U.S. patent application number 11/827522 was filed with the patent office on 2007-11-08 for method and apparatus for inspecting particles or defects of a semiconductor device.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Akira Hamamatsu, Takahiro Jingu, Hidetoshi Nishiyama, Minori Noguchi, Yoshimasa Ooshima, Kenji Watanabe, Tetsuya Watanabe.
Application Number | 20070257214 11/827522 |
Document ID | / |
Family ID | 18774962 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070257214 |
Kind Code |
A1 |
Nishiyama; Hidetoshi ; et
al. |
November 8, 2007 |
Method and apparatus for inspecting particles or defects of a
semiconductor device
Abstract
Conventionally, a particle/defect inspection apparatus outputs a
total number of detected particles/defects as the result of
detection. For taking countermeasures to failures in manufacturing
processes, the particles/defects detected by the inspection
apparatus are analyzed. Since the inspection apparatus outputs a
large number of detected particles/defects, an immense time is
required for analyzing the detected particles/defects, resulting in
a delay in taking countermeasures to a failure in the manufacturing
processes. In the present invention, an apparatus for optically
inspecting particles or defects relates a particle or defect size
to a cause of failure in an inspection result. A data processing
circuit points out a cause of failure from the statistics on the
inspection result, and displays information on the inspection
result. A failure analysis is conducted by setting a threshold for
identifying a failure in each of regions on a semiconductor device
or the like to statistically evaluate detected particles.
Inventors: |
Nishiyama; Hidetoshi;
(Fujisawa, JP) ; Noguchi; Minori; (Mitsukaidou,
JP) ; Ooshima; Yoshimasa; (Yokohama, JP) ;
Hamamatsu; Akira; (Yokohama, JP) ; Watanabe;
Kenji; (Ohume, JP) ; Watanabe; Tetsuya;
(Honzyo, JP) ; Jingu; Takahiro; (Takasaki,
JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
Hitachi High-Technologies Corporation
Tokyo
JP
|
Family ID: |
18774962 |
Appl. No.: |
11/827522 |
Filed: |
July 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11516344 |
Sep 5, 2006 |
7256412 |
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11827522 |
Jul 11, 2007 |
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11302847 |
Dec 13, 2005 |
7115892 |
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11516344 |
Sep 5, 2006 |
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10933977 |
Sep 3, 2004 |
6998630 |
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11302847 |
Dec 13, 2005 |
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09931997 |
Aug 17, 2001 |
6797975 |
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10933977 |
Sep 3, 2004 |
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Current U.S.
Class: |
250/559.41 |
Current CPC
Class: |
G01N 21/8806 20130101;
G01N 21/9501 20130101; G01N 21/94 20130101; G01N 2015/1493
20130101; G01N 21/4738 20130101; G01N 2015/1486 20130101; G01N
21/93 20130101 |
Class at
Publication: |
250/559.41 |
International
Class: |
G01N 21/88 20060101
G01N021/88 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2000 |
JP |
2000-291952 |
Claims
1. An apparatus for inspecting particles or defects comprising:
illuminating means for irradiating light to an object under
inspection; light detecting means for detecting reflected light or
scattered light from the object under inspection; detecting means
for detecting particles or defects based on a signal detected by
the light detecting means; dimension measuring means for processing
the signal to measure a size of each particle or defect; data
processing means for processing an inspection result; and display
means for displaying information on the inspection result, wherein
the data processing means relates a particle or defect size to a
cause of failure to estimate a cause of failure from statistical
processing on the inspection result, and the display means displays
information on the estimated cause of failure, wherein the data
processing means matches the particle or defect sizes measured by
the dimension measuring means with information on pass/fail of the
object under inspection acquired by an electric inspection to
calculate an influence of the particles or the defects on a yield,
and the display means displays a calculation result.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
inspecting particles or defects, and more particularly, to a method
and apparatus for inspecting particles or defects for use in
inspecting particles existing on thin film substrates,
semiconductor substrates, photomasks and so on, and pattern defects
encountered on patterns on such materials, and analyzing the cause
of the defects in the manufacturing of semiconductor chips and
liquid crystal products, wherein the method and apparatus of the
invention display an inspection result in such a form that enables
the user to readily analyze the result and rapidly identify the
cause of failure.
[0002] Conventionally, the technology for detecting defects on
semiconductor devices and so on using an optical measuring means
has been widely known. For example, "Semiconductor Wafer Inspection
Apparatus" described in JP-A-62-89336 discloses a technique for
irradiating a semiconductor substrate with a laser to detect
scattered light from particles, if attached on the semiconductor
substrate, and comparing the detected scattered light with the
result of an inspection, which has been made immediately before on
the same type of semiconductor substrate, to inspect the particles
or defects.
[0003] Also, "Method and Apparatus for Measuring Information on
Particle or Defect Size" described in JP-A-5-273110 discloses a
method of measuring sizes of particles or crystal defects, which
involves irradiating an object under inspection with a laser beam,
receiving scattered light from possible particles or crystal
defects on the object under inspection, and processing the
scattered light to generate an image of the object under inspection
on which the sizes of particles and crystal defects are
measured.
[0004] Also, "Yield Monitoring and Analysis in Semiconductor
Manufacturing" in prescripts of VLSI technology Seminar, pp.
4-42-4-47, in SEMICON Kansai, 1997, discloses an approach for
analyzing the yield from particles detected on a semiconductor
wafer.
[0005] Conventionally, as an approach for managing product
manufacturing processes in manufacturing lines for semiconductor
substrates, thin film substrates and so on, a management approach
is employed for monitoring particles and defects on substrates.
Such a monitoring method involves inspecting particles or pattern
defects on substrates by use of an apparatus for inspecting
particles or defects, monitoring a transition of the number of
particles or defects detected by the inspection apparatus, and
conducting a failure analysis on the particles or defects on
substrates, from which a large number of particles or defects have
been detected.
[0006] However, this prior art approach requires a total time for
the failure analysis equal to the product of the number of detected
particles/defects and a time required for the failure analysis on
one particle/defect. Particularly, the failure analysis requires a
prohibitively long time when the particle/defect inspection
apparatus detects a large number of particles or defects, thereby
giving rise to a problem that the manufacturing of substrates is
delayed.
SUMMARY OF THE INVENTION
[0007] The present invention has been made to solve the problem of
the prior art as mentioned above, and provides a method and
apparatus for inspecting particles or defects for use in inspection
and failure analysis on processes for manufacturing semiconductor
wafers and thin film substrates, which are capable of performing an
inspection in accordance with sizes of particles and pattern
defects or the characteristics of each region on an object under
inspection to take prompt countermeasures to a failure.
[0008] Specifically, the present invention provides a
particle/defect inspection apparatus for measuring an object under
inspection in accordance with an optical approach to detect
particles or defects thereon. The inspection apparatus includes
illuminating means for illuminating light to an object under
inspection, light detecting means for detecting reflected light or
scattered light from the object under inspection, detecting means
for detecting particles or defects based on a signal detected by
the light detecting means, dimension measuring means for processing
the signal detected by the light detecting means to measure the
size of each particle or defect, data processing means for
processing an inspection result, and display means for displaying
information on the inspection result, wherein the data processing
means relates a particle or defect size to a cause of failure to
point out the cause of failure from statistical processing on the
inspection result, and the display means displays information on
the inspection result.
[0009] The present invention also provides a particle/defect
inspecting method for measuring an object under inspection in
accordance with an optical approach to detect particles or defects
thereon. The inspecting method includes a procedure for
illuminating light to an object under inspection, a procedure for
detecting reflected light or scattered light from the object under
inspection, a procedure for detecting particles or defects based on
a detected signal, a procedure for processing the detected signal
to measure the size of each particle or defect, a data processing
procedure for processing an inspection result, and a procedure for
displaying information on the inspection result. The procedures are
executed in this order to relates a particle or defect size to a
cause of failure, wherein the data processing procedure points out
a cause of failure from statistical processing on the inspection
result to display information on the inspection result.
