U.S. patent application number 15/215343 was filed with the patent office on 2016-11-10 for polishing apparatus.
The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Toshifumi KIMBA, Masaki KINOSHITA, Itsuki KOBATA, Yoichi KOBAYASHI, Katsutoshi ONO.
Application Number | 20160325399 15/215343 |
Document ID | / |
Family ID | 46317752 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160325399 |
Kind Code |
A1 |
KOBATA; Itsuki ; et
al. |
November 10, 2016 |
POLISHING APPARATUS
Abstract
A polishing apparatus for polishing a substrate is provided. The
polishing apparatus includes: a polishing table holding a polishing
pad; a top ring configured to press the substrate against the
polishing pad; first and second optical heads each configured to
apply the light to the substrate and to receive reflected light
from the substrate; spectroscopes each configured to measure at
each wavelength an intensity of the reflected light received; and a
processor configured to produce a spectrum indicating a
relationship between intensity and wavelength of the reflected
light. The first optical head is arranged so as to face a center of
the substrate, and the second optical head is arranged so as to
face a peripheral portion of the substrate.
Inventors: |
KOBATA; Itsuki; (Tokyo,
JP) ; KOBAYASHI; Yoichi; (Tokyo, JP) ; ONO;
Katsutoshi; (Tokyo, JP) ; KINOSHITA; Masaki;
(Tokyo, JP) ; KIMBA; Toshifumi; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
46317752 |
Appl. No.: |
15/215343 |
Filed: |
July 20, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14808252 |
Jul 24, 2015 |
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15215343 |
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13330881 |
Dec 20, 2011 |
9401293 |
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14808252 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/013 20130101;
B24B 37/042 20130101; B24B 37/04 20130101; B24B 37/26 20130101;
H01L 22/26 20130101; B24B 37/205 20130101; H01L 21/31053 20130101;
B24B 49/12 20130101; B24B 37/005 20130101; H01L 21/67092 20130101;
H01L 21/68721 20130101; H01L 21/67075 20130101; H01L 21/67253
20130101; B24B 37/10 20130101 |
International
Class: |
B24B 37/26 20060101
B24B037/26; H01L 21/66 20060101 H01L021/66; B24B 49/12 20060101
B24B049/12; B24B 37/013 20060101 B24B037/013; B24B 37/04 20060101
B24B037/04; B24B 37/10 20060101 B24B037/10; H01L 21/3105 20060101
H01L021/3105; B24B 37/005 20060101 B24B037/005 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2010 |
JP |
2010-289209 |
Claims
1. A polishing pad for a substrate polishing apparatus, the
polishing pad being held on a polishing table that is configured to
rotate around its own axis, the polishing pad comprising: a first
surface that is in contact with the polishing table; a second
surface that is opposite to the first surface and is pressed
against a substrate held by a top ring so as to polish the
substrate; a first through-hole extending from the first surface to
the second surface, the first through-hole being configured to
allow the light to pass therethrough from a first optical head
disposed in the polishing table, the first through-hole being
arranged to move in a first path that extends across the center of
the top ring while the polishing pad on the polishing table makes
one revolution, the first path extending from one side to an
opposite side of the top ring in substantially a diametrical
direction; and a second through-hole extending from the first
surface to the second surface, the second thorough-hole being
configured to allow the light to pass therethrough from a second
optical head disposed in the polishing table, the second
through-hole being arranged to move in a second path that extends
across only an annular region of the top ring when the first
through-hole is not present under the top ring while the polishing
pad with the polishing table makes one revolution.
2. The polishing pad according to claim 1, wherein an angle between
a line interconnecting the first through-hole and the center of the
polishing pad and a line interconnecting the second through-hole
and the center of the polishing pad is larger than 0 degrees.
3. The polishing pad according to claim 1, wherein the first
through-hole and the second through-hole are located at opposite
sides with respect to the center of the polishing pad.
4. The polishing pad according to claim 1, wherein a distance from
the center of the polishing pad to the first through-hole is
different from a distance from the center of the polishing pad and
the second through-hole.
5. The polishing pad according to claim 1, wherein the two
through-holes are provided with transparent windows,
respectively.
6. A polishing pad for a substrate polishing apparatus, the
polishing pad being held on a polishing table that is configured to
rotate around its own axis and includes a retainer ring that can
surround a substrate, the polishing pad comprising: a first surface
that is in contact with the polishing table; a second surface that
is opposite to the first surface and is pressed against a substrate
held by a top ring so as to polish the substrate; a first
through-hole extending from the first surface to the second
surface, the first through-hole being configured to allow the light
to pass therethrough from a first optical head disposed in the
polishing table, the first through-hole being arranged to move in a
first path that extends across the center of the top ring while the
polishing pad on the polishing table makes one revolution, the
first path extending from one side to an opposite side of the
retainer ring in substantially a diametrical direction; and a
second through-hole extending from the first surface to the second
surface, the second thorough-hole being configured to allow the
light to pass therethrough from a second optical head disposed in
the polishing table, the second through-hole being arranged to move
in a second path that extends across only an annular region of the
top ring when the first through-hole is not present under the top
ring while the polishing pad with the polishing table makes one
revolution.
7. The polishing pad according to claim 6, wherein an angle between
a line interconnecting the first through-hole and the center of the
polishing pad and a line interconnecting the second through-hole
and the center of the polishing pad is larger than 0 degrees.
8. The polishing pad according to claim 6, wherein the first
through-hole and the second through-hole are located at opposite
sides with respect to the center of the polishing pad.
9. The polishing pad according to claim 6, wherein a distance from
the center of the polishing pad to the first through-hole is
different from a distance from the center of the polishing pad and
the second through-hole.
10. The polishing pad according to claim 6, wherein the two
through-holes are provided with transparent windows,
respectively.
11. A polishing pad for a substrate polishing apparatus, the
polishing pad being held on a polishing table that is configured to
rotate around its own axis and includes a membrane defining a
circular pressure chamber and a plurality of annular pressure
chambers, the polishing pad comprising: a first surface that is in
contact with the polishing table; a second surface that is opposite
to the first surface and is pressed against a substrate held by a
top ring so as to polish the substrate; a first through-hole
extending from the first surface to the second surface, the first
through-hole being configured to allow the light to pass
therethrough from a first optical head disposed in the polishing
table, the first through-hole being arranged to move in a first
path that extends across the center of the top ring while the
polishing pad on the polishing table makes one revolution, the
first path extending from one side to an opposite side of an
outermost one of the plurality of annular pressure chambers in
substantially a diametrical direction; and a second through-hole
extending from the first surface to the second surface, the second
thorough-hole being configured to allow the light to pass
therethrough from a second optical head disposed in the polishing
table, the second through-hole being arranged to move in a second
path that extends across only at least one annular pressure
chamber, corresponding to a peripheral portion of the substrate, of
the plurality of annular pressure chambers when the first
through-hole is not present under the top ring while the polishing
pad with the polishing table makes one revolution.
12. The polishing pad according to claim 11, wherein an angle
between a line interconnecting the first through-hole and the
center of the polishing pad and a line interconnecting the second
through-hole and the center of the polishing pad is larger than 0
degrees.
