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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a defect testing apparatus and a defect
testing method for inspecting a state of generation of defects such as
foreign particles in a fabrication process such as a semiconductor
fabrication process, a liquid-crystal-display fabrication process and a
print-board fabrication process wherein a defect such as a foreign
particle generated in a process to create a pattern on a substrate to
produce an object is detected and analyzed in order to determine a
countermeasure.
In the conventional semiconductor fabrication method, a foreign particle
existing on a semiconductor substrate also known as a wafer causes a
defect such as poor insulation of a wire or a short circuit. Furthermore,
in the case of a miniaturized semiconductor device, an infinitesimal
foreign particle existing in a semiconductor substrate results in poor
insulation of a capacitor or destruction of typically a gate oxide film.
These foreign particles are introduced to get mixed with a semiconductor
material in a variety of states due to a variety of causes. For example, a
foreign particle is generated by a movable part of a transportation
apparatus or a human body. A foreign particle can also be generated as a
result of a chemical reaction in processing equipment using a process gas
or mixed with chemicals or a raw material.
Likewise, if a foreign particle is introduced to get mixed with a pattern,
causing some defects in a process to fabricate a liquid-crystal display
device, the resulting display device is not usable. The process to
fabricate a print board is in the same situation. That is to say, a mixed
foreign particle causes a poor connection and a short circuit in a
pattern.
Prior arts related to apparatuses and methods for detecting defects such as
foreign particles are disclosed in Japanese Patent Laid-open No. Hei
1-250847, Japanese Patent Laid-open No. Hei 6-258239, Japanese Patent
Laid-open No. Hei 6-324003, Japanese Patent Laid-open No. Hei 8-210989 and
Japanese Patent Laid-open No. Hei 8-271437 and referred to as prior arts
1, 2, 3 ,4 and 5 respectively.
In prior art 1, there is described an inspection apparatus for inspecting
surface characteristics of a substrate. The inspection apparatus includes
a storage means for storing desired surface characteristics of the
substrate, a radiation means for radiating a beam to an area on the
surface of the substrate to be inspected all but uniformly, a TDI image
sensor means for forming an image of the area on the surface of the
substrate to which the beam is radiated by the radiation means, and a
comparison means for comparing the image of the area on the surface of the
substrate formed by the TDI image sensor means with the desired surface
characteristics of the substrate stored in the storage means.
In prior art 2, there is described a defect inspecting apparatus comprising
a conveyance means for conveying a substrate having repetitive patterns
with different pitches, a radiation means for forming a plane-wave beam
into a straight line and radiating the plane-wave beam to the substrate, a
space filter, a detector for detecting an optical image formed by an image
formation optical system and supplied to the detector through the space
filter, elimination means for comparing signals, which are generated to
represent the repetitive patterns with large pitches on the substrate and
supplied to the elimination means through the space filter for an
elimination purpose, with each other, and a defect detection means for
detecting a defect caused by typically a very small extraneous material
existing on the substrate on the basis of a signal generated by the
elimination means.
In prior art 3, there is described a defect inspecting apparatus comprising
a detection head, a pitch detection means, an operator processing system,
an extraneous-material data memory, a large-extraneous-material data
memory, a pattern memory, a software processing system, a parameter
transfer means, an extraneous-material memory, a coordinate-data creation
means and a microcomputer wherein the detection head includes a radiation
means, a detection optical system, a space-filter unit, a detector, an
operational amplifier and an A/D converter.
In prior art 4, there is described a very-small-defect detecting apparatus
for detecting a-very smell defect caused by typically a very small
extraneous material having a size in a range of 0.3.mu.m to 0.8 .mu.m or
smaller and existing on a substrate by splitting a laser beam emitted from
a semiconductor laser oscillator into a plurality of optical beams not
interfering each other so as to make intensities of beams reflected by a
thin film created on the substrate smooth or uniform, converging the
optical beams and radiating the converged optical beams at effectively the
same time to the thin film passing the beams at different incidence angles
T1 to Tn, converging lights scattered by a very small defect by using a
light converging lens, and detecting the converged lights by using a
detector such as a TDI image sensor.
