U.S. patent application number 12/222404 was filed with the patent office on 2008-12-25 for electron beam apparatus, a device manufacturing method using the same apparatus, a pattern evaluation method, a device manufacturing method using the same method, and a resist pattern or processed wafer evaluation method.
This patent application is currently assigned to EBARA CORPORATION. Invention is credited to Toshifumi Kimba, Takeshi Murakami, Mamoru Nakasuji, Nobuharu Noji, Tohru Satake, Kenichi Suematsu, Kenji Watanabe.
Application Number | 20080315095 12/222404 |
Document ID | / |
Family ID | 34990502 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080315095 |
Kind Code |
A1 |
Nakasuji; Mamoru ; et
al. |
December 25, 2008 |
Electron beam apparatus, a device manufacturing method using the
same apparatus, a pattern evaluation method, a device manufacturing
method using the same method, and a resist pattern or processed
wafer evaluation method
Abstract
An object of the present invention is to provide an electron
beam apparatus, in which a plurality of electron beams, e.g., four
electron beams, is produced for one optical axis with a relatively
high current achieved for each electron beam. Provided is an
electron beam apparatus comprising: an electron beam emitter (32)
having an electron gun (30), said electron gun (30) disposed along
an optical axis (23) and operable to emit a plurality of off-axis
electron beams along a direction defined by a certain angle with
respect to the optical axis (23); a plurality of apertures (34)
disposed at a location offset from the optical axis (23); and an
electromagnetic lens (7) for forming a magnetic field between the
electron gun (30) and the apertures (34) to control the plurality
of off-axis electron beams emitted from the electron gun (30) so
that the plurality of off-axis electron beams passes through the
apertures (34).
Inventors: |
Nakasuji; Mamoru;
(Kanagawa-ken, JP) ; Satake; Tohru; (Kanagawa-ken,
JP) ; Noji; Nobuharu; (Kanagawa-ken, JP) ;
Murakami; Takeshi; (Tokyo, JP) ; Watanabe; Kenji;
(Kanagawa-ken, JP) ; Kimba; Toshifumi;
(Kanagawa-ken, JP) ; Suematsu; Kenichi;
(Kanagawa-ken, 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: |
34990502 |
Appl. No.: |
12/222404 |
Filed: |
August 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11058216 |
Feb 16, 2005 |
7425703 |
|
|
12222404 |
|
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Current U.S.
Class: |
250/310 |
Current CPC
Class: |
G01N 23/225 20130101;
H01J 2237/0635 20130101; H01J 2237/2817 20130101; H01J 37/28
20130101 |
Class at
Publication: |
250/310 |
International
Class: |
G01N 23/00 20060101
G01N023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2004 |
JP |
2004-043800 |
Mar 2, 2004 |
JP |
2004-057014 |
Mar 23, 2004 |
JP |
2004-084006 |
Claims
1. An electron beam apparatus comprising: an electron beam source
for emitting a primary electron beam; a primary optical system for
guiding said primary electron beam onto a sample surface so as to
scan said sample with said primary electron beam; a secondary
electron detecting unit having a detection surface for detecting a
secondary electron beam emitting from said sample; and a secondary
optical system for guiding an image of said secondary electron beam
emitting from said sample onto the detection surface of said
secondary electron detecting unit to thus form a focused image,
wherein said primary optical system comprises a lens operable to
irradiate said primary electron beam emitted from said electron
beam source in a size larger than a pixel size on said sample
surface, and said secondary optical system comprises a magnifying
lens to magnify the image of said secondary electron beam emitted
from said sample into the focused image on said detection surface,
wherein said detection surface selectively detects the secondary
electron beam emitted from a specific area on the sample
corresponding to said pixel size on the sample surface among the
secondary electron beam which has emitted from said sample and
passed through said magnifying lens.
2. An electron beam apparatus in accordance with claim 1, in which
said detection surface is sized to be substantially equal to or
smaller than a product of the pixel size on said sample surface and
a magnification ratio of said magnifying lens.
3. An electron beam apparatus in accordance with claim 1 or 2, in
which said electron beam apparatus comprises a controller for
controlling said electron beam apparatus, and said secondary
optical system further comprises a deflector, wherein said
controller controls said deflector to be synchronized with the
scanning operation of said primary electron beam over the sample
surface to make a correction so that said secondary electron beam
emanating from the sample as a result of the scanning operation by
said primary electron beam can be focused on said aperture or said
detection surface at any time.
4. An electron beam apparatus in accordance with claim 1, in which
said apparatus comprises a plurality of said magnifying lenses,
wherein a lens in a first stage thereof is defined by a lens set
comprising an electromagnetic lens in combination with an
axisymmetric electrode disposed within said electromagnetic lens
and applied with a positive voltage.
5. An electron beam apparatus in accordance with claim 1, in which
said primary optical system further comprises a multi-aperture for
forming a plurality of primary electron beams from the primary
electron beam emitted from said primary electron beam source, so
that said plurality of primary electron beams formed through said
multi-aperture is available in the scanning on said sample surface.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of application
Ser. No. 11/058,216 filed Feb. 16, 2005, which is based upon and
claims the benefit of priority from prior Japanese Patent
Application No. 2004-043800, filed Feb. 20, 2004, Japanese Patent
Application No. 2004-057014, filed Mar. 2, 2004 and Japanese Patent
Application No. 2004-084006, filed Mar. 23, 2004, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an electron beam apparatus
allowing for an evaluation of a substrate as large as 8 inches or
12 inches with high precision (50 nm pixel to 25 nm pixel) as well
as high throughput. Using a multi-beam is advantageous to achieve
the high throughput, and an electron gun with a greater intensity
of angular current is required to obtain the highly intensified
multi-beam from a single electron gun, which may be represented by
the electron gun of LaB.sub.6 and W hairpin having well-known
angular current intensity values of 10.sup.5 .mu.A/Sr and
3.93.times.10.sup.6 .mu.A/Sr, respectively.
[0003] It can be seen from the comparison in the values of specific
angular current intensity that the value of 10.sup.4 .mu.A/Sr for
TaC is higher than 600 .mu.A/Sr for ZrO/W but lower than
3.93.times.10.sup.6 .mu.A/sr for the W hairpin. The electron gun of
TaC, however, emits intensive beams in the four different
off-optical axial directions and this makes it easier to form the
multi-beam. In this environment, the present invention is directed
to an apparatus aimed at producing a multi-beam with a thermal
electric field emission electron gun using a cathode made of TaC,
for example, and also to a device manufacturing method which allows
for the device to be manufactured with high yield by evaluating a
wafer using the same electron beam apparatus.
[0004] In the background of this field of technology, for example,
in regard to the emission of electrons from a carbide emitter of
transition metal, Kumashiro, et al. have made a detailed report in
their research paper, entitled "Electron emission of carbide
emitter and surface thereof", on the electron emission
characteristics in an emitter employing TaC single crystal and a
polycrystalline thermal emitter (see, the journal, "Applied
physics", Vol. 45, No. 7 (1976)).
[0005] As for the angular current intensity of the electron beam
emitted from the thermal electric field emission electron gun,
there are known values including, for example, 10.sup.4 .mu.A/Sr
for the TaC and 600 .mu.A/Sr for the ZrO/W. The W hairpin has a
problem that a beam current could not be so high.
[0006] There is a problem in an electron gun of the Schottky
cathode made of ZrO/W, LaB.sub.6 or carbide of transition metal
that only a single beam along an optical axis has been used and
inevitably a scanning operation with such a single beam consumes a
lot of time.
[0007] Thus the present invention is directed to solve the
above-described problem, or the problem that the long time is
required to evaluate a large-sized substrate, such as an eight-inch
wafer or a 12-inch wafer, with high precision (50 nm pixel to 25 nm
pixel), and accordingly a first object of the present invention is
to provide an electron beam apparatus allowing a number of electron
beams, for example, four beams of electrons, to be produced for
each optical axis yet with a relatively high current for every
single beam of electrons.
[0008] The present invention further relates to an electron beam
apparatus allowing for an image of a sample having a fine pattern
to be taken with high resolution at a high rate.
[0009] In a practice to take a surface image of a sample, such as a
wafer, according to the prior art, the sample surface is scanned
with a narrowly converged electron beam and thus generated
secondary electrons are detected to produce an SEM image for the
purpose of enhancing the resolution of the image.
[0010] However, as the beam size is reduced, the beam current is
also reduced in proportion to the fourth power of the dimension of
beam diameter. To show one example, assuming that the pixel size is
equal to the beam size, the following relations may be
obtained:
TABLE-US-00001 Beam size Beam current Pixel frequency Frame time
(sec) 0.1 .mu.m.phi. 100 nA 100 MHz 1 sec/mm.sup.2 0.05 .mu.m.phi.
6.25 nA 6.25 MHz 64 sec/mm.sup.2 25 .mu.m.phi. 390 PA 390 KHz 4,096
sec/mm.sup.2 10 .mu.m.phi. 10 PA 10 KHz 1 .times. 10.sup.6
sec/mm.sup.2
Accordingly, since the beam current is reduced exponentially in
association with the reduction of the beam size, the beam current
of the secondary electrons emanating from a sample, such as a
wafer, is reduced, which makes it impossible to increase an S/N
ratio of the image. Due to this, there has been no other choice
than decreasing the scanning rate over the sample with the beam of
primary electrons, or decreasing the pixel frequency exponentially,
in order to increase the emission of the secondary electrons, and
this has led to a problem that a considerably long time period,
that is exponentially increased, is required to scan the image of a
finite area.
[0011] Thus the present invention is also directed to solve the
above-indicated problem, or the problem that if the beam size is
reduced in order to take the surface image of the sample, such as
the wafer, with high resolution, then more time is required to take
the image, and accordingly a second object of the present invention
is to provide an electron beam apparatus that allows for a beam of
electrons having a certain beam size larger than the conventional
beam size to be used for scanning the sample, that takes an image
at a high rate based on the secondary electrons emanating from the
sample and resultantly produces the image with high resolution.
[0012] The present invention further relates to an electron beam
apparatus that carries out a defect inspection and a defect review
of a sample having a fine pattern defined by a minimum line width
not greater than 0.1 .mu.m with high throughput and also to a
device manufacturing method using the same electron beam
apparatus.
[0013] This electron beam apparatus is applicable to improving a
process condition and to classifying a defective wafer by
specifying a factor in developing a defect of bad conductivity
based on an inspection result of the sample from a defect detecting
apparatus. Thus, it is required to acquire the state of the defect
of bad conductivity precisely in order to specify the factor in
developing the defect of bad conductivity, and to address this,
confirming a high resolution image identifying a location of the
defect of bad conductivity, or a bad conductivity defect review,
may be useful.
[0014] Conventionally, a defect detecting apparatus needs a
relatively high beam current due to its nature that a high
throughput is required, and thus has employed an electron optical
system with a compromise resolution performance. On the other hand,
a defect reviewing apparatus has employed an electron optical
system with a compromising level of beam current due to its nature
that a high resolution is required. Thus, since those two
apparatuses use respective beams that are different from each
other, there has been almost no apparatus operable satisfactorily
to provide the defect evaluation in both of the defect detection
and the defect reviewing.
[0015] If both of the defect detecting apparatus and the defect
reviewing apparatus are installed in a clean room, another problem
would be encountered that a large floor area should be necessary.
There would occur an additional problem of large time-loss because
after the detection of the defect by the defect detecting
apparatus, the detected defect has to be searched for in the
separate defect reviewing apparatus.
[0016] Accordingly, a third object of the present invention is to
provide an integrated apparatus that can provide the defect
detection and the defect reviewing in a serial manner in a small
foot print. Another object of the present invention is to provide a
device manufacturing method using the same apparatus.
[0017] The present invention further relates to an electron beam
apparatus, in which a primary electron beam is irradiated on a
sample, and secondary electrons or the like emitting from the
sample are formed into an image in a image-projection optical
system to thereby form a sample image.
[0018] In a conventional electron beam apparatus employing the
image projection optical system according to the prior art, the
primary electron beam is incident upon the sample surface from an
oblique direction with respect to a normal line of the sample and
then deflected into a direction of the normal line by an E.times.B
separator to irradiate the sample.
[0019] However, such an electron beam apparatus as described above
has been had problems, including an increased chromatic aberration
in a secondary electron beam caused by the E.times.B separator, a
bad balance of a primary optical system that has been mounted
obliquely, and an upper limit of irradiation dose imposed by a fact
that the intensity and the emittance of the electron gun are finite
and by a further fact that the secondary electron beam is blurred
due to space charges from the primary electron beams.
[0020] Accordingly, a fourth object of the present invention is
directed to solve the above-described problem and a goal thereof is
to provide an electron beam apparatus that is free from the limited
irradiation dose, the need for the primary optical system and the
chromatic aberration of deflection possibly caused by the E.times.B
separator.
[0021] The present invention further relates to an electron beam
apparatus, and specifically to an electron beam apparatus equipped
with a position measuring device for measuring a position of a
sample table used in the electron beam apparatus that carries out
an evaluation of a sample having a minimum line width not greater
than 0.1 .mu.m with high precision and high throughput.
[0022] Conventionally, an electron beam apparatus of the
above-specified type has been equipped with a position measuring
device for measuring a position of a sample table carrying a
sample, such as a substrate, for the purpose of irradiating an
electron beam to the sample precisely.
[0023] Such a position measuring device is operative in such a
manner that a laser beam from a single laser oscillator is split
into two beams, which are irradiated onto one laser mirror in
parallel with x-axis and the other laser mirror in parallel with
y-axis, respectively, wherein one laser beam is irradiated from the
x-axis side onto the sample table, while the other laser beam is
irradiated from the y-axis side onto the sample table so as to
measure an irradiation point of an electron beam and the x- and
y-directional positions of the sample table accurately.
[0024] It has been conventionally recognized that the sample table,
during its movement, is subject to the Yaw motion to some extent
depending on a tolerance of a stage operable to move the sample
table. In the position measuring device of the prior art, in which
both of the one laser beam irradiated from the x-axis side to the
sample table and the other laser beam irradiated from the y-axis
side to the sample table are directed to one and the same optical
axis, any misalignment of the sample table slightly offset from an
ideal position of the sample table resultant from its Yaw motion
could not be a problem but is negligible, so far as only one
optical axis is used. However, in the electron beam apparatus
having a plurality of optical axes, specifically for a primary
electron beam along an optical axis positioned differently from the
laser axis along which the laser beam is irradiated, the
misalignment would be no more neglected but would problematically
induce what is called Abbe's error. Further, disadvantageously,
there has been a problem that a movable mirror for the laser is
greatly enlarged in size as the sample size becomes larger, and
specifically in the case of a stationary mirror for the laser that
has been fixedly mounted on a sidewall of a sample chamber, there
has been another problem that a measurement error is induced due to
an expansion and a contraction of the sidewall of the sample
chamber.
[0025] Thus the present invention is also directed to solve the
above-described problems, and accordingly, a fifth object thereof
is to provide a position measuring device for a sample table used
in an electron beam apparatus of high precision and high
throughput, which eliminates the Abbe's error even in an apparatus
having a plurality of optical axes. The present invention further
provides an apparatus contemplated advantageously from the
viewpoint of preventing growing in size of the sample table due to
the movable laser mirror and for eliminating any measurement errors
resultant from the expansion and contraction of the sidewall of the
sample chamber.
[0026] The present invention further relates to a method for
evaluating a sample having a pattern defined by a minimum line
width not greater than 0.1 .mu.m with high throughput and also to a
method for manufacturing a device with high yield by using the same
evaluation method.
[0027] To carry out a defect inspection of a semiconductor device,
a CD (Critical Dimension) measurement and a pattern evaluation
including a measurement of alignment accuracy, all by using an
electron beam, a method has been conventionally suggested that a
multi-beam be formed in a single optical system and a scanning
operation be performed with said multi-beam so as to obtain a
two-dimensional image.
[0028] However, such a technique has not yet been known in the
prior art that small sized two-dimensional images obtained from a
plurality of detectors corresponding to respective beams are joined
together so as to produce a single large-sized image. In this
arrangement, the evaluation has been performed as per each beam,
and, inefficiently, this needs a complicated procedure.
[0029] Further, there has been suggested another technology
according to the prior art for producing the multi-beam, in which
electron beam emitted from a plurality of emitters are irradiated
to apertures equally spaced from an optical axis so as to form a
multi-beam.
[0030] However, owing to the features of this technology of the
prior art characterized by a relatively large spacing between beams
of the multi-beam, advantageously it is easier to detect secondary
electrons independently, whereas the beams are located relatively
distant from the optical axis, and this causes drawbacks including
astigmatism and coma aberration in a primary electron beam,
problematically inhibiting the primary beam from being converged to
be narrow.
[0031] Further, in the conventional practice for the CD measurement
or the alignment accuracy measurement, the electron beam is
converged to be 10 nm or narrower and a thus narrowly converged
electron beam is used to measure a line width or a line spacing,
thus performing the measurement operation.
[0032] However, since a beam current is lower due to a smaller beam
size inherent to the prior art, a scanning rate must be reduced in
order to obtain a good S/N ratio and thus improve precision, which
leads to another problem of the throughput being reduced.
[0033] There has been further suggested a method for evaluating a
sample by scanning a sample surface with a plurality of beams,
including a method using a multi-column and a method using an
arrangement of a plurality of beams positioned along a
circumference of a circle around an optical axis.
[0034] However, the method using the multi-column has a drawback
that the throughput would not be improved distinctively since even
with a wafer size as large as 12 inches, all that could be
contemplated is simply to arrange some columns over the wafer, and
at the same time this disadvantageously makes the whole apparatus
expensive. Besides, in the method using an arrangement of the
multi-beam positioned along the circumference of the circle, it is
required to increase the diameter of the circle to generate more
beams, and this would inversely intensify the effect of other
aberrations than the curvature of field, including the astigmatism
and the coma aberration, problematically inhibiting the beam from
being converged to be narrow.
[0035] Accordingly, a sixth object of the present invention is to
provide a method for producing a single large-sized two-dimensional
image by joining together a plurality of small-sized
two-dimensional images corresponding to a plurality of beams.
[0036] Further, a seventh object of the present invention is to
provide a pattern evaluation method that is free from any obstacles
in converging a primary beam to be narrower, and which can provide
an efficient detection of secondary electrons without any cross
talks among them.
[0037] Further, an eighth object of the present invention is to
provide a method for performing a CD measurement and/or measuring
an alignment accuracy with high throughput.
[0038] Further, a ninth object of the present invention is to
provide a pattern evaluation method, in which a multi-beam is
generated proximally to a single optical axis, and secondary
electrons from respective beams in the concurrent scanning with
those beams can be detected efficiently, yet using an electron
optical system having a lesser number of lens stage.
[0039] The present invention further relates to an evaluation
method for evaluating a resist pattern or a subsequently processed
wafer, which enables highly accurate and quick evaluation of a
lithography margin in a resist pattern written by an electron beam
writer and/or in a resist pattern exposed by an ArF, F.sub.2
excimer laser stepper.
[0040] Conventionally, a defect inspection apparatus employing a
light has been used to evaluate the lithography margin or to
determine whether or not an optical proximity effect is adequately
compensated for. However, in the case where the writer of electron
beam direct-writing type or the ArF, F.sub.2 excimer laser stepper
has been employed as the lithography apparatus, a size of a defect
to be detected should be 100 nm or smaller, resulting in a problem
of insufficient resolution of the defect inspection apparatus using
the light.
[0041] In the light of the above problems, a defect inspection
apparatus has been suggested that uses an electron beam instead of
the light so as to enhance the resolution (see, for example, Patent
Document 1 and 2).
[0042] [Patent Document 1]
[0043] Japanese Patent Laid-open Publication No. Sho 63-17523
[0044] [Patent Document 2]
[0045] Japanese Patent Laid-open Publication No. Hei 7-249393
[0046] Accordingly, a tenth object of the present invention is to
provide an evaluation method for evaluating a resist pattern or a
subsequently processed wafer, which allows for measurement of a
lithography margin with high resolution in a short time with a
defect inspection apparatus having a specific performance of
minimum size of defect detection not greater than 100 nm.
SUMMARY OF THE INVENTION
[0047] To accomplish the first object described above, the present
invention provides an electron beam apparatus comprising:
[0048] an electron beam emitter having an electron gun, said
electron gun including a cathode disposed along an optical axis,
and operable to emit a plurality of off-axis electron beams around
said optical axis each along the direction defined by a certain
angle with respect to said optical axis;
[0049] a plurality of apertures each disposed at a location out of
said optical axis; and
[0050] an electromagnetic lens for controlling an on-axis electron
beam and said plurality of off-axis electron beams emitted from
said electron gun so that said plurality of off-axis electron beams
passes through said apertures.
[0051] According to the electron beam apparatus provided by the
first invention of this patent application, owing to its
configuration in which the on-axis electron beam and the off-axis
electron beams emitted from the electron gun are controlled by the
electromagnetic lens so that only the off-axis electron beams are
permitted to pass through the apertures, advantageously it becomes
possible to use the off-axis electron beams that have higher
current than the on-axis electron beam in the inspection of the
sample and thus to achieve a highly precise evaluation thereof.
Further, since the plurality of electron beams can be used to scan
and thus to inspect the sample surface, the present invention
allows for the evaluation of the sample with high throughput.
[0052] To accomplish the second object described above, the present
invention provides an electron beam apparatus comprising:
[0053] an electron beam source for emitting a primary electron
beam;
[0054] a primary optical system for guiding said primary electron
beam onto a sample surface so as to scan said sample with said
primary electron beam;
[0055] a secondary electron detecting unit having a detection
surface for detecting a secondary electron beam emitted from said
sample; and
[0056] a secondary optical system for guiding an image of said
secondary electron beam emitted from said sample onto the detection
surface of said secondary electron detecting unit to thus form a
focused image, wherein
[0057] said primary optical system comprises a converging lens
operable to converge said primary electron beam emitted from said
electron beam source to a size larger than a pixel size on said
sample surface, and
[0058] said secondary optical system comprises: [0059] a magnifying
lens to magnify the image of said secondary electron beam emitted
from said sample into the focused image on said detection surface;
and [0060] an aperture disposed between said magnifying lens and
said detection surface of said secondary electron detecting unit,
and operable to selectively permit only the secondary electron
beams that have been emitted from an area on the sample
corresponding to the pixel size on said sample surface to pass
therethrough from among the secondary electron beams that have been
emitted from said sample and passed through said magnifying
lens.
[0061] According to the second invention, since the primary
electron beams having a beam size sufficiently larger than the
pixel size on the detection surface of the secondary electron
detecting unit are used to scan the sample surface, and only the
specific portions of the secondary electron beams emitted from the
sample that correspond to this pixel are exclusively permitted to
enter the detection surface of the secondary electron beam
detecting unit, advantageously the present invention brings about
an effect that the image can be taken in high resolution at a high
rate.
[0062] To accomplish the third object as described above, the
present invention provides an electron beam apparatus
comprising:
[0063] an electron gun;
[0064] a set of apertures for forming a plurality of primary
electron beams for defect detection (hereafter referred to simply
as an aperture for defect detection) for forming a primary electron
beam emitted from said electron gun into a plurality of primary
electron beams for defect detection to be used to perform a defect
detection;
[0065] an aperture for forming at least one primary electron beam
for defect reviewing (hereafter referred to as an aperture for
defect reviewing) for forming a primary electron beam emitted from
said electron gun into at least one primary electron beam for
defect reviewing to be used to perform a defect reviewing;
[0066] said aperture for defect reviewing being smaller in size
than said aperture for defect detection, thus allowing said primary
electron beam for defect reviewing to be made narrower than said
primary electron beam for defect detection;
[0067] an objective lens for reducing said primary electron beam
for defect detection or said primary electron beam for defect
reviewing transmitted through either one of said aperture for
defect detection or said aperture for defect reviewing to be
focused on a sample;
[0068] a separator for deflecting a secondary electron beam
emitting from the sample; and
[0069] a secondary electron detector for detecting the deflected
secondary electron beam, wherein
[0070] defect detection and defect reviewing are performed by
selecting either of said aperture for defect detection or said
aperture for defect reviewing and using either of said primary
electron beam for defect detection or said primary electron beam
for defect reviewing in association with said selected
aperture.
[0071] Further, in said electron beam apparatus, said aperture for
defect detection and said aperture for defect reviewing may be
arranged in a single aperture plate.
[0072] Alternatively, in said electron beam apparatus, said
aperture for defect detection and said aperture for defect
reviewing may be arranged independently in separate aperture
plates.
[0073] According to the third invention, owing to the configuration
allowing for both of the defect reviewing and the defect detection
of the sample to be performed in the same apparatus, an advantage
of a successfully reduced foot print can be brought about. Further,
this configuration can eliminate such time-consuming work that a
defect is firstly detected in a defect detecting unit and then the
detected defect is searched for in a separate defect reviewing
device, thus advantageously reducing a loss-time and achieving the
reduction in half of a loading and unloading time and a
registration time of the sample.
[0074] To accomplish the fourth object as described above, the
present invention provides an electron beam apparatus
comprising:
[0075] an electron gun comprising a cathode in a ring configuration
for emitting from its tip a primary electron beam composed of a
hollow beam, and an anode and a Wehnelt for controlling a direction
of said hollow beam emitted from said cathode; and
[0076] a lens for converging said hollow beam emitted from said
electron gun to be irradiated on the sample, wherein
[0077] secondary electrons or back scattering electrons emitted
from said sample are focused by said lens into an image.
[0078] Further, said electron beam apparatus may have a
configuration, in which
[0079] said anode has an inner anode that is grounded and an outer
anode that is applied with a voltage, and
[0080] said cathode is disposed in such a position that allows the
primary electron beam to be incident upon the optical axis of the
sample and the secondary electrons or the back scattering electrons
emitting from said sample to be focused into the image by modifying
a lens condition defining a focal distance of said lens and an
irradiation condition in said electron gun defining an emission
direction of the primary electron beam, wherein
[0081] said lens condition of said lens can be controlled by
changing a voltage applied to said lens, and
[0082] said irradiation condition of said electron gun may be
controlled by changing a voltage applied to said outer anode.
