U.S. patent application number 10/464761 was filed with the patent office on 2004-02-12 for inspection method and inspection apparatus using electron beam.
Invention is credited to Funatsu, Ryuichi, Gunji, Yasuhiro, Inada, Yoshikazu, Ninomya, Taku, Nozoe, Mari, Yamamoto, Kenjirou.
Application Number | 20040026633 10/464761 |
Document ID | / |
Family ID | 31177763 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040026633 |
Kind Code |
A1 |
Gunji, Yasuhiro ; et
al. |
February 12, 2004 |
Inspection method and inspection apparatus using electron beam
Abstract
An inspection method and an inspection apparatus using an
electron beam enabling more detailed and quantitative evaluation at
a high throughput level. The method comprises the steps of
irradiating, based on previously prepared information concerning a
defect position on the surface of a sample, the defect and its
vicinity with an electron beam a plurality of times at
predetermined intervals; detecting an electron signal secondarily
generated from the sample surface by the electron beam; imaging an
electron signal detected by the previously specified n-th or later
electron beam irradiation; and measuring the resistance or a
leakage amount of the defective portion of the sample surface in
accordance with the degree of charge relaxation by monitoring the
charge relaxation state of the sample surface based on the electron
beam image information.
Inventors: |
Gunji, Yasuhiro;
(Hitachiota, JP) ; Ninomya, Taku; (Hitachinaka,
JP) ; Funatsu, Ryuichi; (Hitachinaka, JP) ;
Inada, Yoshikazu; (Hitachinaka, JP) ; Yamamoto,
Kenjirou; (Matsudo, JP) ; Nozoe, Mari; (Hino,
JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
20037-1526
US
|
Family ID: |
31177763 |
Appl. No.: |
10/464761 |
Filed: |
June 19, 2003 |
Current U.S.
Class: |
250/492.1 |
Current CPC
Class: |
H01J 2237/2594 20130101;
G01R 31/305 20130101; H01J 37/244 20130101; H01J 2237/24564
20130101; H01J 37/28 20130101; H01J 2237/24592 20130101; H01J
37/268 20130101; H01J 37/222 20130101; H01J 2237/2817 20130101 |
Class at
Publication: |
250/492.1 |
International
Class: |
A61N 005/00; G21G
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2002 |
JP |
2002-180735 |
Claims
What is claimed is:
1. An inspection method using an electron beam comprising the steps
of: irradiating, based on previously prepared information
concerning a defect position on the surface of a sample, the defect
and its vicinity with an electron beam a plurality of times at
predetermined intervals; detecting an electron signal secondarily
generated from the sample surface by the electron beam; imaging the
electron signal detected by the pre-specified n-th or later
electron beam irradiation; and measuring the resistance or a
leakage amount of a defective portion of the sample surface in
accordance with the degree of charge relaxation by monitoring a
charge relaxation state of the sample surface based on the electron
beam image information.
2. The inspection method according to claim 1, wherein the method
comprises displaying image information obtained by the imaging
step.
3. The inspection method according to claim 1, wherein the
previously prepared defect position information is generated based
on defect inspection by continuously moving a sample stage having
the sample placed thereon, and the electron beam irradiation step,
electron signal detection step, and resistance/leakage amount
measurement step are repeated in a state where the sample stage is
moved sequentially and stopped at each defect position based on the
defect position information.
4. The inspection method according to claim 1, wherein the
resistance or leakage amount of each defective portion obtained in
the resistance/leakage amount measurement step is displayed as in a
map on a schematic diagram of the sample organized by type of
defect.
5. An inspection method using an electron beam comprising the steps
of: scanning an electron beam on a sample while continuously moving
a sample table having the sample placed thereon; detecting an
electron signal secondarily generated from the sample surface by
the electron beam; imaging the electron signal; specifying a
defective portion by comparing electron beam images having the same
pattern with each other; generating defect position information
containing at least position information among attribution
information of the defective portion; irradiating the defect and
its vicinity with the electron beam a plurality of times at
predetermined intervals based on the defect position information;
detecting an electron signal secondarily generated from the sample
surface by the electron beam; imaging an electron signal detected
by pre-specified n-th or later electron beam irradiation; and
measuring the resistance or a leakage amount of the defective
portion on the sample surface depending on the degree of charge
relaxation by monitoring the charge relaxation state on the sample
surface in accordance with the electron beam image information.
