U.S. patent application number 12/000126 was filed with the patent office on 2008-05-29 for method for inspecting substrate, substrate inspecting system and electron.
This patent application is currently assigned to EBARA CORPORATION. Invention is credited to Muneki Hamashima, Masahiro Hatakeyama, Tsutomu Karimata, Toshifumi Kimba, Mamoru Nakasuji, Nobuharu Noji, Shin Oowada, Mutsumi Saito, Tohru Satake, Hirosi Sobukawa, Kenji Watanabe, Shoji Yoshikawa.
Application Number | 20080121804 12/000126 |
Document ID | / |
Family ID | 27585755 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080121804 |
Kind Code |
A1 |
Nakasuji; Mamoru ; et
al. |
May 29, 2008 |
Method for inspecting substrate, substrate inspecting system and
electron
Abstract
The present invention relates to a substrate inspection
apparatus for inspecting a pattern formed on a substrate by
irradiating a charged particle beam onto the substrate. The
substrate inspection apparatus comprises: an electron beam
apparatus including a charged particle beam source for emitting a
charged particle beam, a primary optical system for irradiating the
charged particle beam onto the substrate, a secondary optical
system into which a secondary charged particle beam is introduced,
the secondary charged particle beam being emitted from the
substrate by an irradiation of the charged particle beam, a
detection system for detecting the secondary charged particle beam
introduced into said secondary optical system and outputting as an
electric signal, and a process control system for processing and
evaluating the electric signal; a stage unit for holding the
substrate and moving the substrate relatively to said electron beam
apparatus; a working chamber capable of shielding at least an upper
region of the stage unit form outside to control under desired
atmosphere; and a substrate load-unload mechanism for transferring
the substrate into or out of the stage.
Inventors: |
Nakasuji; Mamoru; (Kanagawa,
JP) ; Noji; Nobuharu; (Kanagawa, JP) ; Satake;
Tohru; (Kanagawa, JP) ; Kimba; Toshifumi;
(Kanagawa, JP) ; Hatakeyama; Masahiro; (Kanagawa,
JP) ; Watanabe; Kenji; (Kanagawa, JP) ;
Sobukawa; Hirosi; (Kanagawa, JP) ; Karimata;
Tsutomu; (Kanagawa, JP) ; Yoshikawa; Shoji;
(Tokyo, JP) ; Oowada; Shin; (Kanagawa, JP)
; Saito; Mutsumi; (Kanagawa, JP) ; Hamashima;
Muneki; (Saitama, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
EBARA CORPORATION
Tokyo
JP
|
Family ID: |
27585755 |
Appl. No.: |
12/000126 |
Filed: |
December 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11350009 |
Feb 9, 2006 |
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12000126 |
|
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|
09985331 |
Nov 2, 2001 |
7109483 |
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11350009 |
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Current U.S.
Class: |
250/310 |
Current CPC
Class: |
H01J 2237/082 20130101;
H01J 37/073 20130101; H01J 2237/202 20130101; H01J 2237/24564
20130101; G01N 23/225 20130101; H01J 37/28 20130101; H01J 37/20
20130101; H01J 2237/22 20130101; H01J 37/244 20130101; H01J
2237/20228 20130101; H01J 2237/204 20130101; H01J 2237/2816
20130101; H01J 37/222 20130101; H01J 2237/2817 20130101; H01J 37/06
20130101; H01J 37/185 20130101; H01J 2237/2806 20130101 |
Class at
Publication: |
250/310 |
International
Class: |
H01J 37/285 20060101
H01J037/285 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2000 |
JP |
364076/2000 |
Dec 18, 2000 |
JP |
384036/2000 |
Dec 26, 2000 |
JP |
394138 |
Jan 11, 2001 |
JP |
3654/2001 |
Jan 17, 2001 |
JP |
8998/2001 |
Jan 31, 2001 |
JP |
23422/2001 |
Feb 2, 2001 |
JP |
26468/2001 |
Feb 8, 2001 |
JP |
31901/2001 |
Feb 8, 2001 |
JP |
31906/2001 |
Feb 9, 2001 |
JP |
33599/2001 |
Feb 14, 2001 |
JP |
36840/2001 |
Feb 16, 2001 |
JP |
40421/2001 |
Mar 16, 2001 |
JP |
75863/2001 |
Apr 23, 2001 |
JP |
124219/2001 |
May 28, 2001 |
JP |
158571/2001 |
Nov 17, 2007 |
JP |
351420/2000 |
Claims
1. An inspection apparatus which is arranged in the proximity to at
least one processing apparatus for manufacturing a semiconductor
device, the inspection apparatus evaluating a processed condition
of a wafer after the wafer is processed by the processing
apparatus, the inspection apparatus comprising: a primary optical
system for scanning a surface of a sample by using a plurality of
converged primary electron beams; another optical system for
accelerating, by an objective lens, secondary electron beams
emitted from the sample, the another optical system separating the
secondary electron beams from the primary optical system by an
E.times.B separator to introduce the secondary electron beams into
a secondary optical system, after the introducing, magnifying a
spacing between the secondary electron beams by using at least one
stage lens, and introducing the secondary electron beams to
secondary electron detectors whose number corresponds to that of
the primary electron beams; and an evaluation condition setter for
setting an evaluation condition such that the processed condition
of each wafer should be evaluated within a processing time
necessary for processing one wafer by a processing unit.
2. The inspection apparatus of claim 1, in which the evaluation
condition setter comprises a setter for setting an evaluation area
of the wafer such that the processed condition should be evaluated
only in a specified area on a wafer surface.
3. An inspection apparatus which is arranged in proximity to at
least one processing apparatus for manufacturing a semiconductor
device, the inspection apparatus evaluating a processed condition
of a wafer after the wafer is processed by the processing
apparatus, the inspection apparatus comprising: a primary optical
system for scanning a surface of a sample by using a plurality of
converged primary electron beams; another optical system for
accelerating, by an objective lens, secondary electron beams
emitted from the sample, the another optical system separating the
secondary electron beams from the primary optical system by an
E.times.B separator to introduce the secondary electron beams into
a secondary optical system, after introducing, magnifying a spacing
between the secondary electron beams by using at least one stage
lens, and introducing the secondary electron beams to secondary
electron detectors whose number corresponds to that of the primary
electron beams; and an evaluation condition setter for setting an
evaluation condition such that a processed condition of one lot of
wafers should be evaluated within a processing time necessary for
processing one lot of wafers by the processing unit.
4. The inspection apparatus in accordance with claim 3, in which
the evaluation condition setter comprises a setter for setting an
evaluation area of the wafer such that the processed condition
should be evaluated only in a specified area on a wafer
surface.
5. An inspection apparatus which uses an electron beam, the
apparatus comprising: an electron gun; an irradiator for generating
a plurality of primary electron beams from an electron beam emitted
from the electron gun to irradiate the primary electron beams onto
a wafer; a plurality of secondary electron detectors for detecting
secondary electron beams emitted from a plurality of regions of the
wafer by irradiating the primary electron beams, to obtain a
plurality of sub-image data; and an image source for re-arranging
the detected plurality of sub-image data to generate an image data
of an inspection region on the wafer.
6. The inspection apparatus of claim 5, the apparatus further
comprising: a memory for storing in advance a reference image data
with respect to the wafer to be evaluated; and an evaluator for
evaluating the wafer by comparing the image data generated by the
image source with the reference image data stored in the
memory.
7. The inspection apparatus of claim 6, in which: a stage on which
the wafer is placed is controlled so as to continuously move in the
Y-axis direction; the irradiator is configured such that respective
primary electron beams are driven to simultaneously scan in the
X-axis direction so that irradiation spots of a plurality of
primary electron beams on the wafer are arranged with approximately
equal spacing therebetween in the X-axis direction, and respective
scanning regions may partially be superimposed on each other in the
X-axis direction; and the image source is configured such that
while the sub-image data being re-arranged, the image data of the
wafer surface is generated on the basis of the X and the Y
coordinates of respective primary electron beams.
8. The inspection apparatus in accordance with claim 7, in which:
the image source is configured such that, with respect to areas
overlapping in the X-axis direction, the image source determines a
boundary between the sub-images of a pattern to be evaluated on the
wafer so as not to cross the pattern, and that the image source
generates the image data of the wafer surface.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/350,009, filed Feb. 9, 2006, which was a
divisional of U.S. patent application Ser. No. 09/985,331 filed on
Nov. 2, 2001, which are incorporated by reference in its entirety.
Priority under 35 U.S.C. .sctn..sctn.120 and 121 is hereby claimed
for benefit of the filing date of U.S. patent application Ser. Nos.
09/985,331 and 11/350,009.
BACKGROUND OF THE INVENTION
[0002] In the field of semiconductor processes, the design rule is
going into an age of 100 nm and the production form is on a
transition from a mass production with a few models representative
of a DRAM into a small-lot production with a variety of models such
as a SOC (Silicon on chip). This results in an increase of a number
of processes, and an improvement in an yield for each process must
be essential, which makes more important an inspection for a defect
possibly occurring in each process. The present invention relates
to a substrate inspection method for inspecting a substrate such as
a wafer after respective processes in the semiconductor process by
using an electron beam, a substrate inspection apparatus to be used
therefor and an electron beam apparatus for the inspection
apparatus, and a device manufacturing method using the same method
and apparatuses.
[0003] In conjunction with a high integration of semiconductor
device and a micro-fabrication of pattern thereof, an inspection
apparatus with higher resolution and throughput has been desired.
In order to inspect a wafer substrate of 100 nm design rule for any
defects, a resolution in size equal to or finer than 100 nm is
required, and the increased number of processes resulting from a
high integration of the device has called for an increase in the
amount of inspection, which consequently requires higher
throughput. In addition, as a multilayer fabrication of the device
has been progressed, the apparatus has been further required to
have a function for detecting a contact failure in a via for
interconnecting a wiring between layers (i.e., an electrical
defect). In the current trend, an inspection apparatus of optical
method has been typically used, but it is expected that an
inspection apparatus using an electron beam may soon be of
mainstream, substituting for the inspection apparatus of optical
method in the viewpoint of resolution and of inspection for contact
malfunction. The inspection apparatus of electron beam method,
however, has a weak point in that the inspection apparatus of
electron beam method is inferior to the inspection apparatus of
optical method in the throughput.
[0004] Accordingly, an apparatus having higher resolution and
throughput and being capable of detecting the electrical defects
has been desired to be developed. It has been known that the
resolution in the inspection apparatus of optical method is limited
to 1/2 of the wavelength of the light to be used, and it is about
0.2 .mu.m for an exemplary case of a visible light having put to
practical use.
[0005] On the other hand, in the method using an electron beam,
typically a scanning electron beam method (SEM method) has been put
to practice, wherein the resolution thereof is 0.1 .mu.m and the
inspection time is 8 hours per wafer (20 cm wafer). The electron
beam method has a distinctive feature that it is able to inspect
for any electrical defects (breaking of wire in the wirings, bad
continuity, bad continuity of via). However, the inspection speed
thereof is very low, and so the development of an inspection
apparatus with higher inspection speed has been expected.
[0006] Generally, since an inspection apparatus is expensive and a
throughput thereof is rather lower as compared to other processing
apparatuses, therefore the inspection apparatus has been used after
an important process, for example, after the process of etching,
film deposition, CMP (Chemical-mechanical polishing) planarization
or the like.
[0007] The inspection apparatus of scanning electron microscope
(SEM) using an electron beam will now be described. In the
inspection apparatus of SEM method, the electron beam is focused to
be narrower (the diameter of this beam corresponds to the
resolution thereof) and this narrowed beam is used to scan a sample
so as to irradiate it linearly. On the other hand, moving a stage
in the direction normal to the scanning direction allows an
observation region to be irradiated by the electron beam as a plane
area. The scanning width of the electron beam is typically some 100
.mu.m. Secondary electrons emitted from the sample by the
irradiation of said focused and narrowed electron beam (referred to
as a primary electron beam) are detected by a detector (a
scintillator plus PMT (i.e., photo multiplier tube) or a detector
of semiconductor type (i.e., a PIN diode type) or the like). A
coordinate for an irradiated location and an amount of the
secondary electrons (signal intensity) are combined and formed into
an image, which is stored in a storage or displayed on a CRT (a
cathode ray tube). The above description shows the principle of the
SEM (scanning electron microscope), and defects in a semiconductor
wafer (typically made of Si) in the course of processes may be
detected from the image obtained in this method. The inspection
speed (corresponding to the throughput) is varied in dependence on
an amount of primary electron beam (the current value), a beam
diameter, and a speed of response of the detecting system. The beam
diameter of 0.1 pn (which may be considered to be equivalent to the
resolution), the current value of 100 nA, and the speed of response
of the detector of 100 MHz are the currently highest values, and in
the case using those values the inspection speed has been evaluated
to be about 8 hours for one wafer having the diameter of 20 cm.
This inspection rate, which is extremely lower as compared with the
case using light (not greater than 1/20), has been a big problem
(drawback).
[0008] On the other hand, as a method for improving the inspection
speed or a drawback of the SEM method, new SEM (multi beam SEM)
method using a plurality of electron beams and an apparatus
therefor have been disclosed. In this method, though the inspection
rate can be improved by a number of the plurality of electron
beams, there are other problems that since a plurality of primary
electron beam is irradiated from an oblique direction and a
plurality of secondary electron beam is taken out along an oblique
direction from a sample, the detector receives the secondary
electrons emitted from the sample only along the oblique direction,
that a shadow emerges on an image, and further that secondary
electron signals are mixed together because it is difficult to
separate respective secondary electrons coming from the plurality
of electron beams respectively.
[0009] Conventionally, there has been known an evaluation apparatus
in which a primary electron beam emitted from an electron gun is
focused to be narrower by a lens system to be irradiated onto a
surface of the sample, and then secondary electrons emitted from
the sample are detected to evaluate the sample surface such as a
line width measurement, inspection for the defects thereon or the
like. In this kind of evaluation apparatus, the S/N ratio is
required to be higher than a predetermined value (for example, 22
to 70). In the case where thermal field emission electron gun is
used, it is required to detect the secondary electrons in a range
of 1,000 to 10,000 for each pixel.
[0010] For example, assuming a detection efficiency being 10%,
10.sup.4 to 10.sup.5 pieces of primary electrons have to be
irradiated for each pixel. When converting this value into dose,
dose D (Q/cm.sup.2) may be represented, assuming the pixel size
being 0.1 .mu.m square, as:
D = 10 4 1.6 10 - 19 Q / ( 0.1 10 - 4 ) 2 ~ 10 5 1.6 10 - 19 Q / (
0.1 10 - 4 ) 2 = 16 .mu. c / c m 2 ~ 160 .mu. c / c m 2
##EQU00001##
[0011] Such dose value as in the range of 16 .mu.c/c m.sup.2 to 160
.mu.c/c m.sup.2 is a significantly large value for the wafer
containing a layer of almost completely finished transistor, and
such a dose value may have a negative effect thereon that, for
example, a threshold voltage Vth of the transistor may
increase.
[0012] That is, the conventional evaluation apparatus of
semiconductor wafer has to employ large S/N ratio and thus large
dose, which means when the dose is increased to irradiate large
amount of primary electron beam, the threshold voltage of the
transistor on the wafer is increased, eventually resulting in a
characteristic of the semiconductor device being damaged during the
evaluation of a wafer.
[0013] Further, in the prior art, there has been another problem
that there may occur a location offset between an image of
secondary electron beam obtained by irradiating the primary
electron beam onto the sample surface and a reference image
prepared beforehand, resulting in a deterioration of accuracy in
detecting the defect. This location offset may cause a considerably
serious problem when an irradiation area of the primary electron
beam has an offset with respect to the wafer, and thereby a part of
an inspection pattern drops out of the detecting image of the
secondary electron beam, which cannot be dealt with only by a
technology for optimizing a matching area within the detecting
image. This must be a fatal drawback especially in the inspection
for a fine micro pattern.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to provide a substrate
inspection method capable of inspecting and evaluating a sample
with high throughput and high reliability, and a substrate
inspection apparatus therefor and an electron beam apparatus for
the inspection apparatus.
[0015] Another object of the present invention is to provide a
substrate inspection method capable of employing a desired level of
S/N ratio of a detection signal of a secondary electron even if a
dose of a primary charged particle beam being decreased, and a
substrate inspection apparatus therefor and an electron beam
apparatus for the inspection apparatus.
[0016] Still another object of the present invention is to provide
a substrate inspection method capable of inspecting for any defects
with small amount of information and of selecting either way of
evaluating a large size of wafer and the like with high throughput
or with high accuracy, and a substrate inspection apparatus
therefor and an electron beam apparatus for the inspection
apparatus.
[0017] Still another object of the present invention is to provide
a substrate inspection method in which a plurality of charged
particle beams may be irradiated at once, and either one of an
evaluation with improved measuring accuracy and an evaluation with
improved throughput may be selected because of being equipped with
a storage section storing a lens condition or an axial alignment
condition of a primary optical system and a secondary optical
system corresponding to a pixel size for scanning the sample, and
also to provide a substrate inspection apparatus therefor and an
electron beam apparatus for the inspection apparatus.
[0018] Still another object of the present invention is to provide
a substrate inspection method in which independent of an adjustment
of the lens condition of the primary optical system, a focusing
condition and a magnifying ratio of the secondary optical system
may be adjusted so that a divergence of these values from the
design values may be compensated for so as to accomplish highly
reliable inspection and evaluation, and also to provide a substrate
inspection apparatus therefor and an electron beam apparatus for
the inspection apparatus.
[0019] Still another object of the present invention is to provide
a substrate inspection apparatus in which an angular aperture may
be adjusted independently between the primary and the secondary
optical systems to minimize a number of optical components which
cannot be axially aligned and the lens condition may be adjusted in
both optical systems, and also to provide an electron beam
apparatus for the inspection apparatus.
[0020] Still another object of the present invention is to provide
a substrate inspection method in which in a pattern forming surface
of the sample, an area with many defects expected to occur therein
and an area with wide variation of evaluation values expected
therein are selected so as to irradiate the electron beam or the
light thereon to evaluate such areas with priority, thereby
promoting a quick evaluation, and also to provide a substrate
inspection apparatus therefor and an electron beam apparatus for
the inspection apparatus.
[0021] Still another object of the present invention is to provide
a substrate inspection apparatus comprising at least one of a laser
reflector mirror having a stiffness as high as possible without any
necessity for using a thick base body and another laser reflector
mirror capable of removing recesses on a mirror surface possibly
caused by voids and at the same time retaining a highly accurate
flatness of the mirror surface, and also to provide an electron
beam apparatus for the inspection apparatus.
[0022] Still another object of the present invention is to provide
a substrate inspection method in which a killer defect can be
discriminated from a non-killer defect even if a minimum line width
being 0.1 .mu.m or less, and in addition, an inspection time can be
reduced as compared with the case of the defect inspection
apparatus using the SEM, and also to provide a substrate inspection
apparatus therefor and an electron beam apparatus for the
inspection apparatus.
[0023] Still another object of the present invention is to provide
a substrate inspection method in which an accurate measuring
equipment such as a laser interferometer is installed in a stage
position and thereby a precise inspection may be accomplished even
in the case where a measurement is performed under unstable
temperature condition or a relative vibration exists between an
optical system of an electron beam apparatus and a sample chamber
or a stage, and also to provide a substrate inspection apparatus
therefor and an electron beam apparatus for the inspection
apparatus.
[0024] Still another object of the present invention is to provide
a substrate inspection method in which a single inspection
apparatus has a plurality of functions so that the inspection and
the evaluation of the sample may be performed with small number of
apparatuses, thereby reducing a ratio of a foot print occupied by
the inspection apparatuses in a clean room of a semiconductor
manufacturing equipment, and also to provide a substrate inspection
apparatus therefor and an electron beam apparatus for the
inspection apparatus.
[0025] Still another object of the present invention is to provide
a substrate inspection apparatus which is provided with a
non-contact supporting mechanism by means of a hydrostatic bearing
and a vacuum sealing mechanism by means of differential pumping so
that a pressure difference may be generated between a charged
particle beam irradiating region and a hydrostatic bearing support
section and a gas desorbed from a surface of component facing to
the hydrostatic bearing may be reduced, and also to provide an
electron beam apparatus for the inspection apparatus.
[0026] Still another object of the present invention is to provide
a semiconductor device manufacturing method in which such a
substrate inspection method, a substrate inspection apparatus and a
charged particle beam apparatus for the inspection apparatus as
described above are used in the semiconductor device manufacturing
process to perform a defect inspection and an evaluation of the
sample, thereby improving a yield of device product and preventing
any defective products from being delivered.
[0027] It is to be noted that in the present application, a term
"inspection" is used to mean not only an detection of malfunction
state such as defect but also an evaluation of a detected
result.
[0028] A substrate inspection method according to a first invention
of the present application comprises the steps of:
[0029] (1) emitting a primary charged particle beam from a charged
particle beam source;
[0030] (2) irradiating said generated primary charged particle beam
onto a substrate through a primary optical system;
[0031] (3) introducing a secondary charged particle beam into a
secondary optical system, said secondary charged particle beam
being emitted from said substrate by said irradiation of said
primary charged particle beam;
[0032] (4) detecting said secondary charged particle beam having
been introduced into said secondary optical system and converting
said detected secondary charged particle beam into an electric
signal; and
[0033] (5) processing said electric signal to evaluate said
substrate.
[0034] In an embodiment of said substrate inspection method, said
charged particle beam source may be actuated in a space charge
limited region, so that the primary charged particle beam emitted
from said charged particle beam source may be irradiated onto a
multi aperture plate having a plurality of apertures of said
primary optical system, and thereby the plurality of charged
particle beams having passed through said plurality of apertures
may be formed into an image on the substrate surface. Further, said
charged particle beam source may be actuated in the space charge
limited region, and said charged particle beam source may emit said
primary charged particle beam from a plurality of electron emission
region on a circle corresponding to said plurality of apertures of
the multi aperture plate of the primary optical system.
[0035] Further, in another embodiment of said substrate inspection
method, said substrate inspection method may further comprise a
step (6) in which said detection system detects the secondary
charged particle beam emitted from a plurality of regions on said
substrate to obtain a plurality of sub-image data, and a step (7)
for re-arranging said detected plurality of sub-image data to
generate an image data of the inspection region on the substrate,
and may further comprise a step (8) for storing in advance a
reference image data with respect to the substrate to be evaluated,
and a step (9) for evaluating the substrate by comparing said image
data generated by an image processor with said stored reference
image data.
[0036] Further, in still another embodiment of said substrate
inspection method, said substrate may be controlled so as to
continuously move in the Y-axis direction; respective charged
particle beam are driven to simultaneously scan in the X-axis
direction such that irradiation spots of a plurality of primary
charged particle beams on the substrate are arranged with equal
spacing therebetween in the X-axis direction and respective
scanning regions may partially be superimposed with each other in
the X-axis direction; and while comparing the sub-image data, the X
and the Y coordinates of respective charged particle beams are
taken into account thereby inspecting the surface of the substrate.
Further, in said substrate inspection method, a lens condition or
an axial alignment condition of said primary and said secondary
optical systems corresponding to the pixel size for scanning and
irradiating said substrate may be stored.
[0037] Further, in still another embodiment of said substrate
inspection method, said substrate inspection method may further
comprise the steps of converting said electric signal into a
pattern information and comparing said pattern information with a
reference pattern, wherein a minimum value of distance between
respective charged particle beams in said plurality of charged
particle beams may be controlled to be larger than a value of
resolution of said secondary optical system converted into a value
on the surface of said substrate.
[0038] Further, still another embodiment of said substrate
inspection method may further comprise the steps of converting said
electric signal received from said detection section into a binary
information, converting said binary information into a rectangular
pattern information, and comparing said rectangular pattern
information with the reference pattern.
[0039] In still another embodiment of the substrate inspection
method according to said first invention, for generating an image
of the substrate and evaluating a pattern formed on said substrate
based on said image, said method may further comprise the steps of:
storing a reference image corresponding to said image of the
substrate; reading out said stored reference image; comparing said
image of the substrate with said read-out reference image and
detecting different portions between both images; and classifying
said different portions into such defects including at least
short-circuit, disconnection, convex, chipping, pinhole and
isolation; wherein for generating said image of the substrate, said
method may further comprise the steps of: scanning the substrate
surface by a plurality of beams each focused to be narrower by the
primary optical system; converging the secondary charged particle
beam from the substrate by an objective lens and further separating
said converged secondary charged particle beam from the primary
optical system by an E.times.B separator; magnifying an angle
formed between an orbit of the secondary charged particle beam from
said substrate and an optical axis by the secondary optical system
by using a single stage lens so as to be focused on a multi
apertures for detection; and detecting said focused secondary
charged particle beam by a plurality of detectors.
[0040] Further, in still another embodiment of said substrate
inspection method, in a pattern forming surface of said substrate,
an area with many defects being expected to occur therein and an
area with wide variation of evaluation values being expected
therein may be selected; and the charged particle beam may be
irradiated onto these areas to evaluate such areas with priority;
wherein: in an evaluation of the pattern forming surface whose
whole pattern is formed by dividing said pattern forming surface
into a plurality of areas and forming respective pattern for each
area, said evaluation may be executed by selecting a boundary area
between said divided areas; or in an evaluation of the pattern
forming surface which is formed by dividing the pattern forming
surface into a plurality of adjacent stripes and forming a pattern
for each stripe by a lithography, said evaluation may be executed
by selecting a boundary area between the stripes, a boundary area
between primary fields of view or a boundary area between secondary
fields of view of a pattern projection in the lithography.
[0041] Further, in still another embodiment of said substrate
inspection method, the charged particle beam may be irradiated onto
said pattern forming surface of the substrate, and said pattern may
be evaluated based on said secondary charged particle beam,
wherein, in the pattern forming surface, an area with many defects
being expected to occur therein and an area with wide variation of
evaluation values being expected therein may be selected, and a
central portion of the field of view of the apparatus used for the
present inspection may be located to be superimposed on the
selected areas.
[0042] In still another embodiment of the substrate inspection
method according to said first invention, said method may further
comprise the steps of: detecting an abnormal pattern from the image
data generated by processing said electric signal; and determining
whether or not said detected abnormal pattern is a killer defect
based on a relation thereof with the predetermined reference
pattern; wherein said image processing section may process a
plurality of image data corresponding to said plurality of
secondary charged particle beams simultaneously or in parallel.
[0043] Further, in still another embodiment of said substrate
inspection method, at least two functions selected from the group
consisting of a defect detection of the substrate surface, a defect
review of the substrate surface, a pattern line width measurement,
and a pattern potential measurement may be performed, wherein said
defect detection of the substrate surface may be performed by
comparing the image obtained by the image signal with the pattern
data or by comparing the different dice with each other; said
defect review of the substrate surface may be performed by
observing the image obtained by a scanning of the beam on the
monitor synchronized with a scanning of the primary charged
particle beam on the substrate surface; said pattern line width
measurement may be performed by using a line profile image of the
secondary charged particle beam obtained when the primary charged
particle beam scan the substrate surface in a short side direction
of the pattern; and said pattern potential measurement may be
performed by applying a negative potential to an electrode disposed
in the nearest location to the substrate surface and thereby
selectively driving back the secondary charged particle beam
emitted from the pattern on the substrate surface having a high
potential.
[0044] Still another embodiment of said substrate inspection method
may further comprise a step of setting an evaluation condition such
that a processed condition of each substrate should be evaluated
within a processing time necessary for processing one substrate by
a processing unit, or such that the processed condition of one lot
of substrates should be evaluated within the processing time
necessary for processing one lot of substrates by the processing
unit, wherein said step may further comprise a step of setting an
evaluation area of the substrate such that the processed condition
should be evaluated only in a specified area.
[0045] In still another embodiment of said substrate inspection
method according to the first invention, said inspection method may
further comprise the steps of: obtaining respective images of a
plurality of regions to be inspected each displaced from others
while partially superimposing with each other on said substrate;
storing a reference image; and comparing said obtained images of
the plurality of regions to be inspected with said stored reference
image and thereby determining a defect on said substrate.
[0046] In still another embodiment of said substrate inspection
method, said inspection method may further comprise the steps of:
performing an irradiation of the primary charged particle beam onto
said substrate within a working chamber controlled to be a desired
atmosphere; performing a transfer of said substrate into and out of
said working chamber through a space within a vacuum chamber;
applying a potential to said substrate within said working chamber;
and observing the surface of said substrate and aligning said
substrate to an irradiation location of said primary charged
particle beam.
[0047] A second invention according to the present application
provides an electron beam apparatus in which a primary charged
particle beam is irradiated onto a substrate to emit a secondary
charged particle beam and said secondary charged particle beam is
detected to evaluate the substrate, said apparatus comprising:
[0048] a charged particle beam source for generating the primary
charged particle beam;
[0049] a primary optical system for irradiating a plurality of said
primary charged particle beams onto said substrate while scanning
them relative to said substrate;
[0050] a secondary optical system into which the secondary charged
particle beams emitted from said substrate by the irradiation of
said primary charged particle beams are introduced;
[0051] a detection system for detecting the secondary charged
particle beams introduced into said secondary optical system and
converting the detected secondary charged particle beams into an
electric signals; and
[0052] a process control system for evaluating the substrate based
on said electric signal.
[0053] A third invention according to the present application
provides an electron beam apparatus in which a primary charged
particle beam is irradiated onto a substrate to emit a secondary
charged particle beam and said secondary charged particle beam is
detected to evaluate the substrate, said apparatus comprising:
[0054] a charged particle beam source for emitting the primary
charged particle beam;
[0055] a primary optical system for irradiating a single beam of
said primary charged particle beam onto said substrate while
scanning it relative to said substrate;
[0056] a secondary optical system into which the secondary charged
particle beam emitted from said substrate by the irradiation of
said primary charged particle beam is introduced;
[0057] a detection system for detecting the secondary charged
particle beam introduced into said secondary optical system and
converting the detected secondary charged particle beam into an
electric signal; and
[0058] a process control system for evaluating the substrate based
on said electric signal.
[0059] In an embodiment of the electron beam apparatus according to
the second invention, said charged particle beam source may be set
to actuate within a space charge limited region; a cathode of said
charged particle beam source may be made of monocrystal LaB.sub.6;
and the charged particle beam emitted from the charged particle
beam source may be irradiated onto a multi aperture plate having a
plurality of apertures of said primary optical system, and the
plurality of charged particle beams having passed through said
plurality of apertures may be formed into an image on a surface of
said substrate; or alternatively said charged particle beam source
may be set to actuate within the space charge limited region; said
primary optical system may comprise a multi aperture plate having a
plurality of apertures arranged on a circle; and a plurality of
cathode of the charged particle beam source, each made of
LaB.sub.6, may be arranged on a circle so that each electron
emission region thereof may correspond to each of said plurality of
apertures of said multi aperture plate respectively.