[0083] Further, said electron beam apparatus may have a
configuration, in which,
[0084] said lens comprises a multi-stage of lenses, and
[0085] said electron gun is disposed between the lenses of said
multi-stage of lenses.
[0086] To accomplish the fourth object as described above, the
present invention provides an electron gun comprising:
[0087] a cathode in a ring configuration for emitting a primary
electron beam composed of a hollow beam, and an anode and a Wehnelt
for controlling a direction of said hollow beam emitted from said
cathode, in which
[0088] said cathode is made of cathode material that has been
formed in a pipe shape and operable to emit a primary electron beam
from its end surface by being heated from outside thereof,
[0089] said anode has an inner anode and an outer anode, and
[0090] said Wehnelt has an inner Wehnelt and an outer Wehnelt,
wherein [0091] said inner anode and said inner Wehnelt are disposed
on the inner side with respect to said cathode, and said outer
anode and said outer Wehnelt are disposed on the outer side with
respect to said cathode, wherein
[0092] said inner anode and said outer anode are insulated from
each other and an angle between said hollow beam and the optical
axis can be adjusted by changing a potential difference between
said inner anode and said outer anode, or by isolating said inner
Wehnelt and said outer Wehnelt from each other and changing a
potential difference between said inner Wehnelt and said outer
Wehnelt.
[0093] According to the fourth invention, which has eliminated the
E.times.B separator, advantageously the increase in chromatic
aberration of the secondary electron beam due to the E.times.B
separator can be prevented. Further, since the apparatus employs
the electron gun comprising a ring-shaped cathode but the primary
optical system is no more necessary, such a disadvantage as bad
balance due to the oblique installation of the primary optical
system can be avoided and thus stability can be ensured. Still
further, since the electron gun comprising the ring-shaped cathode
can emit an electron beam having high intensity and high emittance,
allowing the primary electron beam to pass an outside of the
secondary electron beam and thereby preventing any negative effect
from the space charge effect, such an effect can be brought about
that the dose of the electron beam is free from an upper limit.
[0094] To accomplish the fifth object as described above, the
present invention provides a position measuring device for a sample
table in an electron beam apparatus,
[0095] said electron beam apparatus being adapted to perform an
evaluation of a sample by irradiating a plurality of primary
electron beams having a plurality of optical axes onto a sample
carried on a sample table movable along an x-y plane having a
x-axial direction and a y-axial direction,
[0096] said position measuring device comprising: [0097] a first
measuring device operable to irradiate a first laser beam directed
to the sample table along one of the x-axial direction and the
y-axial direction for measuring a position of the sample table
along said one of said axial directions; [0098] a second measuring
device operable to irradiate a second and a third laser beam
directed to the sample table along the other of the x-axial
direction and the y-axial direction for measuring two positions of
the sample table along said other of said axial directions; [0099]
said second laser beams and said third laser beams being irradiated
to said sample table along said other of said axial directions with
an arrangement spaced apart from each other; and [0100] a
controller for detecting a rotation of said sample table within the
x-y plane based on a measurement from said first measuring device
and a measurement from said second measuring device.
[0101] Said position measuring device may further comprise:
[0102] at least one laser source for radiating a laser beam;
and
[0103] a first splitting device for splitting the laser beam
radiated from said laser source into at least two different laser
beams, wherein
[0104] said first measuring device uses one of said beams that have
been split by said splitting means as said first laser beam,
and
[0105] said second measuring device may comprise a second splitting
device for splitting the other of said beams that have been split
by said first splitting means into said second and said third laser
beams.
[0106] Further, said position measuring device may have a
configuration, in which
[0107] said first measuring device comprises a first reflecting
mirror disposed along the other axial direction of said two axial
directions of said sample table, a first guiding device for guiding
said first laser beam that has been split in said first splitting
device toward said first reflecting mirror and a first receiver for
receiving said first laser beam that has been reflected on said
first reflecting mirror;
[0108] said second measuring device comprises a second reflecting
mirror disposed along said one axial direction of said two axial
directions of said sample table; and
[0109] said second splitting device has a second guiding device for
guiding said second laser beam that has been split in said second
splitting device toward said second reflecting mirror, wherein
[0110] said second measuring device may further comprise: [0111] a
third guiding device for guiding said third laser beam that has
been split in said second splitting device toward said second
reflecting mirror; [0112] a second receiver for receiving said
second laser beam that has been reflected on said second reflecting
mirror; and [0113] a third receiver for receiving said third laser
beam that has been reflected on said second reflecting mirror.
[0114] Said position measuring device may have a configuration, in
which
[0115] said first measuring device further comprises a first
stationary mirror installed on a sidewall of an objective lens in
said electron beam apparatus disposed above said sample table, at a
location on said sidewall defined in the first reflecting mirror
side; and
[0116] said first guiding device has a first beam splitter serving
both for guiding said first laser beam that has been split in said
first splitting device toward said first reflecting mirror and for
splitting a fourth laser beam from said first laser beam,
wherein
[0117] said first measuring device may further comprise a first
laser mirror for reflecting and irradiating said fourth laser beam
toward said stationary mirror; and
[0118] said second measuring device may further comprise: [0119] a
second stationary mirror installed on a sidewall of the objective
lens in said electron beam apparatus, at a location on said
sidewall defined in the second reflecting mirror side; [0120] a
second beam splitter serving both for guiding said second laser
beam from said second guiding device toward said second reflecting
mirror and for splitting a fifth laser beam from said second laser
beam; [0121] a second laser mirror for reflecting and irradiating
said fifth laser beam toward said second stationary mirror; [0122]
a third beam splitter serving both for guiding said third laser
beam from said third guiding device toward said second reflecting
mirror and for splitting a sixth laser beam from said third laser
beam; and [0123] a third laser mirror for reflecting and
irradiating said sixth laser beam toward said second stationary
mirror.
[0124] Further, to accomplish the fifth object as described above,
the present invention provides an electron beam apparatus for
evaluating a sample carried on a sample table movable along an x-y
plane having the x-axial direction and the y-axial direction by
irradiating a plurality of primary electron beams having a
plurality of optical axes to said sample, said apparatus
comprising:
[0125] a deflector for deflecting and irradiating said plurality of
primary electron beams to said sample; and
[0126] any one of said position measuring devices for the sample
table as designated above, wherein
[0127] said controller of said position measuring device controls
said deflector based on a rotation within the x-y plane of said
sample table, and said deflector, in response to said control,
deflects each of said plurality of primary electron beams to
compensate for any offset from an ideal course of movement of said
sample and thus corrects the irradiation position of the primary
electron beam on said sample.
[0128] Further, said electron beam apparatus may comprise:
[0129] an objective lens having said plurality of optical axes,
which is disposed above said sample table, wherein
[0130] said objective lens may be an electromagnetic lens in an
integrated structure.
[0131] Further, in said position measuring device,
[0132] said electron beam apparatus may comprise a plurality of
optical systems for forming said plurality of primary electron
beams, wherein
[0133] each of said plurality of optical systems may have an
objective lens having a plurality of optical axes, which is
disposed above said sample table.
[0134] Further, in said position measuring device,
[0135] each of said plurality of optical systems may be adapted to
irradiate a plurality of primary electron beams across said
sample.
[0136] According to the fifth invention, the configuration enables
the measurement at two locations in the sample table along at least
one axial direction of the x-axial direction and the y-axial
direction in order to detect the rotation within the x-y plane of
the sample table, thus an accurate sample evaluation can be
provided, even if the sample table is driven into the Yaw motion.
Further, eight of optical axes, if provided, can make the
evaluation rate as much as eight times as high as that with a
single beam. Therefore, the fifth invention can bring about an
effect that the evaluation of the sample can be provided with high
precision and high throughput.
[0137] To accomplish the sixth object as described above, the
present invention provides a first pattern evaluation method, in
which a plurality of beams is irradiated onto a sample for
evaluating a pattern, said method comprising the steps of:
[0138] a. irradiating an electron beam emitted from an electron gun
over a plurality of apertures;
[0139] b. forming reduced images of respective apertures on a
sample surface;
[0140] c. scanning with said formed images of plurality of beams to
obtain a plurality of two-dimensional images, one for each
beam;
[0141] d. producing a single large-sized two-dimensional image by
joining together said plurality of two-dimensional images obtained
independently for respective beams;
[0142] e. measuring a space along one axial direction between beams
of said plurality of beams; and
[0143] f. adjusting said space to be an integer multiple of a pixel
size.
[0144] In the above method, since the plurality of beams is used
and the spacing between beams along one axial direction is adjusted
to meet the integer multiple of the pixel size in order to form the
large-sized two-dimensional image by joining together the
two-dimensional images obtained by respective beams, it becomes
possible to make an accurate operation of joining images between a
small-sized two-dimensional image obtained by the scanning with one
beam and another small-sized two-dimensional image obtained by the
scanning with an adjacent beam and thus to achieve the pattern
evaluation of high precision.
[0145] Further, to accomplish the sixth object as described above,
the present invention provides a second pattern evaluation method,
in which a plurality of beams is irradiated onto a sample to
evaluate a pattern, said method comprising the steps of:
[0146] a. irradiating an electron beam emitted from an electron gun
over a plurality of apertures;
[0147] b. forming reduced images of respective apertures on a
sample surface;
[0148] c. scanning with said formed images of plurality of beams
along one axial direction by a width of a stripe to obtain a
two-dimensional image; and
[0149] d. during obtaining said two-dimensional image in step (c),
moving the sample table continuously in the other axial direction,
suspending said movement in the other direction upon reaching a
terminal end of a region to be evaluated, and step-moving a stage
in said one axial direction by a width of a stripe, wherein
[0150] an interface between said stripes has concavity and
convexity corresponding to the positions of said plurality of beams
along said one axial direction.
[0151] According to the above method, since in the evaluation of
the pattern with a plurality of beams, the evaluation is provided
for each stripe with the plurality of beams, wherein the interface
between one stripe and another defines concavity and convexity
corresponding to the positions of the plurality of beams along the
one axial direction, therefore this manner can eliminate any
duplicated or skipped scanning but provide an efficient evaluation
with a plurality of beams.
[0152] Further, to accomplish the sixth object as described above,
the present invention provides a third pattern evaluation method,
in which a plurality of beams is irradiated onto a sample to
evaluate a pattern, said method comprising the steps of:
[0153] a. irradiating an electron beam emitted from an electron gun
over a plurality of apertures;
[0154] b. forming reduced images of respective apertures on a
sample surface;
[0155] c. scanning with said formed images of plurality of beams
along one axial direction to obtain a plurality of two-dimensional
images by signals from detectors, each associated with one
beam;
[0156] d. moving the position of said two-dimensional image by a
predetermined distance both in the x-axial direction and the
y-axial direction between respective beams on the sample to thereby
join said two-dimensional images to be formed into a single
two-dimensional image encompassing a larger area.
[0157] According to the above method, since in the evaluation of
the pattern with a plurality of beams, the position of the
small-sized two-dimensional image obtained from each beam is
shifted by the predetermined distances along both of the x-axis and
the y-axis between the beams on the sample for joining the images,
therefore it becomes possible to obtain the resultant large-sized
two-dimensional image formed by joining together all of the
small-sized two-dimensional images obtained from the plurality of
beams.
[0158] Further, to accomplish the sixth object as described above,
the present invention provides a fourth pattern evaluation method,
in which a plurality of beams is irradiated onto a sample to
evaluate a pattern, said method comprising the steps of:
[0159] a. generating a plurality of beams;
[0160] b. scanning with a plurality of beams across a mark having
an x-directional patterned side or a y-directional patterned side
and detecting generated electrons from respective beams by
detectors, each associated with one beam, so as to form a plurality
of two-dimensional images;
[0161] c. joining together said plurality of two-dimensional images
from respective detectors based on a predetermined value of
inter-beam distance;
[0162] d. modifying the inter-beam distance to produce a normal
geometry of the mark image that has been obtained in the joining
step, re-joining the images, and then storing a particular
inter-beam distance that can produce a most normal mark image;
and
[0163] e. obtaining a plurality of two-dimensional images of the
sample to be evaluated by respective beams and joining together
said plurality of two-dimensional images obtained from respective
beams by using said stored value of the inter-beam distance so as
to obtain a single two-dimensional image encompassing a larger area
of the sample.
[0164] According to the method as described above, since in forming
a large-sized two-dimensional image by joining together a plurality
of small-sized two-dimensional images obtained from respective
beams, not only the position of the small-sized two-dimensional
image is shifted by the predetermined distance along both of the x-
and the y-axial directions between the beams on the sample for
joining the images, but also the inter-beam distance is modified
for joining images to thereby compensate for the actual offset so
as to create the normal geometry of the mark image to be obtained
by joining, therefore it becomes possible to obtain the resultant
large-sized two-dimensional image of high precision.
[0165] Further, to accomplish the seventh object as described
above, the present invention provides a fifth pattern evaluation
method, in which a pattern formed on a substrate is scanned by a
multi-beam and secondary electrons emitting from scanning points
are detected to evaluate said pattern, said method comprising the
steps of:
[0166] a. accelerating an electron beam emitted from an electron
gun up to AKV;
[0167] b. irradiating said accelerated electron beam over an
aperture plate having a plurality of apertures;
[0168] c. reducing a plurality of beams, that has been formed
through said apertures, into images on a sample applied with a
voltage of -BkV for scanning said sample;
[0169] d. extending a spacing between groups of secondary electrons
emanating from the scanning points and guiding them to a detector;
and
[0170] e. detecting said groups of secondary electrons
independently by said detector to form two-dimensional images,
wherein
[0171] said AkV and BkV are defined as A-B=.ltoreq.0.6 kV, and said
groups of secondary electrons have a common passage defined by a
two-stage lens which are shared with the primary electron
beams.
[0172] According to the above method, in the electron optical
system having the two-stage of lenses defining the common passage
for the primary and the secondary electron beams, the ratio of the
landing energy of the primary electron beam to the energy of the
secondary electron beam is considerably smaller than that
associated with the prior art, and so the focal condition can be
easily adjusted to be compatible between the primary beam and the
secondary beam, which can help form the multi-beam in the vicinity
of a single optical axis.
[0173] Further, to accomplish the seventh object as described
above, the present invention provides a sixth pattern evaluation
method, in which a pattern formed on a substrate is scanned by a
multi-beam, and secondary electrons emitting from scanning points
are detected to evaluate said pattern, said method comprising the
steps of:
[0174] a. accelerating an electron beam emitted from an electron
gun up to AKV;
[0175] b. shaping said electron beam by means of a plurality of
apertures into a multi-beam;
[0176] c. reducing said multi-beam into images on a sample applied
with a voltage of -BkV for scanning said sample;
[0177] d. extending a spacing between groups of secondary electrons
emitted from the scanning points and guiding them to a detector;
and
[0178] e. detecting said groups of secondary electrons
independently by said detector to form two-dimensional image,
wherein
[0179] said AkV and BkV are defined as A-B.ltoreq.0.3 (kV), and
said groups of secondary electrons have a common passage defined by
one-stage of lens which are shared with the primary electron
beams.
[0180] According to the above method, in the electronic optical
system having the one-step of lens defining the common passage of
the primary and the secondary electron beams, a similar operational
effect to the above sixth pattern evaluation method can be
obtained.
[0181] Further, to accomplish the seventh object as described
above, the present invention provides a seventh pattern evaluation
method, in which a pattern formed on a substrate is scanned by a
multi-beam and secondary electrons emanating from scanning points
are detected to evaluate said pattern, said method comprising the
steps of:
[0182] a. accelerating an electron beam emitted from an electron
gun up to AKV;
[0183] b. shaping said electron beam by means of a plurality of
apertures into a multi-beam;
[0184] c. reducing said multi-beam into images on a sample applied
with a voltage of -BkV for scanning said sample; and
[0185] d. detecting said groups of secondary electrons emanating
from said scanning points to form a plurality of two-dimensional
images, wherein
[0186] said AkV and BkV are defined as A-B.ltoreq.0.5 (kV), and a
lens most proximal to the sample and used in common by the primary
and the secondary electron beams includes an electromagnetic
lens.
[0187] According to the above method, in the electron optical
system having the lens most proximal to the sample and defining the
common passage for both of the primary and the secondary electron
beams, which includes the electromagnetic lens, a similar
operational effect to the above sixth pattern evaluation method can
be obtained.
[0188] Further, to accomplish the seventh object as described
above, the present invention provides an eighth pattern evaluation
method, in which a pattern formed on a substrate is scanned by a
multi-beam, and secondary electrons emanating from scanning points
are detected to evaluate the pattern, said method comprising the
steps of:
[0189] a. accelerating an electron beam emitted from an electron
gun up to AKV;
[0190] b. irradiating said accelerated electron beam over an
aperture plate having a plurality of apertures,
[0191] c. reducing a multi-beam, which has been shaped through said
aperture plate, into images on a sample applied with a voltage of
-BkV for scanning said sample;
[0192] d. extending a spacing between groups of secondary electrons
emitting from the scanning points and guiding them to a detector;
and
[0193] e. detecting said groups of secondary electrons
independently by said detector to form a plurality of
two-dimensional images, wherein
[0194] said AkV and BkV are defined as A-B.ltoreq.0.5 kV, and a
lens most proximal to said sample includes an electromagnetic
lens.
[0195] According to the above method, in the electron optical
system having the lens most proximal to the sample and defining the
common passage for both of the primary and the secondary electron
beams, which includes the electromagnetic lens, a similar
operational effect to the above sixth pattern evaluation method can
be obtained.
[0196] To accomplish the seventh object as described above, the
present invention provides a ninth pattern evaluation method in
accordance with any one of the above-defined fifth to eighth
pattern evaluation methods, in which said electron optical system
has a plurality of optical axes with the optical axes projected
along one axial direction being equally spaced.
[0197] According to the above method, owing to the configuration
allowing said electron optical system to have a plurality of
optical axes, the method can improve, in addition to those
advantages associated with the above different methods, the
throughput in proportion to the number of optical axes.
[0198] To accomplish the eighth object as described above, the
present invention provides a tenth pattern evaluation method, in
which a multi-beam is used to evaluate a pattern, said method
comprising the steps of:
[0199] a. irradiating an electron beam emitted from a thermionic
emission electron gun over an aperture plate having a plurality of
apertures;
[0200] b. reducing said electron beam, which has passed through
said aperture plate, to be focused on a sample;
[0201] c. scanning with respective beams of the multi-beam
concurrently in the direction orthogonal to a patterned side;
[0202] d. detecting a secondary corpuscular beam emitted from
scanning points by a multi-detector corresponding to the
multi-beam, and obtaining and storing a plurality of signal
waveforms; and
[0203] e. calculating a CD value or a pattern spacing from the
plurality of signal waveforms corresponding to said multi-beam.
[0204] Further, to accomplish the eighth object as described above,
the present invention provides an eleventh pattern evaluation
method in accordance with the above-defined tenth pattern
evaluation method, in which the beams of said multi-beam are
aligned along a straight line not in parallel with the x-axis or
the y-axis.
[0205] According to those tenth and eleventh pattern evaluation
methods, since the CD value or the spacing between the patterns can
be calculated from the number of signal waveforms corresponding to
the beams of the multi-beam, the measuring time required in the
evaluation of the CD value or the pattern spacing can be shortened
by an inverse of the number of beams.
[0206] Further, to accomplish the eighth object as described above,
the present invention provides a twelfth pattern evaluation method,
in which a multi-beam is used to evaluate a pattern, said method
comprising the steps of:
[0207] a. irradiating an electron beam emitted from a thermionic
emission electron gun over an aperture plate having a plurality of
apertures;
[0208] b. reducing said electron beam, which has passed through
said aperture plate, to be focused on a sample;
[0209] c. scanning with respective beams of the multi-beam
concurrently in the direction orthogonal to a patterned side;
[0210] d. detecting a secondary corpuscular beam emitted from
scanning points by a multi-detector corresponding to the
multi-beam, and obtaining and storing a plurality of signal
waveforms;
[0211] e. moving the multi-beam serially by one-pixel in the
direction parallel with a patterned side and then repeating the
steps of (c) and (d);
[0212] f. forming a two-dimensional image of said pattern from a
plurality of signal waveforms corresponding to said multi-beam;
and
[0213] g. calculating an edge roughness from the pattern obtained
in the step (f).
[0214] According to the above method, since the edge roughness is
calculated from the number of signal waveforms corresponding to the
beams of the multi-beam, the measuring time required in the
evaluation of the edge roughness can be shortened by an inverse of
the number of beams.
[0215] Further, to accomplish the eighth object as described above,
the present invention provides a thirteenth pattern evaluation
method in accordance with any one of the above-defined tenth to
twelfth pattern evaluation methods, in which said electron gun has
a thermionic emission cathode and actuates said cathode under a
space charge limited condition.
[0216] According to the above method, in any one of the
above-defined tenth to twelfth pattern evaluation methods, a shot
noise can be reduced.
[0217] Further, to accomplish the ninth object as described above,
the present invention provides a fourteenth pattern evaluation
method, in which a plurality of beams is used to scan a sample
surface to thereby evaluate said sample, said method comprising the
steps of:
[0218] a. adjusting an emission angle of an electron beam emitted
from an electron gun by means of an anode having at least two
electrodes;
[0219] b. converging said electron beam with said emission angle
already adjusted, by a condenser lens to form a crossover in an NA
aperture;
[0220] c. forming a multi-beam with a multi-aperture disposed in
the vicinity of said condenser lens;
[0221] d. forming an image of the NA aperture by a reduction lens
in the vicinity of a principal plane of an objective lens;
[0222] e. focusing a reduced image of the multi-aperture on a
sample surface by a reduction lens and the objective lens;
[0223] f. scanning with the multi-beam across the sample surface,
while applying a dynamic focusing;
[0224] g. accelerating secondary electrons emanating from the
sample by the objective lens to allow them to pass through the
objective lens;
[0225] h. deflecting the secondary electrons by an E.times.B
separator to advance toward a secondary optical system;
[0226] i. extending a spacing between beams of the multi-beam of
secondary electrons and detecting them on a plurality of detectors;
and
[0227] j. detecting beams of the multi-beam of secondary electrons
independently to form a two-dimensional image for evaluating the
sample.
[0228] According to the above method, since the emission angle
and/or the crossover size of the beam from the electron gun can be
adjusted by the lens including a plurality of anodes, therefore the
required lens can be simplified into one-step of lens and its
associated axial-aligning device is no more necessary but the
multi-beam can be formed with a thus simplified optical system.
[0229] Further, to accomplish the ninth object as described above,
the present invention provides a fifteenth pattern evaluation
method, in which a plurality of beams is used to scan a sample
surface to thereby evaluate said sample, said method comprising the
steps of:
[0230] a. focusing an electron beam emitted from an electron gun in
an NA aperture by a condenser lens;
[0231] b. focusing an image of said NA aperture by a reduction lens
in the vicinity of a principal plane of an objective lens;
[0232] c. forming a multi-beam by means of a multi-aperture
disposed in front of or behind a condenser lens;
[0233] d. focusing said multi-beam on the sample surface by a
reduction lens and the objective lens;
[0234] e. scanning with the multi-beam across the sample, while
applying dynamic focusing;
[0235] f. accelerating secondary electrons emitting from the
scanning points by the objective lens to allow them to pass through
the objective lens;
[0236] g. deflecting the secondary electrons by an E.times.B
separator to advance toward a secondary optical system;
[0237] h. extending a spacing between beams of a multi-beam of
secondary electrons and detecting them by a plurality of detectors;
and
[0238] i. detecting beams of the multi-beam of secondary electrons
independently to form a two-dimensional image for evaluating the
sample, wherein
[0239] an electric field intensity in the vicinity of said sample
can be adjusted within a range of 1.5 kV/mm to 5.5 kV/mm.
[0240] According to the above method, during a series of evaluation
processes in which the multi-beam is focused on the sample surface
to scan it and to thereby produce the two-dimensional image for
evaluating the pattern of the sample, the electric field intensity
in the vicinity of the sample can be adjusted in a range of 1.5
kV/nm to 5.5 kV/nm, and thus the invention can successfully provide
the pattern evaluation method in which the out-of-focus level of
the secondary electrons on the detector can be reduced by adjusting
the electric field intensity appropriately according to the
features on the sample surface, and which is free from a fear of
discharge that might be otherwise induced between the lens and the
sample.
[0241] Further, to accomplish the ninth object as described above,
the present invention provides a sixteenth pattern evaluation
method, in which a plurality of beams is used to scan a sample
surface to thereby evaluate said sample, said method comprising the
steps of:
[0242] a. irradiating an electron beam emitted from an electron gun
having a thermionic emission cathode over a multi-aperture;
[0243] b. focusing the electron beam, which has passed through the
multi-aperture, in an NA aperture;
[0244] c. reducing a group of electron beams, which have been
separated independently through the multi-aperture, by a reduction
lens and an objective lens to scan the sample surface;
[0245] d. accelerating secondary electrons emitting from the
scanning points on the sample by the objective lens to allow them
to pass through the objective lens;
[0246] e. deflecting the secondary electrons by an E.times.B
separator to advance toward a secondary optical system;
[0247] f. extending a spacing between beams of the multi-beam of
secondary electrons and detecting them by a plurality of detectors;
and
[0248] g. detecting beams of the multi-beam of secondary electrons
independently to form a two-dimensional image for evaluating the
sample, wherein
[0249] an arrangement of said multi-beam is defined by an array of
m-row.times.n-column, in which a spacing between i-row, j-column
and i+1-row, j-column is substantially equal to the spacing between
i-row, j-column and i-row, j+1-column.
[0250] According to the above method, the beams in the primary
optical system can have a higher resolution than the beams in the
secondary optical system and also a maximum possible number of
beams can be arranged in a smallest possible circle under the
condition that the beams are equally spaced along the one axial
direction, and this allows the beams to be converged narrow without
inversely increasing the astigmatism and/or the coma
aberration.