13. The polishing pad according to claim 11, wherein the first
through-hole and the second through-hole are located at opposite
sides with respect to the center of the polishing pad.
14. The polishing pad according to claim 11, wherein a distance
from the center of the polishing pad to the first through-hole is
different from a distance from the center of the polishing pad and
the second through-hole.
15. The polishing pad according to claim 11, wherein the two
through-holes are provided with transparent windows, respectively.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. application Ser.
No. 14/808,252, filed Jul. 24, 2015, which is a Divisional of U.S.
patent application Ser. No. 13/330,881, filed Dec. 20, 2011, now
U.S. Pat. No. 9,401,293, issued Jul. 26, 2016, which claims the
benefit of Japanese Patent Application No. 2010-289209, filed Dec.
27, 2010, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a polishing apparatus for
polishing a surface of a substrate, such as a semiconductor wafer,
and more specifically to a polishing apparatus and a polishing
method which obtain a film-thickness distribution over the entire
substrate surface including a central portion and a peripheral
portion thereof during polishing of the substrate and control a
load on the substrate based on the film-thickness distribution.
[0004] 2. Description of the Related Art
[0005] A CMP (chemical mechanical polishing) apparatus is widely
known as equipment for polishing a surface of a substrate, such as
a semiconductor wafer. This CMP apparatus polishes the surface of
the substrate by pressing the substrate against a polishing pad on
a rotating polishing table while supplying a polishing liquid onto
the polishing pad. The CMP apparatus typically has a film-thickness
measuring device for measuring a film thickness or a signal
equivalent to the film thickness. The CMP apparatus having such a
film-thickness measuring device controls a polishing load on the
substrate based on a measured value of the film thickness obtained
from the film-thickness measuring device and to determine a
polishing end point. An eddy current sensor or an optical sensor is
generally used as the film-thickness measuring device.
[0006] FIG. 1 is a plan view showing a positional relationship
between film-thickness measuring device of a conventional CMP
apparatus and substrate. A film-thickness measuring device 100 is
provided in a polishing table 102 so as to face a substrate W on a
polishing pad 105. The film-thickness measuring device 100 measures
the film thickness at multiple measuring points on the substrate W
while moving across the substrate W each time the polishing table
102 rotates. In the conventional CMP apparatus, the film-thickness
measuring device 100 is arranged so as to pass through the center
of the substrate W, as shown in FIG. 1. This is for the purpose of
measuring the film thickness at multiple measuring points
distributed in a radial direction of the substrate W, as shown in
FIG. 2.
[0007] There exist microcircuit patterns on the surface of the
substrate to be polished. In some regions on the substrate, the
existence of such circuit patterns could cause a difference in
obtained data indicating the film thickness (e.g., voltage value or
current value in the case of using the eddy current sensor,
relative reflectance in the case of using the optical sensor) even
when the film thickness is the same. Thus, in order to avoid such
an influence of the circuit patterns, smoothing is performed on the
data.
[0008] The CMP apparatus determines the polishing loads on multiple
regions (e.g., a central portion, an intermediate portion, a
peripheral portion) of the substrate based on a film-thickness
profile obtained during polishing and polishes the substrate so as
to make the film thickness uniform. However, in the conventional
CMP apparatus, an accurate film thickness cannot be obtained in the
peripheral portion of the substrate because of the smaller number
of measuring points on this potion. This problem will be explained
with reference to FIG. 2. FIG. 2 is a view showing measuring points
on the substrate at which film-thickness measurement is performed
while the polishing table makes one revolution. The peripheral
portion of the substrate is an outermost annular portion having a
width ranging from 10 mm to 20 mm. Because of its narrow width, the
number of measuring points on the peripheral portion is small, as
can be seen from FIG. 2.
[0009] The peripheral portion of the substrate is most likely to be
affected by the polishing load and the polishing liquid, and
therefore the film thickness is likely to vary greatly during
polishing as compared with other regions. Moreover, an initial film
thickness in the peripheral portion of the substrate is, in many
cases, larger than that in other regions. Thus, it is necessary to
accurately measure and monitor the film thickness in the peripheral
portion during polishing of the substrate. However, as described
above, it is difficult to obtain an accurate film thickness in the
peripheral portion because of the smaller number of measuring
points on this portion.
[0010] FIG. 3 is a graph showing a change in the measured value of
the film thickness in the central portion of the substrate and a
change in the measured value of the film thickness in the
peripheral portion of the substrate. In FIG. 3, a vertical axis
represents measured value (estimated value) of the film thickness
obtained by the optical sensor, and a horizontal axis represents
polishing time. As can be seen from FIG. 3, the film thickness in
the central portion (see FIG. 2) of the substrate decreases
gradually with the polishing time, while the film thickness in the
peripheral portion (see FIG. 2) varies irregularly. This is because
the small number of measuring points in the peripheral portion
cannot provide sufficient data for the smoothing. In particular,
when the polishing table rotates at a high speed, the number of
measuring points in the peripheral portion becomes even
smaller.
[0011] As described above, it is difficult to obtain
highly-accurate film-thickness data in the peripheral portion of
the substrate, and consequently a highly-accurate film-thickness
profile of the substrate cannot be obtained during polishing. As a
result, it has been difficult to obtain a desired film-thickness
profile through feedback of the film-thickness profile to the
polishing load.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in view of the above
drawback. It is therefore an object of the present invention to
provide a polishing apparatus and a polishing method capable of
obtaining highly-accurate film-thickness data over a substrate
surface in its entirety including a central portion and a
peripheral portion.
[0013] One aspect of the present invention for achieving the above
object is to provide an apparatus for polishing a substrate having
a film thereon by bringing the substrate into sliding contact with
a polishing pad. The apparatus includes: a rotatable polishing
table for holding the polishing pad; a top ring configured to hold
the substrate and to press a surface of the substrate against the
polishing pad; at least one light source configured to emit light;
a first optical head configured to apply the light to the surface
of the substrate and to receive reflected light from the substrate;
a second optical head configured to apply the light to the surface
of the substrate and to receive reflected light from the substrate;
at least one spectroscope configured to measure at each wavelength
an intensity of the reflected light received by the first optical
head and the second optical head; and a processor configured to
produce a spectrum from the intensity of the reflected light at
each wavelength measured by the spectroscope and to determine a
thickness of the film of the substrate from the spectrum produced.
The spectrum indicates a relationship between intensity and
wavelength of the reflected light. The first optical head is
arranged so as to face a center of the substrate held by the top
ring, and the second optical head is arranged so as to face a
peripheral portion of the substrate held by the top ring.
[0014] In a preferred aspect of the present invention, the second
optical head is located outwardly of the first optical head with
respect to a radial direction of the polishing table.
[0015] In a preferred aspect of the present invention, the second
optical head is located inwardly of the first optical head with
respect to a radial direction of the polishing table.
[0016] In a preferred aspect of the present invention, the first
optical head and the second optical head are located at different
positions with respect to a circumferential direction of the
polishing table.
[0017] In a preferred aspect of the present invention, a line
connecting the first optical head to the center of the polishing
table and a line connecting the second optical head to the center
of the polishing table meet at an angle of substantially 180
degrees.