[0060] Further, in an embodiment of the electron beam apparatus
according to the second invention, said detection system may detect
the secondary charged particle beam emitted from a plurality of
regions of said substrate to obtain a plurality of sub-image data,
and said electron beam apparatus may further comprise an image
processor for re-arranging said detected plurality of sub-image
data to generate an image data of the inspection region on the
substrate, wherein, said electron beam apparatus may further
comprise a memory for storing in advance a reference image data
with respect to the substrate to be evaluated, and an evaluator for
evaluating the substrate by comparing said image data generated by
said image processor with said reference image data stored in said
memory. In said case, said substrate may be controlled so as to
continuously move in the Y-axis direction; said primary optical
system may be configured such that respective charged particle
beams are driven to simultaneously scan in the X-axis direction so
that irradiation spots of a plurality of charged particle beams on
the substrate are arranged with approximately equal spacing
therebetween in the X-axis direction, and respective scanning
regions may partially be superimposed with each other in the
X-direction; and said image processor is configured such that while
said sub-image data being re-arranged, the X and the Y coordinates
of respective charged particle beams should be taken into account
to generate the image data of the substrate surface.
[0061] Further, in another embodiment of the electron beam
apparatus according to the second invention, said apparatus may
further comprise a storage section for storing a lens condition or
an axial alignment condition of said primary and said secondary
optical systems corresponding to a pixel size with which said
primary charged particle beams are irradiated onto said substrate
while scanning them relative to said substrate.
[0062] Further, in an embodiment of the electron beam apparatus
according to the third invention, said apparatus may further
comprise a storage section for storing a lens condition or an axial
alignment condition of said primary and said secondary optical
systems corresponding to a pixel size with which said primary
charged particle beams are irradiated onto said substrate while
scanning it relative to said substrate.
[0063] Further, in another embodiment of the electron beam
apparatus according to the third invention, said apparatus
comprises, said electronic optical system may further comprise: at
least one stage of axially symmetric lens comprising an electrode
made by processing an insulating material and applying a metal
coating onto a surface thereof; a plurality combinations of said
charged particle beam source, said primary optical system and said
secondary optical system, each of said combinations comprising an
optical column; and a storage section for storing a lens condition
or an axial alignment condition of said primary and said secondary
optical systems corresponding to a pixel size used for scanning
said substrate.
[0064] Further, in another embodiment of the electron beam
apparatus according to the second invention, in said apparatus,
said process control system may comprise a secondary charged
particle beam processing section, wherein said secondary charged
particle beam processing section comprises a converter for
converting said electric signal into a pattern information, and a
comparator for comparing said pattern information with the
reference pattern, wherein a minimum value of distance between
respective charged particle beams in said plurality of charged
particle beams may be controlled to be larger than a value of
resolution of said secondary optical system converted into a value
on the surface of said substrate.
[0065] Further, in another embodiment of the electron beam
apparatus according to the second and the third inventions, in said
apparatus, said process control system may comprise said image
processing section, wherein said image processing section may
comprise a converter for converting said electric signal received
from said detection section into a binary information, a converter
for converting said binary information into a rectangular pattern
information, and a comparator for comparing said rectangular
pattern information with the reference pattern. In this case, said
primary and said secondary optical systems may be accommodated in
an optical column, wherein said primary optical system may
comprise, in said optical column, at least one axially symmetric
lens made of insulating material with an electrode formed on a
surface thereof by metal coating.
[0066] Further, in another embodiment of the electron beam
apparatus according to the second invention, generating an image of
the substrate and evaluating a pattern formed on said substrate
based on said image may be performed by: storing a reference image
corresponding to said image of the substrate; reading out said
stored reference image; comparing said image of the substrate with
said read-out reference image and detecting different portions
between both images; and classifying said different portions into
such defects including at least short-circuit, disconnection,
convex, chipping, pinhole and isolation; wherein said generating
the image of the substrate is performed by: scanning the substrate
surface by a plurality of beams each focused to be narrower by the
primary optical system; converging the secondary charged particle
beam from the substrate by an objective lens and further separating
said converged secondary charged particle beam from the primary
optical system by an E.times.B separator; focusing a secondary
charged particle beam image from said substrate on a multi aperture
for detection with an angle formed between a secondary electron
orbit and an optical axis being magnified, by said secondary
optical system using at least one stage of lens; and detecting said
focused secondary charged particle beam by a plurality of
detectors; wherein said electron beam apparatus may further
comprise (1) a function for pre-aligning said substrate, (2) a
function for registering in advance a recipe for performing an
inspection of said substrate, (3) a function for reading out a
substrate number formed on said substrate, (4) a function for
reading out a recipe corresponding to said substrate by using said
read-out substrate number, (5) a function for performing an
inspection based on said read-out recipe, (6) a function for
registering in advance an inspection pattern image for said
substrate, (7) a function for reading out and displaying said
registered inspection pattern image, (8) a function for moving said
substrate based on a specification on said inspection pattern image
or a direction of said recipe so that said specified or directed
inspection point may approach a desired location, (9) a function
for registering in advance a reference image for said specified or
directed inspection point, (10) a function for forming said
reference image for said specified or directed inspection point and
positioning said inspection point by comparing an image for
positioning said specified or directed inspection point with a
reference image for positioning said inspection point, (11) a
function for forming an image for inspecting said positioned
inspection point, (12) a function for storing said reference image
for inspecting said positioned inspection point, (13) a function
for displaying said image for inspection and said reference image
for inspection, (14) a function for comparing said both images to
detect different portions therebetween, (15) a function for
classifying said different portions into such defects including at
least short-circuit, disconnection, convex, chipping, pinhole and
isolation, (16) a function for classifying the size of said
respective defects including at least short-circuit, disconnection,
convex, chipping, pinhole and isolation, (17) a function for
irradiating a probe onto said different portions on said substrate
so as to physically analyze, (18) a function for overwriting said
inspection pattern image with a classification result of the
different portions of said specified or directed inspection point,
(19) a function for calculating a defect density of all defects as
well as respective defects classified by type or size for
respective chips, substrates and a specified substrate when said
substrate is a substrate, (20) a function for registering in
advance a defect size-critical rate table for said respective
defect types, (21) a function for calculating a yield for
respective chips, substrates and a specified substrate based on
said defect size-critical rate table for said respective defect
types, (22) a function for registering a different portion
detection result of said specified inspection point, a
classification result of said different portions, and a calculation
result of said respective defect densities and yields, and (23) a
function for outputting said registered respective inspection
results and calculation results.
[0067] Further, in another embodiment of the electron beam
apparatus according to the second invention, said primary optical
system may comprise a aperture plate for forming said primary
charged particle beam into a plurality of beams, and an E.times.B
separator, wherein an aperture determining an angular aperture for
said primary optical system may be disposed between said aperture
plate and said E.times.B separator, or alternatively, said primary
optical system may further comprise a condenser lens for focusing
said primary charged particle beam emitted from said charged
particle beam source to form a crossover image, and the apertures
for forming said primary charged particle beam into a plurality of
beams, wherein said apertures may be disposed between said
condenser lens and said crossover image, and an numerical aperture
for said primary optical system may be adjusted by changing a
magnifying ratio of said crossover image or adjusted to a design
value, or alternatively, said primary optical system may further
comprise a condenser lens for focusing said primary charged
particle beam emitted from said charged particle beam source to
form a first crossover image, and a aperture plate for forming said
primary charged particle beam into a plurality of beams, wherein
said aperture plate may be disposed between said condenser lens and
said first crossover image, and said secondary optical system may
further comprise a condenser lens for focusing said plurality of
secondary charged particle beam to form a second crossover
image.
[0068] In another embodiment of the electron beam apparatus
according to said first and said second inventions, in a pattern
forming surface of said substrate, an area with many defects being
expected to occur therein and an area with wide variation of
evaluation values being expected therein may be selected, and the
charged particle beam may be irradiated onto these areas to
evaluate such areas with priority, and in this case, in an
evaluation of the pattern forming surface whose whole pattern is
formed by dividing said pattern forming surface into a plurality of
areas and forming respective pattern for each area, said evaluation
may be executed by selecting a boundary area between said divided
areas, or alternatively, in an evaluation of the pattern forming
surface which is formed by dividing said pattern forming surface
into a plurality of adjacent stripes and forming a pattern for each
stripe by a lithography, said evaluation may be executed by
selecting a boundary area between the stripes, a boundary area
between primary fields of view of a pattern projection in the
lithography or a boundary area between sub-fields of view.
[0069] In another embodiment of the electron beam apparatus
according to said second and said third inventions, the charged
particle beam is irradiated onto a pattern forming surface of said
substrate, and said pattern is evaluated based on said secondary
charged particle beam, wherein, in said pattern forming surface, an
area with many defects being expected to occur therein and an area
with wide variation of evaluation values being expected therein may
be selected, and a central portion of the field of view of the
apparatus may be positioned to be superimposed on said selected
areas, or alternatively, said process control unit may comprise a
secondary charged particle beam signal processing section, a
detector for detecting an abnormal pattern from an image data
generated in said secondary charged particle beam processing
section and a determining system for determining whether or not
said detected abnormal pattern is a killer defect based on a
relation thereof with a predetermined reference pattern.
[0070] In another embodiment of the electron beam apparatus
according to said first and said second inventions, said apparatus
may further comprise at least two functions selected from the group
consisting of a defect detection of a substrate surface, a defect
review of the substrate surface, a pattern line width measurement,
and a pattern potential measurement. In the electron beam apparatus
of this embodiment, said defect detection of the substrate surface
may be performed by comparing an image obtained by an image signal
with a pattern data or by comparing different dice with each other,
said defect review of the substrate surface may be performed by
observing an image obtained by a scanning of the beam on a monitor
synchronized with a scanning of the primary charged particle beam
on the substrate surface, said pattern line width measurement may
be performed by using a line profile image of the secondary charged
particle beam obtained when the primary charged particle beam scans
the substrate surface in a short side direction of the pattern, and
said pattern potential measurement may be performed by applying a
negative potential to an electrode disposed in the nearest location
to the substrate surface and thereby selectively driving back the
secondary charged particle beam emitted from the pattern on the
substrate surface having a high potential.
[0071] In another embodiment of the electron beam apparatus
according to said second and said third inventions, said apparatus
may further comprise an evaluation condition setter for setting an
evaluation condition such that a processed condition of each
substrate should be evaluated within a processing time necessary
for processing one substrate by a processing unit, or
alternatively, said apparatus may further comprise an evaluation
condition setter for setting an evaluation condition such that a
processed condition of one lot of substrates should be evaluated
within a processing time necessary for processing one lot of
substrates by a processing unit. In this case, said evaluation
condition setter may comprise a setter for setting an evaluation
area of the substrate such that the processed condition should be
evaluated only in a specified area on a substrate surface.
[0072] In another embodiment of the electron beam apparatus
according to said second and said third inventions, said process
control unit may comprise an image obtaining device for obtaining
respective images of a plurality of regions to be inspected each
displaced from others while partially superimposing with each other
on said substrate, a memory for storing a reference image, and a
defect determining system for comparing said images of the
plurality of regions to be inspected obtained by said image
obtaining device with said reference image stored in said memory
and thereby determining a defect on said substrate.
[0073] Further, in another embodiment of the electron beam
apparatus according to said second and said third inventions, a
plurality of optical systems each including said charged particle
beam source, said primary optical system, said secondary optical
system and said detection system may be arranged on one substrate
to be inspected.
[0074] Further, in another embodiment of the electron beam
apparatus according to said second and said third inventions, said
primary optical system may comprise an objective lens, wherein an
electrostatic lens, which configures said objective lens, may have
an inner section made of ceramic material having a low linear
expansion coefficient which is integrally configured with another
ceramic material disposed outside thereof, and a plurality of
electrodes may be formed on a surface of the ceramic material of
said inner section by metal coating, wherein each of said plurality
of electrodes may be arranged respectively to be axially
symmetric.
[0075] Further, in another embodiment of the electron beam
apparatus according to said second and said third inventions, said
primary optical system may comprise an objective lens, wherein an
electrostatic lens, which configures said objective lens, may have
an inner section made of ceramic material capable of being
machined, which is adhesively fixed to another ceramic material
disposed outside thereof; and a plurality of electrodes may be
formed on a surface of the ceramic material of said inner section
by metal coating, wherein each of said plurality of electrodes may
be arranged respectively to be axially symmetric.
[0076] A fourth invention according to the present application
provides a substrate inspection apparatus for inspecting a pattern
formed on a substrate by irradiating a charged particle beam onto
said substrate, said apparatus comprising:
[0077] an electron beam apparatus comprising: a charged particle
beam source for emitting a charged particle beam; a primary optical
system for irradiating said charged particle beam onto said
substrate; a secondary optical system into which a secondary
charged particle beam is introduced, said secondary charged
particle beam being emitted from said substrate by an irradiation
of said charged particle beam; a detection system for detecting
said secondary charged particle beam introduced into said secondary
optical system and outputting as an electric signal; and a process
control system for processing and evaluating said electric
signal;
[0078] a stage unit for holding said substrate and moving said
substrate relatively to said electron beam apparatus;
[0079] a working chamber capable of shielding at least an upper
region of said stage unit form outside to control under desired
atmosphere; and
[0080] a substrate transfer mechanism for transferring said
substrate into or out of said stage.
[0081] In an embodiment of the substrate inspection apparatus
according to said fourth invention, said apparatus may further
comprise a laser interferometer for detecting a location of said
stage unit, wherein, said primary optical system may comprise an
objective lens which is configured by an axially symmetric
electrostatic lens at least whose outer section is made of ceramic
material having a low linear expansion coefficient, and a reference
mirror of said laser interferometer may be mounted on said outer
section of said electrostatic lens.
[0082] In another embodiment of said substrate inspection
apparatus, said apparatus may further comprise a laser
interferometer which includes a laser reflection mirror mounted at
least on said stage unit or formed by polishing a part of member of
said stage unit and is used for measuring a location of said stage
by reflecting a laser with said laser reflection mirror, wherein
said laser reflection mirror may be formed by a base body made of
SiC ceramic.
[0083] In another embodiment of the substrate inspection apparatus
according to said fourth invention, a plurality of optical columns
each including said charged particle beam source, said primary
optical system, said secondary optical system and said detection
system may be arranged therein in parallel; and a laser
interferometer which includes a laser reflection mirror mounted at
least on said stage unit or formed by polishing a part of member of
said stage unit and is used for measuring a location of said stage
by reflecting a laser with said laser reflection mirror may,
wherein said laser reflection mirror may be formed by a base body
made of SiC ceramic, and each of said plurality of optical columns
may comprise at least one stage of axially symmetric lens with an
outer diameter processed to be small size by machining a ceramic
and selectively applying a metal coating on a surface thereof.
[0084] In another embodiment of said substrate inspection
apparatus, said stage unit may be provided with a non-contact
supporting mechanism by means of a hydrostatic bearing and a vacuum
sealing mechanism by means of differential pumping, a divider may
be provided for making a conductance smaller between a region on a
surface of said substrate where said primary charged particle beam
is to be irradiated and a hydrostatic bearing support section of
said stage unit, so that a pressure difference may be generated
between said charged particle beam irradiating region and said
hydrostatic bearing support section.
[0085] In another embodiment of said substrate inspection
apparatus, a table of said stage unit may be accommodated in a
housing and supported in a non-contact manner by a hydrostatic
bearing, said housing accommodating said stage may be vacuumed, and
a differential pumping mechanism for evacuating a region on a
surface of said substrate where said primary charged particle beam
is to be irradiated may be provided so as to surround a portion of
said electron beam apparatus where said primary charged particle
beam is to be irradiated onto said substrate surface.
[0086] Further in another embodiment of said substrate inspection
apparatus, said apparatus may further comprise a vibration
isolation unit for isolating a vibration from a floor to said
vacuum chamber.
[0087] Further, in another embodiment of said substrate inspection
apparatus, said apparatus may further comprise a potential applying
mechanism disposed in said working chamber for applying a potential
to said object to be inspected, and an alignment control unit for
observing a surface of said object to be inspected and controlling
an alignment thereof in order to position said object to be
inspected with respect to said electron optical system.
[0088] Further, in another embodiment of said substrate inspection
apparatus, said electron beam apparatus may be any electron beam
apparatus defined in either of claim 24 to 55.
[0089] A fifth invention according to the present application
provides a semiconductor device manufacturing method comprising a
step of evaluating a semiconductor substrate in a course of
processes or after having been completed by using either of the
substrate inspection method, the electron beam apparatus or the
substrate inspection apparatus, described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0090] FIG. 1 is a cross-sectional elevational view taken along a
line A-A of FIG. 2, illustrating main components of an inspection
apparatus according to the present invention;
[0091] FIG. 2 is a cross-sectional plan view taken along a line B-B
of FIG. 1, illustrating the main components of the inspection
apparatus shown in FIG. 1 according to the present invention;
[0092] FIG. 3 is a cross sectional view of an alternative
embodiment of a cassette holder;
[0093] FIG. 4 is a cross sectional view taken along a line C-C of
FIG. 1, illustrating a mini-environment chamber shown in FIG.
1;
[0094] FIG. 5 is a cross sectional view taken along a line D-D of
FIG. 2, illustrating a loader housing shown in FIG. 1;
[0095] FIG. 6 is an enlarged view of a wafer rack, wherein (A) is a
side elevational view and (B) is a cross sectional view taken along
a line E-E of (A);
[0096] FIG. 7 shows an alternative embodiment of a main housing
support system;
[0097] FIG. 8 is a diagram illustrating a general configuration of
an electronic optical system of the inspection apparatus shown in
FIG. 1;
[0098] FIG. 9 shows a positional relationship between apertures in
a multi aperture plate used in an primary optical system of the
electron optical system shown in FIG. 8;
[0099] FIG. 10 illustrates an electron gun operating condition of
the electron optical system shown in FIG. 8;
[0100] FIG. 11 illustrates an E.times.B separator;
[0101] FIG. 12 illustrates a scanning/irradiating method of a
primary electron beam on a wafer;
[0102] FIG. 13 is a block diagram illustrating a configuration of
an image data processing section shown in FIG. 8;
[0103] FIG. 14 illustrates an operation of an image data
re-arranging device shown in FIG. 13;
[0104] FIG. 15 shows a potential applying mechanism;
[0105] FIG. 16 illustrates an electron beam calibration mechanism,
wherein (A) is a side elevational view and (B) is a plan view;
[0106] FIG. 17 is a schematic diagram of an alignment control
device for a wafer;
[0107] FIG. 18 is a block diagram illustrating a flow of inspection
algorism;
[0108] FIG. 19 is a flow chart illustrating an embodiment of a
semiconductor device manufacturing method according to the present
invention;
[0109] FIG. 20 is a flow chart illustrating a lithography process,
a core process in a wafer processing processes of FIG. 19;
[0110] FIG. 21 illustrates an arrangement of optical columns
barrels in the electron beam apparatus;
[0111] FIG. 22 illustrates an evaluation region in an alternative
embodiment of the inspection method;
[0112] FIG. 23 is an enlarged view of an area encircled by a circle
Cr of FIG. 22;
[0113] FIG. 24(A) is a diagram for illustrating a pattern line
width inspection, and FIG. 24(B) is a diagram for illustrating a
potential contrast measurement of a pattern;
[0114] FIG. 25 shows another embodiment of a stage unit used in the
substrate inspection apparatus according to the present invention,
wherein (A) is an elevational view and (B) is a side elevational
view;
[0115] FIG. 26 is a detailed perspective view of a hydrostatic
bearing section shown in FIG. 25;
[0116] FIG. 27 shows another embodiment of a stage unit and an
embodiment of evacuating system on a tip of the optical column used
in the substrate inspection apparatus according to the present
invention;
[0117] FIG. 28 shows another embodiment of the stage unit and the
evacuating system on a tip of the optical column used in the
substrate inspection apparatus according to the present
invention;
[0118] FIG. 29 shows still another embodiment of the stage unit and
the evacuating system on a tip of the optical column used in the
substrate inspection apparatus according to the present
invention;
[0119] FIG. 30 shows still another embodiment of the stage unit and
the evacuating system on a tip of the optical column used in the
substrate inspection apparatus according to the present
invention;
[0120] FIG. 31 shows another embodiment of a vacuum chamber and an
XY stage used in the substrate inspection apparatus according to
the present invention;
[0121] FIG. 32 shows an example of a differential pumping mechanism
installed in the system shown in FIG. 31;
[0122] FIG. 33 shows a circulation piping system of gas for the
system shown in FIG. 31;
[0123] FIG. 34 is a diagram illustrating a general configuration of
another embodiment of the electron beam apparatus according to the
present invention;
[0124] FIG. 35 is a schematic diagram illustrating a potential
distribution in a potential contrast measurement;
[0125] FIG. 36 is a diagram illustrating a relation between a pulse
potential applied to a blanking deflector and an incident beam
current onto a sample in a potential measurement of high time
resolution;
[0126] FIG. 37 is a flow chart illustrating an inspection procedure
according to the present invention;
[0127] FIG. 38 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0128] FIG. 39 is a diagram for explaining a wafer inspection
method according to the present invention, illustrating a pattern
defect detection;
[0129] FIG. 40 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0130] FIG. 41 is a diagram illustrating an embodiment of a
scanning electron beam apparatus to which a feature of the electron
beam apparatus of FIG. 40 is applied;
[0131] FIG. 42 illustrates an arrangement of the optical systems in
the electron beam apparatus;
[0132] FIG. 43 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0133] FIG. 44 illustrates a configuration of an electrostatic
lens, which configures an object lens, installed in the electron
beam apparatus shown in FIG. 43;
[0134] FIG. 45 is a diagram illustrating an embodiment of a
scanning electron beam apparatus to which a feature of the
apparatus shown in FIG. 43 is applied;
[0135] FIG. 46 is a block diagram illustrating a preferred
manufacturing process of a laser reflection mirror shown in FIG.
44;
[0136] FIG. 47 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0137] FIG. 48 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0138] FIG. 49 illustrates how to discriminate a killer defect from
a non-killer defect in an inspection by the electron beam apparatus
of FIG. 48;
[0139] FIG. 50 is a diagram illustrating a general configuration of
still another embodiment of the electron beam apparatus according
to the present invention;
[0140] FIG. 51 illustrates an aperture plate having a plurality of
apertures installed in the electron beam apparatus shown in FIG.
50;
[0141] FIG. 52 illustrates an example in which is arranged a
plurality of optical systems each having an integrated electron
beam apparatus according to the present invention;
[0142] FIG. 53 is a diagram illustrating a general configuration of
another embodiment of the defect inspection apparatus using the
electron beam apparatus according to the present invention;
[0143] FIG. 54 illustrates an example of a plurality of images to
be inspected obtained by the defect inspection apparatus of FIG. 53
as well as a reference image;
[0144] FIG. 55 is a flow chart illustrating a flow of a main
routine for wafer inspection in the defect inspection apparatus of
FIG. 53;
[0145] FIG. 56 is a flow chart illustrating a detailed flow of a
sub-routine in a process for obtaining a plurality of image data to
be inspected in FIG. 55;
[0146] FIG. 57 is a flow chart illustrating a detailed flow of a
sub-routine in a comparison process in FIG. 55; and
[0147] FIG. 58 is a conceptual diagram illustrating a plurality of
regions to be inspected, each being displaced from others while
partially superimposing with each other on a surface of the
semiconductor wafer.
DETAILED DESCRIPTION OF THE INVENTION
[0148] There will now be described preferred embodiments of the
present invention as a substrate inspection apparatus for
inspecting a substrate or a wafer as an object to be inspected
having a pattern formed on a surface thereof, with reference to the
attached drawings.
[0149] Referring to FIGS. 1 and 2, main components of a substrate
inspection apparatus 1 according to an embodiment of the present
invention is shown by an elevational view and a plan view.
[0150] The semiconductor testing apparatus 1 of this embodiment
comprises a cassette holder 10 for holding cassettes which stores a
plurality of wafers; a mini-environment chamber 20; a main housing
30 which defines a working chamber; a loader housing 40 disposed
between the mini-environment chamber 20 and the main housing 30 to
define two loading chambers; a loader 60 for loading a wafer from
the cassette holder 10 onto a stage device 50 disposed in the main
housing 30; and an electro-optical device 70 installed in the
vacuum main housing 30. These components are arranged in a
positional relationship as illustrated in FIGS. 1 and 2. The
semiconductor testing apparatus 1 further comprises a pre-charge
unit 81 disposed in the vacuum main housing 30; a potential
applying mechanism 83 (see in FIG. 15) for applying a to a wafer;
an electron beam calibration mechanism 85 (see in FIG. 16); and an
optical microscope 871 which forms part of an alignment controller
87 for aligning the wafer on the stage device 50.
Cassette Holder
[0151] The cassette holder 10 is configured to hold a plurality
(two in this embodiment) of cassettes 14 (for example, closed
cassettes such as SMIF,FOUP manufactured by Assist Co.) in which a
plurality (for example, 25) of wafers are placed side by side in
parallel, oriented in the vertical direction. The cassette holder
can be arbitrarily selected for installation adapted to a
particular loading mechanism. Specifically, when a cassette,
carried to the cassette holder 10, is automatically loaded into the
cassette holder 10 by a robot or the like, the cassette holder 10
having a structure adapted to the automatic loading can be
installed. When a cassette is manually loaded into the cassette
holder 10, the cassette holder 10 having an open cassette structure
can be installed. In this embodiment, the cassette holder 10 is the
type adapted to the automatic cassette loading, and comprises, for
example, an up/down table 11, and an elevation mechanism 12 for
moving the up/down table 11 up and down. The cassette 14 can be
automatically set onto the up/down table 11 in the position
indicated by chain lines in FIG. 2. After the setting, the cassette
c is automatically rotated to the position indicated by solid lines
in FIG. 2 so that it is directed to the axis of pivotal movement of
a first carrier unit within the mini-environment chamber 20. In
addition, the up/down table 11 is moved down to the position
indicated by chain lines in FIG. 1. In this way, the cassette
holder 10 for use in automatic loading, or the cassette holder 10
for use in manual loading may be both implemented by those in known
structures, so that detailed description on their structures and
functions are omitted.
[0152] As an alternative embodiment for the above described
cassette holder 10 and cassette 14, such a device 10a as shown in
FIG. 3 may be considered. This device 10a holds a plurality of
substrates W with a diameter of 300 mm in a substrate carrier box
15a with each substrate being separated from others. This substrate
carrier box 15a has a box main body 151 disposed on a stationary
table 11a, and conveys and stores the wafers W horizontally and
parallelly with each other as each contained in a slot-like pocket
(not shown) fixedly mounted in said box main body. The box main
body 151a of the substrate carrier box 15a has an opening in a side
facing to a mini-environment chamber, and said opening is designed
to be selectively opened or closed by a door 152a for carrying
in/out the substrate, said door being provided in a housing 22 of
the mini-environment chamber. This door 152a for carrying in/out
the substrate is designed to be opened/closed by an automatic door
opening/closing unit, though not shown. The device 10a comprises a
lid body 153a, which is disposed in an opposite side of said
opening facing to the mini-environment chamber, for covering
another opening through which filters and a fun motor are to be
attached or detached, said slot like pocket (not shown) for holding
the substrate, a UPA filter 155a, a chemical filter 156a, and a fun
motor 157a. In this embodiment also, the wafer W is carried in or
out by a first transfer unit 61 of robot type in a loader 60.
[0153] It is to be noted that the substrate or the wafer received
in the cassette 14 is a wafer to be subjected to an inspection,
wherein said inspection is performed after or in a course of a
process for processing the wafer in the semiconductor manufacturing
process. In specific, such a substrate or a wafer as having been
subjected to a film deposition process, a CMP process, or an ion
implantation process, a wafer with a wiring pattern formed thereon
or a wafer with a wiring pattern not yet formed thereon is received
in the cassette. Since a plurality of wafers is received in the
cassette 14 so as to be arranged horizontally and parallelly
placing a space therebetween and stacked vertically, an arm of the
first transfer unit is designed to be movable vertically so that a
wafer in any position may be caught by said first transfer unit as
will be described later.
Mini-Environment Chamber
[0154] In FIGS. 1, 2 and 4, the mini-environment chamber 20
comprises a housing 22 which defines a mini-environment space 21
that is controlled for an atmosphere; a gas circulating device 23
for circulating a gas such as clean air within the mini-environment
space 21 for the control; a discharging device 24 for recovering a
portion of air supplied into the mini-environment space 21 for
discharging; and a pre-aligner 25 for roughly aligning a substrate,
i.e., a wafer under testing, which is placed in the
mini-environment space 21.
[0155] The housing 22 has a top wall 221, a bottom wall 222, and
peripheral wall 223 which surrounds four sides of the housing 22 to
provide a structure for isolating the mini-environment space 21
from the outside. For controlling the atmosphere in the
mini-environment space 21, the gas circulating device 23 comprises
a gas supply unit 231 attached to the top wall 221 within the
mini-environment space 21 as illustrated in FIG. 4 for cleaning a
gas (air in this embodiment) and delivering the cleaned gas
downward through one or more gas delivering ports (not shown) in
laminar flow; a recovery duct 232 disposed on the bottom wall 222
within the mini-environment space for recovering air which has
flown down to the bottom; and a conduit 233 for connecting the
recovery duct 232 to the gas supply unit 231 for returning
recovered air to the gas supply unit 231. In this embodiment, the
gas supply unit 231 takes about 20% of air to be supplied, from the
outside of the housing 22 for cleaning. However, the percentage of
gas taken from the outside may be arbitrarily selected. The gas
supply unit 231 comprises an HEPA or ULPA filter in a known
structure for creating cleaned air. The laminar downflow of cleaned
air is mainly supplied such that the air passes a carrying surface
formed by the first carrier unit, later described, disposed within
the mini-environment space 21 to prevent dust particles, which
could be produced by the carrier unit, from attaching to the wafer.
Therefore, the downflow nozzles need not be positioned near the top
wall as illustrated, but is only required to be above the carrying
surface formed by the carrier unit. In addition, the air need not
either be supplied over the entire mini-environment space 21. It
should be noted that an ion wind may be used as cleaned air to
ensure the cleanliness as the case may be. Also, a sensor may be
provided within the mini-environment space 21 for observing the
cleanliness such that the apparatus is shut down when the
cleanliness is degraded. An access port 225 is formed in a portion
of the peripheral wall 223 of the housing 22 that is adjacent to
the cassette holder 10. A gate valve in a known structure may be
provided near the access port 225 to shut the access port 225 from
the mini-environment chamber 20. The laminar downflow near the
wafer may be, for example, at a rate of 0.3 to 0.4 m/sec. The gas
supply unit 231 may be disposed outside the mini-environment space
21 instead of within the mini-environment space 21.
[0156] The discharging device 24 comprises a suction duct 241
disposed at a position below the wafer carrying surface of the
carrier unit and below the carrier unit; a blower 242 disposed
outside the housing 22; and a conduit 243 for connecting the
suction duct 241 to the blower 242. The discharging device 24 sucks
a gas flowing down around the carrier unit and including dust,
which could be produced by the carrier unit, through the suction
duct 241, and discharges the gas outside the housing 22 through the
conduits 243, 244 and the blower 242. In this event, the gas may be
emitted into an exhaust pipe (not shown) which is laid to the
vicinity of the housing 22.
[0157] The aligner 25 disposed within the mini-environment space 21
optically or mechanically detects an orientation flat (which refers
to a flat portion formed on the outer periphery of a circular
wafer) formed on the wafer, or one or more V-shaped notches formed
on the outer peripheral edge of the wafer to previously align the
position of the wafer in a rotating direction about the axis
O.sub.1-O.sub.1 at an accuracy of approximately .+-. one degree.