[0251] Further, to accomplish the ninth object as described above,
the present invention provides a seventeenth pattern evaluation
method in accordance with any one of the above-defined fourteenth
to sixteenth pattern evaluation methods, in which plural sets of
said electron gun, said primary optical system, said secondary
optical system and said detecting system are disposed over a single
wafer, wherein the lens of said primary optical system includes a
plurality of electrodes in a stack on a single substrate of
ceramics, each of said electrodes having a number of holes
corresponding to a number of optical axes in association with the
number of optical systems arranged.
[0252] According to the above method, the throughput in the pattern
evaluation can be improved in proportion to the number of optical
systems used, yet with the simple structure which facilitates the
fabrication and assembling of the electron optical system for
providing the pattern evaluation, thus allowing building of the
system at a lower cost.
[0253] Further, the present invention is characterized in that in
manufacturing devices, an evaluation of a wafer in the course of or
after processing is provided by using any one of the above-defined
pattern evaluation methods.
[0254] According to the above method, the device manufacturing
method having each different advantage associated with each pattern
evaluation method can be obtained.
[0255] To accomplish the tenth object as described above, the
present invention provides an evaluation method for evaluating a
resist pattern formed by an electron beam direct writer and/or an
exposing device, such as an excimer laser stepper, or a
subsequently processed wafer, said method comprising the step
of:
[0256] preparing an exposed wafer through a process in which a dose
is changed by steps in a row direction, while a focal condition is
changed by steps in a column direction, with respect to a plurality
of dies arranged in matrix on a wafer, so that the exposure can be
carried out with the dose and the focal condition changing in
two-dimensional matrix;
[0257] measuring a predetermined number of line width at a
predetermined locations for each of said plurality of dies;
[0258] making a determination on each die whether or not a line
width thereof falls in a predetermined range based on said
measurement;
[0259] applying a defect inspection to the die having the line
width falling in said range; and
[0260] evaluating a lithography margin from a resultant defect
distribution obtained in the previous step.
[0261] Further, the present invention provides an evaluation method
in accordance with the above-defined evaluation method, in which
said step of applying a defect inspection comprises:
[0262] irradiating an electron beam to a region including a
plurality of pixels on said wafer; and
[0263] magnifying secondary electrons or back-scattered electrons
emitting from said region on said wafer by an optical system to
obtain a two-dimensional image.
[0264] Further, the present invention provides an evaluation method
in accordance with the above-defined evaluation method, in which it
is determined whether or not said detected defect is resultant from
the lithography.
[0265] Further, the present invention provides an evaluation method
in accordance with the above-defined evaluation method, in which
said defect resultant from the lithography is a defect induced by
an excessive or insufficient correction to the proximity
effect.
[0266] Further, the present invention provides an evaluation method
in accordance with the above-defined evaluation method, in which
said step of applying a defect inspection comprises a step of
performing a defect detection of said die by scanning with the
electron beam in the direction orthogonal to one axial direction,
while moving said wafer continuously in said one axial
direction.
[0267] Furthermore, the present invention provides a semiconductor
device manufacturing method which employs any one of the
above-defined evaluation methods.
[0268] Those and other objects, features and advantages of the
present invention will be apparent by reading the following
description with reference to the attached drawings showing
illustratively preferred embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0269] FIG. 1 is a schematic view showing an electron beam
apparatus according to an embodiment of a first invention;
[0270] FIG. 2 is a plan view of an anode;
[0271] FIG. 3 is a schematic diagram for illustrating how to adjust
a rotation of a group of beams by using an electromagnetic lens
13;
[0272] FIG. 4 is a schematic view showing an electron beam
apparatus according to an embodiment of a second invention;
[0273] FIG. 5 is a sectional view of an objective lens 2-3;
[0274] FIG. 6 is a schematic diagram illustrating a relationship
among a pixel area 2-18 on a sample, an outer diameter of a primary
electron beam 2-17 used in scanning the sample surface and an
aperture 2-8 in a detection surface, which has been magnified by
magnifying lenses 2-3, 2-6 and 2-7. Secondary electrons emitting
from the outside of the pixel 2-8 (shown by dotted lines) are
inhibited from passing through the aperture 2-8;
[0275] FIG. 7 is a schematic diagram, wherein FIG. 7a shows a
schematic view of an electron beam apparatus according to another
embodiment of the second invention, FIG. 7b shows a schematic view
of a multi-aperture 2-45 and FIG. 7c shows a schematic view of a
multi-aperture 2-58 disposed in front of a detector 2-60,
respectively;
[0276] FIG. 8 is a schematic diagram, wherein FIG. 8a shows a
schematic view of the multi-aperture 2-45 and FIG. 8b shows a state
of scanning of the primary electron beams that have passed through
the multi-aperture 2-45 shown in FIG. 7a;
[0277] FIG. 9 is a schematic diagram showing a structure of an
objective lens 2-50;
[0278] FIG. 10 is a schematic diagram of an electron beam apparatus
according to an embodiment of a third invention;
[0279] FIG. 11 is a plan view of an aperture plate;
[0280] FIG. 12 is a plan view of an NA aperture;
[0281] FIG. 13 is a schematic diagram showing a coupling between an
aperture plate and an actuator;
[0282] FIG. 14 is a schematic diagram showing how to scan with
electron beams along with apertures;
[0283] FIG. 15 is a diagram schematically illustrating a formation
of an focused image in an electron beam apparatus with a
image-projection optical system according to an embodiment of a
fourth invention;
[0284] FIG. 16 is a fragmentally sectional view schematically
showing an electron gun according to an embodiment of the fourth
invention;
[0285] FIG. 17 is a diagram schematically illustrating a formation
of an focused image in an electron beam apparatus with a
image-projection optical system according to another embodiment of
the fourth invention;
[0286] FIG. 18 is a fragmentally sectional view schematically
showing an electron gun according to another embodiment of the
fourth invention;
[0287] FIG. 19 is a schematic plan view of a position measuring
device for a sample table in an electron beam apparatus according
to an embodiment of a fifth invention;
[0288] FIG. 20 is a schematic sectional view taken along the A-A'
line of FIG. 19;
[0289] FIG. 21 is a schematic sectional view taken along the B-B'
line of FIG. 19;
[0290] FIG. 22 is a schematic sectional view taken along the C-C'
line of FIG. 19;
[0291] FIG. 23 is a diagram illustrating how to compensate for the
Yaw motion according to the present invention;
[0292] FIG. 24 is a partial enlarged view of FIG. 23;
[0293] FIG. 25 is a diagram schematically showing an electron
optical column used in a pattern evaluation method of a sixth
invention;
[0294] FIG. 26 is a diagram schematically showing an inter-beam
adjusting method in a pattern evaluation method according to a
first embodiment of the sixth invention;
[0295] FIG. 27 is a diagram showing a feature in an interface
between stripes in a pattern evaluation method according to a
second embodiment of the sixth invention;
[0296] FIG. 28 is a diagram schematically illustrating an outline
of joining operation of small-sized images in a pattern evaluation
method according to a third embodiment of the sixth invention;
[0297] FIG. 29 is a diagram schematically showing an electron
optical system used in a pattern evaluation method of a seventh
invention;
[0298] FIG. 30 illustrates three different cases for determining a
concurrent focal condition for a primary and a secondary beam in
the seventh invention;
[0299] FIG. 31 is a diagram showing a second embodiment of the
seventh invention, schematically illustrating an apparatus
including a plurality of optical systems, each with a multi-beam
formed around a single optical axis;
[0300] FIG. 32 is a sectional view showing the apparatus of the
second embodiment of the seventh invention, illustrating one case,
by way of example, where a plurality of optical elements is made of
ceramic plates stacked in the z-axial direction;
[0301] FIG. 33 is a diagram schematically showing an electron
optical system used in a pattern evaluation method of an eighth
invention;
[0302] FIG. 34 is a diagram illustrating a pattern evaluation
method of the eighth invention, wherein (A) shows an outline of a
CD measurement, (B) shows an outline of aligning accuracy
measurement and (C) shows an outline of edge roughness measurement,
respectively;
[0303] FIG. 35 is a diagram schematically showing an electron
optical system used in a pattern evaluation method according to a
ninth invention;
[0304] FIG. 36 is a diagram schematically showing a second
electronic optical system used in the ninth invention;
[0305] FIG. 37 is a flow chart showing a semiconductor device
manufacturing process;
[0306] FIG. 38 is a flow chart showing a lithography process in the
semiconductor device manufacturing process of FIG. 37;
[0307] FIG. 39 is a diagram for illustrating an embodiment of an
evaluation method of a resist pattern or a processed wafer
according to a tenth invention;
[0308] FIG. 40 is a diagram for illustrating a configuration of one
die and an area having the priority in the inspection in FIG.
39;
[0309] FIG. 41 is a diagram schematically showing an exemplary
structure of a defect inspection apparatus applicable to an
evaluation method of a resist pattern or a processed wafer
according to the tenth invention; and
[0310] FIG. 42 is a diagram for illustrating a scanning operation
performed by the defect inspection apparatus shown in FIG. 41.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0311] Preferred embodiments of the present invention will now be
described with reference to the attached drawings.
First Example
[0312] First, an overview of an electron beam apparatus according
to the first invention will be presented.
[0313] An electron beam apparatus according to an embodiment of the
present invention as shown in FIG. 1 comprises an electron beam
emitter section 32 having an electron gun 30, a plurality of
apertures 34 disposed at a location out of an optical axis 23 and
an electromagnetic lens 7 operable to control an on-axis electron
beam and a plurality of off-axis electron beams emitted from the
electron gun 30 so that said plurality of off-axis electron beams
may pass through the apertures 34.
[0314] The electron beam emitter section 32 comprises two electron
guns 30 and a housing 38 serving for holding the electron guns 30
as well as defining an electron gun chamber 5, and an ion pump 6
for evacuating the electron gun chamber 5 to high vacuum is
attached to the housing 38. Further, each of the electron guns 30
is connected with a mechanism 28 for activating the electron gun 30
mechanically. Although, in the illustrated embodiment, the electron
beam apparatus includes two electron guns 30, the present invention
is not limited to this, but only one or two or more electron guns
30 may be arranged.
[0315] Each of the electron guns 30 emits a single on-axis electron
beam along the optical axis 23 and also a plurality of off-axis
electron beams around said on-axis electron beam along the optical
axis 23. In the illustrated embodiment, the electron gun 30 emits
four off-axis electron beams that are equally spaced along a circle
surrounding the on-axis electron beam. However, the present
invention is not limited to the four off-axis electron beams but
may include at least two or more off-axis electron beams. The
electron gun 30 has a cathode 36 and an anode 3. The cathode 36 is
made up of ZrO/W chip 1 that has been spot-welded to a tungsten
heater 2. It is to be noted that such a cathode 36 is commercially
available in the market. The electron gun 30 may be made either one
of ZrO/W, carbide of transition metal or a Schottky cathode 36, for
example. The anode 3 is disposed at a location not much away from
the ZrO/W chip 1 of the electron gun 30.
[0316] As shown in FIG. 2, the anode 3 is provided with four
apertures of 10 .mu.m.phi. at four positions out of the optical
axis 23 symmetrically along a circle surrounding the optical axis
23. The anode 3 is grounded and the ZrO/W chip 1 is applied with a
voltage of -4.5 kV. This diode structure can induce the Schottky
emission effect. The electron beams emitted from the ZrO/W chip 1
include a single on-axis electron beam along the optical axis 23
and the four off-axis electron beams around the on-axis electron
beam along the optical axis 23. A conventional apparatus has
employed only one on-axis electron beam that is emitted in the
direction of the optical axis 23. However, since the four off-axis
electron beams are associated with extremely high current level as
compared to the on-axis electron beam, the on-axis electron beam is
hereby discarded but the four off-axis electron beams 34 are
permitted to pass through the apertures 34.
[0317] The electromagnetic lens 7 forms a magnetic field extending
to the anode 3 region. To explain this more specifically, the
magnetic field extends from the ZrO/W chip 1 of the electron gun 30
to the vicinity downstream to the anode 3 so that among the
electron beams emitted from the ZrO/W chip 1, the four off-axis
electron beams can exclusively pass through the apertures 34.
[0318] The electromagnetic lens 7 defines a circular configuration
in the vicinity of the optical axis 23 viewed from the electron gun
30 side and includes an upstream recess 50 formed in a central
portion of its surface defined in the electron gun side, with which
a part of the electron gun chamber 5 is fitted. The electromagnetic
lens 7 further includes a downstream recess 51 substantially in the
same configuration as the upstream recess 50.
[0319] The electromagnetic lens 7 comprises a pair of annular coils
7-1 and 7-2 positioned around the optical axis 23, a central
magnetic pole 7-3 interposed between said pair of coils, an
upstream magnetic pole 7-4 disposed in the upstream side of the
central magnetic pole with respect to the optical axis and, a
downstream magnetic pole 7-5 disposed in the downstream side of the
central magnetic pole with respect to the optical axis. The central
magnetic pole 7-3, the upstream magnetic pole 7-4 and the
downstream magnetic pole 7-5 are made of ferromagnetic material,
respectively. The upstream magnetic pole 7-4 and the downstream
magnetic pole 7-5 are also serving as a magnetic circuitry covering
the pair of annular coils 7-1 and 7-2.
[0320] The electromagnetic lens 7 further includes an opening 60 in
a location facing the electron gun 30, which is formed through the
central, the upstream and the downstream magnetic poles for
permitting the electron beam to pass therethrough. The anode 3
provided with the four apertures 34 is disposed within the opening
in the vicinity of the downstream magnetic pole. The magnetic field
is produced within the opening with the aide of the central, the
upstream and the downstream magnetic poles so as to control the
electron beam passing through the opening such that only the
off-axial electron beams may pass through the corresponding
apertures 34.
[0321] The pair of coils consists of the upstream coil 7-1 disposed
in the upstream side of the central magnetic pole and the
downstream coil 7-2 disposed in the downstream side of the central
magnetic pole. The upstream and the central magnetic poles together
with the upstream coil define an upstream lens. The downstream and
the central magnetic poles 7-5, 7-3 together with the downstream
magnetic pole 7-3 define a downstream lens. Thus, the central
magnetic pole 7-3 is serving as a common magnetic pole between the
upstream lens and the downstream lens. The four off-axis electron
beams emitted from the ZrO/W chip 1 are converged while being
rotated by these two lenses or the upstream and the downstream
lenses. The intensity of the convergence and the rotation angle of
the electron beams are controlled appropriately such that the four
off-axial electron beams may pass through the apertures 34 disposed
in the anode 3. That is, the upstream coil and the downstream coil
are applied with respective currents in opposite directions and the
intensity of the currents and the ratio between the currents are
appropriately controlled. Controlling of the lens intensity can
tune the intensity of the convergence (i.e., the R direction, or
the radial direction, with respect to the optical axis 23) and the
controlling of the current ratio between the upstream lens and the
downstream lens can tune the rotation angle (i.e., the .theta.
direction, or the rotational direction). The axial alignment of the
electron beams relative to the electromagnetic lens 7 may be
provided by the mechanism 28 for moving the electron gun 30
mechanically.
[0322] Axial aligning coils 9 and 10, an NA aperture 12 and an
electromagnetic lens 13 are disposed in this order downstream to
the apertures 34. The electromagnetic lens 13 has the same
structure as the electromagnetic lens 7. The axial aligning coil 9
is fitted in a recess of the electromagnetic lens 7 in the
downstream side thereof and the axial aligning coil 10 is fitted in
a recess of the electromagnetic lens 13 in the upstream side
thereof, respectively. The NA aperture 12 is arranged at a location
a little closer to the sample than the axial aligning coil 10 and
the electron beam having passed through the NA aperture 12 is
controlled by the electromagnetic lens 13. In the downstream side
of the electromagnetic lens 13 are disposed an axial aligning
deflector 24, a first scanning deflector 25, E.times.B deflectors
15 and 16, a scanning deflector 17, an electromagnetic lens 14, an
axisymmetric electrode 21 and a sample 22 in this order. The
electron beam apparatus of this illustrated embodiment further
comprises a secondary optical system. The axial aligning deflector
24 is fitted in a recess of the electromagnetic lens 13 in the
downstream side thereof. The electromagnetic lens 14 includes a gap
20 defined in the side facing to a sample 22, and a lens effect
induced by an on-axis magnetic field produced by the gap 20 and an
electric field produced by the axisymmetric electrode 21, the
sample surface and the electromagnetic lens 14 causes a reduced
image of the aperture 34 to be focused on the surface of the sample
22. That is, a plurality of apertures 34 are firstly reduced by a
reduction lens 13, and the resultant image thereof is further
reduced by an objective lens (a synthetic lens system comprising
the electromagnetic lens 14 in combination with an electrostatic
lens implemented by the electrode 21 and the like) to form a
multi-beam in a size of 50 nm.phi. to 100 nm.phi. on the sample 22.
Although the electromagnetic lens 14, similarly to the
electromagnetic lens 7, 13, has a circular configuration viewed
from the upstream side, it includes two recesses formed only in the
periphery of the region in upstream side defining the passage of
the electron beam. The E.times.B deflectors 15 and 16 and the
scanning deflector 17 are fitted in the recess.
[0323] The four off-axial electron beams having passed through the
apertures 34 form a crossover in the NA aperture 12 with the aid of
the convergence effect from the electromagnetic lens 7. The axial
aligning with respect to the NA aperture 12 and the electromagnetic
lens 13 is carried out by the axial aligning coils 9 and 10. The
off-axis electron beams passed through the NA aperture 12 are
focused by the electromagnetic lens 13 in position on a principal
plane of the objective lens 14, 21, so that the lens aberration in
the formation of the images of the apertures 34 on the sample
surface can be minimized. As for the electromagnetic lens 13,
similarly to the electromagnetic lens 7, the lens intensity and the
rotation are independently controllable, and this works to control
the orientation on the sample of the four off-axis electron beams
that have passed through the apertures 34, so that the four
off-axis electron beams projected along the y-axis are all equally
spaced, as shown in FIG. 3. After having been adjusted by the
electromagnetic lens 13, the four off-axis electron beams are
subject to the axial aligning relative to the objective lens 14, 21
by the axial aligning deflector 24. The electron beams are focused
into images on the sample 22 by the objective lens 14, 21 and
driven by the scanning deflector 25, 17 to scan the sample 22.
Secondary electrons emanating from the scanning points on the
sample 22 are accelerated by the electric field produced by a
positive voltage applied to the axisymmetric electrode 21 and a
negative voltage applied to the sample 22 and deflected by the
E.times.B deflector 15, 16 toward a secondary optical system 26.
The magnifying lens 18 creates magnified images of the secondary
electrons on the detector 19, where the secondary electrons
originated from the four off-axis electron beams can be detected
without any interference therebetween and resultantly SEM images of
four channels per one optical axis 23 can be created.
[0324] The electron beam apparatus comprises the electromagnetic
lens 7 and the aperture 34 in the anode 3 disposed in the location
out of the optical axis 23, wherein the electromagnetic lens 7 can
be adjusted such that the plurality of electron beams emitted from
the ZrO/W cathode 36 may pass through the apertures 34. This allows
the most intensive four off-axis electron beams among a plurality
of electron beams emitted from the ZrO/W cathode 36 to be
accurately aligned with the positions of the apertures 34 by using
the electromagnetic lens 7, which means that the magnified and
uniformly intensified four electron beams can be obtained, thus
realizing a highly precise evaluation. Further advantageously, the
present invention using the four off-axis electron beams for the
scanning operation on the sample can provide the evaluation of a
substrate with high throughput.
[0325] Further, in the present invention, the orientation of the
group of four off-axis electron beams in the rotational direction
on the sample can be adjusted by the electromagnetic lens 13, and
the crossover position can be controlled to meet the requirement to
reduce the aberration in the vicinity of the objective lens 14, 21,
as well.
[0326] The electron gun chamber 5 in the above-illustrated
embodiment is isolated from the sample 22 by the apertures 34 and
the NA apertures 12 defining orifices of low vacuum conductance, in
which the space between the orifices is exhausted by an ion pump
11, contributing to longer operating life and stable operation of
the ZrO/W cathode.
Second Example
[0327] A first embodiment using a single beam embodying the second
invention will now be described with reference to FIG. 4. An
electron beam apparatus of this illustrated embodiment comprises an
electron gun 2-1 serving as an electron beam source emitting a
primary electron beam 2-13, a primary optical system 2-30 for
guiding the primary electron beam onto a sample 2-4 to scan said
sample 2-4 with the primary electron beam, a secondary electron
detecting unit 2-9 having a detection surface 2-16 for detecting a
secondary electron beam 2-14 emitting from the sample 2-4, a
secondary optical system 2-40 for guiding the secondary electron
beam 2-14 emitting from the sample 2-4 to be focused into an image
on the detection surface 2-16 of the secondary electron detecting
unit 2-9 and a controller 2-100 for controlling the electron beam
apparatus.
[0328] The electron gun 2-1 of thermionic beam source type has been
employed, in which electrons are emitted by heating an electron
emission material (cathode). The electron emission material
(emitter) serving as the cathode has employed lanthanum hexaboride
(LaB.sub.6). The electron beam source used herein may be of
electric field emission type or of thermal electric field emission
type. For the SEM type of apparatus, the electron beam source of
Schottky emission type or of thermal electric field emission type
is used.
[0329] The primary optical system 2-30 comprises a condenser lens
2-2, 2-3 for irradiating the primary electron beam 2-13 emitted
from the electron gun 2-1 in a larger size than a pixel size
defined on the sample surface and a scanning deflector 2-11 for
performing a raster scanning with the primary electron beam on the
sample 2-4.
[0330] In the illustrated embodiment, the condenser lens is
composed of a condenser lens 2-2 and an objective lens 2-3. The
condenser lens 2-2 is disposed in the sample side with respect to
the electron gun 2-1 or downstream to the electron gun 2-1, and the
objective lens 2-3 is disposed downstream to the condenser lens 2-2
and immediately upstream to the sample 2-4. The condenser lens 2-2
and the objective lens 2-3, thus arranged to serve as the
converging lens system, can converge the primary electron beam
emitted from the electron gun 2-1 to a size two or three times as
large as the pixel size on the sample.
[0331] The scanning deflector 2-11 is disposed immediately
downstream to the condenser lens 2-2. The scanning deflector 2-11
is controlled by the controller 2-100, in which the deflector 2-11
in response to the instruction from the controller 2-100 deflects
the primary electron beam, that has been converged to the specified
size through the condenser lens 2-2, to thereby provide the raster
scanning with the primary electron beam 2-13 on the sample 2-4.
[0332] The primary optical system 2-30 further comprises an
E.times.B separator 2-5 for deflecting the primary electron beam,
that has passed through the condenser lens 2-2 and the scanning
deflector 2-11, toward the sample 2-4 via the objective lens 2-3.
The E.times.B separator 2-5 forms the electric field and the
magnetic field in directions orthogonal to each other, and
specifically the E.times.B separator 2-5 embodies a unit of
deflection optical system having the electric field and the
magnetic field crossing at a right angle. Selective application of
the electromagnetic field can control the electron beam entering
the field from one direction to be deflected at a specified angle
and the electron beam entering the field from the opposite
direction to be deflected at a specified angle in the effect from a
force applied by the electric field and a force applied by the
magnetic field. The E.times.B separator 2-5 deflects the primary
electron beam 2-13 that has passed through the condenser lens 2-2
and the scanning deflector 2-11 so that the electron beam 2-13 can
be irradiated vertically onto the sample 2-4, and also deflects the
secondary electron beam 2-14 emanating from the sample 2-4 toward
the secondary electron detecting unit 2-9. Although the E.times.B
separator has been herein explained to be included in the primary
optical system 2-30, it may be included in the secondary optical
system 2-40 or may be included in both or neither of the primary
and/or the secondary optical systems, 2-30 and 2-40.
[0333] The reason the angle formed between the primary electron
beam 2-13 and a normal line 2-A of the sample surface is 3.alpha.,
while an angle formed between the secondary electron beam 2-14 and
the normal line 2-A of the sample surface is .alpha. is that this
can reduce the chromatic aberration due to the E.times.B separator
2-5. A detailed description can be found in Japanese Patent
Application No. 2000-335756 and International Patent Application
No. PCT/JP01/054949. The contents of those applications are hereby
incorporated by reference in their entirety.
[0334] The secondary optical system 2-40 comprises the objective
lens 2-3 for adjusting the locus of the secondary electron beam
2-14 emitting from the sample 2-4 to thereby reduce the aberration,
magnifying lenses 2-6 and 2-7 for focusing a magnified image of the
secondary electron beam on the detection surface 2-16, an NA
aperture 2-10 interposed between the magnifying lenses 2-6 and 2-7,
a correction deflector 2-12 interposed between the magnifying lens
2-7 and the detection surface 2-16 of the secondary electron
detecting unit, and an aberration reducing aperture 2-8 interposed
between the correction deflector 2-12 and the detection surface
2-16 of the secondary electron detecting unit.
[0335] The objective lens 2-3 is serving both for focusing the
primary electron beam 2-13 on the surface of the sample 2-4 and for
converging the secondary electron beam 2-14 emanating from the
samples 2-14 to be a narrow beam directed to the E.times.B
separator 2-5. A specific structure of the objective lens 2-3 is
shown in FIG. 5. The objective lens 2-3 comprises an
electromagnetic lens 2-22 having an annular coil 2-26 centered on
the optical axis 2-19 and surrounded by a permalloy core 2-28 and a
tubular cylindrical electrode 2-20 disposed along the central axis
line of the electromagnetic lens or the optical axis 2-19. The
electromagnetic lens 2-22 has an annular configuration with a space
2-32 defined in the central region thereof. The cylindrical
electrode 2-20 is disposed within the space 2-32 of the
electromagnetic lens 2-22 at a location in its sample 2-4 side and
partially extending beyond a lower magnetic pole 2-34 of the
electromagnetic lens 2-22 toward the sample 2-4 side. A part of the
permalloy core 2-28 constitutes an upper magnetic pole 2-36 of the
electromagnetic lens 2-22. An annular gap 2-24 is defined in the
upper magnetic pole 2-36 in its sample side. Thus, the objective
lens 2-3 comprises an ordinary electromagnetic lens having the gap
2-4 defined in the optical axis 2-19 side. An on-axis magnetic
field distribution 2-21 of the objective lens 2-3 has its maximum
value seen in the central region of the gap 2-24 and substantially
zero value on the sample 2-4 surface. The sample 2-4 is applied
with a negative voltage by a first variable voltage source 2-38,
and the cylindrical electrode 2-20 is applied with a high positive
voltage by the second variable voltage source 2-39. Owing to this,
an electric field is formed between the sample 2-4 and the
cylindrical electrode 2-20. Accordingly, the secondary electron
beam emitted from the sample 2-4 is accelerated in the electric
field produced by the sample 2-4 and the cylindrical electrode 2-20
and consequently has been highly energized at the time of
convergence by the electromagnetic lens 2-22. Owing to this, the
on-axis chromatic aberration coefficient of the objective lens 2-3
can be reduced and thus produce a lower aberration. The objective
lens 2-3 is included in both of the primary and the secondary
optical systems, 2-30 and 2-40.