In prior art 5, there is described an extraneous-material inspecting
apparatus comprising a radiation optical system for radiating a beam
generated by a light source to a sample comprising repetitive chips, a
detection optical system including a linear image sensor for receiving
lights reflected and scattered by the sample and for converting the
reflected and scattered lights into a signal, and an interchip comparison
means for comparing signals output by the linear image sensor employed in
the detection optical system for the repetitive chips in order to detect a
comparison mismatch as existence of an extraneous material on the sample,
wherein the radiation optical system includes, a shading correction plate
having a plurality of curved transmission portions created thereon for an
intensity distribution of the beam generated by the light source to
correct the beam radiation so as to give an all but equal phase
distribution in the straight-line transversal direction and an all but
uniform radiation intensity in the straight-line longitudinal direction,
and a light converging subsystem for converging the radiated beam and
radiating the converged beam to the sample in a slanting direction with
respect to the surface of the sample.
In the prior arts described above, however, it is not easy to detect a
defect cause by a very small extraneous material with a size of about 0.1
.mu.m or smaller existing on a substrate, on which repetitive patterns
coexist with non-repetitive patterns, with a high degree of sensitivity
and at a high speed.
This is because, with the prior arts described above, the farther the
distance from a location in an inspected area to the optical axis of the
detection optical system, the lower the MTF (Modulation Transfer Function)
for the location so that the illumination intensity of the radiated light
in regions surrounding the inspected area is not sufficient, making it
difficult to inspect a defect with a high degree of sensitivity and at a
high speed.
SUMMARY OF THE INVENTION
It is thus an object of the present invention addressing the problems
described above to provide a defect inspecting apparatus and a defect
inspection method that are capable of inspecting an area of inspection
also for a defect caused by typically a very small extraneous material
having a size of about 0.1 .mu.m or smaller with a high degree of
sensitivity and at a high speed by effectively utilizing the light
quantity of a Gaussian optical beam emitted by an ordinary low-cost light
source.
It is another object of the present invention to provide a defect
inspecting apparatus and a defect-inspection method that are capable of
inspecting an area of inspection also for a defect caused by typically a
very small extraneous material having a size of about 0.1 .mu.m or smaller
by employing a TDI image sensor for receiving an optical image based on a
DUV (Distant Ultra Violet) laser beam obtained from a substrate being
inspected.
It is a further object of the present invention to provide a defect
inspecting apparatus and a defect inspection method that are capable of
inspecting an area of inspection also for a defect caused by typically a
very small extraneous material having a size of about 0.1 .mu.m or smaller
with a high degree of sensitivity and at a high speed by effectively
utilizing the light quantity of a beam emitted by a lamp serving as a
light source and by solving the problem of an insufficient illumination
intensity in regions surrounding an area of detection on a substrate
serving as an object of inspection with the insufficient illumination
intensity caused by the fact that, the farther the distance from a region
to the optical axis of the detection optical system, the lower the MTF for
the region.
It is a still further object of the present invention to provide a defect
inspecting apparatus and a defect inspection method that are capable of
inspecting an area of inspection also for a defect caused by typically a
very small extraneous material having a size of about 0.1 .mu.m or smaller
with a high degree of sensitivity and at a high speed by effectively
utilizing the light quantity of a Gaussian optical beam emitted by an
ordinary low-cost light source and by solving the problem of an
insufficient illumination intensity in regions surrounding an area of
detection on a substrate serving as an object of inspection with the
insufficient illumination intensity caused by the fact that, the farther
the distance from a region to the optical axis of the detection optical
system, the lower the MTF for the region.
In order to achieve the objects described above, the present invention is
characterized in that, in an area with a minimum illumination intensity in
an illumination-intensity distribution within a radiation range, radiation
of a beam is implemented to give a maximum illumination intensity and the
S/N ratio of a signal representing a detected beam is maximized in order
to improve the detection sensitivity and to increase the throughput.
That is to say, the present invention is characterized in that, by
radiating a Gaussian optical beam to an area of detection on a substrate
serving as an object of inspection with the Gaussian optical beam shaped
to provide a maximum illumination intensity on the outermost circumference
(or the periphery) of the area of detection, the sensitivity (the S/N
ratio) on the outermost circumference in a detector can be increased and a
defect caused by typically a very small extraneous material existing in
the area of detection can be detected with a high degree of sensitivity
and at a high speed. It should be noted that, by a maximum illumination
intensity, an illumination intensity of about 60% of the illumination
intensity at the center of the area of detection is meant.