The pre-aligner forms part of a mechanism for determining the
coordinates of an object under testing and is responsible for rough
alignment of an object under testing. Since the pre-aligner itself
may be of a known structure, description on its structure and
operation is omitted.
[0158] Although not shown, a recovery duct for the discharger 24
may also be provided below the pre-aligner such that air including
dust, emitted from the pre-aligner, is discharged to the
outside.
Main Housing
[0159] In FIGS. 1 and 2, the main housing 30, which defines the
working chamber 31, comprises a housing body 32 that is supported
by a housing supporting device 33 fixed on a vibration isolator 37
disposed on a base frame 36. The housing supporting device 33
comprises a frame structure 331 assembled into a rectangular form.
The housing body 32 comprises a bottom wall 321 securely fixed on
the frame structure 331; a top wall 322; and a peripheral wall 323
which is connected to the bottom wall 321 and the top wall 322 and
surrounds four sides of the housing body 32, and isolates the
working chamber 31 from the outside. In this embodiment, the bottom
wall 321 is made of a relatively thick steel plate to prevent
distortion due to the weight of equipment carried thereon such as
the stage device. Alternatively, another structure may be employed.
In this embodiment, the housing body 32 and the housing supporting
device 33 are assembled into a rigid construction, and the
vibration isolator 37 prevents vibrations from the floor, on which
the base frame 36 is placed, from being transmitted to the rigid
structure. A portion of the peripheral wall 323 of the housing body
32 that adjoins the loader housing 40, later described, is formed
with an access port 325 for introducing and removing a wafer.
[0160] The vibration isolator 37 may be either of an active type
which has an air spring, a magnetic bearing and so on, or a passive
type likewise having these components. Since any known structure
may be employed for the vibration isolator 37, description on the
structure and functions of the vibration isolator itself is
omitted. The working chamber 31 is held in a vacuum atmosphere by a
vacuum system (not shown) in a known structure. A controller 2 for
controlling the operation of the overall apparatus is disposed
below the base frame 36.
[0161] The vacuum system described above is composed of a vacuum
pump, a vacuum valve, a vacuum gauge, a vacuum pipe and the like,
though each being not shown, and exhausts to vacuum an electronic
optical system, a detector section, a working chamber and a loading
chamber which will be described later, according to a predetermined
sequence. In each of those sections, the vacuum valve is controlled
so as to accomplish a required vacuum level. The vacuum level is
regularly monitored, and in the case of irregularity, an interlock
function executes an emergency control such as an interception of
communication between the chambers or between the chamber and the
evacuating system by an isolation valve, though not shown, to
secure the vacuum level for each section. As for the vacuum pump, a
turbo molecular pump may be used for main exhaust, and a dry pump
of Root type may be used as a roughing vacuum pump. A pressure at
an inspection spot (an electron beam irradiating section) or in the
working chamber is practically in a range of 10.sup.-3 to 10.sup.-5
Pa, preferably in a range of 10.sup.-4 to 10.sup.-6 Pa as shifted
by one digit down.
Loader Housing
[0162] In FIGS. 1, 2 and 5, the loader housing 40 comprises a
housing body 43 which defines a first loading chamber 41 and a
second loading chamber 42. The housing body 43 comprises a bottom
wall 431; a top wall 432; a peripheral wall 433 which surrounds
four sides of the housing body 43; and a partition wall 434 for
partitioning the first loading chamber 41 and the second loading
chamber 42 such that both the loading chambers can be isolated from
the outside. The partition wall 434 is formed with an aperture,
i.e., an access port 435 for passing a wafer between both the
loading chambers. Also, portions of the peripheral wall 433 that
adjoin the mini-environment chamber 20 and the main housing 30 is
formed with access ports 436 and 437, respectively. The housing
body 43 of the loader housing 40 is carried on and supported by the
frame structure 331 of the housing supporting device 33. This
prevents the vibrations of the floor from being transmitted to the
loader housing 40 as well. The access port 436 of the loader
housing 40 is in alignment with the access port 226 of the housing
22 of the mini-environment chamber 20, and a gate valve 27 is
provided for selectively isolating a interaction between the
mini-environment space 21 and the first loading chamber 41. The
gate valve 27 has a sealing material 271 which surrounds the
peripheries of the access ports 226, 436 and is fixed to the side
wall 433 in close contact therewith; a door 272 for isolating air
from flowing through the access ports in cooperation with the
sealing material 271; and an actuator 273 for moving the door 272.
Likewise, the access port 437 of the loader housing 40 is in
alignment with the access port 325 of the housing body 32, and a
gate valve 45 is provided for selectively isolating a intraction
between the second loading chamber 42 and the working chamber 31 in
a hermetic manner. The gate valve 45 comprises a sealing material
451 which surrounds the peripheries of the access ports 437 and 325
and is fixed to side walls 433 and 323 in close contact therewith;
a door 452 for isolating air from flowing through the access ports
in cooperation with the sealing material 451; and an actuator 453
for moving the door 452. Further, the aperture formed through the
partition wall 434 is provided with a gate valve 46 for closing the
aperture with the door 461 to selectively isolating a interaction
between the first and second loading chambers in a hermetic manner.
These gate valve 27, 45, 46 are configured to provide air-tight
sealing for the respective chambers when they are in a closed
state. Since these gate valve may be implemented by known ones,
detailed description on their structures and operations is omitted.
It should be noted that a method of supporting the housing 22 of
the mini-environment chamber 20 is different from a method of
supporting the loader housing 40. Therefore, for preventing
vibrations from being transmitted from the floor through the
mini-environment chamber 20 to the loader housing 40 and the main
housing 30, a vibration-absorption damping material may be disposed
between the housing 22 and the loader housing 40 to provide
air-tight sealing for the peripheries of the access ports.
[0163] Within the first loading chamber 41, a wafer rack 47 is
disposed for supporting a plurality (two in this embodiment) of
wafers spaced in the vertical direction and maintained in a
horizontal position. As illustrated in FIG. 6, the wafer rack 47
comprises posts 472 fixed at four corners of a rectangular
substrate 471, spaced from one another, in an upright position.
Each of the posts 472 is formed with supporting devices 473 and 474
in two stages, such that peripheral edges of wafers W are carried
on and held by these supporting devices. Then, leading ends of arms
of the first and second carrier units, later described, are brought
closer to wafers from adjacent posts and grab the wafers.
[0164] The loading chambers 41 and 42 can be controlled for the
atmosphere to be maintained in a high vacuum condition (at a
pressure of 10.sup.-5 to 10.sup.-6 Pa) by a pumping system (not
shown) in a known structure including a vacuum pump for the working
chamber, not shown. In this event, the first loading chamber 41 may
be held in a low vacuum condition as a low vacuum chamber, while
the second loading chamber 42 may be held in a high vacuum
condition as a high vacuum chamber, to effectively prevent
contamination of wafers. The employment of such a structure allows
a wafer, which is accommodated in the loading chamber and is next
subjected to the defect testing, to be carried into the working
chamber without delay. The employment of such a loading chambers
provides for an improved throughput for the defect testing, and the
highest possible vacuum condition around the electron source which
is required to be kept in a high vacuum condition, together with
the principle of a multi-beam type electron system, later
described.
[0165] The first and second loading chambers 41 and 42 are
connected to a vacuum exhaust pipe and a vent pipe for an inert gas
(for example, dried pure nitrogen) (neither of which are shown),
respectively. In this way, the atmospheric state within each
loading chamber is attained by an inert gas vent (which injects an
inert gas to prevent an oxygen gas and so on other than the inert
gas from attaching on the surface). Since an apparatus itself for
implementing the inert gas vent is known in structure, detailed
description thereon is omitted.
[0166] In the testing apparatus according to the present invention
which uses an electron beam, when representative lanthanum
hexaboride (LaB.sub.6) used as an electron source for an
electro-optical system, later described, is once heated to such a
high temperature that causes emission of thermal electrons, it
should not be exposed to oxygen within the limits of possibility so
as not to shorten the lifetime. The exposure to oxygen can be
prevented without fail by carrying out the atmosphere control as
mentioned above at a stage before loading a wafer into the working
chamber in which the electron-optical system is disposed.
Stage Device
[0167] The stage device 50 comprises a fixed table 51 disposed on
the bottom wall 301 of the main housing 30; a Y-table 52 movable in
a Y-direction on the fixed table 51 (the direction vertical to the
drawing sheet in FIG. 1); an X-table 54 movable in an X-direction
on the Y-table 52 (in the left-to-right direction in FIG. 1); a
turntable 56 rotatable on the X-table; and a holder 57 disposed on
the turntable 56. A wafer is releasably held on a wafer carrying
surface 571 of the holder 57. The holder 57 may be of a known
structure which is capable of releasably grabbing a wafer by means
of a mechanical or electrostatic chuck feature. The stage device 50
uses servo motors, encoders and a variety of sensors (not shown) to
operate a plurality of tables as mentioned above to permit highly
accurate alignment of a wafer held on the carrying surface 571 by
the holder 57 in the X-direction, Y-direction and Z-direction (in
the up-down direction in FIG. 1) with respect to an electron beam
irradiated from the electro-optical device, and in a direction
about the axis normal to the wafer supporting surface (.theta.
direction). The alignment in the Z-direction may be made such that
the position on the carrying surface of the holder, for example,
can be finely adjusted in the Z-direction. In this event, a
reference position on the carrying surface is sensed by a position
measuring device using a laser of an extremely small diameter (a
laser interferometer) to control the position by a feedback
circuit, not shown. Additionally or alternatively, the position of
a notch or an orientation flat of a wafer is measured to sense a
plane position or a rotational position of the wafer relative to
the electron beam to control the position of the wafer by rotating
the turntable 54 by a stepping motor which can be controlled in
extremely small angular increments. In order to maximally prevent
particle produced within the working chamber, servo motors 531, 531
and encoders 522, 532 for the stage device 50 are disposed outside
the main housing 30. Since the stage device 50 may be of a known
structure used, for example, in steppers and so on, detailed
description on its structure and operation is omitted. Likewise,
since the laser interferometer may also be of a known structure,
detailed description on its structure and operation is omitted.
[0168] It is also possible to establish a basis for signals which
are generated by previously inputting a rotational position, and
X-, Y-positions of a wafer relative to the electron beam in a
signal detecting system or an image processing system, later
described. The wafer chucking mechanism provided in the holder is
configured to apply a voltage for chucking a wafer to an electrode
of an electrostatic chuck, and the alignment is made by pinning
three points on the outer periphery of the wafer (preferably spaced
equally in the circumferential direction). The wafer chucking
mechanism comprises two fixed aligning pins and a push-type clamp
pin. The clamp pin can implement automatic chucking and automatic
releasing, and constitutes a conducting spot for applying the
voltage. While in this embodiment, the X-table is defined as a
table which is movable in the left-to-right direction in FIG. 2;
and the Y-table as a table which is movable in the up-down
direction, a table movable in the left-to-right direction in FIG. 2
may be defined as the Y-table; and a table movable in the up-down
direction as the X-table.
Loader
[0169] The loader 60 comprises a robot-type first carrier unit 61
disposed within the housing 22 of the mini-environment chamber 20;
and a robot-type second carrier unit 63 disposed within the second
loading chamber 42.
[0170] The first carrier unit 61 comprises a multi-node arm 612
rotatable about an axis O.sub.1-O.sub.1 with respect to an actuator
611. While an arbitrary structure may be used for the multi-node
arm, the multi-node arm in this embodiment has three parts which
are pivotably attached to each other. One part of the arm 612 of
the first carrier unit 61, i.e., the first part closest to the
actuator 611 is attached to a rotatable shaft 613 by a driving
mechanism (not shown) of a known structure, disposed within the
actuator 611. The arm 612 is pivotable about the axis
O.sub.1-O.sub.1 by means of the shaft 613, and radially telescopic
as a whole with respect to the axis O.sub.1-O.sub.1 through
relative rotations among the parts. At a leading end of the third
part of the arm 612 furthest away from the shaft 613, a holding
device 616 in a known structure for holding a wafer, such as a
mechanical chuck or an electrostatic chuck, is disposed. The
actuator 611 is movable in the vertical direction by an elevating
mechanism 615 in a known structure.
[0171] The first carrier unit 61 extends the arm 612 in either a
direction M1 or a direction M2 of two cassettes 14 held in the
cassette holder 10, and removes a wafer accommodated in a cassette
14 by carrying the wafer on the arm or by grabbing the wafer with
the chuck (not shown) attached at the leading end of the arm.
Subsequently, the arm is retracted (in a position as illustrated in
FIG. 2), and then rotated to a position at which the arm can extend
in a direction M3 toward the prealigner 25, and stopped at this
position. Then, the arm is again extended to transfer the wafer
held on the arm to the prealigner 25. After receiving a wafer from
the prealigner 25, contrary to the foregoing, the arm is further
rotated and stopped at a position at which it can extend to the
second loading chamber 41 (in the direction M3), and transfers the
wafer to a wafer rack 47 within the second loading chamber 41. For
mechanically grabbing a wafer, the wafer should be grabbed on a
peripheral region (in a range of approximately 5 mm from the
peripheral edge). This is because the wafer is formed with device
construction (circuit patterns) over the entire surface except for
the peripheral region, and grabbing the inner region would result
in failed or defective devices.
[0172] The second carrier unit 63 is basically identical to the
first carrier unit 61 in structure except that the second carrier
unit 63 carries a wafer between the wafer rack 47 and the carrying
surface of the stage device 50, so that detailed description
thereon is omitted.
[0173] In the loader 60, the first and second carrier units 61 and
63 each carry a wafer from a cassette held in the cassette holder
10 to the stage device 50 disposed in the working chamber 31 and
vice versa, while remaining substantially in a horizontal position.
The arms of the carrier units are moved in the vertical direction
only when a wafer is removed from and inserted into a cassette,
when a wafer is carried on and removed from the wafer rack, and
when a wafer is carried on and removed from the stage device 50. It
is therefore possible to smoothly carry a larger wafer, for
example, a wafer having a diameter of 30 cm.
[0174] Next, how a wafer is carried will be described in sequence
from the cassette 14 held by the cassette holder 10 to the stage
device 50 disposed in the working chamber 31.
[0175] As described above, when the cassette is manually set, the
cassette holder 10 having a structure adapted to the manual setting
is used, and when the cassette is automatically set, the cassette
holder 10 having a structure adapted to the automatic setting is
used. In this embodiment, as the cassette 14 is set on the up/down
table 11 of the cassette holder 10, the up/down table 11 is moved
down by the elevating mechanism 12 to align the cassette c with the
access port 225.
[0176] As the cassette is aligned with the access port 225, a cover
(not shown) provided for the cassette is opened, and a cylindrical
cover is applied between the cassette 14 and the access port 225 of
the mini-environment to block the cassette and the mini-environment
space 21 from the outside. Since these structures are known,
detailed description on their structures and operations is omitted.
When the mini-environment chamber 20 is provided with a gate for
opening and closing the access port 225, the gate is operated to
open the access port 225.
[0177] On the other hand, the arm 612 of the first carrier unit 61
remains oriented in either the direction M1 or M2 (in the direction
M1 in this description). As the access port 225 is opened, the arm
612 extends to receive one of wafers accommodated in the cassette
at the leading end. While the arm and a wafer to be removed from
the cassette are adjusted in the vertical position by moving up or
down the actuator 611 of the first carrier unit 61 and the arm 612
in this embodiment, the adjustment may be performed by moving up
and down the up/down table 11 of the cassette holder 10, or
performed by both.
[0178] As the arm 612 has received the wafer, the arm 621 is
retracted, and the gate is operated to close the access port (when
the gate is provided). Next, the arm 612 is pivoted about the axis
O.sub.1-O.sub.1 such that it can extend in the direction M3. Then,
the arm 612 is extended and transfers the wafer carried at the
leading end or grabbed by the chuck onto the prealigner 25 which
aligns the orientation of the rotating direction of the wafer (the
rotational direction about the central axis vertical to the wafer
plane) within a predetermined range. Upon completion of the
alignment, the carrier unit 61 retracts the arm 612 after a wafer
has been received from the prealigner 25 to the leading end of the
arm 612, and takes a posture in which the arm 612 can be extended
in a direction M4. Then, the door 272 of the gate valve 27 is
operated to open the access ports 223, 236, and the arm 612 is
extended to place the wafer on the upper stage or the lower stage
of the wafer rack 47 within the first loading chamber 41. It should
be noted that before the gate valve 27 opens the access ports to
transfer the wafer to the wafer rack 47, the aperture 435 formed
through the partition wall 434 is closed by the door 461 of the
gate valve 46 in an air-tight state.
[0179] In the process of carrying a wafer by the first carrier
unit, clean air flows (as a downflow) in laminar flow from the gas
supply unit 231 disposed on the housing of the mini-environment
chamber to prevent particle from attaching on the upper surface of
the wafer during the carriage. A portion of the air near the
carrier unit (in this embodiment, about 20% of the air supplied
from the supply unit 231, mainly contaminated air) is drawn from
the suction duct 241 of the discharging device 24 and emitted
outside the housing. The remaining air is recovered through the
recovery duct 232 disposed on the bottom of the housing and
returned again to the gas supply unit 231.
[0180] As the wafer is placed into the wafer rack 47 within the
first loading chamber 41 of the loader housing 40 by the first
carrier unit 61, the gate valve 27 is closed to seal the loading
chamber 41. Then, the first loading chamber 41 is filled with an
inert gas to expel air. Subsequently, the inert gas is also
evacuated so that a vacuum atmosphere dominates within the loading
chamber 41. The vacuum atmosphere within the loading chamber 41 may
be at a low vacuum degree. When a certain degree of vacuum is
provided within the loading chamber 41, the gate valve 46 is
operated to open the access port 434 which has been sealed by the
door 461, and the arm 632 of the second carrier unit 63 is extended
to receive one wafer from the wafer receiver 47 with the holding
device at the leading end (the wafer is carried on the leading end
or held by the chuck attached to the leading end). Upon completion
of the receipt of the wafer, the arm 632 is retracted, followed by
the gate 46 again operated to close the access port 435 by the door
461. It should be noted that the arm 632 has previously taken a
posture in which it can extend in the direction N1 of the wafer
rack 47 before the gate 46 is operated to open the access port 435.
Also, as described above, the access ports 437, 325 have been
closed by the door 452 of the gate valve 45 before the gate valve
46 is operated to block the interaction between the second loading
chamber 42 and the working chamber 31 in an air-tight condition, so
that the second loading chamber 42 is evacuated.
[0181] As the gate valve 46 is operated to close the access port
435, the second loading chamber 42 is again evacuated at a higher
degree of vacuum than the first loading chamber 41. Meanwhile, the
arm of the second carrier unit 61 is rotated to a position at which
it can extend toward the stage device 50 within the working chamber
31. On the other hand, in the stage device 50 within the working
chamber 31, the Y-table 52 is moved upward, as viewed in FIG. 2, to
a position at which the center line X.sub.0-X.sub.0 of the X-table
54 substantially matches an X-axis X.sub.1-X.sub.1 which passes a
pivotal axis O.sub.2-O.sub.2 of the second carrier unit 63. The
X-table 54 in turn is moved to the position closest to the leftmost
position in FIG. 2, and remains awaiting at this position. When the
second loading chamber 42 is evacuated to substantially the same
degree of vacuum as the working chamber 31, the door 452 of the
gate valve 45 is moved to open the access ports 437, 325, allowing
the arm 632 to extend so that the leading end of the arm 632, which
holds a wafer, approaches the stage device 50 within the working
chamber 31. Then, the wafer is placed on the carrying surface 571
of the stage device 50. As the wafer has been placed on the
carrying surface 571, the arm is retracted, followed by the gate
valve 45 operated to close the access ports 437, 325.
[0182] The foregoing description has been made on the operation
until a wafer in the cassette 14 is carried and placed on the stage
device. For returning a wafer, which has been carried on the stage
device and processed, from the stage device to the cassette 14, the
operation reverse to the foregoing is performed. Since a plurality
of wafers are stored in the wafer rack 47, the first carrier unit
61 can carry a wafer between the cassette and the wafer rack 47
while the second carrier unit 63 is carrying a wafer between the
wafer rack 47 and the stage device 50, so that the testing
operation can be efficiently carried out.
[0183] In specific, when there are a wafer W, which has been
already processed, and a wafer W, which has not yet been processed,
in a wafer rack 47 in the first loading chamber, at first, the
wafer which has not yet been processed is transferred to the stage
50 and the processing is started. During this processing, the wafer
which has already been processed is transferred from the stage 50
to the wafer rack 47. On the other hand, the other which has not
yet been processed is picked up from the wafer rack 47 again by the
arm, which after having been positioned by a pre-aligner, is
further transferred to the wafer rack 47 of a loading chamber 41.
This procedure may allow, in the wafer rack 47, the wafer A which
has already been processed to be substituted by the wafer which has
not yet been processed, during the wafer being processed.
[0184] Alternatively, depending on the way how to use such an
apparatus for executing an inspection and/or an evaluation, a
plurality of stage units 50 may be arranged in parallel, so that
the wafers may be transferred from one wafer rack 47 to each of the
stage units 50 thereby applying a similar processing to a plurality
of wafers.
Modifications of Main Housing
[0185] FIG. 7 illustrate exemplary modifications to the method of
supporting the main housing 30. In an exemplary modification
illustrated in FIG. 7(B), a housing supporting device 33c is made
of a thick rectangular steel plate 331c, and a housing body 32c is
placed on the steel plate. Therefore, the bottom wall 321c of the
housing body 32c is thinner than the bottom wall 222 of the housing
body 32 in the foregoing embodiment. In an exemplary modification
illustrated in FIG. 7(B), a housing body 32c and a loader housing
40c are suspended by a frame structure 336c of a housing supporting
device 33c. Lower ends of a plurality of vertical frames 337c fixed
to the frame structure 336c are fixed to four corners of a bottom
wall 321c of the housing body 32c, such that the peripheral wall
and the top wall are supported by the bottom wall. A vibration
isolator 37c is disposed between the frame structure 336c and a
base frame 36c. Likewise, the loader housing 40 is suspended by a
suspending member 49c fixed to the frame structure 336. In the
exemplary modification of the housing body 32c illustrated in FIG.
7(B), the housing body 32c is supported in suspension, the general
center of gravity of the main housing and a variety of devices
disposed therein can be brought downward. The methods of supporting
the main housing and the loader housing, including the exemplary
modifications described above, are configured to prevent vibrations
from being transmitted from the floor to the main housing and the
loader housing.
[0186] In another exemplary modification, not shown, the housing
body of the main housing is only supported by the housing
supporting device from below, while the loader housing may be
placed on the floor in the same way as the adjacent
mini-environment chamber. Alternatively, in a further exemplary
modification, not shown, the housing body of the main housing is
only supported by the frame structure in suspension, while the
loader housing may be placed on the floor in the same way as the
adjacent mini-environment chamber.
Electron Beam Apparatus
[0187] An electron optical apparatus 70 (hereafter simply refer to
an electron beam apparatus) of this embodiment will be explained
hereafter. The electron beam apparatus 70 comprises a optical
column 701 fixedly mounted to a housing 32, said optical column
containing an electron gun 71a as a device for emitting a charge
particle beam, a primary electron optical system 72 (hereafter
simply referred to as a primary optical system) for irradiating a
electron beam (hereafter, a electron beam is used for one example
of a charge particle beam) emitted from the electron gun 71 to a
sample or substrate and a secondary electron optical system 74
(hereafter simply referred to as a secondary optical system) to
which a secondary electron emitted from the substrate is
introduced, a detecting system 76, and a process control system, as
schematically illustrated in FIGS. 8 and 9.
[0188] A thermal electron beam source is employed as an electron
beam source. An electron emitting member (emitter) is made of
LaB.sub.6. Other material may be used for the electron emitting
member so far as it has a high melting point (low vapor pressure at
high temperature) and a small work function. In order to generate a
plurality of electron beams, two kinds of method may be used. One
is such a method in which firstly a single electron beam is emitted
from a single emitter (having a single projection) and then is
passed through a thin plate with a plurality of apertures formed
therein (aperture plate) to generate a plurality of electron beams,
while in the other method, a plurality of projections is formed on
the emitter so that a single electron beam may be emitted from a
single projection and thereby a plurality of electron beams may be
emitted as a whole. In either method, the electron beam is
generated by taking advantage of such a nature that the projection
facilitates a high intensity discharge occurs at a tip thereof. The
electron beam generated in the other types of electron beam source
such as a thermal field emission type electron beam source may be
used.
[0189] It is to be noted that the thermal electron beam source is
of such a method in which the electron emitting member is heated to
emit electrons, while the thermal field emission electron beam
source is of such a method in which a high electric field is
applied to the electron emitting member to emit an electron and
further the electron beam emitting section is heated so as to
stabilize the electron emission.
[0190] The present invention has paid attention to the fact that a
shot noise in the secondary electron can be reduced by lowering the
shot noise in the primary electron beam because a main part of the
shot noise in the secondary electron comes from that of the primary
electron beam, and accordingly the electron gun 71 of this
embodiment is constructed so that a desired degree of S/N ratio of
the detection signal of the secondary electron may be accomplished
even if a quantity of radiation of the primary electron beam is
rather small.
[0191] A method for reducing the shot noise in the primary electron
beam will be described below.
[0192] Under a condition where the electron gun is controlled by a
cathode temperature, that is, the electron gun is operating in a
temperature limited region, a shot noise i.sub.n emitted from the
electron gun may be represented by the expression below: (See
"Communication engineering handbook" edited by The Institution of
Telecommunications Engineers, 1957, p. 471.)
i.sub.n.sup.2=2eI.sub.pB.sub.f (1)
where, i.sub.n.sup.2 is a mean square of a noise current, e is a
charge of an electron, I.sub.p is an anode current and B.sub.f is a
frequency bandwidth of a signal amplifier. When the electron flow
is in a space charge limited region, the expression (1) may be
rewritten as:
i.sub.n.sup.2=.GAMMA..sup.22eI.sub.pB.sub.f (2)
where, .GAMMA..sup.2 is a shot noise reduction factor and is
smaller than 1.
[0193] When the cathode temperature is high enough, .GAMMA..sup.2
moves to about 0.018 at the lowest, and the noise current lowers
down to 13% of that in the case of the temperature limited region.
Assuming that the secondary electron is nearly equal to the primary
electron (secondary electron.apprxeq.primary electron), the S/N
ratio in this case may be expressed as:
S / N = I p / { .GAMMA. ( 2 e I p B f ) 1 / 2 } = 1 / .GAMMA. ( I p
/ ( 2 e B f ) 1 / 2 } = n 1 / 2 / ( .GAMMA. 2 1 / 2 ) ( 3 )
##EQU00002##
When .GAMMA.=0.13 is applied to the expression (3), the S/N ratio
can be expressed as:
S/N=7.7(n/2).sup.1/2 (4)
where, n is a number of the secondary electrons per pixel.
[0194] That is, the electron gun operating in the space charge
limited region exhibits a performance equivalent to that in the
case where, in comparison with the case of the electron gun
operating in the temperature limited region (TFE case), the 59
(=1/.GAMMA..sup.2=1/0.13.sup.2) times as much as electrons may be
required per pixel. Since the latter has higher intensity than that
of the former by approximately two digits, the latter has a
possibility to be required larger beam current than the former by
two digits when assuming the same beam diameter and the same
optical system for both of them, but when a new optical system
suitable for the former is designed, the latter may provide the
beam current larger than that of the former by one digit. The S/N
ratio of the latter is 1/55 of that of the former. In other words,
in the electron gun in the space charge limited region, the
measuring time and the dose may be as small as 0.18 times
(10/55.apprxeq.0.18) and 1/55 of those of the electron gun in the
temperature limited region, respectively.
[0195] Whether or not the electron gun is operating in the space
charge limited region can be examined by a method described below
with reference to FIG. 10.
[0196] FIG. 10[A] shows a relation between an electron gun current
and a cathode heating current. In FIG. 10(A), a region Q.sub.1 is
the region wherein the electron gun current hardly increases in
response to an increase of the cathode heating current, that is,
this region Q.sub.1 is the space charge limited region.
[0197] On the other hand, FIG. 10[B] shows a relation between the
electron gun current and an anode voltage. In FIG. 10(B) a region
Q.sub.2 is the region wherein the electron gun current sharply
increases in response to an increase of the anode voltage, that is,
this region Q.sub.2 is also the space charge limited region.
[0198] As is obvious from the above description, the electron gun
may be determined to be operating in the space charge limited
region if the cathode heating current of the electron gun is
increased to measure the electron gun current and said electron gun
current is observed to be in the saturated condition, the region
Q1, or if the anode voltage of the electron gun is increased to
measure the electron gun current and said electron gun current is
observed to be in the steeply changing region. Accordingly, the
condition for operating the electron gun in the space charge
limited region may be determined.
[0199] In the electron gun 71, the heating current or the anode
voltage (voltage applied to an anode 712) is set such that the
electron gun 71 may operate in the space charge limited region, as
described above. A cathode 711 of the electron beam 71 is made of
monocrystal LaB.sub.6 and has nine projections each provided with a
tip of trapezoidal cone shape, though not shown. These projections
are arranged along a circle so that each of them corresponds to
each of a plurality of apertures in a first multi aperture plate,
which will be described later with reference to FIG. 9. Each tip of
these projections has a curvature of radius of about 30 .mu.m.
Since each electron beam is emitted only from a vicinity of the tip
of trapezoidal cone projection, in the case of relatively high
electron gun current such as about 1 mA, for the voltage of 1 kV,
the intensity of 1.times.10.sup.4 A/cm.sup.2 sr (1 kV) may be
obtained.
[0200] The primary optical system 72 serves to irradiate the
primary electron beam emitted from the electron beam 71 onto a
surface of a substrate or wafer W to be inspected, and comprises:
an electrostatic lens or a condenser lens 721 for focusing the
primary electron beam; a first multi aperture plate 723 disposed
below said condenser lens 721 and provided with a plurality of
apertures formed therein for forming the primary electron beam into
a plurality of electron beams or multi-beams; another electrostatic
lens or a reduction lens 725 for reducing the primary electron
beams; an E.times.B separator 726 including an electromagnetic
deflector 727 and an electrostatic deflector 728; and an objective
lens 729, each being arranged in this order placing the condenser
lens 721 at a top position as shown in FIG. 8 such that an optical
axis OA.sub.1 of the primary electron beam emitted from the
electron gun is perpendicular to the surface of the object or wafer
W to be inspected.
[0201] In order to eliminate an effect of field curvature
aberration possibly caused by the reduction lens 725 and the
objective lens 729, a plurality of apertures 7231 (nine apertures
in this embodiment) formed in the multi aperture plate 723 is
arranged along a circle around a center of the optical axis
OA.sub.1, such that projected points of the apertures onto X-axis
may be equally spaced by Lx, as shown in FIG. 9. Each of the
apertures may be, for example, a circle with a diameter of about 1
to 10 microns, and also it may be of square shape. Further, a
position of the first multi aperture plate 723 is necessary to be
adjusted such that the aperture may be positioned in a point where
the primary electron beam emitted from the electron beam 71 has the
greatest intensity. For this purpose, the multi aperture plate 723
is mounted on at least one stage of an XY stage allowing a movement
in a plane including the multi aperture plate 723, a Z stage
allowing a movement in a direction perpendicular to the plane
including the multi aperture plate 723 and a .theta. stage allowing
a rotation of the plane including the multi aperture plate 723, and
at least one stage of the XY stage, the Z stage and the 0 stage
each holding the multi aperture plate is adjusted such that the
intensity of the plurality of electron beams formed by the multi
aperture plate 723 should be uniform and greatest.