[0336] The magnifying lenses 2-6 and 2-7 may be made of electron
lens having a function for magnifying an electron beam image,
respectively.
[0337] The NA aperture 2-10 is disposed between the magnifying
lenses 2-6 and 2-7 to remove the electron beams emitted from the
sample 2-4 at a large angle. In the illustrated embodiment, since
the secondary electron beam emitted vertically from the sample 2-4,
after having passed through the objective lens 2-3, intersects with
the optical axis 2-19, the NA aperture 2-10 is preferably disposed
at the location of the intersection or on its conjugate plane. This
arrangement allows control and reduction of the aberration to a
desired level.
[0338] The correction deflector 2-12 is controlled by the
controller 2-100, in which the correction deflector 2-12, in
response to the instruction from the controller 2-100, deflects the
trajectory of the secondary electron beam 2-14 so that the image to
be produced by the secondary electron beam 2-14 can be always
formed on the aberration reducing aperture 2-8. More specifically,
the correction deflector 2-12 in response to the instruction from
the controller 2-100 actuates in synchronism with the operation of
the scanning deflector 2-11 that is driving the primary electron
beam to scan the sample 2-4, and corrects the trajectory of the
secondary electron beam in synchronism with the scanning operation
of the primary electron beam, so that the image of the secondary
electron beam 2-14 emitting from the specified area of the sample
2-4 which is scanned by the primary electron beam 2-13 and
corresponds to the pixel size defined on the detecting surface 2-16
can be formed over the aberration reducing aperture 2-8 at any
times.
[0339] The aberration reducing aperture 2-8 allows only such a
secondary electron beam to pass therethrough that has emitted from
a specified area on the sample 2-4 corresponding to the pixel size
on the detection surface 2-16 of the secondary electron detecting
unit 2-9 among the secondary electron beams that have emanated from
the sample 2-4 and passed through the magnifying lenses 2-6 and
2-7. The aberration reducing aperture 2-8 has a size substantially
equal to a product of the pixel size on the sample surface and the
magnification of the magnifying lenses 2-3, 2-6 and 2-7.
Alternatively, the effective detection area of the detection
surface 2-16 may be made equal to the size of the aperture 2-8, and
in that case the aperture 2-8 may be eliminated. In case where the
secondary optical system suffers from large aberration, the
aperture 2-8 may be formed to be slightly smaller in its size than
the product of the pixel size on the sample and the magnification
scale of said magnifying lens to thereby reduce the effect of the
aberration from the secondary optical system.
[0340] The controller 2-100 may be implemented by a general-purpose
personal computer in one example. The computer comprises a
controller main unit 2-144 for executing a control operation of the
scanning deflector 2-11, the correction deflector 2-12 and the
secondary electron detecting unit 2-9 and also an arithmetic
operation in accordance with a specified program, a CRT 2-113 for
indicating results from those operations and secondary electron
images, and an input section 2-150, such as a keyboard or a mouse,
allowing for an operator to input a command. It is a matter of
course that the controller 2-100 may be made of hardware dedicated
for the defect inspection apparatus or a workstation, for
example.
[0341] The controller main unit 2-144 includes a CPU, a RAM, a ROM
and a variety of control substrates, such as a video substrate,
though not shown. The controller main unit 2-144 is connected with
a storage device 2-152. The storage device 2-152 may be made of
hard disk, for example. On the storage device 2-152 are allocated a
secondary electron image storage area 2-154 for storing the
secondary electron image data of the sample 2-4 received from the
secondary electron detecting unit 2-9 and a reference image storage
area 2-156 for storing in advance the reference image data of the
sample containing no defect. The storage device 2-152 further
contains a control program for controlling the entire electron beam
apparatus, especially for controlling the scanning deflector 2-11,
the correction deflector 2-12 and the secondary electron detecting
unit 2-9, an evaluation program for evaluating the sample, and a
control program 2-158 for making a compensation or a correction to
any possible deviation from a design parameter value with respect
to a position, an orientation (rotational position) or a distance
between the beams of a plurality of primary electron beams
irradiated to the sample. The image data representing the scanned
surface of the sample 2-20 and stored in the secondary electron
image storage area 2-154 is compared with the reference image data
of the sample containing no defects that has been previously stored
in the reference image storage area 2-156 to thereby detect the
defect in the sample 2-4.
[0342] A general operation of the electron beam apparatus according
to the above-illustrated embodiment will now be described.
[0343] The primary electron beam 2-13 is emitted from the electron
gun 2-1 in the direction angled by 3.alpha. relative to the normal
line 2-A of the sample surface, converged by the condenser lens 2-2
and deflected by the E.times.B separator so as to be directed
toward the sample 2-4. Further, the primary electron beam 2-13 is
converged to be two to three times as large as the pixel size on
the sample surface and thus directed to the sample 2-4. The primary
electron beam is driven by the deflector 2-11 to perform the raster
scanning across the sample 2-4.
[0344] The secondary electrons emanating from the sample 2-4 in the
wide range of direction within .+-.90.degree. are accelerated by
the accelerating electric field for the secondary electrons
produced by the axisymmetric cylinder 2-20 contained in the
objective lens 2-3 and the sample 2-4 and then converged by the
electromagnetic lens 2-22 to be a narrow beam, which in turn passes
through the objective lens 2-3 as indicated by the locus 2-14 of
the secondary electron. This can reduce the aberration of the
objective lens 2-3. The secondary electron beam 2-14 having passed
through the objective lens 2-3 is deflected by the E.times.B
separator 2-5 at an angle of .alpha. relative to the normal line
2-A of the sample surface. The secondary electron beam is magnified
by the magnifying lenses 2-6 and 2-7 to form an enlarged image over
the aberration reducing aperture 2-8, where only some of those
secondary electron beams that have been emitted from the specific
area of the sample corresponding to the pixel size on the detection
surface 2-16 of the secondary electron detecting unit 2-9 are
allowed to pass through the aberration reducing aperture 2-8. The
controller 2-100 synchronizes the correction deflector 2-12 with
the scanning operation of the primary electron beam on the sample
2-4 to make a correction, so that the image of the secondary
electron beam emitting from the specified area of the sample 2-4
which is scanned by the primary electron beam and corresponds to
the pixel size defined on the detecting surface 2-16 can be formed
over the aberration reducing aperture 2-8 at any time. The
secondary electron beam having passed through the aberration
reducing aperture 2-8 is detected by the secondary electron
detecting unit 2-9 to produce the SEM image. In this regard, the
effective detection area of the detection surface 2-16 may be made
equal to the size of the aperture 2-8, and in that case the
aperture 2-8 may be omitted.
[0345] FIG. 6 shows a relationship between a pixel and an outer
diameter 2-17 of the primary electron beam used to scan the sample
2-4. The outer diameter 2-17 of the primary electron beam used for
the scanning has been converged on the sample 2-4 to have a
diameter larger than the pixel size defined thereon. If the NA
aperture is properly sized, the aberration of the objective lens
2-3 is reduced sufficiently to allow only the secondary electron
beams that have been emitted from the specific region 2-18 on the
sample corresponding to the pixel area on the detection surface
2-16 of the secondary electron detecting unit 2-9 to pass through
the aberration reducing aperture 2-8, but intercept the rest of the
secondary electron beams that have been emitted from the other
region than the region 2-18 corresponding to said pixel area not to
enter the secondary electron detecting unit 2-9. Owing to this,
although the primary electron beam used for the scanning is large
in size, this configuration only allows the information limited in
the sample region 2-18 corresponding to the pixel area to enter the
secondary electron detecting unit 2-9 and thus an SEM image of
better resolution can be obtained.
[0346] The calculated pixel frequency and frame time in this case
are listed as follows. It is to be noticed that the transmission
rate of the secondary electrons is hereby assumed to be 25%.
TABLE-US-00002 Beam current Pixel Pixel size Beam size in a pixel
frequency Frame time 0.1 .mu.m.phi. 0.2 .mu.m.phi. 16 .times. 100
nA 400 MHz** 0.25 sec/mm.sup.2 0.05 .mu.m.phi. 0.2 .mu.m.phi. 400
nA 100 MHz 4 sec/mm.sup.2 0.025 .mu.m.phi. 0.2 .mu.m.phi. 100 nA 25
MHz 64 sec/mm.sup.2* 10 .mu.m.phi. 0.2 .mu.m.phi. 16 nA 4 MHz 2.5
.times. 10.sup.3 sec/mm.sup.2*** *{1 mm.sup.2/(0.025 .times.
10.sup.-3).sup.2} .times. {1/(25 .times. 10.sup.6)} = 64 sec; **16
.times. 100 .times. 0.25 MHz = 400 MHz; ***{1 mm.sup.2/(0.01
.times. 10.sup.-3).sup.2} .times. {1/(4 .times. 10.sup.6)} = 2.5
.times. 10.sup.3 sec.
[0347] As seen from the comparison of the above table with the
table in P2, the present invention has an overwhelming advantage
over the prior art. Especially the present invention is
advantageous in a small pixel.
Third Example
[0348] An electron beam apparatus according to a second embodiment
of the second invention will now be described with reference to
FIG. 7. FIG. 7 is a schematic view of an electron beam apparatus
according to the second embodiment of the present invention, in
which a primary electron beam is composed of a multi-beam. This
electron beam apparatus, as shown in FIG. 7(a), comprises an
electron gun 2-41 serving as an electron beam source for emitting a
primary electron beam, a primary optical system 2-42 for guiding
the primary electron beam onto a sample 2-53 to scan the sample
2-53 with the primary electron beam, a secondary electron detecting
unit 2-59 including a plurality of secondary electron beam
detectors provided with detection surfaces 2-61 for detecting a
secondary electron beam emanating from the sample 2-53, a secondary
optical system 2-54 for guiding the secondary electron beam
emitting from the sample 2-53 to be focused into an image on the
detection surface 2-61 of the secondary electron detecting unit
2-59 and a controller 2-100 for controlling the electron beam
apparatus.
[0349] The electron gun 2-41 has the same configuration as that of
the first embodiment. The primary optical system 2-42 comprises
condenser lenses 2-43, 2-44 and 2-46, a multi-aperture 2-45, an NA
aperture 2-47, scanning deflectors 2-77 and 2-78, and an objective
lens 2-50.
[0350] The multi-aperture 2-45 is disposed at a location
immediately downstream to the condenser lens 2-44. The
multi-aperture 2-45 is composed of 16 apertures, 2-45a, 2-45b,
2-45c . . . , wherein the primary electron beam emitted from the
electron gun 2-41 passes through the multi-aperture 2-45 to be
formed into sixteen primary electron beams in total to be used in
scanning the sample 2-53. The plurality of apertures formed in the
multi-aperture 2-45 is shifted in the rotational direction by an
angle of .theta. as indicated in FIG. 7(b) relative to the
coordinate x-y on the sample 2-53. Although the illustrated
embodiment has employed 16 apertures, the number of apertures used
is not limited to 16.
[0351] The condenser lenses 2-43 and 2-44 are disposed at locations
defined in the sample side with respect to the electron gun 2-41 or
downstream to the electron gun 2-41 and upstream to the
multi-aperture 2-45. With the aid of the condenser lenses 2-43 and
2-44 arranged in this configuration, the primary electron beam
emitted from the electron gun 2-41 is converged by two steps to
thereby adjust the irradiation area of the primary electron beam
for the irradiation over the multi-aperture 2-45. The primary
electron beam having passed through the multi-aperture 2-45 is
formed into a plurality of electron beams, 16 beams of primary
electrons in the illustrated embodiment.
[0352] The NA aperture 2-47 is interposed between the condenser
lenses 2-44 and 2-46, and a crossover image of the primary electron
beam that has passed through the multi-aperture is formed in the NA
aperture 2-47. The NA aperture helps reduce the aberration. The
crossover image formed in the NA aperture 2-47 is focused into an
image on a principal plane of an objective lens 2-50.
[0353] The condenser lens 2-46 is disposed downstream to the NA
aperture 2-47 and the objective lens 2-50 is disposed immediately
upstream to the sample 2-53. The condenser lens 2-46 serves to
focus the crossover image formed in the NA aperture 2-47 on the
principal plane of the objective lens so that every one of the 16
primary electron beams has a size two to three times as large as a
pixel size on the sample surface.
[0354] The scanning deflectors 2-77 and 2-78 are arranged
downstream to the condenser lens 2-46 in two steps. The scanning
deflectors 2-77 and 2-78 are under the control of the controller
2-100, wherein in response to an instruction from the controller
2-100, the scanning deflectors 2-77 and 2-78 deflects the primary
electron beams that have passed through the condenser lens 2-46 and
thus converged into the specified size and thereby provides raster
scanning with the primary electron beams in the x-axial direction
across the sample 2-53. In addition, the sample table is moved
continuously in the y-axial direction, and these x- and y-axial
motions provide two-dimensional scanning operation with the primary
electron beams on the sample.
[0355] The primary optical system 2-42 further comprises an
E.times.B separator 2-48, 2-49 for deflecting the 16 primary
electron beams having passed through the scanning deflector 2-78
toward the sample 2-53 via the objective lens 2-50. The
configuration, operation and function of the E.times.B separator
2-48, 2-49 are the same as in the first embodiment. An optical path
is defined between the E.times.B separator 2-48, 2-49 and the
sample 2-53 for the common passage of the primary and the secondary
electron beams.
[0356] An angle formed by the primary electron beam and the normal
line 2-A of the sample surface is 3.alpha. and an angle formed by
the secondary electron beam and the sample surface is .alpha.,
similarly to the first embodiment.
[0357] The secondary optical system 2-54 comprises the objective
lens 2-50 for controlling the loci of 16 groups of secondary
electron beams emanating from the sample 2-53 corresponding to the
number of 16 of the primary electron beams to thereby reduce the
aberration, magnifying lenses 2-55 and 2-56 for focusing the
secondary electron beam into a magnified image on the detection
surface 2-61, correction deflectors 2-79 and 2-80 disposed
downstream to the magnifying lenses 2-55 and 2-56, respectively, an
NA aperture 2-74 disposed between the magnifying lens 2-56 and the
deflector 2-80 and a multi-aperture 2-58 disposed in front of the
secondary electron detecting unit 2-59.
[0358] The objective lens 2-50 is serving both for focusing the
primary electron beam on the surface of the sample 2-53 and for
converging the secondary electron beam emanating from the sample
2-53 to be narrow toward the E.times.B separator 2-49, and the
structure of the objective lens 2-50 is similar to the objective
lens 2-3 in the first embodiment as shown in FIG. 5. The objective
lens 2-50 allows for the common passage of the primary and the
secondary electron beams.
[0359] The function of the magnifying lens 2-55, 2-56 is similar to
that in the first embodiment.
[0360] The NA aperture 2-74 eliminates any electron beams that have
been emitted at a large angle relative to the normal line of the
sample 2-53. This can control the aberration to meet a desired
size. The NA aperture 2-47 may be omitted, if it is not required to
reduce the aberration further.
[0361] The correction deflector 2-79 is under the control of the
controller 2-100, wherein in response to an instruction from the
controller 2-100, the correction deflector 2-79 deflects the locus
of the secondary electron beam so that the crossover image produced
by the secondary electron beam can be formed over the NA aperture
2-74 at any time. More specifically, the correction deflector 2-79
is actuated in synchronism with the operations of the scanning
deflectors 2-77 and 2-78, which drive the primary electron beam to
scan the sample 2-53, in response to the instruction from the
controller 2-100 so that the locus of the secondary electron beam
may be corrected in synchronism with the scanning operation of the
primary electron beam, and thereby the crossover image produced by
the secondary electron beam can be formed over the NA aperture 2-74
at any time.
[0362] The correction deflector 2-80 is also controlled by the
controller 2-100, wherein in response to an instruction from the
controller 2-100, the correction deflector 2-80 deflects the locus
of the secondary electron beam so that the image of the secondary
electron beam having passed through the NA aperture 2-74 may be
formed over the multi-aperture 2-58 in front of the corresponding
detector 2-60 at any time. More specifically, the correction
deflector 2-80 is also actuated in synchronism with the operations
of the scanning deflectors 2-77 and 2-78, which drive the primary
electron beam to scan the sample 2-53, in response to the
instruction from the controller 2-100 so that the locus of the
secondary electron beam may be corrected in synchronism with the
scanning operation of the primary electron beam and thereby the
image of the secondary electron beam having passed through the NA
aperture 2-74 can be formed over the corresponding multi-aperture
2-58 in front of the detector 2-60 at any time.
[0363] The multi-aperture 2-58 in front of the detector 2-60 allows
only such a secondary electron beam to pass therethrough that has
emanated from a specified area of the sample 2-53 corresponding to
the pixel size on the detection surface 2-61 among the secondary
electron beams that have emitted from the sample 2-53 and passed
through the magnifying lenses 2-50, 2-55 and 2-56. Each of the
apertures of the multi-aperture 2-58 in front of the detector 2-60
has a size substantially equal to a product of the pixel size of
the detector 60 on the corresponding sample surface and the
magnification factor of the magnifying lenses 2-50, 2-55 and
2-56.
[0364] The multi-aperture 2-58 includes a plurality of apertures
corresponding to a plurality of primary electron beams. In the
illustrated embodiment, since 16 pieces of the primary electron
beams have been formed by the multi-aperture 2-45 disposed
downstream to the electron gun 2-41, correspondingly the
multi-aperture 2-58, as shown in FIG. 7(c), is composed of 16
apertures, 2-58a, 2-58b, 2-58c . . . . Similarly to the
multi-aperture 2-45, the multi-aperture 2-58 is shifted in the
rotational direction by an angle of .theta.. The multi-aperture
2-58 is arranged in a position so that the 16 pieces of secondary
electron beams emanating from the irradiation points on the sample
2-53 by the primary electron beams can be focused into 16 pieces of
enlarged images through the magnifying lenses 2-50, 2-55 and 2-56
over respectively associated apertures of the multi-aperture
2-58.
[0365] The secondary electron detecting unit 2-59 includes a
plurality of secondary electron detectors 2-60. More specifically,
the secondary electron detecting unit 2-59 comprises 16 pieces of
secondary electron detectors, 2-60a, 2-60b, 2-60c . . . ,
corresponding to the 16 pieces of primary electron beams. The
secondary electron detectors 2-60a, 2-60b, 2-60c . . . are arranged
in association with the 16 apertures of the multi-aperture 2-58,
2-58a, 2-58b, 2-58c . . . , respectively. The secondary electron
detectors are all independent from one another and individually
have the detection surfaces, 2-61a, 2-61b, 2-61c . . . . Each of
the detection surface 2-61a, 2-61b, 2-61c . . . is positioned
correspondingly to each associated aperture 2-58a, 2-58b, 2-58c . .
. . Each of the 16 groups of secondary electron beams emanating
from the sample 2-53 passes through its associated aperture of the
multi-aperture 2-58 and detected by its associated secondary
electron beam detector 2-60. Although FIG. 7 shows as if only a
single secondary electron beam passes through the aperture 2-58c,
this is intended to illustrate the embodiment clearly in a
simplified manner, and the other 15 secondary electron beams are
hereby omitted. This implies that the image of the sample surface
is formed on a surface of the multi-aperture 2-58. Accordingly, the
image of the secondary electrons from the incident point of the
beam which has passed through the aperture 2-45a is formed over the
aperture 2-58a, and similarly the images of the secondary electrons
from the incident points of the beams which have passed through the
apertures 2-45b, 2-45c, 2-45d . . . can be formed over respective
associated apertures 2-58b, 2-58c, 2-58d . . . , respectively.
[0366] The controller 2-100 is similar to that in the first
embodiment.
[0367] A general operation of the electron beam apparatus according
to the above-illustrated embodiment will now be described.
[0368] The primary electron beam is emitted from the electron gun
2-41 in the direction angled by 3.alpha. relative to the normal
line of the sample surface and magnified by the condenser lenses
2-43 and 2-44 in two steps so that the primary electron beam may be
irradiated onto the multi-aperture 2-45 appropriately. Then, the
primary electron beam passes through the multi-aperture 2-45
including a plurality of apertures to be formed into a plurality of
primary electron beams, which in turn forms a crossover image in
the NA aperture 2-47, converged by the condenser lens 2-46 and
deflected by the E.times.B separator 2-48, 2-49 toward the sample
2-53. Each of the plurality of primary electron beams is further
converged by the objective lens 2-50 to be two to three times as
large as the pixel size on the sample surface and projected onto
the sample 2-53. The primary electron beams is driven by the
scanning deflectors 2-77 and 2-78 so as to perform the raster
scanning in the x-axial direction. In the case where the
multi-aperture 2-45 defines the array as shown in FIG. 8(a), the
raster scanning is performed as shown in FIG. 8(b), thus achieving
a highly efficient scanning encompassing 16 pixels.times.scanning
width per one scanning operation.
[0369] The secondary electron beam emitting from the sample 2-53 in
the wide range of direction within .+-.90.degree. is converged into
a narrow beam and passes through the objective lens 2-49, as is the
case in the first embodiment. This helps reduce the aberration of
the objective lens 2-50. The secondary electron beam having passed
through the objective lens 2-50 is deflected by the E.times.B
separator 2-48, 2-49 in the direction defined by an angle .alpha.
relative to the normal line 2-A of the sample surface. The
secondary electron beam is magnified by the magnifying lens 2-55,
2-56 and deflected in its locus by the correction deflector 2-79 to
form a crossover image on the NA aperture 2-74. The secondary
electron beam having passed through the NA aperture 2-74 is
deflected in its locus by the deflector 2-80 to produce a magnified
image over the multi-aperture 2-58 in front of the detector 2-60,
wherein only some of those secondary electron beams that have been
emitted from the specified region of the sample corresponding to
the pixel size on the detection surface 2-61 of the secondary
electron detecting unit 2-59 are allowed to pass through the
multi-aperture 2-58 in front of the detector 2-60. This can
eliminate the aberration. The 16 pieces of secondary electron beams
are deflected by the correction deflectors 2-79 and 2-80,
concurrently pass through respective associated apertures of the
multi-aperture 2-58 in front of the deflectors 2-60 and then are
detected by the associated detectors 2-60. An output signal from
each detector 2-60 is sent to the controller 2-100, where the SEM
image is formed based on the output signal from each detector 2-60.
At this time, the positional correction is applied according to the
beam position of the multi-beam, and a single SEM image is formed
by using the 16 detector units. If the NA aperture of the secondary
optical system is omitted, the lens of the structure shown in FIG.
9, which comprises a gap defined in the sample side, may be used as
the objective lens. In that case, since the axial magnetic field is
not zero on the sample, the principal ray of the secondary
electrons never intersects with the optical axis, and so the
aperture cannot be placed. This circumstance requires that the size
of the aperture in front of the detector is made smaller to thereby
reduce the aberration.
[0370] The objective lens 2-50 may employ the structure shown in
FIG. 5, or alternatively may take the structure of FIG. 9. The
primary electron beam is entered at an angle of 3.alpha. relative
to the optical axis of the objective lens 2-50, deflected by the
E.times.B separator 2-48, 2-49 to be in alignment with the optical
axis, and formed into a plurality of beams by the objective lens
2-50 on the sample 2-53, and then the secondary electrons emanating
from the sample 2-53 are converged to be narrow and focused into a
plurality of secondary electron images in the vicinity of the
principal plane of deflection of the E.times.B separator 2-48,
2-49. The beam is deflected to the -.alpha. direction by the
electrostatic deflector 2-48 of the E.times.B separator and
deflected to the +2.alpha. direction by the electrostatic deflector
2-49 of the E.times.B separator, resulting in the total deflection
in the .alpha. direction. Accordingly, the secondary optical system
2-54 is disposed in the .alpha. direction. Actually, from the fact
that the primary beam incident from the 3.alpha. direction has a
slightly higher energy than the secondary electrons leaving in the
.alpha. direction, it is considered that the deflection angle of
the primary beam is around 2.7.alpha. not 3.alpha.. The deflector
2-78 serving as the second step deflector for the primary electrons
may be arranged at the location 2-51 of FIG. 9. Preferably, the
element 2-51 may employ an electrostatic deflector. The element
2-52 is an axisymmetric circular disk to be applied with a positive
voltage. A lens gap 2-64 is open in the sample side and preferably
the angles formed by the gap surfaces and the optical axis,
.theta..sub.1, .theta..sub.2, may be equal to or greater than
45.degree..
Fourth Example
[0371] An overview of an electron beam apparatus according to an
embodiment of the third invention will now be presented.
[0372] FIG. 10 is a schematic diagram of an electron beam apparatus
according to an embodiment of the present invention. The electron
beam apparatus of the illustrated embodiment comprises a primary
optical system for guiding the primary electron beam onto a sample
so as to scan the sample with the primary electron beam and a
secondary optical system for detecting secondary electrons emitting
from the sample.