[0018] In a preferred aspect of the present invention, the second
optical head is located outwardly of the polishing table.
[0019] In a preferred aspect of the present invention, the
apparatus further includes a controller for determining load on the
substrate. The top ring has a mechanism configured to press a
central portion and the peripheral portion of the substrate
independently against the polishing pad, and the controller is
configured to determine loads of the top ring on the central
portion and the peripheral portion based on a film thickness at the
central portion and a film thickness at the peripheral portion.
[0020] Another aspect of the present invention is to provide an
apparatus for polishing a substrate having a film thereon by
bringing the substrate into sliding contact with a polishing pad.
The apparatus include: a rotatable polishing table for holding the
polishing pad; a top ring configured to hold the substrate and to
press a surface of the substrate against the polishing pad; and a
first film-thickness sensor and a second film-thickness sensor each
configured to measure a thickness of the film of the substrate. The
first film-thickness sensor is arranged so as to face a center of
the substrate held by the top ring, and the second film-thickness
sensor is arranged so as to face a peripheral portion of the
substrate held by the top ring.
[0021] Still another aspect of the present invention is to provide
a method of polishing a substrate having a film thereon by bringing
the substrate into sliding contact with a polishing pad. The method
includes: rotating a polishing table holding the polishing pad;
pressing a surface of the substrate against the rotating polishing
pad; applying light to the surface of the substrate from a first
optical head arranged so as to face a center of the substrate and
receiving reflected light from the substrate by the first optical
head; applying light to the surface of the substrate from a second
optical head arranged so as to face a peripheral portion of the
substrate and receiving reflected light from the substrate by the
second optical head; measuring at each wavelength an intensity of
the reflected light received by the first optical head and the
second optical head; producing a spectrum from the measured
intensity, the spectrum indicating a relationship between intensity
and wavelength of the reflected light; and determining a thickness
of the film of the substrate from the spectrum.
[0022] In a preferred aspect of the present invention, the first
optical head and the second optical head apply the light to the
surface of the substrate and receive the reflected light from the
substrate at different times.
[0023] In a preferred aspect of the present invention, the first
optical head and the second optical head apply the light to the
surface of the substrate and receive the reflected light from the
substrate alternately at substantially constant time intervals.
[0024] In a preferred aspect of the present invention, the
peripheral portion of the substrate is an outermost annular portion
of the substrate, and a width of the peripheral portion is in a
range of 10 mm to 20 mm.
[0025] According to the present invention, the tip of the second
optical head moves along the peripheral portion of the substrate
with the rotation of the polishing table. Therefore, the number of
measuring points on the peripheral portion is increased, so that
more highly accurate film thickness can be obtained. As a result, a
highly-accurate film-thickness profile (i.e., a film-thickness
distribution along the radial direction of the substrate) can be
created during polishing, and a desired film-thickness profile can
be obtained based on the created film-thickness profile.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a plan view showing a positional relationship
between film-thickness measuring device of a conventional CMP
apparatus and substrate;
[0027] FIG. 2 is a view showing measuring points on the substrate
at which film-thickness measurement is performed while a polishing
table makes one revolution;
[0028] FIG. 3 is a graph showing a change in measured value of the
film thickness in a central portion of the substrate and a change
in measured value of the film thickness in a peripheral portion of
the substrate;
[0029] FIG. 4A is a schematic view showing the principle of
determining a film thickness based on a spectrum of a reflected
light from a substrate;
[0030] FIG. 4B is a plan view showing a positional relationship
between the substrate and a polishing table;
[0031] FIG. 5 is a graph showing spectra of the reflected light
obtained by performing a polishing simulation on the substrate
shown in FIG. 4A based on the theory of interference of light;
[0032] FIG. 6 is a cross-sectional view schematically showing a
polishing apparatus according to an embodiment of the present
invention;
[0033] FIG. 7 is a plan view showing arrangement of a first optical
head having a first light-applying unit and a first light-receiving
unit and a second optical head having a second light-applying unit
and a second light-receiving unit;
[0034] FIG. 8 is a view showing paths of a tip of the second
optical head described on a surface of the substrate;
[0035] FIG. 9 is an example of a film-thickness profile produced by
a processor;
[0036] FIG. 10 is a cross-sectional view showing an example of a
top ring having a pressing mechanism for pressing plural regions of
the substrate independently;
[0037] FIG. 11 is a diagram showing film-thickness profiles;
[0038] FIG. 12 is a plan view showing another example of
arrangement of the first optical head and the second optical
head;
[0039] FIG. 13 is a view showing paths of the tip of the second
optical head shown in FIG. 12;
[0040] FIG. 14 is a plan view showing still another example of
arrangement of the first optical head and the second optical
head;
[0041] FIG. 15 is a view showing an example in which a common
spectroscope and a common light source are provided for the first
optical head and the second optical head;
[0042] FIG. 16 is a plan view showing still another example of
arrangement of the first optical head and the second optical
head;
[0043] FIG. 17 is a plan view showing still another example of
arrangement of the first optical head and the second optical
head;
[0044] FIG. 18 is a plan view showing still another example of
arrangement of the first optical head and the second optical
head;
[0045] FIG. 19 is a plan view showing an example in which a third
optical head is provided in addition to the first optical head and
the second optical head;
[0046] FIG. 20 is a plan view showing another example of
arrangement of the first optical head, the second optical head, and
the third optical head;
[0047] FIG. 21 is a plan view showing still another example of
arrangement of the first optical head, the second optical head, and
the third optical head;
[0048] FIG. 22 is a plan view showing still another example of
arrangement of the first optical head, the second optical head, and
the third optical head;
[0049] FIG. 23 is a plan view showing another example of
arrangement of the second optical head;
[0050] FIG. 24 is a plan view showing still another example of
arrangement of the second optical head; and
[0051] FIG. 25 is a cross-sectional view showing a modified example
of the polishing apparatus shown in FIG. 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0052] Embodiments of the present invention will be described below
with reference to the drawings. FIG. 4A is a schematic view showing
the principle of determining a film thickness based on a spectrum
of a reflected light from a substrate, and FIG. 4B is a plan view
showing a positional relationship between the substrate and a
polishing table. As shown in FIG. 4A, a substrate W, to be
polished, has an underlying layer (e.g., a silicon layer) and a
film (e.g., a dielectric film, such as SiO.sub.2, having a property
of light permeability) formed on the underlying layer. A surface of
the substrate W is pressed against a polishing pad 22 on a rotating
polishing table 20, so that the film of the substrate W is polished
by sliding contact with the polishing pad 22.
[0053] A light-applying unit 11 and a light-receiving unit 12 are
arranged so as to face the surface of the substrate W. The
light-applying unit 11 is coupled to a light source 16, and light
emitted by the light source 16 is directed to the surface of the
substrate W by the light-applying unit 11. The light-applying unit
11 applies the light in a direction substantially perpendicular to
the surface of the substrate W, and the light-receiving unit 12
receives the reflected light from the substrate W. The light
emitted by the light source 16 is multiwavelength light. As shown
in FIG. 4B, the light is applied to the surface of the substrate W
each time the polishing table 20 makes one revolution. A
spectroscope 14 is coupled to the light-receiving unit 12. This
spectroscope 14 is configured to disperse the reflected light
according to wavelength and to measure the intensity of the
reflected light at each wavelength.