[0202] The primary optical system 72 further comprises: an
electrostatic deflector 731 for blanking; an electrostatic
deflector 733 for deflecting the primary electron beam so as to
cause a scanning motion; a knife edge 732 for blanking; and an
axially symmetric electrode 737 disposed between the objective lens
729 and the wafer W. The axially symmetric electrode 737 is held to
be, for example, a potential of -10V with respect to a potential 0V
of the wafer.
[0203] Then the E.times.B separator 726 will be described with
reference to FIG. 11. FIG. 11[A] shows an E.times.B separator
according to a first embodiment of the present invention. This
separator consists of the electrostatic deflector 728 and the
electromagnetic deflector 727, and is shown in FIG. 11 by a cross
sectional views projected onto an X-Y plane perpendicular to the
optical axis OA.sub.1 (perpendicular to the paper of the
drawing).
[0204] The electrostatic deflector 728 comprises a pair of
electrodes (electrostatic deflecting electrodes) 7281 disposed in a
vacuum container and generates an electric field in the
X-direction. Each of these electrostatic deflecting electrodes 7281
is mounted to a vacuum wall 7283 of the vacuum container via an
insulating spacer 7282, and a distance Dp between these electrodes
is designed to be shorter than a length 2Lp along the Y-direction
of the electrostatic deflecting electrodes 7281. Owing to this
design, an area where an electric field intensity generated around
a Z axis or the optical axis OA.sub.1 is uniform may be made
relatively wider, wherein ideally if Dp<Lp, the area with
uniform electric field intensity could be made further wider.
[0205] That is, since in an area within a distance of Dp/2 from an
end of the electrode, the electric field intensity is not uniform,
the area with almost uniform electric field intensity is in a
central area or 2Lp-Dp area which excludes the end areas with
non-uniform electric field intensity. This means that a condition
of existence of the uniform electric field intensity is 2Lp>Dp,
and in addition, designing to be Lp>Dp makes the uniform
electric field area further wider.
[0206] On an outside of the vacuum wall 7283 is provided an
magnetic deflector for generating a magnetic field in the
Y-direction. The magnetic deflector 727 comprises an magnetic coil
7271 and another magnetic coil 7272, wherein each of these coils
generates a magnetic field in the X- and the Y-directions
respectively. It is to be noted that although the magnetic field in
the Y-direction can be generated only by the coil 7272, the coil
7271 for generating the magnetic field in the X-direction is also
mounted in order to improve an orthogonality between the electric
field and the magnetic field. That is, the orthogonality between
the electric field and the magnetic field can be improved by
offsetting a magnetic field component in the +X direction generated
by the coil 7272 with a magnetic field component in the -X
direction generated by the coil 7271.
[0207] Each of these coils 7271 and 7272 for generating magnetic
field is constituted of two pieces in order to be arranged on the
outside of the vacuum container, so that these two pieces may be
attached onto the vacuum wall 7283 from both sides respectively and
may be clamped tightly by screw or the like at a portion 7 so as to
be made into one unit.
[0208] An outermost layer 7273 of the E.times.B separator is
constructed as a yoke made of permalloy or ferrite. Similar to the
coils 7271 and 7272, the outermost layer 7273 may be made as two
pieces and attached onto an outside of the coil 7272 to be formed
into one unit by screwing at a portion 7274.
[0209] FIG. 11[B] shows another E.times.B separator according to a
second embodiment of the present invention by a cross sectional
view projected on a plane orthogonal to the optical axis. This
E.times.B separator according to the second embodiment is different
from that of the first embodiment shown in FIG. 11[A] in that six
poles of electrostatic deflecting electrodes 7281' are provided
therein. In FIG. 11[B], any components corresponding to those of
the E.times.B separator shown in FIG. 11[A] will be designated by
the same reference numerals added by "'" (dash), and the
description therefor will be omitted. To each of these
electrostatic deflecting electrodes 7281' is applied a voltage
proportional to cos .theta..sub.i, which is represented as kcos
.theta..sub.i (k is constant), where .theta..sub.i (i=0, 1, 2, 3,
4, 5) is an angle formed between a line connecting a center of each
electrode to the optical axis and a direction of the electric field
(X-axis direction). It is to be noted that the .theta..sub.i is an
arbitrary angle.
[0210] Since also the second embodiment shown in FIG. 11[B] can
generate only the electric field in the X-axis direction similar to
the first embodiment, coils 7271' and 7272' for generating the
magnetic fields of X-axis direction and of Y-axis direction,
respectively, are provided to correct the orthogonality.
[0211] The embodiment shown in FIG. 11[B] can make the area with
uniform electric field intensity further wider than the embodiment
shown in FIG. 11[A].
[0212] Although the coil for generating magnetic field has been
formed into a saddle type in the embodiments shown in FIGS. 11[A]
and 11[B], a coil of toroidal type may be employed.
[0213] The secondary optical system 74 comprises two magnifying
lenses 741 and 743, which make up a two stage electrostatic lens,
for passing therethrough a secondary electron separated from the
primary optical system by the E.times.B separator 727, and a second
multi aperture plate 745. Each of apertures 7451 formed in the
second multi aperture plate 745 is adapted, as shown by a broken
line in FIG. 9, to correspond one-to-one to each of the apertures
7231 formed in the first multi aperture plate 723 of the primary
optical system, wherein the aperture 7451 of the second multi
aperture plate 745 is a circular hole with a diameter larger than
that of the aperture 7231 of the first multi aperture plate
723.
[0214] The detection system 76 comprises a plurality of detectors
761 (nine detectors in this embodiment) each disposed corresponding
to and adjacent to each aperture 7451 of the second multi aperture
plate 745 of the secondary optical system 74, and each of the
detectors 761 is electrically connected to an image data processing
section 771 of the process control system 77 via an A/D converter
(including amplifier) 763. It is to be noted that though only one
detector 761 has been connected to the image processing section 771
in FIG. 8, respective detectors are connected to the image data
processing section via respective independent A/D converters 763.
Further, the image processing section 771 is also connected to the
electrostatic deflector 733 so that a scanning signal for
deflecting the primary electron beam may be supplied to the
electrostatic deflector 733. As an element for the detectors may be
used, for example, a PN junction diode which directly detects an
electron beam intensity or a PMT (photomultiplier) which detect a
light emitting intensity through a scintillator which becomes
luminous by electron.
[0215] The image processing section 771 may convert an electric
signal supplied from respective A/D converter 763 to a binary
information by setting an appropriate threshold voltage, and then
may convert the binary signal into an image data. For this purpose,
the scanning signal for deflecting the primary electron beam, which
is supplied from the electrostatic deflector 733 to the image
processing section 771, may be used. The image processing section
771 may compare the obtained image data with a reference circuit
pattern, while storing thus obtained image data in an appropriate
memory. Thereby, a plurality of circuit patterns, or the same
number of circuit patterns with that of the primary electron beams,
on the wafer W may be subjected to the inspection
simultaneously.
[0216] It is to be noted that in the embodiment shown in FIG. 8,
the image data processing section 771 can use various kinds of
reference circuit patterns in order to compare therewith an image
data representing a certain circuit pattern on the wafer W, that
is, for example, an image data obtained in the same place on the
other chip different from that scanned for generating said image
data to be compared may be used.
[0217] An operation of the electron beam apparatus with an above
configuration will now be described. The primary electron beam
emitted from the electron gun 71 is converged by the condenser lens
721 in the primary optical system 72 to form a crossover at a point
P1 of knife edge 732. On the other hand, the primary electron beam
converged by the condenser lens 721 passes through the plurality of
apertures 7231 of the multi-aperture plate 723 to form into a
plurality of primary electron beams (nine beams in this
embodiment), which are focused by the reducing lens 725 so as to be
projected onto a point P2. After being focused onto the point P2,
the beams are further focused onto a surface of a wafer W by the
objective lens 729. On the other hand, the deflecter 733 disposed
between the reducing lens 725 and the objective lens 726 deflects
the primary electron beams so as to scan the surface of the wafer
W.
[0218] The plurality of focused primary electron beams are
irradiated onto the wafer W at a plurality of points thereon, and
secondary electrons are emitted from said plurality of points.
Those secondary electrons are attracted by an electric field of the
objective lens 729 to be converged narrower, and then deflected by
the E.times.B separator 726 so as to be introduced into the
secondary optical system 74. The secondary electron image is
focused on a point P3 which is much closer to the deflector 726
than the point P2. This is because the primary electron beam has
the energy of 500 eV on the surface of the wafer, while the
secondary electron beam only has the energy of a few eV.
[0219] Each of the images of the secondary electrons focused at the
point P3 is focused by the two-stage magnifying lenses 741 and 743
onto each of the corresponding apertures 7451 of the multi-aperture
detection plate 745 to be formed into an image, so that each of the
detectors 761 disposed correspondingly to each of the apertures
7451 detects the image. Each of the detectors 761 thus detects the
electron beam and converts it into an electric signal
representative of its intensity. The generated electric signals are
output from respective detectors 761, and after being converted
respectively into digital signals by the A/D converter 763, they
are input to the image processing section 771 of the process
control system 77. The image processing section 763 converts the
input digital signals into image data. Since the image processing
section 763 is further supplied with a scanning signal for
deflecting the primary electron beam, the image processing section
763 can display an image representing the surface of the wafer.
Comparing this image with a reference pattern that has been pre-set
in a setting device (not shown) allows to determine whether or not
the pattern on the wafer W being inspected (evaluated) is
acceptable.
[0220] Further, the line width of the pattern formed on the surface
of the wafer W can be measured in such a way that the pattern to be
measured on the wafer W is moved by a registration to the proximity
of the optical axis of the primary optical system, and the pattern
is then line-scanned to extract the line width evaluation signal,
which in turn is appropriately calibrated.
[0221] Irradiation of the primary electron beams onto a wafer while
scanning them with respect to the wafer may be practiced as shown
in FIG. 12. For simplicity of explanation, a case wherein the
number of electron beams are four (EB1 to EB4) will be explained.
Each irradiation point Ebp1 to Ebp4 of each primary electron beam
designates the irradiating point of the primary electron beams
which scans from the left side to the right side in the X direction
in corresponding, respective scanning areas SA1 to SA2. The size of
one electron beam is determined such that each primary electron
beam can scan the area having a width of 50 .mu.m. When the
irradiation point of the electron beam reaches the right side in
the corresponding scanning area, the irradiating point is moved
back to the left side of the scanning area. On the other hand the
stage device continuously moves the wafer with predetermined speed
in the Y direction.
[0222] In this regard, it is required to make special arrangements
in order to minimize the affection by the three aberrations, i.e.,
the distortion caused by the primary optical system, the axial
chromatic aberration, and the filed astigmatism, when the primary
electron beams passed through the apertures of the multi-aperture
plate 723 in the primary optical system are focused onto the
surface of the wafer W and then the secondary electrons emitted
from the wafer W are formed into an image on the detector 761.
[0223] It is to be noticed that, with respect to the relationship
between the spacing of a plurality of primary electron beams and
the secondary optical system, any space between the primary
electron beams made longer than the aberration by the secondary
optical system may eliminate the cross talks among the plurality of
beams.
[0224] Although there has been described above an example in which
a plurality of tips of the cathode of the electron gun is arranged
along a circle, the plurality of tips may be arranged on a line. In
that case, the apertures formed on the first multi aperture plate
723 as well as those on the second multi aperture plate 745 must be
arranged along respective lines at positions corresponding to the
tips of the cathode.
[0225] According to an actual machine test having been conducted by
using the electron beam apparatus shown in FIG. 8, a beam current
of 3 nA was obtained as a beam current for each of nine electron
beams when a beam diameter of 10 nm was employed. In comparison
with the beam current of 150 nA during an operation within the
temperature limited region, the S/N ratio was in a comparative
degree. Since a total beam current of the nine electron beams was
27 nA, which was small enough in comparison with the 150 nA, a beam
blur possibly caused by the space charge effect had almost no
effect. Further, because of nine electron beams being used, nine
times as fast as inspection speed may be expected in comparison
with a case of one electron beam.
[0226] Then, with reference to FIG. 13, a detailed configuration of
the image data processing section 771 of the electron beam
apparatus shown in FIG. 8 will be described. The image data
processing section 771 comprises a sub-image data storage sub
system 7711, an image data re-arranging sub system 7712, an
inter-sub-image overlap processing sub system 7713, an inspection
image data storage sub system 7714, a reference image data storage
sub system 7715, and a comparison sub system 7716. The sub-image
data storage sub system 7711 serves to receive and to store a
sub-image data detected by each detector 761 for detecting the
secondary electron, and has a storage area corresponding to each
detector. The image data re-arranging sub system 7712 serves to
re-arrange the sub-image data stored in the sub-image data storage
sub system 7711 so as to match the X-Y coordinates of respective
multi beams, while the inter-sub-image overlap processing sub
system 7713 serves to determine a boundary between the sub-images
and/or to decide either of the sub-image data should be employed.
Re-arranged image data is stored in the inspection image data
storage sub system 7714. The comparison sub system 7716 compares
the image data stored in the inspection image data storage sub
system 7714 with the reference image data stored in the reference
image data storage sub system 7715, and outputs a result of the
comparison.
[0227] FIG. 14 illustrates an operation of the image data
re-arranging sub system 7712 shown in FIG. 13. As having been
described with reference to FIG. 8, the first and the second multi
aperture plates 723 and 745 are designed such that arrangement
positions of the apertures in the first and the second multi
aperture plates 723 and 745 (and the detectors 761) may relatively
correspond to each other, and projected points on the X-axis of the
beam spots irradiated through the apertures in the first multi
aperture plate 723 onto the wafer W may be spaced with
approximately equal distances. Therefore, the beam spots generated
when the multi beams having passed through the plurality of
apertures in the first multi aperture plate 723 are irradiated onto
the wafer W are also spaced with approximately equal distances when
they are projected onto the X-axis. That is, in FIG. 14, when the
X-Y coordinates of the multi beams (i.e. beam spots) EB1 to EB9
formed along a circle around a center of the optical axis are
designated by (x.sub.1, y.sub.1).about.(x.sub.9, y.sub.9), a
relation thereof may be expressed as:
x.sub.1-x.sub.2.apprxeq.x.sub.2-x.sub.9.apprxeq.x.sub.9-x.sub.3.apprxeq.-
x.sub.3-x.sub.8.apprxeq.x.sub.8-x.sub.4.apprxeq.x.sub.4-x.sub.7.apprxeq.x.-
sub.7-x.sub.5.apprxeq.x.sub.5-x.sub.6.apprxeq.Lx (constant, as
shown in FIG. 9).
[0228] When a sample or the wafer W is evaluated by using the
electron beam apparatus shown in FIG. 8, the multi beams EB1 to EB
9 are simultaneously irradiated onto the wafer W while continuously
moving the stage unit 50 on which the wafer W is mounted in the
Y-axis direction and at the same time controlling the multi beams
so as to scan in the X-direction by a line width d+.DELTA.. That
is, adjacent two beams are controlled so as for their scanning
areas to overlap with each other in the X-direction by .DELTA..
Thus, when the areas scanned by the multi beams EB1 to EB9 are
designated by SA1 to SA9, the multi beams EB1 to EB9 raster-scan
the corresponding areas SA1 to SA9 respectively.
[0229] The secondary electron beams emitted from a surface of the
wafer W by an irradiation of the multi beams are passed through the
apertures of the second multi aperture plate 745 to be detected by
the corresponding detectors 761 for detecting the secondary
electrons, and what are detected by the detectors 761 are stored in
the respective storage areas in the sub-image data storage sub
system 7711 as the sub-image data. The image re-arranging sub
system 7712 re-arranges the sub-image data stored in the storage
sub system 7711 so as to be arranged in a order of the detectors
from 761-1 to 761-9 (wherein, the detectors 761-1 to 761-9
correspond to the multi beams EB1 to EB9 respectively), that is, in
the area order of SA1, SA2, SA9, SA3, SA8, SA4, SA7, SA5, and then
SA6.
[0230] At that time, the displacement of the detectors 761-1 to
761-9 in the Y-axis direction should be taken into account. For
example, as to the detectors 761-1 and 761-2, time T necessary for
the movement of the stage unit 50 by a distance y.sub.2-y.sub.1 is
measured in advance and arranges the image data rearranging sub
system 7712, adjacent to a sub-image data from the detector 761-1
obtained by a certain scanning in the X-axis direction, another
sub-image data obtained from the detector 761-2 at the time T after
said certain scanning. Thereby, not only an arrangement relation of
the X coordinate but also the Y coordinate value of the image data
adjacently arranged in the X-direction can be made coincident with
each other. Alternative method may be employed in which the
distance y.sub.2-y.sub.1 is converted into a number of the pixels
so as to displace their position by that number of pixels.
[0231] The overlap .DELTA. between adjacent two areas is determined
by the inter-sub-image overlap processing sub system 7653, for
example, in such a manner as described below. An area (B) in FIG.
14 designates the overlap between the areas SA1 and SA2, and Pt in
the area (B) in FIG. 14 designates a pattern to be evaluated,
wherein a boundary line Bol is determined within the overlap A so
as not to cross the pattern such that a sub-image data from the
detector 761-1 corresponding to the beam EB1 is employed for a
right side area of the boundary Bol and anther sub-image data from
the detector 761-2 corresponding to the beam EB2 is employed for a
left side area of the boundary Bol, and then these sub-image data
are combined. That is, the boundary is determined in such a manner
that the crossing of the boundary between the sub-images with the
patterns may be minimized. Other overlaps may be processed in the
same manner.
[0232] Among these image data combined in the manner described
above, only the image data within an area to be inspected EA of the
wafer W are stored in the inspection image data storage sub system
7714.
[0233] When all the image data within an area to be inspected EA on
the wafer W cannot be obtained by a single scanning, that is, as
shown in FIG. 14, when there still exists an area to be scanned in
the right side of the area SA6, the stage unit 50 may be shifted in
the X-axis direction so that the new area adjacent to the area SA6
can be scanned by the beam EB1 to obtain the image data in the same
manner as described above.
[0234] When any defects is to be detected, the comparison sub
system 7716 compares the image data stored in the inspection image
data storage sub system 7714 with the reference image data stored
in the reference image data storage sub system 7715, so that the
defect on the wafer W may be detected. Alternatively, a plurality
of combined images for a plurality of wafer expected to have the
same pattern may be obtained to compare the image data with each
other, thereby determining there being the defect at a portion of a
certain wafer when said portion exhibits an image data different
from other most image data.
[0235] When a line width is to be detected, an appropriate method
may be employed to measure the line width.
[0236] Although there has been described the case where the X
coordinates of the beam spots of the primary electron beams are
spaced with approximately equal distances, they may not be
necessarily spaced with equal distance. Alternatively, for example,
distances between beams in the X-axis direction may be measured to
be converted into a number of pixels, thereby shifting the images
by this number of pixels. In this case, the distance on the X
coordinate between the irradiation spots may be varied.
Pre-Charge Unit
[0237] As shown in FIG. 1, a pre-charge unit 81 is disposed in a
working chamber 31, adjacent to a optical column 701 of an
electronic optical apparatus 70. Since this inspection apparatus is
of a type in which an electron beam is irradiated a substrate or
wafer to be inspected by scanning it, and thereby a device pattern
or the like formed on a surface of the wafer is inspected,
information such as secondary electrons emitted by the irradiation
of the electron beam is utilized as an information of the wafer
surface. Sometimes, depending on a condition including a material
of the wafer, an energy level of the irradiated electron or the
like, the wafer surface may be charged-up. Further, depending on
the locations on the wafer, some locations might be more strongly
charged-up than other locations. If there are non-uniform
distribution in a charging amount on the wafer, the information of
the secondary electron beam is made to be non-uniform, which makes
it hard to obtain an accurate information.
[0238] Accordingly, in the present embodiment, there is provided a
pre-charge unit 81 having a charged particle irradiating section
811 in order to prevent this non-uniform distribution. In order to
prevent a non-uniform distribution in charging, before the
electrons for inspection being irradiated onto a predetermined
location of the wafer to be inspected, the charged particles are
irradiated from the charged particle irradiating section 811 of the
pre-charge unit thereto, thus preventing the non-uniform charging
from occurring. The charging on the wafer surface is detected by
forming and evaluating an image of the wafer surface in advance,
and based on a result of the detection, the pre-charge unit 81 is
operated. Further, in this pre-charge unit, the primary electron
beam may be irradiated with some gradation.
[0239] In this pre-charge unit, the primary electron beam may be
irradiated with an out of focus condition.
[0240] In some method for inspecting a sample for any electric
defects, such a fact may be used that when a portion to be
insulated is not in the insulated condition by some reason, a
voltage in that portion is different from that in the insulated
condition.
[0241] This is conducted in such a manner that firstly a voltage
difference is generated between a voltage in a portion to be
insulated essentially and that of another portion which should have
been insulated but is not in the insulated condition due to some
reason, by applying a charge to the sample in advance; secondly the
data with voltage difference is obtained by irradiating the beam
according to the present invention; and finally a non-insulated
condition is detected by analyzing the obtained data.
Potential Applying Mechanism
[0242] Referring next to FIG. 15, the potential applying mechanism
83 applies a potential of plus or minus several volts to a carrier
of a stage, on which the wafer is placed, to control the generation
of secondary electrons based on the fact that the information on
the secondary electrons emitted from the wafer (secondary electron
yield) depend on the potential on the wafer. The potential applying
mechanism 83 also serves to decelerate the energy originally
possessed by irradiated electrons to provide the wafer with
irradiated electron energy of approximately 100 to 500 eV.
[0243] As illustrated in FIG. 15, the potential applying mechanism
83 comprises a voltage applying device 831 electrically connected
to the carrying surface 571 of the stage device 50; and a charging
detection/voltage determining system (hereinafter
detection/determining system) 832. The detection/determining system
832 comprises a monitor 833 electrically connected to an image
forming unit 771 of the detecting system 76 in the electron beam
apparatus 70; an operator 834 connected to the monitor 833; and a
CPU 835 connected to the operator 834. The CPU 835 supplies a
signal to the voltage applying device 831.
[0244] The potential applying mechanism 83 is designed to find a
potential at which the wafer under testing is hardly charged, and
to apply such potential to the carrying surface 541.
Electron Beam Calibration Mechanism
[0245] Referring next to FIG. 16, the electron beam calibration
mechanism 85 comprises a plurality of Faraday cups 851, 852 for
measuring a beam current, disposed at a plurality of positions in a
lateral region of the wafer carrying surface 541 on the turntable.
The Faraday cups 851 are used for a fine beam (approximately .phi.2
.mu.m), while the Faraday cups 852 are used for thick beams
(approximately .phi.30 .mu.m). The Faraday cups 851 for a fine beam
measures a beam profile by driving the turntable step by step,
while the Faraday cups 852 for a wide beam measure a total amount
of currents. The Faraday cups 851, 852 are mounted on the wafer
carrying surface 541 such that their top surfaces are coplanar with
the upper surface of the wafer W carried on the carrying surface
541. In this way, the primary electron beam emitted from the
electron gun is monitored at all times. This is because the
electron gun cannot emit a constant electron beam at all times but
varies in the emitting amount as it is used over time.
Alignment Controller
[0246] The alignment controller 87, which aligns the wafer W with
the electron optical apparatus 70 using the stage system 50,
performs the control for rough alignment through wide field
observation using the optical microscope 871 (a measurement with a
lower magnification than a measurement made by the electron optical
system); high magnification alignment using the electron optical
system of the electron optical apparatus 70; focus adjustment;
testing region setting; pattern alignment; and so on. The wafer is
tested at a low magnification using the optical system in this way
because an alignment mark must be readily detected by an electron
beam when the wafer is aligned by observing patterns on the wafer
in a narrow field using the electron beam for automatically testing
the wafer for patterns thereon.
[0247] The optical microscope 871 is disposed on the housing 30
(alternatively, may be movably disposed within the housing 30),
with a light source, not shown, being additionally disposed within
the housing 30 for operating the optical microscope. The electron
optical system for observing the wafer at a high magnification
shares the electron optical systems (primary optical system 72 and
secondary optical system 74) of the electron optical apparatus 70.
The configuration may be generally illustrated in FIG. 17. For
observing a point to be observed on a wafer at a low magnification,
the X-stage 54 of the stage device 50 is moved in the X-direction
to move the point to be observed on the wafer into a view field of
the optical microscope 871. The wafer is viewed in a wide field by
the optical microscope 871, and the point to be observed on the
wafer is displayed on a monitor 873 through a CCD 872 to roughly
determine a position to be observed. In this event, the
magnification of the optical microscope may be changed from a low
magnification to a high magnification.
[0248] Next, the stage device 50 is moved by a distance
corresponding to a spacing .delta.x between the optical axis of the
electron optical apparatus 70 and the optical axis of the optical
microscope 871 to move the point to be observed on the wafer,
previously determined by the optical microscope 871, to a point in
the field of the electron optical apparatus 70. The distance
.delta.x between the axis O.sub.3-O.sub.3 of the electron optical
apparatus and the axis O.sub.4-O.sub.4 of the optical microscope
871 is previously known (while it is assumed that the
electron-optical system 70 is deviated from the optical microscope
871 in the direction along the X-axis in this embodiment, they may
be deviated in the Y-axis direction as well as in the X-axis
direction), such that the point to be observed can be moved to the
viewing position by moving the stage device 50 by the distance
.delta.x. The point to be observed has been moved to the viewing
position of the electron optical apparatus 70, the point to be
observed is imaged by the electron optical system at a high
magnification for storing a resulting image or displaying the image
on the monitor 765 through the CCD 761.
[0249] After the point to be observed on the wafer imaged by the
electron optical system at a high magnification is displayed on the
monitor 765, displacement of the stage device 50 with respect to
the center of rotation of the turntable 54 in the wafer rotating
direction, that is displacement .delta..theta. of the stage device
50 with respect to the optical axis O.sub.3-O.sub.3 of the electron
optical system in the wafer rotating direction are detected in a
known method, and displacement of a predetermined pattern with
respect to the electron optical apparatus in the X-axis and Y-axis
is also detected. Then, the operation of the stage device 50 is
controlled to align the wafer based on the detected values and data
on a testing mark attached on the wafer or data on the shape of the
patterns on the wafer which have been acquired in separation.
Control System
[0250] A control system comprises a main controller, a controlling
controller, and a stage controller as main components, though not
shown.
[0251] The main controller is provided with a man-machine interface
through which an operator manipulates the main controller (a
variety of commands/instructions, an entry of recipe and the like,
direction of inspection start, switching between an automatic and a
manual inspection modes, an input of all of the commands required
in the manual inspection mode and so forth). In addition, the main
controller also performs such jobs as: a communication with a host
computer in a plant; a control of the vacuum evacuating system; a
transfer of a sample such as a wafer; a control of position
alignment; a transmission of commands or information to other
controlling controllers or the stage controller; and a receipt of
information or the like. Further, the main controller also is in
charge of such functions as: an acquisition of an image signal from
an optical microscope; a stage vibration compensating function for
compensating for possible deterioration in image by feeding back a
fluctuating signal of the stage to the electronic optical system;
and an automatic focal point compensating function for detecting a
displacement of a usage observation point in the Z direction (the
direction along the optical axis OA.sub.1 of the first optical
system) and feeding it back to the electron optical system so as to
automatically compensating for the focal point. The
transmitting/receiving operation of the feedback signal or the like
to/from the electronic optical system as well as the
transmitting/receiving operation of the signal to/from the stage
are performed via the controlling controller or the stage
controller respectively.
[0252] The controlling controller is mainly in charge of a control
of the electron optical system (such as a control of high precision
power source for the electron gun, the lenses, the aligner, the
Wien filter or the like). In specific, the controlling controller
performs, for example, such a control (continuous control)
operation as an automatic voltage setting for respective lens
systems and the aligner in response to respective operation modes,
so that a constant electron current may be regularly irradiated
onto the irradiation region even if the magnification is changed,
and the voltage to be applied to respective lens systems, the
aligner or the like may be automatically set in response to the
magnification.
[0253] The stage controller is mainly in charge of a control for a
movement of the stage to allow a precise movement in the X- and the
Y-directions on the order of .mu.m (with tolerance of about +/-0.5
.mu.m). Further, in the present stage, a control in the rotational
direction (.theta. control) is also performed with a tolerance
equal to or less than about +/-0.3 seconds.
Inspection Procedure
[0254] Generally, since an inspection apparatus using an electron
beam is rather expensive and also the throughput thereof is rather
lower than that provided by other processing apparatuses, this type
of inspection apparatus is currently applied to a wafer after an
important process (for example, etching, film deposition, or CMP
(chemical and mechanical polishing) planarization process) which is
considered that the inspection is required most.
[0255] A wafer W to be inspected is, after having been positioned
on an ultra precise stage unit through a loading chamber, secured
by an electrostatic chucking mechanism or the like, and then a
detect inspection is conducted according to a procedure (inspection
flow) shown in FIG. 18. At first, if necessary, a position of each
of dice is checked and/or a height of each location is sensed, and
those values are stored. Adding to that, an optical microscope is
used to obtain an optical microscope image in an area to be
observed possibly including defects or the like, which may also be
used in, for example, the comparison with an electron beam image.
Then, recipe information corresponding to the kind of the wafer
(for example, after which process the inspection should be applied;
which is the wafer size, 200 mm or 300 mm, and so on) is entered
into the apparatus, and subsequently, after a designation of an
inspection place, a setting of an electronic optical system and a
setting of an inspection condition having being executed, a defect
inspection is conducted typically at real time while simultaneously
obtaining the image. A fast data processing system with an
algorithm installed therein executes an inspection, such as the
comparisons between cells, between dice or the like, and any
results would be output to a CRT or the like and stored in a
memory, if desired. Those defects include a particle defect, an
irregular shape (a pattern defect) and an electric defect (a broken
wire or via, a bad continuity or the like), and the fast data
processing system also can automatically and at real-time
distinguish and categorize them according to a defect size, or
whether their being a killer defect (a critical defect or the like
which disables a chip). The detection of the electric defect may be
accomplished by detecting an irregular contrast. For example, since
a location having a bad continuity would generally be charged into
positive level by an electron beam irradiation (about 500 eV) and
thereby its contrast would be decreased, the location of bad
continuity can be distinguished from normal locations. The electron
beam irradiation device in that case designates an electron beam
source (source for generating thermoelectron, UV/photoelectron)
with lower potential (energy) arranged in order to emphasize the
contrast by a potential difference, in addition to the electron
beam irradiation device used for a regular inspection. Before the
electron beam for inspection being irradiated against the objective
region for inspection, the electron beam having that lower
potential energy is generated and irradiated.