[0373] The primary optical system comprises an electron gun 3-32
for emitting a primary electron beam, a plurality of apertures 3-21
for defect detecting for forming the primary electron beam emitted
from the electron gun 3-32 into a plurality of defect detecting
primary electron beams to perform defect detection, at least one
aperture 3-22 for defect reviewing for forming the primary electron
beam emitted from the electron gun 3-32 into at least one primary
electron beam for defect reviewing to perform defect reviewing,
axial aligning deflectors 3-7, 3-9, 3-10 and 3-13, a condenser lens
3-8, an NA aperture 3-11, a reduction lens 3-12, scanning
deflectors 3-14 and 3-17 for driving the primary electron beam to
scan a sample 3-20 and an objective lens 3-18 for reducing the
primary electron beam to be focused on the sample 3-20.
[0374] The electron gun 3-32 comprises a W filament for heating a
ZrO/W cathode, a Schottky shield 3-2 and a first, a second and a
third anodes 3-3, 3-4, 3-5. The cathode may be made of one selected
from a group consisting of ZrO/W, LaB.sub.6, carbide of transition
metal, and Schottky cathode, and in the illustrated embodiment, the
cathode is made of ZrO/W. For the cathode, if made of carbide of
transition metal, such as TaC, the electron beams are emitted in
four or eight different directions along the periphery around an
optical axis 3-33. For the cathode made of LaB.sub.6, owing to its
intensive emittance, a number of multi-beams may be formed in the
vicinity of the optical axis.
[0375] A plurality of apertures 3-21 for defect detecting and at
least one aperture 3-22 for defect reviewing are disposed behind or
downstream to the third anode. In the illustrated embodiment, the
apertures 3-21 for defect detecting are arranged at four locations
out of the optical axis 3-33 symmetrically along the
circumferential direction, and the aperture 3-22 for defect
reviewing is arranged at one location out of the optical axis 3-33.
Further, both of the apertures 3-21 for defect detecting and the
aperture 3-22 for defect reviewing are formed in a single aperture
plate 3-6 as shown in FIG. 11. However, only the apertures 3-21 for
defect detecting may be disposed in the aperture plate 3-6 but the
aperture 3-22 for defect reviewing may be disposed in a separate
aperture plate, though not shown. The aperture 3-22 for defect
reviewing is smaller in size than the aperture 3-21 for defect
detecting, and this may help converge the primary electron beam for
defect reviewing to be narrower than the defect detecting primary
electron beam. Further regarding the size, the primary electron
beam for defect reviewing may be sized one-half of or smaller than
said defect detecting primary electron beam. In the illustrated
embodiment, the aperture 3-21 for defect detecting has a size of 30
.mu.m.phi., which makes it difficult for the gas to be relieved and
thus reduces vacuum conductance, and accordingly it also serves to
maintain an electron gun chamber in a high vacuum condition.
[0376] The aperture plate 3-6 is attached to a housing (not shown)
of the electron beam apparatus so that it can move in the direction
crossing the optical axis 3-33. That is, as shown in FIG. 13, the
aperture plate 3-6 is fixed to one end of a bellows 3-35 in vacuum,
and the bellows 3-35 in the other end thereof is fixed to a vacuum
wall 3-36 via a fitting for mounting the bellows 3-35. The bellows
3-35 in the one end thereof is attached to an actuator 3-37 for
making it movable in one axial direction. Accordingly, by moving
the aperture plate 3-6 to make the point A of the aperture plate
3-6 in alignment with the optical axis 3-33, the primary electron
beam from the electron gun 3-32 can be irradiated exclusively over
the aperture 3-21 for defect detecting. By moving the aperture
plate 3-6 to make the point B of the aperture plate 3-6 in
alignment with the optical axis 3-33, the primary electron beam
from the electron gun 3-32 can be irradiated exclusively over the
aperture 3-22 for defect reviewing. For performing the defect
detection of the sample 3-20, the aperture plate 3-6 is moved so
that the point A of the aperture plate 3-6 is aligned with the
optical axis 3-33, while for performing the defect reviewing of any
defects, if detected, the aperture plate 3-6 is moved so that the
point B of the aperture plate 3-6 is aligned with the optical axis
3-33. The housing of the electron beam apparatus is provided with a
monitor which allows to monitor a condition in the electron beam
apparatus from outside thereof. This allows for an operator to
choose whether the primary electron beam from the electron gun 3-32
should be irradiated exclusively over the aperture 3-21 for defect
detecting or exclusively over the aperture 3-22 for defect
reviewing, while viewing the primary electron beam from the outside
of the vacuum via the monitor. That is, if the aperture 3-21 for
defect detecting is selected, the primary electron beam for defect
detection may be used to perform the defect detection, or if the
aperture 3-22 for defect reviewing is selected, the primary
electron beam for defect reviewing may be used to perform the
defect reviewing. Although in the illustrated embodiment, the
operator can manually move the aperture plate, the aperture plate
may be moved by means of the actuator 3-37. If the aperture 3-21
for defect detecting and the aperture 3-22 for defect reviewing are
arranged in two separate aperture plates, respectively, the
aperture plates may be exchanged with each other so as to place the
desired aperture(s) in the electron beam apparatus.
[0377] The condenser lens 3-8 is disposed at a location defined in
the sample 3-20 side or downstream with respect to the aperture
plate 3-6, and the NA aperture 3-11 is disposed downstream to the
condenser lens 3-8. The primary electron beam having passed through
the aperture 3-21 for defect detecting or the aperture 3-22 for
defect reviewing forms a crossover in the NA aperture 3-11 by the
condenser lens 3-8. The NA aperture, if configured in a square
having a sufficiently larger area than the crossover size 3-31 as
shown in FIG. 12, can facilitate the measurement of the crossover
size and also prevent the occurrence of intensity fluctuation of
the primary electron beam even in the vibration or drifting of the
crossover position. Since the aperture angle is determined by the
crossover diameter, the control of the beam current and the
resolution can be carried out without exchanging the NA
apertures.
[0378] The reduction lens 3-12 is disposed downstream to the NA
aperture 3-11 and operable to magnify the crossover having passed
through the NA aperture 3-11 into a focused image on the principal
plane of the objective lens 3-18. An exciting condition of the
reduction lens 3-12 has been designed so that the aberration in the
focusing of the four primary electron beams for defect detection on
the sample 3-20 can be reduced.
[0379] The scanning deflectors 3-14 and 3-17 are disposed
downstream to the reduction lens 3-12 and are operable to deflect
the primary electron beam for scanning the sample 3-20.
[0380] The objective lens 3-18 is disposed downstream to the
deflector 3-17 and operable to reduce the primary electron beam to
be focused on the sample 3-20.
[0381] The axial aligning deflector 3-7 is interposed between the
aperture plate 3-6 and the condenser lens 3-8, the axial aligning
deflectors 3-9 and 3-10 are interposed between the condenser lens
3-8 and the NA aperture 3-11, and the axial aligning deflector 3-13
is interposed between the reduction lens 3-12 and the scanning
deflector 3-14, and they are operable to provide the axial
alignment with respect to the condenser lens 3-8, the NA aperture
3-11 and the objective lens 3-18, respectively.
[0382] The secondary optical system comprises an axisymmetric
electrode 3-19 for accelerating the secondary electron beam, the
objective lens 3-18 for converging the accelerated secondary
electron beam, an E.times.B separator 3-15, 3-16 for deflecting the
secondary electron beam emitted from the sample 3-20, magnifying
lenses 3-23 and 3-24, axial aligning deflectors 3-27 and 3-28, an
aperture 3-25 and a secondary electron detector 3-26.
[0383] The axisymmetric electrode 3-19 is disposed in a location
defined in the secondary electron detector 3-26 side a bit away
from the sample 3-20, wherein the secondary electron beam emitting
from the sample 3-20 is accelerated by the electric field produced
by the negative voltage applied to the sample 3-20 and the
axisymmetric electrode 3-19.
[0384] The E.times.B separator 3-15, 3-16 is, along with the
objective lens 3-18, disposed between the axisymmetric electrode
3-19 and the magnifying lens 3-23. The E.times.B separator 3-15,
3-16 forms the electric field and the magnetic field in orthogonal
directions from each other and thus provides a unit of deflection
optical system with the electric field and the magnetic field
crossed at a right angle. Selective application of the
electromagnetic field can control the electron beam entering the
field from one direction to be deflected at a specified angle and
the electron beam entering the field from the opposite direction to
be deflected at a specified angle different from said angle for the
former in the effect from a force applied by the electric field and
a force applied by the magnetic field. The E.times.B separator
3-15, 3-16 deflects the secondary electron beam emanating from the
sample 3-20 to be directed toward the secondary electron detector
3-26.
[0385] The magnifying lenses 3-23 and 3-24 are disposed between the
E.times.B separator 3-15, 3-16 and the aperture 3-25, respectively,
and are operable to magnify the image of the secondary electron
beam to form an enlarged image over the aperture 3-25 in front of
the secondary electron detector 3-26. Since the aberration of the
secondary optical system is determined by the objective lens 3-18,
the magnifying lenses 3-23 and 3-24 are composed of the
electrostatic lens.
[0386] The aperture 3-25 is disposed in front of the secondary
electron detector 3-26. The aperture 3-25 includes four apertures
corresponding to the apertures 3-21 for defect detecting, over
which the enlarged images of the secondary electron beams are
formed.
[0387] The axial aligning deflectors 3-27 and 3-28 are disposed in
the secondary electron detector side with respect to the magnifying
lenses 3-23 and 3-24, respectively, and are operable to provide the
axial alignment of the secondary electron beam with the magnifying
lens 3-24 and the aperture 3-25, respectively.
[0388] The secondary electron detector 3-26 is composed of a
scintillator, a photomultiplier (photoelectron multiplier) and the
like, and is operable to detect the four pieces of secondary
electron beams having passed through the apertures 3-25 and convert
thus detected secondary electron beams into corresponding four
analog signals.
[0389] The secondary electron detector 3-26 is connected to the
image forming circuit 3-30 via an A/D converter 3-29. The four
analog signals output from the secondary electron detector 3-26 are
converted into digital signals by the A/D converter 3-29, with
which the SEM image by four-channel is formed in the image forming
circuit 3-30. The image forming circuit 3-30 is configured
similarly to the controller 3-100 as discussed above, in which said
SEM image by four-channel is compared to the previously stored
reference image data on the sample containing no defects to thereby
detect any defects in the sample, and if the defect exists in the
sample, the coordinate of the defect is stored. The comparison may
employ the cell-to-cell detection method, in which the images are
compared between the cell portions of the same type on the same die
or the die-to-die detection method, in which the comparison is made
between the same pattern regions in different dies.
[0390] The general operation of the electron beam apparatus
according to the illustrated embodiment will now be described.
[0391] In the defect detection, the primary electron beam emitted
from the electron gun 3-32 is irradiated to the aperture 3-21 for
defect detecting to be formed into four primary electron beams for
defect detection. The electron gun 3-32 emits a primary electron
beam in the optical axis direction, while at the same time, it also
emits a plurality of primary electron beams around the optical axis
angled thereto. The primary electron beam emitted along the optical
axis is blocked by the aperture plate 3-6 but only the plurality of
primary electron beams emitted out of the optical axis is permitted
to pass through the apertures 3-21 for defect detecting so as to be
formed into the above-discussed four primary electron beams for
defect detection. Each of the apertures 3-21 for defect detecting
is sized to 30 .mu.m.phi., wherein the primary electron beams for
defect detection having passed through the apertures are reduced by
the condenser lens 3-8, the reduction lens 3-12 and the objective
lens 3-18 so that the resultant four small-sized primary electron
beams for defect detection can be formed on the sample 3-20. Those
four primary electron beams for defect detection are deflected in
two steps by the scanning deflectors 3-14 and 3-17 to thereby
perform the raster scanning on the sample for carrying out the
defect inspection of the sample 30. Based on the fact that the
primary electron beams emitted in four different directions from
the electron gun 3-32 are associated with much higher current level
than the primary electron beam emitted in the optical axis
direction, the beam current around 400 nA could be obtained with a
beam diameter of 50 nm. Owing to this, the primary electron beams
for defect detection can perform the scanning operation across the
sample 3-20 at the pixel frequency of 400 MHz. With the beam
current of 100 nA and the pixel frequency of 100 MHz, the number of
electrons per pixel would be 4050, implying that a signal of
satisfactory S/N ratio could have been obtained. With the four
times high beam current, even if scanning is applied at the four
times high frequency, the signal of the same S/N ratio can be
obtained. Further, using the four primary electron beams allows the
SEM image by four channels to be obtained and thus the defect
inspection to be performed at the scanning rate of 1.6 GHz (400
MHz.times.4) of equivalent frequency. Each of the secondary
electron beams emanating from the four scanning points on the
sample 3-20 upon scanning with the four primary electron beams for
defect detection over the sample 3-20 is accelerated in the
electric field produced by the negative voltage applied to the
sample and the axisymmetric electrode 3-19 disposed under the
electromagnetic lens 3-18, and each of the beams is converged to be
narrow to pass through the objective lens 3-18 and then deflected
by the E.times.B separator 3-15, 3-16, to be guided into the
secondary optical system. The secondary electron beams are
magnified by the two step of magnifying lens 3-23 and 3-24 and
formed into enlarged images over the aperture 3-25 comprising the
four apertures, and those secondary electron beams that have passed
through the apertures 3-25 are detected by the secondary electron
detectors 3-26 so as to create the SEM image by four channels in
the image forming circuit 3-30. At this stage, the positions of the
four primary electron beams for defect detection have been
previously measured and the measured values have been previously
stored in the image forming circuit 3-30. The image forming circuit
3-30 synthesizes the four pieces of SEM image while at the same
time compensating for the misalignment among those primary electron
beams for defect detection. In the formation of this image, a
scanning signal is input to the image forming circuit 3-30, with
which the four pieces of SEM image can be synthesized. The axial
alignment of the secondary electron beam to the magnifying lens
3-23 is carried out by the E.times.B separator 3-15, 3-16, the
axial alignment to the lens 3-24 is carried out by the aligning
deflector 3-27, and the axial alignment to the aperture 3-25 is
carried out by the aligning deflector 3-28. Since the magnifying
lenses 3-23 and 3-24 are composed of the electrostatic lenses, the
secondary optical system is light in weight and advantageously does
not suffer from vibration, though having no vertical arrangement
like the primary optical system. The image forming circuit 3-30
compares the SEM image by four channels with the reference image of
the sample containing no defect to thereby detect any defects in
the sample.
[0392] When the defect detection has been completed across the
sample 3-20 entirely, then image forming circuit 3-30 stores the
coordinate of the detected defect. Based on this information, the
operator moves the aperture plate 3-6 so that the point B of the
aperture plate 3-6 is in alignment with the optical axis 3-33 and
thus makes a control so that the primary electron beam from the
electron gun 3-32 can be irradiated exclusively over the aperture
3-22 for defect reviewing.
[0393] Then, based on the coordinate information of the defect, the
primary electron beam for defect reviewing is aligned with the
position of each defect on the sample 3-20 in sequence, where the
movement of the stage is suspended and the defect reviewing is
performed. The defect reviewing operation is carried out in
accordance with the same procedure as the defect detection, with an
exception that the different primary electron beam is used in the
defect reviewing as discussed above. To perform the defect
reviewing, the primary electron beam emitted from the electron gun
3-32 is irradiated over the aperture 3-22 for defect reviewing. In
the defect reviewing, since the moving of the stage consumes the
majority of time over the image taking, even a single electron beam
for defect reviewing can provide the two-dimensional image at a
sufficiently high rate. Owing to this, the illustrated embodiment
has employed the aperture 3-22 for defect reviewing having a single
aperture. However, the aperture 3-22 for defect reviewing may
include four apertures and thus four electron beams for defect
reviewing can be used, depending on the different conditions. In
the defect reviewing, the pixel size on the secondary electron
detector 3-26 is required to be equal to or smaller than 25 nm
pixel. Accordingly, the beam size of the electron beam for defect
reviewing is also required to be equal to or smaller than 25 nm.
When a single electron beam for defect reviewing is used, one of
the four detectors 3-26 may be used. If the aperture 3-22 for
defect reviewing include four apertures, sizing each of four
apertures to be equal to or smaller than one-half of the each
aperture size of the four apertures for defect detecting 3-22 may
advantageously allow to change the beam size without any
modifications required in the lens condition.
[0394] Assuming that, for example, in the defect reviewing, the SEM
image of 10 .mu.m square would be obtained at 100 MHz, the time
required, T, is expressed as follows, with the pixel size of 25 nm
square:
T = { 10 m .times. 10 m / ( 25 .times. 10 - 3 ) 2 } .times. 10 - 8
sec = 1.6 .times. 10 - 3 sec , ##EQU00001##
indicating that the moving of the stage requires a much longer time
period (100.about.500 ms). Therefore, in the above case, it is not
necessary to use the four electron beams for defect reviewing but
the scanning operation can be still performed only with a single
electron beam for defect reviewing as practiced in the illustrated
embodiment.
[0395] However, if the beam size of 10 nm.phi. and the pixel size
of 10 nm square are used, the beam current around 400 nA can be
obtained with the beam diameter of 50 nm and accordingly the beam
current is reduced to 400 nA.times.(10/50).sup.4=0.64 nA. As a
result, a single electron beam for defect reviewing cannot be
driven to scan at the pixel frequency of 100 MHz but can be only at
the frequency of 0.64 MHz. Under this condition, the time required,
T, for obtaining the SEM image of 10 .mu.m square is calculated as
follows:
T = { 10 m .times. 10 m / ( 10 .times. 10 - 3 ) 2 } .times. { 1 /
0.64 .times. 10 - 6 } sec = 1.56 sec , ##EQU00002##
indicating that the time T exceeds the stage moving time. In such a
case, the aperture for defect reviewing composed of four apertures,
each defining the 1/4 diameter, may be used and thus the scanning
operation may be performed with the total of four electron beams
for defect reviewing. In that case, the time T will be 0.39 sec,
which is substantially as long as the stage moving time.
Fifth Example
[0396] An overview of an electron beam apparatus according to an
embodiment of the fourth invention will now be presented.
[0397] FIG. 15 shows a diagram of an electron beam apparatus of
image projection optical system focusing a beam into an image
according to one embodiment of the present invention.
[0398] An electron beam apparatus using an image projection optical
system in the illustrated embodiment comprises an electron gun
4-40, a secondary optical system for detecting secondary electron
beam or back scattering electrons emitting from a sample, and a
detecting unit 4-1 for detecting the secondary electron beam or the
back scattering electrons, as shown in FIG. 15. As such, the
electron beam apparatus of this embodiment comprises no primary
optical system for irradiating the primary electron beam in the
oblique direction relative to the normal line of the sample surface
and no E.times.B separator for deflecting the primary electron beam
entered from the oblique direction toward the direction along the
normal line, but the electron gun 4-40 is arranged in the secondary
optical system.
[0399] The electron gun 4-40 has a ring-shaped cathode 4-29 for
emitting a primary electron beam defining a hollow beam from a tip
portion thereof, an anode 4-22, 4-26 for controlling the direction
of the hollow beam emitted from the cathode 4-29 and a Wehnelt
4-22, 4-25, as shown in FIG. 16. The anode has an inner anode 4-22
that is grounded and an outer cathode 4-26 that is applied with a
voltage. In the apparatus according to the prior art, since there
is a site where the primary electron beam and the secondary
electron beam are sharing a common optical path, the out-of-focus
level of the secondary electron beam due to the space charge effect
from the primary electron beam may exceed an ignorable value. In
the hollow beam of the present case, owing to the configuration
allowing the primary electron beam to pass the outer side of the
secondary electron beam, there should be induced no out-of-focus of
the secondary electron beam even with any increase in the primary
electron beams. The irradiation condition of the electron gun 4-40
for determining the emission direction of the primary electron beam
can be controlled by adjusting the voltage applied to the outer
anode 4-26.
[0400] The secondary optical system comprises a doublet lens 404
for focusing the secondary electrons or the back scattering
electrons (also referred to as reflected electrons) emanating from
the sample 4-6 into an image of the sample 4-6 and magnifying
lenses 4-2 and 4-3 for magnifying the focused secondary electron
beam and the like.
[0401] The doublet lens 4-4 is interposed between the sample 4-6
and the magnifying lenses 4-2 and 4-3, and comprises a pair of
electron lenses 4-5a and 4-5b. If the voltage applied to the
electron lenses 4-5a and 4-5b is changed, a focal distance of the
doublet lens is changed to thereby allow the control of the lens
condition. The electron gun 4-40 is interposed between the electron
lenses 4-5a and 4-5b and designed to provide an irradiation onto
the sample 4-6 if there is a lens effect from the electron lens
4-5a.
[0402] The NA aperture 4-13 is interposed between the pair of
electron lenses 4-5a and 4-5b and is operable to eliminate the
electron beam emanating from the sample 4-6 at a large angle
relative to the normal line of the sample 4-6.
[0403] The magnifying lenses 4-2 and 4-3 are disposed between the
doublet lens 4-4 and the detecting unit 4-1 or downstream to the
doublet lens 4-4 and are operable to magnify in two steps the
sample image focused by the doublet lens 4-4.
[0404] The detecting unit 4-1 is disposed downstream to the
magnifying lens 4-2, and comprises a scintillator and a CCD for
detecting the secondary electron beams or the like to form an
enlarged image of the sample.
[0405] The electron gun 4-40 must be able to provide an irradiation
in the vicinity of the optical axis 4-21 under both lens conditions
for the secondary electrons and the back scattering electrons.
Further, the electron gun 4-40 must be placed in a specified
location where the secondary electrons and the back scattering
electrons from the sample 4-6 would not interfere with the
components of the electron gun. To address this, the electron gun
4-40 is placed in the location where the loci of the primary
electrons under said two lens conditions intersect with each other
on the assumption that the primary electrons have been emitted at a
sufficiently large angle from the optical axis 4-21. At this
specified location, both of the primary electron beam 4-9 for the
secondary electrons and the primary electron beam 4-8 for the back
scattering electrons can be used. Such a location 4-10 where the
trajectories of the primary electron beams intersect under both
lens conditions, one for the secondary electrons and the other for
the back scattering electrons, can be determined through a
simulation. Although in the illustrated embodiment, the placement
of the electron gun 4-40 has been selected to be a location 4-10
where the loci of the primary electron beams under the lens
condition for the secondary electrons and the lens condition for
the back scattering electrons intersect, the electron gun 4-40 may
not be used in common to satisfy both conditions but separate
electron guns may be placed, one for the secondary electrons and
the other for the back scattering electrons.
[0406] It is to be noted that the primary electron beam 4-9 for the
secondary electrons and the primary electron beam 4-8 for the back
scattering electrons are associated with different angles relative
to the optical axis 4-21, as shown in FIG. 15.
[0407] A general operation of the electron beam apparatus according
to the illustrated embodiment will now be described.
[0408] The hollow beam defining the primary electron beam emitted
from the electron gun 4-40 placed in the location 4-10 in the
direction along the trajectory shown by 4-9 or 4-8 is focused by
one lens element 4-5a of the doublet lens onto the optical axis
4-21 of the sample 4-6. At that time, the primary electron beam for
the secondary electrons follows the trajectory 4-9, and the primary
electron beam for the back scattering electrons follows the
trajectory 4-8. The secondary electrons or the back scattering
electrons emitting from the sample 4-6 follow the locus indicated
by 4-7 and are formed into a parallel beam by the one lens element
4-5a of the doublet lens, which is in turn focused by the other
lens element 4-5b of the doublet lens into an image on an image
plane 4-12 of the doublet lens. The image of the sample is further
magnified by the magnifying lenses 4-3 and 4-2 to form a
two-dimensional image on the detecting unit 4-1.
[0409] The structure of the electron gun 4-40 will now be described
with reference to FIG. 16.
[0410] FIG. 16 schematically shows a partial sectional view of the
electron gun 4-40 according to one embodiment of the present
invention. In FIG. 16, the electron gun 4-40 is illustrated as cut
away along the optical axis 4-21.
[0411] The electron gun 4-40 of the illustrated embodiment has a
structure of rotation symmetry around the optical axis 4-21 and
comprises the ring-shaped cathode 4-29 for emitting the primary
electron beam defining the hollow beam from the tip portion
thereof, the anode 4-22, 4-26 for controlling the direction of the
hollow beam emitted from the cathode 4-29 and the Wehnelt 4-22,
4-25 for controlling the beam current value and the convergence
condition of the beam, as already described.
[0412] The cathode 4-29 is centered around the optical axis 4-21
and extends circumferentially around the optical axis 4-21. The
cathode 4-29 comprises an annular support section 4-29a extending
in parallel with the optical axis 4-21 in the up-and-down direction
in the drawing, an annular step section 4-29b extending inward in
the radial direction from the bottom end of the support section
4-29a and an annular emitter section 4-29c extending in parallel
with the optical axis 4-21 from the inner end of the step section
4-29b, wherein said support section 4-29a, step section 4-29b and
emission section 4-29c are together formed as an integral element.
The support section 4-29a is carried by the Wehnelt 4-24 via an
annular insulating spacer 4-32 and the support section 4-29a
supports the emitter section 4-29c via the step section 4-29c. The
emitter section 4-29c defines a tapered tip portion 4-29d in its
bottom end and is adapted to emit a hollow beam in a circular ring
configuration from this tip portion 4-29d.
[0413] The cathode 4-29 is made of hafnium (Hf) assuming a
ring-shape whose end surface has been sharpened so that the
emission of electrons takes effect exclusively from the tip portion
4-29d. The cathode 4-29 may be made of sintered compact of
LaB.sub.6, Ta or the like.
[0414] The anode 4-22, 4-26 is centered around the optical axis
4-21 and comprises an inner anode 4-22 and an outer anode 4-26. The
inner anode 4-22 is disposed in the inside with respect to the
cathode 4-29, while the outer anode 4-26 is disposed in the outside
with respect to the cathode 4-29.
[0415] The inner anode 4-22 is grounded and thus has a potential of
zero, defining a ground electrode. On the other hand, the outer
anode 4-26 is adapted to be applied with a voltage of any desired
value, wherein a potential difference produced between the inner
anode 4-22 and the outer anode 4-26 can control the direction of
the hollow beam emitted from the cathode 4-29.