In addition, the present invention also provides a defect inspection method
and an apparatus adopting the method comprising the steps of:
using a radiation optical system including a radiation light source to
radiate a Gaussian light beam to an area of detection on a substrate
serving as an object of inspection and having a circuit pattern created
thereon wherein the Gaussian light beam is shaped to give an
illumination-intensity distribution of a Gaussian distribution having a
standard deviation about equal to the distance from the optical axis of
the area of detection to the periphery of the area of detection;
using a detection optical system to form an optical image of the area of
detection on the substrate serving as an object of inspection by radiation
of the shaped Gaussian light beam to a photo-sensitive surface of a
detector corresponding to the area of detection;
detecting a picture signal corresponding to the area of detection and
originating from the detector; and
detecting a defect caused by typically an extraneous material existing in
the area of detection on the basis of the detected picture signal.
Furthermore, the present invention also provides a defect inspection method
and an apparatus adopting the method comprising the steps of:
using a radiation optical system to radiate a Gaussian light beam to an
area of detection on a substrate serving as an object of inspection and
having a circuit pattern created thereon wherein the Gaussian light beam
is shaped by adaptation of the diameter or the longitudinal length of the
beam to the distance between peripheries having the optical axis of the
area of detection as the center thereof so that the ratio of the
illumination intensity on the peripheries of the area of detection to the
illumination intensity at the center of the area of detection is in a
range of about 0.46 to about 0.73 or, ideally, in a range of about 0.54 to
about 0.67;
using a detection optical system to form an optical image of the area of
detection on the substrate serving as an object of inspection by radiation
of the shaped Gaussian light beam to a photo-sensitive surface of a
detector corresponding to the area of detection;
detecting a picture signal corresponding to the area of detection and
originating from the detector; and
detecting a defect caused by typically an extraneous material existing in
the area of detection on the basis of the detected picture signal.
Moreover, in the defect inspection method and the apparatus adopting the
method provided by the present invention, the Gaussian light beam has a
slit shape and the substrate serving as an object of inspection is moved
relatively to the Gaussian light beam with a slit shape in a direction
crossing the longitudinal direction of the Gaussian light beam.
Further, in the defect inspection method and the apparatus adopting the
method provided by the present invention, the detector is a TDI image
sensor.
In addition, in the defect inspection method and the apparatus adopting the
method provided by the present invention, the shaped Gaussian light beam
is radiated to the area of radiation on the substrate serving as an object
of inspection in a slanting direction with respect to the surface of the
area.
Furthermore, the present invention also provides a defect inspection method
and an apparatus adopting the method comprising the steps of:
using a radiation optical system to radiate a Gaussian light beam to an
area of detection on a substrate serving as an object of inspection and
having a circuit pattern created thereon wherein the Gaussian light beam
is shaped wherein the Gaussian light beam is shaped by adaptation of the
diameter or the longitudinal length of the beam to the distance between
peripheries having the optical axis of the area of detection as the center
thereof so that the ratio of the illumination intensity on the peripheries
of the area of detection to the illumination intensity at the center of
the area of detection is in a range of about 0.46 to about 0.73 or,
ideally, in a range of about 0.54 to about 0.67;
using a detection optical system to form an optical image of the area of
detection on the substrate serving as an object of inspection by radiation
of the shaped Gaussian light beam to a photo-sensitive surface of a
detector corresponding to the area of detection;
detecting a picture signal corresponding to the area of detection and
originating from the detector; and
detecting a defect caused by typically an extraneous material existing in
the area of detection on the basis of the detected picture signal.
Moreover, the present invention also provides a defect inspection method
and an apparatus adopting the method comprising the steps of:
using a radiation optical system to radiate a DUV beam to an area of
detection on a substrate serving as an object of inspection and having a
circuit pattern created thereon;
using a detection optical system to form an optical image of the area of
detection on the substrate serving as an object of inspection by radiation
of the shaped DUV beam on a DUV-light-sensitive surface of a TDI image
sensor corresponding to the area of detection;
detecting a picture signal corresponding to the area of detection and
originating from the TDI image sensor; and
detecting a defect caused by typically an extraneous material existing in
the area of detection on the basis of the detected picture signal.