Cleaning of Electrode
[0256] As the electron beam apparatus according to the present
invention being operated for a long time, an organic substance
would be deposited on a variety of electrodes used for forming or
changing the electron beam. Since the insulating material gradually
depositing on the surface of the electrodes by the electric charge
affects reversely on the forming or deflecting mechanism for the
electron beam, accordingly those deposited insulating material must
be removed periodically. To remove the insulating material
periodically, an electrode adjacent to the region where the
insulating material has been deposited is used to generate the
plasma of hydrogen, oxygen, fluorine or compound including them
(HF, O.sub.2, H.sub.2O, C.sub.MF.sub.N or the like) in the vacuum
and to control the plasma potential in the space to be a potential
level (several kV, for example, 20V-5 kV) where the spatter would
be generated on the electrode surface, thereby allowing only the
organic substance to be oxidized, hydrogenated or fluorinated and
thereby removed.
[0257] Next, an embodiment of a method of manufacturing a
semiconductor device according to the present invention will be
described with reference to FIGS. 19 and 20.
[0258] FIG. 19 is a flow chart illustrating an embodiment of a
method of manufacturing a semiconductor device according to the
present invention. Manufacturing processes of this embodiment
include the following main processes:
[0259] (1) a wafer manufacturing process for manufacturing a wafer
(or a wafer preparing process for preparing a wafer);
[0260] (2) a mask manufacturing process for manufacturing masks for
use in exposure (or mask preparing process for preparing
masks);
[0261] (3) a wafer processing process for performing processing
required to the wafer;
[0262] (4) a chip assembling process for cutting one by one chips
formed on the wafer and making them operable; and
[0263] (5) a chip testing process for testing complete chips.
[0264] The respective main processes are further comprised of
several sub-processes.
[0265] Among these main processes, the wafer fabricating process
set forth in (3) exerts critical affections to the performance of
resulting semiconductor devices. This process involves sequentially
laminating designed circuit patterns on the wafer to form a large
number of chips which operate as memories, MPUs and so on. The
wafer fabricating process includes the following sub-processes:
[0266] (A) a thin film forming sub-process for forming dielectric
thin films serving as insulating layers, metal thin films for
forming wirings or electrodes, and so on (using CVD, sputtering and
so on);
[0267] (B) an oxidation sub-process for oxidizing the thin film
layers and the wafer substrate;
[0268] (C) a lithography sub-process for forming a resist pattern
using masks (reticles) for selectively fabricating the thin film
layers and the wafer substrate;
[0269] (D) an etching sub-process for fabricating the thin film
layers and the substrate in conformity to the resist pattern
(using, for example, dry etching techniques);
[0270] (E) an ion/impurity implantation/diffusion sub-process;
[0271] (F) a resist striping sub-process; and
[0272] (G) a sub-process for testing the fabricated wafer;
[0273] As appreciated, the wafer fabrication process is repeated a
number of times equal to the number of required layers to
manufacture semiconductor devices which operate as designed.
[0274] FIG. 20 is a flow chart illustrating the lithography
sub-process which forms the core of the wafer processing process in
FIG. 12. The lithography sub-process includes the following
steps:
[0275] (a) a resist coating step for coating a resist on the wafer
on which circuit patterns have been formed in the previous
process;
[0276] (b) a resist exposing step;
[0277] (c) a developing step for developing the exposed resist to
produce a resist pattern; and
[0278] (d) an annealing step for stabilizing the developed resist
pattern.
[0279] Since the aforementioned semiconductor device manufacturing
process, wafer fabrication process and lithography process are well
known, and therefore no further description will be required.
[0280] When the defect testing method and defect testing apparatus
according to the present invention are used in the testing
sub-process set forth in (G), any semiconductor devices even having
submicron (sized) patterns can be tested at a high throughput, so
that a total inspection can also be conducted, thereby making it
possible to improve the yield rate of products and prevent
defective products from being shipped.
[0281] It is to be noted that although in the above embodiment,
there has been described an example shown in FIGS. 1 and 2 where
only a single electron beam apparatus 70 is installed, a plurality
of electron beam apparatuses may be arranged side-by-side, as shown
in FIG. 21, to inspect a plurality of regions simultaneously.
[0282] That is, FIG. 21(A) is a plan view of an example of
arrangement where four optical columns (each optical column
includes one electron beam apparatus respectively) are arranged on
a line, while FIG. 21(B) is a plan view of another example of
arrangement where six optical columns, each having an optical axis
OA.sub.2, are arranged in a matrix of two rows by three columns. In
the examples shown in FIGS. 21(A) and 21(B), a single optical
columns irradiates a plurality of electron beams (each one is
designated by a symbol "EB"), which is then detected by a multi
detector. The multi detector comprises a plurality of detector
elements 761, each detecting a single electron beam EB. A maximum
outer diameter of an area on a wafer surface irradiated by a
plurality of electron beams of one optical column is designated
respectively by symbols Sr1 to Sr6. In the examples shown in FIGS.
21(A) and 21(B), each of the plurality of optical columns is
arranged so as not to interface with each other, so that a wide
area of wafer surface may be inspected by a number of optical
columns at once, thereby accomplishing high throughput in the wafer
inspection process. In the example shown in FIG. 21(A), the wafer
surface is continuously moved in a direction perpendicular to the
row of the optical columns (designated by an arrow Ar1) in order to
inspect entire wafer W.
Variation of the Inspection Apparatus
[0283] Then, a specific example of an inspection method of a
circuit pattern formed on a substrate or the wafer W will be
described. FIGS. 22 and 23 show typical example in the case of
forming a circuit pattern by using an electron beam lithography.
That is, a semiconductor chip SCT is divided into a plurality of
stripes St extending in a Y-axis direction with a width in a
X-direction of, for example, 5 mm, and a mask pattern is
transferred onto the wafer while continuously moving the stage unit
50 with said semiconductor chip mounted thereon along each stripe
in the Y-direction. Further, one stripe is divided into a plurality
of primary fields of views, each being defined by a Y-direction
size of 250 .mu.m and an X-direction size of 5 mm and designated by
VFp, which in turn is further divided into a plurality of secondary
fields of view, each being defined by 250 .mu.m square and
designated by VFs, wherein the transfer is executed for each
secondary field of view. That is, one mask is prepared for each
secondary field of view, which is a component of the primary field
of view, and a circuit portion is transferred by scanning with the
beam each secondary field of view one-by-one.
[0284] When the circuit pattern is formed by the above-described
method, a portion where the defect is most likely to occur is in a
boundary between one stripe St and an adjacent stripe St, a portion
where the defect is second-most likely to occur is in a boundary
between the primary fields of view VFps, and a portion where the
defect is third-most likely to occur is in a boundary between the
secondary fields of view VFss. A portion with the widest
fluctuation exhibits in the same order of boundary portion between
stripes, that between the primary fields of view, and that between
the secondary fields of view.
[0285] Accordingly, in this embodiment, an evaluation apparatus is
equipped with an inspection mode for inspecting each boundary
between the stripes designated by BAst with a width of 200 .mu.m
(seven portions in FIG. 22). When more precise evaluation is
expected, a mode for inspecting a boundary area between the primary
fields of view designated as BAp should be employed, and more
preferably a mode for inspecting a boundary area between the
secondary fields of view designated as BAs should be employed
additionally. Applying a sampling inspection with a certain
priority as described above allows most defects to be detected
while reducing an inspection time to be several to several ten
percents in comparison with the case of 100% inspection.
[0286] In the electron beam apparatus, the optical system has small
aberration and distortion in a central portion of the field of
view, and accordingly a reliable evaluation may be accomplished
when the central portion of the field of view is used for the
measurement. That is, a probability of missing any defects may be
made lower when the boundary area could be necessarily evaluated by
using the central portion of the field of view, as showing the
stripe width by BAo, even if both of the boundary area and the
other areas are to be inspected together. Moreover, a probability
of determining normal patterns as defects may be made lower.
[0287] The deflectors for scanning 733 and 728 are adapted to scan
the surface of the wafer W with the irradiation points of the
primary electron beam in the X-direction, and a scanning distance
is controlled to be "an X-directional distance between irradiation
points of the primary electron beams plus .alpha.". That is, the a
designates a dimension in the X-direction of the area to be double
scanned, which is 0.3 to 3 mm.
[0288] When the boundary between the stripes on the surface of the
wafer W is to be inspected in this electron beam apparatus, the
stage unit 50 continuously moves the wafer in the Y-direction for
the inspection. During this operation, the scanning deflectors 733
and 728 control the irradiation point of each primary electron beam
to scan in the X-direction by the X-directional distance between
the electron beams plus .alpha.. For example, the boundary between
the stripes described above is to be inspected by a width of 200
.mu.m, the X-directional distance between the primary electron beam
irradiation points is set to be 23 .mu.m, then each primary
electron beam irradiation point scans a width of 23+.alpha., and as
a whole, an inspection width of 23.times.9+.alpha. (=200
.mu.m+.alpha.) may be accomplished.
[0289] Upon executing a defect inspection, the image obtained by
scanning as described above is compared with an image without
defect, which has been stored previously in a memory, to detect any
defective portions automatically.
[0290] FIG. 24(A) shows an example for measuring a line width. An
actually formed pattern Pt2 is scanned in an Ar2 direction to
obtain an actual intensity signal of secondary electron Si, wherein
a width ws of this signal continuously exceeding a threshold level
SL determined previously through calibration may be measured as a
line width of the pattern Pt2. If any line width measured in this
way does not fall in a predetermined range, then this pattern may
be determined to have a defect.
[0291] FIG. 24(B) shows an example for measuring a potential
contrast of a pattern formed on the wafer. In the structure shown
in FIG. 8, to the axially symmetrical electrode 737 disposed
between the objective lens 729 and the wafer 5 has been applied,
for example, a potential of -10V relative to a wafer potential of
0V. At that time, an equipotential surface of -2V is assumed to be
drawn in a shape as indicated by EpS. It is to be assumed herein
that patterns Pt3 and Pt4 are at the potentials of -4V and 0V
respectively. In this case, since a secondary electron emitted from
the pattern Pt3 has an upward velocity equivalent to the kinetic
energy of 2 eV in the -2V equipotential surface EpS, the secondary
electron overcomes that potential barrier EpS and escapes from the
equipotential surface Ve as indicated by an orbit Tr1, which would
be detected by the detector 761. On the other hand, a secondary
electron emitted from the pattern Pt4 can not overcome the
potential barrier of -2V and is driven back to the wafer surface as
indicated by an orbit Tr2, which would not be detected.
Accordingly, a detected image for the pattern Pt3 appears to be
brighter, while the detected image for the pattern Pt4 appears to
be darker. Thus the potential contrast can be obtained. If the
brightness and the potential for a detected image have been
calibrated in advance, the potential of the pattern can be measured
from the detected image. Further, based on that potential
distribution, the pattern can be evaluated on any defective
portions.
[0292] Each of the detectors 761 converts the detected secondary
electron beam into an electric signal indicative of an intensity
thereof. The electric signals thus output from respective detectors
are, after having been amplified respectively by the amplifier 763,
received by the image processing section 771 of the process control
system 77 and converted into image data. Since the image processing
section 771 is further supplied with a scanning signal for
deflecting the primary electron beam, the image processing section
771 can display an image representing the surface of the wafer W.
Comparing this image with the reference pattern allows any defects
in the wafer W to be detected.
[0293] Further, a line width of the pattern to be evaluated on the
wafer W can be measured in such a manner that firstly a pattern to
be evaluated on the wafer is moved by registration to a position
near to the optical axis of the primary optical system, secondly a
line width evaluation signal is taken out by line-scanning and then
said signal is calibrated appropriately.
Stage Unit and Variation Thereof
[0294] Referring to FIGS. 25 to 30, other embodiments of the stage
unit will be described. These embodiments of the stage unit relate
to an improvement of a structure using a well known hydrostatic
bearing. In FIGS. 25 to 30, those components corresponding to those
of the housing, the stage unit, and the electronic optical system
shown in FIG. 1 or 2 will be designated by the same reference
numerals with any one of suffixes "d" to "f" added thereto. In some
embodiments, common components will be designated by the same
reference numerals.
[0295] Referring to FIG. 25, in a chamber 31d vacuum-exhausted via
a vacuum exhaust pipe 309d, a stage unit 50d comprises: a
stationary table 51d of box type (open to above) fixed to a housing
30d; an X table 54d of box type also, which is operatively mounted
in said stationary table 51d so as to be movable in an X-direction
(lateral direction in FIG. 25(A)); a Y-directionally movable
section or a Y table 52d which is operatively mounted in said
X-directionally movable section or the X table 54d so as to be
movable in a Y-direction (lateral direction in FIG. 25(B)); and a
turn table 56d mounted on the Y table 52d. The wafer W is
detachably held by a well-known holder (not shown) installed on the
turn table 56d. A bottom face 543d and a side face 544d of the X
table 54d, each facing to guide faces 511d and 512d of the
stationary table 51d, respectively, are provide with a plurality of
hydrostatic bearings 58d, and owing to an operation of this
hydrostatic bearings 58d, the X table 54d can be moved in the
X-direction (lateral direction in FIG. 25(A)) while maintaining
micro gap against the guide faces. Further, a bottom face 523d and
a side face 524d of the Y table 52d, each facing to guide faces
541d and 542d of the X table 54d, respectively, are provide with a
plurality of hydrostatic bearings 58d, and owing to the operation
of this hydrostatic bearings 58d, the Y table 52d can be moved in
the Y-direction (lateral direction in FIG. 25(B)) while maintaining
micro gap against the guide faces. In addition, a differential
pumping mechanism is arranged around the hydrostatic bearing so
that a high pressure gas supplied to the hydrostatic bearing does
not leak into the vacuum chamber 31d. This configuration is
illustrated in FIG. 26. Around the hydrostatic bearing 58d are
formed double grooves 581d and 582d 58d which are always
vacuum-pumped by a vacuum pipe and a vacuum pump, though not shown.
Owing to these structures, the X table is operatively supported in
the vacuum in non-contact manner so as to be movable in the
X-direction, and also the Y table is operatively supported in the
vacuum in non-contact manner so as to be movable in the
Y-direction. These double grooves 581d and 582d are formed on a
surface on which the hydrostatic bearing is provided so as to
surround said hydrostatic bearing. The hydrostatic bearing may be
of well-known structure, and the detailed description therefor will
be omitted.
[0296] A division plate 525d is attached onto an upper face of the
Y table 52d of the stage unit 50d, wherein said division plate 525d
overhangs to a great degree approximately horizontally in the +Y
direction and the -Y direction (lateral direction in FIG. 25[B]),
so that between an upper face of the X table 54d and the division
plate 525d may be always provided a restrictor 526d with small
conductance therebetween. Also, a similar division plate 545d is
attached onto an upper face of the X table 54d so as to overhang in
the +/-X direction (lateral direction in FIG. 25[A]), so that a
restrictor 546d may be constantly formed between an upper face of a
stationary table 51d and the division plate 545d.
[0297] In this way, since the restrictor 526d and 546d are
constantly formed wherever the turn table 56d may move to, and the
restrictors 526d and 546d can prevent the movement of a discharged
gas even if a gas is discharged or leaked along the guide face
511d, 512d, 541d or 542d upon movement of the X table or the Y
table, a pressure increase can be significantly controlled to low
level in a space G1 adjacent to the wafer to which the charged
particle beam is to be irradiated.
[0298] Since the grooves for differential pumping formed
surrounding the hydrostatic bearings 58d work for evacuating,
therefore in a case where the restrictor 526d and 546d have been
formed, the discharged gas from the guiding faces is mainly
evacuated by those differential pumping sections. Owing to this,
the pressure in those spaces G2 and G3 within the stage are kept to
be higher level than the pressure within the chamber 31d.
Accordingly, if there are more portions provided for vacuum-pumping
the spaces G2 and G3 in addition to the evacuating grooves 581d and
582d, the pressure within the spaces G2 and G3 can be decreased,
and the pressure rise of the space G1 in the vicinity of the wafer
can be controlled to be further low. For this purpose, evacuating
channels 517d and 547d are provided. The evacuating channel 517d
extends through the stationary table and the housing to communicate
with an outside of the housing. On the other hand, the evacuating
channel 547d is formed in the X table 54d and opened in an under
face thereof.
[0299] It is to be noted that though arranging the division plates
545d and 525d might cause a problem requiring the chamber 31d to be
extended so as not to interfere with the division plates, this can
be improved by employing those division plates of stretchable
material or structure. There may be suggested one embodiment in
this regard, which employs the division plates made of rubber or in
a form of bellows, and the ends portions thereof in the direction
of movement are fixedly secured respectively, so that each end of
the division plate 525d is secured to the X table 54d and that of
the division plate 545d to an inner wall of the housing 30d.
[0300] FIG. 27 shows another embodiment of the stage unit and other
units surrounding the optical column.
[0301] In this embodiment, a cylindrical divider 91e is disposed
surrounding a tip portion of an optical column 701d or an electron
beam irradiating section 702d, so that a restrictor may be produced
between an upper face of the wafer W and the cylindrical divider
91e. In such configuration, even if the gas is desorbed from the XY
stage to increase the pressure within the chamber 31d, since a
space G5 within the divider has been isolated by the divider 91e
and exhausted with a vacuum pipe 703d, there could be generated a
pressure deference between the pressure in the chamber 31d and that
in the space G5 within the divider, thus to control the pressure
rise in the space G5 within the divider to be low. Preferably, the
gap between the divider 91e and the wafer surface should be
approximately some ten .mu.m to some mm, depending on the pressure
levels to be maintained within the chamber 31d and in the
surrounding of the irradiating section 702d. It is to be understood
that the interior of the divider 91e is made to communicate with
the vacuum pipe by the known method.
[0302] On the other hand, the charged particle beam irradiation
apparatus or the electronic optical system may sometimes apply a
high voltage of about some kV to the wafer W, and so it is feared
that any conductive materials located adjacent to the wafer could
cause an electric discharge. In this case, the divider 91e made of
insulating material such as ceramic may be used in order to prevent
any discharge between the wafer W and the divider 91e.
[0303] It is to be noted that a ring member 561e arranged so as to
surround the wafer W (sample) is a plate-like adjusting part
fixedly attached to a holder (not shown) mounted on the turn table
56d and is set to have the same height with the wafer so that a
micro gap G6 may be formed throughout a full circle of the tip
portion of the divider 91e even in a case of the charged particle
beam being irradiated against an edge portion of the sample such as
the wafer. Thereby, whichever location on the wafer W may be
irradiated by the charged particle beam, the constant micro gap G6
can be always formed in the tip portion of the divider 91e so as to
maintain the pressure stable in the space G5 surrounding the
optical column tip portion.
[0304] FIG. 28 shows another embodiment in which a differential
pumping system is provided on a tip portion of the optical
column.
[0305] A division member 91f having a differential pumping
structure integrated therein is arranged so as to surround the
electron beam irradiating section 702d of the optical column 701d.
The division member 91f is cylindrical in shape and has a circular
channel 911f formed inside thereof and an evacuating path 912f
extending upwardly from said circular channel 911f. Said evacuating
path 912f is connected to a vacuum pipe 914f via an inner space
913f. A micro space as narrow as some ten .mu.m to some mm is
formed between a lower end of the division member 91f and the upper
face of the Wafer W.
[0306] With such configuration as described above, even if the gas
is discharged from the stage in association with the movement of
the stage resulting in an increase of the pressure within the
chamber 31d, and eventually is to possibly flow into the space of
the tip portion or the charged particle beam irradiating section,
that is, the electron beam irradiating section 702d, the gas is
prevented from flowing into the electron beam irradiating section
by the division member 91f, which has reduced the gap between the
wafer W and itself so as to make the conductance very low, thus to
reduce the flow-in rate. Further, since any gas that has flown into
is allowed to be exhausted through the circular channel 911f to the
vacuum pipe 914f, there will be almost no gas remained to flow into
the space G5 surrounding the electron beam irradiating section
702d, and accordingly the pressure of the space surrounding the
electron beam irradiating section 702d can be maintained to be a
desired high vacuum level.
[0307] FIG. 29 shows still another embodiment in which a
differential pumping system is provided on a tip portion of the
optical column.
[0308] A division member 91g is arranged so as to surround the
electron beam irradiating section 702d in the chamber 31d and
accordingly to isolate the electron beam irradiating section 702d
from the chamber 31d. This division member 91g is coupled at a
central portion thereof 911g to a refrigerating machine 913g via a
support member 912g made of material of high thermal conductivity
such as copper or aluminum, and is kept as cool as -100.degree. C.
to -200.degree. C. A part 914g of the division member 91g is
provided for blocking a thermal conduction between the cooled
central portion 911g and the optical column and is made of material
of low thermal conductivity such as ceramic, resin or the like.
Further, a part 915g of the division member 91g is made of
insulating material such as ceramic or the like and is attached to
the lower end of the division member 91g so as to prevent any
electric discharge between the wafer W and the division member
91g.
[0309] With such configuration as described above, any gas
molecules attempting to flow into the space surrounding the charged
particle beam irradiating section from the chamber 31d are blocked
by the division member 91g, and even if there are any molecules
successfully flown into the space, they are frozen to be captured
on the surface of the division member 91g, thus allowing the
pressure in the space surrounding the charged particle beam
irradiating section 702d to be kept low. It is to be noted that a
variety type of refrigerating machines may be used for the
refrigerating machine in this embodiment, for example, a cooling
machine using liquid nitrogen, a He refrigerating machine, a
pulse-tube type refrigerating machine or the like.
[0310] FIG. 30 shows still another embodiment including a variation
of the stage unit and a structure of the optical column with a
division member installed on a tip thereof.
[0311] The division plates 545d and 525d are respectively arranged
on the X table and the Y table, similarly to those illustrated in
FIG. 25, and thereby, if a holder (not shown) for holding the wafer
is moved to any locations, the space G5 within the stage is
separated from the inner space of the chamber 31d by those division
plates via the restrictions 546d and 526d. Further, another divider
91e similar to that as illustrated in FIG. 27 is formed surrounding
the electron beam irradiating section 702d so as to separate a
space G5 accommodating the electron beam irradiating section 702d
therein from the interior of the chamber 31d with a restriction G6
disposed therebetween. Owing to this, upon movement of the stage,
even if the gas having been adsorbed onto the stage is desorbed
into the space G2 to increase the pressure in this space, the
pressure increase in the chamber 31d is kept to be low, and the
pressure increase in the space G5 is also kept to be much lower.
This allows the pressure in the space G5 for irradiating the
electron beam to be maintained at low level. Alternatively,
employing the division member 91f having the differential pumping
mechanism integrated therein as shown in FIG. 28, or the division
member 91g cooled with the refrigerating machine as shown in FIG.
29 allows the space G5 to be maintained stably with further lowered
pressure.
[0312] FIG. 31 shows still another embodiment of the stage unit and
the differential pumping system. Since a general configuration of
this embodiment is different from those shown in FIGS. 25 to 30,
those corresponding components are designated by the same reference
numerals with a suffix "h" added thereto.
[0313] A pedestal 511h of the fixed table 51h of the stage device
50h is fixedly mounted on a bottom wall of the housing 30h, and a Y
table 52h movable in the Y direction (the vertical direction on
paper in FIG. 31) is disposed on the pedestal 511h. Convex portions
522h and 523h are formed on opposite sides (the left and the right
sides in FIG. 31) of the Y table 52h respectively, each of which
projects into a concave groove formed on a side facing to the Y
table in either of a pair of Y directional guides 512h and 513h
mounted on the pedestal 511h. The concave groove extends
approximately along the full length of the Y directional guide in
the Y direction (the vertical direction on paper in FIG. 31). A
top, a bottom and a side faces of respective convex portions
protruding into the grooves are provided with known hydrostatic
bearings 58h respectively, through which a high-pressure gas is
blown out and thereby the Y table 52h is supported by the Y
directional guides 512h and 513h in non-contact manner so as to be
movable smoothly reciprocating in the Y direction. Further, a
linear motor 514h of known structure is arranged between the
pedestal 511h and the Y table 52h for driving the Y table in the Y
direction. The Y table is supplied with the high-pressure gas
through a flexible pipe 526h for supplying a high-pressure gas, and
the high-pressure gas is further supplied to the above-described
hydrostatic bearings 58h though a gas passage (not shown) formed
within the Y table. The high-pressure gas supplied to the
hydrostatic bearings blows out into a gap of some microns to some
ten microns formed respectively between the bearings and the
opposing guide planes of the Y directional guide so as to position
the Y table accurately with respect to the guide planes in the X
and Z directions (up and down directions in FIG. 31).
[0314] The X table 54h is disposed on the Y table so as to be
movable in the X direction (the lateral direction in FIG. 31). A
pair of X directional guides 522h and 523h (only 522h is
illustrated) with the same structure as of the Y directional guides
512h and 513h is arranged on the Y table 52h with the X table 54h
sandwiched therebetween. Concave grooves are also formed in the X
directional guides on the sides facing to the X table and convex
portions are formed on opposite sides of the X table (sides facing
to the X directional guides). The concave groove extends
approximately along the full length of the X directional guide. A
top, a bottom and a side faces of respective convex portions of the
X table 54h protruding into the concave grooves are provided with
hydrostatic bearings (not shown) similar to those hydrostatic
bearings 58h in the similar arrangements. A linear motor 524h of
known configuration is disposed between the Y table 52h and the X
table 54h so as to drive the X table in the X direction. Further,
the X table 54h is supplied with a high-pressure gas through a
flexible pipe 546h, and thus the high-pressure gas is supplied to
the hydrostatic bearings. The X table 54h is supported highly
precisely with respect to the Y directional guide in a non-contact
manner by way of said high-pressure gas blowing out from the
hydrostatic bearings to the guide planes of the X directional
guides. The vacuum chamber 31h is evacuated through vacuum pipes
309h, 518h and 519h coupled to a vacuum pump of known structure.
Those pipes 518h and 519h pass through the fixed table 51h to the
top surface thereof to open their inlet sides (inner side of the
vacuum chamber) in the proximity of the locations to which the
high-pressure gas is ejected from the stage device, so that the
pressure in the vacuum chamber may be prevented to the utmost from
rising up by the blown-out gas from the hydrostatic bearings.
[0315] A differential pumping mechanism 92h is arranged so as to
surround the tip portion of the optical column 701h or the charged
particles beam irradiating section 702h, so that the pressure in a
charged particles beam irradiation space G5 can be controlled to be
sufficiently low even if there exists high pressure in the vacuum
chamber 31h. That is, an annular member 921h of the differential
pumping mechanism 92h mounted around the charged particle beam
irradiating section 702h is positioned with respect to the housing
30h so that a micro gap (in a range of some microns to some-hundred
microns) G7 can be formed between the lower face thereof (the
surface facing to the wafer) and the wafer, and an annular groove
922h is formed in the lower face thereof. The annular groove 922h
is coupled to a vacuum pump or the like, though not shown, through
an evacuating pipe 923h. Accordingly, the micro gap g5 can be
exhausted through the annular groove 922h and the evacuating pipe
923h, and if any gaseous molecules from the chamber 31h attempt to
enter the space G5 circumscribed by the annular member 921h, they
may be exhausted. Thereby, the pressure within the charged particle
beam irradiation space G5 can be maintained to be low and thus the
charged particle beam can be irradiated without any troubles. The
annular groove 922h may be made doubled or tripled, depending on
the pressure in the chamber and the pressure within the charged
particle beam irradiation space G5.
[0316] Typically, dry nitrogen is used as the high-pressure gas to
be supplied to the hydrostatic bearings. If available, however, a
much higher-purity inert gas should be preferably used instead.
This is because any impurities, such as water contents, oil and fat
contents or the like, included in the gas could stick on the inner
surface of the housing defining the vacuum chamber or on the
surfaces of the stage components leading to the deterioration in
vacuum level, or could stick on the sample surface leading to the
deterioration in vacuum level in the charged particle beam
irradiation space.
[0317] It should be appreciated that though typically the wafer is
not placed directly on the X table, but may be placed on a sample
table having a function to detachably carry the sample and/or a
function to make a fine tuning of the position of the sample
relative to the stage device 50, an explanation therefor is omitted
in the above description for simplicity due to the reason that the
presence and structure of the sample table has no concern with the
principal concept of the present invention.
[0318] Since a stage mechanism of a hydrostatic bearing used in the
atmospheric pressure can be used in the above-described charged
particle beam apparatus mostly as it is, a high precision stage
having an equivalent level of precision to those of the stage of
high-precision adapted to be used in the atmospheric pressure,
which is typically used in an exposing apparatus or the likes, may
be accomplished for an XY stage to be used in a charged particle
beam apparatus with equivalent cost and size.
[0319] It should be also appreciated that in the above description,
the structure and arrangement of the hydrostatic guide and the
actuator (the linear motor) have been explained only as an example,
and any hydrostatic guides and actuators usable in the atmospheric
pressure may be applicable.
[0320] FIG. 32 shows an example of numeric values representative of
the dimensions of the annular grooves 922 formed in the annular
member 921 of the differential pumping mechanism. In this example,
a doubled structure of annular grooves 922h and 922h' which are
separated from each other in the radial direction is provided.
[0321] The flow rate of the high-pressure gas supplied to the
hydrostatic bearing is typically in the order of about 20 L/min (in
the conversion into the atmospheric pressure). Assuming that the
vacuum chamber C is evacuated by a dry pump having a function of
pumping speed of 20000 L/min through a vacuum pipe with an inner
diameter of 50 mm and a length of 2 m, the pressure in the vacuum
chamber will be about 160 Pa (about 1.2 Torr). At that time, with
the applied size of the annular member 921h, the annular groove and
others of the differential pumping mechanism as illustrated in FIG.
32, the pressure within the charged particles beam irradiation
space G5 can be controlled to be 10.sup.-4 Pa (10.sup.-6 Torr).
[0322] FIG. 33 shows a vacuum chamber 31h defined by the housing
30h and a evacuating circuit 93 for the differential pumping
mechanism. The vacuum chamber 31h is connected to a dry vacuum pump
932 via vacuum pipes 931a and 931b of the evacuating circuit 93. An
annular groove 922h of a differential pumping mechanism 92h is
connected with an ultra-high vacuum pump or a turbo molecular pump
933 via a vacuum pipe 931c connected to an exhaust port 923h.
Further, the interior of a optical column 701h is connected with a
turbo molecular pump 934 via a vacuum pipe 931d connected to an
exhaust port 903. Those turbo molecular pumps 933, 934 are
connected to the dry vacuum pump 932 through vacuum pipes 931e,
931f. (In FIG. 33, the single dry vacuum pump has been used to
serve both as a roughing vacuum pump of the turbo molecular pump
and as a pump for vacuum pumping of the vacuum chamber, but
alternatively multiple dry vacuum pumps of separate systems may be
employed for pumping, depending on the flow rate of the
high-pressure gas supplied to the hydrostatic bearings of the XY
stage, the volume and inner surface area of the vacuum chamber and
the inner diameter and length of the vacuum pipes.)