[0010] These and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block diagram generally illustrating the
configuration of an apparatus for inspecting particles or defects
according to the present invention;
[0012] FIG. 2 is a block diagram of the apparatus for inspecting
particles or defects according to the present invention when it is
operated as a component of a system;
[0013] FIG. 3A is a diagram showing image data when a particle
exists;
[0014] FIG. 3B is a three-dimensional graph showing a distribution
of signal strength when particle data is measured;
[0015] FIGS. 4A and 4B are three-dimensional graphs for comparing
distributions of two types of signal strengths;
[0016] FIG. 4C is a graph for explaining how a maximum is
calculated for the signal strength;
[0017] FIGS. 5A to 5C are graphs showing the relationship between
the particle size and the number of detected particles depending on
different causes of failure;
[0018] FIG. 6 is a graph showing the relationship between the
number of detected particles and the particle size;
[0019] FIG. 7 is a histogram showing the relation-ship between the
number of detected particles and the particle size;
[0020] FIGS. 8A and 8B are diagrams clearly illustrating particles
of a particular size on a wafer;
[0021] FIGS. 9A to 9C are graphs each showing in time series a
transition of the number of detected particles having a particular
size;
[0022] FIG. 10 is a front view of a screen which displays for the
user a cause of failure which results in the generation of
particles;
[0023] FIG. 11 is a plan view schematically illustrating regions on
a semiconductor wafer;
[0024] FIGS. 12A and 12B are plan views each clearly showing
particles of a particular size on a wafer when particle data is
managed separately for each region;
[0025] FIG. 13 is a graph (No. 1) showing the relationship between
the particle size and the number of detected particles in each of
regions;
[0026] FIG. 14 is a graph (No. 2) showing the relationship between
the particle size and the number of detected particles in each of
regions;
[0027] FIG. 15 is a graph for explaining the relationship between a
maximum of signal strength generated by the apparatus for
inspecting particles or defects according to the present invention
and the particle size;
[0028] FIG. 16 is a block diagram illustrating the apparatus for
inspecting particles or defects according to the present invention
which is operated as a system together with a review apparatus;
[0029] FIG. 17A is a three-dimensional graph showing a distribution
of a saturated signal strength;
[0030] FIG. 17B is a graph for explaining how a maximum is
calculated for the signal strength;
[0031] FIG. 17C is a plan view of a particle showing a major axis
and a minor axis of the particle;
[0032] FIG. 18A is a block diagram generally illustrating the
configuration of an inspection apparatus which has a function of
distinguishing particles from scratches;
[0033] FIG. 18B is a diagram for explaining a method of
distinguishing particles from scratches;
[0034] FIG. 19 is a block diagram illustrating a method of
calculating the particle size when using the method of
distinguishing particles from scratches;
[0035] FIG. 20 is a histogram showing the relation-ship between the
number of detected particles and the particle size for a plurality
of objects under inspection;
[0036] FIG. 21 is a histogram showing the relation-ship between the
number of detected particles/scratches and the particle/scratch
size separately for particles and scratches;
[0037] FIG. 22 is a front view of a display showing a method of
displaying detected particles of particular sizes in the apparatus
for inspecting particles or defects according to the present
invention;
[0038] FIG. 23 is a plan view of a wiring pattern for explaining
the relationship between the wiring pattern and a particle
size;
[0039] FIG. 24 is a graph showing the relationship between a
detection sensitivity and the influence of particles on a yield,
when the apparatus for inspecting particles or defects according to
the present invention is used;
[0040] FIG. 25 is a graph showing an example of calculating the
influence on the yield for each manufacturing step;
[0041] FIG. 26 is a graph showing the relationship between the
particle size and the number of detected particles when standard
particles are measured by the apparatus for inspecting particles or
defects according to the present invention;
[0042] FIG. 27 is a graph showing the relationship between the
particle size and the number of detected particles before
calibrating the sensitivity for the size of detectable particles in
the apparatus for inspecting particles or defects according to the
present invention;
[0043] FIG. 28 is a graph showing the relationship between particle
sizes measured by the inspection apparatus according to the present
invention and sizes measured by SEM when the sensitivity for the
size of detectable particles is calibrated in the apparatus for
inspecting particles or defects according to the present
invention;
[0044] FIG. 29 is a plan view of a wafer for explaining a method of
calculating the influence on the yield from the presence or absence
of particles;
[0045] FIGS. 30A and 30B are graphs showing correlations of
particle sizes measured by the apparatus for inspecting particles
or defects according to the present invention to particle sizes
measured by SEM, where FIG. 30A shows a correlation of particle
sizes measured on a wafer having a one-layer pattern to particle
sizes measured by SEM, and FIG. 30B is a graph showing a
correlation of particle sizes measured on a wafer having a
multi-layer pattern to particle sizes measured by SEM;
[0046] FIG. 31 includes a graph showing a correlation of particle
sizes measured by the apparatus for inspecting particles or defects
according to the present invention to particle sizes measured by
SEM, and SEM photographs of detected particles;
[0047] FIG. 32 is a histogram showing the relation-ship between
particle sizes and the number of the particles measured by the
apparatus for inspecting particles or defects according to the
present invention;
[0048] FIG. 33A is a graph showing the relationship between
particle sizes measured by the apparatus for inspecting particles
or defects according to the present invention, and the yield;
[0049] FIGS. 33B and 33C are plan views of wafers each showing a
distribution of detected particles on the wafer;
[0050] FIG. 34 is a graph showing an exemplary display of the
accumulated number of particles by size, using the apparatus of
inspecting particles or defects according to the present invention;
and
[0051] FIG. 35 is a graph showing the relationship between particle
sizes and the number of the particles measured by the apparatus for
inspecting particles or defects according to the present invention,
together with a distribution of the detected particles.
DESCRIPTION OF THE EMBODIMENTS
[0052] In the following, each of embodiments according to the
present invention will be described with reference to the
accompanying drawings.
[Configuration and Operation of Apparatus for Inspecting Particles
or Defects according to the Present Invention]
[0053] First, the configuration and operation of an apparatus for
inspecting particles or defects according to the present invention
will be described with reference to FIGS. 1 and 2.
[0054] FIG. 1 is a block diagram illustrating the configuration of
the apparatus for inspecting particles or defects according to the
present invention.
[0055] FIG. 2 is a block diagram of the apparatus for inspecting
particles or defects according to the present invention when it is
operated as a component of a system.
[0056] While the following description on the embodiment will be
made on an example in which a semiconductor wafer is inspected for
particles possibly attached thereon, the present invention can be
applied to an apparatus for inspecting pattern defects other than
particles. Also, the present invention is not limited to
semiconductor wafers but can be applied to thin film substrates,
photomasks, TFT, PDP and so on.
[0057] The apparatus for inspecting particles or defects according
to the present invention comprises an illumination optical system
101; a detection optical system 103; a light detector unit 104; a
signal processing circuit 105; a data display unit 106; a stage
assembly 107; an auto-focus illumination unit 108; and an
auto-focus light receiver unit 109.
[0058] For conducting an inspection, an object under inspection 102
is placed on the stage assembly 107 and irradiated by the
illumination optical system 101, and scattered light from the
object under inspection 102 is condensed by the detection optical
system 103. Then, the light detector unit 104 detects the scattered
light from the object under inspection 102. The scattered light
detected by the light detector unit 104 is opto-electrically
transduced, and processed by the signal processing circuit 105 to
detect particles and measure their sizes.
[0059] The object under inspection 102 is moved in the horizontal
direction by the stage assembly 107, and also moved in the vertical
direction by the auto-focus illumination unit 108 and auto-focus
light receiver unit 109 such that the object under inspection 102
is positioned at the focal point of the detection optical system
103. Thus, particles can be detected and their sizes be measured
over the entire area of the object under inspection 102. Then, the
result of detection is displayed on the data display unit 106.
[0060] Here, the illumination optical system 101 is configured to
irradiate the object under inspection 102 with light, for example,
from a laser light source such as Ar laser, semiconductor laser,
YAG laser and UV laser, or a white light source such as an Xe lamp
and Hg lamp, using a beam expander, a collimator lens, a
cylindrical lens or the like. The illumination optical system 101
is adjusted such that the light is irradiated at the focal point of
the detection optical system 103.
[0061] Here, for selecting an appropriate light source, a light
source having a short wavelength is preferred as the illumination
light source for improving the sensitivity for detecting particles,
so that a YAG laser, Ar laser and UV laser are suitable.
Alternatively, for reducing the size and cost of the apparatus, a
semiconductor laser is suitable. Further alternatively, a white
light source is suitable as the illumination light source for
reducing interference by an optically transparent thin film which
may be formed on an object under inspection.
[0062] As to the shape of irradiating light, a circular
illumination or a liner illumination may be used for irradiation.
The illumination light may be or may not be collimated light. For
increasing the amount of light on an object under inspection per
unit area, the power of the illumination light source may be
increased, or the illumination light may be illuminated with high
numerical aperture (NA).
[0063] Next, the detection optical system 103 has optical lenses
configured such that from the light emitted from the illumination
optical system 101, scattered light from the object under
inspection 102 is condensed on the light detector unit 104. Also,
the detection optical system 103 also has the ability to optically
process the scattered light, for example, make modification,
adjustment and so on to the optical characteristics of the
scattered light using a polarizer and a spatial filter.
[0064] When a polarizer is used for optical processing, the
polarizer is preferably set up in a direction in which P-polarized
light is transmitted when S-polarized light is irradiated. On the
other hand, the polarizer is preferably set up on a direction in
which S-polarized light is transmitted when P-polarized light is
irradiated. When a spatial filter is used, collimated light is
suitably used as the illumination light for improving the
performance of detecting particles.
[0065] The light detector unit 104 is used to receive the scattered
light condensed by the detection optical system 103 for
opto-electrically transducing the scattered light, and is
implemented, for example, by a TV camera, a CCD linear sensor, a
TDI sensor, an anti-blooming TDI sensor, and a photomultiplier.
[0066] For selecting a device for the light detector unit 104, a
photomultiplier is suitable in use for detecting feeble light.
Alternatively, a TV camera is suitable for rapidly capturing a
two-dimensional image. When the detection optical system 103
comprises a focusing system, a TV camera, a CCD linear sensor, a
TDI sensor, or an anti-blooming TDI sensor is suitable. When the
detection optical system 103 comprises a light condenser system, a
photomultiplier may be used. In addition, when the light detector
unit 104 receives light over a wide dynamic range, i.e., if the
sensor is saturated by incident light, the sensor may be
additionally provided with an anti-blooming function.
[0067] Next, the signal processing circuit 105 comprises a section
for detecting particles, and a section for measuring the size of a
particle. For detecting particles, the signal processing circuit
105, for example, binarizes an input signal, determines a signal
equal to or larger than a binarization threshold as a particle, and
outputs the result of determination. While the signal processing
circuit 105 also measures particle sizes, details on associated
processing will be described later. The stage assembly 107 in turn
has functions of, for example, moving the object under inspection
102 in the horizontal and vertical directions, and rotating the
object under inspection 102. The auto-focus illumination unit 108
converges light emitted, for example, from a white light source
such as an Hg lamp or a laser light source such as He--Ne onto the
object under inspection 102. Here, the wavelength of a light source
used in the auto-focus illumination unit 108 is preferably
different from that of a light source used in the illumination
optical system 101.
