U.S. patent application number 12/783318 was filed with the patent office on 2010-09-09 for surface inspection with variable digital filtering.
This patent application is currently assigned to Hitachi High-Technologies Corporation. Invention is credited to Takahiro Jingu, Kazuo Takahashi.
Application Number | 20100225907 12/783318 |
Document ID | / |
Family ID | 38987428 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100225907 |
Kind Code |
A1 |
Takahashi; Kazuo ; et
al. |
September 9, 2010 |
SURFACE INSPECTION WITH VARIABLE DIGITAL FILTERING
Abstract
A semiconductor wafer, which is an inspection object, is stuck
by vacuum on a chuck and this chuck is mounted on an inspection
object movement stage consisting of a rotational stage and a
translational stage, located on a Z-stage. The rotational stage
provides a rotational movement and the translational stage provides
a translational movement. And when a foreign particle or a defect
on an inspection object surface is detected, the parameter of
digital filtering is dynamically changed during inspection, and the
foreign particle or the defect is differentiated using the result
after removing a low frequency fluctuation component to be a noise
component.
Inventors: |
Takahashi; Kazuo; (Ninomiya,
JP) ; Jingu; Takahiro; (Takasaki, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
Hitachi High-Technologies
Corporation
Tokyo
JP
|
Family ID: |
38987428 |
Appl. No.: |
12/783318 |
Filed: |
May 19, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11878197 |
Jul 23, 2007 |
|
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12783318 |
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Current U.S.
Class: |
356/237.5 |
Current CPC
Class: |
G01N 21/8851 20130101;
G01N 21/956 20130101 |
Class at
Publication: |
356/237.5 |
International
Class: |
G01N 21/17 20060101
G01N021/17 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2006 |
JP |
2006-207342 |
Claims
1. A surface inspection apparatus for detecting a foreign particle
or a defect present on an inspection object surface or inside the
proximity of the surface, comprising: an inspection object movement
stage having a rotational movement unit and a translational
movement unit configured so as to be able to scan said inspection
object at an approximately constant rotational angular speed; a
laser beam source; an illumination unit irradiating an laser beam
emitted from said laser beam source on an illumination spot of a
predetermined size on the inspection object surface; a
scattered/diffracted/reflected light detection unit, wherein an
irradiating light detects a scattered/diffracted/reflected light at
said illumination spot and converts to an electric signal; an A/D
converter for conversion of said electric signal into digital data;
a particle diameter calculation device for calculating a size of
the foreign particle or the defect from the digital data obtained
by said A/D conversion; wherein said A/D conversion unit executes
sampling of said electric signal at approximately constant sampling
time intervals, and said particle diameter calculation device
executes detection of the foreign particle/defect by using a result
of a removal treatment of an undesired low frequency fluctuation
component on the digital data obtained by said A/D converter.
2-18. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for inspecting a
foreign particle or a defect and the like present on a surface of
an inspection object, and an apparatus for inspecting the foreign
particle, the defect or the like.
[0002] In a surface inspection, for example, a circuit is formed by
pattern transfer on a bare-wafer and following etching, in a
manufacturing process for a semiconductor device. In various
manufacturing processes of a semiconductor device for forming a
circuit, a foreign particle or a defect and the like attached on a
bare-wafer surface accounts for a significant factor of lowering a
yield. A foreign particle or a defect attached on a wafer surface
is controlled in each step of manufacturing processes, and an
apparatus to detect a foreign particle attached on a bare-wafer
surface or a defect present on a wafer surface and the like with
high sensitivity and high throughput, is a wafer surface inspection
apparatus.
[0003] Methods to detect a foreign particle or a defect on a wafer
surface are mainly classified into methods using a charged particle
beam of an electron beam or the like and methods using a light
beam, and the methods using a light beam include a method to take
an image of a wafer surface by using a camera and analyze image
information and a method to detect a scattered light on a wafer
surface by a light receiving element like a photoelectron
multiplier tube and analyze the extent of light scattering. The
latter includes JP-A-63-143830.