[0054] A processor 15 is coupled to the spectroscope 14. This
processor 15 is configured to read measurement data obtained by the
spectroscope 14 and to produce intensity distribution of the
reflected light from the measured values of the light intensity.
More specifically, the processor 15 produces a spectrum (spectral
profile) which indicates the light intensity at each of the
wavelengths. This spectrum is expressed as a line graph indicating
a relationship between wavelength and intensity of the reflected
light. The processor 15 is further configured to determine the film
thickness of the substrate W from the spectrum and to determine a
polishing end point. A general-purpose computer or a dedicated
computer can be used as the processor 15. The processor 15 performs
predetermined processing steps according to a program (or computer
software).
[0055] FIG. 5 is a graph showing spectra of the reflected light
obtained by performing a polishing simulation on the substrate
shown in FIG. 4A based on the theory of interference of light. In
FIG. 5, a horizontal axis represents wavelength of light, and a
vertical axis represents relative reflectance derived from the
intensity of the light. The relative reflectance is an index that
indicates the intensity of light. More specifically, the relative
reflectance is a ratio of the intensity of the reflected light to a
predetermined reference intensity. By dividing the intensity of the
reflected light (i.e., the actually measured intensity) by the
predetermined reference intensity, noise components are removed and
therefore intensity of the light with no noise can be obtained. The
predetermined reference intensity may be an intensity of the
reflected light obtained when polishing a silicon wafer with no
film thereon in the presence of water. Instead of the relative
reflectance, the intensity of the light may be used as it is.
[0056] The spectrum is an arrangement of the light intensity in the
order of wavelength and indicates the light intensity at each
wavelength. The spectrum varies depending on the film thickness.
This phenomenon is due to interference between light waves.
Specifically, the light, applied to the substrate, is reflected off
an interface between a medium (e.g., water) and the film and an
interface between the film and the underlying layer beneath the
film. The light waves from these interfaces interfere with each
other. The manner of interference between the light waves varies
according to the thickness of the film (i.e., a length of an
optical path). As a result, the spectrum of the reflected light
from the substrate varies depending on the thickness of the film,
as shown in FIG. 5.
[0057] The processor 15 determines the film thickness from the
spectrum obtained. A known technique can be used for determining
the film thickness from the spectrum. For example, there is a
method of estimating a film thickness by comparing a spectrum
obtained during polishing (i.e., an actually measured spectrum)
with prepared reference spectra, as disclosed in Japanese laid-open
patent publication No. 2009-505847. This method includes the steps
of comparing the spectrum at each point of time during polishing
with the plural reference spectra and determining a film thickness
from a reference spectrum whose shape is most similar to the shape
of the measured spectrum. The plural reference spectra are prepared
in advance by polishing a substrate that is identical or similar to
the substrate to be polished. Each reference spectrum is associated
with a film thickness at a point of time when that reference
spectrum is obtained. Therefore, the current film thickness can be
estimated from the reference spectrum having a shape that is most
similar to that of the spectrum obtained during polishing.
[0058] The processor 15 is coupled to a controller 19 for
determining polishing conditions, such as a polishing load on the
substrate. The spectrum created by the processor 15 is sent to the
controller 19, which then determines an optimum polishing load for
achieving a target film-thickness profile based on the spectrum
obtained during polishing and controls the polishing load on the
substrate, as will be described later.
[0059] FIG. 6 is a cross-sectional view schematically showing a
polishing apparatus according to an embodiment of the present
invention. The polishing apparatus includes the polishing table 20
for supporting the polishing pad 22 thereon, a top ring 24
configured to hold the substrate W and to press the substrate W
against the polishing pad 22, and a polishing liquid supply
mechanism 25 configured to supply a polishing liquid (slurry) onto
the polishing pad 22. The polishing table 20 is coupled to a motor
(not shown in the drawing) provided below the polishing table 20,
so that the polishing table 20 can rotate about its own axis. The
polishing pad 22 is secured to an upper surface of the polishing
table 20.
[0060] The polishing pad 22 has an upper surface 22a, which
provides a polishing surface for polishing the substrate W. The top
ring 24 is coupled to a motor and an elevating cylinder (not shown
in the drawing) via a top ring shaft 28. With these configurations,
the top ring 24 can move in the vertical direction and can rotate
about the top ring shaft 28. The top ring 24 has a lower surface
which is configured to hold the substrate W by a vacuum suction or
the like.
[0061] The substrate W, held on the lower surface of the top ring
24, is rotated by the top ring 24, and is pressed by the top ring
24 against the polishing pad 22 on the rotating polishing table 20.
Simultaneously, the polishing liquid is supplied onto the polishing
surface 22a of the polishing pad 22 from the polishing liquid
supply mechanism 25. The surface of the substrate W is polished in
the presence of the polishing liquid between the surface of the
substrate W and the polishing pad 22. A relative movement mechanism
for providing sliding contact between the substrate W and the
polishing pad 22 is constructed by the polishing table 20 and the
top ring 24.
[0062] The polishing table 20 has holes 30A and 30B whose upper
ends lying in the upper surface of the polishing table 20. The
polishing pad 22 has through-holes 31A and 31B at positions
corresponding to the holes 30A and 30B, respectively. The hole 30A
and the through-hole 31A are in fluid communication with each
other, and the hole 30B and the through-hole 31B are in fluid
communication with each other. Upper ends of the through-holes 31A
and 31B lie in the polishing surface 22a. The holes 30A and 30B are
coupled to a liquid supply source 35 via a liquid supply passage 33
and a rotary joint 32. During polishing, the liquid supply source
35 supplies water (preferably pure water) as a transparent liquid
into the holes 30A and 30B. The water fills spaces formed by the
lower surface of the substrate W and the through-holes 31A and 31B,
and is expelled therefrom through a liquid discharge passage 34.
The polishing liquid in the through-holes 31A and 31B is discharged
together with the water and thus a path of the light is secured.
The liquid supply passage 33 is provided with a valve (not shown in
the drawing) configured to operate in conjunction with the rotation
of the polishing table 20. The valve operates so as to stop the
flow of the water or reduce the flow of the water when the
substrate W is not located over the through-holes 31A and 31B.
[0063] The polishing apparatus has an optical film-thickness
measuring device for measuring the film thickness according to the
above-described method. This optical film-thickness measuring
device includes light sources 16a and 16b for emitting light, a
first light-applying unit 11a configured to direct the light,
emitted by the light source 16a, to the surface of the substrate W,
a first light-receiving unit 12a configured to receive the
reflected light from the substrate W, a second light-applying unit
11b configured to direct the light, emitted by the light source
16b, to the surface of the substrate W, a second light-receiving
unit 12b configured to receive the reflected light from the
substrate W, spectroscopes 14a and 14b configured to disperse (or
break) the reflected light according to the wavelength and to
measure the intensity of the reflected light over a predetermined
wavelength range, and the processor 15 configured to produce the
spectrum from the measurement data obtained by the spectroscopes
14a and 14b and to determine the film thickness of the substrate W
based on the spectrum. The spectrum indicates light intensities
distributed over the predetermined wavelength range and indicates a
relationship between intensity and wavelength of the light.