[0068] Next, the auto-focus light receiver unit 109 is a section
for receiving a portion of emitted from the auto-focus illumination
unit 108, which is reflected from the object under inspection 102,
and may comprise a sensor capable of detecting the position of
light, such as a position sensor. Information acquired by the
auto-focus light receiver unit 109 is sent to the stage assembly
107 for controlling the stage. While in the embodiment illustrated
in FIG. 1, the illumination optical system 101 illuminates the
object under inspection 102 from one direction, the illumination
optical system 101 may be configured to illuminate the object under
inspection 102 from two directions. Further, while the example of
FIG. 1 has one each of the detection optical system 103 and
detector unit 104 to detect the object under inspection 102 in one
direction, the inspection apparatus may comprise two or more sets
of these components such that the object under inspection 102 is
detected in two or more directions.
[0069] Next, FIG. 2 illustrates a system which is configured using
the apparatus for inspecting particles or defects according to the
present invention. Specifically, the system comprises the particle
inspection apparatus 1301 of the present invention; a data server
1302; a review apparatus 1303; an electric testing apparatus 1304;
an analyzer 1305; and a network 1306 for interconnecting the
respective components. In this system, the review apparatus 1303
is, for example, a measuring SEM; the electric testing apparatus
1304 is a tester; and the analyzer 1305 is an apparatus for
analyzing components of particles such as EDX. The data server 1302
is a computer which can collect and accumulate inspection data from
the particle inspection apparatus 1301; results of reviews from the
review apparatus 1303; results of tests from the electric testing
apparatus 1304; and results of analyses from the analyzer 1305. The
network 1306 is a communication network, for example, based on the
Ethernet.
[0070] Next described will be the operation of the system using the
apparatus for inspecting particles or defects. After an inspection
has been made in the particle inspection apparatus 1301, particles
for which appropriate countermeasures should be taken are selected
by a method as described above. Information on selected particles
is added to the result of inspection by the particle inspection
apparatus 1301, for example, serial numbers allocated to particles
when they were detected, information on the positions of particles,
information on the sizes of particles, and so on, and transmitted
to the data server 1302 through the network 1306. For adding the
information on the selected particles, for example, a flag may be
added to the result of detection to indicate whether or not
appropriate countermeasures are required. Then, for investigating
particles detected by the particle inspection apparatus 1301 in
greater detail, the object under testing is conveyed to the review
apparatus 1303. The object under testing may be manually conveyed
or mechanically conveyed.
[0071] After the object under testing has been conveyed to the
review apparatus 1303, the review apparatus 1303 accesses the data
server 1302 to receive the result of detection from the data server
1302 through the network 1306. Then, a review is started using the
received result of detection. In this event, the particles which
require countermeasures are preferentially reviewed, using the
information added by the particle inspection apparatus 1301,
thereby making it possible to rapidly analyze particles which can
cause a failure. Similarly, the analyzer 1305 can also analyze
preferentially the particles which require countermeasures based on
the information added by the particle inspection apparatus 1301,
thereby making it possible to rapidly advance an analysis on the
cause of a failure.
[0072] These review data and result of analysis may be accumulated
in the data server 1302, such that they are matched with results of
testing in the electric testing apparatus 1304 to confirm whether
or not a failure is eventually determined. If a failure is not
eventually identified, the data server 1302 transmits data for
changing the criteria for selecting particles which require
countermeasures to the particle inspection apparatus 1301, so that
the particle inspection apparatus 1301 changes the criteria for
determining whether or not countermeasures are required, thereby
making it possible to more accurately select particles which
require countermeasures and to readily take appropriate
countermeasures to a failure in the semi-conductor manufacturing
process.
[0073] While the foregoing description has been made for an example
in which data is transmitted and received through a network, the
transmission/reception of data need not be performed through a
network, but data may be delivered through a removable recording
medium or sheets of paper on which data are printed out.
[0074] Next described will be another manner of using the particle
inspection apparatus 1301 according to the present invention in
combination of the review apparatus 1303. FIG. 16 shows a portion
of FIG. 2 extracted therefrom. In FIG. 16, an inspection apparatus
1601 is, for example, the apparatus for inspecting particles or
defects of the present invention, and a review apparatus 1602, for
example, a measuring SEM, reviews particles or defects on an object
under inspection. Also, a network 1603 transmits/receives data
between the inspection apparatus 1601 and the review apparatus
1602, and is implemented, for example, by a system connected
through the Ethernet. Next, the operation will be described. It
should be noted that in the following description, particles are
taken as an example.
[0075] First, the inspection apparatus 1601 inspects particles on
an object under inspection, and adds, for example, serial numbers
allocated to particles when they are detected, information on
positions of particles, and information on sizes of particles to
the result of inspection. The resultant inspection data is
transmitted to the review apparatus 1602 through the network 1603.
After the object under inspection is conveyed to the review
apparatus 1602, the particles are reviewed in the review apparatus
1602. In this event, a scaling factor for reviewing in the review
apparatus may be adjusted in accordance with the information on the
particle sizes measured by the inspection apparatus 1602 to perform
an efficient reviewing operation. Specifically, when the particle
size information acquired from the inspection apparatus 1601 shows
a small particle, this particle is reviewed at a high scaling
factor, so that details on the small particle can be rapidly
observed. On the other hand, if the particle size information
indicates a large particle, this particle is reviewed at a low
scaling factor, so that the large particle can be reviewed without
extending off a review screen, thereby making it possible to
rapidly observe an entire image of the particle. For example, when
the inspection data transmitted from the inspection apparatus 1601
indicates a particle, the size of which is 0.1 .mu.m, this particle
is reviewed by adjusting the scaling factor such that the review
apparatus 1601 covers a field of view which spans 1 .mu.m. On the
other hand, when a particle has a size of 10 .mu.m, the scaling
factor is adjusted such that the review apparatus 1601 covers a
field of view which spans 100 .mu.m. In this way, the review
apparatus 1602 allows the user to efficiently review small
particles to large particles to rapidly analyze detected
particles.
[0076] This embodiment has been described for an example in which
particle size information is outputted from the inspection
apparatus 1601, and the scaling factor is adjusted in accordance
with the size information in the review apparatus 1602. As an
alternative method, information on the review scaling factor and
the field of view for reviewing in the review apparatus 1602 may be
added to the inspection data.
[0077] Also, this embodiment has been described for an example in
which a particle is reviewed in the field of view which spans an
area ten times wider than the size of the particle by adjusting the
review scaling factor for the review apparatus 1602. However, the
scaling factor may be any other value. Also, if the accuracy of
particle position information is known in the inspection apparatus
1601, a particle may be reviewed at a scaling factor based on the
particle size information in consideration of the accuracy of the
position information.
[0078] Further, while this embodiment has been described for an
example in which a particle is reviewed by the review apparatus
1602, the foregoing approach may be applied when a particle is
reviewed by the apparatus for inspecting particles or defects of
the present invention.
[Measurement of Size of Particle]
[0079] Next, description will be made on the processing for
measuring the size of a particle using the method and apparatus for
inspecting particles or defects according to the present
invention.
[0080] FIGS. 3A, 3B are a diagram showing image data when a
particle exists, and a diagram showing a distribution of signal
strength when particle data is measured.
[0081] FIGS. 4A to 4C are diagrams for comparing distributions of
two types of signal strengths, and an explanatory diagram for
showing how a maximum is calculated for the signal strength.
[0082] FIG. 3A shows an example of image processed by the signal
processing circuit 105 when a particle exists, where particle data
201 can be seen in a central portion of the image. The particle
data 201 is outputted from the light detector unit 104, and
captured by the signal processing circuit 105 as data having a
contrast value. FIG. 3B shows FIG. 3A in a three-dimensional
representation, where x- and y-axes are coordinate axes for
determining a position within the image, and z-axis represents the
signal strength. Signal strengths are plotted at corresponding
positions, and connected by lines. In FIG. 3B, a waveform 202
indicates waveform data of the particle data 201. This waveform 202
can be approximated to a Gaussian distribution from the nature of
the illumination optical system 101 and the detection optical
system 103, and the width and height of the Gaussian distribution
vary depending on the size of a particle on the object under
inspection 102. Further, the width and height of the distribution
also vary depending on the luminance of the laser illumination used
in the illumination optical system 101. Therefore, the shape of a
distribution and the amount of feature may have been previously
measured for a variety of standard particles using the inspection
apparatus of the present invention configured as described above,
such that the detected waveform 202 is compared with the results of
measurements made on the standard particles to acquire information
on the size of the detected particle.
[0083] A method of comparing the waveform 202 of the particle with
the waveforms of the standard particles may involve previously
measuring the total sum (integral) of the signal strengths in the
region occupied by the particle data 201, i.e., data on the volume
of the waveform 202, and comparing the volume data of the particle
data 201 with the volume data of the standard particles. However,
if the illumination optical system 101 differs in luminance when
the standard particles are measured and when particles on the
object under inspection are measured, the respective volume data
are divided by the luminances of the illumination optical system
101 for normalization, or the volume data of the particle data 201
or the standard particles is multiplied by the ratio of luminances
to correct the volume data.
[0084] As an alternative method of comparing waveforms, a maximum
signal strength value in the waveform 202 or the width of the
waveform 202 may be compared.
[0085] A method of calculating a maximum signal strength value will
be explained with reference to FIGS. 4A to 4C. FIGS. 4A, 4B show
exemplary waveforms of particle data, similar to the waveform 202.
Specifically, FIG. 4A shows an example in which a signal waveform
of particle data acquired by the light detector unit 104 is in the
shape of pinnacle having a peak, indicating that the signal does
not reach a saturation region of the light detector unit 104. FIG.
4B in turn shows an exemplary signal waveform of particle data
which presents a plateau shape at the peak, indicating that the
signal reaches the saturation region of the light detector unit 104
and does not include data exceeding the saturation region.
[0086] The maximum signal strength value is defined as the value
which is determined as maximum as a result of comparison between
signal strengths at respective pixels of the waveform, when
particle data draws a signal waveform as shown in FIG. 4A, i.e., a
signal strength at the peak point 301. On the other hand, when
particle data draws a signal waveform as shown in FIG. 4B, a
calculation is performed as described below to find a maximum
signal strength value.