[0323] A high-purity inert gas (N.sub.2 gas, Ar gas or the like) is
supplied to a hydrostatic bearing of the stage device 50h through
flexible pipes 526h, 546h. Those gaseous molecules blown out of the
hydrostatic bearing are diffused into the vacuum chamber and
evacuated by the dry vacuum pump 932 through exhaust ports 309h,
518h and 519h. Further, those gaseous molecules having flown into
the differential pumping mechanism and/or the charged particles
beam irradiation space are sucked from the annular groove 922h or
the tip portion of the optical column 701h and exhausted through
the exhaust ports 923h and 703h by the turbo molecular pumps 933
and 934, and then those gaseous molecules, after having been
exhausted by the turbo molecular pumps, are further exhausted by
the dry vacuum pump 932. In this way, the high-purity inert gas
supplied to the hydrostatic bearing is collected into the dry
vacuum pump and then exhausted away.
[0324] On the other hand, the exhaust port of the dry vacuum pump
932 is connected to a compressor 935 via a pipe 931g, and an
exhaust port of the compressor 935 is connected to flexible pipes
546h and 526h via pipes 931h, 931i and 931k and regulators 936 and
937. With this structure, the high-purity inert gas exhausted from
the dry vacuum pump 932 is compressed again by the compressor 935
and then the gas, after being regulated to an appropriate pressure
by regulators 936 and 937, is supplied again to the hydrostatic
bearings of the stage device.
[0325] In this regard, since the gas to be supplied to the
hydrostatic bearings is required to be as highly purified as
possible in order not to have any water contents or oil and fat
contents included therein, as described above, the turbo molecular
pump, the dry pump and the compressor are all required to have such
structures that they prevent any water contents or oil and fat
contents from entering the gas flow path. It is also considered
effective that a cold trap, a filter 938 or the like is provided in
the course of the outlet side piping 931h of the compressor so as
to trap the impurities such as water contents or oil and fat
contents, if any, included in the circulating gas and to prevent
them from being supplied to the hydrostatic bearings.
[0326] This may allow the high purity inert gas to be circulated
and reused, and thus allows the high-purity inert gas to be saved,
while the inert gas would not remain desorbed into a room where the
present apparatus is installed, thereby eliminating a fear that any
accidents such as suffocation or the like would be caused by the
inert gas.
[0327] A circulation piping system is connected to a high-purity
inert gas supply source 939, which serves both to fill up with the
high-purity inert gas all of the circulation systems including the
vacuum chamber C, the vacuum pipes 931a to 931e, and the pipes in
compression side 931f to 9311, prior to the starting of the gas
circulation, and to supply a deficiency of gas if the flow rate of
the circulation gas decreases by some reason. Further, if the dry
vacuum pump 932 is further provided with a function for compressing
up to the atmospheric pressure or more, it may be employed as a
single pump so as to serve both as the dry vacuum pump 932 and the
compressor 935.
[0328] As the ultra-high vacuum pump to be used for evacuating the
optical column, other pumps including an ion pump and a getter pump
may be used instead of the turbo molecular pump. It should be
appreciated that if these pumps of an accumulating type is used, a
circulating piping system may not be provided for the optical
column. Further, instead of the dry vacuum pump, a dry pump of
other type, for example, a dry pump of diaphragm type may be
used.
ALTERNATIVE EMBODIMENT OF ELECTRON BEAM APPARATUS
[0329] FIGS. 34 to 37 show an alternative embodiment of the
electron optical apparatus or the electron beam apparatus
designated generally by reference numeral 70i. In these drawings,
the same components as those in the electron beam apparatus shown
in FIG. 8 are designated respectively by the same reference
numerals and detailed explanations on the structure and function
thereof will be omitted. Besides, components different from those
in FIG. 8 are designated respectively by the same reference
numerals, each added with a suffix "i". Further, in the following
description of each of the embodiments for the case with a
multi-aperture plate included in a first and a second optical
systems, since the relationship between the first and the second
multi-aperture plates is same as that illustrated in FIG. 9,
therefore an illustration and an explanation therefor will be
omitted.
[0330] In the present embodiment, a configuration of an electron
beam apparatus is same as that of the electronic optical apparatus
shown in FIG. 8, with the exception that a secondary optical system
thereof 74i only has a single lens and that a detection system
thereof 76i comprises a pattern memory 772 connected to an image
data processing section 771 of a process control system 77i.
[0331] In this apparatus, secondary electron images are detected by
a set of detectors 761 of the detection system 76i disposed behind
apertures 7451 of a multi-aperture plate 745 of the secondary
optical system 74i without any cross talks with respect to one
another, and then formed into images in the image data processing
section 771 that is an image forming unit. Further, an image for a
sample pattern is formed from pattern data and is stored separately
in the pattern memory 772, and thereby an image comparing circuit
attached to the image data processing section 771 makes a
comparison of the pattern image with an image formed from the
secondary electron images to classify a defect into any one of a
classification group consisting of short-circuit, disconnection,
convex, chipping, pinhole and isolation.
[0332] Further, upon measuring a potential of a pattern on a wafer
W, a potential lower than that in a surface of the wafer is applied
to an axially symmetric electrode 737 to select the secondary
electrons from the sample or wafer W based on their energies such
that some are permitted to pass through to an objective lens 729
side and some are driven back onto the wafer W side thus to measure
a voltage of the pattern. This allows more secondary electrons
originated from a pattern having a lower potential to be detected
and fewer secondary electrons originated from a pattern having a
higher potential to be detected, and thereby allows the potential
of the pattern on the sample to be measured based on a quantity of
the detected secondary electrons being large or small.
[0333] For example, it is assumed that an equipotential surface of
0V has such a profile around the electrode 737 as illustrated in
FIG. 35, when a voltage of -10V is applied to said electrode 737.
In that case, the secondary electron emitted from the pattern
having the potential of -2V with the given energy of 0V can run
over the potential barrier of 0V thus to be detected, because that
secondary electron should still has the energy retained at the
level of 1 eV at the equipotential surface of 0 eV, while on the
other hand, the secondary electron emitted from the pattern having
the potential of +2V with the given energy of 0 eV is only
permitted to go up to the equipotential surface of 2 eV, which
forces the secondary electron to return back toward the sample and
the secondary electron would not be anyhow detected. Accordingly,
the image for the pattern of -2V is formed to be brighter, while
the image for the pattern of 2V is formed to be darker. Thus the
potential contrast may be measured.
[0334] Further, when a potential measurement of high time
resolution is to be performed, a pulse voltage may be applied to a
blanking deflector 731 to deflect the beam and thereby to block
said beam by a blanking knife edge 734 so as to form it into a
multi-beam in the form of short pulses, thereby accomplishing the
above-described measurement.
[0335] For example, if such pulse voltages as illustrated
respectively by [A] and [B] of FIG. 36 are applied to electrodes of
the blanking deflector 731 disposed in the left and the right sides
with respect thereto, then such a pulsed beam current as
illustrated by [C] of FIG. 36 would be entered onto the wafer.
Accordingly, if the pulsed electron beam is entered to the pattern
and the secondary electrons emitted at that time are detected, the
potential of the pattern can be measured with the time resolution
having said pulse width. It is to be noted that those dotted lines
between the blanking deflector 731 and the blanking knife edge 732
in the drawing designate electron beam orbits at the time of
blanking.
[0336] An inspection procedure by using said electron beam
apparatus of the present invention will now be described.
[0337] FIG. 37 shows an example of the inspection procedure
according to the present invention. A wafer 11 subject to an
inspection is taken out of a wafer cassette (1) and then
pre-aligned, while at the same time a wafer number reader, though
not shown, reads out a wafer number having been formed on this
wafer (2). The wafer number is unique to an individual wafer. The
read-out wafer number is used as a key to read out a recipe
corresponding to this wafer (3), said recipe having been registered
in advance. The recipe includes the inspection procedure and/or the
inspection condition defined for this wafer.
[0338] Subsequent operations may be performed automatically or
semi-automatically according to the read-out recipe. After the
wafer number having been read-in, the wafer W is transferred and
mounted onto an XY stage in a sample chamber held into a vacuum
(4). The wafer W loaded on the XY stage is aligned by the primary
and the secondary optical systems installed within the sample
chamber (5). The alignment operation may be performed in such a
manner that an enlarged image of the alignment pattern formed on
the wafer W is compared with a reference image registered in
advance for the alignment in association with the recipe and then a
stage position coordinate is corrected such that the alignment
image can be superposed exactly on the reference image. After the
alignment, a wafer image (an inspection pattern image)
corresponding to this wafer is read out and indicated on a display
(6). The wafer image shows a required inspection point and a
history for this wafer.
[0339] After the wafer image having been indicated, an operator
specifies a point corresponding to a position desired to be
inspected among the inspection points shown on the wafer image (7).
Once the inspection point is specified, the stage moves and brings
the wafer W subject to the inspection to such a location that the
specified inspection point thereon may be positioned directly below
the electron beam (8). After this movement, the scanning electron
beam is irradiated onto the specified inspection point, and an
image for the purpose of positioning with a relatively low
magnification is formed thereon. Then, similarly to the aligning
procedure, the formed image is compared with a reference image
corresponding to the specified inspection point, which has been
registered in advance for positioning, and a precise positioning is
performed so that the formed image may be superposed exactly on the
reference image (9). The positioning may be accomplished by, for
example, a fine-adjustment of the region to be scanned by the
electron beam.
[0340] If appropriately positioned, the wafer should be located
such that the region to be inspected is in an approximately central
location of the screen, that is, a location directly below the
electron beam. In this state, an image in the inspection region to
be used for an inspection with a high magnification may be formed
(10). The image to be used for the inspection is compared with a
reference image corresponding to this region to be inspected, which
has been registered in advance for the inspection in association
with the recipe, and then a different portion between those two
images is detected (11). The different portion is considered as a
pattern defect. The pattern defect may be classified into such
defect groups including at least short-circuit, disconnection,
convex, chipping, pinhole and isolation (12).
[0341] Subsequently, the convex and the isolation defects are
classified according to the size, in which a distance to an
adjacent pattern is defined by a unit representing a minimum space
and a subtending length (a length of a shadow of a defect projected
to a pattern) by a unit representing a minimum pattern width. On
the other hand, the pinhole and the chipping defects are classified
according to the size, in which a width of a pattern including
either of said defects is used as a unit defining the size in the
width direction and a minimum pattern width is used as a unit in
the longitudinal direction (13). It is to be noted that the minimum
pattern width and the minimum space are values to be defined based
on a pattern design rule for the device subject to the inspection
and these values should have been registered prior to the
inspection.
[0342] After the defect determination and the classification
thereof regarding to the specified inspection point having been
completed, the classification result is stored in the inspection
database while being used to overwrite the specified inspection
point on the wafer image. Thus the inspection procedure for one
location comes to the end as described above.
[0343] If there are remaining any inspection locations, a
subsequent inspection point may be specified on the wafer image,
and the operations following to the step of specifying the
inspection point in FIG. 37 may be repeated. After full range of
inspection on said wafer having been finished, a density and/or a
yield for a total defect, for each classified defect, and for each
defect distinguished by size is calculated for each chip or wafer
(14). The calculation of the yield may be executed by using a
critical rate table of defect size for the respective defect types
registered in advance. The critical rate table of defect size has
been prepared to correlate each of the defects including the
convex, chipping, pinhole and isolation, which have been classified
by size, with each unique critical rate. These calculation results
may be stored in the inspection database together with the
inspection result (14), and output to be used at any times as
desired (15).
[0344] If there remains any wafers to be measured in a wafer
cassette, a subsequent wafer is taken out of the wafer cassette and
then inspected according to the procedure shown in FIG. 37. The
density and the yield for a plurality of wafer are also calculated
similarly to the case of the wafer as described above.
[0345] It is to be appreciated that if the electron beam apparatus
is further equipped with additional analyzing functions by means
of, for example, a characteristic X-ray analyzer or an Auger
electron analyzer, it may become possible to obtain analytic data
of the inspection point such as data including a defective
composition in addition to the classification in the defect
determination based on the inspection image.
Further Alternative Embodiment of Electron Beam Apparatus
[0346] FIGS. 38 and 39 show an alternative embodiment of the
electron beam apparatus designated generally by reference numeral
70j. In FIGS. 38 and 39, the same components as those in the
electron beam apparatus shown in FIG. 8 are designated respectively
by the same reference numerals and detailed explanations on the
structure and function thereof will be omitted. Besides, components
different from but similar to those in FIG. 8 are designated
respectively by the same reference numerals, each added with a
suffix "j".
[0347] An electron beam apparatus according to this embodiment is
same as the electron optical apparatus as shown in FIG. 8 with the
exception that an aperture plate 735 defining an aperture is
located at a point P1 where a crossover of a primary optical system
72j is formed, that an aperture plate 747 defining an aperture is
located at a point P4 where a crossover of a secondary optical
system 74j is formed, and that the secondary optical system 74j
comprises an electrostatic deflector 746.
[0348] In the electron beam apparatus of the present embodiment, a
plurality of secondary electron beams emitted from respective
irradiation spots on a wafer W is guided to a detector through the
secondary optical system 74j. In a stage prior to a magnifying lens
743, the electrostatic deflector 746 is arranged so as to function
as an axially aligning device for the magnifying lens 743. Further,
the aperture plate 747 defining the aperture is arranged at the
location P4 where the second crossover image is formed so as to
obtain the resolution of the second optical system.
[0349] Herein, any cross talks among a plurality of beams may be
avoided by making a spacing between a plurality of primary electron
beams be greater than the resolution of the secondary optical
system as converted into the value on the wafer surface. The
spacing between the irradiation spots is scanned by said
electrostatic deflector 746. This allows an image to be created in
the same principle as of the SEM and also with a throughput
proportional to the number of beams. Since chromatic aberration can
be reduced by controlling an angle of deflection of the
electrostatic deflector 746 to a value proximal to -1/2 of an angle
of electromagnetic deflection by an E.times.B separator 726,
therefore the deflection would not increase the beam diameter
excessively.
[0350] Each of detecting elements of a detector 761 is connected
via each of amplifiers 763 to an image data processing section 771
of a process control system 77 for converting a detection signal to
the image data. Since the image data processing section 771 is
supplied with the same scanning signal as that given to a deflector
733 for deflecting the primary electron beam, the image data
processing section 771 can figure out an image representative of
the scanned surface of the wafer W from the detection signal
obtained during the beam scanning.
[0351] As can be seen obviously from FIG. 38, since a portion in
the optical path common to the primary optical system and the
secondary optical system is the portion from the E.times.B
separator 726 through an objective lens 729 up to the wafer W, the
number of common optical parts has been successfully decreased.
Owing to this, even if the lens condition for the objective lens
729 was matched to the primary electron beam, a focusing condition
for the secondary electron beam can be adjusted by using the
magnifying lenses 741 and 743. The latter, the magnifying lens 743
is to magnify an angle .theta.1 made by an orbit of the secondary
electron and the optical axis OA.sub.2 to .theta.2.
[0352] In addition, although the axial alignment with respect to
the objective lens 729 is performed favorably to the primary
electron beams by applying an axial aligning power supply voltage
onto the deflector 728 in superposition to its due voltage, the
axial mismatch of the secondary electron beam due to the axial
alignment favorable to the primary electron beam can be compensated
for by using the axial aligner for the secondary optical system or
the deflector 746.
[0353] As for the aperture plate defining the aperture, two
aperture plates has been employed, one of which is the aperture
plate 735 for passing only the primary electron beam therethrough
disposed at the location P1 where the first cross over image is
formed, and the other of which is another aperture plate 747 for
passing only the secondary electron beam therethrough disposed at
the location P4 where the second cross over image is formed,
thereby allowing an optimal aperture diameter to be selected
individually. Employing a size of an aperture of the objective lens
729 sufficiently greater than the diameter of the cross over herein
and zooming the objective lenses 721 and 725 so as to make the
cross over size variable at the position of the objective lens 729
can make an angular aperture selectable. This allows the angular
aperture to be adjusted to a desired optimal value within a range
determined by the trade-off between the low aberration and the high
beam current by only using an electric signal without exchanging
apertures.
[0354] As for the location of the aperture of the secondary optical
system, such a condition should be satisfied that the secondary
electron image could be focused on the detector 761 by the
magnifying lenses 741 and 743. Then, the aperture is to be moved
along the optical axis OA.sub.2 until the location where every
secondary electron beam may have the same intensity when the wafer
with the inspected surface having a uniform emission characteristic
has been used, and at that location, the aperture of the secondary
optical system should be fixed. This position is the location in
the optical axis direction where the principal ray from the wafer
would cross the optical axis as illustrated.
[0355] In a pattern defect inspection method for a wafer W by way
of the pattern matching, a control section which is not shown but
has been provided for controlling the electron beam apparatus
executes a comparative matching between a secondary electron beam
reference image of a wafer having no defect which has been stored
in a memory thereof in advance and an actually detected secondary
electron beam image so as to calculate a similarity between those
two images. For example, if the calculated similarity is not
greater than a threshold, it is determined that "a defect exists"
and if the calculated similarity is greater than the threshold, it
is determined that "no defect exists". At this stage, the detected
image may be displayed on a CRT, though not shown. Thereby, an
operator can make a final confirmation and thus evaluate whether
the wafer W has actually a defect or not. Further, the images may
be compared to see a matching in segment by segment base so as to
detect automatically the segment including the defect. In that
case, preferably an enlarged image representing the defective
segment should be displayed on the CRT.
[0356] Still further, for a wafer having a number of same dice, the
detected images may be compared between the detected dice so as to
detect the defective part without the need for using the reference
image as described above. For example, FIG. 39 [A] shows an image
Im1 for a firstly detected die and another image Im2 for a
secondarily detected die. If it is determined that another image
for a thirdly detected die is same as or similar to the first image
Im1, then it can be determined that the second die image Im2 has a
defect in the segment Nt, and thus a defective part can be
detected. At this stage, the detected image may be displayed on the
CRT while marking the segment determined to be defective.
[0357] It is to be noted that to measure a line width of a pattern
or a potential contrast of the pattern formed on the wafer, the
operation may be performed in the manner as described in
conjunction with FIG. 24, and the explanation thereof will be
omitted.
[0358] Referring to FIG. 38, since a blanking deflector 731 has
been provided, said deflector 731 may be used to deflect the
primary electron beam toward the aperture at the cross over image
formation point in a predetermined cycle so as to permit the beam
to pass therethrough for a short period and to block it for the
rest of the period, which will be repeated, then it will be
possible to form a bundle of beams having a short pulse width. If
such a beam having a short pulse width is used to measure the
potential on the wafer as described above, the device operation
characteristics can be analyzed with high time resolution. That is,
the present electron beam apparatus can be used as what is called
an EB tester.
Further Alternative Embodiment of Electron Beam Apparatus
[0359] FIG. 40 shows an alternative embodiment of the electron
optical apparatus or the electron beam apparatus designated
generally by reference numeral 70k. In FIG. 40, the same components
as those in the electron beam apparatus shown in FIG. 8 are
designated respectively by the same reference numerals and detailed
explanations on the structure and function thereof will be omitted.
Besides, components different from but similar to those in FIG. 8
are designated respectively by the same reference numerals, each
added with a suffix "k".
[0360] The electron beam apparatus according to the present
embodiment is same as the embodiment of FIG. 8 with the exception
that the apparatus further comprises a mode determining circuit 775
connected to an image data processing section 771 of a process
control system 77k, that said mode determining circuit 775 is
provided with a CPU 776, a memory section 777 connected to said CPU
776 and an operator console 778, and that said memory section is
connected to respective components in a primary optical system 72
and a secondary optical system 74.
[0361] In the electron beam apparatus of the present embodiment, a
secondary electron image is formed on one of a plurality of
apertures 7451 of a second multi-aperture plate 745 by magnifying
lenses 741 and 743, and this second electron image is detected by
each of detectors 761. Each of those detectors 761 converts the
detected secondary electron image into an electric signal
representing an intensity thereof. In this way, the electric signal
output from each of the detectors, after having been amplified by
the corresponding amplifier 763, is entered into the image data
processing section 771 of the process control system 77k and
converted into an image data in this image data processing section.
Since the image data processing section 771 is further supplied
with the scanning signal for deflecting the primary electron beam,
the image data processing section 771 may display an image
representative of the surface of a sample or a wafer W. By
comparing this image with a reference pattern allows a defect in
the wafer to be detected, and further, by moving the pattern to be
evaluated on the wafer W to a location proximal to an optical axis
OA.sub.1 of the primary optical system 72 by way of registration
and then line-scanning this pattern, a line width evaluation signal
for the pattern formed on the top surface of the sample can be
extracted, which is further calibrated appropriately so as to
measure the line width of the pattern.
[0362] In the case for evaluating a wafer having a pattern with a
minimum line width of 0.1 .mu.m, if there are some evaluation modes
available for the electron beam apparatus, including a mode using a
pixel size of 0.2 .mu.m for performing an evaluation with high
throughput, another mode using the pixel size of 0.1 .mu.m for
performing an evaluation with higher precision but the throughput
deteriorated to one-quarter of that by the first mode, and further
the other mode using the pixel size of 0.05 .mu.l for allowing an
evaluation with much higher precision but the throughput further
deteriorated to one-quarter of that by said another mode, then such
electron beam apparatus may advantageously works for many uses.
[0363] On the other hand, when the pixel size is changed, the beam
size and thus a scanning dimension need to change in association
with the change in pixel size. To change the scanning dimension, it
is only required to change a voltage to be applied to the
deflector. In contrast, to change the beam size, it is required to
change many parameters.
[0364] In FIG. 40, the primary electron beam, after having passed
through a plurality of apertures 7231 of the multi-aperture plate
723 is focused by a reduction lens 725 and an objective lens 729.
Accordingly, conditions for the reduction lens 725 and the
objective lens 729 may be determined and stored in the memory
section in advance, so that the zooming effect from those two
lenses may be used to change a reduction ratio to form a beam in a
size suitable for each of the pixel sizes of 0.05 .mu.m, 0.1 .mu.m
and 0.2 .mu.m, and the appropriate condition may be extracted and
established at each time when the mode is changed. From the
viewpoint of the secondary optical system, since the objective lens
is determined by the condition for the primary optical system, the
above-described method is not applicable to the secondary optical
system. In the secondary optical system, the lens condition may be
determined such that the secondary electrons or a principal ray
emitted from the sample in a right angle with respect to the
surface thereof can be entered exactly into each of the apertures
7451 of the second multi-aperture plate 745 of the secondary
optical system by at least one-step of lens arranged downstream to
an E.times.B separator 727. These lens conditions and axial
aligning conditions for each of those three modes may be stored in
the memory section 777 of the mode determining circuit. Then, the
input from the operator console 778 may control the CPU 776 to
extract the conditions and to reset the values appropriately at
each time when the mode is changed.
[0365] FIG. 41 shows an embodiment in which a mode determining
circuit similar to that in preceding embodiment is applied to an
electron beam apparatus of the scanning type for irradiating a
single electron beam, which is designated generally by reference
numeral 70m. In FIG. 41, components corresponding to those in the
preceding FIG. 40 are designated by the same reference numerals,
each added with a suffix "m".
[0366] In this embodiment, since a condenser lens 721 m has
substantially the same structure as that of an objective lens 729m,
therefore the condenser lens is representatively explained in
detail.
[0367] The condenser lens 721m, which is an electrostatic axially
symmetric lens, comprises a main body 7210 made of ceramic. This
main body 7210 is formed to be annular in plan view to define a
circular opening 7211 in a central portion thereof, and an inner
circle side thereof is divided into three plate-like sections 7212
to 7214 spaced to one another in a longitudinal direction (the
direction along the optical axis) in FIG. 41. An outer surface of
the ceramic made main body 7210, especially the outer surface of
the plate-like sections 7212 to 7214, is coated with metal coating
films 7212' to 7214'. These coating films 7212' to 7214' serve as
electrodes respectively, in which to the coating films 7212' and
7214' is applied respectively a voltage having a level approximate
to the ground side, while to the central coating film 7213' is
applied a positive or a negative high voltage having a high
absolute value through the electrode fitting 7215 provided on the
main body 7210, thereby to serve as a lens. Such lens is allowed to
be of high processing accuracy and to be made smaller in an outer
diameter because each element thereof is formed out from a single
piece of ceramic by machining and finishing simultaneously.
[0368] In the electron beam apparatus of the above embodiment,
since the outer diameter of the lens can be made smaller, the
diameter of the optical column containing the electron beam
apparatus also may be reduced. Therefore, it becomes possible to
arrange a plurality of optical columns for one piece of sample such
as a wafer having a larger diameter. For example, the array of four
pieces of optical columns in the X direction by two rows in the Y
direction, that is, eight optical columns 701m in total may be
arranged for one piece of sample, as shown in FIG. 42. In this
arrangement, the distances between optical axes of respective
optical systems projected in the X-axis direction are made all
equal. Employing such an arrangement can eliminate a not-evaluated
region or a doubly evaluated region with several times of
mechanical scanning. Then, when the stage (not shown) holding the
wafer W is continuously moved in the Y-direction and each of the
optical columns scans in the X direction with a width of 1.1 mm,
then a 8 mm wide region can be evaluated with one time of
mechanical scanning. It is to be appreciated that a 50 .mu.m wide
region should be doubly evaluated.
[0369] The lens conditions and axial aligning conditions for each
of the modes may be measured in advance and stored in the memory
section 777 belonging to the mode determining circuit 775, and
then, an input from the operator console 778 controls the CPU 776
to extract the conditions and reset the values appropriately at
each time when the mode is changed.
Further Alternative Embodiment of Electron Beam Apparatus
[0370] FIGS. 43 and 44 show an alternative embodiment of the
electronic optical apparatus or the electron beam apparatus
designated generally by reference numeral 70n. In FIGS. 43 and 44,
the same components as those in the electron beam apparatus shown
in FIG. 8 are designated respectively by the same reference
numerals and detailed explanations on the structure and function
thereof will be omitted. Besides, components different from but
similar to those in FIG. 8 are designated respectively by the same
reference numerals, each added with a suffix "n".
[0371] The electron beam apparatus according to the present
embodiment is same as the embodiment of FIG. 8 with the exception
that the apparatus further comprises a laser interferometer in
association with the stage unit and the objective lens, and that an
aperture plate is arranged at a point P1 where a cross over is
formed.
[0372] FIG. 44 illustrates in detail a specific structure of an
electrostatic lens which constitutes an objective lens 729n shown
in FIG. 43. The objective lens 729n is formed into an axially
symmetric structure centering around an optical axis OA.sub.1,
wherein only a right half-portion thereof is shown in a sectional
view of FIG. 44.
[0373] The objective lens 729 may be fabricated in the following
manner. Primarily, a metal bar 7299 is embedded into a ceramic
material, which can be shaped by machining, so as to form a
circularly cylindrical part 7290. Secondarily, the ceramic material
is machined with a lathe in order to form an upper electrode
section 7292, a central electrode section 7293, a lower electrode
section 7294 and an axially symmetric electrode section 7295. Then,
the masking is applied to those portions where the surface of the
ceramic material is to be exposed for insulation, and a metal
plating is applied to the remaining surface portions of the ceramic
material by way of electroless plating, thereby forming an upper
electrode 7292', a central electrode 7293', a lower electrode 9294'
and an axially symmetric electrode 7295'.
[0374] The upper electrode 7292' is supplied with a voltage from a
lead 7296 connected to a top surface thereof. The central electrode
7293' and the lower electrode 7294' are supplied with voltages from
leads 7297 via a pair of metal bars 7299. It is to be noticed that
a vacuum sealing is not necessary to the metal bar 7299. The
axisymmetric electrode 7295' is supplied with a voltage from a lead
7298 connected to a lower face thereof.
[0375] A cylindrical part made of ceramic having such a
configuration as described above may be fabricated small in size,
and then a ceramic member 7300 having a low coefficient of linear
expansion (e.g., NEXCERAN113 available from Nippon Steel
Corporation) is adhered onto the outer side thereof. Then, a planer
stationary laser mirror 7301 is fixedly adhered to the outer side
of said ceramic member 7300. The stationary laser mirror 7301 may
be formed by polishing a side of the ceramic member 7300 subject to
the laser beam to be a mirror-surface.
[0376] The integration of the stationary laser mirror 7301 into the
objective lens 729n (fixing by adhesion or integration in
structure) makes it possible that in case of the vibration of the
optical system in the X-Y plane direction in addition to the
vibration of the stage unit as the matter of course, the laser
interferometer measures a displacement of the electron beam due to
such vibration and the beam position may be accordingly
compensated. That is, even if the objective lens 729n vibrates in
the x-y direction, a variation in relative distance with respect to
the stage 50n can be measured by the laser interferometer 94 and
thereby the compensation may be applied to the beam so as to offset
the variation. In this manner, a relative micro-vibration between
the optical system and the stage can be compensated and thereby an
image distortion due to the vibration of the optical system can be
reduced.
[0377] An evaluation such as a defect inspection of a pattern
formed on a surface of a wafer W which is a sample is to be
accomplished by using the electron beam apparatus shown in FIG. 43,
an electrostatic deflector 733 and a magnetic deflector 728 of a
Wien filter or an E.times.B separator 726 should be operated
interlockingly and at the same time an X table and a Y table of a
stage unit 50n are to be moved, so that a plurality of primary
electron beams may scan the surface of the wafer W in the
X-direction while continuously moving the wafer W in the
Y-direction, thus scanning the overall surface of the wafer W. That
is, after the stage unit 50n having been moved to place the wafer W
at a scanning starting end, the stage unit is moved continuously in
the Y-direction while controlling a plurality of primary electron
beams to scan in the X-direction with an amplitude slightly greater
than a distance between respective primary electron beams, Lx
(shown in FIG. 9). This means that the wafer could have been
scanned in the region extending along the Y-direction having a
width w equivalent to full scanning distance of the plurality of
primary electron beams in the X-direction, and a signal in
association with the scanning in said region would be output from a
detector 761.
[0378] Subsequently, after the stage unit having been moved in the
X-direction by a step equivalent to the width w, the table of the
stage unit 50 is continuously moved in the Y-direction while
controlling the plurality of primary electron beams to scan the
wafer W in the X-direction by the distance equivalent to the width
w. Thereby, another region of the width w adjacent to the region
having been previously scanned would have been scanned both in the
X- and the Y-directions. After this, the similar operations may be
repeated to scan the overall surface of the wafer W, and the signal
obtained as a result of scanning operations from the detector 761
may be processed so as to evaluate the wafer W.
[0379] It is to be appreciated that, preferably, the laser
interferometer 94 should be employed in order to precisely control
the movement of the stage unit 50n. To achieve this, the X table
and the Y table of the stage unit are provided with movable laser
mirrors 941, while a laser interferometer 942 with a built-in laser
oscillator 943, a stationary laser mirror 946 (which may be the
same mirror as the reference mirror 7301 of FIG. 44) secured
fixedly to the objective lens, a reflection mirror 944 and a
dichroic mirror 945 are mounted respectively in appropriate
locations on the stationary side as illustrated, so that a position
of the stage can be calculated based on the interference between
the light which has followed an optical path from the laser
oscillator 943.fwdarw.the dichroic mirror 945.fwdarw.the reflection
mirror 944.fwdarw.the stationary laser mirror 946 (7301).fwdarw.the
reflection mirror 944 the dichroic mirror 945.fwdarw.the laser
interferometer 942 and the light which has followed another optical
path from the laser oscillator 943.fwdarw.the dichroic mirror
945.fwdarw.the stationary laser mirror 941.fwdarw.the dichroic
mirror 945.fwdarw.the laser interferometer 942.
