U.S. patent application number 12/187060 was filed with the patent office on 2008-12-04 for wafer surface inspection apparatus and wafer surface inspection method.
This patent application is currently assigned to HITACHI HIGH-TECHNOLOGIES CORPORTION. Invention is credited to Masayuki Hachiya, Kazuhiro Zama.
Application Number | 20080297782 12/187060 |
Document ID | / |
Family ID | 37851589 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080297782 |
Kind Code |
A1 |
Zama; Kazuhiro ; et
al. |
December 4, 2008 |
WAFER SURFACE INSPECTION APPARATUS AND WAFER SURFACE INSPECTION
METHOD
Abstract
A wafer surface inspection method and apparatus of high
sensitivity, and free from performance degradation in terms of
cleanliness, coordinate repeatability of foreign particles and the
like. Gas for cooling is sprayed onto a laser irradiation position
on the wafer surface to prevent an increase in temperature of the
foreign particles and to suppress break-down of the foreign
particles.
Inventors: |
Zama; Kazuhiro; (Mito,
JP) ; Hachiya; Masayuki; (Tokorozawa, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
HITACHI HIGH-TECHNOLOGIES
CORPORTION
Tokyo
JP
|
Family ID: |
37851589 |
Appl. No.: |
12/187060 |
Filed: |
August 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11501922 |
Aug 10, 2006 |
7420668 |
|
|
12187060 |
|
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Current U.S.
Class: |
356/237.4 |
Current CPC
Class: |
G01N 21/9501 20130101;
G01N 21/94 20130101; G01N 2021/151 20130101 |
Class at
Publication: |
356/237.4 |
International
Class: |
G01N 21/88 20060101
G01N021/88 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2005 |
JP |
2005-233314 |
Claims
1-3. (canceled)
4. An optical inspection apparatus comprising: a stage which moves
a substrate relative to a laser beam; a light irradiation unit
which irradiates foreign particles on the substrate with the laser
beam; a light detection unit which detects light scattered from the
foreign particles; a gas spraying unit which supplies a gas to said
foreign particles; and at least one of a dust control unit and a
dehumidifier unit disposed in a gas flowing path of the gas
supplying unit.
5. An optical inspection apparatus according to claim 4, wherein
said gas supplying unit includes a gas spraying unit.
6. An optical inspection apparatus according to claim 4, wherein
said substrate is a semiconductor wafer, a glass substrate or a
disk substrate.
7. An optical inspection apparatus according to claim 4, wherein
said dust control unit includes a filter.
8. An optical inspection apparatus according to claim 4, wherein
said dehumidifier unit includes an air dryer.
9. An optical inspection apparatus according to claim 4, wherein
the gas is dry air, nitrogen gas, helium or argon.
10. An optical inspection apparatus according to claim 5, wherein
the gas spraying unit includes a supply pipe.
11. An optical inspection apparatus according to claim 5, wherein
the said gas spraying unit includes a supply path open/close
unit.
12. An optical inspection apparatus according to claim 5, wherein
the said gas spraying unit includes at least one of a flow rate
measuring unit and a flow rate variable unit.
13. An optical inspection apparatus according to claim 5, wherein
the said gas spraying unit sprays gas at least during the time in
which the laser beam is irradiated.
14. An optical inspection apparatus according to claim 5, wherein a
dew point of the gas is controlled.
15. An optical inspection apparatus according to claim 5, wherein
at least one of a flow rate and a flow velocity of the gas is
controlled based on an energy density of the laser beam.
16. An optical inspection apparatus according to claim 5, further
comprising a display unit which is adapted to display a relation
between an output power of the laser beam and a flow rate of the
gas.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a surface inspection
apparatus and a surface inspection method of a subject to be
inspected, and relates for example to a wafer surface inspection
apparatus and a wafer surface inspection method for inspecting for
foreign particles or foreign matter, defects and the like on a
semiconductor wafer surface in a manufacturing process of a
semiconductor device.