[0004] In a surface detection apparatus of a method in which a
laser beam is irradiated on a wafer, generally a laser beam is
irradiated on a wafer surface and a scattered light generated from
a foreign particle by the irradiation, is detected by a detector
and A/D-converted, and then the size of a foreign particle/defect
is calculated from digital data obtained after A/D conversion. To
attain high throughput of inspection, a method is adopted that an
inspection table, where a work (a wafer) is mounted, is rotated at
high speed, and a stage where the inspection table is horizontally
mounted in uniaxial direction, is scanned. Based on size
information on a foreign particle/defect and coordinate information
from the stage, a foreign particle/defect map on an entire surface
of the work is calculated.
[0005] Aside from a signal generated from a foreign particle/defect
of a detection object, reflected light from an inspection object
includes a low frequency fluctuation component depending on surface
condition, film type or film thickness, and surface roughness. In
addition, influenced by vibration or the like from an inspection
object movement unit, a low frequency component is generated. This
low frequency component is not constant, because it is decided by
parameters consisting of a size of illumination light, a speed of
the inspection object movement unit and movement position.
[0006] Conventionally, though the frequency component was removed
or controlled by an analogue filter, since it is difficult for a
Cut-off frequency setting to be flexibly varied as being determined
by a circuit constant, it was difficult to respond to each of the
conditions described above.
[0007] In addition, considering distortion of a passing signal,
since a passing signal band is required to have a margin, it was
hard to have an attenuation frequency band sufficiently wide, and
it was difficult for the low frequency component to be removed or
controlled accurately.
[0008] Accordingly, since a detection determination threshold level
has to be raised by the degree of the low frequency fluctuation
component remaining after passing the analogue filter, there
remained a problem that detection sensitivity was deteriorated by
this degree.
[0009] In addition, depending on surface condition, film type or
film thickness, and surface roughness, reflected light generated
from a foreign particle/defect varies itself, therefore there was a
problem that it was difficult to respond only with a fixed
threshold.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide a surface
inspection apparatus and a surface inspection method enabling to
respond to a wide variety of wafers with a different kind of film
type, film thickness, surface roughness and crystal orientation or
the like.
[0011] In addition, another object of the present invention is to
provide a surface inspection apparatus and a surface inspection
method enabling to reduce the influence received from an inspection
object movement unit of the inspection apparatus itself, and
enhance the accuracy of detection determination.
[0012] According to one embodiment of the present invention, in
digital filtering of a signal obtained by a surface inspection, at
least one parameter for the digital filtering is dynamically varied
during inspection.
[0013] According to another embodiment of the present invention, in
digital filtering of a signal obtained by a surface inspection, at
least one parameter for the digital filtering is controlled in
response to a radius of an inspection object.
[0014] According to still another embodiment of the present
invention, a surface inspection apparatus for detecting a foreign
particle or a defect present on an inspection object surface or
inside the proximity of the surface is configured so as to detect a
foreign particle/defect by using results obtained by a removing
treatment of an undesired low frequency fluctuation component.
[0015] It is desirable that the removing treatment of the undesired
low frequency fluctuation component be accomplished by a digital
filtering treatment of plurality of digital data obtained from a
signal received at the surface inspection.
[0016] It is desirable that the digital filtering treatment be a
frequency band limitation filtering treatment which removes the
undesired low frequency fluctuation component.
[0017] It is desirable that the frequency band limitation filtering
treatment be a low-pass filtering treatment which extracts the
undesired low frequency fluctuation component and be configured so
as to subtract the result of the low-pass filtering treatment from
the digital data.
[0018] It is desirable that the frequency band limitation filtering
treatment be a high-pass filtering treatment or a band-pass
filtering treatment which removes the undesired low frequency
fluctuation component.
[0019] In addition, it is desirable that the Cut-off frequency of
the digital filtering treatment be variable.
[0020] In addition, it is desirable that the Cut-off frequency of
the frequency band limitation filtering treatment be determined
based on any one or a combination of plurality of (1) a main
scanning rotational speed of an inspection object movement stage,
(2) coordinate position in the sub-scanning direction obtained by
the above coordinate detection unit (3) a size of an illumination
spot, and be set every time when a condition varies.