[0416] The inner anode 4-22 comprises a zero potential electrode
section 4-22a for controlling the direction of the hollow beam and
a support section 4-22b for producing the zero potential over the
optical axis, said zero potential electrode section 4-22a and said
support section 4-22b together defining an integral element. The
support section 4-22b is formed into a circular cylindrical
configuration extending in one direction in parallel with the
optical axis 4-21 and fixed to the housing of the electron beam
apparatus by using a member that is not shown in the drawing. The
zero potential electrode 4-22a is formed into an annular and flat
plate extending from the bottom end of the support section 4-22b in
the direction orthogonal to the optical axis 4-21 and outwardly in
the radial direction.
[0417] The outer anode 4-26 is disposed on the radially outside
with respect to the inner anode 4-22 and extends circumferentially
around the optical axis 4-21, thus defining an annular structure.
Further, the outer anode 4-26 is disposed on the radially outside
with respect to the inner anode 4-22 with a space placed
therebetween, which defines an annular path 4-22 allowing the
hollow beam to pass therethrough.
[0418] The outer anode 4-26 comprises an electrode section 4-26a
for controlling the direction of the hollow beam and a support
section 4-26b for supporting the electrode section 4-26a, said zero
potential electrode section 4-22a and said support section 4-26b
together defining an integral element as insulated from each
other.
[0419] The support section 4-26b is formed into a circular cylinder
extending in parallel with the optical axis 4-21 and fixed to the
housing of the electron beam apparatus as insulated therefrom by
using a member that is not shown in the drawing. The support
section 4-26b of the outer anode 4-26 extends along and in parallel
with the support section 4-22b of the inner anode 4-22. Further,
the support section 4-26b is disposed radially outside of the
support section 4-22b with a space placed therebetween, in which
the cathode 4-29, the Wehnelt 4-24, 4-25 and other elements are
arranged.
[0420] The electrode section 4-26a is formed into an annular and
flat plate extending from the bottom end of the support section
4-26b in the direction orthogonal to the optical axis 4-21 and
inward in the radial direction. Further, the electrode section
4-26a is opposite to the flat-plate section 4-22a of the inner
anode 4-22 to be flush therewith via the annular path 4-22c
interposed therebetween.
[0421] The inner anode 4-22 is grounded or earthed as explained
previously, and this arrangement prevents the potential of the
electron gun 4-40 from affecting the locus of the secondary
electrons on the optical axis. The outer anode 4-26 is insulated
from the inner anode 4-22, and so the application of the voltage
different from the ground to the outer anode 4-26 can control the
hollow beam defining the primary electron beam appropriately such
that the emission of the beam can be directed to the inward 4-31
direction or the outward 4-30 direction and/or the beam can be
formed into a convergent beam or a divergent beam. In this
connection, if the beam is to be guided in the direction of 4-31, a
negative voltage should be applied to the outer anode 4-26, or if
the beam is to be guided in the direction of 4-30, a positive
voltage should be applied to the outer anode 4-26. In this way, the
annular path 4-22c has a certain width in the radial direction so
as to permit the control for changing the direction of the hollow
beam to be carried out with some allowable angle range. The cathode
4-29 is positioned such that the tip portion thereof 4-29d is in
the same radial position as the annular path 4-22 so that the angle
range determining the direction of the hollow beam can be changed
as much as possible.
[0422] The Wehnelt 4-24, 4-25 is formed into an annular
configuration centered around the optical axis 4-21, extending in
parallel with the optical axis 4-21 with its width expanded toward
the bottom in the drawing.
[0423] The Wehnelt 4-24, 4-25 comprises an inner Wehnelt 4-24 and
an outer Wehnelt 4-25. The inner Wehnelt 4-24 is disposed in the
inside with respect to the cathode 4-29, and the outer Wehnelt 4-25
is disposed on the outside with respect to the cathode 4-29.
[0424] The inner Wehnelt 4-24 comprises an electrode section 4-24a
for controlling the emission of the primary electron beam and a
support section 4-24b for supporting the electrode section 4-24a,
said electrode section 4-24a and said support section 4-24b
together defining an integral element. The support section 4-24b
comprises a circular cylindrical section 4-24b1 extending in
parallel with the optical axis 4-21 and a truncated cone section
4-24b2 extending from the bottom end of the circular cylindrical
section at an angle toward the radially inward direction. The
electrode section 4-24a defines a circular cylindrical
configuration extending from the bottom end of the truncated cone
section 4-24b2 in parallel with the optical axis 4-21.
[0425] The outer Wehnelt 4-25 has an electrode section 4-25a for
controlling the emission of the primary electron beam and a support
section 4-25b for supporting the electrode section 4-25a, said
electrode section 4-25a and said support section 4-25b together
defining an integral element. The electrode section 4-25a is
supported by the inner Wehnelt 4-24 via an insulation spacer that
is not shown in the drawing. The support section 4-25b is disposed
on the radially outside with respect to the support section 4-24b
of the inner Wehnelt 4-24 and defines a space therebetween, in
which the tip portion 4-29d of the cathode is arranged. The support
section 4-25b comprises a circular cylindrical section 4-25b1
extending in parallel with the optical axis 4-21 and a truncated
cone section 4-25b2 extending from the bottom end of the circular
cylindrical section at an angle toward the radially outward
direction. Thus, the truncated cone section 4-25b2 of the outer
Wehnelt 4-25 and the truncated cone section 4-24b2 of the inner
Wehnelt 4-24 together secure a space expanding toward downstream
side of the tip portion 4-29d of the cathode so as to prevent the
divergence of the hollow beam emitted from the tip portion 4-29d of
the cathode.
[0426] The configuration of the Wehnelt 4-24, 4-25 may be
determined through the simulation. The Wehnelt 4-24, 4-25 can be
used to control the primary electron beam in a similar manner to
the anode 4-22, 4-26 by insulating the inner Wehnelt 4-24 from the
outer Wehnelt 4-25 and applying a voltage different from the ground
to the outer Wehnelt 4-25 so that the emission of the primary
electron beam can be guided in the inward direction 4-31 or outward
direction 4-30. The control of the emission direction of the
primary electron beam is carried out only by the anode 4-22, 4-26.
The Wehnelt 4-24, 4-25 has a function for controlling the beam
amount and preventing the divergence of the beam.
[0427] The electron gun 4-40 may further comprise a sub-cathode
4-28 and a shield 4-27 for the sub-cathode 4-28. The sub-cathode
4-28 has an annular configuration centered around the optical axis
4-21 and is disposed on the radially outside with respect to the
cathode 4-29. The sub-cathode 4-28 is made of tungsten filament and
is disposed on the outside with respect to the cathode 4-29 with a
certain distance placed therebetween in the circumferential
direction centered on the optical axis 4-21. The shield 4-27 for
the sub-cathode 4-28 is a shield serving for directing all of the
electrons from the sub-cathode 4-28 into the cathode 4-29 and may
be applied with a voltage of 20.1 kV, for example.
[0428] The insulation spacer 4-23 couples the inner Wehnelt 4-24
with the inner anode 4-22 and the insulation spacer 4-32 couples
the cathode 4-29 with the inner Wehnelt 4-24. The reason they have
different diameters resides in that the longer insulation length
should be secured so as to avoid discharging.
[0429] A general operation of the electron gun 4-40 according to
the illustrated embodiment will now be described.
[0430] A voltage around -20 kV is applied to the cathode 4-28 to
cause an electro-bombardment toward the cathode 4-29 (the
electro-bombardment method is one of the known methods for
degassing the components such as an electrode in an ion source for
an ionization vacuum gauge or a mass spectrometer with a
hot-cathode. A detailed description can be found in the Japanese
Patent Laid-open Publication No. Hei 06-150875, for example.) so as
to induce a current flow of about 1 mA to thereby heat the cathode
4-29 with the power of
(20-4.5).times.10.sup.3.times.1.times.10.sup.-3 W. In this stage,
the cathode 4-29 is applied with the voltage of -4.5 kV. Through
this procedure, the primary electron beam is emitted from the
cathode. The emission direction of the primary electron beam can be
controlled by applying the voltage different from the ground to the
outer anode 4-26.
[0431] Since such an electron gun 4-40 as described above has a
large cathode 4-29 area on the order of 10
.mu.m.times.2.pi..times.3 mm.apprxeq.2.times.10.sup.-1 mm.sup.2 and
advantageously the tip portion of the cathode 4-29 can be applied
with an intensive electric field, the primary electron beam of high
intensity can be extracted. Therefore, with such an electron gun,
it becomes possible to irradiate the beam having the beam current
of some mA onto an area having a diameter as large as 200 .mu.m
without any problem, which allows the image projection optical
system to be actuated in the very bright environment and thus helps
increase the number of electrons per pixel, resulting in an image
of good S/N ratio to be obtained. Furthermore, since this
irradiation method can eliminate the use of the E.times.B
separator, there would be induced no chromatic aberration from
deflection in the image of secondary electron beam which otherwise
could have caused by the E.times.B separator. Since this
arrangement further eliminates the use of the obliquely installed
primary optical system, the mechanical resonance frequency can be
increased to make the apparatus more robust to the vibrations.
Further, as clearly seen from FIG. 15, the primary electron beam
has its passage in the outside to the locus 7 of the secondary
electron beam, and so there would be no chance that the space
charge from the primary electron beam stimulates the out-of-focus
of the secondary electron beam. The omission of the primary optical
system can reduce costs by just that much.
Sixth Example
[0432] FIG. 17 shows an electron beam apparatus of image projection
optical system focusing a beam into an image according to another
embodiment of the fourth invention. Elements similar to those in
the first embodiment are designated by the same reference numerals
and the detailed explanation thereof is hereby omitted but the
description is only given of different points. The electron beam
apparatus according to the second embodiment is different in
comparison with the first embodiment in that a different type of
electron gun is used. As it is, the electron gun according to the
illustrated embodiment will now be described with reference to FIG.
18.
[0433] Although the electron gun 4-40 of the first embodiment has
employed the configuration in which the cathode 4-29 is heated by
the sub-cathode 4-28 so as to emit the primary electron beam, the
present embodiment has employed a photo-cathode 4-29 taking
advantage of photoelectric effect to emit the primary electron
beam. Owing to this, an electron gun 4-50 according to the present
embodiment is different from the electron gun 4-40 according to the
first embodiment in the configuration and material of the cathode
4-29. Further, instead of the sub-cathode 4-28 and the shield 4-27,
the electron gun 4-50 comprises an optical fiber 4-33, a
longer-wave cut filter 4-35 and a high pressure mercury lamp
4-37.
[0434] A cathode 4-29' of the electron gun 4-50 according to the
second embodiment is centered on the optical axis 4-21 and extends
circumferentially around the optical axis 4-21. The cathode 4-29'
comprises an annular support section 4-29a' extending in parallel
with the optical axis 4-21 in the up-and-down direction in the
drawing, a truncated cone section 4-29b extending at an angle
toward the radially inward direction from the bottom end of the
support section 4-29a', and an annular emitter section 4-29c'
extending in parallel with the optical axis 4-21 from the inner end
of the truncated cone section 4-29b', said support section 4-29a',
truncated cone section 4-29b' and emitter section 4-29c' defining
an integral element. The support section 4-29a' is supported by the
Wehnelt 4-24 via the annular insulation spacer 4-32 and it supports
the emitter section 4-29c' via the truncated cone section 4-29b'.
The emitter section 4-29c' defines a tapered tip portion 4-29d' in
the bottom end thereof, from which a hollow beam in a circular ring
configuration is emitted. The cathode 4-29' is made of silica glass
with its tip portion coated with platinum in the ring-shape and
with its inner and outer sides vapor-deposited with aluminum.
[0435] The optical fiber 4-33 is connected at its one end to the
top end of the support section 4-29a' of the cathode 4-29' while
the other end thereof is connected to the long-wave cut filter
4-35. Further, the high pressure mercury lamp 4-37 is coupled to
the long waver cut filter 4-35.
[0436] The light emitted from the high pressure mercury lamp 4-37
has its long-wave components filtered out by the long-wave cut
filter 4-35 and then guided through the optical fiber 4-33 into the
cathode 4-29'. When the light enters the cathode 4-29' and thus the
photoelectric material, platinum, the photoelectric effect is
developed and thereby the primary electron beam is emitted from the
tip portion 4-29d'.
[0437] The use of the photo-cathode can solve the problem of
temperature rise resultant from the heating of the cathode 4-29 to
induce the emission of the primary electron beam.
Seventh Example
[0438] An overview of an electron beam apparatus according to an
embodiment of the fifth invention will now be presented.
[0439] FIGS. 19 and 20 show a position measuring device for a
sample table of an electron beam apparatus according to an
embodiment of the present invention. FIG. 19 is a plan view and
FIG. 20 is a schematic sectional view taken along the A-A' line of
FIG. 19.
[0440] The position measuring device of the illustrated embodiment
is provided to measure a position of the sample table of the
electron beam apparatus.
[0441] The electron beam apparatus irradiates a plurality of
primary electron beams having a plurality of optical axes over a
sample 5-22 loaded on a sample table 5-32 adapted to be movable
along the x-y plane having the x-axial direction and the y-axial
direction.
[0442] The position measuring device of the illustrated embodiment
comprises a laser source 5-1 for emitting a laser beam 5-400, a
first splitting device 5-2 for splitting the laser beam 5-400
emitted from the laser source 5-1 into two separate laser beams
5-402 and 5-404, a first measuring device 5-200 for measuring the
position of the sample table 5-32 along the x-axial direction by
using one of the two separate laser beams or a first laser beam
5-402, a second measuring device 5-300 for measuring two positions
of the sample table 5-32 along the y-axial direction by using the
other 5-404 of the two separate beams, and a controller 5-100 for
detecting a rotational amount of the sample table 5-32 in the x-y
plane based on the measurement from the second measuring device
5-300.
[0443] The first splitting device 5-2 comprises a beam splitter 5-2
in the present embodiment. The beam splitter 5-2 is operable to
split the laser beam emitted from the laser source 5-1 into the
first laser beam 5-402 and the second laser beam 5-404.
[0444] The first measuring device 5-200 comprises a x-movable laser
mirror 5-12 serving as a first reflecting mirror disposed along the
y-axial direction in the sample table 5-32, a first guiding device
5-9 for guiding the first laser beam 5-402, that has been split in
the beam splitter 5-2, toward the x-movable laser mirror 5-12, a
laser receiver 5-3 serving as a first receiver for receiving the
first laser beam reflected by the first reflecting mirror 5-12, and
a x-directional stationary laser mirror 5-11 serving as a first
stationary mirror installed on a sidewall of an objective lens 5-20
of the electron beam apparatus disposed above the sample table
5-32, at a location on said sidewall defined in the x-movable laser
mirror 5-12 side thereof.
[0445] The first guiding device 5-9 comprises the first beam
splitter 5-9 in the illustrated embodiment. The beam splitter 5-9
is operable to guide the first laser beam 5-402 split in the beam
splitter 5-2 toward the first reflecting mirror 5-12, while
splitting a fourth laser beam 5-406 from the first laser beam
5-402.
[0446] The first measuring device further comprises a laser mirror
5-33 serving as a first laser mirror for reflecting the fourth
laser beam 5-406 to be irradiated toward the x-directional
stationary laser mirror 5-11.
[0447] The position measuring device of the present embodiment
further comprises a laser reflector 5-4 for reflecting the second
laser beam 5-404 split in the beam splitter 5-2, toward the second
measuring device 5-300. The laser reflector 5-4 guides the other
laser beam 5-404 split in the beam splitter 5-2 and directed along
the y-axial direction, into the second measuring device 5-300. The
position measuring device of the illustrated embodiment includes
the laser reflector 5-4 for the reason that it has only one laser
source.
[0448] A second measuring device 5-300 comprises a beam splitter
5-5 for splitting a third laser beam 5-410 from the second laser
beam 5-404 reflected by the laser reflector 5-4, a y-moving laser
mirror 5-13 serving as a second reflecting mirror disposed along
the x-axial direction in the sample table 5-32, a laser mirror 5-7
serving as a third guiding device for guiding the third laser beam
5-410 split in the beam splitter 5-5, toward the y-movable laser
mirror 5-13, a laser receiver 5-6 serving as a second receiver for
receiving the second laser beam 5-404 reflected by the y-movable
laser mirror 5-13, and a laser receiver 5-8 serving as a third
receiver for receiving the third laser beam 5-410 reflected by the
y-moving laser mirror 5-13. The beam splitter 5-5 is also serving
as a second guiding device for guiding the second laser beam 5-404
toward the y-moving laser mirror 5-13.
[0449] The second measuring device 5-300 comprises a y-directional
stationary laser mirror 5-60 serving as a second stationary mirror
installed on a sidewall of the objective lens 5-20 of the electron
beam apparatus, at a location on said sidewall defined in the
y-moving laser mirror 5-13 side thereof, a beam splitter 5-42 for
guiding the second laser beam 5-404 from the beam splitter 5-5
toward the y-moving laser mirror 5-13, while splitting a fifth
laser beam 5-412 from the second laser beam 5-404, a second laser
mirror 5-62 for reflecting the fifth laser beam 5-412 to be
irradiated toward the y-directional stationary laser mirror 5-60, a
beam splitter 5-41 serving as a third beam splitter for guiding the
third laser beam 5-410 reflected by the laser mirror 5-7, toward
the y-moving laser mirror 5-13, while splitting a sixth laser beam
5-414 from the third laser beam 5-410, and a third laser mirror
5-63 for reflecting the sixth laser beam 5-414 to be irradiated
onto the y-directional stationary laser mirror 5-60.
[0450] The electron beam apparatus for evaluating the sample 5-22
comprises eight optical axes indicated by 5-23, 5-24, 5-25, 5-26,
5-83, 5-84, 5-85 and 5-86 above the sample 5-22 fixedly loaded on
the sample table 5-32. A set of elements including an electron gun
consisting of a ZrO/W cathode 5-14, a Schottky shield 5-15 and an
anode 5-16, a condenser lens 5-17 capable of controlling a rotation
of a primary electron beam emitted from the electron gun, a
multi-aperture 5-31, an NA aperture 5-18, a reduction lens 5-19 and
an objective lens 5-20 is arranged along each of the eight optical
axes on a single sample 5-22. In the evaluation of the sample 5-22,
the eight primary electron beams are driven concurrently in the
x-direction to perform the scanning motion, while driving an
actuator, though not shown, so as to move the sample table 5-32
continuously in the y-direction, and secondary electron beams
emanating from the scanning points are accelerated by an
axisymmetric electrode 5-21. The axisymmetric electrode 5-21 is
disposed below the objective lens 5-20 and formed to be
axisymmetric in the vicinity of each optical axis. The secondary
electron beams accelerated by the axisymmetric electrode 5-21 are
converged by the objective lens 5-20 having a gap defined in the
sample 5-22 side thereof and deflected by an E.times.B separator,
though not shown, in the direction deviating from the optical axis
into corresponding detectors, 5-27, 5-28, 5-29, 5-30, 5-87, 5-88,
5-89, 5-90, where they are detected. Four secondary electron beams
which are equally spaced from any adjacent beams when projected on
the y-axis are produced for each optical axis, and each of those
four secondary electron beams is detected independently by each
associated detector. The SEM image by 32 channels is generated from
secondary electron signal by 8.times.4=32 channels from those
detectors, so that the evaluation of the sample with high
throughput can be carried out, while at the same time, movement of
the sample table can be reduced because the sample table is only
required to move in the x-direction by a distance equivalent to an
interval between the adjacent optical axes.
[0451] In the position measuring device according to the present
embodiment, the x-movable laser mirror 5-12 is formed by a surface
of the sample table oriented in parallel with the y-axis, which has
been mirror polished, and the y-movable laser mirror 5-13 is formed
by a surface of the sample table oriented in parallel with the
x-axis, which has been mirror polished. When the sample table is
made of silicon carbide ceramics, which include many voids, such a
material having substantially no void, including ZrO, highly
purified alumina and silica, may be first attached onto the side
surface of the sample table and then the resultant surface may be
mirror polished.
[0452] The laser beam 5-400 emitted from the laser oscillator 5-1
is split by the beam splitter 5-2 into the first laser beam 5-402
that is advanced straight for the x-measurement and the second
laser beam 5-404 that is reflected in the y-axial direction for the
y-measurement. The first laser beam 5-402 is split by the beam
splitter 5-9 into two beams, the first laser beam 5-402 and the
fourth laser beam 5-406. The fourth laser beam 5-406 is reflected
at a right angle by the laser mirror 5-33 and irradiated on the
stationary laser mirror 5-11 installed on the outside of the
objective lens 5-20. The fourth laser beam 5-406 reflected by the
stationary laser mirror 5-11 is further reflected by the laser
mirror 5-33 to be advanced straight through the beam splitter 5-9
into the laser receiver 5-3. On the other hand, the first laser
beam 5-402 transmitted through the beam splitter 5-9 is reflected
by the x-moving laser mirror 5-12 installed in the sample table
5-32 and then reflected by the beam splitter 5-9 to enter the laser
receiver 5-3. The speed of the moving mirror can be measured by the
interference of the fourth laser beam 5-406 from the stationary
laser mirror 5-11 with the first laser beam 5-402 from the x-moving
laser mirror 5-12. This speed may be integrated by a counter
installed in the laser receiver 5-3. More specifically, a
fluctuation of the signal resultant from the interference of the
first laser beam 5-402 from the x-moving laser mirror 5-12 with the
fourth laser beam 5-406 reflected by the stationary laser mirror
5-11 is converted into a pulse form, from which the speed of the
moving mirror is calculated and the calculated speed is further
integrated so as to determine a travel distance of the sample table
in the x-axial direction.
[0453] On the other hand, the second laser beam 5-404 split by the
beam splitter 5-2 is reflected at a right angle by the laser
reflector 5-4 and split by the beam splitter 5-5 into two beams,
the second laser beam 5-404 and the third laser beam 5-410.
[0454] The second laser beam 5-404 is split by the beam splitter
5-42 into the second laser beam 5-404 and the fifth laser beam
5-412 as shown in FIG. 21. The fifth laser beam 5-412 is reflected
at a right angle by the second laser mirror 5-62 and irradiated on
the y-directional stationary laser mirror 5-60 installed on the
outside of the objective lens 5-20. The fifth laser beam 5-412
reflected by the stationary laser mirror 5-60 is further reflected
by the second laser mirror 5-62 and the beam splitter 5-42 and
advanced straight through the beam splitter 5-5 into the laser
receiver 5-6. On the other hand, the second laser beam 5-404
transmitted through the beam splitter 5-42 is irradiated onto and
thus reflected by the y-moving laser mirror 5-13 installed on the
sample table 5-32 and advanced straight through the beam splitters
5-42 and 5-5 into the laser receiver 5-6. A fluctuating signal is
produced from the interference of the laser beam from the
y-directional stationary laser mirror 5-60 with the laser beam from
the y-moving laser mirror 5-13, and this signal is shaped into the
pulse form, which is in turn counted to determine the speed of the
movable mirror. This speed is integrated by the counter installed
in the laser receiver 5-6 and similarly the travel distance of the
sample table in the y-axial direction is calculated.
[0455] Further, although FIG. 21 only shows an optical path of the
second laser beam, behind that of the second laser beam, the third
laser beam 5-410 follows a similar optical path as shown in FIG.
22. The third laser beam 5-410 is reflected at a right angle by the
beam splitter 5-7 and then split by the beam splitter 5-41 into the
third laser beam 5-410 and the sixth laser beam 5-414. The sixth
laser beam 5-414 is reflected at a right angle by the third laser
mirror 5-63 and then reflected by the y-directional stationary
laser mirror 5-60 installed on the outside of the objective lens
5-20, and the beam is further reflected by the third laser mirror
5-63 and the beam splitter 5-41 and then advanced straight through
the beam splitter 5-7 into the laser receiver 5-8. On the other
hand, the third laser beam 5-410 transmitted through the beam
splitter 5-41 is reflected by the y-moving laser mirror 5-13
installed on the sample table 5-32 and advanced straight through
the beam splitter 5-41 and 5-7 into the laser receiver 5-8. The
fluctuating signal is obtained by the interference of the laser
beam from the y-directional stationary laser mirror 5-60 with the
laser beam from the y-moving laser mirror 5-13, and the obtained
signal is shaped into the pulse form, which is in turn counted to
thus measure the speed of the moving mirror. This speed is
integrated by the counter installed in the laser receiver 5-8 and
similarly the travel distance of the sample table in the y-axial
direction can be calculated.
[0456] The values calculated in the laser receivers 5-3, 5-6, 5-8
are sent to the controller 5-100, which determines the rotational
amount of the sample table 5-32 within the x-y plane based on the
calculated values of the positions of the sample table 5-32
measured at the two locations by the y-axis directional laser
beam.
[0457] The correction method for Abbe's error according to the
present invention will now be described. Reference numerals 5-41,
5-42 found in FIG. 23 designate the beam splitter 5-41, 5-42 shown
in FIG. 19, each of which is composed of a translucent mirror for
splitting the laser beam into two beams, one directed to the
y-directional stationary laser mirror 5-60 installed on the outside
of the objective lens 5-20 and the other directed to the y-moving
laser mirror 5-13 on the sample table 5-32. Reference numeral 5-43
presents an ideal orientation of the sample table 5-32, and
reference numeral 5-44 presents the orientation of the sample table
5-32 at the moment when the Yaw motion of the sample table has been
triggered from the tolerance in moving the sample. The difference
in readings of the y-coordinate of the sample table 5-32 measured
by the laser receivers 5-8 and 5-6 is divided by the value of
spacing, 1, between the beam splitters 5-41 and 5-42, and the
rotational amount .delta.(radian) for the sample table 5-32 can be
calculated.
[0458] Assuming that a distance in the y-axial direction between
adjacent optical axes (e.g., the optical axis 5-83 and the optical
axis 5-23) is denoted as "2b" and a distance in the x-axial
direction between said adjacent optical axes is denoted as "a". It
is also assumed that the rotational amount .delta. of the sample
table 5-32 is measured in a clockwise rotation. A difference in the
readings of the coordinate by the x-directional laser measuring
device 5-3 and the y-directional laser measuring device 5-8 can be
determined in the following manner. Although the sample table is
rotated by .delta. in the clockwise direction in FIG. 23, there is
no error produced from the rotation at the intersection 5-500 of
the x-laser axis 5-3 with the y-laser axis 5-8. The error induced
by the rotation at a certain point increases as it goes farther
from the intersection 5-500.