[0087] First, in the saturation region 302, maximum lengths of the
saturation region are calculated in the x- and y-directions,
respectively. FIG. 4C shows a cross-section of FIG. 4B taken along
the maximum length region. In FIG. 4C, the horizontal axis is a
coordinate axis representing the position in the maximum length
region, while the vertical axis is a coordinate axis representing
the signal strength. The signal strength 303 indicates the
saturation level of the light detector unit 104. On this
cross-section, three or more unsaturated signals 304 are selected.
Here, description is made on the assumption that three points are
selected. As points to be selected, three points having the largest
signal strengths are selected from unsaturated signals on the
cross-section. Assuming that the three points are at coordinates
x1, x2, x3, and have signal strengths z1, z2, z3, respectively,
equations representing Gaussian distributions are derived using
unknown numbers k, .sigma., u:
z1=k/.sigma.exp(-(x1-u).sup.2/(2-.sigma..sup.2))
z2=k/.sigma.exp(-(x2-u).sup.2/(2.sigma..sup.2))
z3=k/.sigma.exp(-(x3-u).sup.2/(2.sigma..sup.2)) The unknown values
k, .sigma., u can be found by solving the simultaneous equations.
Then, the maximum signal strength value in FIG. 3B can be
calculated using the resulting values of k, .sigma. as follows:
k/.sigma.
[0088] It should be noted that although the example shown herein
uses the unknown value u for calculating the maximum signal
strength value, the unknown value U need not be used. In this case,
two points are selected from the unsaturated signals 304. Selected
signal points are those having the largest signal strengths from
unsaturated signals on the cross-section. Assuming that the two
points are at coordinates x1, x2, and have signal strengths z1, z2,
respectively, equations representing Gaussian distributions are
derived using unknown numbers k, .sigma.:
z1=k/.sigma.exp(-(x1).sup.2/(2.sigma..sup.2))
z2=k/.sigma.exp(-(x2).sup.2/(2.sigma..sup.2))
[0089] Since the unknown values k, a can be found by solving the
simultaneous equations, the maximum signal strength value in FIG.
3B can be calculated using the values of k, .sigma. as follows:
k/.sigma.
[0090] A particle size can be measured by comparing the maximum
signal strength value derived from the foregoing calculation for a
detected particle with those for the standard particles.
[0091] Next, another embodiment for calculating the maximum signal
strength value will be described with reference to FIG. 17.
[0092] FIGS. 17A to 17C are a graph showing a signal distribution
of particle data which presents a plateau shape at the peak; a
diagram showing the shape of the saturated signal portion; and an
explanatory diagram for explaining how the maximum signal strength
value is calculated. FIG. 17A shows the relationship between a
signal waveform 1701 and a peak region 1702, wherein the peak
region 1702 in the signal waveform 1701 does not include data
exceeding the saturated level since the peak region 1702 reaches
the saturation region of the light detector unit 104. FIG. 17B
shows a cross-section of the signal waveform 1701, where the
vertical axis represents the signal strength, and the horizontal
axis represents the pixel position in the signal. In FIG. 17B, a
saturation level 1703 indicates the saturation level of the light
detector unit 104, and a signal width 1704 indicates the width of
the peak region 1702. Also, a signal strength 1705 is a maximum
signal strength value which is generated when an unsaturable
detector is used for the light detector unit 104.
[0093] Next explained is a method of calculating the maximum signal
strength value 1705 from the saturated signal waveform 1701.
Assuming that the saturation level 1703 is represented by SL; the
signal width 1704 by SW, and the signal strength 1705 by PL, the
illustrated waveform is approximated to a Gaussian distribution to
derive the following equations:
SL=k/.sigma.exp(-(-SW/2).sup.2/(2.sigma..sup.2)) PL=k/.sigma. where
k is a coefficient, and .sigma. is a value calculated from the
configuration of the optical system in the apparatus for inspecting
particles and defects of the present invention.
[0094] Therefore, from the two equations, PL is calculated as
follows: PL=SL/exp(-(-SW/2).sup.2/(2.sigma..sup.2)) Here, since SL
indicates the output of the light detector unit 104 when it is
saturated, SL represents 255 gradation levels when an A/D converter
of the light detector unit 104 has a 8-bit resolution. .sigma. is
given a value from zero to one depending on the configuration of
the optical system. Next, a method of calculating SW will be
described. FIG. 17C shows the shape of the peak region 1702, in
other words, a region in which the light detector unit 104 is
saturated. FIG. 17C includes a saturation region 1706 and a signal
width 1704. Since the signal waveform 1701 is regarded as a
Gaussian distribution, the saturation region 1706 can be assumed to
be circular. Therefore, assuming that the signal width 1704 is
represented by SW, and the saturation region 1706 by SA, SW is
calculated by: SW=2 {square root over ((SA/.sigma.))} In the above
equation, (A) represents a calculation of a square root of A, and
.pi. is the Ludolphian number. The saturation region 1706 may be
comprised of the number of pixels in which the light detector unit
104 is saturated. Here, a saturated pixel may be represented by a
maximum of the output from the A/D converter of the light detector
unit 104, and may be set in consideration of electric noise in the
light detector unit 104. For example, when the A/D converter has an
8-bit resolution, the output represents a maximum of 255 gradation
levels. It may be thought that the output at 245th gradational
level or higher is saturated if electric noise accounts for 10
gradation levels.
[0095] If the signal waveform 1701 is not saturated, a similar
calculation may be performed using a maximum of the signal waveform
1701 as the saturation level 1703.
[0096] Since the maximum signal strength value can be calculated
from the foregoing process, the size of a detected particle can be
measured by comparing the values calculated using the standard
particles with a value calculated using the detected particle.
[0097] While the foregoing description has been made for the
maximum signal strength value as an example, the integral of signal
strength over particle data may be used instead of the maximum
signal strength value. In this case, the integral of signal
strength over particle data may be calculated by adding contrast
values of respective pixels in the detected particle signal. Also,
while the foregoing embodiment employs an 8-bit A/D converter, an
A/D converter having 10 bits or more may be used. Further, while
the foregoing embodiment has been described for an example of
calculating the signal width 1704 as the diameter of a circle, a
width of the saturation region which indicates a maximum length or
a minimum length may be used instead of the diameter.
[0098] In the description on the configuration of the apparatus,
the illumination optical system 101 uses laser light as an example
in the foregoing embodiment. Alternatively, white light may be used
instead of laser light. Also, when an object under testing has
repeated circuit patterns, the foregoing measurement of the size
may be made after taking a difference between an image of the
repeated pattern on which no particle exists and an image of the
same on which a particle exists. Also, irrespective of the presence
or absence of repeated patterns, if data on scattered light or data
on reflectivity associated with the circuit pattern or a film, for
example, an oxide film or a metal film, can be acquired beforehand,
such data may be used to correct data on the size of a particle on
the circuit pattern or the film. Furthermore, while the foregoing
embodiment measures the size of a particle by comparing it with the
sizes of standard particles, the size of the particle may be
compared with a particle, the size of which is known, instead of
the standard particles.
[0099] Next, an exemplary method of calculating a particle size
from the maximum signal strength value will be described with
reference to FIG. 15 when using data on a particle, the size of
which is known. FIG. 15 is a graph in which the horizontal axis
represents a maximum signal strength value of particle acquired
from the apparatus for inspecting particles or defects according to
the present invention, and the vertical axis represents the
particle size. Here, the maximum signal strength values of
particles are calculated by the aforementioned method, while the
size of a particle is derived by measuring a horizontal dimension
and a vertical dimension of the particle using a review apparatus
such as a measuring SEM, multiplying the horizontal dimension by
the vertical dimension, and taking a square root of the product. In
FIG. 15, a plot point 1501 indicates data on a particle, so that
FIG. 15 indicates data on a plurality of particles. An approximate
curve 1502 is calculated by a least-square method based on the data
at the plot points 1501. In this event, the approximate curve can
be expressed by an equation y=ax+b when the horizontal axis of the
graph is represented by x, and the vertical axis of the same by y,
where, a and b are values found by a least-square method.
[0100] For calculating a particle size from a maximum signal
strength value, a relational expression between the maximum signal
strength value and the particle size is found and is used to
calculate the particle size from the maximum signal strength
value.
[0101] Next, the operation will be described. First, the
approximate curve 1502 has been previously calculated by the
aforementioned method. Next, an object under inspection is
inspected using the apparatus for inspecting particles or defects
according to the present invention. Then, a maximum signal strength
value for the particle is calculated as described above during the
inspection. In this event, using the approximate curve, the maximum
signal strength value is substituted into x of the approximate
curve to calculate y which is determined as the particle size.
[0102] Examples of the results calculated by the foregoing method
are shown in FIGS. 30A, 30B and 31. FIGS. 30A, 30B are graphs,
wherein the horizontal axis represents the particle size calculated
from signal outputted from the apparatus for inspecting particles
or defects according to the present invention, and the vertical
axis represents the particle size measured by a measuring SEM. A
plot point 3101 corresponds to information on one particle. A
straight line 3102 in turn represents an approximate line when each
of plot points 3101 is least-mean-square approximated, and a value
3103 indicates a correlation value at the plot point 3101.
[0103] Further, FIG. 30A shows the result of measuring sizes of
particles detected on a wafer having a one-layer pattern, and FIG.
30B shows, by way of example, the result of measuring sizes of
particles detected on a wafer having a multi-layer pattern.
[0104] FIG. 31 shows, by way of example, SEM photo-graphs of used
particles in addition to the particle sizes calculated from signals
outputted from the apparatus for inspecting particles or defects
according to the present invention on the horizontal axis, and the
particle sizes measured by the measuring SEM on the vertical axis,
in a manner similar to FIGS. 30A, 30B.