6. An inspection apparatus using an electron beam comprising: a
sample table for sample placement; a stage mechanism unit for
continuously moving the sample table; an electron source; an
electron optics system for applying and scanning an electron beam
from the electron source on the sample; a detector for detecting an
electron signal secondarily generated from the sample surface by
the electron beam; an image processing unit for imaging the
electron signal and specifying a defective portion by comparing
electron beam images having substantially the same pattern with
each other; and a defect position information generating unit for
generating defect position information including at least position
information among attribute information of the defective position,
wherein the electron optics system has further a function to
irradiate, based on the defect position information, a defect and
its vicinity with the electron beam at predetermined intervals a
plurality of times, the detector detects the electron signal
secondarily generated from the sample surface by the electron beam,
the image processing unit has a function to image the electron
signal detected by the pre-specified n-th or later electron beam
irradiation, and the inspection apparatus further comprises a
resistance/leakage amount measurement part for monitoring the
charge relaxation state of the sample surface according to the
electron beam image information and measuring the resistance or a
leakage amount of the defective portion on the sample surface
depending on the degree of charge relaxation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an inspection method and an
inspection apparatus using an electron beam, both of which inspect
a sample such as a semiconductor device having micro-fabricated
patterns, a substrate, a photomask (a mask having patterns formed
thereon, which is used for exposing patterns on a substrate), and a
liquid crystal plate.
[0003] 2. Description of the Related Art
[0004] Semiconductor devices such as memories and microcomputers
used for computers, etc. are manufactured through the repetition of
transcription processes such as exposing, lithographing, or etching
patterns such as circuits, which are formed on photomasks. In the
manufacturing process of semiconductor devices, the manufacturing
yield is greatly affected by several factors. These include whether
or not the results of the lithography process, etching process, or
other processes involved are satisfactory. Yield is also affected
by the presence or absence of foreign matter of the like.
Therefore, in order to detect early or in advance the occurrence of
abnormalities or defects, patterns on a semiconductor wafer are
inspected at the end of each manufacturing process.
[0005] As one example of a method for inspecting defects present in
a pattern on a semiconductor wafer, an optical visual inspection
apparatus has been put into practice, wherein the comparison of
patterns is performed using optical images obtained through light
irradiation of a semiconductor wafer. However, as circuits have
miniaturized (micro) patterns and complicated shapes, and as
materials used for circuits have become diversified, it is
difficult to detect these defects using optical images. Thus, a
method and an apparatus for inspecting a pattern using an electron
beam image that has higher resolution than an optical image have
been put into practice.
[0006] Known are technologies disclosed, for example, in JP Patent
Publication (Kokai) No. 59-192943, JP Patent Publication (Kokai)
No. 5-258703, Sandland, et al., "An electron-beam inspection system
for x-ray mask production," J. Vac. Sci. Tech. B, Vol. 9, No. 6,
pp. 3005-3009 (1991), Meisburger, et al., "Requirements and
performance of an electron-beam column designed for x-ray mask
inspection," J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3010-3014
(1991), Meisburger, et al., "Low-voltage electron-optical system
for the high-speed inspection of integrated circuits," J. Vac. Sci.
Tech. B, Vol. 10, No. 6, pp. 2804-2808 (1992), Hendricks, et al.,
"Characterization of a New Automated Electron-Beam Wafer Inspection
System," and SPIE Vol. 2439, pp. 174-183 (Feb. 20-22, 1995).
[0007] In order to achieve high throughput and highly accurate
inspections in line with the increase of wafer bore diameter and
the miniaturization of circuit patterns, there is a need to obtain
a high SN image at very high speeds. To this end, the number of
electrons emitted through the use of a larger beam, with a current
1,000 times or more (100 nA or more) greater than that of an
ordinary scanning electron microscope (hereinafter referred to as
an SEM), should be preserved to ensure the maintenance of a high SN
ratio. Further, it is essential to detect secondary electrons
generated from a substrate and reflected electrons at high speeds
and with high efficiency.
[0008] Furthermore, in order to prevent a semiconductor substrate
with a insulating film such as a resist from being affected by
charging, it is necessary to apply a low accelerated electron beam
of 2 keV or less. This technology is disclosed in the "Electron/Ion
beam handbook (2nd edition)," edited by the 132nd Committee of
Japan Society for the Promotion of Science, pp. 622-623, Nikkan
Kogyo Shimbun (1986). However, the use of the low accelerated
electron beam with a large current generates aberrations due to the
space charge effect, and thereby high-resolution observation has
been difficult.
[0009] As a method for solving this problem, a technology wherein a
highly accelerated electron beam is decelerated directly before a
sample and is applied to the sample substantially as a low-speed
accelerated electron beam is known. Such technology is disclosed
in, for example, JP Patent Publication (Kokai) No. 2-142045 and JP
Patent Publication (Kokai) No. 6-139985.
[0010] With respect to an inspection apparatus using the above SEM,
the following problems have yet to be solved.
[0011] One problem is that detailed evaluation is impossible
because the presence of defects is digitally judged as being 0 or
1, and during this period analog judgment cannot be performed.
Taking a non-opening defect of a plug hole bottom as an example,
this means that it is conventionally judged to be conductive or
non-conductive, but in contrast there also exists an intermediate,
semi-conductive state. However, a plug is originally required to
permit low resistance and ohmic connections among levels of
wirings. In view of this point, it can be said that a detailed
analog evaluation should be conducted using the resistance.