[0064] The first light-applying unit 11a, the first light-receiving
unit 12a, the second light-applying unit 11b, and the second
light-receiving unit 12b are each constructed by optical fiber. The
first light-applying unit 11a and the first light-receiving unit
12a constitute a first optical head (i.e., an optical
film-thickness measuring head) 13A, and the second light-applying
unit 11b and the second light-receiving unit 12b constitute a
second optical head (i.e., an optical film-thickness measuring
head) 13B. The first light-applying unit 11a is coupled to the
light source 16a, and the second light-applying unit 11b is coupled
to the light source 16b. The first light-receiving unit 12a is
coupled to the spectroscope 14a, and the second light-receiving
unit 12b is coupled to the spectroscope 14b.
[0065] A light emitting diode (LED), a halogen lamp, a xenon flash
lamp, or the like, which emits multi-wavelength light, can be used
for the light sources 16a and 16b. The first light-applying unit
11a, the first light-receiving unit 12a, the second light-applying
unit 11b, the second light-receiving unit 12b, the light sources
16a and 16b, and the spectroscopes 14a and 14b are provided in the
polishing table 20 and are rotated together with the polishing
table 20. The first light-applying unit 11a and the first
light-receiving unit 12a are located in the hole 30A formed in the
polishing table 20, and tips of the first light-applying unit 11a
and the first light-receiving unit 12a are adjacent to the surface,
to be polished, of the substrate W. Similarly, the second
light-applying unit 11b and the second light-receiving unit 12b are
located in the hole 30B formed in the polishing table 20, and tips
of the second light-applying unit 11b and the second
light-receiving unit 12b are adjacent to the surface, to be
polished, of the substrate W.
[0066] The first light-applying unit 11a and the first
light-receiving unit 12a are arranged perpendicularly to the
surface of the substrate W, so that the first light-applying unit
11a applies the light to the surface of the substrate W
perpendicularly. Similarly, the second light-applying unit 11b and
the second light-receiving unit 12b are arranged perpendicularly to
the surface of the substrate W, so that the second light-applying
unit 11b applies the light to the surface of the substrate W
perpendicularly.
[0067] The first light-applying unit 11a and the first
light-receiving unit 12a are arranged so as to face the center of
the substrate W held by the top ring 24. Therefore, as shown in
FIG. 4B, each time the polishing table 20 rotates, the tips of the
first light-applying unit 11a and the first light-receiving unit
12a move across the substrate W and the light is applied to regions
including the center of the substrate W. This is for the purpose of
measuring the film thickness over the entire surface of the
substrate W, including a central portion of the substrate W,
through the first light-applying unit 11a and the first
light-receiving unit 12a passing through the center of the
substrate W. The processor 15 can therefore produce a
film-thickness profile (i.e., a film-thickness distribution) based
on the film thickness data measured.
[0068] The second light-applying unit 11b and the second
light-receiving unit 12b are arranged so as to face a peripheral
portion of the substrate W held by the top ring 24. The tips of the
second light-applying unit 11b and the second light-receiving unit
12b move along the peripheral portion of the substrate W each time
the polishing table 20 rotates. Therefore, the light is applied to
the peripheral portion of the substrate W each time the polishing
table 20 rotates.
[0069] During polishing, the substrate W is irradiated with the
light from the first light-applying unit 11a and the second
light-applying unit 11b. The light from the first light-applying
unit 11a is reflected off the surface of the substrate W, and the
reflected light is received by the first light-receiving unit 12a.
The light from the second light-applying unit 11b is reflected off
the surface of the substrate W, and the reflected light is received
by the second light-receiving unit 12b. While the substrate W is
irradiated with the light, the water is supplied into the hole 30A
and the through-hole 31A, so that the space formed between the
surface of the substrate W and the respective tips of the first
light-applying unit 11a and first light-receiving unit 12a is
filled with the water. Similarly, while the substrate W is
irradiated with the light, the water is supplied into the hole 30B
and the through-hole 31B, so that the space formed between the
surface of the substrate W and the respective tips of the second
light-applying unit 11b and second light-receiving unit 12b is
filled with the water.
[0070] The spectroscope 14a is configured to disperse the reflected
light sent from the first light-receiving unit 12a according to
wavelength and to measure the intensity of the reflected light at
each wavelength. Similarly, the spectroscope 14b is configured to
disperse the reflected light sent from the second light-receiving
unit 12b according to wavelength and to measure the intensity of
the reflected light at each wavelength. The processor 15 creates
the spectrum from the intensity of the reflected light measured by
the spectroscope 14a and the spectroscope 14b. The spectrum shows a
relationship between the intensity and the wavelength of the
reflected light. Further, the processor 15 determines the current
film thickness of the substrate W using the previously-described
known technique.
[0071] FIG. 7 is a plan view of arrangement of the first optical
head 13A having the first light-applying unit 11a and the first
light-receiving unit 12a and the second optical head 13B having the
second light-applying unit 11b and the second light-receiving unit
12b. As shown in FIG. 7, the center of the substrate W is located
on a path of the first optical head 13A, and the peripheral portion
of the substrate W is located on a path of the second optical head
13B. As can be seen from FIG. 7, the second optical head 13B moves
across only the peripheral portion of the substrate W and its
travelling direction is approximately in the circumferential
direction of the substrate W.
[0072] The first optical head 13A and the second optical head 13B
are arranged along the radial direction of the polishing table 20.
Therefore, a line connecting the first optical head 13A to the
center O of the polishing table 20 and a line connecting the second
optical head 13B to the center O of the polishing table 20 meet at
an angle of 0 degree. The second optical head 13B is located
outwardly of the first optical head 13A with respect to the radial
direction of the polishing table 20. Specifically, a distance
between the second optical head 13B and the center O of the
polishing table 20 is longer than a distance between the first
optical head 13A and the center O of the polishing table 20.
[0073] FIG. 8 is a view showing the paths of the tip of the second
optical head 13B described on the surface of the substrate W. More
specifically, FIG. 8 shows the paths of the second optical head 13B
when the polishing table 20 makes two revolutions. As can be seen
from FIG. 8, the second optical head 13B moves along the peripheral
portion of the substrate W as the polishing table 20 rotates. As a
result, the number of measuring points on the peripheral portion
becomes larger than the number of measuring points shown in FIG. 2
in the conventional CMP apparatus. Therefore, the film thickness in
the peripheral portion of the substrate W can be determined
accurately from the larger number of measurement data.
[0074] In this specification, the peripheral portion of the
substrate is an outermost annular portion of the substrate, as
shown in FIG. 8, and a width thereof is in the range of 10 mm to 20
mm. For example, in the case of a substrate having a diameter of
300 mm, the width of the annular peripheral portion is about 10 mm.
The peripheral portion is a region where devices are formed. The
peripheral portion of the substrate is most likely to be affected
by the polishing load and the polishing liquid during polishing,
and therefore the film thickness is likely to vary greatly during
polishing as compared with other regions. Therefore,
highly-accurate monitoring of the film thickness is required during
polishing.