[0105] While this embodiment calculates a square root of the
vertical dimension and the horizontal dimension of each particle,
the size of a particle may be defined as the larger one of the
vertical dimension and the horizontal dimension of the particle, or
an average value of the vertical dimension and the horizontal
dimension of the particle. Alternatively, the major axis of a
particle may be used, or the minor axis of the particle may be
used. Further, the approximate curve may be a first-order curve,
i.e., a straight line, or a higher-order curve, a logarithmic curve
or an exponential curve, or a combination of a plurality of
curves.
[0106] If the provision of different approximate curves for
respective shapes of particles results in a better correlation of
the particle sizes calculated as described above to the particle
sizes measured using the measuring SEM, a different approximate
curve may be used for each shape of particle. Here, the difference
in the shape of a particle refers to, for example, the difference
between a spherical particle and a flat plate-shaped particle, or
the difference between a particle and a scratch, when the
difference lies in the ratio of the particle size measured from
above to the particle size measured from the side.
[0107] Now, a method of distinguishing a particle from a scratch
will be described with reference to FIGS. 18A, 18B. FIG. 18A
illustrates the configuration for discriminating between a particle
and a scratch, and FIG. 18B shows how they are discriminated. FIG.
18A comprises a substrate 1801; a particle 1802; epi-illumination
light 1803 which illuminates the substrate from a perpendicular
direction; oblique illumination light 1804; a light detector 1805;
a storage circuit 1806; and a comparator circuit 1807. In the
illustrated configuration, the epi-illumination light 1803 is
emitted to the substrate at an angle close to a direction
perpendicular to the surface of the substrate 1801, while the
oblique illumination light 1804 is emitted to the substrate 1801 at
an angle close to a direction horizontal to the substrate 1801.
Their light sources may be an Ar laser, a YAG laser, or the like,
by way of example. The light detector 1805, in turn, may be a TV
camera, a CCD linear sensor, a TDI sensor, or a
photomultiplier.
[0108] Next, the operation will be described. A particle or a
scratch is irradiated with the epi-illumination light 1803 to
detect scattered light from the particle or scratch by the light
detector 1805. The amount of scattered light is stored in the
storage circuit 1806. Subsequently, the irradiation of the
epi-illumination light 1803 is stopped, and the oblique
illumination light 1804 is irradiated to the particle or scratch to
detect scattered light from the particle or scratch by the light
detector 1805. The amount of scattered light is stored in the
storage circuit 1806. Next, the light intensities, or the amounts
of scattered light stored in the storage circuit 1806 are compared
by the comparator circuit 1807. The comparator circuit 1807
calculates the ratio of the amount of scattered light when the
epi-illumination light 1803 is irradiated to the amount of
scattered light when the oblique illumination light 1804 is
irradiated, and compares the ratio with a previously determined
threshold to determine a particle or a scratch. A determination
method used herein may take advantage of the fact that a particle
has a smaller ratio of the amounts of scattered light, and a
scratch has a larger ratio, as shown in FIG. 18B.
[0109] Next, a method of calculating a particle size when there are
a plurality of approximate curves will be described with reference
to FIG. 19. FIG. 19 comprises a storage unit 1901 for storing a
maximum of detected signals; a discrimination unit 1902 for
discriminating between a particle and a scratch; a conversion curve
selection unit 1903; and a particle size calculation unit 1904.
[0110] Next, the operation will be described. First, a conversion
equation for calculating a particle size from a maximum signal
strength value using the aforementioned method has been created for
each of a particle and a scratch in the apparatus of inspecting
particles or defects according to the present invention and stored
in the conversion curve selection unit 1903. Next, a wafer is
inspected by the inspection apparatus. In this event, a maximum
signal strength value of a detected substance is stored in the
storage unit 1901. Next, the discrimination unit 1902 determines
whether the detected substance is a particle or a scratch by the
aforementioned method. Based on this determination, a conversion
curve is selected from the conversion curve selection unit 1903,
and the selected conversion curve and the maximum signal strength
value stored in the storage unit 1901 are inputted to the particle
size calculation unit 1904 to calculate the size of the
particle.
[0111] While the foregoing embodiment has described for an example
in which a conversion curve is set according to the shape of a
particle and a defect, a different approximate curve may be used
according to the position on an object under inspection at which a
particle is detected, for example, whether a particle on a circuit
pattern or a particle on a region without patterns. Alternatively,
a different approximate curve may be used depending on the surface
state of an object under inspection, for example, whether the
surface is coated with an aluminum film or a tungsten film.
[Method of Calibrating Measured Particle Size]
[0112] Next described will be a method of calibrating a particle
size measured by the apparatus for inspecting particles or defects
according to the present invention. This calibration may be used,
for example, when the amount of illumination light has changed due
to a deterioration in the illumination optical system in the
apparatus for inspecting particles or defects according to the
present invention.
[0113] An exemplary calibrating method will be described. First,
mirror wafers with standard particles having known sizes attached
thereto is prepared as calibration wafers. Two or more types of
standard particles are preferably prepared. For example, a standard
particle of 0.2 .mu.m and a standard particle of 0.6 .mu.m are
attached to mirror wafers, respectively. Next, these wafers are
inspected by the apparatus for inspecting particles or defects
according to the present invention to display the sizes of detected
particles. In this event, if the inspection apparatus does not
fail, peaks will appear at 0.2 .mu.m and 0.6 .mu.m on the scale of
the histogram.
[0114] For example, FIG. 26 is a graph showing the number of
detected particles on the vertical axis, and sizes of the detected
particles on the horizontal axis. As can be seen in FIG. 26, the
number of detected particles is increased at 0.2 .mu.m and 0.6
.mu.m on the scale. In contrast to FIG. 26, FIG. 27 shows an
example when the laser light source used in the illumination
optical system 101 has deteriorated to reduce the amount of
illumination light to one half, wherein the number of detected
particles is increased at 0.1 .mu.m and 0.3 .mu.m on the scale. In
other words, FIG. 27 shows an example in which a reduced amount of
illumination light results in a less amount of scattered light, so
that particle sizes are measured smaller than correct values.
[0115] Next explained will be a method of calculating a calibration
coefficient for calibrating the inspection apparatus. Assume first
that the size of the standard particle inspected above is SS, and
the size of a particle measured by the inspection apparatus of the
present invention is IS. In this event, since a reduced amount of
illumination light is calculated from the ratio of SS to IS, the
calibration coefficient, designated VR, is calculated by: VR=SS/IS
Therefore, the calibration may be accomplished by increasing the
amount of illumination light by a factor of VR or by multiplying a
conversion equation for calculating the a particle size from the
amount of scattered light by VR. Specifically, in the
aforementioned example, assuming that the size SS of the standard
particle is 0.2 .mu.m and the size IS of the particle measured by
the inspection apparatus is 0.1 .mu.m, the calibration coefficient
VR is calculated as: VR=2 so that the amount of illumination light
may be increased twice.
[0116] While the foregoing example has employed a wafer with a
standard particle of a known size attached thereto as a calibration
wafer, the calibration wafer is only required to have a particle or
a defect of known size attached thereto, so that a wafer having a
defect of known size intentionally created therein may be used
instead.
[0117] Next, another calibration method will be described with
reference to FIG. 2.
[0118] This is a method which uses values measured by the review
apparatus as particle sizes. First, an inspection is made in the
particle inspection apparatus 1301, and information on selected
particles is added to the results of inspection by the particle
inspection apparatus 1301, for example, serial numbers allocated to
particles when they were detected, information on the positions of
the particles, information on the sizes of the particles, and so
on, and transmitted to the data server 1302 through the network
1306. After the wafer has been conveyed to the review apparatus
1303, the wafer is reviewed by the review apparatus 1303, and
information on particle sizes measured therein is added to the
inspection result. Here, the particle size information is derived,
when using, for example, a measuring SEM as the review apparatus
1303, by measuring the horizontal dimension and vertical dimension
of a particle using the measuring SEM, multiplying the horizontal
dimension by the vertical dimension, and taking a square root of
the product. Next, the information added to the inspection result
is transmitted to the data server 1302, and the added information
is received by the particle inspection apparatus 1301 to calibrate
the particle size information outputted from the particle
inspection apparatus 1301 based on the size information.
[0119] The calibration method will be described with reference to
FIG. 28. FIG. 28 is a graph showing the information on the size of
each particle measured by the particle inspection apparatus 1301 on
the horizontal axis, and the information on the size measured by
the review apparatus 1303 on the vertical axis. In FIG. 28, a plot
point 2901 indicates information on the size of the same particle,
so that FIG. 28 plots information on a plurality of particles.
Here, if the particle sizes are correctly measured, plot points
2901 should be arranged along a straight line 2902. The calibration
method first finds an approximate line for the data of the plot
points 2901 through a least-square method or the like. This
approximate line is the straight line 2903 which is expressed by an
equation: y=ax+b where x represents the size of a particle measured
by the inspection apparatus on the horizontal axis, and y
represents the size of the particle measured by the review
apparatus 1303 on the vertical axis. Also, a and b are values found
by a least-square method. Next, the particle is inspected by the
apparatus for inspecting particles or defects according to the
present invention, the size of the particle is measured, and the
measured size is substituted into x in the above equation. The
resulting value y is determined as the size of the particle after
calibration.
[0120] While the linear approximation has been described as the
calibration method, the approximation may be made to a higher order
curve, a logarithmic curve, an exponential curve, or a combination
of curves. In addition, a wafer for use in calibrating the particle
size is not limited to one, but a plurality of wafers may be
used.
[0121] In the foregoing description, particles are inspected using
scattered light. This method is advantageous in that particles can
be efficiently found. Also advantageously, when particle sizes are
calculated by the aforementioned method, particles can be found
without requiring a special light source for measuring the sizes,
and measurements of the sizes can be made with scattered light from
the same light source.
[Analysis on Cause of Failure and Display of Result]
[0122] Next, description will be made on a procedure for analyzing
a cause of failure and a procedure for displaying the result of
analysis to the user when particle sizes are measured using the
apparatus for inspecting particles or defects according to the
present invention.