[0002] In a manufacturing process of a semiconductor device, a
circuit is formed by transferring a pattern onto a bare wafer and
etching the same. In the manufacturing processes of various
semiconductor devices during which circuits are formed, foreign
particles adherent to the wafer surface, defects and the like
become major factors causing a decrease in yield. The foreign
particles adherent to the wafer surface and the defects are managed
in each manufacturing process, and a wafer surface inspection
apparatus detects the foreign particles adherent to the bare wafer
surface, the defects present on the wafer surface and the like with
high sensitivity and with high throughput.
[0003] The methods of inspecting for foreign particles and defects
on the wafer are largely classified into those using a charged
particle beam such as an electron beam or the like and those using
light. The methods using light include one that uses a camera to
take an image of the wafer surface to analyze the image
information, and one that uses a light receiving element like a
photomultiplier tube to detect scattered light on the wafer surface
to analyze the degree of scattering of light. For example, in a
surface inspection apparatus of the type irradiating the surface of
the wafer with a laser beam, the scattered light from foreign
particles caused by irradiation with the laser beam is detected by
a detector and is subjected to analog-to-digital conversion to be
output as coordinate data. To increase the throughput of
inspection, an inspection table with a work (wafer) mounted thereon
is rotated at high speed, and a stage mounted with the inspection
table is scanned horizontally in an axial direction. As a surface
inspection apparatus of this type, one described in JP-A-55-102233,
for example, is known.
SUMMARY OF THE INVENTION
[0004] In the method of irradiating a wafer surface with a laser
beam and detecting scattered light from foreign particles or
defects, detection sensitivity would be improved if the density of
energy of laser irradiation is increased. However, it has become
found that when the foreign particles are made of organic matter
prone to break down, the foreign particles may be broken down
(destructed) by heat of the laser irradiation, in which case the
particles broken down would fly around the area and adhere to the
wafer surface to thereby contaminate the wafer. Conventional
inspection apparatuses use laser of low power, and thus, such
phenomenon of destruction of foreign particles by the laser beam
did not occur. However, with an increase in sensitivity of
detection of foreign particles, laser of high power has come to be
used, and thus, the phenomenon of destruction of foreign particles
by laser irradiation has begun to emerge. Further, in the wafer
surface inspection apparatus, inspection is carried out while
rotating the work (wafer) to be measured, as described above. Thus,
the destructed particles would fly around the area and adhere to
the wafer surface in a spiral fashion over a wide area, to
contaminate the wafer.
[0005] For a wafer surface inspection apparatus, high cleanliness
and high precision coordinate repeatability of foreign particles
are required. The wafer contamination attributable to the
destruction of foreign particles, however, would degrade such
performance. To address this problem, although the density of
energy of laser irradiation may be decreased to avoid destruction
of foreign particles, it would lower detection sensitivity as well.
Accordingly, there is a demand for a method that can prevent
destruction of foreign particles attributable to laser without
lowering the detection sensitivity.
[0006] An object of the present invention is to provide a wafer
surface inspection apparatus that is highly sensitive and free of
degradation of device performance in terms of cleanliness,
coordinate repeatability of foreign particles and the like.
[0007] It is considered that foreign particles are broken down
(destructed) by irradiation with a laser beam because the
temperature of the particles increases due to the irradiation with
the laser beam. Thus, by spraying gas for cooling onto the laser
irradiation position on the wafer, the increase in temperature of
the foreign particles can be prevented to suppress destruction of
the foreign particles. The conditions for spraying gas for cooling
depend on the density of energy at the point of laser irradiation.
That is, when the density of energy is large, it is necessary to
increase the flow velocity and the flow rate of the gas for cooling
to increase the amount of heat radiation from the foreign
particles.
[0008] JP-A-55-102233 describes that upon detection of foreign
particles on the wafer, air is blown to blow off the particles.
However, the foreign particles generally adhere to the wafer so
firmly that they would not be blown off by just blowing the air.