[0459] The sample table coordinate subject to the irradiation of
the optical axis 5-83 is represented by the coordinate 5-503 that
has been rotated in the counter-clockwise direction by .delta.
around the intersection 5-500 from the readings of the laser
measuring devices 5-3 and 5-8. If the value of .delta. is small,
the triangle (5-83, 5-503, 5-502) is analogous to the triangle
(5-500, 5-501, 5-502), and the angle (5-503, 5-83, 5-502) is
represented by .DELTA.. The distance between the point 5-83 and the
point 5-503 is:
{square root over ((2.5a).sup.2+b.sup.2.delta.)} (Equation 1)
[0460] The quantity of correction for the y-coordinate of the
optical axis 5-83 is determined from FIG. 24 in the following
equation:
b - ( 3.5 a ) 2 + b 2 .delta. cos .DELTA. = b - ( 3.5 a ) 2 + b 2
.delta. 3.5 a b - ( 3.5 a ) 2 + b 2 = b - 3.5 a .delta. ( Equation
2 ) ##EQU00003##
[0461] On the other hand, the quantity of correction for the
x-coordinate is determined from FIG. 24 in the following
equation:
( 3.5 a ) 2 + b 2 .delta. sin .DELTA. = ( 3.5 a ) 2 + b 2 .delta. b
( 3.5 a ) 2 + b 2 = b .delta. ( Equation 3 ) ##EQU00004##
[0462] The quantity of correction for the y-coordinate of the
optical axis 5-23 is similarly determined to be
-b-2.5a.delta.,
and the quantity of correction for the x-coordinate turns to be
+b.delta..
[0463] The correction amount to the y-coordinate for the optical
axis 5-84 is determined to be
b-1.5a.delta.,
[0464] and the correction amount to the x-coordinate turns to be
-b.delta..
[0465] The quantity of correction for the y-coordinate of the
optical axis 5-24 is determined to be
-b-0.5a.delta.,
[0466] and the quantity of correction for the x-coordinate turns to
be
b.delta..
[0467] The quantity of correction for the y-coordinate of the
optical axis 5-85 is determined to be
b-0.5a.delta.,
[0468] and the quantity of correction for the x-coordinate turns to
be
-b.delta..
[0469] The quantity of correction for the y-coordinate of the
optical axis 5-25 is determined to be
-b+1.5a.delta.,
and the quantity of correction for the x-coordinate turns to be
b.delta..
[0470] The quantity of correction for the y-coordinate of the
optical axis 5-86 is determined to be
b+2.5a.delta.,
[0471] and the quantity of correction for the x-coordinate turns to
be
-b.delta..
[0472] The quantity of correction for the y-coordinate of the
optical axis 5-26 is determined to be
b+3.5a.delta.,
[0473] and the quantity of correction for the x-coordinate turns to
be
b.delta..
Eighth Example
[0474] FIG. 25 is a schematic diagram illustrating an electron
optical system used in a pattern evaluation method in a first
embodiment of the sixth invention. An electron beam emitted from an
electron gun 1 is axially aligned by an axial-aligning deflector 27
with a condenser lens 2 and a multi-aperture 3. A beam having
passed through the multi-aperture is axially aligned by an
axial-aligning deflector 28 with an NA aperture 4 and a reduction
lens 5. The multi-aperture forms the beam into a reduced image at
the point of 26 and the beam is further focused by an objective
lens 11 into an image of a multi-beam consisting of 6 to 20 beam
elements on a sample 12. The multi-beam is driven by a two-stage of
deflectors 29 and 10 to scan the sample 12 in on-axial direction
across a range equivalent to the width of a stripe, while the
scanning operation by the deflector and the moving of the sample
table are carried out in the other-axial direction, to thereby
obtain a two-dimensional image. Secondary electrons emanating from
the sample 12 are accelerated and converged by the objective lens
11, and separated from the primary optical system by an E.times.B
separator 9 into the secondary optical system, where an electron
image is magnified by magnifying lenses 13 and 14, multiplied by a
MCP detector 15, absorbed by a multi-anode 16, and converted into
an electric signal by a resistor 17, with which a two-dimensional
image is formed by an amplifierA/D converter and image forming
circuit 18 and then stored in a memory of a CPU 7. In this regard,
the stripe designates an area available for the evaluation provided
by one time of continuous movement of the stage (sample carrier)
and defines an area equivalent to a product of the scanning width
by the deflector and the size of the sample in the other-axial
direction, which contains a pattern subject to the evaluation on
the inside and the interface thereof.
[0475] Before starting the evaluation of the sample, the scanning
with the multi-beam 20-25 is applied to a L-shaped marker 19 (shown
in the lower right section of FIG. 25) prepared always on the
stage, and the secondary electrons emanating from each beam are
detected by each detector, with which each small-sized
two-dimensional image is produced. The resultant images are joined
together based on the design values for respective positions of the
multi-beam.
[0476] Assuming that such a pattern as represented by 8 (shown in
the left-hand side of FIG. 25) was obtained as a result of the
joining operation of the images, a joint site indicated by 30 is
found between adjacent small-sized two-dimensional images. It can
be determined from an amount of discontinuity in the joint site how
much is the actual deviation in the x-direction from an original
design value. If the actual deviation from the design value in the
x-coordinate indicative of the position of each beam of the
multi-beam can be successfully corrected, the deviation in 30 will
be eliminated. For example, in the case indicated by 30, where the
pattern produced by the lower beam is offset in the right-hand
direction with respect to the upper pattern, the x-coordinate of
the lower beam should be offset in the left-hand direction over the
design value. The correction to the actual deviation can be
performed while viewing the image.
[0477] A y-directional spacing between beams in the multi-beam will
now be described. Assuming in this system that the pixel size is
100 nm, the beam spacing is 1 .mu.m and the number of beams is 10,
an exemplary signal waveform obtained by scanning the pattern, P,
having the y-directional dimension of 9 .mu.m is shown in the lower
section of FIG. 26. The entire position of the multi-beam 31-40 is
fine-tuned in the y-direction so that the amplitude of the waveform
of the signal from the top beam 31 may be equivalent to 50% of the
amplitude of the waveform from the intermediate beams 32-39, as
shown in FIG. 26. That is, if the amplitude of the signal waveform
from the top beam 31 is smaller than the 50% amplitude, this
indicates that the beam 31 is scanning the region above (out of)
the pattern, and so tuning should be performed to move the entire
beam downward. Through this operation, the beam position is tuned
such that the signal waveform from the top beam 31 defines the
amplitude of 50% (i.e. such that a half of the top beam 31 covers
the edge of the pattern), and then the waveform from the bottom
beam 40 is examined. At this time, it may be found that if the
amplitude of the waveform from the beam 40 exceeds 50% of the
amplitude of the waveform from the intermediate beams 32-39 as
indicated by the solid line, then the spacing between beams in the
y-direction is too small, while on the contrary, if the amplitude
of the waveform from the beam 40 is below 50% as indicated by the
dotted line, the spacing is too large. That is, the spacing in the
y-direction between the beams in a plurality of beams has been
accurately measured. If the spacing is too narrow, the exciting
voltage of the reduction lens should be increased so as to shorten
the focal distance of this lens and make the reduction ratio
approaching to zero, or if the spacing is too wide, the control
should be provided to make the reduction ratio approaching to 1.
Since this measuring method employs the measurement multiplied by
10 to evaluate the spacing between adjacent beams, the adjustment
of high precision can be provided. In this way, the present
invention has successfully achieved the accurate matching of the
beam spacing 1 .mu.m with the pixel size 100 nm multiplied by 10
(integer multiple).
[0478] In this way, the distance between the beams is adjusted, and
in the condition that the adjusted beam distance has been stored,
the small-sized two-dimensional images are obtained and joined in
accordance with the distance between the beams that has been
already stored as described above to thereby successfully form a
large-sized two-dimensional image of high precision.
Ninth Example
[0479] FIG. 27 shows a second example of the sixth invention.
[0480] If a single beam is used for the scanning as practiced in
the prior art, from the fact that the x-coordinates of the starting
points of the scanning, 41, 42, 43 and the x-coordinates of the end
points of the scanning, 47, 48, 49, are respectively the same for
the first scanning operation (starting point 41, scanning 44, end
point 47) and the second and the third scanning operations as shown
in FIG. 27(A), the interfaces 50, 51 may be straight lines parallel
with the y-axis. However, in use of the multi-beam, where the
respective beams have the different x-directional coordinates as
indicated by 20-25 in FIG. 25, the x-coordinates of the starting
points 31-40 of those beams are different. It is a matter of course
from the same scanning time period that the x-coordinates of their
end points of scanning are also all different. Taking this into
account, it is suggested that the interface between the stripe in
the left-hand side (white) and the stripe in the right-hand side
(with scanning lines) should be in a concavo-convex configuration
corresponding to the beam positions in the x-direction, as shown in
FIG. 27(B). As a result, there would be no more chance of any
overlapped scanning and thus any excessive irradiation, and any
regions to be left not-evaluated due to insufficient scanning. To
obtain the two-dimensional image in the scanning method of FIG. 27,
assuming that the position of the image obtained by the signal from
the beam of 31 is (0, 0), the images may be joined in such a manner
that the position of the small-sized image obtained by the signal
from the beam of 32 is shifted by (x.sub.1,2, y.sub.1,2) and the
position of the small-sized image obtained by the signal from the
beam of 33 is shifted by (x.sub.1,3, y.sub.1,3), generally by
(x.sub.i,i, y.sub.1,i).
Tenth Example
[0481] FIG. 28 shows a third example of the sixth invention.
[0482] This example illustrates a method for forming the
large-sized two-dimensional image from small-sized two-dimensional
images when the pattern 57 is to be evaluated by a plurality of
beams 51 to 56.
[0483] The y-directional distance between any adjacent beams of the
respective beams 51-56 is equal
(.DELTA.y.sub.51-52=.DELTA.y.sub.52-53=.DELTA.y.sub.53-54=.DELTA.y.sub.54-
-55=.DELTA.y.sub.55-56), for example, 1 .mu.m, and the
x-directional distance between the adjacent beams is also equal
(.DELTA.x.sub.51-52=.DELTA.x.sub.52-53=.DELTA.x.sub.54-55=.DELTA.x.sub.55-
-56), for example, 0.3 .mu.m, wherein the x-coordinates of the
beams 51 and 54 are equal (x.sub.51=x.sub.54).
[0484] As shown in FIG. 28(A), each of the beams 51-56 is driven to
make a scanning operation by the width of the stripe in the
x-direction, while moving the pixel by the distance between the
beams in the y-direction, and thereby the small-sized
two-dimensional images 51a-56a can be obtained from the signals
corresponding to respective beams. It is to be noted that the beam
56 resides out of the pattern and accordingly no corresponding
image exists. The large-sized two-dimensional image can be obtained
by making a correction to the distance between the beam positions
for the small-sized two-dimensional images. Taking the above
example of the beam positions by way of illustration, the
two-dimensional image 58 having a continuous pattern can be
obtained through the correction applied in such a way that, taking
the image obtained from the beam 51 as a reference, the image 52a
obtained from the beam 52 is shifted by 1 .mu.m in the y-direction
and by -0.3 .mu.m in the x-direction, the image 53a obtained from
the beam 53 is shifted by 2 .mu.m in the y-direction and by -0.6
.mu.m in the x-direction, the image 54a obtained from the beam 54
is shifted by 3 .mu.m in the y-direction and by 0 .mu.m in the
x-direction, and the image 55a obtained from the beam 55 is shifted
by 4 .mu.m in the y-direction and by -0.3 .mu.m in the x-direction.
It is a matter of course that also in this example, preferably the
spacing between respective beams 51-56 in the y-direction should be
adjusted to be an integer multiple of the pixel size, as described
previously.
[0485] Since the spacing between the beams of the multi-beam in the
direction of the continuous movement of the sample table is defined
by the integer multiple of the pixel size in this illustrated
embodiment, a small-sized two-dimensional image obtained from the
scanning with one beam and another small-sized two-dimensional
image obtained from the scanning with an adjacent beam can be
joined precisely in an accurate manner so as to create a
large-sized two-dimensional image.
Eleventh Example
[0486] FIG. 29 shows an electron optical system used in an
embodiment of the seventh invention. An electron gun 101 has a
single crystal LaB.sub.6 cathode having a radius of curvature of 30
.mu.m in the tip portion, from which an electron beam is emitted to
irradiate over a multi-aperture 102 disposed in the vicinity of the
optical axis to be formed into a multi-beam. The multi-beam from
the multi-aperture is converged by a condenser lens 103 to form a
crossover in an NA aperture 105, and then the multi-beam is
converged by a reduction lens 104, and further reduced by a first
objective lens 106 and a second objective lens 108 to be formed
into an image on a sample surface 109 while being driven by
electrostatic deflectors 142 and 143 to scan the sample surface.
Since an E.times.B separator 107 is disposed at a location
different from the point of image formation of the primary beam,
the chromatic aberration from the deflection is induced in the
primary beam. To avoid this, the present invention has set the
deflection amount by the electromagnetic deflector of the E.times.B
separator 107 as two times as large as the deflection amount by the
electrostatic deflector thereof to thereby prevent the deflection
chromatic aberration of the primary beam from being induced. In
this condition, to allow the beam to pass through the center of the
first objective lens 106, the pre-deflection is carried out by a
deflector 144. Further, assuming the trajectory of the principal
ray of the primary electron beam follows 110, it may pass through
the center of the second objective lens 108 but enter a location a
bit away from the optical axis on the sample 109. The secondary
electrons emitting from this site follow the trajectory indicted by
the dotted line 111 and are further deflected by the E.times.B
separator 107 into a secondary optical system 112. The spacing
between the beams is extended by a magnifying lens 113, and each
beam of the multi-beam is multiplied by a MCP 115, absorbed by a
multi-anode 116 and converted into a voltage signal by a resistor
118, which is in turn multiplied by 119 and A/D-converted into a
two-dimensional signal, which is stored in a memory 120. It is to
be noted that reference numeral 114 designates a deflector, 117 a
lead wire, 141 a detector fixing plate in FIG. 29. In addition,
FIG. 29 shows a plan view of the detector in the lower right
section thereof.
[0487] In this connection, in order to form a magnified image on an
incident plane of the MCP 115 by the magnifying lens 113, it is
necessary for the secondary electrons emitting from the sample 109
to form the magnified image at a position proximal to the principal
plane of the magnifying lens 113 with the aide of the lenses 108
and 106, and further it is necessary to form the magnified image of
the secondary electrons in the position proximal to the principal
plane of the magnifying lens 113 as described above specifically
under the lens condition for focusing the primary beam on the
sample 109 by the lenses 106, 108. This condition is referred to as
"the concurrent focusing condition of the primary and the secondary
beams".
[0488] The concurrent focusing condition of the primary and the
secondary beams will be determined by using FIG. 30.
[0489] FIG. 30 illustrates three different types of optical system
defining the common passage of the primary and the secondary beams,
wherein FIG. 30(A) shows a system including one-stage of objective
lens, FIG. 30(B) shows the same system as FIG. 29 and FIG. 30(C)
shows the system in which the objective lens includes an
electromagnetic lens. FIG. 30(B) corresponds to the system of FIG.
29, and FIGS. 30 (A) and (C) show variations of the system of FIG.
25.
[0490] FIG. 30(A) illustrates a case allowing for the common
passage of the primary and the secondary beams only through
one-stage of lens. Assuming that the typical primary beam used in
the prior art is of 0.3 kV or higher, the secondary electrons
accomplish its focal condition at a point immediately above the
objective lens 108 and before the E.times.B separator 107, implying
that the object point distance of the magnifying lens 113 is too
long, and so if the lens 113 is used as a magnifying lens, the
secondary optical system becomes too long. To place an image point
of the secondary beam near to 124 under the lens condition
satisfying the focal condition of the primary beam, it has been
found from a simple simulation that the landing energy of the
primary beam should be controlled to 300 V or lower. It is to be
noted that in the drawing, reference numeral 121 is a diagram of
the primary beam image formation, 122 is a diagram of the secondary
beam image formation and 123 is a first reduction image of the
multi-beam.
[0491] If the primary and the secondary beams have a common passage
through the lenses 106 and 108 as shown in FIG. 30(B), the
requirement of the landing energy to meet the concurrent focusing
condition of the primary and the secondary beams can be relaxed, so
that the landing energy of 600 V or lower for the primary electron
beam has still allowed the image point of the secondary electrons
to be focused at the location 124 before the magnifying lens 113.
If this landing energy is set at 600 V or higher, the locus 121 of
the primary beam exhibits divergence toward the top in the drawing,
resulting in a large diameter at the position of the lens 106,
which leads to an increase in aberration of the primary beam.
[0492] The description will now be directed to FIG. 30(C). In the
illustrated embodiment, the objective lens 108 has employed a
synthetic lens composed of an electromagnetic lens and an
electrostatic lens. The portion containing no ferromagnetic
material in the magnetic circuit, or the lens gap 125, is defined
in the sample side, and the z position producing a maximum on-axis
magnetic field of the lens is defined in the sample side with
respect to the gap. At the z position associated with the maximum
on-axis magnetic field, the beam is most intensively subject to the
focusing effect. An electrode 126 for applying a positive high
voltage is disposed in the vicinity of said z position so as to
reduce the (energy range/beam energy at the lens position) ratio to
thereby reduce the axial chromatic aberration. That is, said ratio
has been reduced by increasing the denominator. Since the lens
effect of the electromagnetic lens is in inverse proportion to the
square root of the beam energy and the lens effect of the
electrostatic lens is in inverse proportion to the beam energy,
therefore in this case, essentially the landing voltage of the
primary beam can be made considerably high as compared to the 300 V
of the case of (A) including only one-step of electrostatic lens.
It has been found as a result of the simulation that the landing
voltage of 500 V or lower can provide a practical position
acceptable for both of the object point 123 of the primary beam and
the image point 124 of the secondary beam.
Twelfth Example
[0493] FIG. 31 shows an electron optical system according to a
second embodiment of the seventh invention. FIG. 31 includes a
plurality of optical systems shown in FIG. 29 arranged along a
straight line. In this embodiment, a plurality of apertures 172,
174 corresponding to respective optical axes is formed in a ceramic
substrate 170 with metal coating 173 applied in the periphery of
the apertures and thus configured plates are fabricated by a
desired number and further assembled by using knock pins 171 to
provide a primary optical system defined from an electron gun 101
to the lower pole of the objective lens 108. FIG. 32 shows
reference numerals corresponding to the above-described optical
elements in its right-hand side. In the drawing, reference numeral
101 designates an electron gun, 102 a multi-aperture plate, 103 a
condenser lens, 104 a condenser lens, 106 a reduction lens, 107 an
E.times.B separator, 108 an objective lens, 109 a sample, 113 a
magnifying lens of a secondary optical system, 115 an MCP, 116 a
multi-anode, and each of 142, 143 and 144 an electrostatic
deflector. Further, as to the secondary optical system, the optical
axes extend obliquely in opposite directions for every adjacent
optical axis of the primary optical system disposed along the
straight line, and so the spacing between adjacent optical axes in
the secondary optical system would be expanded by a multiple of
two, meaning that there should be no problem, if the secondary
optical system is fabricated individually for each one of the
optical axes. That is, in FIG. 32, since the secondary optical
system is arranged such that the optical axes 111 and 113 are
directed to the front surface of the sheet and the optical axes 112
and 114 are directed to the back surface of the sheet, meaning that
the spacing between adjacent axes of the secondary optical system
refers to the spacing between 111 and 113 or the spacing between
112 and 114, which is equivalent to the double of the spacing
between 111 and 112. Therefore, the secondary optical system may be
constructed independently for each optical axis as practiced in the
prior art.
[0494] According to the illustrated embodiment, since the ratio of
(the landing energy of the primary electron beam/the energy of
secondary electrons) is relatively small, such as (600 eV/2 eV)=300
or lower (the case A of FIG. 30), (300 eV/2 eV)=150 or lower (the
case B), and (500 eV/2 eV)=250 or lower (the case C), as compared
to the conventional (1000 eV/2 eV)=500, and accordingly the
concurrent focusing condition of the primary and the secondary
beams could be easily satisfied, therefore it becomes possible to
form a multi-beam in the vicinity of the single optical axis in the
primary optical system and detect the secondary electrons
independently without any cross talk among them.
Thirteenth Example
[0495] FIG. 33 shows an overview of an electron optical system used
in an embodiment of the eighth invention. The electron gun
comprises a LaB.sub.6 single crystal cathode 201, a Wehnelt 202 and
an anode 203, in which the cathode 201 is actuated under the space
charge limited condition to thereby reduce the shot noise
effectively to one-quarter of or lower than that obtained by using
the Schottky cathode, and a satisfactory S/N ratio can be
accomplished with the number of electrons on the order of 250 per
pixel. Accordingly, the evaluation of such a resist as ArF resist
whose resist feature is more apt to change by the irradiation of
the electron beam can be provided without causing any deformation
over the resist.
[0496] An electron beam emitted from the electron gun is converged
by a condenser lens 204 and irradiated over a multi-aperture 205 to
be formed into a crossover in an NA aperture 224. The beam that has
been formed into a plurality of beams through the multi-aperture
205 is reduced by the reduction lens 206 and the objective lens 208
so as to form a narrowly converged multi-beam on a sample 209.
Those beams of the multi-beam are driven by an electrostatic
deflector 223 and an electrostatic deflector of an EB separator 207
to scan the sample 209. Since the sample 209 is applied with a
voltage of -4 kV, for example, the secondary electrons emitted from
the scanning points on the sample are accelerated toward the
objective lens 208, converged into a narrow bundle of beams with
the spacing between beams extended, and ultimately formed into a
secondary electron image in the vicinity of the E.times.B separator
207. A secondary beam is deflected by the E.times.B separator 207
at an angle of about 20.degree. relative to the primary beam and
adjusted in its magnification by magnifying lenses 210 and 211 of a
secondary optical system to be focused into an image on an incident
plane of an MCP 213 with an arrangement corresponding to a pitch of
a multi-anode 214 disposed behind the MCP 213. The electrons from
each beam are multiplied in the MCP 213, and each beam is
independently absorbed in the multi-anode 214 and converted into a
voltage signal by a resistor 215 and further into a digital signal
by a group of preamplifiers and A/D converters 216, to which a
variety of processing is applied in a two-dimensional image forming
circuit 217 and the processed image data is stored in a memory
218.
[0497] The multi-beam is aligned along a line extending to the
direction of about 45.degree. as indicated by 222 in the lower
right section of the drawing. A signal waveform in the scanning of
a y-line 219 in the x-direction is shown in (A) of FIG. 34, and a
signal waveform in the scanning of two x-line patterns 220, 221 in
the y-direction is shown in (B) of FIG. 34. In addition, the method
for measuring edge roughness is illustrated in (C) with respect to
the y-line.
[0498] During the CD measurement shown in FIG. 34(A), the
processing is applied to the signal waveform directly without any
pre-processing prior to the formation of the two-dimensional image.
That is, a threshold value 231 is applied to each of the seven
signal waveforms 232, and a time interval 233 between the times
when the waveform traverses the threshold value is determined,
which in turn is converted to a dimension by using a scanning rate
and finally a CD value may be determined for each beams of the
multi-beam and averaged among them, or alternatively the signal
waveform 232 may be applied with the positional adjustment by a
time period corresponding to a difference in spacing between the
beams in the x-direction and the resultant signal waveforms may be
added and averaged to determine the time interval 233 with the
improved S/N ratio.
[0499] Instead of the threshold method, tangential lines 234 and
235 may be applied to the leading edge and the trailing edge of the
signal waveform, wherein intersections of the tangential lines with
a base line 236 of the signal are determined, and then a time
difference 237 therebetween is determined and converted to a
dimension. Which of the methods, the threshold method or the method
using the tangential line is to be employed may be determined
depending on the material of the pattern, the vertical structure
and so on.
[0500] An aligning precision measuring method shown in FIG. 34(B)
will now be described. For the measurement of the aligning
precision in the y-direction, the multi-beam 222 is moved to the
vicinity of a pattern 221 formed in the following layer located in
the vicinity of the pattern 220 formed in the previous layer, and
then the scanning is carried out with the multi-beam all together
in the y-direction concurrently. The signal waveform from the
detector associated with each beam during this operation is
represented in (B) of FIG. 34. The sharper edge in the leading edge
and the trailing edge of the waveform is selected, and a time
interval or a distance 238 between intersections of the selected
edge with the threshold value 231 should be determined. In this
case, since, differently from the case of (A) where both of the
leading edge and the trailing edge of the signal waveforms are
used, either one of the leading edge or the trailing edge of the
signal waveform may be used in determining the threshold value, the
value representing the most sharp leading edge or trailing edge of
the signal waveform, typically the value equivalent to 50% of the
amplitude may be selected. It is a matter of course that the
aligning precision may be calculated by approximating the leading
edges or the trailing edges by the tangential lines 234, wherein
the time 239 is determined from the intersections of the tangential
lines with the base line, and thus determined time is converted to
the distance, which in turn is compared to the design value to thus
calculate the aligning precision.
[0501] An example of the eighth invention will now be described in
connection with the method for measuring the edge roughness. The
multi-beam is moved to the vicinity of the y-pattern 240, and then
driven to perform the scanning operation in the x-direction. If the
interval between respective beams in the y-direction encompasses a
few pixels, then the multi-beam performs the scanning operation
while each beam is shifted by one pixel in the y-direction, as
shown in 241-245, and this operation is repeated until the scanning
has been finished entirely for the every inter-beam distance to
thereby obtain the two-dimensional image. As it is, the edge
roughness can be measured from the measurement of a P-P value or an
effective value of the concavo-convex area based on the obtained
image as designated by 246, 247. In this regard, it is necessary to
slow down the pixel frequency of the signal waveform in each
scanning operation so that a good S/N ratio can be obtained.