Further, the present invention also provides a defect inspection method and
an apparatus adopting the method comprising the steps of:
using a radiation optical system to radiate a DUV beam to an area of
detection on a substrate serving as an object of inspection and having a
circuit pattern created thereon wherein the DUV beam is shaped to give an
illumination-intensity distribution of a Gaussian distribution having a
standard deviation about equal to the distance from the optical axis of
the area of detection to the periphery of the area of detection;
using a detection optical system to form an optical image of the area of
detection on the substrate serving as an object of inspection by radiation
of the shaped DUV beam on a DUV-light-sensitive surface of a TDI image
sensor corresponding to the area of detection;
detecting a picture signal corresponding to the area of detection and
originating from the TDI image sensor; and
detecting a defect caused by typically an extraneous material existing in
the area of detection on the basis of the detected picture signal.
According to a configuration described above, a problem of an insufficient
illumination intensity on the periphery of an area of detection on a
substrate serving as an object of inspection caused by the fact that, the
farther the distance from a region to the optical axis of the detection
optical system, the lower the MTF (Modulation Transfer Function) for the
region, is solved by effectively utilizing the light quantity of a
Gaussian light beam emitted by an ordinary low-cost light source, making
it possible to detect also a defect caused by typically a very small
extraneous material with a size in a range of about 0.1 .mu.m s to about
0.5 .mu.m or even a defect caused by typically a very small extraneous
material with a size smaller than 0.1 .mu.m with a high degree of
sensitivity and at a high speed.
In addition, according to configuration described above, an optical image
based on a DUV (Distant Ultra Violet) laser beam such as an excima laser
obtained from a substrate serving as an object of inspection can be
received by a TDI image sensor, making it possible to detect also a defect
caused by typically a very small extraneous material with a size in a
range of about 0.1 .mu.m to about 0.5 .mu.m or even a defect caused by
typically a very small extraneous material with a size smaller than 0.1
.mu.m.
Furthermore, according to a configuration described above, a problem of an
insufficient illumination intensity on the periphery of an area of
detection on a substrate serving as an object of inspection caused by the
fact that, the farther the distance from a region to the optical axis of
the detection optical system, the lower the MTF for the region, is solved
by effectively utilizing the light quantity of a beam emitted by a lamp
serving as a light source, making it possible to detect also a defect
caused by typically a very small extraneous material with a size of about
0.1 .mu.m or smaller in the area of detection with a high degree of
sensitivity and at a high speed. It should be noted that the detection is
moved from one area to another over the substrate serving as an object of
inspection.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the configuration of a fourth embodiment
implementing a defect inspecting apparatus provided by the present
invention in a simple and plain manner;
FIG. 2(a) is a diagram showing an embodiment implementing an illumination
optical system employed in the fourth embodiment implementing a defect
inspecting apparatus of FIG. 1 in concrete terms as seen from a position
on the y axis; and FIG. 2(b) is a diagram showing the same in concrete
terms as seen from a position on the x axis;
FIG. 3 is an explanatory diagram used for describing a basic concept of
shaping a slit-shaped Gaussian beam by means of an illumination optical
system to increase the illumination efficiency;
FIGS. 4(a) and 4(b) are explanatory diagrams used for describing an
image-pickup method to receive a light representing an optical image in an
area of detection on a substrate being inspected by using a TDI image
sensor as a detector;
FIG. 5 is a diagram showing variations in illumination f(x.sub.0) at a
periphery (x.sub.0 =1) of a detection area with changes in standard
deviation .sigma. (corresponding to the width of illumination) of a
Gaussian Beam;
FIG. 6 is a diagram showing variations in illumination f(x.sub.0) with
changes in distance x.sub.0 from the optical axis of a detection area for
a radiated Gaussian beam at standard deviations .sigma. of 0.5, 1 and 2;
FIG. 7 is a diagram showing the configuration of the second embodiment
implementing a defect inspecting apparatus provided by the present
invention in a simple and plain manner.
FIGS. 8(a) and 8(b) are explanatory diagrams used for describing an
embodiment implementing a TDI image sensor capable of receiving a DUV
light;
FIG. 9 is a diagram showing the configuration of an embodiment implementing
a signal processing system capable of inspecting an object by detection of
a signal generated by a defect caused by typically a very small extraneous
material with a size of about 0.1 .mu.m or smaller by discrimination of a
false-information signal;
FIG. 10 is a diagram showing the configuration of another embodiment
implementing the radiation optical system employed in the first embodiment
implementing the defect inspecting apparatus shown in FIG. 1;
FIG. 11 is an explanatory diagram showing a case in which the illumination
intensity on the periphery of an area of detection is increased by using
the radiation optical system shown in FIG. 10 to effectively utilize the
light quantity of a beam emitted by a lamp serving as a light source and
make use of the orientability of the beam emitted by the lamp serving as a
light source; and
FIG. 12 is a diagram showing an illumination distribution over an area of
detection obtained by using the radiation optical system shown in FIGS. 10
and 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Some preferred embodiments implementing a defect inspecting apparatus and
method provided by the present invention, are explained by referring to
diagrams as follows.