Rather, blowing off the foreign particles would pose another
problem that the range of contamination would increase. In the
present invention, gas of high cleanliness enough to cool the
foreign particles is sprayed at the flow velocity and the flow rate
with which the foreign particles would not be blown off. Further,
in JP-A-55-102233, the air is blown before analysis, i.e., before
irradiation of light, to blow off the foreign particles. In
contrast, in the present invention, the gas for cooling is sprayed
onto the laser irradiation position at the same time as irradiation
of the laser beam, in order to cool the foreign particles being
irradiated with the laser beam.
[0009] Namely, the wafer surface inspection apparatus according to
an aspect of the present invention includes: a table holding a
semiconductor wafer; light irradiation means for irradiating a
small area on a surface of the semiconductor wafer held on the
table with a laser beam; light detection means for detecting light
scattered from the semiconductor wafer by irradiation with the
laser beam; table drive means for rotating and concurrently
linearly moving the table with respect to the light irradiation
means; and gas spraying means for spraying gas onto the area on the
semiconductor wafer irradiated with the laser beam by the light
irradiation means. Preferably, the apparatus has a control unit
controlling the light irradiation means and the gas spraying means,
and the light irradiation means and the gas spraying means are
controlled by the control unit such that the gas is sprayed from
the gas spraying means at least while the beam is irradiated from
the light irradiation means.
[0010] According to the present invention, irradiation of laser and
spraying of gas with respect to the wafer are carried out at the
same time and for the same location. This can increase the density
of energy of irradiated laser at the limit of not destroying the
foreign particles, compared to the conventional case. Accordingly,
it is possible to carry out the inspection without destructing the
foreign particles, while preventing lowering of detection
sensitivity.
[0011] Other objects, features and advantages of the present
invention will become apparent from the following description of
the embodiments of the present invention when taken with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram showing a schematic configuration of a
wafer surface inspection apparatus according to the present
invention.
[0013] FIG. 2 is a configuration diagram (piping system diagram) of
an air blow unit.
[0014] FIG. 3A shows that contamination in a spiral form has
occurred with a conventional inspection method.
[0015] FIG. 3B shows a result of inspection by a method of the
present invention.
[0016] FIG. 4 shows the relation between the laser power and the
gas spraying flow rate having an effect of suppressing destruction
of foreign particles.
[0017] FIG. 5 is a diagram (piping system diagram) showing an air
blow unit incorporating a mass flow controller.
[0018] FIG. 6 shows a setting screen of gas flow rate and a
displayed state of scatter plot.
DESCRIPTION OF THE EMBODIMENTS
[0019] The inspection method and the inspection apparatus of the
present invention are applicable to a flat plate-shaped subject to
be inspected, such as a semiconductor wafer, a glass substrate for
a liquid crystal panel, a disk substrate and the like. In the
following, embodiments of the present invention will be described
with reference to the drawings, taking a semiconductor wafer as an
example.
[0020] FIG. 1 shows a schematic configuration of a foreign particle
inspection apparatus of the present invention incorporating gas
spraying means (gas spraying unit).
[0021] A semiconductor wafer 5 that is the subject to be inspected
is rested on an inspection table 6, serving also as holding means
(holder) or vacuum suction means (vacuum suction device), and is
clamped or held with vacuum. A scanning stage 8 is mounted with an
air spindle motor 7 to which inspection table 6 is attached, and is
capable of generally horizontal movement backwards and forthwards
in an axial direction. Air spindle motor 7 rotates at high speed in
the .theta. direction while controlling inspection table 6 to a
prescribed speed, and at the same time, the scanning stage 8 moves
inspection table 6 in the scanning direction. A detection system 2
and a laser irradiation position 10 are stationary. Semiconductor
wafer 5 relatively moves with respect to laser irradiation position
10, so that the area of laser irradiation position 10 is cooled by
fixedly providing the gas spraying means at an arbitrary position.
The gas spraying means is constructed by eliminating sliding parts
to the greatest possible extent, to restrict generation of dust
from the gas spraying means.