[0380] In the laser interferometer 94 of FIG. 43, the
interferometer for either one of the X-axis or the Y-axis direction
has been illustrated, and the interferometer for the other
direction has been omitted. However, in practice, the
interferometer should be provided for both of the X-axis and the
Y-axis directions as a matter of course. For example, as for the
movable mirror 941, orthogonal side faces of the X and the Y tables
of the stage unit may be provided with movable mirrors for the
X-axis and for the Y-axis, respectively.
[0381] If the wafer W is a semiconductor wafer, then instead of the
above-described evaluation method, the following method may be
taken to evaluate the wafer W. That is, a marker may be arranged at
an appropriate location on the surface of the wafer W, such that
only the one electron beam among a plurality of primary electron
beams, which has been formed by one aperture of a multi-aperture
plate 723, may be allowed to scan said marker and an output from
the detector at that time of scanning is extracted to detect the
position of the marker. Thereby, a physical relationship between
the wafer W and the primary electron beam can be determined, and
therefore, if an orientation of a circuit pattern formed on the
surface of the wafer W with respect to the X- and the Y-directions
have been determined in advance, a plurality of primary electron
beams could be guided to the correct position to meet said circuit
pattern and the beams therein could scan the circuit pattern,
thereby accomplishing the evaluation of the circuit pattern on the
wafer W.
[0382] Further, the line width of the pattern on the surface of the
wafer W can be measured in such a way that first a pattern to be
evaluated on the wafer W is moved by registration to the proximity
to the optical axis of the primary optical system and the wafer W
is line-scanned with the primary electron beam to detect the
secondary electron beam, and then a signal corresponding to this
secondary electron beam is detected to extract a signal for
evaluating the line width of the circuit pattern on the surface of
the wafer W, which is then calibrated appropriately thus to measure
the line width of the pattern on the surface of the wafer W.
[0383] FIG. 45 shows an embodiment in which a mode determining
circuit having a principle similar to that of the above-described
embodiment is applied to an electron beam apparatus of scanning
type for irradiating a single electron beam, which is designated
generally by reference numeral 70p. In FIG. 45, components
corresponding to those in the embodiment of FIG. 43 are designated
by the same reference numerals, each added with a suffix "p".
[0384] An electron gun 71p comprises an anode 713p and a cathode
711p so as to emit a primary electron beam having a cross over with
a diameter of approximately 10 microns. Thus emitted, the primary
electron beam passes through an axial aligning deflectors 731p,
731p' and further through the condenser lens 721p, where being
converged, and further passes through a deflector 733p and a Wien
filter or an E.times.B separator 726p, and thereafter the beam is
focused by an objective lens 729p so as to be formed into an image
on the proximity to a plurality of circuit patterns in the shapes
of, for example, rectangles formed on a surface of a wafer W loaded
on a stage unit 50. Deflectors 10 and 40 control the primary
electron beam to scan the wafer W.
[0385] Secondary electron beam emitted from the pattern on the
wafer W as the result of the scanning with the primary electron
beam is accelerated by an electric field of the objective lens 729p
and deflected by the Wien filter 726 to deviate from an optical
axis OA.sub.1 thus to be separated from the primary electron beam.
Then, the secondary electron beam is detected by a secondary
electron detector 761p. The secondary electron detector 761p
outputs an electric signal representing an intensity of the
secondary electron beam entered therein. The electric signal output
from this detector 761p is input to an image data processing
section 771 of a process control system 77p after having been
amplified by a corresponding amplifier (not shown).
[0386] As shown in FIG. 45, the electron gun 71p, the axial
aligning deflectors 731p, 731p', the condenser lens 721p, the
deflector 733p, the Wien filter 726p, the objective lens 729p and
the secondary electron beam detector 761p are all accommodated
within an optical column 701p having a diameter corresponding to a
given area of the wafer W, thus composing a single unit of electron
beam scanning and detection system, which is used to scan the
circuit pattern on the wafer W. In practice, a plurality of dice
has been formed on the surface of the wafer W. Other electron beam
scanning/detection systems (not shown) each having a similar
configuration to the above-described electron beam scanning and
detection system is arranged in parallel with the optical column
701p so as to be used to scan the same location on a different die
on the wafer W.
[0387] Although the electron beam scanning and detection system
operates in the same manner as in the preceding explanations, what
is different is that the electric signal output from the secondary
electron detection system of each of the electron beam
scanning/detection systems, which is constructed as one beam/one
detector per one optical column, is entered into the image data
processing section 771 of the process control system 77. Then, the
image data processing section 771 converts the electric signal
entered from each of the detection systems into a binary
information, and further converts this binary information into an
image data with reference to the electron beam scanning signal. To
accomplish this, a signal waveform having given to the
electrostatic deflector 733p is supplied to the image data
processing section 771. The image data obtained for each of the
dice formed on the surface of the wafer W is compared with a
reference die pattern while being accumulated in an appropriate
memory.
[0388] This allows a defect to be detected for every one of the
plurality of die patterns formed on the surface of the wafer W.
[0389] It is to be noted that similarly to the above-described
embodiments, also in the embodiment shown in FIG. 45, a variety of
circuit patterns may be used as the reference circuit pattern to be
used by the image data processing section 771 for making a
comparison with a specific image data representing a certain die
pattern on the wafer W, and for example, such image data obtained
from the CAD data of the die pattern, to which the scanning has
been applied so as to generate said specific image data, may be
used.
[0390] The Wien filter or the E.times.B separator 726p comprises an
electrostatic deflector 728p and an electromagnetic deflector 727p
arranged so as to circumscribe said electrostatic deflector 728p.
As this magnetic deflector 727p, preferably a permanent magnet made
of platinum alloy may be used instead of an electromagnetic coil.
This is because applying a current in a vacuum environment is not
adequate. Further, the deflector 733p functions both as the axial
aligner for aligning the direction of the primary electron beam
with the axis of the objective lens 729p and the scanner.
[0391] Since the method for fabricating the condenser lens 721p and
the objective lens 729p may be same as the method for fabricating
the condenser lens and the objective lens in the embodiment shown
in FIG. 41, a detailed explanation thereof will be omitted.
[0392] As described before, since the condenser lens 721p and the
objective lens 729p are fabricated by way of machining the ceramic,
it is possible to process those lenses with high level of precision
and to reduce the outer diameters thereof. Accordingly, if the
outer diameters of the condenser lens 2 and the objective lens 729p
are reduced to, for example, not greater than 20 mm, then six or
eight electron beam apparatuses can be arranged for one piece of
wafer by employing such an array of the optical column as shown in
FIG. 42 in the case of the inspection of the wafer having a
diameter of 200 mm with a range for inspection defined by a
diameter of 140 mm, the throughput in increased by 6 or 8
times.
[0393] It is to be appreciated that the laser reference reflection
mirrors to be mounted on the objective lens and the stage unit may
be fabricated according to the fabrication processes shown in FIG.
46.
[0394] In the method, as shown in FIG. 46, primarily SiC ceramic
was processed to have a dimension defined by a sectional area of 30
mm.times.30 mm and a length of 35 cm (STP 1). A laser reflecting
surface thereof was ground to be a fine obscured glass like face
having a rough but high flatness surface (STP 2). Subsequently, a
CVD apparatus was used to apply a film deposition thereto up to a
level to fill in sufficiently a void on the reflecting surface due
to a void formed inside thereof and the rough surface (20 .mu.m
thick in one example) (STP4). In that stage, in order to fill in
the void and the like efficiently, the mirror was inclined so as to
form an angle of approximately 45 degrees between the vertical line
and the reflecting surface and left in this condition for a long
time period thus to form the film.
[0395] After that, a mirror polishing was applied to the object
(STP 6). Since the surface prior to the deposition by the CVD was
in the fine obscured glass like condition, even at the time of
polishing, there would never occur a separation between the main
body and the CVD film. After the mirror polishing, a multi-layer
reflection film or titanium, gold or the like was used to form a
reflecting film (STP 8).
Further Alternative Embodiment of Electron Beam Apparatus
[0396] FIG. 47 shows an alternative embodiment of the electronic
optical apparatus or the electron beam apparatus designated
generally by reference numeral 70q. In FIG. 47, the same components
as those in the electron beam apparatus shown in FIG. 43 are
designated respectively by the same reference numerals and detailed
explanations on the structure and function thereof will be omitted.
Besides, components different from but similar to those in FIG. 43
are designated respectively by the same reference numerals, each
added with a suffix "q".
[0397] The electron beam apparatus according to this embodiment is
same as the electron beam apparatus shown in FIG. 43 with the
exception that an aperture plate 747 is disposed at a point P4 in a
secondary optical system 74q where a cross over is formed, that the
secondary optical system comprises an electrostatic deflector 746
and that a detection system comprises a control section 78.
[0398] In this embodiment, each of the detectors 761 is connected
via each of the amplifier 763 to an image data processing section
771 of a process control system 77q for converting a detection
signal into an image data. Since the image data processing section
771 is supplied with the same scanning signal as that given to a
deflector 733 for deflecting the primary electron beam, the image
data processing section 771 can figure out a secondary electron
pattern image for a pattern formed on a wafer W from the detection
signal obtained during the beam scanning.
[0399] The image data processing section 771 is operatively
connected with the control section 780 so as to be capable of
performing a data communication therebetween. This control section
780 executes an evaluation on the wafer W based on the secondary
electron pattern image generated by the image data processing
section while controlling and managing the whole electron beam
apparatus.
[0400] The control section 780 is connected with a display section
782 for indicating an evaluation result or the like and an input
section 781 for entering a command of an operator. The display
section 782 may be made up of a CRT or a liquid-crystal display and
may indicate a defective pattern, a secondary electron pattern
image, the number of defective locations and so on.
[0401] The wafer W may be placed on a stage unit 50n. This stage
unit is configured such that it can move within a horizontal plane
in the X and the Y directions with the wafer W placed thereon in
response to the command from the control section 78. That is, the
stage unit 50n enables the wafer W to move in the X and the Y
directions with respect to the primary and the secondary optical
systems. Since a laser interferometer 94 to be arranged in
conjunction with the stage unit and an objective lens has the same
structure and function as those of the apparatus shown in FIG. 43,
detailed explanations thereof will be omitted.
[0402] A laser reflection mirror 941 provided in the form of a
movable mirror requires to be at least 30 cm long for evaluating a
12-inch wafer W, and to be further longer for the YAW measurement
or for aligning an optical axis OA.sub.1 of the primary optical
system onto a fixed marker or a Faraday cup of the stage device
50n, being around 40 cm long in most cases. In the present
embodiment, a base body of such a long laser reflection mirror 941
is made of highly rigid SiC ceramic without increasing the
thickness thereof. If a side face of a top surface member of the
stage device is formed as the reflection mirror, then the rigidity
can be further improved.
[0403] Preferably, a laser reflection mirror 946 provided in the
form of a reference mirror may be attached to a ring, which is made
of ceramic having a coefficient of linear expansion almost equal to
0 and has been attached to an outer cylinder of the objective lens
729, in order to avoid an affection from thermal expansion of the
optical column. This reference mirror 946 may be made of SiC
ceramic similarly to the movable mirror 941.
[0404] An operation of the electron beam apparatus according to the
present embodiment will now be described. As can be seen obviously
from FIG. 47, since a portion in the optical path common to the
primary optical system and the secondary optical system is the
portion from an E.times.B separator 727 through the objective lens
729 up to the wafer W, the number of common optical parts has been
successfully decreased. Owing to this, even if the lens condition
for the objective lens 729 was matched to the primary electron
beam, a focusing condition for the secondary electron beam can be
adjusted by using magnifying lenses 741 and 743. In addition,
although the axial alignment with respect to the objective lens 729
is performed favorably to the primary electron beams by applying an
axial aligning power supply voltage onto the deflector 733 in
superposition to its due voltage, the axial mismatch of the
secondary electron beam due to the axial alignment favorable to the
primary electron beam can be compensated for by using the axial
aligner for the secondary optical system or the electrostatic
deflector 746.
[0405] As for the aperture plates 735, 747 defining numerical
apertures, two aperture plates has been employed, one of which is
disposed at the location where the first cross over image is formed
(an installation point of an opening aperture 4) and only the
primary electron beam passes therethrough, and the other of which
is disposed at the location where the second cross over image is
formed (an installation point of an opening aperture 747) and only
the secondary electron beam passes therethrough, thereby allowing
an optimal aperture diameter to be selected individually. Employing
a size of an aperture of the objective lens 729 sufficiently
greater than the diameter of the cross over herein and zooming the
objective lenses 721 and 725 so as to make the cross over size
variable at the position of the objective lens 729 can make an
angular aperture selectable. This allows the angular aperture to be
adjusted to a desired optimal value within a range determined by
the trade-off between the low aberration and the high beam current
by only using an electric signal without exchanging apertures.
[0406] As for the location of the aperture of the secondary optical
system, such a condition should be satisfied that the secondary
electron image could be focused on the detector 761 by the lenses
741 and 743. Then, the aperture is to be moved along the optical
axis (Z) until the location where every secondary electron beam may
have the same intensity when the wafer with the inspected surface
having a uniform emission characteristic has been used, and at that
location, the aperture of the secondary optical system should be
fixed. This position is the location in the optical axis direction
where the principal ray from the wafer would cross the optical axis
as illustrated.
[0407] A process for obtaining the secondary electrons is as
follows. The primary electron beam emitted from the electron gun 71
is focused by the condenser lens 721 to form a cross over at a
point P1. Since, passing through a plurality of apertures 7231 of
the first multi aperture plate 723 on the way to the point P1, the
primary electron bean is formed into a plurality of beams. The
plurality of beams is focused on a point P2 by the reduction lens
725 and further focused through the objective lens 729 to be formed
into an image on the wafer W. Thus, on the wafer W, a plurality of
irradiation spots each having almost the same intensity is formed
by the primary electron beam, and then the secondary electrons are
emitted from those irradiation spots respectively. During this
period, the electrostatic deflector 733 deflects the primary
electron beam so as to scan a certain region slightly larger than
the spacing between adjacent two beams. This deflection allows the
irradiation spots on the wafer to scan in the beam aligning
direction with no region left not-scanned.
[0408] The multi-beam consisting of the secondary electrons emitted
from the respective irradiation spots on the wafer is accelerated
by the electric field of the objective lens 7 and converged to be
narrower, and then reaches to an E.times.B separator 726, where the
multi-beam is deflected by a field (E.times.B) generated therein
into the direction at a specified angle with respect to the optical
axis OA.sub.1 to proceed along the optical axis OA.sub.2 of the
secondary optical system 74q. The secondary electron image is
focused on the point P3 that is closer to the objective lens 729
than the point P2. This is because typically each of the secondary
electron beams only has an energy of some eV, while each of the
primary electron beams having the energy of, for example, 500 eV on
the wafer. The multi-beam consisting of those secondary electron
beams is magnified by the magnifying lenses 741 and 743, and after
having passed through the plurality of apertures 7451 of the second
multi-aperture plate 745, each beam of the multi-beam is detected
by the detector 761. The detection signal is sent to the image data
processing section 771 of the process control system 77q via the
amplifier 763 to form the secondary electron image pattern.
[0409] The stage unit 50n moves the wafer W sequentially or
continuously by a predetermined width synchronously so as to allow
the multi-beam to scan the overall surface of the wafer to be
inspected. At this point of time, in the laser interferometer 94, a
laser oscillator 943 oscillates a laser beam. The oscillated laser
beam is split into two beams by a half mirror or a dichroic mirror
945. One of the beams which has passed through the half mirror 945
reaches to the movable mirror 941, while the other beam is
reflected by a total reflection mirror 944 and reaches to the
reference mirror 946, thus each of two beams being reflected. The
beam reflected by the movable mirror 941 passes through the half
mirror 945 and guided to a receiver or a laser interferometer 942,
while the beam reflected by the reference mirror 946 is reflected
again by the total reflection mirror 944 and the half mirror 945 to
be guided to the receiver 942. Thus, the receiver 942 detects an
interference light of the reflected beams from the movable mirror
941 and the reference mirror 946. The detection signal is sent to
the control section 780, where a distance between the movable
mirror 941 and the reference mirror 946 along the X and Y
directions, i.e., an XY coordinate position of the X and the Y
tables of the stage unit 50n, is calculated based thereon.
[0410] The control section 780, based on the XY coordinate position
of the X and the Y tables of the stage unit 50n, controls the
movement of the stage unit 50n so as to inhibit any area from being
left not-scanned with the multi-beam. In the present embodiment,
since the base bodies of the laser reflection mirrors 941, 946 have
been made of highly rigid SiC, the flatness of the mirror surfaces
can be maintained highly precisely without increasing the thickness
thereof. This enables the highly precise position control of the
stage unit 50n, thus allowing the accurate secondary electron beam
image to be obtained. Besides, the laser reflection mirror which
has been made thin is space-saving. Further, the movable mirror 941
which has been made lighter in weight can reduce the load in moving
the stage.
[0411] Based on the secondary electron beam image pattern formed in
the manner as described above, the control section 780 performs,
for example, an evaluation of the wafer as follows.
[0412] In a defect inspection method by way of the pattern matching
applied to the wafer W, the control section 780 makes a comparative
matching between a secondary electron beam reference image for a
wafer having no defect, which has been stored in the memory in
advance, and an actually detected secondary electron beam image and
calculates a similarity therebetween. For example, if the
similarity indicates a value not greater than a threshold, it is
determined that "a defect exists", and if the similarity indicates
a value greater than the threshold, it is determined that "no
defect exists". At this stage, the detected image may be displayed
on the display section 782. This enables an operator to confirm and
evaluate finally on whether or not the wafer is defective. Further,
every segmental region within the image may be comparatively
matched to one another so as to automatically detect the segmental
region having a defect. At this stage, preferably, an enlarged
image of the defective region should be displayed on the display
section 782.
[0413] A method for measuring a line width of a pattern formed on a
wafer and a method for measuring a voltage contrast of the pattern
may be same as those described before in conjunction with FIG. 24,
and the explanations thereof will be omitted.
[0414] In FIG. 47, if a blanking deflector 731 is arranged so as to
deflect the primary electron beam toward an aperture of the
aperture plate 735 disposed in the cross over image formation point
at a predetermined cycle and thereby to permit said beam to pass
therethrough for a short period and to block it for the rest of the
period, which will be repeated, then it will be possible to form a
bundle of beams having a short pulse width. If such a beam having a
short pulse width is used to measure the potential on the wafer as
described above, the device operation can be analyzed with high
time resolution. That is, the present electron beam apparatus can
be used as what is called an EB tester.
Further Alternative Embodiment of Electron Beam Apparatus
[0415] FIGS. 48 and 49 show an alternative embodiment of the
electronic-optical apparatus or the electron beam apparatus
designated generally by reference numeral 70r. In FIGS. 48 and 49,
the same components as those in the electron beam apparatus shown
in FIG. 43 are designated respectively by the same reference
numerals and detailed explanations on the structure and function
thereof will be omitted.
[0416] The electron beam apparatus according to the present
embodiment is same as the electron beam apparatus shown in FIG. 43
with the exception that a detection system thereof comprises a
control unit 775r similar to the mode determining circuit arranged
in the electron beam apparatus shown in FIG. 40. Accordingly, the
following discussion is directed only to the part relating to the
detecting and scanning.
[0417] Each of the detectors 761 outputs an electric signal
representing an intensity of an incident secondary electron beam
thereto. Each of those electric signals, after having been
amplified by each corresponding amplifier 763, is input to an image
data processing section 771 of a process control system 77r. The
image data processing section 771 converts the electric signal
supplied from each of the amplifiers 763 into an image data. This
can be done because the image data processing section 771 is also
supplied with a scanning signal having given to an electrostatic
deflector 733 for deflecting the primary electron beam. Thus, the
image data processing section 771 outputs a set of image data for
respective circuit patterns formed on a wafer W all at once.
[0418] A plurality of image data output from the image data
processing section 771 is sequentially stored into a memory 777r
under a control of a computer 776r running according to an
operational command from a console 778r. The memory 777r comprises
an image memory section for accumulating the plurality of image
data obtained sequentially corresponding to the scanning of the
circuit pattern in this way, a reference pattern database for
accumulating reference patterns to be used for comparing with the
image data obtained by the scanning and thereby determining whether
or not an irregular pattern exists, and a determining pattern
database for accumulating patterns to be used for determining
killer defects and other patterns to be used for determining
non-killer defects. With this configuration, the computer 776r can
work out to compare the image data obtained from a certain circuit
pattern with that of the reference pattern and to distinguish the
killer defect from the non-killer defect by using said determining
pattern database.
[0419] Besides, the computer 776r has been programmed to control
the scanning of the wafer W with the primary electron beam so that
the defect inspection apparatus shown in FIG. 49 may be used to
execute an evaluation such as a defect inspection of a pattern
formed on a surface of the wafer W. That is, the computer 776r
controls an electrostatic deflector 733 and an magnetic deflector
727 of a Wien filter or an E.times.B separator 726 to work
interlockingly so as to scan the surface of the wafer W in the X
direction with a plurality of beams, while controlling the stage
unit 50n to move the wafer W continuously in the Y direction,
thereby accomplishing the scanning of the overall surface of the
wafer W.
[0420] To explain in more specific, after having controlled the
stage unit 50n to move and place the wafer W at a scanning starting
end, the computer 776 further controls the stage unit to move
continuously in the Y-direction while controlling a plurality of
primary electron beams to scan in the X-direction with an amplitude
slightly greater than a distance between respective primary
electron beams, Lx (shown in FIG. 9). This means that the wafer
could have been scanned in the region extending along the
Y-direction having a width w equivalent to full scanning distance
of the plurality of primary electron beams in the X-direction, and
a signal in association with the scanning in said region would be
output from a detector 761.
[0421] Subsequently, after the X table of the stage unit 50n having
been moved in the X-direction by a step equivalent to the width w,
the Y table of the stage unit 50n is continuously moved in the
Y-direction while controlling the plurality of primary electron
beams to scan the wafer W in the X-direction by the distance
equivalent to the width w. Thereby, another region of the width w
adjacent to the region having been previously scanned would have
been scanned both in the X- and the Y-directions. After this, the
similar operations may be repeated thus to scan the overall surface
of the wafer W, and the signal obtained as a result of scanning
operations from the detector 761 may be processed so as to evaluate
the wafer W.
[0422] It is to be noted that a distance measuring operation of the
stage unit is same as that in the embodiment described in
conjunction with FIG. 43, and the explanation thereof will be
omitted.
[0423] If the wafer W is a semiconductor wafer, the following
method may be employed to evaluate the wafer W. That is, a marker
may be arranged at an appropriate location on the surface of the
wafer W, such that only the one electron beam among a plurality of
primary electron beams, which has been formed by one aperture of a
multi-aperture plate 723, may be allowed to scan said marker and an
output from the detector at that time of scanning is extracted thus
to detect the position of the marker. Thereby a physical
relationship between the wafer W and the primary electron beam can
be determined, and therefore if an arrangement of a circuit pattern
formed on the surface of the wafer W with respect to the X- and the
Y-directions have been determined in advance, a plurality of
primary electron beams could be guided to the correct position to
meet said circuit pattern and the beams therein could scan the
circuit pattern, thereby accomplishing the evaluation of the
circuit pattern on the wafer W.
[0424] Further, the line width of the pattern on the surface of the
wafer W can be measured in such a way that first a pattern to be
evaluated on the wafer W is moved by registration to the proximity
to the optical axis of the primary optical system and the wafer W
is line-scanned with the primary electron beam to detect the
secondary electron beam, and then a signal corresponding to this
secondary electron beam is detected to extract a signal for
evaluating the line width of the circuit pattern on the surface of
the wafer W, which is then calibrated appropriately thus to measure
the line width of the pattern on the surface of the wafer W.
[0425] It is to be appreciated that forming an image of each one of
the secondary electron beams on each corresponding one of those
apertures of the second multi-aperture plates 745 or, in other
words, aligning the orbit of the secondary electron beam, Tr2, with
each corresponding one of those apertures of the second
multi-aperture plate 745 will be possible if one piece of lens is
arranged downstream to the E.times.B separator 726, which may
facilitate said image formation or alignment of the secondary
electron beam by changing an excitation of the magnifying lens 743
and shifting the cross over point P3. Although these adjustments
may cause a mismatch in the focusing condition for the secondary
electron beam, if the aperture of the second multi-aperture plate
745 was formed so as to have a larger diameter, then the secondary
electron detection efficiency would not be deteriorated, and
accordingly the above adjustments would never cause any
disadvantages to the defect inspection.
[0426] Now, referring to FIG. 49 [A], [B] and [C], there will be
described how the computer 776r in the electron beam apparatus of
FIG. 48 works to distinguish a killer defect from a non-killer
defect. As having been described before, as a plurality of
semiconductor chips on the wafer W is scanned all at once with a
plurality of electron beams, image data representing the circuit
pattern on each of the semiconductor chip is accumulated one after
another in the memory 777r. Then, the operator, at any appropriate
point of time when the memory 777r has stored the accumulated image
data for some parts or all parts of each circuit pattern, sends a
command to the computer 776r from the console 778r to execute a
defect inspection operation. The computer 776r has been programmed
to execute in response to said command the operation comprising the
steps of:
[0427] (1) reading out a part of the image data for the circuit
pattern of one of the semiconductor chips and the image data for
the reference pattern corresponding thereto from the memory
777r;
[0428] (2) making a comparison between said two image data;
[0429] (3) as a result of the comparison, identifying a normal
pattern and an abnormal pattern and then taking out the image data
containing the abnormal pattern;
[0430] (4) comparing said taken-out image data with the contents of
the determining pattern database in the memory 777r and determining
whether the abnormal pattern is considered to be the killer defect
or the non-killer defect;
[0431] (5) subsequently, executing said steps from (1) to (4) for
all other parts of the image data obtained from the scanning thus
to end the defect inspection of the circuit pattern for the current
semiconductor chip; and then
[0432] (6) repeating said steps from (1) to (5) for the image data
obtained from the scanning for every remaining semiconductor chips
one by one, thus to complete the defect inspection for all of the
semiconductor chips to be inspected.
[0433] Herein, there will now be described an algorithm for
determining whether the location determined to be the abnormal
pattern is the killer defect or the non-killer defect. This
algorithm is based on such an empirical rule that "although the
obtained image data is representative of the abnormal pattern, it
should be considered with a considerably high probability that said
location is actually of a conductive material". Then, it is assumed
that as the result of the scanning of a certain circuit pattern,
three kinds of images as shown in FIG. 49 [A], [B] and [C] were
obtained as the images including the abnormal patterns. In the
drawings, those white rectangular portions Ptn without hatching are
the images representative of the normal patterns and those
rectangular portions Pta-1, Pta-2 with hatching are the images
representative of the abnormal patterns. Among those rectangular
patterns corresponding to the abnormal patterns, the rectangular
portion Pta-1 shown in [A] is in contact with a single rectangular
portion Ptn, the rectangular portion Pta-1 shown in [B] has no
contact with any rectangular portions Ptn, and the rectangular
portions Pta-2 shown in [C] are in contact with two or more
rectangular portions Ptn, respectively. Then, based on said
empirical rule, the algorithm determines that the rectangular
portions Pta-1 shown in [A] and [B] are the non-killer defects but
the rectangular portions Pta-2 shown in [C] are the killer
defects.
[0434] With respect to an image of a contact hole layer, the
computer 776r works according to said algorithm to determine that
an abnormal pattern overlapping with the contact hole is a killer
defect and an abnormal pattern having no contact with the contact
hole is a non-killer defect. Besides, with respect to an image of a
gate layer, the computer 776r works to determine such that an
abnormal pattern located within the predetermined range proximal to
the gate pattern is indicative of a killer defect and therefore the
abnormal pattern located away from the gate pattern by a
predetermined distance or much farther is a non-killer defect.
[0435] It is to be appreciated that the determining pattern
database within the memory 777r may be updated by adding a newly
found abnormal pattern at each time when the new abnormal pattern
is found so as to be determined on whether it is the killer defect
or the non-killer defect during the computer 776r being operative
for the defect inspection.
Further Alternative Embodiment of Electron Beam Apparatus
[0436] FIGS. 50 to 52 show an alternative embodiment of the
electronic optical apparatus or the electron beam apparatus
designated generally by reference numeral 70s. In FIGS. 50 to 52,
the same components as those in the electron beam apparatus shown
in FIG. 8 are designated respectively by the same reference
numerals and detailed explanations on the structure and function
thereof will be omitted.
[0437] In FIG. 50, an electron gun for emitting an electron beam is
designated by reference numeral 71s, a primary optical system by
72s, a multi-aperture plate provided with a plurality of small
apertures by 723s, a lens by 721s, electromagnetic deflectors by
731s and 733s, an E.times.B separator by 726s, an objective lens by
729s, a secondary optical system by 74s, lenses by 741s and 743s,
and a detector for detecting a secondary electron beam by 761s.
Reference numeral 771s designates an image forming unit of a
process control system 77s, and 779s designates a scanning control
unit, which functions to supply the deflectors 731s and 733s with
scanning signals for scanning the electron beam. The multi-aperture
plate 723s may be provided with, for example, nine apertures
(3.times.3) as shown in FIG. 51 [A] or seven apertures (1.times.7)
as shown in FIG. 51 [B]. It is to be appreciated that the
arrangement and the number of those apertures are not limited to
those illustrated in FIG. 51, but any aperture pattern may be
arbitrarily employed if appropriate.
[0438] In the apparatus shown in FIG. 50, an electron beam emitted
from the electron gun 71s is formed into a plurality of beams by a
plurality of apertures of the aperture plate 723s, and these beams
are formed into images on a surface of a wafer W through the lenses
721s and 729s, while simultaneously the plurality of electron beam
is controlled by the deflectors 731s and 733s so as to scan the
surface of the wafer W. Under the condition where a stage holding
the wafer W has been fixed, the scanning control unit 779s controls
the deflectors 731s and 733s to cause the electron beams to scan in
the X-axis and the Y-axis directions. Thereby, with the wafer W
being fixed, between those spots having formed on the wafer surface
at the point of time to, other spots are sequentially formed at the
points of time t.sub.1, t.sub.2, . . . , and in this way,
eventually the electron beam spots are formed at all of the points
within a predetermined area on the surface of the wafer W. Then,
the stage with the wafer W loaded thereon is moved, and another
area adjacent to the previously scanned area is similarly
scanned.
[0439] A secondary electron beam emitted by forming an image of the
electron beam on the wafer W is deflected by the E.times.B
separator 726s, and detected by the detector 761s through the
lenses 741s and 743s of the secondary optical system, where the
detected beam is converted into an electric signal and is supplied
as a detector output signal to the image forming unit 771s.
[0440] In the apparatus shown in FIG. 50, for example, the
multi-aperture plate 723s provided with nine apertures as shown in
FIG. 51 [A] is used to form nine electron beam spots on the surface
of the wafer, and accordingly the detector 761s is provided with
nine detecting elements corresponding to the array of the apertures
of the multi-aperture plate 723s so as to detect the secondary
electron beams from those nine spots respectively.