[0075] The substrate W is polished by the sliding contact between
the substrate W and the polishing pad 22 and by chemical action of
the polishing liquid. Therefore, portions of the polishing pad 22
where the first optical head 13A and the second optical head 13B
are provided do not contribute to polishing of the substrate W. As
can be seen from FIG. 8, the second optical head 13B passes through
only the peripheral portion of the substrate W and does not pass
through other portions. Therefore, the influence of the second
optical head 13B on the substrate polishing can be minimized.
[0076] In the case where the polishing table 20 has a larger
diameter than that of the substrate W, the slower the polishing
table 20 rotates, the longer time it takes for the second optical
head 13B to pass through the substrate W. Therefore, for example,
the polishing table 20 may rotate at a speed of 50 min.sup.-1 or
less during polishing of the substrate W. Alternatively, the
rotational speed of the polishing table 20 may be lowered to less
than a preset rotational speed in predetermined time intervals
during polishing of the substrate W.
[0077] In in-situ measurement in which the film thickness is
measured during polishing of the substrate, the polishing liquid
may affect the measurement of the film thickness. In particular, in
the optical film-thickness measuring device, the light may be
blocked by the polishing liquid and as a result highly-accurate
measurement may not be performed. Thus, in order to remove the
influence of the polishing liquid on the film-thickness
measurement, pure water may be supplied onto the polishing pad 22
regularly while the substrate is polished (i.e., water-polished)
and the film thickness of the substrate may be measured during
supply of the pure water.
[0078] The processer 15 produces the film-thickness profile from a
combination of the film-thickness values obtained through the first
optical head 13A and the film-thickness values obtained through the
second optical head 13B. FIG. 9 is an example of the film-thickness
profile produced by the processor 15. As shown in FIG. 9, the
film-thickness profile is composed of a large number of
film-thickness values that have been determined by the processer
15. The film-thickness values (indicated by .DELTA.) obtained using
the first optical head 13A are allotted to portions other than the
peripheral portion of the substrate W, and the film-thickness
values (indicated by .largecircle.) obtained using the second
optical head 13B are allotted to the peripheral portion of the
substrate W. In this manner, the film-thickness values obtained
through the second optical head 13B are used to create a part of
the film-thickness profile corresponding to the peripheral portion
of the substrate W. Therefore, the processer 15 can produce the
highly-accurate film-thickness profile from the center to the
peripheral portion of the substrate W.
[0079] The film-thickness profile is a film-thickness distribution
that indicates a film thickness in each region of the substrate W.
By adjusting the polishing load on each region of the substrate
during polishing, a desired film-thickness profile or a desired
polishing profile (i.e., a profile indicating a distribution of
amounts of film removed) can be obtained. The top ring 24 has a
mechanism capable of independently pressing plural regions
(including the central portion and the peripheral portion) of the
substrate W. The top ring 24 having such a mechanism will be
described below with reference to FIG. 10.
[0080] FIG. 10 is a cross-sectional view showing an example of the
top ring 24 having the pressing mechanism for pressing plural
regions of the substrate independently. The top ring 24 has a top
ring body 51 coupled to the top ring shaft 28 via a universal joint
50, and a retainer ring 52 provided on a lower portion of the top
ring body 51. The top ring 24 further has a circular flexible
membrane 56 to be brought into contact with the substrate W, and a
chucking plate 57 that holds the membrane 56. The membrane 56 and
the chucking plate 57 are disposed below the top ring body 51. Four
pressure chambers (air bags) P1, P2, P3, and P4 are provided
between the membrane 56 and the chucking plate 57. The pressure
chambers P1, P2, P3, and P4 are formed by the membrane 56 and the
chucking plate 57. The central pressure chamber P1 has a circular
shape, and the other pressure chambers P2, P3, and P4 have an
annular shape. These pressure chambers P1, P2, P3, and P4 are in a
concentric arrangement.
[0081] Pressurized fluid (e.g., pressurized air) is supplied into
the pressure chambers P1, P2, P3, and P4 or vacuum is developed in
the pressure chambers P1, P2, P3, and P4 by a pressure-adjusting
device 70 through fluid passages 61, 62, 63, and 64, respectively.
The pressures in the pressure chambers P1, P2, P3, and P4 can be
changed independently to thereby independently adjust loads on four
regions of the substrate W: the central portion, an inner
intermediate portion, an outer intermediate portion, and the
peripheral portion. Further, by elevating or lowering the top ring
24 in its entirety, the retainer ring 52 can press the polishing
pad 22 at a predetermined load.
[0082] A pressure chamber P5 is formed between the chucking plate
57 and the top ring body 51. Pressurized fluid is supplied into the
pressure chamber P5 or vacuum is developed in the pressure chamber
P5 by the pressure-adjusting device 70 through a fluid passage 65.
With this operation, the chucking plate 57 and the membrane 56 in
their entirety can move up and down. The retainer ring 52 is
arranged around the substrate W so as to prevent the substrate W
from coming off the top ring 24 during polishing. The membrane 56
has an opening in a portion that forms the pressure chamber P3, so
that the substrate W can be held by the top ring 24 via the vacuum
suction by producing vacuum in the pressure chamber P3. Further,
the substrate W can be released from the top ring 24 by supplying
nitrogen gas or clean air into the pressure chamber P3.
[0083] The pressure-adjusting device 70 is coupled to the
controller 19. The polishing loads on the respective portions of
the substrate W, i.e., the internal pressures of the pressure
chambers P1, P2, P3, and P4, are determined by the controller 19.
The controller 19 is coupled to the above-described processor 15,
and the film-thickness profile produced by the processor 15 is sent
to the controller 19. The controller 19 controls the internal
pressures of the pressure chambers P1, P2, P3, and P4 through the
pressure-adjusting device 70. Specifically, the controller 19
determines target internal pressures of the pressure chambers P1,
P2, P3, and P4 such that the film-thickness profile obtained during
polishing coincides with a target film-thickness profile, and sends
command signals of the target internal pressures to the
pressure-adjusting device 70. The pressure-adjusting device 70 then
adjusts the internal pressures of the pressure chambers P1, P2, P3,
and P4 based on the command signals sent from the controller 19.
With these operations, the top ring 24 can press the respective
portions of the substrate W at optimum loads, respectively. It is
also possible to control an internal pressure of only one of the
pressure chambers (e.g., the internal pressure of the pressure
chamber P4 corresponding to the peripheral portion of the substrate
W) based on the film-thickness profile obtained. In this
embodiment, the second optical head 13B is arranged in a position
corresponding to the pressure chamber P4.
[0084] FIG. 11 is a diagram showing a film-thickness profile at a
polishing initial stage, a target film-thickness profile, a
film-thickness profile when polishing a substrate while performing
a feedback control of the polishing loads based on the
film-thickness profile obtained during polishing, and a
film-thickness profile when polishing a substrate without
performing the feedback control. The diagram of FIG. 11 shows
polishing results of the substrate having an initial film-thickness
profile in which the film in the peripheral portion is thicker than
the film in the other portions. As can be seen from FIG. 11, as a
result of polishing the substrate while performing the feedback
control of the polishing loads based on the film-thickness profile,
a film-thickness profile that is similar to the target
film-thickness profile is obtained. In contrast, when the feedback
control is not performed, a desired film-thickness profile is not
obtained.