By the way, with semiconductor devices miniaturized more and more, a
further increase in yield is also required. To put it in detail, a circuit
pattern created on a semiconductor substrate such as a semiconductor wafer
for making such semiconductor devices is subjected to super
miniaturization with a design rule of 0.3 to 0.2 .mu.m or even smaller.
For this reason, a foreign particle existing on the semiconductor
substrate causes a semiconductor device created on the substrate to
operate abnormally even if the foreign particle is an infinitesimal
molecule with a size of about 0.1 .mu.m or smaller or a particle with a
size close to that at an atomic level.
In such a state of the art to fabricate a semiconductor device, the defect
inspecting apparatus provided by the present invention for detecting a
defect such as a foreign particle is required to have a capability of
inspecting a defect such as an infinitesimal foreign particle existing on
a semiconductor substrate such as a semiconductor wafer, on which a
circuit pattern undergoing a super-miniaturization by a design rule of 0.3
to 0.2 .mu.m or even smaller exists, with a high degree of sensitivity at
a high speed.
FIG. 1 is a diagram showing the first embodiment implementing a defect
inspecting apparatus provided by the present invention for detecting a
defect such as a foreign particle in a simple and plain manner. FIG. 2 is
a diagram showing an embodiment implementing an illumination optical
system employed in the defect inspecting apparatus.
As shown in FIG. 1, the defect inspecting apparatus for detecting a defect
such as a foreign particle comprises: stage 201 for mounting an inspection
object 1 such as a semiconductor device or a semiconductor wafer on which
a super-miniaturized circuit pattern with a defect thereof to be detected
has been created; an illumination-light source 101 implemented by a
laser-beam source such as a semiconductor laser, an argon laser, a YAG-SHG
laser or an excima laser; an illumination optical system 102 for radiating
a high-luminance light emitted by the illumination-light source (laser
source) 101 to an illumination area 2 on the inspection object 1 from a
slanting direction as a slit-shaped Gaussian beam 107 having a
illumination distribution close to the Gaussian distribution as shown in
FIG. 3; a detection optical system 301 comprising an image formation lens
includes an objective lens which are used for forming an image from
reflection lights, or diffraction lights or scattered lights obtained by a
detection area 3; detector 302 each implemented typically by a TDI image
sensor or a CCD image sensor having a photo-sensitive surface
corresponding to the detection area 3; and an image-signal processing unit
401 for detecting a defect such as a foreign particle from an image signal
output by the detector 302.
It should be noted that the defect inspecting apparatus also has an
automatic focus control system for controlling formation of an image of
the surface of the inspection object 1 on the photo-sensitive surface of
the detector 302.
The detection optical system 301 may be formed of a spatial filter unit for
shielding diffraction light coming from repetitive patterns having a small
pitch formed on a substrate to be inspected, and Fourier transform lens as
described in Japanese Patent Laid-open Nos. Hei 6-258239 and Hei 6-324003.
The actual configuration of the illumination-light optical source 101 and
the illumination optical system 102 is shown in FIG. 2. In the figure,
reference numeral 103 denotes a concave or convex lens for enlarging the
diameter of a laser beam 106 emitted by the illumination-light source 101.
Reference numeral 104 denotes a collimate lens for converting a laser beam
output by the concave or convex lens 103 with an expanding diameter into
substantially parallel beams. Reference numeral 105 denotes a cylindrical
lens with a conical surface for converging the substantially parallel
beams obtained as a result of the conversion in the collimate lens 104 in
the direction of the y axis and for radiating the converged beams to an
illumination area 2 on the inspection object 1 as a slit-shaped Gaussian
beam 107 having an illumination distribution close to the Gaussian
distribution as shown in FIG. 3. The cylindrical lens 105 serves as an
optical system having a converging function in the direction of the y
axis.