[0022] A laser beam 11 irradiated from a laser light source 20 is
reflected by a mirror 4 to pass through a projecting portion 3, and
is then directed to laser irradiation position 10 on the surface of
semiconductor wafer 5. With laser irradiation position 10 being
fixed, semiconductor wafer 5 is moved relatively in the scanning
direction while being rotated at high speed in the .theta.
direction, to detect foreign particles on the entire surface of
semiconductor wafer 5. As laser irradiation position 10 is
irradiated with laser beam 11, scattered light is generated from
foreign particles or defects, which scattered light is detected by
detection system 2. Gas 9 of high cleanliness is sprayed onto laser
irradiation position 10 of semiconductor wafer 5 from gas spraying
unit 1 continuously at least during the time in which laser beam 11
is irradiated.
[0023] In the example shown in FIG. 1, the gas spraying direction
from gas spraying unit 1 to laser irradiation position 10 is
opposite to the irradiation direction of the laser beam. The gas
spraying direction does not affect cooling efficiency of the area
of laser irradiation position 10, and similar effects can be
obtained when it is set to any direction with respect to the laser
irradiation direction. As the gas for cooling, dry air or nitrogen
gas, or gas exhibiting high thermal conductivity, such as helium,
argon or the like, may be used.
[0024] Laser light source 20 and gas spraying unit 1 are controlled
by a CPU or processing device 21. The output of detection system 2
is subjected to analog-to-digital conversion, and is input to CPU
or processing device 21. Rotation angle data of air spindle motor 7
and position data of scanning stage 8 are also input to CPU or
processing device 21. When the output of detection system 2 exceeds
a predetermined threshold value, CPU or processing device 21
obtains the coordinate on the wafer from the rotation angle data of
air spindle motor 7 and the position data of scanning stage 8, and
stores the same as defect coordinate data.
[0025] FIG. 2 is a schematic diagram showing an air circuit of the
gas spraying unit 1. The air circuit includes pressurizing means
(pressurizing device) of gas 17, made of a compressor 19 or the
like, dehumidifier means (dehumidifier device) made of an air dryer
(not shown) or the like, supply path open/close means (supply path
open/close device) made of an air valve 12 or the like, flow rate
measuring means (flow meter) made of a purge meter 13, MFM (mass
flow meter) or the like, flow rate variable means (flow rate
variable device) made of a speed controller 16, needle valve or the
like, dust control means (dust control device) arranged in a
plurality of stages, made of two or more filters or the like, and a
supply pipe 30 for connecting these elements. The overall supply of
gas 17 is controlled via CPU or processing device 21.
[0026] The pressurizing means and the dehumidifier means in the
configuration may be substituted with dry air supplied as the plant
utilities on the semiconductor manufacturing line, or may be
provided individually for the inspection apparatuses. In either
case, similar effects can be obtained. In order to use a gas type
different from the air or to suppress disturbance from the plant
side, it is preferable to mount them individually to the inspection
apparatuses. When placing greater importance on downsizing and
manufacturing cost of the inspection apparatuses, it is preferable
to substitute them with the dry air.
[0027] As shown in the figure, gas 17 increased to a prescribed
pressure by compressor 19 is controlled to a prescribed dew point
by the air dryer, and is supplied through supply pipe 30. Inflow
gas 17, of which supply and shut-off is controlled by valve 12,
passes through purge meter 13 that measures a flow rate of gas 17.
Thereafter, gas 17 is adjusted by speed controller 16 to the flow
rate that would not contaminate the wafer. After passing through a
first filter 14 (first dust control means) and a second filter 15
(second dust control means), the gas is sprayed onto the surface of
semiconductor wafer 5 as sprayed gas 18. Foreign particles (dust)
within gas 17 are removed (captured) by first filter 14 (first dust
control means) and second filter 15 (second dust control means)
provided in a plurality of stages, and thus, sprayed gas 18 is
sprayed as the gas of high cleanliness. It is noted that speed
controller 16 and purge meter 13 may be configured with flow rate
control means (flow rate control device) such as a MFC 31 (mass
flow controller) or the like, serving as both the flow rate
measuring means and the flow rate variable means, as shown in FIG.