[0012] Further, refresh defects of DRAMs, transistor leakage
defects of flash memories, or the like, though they are categorized
as the same type of electric characteristic defects, are caused by
a micro leakage current of a pn junction, and these defects are
difficult to detect even with an SEM inspection apparatus. JP
Patent Publication (Kokai) No. 2002-9121 discloses attempts to
detect the above defects by intermittently applying an electron
beam in a condition where a junction is charged in a reverse biased
state, and detecting the defect as an electric potential contrast
image using a state where the charge is relaxed through a junction
leakage current.
[0013] However, in this method, since the irradiation of the
electron beam at the same location is repeated many times, it is
necessary to move a wafer in a step-and-repeat manner. Therefore,
when stationary time of a stage mechanism or time lost through
stage control is taken into consideration, a problem arises, in
which the throughput, evaluated in terms of the time required for
one semiconductor substrate, deteriorates.
SUMMARY OF THE INVENTION
[0014] The present invention has been accomplished in view of the
above points, and thus has an object of providing an inspection
method and an inspection apparatus using an electron beam, which
enables a high throughput of more detailed and quantitative
evaluation, by using an SEM inspection apparatus as technology for
inspecting characteristic electric defects that are difficult to
detect through optical images and by making it possible not only to
judge conductiveness or non-conductiveness, etc., but also to
measure the resistance or a leakage current amount at a pn
junction.
[0015] An embodiment of the present invention is an inspection
apparatus using an electron microscope for detecting a defect on a
pattern of a sample based on a detection signal of secondary
charged particles generated by scanning an electron beam, wherein a
rough inspection for narrowing down defect candidates is first
conducted and defect review is performed, and then the resistance
or leakage amount of a defective portion is measured.
[0016] More specifically, a method of the present invention
comprises the steps of: irradiating, based on previously prepared
information concerning a defect position on the surface of a
sample, the defect and its vicinity with an electron beam a
plurality of times at predetermined intervals; detecting an
electron signal secondarily generated from the sample surface by
the electron beam; imaging the electron signal detected by the
previously specified n-th or later electron beam irradiation; and
measuring the resistance or a leakage amount of a defective portion
of the sample surface in accordance with the degree of charge
relaxation by monitoring a charge relaxation state of the sample
surface based on information of the electron beam image.
[0017] This specification includes part or all of the contents as
disclosed in the specification and/or drawings of Japanese Patent
Application No. 2002-180735, which is a priority document of the
present application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a vertical cross sectional view showing a
configuration of a SEM type visual inspection apparatus.
[0019] FIG. 2 is a function block diagram of an embodiment of the
present invention.
[0020] FIG. 3 is a flow chart showing an inspection procedure.
[0021] FIG. 4 is a flow chart showing an inspection procedure.
[0022] FIG. 5 is a relationship diagram illustrating a principle
for measuring the resistance of a defective portion.
[0023] FIG. 6 is a plan view of a wafer holder.
[0024] FIG. 7 is a screen view showing an example display on a
monitor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Preferred embodiments of the present invention will
hereinafter be described with reference to the accompanying
drawings.
[0026] FIG. 1 is a vertical cross sectional view illustrating a
configuration of an SEM type visual inspection apparatus 1 as one
example of an inspection apparatus using a scanning electron
microscope to which the present invention is applied. The SEM type
visual inspection apparatus 1 comprises an inspection chamber 2,
the inside of which is evacuated, and a spare chamber (not shown in
the present embodiment) for conveying a sample substrate 9 into the
inspection chamber 2. These inspection chamber 2 and spare chamber
are configured so that they are independently evacuated. In
addition to the above inspection chamber 2 and spare chamber, the
SEM type visual inspection apparatus 1 is composed of an image
processing unit 5, a controller 6, and a secondary electrons
detection unit 7.
[0027] The inside of the inspection chamber 2 is roughly divided
into an electron optics system 3, a sample chamber 8, and an
optical microscope unit 4. The electron optics system 3 comprises
an electron gun 10, an electron-beam drawing electrode 11, a
condenser lens 12, a blanking deflector 13, a scan deflector 15, a
diaphragm 14, an objective lens 16, a reflecting plate 17, and an
ExB deflector 18. A secondary electron detector 20 of the secondary
electrons detection unit 7 is disposed above the objective lens 16
in the inspection chamber 2. An output signal of the secondary
electron detector 20 is amplified by a preamplifier 21 provided
outside the inspection chamber 2, which in turn is converted into
digital data by an AD converter 22.
[0028] The sample chamber 8 comprises a sample table 30, an X stage
31, a Y stage 32, a position monitoring length-measuring device 34,
and a sample substrate height measuring device 35. The optical
microscope unit 4 is located in the vicinity of the electron optics
system 3 lying within the inspection chamber 2 and is installed at
a position where they are distant from each other to such an extent
that they do not exert influence on each other. The distance
between the electron optics system 3 and optical microscope unit 4
is known. Further, the X stage 31 or the Y stage 32 moves forward
and backward alternately between the electron optics system 3 and
the optical microscope unit 4. The optical microscope unit 4
comprises a light source 40, an optical lens 41, and a CCD camera
42.