[0123] FIGS. 5A to 5C are diagrams showing that the relationship
between particle sizes and the number of detected particles changes
due to a cause of failure.
[0124] FIG. 6 is a line graph showing the number of detected
particles and particle sizes.
[0125] FIG. 7 is a histogram showing the number of detected
particles and particle sizes.
[0126] FIGS. 8A, 8B are schematic diagrams each clearly showing
particles of a particular size on a wafer;
[0127] FIGS. 9A to 9C are graphs each showing a transition of the
number of detected particles for each articular size.
[0128] FIG. 10 is a diagram illustrating a screen for displaying to
the user a cause by which particles are generated.
[0129] FIG. 20 is a histogram showing the number of detected
particles and the particle sizes on a plurality of wafers.
[0130] FIG. 21 is another histogram separately showing detected
particles and scratches on a wafer.
[0131] One important idea of the present invention is to use
particle size information for analyzing a cause of failure. The
following description will be made on the effectiveness of using
the particle size information for analyzing a cause of failure.
[0132] Assume herein that particles have been detected from a wafer
processed by a semiconductor manufacturing apparatus, for example,
an etching apparatus, and the relationship between particle sizes
and the number of detected particles are as shown in FIGS. 5A to
5C. A region 401 in FIG. 5A shows a distribution of particles
steadily generated in a process of an etching apparatus. In this
case, the particle sizes concentrate in a range from a to b, so
that a gently-sloping mountain is formed.
[0133] On the other hand, FIG. 5B shows an exemplary distribution
of particles which are generated when the apparatus is faulty. In
this case, large particles (a range of sizes larger than c) are
frequently generated as shown in a region 402, in addition to the
particles in the steady state shown in the region 401. It is
contemplated that the cause for such large particles is deposits on
the inner wall surface of the etching apparatus are peeled off the
wall surface during the etching process. FIG. 5C also shows an
exemplary distribution of particles which are generated when a
failure occurs. In this case, FIG. 5C shows that particle sizes
also concentrate in a range from d to e in addition to the
particles in the steady state. It is contemplated that the cause
for such particles is particular patterns which are peeled off and
dispersed during the etching process.
[0134] As described above, in manufacturing apparatuses for
semiconductor or the like, there is a relationship between the
sizes of generated particles and the cause by which the particles
are generated, so that the cause for particles generated in a
certain manufacturing apparatus can be immediately known by
managing the generation of particles of particular sizes. In other
words, by investigating the relation-ship between the size of
particles and the number of generated particles, the cause of
failure can be revealed.
[0135] It should be understood that the values a-e of course depend
on particular manufacturing apparatuses, manufacturing processes
and so on. Also, particles generated by a different cause may
exhibit a different distribution of size, so that it is preferred
to prepare data which conforms to a particle size distribution for
each cause. In addition, while this embodiment intends to identify
the cause for generated particles in two ranges, the range of
particle size may be divided into more than two ranges.
[0136] Next, description will be made on a specific function of
analyzing a cause of failure.
[0137] First described is how the particle sizes and the number of
detected particles are displayed on the data display unit 106. The
data display unit 106 displays a graph showing a particle size
distribution as described above, i.e., a graph which allows the
user to understand the relationship between particle sizes and the
number of detected particles. FIG. 6 is a graph showing the
particle size on the horizontal axis and the number of detected
particles on the vertical axis. A point 501 indicates the number of
detected particles of certain size. In this exemplary graph, data
on the number of detected particles is provided in increments of
0.1 .mu.m. A curve 502 is a line connecting the points 501. By
displaying the graph as in this embodiment, it can be immediately
seen how particles detected from an object under inspection 102 are
distributed.
[0138] In the graph of FIG. 6, a minimum value on the horizontal
axis may be a minimal detectable dimension of the particle
inspection apparatus, or a particle size which should be managed on
a semiconductor manufacturing line. Also, the scale may be
represented in a logarithmic or linear form. The unit of scale may
be variable. Further, a displayed range of each axis may be fixed
or variable. For example, particles generated by a particular cause
alone may be displayed by displaying particles of a particular
size. The contents represented on the vertical axis and the
horizontal axis may be replaced with each other. Instead of the
number of detected particles, the density of particles may be
shown. Further, while this embodiment displays a graph, an average
value of the graph, and a standard deviation or variance of the
graph may also be displayed other than the graph. Also, while this
embodiment displays particle data on one wafer as one graph, the
graph need not be displayed for only one wafer. An average value, a
standard deviation and a variance of particle data on a plurality
of wafers may be displayed, and particle data on a plurality of
wafers may be displayed side by side.
[0139] The graph may be displayed in histogram as shown in FIGS. 7
and 32. The graphs on these figures indicate the particle size on
the horizontal axis, and the number of detected particles on the
vertical axis, similarly to FIG. 6. These graphs display the
particle size on the horizontal line divided into certain sections.
FIG. 7 shows data sections in increments of 0.2 .mu.m. FIG. 32 in
turn shows data sections in increments of 0.1 .mu.m, wherein
particles having the size equal to or more than 5 .mu.m are counted
in a bar graph 3301, and a histogram for particles having the size
smaller than 1.1 .mu.m and a histogram for particles having the
size equal to or larger than 1.1 .mu.m are displayed in different
colors, by way of example. In addition, a function may be added for
displaying information on the positions of a detected particles in
a selected portion of a bar graph. Also, a review image may be
displayed for the detected particles in the selected portion.
[0140] FIG. 34 shows another example of graphical representation.
FIG. 34 shows an example in which the particle size is set on the
horizontal axis, and an accumulated number of particles is set on
the vertical axis. Here, the accumulated number refers to the
number of detected particles of a certain size or larger.
[0141] FIG. 35 shows a further example of graphical representation.
FIG. 35 shows an example in which the particle size is set on the
horizontal axis, and the number of detected particles is set on the
vertical axis, with a curve 3601 indicative of the number of
detected particles, and an equation expressing the curve 3601
indicative of the number of detected particles additionally
indicated in the graph. In the equation 3601, x represents the
particle size, and y the number of detected particles. The equation
3601 is an approximate equation derived from the number of detected
particles for each particle size. The curve 3601 represents the
equation 3602.
[0142] FIG. 20 shows a further example of graphical representation.
While the example in FIG. 7 displays data for one wafer, data on a
plurality of wafers may be displayed side by side as shown in FIG.
20. Specifically, FIG. 20 is an example in which the number of
detected particle is set on one of three coordinate axes; the
particle size on another axis; and the wafer number on the
remaining axis. In this example, data sections for the particle
size are set in increments of 0.1 .mu.m from zero to 1 .mu.m,
particles having sizes equal to or larger than 1 .mu.m are counted
on the same bar graph, and the total number of detected particles
is also displayed in the graph. As is the case with FIG. 6, an
average value, standard deviation and variance may also be
displayed on the graph of FIG. 20.
[0143] FIG. 21 shows a further example of graphic representation.
FIG. 21 shows an example in which displayed data are classified
into particles and scratches and also classified by size.
[0144] Next, description will be made on a function of displaying
information on the positions of detected particles. FIG. 8A shows
information on the positions of all particles detected by a
particle inspection.
[0145] In FIG. 8A, detected particles 702 exist within a contour
701 of an 8-inch semiconductor wafer. In this event, as a mouse is
click once or twice on a bar graph 601 in FIG. 7, the section of
the bar graph 601, i.e., displayed particles 703 of sizes ranging
from 2.8 .mu.m to 3.0 .mu.m in FIG. 8A are changed as shown in FIG.
8B. The inspection apparatus has such a function so that the user
can immediately find the positions on an object under inspection
102 of particles having sizes in a particular range.
[0146] FIG. 22 shows an exemplary result of a particle inspection
displayed after the inspection.
[0147] The display in FIG. 22 comprises an inspection map 2201
indicative of the positions at which particles are detected; a
histogram 2202 for the sizes of the detected particles; a review
button 203; a review image 2204 of the detected particles;
particles 2205; a particle size data section 2206 to be reviewed.
The review image 2204 is displayed centered at the particle 2205.
In this example, particles having sizes ranging from 2.8 .mu.m to
3.0 .mu.m in the data section 2206 are selected.
[0148] In operation, after particles are inspected by the apparatus
for inspecting particles or defects according to the present
invention, the inspection map 2201 is displayed as information on
the positions of the particles, and the histogram 2202 is displayed
as information on particle sizes. Then, the data section 2206 is
selected as a particle size to be reviewed. Clicking on the review
button 2203 causes the review image 2204, provided by the apparatus
for inspecting particles or defects of the present invention, to be
displayed. Here, the review image 2204 may be an image generated
from scattered laser light, or an image captured by a
microscope.
[0149] Next, a management approach applied when the statistics are
collected in time series on particles having a particular size will
be described with reference to FIGS. 9A to 9C.
[0150] FIG. 9A shows a transition of the total sum of all
particles, irrespective of the size, detected by the particle
inspection apparatus, in time series for wafers processed in the
same process by the same manufacturing apparatus. FIG. 9C shows a
transition of the total sum of particles having sizes ranging from
2.8 to 3.0 [.mu.m], shown in the example of FIG. 7, in time series.
FIG. 9B shows a transition of the total sum of the remaining
particles in time series.
[0151] Thresholds 1001, 1002, 1003 indicate management reference
values for the number of particles in the three cases. When
particles exceeding these thresholds are detected, this means that
an associated wafer is diagnosed as defective. Specifically, it is
determined from FIG. 9A that a peak value 1004 near an inspection
time A is unusually high.
[0152] However, while a certain failure may be guessed from the
statistics shown in FIG. 9A, its cause cannot be revealed.