It should be noted that the concave or convex lens 103 and the collimate
lens 104 constitute a beam expander for enlarging the diameter of the
laser beam 106. Thus, the illumination optical system 102 can be regarded
as a system comprising the beam expander, the cylindrical lens 105 and a
mirror as described in Japanese Patent Laid-open Nos. Hei 6-258239 and Hei
6-324003. The beam expander typically comprises a collimate lens, a
concave lens and a receiver lens. As described above, the cylindrical lens
105 is used for converging the substantially parallel beams obtained as a
result of the conversion in the beam expander in the direction of the y
axis and for radiating the converged beams to an illumination area 2 on
the inspection object 1 as a slit-shaped Gaussian beam 107 having an
illumination distribution close to the Gaussian distribution as shown in
FIG. 3. The mirror reflects the slit-shaped Gaussian beam 107 output by
the cylindrical lens 105 and radiates the beam 107 to the inspection
object 1 in a slanting direction.
By the way, by changing the distance b between the concave or convex lens
103 and the collimate lens 104 or the distance between the concave lens
and the receiver lens in the configuration described above, the
x-direction width of the luminance beam having an illumination
distribution substantially resembling the Gaussian distribution can be
altered. That is to say, by adjusting the beam expander, the x-direction
length Lx of the illumination area 2 (or the slit-shaped beam 107) having
an illumination distribution substantially resembling the Gaussian
distribution can be changed. In addition, by varying the distance between
the conical lens 104 and the inspection object 1, the y-direction length
Ly of the illumination area 2 (or the slit-shaped beam 107) having an
illumination distribution substantially resembling the Gaussian
distribution can also be changed.
A detection area 3 shown in FIG. 3 is an area on the inspection object 1 to
be inspected by using a TDI image sensor or a CCD image sensor. In the
case of a TDI image sensor, for example, the dimensions of each pixel are
typically 27 .mu.m.times.27 .mu.m. The TDI image sensor is typically a
64.times.4,096 CCD image-pickup sensor which comprises 64 rows in the TDI
(Time Delay Integration) direction and 4,096 columns in the MUX direction,
and operates in a TDI mode. That is to say, the TDI image sensors 302a has
a configuration comprising n stages of line sensors as shown in FIG. 4
where n is typically 64. A line rate rt is the amount of information
output by the sensor which is the line sensors in this case. At a line
rate rt, accumulated charge is transferred through lines 1, 2 and so on,
from one line to another. By synchronizing the movement speed of the
y-axis stage 201 for moving the inspection object 1 in the direction of
the y axis with the line rate rt, an image 6 based on a scattered light
and a diffraction light generated by typically an infinitesimal foreign
particle 5 is accumulated for a long time it takes to transfer the charge
to the line n so that a defect such as an infinitesimal foreign particle
can be detected with a high degree of sensitivity. In this image sensor,
the image of a defect such as an infinitesimal foreign particle is
detected as a sum of intensities of a scattered light and a diffraction
light traveling from the line 1 to the line n. However, a scattered light
or a diffraction light coming from the same point on the object of
inspection and reaching the lines is timewise entirely incoherent.
As described above, a beam emitted by the illumination-light source 101 is
converted by the illumination optical system (or the radiation optical
system) 102 into a slit-shaped Gaussian beam 107 which is radiated to the
surface of the inspected substrate 1 on the stage 201 typically in a
slanting direction to form an illumination area 2 on the surface. While
the inspected substrate 1 is being moved in the direction of the y axis by
moving the stage 201 in the direction of the y axis, the detector 302a
implemented typically by a TDI image sensor transfers electric charge
accumulated in each pixel from one line to another at a line rate rt
synchronized with the movement speed of the stage 201. In this way, while
an optical image of the detection area 3 on the inspected substrate 1
formed by the detection optical system 301 is being picked up, each pixel
(or each device) along the width H of the detection area 3 is scanned to
generate a detection signal which is then supplied to the image-signal
processing unit 401. By processing the detection signal in the
image-signal processing unit 401, it is possible to detect a defect such
as an infinitesimal foreign particle existing in the detection area 3 with
a high degree of sensitivity and at a high speed.
By using the TDI image sensor 302a as described above, it is possible to
compute a total of illumination values of a scattered light or a
diffraction light generated by a defect such as an infinitesimal foreign
particle where (quantity of light=illumination value.times.time) and,
hence, to increase the sensitivity. In addition, once the slit-shaped beam
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