG. 23) is
adopted. The light blocking plate 39 allows to detect only foreign
particles existing on the transparent substrate 21. That is, the
scattered light only from the point D (FIG. 24) on the transparent
substrate 21 can be detected.
If the slit 39 is disposed on a plane 83 perpendicular to the
optical axis 81 of the focusing lens, points other than those on
the optical axis are defocused, hence the effect for blocking the
abnormally scattered light is suppressed as shown in FIG. 26.
Reference numerals 39a, 88, and 85 indicate the slit plate, the
aperture of the slit plate, and the image focusing trace produced
by the scanning line for detecting foreign particles, respectively;
further, reference numeral 86 indicates a focusing trace of the
scattered light from the lower surface and E.sub.1 and E.sub.3
represent the sizes of spots made by abnormally scattered light. As
can be seen from this diagram, the overlapped portion with the
scattered light to be detected, so that discrimination of the
abnormally scattered light from the scattered light to be detected
becomes impossible.
However, if the slit 39b is inclined to fall just on to the image
focusing plane 82 depicted in FIG. 25, the slit condition becomes
as shown in FIG. 26, thus the discrimination between the scattered
lights explained above is enabled.
In this case, the inclination .phi. of the image focusing plane is
given by the following formula, ##EQU1## where m is the
magnification of the condenser lens 40 on the optical axis 81. When
the value of m is great, the value of .phi. becomes shall and the
inclination of the slit increases, so the light detection becomes
difficult. For example, if the value of m is set as approximately
0.27 for the .beta. equals to 15.degree., the value of .phi. is
approximately 45.degree., hence it is possible to dispose the slit
easily. Although the condition varies depending on the value of
.beta., the magnification of the condenser lens must be equal to or
less than one.
Since the spot size of the laser beam irradiated on the transparent
substrate is fixed, the sizes of spot image of I', O', and J'
obtained by focusing the spots I, O, and J as shown in FIG. 25 vary
because of the different magnification. This applies also to the
traces of abnormally scattered light, thus the lines 86 and 85 are
not parallel in FIGS. 26 and 27.
To retain a satisfactory discriminating ratio between foreign
particle and the others and to increase the tolerance for the
fluctuation of a spot in the X direction based on above-mentioned
characteristics, the shape of the slit 39c need only be modified as
illustrated in FIG. 28. In this case, the width of the slit 39C
must be greater than the size of a laser spot image including the
effect of the aberration caused by the condenser lens.
Although the slit is placed between the condenser lens 40 and the
photoelectric multiplier 38, it is further preferable to disperse a
field lens 88 for focusing light between the slit 39c and the
photoelectric multiplier 38. This is because the photoelectric
multiplier cannot be placed sufficiently near the slit due to the
inclination of the slit, and the scattered light cannot be gathered
on a light receiving surface 89 of the photoelectric multiplier
without the field lens.
A scattered light detecting optical system is constructed based on
the configuration depicted in FIG. 29. The scattered light
detecting sensibility is improved by inserting an ND filter at an
intermediate point of the optical path in some cases.
When the slit 39c is installed, the slit position must be correctly
arranged relative to the laser beam scanning line trace produced by
the condenser lens. For this purpose, a fine adjustment mechanism
must be provided only for the slit in the scattered light detecting
optical system. In FIG. 29, at least fine adjustment in the x and y
directions is indispensable, hence a rotating fine adjusting
mechanism for the x- and y-directional adjustment is provided if
necessary.
According to the present embodiment, since the abnormally scattered
light from the pattern and foreign particles on the lower surface
of the substrate, the pellicle and the like which may hinder the
proper inspection can be completely ignored, the rate of erroneous
foreign particle detection is reduced, the time period required for
the visual check after the automatic inspection is minimized, and
the number of cleaning operations is decreased; thereby
contributing to the production cost reduction and productivity
improvement.
According to the present invention as explained above, the foreign
particle inspection can be conducted with a simple foreign particle
detecting apparatus which detects foreign particles on a substrate
at a high speed while feeding the substrate to a predetermined
direction. Furthermore, the magnitude of the scattered light from
foreign particles can be effectively detected without being
affected by the pellicle frame on the substrate surface and the
circuit pattern formed on the substrate, wherein a particle as
small as 2 .mu.m can be detected. As the inclination angles .alpha.
and .beta. decreases, the change in the polarization angle can be
more effectively detected. Although the detecting sensibility is
improved in this case, the inclination angles .alpha. and .beta.
are preferably set as 22.5.degree..+-.15.degree. because of the
influence from the pellicle frame.
* * * * *