[0021] In addition, when the above particle diameter calculation
device determines the Cut-off frequency of the frequency band
limitation filtering treatment, it is desirable to use further any
one or a combination of plurality of (1) type or thickness of film
formed (2) surface roughness (3) crystal orientation (4) warpage
amount, on an inspection object surface.
[0022] According to the present invention, even in the case of
different surface conditions of an inspection object, as it is
possible to reduce the low frequency component of the reflected
light, it is not necessary to raise a detection determination
threshold level, therefore a weak signal can be detected and an
inspection object can be accurately measured.
[0023] Alternatively, because reduction of the low frequency
component of the reflected light is enabled in each condition of a
size of illumination light, a speed of an inspection object
movement unit or movement position, a proper threshold can be
set.
[0024] Alternatively, even in the case that surface condition of an
inspection object differs depending on film type or film thickness,
surface roughness, inspection can be executed with the same
performance as in the case of a standard wafer.
[0025] Alternatively, because of no signal distortion caused by
analogue filtering, a passing signal has no distortion and it is
possible to narrow passing band width and further to obtain
symmetric attenuation property in both bands, therefore, an
accurate inspection can be accomplished.
[0026] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a schematic configuration according to one
embodiment of the present invention.
[0028] FIG. 2A shows a side view of an illumination spot according
to one embodiment of the present invention.
[0029] FIG. 2B shows a plan view of an illumination spot according
to one embodiment of the present invention.
[0030] FIG. 3 shows scanning according to one embodiment of the
present invention.
[0031] FIG. 4 shows the difference (the signal width difference) of
a foreign particle/defect signal caused by the scanning position
difference according to one embodiment of the present invention
[0032] FIG. 5 shows a foreign particle/defect signal and a
threshold according to one embodiment of the present invention.
DESCRIPTION OF THE INVENTION
[0033] Although the following description will be made below on
embodiments of the present invention using the accompanying
drawings, the apparatus and the method according to the present
invention are not limited to the configurations shown in each
drawing and various changes and modifications may be made within
the spirit of the invention.
[0034] FIG. 1 shows first embodiment of a foreign particle/defect
inspection apparatus using a foreign particle/defect detection
method according to the present invention. The semiconductor wafer
100, which is an inspection object, is stuck fast to the chuck 101
by vacuum and this chuck 101 is mounted on the Z-stage 105 via the
inspection object movement stage 102 configured with a rotational
movement unit, which is capable of scanning with a nearly constant
rotational angle speed, consisting of the rotational stage 103, and
a translational movement unit consisting of the translational stage
104. The rotational movement .theta. is carried out on the
rotational stage 103 and the translational movement r is carried
out on the translational stage 104.
[0035] FIGS. 2A and 2B are a plan view and a side view showing the
illumination/detection optical system 110 located above the
semiconductor wafer 100. An illumination unit according to the
present embodiment uses a laser light source as the light source
200 of an illumination light. The irradiating light 201 consisting
of a laser light shot from the light source 200 enters into the
irradiating lens 202 and the illumination spot 203 with a
predetermined size is formed. The irradiating light 201 is, for
example, P polarization, and is configured so as to enter obliquely
with approximately Brewster's angle to crystal Si, on a surface of
the semiconductor wafer 100, which is an inspection object.
Therefore, the illumination spot 203 is substantially oval-shaped,
and the inside area of a contour line where illuminance comes down
to 1/e.sup.2 (e: base of natural logarithm) of that at the center
of the illumination spot 203, is defined anew as the illumination
spot.
[0036] The width 204 in the long axis direction of the illumination
spot 203 is described as d1 and the width 209 in the short axis
direction of the same is described as d2. With the illumination
spot 203, .theta.-scanning 208 is executed as indicated by the
dotted arrow in FIG. 2B.
[0037] As shown in FIG. 3, by changing and combining with time the
rotational movement 8 and the translational movement r, the
inspection object movement stage 102 causes relatively the
illumination spot 203 to scan spirally on the approximately whole
surface of the semiconductor wafer 100. While the rotation stage
rotates one turn, scanning moves as much as the distance .DELTA.r.
When .DELTA.r>d1, because an illumination light is not radiated
on the semiconductor wafer 100 in spiral scanning and gap area not
to be inspected is formed, normally a setting of .DELTA.r<d1 is
used. Although, in the present embodiment, scanning of the
illumination spot 203 is executed from the inner periphery toward
the outer periphery of the semiconductor wafer 100, the reverse
scanning direction is acceptable.