[0029] The image processing unit 5 comprises a first image storage
part 46, a second image storage part 47, an operation part 48, and
a defect determination part 49. A captured electron-beam image or
optical image is displayed on a monitor 50.
[0030] Operation instructions and operating conditions used for the
respective parts of the apparatus are inputted to and outputted
from the controller 6. Conditions such as accelerating voltage,
deflected width and a deflection speed of an electron beam at the
occurrence of the electron beam, timings for capturing signals by
the secondary electrons detection unit 7, a sample table traveling
speed, and others have been inputted in advance to the controller 6
so that they can be arbitrarily or selectively set depending on
purposes. The controller 6 monitors shifts or displacements in
position and height from signals outputted from the position
monitoring length measuring device 34 and the sample substrate
height measuring device 35 by the use of the correction control
circuit 43. Based on the results of the monitoring, the controller
6 enables the correction control circuit 43 to generate a
correction signal, and to send the correction signal to the
objective lens source 45 and a scan signal generator 44, so that an
electron beam is always applied to the proper position.
[0031] In order to obtain an image of the sample substrate 9, a
thinly-focused electron beam 19 is applied to the sample substrate
9 to thereby produce secondary electrons 51. They are detected in
synchrony with the scanning of the electron beam 19 and the
movements of the X stage 31 and the Y stage 32, thereby obtaining
the image of the sample substrate 9.
[0032] It is essential to enhance the inspection speed for the SEM
type visual inspection apparatus. Therefore, unlike an ordinary
conventional type of SEM, the SEM type visual inspection apparatus
does not perform the scanning of an electron beam of an
electron-beam current on the order of pA at low speeds, perform the
scanning a large number of times, or perform the superimposition of
respective images on one another. Further, for the purpose of
restricting charging on an insulating material, it is necessary to
scan the electron beam once or several times at high speed, rather
than many times. Thus, in the present embodiment, an electron beam
having a larger current of, for example, 100 nA, which is about
1,000 times or more greater than that of a conventional SEM, is
scanned once alone to thereby form an image.
[0033] A diffusion refill-type thermofield emission electron source
is used for an electron gun 10. The use of this electron gun 10
makes it possible to ensure an electron beam current remains stable
as compared with, for example, a tungsten filament electron source
and a cold field emission type electron source. Therefore, an
electron beam image that shows little change in brightness can be
obtained. Further, since the electron gun 10 enables the electron
beam current to be set at a high level, the high-speed inspection
described below can be realized. The electron beam 19 is drawn from
the electron gun 10 by applying a voltage between the electron gun
10 and the drawing electrode 11.
[0034] The electron beam 19 is accelerated by applying a negative
potential with a high voltage to the electron gun 10. This enables
the electron beam 19 to move to the sample table 30 by means of
energy equivalent to the potential, followed by convergence on the
condenser lens 12. Further, the electron beam 19 is thinly-focused
by the objective lens 16 to be applied to the sample substrate 9
mounted on the X stage 31 and the Y stage 32 placed on the sample
table 30. The sample substrate 9 is a semiconductor wafer, a chip,
or a substrate having a micro-fabricated circuit pattern such as a
liquid crystal, a mask, or the like. The scan signal generator 44
for generating a scan signal and a blanking signal is connected to
the blanking deflector 13, and the objective lens source 45 is
connected to the objective lens 16.
[0035] To the sample substrate 9, negative voltage can be applied
by a high-voltage power supply 36. By adjusting the voltage of this
high-voltage power supply 36, the electron beam 19 is decelerated
and electron beam irradiation energy applied to the sample
substrate 9 can be adjusted to an optimum value without changing
the potential of the electron gun 10.
[0036] The secondary electrons 51 generated by applying the
electron beam 19 to the sample substrate 9 are accelerated under
the negative voltage applied to the sample substrate 9. The ExB
deflector 18 is disposed above the sample substrate 9. The
deflector 18 is used for turning the orbit of secondary electrons
by means of both electric and magnetic fields without affecting the
orbit of the electron beam 19. This enables the accelerated
secondary electrons 51 to be deflected in a predetermined
direction. The intensities of the electric and magnetic fields
applied to the ExB deflector 18 allow adjustments to the amount of
deflection of secondary electrons. In addition, these electric and
magnetic fields can be varied in conjunction with the negative
voltage applied to the sample substrate 9.
[0037] The secondary electrons 51 deflected by ExB deflector 18
collide with the reflecting plate 17 under predetermined
conditions. The reflecting plate 17 has a conical shape and also
has a function as a shield pipe to shield the electron beam 19
applied to the sample substrate 9. When the accelerated secondary
electrons 51 collide with this reflecting plate 17, second
secondary electrons 52, having energy from a few eV to 50 eV, are
produced from the reflecting plate 17.
[0038] The secondary electrons detection unit 7 has the secondary
electron detector 20 provided within the evacuated inspection
chamber 2. A preamplifier 21, an AD converter 22, an optical
converting means 23, optical transmission means 24, an electric
converting means 25, a high-voltage power supply 26, a preamplifier
drive source 27, an AD converter drive source 28, and a reverse
bias source 29 are provided outside the inspection chamber 2, which
constitutes the secondary electrons detection unit 7.