5. This allows gas 17 to be supplied at a stable flow rate with
accuracy, without being affected by variation in pressure of
compressor 19. Accordingly, the cooing performance by sprayed gas
18 is stabilized, and thermal destruction of foreign particles can
be suppressed effectively, and thus, coordinate repeatability of
the foreign particles improves.
[0028] The set value of the flow rate of gas 17, controlled by MFC
31, is set in a freely changeable manner via a setting screen
provided on display means (not shown) formed with a CRT or flat
panel display, using input means (input unit) 5 (not shown) formed
with a keyboard, touch panel, mouse or the like. The input set
value is registered to CPU or processing device 21. CPU or
processing device 21, based on the flow rate set value, controls
via MFC 31 such that the prescribed flow rate of gas 17 is
maintained in a stable manner.
[0029] FIG. 6 shows a flow rate setting screen of the present
embodiment. It is configured such that the set value of flow rate
supplied from gas spraying unit 1 can be input, via an input device
520, to a flow rate set value input space 33 that is displayed on
the setting screen 32 provided on the display means (display
device). The flow rate of gas 17 is controlled in the
above-described manner, based on the set value.
[0030] Although the flow rate of gas 17 is set via input space 33
in the present embodiment, not limited to input space 33, it may be
set via another screen opened with an icon or button provided on
the setting screen. Any screen enabling setting of at least the set
value of flow rate of gas 17 may be used.
[0031] FIGS. 3A and 3B show the effect of suppressing thermal
destruction of foreign particles by the gas spraying means.
[0032] FIG. 3A shows a map (distribution of foreign particles) of
the wafer in the state of occurrence of contamination in a spiral
fashion (detection sensitivity: 40 nm or more). It shows that, with
the inspection carried out by a conventional method without
spraying of gas, foreign particles adherent to the wafer are
destroyed by laser irradiation and scattered around the area, which
adhere to the wafer in the shape of bands. The foreign particles
are distributed in a spiral manner from the inner side toward the
outer side, because the inspection was carried out while rotating
the wafer, causing the scattered foreign particles to move outward
along the flow of the air that occurs from the inner side toward
the outer side on the wafer surface during inspection due to
viscosity of the air.
[0033] FIG. 3B shows a map of the wafer in the state of absence of
spiral contamination (detection sensitivity: 40 nm or more). The
inspection was conducted under the conditions exactly the same as
in FIG. 3A, except that the gas was sprayed onto the laser
irradiation area on the wafer.
[0034] Spiral contamination as in FIG. 3A has not occurred, showing
a significant effect of suppressing thermal destruction of foreign
particles by the gas spraying means. It is noted that the
inspection was carried out in the following order: (1) perform
inspection of the initial state, (2) cause foreign particles to
adhere, (3) conduct measurement of FIG. 3B, and (4) conduct
measurement of FIG. 3A. That is, FIGS. 3A and 3B are diagrams
confirming that the foreign particles are destroyed in the absence
of gas spraying, after confirming presence of the gas spraying
effect.
[0035] FIG. 4 shows the relation between the laser power and the
flow rate of sprayed gas having the effect of suppressing
destruction of foreign particles, obtained through experiments.
[0036] The experimental conditions are as follows:
[0037] (1) laser wavelength: 532 nm
[0038] (2) laser spot diameter: elliptical shape of 50
.mu.m.times.10 .mu.m
[0039] (3) spindle rotational speed: 1500 r/min
[0040] (4) stage feed pitch: 20 .mu.m
[0041] (5) foreign particle detection sensitivity: 40 nm
[0042] (6) inner diameter of gas (air) spraying nozzle: 2.5 mm
[0043] (7) evaluated wafer: bare wafer of .phi. 300 mm
[0044] (8) air spraying angle (elevation angle): 23.degree.
[0045] The experimental methodology is as follows:
[0046] (1) Perform measurement of the wafer in the initial
state.