[0038] In addition, in the embodiment, in the approximately whole
area from the inner periphery toward the outer periphery of the
semiconductor wafer 100, the rotational stage 103 is driven at a
approximately constant angular speed and the translational stage
104 is driven nearly at a constant linear speed. FIG. 4 shows, as a
result of the above, the relative movement linear speed of the
illumination spot 203 to the surface of the semiconductor wafer
100, becomes larger at the outer periphery area compared with that
at the inner periphery area.
[0039] On the inspection object movement stage 102, the inspection
coordinate detection device 106 is provided in order to detect the
main-scanning coordinate position .theta. and the sub-scanning
coordinate position r. Although, in the present embodiment, as a
means of obtaining position information, a rotary encoder (primary
position acquisition section) of an optical scanning type is used
to detect the main-scanning coordinate position .theta., and a
linear encoder (secondary position acquisition section) of an
optical scanning type is used to detect the sub-scanning coordinate
position r, instead of both encoders, other type detectors with a
different detection principle may be used as long as a sensor
capable of detecting an angle or a position on a straight line with
high accuracy is used.
[0040] The collecting lens 205 is configured so as to collect a
scattered light with a low elevation angle in order to collect
efficiently the scattered light even from a minute foreign particle
which follows Rayleigh scattering. In this configuration, the
scattered light from the foreign particle/defect 206 passes the
collecting lens 205 and is detected by a light detection unit
consisting of the light detector 207. The light detector 207, which
detected the scattered light, converts the scattered light to an
electric signal (an inspection signal) and outputs as a scattered
light signal. Although, in the present embodiment, a photoelectron
multiplier tube is used as the light detector 207, other light
detectors with different detection principles may be used as long
as the light detector can detect a scattered light from a foreign
particle with high sensitivity.
[0041] As described above, in the present embodiment, in the
approximately whole area from the inner periphery toward the outer
periphery of the semiconductor wafer 100, the rotational stage 103
is driven at an approximately constant angular speed, and the
relative movement linear speed of the illumination spot 203 to the
surface of the semiconductor wafer 100 becomes bigger at the outer
periphery compared with that at the inner periphery. Therefore, a
time period while a foreign particle on the semiconductor wafer 100
crosses the short axis 209 and the width d2 of the illumination
spot 203, is smaller in the case where the foreign particle is
present in an outer periphery area of the semiconductor wafer 100
compared with that in the case where present in an inner periphery
area. Therefore, as shown in FIG. 4, time-varying wave form of a
signal intensity of the scattered light signal obtained by the
light detector 207 via the amplifier 111 has generally the smaller
half bandwidth of signal peak, in the outer periphery area, that
is, in the case where the foreign particle is present in the larger
radius area of the scanning direction.
[0042] Then, a signal treatment according to the present embodiment
will be explained below. After the scattered light signal, which is
converted to an electric signal (an inspection signal) by the light
detector 207, is amplified by the amplifier 111, the scattered
light signal is sampled every sampling time interval .DELTA.T
predetermined by A/D conversion unit consisting of A/D converter
112, and converted to digital data. The sampling time interval
.DELTA.T is determined so as to be able to sample the signal wave
form shown in FIG. 4 with sufficient time resolution. For example,
when the half bandwidth in the most outer periphery area having the
minimum signal wave form width as shown in FIG. 4, is described as
.DELTA.Sout, .DELTA.T is determined as .DELTA.T=.DELTA.Sout/10. By
this sampling, a group of time series digital data corresponding to
the signal wave form shown in FIG. 4. are obtained.
[0043] Incidentally, the group of time series digital data includes
the signal component 500 of low frequency as shown in FIG. 5 in
addition to intensity information of the scattered light
corresponding to a size of the detected foreign particle/defect,
which is essentially needed. Generally, the signal component of low
frequency does not become a fixed value because it varies depending
on a main scanning rotational speed of the inspection object
movement stage, coordinate information in the scanning direction
obtained by the coordinate detection unit, the size of the
illumination spot, and further, type or thickness of film formed,
surface roughness, crystal orientation and warpage amount on the
inspection object surface. Therefore, in order to calculate
correctly a size of the foreign particle/defect, it is necessary to
remove the influence from the low frequency component.