[0039] The secondary electrons detector 20 of the secondary
electrons detection unit 7 is placed above the objective lens 16
inside the inspection chamber 2. The secondary electrons detector
20, preamplifier 21, AD converter 22, optical converting means 23,
preamplifier drive power source 27, and AD converter drive power
source 28 are rendered floating at a positive potential by the
high-voltage power supply 26. The second secondary electrons 52
generated from the collision of the secondary electrons 51 with the
reflecting plate 17 are introduced into the secondary electrons
detector 20 under the action of a drawing electric field created by
the positive potential.
[0040] The secondary electrons detector 20 is configured so as to
detect the second secondary electrons 52 generated by the collision
of the secondary electrons 51 with the reflecting plate 17 in
conjunction with the time when the electron beam 19 is scanned. An
output signal of the secondary electrons detector 20 is amplified
by the preamplifier 21 provided outside the inspection chamber 2,
which in turn is converted into digital data by the AD converter
22.
[0041] The AD converter 22 is configured so as to convert an analog
signal detected by the secondary electrons detector 20 into a
digital signal immediately after the preamplifier 21 amplifies the
signal, and then transmit the signal to the image processing unit
5. Since the detected analog signal is digitized and transmitted
immediately after its detection, a signal having a higher speed and
S/N ratio than a conventional signal can be obtained.
[0042] The sample substrate 9 is mounted on the X stage 31 and the
Y stage 32. Either one of a method for stopping the X stage 31 and
the Y stage 32 upon the execution of an inspection to thereby
two-dimensionally scan the electron beam 19, and a method for
sequentially moving the X stage 31 and the Y stage 32 in a Y
direction at a constant speed upon the execution of the inspection
to thereby linearly scan the electron beam 19 in an X direction can
be selected. In the case of inspecting a relatively small specific
given area, the former method of stopping the sample substrate 9
for inspection is effective. In the case of inspecting a relatively
wide area, the method of consecutively moving the sample substrate
9 at a constant speed for inspection is effective. In addition,
when blanking on the electron beam 19 is necessary, the electron
beam 19 is deflected by the blanking deflector 13 so that the
electron beam is controlled so as not to pass through the diaphragm
14.
[0043] In the present embodiment, a laser interference-based
wavemeter is used as the position monitoring length-measuring
device 34 for monitoring the positions of the X stage 31 and the Y
stage 32. The positions of the X stage 31 and the Y stage 32 can be
monitored in real time, and the results thereof are to be
transferred to the controller 6. Further, the present embodiment is
configured so that data items concerning the numbers of revolutions
of motors used for the X stage 31, Y stage 32, etc. are also
transferred from their drivers to the controller 6 in the same
manner. The controller 6 is able to accurately grasp each area and
position irradiated with the electron beam 19 based on these data
items. Therefore, when a position irradiated with the electron beam
19 is deviated from an intended position, the correction control
circuit 43 can correct the position in real time, if necessary.
Further, areas irradiated with the electron beam 19 can be stored
for every sample substrate 9.
[0044] The sample substrate height measuring device 35 utilizes an
optical measuring instrument, e.g., a laser interference measuring
instrument or a reflected-light type measuring instrument for
measuring the position change of reflected light. It is configured
so as to measure the height of the sample substrate 9 mounted on
the X stage 31 and the Y stage 32 in real time. The present
embodiment employs a method comprising the steps of applying a
slender white light transmitted through a slit to the sample
substrate 9 through a transparent window, detecting the position of
the reflected light thereof by a position detecting monitor, and
calculating the amount of height change from the variation in
position. Based on data measured by this optical height measuring
device 35, the focal distance of the objective lens 16 is
dynamically corrected, whereby the electron beam 19 that is focused
on each area to be inspected can be always applied. Further,
warpage or height distortion of the sample substrate 9 is measured
in advance before the application of the electron beam, and based
on the data thereof, the objective lens 16 may also be configured
so that correction conditions thereof are set for each inspected
area.
[0045] The image processing unit 5 comprises a first image storage
part 46, a second image storage part 47, an operation part 48, a
defect determination part 49 and a monitor 50. An image signal on
the sample substrate 9 detected by the secondary electrons detector
20 is amplified by the preamplifier 21 and digitized by the AD
converter 22. Thereafter it is converted into a light signal by an
optical converting means 23 and transmitted by an optical
transmitting means 24. Then, it is converted again into an electric
signal by an electric converting means 25, and the thus obtained
signal is stored in the first or second image storage part 46 or
47. The operation part 48 performs an alignment between the image
signal stored in the first image storage part 46 and the image
signal stored in the second image storage part 47, standardization
of signal level, and various image processes for removing noise
signals. It also computes both the image signals for comparison.
The defect determination part 49 compares the absolute value of the
differential image signal computed for comparison by the operation
part 48 with a predetermined threshold value. When the level of the
differential image signal is larger than the predetermined
threshold value, the defect determination part 49 judges their
pixels as defect candidates, and their positions, the number of
defects, etc. are displayed on the monitor 50.