[0153] On the other hand, when particles are managed by size in
accordance with the inspection approach of the present invention, a
remarkable peak 1005 appears at A time in FIG. 9C, so that it is
understood that particles having sizes ranging from 2.8 to 3.0
[.mu.m] particularly concentrate in a lot which was inspected at
that time. Thus, from the fact that no section exceeds the
threshold in FIG. 9B and the peak value 1005 is sensed in FIG. 9C,
the user can guess by the reason shown in FIGS. 5A to 5C that
patterns of these sizes peeled off and scattered on wafers during
an etching process can be the cause for an unusual increase in the
number of particles, and therefore immediately take effective
countermeasures to the failure, such as checking the etching
apparatus.
[0154] Next, an example of displaying a cause of failure to the
user will be described with reference to FIG. 11.
[0155] The apparatus for inspecting particles or defects according
to the present invention has a function of analyzing the particle
size and the number of detected particles to display a cause of
failure to the user.
[0156] For example, assume that a graph as shown in FIG. 7 results
from an inspection, taking the cause of failure shown in FIG. 5C as
a model. Assume also that a section d-e in FIG. 5C corresponds to
the particle size range of 2.8 .mu.m to 3.0 .mu.m in FIG. 7.
Therefore, when the result of inspection shown in FIG. 7 is
obtained, the screen shown in FIG. 9 is displayed to clarify the
user the result of analysis on the cause of failure.
[0157] Next described is another exemplary management approach
based on the particle size. Particles detected by the inspection
apparatus may be classified into those which cause a failure, and
those which do not cause a failure. Specifically, if particles are
smaller than wire widths and spaces between wires in a wiring
pattern created on a wafer, such particles cause no failure in many
cases. Therefore, detected particles having a certain size or more
may be managed as a possible cause of failure.
[0158] Next, description will be made on an exemplary method of
calculating a particle size to be managed. FIG. 23 shows the
relationship between a wiring pattern 2401 having a wire width W1,
a wiring pattern 2402 having a wire width W2 and a wiring pattern
having a wire width W3 on a wafer, and a particle 2404. When this
particle 2404 is conductive, the particle 2404 attached, for
example, at a position 2405 to connect the wiring pattern 2401 and
wiring pattern 2402 would cause the wiring pattern 2401 and wiring
pattern 2402 to short-circuit through the particle 2404, with the
result that this chip becomes defective. As such, assuming that the
distance between the wiring pattern 2401 and wiring pattern 2402 is
S1, and the distance between the wiring pattern 2402 and wiring
pattern 2403 is S2, the particle 2404 which can short-circuit the
wiring pattern 2402 to another wire has a size of S1 or S2 or more.
Particularly, a particle having a size of (S1+W2+S2) will
short-circuit wires with possibility of 100%.
[0159] Therefore, when the wiring patterns have the widths and
distance between wires as defined above, the size of a particle
causing a failure is given by: MIN (S1,S2) where MIN (A, B)
indicates the smaller value of A and B when they are compared.
[0160] It should be noted that the example shown herein is a
calculation for the most strict condition in management. If the
condition is less strict, larger particles may be managed.
[0161] By determining a particle size to be managed in each
manufacturing process by the calculation described above and
monitoring fluctuations in the number of detected particles having
the managed size or more, it is possible to sense the occurrence of
a failure without delay. A monitoring method used herein may
involve previously calculating an average and standard deviation of
the number of particles under management detected, for example,
from several to several tens of wafers, monitoring the number of
particles based on a monitoring threshold calculated by: Monitoring
Threshold=Average+kStandard Deviation and analyzing a cause of
failure and taking countermeasures to wafers on which the number of
detected particles exceeds the monitoring threshold. In the above
equation, k is a constant which may be set to k=3, for example,
when it is desired that the failure analysis is conducted for
approximately 0.3% of all wafers.
[0162] Next described is another method of calculating a particle
size to be managed. This method calculates the influence of
particles exerted on the yield of wafers from the presence or
absence of particles detected on one wafer, and determination made
to chips on which the particles are detected as to whether they are
non-defective or defective, and manages a particle size at which
the calculated influence present a maximum.
[0163] A method of calculating the influence on the yield will be
described with reference to FIG. 29. FIG. 29 shows chips on a wafer
classified according to the presence or absence of particles, and
non-defective and defective chips. Specifically, FIG. 29 shows
chips 3001 (hereinafter labeled "Gn") on which no particles have
been detected and which are non-defective; chips 3002 (hereinafter
labeled "Bn") on which no particles have been detected but which
are defective; chips 3003 (hereinafter labeled "Gp") on which
particles have been detected but which are non-defective; and chips
3004 (hereinafter labeled "Bp") on which particles have been
detected and which are defective. Here, whether or not particles
have been detected on a certain chip may be determined based on the
position information in the result of an inspection performed by
the apparatus for inspecting particles or defects according to the
present invention. Also, determination as to whether a certain chip
is non-defective or defective may be made using, for example, the
result of an electric inspection.
[0164] First, assuming that the yield of a certain wafer is Y, and
the yield of chips on which no particles have been detected is Yn,
the influence dY of detected particles on the yield of the wafer is
defined as: dY=Yn-Y Since Y is the yield of the wafer, Y can be
expressed by: Y=Yn(1-.gamma.)+Yp.gamma. where Yp is the yield of
chips on which particles have been detected, and .gamma. is the
proportion of chips on which particles have been detected with
respect to the total number of chips (hereinafter called the
"particle occurrence frequency").
[0165] Here, using the aforementioned Gn, Bn, Gp, Bp:
Y=(Gn+Gp)/(Gn+Bn+Gp+Bp) Yn=Gn/(Gn+Bn) Yp=Gp/(Gp+Bp)
.gamma.=(Gp+Bp)/(Gn+Bn+Gp+Bp) can be derived.
[0166] Therefore, dY can be expressed as follows: dY = .times. Yn -
Y = .times. Yn - ( Yn ( 1 - .gamma. ) + Yp .gamma. ) = .times. ( Yn
- Yp ) .gamma. = .times. Yn ( 1 - Yp / Yn ) .gamma. ##EQU1## Here,
assuming that the probability of a chip deter-mined as defective
due to particles is represented by F (hereinafter called the
"critical probability"), Yp can be expressed by: Yp=Yn(1-F)
[0167] Rewriting the above equation for F, F=1-Yp/Yn so that dY can
be expressed by: dY=YnF.gamma.
[0168] Here, the particle occurrence frequency .gamma. is larger as
a particle detection sensitivity is higher, and smaller as the
particle detection sensitivity is lower. This is because a higher
detection sensitivity contributes to detection of a larger number
of particles. The critical probability F in turn is smaller as the
particle detection sensitivity is higher, and larger as the
particle detection sensitivity is lower. This is because although a
higher sensitivity contributes to detection of smaller particles,
those particles which are smaller than the distance between wiring
patterns do not cause a failure such as short-circuiting.
[0169] Therefore, when the influence dY on the yield is calculated,
the particle sizes used in the calculation are limited. The
particle size which maximizes the influence dY on the yield
indicates the minimum particle size to be managed. The limitation
on the particle sizes refers to using those data on particles
having a certain size or more.
[0170] FIG. 24 shows an exemplary result of calculating the
influence dY on the yield. FIG. 24 shows the influence dY on the
yield on the vertical axis, and the particle size used in
calculating the influence dY on the yield on the horizontal axis.
For example, in FIG. 24, a point 2501 indicates that the influence
dY on the yield is 0.1 as a result of the calculation using data on
particles having sizes equal to or more than 0.1 .mu.m, and a point
2502 indicates that the influence dY on the yield is 0.8 as a
result of the calculation using data on particles having sizes
equal to or more than 0.4 .mu.m. Here, using data on particles
having the sizes equal to or more than 0.1 .mu.m means that the
calculation is performed on the assumption that among detected
particles, chips on which particles of 0.1 .mu.m or more have been
detected are regarded as chips on which particles are attached, and
chips on which particles less than 0.1 .mu.m have been detected or
no particles have been detected are regarded as chips on which no
particles are attached. Thus, it is appreciated from FIG. 24 that
the influence dY on the yield is the largest when it is calculated
using data on particles of 0.4 .mu.m or more, so that particles of
0.4 .mu.m or more should be managed.
[0171] While the foregoing embodiment shows that the particle size
is changed in increments of 0.1 .mu.m, the increment may be 0.2
.mu.m or any other value. Also, while the foregoing embodiment has
been described for an example which determines the particle size
that exerts the largest influence dY on the yield as the method of
determining a particle size to be managed, the particle size to be
managed need not be the particle size that exerts the largest
influence, but may be a particle size that presents a value close
to the largest influence dY on the yield, for example, a value
equal to or more than the largest influence dY multiplied by
0.9.
[0172] FIGS. 33A to 33C show another exemplary result of
calculation. FIGS. 33A to 33C show the result of calculating the
influence dY on the yield; and particle detection maps at that
time. FIG. 33A shows, by way of example, that the influence dY on
the yield is calculated in increments of approximately 0.07 .mu.m
of particle size, and values on the vertical axis are represented
in percent. FIG. 33B is a particle detection map which displays all
particles detected by the apparatus for inspecting particles or
defects according to the present invention, and FIG. 33C is a
particle detection map which shows extracted particles having the
sizes equal to or more than 1.1 .mu.m. The value of 1.1 .mu.m
indicates the particle size that exerts the largest influence dY on
the yield in FIG. 33A. It is therefore understood that particles
may be managed based on the particle detection map of FIG. 33C.
[0173] Next, description will be made on an approach for managing a
semiconductor device manufacturing process when the influence dY on
the yield is used for the management. FIG. 25 shows a graph which
sets the aforementioned influence dY on the yield on the vertical
axis, and a semiconductor manufacturing process on the horizontal
axis. Specifically, the horizontal axis shows steps in the process
in which particles are inspected using the apparatus for inspecting
particles or defects according to the present invention.