[0085] In general, the same type of substrate is polished under the
same polishing conditions. However, since the polishing pad 22 and
the retainer ring 52 of the top ring 24, which are consumables of
the polishing apparatus, wear away gradually with the polishing
time, the film-thickness profile obtained varies gradually even
under the same conditions. Such a variation in the film-thickness
profile is remarkable particularly in the peripheral portion of the
substrate. This is because the polishing load tends to concentrate
on the peripheral portion of the substrate and this peripheral
portion is likely to be subject to the influence of the wear of the
retainer ring 52 and the polishing pad 22. According to the
above-described embodiment, because the film thickness in the
peripheral portion of the substrate can be measured accurately,
polishing error due to the wear of the polishing pad 22 and/or the
retainer ring 52 can be detected. Specifically, the wear of the
polishing pad 22 and/or the retainer ring 52 can be detected based
on a change with time in the film thickness in the peripheral
portion of the substrate. For example, if a desired film thickness
cannot be achieved even under the same polishing conditions, then
it can be judged that the polishing pad 22 and/or the retainer ring
52 has worn away. In this manner, the film-thickness measurement
data at the peripheral portion of the substrate can be used not
only for the real-time feedback control of the polishing load on
the substrate, but also for the wear detection of the consumables,
such as the polishing pad 22 and the retainer ring 52.
[0086] FIG. 12 is a plan view showing another example of
arrangement of the first optical head 13A and the second optical
head 13B. The arrangement of the first optical head 13A and the
second optical head 13B shown in FIG. 12 is basically the same as
the arrangement shown in FIG. 7, but differs in that the second
optical head 13B is closer to the center O of the polishing table
20 than the first optical head 13A is. Specifically, in the example
shown in FIG. 12, the second optical head 13B is located inwardly
of the first optical head 13A with respect to the radial direction
of the polishing table 20. As a result, a distance between the
second optical head 13B and the center O of the polishing table 20
is shorter than a distance between the first optical head 13A and
the center O of the polishing table 20.
[0087] FIG. 13 is a view showing paths of the second optical head
13B shown in FIG. 12, and more specifically shows the paths of the
second optical head 13B when the polishing table 20 makes two
revolutions. As can be seen from FIG. 13, the second optical head
13B moves along the peripheral portion of the substrate W as the
polishing table 20 rotates. Therefore, the film thickness in the
peripheral portion can be measured at more measuring points.
Furthermore, as can be seen from the comparison between the paths
shown in FIG. 8 and the paths shown in FIG. 13, the path of the
second optical head 13B shown in FIG. 13 is longer than the path of
the second optical head 13B shown in FIG. 8. Therefore, with the
arrangement shown in FIG. 12, the film thickness in the peripheral
portion can be measured at more measuring points. On the other
hand, since the second optical head 13B does not contribute to
polishing of the substrate W, it is preferable that the path of the
second optical head 13B be short, from the standpoint of
improvement of a polishing rate (i.e., a removal rate of the film).
While the arrangement shown in FIG. 7 provides slightly less
measuring points in the peripheral portion of the substrate W as
compared with the arrangement shown in FIG. 12, the arrangement
shown in FIG. 7 is preferable from the standpoint of improvement of
a polishing performance.
[0088] FIG. 14 is a plan view showing still another example of
arrangement of the first optical head 13A and the second optical
head 13B. As shown in FIG. 14, the first optical head 13A and the
second optical head 13B are located at opposite sides with respect
to the center O of the polishing table 20. More specifically, a
line connecting the first optical head 13A to the center O of the
polishing table 20 and a line connecting the second optical head
13B to the center O of the polishing table 20 meet at an angle of
substantially 180 degrees. FIG. 14 shows a state in which the first
optical head 13A is facing the center of the substrate W (described
by a solid line) and a state in which the second optical head 13B
is facing the peripheral portion of the substrate W (described by a
dotted line). The second optical head 13B is located outwardly of
the first optical head 13A with respect to the radial direction of
the polishing table 20.
[0089] In the above-discussed examples shown in FIG. 7 and FIG. 12,
the first optical head 13A and the second optical head 13B apply
the light to the substrate W and receive the light from the
substrate W substantially simultaneously. In the example shown in
FIG. 14, the first optical head 13A and the second optical head 13B
apply the light to the substrate W and receive the light from the
substrate W at different timings.
[0090] As described above, in the arrangement shown in FIG. 14, the
film thickness at the central portion of the substrate W and the
film thickness at the peripheral portion of the substrate W are
measured at different times. Therefore, it is possible to use one
spectroscope for receiving both the reflected light from the first
optical head 13A and the reflected light from the second optical
head 13B. That is, even if one spectroscope receives the reflected
light from the central portion of the substrate W and the reflected
light from the peripheral portion of the substrate W, these
reflected lights are not superimposed in the spectroscope. Further,
it is also possible to connect one light source to the first
optical head 13A and the second optical head 13B selectively. Next,
an example having a common spectroscope and a common light source
will be described with reference to FIG. 15.
[0091] As shown in FIG. 15, the first light-applying unit 11a and
the second light-applying unit 11b are coupled to a light source 16
through a first optical switch 40A. This first optical switch 40A
is configured to couple the light source 16 to one of the first
light-applying unit 11a and the second light-applying unit 11b
selectively. Similarly, the first light-receiving unit 12a and the
second light-receiving unit 12b are coupled to a spectroscope 14
through a second optical switch 40B. The optical switch is a device
for switching light-transmission route. A typical type of optical
switch has a mirror for changing a travelling direction of light
and switches the light-transmission route by reflecting incident
light. Other than the optical switch using the mirror, a waveguide
optical switch may be used. This type of optical switch uses a
material whose index of refraction varies upon input of heat or
electricity. These known optical switches can be used as the first
optical switch 40A and the second optical switch 40B.
[0092] In the above-described structure, when the first optical
head 13A moves across the substrate W, the light source 16 and the
spectroscope 14 are coupled to the first light-applying unit 11a
and the first light-receiving unit 12a by the optical switches 40A
and 40B. When the second optical head 13B moves across the
substrate W, the light source 16 and the spectroscope 14 are
coupled to the second light-applying unit 11b and the second
light-receiving unit 12b by the optical switches 40A and 40B. In
this manner, by using the optical switches 40A and 40B, the light
source 16 and the spectroscope 14 can be coupled to the first
optical head 13A or the second optical head 13B alternately.
[0093] In the example shown in FIG. 14, the first optical head 13A
and the second optical head 13B are arranged at substantially equal
intervals in a circumferential direction of the polishing table 20,
so that the first optical head 13A and the second optical head 13B
apply the light to the substrate W and receive the reflected light
from the substrate W alternately at substantially constant time
intervals. Therefore, the processor 15 can secure a sufficient time
for processing the measurement data (i.e., data containing measured
values of the intensity of the reflected light) sent from the
spectroscope 14.