[0046] Next, the operation of each part of the inspection apparatus
shown in FIG. 1 will be described according to the inspection
procedure shown in FIG. 3. FIG. 3 shows a flowchart of the
inspection procedure.
[0047] First, a wafer cassette having a wafer placed on the desired
shelf is placed on a cassette placement part of a wafer
transportation system (Step 310 of FIG. 3).
[0048] Next, in order to specify the wafer to be inspected, the
number of the cassette shelf having the wafer placed thereon is
entered through an operation screen. Then, through the operation
screen various inspection conditions are inputted (Step 320 of FIG.
3). The inspection condition parameters to be inputted include
those involving electron beam current, electron beam irradiation
energy, scanning speed and signal detection sampling clock, the
area to be inspected, and various types of information regarding
the wafer to be inspected. Further, the content concerning whether
a plurality of wafers are to be automatically and continuously
inspected one by one, whether one wafer is to be inspected
continuously under different conditions, or the like are inputted
as inspection condition parameters. These parameters can be
individually inputted, but usually the combinations of the above
various inspection condition parameters are stored in a database as
inspection condition data files. Therefore, it is necessary to
select and input one file among inspection condition data files.
When the input of these conditions is completed (Step 320 of FIG.
3), the inspection starts (Step 330 of FIG. 3).
[0049] When automatic inspection starts, a predetermined wafer is
first transported into the inspection apparatus. When wafers to be
inspected have different diameters, or when wafers have different
shapes falling between those of the orientation flat type and notch
type, the wafer transportation system can deal with these cases by
replacing one holder for placing a wafer with another in accordance
with the sizes or shapes of wafers. The wafer to be inspected is
transported from the wafer cassette onto the wafer holder by the
wafer loader, which includes an arm and a preliminary vacuum
chamber. The wafer is securely held and subjected to evacuation
together with the holder inside the wafer loader, and then
transported to the inspection chamber that has already been
evacuated by the evacuation system (Step 340 of FIG. 3). When the
wafer is loaded, electron beam irradiation conditions for each part
are set by an electron optics system controller based on the above
inputted inspection condition parameters.
[0050] FIG. 6 is a plane view of a wafer holder 750 on which a
wafer 760 is placed. The wafer holder 750 as shown in FIG. 6 has a
beam calibration pattern 770 placed thereon. A stage moves so that
the beam calibration pattern comes beneath the electron optics
system (Step 350 of FIG. 3), and an electron beam image of the beam
calibration pattern 770 is obtained for making focal and astigmatic
adjustments according to the obtained image. Then, the stage moves
further so that the electron optics system is located above a
specific point of the wafer to be inspected to obtain an electron
beam image of the wafer and to adjust a contrast image or the like.
At this time, when it is necessary to modify the electron beam
irradiation conditions, etc., the parameters are modified and the
beam calibration can be performed again. At the same time the
height of the wafer is obtained by the height detector, a wafer
height detection system computes the correlation between the height
information and electron beam focusing conditions. Thereafter,
whenever an electron beam image is obtained, an automatic
adjustment of the focusing conditions is made based on the results
of the wafer height detection, without the need for focusing each
time. This enables electron beam images to be obtained continuously
and at high speeds (Step 360 of FIG. 3).
[0051] When the input of the electron beam irradiation conditions
and the focal/astigmatic adjustment are completed, alignment is
performed in accordance with two points on the wafer (Step 370 of
FIG. 3).
[0052] After the alignment is completed, the rotation or coordinate
values are corrected based on the results of the alignment. Then,
the stage moves so that the electron optics system is located above
a second calibration pattern 780 placed on the wafer holder 750 as
shown in FIG. 6 (Step 380 of FIG. 3). The second calibration
pattern 780 is a transistor or a pattern corresponding to a
transistor having a normal junction formed thereon in advance.
Using that pattern, the brightness of a normal portion is
calibrated. Based on the results of the calibration, the electron
optics system is located above the wafer to obtain an image of a
pattern point on the wafer and perform brightness adjustment: in
other words, calibration (Step 390 of FIG. 3).
[0053] After the calibration is completed, the inspection is
performed (Step 400 of FIG. 3). With respect to the inspection
method, while the stage is continuously moved to conduct the
inspection of specified areas, the image processing is carried out
on a real-time basis and an image of a defect occurrence point is
automatically stored (Step 410 of FIG. 3). Then, the inspection
result is displayed on the monitor 50, and the data is outputted to
the outside through a data conversion part (Step 420 of FIG.
3).
[0054] For inputting the inspection conditions (Step 320 of FIG.
3), when the condition is set wherein one point is inspected
several times under different conditions, a charge elimination
process is carried out on the area that has been once inspected
(Step 440 of FIG. 3). Although a charge-elimination part is not
shown in FIG. 1, the charge elimination process is carried out, for
example, by the application of ultraviolet light.