[0174] Next, the operation will be described. First, an inspection
is conducted in each of the steps in the process shown on the
horizontal axis using the same wafer. Next, at the time each of
chips on the wafer is determined as non-defective or defective, the
aforementioned influence dY on the yield is calculated for each
step. FIG. 25 is an example of calculating the influence dY on the
yield in each step. For example, a point 2601 indicates that the
influence dY on the yield is 0.8 when calculated using particles
detected in a step labeled "Step 4" in the process. In this way,
the influence dY on the yield is calculated in each step, and
countermeasures are taken preferentially from a step which presents
a larger influence dY on the yield, thereby making it possible to
take countermeasures from a step which is more likely to cause a
failure.
[0175] In the foregoing embodiment, all data on particles detected
in each step are used for calculating the influence dY. For
particles which have been known that they had occurred in a
different step, the influence dY on the yield may be calculated
using the remaining data except for the data on the particles. For
removing data, for example, information on the position of
particles detected in Step 1 in FIG. 25 may be compared with
information on the position of particles detected in Step 2, and
the particles previously detected in Step 1 may be deleted from
data on particles in Step 2.
[0176] Also, the foregoing embodiment has been described for the
management of particle size using the influence dY on the yield
expressed by: dY=YnF.gamma. When a failure caused by a process is
eliminated by improving the process management, dY=F.gamma. may be
used by setting the aforementioned Yn to one (Yn=1). The approach
of the present invention may also be applied to any index for
calculating the influence of particles. For example, for memory
products such as DRAM, the number of defective bits caused by each
particle may be used as an index.
[0177] The foregoing embodiment is advantageous in that since
wiring pattern widths and space widths in a semiconductor device
are only required as information for determining whether a particle
causes a failure in the example described with reference to FIG.
23, a particle size to be managed can be determined at the time the
design of a semiconductor device is definite. The example described
with reference to FIG. 29, in turn, is advantageous in that it
employs an index including a consideration of information such as
short-circuiting of wires due to the height of a particle, and so
on, as well as the width of the particle, so that the actual state
of device can be known.
[Inspection on Particles by Region and Analysis on Cause of
Failure]
[0178] Next, description will be made on an embodiment which
manages particle data by region on a wafer to take countermeasures
using the apparatus for inspecting particles or defects according
to the resent invention.
[0179] FIG. 11 schematically illustrates regions on semiconductor
wafer.
[0180] FIGS. 12A, 12B are schematic diagrams each clearly showing
particles of a particular size on a wafer when particle data is
managed separately for each region;
[0181] FIGS. 13, 14 are graphs each showing the number of detected
particles by size in each region.
[0182] Generally, when a chip pattern is formed on a semiconductor
wafer, the pattern is not always formed uniformly, but some region
in the pattern exhibits a higher pattern forming density while
another region in the pattern exhibits a lower pattern forming
density. For example, assuming that a chip illustrated in FIG. 11
is a microprocessor, the pattern is divided, for example, into a
region 1101 for memory cell circuits; a region 1102 for data
input/output circuits; and a region 1103 in which no circuit
pattern exists. Generally, these regions 1101, 1102, 1103 differ in
circuit pattern integration degree from one another. As a result,
different sizes of particles would cause failures in the respective
regions. In other words, the particle size which should be managed
and analyzed differs from one region to another in a chip.
[0183] Specifically stated, for example, when a particle of size
.alpha. or more would cause the chip to be defective in the region
1101; a particle of size .beta. or more in the region 1102; and a
particle of size .gamma. or more in the region 1103, information on
these regions and information on particle size which causes the
chip to be defective in each of these regions are previously stored
in the inspection apparatus as management data. The information on
the regions and information on particle size causing the defective
chip may be directly entered on a screen which may be provided on
the inspection apparatus for entering coordinate values and
particle size, or regions may be selected from an optical image
captured by a TV camera or the like. Alternatively, data may be
downloaded from a higher rank system, or data may be read into the
inspection apparatus from a removable storage medium, for example,
a floppy disk.
[0184] By providing the inspection apparatus with the information
on the regions and the information on particle sizes which cause
the chip to be defective, an object under inspection is inspected.
Then, a region is determined from information on the position of a
detected particle in the inspection apparatus, and the information
on the detected particle size is compared with the information on
particle sizes which cause the chip to be defective, to determine
whether or not the detected particle will cause a failure.
[0185] As a result, particles determined as a cause of failure and
particles not determined as a cause of failure are displayed in
different forms, such that the particles determined as a cause of
failure are distinctively displayed to the user, thereby allowing
the user to be immediately aware of the particles which cause a
failure.
[0186] The foregoing approach will be shown in a specific manner
with reference to FIGS. 12A, 12B.
[0187] A wafer shown in FIGS. 12A, 12B is displayed with the
positions of detected particles 1202 indicated thereon. Since the
result of detection has been displayed as shown in FIG. 12A in the
prior art, an analysis on the cause of failure involves selecting
proper particles and analyzing the selected particles. Therefore,
the prior art suffers from a low probability that particles which
should be essentially analyzed can be selected, and a long time
required for the analysis on the cause of failure. On the contrary,
by displaying in a different form those particles which have been
determined as the cause of failure using the foregoing
determination, i.e., particles 1203 which should be analyzed as
shown in FIG. 12B, it is possible to readily select the particles
1203 which should be analyzed from detected particles, to increase
the probability that the particles which should be analyzed can be
selected, and to rapidly analyze the cause of failure. In FIG. 11,
for displaying different regions in different manners, they are
displayed in different patterns. Alternatively, these region may be
displayed in different colors or sizes. Further alternatively,
displayed particles may be limited to those which cause a failure.
Also, while the foregoing embodiment divides a chip into several
regions, the wafer surface may be divided, for example, in
accordance with the distance from the center of the wafer to the
wafer edge, and different particle sizes may be managed in
different regions. Furthermore, the layout of semiconductor chips
may be displayed on the wafer shape 1201.
[0188] Next, description will be made on an approach for inspecting
the number of particles detected in respective regions to take
countermeasures to a failure with reference to FIGS. 13 and 14.
[0189] In this example, a wafer is divided into three regions,
designated Region A, Region B, Region C, in each of which the
number of particles is detected. Then, the result is displayed to
the user in the form of graph for each region.
[0190] For example, as shown in FIG. 13, the horizontal axis
represents the particle size, and the vertical axis represents the
number of detected particles, wherein different colors are
allocated to Region A, Region B, Region C, respectively, the
particles are displayed by size in graphical representation, and
the numbers of particles falling under the same size category in
the three regions are displayed side by side.
[0191] Alternatively, as shown in FIG. 14, the numbers of particles
falling under the same size category may be displayed in stack.
[0192] Specifically, the three regions may be a memory cell region,
a circuit region other than memory circuit, and region without
circuit pattern, for example, on a semiconductor wafer. By
displaying these regions as shown in FIGS. 13 and 14, the
management of particles by region is facilitated. The information
on the regions may be directly entered on a screen which may be
provided on the inspection apparatus for entering coordinate values
and particle size, or regions may be selected from an optical image
captured by a TV camera or the like. Alternatively, data may be
downloaded from a higher rank system, or data may be read into the
inspection apparatus from a removable storage medium, for example,
a floppy disk.
[0193] Next described will be an approach for counting the number
of detected particles by size in each of regions to find out
defective products.
[0194] As described above, the particle size determined as a cause
of failure differs from one region to another. In a certain region
which does not include very fine circuits, even a relatively large
particle would not be regarded as a cause of failure. On the other
hand, in another region which includes fine circuits, even a
relatively small particle could cause a trouble. In this way,
thresholds over which an alarm is generated are designated by
.alpha., .beta., .gamma. for Region A, Region B, Region C,
respectively. For example, in the example shown in FIGS. 13, 14,
assume:
[0195] .alpha.=1.0 [.mu.m]
[0196] .beta.=1.6 [.mu.m]
[0197] .gamma.=2.0 [.mu.m]
[0198] With these thresholds, the total sum of detected particles
exceeding the threshold set for each region is as follows:
[0199] Region A . . . 24
[0200] Region B . . . 3
[0201] Region C . . . 1
[0202] Even though a very large number of particles are apparently
detected in Region C, they do not significantly affect the quality
of a product. On the other hand, particles detected in Region A,
the number of which is not so large as in Region C, is highly
likely to affect the quality of the product, so that the product
could be determined as defective due to the particles attached on
Region A with a high probability. In this way, a reasonable
inspection can be conducted in accordance with the characteristic
of each region by setting a threshold of particle size for each
region, over which a particle detected therein is regarded as a
cause of failure, counting the total sum of detected particles
exceeding the threshold in each region, determining whether the
object under testing is non-defective or defective, and displaying
the user to the result of determination.
[About Optical System in Apparatus for Inspecting Particles or
Defects]
[0203] In the foregoing description on the present invention, the
optical system in the apparatus for inspecting particles or defects
employs scattered light to detect particles and measure the sizes
of the particles. The approach of the present invention, however,
can be applied to an optical system which relies on reflected light
to detect particles or defects and measure the sizes thereof.
Generally, the optical system relying on scattered light exhibits a
high inspection efficiency but a low measurement accuracy. On the
contrary, the optical system relying on reflected light exhibits a
low inspection efficiency, but a high measurement accuracy. The
approach of the present invention can be applied to either of the
optical systems.
[0204] As appreciated from the foregoing, the present invention
provides an apparatus and method for inspecting particles ore
defects, which are suitable for use in inspecting particles or
defects in processes for manufacturing semiconductor wafers or thin
film substrates and conducting a failure analysis based on the
inspection result. The inspection apparatus and method are capable
of rapidly taking countermeasures to a failure by conducting an
inspection and a failure analysis in accordance with the
characteristics of particles and patterns or the characteristics of
regions on an object under inspection.
[0205] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present invention is therefore to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and range of equivalency of the claims are therefore intended to be
the embraced therein.
* * * * *