[0441] The image forming unit 771s is also supplied with the
scanning signal from the scanning control unit 779s, and the
detector output signal is associated with the scanning signal and
stored in an image data memory (not shown) as a signal
representative of a pixel position. With this signal, the image
forming unit 771s can form a surface image of the wafer W.
[0442] The image representing the wafer surface which has been
formed in such a manner as described above is compared in a
mismatch/match detecting unit (not shown) as per pixel with a
reference image pattern or an image pattern with no defect stored
in advance, and if any mismatching pixel is found out, then it may
be determined that the wafer has a defect. Further, the image
representing the wafer surface may be displayed on the monitor
screen, and in that case an experienced operator or the like may
monitor the image to inspect the wafer surface for any defects.
[0443] Still further, upon measuring a line width of a wiring
pattern or an electrode pattern formed on a wafer, a pattern area
to be evaluated is moved to a location on or near to an optical
axis and said area is line-scanned to take out an electric signal
to be used for evaluating the line width, and then the signal is
calibrated as needed thereby to detect the line width.
[0444] With an evaluation apparatus having such a structure as
above, the present invention has suggested a method for inspecting
the wafer surface which has been processed by a processing
apparatus, in which the evaluation apparatus is arranged in the
proximity to the processing apparatus and further a controller (not
shown) controls an overall operation of the evaluation apparatus to
inspect only a region consisting of a predetermined location or a
plurality of predetermined areas on the wafer surface so that an
inspection time for a wafer may be made approximately equal to a
processing time per wafer of said processing apparatus. In this
control, at first the wafer is secured onto the stage of the
evaluation apparatus, and then minimal required evaluation
parameter of a wafer and a processing time required per wafer are
input into the controller of the evaluation apparatus. The
evaluation parameter may be, for example, a fluctuation of a
minimum line width in the case of the processing apparatus being a
lithography apparatus, and a defect inspection in the case of the
processing apparatus being an etching apparatus. Subsequently, the
controller determines an evaluation area or a region to be
inspected on the wafer based on the entered evaluation parameter
and the entered necessary processing time so that the time required
per wafer for evaluating a processed condition of the wafer may be
made within or approximately equal to the processing time required
per wafer.
[0445] Since the inspection is only applied to the predetermined
area and inevitably the range of movement of the wafer W within the
evaluation apparatus should be made smaller, therefore a foot print
of the evaluation apparatus can be reduced in comparison with the
case where the inspection is applied to the entire area on the
wafer. Further, since the evaluation time has been made
approximately equal to the processing time, and accordingly the
throughput of the evaluation apparatus is also approximately equal
to that of the processing apparatus, therefore if any defect is
found out, it will be more easier to find out any irregular
operation in the processing apparatus corresponding to the
defective condition.
[0446] It is to be appreciated that the inspection apparatus may
comprise a plurality of optical column units arranged in an array
as shown in FIG. 52, each unit of the optical column including the
electron beam apparatus shown in FIG. 50. That is, FIG. 52 [A]
schematically shows an array of the electron beam spots on the
wafer W in the case of six optical columns arranged in the array of
2 rows.times.3 columns, each including the multi-aperture plate
723s with nine apertures as shown in FIG. 51[A]. On the other hand,
FIG. 52 [B] schematically shows an array of the electron beam spots
on the wafer W in the case of four optical columns arranged in
line, each including the multi-aperture plate 723s with seven
apertures arranged in line as shown in FIG. 51[B].
[0447] In FIG. 52, a group of beam spots generated by each of the
optical columns is indicated by a circle designated with the
reference BG, and a straight line R extending from the center of
each circle indicates the direction of the emission of the
secondary electron beam in each of the optical columns, that is,
the orientation of the secondary electron beam detection system
comprising the lenses 741s and 743s and the detector 761s. As shown
in FIG. 52 [A] and [B], the secondary electron beam detection
systems have been arranged so as not to interfere with one another,
and with such arrangement, a plurality of optical columns may be
installed in the efficient manner thus to prevent the foot print
for the entire evaluation apparatus from being oversized.
[0448] It is to be noted that the arrangement and the number of the
plurality of optical columns, as a matter of course, are not
limited to those shown in FIG. 52 [A] and [B]. In the case where
the optical columns in the array of 1.times.N as shown in FIG. 52
[B] is employed, the wafer W may be moved continuously in the
direction indicated by the arrow "a", if appropriate.
[0449] Also, in the second embodiment using a plurality of optical
systems, similarly to the first embodiment, the evaluation
apparatus may be placed in the proximal to the processing apparatus
and furthermore the control system (not shown) may control the
operation thereof such that the inspection time for a wafer can be
made approximately equal to the processing time per wafer of said
processing apparatus. In that case, the wafer may be inspected with
a full-face inspection or with a partial inspection limited to a
predetermined region on the wafer surface depending on the
processing time, and the important point is that the inspection
operation would be controlled such that the processing time per
wafer should be approximately matched to the inspection time per
wafer. In this case also, the range necessary for moving the wafer
can be made smaller, and thereby the foot print for the evaluation
apparatus can be reduced. Besides, since the throughput of the
evaluation apparatus is made approximately equal to the throughput
of the processing apparatus, if a defect is found out, it will be
much easier to find out an irregular operation in the processing
apparatus.
[0450] Further, upon evaluating a processed condition in a
processing apparatus with an especially shorter processing time, a
sampling inspection on the basis of one for every two wafers or one
for every three wafers may be employed so as to make a better
matching between the throughputs per lot.
Further Alternative Embodiment of Electron Beam Apparatus
[0451] Now, referring to FIGS. 53 to 59, a defect inspection of a
pattern formed on a wafer will be described in detail. It is to be
noted that in FIG. 53, an embodiment in which an inspection
apparatus is applied to what is called an electron beam apparatus
of the multi-beam type is designated generally by a reference
numeral 70t, and components corresponding to those in the preceding
embodiments are designated by the same reference numerals, each
added with a suffix "t", wherein explanations of the structure and
function of those components will be omitted and only the contents
which have been newly added may be explained in detail.
[0452] In FIG. 53, the reference numeral 71t denotes an electron
gun for emitting a primary electron beam, 721t denotes an
electrostatic lens for converging the emitted primary electron
beam, 726t denotes an E.times.B deflector which allows the
appropriately shaped primary electron beam to advance straight in
the field consisting of an electric field and a magnetic field
crossing orthogonally with each other so as to impinge upon a
semiconductor wafer W at an approximately right angle, 729t denotes
an objective lens for forming the deflected primary electron beam
into an image on the wafer W, 50t denotes a stage unit capable of
moving within a horizontal plane with the wafer W loaded thereon,
741t denotes an electrostatic lens for forming a secondary electron
beam emitted from the wafer W by the irradiation of the primary
electron beam into an image, and 761t denotes a detector for
detecting individually an intensity of each beam for each of the
formed images. A signal from the detector 761t is input into an
image forming circuit 765t thus to form a secondary electron image.
The electron beam apparatus in this embodiment further comprises a
process control system 77t for executing an operation for detecting
a defect on the wafer W based on the secondary electron image
detected by the detector 761t while controlling the whole
apparatus. It is to be appreciated that although an image by
scattered electrons or reflected electrons may be obtained as said
secondary electron image other than the image by the secondary
electrons, herein, the case where the obtainment of the secondary
electron image is selected will be described exclusively.
[0453] Further, a deflecting electrode 733t is interposed between
an objective lens 729t and the wafer W for deflecting an angle of
incidence of the primary electron beam to the wafer W by the
electric field or the like. This deflecting electrode 733t is
connected with a deflection controller 75t for controlling an
electric field of said deflecting electrode 733t. This deflection
controller 75t is connected to the process control system 77t and
controls said deflecting electrode 733t so that the deflecting
electrode 733t can generate the electric field in response to a
command from the process control system 77t. It is to be noted that
the deflection controller 75t may be implemented as a voltage
controller for controlling a voltage to be applied to the
deflecting electrode 733t.
[0454] The detector 761t may have any arbitrary structure so far as
it can convert the secondary electron image formed by the
electrostatic lens 741t into a signal, which can be processed in a
subsequent stage.
[0455] The process control system 77t may be constituted of a
general-purpose personal computer and the like as shown in FIG. 53.
This computer may comprise a control section main body 791 for
executing a variety of controls and arithmetic processing according
to a predetermined program, a CRT 796 for indicating a processing
result of the main body 791 and an input section 797 such as a key
board or a mouse for enabling an operator to input a command. As a
matter of course, the process control system 77t may be constituted
of a hardware dedicated to a defect inspection apparatus or a
workstation.
[0456] The control section main body 791 comprises a variety of
control boards, including a CPU, a RAM, a ROM, a hard disk, and a
video board. A secondary electron image memory area 792 has been
allocated on a memory such as the RAM or the hard disk for storing
the electric signal received from the detector 761t, i.e., the
digital image data of the secondary electron image for the wafer W.
Further, on the hard disk, there is a reference image memory
section 793 for storing beforehand a reference image data for the
wafer having no defect. Still further, on the hard disk, in
addition to the control program for controlling the whole unit of
the defect inspection apparatus, a defect detection program 794 is
stored for reading the secondary electron image data from the
memory area 792 and automatically detecting a defect in the wafer W
based on said image data according to the predetermined algorithm.
This defect detection program 794, as will be described in more
detail later, has such a function that it performs a matching of
reference image read out from the reference image memory section
793 to an actually detected secondary electron image in order to
automatically detect any defective parts, so that it may indicate a
warning to the operator when it determines there is the defect
existing. In this regard, the CRT 796 may be designed to display
the secondary electron image EIm on the display section
thereof.
[0457] An operation of the defect inspection apparatus according to
the first embodiment will now be described by taking flow charts of
FIG. 55 to 57 as examples.
[0458] First of all, as shown in the flow of the main routine of
FIG. 55, the wafer W to be inspected is placed on the stage 50t
(step 1000). This step may be performed in the mode that the loader
automatically sets the wafers W one after another onto the stage
unit 50t as explained above.
[0459] Then, images for a plurality of regions to be inspected are
respectively obtained, which are displaced one from another while
being superimposed partially one on another on the XY plane of the
surface of the wafer W (Step 1002). Each of said plurality of
regions to be inspected, from which the image is to be obtained,
is, for example, a rectangular region on the wafer surface TS to be
inspected as designated by reference numerals RA1, RA2, . . . ,
Rak, . . . in FIG. 59, each of which is observed to be displaced
relative to one another while being partially superimposed one on
another around the inspection pattern TPt of the wafer. For
example, 16 pieces of images TAI for the regions to be inspected
(the images to be inspected) may be obtained as shown in FIG. 54.
Herein, for the image shown in FIG. 54, each segment of rectangular
shape corresponds to one pixel (or a block, whose unit is greater
than the unit of pixel), and among those segments, shaded ones
correspond to the imaged area of the pattern on the wafer W. This
step 1002 will be described in more detail later with reference to
the flow chart of FIG. 56.
[0460] Then, the image data for the plurality of regions to be
inspected, which have been obtained at Step 1002, are compared
respectively with the reference image stored in the memory section
793 to look for any matching (Step 1004 in FIG. 55), and it is
determined whether or not there is a defect existing in the wafer
inspection surface encompassed by said plurality of regions to be
inspected. This process performs, what is called, the matching
operation between image data, which will be explained later in
detail with reference to the flow chart shown in FIG. 57.
[0461] If the result from the comparing process at Step 1004
indicates that there is a defect in the wafer inspection surface
encompassed by said plurality of regions to be inspected (Step
1006, affirmative determination), the process gives a warning to
the operator indicating the existence of the defect (Step 1008). As
for the way of warning, for example, the display section of the CRT
796 may display a message notifying the operator that there is a
defect, or at the same time may additionally display a magnified
secondary electron image EIm of the pattern determined to have the
defect. Such defective wafers may be immediately taken out of the
stage device to be stored in another storage separately from those
wafers having no defect (Step 1010).
[0462] If the result from the comparing process at Step 1004
indicates that there is no defect in the wafer W (Step 1006,
negative determination), it is determined whether or not there are
remained more regions to be inspected for the wafer W currently
treated as the inspection object (Step 1012). If there are more
regions remained for inspection (Step 1012, affirmative
determination), the stage device 50t is driven to move the wafer W
so that other regions to be further inspected are positioned within
the irradiating region of the primary electron beam (Step 1014).
Subsequently, the process goes back to Step 1002 to repeat the
similar operations for said other regions to be inspected.
[0463] If there is no more regions remained to be further inspected
(Step 1012, negative determination), or after a drawing out
processing of the defective wafer (Step 1010), it is determined
whether or not the current wafer treated as the inspection object
is the last wafer to be inspected, that is, whether or not there
are any wafers remaining for the inspection in the loader, though
not shown (Step 1016). If the current wafer is not the last one
(Step 1016, negative determination), the wafers having been
inspected already are stored in a predetermined storing location,
and a new wafer which has not been inspected yet is set instead on
the stage device (Step 1018). Then, the process goes back to Step
1002 to repeat the similar operations for said wafer. In contrast,
the current wafer is the last one (Step 1016, affirmative
determination), the wafer having been inspected is stored in the
predetermined storing location to end the whole process.
[0464] Then, the process flow of the step 1002 will now be
described with reference to the flow chart of FIG. 56.
[0465] In FIG. 56, first of all, an image number "i" is set to the
initial value "1" (Step 1020). This image number is an
identification number assigned serially to each of the plurality of
images for the regions to be inspected. Secondary, an image
position (X.sub.i, Y.sub.i) is determined for the region to be
inspected as designated by the set image number i (Step 1022). This
image position is defined as a specific location within the region
to be inspected for bounding said region, for example, a central
location within said region. Currently, i=1 defines the image
position as (X.sub.1, Y.sub.1), which corresponds, for example, to
a central location of the region to be inspected RA1 as shown in
FIG. 59. The image position has been determined previously for
every image region to be inspected, and stored, for example, in the
hard disk of the process control system 77t to be read out at Step
1022.
[0466] Then, the deflection controller 75t applies a potential to
the deflecting electrode 733t (Step 1024 in FIG. 56) so that the
primary electron beam passing through the deflecting electrode 733t
of FIG. 53 may be irradiated onto the image region to be inspected
in the image position (X.sub.i, Y.sub.i) having determined at Step
1022.
[0467] Then, the electron gun 71t emits the primary electron beam,
which goes through the electrostatic lens 721t, the E.times.B
separator 726t, the objective lens 729t and the deflecting
electrode 733t, and eventually impinges upon a surface of the set
wafer W (Step 1026). At that time, the primary electron beam is
irradiated onto the image region to be inspected at the image
position (X.sub.i, Y.sub.i) on the wafer inspection surface TS.
When the image number i=1, the region to be inspected is RA1.
[0468] Secondary electrons are emitted from the region to be
inspected, on which the primary electron beam has been irradiated.
Then, the generated secondary electron beam is formed into an image
on the detector 761t with a predetermined magnification by the
electrostatic lens 741t of the magnified projection system. The
detector 761t detects the imaged secondary electron beam, and
converts it into an electric signal or a digital image data for
each detecting element and outputs this signal (Step 1028). Then,
the detected digital image data for the image number is transmitted
to the secondary electron image memory area 792 (Step 1030).
[0469] Subsequently, the image number i is incremented by 1 (Step
1032), and it is determined whether or not the incremented image
number (i+1) is greater than a constant value "i.sub.MAX" (Step
1034). This i.sub.MAX is the number of images to be obtained for
inspection, which is "16" for the above example of FIG. 54.
[0470] If the image number i is not greater than the constant value
i.sub.MAX (Step 1034, negative determination), the process goes
back to Step 1022 again, and determines again the image position
(X.sub.i+1, Y.sub.i+1) for the incremented image number (i+1). This
image position is a position shifted from the image position
(X.sub.i, Y.sub.i) having determined in the previous routine by a
specified distance (.DELTA.X.sub.i, .DELTA.Y.sub.i) in the
X-direction and/or the Y-direction. The region to be inspected in
the example of FIG. 59 is at the location (X.sub.2, Y.sub.2), i.e.,
the rectangular region RA2 indicated with the dotted line, which
has been shifted from the position (X.sub.1, Y.sub.1) only in the
Y-direction. It is to be noted that the value for (.DELTA.X.sub.i,
.DELTA.Y.sub.i) (i=1, 2, . . . i.sub.MAX) may have been determined
appropriately from the data indicating practically and
experimentally how much is the displacement of the pattern TPt on
the wafer inspection surface TS from the field of view of the
detector 761t and the number and the area of the regions to be
inspected.
[0471] Then, the operations for Step 1022 to Step 1032 are repeated
for i.sub.MAX pieces of region to be inspected. These regions to be
inspected are continuously displaced while being partially
superimposed one on another on the wafer inspection surface TS so
that the image position after k times of shifting (X.sub.k,
Y.sub.k) corresponds to the inspection image region RAk, as shown
in FIG. 59. In this way, the 16 pieces of inspection image data
exemplarily illustrated in FIG. 54 are obtained into the image
memory area 792. It is observed that a plurality of images TAI
obtained for the regions to be inspected (i.e., inspection images)
contains partially or fully the image Ipt of the pattern TPt on the
wafer inspection surface TA, as illustrated in FIG. 54.
[0472] If the incremented image number i has become greater than
i.sub.MAX (Step 1034, affirmative determination), the process
returns out of this subroutine and goes to the comparing process
(Step 1004) in the main routine of FIG. 55.
[0473] It is to be noted that the image data that has been
transferred to the memory at Step 1030 is composed of intensity
values of the secondary electrons for each pixel (so-called, raw
data) detected by the detector 761t, and these data may be stored
in the memory area 792 after having been processed through various
operations in order to use for performing the matching operation
relative to the reference image in the subsequent comparing process
(Step 1004 of FIG. 55). Such operations includes, for example, a
normalizing process for setting a size and/or a density of the
image data to be matched with the size and/or the density of the
reference image data, or the process for eliminating as a noise the
isolated group of elements having the pixels not greater than the
specified number. Further, the image data may be converted by means
of data compression into a feature matrix having extracted features
of the detected pattern rather than the simple raw data, so far as
it has not negatively affect on the accuracy in detection of the
highly precise pattern. Such feature matrix includes, for example,
m.times.n feature matrix, in which a two-dimensional inspection
region composed of M.times.N pixels is divided into m.times.n
(m<M, n<N) blocks, and respective sums of intensity values of
the secondary electrons of the pixels contained in each block (or
the normalized value defined by dividing said respective sums by a
total number of pixels covering all of the regions to be inspected)
should be employed as respective components of the matrix. In this
case, the reference image data also should have been stored in the
same form of representation. The image data in the context used in
the embodiments of the present invention includes, of course, not
only a simple raw data but also any image data having the feature
extracted by any arbitrary algorithms as described above.
[0474] The process flow for Step 1004 will now be described with
reference to the flow chart of FIG. 57.
[0475] First of all, the CPU in the process control system 77t
reads the reference image data out of the reference image memory
section 793 (FIG. 53) onto the working memory such as the RAM or
the like (Step 1040). This reference image is identified by
reference numeral SIm in FIG. 54. Then, the image number "i" is
reset to 1 (Step 1042), and then the inspection image data for the
image number i is reads out onto the working memory (Step
1044).
[0476] Then, the read out reference image data is compared with the
data of the image "i" for any matching to calculate a distance
value "D.sub.i" between both data (Step 1046). This distance value
D.sub.i indicates a similarity level between the reference image
and the image to be inspected "i", wherein a greater distance value
indicates the greater difference between the reference image and
the inspection image. Any unit of amount may be used for said
distance value Di so far as it may represent the similarity level.
For example, if the image data is composed of M.times.N pixels, the
secondary electron intensity (or the amount representative of the
feature) of each pixel may be considered as each of the position
vector elements of M.times.N dimensional space, so that an
Euclidean distance or a correlation coefficient between the
reference image vector and the image "i" vector in the M.times.N
dimensional space may be calculated. It will be easily appreciated
that any distance other than the Euclidean distance, for example,
the urban area distance may be calculated. Further, if the number
of pixels is huge, which increases the amount of the operation
significantly, then the distance value between both image data
represented by the m.times.n feature vector may be calculated as
described above.
[0477] Subsequently, it is determined if the calculated distance
value D.sub.i is smaller than a predetermined threshold Th (Step
1048). This threshold Th is determined experimentally as a
criterion for judging a sufficient matching between the reference
image and the image to be inspected. If the distance value D.sub.i
is smaller than the predetermined threshold Th (Step 1048,
affirmative determination), the process determines that the
inspection plane TS of the wafer W has "no defect" (Step 1050) and
returns out of this sub routine. That is, if there has been found
at least one image among those inspection images matching to the
reference image, the process determines there is "no defect".
Accordingly, since the matching operation shall not necessarily be
applied to every inspection image, the high-speed judgment becomes
possible. As for the example of FIG. 54, it is observed that the
image to be inspected at the column 3 of the row 3 is approximately
matching to the reference image without any offset thereto.
[0478] When the distance value D.sub.i is equal to or greater than
the threshold Th (Step 1048, negative determination), the image
number "i" is incremented by 1 (Step 1052), and then it is
determined whether or not the incremented image number (i+1) is
greater than the predetermined value i.sub.MAX (Step 1054).
[0479] If the image number "i" is not greater than the
predetermined value i.sub.MAX (Step 1054, negative determination),
the process goes back to Step 1054 again, reads out the image data
for the incremented image number (i+1), and repeats the similar
operations.
[0480] If the image number "i" is greater than the predetermined
value i.sub.MAX (Step 1054, affirmative determination), then the
process determines that said inspection plane TS of the wafer W has
"a defect existing" (Step 1056), and returns out of the sub
routine. That is, if any one of the images to be inspected is not
approximately matching to the reference image, the process
determined that there is "a defect existing".
[0481] Although in the above embodiment, the inspection method has
been described in conjunction with the electron beam apparatus of
the multi-beam type, one selected from a variety of types, the
inspection method according to this embodiment is also applicable
to, for example, an electron beam apparatus of the scanning type as
illustrated in FIG. 45. However, herein, an illustration of such
electron beam apparatus should be omitted for the simplicity.
[0482] It is to be appreciated that although in the above
description for the embodiment, each of the electron beam
apparatuses having individually a characteristic portion has been
distinctively explained, a single electron beam apparatus may
include a plurality of characteristic portions described above in
combination.
EFFECT OF THE INVENTION
[0483] According to a method for inspecting a substrate, a
substrate inspection apparatus and a charged particle beam
apparatus to be used in said substrate inspection apparatus, the
following effect may be brought about.
[0484] (1) Since the electron beam consisting of a plurality of
primary charged particle beams is irradiated onto and thereby to
scan the sample all at once so as to obtain a plurality of
sub-image data, and said sub-image data are rearranged based on the
consideration of the X-Y coordinates thereof and then synthesized
so as to obtain the image data for the region to be inspected on
the wafer, throughput of the apparatus can be increased
distinctively.
[0485] (2) Since the electron gun for emitting the charged particle
beam has been designed so as to be operated in the space charge
limited region, the S/N ratio can be increased to a great degree as
compared with the case where the electron gun is operated in the
temperature limited region according to the prior art. Accordingly,
the S/N ratio of equivalent level to that having accomplished by
the prior art can be obtained with lower beam current.
[0486] (3) Since even if a plurality of primary electron beams are
used to scan the sample wafer all at once, the S/N ratio of a
predetermined level can be obtained with still lower beam current,
therefore a blur of the beam due to the space charge effect can be
reduced to negligibly low level.
[0487] (4) Since the electron beam apparatus can be operated by
quickly selecting either of a mode allowing for a precise
evaluation yet with a small throughput or another mode allowing for
a rough evaluation still with a large throughput, the efficient
inspection or evaluation of the sample can be accomplished.
[0488] (5) Since the electrostatic lens is made by machining a
single block of insulating material, and thereby the high precision
lens of smaller diameter can be produced, the electron beam
apparatus can be made compact and a plurality of optical columns
can be arranged collectively for the wafer having a large diameter
thus to accomplish an inspection and/or evaluation with high
throughput.
[0489] (6) Since the circuit pattern formed on a surface of the
sample is captured as the rectangular pattern information rather
than the 0 and 1 binary information, it will become possible to
improve a capacity of a memory for accumulating said image
patterns, a rate of data transmission and a rate of data comparison
to a great degree (this effect may appear significant specifically
in a layer of lower pattern density such as a contact hole layer or
a gate layer)
[0490] (7) Since at least one step of lens is used to magnify the
secondary electron image, the focusing condition and/or the
magnification for the secondary optical system is made adjustable
separately from the adjustment of the lens condition for the
primary optical system, therefore any offsets from those design
values can be compensated and also any detected defects can be
classified so as to detect a critical defect accurately and
quickly.
[0491] (8) Since in the semiconductor manufacturing process, the
inspection can be applied intensively only to a region where the
defect is apt to occur, the inspection time can be shortened and
substantially all the defects required to be detected can be
accordingly detected.
[0492] (9) Since the bulk material of highly rigid SiC ceramic has
been employed for the laser reflection mirror to be used in the
laser interferometer, a distortion or a bowing of the mirror
surface can be eliminated thus to improve a precision of flatness
thereof without thickening the base body and also an erroneous
detection in the position measurement can be prevented, and in
addition, the weight of the stage as well as a space necessary for
moving the stage can be reduced.
[0493] Further, since the laser reflection mirror according to the
present invention is made in such a manner that the SiC ceramic
base body is treated with a SiC film deposition to be covered
therewith and then is polished to be a mirror-surface, therefore
such an advantageous effect can be provided in that there is no
fear of film stripping due to the aging. Still further, in the film
deposition of SiC, if the SiC is deposited from various directions
diagonal with respect to the surface of the base body, then a
concave problem in the mirror surface caused by a void can be
appropriately dissolved thus to maintain the high level of flatness
on the mirror surface.
[0494] Further, since a portion common to the primary and the
secondary optical systems has been minimized while satisfying the
requirement, in addition to the effects described above, there has
been provided another advantage that the primary and the secondary
optical systems can be adjusted almost independently, and in that
case, a cross talk between electron beams can be eliminated by
making a spacing between the primary electron beams greater than a
resolution of the secondary optical system as converted into a
surface of the sample.
[0495] (10) Since a single electron optical column has been
provided with at least one step of axially symmetric lens which is
made by machining a block of ceramic and selectively applying a
metal coating onto a surface thereof so as to accomplish a reduced
outer diameter, in addition to the effects described above, there
has been provided another advantage that a plurality of
electronic-optical optical columns can be arranged in parallel over
one piece of sample thus to improve the throughput of the
inspection or evaluation of the sample.
[0496] (11) Further, according to the device manufacturing method
of the present invention, since the above-described electron beam
apparatus can be used to evaluate the wafer during being processed
or after having been processed with high throughput as well as with
high level of accuracy, such advantageous effects can be obtained
that a yield of the product is improved and the delivery of any
defective products is prevented.
[0497] (12) Since a killer defect and a non-killer defect can be
distinguished from each other automatically even for a region
having a minimum line width of not greater than 0.1 micron, it will
become possible to provide a highly reliable defect inspection.
[0498] (13) Since a new pattern for either of a killer defect and a
non-killer defect can be added into a database at each time when it
has been found during a defect inspection period, it will become
possible to provide a user friendly apparatus.
[0499] (14) Since the image data obtained from the adjacent
secondary electron beams can be used to detect a mismatching
portion and/or a defect, it will become possible to reduce a memory
capacity for accumulating the image data.
[0500] (15) Since at least the outer side of the electrostatic lens
to be used as the objective lens has been made of ceramic material
having a low coefficient of linear expansion and further the
stationary laser mirror is attached to this ceramic material or the
ceramic material itself has been mirror-finished to form the
stationary laser mirror, therefore it will be possible to provide
an accurate evaluation of the sample even in the circumstance of
low stability in temperature or in the case of relative vibration
occurring between the optical system and the sample chamber.
[0501] (16) Since a single unit of apparatus can perform a
multi-purpose inspection, measurement and evaluation including a
defect inspection, a defect reviewing, a pattern line width
measurement, and a pattern potential measurement, such a problem
can be prevented that a large foot print in a clean room has been
occupied by the inspection apparatus, and as a result, a larger
number of device manufacturing apparatuses is allowed to be
arranged therein, thereby providing an efficient way for using the
clean room.
[0502] Further, with a plurality of optical columns to be arranged
and a multi-beam for irradiating the sample surface and
correspondingly a plurality of detecting elements to be arranged
for each of the optical columns, a throughput of the inspection
process (a volume of inspection per unit time) can be
increased.
[0503] (17) Since the electron beam apparatus and the inspection
apparatus can be made compact and at the same time a throughput of
the electron beam apparatus can be matched with a throughput of the
processing apparatus of the wafer, and thereby an operation in the
processing apparatus can be checked at real time when the wafer
containing the defect is detected, such a fear can be reduced that
the wafers containing defects might be undesirably fabricated
continuously.
[0504] (18) Since the stage can exhibit a highly precise
positioning ability within the vacuum atmosphere and further the
pressure in the charged particle beam irradiating location is
hardly increased, the processing with the charged particle beam
against the sample can be performed with high level of
accuracy.
[0505] (19) The gas which has been desorbed from the hydrostatic
bearing support section is almost completely blocked by the divider
and thereby it hardly run over the divider to reach onto the
charged particle beam irradiating region side. This can help
further stabilize a vacuum level in the charged particle beam
irradiating location.
[0506] (20) Since an inspection apparatus can be provided, in which
the stage has a highly accurate positioning function and a vacuum
level in the charged particle beam irradiating region is stable, it
will be possible to provide the inspection apparatus with higher
inspection performance and without any fear of contamination to the
sample.
[0507] (21) Since such an exposing apparatus can be provided, in
which the stage has a highly accurate positioning function and a
vacuum level in the charged particle beam irradiating region is
stable, it will be possible to provide the exposing apparatus with
higher exposing accuracy and without any fear of contamination to
the sample.
[0508] (22) The stage having a similar configuration to the stage
of the hydrostatic bearing type which has been typically used in
the atmosphere (a stage supported by the hydrostatic bearing having
no differential pumping mechanism) can be used to provide a stable
processing by the charged particle beam against a sample on the
stage.
[0509] (23) Since it has become possible to minimize the affection
to the vacuum level in the charged particle beam irradiating
region, the processing by the charged particle beam against the
sample can be stabilized.
[0510] (24) It has become possible to provide at a low price the
exposing apparatus in which the stage has a highly accurate
positioning function and a vacuum level in the charged particle
beam irradiating region is stable.
[0511] (25) Since the present invention allows a plurality of
images to be taken for a plurality of regions to be inspected each
displaced from others while partially superimposing with each other
on the sample and also allows each of these images subject to the
inspection to be compared with the reference image thus to detect a
defect in the sample, therefore such an advantageous effect can be
obtained that a deterioration in the defect detecting accuracy due
to the position mismatch between the image subject to the
inspection and the reference image is prevented.
[0512] (26) Since the present invention allows the above-described
charged particle beam apparatus to be used to evaluate the wafer
during being processed or after having been processed, such an
advantageous effect has been obtained that the highly accurate
evaluation may be accomplished, a yield in the device manufacturing
process may be improved and any defective products can be prevented
from being delivered.
* * * * *