[0055] Then, an inspection is carried out again under different
electron beam irradiation conditions (Step 400 of FIG. 3). In this
way, when the inspection is completed, the wafer is unloaded and
the inspection is finished (Step 430 of FIG. 3).
[0056] FIG. 2 is a function block diagram showing an embodiment of
the present invention. The inspection performed in accordance with
the inspection procedure described above is regarded as a rough
inspection. Based on the results of this rough inspection, defect
candidates are narrowed down. Thereafter, detailed inspection as
shown below is carried out.
[0057] Namely, the inspections performed and the output of results
obtained at Steps 400, 410, and 420 of FIG. 3 are represented as
defect information 220 outputted from the image processing unit 5
in FIGS. 2 (a) and (b). Based on this defect information 220,
defect position information 240 is generated by a defect position
information generating unit 230. The stage is moved so as to bring
a defect position indicated by the defect position information 240
underneath the electron optics system, and a resistance/leakage
amount measuring unit 250 measures the resistance and a leakage
amount 260 (detailed inspection).
[0058] Since the rough inspection of the entire wafer is conducted
at high speed by continuously moving the stage to narrow down
defect candidates, and then a detailed inspection is conducted,
which takes more time, the entire inspection efficiency can be
greatly improved.
[0059] In FIG. 2(b), the stage is moved based on the defect
position information 240, and a defect is reviewed by a defect
review processing unit 270. Thereafter, the resistance and leakage
amount are measured. While doing this, defect candidates are
further narrowed down by defect review, and the inspection
efficiency can be further enhanced.
[0060] FIG. 4 is a flow chart showing an inspection procedure. With
reference to FIG. 4, the inspection procedure shown in FIG. 2(b) is
described in detail.
[0061] First, a wafer cassette having a wafer placed on a desired
shelf is placed on a cassette placement part of a wafer
transportation system (Step 510 of FIG. 4).
[0062] Next, in order to specify a wafer to be inspected, the
number of the cassette shelf having the wafer placed thereon is
entered through an operation screen. Then, through the operation
screen the results of a rough inspection previously conducted are
inputted (Step 520 of FIG. 4). The input contents include file
names storing the inspection results.
[0063] When the input is completed, a defect review starts (Step
530). Once automatic defect review starts, first the predetermined
wafer is transported into the inspection apparatus and then
transported to an inspection chamber that has been already
evacuated by the evacuation system (Step 540 of FIG. 4).
[0064] When the wafer is loaded, the stage is moved so as to bring
a defect position underneath the electron optics system based on
the defect position information as the above inputted results of
the rough inspection (Step 550). The defect is displayed on the
monitor 50 for reviewing (Step 560).
[0065] Thereafter, the process is shifted to a resistance
measurement mode (Step 600).
[0066] Next, the electron beam irradiation condition is tentatively
set at Step 610. Since the principle disclosed in JP Patent
Publication (Kokai) No. 2002-9121 described above is used for
measurement, an electron beam current amount, an XY scanning size,
an irradiation interval, the number of irradiation times, etc. are
tentatively set. At Step 620, an image corresponding to these
conditions is displayed, and it is judged whether these conditions
are suitable for measurement at Step 630. If the conditions are not
suitable, the process returns to Step 610 to adjust the conditions.
After suitable conditions are determined, the resistance of the
defective portion is measured at Step 640.
[0067] Thereafter, the resistance measurement mode is finished, and
the results of review, the results of resistance measurement, or
the like are outputted at Step 570. With respect to subsequent
defects, the same processes are repeated. Then, after the processes
for all the defects are finished, the wafer is unloaded at Step 590
and then the process is finished.
[0068] FIG. 5 is a relationship diagram illustrating a principle
for measuring the resistance of a defective portion. The horizontal
axis represents time, and the vertical axis represents the amount
of electron beam irradiation and charged voltage, or SEM image
brightness. The detailed principle of a method for resistance
measurement of a defective portion is disclosed in JP Patent
Publication (Kokai) No. 2002-9121. FIG. 5 shows an example plug
having a shorter charge relaxation time than a plug having a pn
junction with a normal electron beam irradiation interval
T.sub.int. In this case, after electron beam is applied a plurality
of times, a difference between the normal plug 700 and leakage
defect plug 710 in SEM image brightness occurs as shown in the
figure. When the difference is classified quantitatively, the
degree of leakage, namely the resistance component, can be
estimated. For example, when the difference is larger, the
resistance is estimated to be smaller.
[0069] FIG. 6 is a plane view of a wafer holder as mentioned above.
Several types of leakage samples generated from a normal pn
junction are prepared in the second calibration pattern 780
provided on the wafer holder 750, and these are compared with the
SEM image brightness of each defective portion. This enables more
accurate quantitative evaluation. By doing this, the estimation of
absolute resistance can be achieved.