[0502] According to the eighth invention, the evaluation of the
pattern requires relatively shorter time corresponding to a number
of beams, and thus the time required for the measurement can be
shortened.
Fourteenth Example
[0503] FIG. 35 shows a schematic diagram of an electron optical
system used in a pattern evaluation method according to an
embodiment of the ninth invention.
[0504] The electron gun comprises an LaB.sub.6 cathode 301, a
Wehnelt electrode 302 and a triple-electrode anode 303, in which a
positive voltage is applied to a central electrode of the
triple-electrode anode 303 to thereby define a convex lens of a
small spherical aberration. An appropriate control of the focusing
effect of this convex lens can adjust the irradiation area on the
multi-aperture 307. Alternatively, an NA value (focusing half
angle) of a primary beam on a sample 317 can be controlled by
modifying a size of a crossover formed in an NA aperture 309 by
changing a focal distance of the lens. In either case, the primary
beam emitted from the electron gun 301, 302, 303 is axially aligned
by axial aligning deflectors 331 and 332 with a condenser lens 305
and the multi-aperture 307. In the condenser lens 305, an exciting
voltage is determined so as to focus the crossover on the NA
aperture 309. The electron beam passes through the multi-aperture
307 to be formed into a multi-beam, which is axially aligned by a
two-step of axial aligning deflectors 333 and 334 with both of the
NA aperture 309 and a reduction lens 310, reduced by a reduction
lens 310 and an objective lens 315 to be focused on the surface of
the sample 317, and at the same time, driven by deflectors 311 and
314 to perform a raster scanning across the sample 317. During the
scanning operation across the sample with the multi-beam, the
dynamic focusing is applied to the multi-beam, that is, the
converging power of the lens is changed in synchronism with the
scanning operation to compensate for the aberration due to the
curvature of field, so that the multi-beam may be always focused on
the sample surface. Secondary electrons emitting from scanning
points of the multi-beam on the sample are accelerated and
converged by an accelerating electric field generated by the
objective lens 315 and the sample 317 for the secondary electrons
in the vicinity of the sample, and after passing through the
objective lens 315, the secondary electrons are deflected by an
E.times.B separator 313 so as to be directed to a secondary optical
system, where a spacing between the beams of secondary electrons is
extended by a two-stage of magnifying lens 319, 321, and also a
zooming operation is applied thereto so that the spacing between
the images of secondary electrons may be equal to the interval
between secondary electron detectors 323. In this connection, the
simulation has shown that the higher is the intensity of the
electric field in the vicinity of the surface of the sample 317,
the smaller is the out-of-focusing of the secondary electron image
on the detector 323. However, if the electric field intensity is
too high, resultantly the discharge is induced between the lens 315
and the sample 317, possibly leading to a destroyed sample.
Accordingly, the voltage to be applied to a lower electrode of the
lens 315 is determined so that the critically intensified electric
field that would not cause any discharge between the lens 315 and
the sample 317 can be produced over the wafer surface. The electric
field intensity that triggers the discharge in the sample is not
constant but depends on the condition in the surface of the sample,
wherein, for example, if such a projection like a via is present in
a wafer surface, a locally intensified electric field could be
formed even with an average electric field intensity as low as 1.6
kV/mm resulting in the discharge at that point. As for a flat wafer
with a film of SiO.sub.2 deposited on the surface thereof, the
electric field intensity that could induce discharging is as high
as 6 kV/mm.
[0505] Accordingly, the voltage applied to the lower electrode
should be once made variable within a range allowing the average
electric field intensity formed between the sample 317 and the
lower electrode to fall in a range of 1.5 kV/mm to 5.5 kV/mm,
wherein the voltage applied to the lower electrode may be
appropriately selected to be 1.5 kV/mm that is a bit lower than 1.6
kV/mm for the evaluation of the sample containing a via or 5.5
kV/mm that is a bit lower than 6 kV/mm for the evaluation of the
sample deposited with the SiO.sub.2 film. This can eliminate the
possibility of discharging to be induced and provides a feature of
the secondary optical system that the out-of-focusing of the
secondary electron image can be minimized.
[0506] The arrangement of the primary electron beams involves a
requirement that the distance between adjacent beams of the primary
electron beam should be made larger than a resolution of the
secondary optical system and also that the beam intervals, d,
between any adjacent beams projected on the y-axis are all equal.
FIG. 35 shows in its left-hand side by .largecircle. marks an
example of the arrangement of the beams that can meet
above-discussed two requirements and in which a certain number of
beams can be arranged in as small circle as possible. In the
illustrated example, the total of 16 beams in an array of
4-row.times.4-column are successfully positioned within the circle
335. If fourteen beams, they are all positioned within the circle
336. Thus, in order to accommodate a specified number of beams in
as small circle as possible, assuming that each beam is designated
by i-th in the x-direction and j-th in the y-direction, it is
required that the distance 328 between the adjacent beams (i, j)th
and (i, j+1)th should be approximately equal to the distance 329
between the adjacent beams (i, j+1)th and (i+1, j)th.
[0507] It is to be noted that in FIG. 35, reference numeral 316
designates a positive high-voltage power supply, 318 a negative
voltage power supply, 320, 322 an axial aligning deflector, 323 a
scintillator, 324 a light guide, 325 a PMT, 326 an A/D converter
and 327 an image forming device.
Fifteenth Example
[0508] FIG. 36 shows an electron optical system used in a pattern
evaluation method according to a second example of the ninth
invention. An electron beam emitted from an electron gun 361 is
subject to the focusing effect of a triple-electrode anode 374 to
once form a crossover 379, and the beams divergent therefrom
irradiate a multi-aperture 362 to be formed into a multi-beam.
Those beams are reduced by a condenser lens 363 and an objective
lens 365 to be focused on a sample 366. The multi-beam is driven by
an electrostatic deflector 375 and an electrostatic deflector 376
of an E.times.B separator 364 to perform the scanning operation
across the sample 366, and secondary electrons emitting from the
scanning points are narrowly converged by applying a positive high
voltage 377 to an electrode 365' disposed at the lowest position in
the objective lens 365, and after passing through the objective
lens 365, deflected by the E.times.B separator 364 toward a
secondary optical system, where an interval between groups of
secondary electrons in the multi-beam is expanded by a magnifying
lens 367, and the secondary electrons are converted into a light by
a scintillator 368 and further into an electric signal by a light
guide 379 and a photomultiplier 369, which is used subsequently in
a plurality of A/D converter, an image forming circuit to form a
two-dimensional image. Further, the sample 366 is applied with a
negative high voltage 378, and the primary beam is irradiated with
a low landing energy on the order of 200 V.
[0509] FIG. 36 shows an arrangement of a plurality of the
above-discussed optical systems along a straight line as is the
case with FIG. 31.
[0510] Further, similarly to the example of FIG. 32, as to the
E.times.B separator and/or the electrostatic deflectors, the lenses
and the like, a plurality of apertures 372, 374 corresponding to
optical axes is formed in a ceramic substrate 370 with metal
coating applied in the periphery of the apertures and thus
configured plates are fabricated by a desired number and further
assembled by using knock pins 371 in the necessary Z-positions to
provide a primary optical system defined from the electron gun 361
to the lowest pole of the objective lens 365. Further, as to the
secondary optical system, since the optical axis extends obliquely
in the opposite direction (in the front surface and the back
surface of the paper) for any adjacent optical axes with respect to
the optical axes of the primary optical system disposed along the
straight line, and so the pitch between adjacent optical axes of
the secondary optical system would have a double distance of that
of the primary optical system, therefore the secondary optical
system can be fabricated in a conventional lens structure.
[0511] According to the illustrated embodiment, since the emission
angle and/or the crossover size of the beam from the electron gun
is controlled by the lens including a plurality of anodes, a
necessary lens may be simplified into a single stage lens and its
associated aligning device is no more necessary, and accordingly
the optical axis length can be also made shorter, thus facilitating
the formation of the multi-beam with a simplified optical
system.
Sixteenth Example
[0512] FIG. 37 shows a pattern evaluation method illustrated in the
above embodiment applied to a wafer evaluation in a semiconductor
device manufacturing process.
[0513] An example of a device manufacturing process will be
described with reference to a flow chart of FIG. 37.
[0514] This manufacturing process includes the following main
processes.
[0515] (1) A wafer manufacturing process for fabricating a wafer
(or wafer preparing process for preparing a wafer) (Step 10)
[0516] (2) A mask manufacturing process for fabricating a mask to
be used in the exposure (or a mask preparing process for preparing
a mask) (Step 11)
[0517] (3) A wafer processing process for performing any processing
treatments necessary for the wafer (Step 12)
[0518] (4) A chip assembling process for cutting out those chips
formed on the wafer one by one to make them operative (Step 13)
[0519] (5) A chip inspection process for inspecting an assembled
chip (Step 14)
[0520] It is to be noted that each of these main processes further
comprises several sub-processes.
[0521] Among the main processes, one that has a critical effect on
the performance of the semiconductor device is the wafer processing
process. In this wafer processing process, the designed circuit
patterns are deposited on the wafer one on another, thus to form
many chips, which will function as memories or MPUs. This wafer
processing process includes the following sub-processes.
[0522] (1) A thin film deposition process for forming a dielectric
thin film to be used as an insulation layer, a metallic thin film
to be formed into a wiring section or an electrode section, and the
like (by using the CVD or the sputtering process)
[0523] (2) An oxidizing process for oxidizing thus formed thin film
layers and the wafer substrate
[0524] (3) A lithography process for forming a resist pattern by
using a mask (reticle) in order to selectively process the thin
film layers and/or the wafer substrate
[0525] (4) An etching process for processing the thin film layers
and/or the wafer substrate in accordance with the resist pattern
(by using, for example, the dry etching technology)
[0526] (5) An ions/impurities implant and diffusion process
[0527] (6) A resist stripping process
[0528] (7) An inspection process for inspecting the processed
wafer
[0529] It is to be noted that the wafer processing process must be
performed repeatedly as desired depending on the number of layers
contained in the wafer, thus to manufacture a semiconductor device
that will be able to operate as designed.
[0530] FIG. 38 shows a flow chart showing the lithography process
included as a core process in said wafer processing process. The
lithography process comprises the respective processes as described
below.
[0531] (1) A resist coating process for coating the wafer having a
circuit pattern formed thereon in the preceding stage with the
resist (Step 20)
[0532] (2) An exposing process for exposing the resist (Step
21)
[0533] (3) A developing process for developing the exposed resist
to obtain the pattern of the resist (Step 22)
[0534] (4) An annealing process for stabilizing the developed
resist pattern (Step 23)
[0535] A known process is applied to each of the semiconductor
device manufacturing process, the wafer processing process and the
lithography process described above.
[0536] When a pattern evaluation method according to the
above-defined respective embodiments is used in the above-described
inspection process of (7), any defects can be detected with high
precision without any image disorders of the secondary electron
image even on a semiconductor device having a fine pattern,
enabling an improvement in yield of the products as well as the
prevention of shipping of any defective products.
[0537] It is to be noted that the pattern evaluation according to
the present invention is applicable to a broad range of pattern
evaluation of a sample, including a defect inspection, a line width
measurement, an aligning precision measurement, a potential
contrast measurement for a sample such as a photo mask, a reticle,
a wafer and so on.
Seventeenth Invention
[0538] An embodiment of an evaluation method of a resist pattern or
a subsequently processed wafer according to the tenth invention
will now be described with reference to FIGS. 39 to 42.
[0539] In the tenth invention, in order to evaluate a pattern
formed on a wafer by using an electron beam direct writer or a
pattern exposure system such as an excimer laser stepper, firstly
such a wafer is prepared in which dies in an array defined by rows
and columns on the wafer have been finished with the exposing and
developing process with the dose and the focal condition modified
in a two-dimensional matrix on the wafer by changing the dose in a
step-by-step manner in the row direction and changing the focal
condition in a step-by-step manner in the column direction.
[0540] That is, FIG. 39 shows an example of a 12-inch wafer created
by the electron beam writer (not shown) with the dose and the focal
condition that are changed in the two-dimensional matrix as
discussed above. For example, the wafer 11' may contain a plurality
of dies in a size of 20 mm.times.40 mm that have been formed by
using the electron beam writer with the different dose in the row
direction of 0.9, 0.95, 1.00, 1.05, 1.10, 1.15 (.times.10.sup.-6
coulomb/cm.sup.2) and the focal condition in the column direction
changing from 0.7 .mu.m over-focusing to 0.6 .mu.m under-focusing
by every 0.1 .mu.m.
[0541] For example, each of the dies 12' positioned in the top row
of the wafer 11' is associated with the dose of 0.90
(.times.10.sup.-6 coulomb/cm.sup.2), and the focal condition has
been changed from the left die to the right die sequentially by
changing the objective lens current within the range of -0.4 .mu.m
to +0.3 .mu.m by every 0.1 .mu.m. Similarly, each of the dies
positioned in the second row from the top of the wafer 11' is
associated with the dose of 0.95 (.times.10.sup.-6
coulomb/cm.sup.2), and the focal condition has been changed from
the left die to the right die sequentially within the range of -0.6
.mu.m to +0.5 .mu.m by every 0.1 .mu.m.
[0542] In thus prepared wafer 11', a CD measuring device measures a
line width of each die at a predetermined position by a desired
number per die. Specifically, after the wafer 11' has been exposed
and developed, the measurement of the line width of a predetermined
pattern of every die is performed at five positions in each die by
the CDSEM. It is assumed that as a result, the hatched die 12'
identified with the diagonal lines falling toward the right has the
line width (the width of the exposed region) smaller than 90 nm,
which should have been 100 nm in design size, and it is determined
that the design specification has not been satisfied. It is further
assumed that the hatched die 13' identified with the diagonal lines
rising toward the right has the line width (the width of the
exposed region) of 110 nm or greater, which should have been 100 nm
in design size, and it is determined that the design specification
has not been satisfied. It can be determined from the result that
the not-hatched die is free from any failure measured in line width
and worthy of application of the defect inspection. Such a die is
then applied with the defect inspection to detect a defect as will
be discussed below.
[0543] In evaluating a lithography margin, the proximity effect
should be most critical in the vicinity of interface between a
memory cell 22' and a peripheral pattern area 23'. The inspection
of those regions with the electrons is efficient. In the present
invention, since each die 21' has a central memory cell 22' and its
adjacent peripheral pattern area 23', it is efficient that the
interface region associated with the varied pattern density should
be examined preferentially by a defect inspection apparatus. An
elongated scanning area 24', 25' including said interface region is
specified in opposite sides of the memory cell 22'. The scanning
area 24', 25' is specified such that one-half of a single stripe is
defined in the memory cell area 22' and the other half of the
stripe is defined in the peripheral pattern area 23'.
[0544] In actual practice, for the defect inspection, each die 21'
is divided into a plurality of stripes, which contains the scanning
area 24', 25' and each having a width corresponding to the scanning
area, and the scanning operation is carried out for each stripe. As
shown in FIG. 40, assuming that in the scanning area 24', 25', a
longitudinal direction is designated as y-direction and a direction
orthogonal to the y-direction is designated as x-direction, in
order to perform the defect inspection of the wafer 11', the defect
inspection apparatus irradiates in the x-direction by a length
corresponding to the width of one stripe with an electron beam of
rectangular-shape in its sectional view, while moving the wafer 11'
continuously in the y-direction, to thereby complete the scanning
over one stripe, and then the apparatus performs the same procedure
for the scanning over the adjacent stripe. These steps of procedure
are repeated to complete the scanning operation across each
scanning area 24', 25' so as to examine to see whether there is a
defect.
[0545] FIG. 41 shows an exemplary structure of a defect inspection
apparatus that can be used in an evaluation method of a resist
pattern or a processed wafer according to the tenth invention for
carrying out the above-described evaluation. A primary beam 32'
emitted from an electron gun 31' having a cathode of LaB.sub.6 is
converged by a condenser lens 33' to form a crossover in an NA
aperture 35'. During this step, any electron beams out of the field
are removed by a beam shaping aperture 34' of rectangular shape
disposed immediately below the condenser lens 33'. The primary beam
32' having passed through the condenser lens 33' forms a
rectangular beam on a conjugate plane 41' for a wafer W provided by
a doublet-type objective lens 39', 40'.
[0546] This rectangular beam is deflected by an E.times.B separator
38' toward the direction of normal line of the wafer W and focused
by the objective lens 39', 40' on the surface of the wafer W. At
this time, the trajectory 42' of the primary beam follows a
different path away from the trajectory of a secondary beam 43',
and so there would be no more fear that the blur of the secondary
beam 43' is enhanced by the effect of the space charge pertaining
to the primary beam 32'.
[0547] The primary beam 32' thus formed by the primary optical
system may irradiate an area larger by about 10 .mu.m than an area
defined by 51.2 .mu.m.times.25.6 .mu.m, for example, on the surface
of the wafer W. The primary beam 32' is driven by an electrostatic
deflector 37' with eight-poles to perform a scanning operation in a
direction orthogonal to the paper along a shorter side of the
rectangle by a scanning width of 205 .mu.m, for example, while at
the same time, the table (not shown) carrying the wafer W thereon
is moved continuously in the direction orthogonal to said scanning
direction.
[0548] The wafer W is applied with a voltage of -4 kV. Accordingly,
the secondary beam 43' emanating from the scanned wafer W is
accelerated in the normal line direction of the wafer W and
converged through the objective lens 40', 39' to form an enlarged
image on the deflecting support point of the E.times.B separator
38'. Since the objective lens 39', 40' is designed in a
configuration proximal to the symmetric doublet lens, the
distortion and the magnification chromatic aberration has been
reduced to be low. The secondary beam 43' passing through the
E.times.B separator 38' without being deflected thereby is
magnified by the magnifying lenses 45', 46' and 48' so as to form
an enlarged image of the wafer W in front of an MCP (multi-channel
plate) 49'.
[0549] In the illustrated secondary electronic optical system, in
synchronism with the scanning operation of the primary beam 32', a
correction is applied to the path of the secondary beam 43' by the
deflector 44' so that the secondary beam 43' may pass through the
vicinity of the center of the magnifying lens 45', and further a
deflection correction is applied by the deflector 47' in order to
reduce the aberration. Owing to this, since the aberration induced
in the secondary beam 43' is limited almost to that caused by the
initial two-stage of lenses 39', 40', the secondary electron
optical system can be of low aberration.
[0550] After the number of electrons in each pixel of the secondary
beam image has been multiplied by about 10.sup.4 by a MCP 49, the
secondary beam 43' is converted to an image of light by a
scintillator plate 50'. At this time, although an accelerating
voltage is applied between the back surface of the MCP 49' and the
scintillator plate 50', owing to a gap on the order of 500 .mu.m
provided between the back surface of the MCP 49' and a front
surface of the scintillator plate 50', the secondary beam could be
diverted over a range of 30.mu. in the front surface of the
scintillator even when the secondary beam having the electron
number distribution of delta function enters the front surface of
the MCP 49. Accordingly, it is preferred that the magnification of
the secondary electron optical system may be selectively set to
such a magnification that the pixel of 100 nm, for example, on the
surface of the wafer W can be magnified to 60 .mu.m or more on the
front surface of the scintillator plate 50', or magnified by a
multiple of 600 or more.
[0551] The image of light formed in the scintillator plate 50' is
focused by a relay lens 51' on a light acceptance surface of a TDI
camera 52'. It is to be noted that a difference in size between a
pixel in the TDI camera 52' and a pixel in the scintillator plate
50' can be compensated for by selecting the magnification of the
relay lens 51' appropriately.
[0552] Steps for carrying out a defect inspection of the wafer in
accordance with an evaluation method of a resist pattern or a
processed wafer according to the tenth invention will now be
described with reference to FIG. 42. As already explained with
respect to FIG. 40, the scanning operation for a single die 61' is
carried out for each of the plurality of stripes 62' defining the
width in the x-direction in a range of 100 .mu.m to 200 .mu.m. A
sectional geometry 63' of the electron beam formed by the defect
inspection apparatus shown in FIG. 41 is substantially rectangular
on the surface of the wafer 11'. The primary electron beam has a
sufficiently uniform intensity within a specific rectangular
irradiation area 66' enclosed by the y-directional sides 64' and
the x-directional sides 65' in the sectional geometry 63'. FIG. 42
indicates that said irradiation area 66' contains a plurality of
pixels, 67', 68', 69', 70' . . . .
[0553] While moving the wafer 11' continuously in the +y direction,
the defect inspection apparatus moves the electron beam in the +x
direction from one end of a single stripe 62' by every pixel width
until it reaches the other end, then the beam makes a flyback to
the original one end. Specifically, when the side 71' positioned in
the right-hand side of the irradiation area 66' in the diagram
reaches the left end of the single stripe 62', the defect
inspection apparatus starts the detection of the secondary
electrons. When the electron beam has traveled from this starting
point toward the right by one pixel width on the stripe, meaning
that the irradiation area 66' has been transferred by one pixel
width, the secondary electron signal indicative of the secondary
electrons detected from the pixel falling in the irradiation area
66' among those pixels aligned in the y-direction at the left-most
side of the stripe 62' is input to the first pixel column of the
TDI camera 52' (FIG. 41).
[0554] When the electron beam has been advanced across the stripe
62' toward the right further by one pixel width, the secondary
electron signal held in the first pixel column of the TDI camera
52' is transferred to the left, so that the secondary electron
signal indicative of the secondary electrons detected from the
pixel falling in the irradiation area 66' among those pixels
aligned in the y-direction at the left-most side of the stripe 62'
is input to the first pixel column, and the secondary electron
signal indicative of the secondary electrons detected from the
pixel falling in the irradiation area 66' among those pixels
aligned in the y-direction at the second from the left of the
stripe 62' is input to the second pixel column.
[0555] In this way, each time the electron beam is shifted across
the stripe 62' toward the right by the width corresponding to one
pixel, the secondary electron signal from the pixel falling in the
irradiation area 66' among those pixels aligned in the y-direction
at the left-most side of the stripe 62' is transferred to the left
and accumulated in the TDI camera 52'. Finally, when the side 64'
positioned in the left end of the rectangle 66' has passed the
pixel aligned in the y-direction at the left-most side of the
stripe 62', the pixel of the TDI camera 52' outputs a signal
corresponding to the secondary electron signal from the pixel
aligned at the left-most side of the stripe 62'.
[0556] A similar operation is repeated and when the side 64'
positioned at the left side of the irradiation area 66' has passed
the right end 72' of the stripe 62', the secondary electron signal
from a pixel falling in the irradiation area 66' among the pixels
aligned in the y-direction at the right-most side of the stripe 62'
is output and thus a one-cycle of the x-directional scanning
operation has been completed. When the one-cycle of scanning
operation has been completed, the defect inspection apparatus makes
a flyback of the electron beam to the left end of the stripe 62'.
Since the stage is continuously moving in the y-direction, the die
61' has been moved in the +y direction by a distance corresponding
to the length of the side 64'. After that, a scanning operation
similar to that discussed above is commenced.
[0557] Actually, since the wafer 11' and thus the die 61' is moved
continuously in the +y direction in the duration of each scanning
operation, the electron beam 61' will be driven also in the -y
direction so as to compensate for the moving rate in the +y
direction of the die 61'. However, since the sectional geometry 63'
of the electron beam has a certain size of irradiation area 66'
sufficient to cover a specified number of pixels arranged in the
vertical and horizontal directions with some margin, it is not
necessary to perform the scanning of extra high precision. If the
vibration of the wafer 11' or the uneven rate of moving speed of
the wafer 11' in the y-direction is detected, a positional
correction is made in the secondary electron optical system so that
the position to be measured on the stripe can be formed into an
image correctly on the MCP 49'.
[0558] In FIG. 42, when the scanning of one die 61' has been
completed, subsequently the scanning is applied to a die 73'
adjacent to the die 61' in the y-direction, and in this way when
the scanning has been completed across one stripe 62' to the die at
the end of the wafer 11' in the +y direction, then the defect
inspection apparatus performs the scanning operation across a
stripe 74' adjacent to the stripe 62', while moving the wafer 11'
in the -y direction mechanically.
[0559] The defect inspection apparatus determines whether thus
detected defect is resultant from the lithography or other types of
defect, such as those from particle or the like, and in accordance
with the determination, eliminates those defects having no
connection with the lithography condition, such as the defect from
particle, but picks up exclusively the defects having a connection
with the lithography, such as abnormal pattern from the excessive
or insufficient compensation for the proximity effect, wherein the
distribution of the defect generation resultant from the
lithography is examined to evaluate the lithography margin. As a
result, the die 14' indicated with a circle mark in FIG. 39
represents the die containing no defect resultant from the
lithography.
[0560] In this case, it can be concluded from the evaluation as
described above that the lithography margin is in a range of 0.1
.mu.m over-focusing to 0.2 .mu.m under-focusing, and the dose is in
a range of 1.0 .mu.c/m.sup.2 to 1.10 .mu.c/m.sup.2.
[0561] The evaluation method of a resist pattern or a processed
wafer according to the tenth invention can be effectively applied
to a semiconductor device manufacturing method shown in FIG. 37 and
FIG. 38, for example.
[0562] If the evaluation method of a resist pattern according to
the tenth invention is used in the chip inspection process in the
sixteenth example to carry out the defect inspection, any defects
can be detected with high throughput even on a semiconductor device
having a fine pattern, enabling not only the 100 percent inspection
but also the improvement in yield of the products as well as the
prevention of shipping of any defective products.
[0563] As can be understood from the above description, since the
use of the electron beam can achieve the resolution of 0.1 .mu.m or
lower over the resolution of 0.1 .mu.m or higher obtainable by the
light, the present invention can bring about a particularly
advantageous effect that the lithography margin can be measured
with a high resolution over the defect inspection of optical method
of the prior art. Since in the present invention, the defect
inspection is not applied to every single die but only to the die
having a normal line width, the time required for the defect
inspection can be shortened.
* * * * *