[0047] (2) Intentionally cause foreign particles that would readily
be destroyed (e.g., organic matter) to adhere to the wafer
surface.
[0048] (3) Perform measurement in the state where air is sprayed
onto the portion irradiated with laser.
[0049] (4) Perform measurement in the state where air is not
sprayed onto the portion irradiated with laser.
[0050] (5) Determine that there is the air spraying effect and mark
".largecircle." when spiral contamination does not occur in (3) but
occurs in (4).
[0051] (6) Determine that there is no air spraying effect and mark
"X" when spiral contamination occurs in (3).
[0052] (7) Determine that adherence of foreign particles is
insufficient when no spiral contamination occurs in both (3) and
(4), and cause the foreign particles to adhere again and perform
measurement of (3) and (4).
[0053] (8) Conduct evaluation of (2) through (7) using the air
spraying flow rate [l/min] and the laser power [mW] as
parameters.
[0054] The method for determining the air spraying effect is as
follows. The state after measurement is compared with the initial
state before adherence of the foreign particles. It is determined
that there is no air spraying effect if there is spiral
contamination as shown in FIG. 3A or the track of destruction of
the foreign particles. In contrast, it is determined that there is
the air spraying effect if there is no spiral contamination
compared with the initial state.
[0055] It has been confirmed that the spraying of the air has an
effect of reducing the range of contamination even in the area
shown by X where the foreign particles are destroyed. This is
presumably because the flow of the air on the wafer surface during
inspection is disturbed by the sprayed air, making it difficult for
them to adhere to the wafer.
[0056] It is understood from the result of FIG. 4 that the gas
spraying flow rate required to suppress destruction of foreign
particles increases as the laser power increases, and that the flow
rate of at least 15 l/min or more is required with the laser power
of 500 mW or more that is necessary for detection of fine foreign
particles. It however has been confirmed that the gas supplied with
the flow rate exceeding 30 l/min would likely blow off the adhered
foreign particles. As such, it is desirable that the flow rate of
gas 17 is set preferably in the range of 15 to 30 l/min to
guarantee the performance of foreign particle repeatability. More
desirably, using the following expression 1 obtained from the
result of FIG. 4, the flow rate is set preferably in the range of
not lower than the flow rate obtained from the expression 1 and not
greater than 30 l/min:
y=0.015x+7.5 (expression 1)
where y is the spraying flow rate of gas 17 (l/min), and x is the
laser power (mW). When gas of high thermal conductivity, such as
helium gas or the like, is used, a greater effect of suppressing
thermal destruction can be obtained with the less flow rate of gas
17, which can improve both the detection sensitivity and the
foreign particle repeatability.
[0057] Further, the relation between the laser power and the
spraying flow rate shown in FIG. 4 is displayed as a scatter plot
34 on the setting screen provided on the display means shown in
FIG. 6 or on a screen of database separately provided. By
displaying scatter plot 34 as the reference data, it is possible to
prevent a setting error of flow rate of gas 17 with respect to the
laser power. Furthermore, it is configured to allow an alarm
message to be displayed on the display means or the registration to
be rejected, when the flow rate setting of gas 17 out of the
relation of FIG. 4 with respect to the laser power is input, based
on the expression 1 above and the upper limit of the flow rate.
[0058] As described above, according to the present embodiment, gas
of high cleanliness is sprayed, which ensures that inspection of
the wafer is carried out while maintaining the conventional
cleanliness. The adhered foreign particles are not blown off, which
ensures that the conventional performance of foreign particle
repeatability is maintained. Further, according to the present
embodiment, it is possible to increase the density of laser energy
at the limit of not destroying the foreign particles. Even in the
event that the laser beam is irradiated exceeding the laser energy
density at the limit of not destroying the foreign particles, the
range of scattering of the destroyed foreign particles can be made
smaller than in the conventional case.
[0059] Although the embodiments of the present invention have been
described above, it will be apparent to a person skilled in the art
that the present invention is not limited thereto, but various
changes and modifications are possible within the spirit of the
present invention and within the scope of the appended claims.
* * * * *