[0070] FIG. 7 is a screen view showing an example display on a
monitor. The example display of FIG. 7 includes the measurement
results concerning the resistance of defects. On left side of a
screen 800, a wafer map 810 is displayed, and defects are indicated
on the map by circular signs. Portions where leakage defects occur
are indicated as a distribution pattern. In an area 820, legends
for the distribution pattern of leakage defective portions as shown
in the wafer map 810 are displayed, and in this example, the
resistance is classified into three types. Each type may be
distinguished by color to easily and visually identify them. In the
figure, "XX" and "YY" practically represent specific values of the
resistance. These values can be arbitrarily set. Further, the
conditions at the time of measuring the resistance in this example
are displayed in an area 830. An electron beam current amount, a
scanning size in each direction of X or Y axis, an irradiation
interval of the electron beam, and the number of times for electron
beam irradiation on the same area are displayed in an area 832, an
area 834, an area 836, and an area 838, of the area 830,
respectively.
[0071] Defects such as leakage defects are greatly affected by
process conditions, and therefore, for example, some defects are
likely to occur around the wafer. According to this embodiment,
such distribution characteristic can be more accurately
grasped.
[0072] Although defects such as leakage defects are indicated on
the distribution on the wafer in this embodiment, they may be
indicated as a distribution on each chip of the wafer. In this
case, the wafer map 810 as shown in FIG. 7 may display one chip or
a plurality of chips.
[0073] The above embodiments according to the present invention are
summarized as follows.
[0074] A method is provided, which comprises the steps of:
irradiating, based on previously prepared information concerning a
defect position on the surface of a sample, the defect and its
vicinity with an electron beam a plurality of times at
predetermined intervals; detecting an electron signal secondarily
generated from the sample surface by the electron beam; imaging an
electron signal detected by the previously specified n-th or later
electron beam irradiation; and measuring the resistance or a
leakage amount of a defective portion of the sample surface in
accordance with the degree of charge relaxation by monitoring a
charge relaxation state of the sample surface based on the electron
beam image information.
[0075] The method may further comprise displaying image information
obtained by the imaging step.
[0076] Further, the previously prepared defect position information
is generated based on defect inspection by continuously moving a
sample stage having a wafer placed thereon. The electron beam
irradiation step, electron signal detection step, and
resistance/leakage amount measurement step are repeated in a state
where the sample stage is moved sequentially and stopped at each
defect position based on the defect position information.
[0077] Furthermore, the resistance or leakage amount of each
defective portion obtained in the resistance/leakage amount
measurement step is displayed as in a map on a schematic diagram of
the wafer organized by type of defect.
[0078] Moreover, a method is provided comprising the steps of:
scanning an electron beam on a wafer while continuously moving a
sample table having the wafer placed thereon; detecting an electron
signal secondarily generated from the wafer surface by the electron
beam; imaging the electron signal; specifying a defective portion
by comparing electron beam images having the same pattern with each
other; generating defect position information containing at least
position information among attribution information of the defective
portion; irradiating the defect and its vicinity with the electron
beam a plurality of times at predetermined intervals based on the
defect position information; detecting an electron signal
secondarily generated from the wafer surface by the electron beam;
imaging an electron signal detected by the pre-specified n-th or
later electron beam irradiation; and measuring the resistance or a
leakage amount of the defective portion on the wafer surface
depending on the degree of charge relaxation by monitoring a charge
relaxation state on the wafer surface in accordance with the
electron beam image information.
[0079] In addition, an inspection apparatus is provided, which
comprises a sample table for wafer placement; a stage mechanism
unit for continuously moving the sample table; an electron source;
an electron optics system for applying and scanning an electron
beam from the electron source on the wafer; a detector for
detecting an electron signal secondarily generated from the wafer
surface by the electron beam; an image processing unit for imaging
the electron signal and specifying a defective portion by comparing
electron beam images having the same pattern with each other; and a
defect position information generating unit for generating defect
position information including at least position information among
attribute information of a defective position. Here, the electron
optics system has a function to irradiate, based on the defect
position information, a defect and its vicinity with the electron
beam at predetermined intervals a plurality of times. The detector
detects the electron signal secondarily generated from the wafer
surface by the electron beam, and the image processing unit has a
function to image the electron signal detected by the pre-specified
n-th or later electron beam irradiation. The apparatus further
comprises a resistance/leakage amount measurement part for
measuring the resistance or a leakage amount of the defective
portion on the wafer surface depending on the degree of charge
relaxation by monitoring the charge relaxation state of the wafer
surface according to the electron beam image information.
[0080] As described above, it is possible to obtain an inspection
method and an inspection apparatus enabling more detailed and
quantitative evaluation at a high throughput level, by using an SEM
type inspection apparatus as a technology for inspecting electric
characteristic defects that are difficult to be detected by optical
images, and making it possible not only to judge conductiveness or
non-conductiveness but also to measure the resistance or a leakage
current amount at a pn junction.
EFFECT OF THE INVENTION
[0081] As mentioned above, the present invention provides an
inspection method and an inspection apparatus using an electron
beam, which enables more detailed and quantitative evaluation at a
high throughput level.
[0082] All publications, patents and patent applications cited
herein are incorporated herein by reference in their entirety.
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