[0094] While the second optical head 13B is arranged outwardly of
the first optical head 13A with respect to the radial direction of
the polishing table 20 in the example of FIG. 14, the second
optical head 13B may be arranged inwardly of the first optical head
13A with respect to the radial direction of the polishing table 20
as shown in FIG. 16. Specifically, the line connecting the second
optical head 13B to the center O of the polishing table 20 may be
shorter than the line connecting the first optical head 13A to the
center O of the polishing table 20. In this case also, the same
effects as in the examples shown in FIG. 14 and FIG. 15 can be
obtained.
[0095] FIG. 17 is a plan view showing still another example of
arrangement of the first optical head 13A and the second optical
head 13B. In the previously-discussed example shown in FIG. 14, the
first optical head 13A and the second optical head 13B are in
alignment with each other. In FIG. 17 the second optical head 13B
is arranged in a different position than a position of the first
optical head 13A with respect to the circumferential direction the
polishing table 20. FIG. 17 shows a state in which the first
optical head 13A is facing the center of the substrate W (described
by a solid line) and a state in which the second optical head 13B
is facing the peripheral portion of the substrate W (described by a
dotted line). In this example, the line connecting the first
optical head 13A to the center O of the polishing table 20 and the
line connecting the second optical head 13B to the center O of the
polishing table 20 meet at an angle of about 120 degrees. In this
example also, the film thickness at the central portion of the
substrate W and the film thickness at the peripheral portion of the
substrate W are measured at different times. Therefore, the single
light source 16 and the single spectroscope 14 can be used for the
first optical head 13A and the second optical head 13B selectively
as shown in FIG. 15.
[0096] While the second optical head 13B is arranged outwardly of
the first optical head 13A with respect to the radial direction of
the polishing table 20 in the example of FIG. 17, the second
optical head 13B may be arranged inwardly of the first optical head
13A with respect to the radial direction of the polishing table 20
as shown in FIG. 18.
[0097] FIG. 19 is a plan view showing an example in which a third
optical head 13C is provided in addition to the first optical head
13A and the second optical head 13B. The third optical head 13C has
the same structure as the above-discussed first optical head 13A
and the second optical head 13B. The third optical head 13C is
coupled to a light source and a spectroscope (not shown). As shown
in FIG. 19, the first optical head 13A, the second optical head
13B, and the third optical head 13C are arranged along the radial
direction of the polishing table 20. The second optical head 13B
and the third optical head 13C are located outwardly of the first
optical head 13A.
[0098] The arrangement of the first optical head 13A and the second
optical head 13B is the same as the arrangement shown in FIG. 7.
The third optical head 13C is located in an intermediate point
between the first optical head 13A and the second optical head 13B.
Specifically, a distance between the first optical head 13A and the
third optical head 13C is substantially the same as a distance
between the third optical head 13C and the second optical head 13B.
The position of the third optical head 13C corresponds to an
intermediate portion located between the central portion and the
peripheral portion of the substrate. The second optical head 13B is
located in a position corresponding to the above-described pressure
chamber P4, and the third optical head 13C is located in a position
corresponding to the above-described pressure chamber P2 or the
pressure chamber P3. Therefore, a more highly-accurate
film-thickness profile can be obtained.
[0099] FIG. 20 is a plan view showing another example of
arrangement of the first optical head 13A, the second optical head
13B, and the third optical head 13C. The arrangement shown in FIG.
20 is basically the same as the arrangement shown in FIG. 19, but
differs in that the second optical head 13B and the third optical
head 13C are located inwardly of the first optical head 13A with
respect to the radial direction of the polishing table 20. In this
example also, the second optical head 13B is located in a position
corresponding to the peripheral portion of the substrate, and the
third optical head 13C is located in a position corresponding to
the intermediate portion located between the central portion and
the peripheral portion of the substrate.
[0100] FIG. 21 is a modified example of the arrangement shown in
FIG. 19, and FIG. 22 is a view showing a modified example of the
arrangement shown in FIG. 20. As shown in FIG. 21 and FIG. 22, the
third optical head 13C may be located closer to the second optical
head 13B than to the first optical head 13A. According to these
arrangements, the film thickness of the intermediate portion near
the peripheral portion of the substrate can be measured using the
third optical head 13C.
[0101] FIG. 23 is a plan view showing another example of
arrangement of the second optical head 13B. In this example, the
second optical head 13B is arranged outwardly of the polishing
table 20. The position of the first optical head 13A is the same as
in the above-discussed examples. The position of the second optical
head 13B is fixed and is supported by a support member (not shown).
The second optical head 13B does not rotate together with the
polishing table 20. In this example, the top ring 24 (see FIG. 6)
oscillates in the radial direction of the polishing table 20 during
polishing as indicated by arrow S such that the peripheral portion
of the substrate W protrudes from the polishing pad 22 on the
polishing table 20. Therefore, the second optical head 13B can
apply the light to the exposed peripheral portion of the substrate
W and can receive the reflected light from the substrate W.
[0102] FIG. 24 is a plan view showing still another example of
arrangement of the second optical head 13B. In this example, as
shown in FIG. 24, the second optical head 13B is located at the
center of the polishing table 20. The top ring 24 is configured to
oscillate in the radial direction of the polishing table 20 as
indicated by arrow T such that the peripheral portion of the
substrate W is moved to the center of the polishing table 20.
Therefore, in this example also, the second optical head 13B can
apply the light to the peripheral portion of the substrate W and
can receive the reflected light from the substrate W.
[0103] FIG. 25 is a cross-sectional view showing a modified example
of the polishing apparatus shown in FIG. 6. In the example shown in
FIG. 25, the liquid supply passage, the liquid discharge passage,
and the liquid supply source are not provided. Instead, transparent
windows 45A and 45B are provided in the polishing pad 22. The
light-applying units 11a and 11b direct the light to the surface of
the substrate W on the polishing pad 22 through the transparent
windows 45A and 45B, and the light-receiving units 12a and 12b
receive the reflected light from the substrate W through the
transparent windows 45A and 45B. The other structures are the same
as those of the polishing apparatus shown in FIG. 6. The
transparent windows 45A and 45B can be applied to the examples
shown in FIG. 7 through FIG. 24.
[0104] Although two or three optical heads are provided in the
above examples, the present invention is not limited to them. Four
or more optical heads may be provided so long as at least one
optical head is arranged so as to face the peripheral portion of
the substrate. Moreover, the present invention is not limited to
the optical film-thickness measuring device, and can be applied to
other type of film-thickness measuring device, such as eddy current
sensor. For example, according to the above-discussed examples
shown in FIG. 7 through FIG. 24, a first eddy current sensor
(film-thickness sensor) may be arranged so as to face the center of
the substrate, and a second eddy current sensor may be arranged so
as to face the peripheral portion of the substrate.
[0105] The previous description of embodiments is provided to
enable a person skilled in the art to make and use the present
invention. Moreover, various modifications to these embodiments
will be readily apparent to those skilled in the art, and the
generic principles and specific examples defined herein may be
applied to other embodiments. Therefore, the present invention is
not intended to be limited to the embodiments described herein but
is to be accorded the widest scope as defined by limitation of the
claims and equivalents.
* * * * *