[0044] Consequently in the present embodiment, toward the digital
data from the A/D converter 112, the data of only the low frequency
component is generated by the variable low-pass filter 114
treatment as one example of digital filtering, followed by
subtraction by the subtracter 115 from data obtained by the A/D
converter 112 (digital filtering section) and only the intensity
information of the scattered light corresponding to the size of the
foreign particle/defect is extracted.
[0045] Here, the Cut-off frequency which is one example of a
parameter of the variable low-pass filter 114, is dynamically
controlled by the calculator 116 (parameter changing section),
based on the information including rotational speed of an
inspection object movement stage, coordinate position in the
scanning direction obtained by the coordinate detection unit, size
of the illumination spot, further, type or thickness of film
formed, surface roughness, crystal orientation and warpage amount
on the inspection object surface. The calculation parameter of this
calculator is based on information from the inspection coordinate
detection device 106 and the upper CPU 107.
Cut-off frequency=1/(short radius of illumination spot/rotational
speed/(2*circle ratio*radius coordinate position))/A
"A" is specified from film type, film thickness, surface roughness,
crystal orientation and warpage amount.
[0046] Film type, film thickness, surface roughness, crystal
orientation and warpage amount are set by a user via an input unit
not shown, and calculated in an inspection apparatus. As this input
unit, a pointing device such as a keyboard or a mouse may be used.
In addition, an independent memory in which necessary information
described above is stored, may be input into the inspection
apparatus via an interface not shown.
[0047] The scattered light intensity value obtained as a result of
the data processing, is compared with the predetermined detection
threshold in the foreign particle/defect determination device 108,
and the foreign particle/defect determination device 108 generates
foreign particle/defect determination information if the scattered
light intensity value is not less than the threshold. When the
foreign particle/defect determination information is generated, the
foreign particle/defect coordinate detection device 109 calculates
the coordinate position of the detected foreign particle/defect
based on information from the inspection coordinate detection
device 106. In addition, the particle diameter calculation device
117 calculates the size of the foreign particle/defect detected
from the scattered light intensity value.
[0048] In this manner, in the present embodiment, toward the signal
obtained by the amplifier 111, after removing the influence of the
low frequency component by the variable low-pass filtering
treatment, the size of the foreign particle/defect is calculated.
By execution of parameter changing treatment where parameter of
this digital filtering is varied dynamically during inspection, as
shown in FIG. 5, even in the case of superposition 501 of the
foreign particle/defect signal on the low frequency component, the
low frequency component removal 502 causes the foreign
particle/defect signal to be the detection signal 506 after the
present embodiment, and since the offset by the extent of the
signal component 500 of the low frequency wave is not necessary
like the conventional threshold 504 and can be used as the
threshold 505 after the present embodiment, the foreign
particle/defect signal 503 which has not been detected
conventionally, can be properly detected.
[0049] Although, in the present embodiment, after the undesired low
frequency fluctuation component is extracted by the low-pass
filtering treatment, the subtraction thereof from the original data
provides the removal of the low frequency fluctuation component,
the configuration is obviously accepted where a high-pass filtering
treatment or a band pass filtering treatment in which the low
frequency fluctuation component is removed directly.
[0050] The result of the surface inspection is output from an
output unit not shown. As the output unit, a printing unit such as
a display unit or a printer and the like, may be used. In addition,
result information may be stored in a memory built in the
inspection apparatus via an interface not shown. Alternatively, the
result information may be stored in an independent memory via an
interface not shown.
[0051] It should be noted that, according to the present
embodiment, although foreign particles/defects on the inspection
surface are differentiated by the electric signal (inspection
signal) based on the scattered light, it is not limited to this
method, furthermore, by providing a light detecting unit where a
diffracted light or a reflected light, which is emitted by the
irradiating light from the inspection object, is detected and
converted to an electric signal (inspection signal),
differentiation of foreign particles/defects can be accomplished by
the electric signal (inspection signal).
[0052] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *