U.S. patent application number 14/539315 was filed with the patent office on 2015-03-12 for polishing method, polishing apparatus and polishing tool.
The applicant listed for this patent is EBARA CORPORATION, OSAKA UNIVERSITY. Invention is credited to Junji MURATA, Takeshi OKAMOTO, Shun SADAKUNI, Yasuhisa SANO, Keita YAGI, Kazuto YAMAUCHI.
Application Number | 20150068680 14/539315 |
Document ID | / |
Family ID | 44167441 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150068680 |
Kind Code |
A1 |
SANO; Yasuhisa ; et
al. |
March 12, 2015 |
POLISHING METHOD, POLISHING APPARATUS AND POLISHING TOOL
Abstract
A polishing method and a polishing apparatus finish a surface of
a substrate of a compound semiconductor containing an element such
as Ga or the like to a desired level of flatness, so that the
surface can be flattened with high surface accuracy within a
practical processing time. In the presence of water, such as weak
acid water, water with air dissolved therein, or electrolytic ion
water, the surface of the substrate made of a compound
semiconductor containing either one of Ga, Al, and In and a surface
of a polishing pad having an electrically conductive member in an
area of the surface which is held in contact with the substrate)
are relatively moved while being held in contact with each other,
thereby polishing the surface of the substrate.
Inventors: |
SANO; Yasuhisa; (Osaka,
JP) ; YAMAUCHI; Kazuto; (Osaka, JP) ; MURATA;
Junji; (Osaka, JP) ; OKAMOTO; Takeshi; (Osaka,
JP) ; SADAKUNI; Shun; (Osaka, JP) ; YAGI;
Keita; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSAKA UNIVERSITY
EBARA CORPORATION |
Osaka
Tokyo |
|
JP
JP |
|
|
Family ID: |
44167441 |
Appl. No.: |
14/539315 |
Filed: |
November 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13511802 |
May 24, 2012 |
8912095 |
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PCT/JP2010/072837 |
Dec 14, 2010 |
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14539315 |
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Current U.S.
Class: |
156/345.12 |
Current CPC
Class: |
H01L 21/02024 20130101;
B24B 49/12 20130101; B24B 37/30 20130101; H01L 21/32125 20130101;
B24B 37/042 20130101; B24B 37/10 20130101; B24B 37/0053
20130101 |
Class at
Publication: |
156/345.12 |
International
Class: |
H01L 21/321 20060101
H01L021/321 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2009 |
JP |
2009-284491 |
Dec 15, 2009 |
JP |
2009-284493 |
Dec 15, 2009 |
JP |
2009-284494 |
Claims
1-52. (canceled)
53. A polishing tool comprising: an elastic base made of at least
one of elastic materials including rubber, resin, foamable resin,
and non-woven fabric; an electrically conductive member disposed on
the elastic base in an area held in contact with at least the
substrate; and an intermediate film interposed between the elastic
base and the electrically conductive member for increasing adhesion
therebetween.
54. The polishing tool according to claim 53, wherein the
intermediate film is made of carbon or chromium.
55. The polishing tool according to claim 53, wherein the elastic
base has grooves defined in a surface thereof for efficiently
supplying the processing liquid.
56. The polishing tool according to claim 53, wherein the elastic
base has a number of through-holes for passing at least one of
light and an ion current therethrough.
57. A polishing apparatus comprising: a container for holding a
processing liquid therein; the polishing tool recited in claim 53,
the polishing tool being disposed in the container while being
immersed in the processing liquid; a substrate holder for holding
the substrate and bringing the substrate into contact with the
polishing tool while immersing the substrate in the processing
liquid in the container; and a moving mechanism for relatively
moving the polishing tool and the substrate held by the substrate
holder while the polishing tool and the substrate are in contact
with each other.
58. The polishing apparatus according to claim 57, wherein the
processing liquid comprises a pH buffer solution of a neutral pH
which contains Ga ions, and the substrate is made of a
semiconductor containing an element of Ga.
59. A polishing apparatus comprising: the polishing tool recited in
claim 53; a substrate holder for holding a substrate and bringing
the substrate into contact with the polishing tool; a moving
mechanism for relatively moving the polishing tool and the
substrate held by the substrate holder while the polishing tool and
the substrate are in contact with each other; and a processing
liquid supply section for supplying a processing liquid to a
contacting region of the polishing tool and the substrate held by
the substrate holder.
60. The polishing apparatus according to claim 59, wherein the
processing liquid comprises a pH buffer solution of a neutral pH
which contains Ga ions, and the substrate is made of a
semiconductor containing an element of Ga.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing method and a
polishing apparatus, and more particularly to a polishing method
and a polishing apparatus for performing the planarization
polishing of a surface (surface to be processed) of a substrate
such as a single substrate made of a compound semiconductor
containing an element such as Ga, Al, In, or the like, or a bonded
substrate (epitaxial substrate) on which a compound semiconductor
containing an element such as Ga, Al, In, or the like is mounted.
The present invention is also related to a polishing method and a
polishing apparatus, such as a catalyst-referred chemical
processing system, for performing the planarization polishing of a
surface (surface to be processed) of a substrate while monitoring
the progress of a polishing process in order to determine the
timing of an endpoint of the polishing process. (e.g., stoppage of
polishing process or change of polishing conditions). Furthermore,
the present invention relates to a polishing tool provided in such
as the catalyst-referred chemical processing system.
BACKGROUND ART
[0002] The applicant has proposed a catalyst-referred chemical
processing system for processing a surface (surface to be
processed) of a substrate by placing the substrate in an acid
processing solution, placing an acid or basic solid catalyst in
contact with or in close proximity with the surface of the
substrate, and eluting surface molecules of the surface which is
held in contact with or in close proximity with the solid catalyst
into the acid processing solution (see Japanese laid-open patent
publication No. 2008-121099). According to the catalyst-referred
chemical processing system, the surface of the substrate
(workpiece) is irradiated with light, preferably ultraviolet light,
or a voltage is applied between the substrate and the solid
catalyst, to promote oxidization of the surface for an increasing
machining rate. The catalyst-referred chemical processing system
makes it possible to planarize the surface of the substrate with
only a chemical action while causing little damage to the surface
of the substrate. However, it is generally difficult to planarize a
surface of a single substrate made of a compound semiconductor
containing an element Ga, for example, to a sufficiently highly
accurate surface roughness within a practical given period of
time.
[0003] Demands for finer and multi-layered interconnects for highly
integrated semiconductor devices in recent years require that the
surface of films such as metal films on the surface of substrates
such as semiconductor wafers or the like be planarized to a high
degree. To meet such demands, it has widely been customary to
planarize the surface of films on the surface of substrates by
removing surface irregularities therefrom according to chemical
mechanical polishing (CMP). In a chemical mechanical polishing
process, it is necessary while a film is being polished to monitor
the polished state of the film in order to stop polishing the film
at a desired position. Therefore, it has been the general practice
to monitor the polished state of an electrically conductive metal
film formed on a surface of a substrate by applying an inductive
magnetic field to the metal film and detecting the rate of
attenuation of an eddy current generated in the surface of the
metal film with an eddy current sensor for thereby measuring the
thickness of the metal film.
[0004] The applicant has proposed an apparatus for monitoring the
polished state of a film formed on a surface of a substrate by
applying light to a surface (surface to be polished) of a film on a
surface of a substrate, breaking up the light reflected from the
surface into spectral data with a spectrometer, and measuring the
thickness of the film based on the spectral data (see Japanese
laid-open patent publication No. 2004-154928).
[0005] The applicant has also proposed a polishing method of
polishing a surface (surface to be polished) of a semiconductor
substrate by holding the surface of the semiconductor substrate and
a contact platen (polishing tool), at least the surface of which is
made of a catalyst, in contact with each other and moving them
relative to each other within a processing liquid, as a polishing
method of precisely and efficiently polishing a semiconductor
substrate of a hard-to-process material such as Sic, GaN, or the
like (see Japanese laid-open patent publication No. 2009-117782).
The contact platen comprises, for example, a base of molybdenum or
the like and a catalyst of platinum or the like which is attached
to a surface of the base.
SUMMARY OF INVENTION
Technical Problem
[0006] The applicant has found that when a substrate of a compound
semiconductor containing an element Ga is immersed in a processing
liquid comprising a pH buffer solution of a neutral pH which
contains Ga ions, and light is applied to the surface of the
substrate or a bias potential is applied to the substrate, a Ga
oxide is formed on the surface of the substrate, and the formed Ga
oxide can be polished away by holding the Ga oxide and a polishing
platen (polishing tool) in contact with each other and moving them
relative to each other (see Japanese patent application No.
2009-78234).
[0007] However, it has been discovered that if light is applied to
the surface of the substrate or a bias potential is applied to the
substrate to form a Ga oxide, and the Ga oxide is polished away to
flat the surface of the substrate of the compound semiconductor
containing the element Ga, then it takes a long time to polish the
surface of the substrate until the polished surface achieves a
desired level of flatness or the polished surface fails to achieve
a sufficient level of flatness.
[0008] For example, in a process of fabricating a substrate made of
a semiconductor alone, called a bare substrate, a mass of
semiconductor material known as an ingot is cut into substrates,
and thereafter each surface of the substrate is polished for
removing damage therefrom.
[0009] Heretofore, however, although the progress of the polishing
process can be monitored for the purposes of removing a film formed
on a surface of a substrate and planarizing the surface of the film
based on the measuring principles, the progress of the polishing
process cannot be monitored for the purpose of removing damage from
a surface of a substrate free of a film, such as a bare
substrate.
[0010] It has been found that if a contact platen (polishing tool)
is constructed of a base cut to a certain shape and a catalyst
attached to a surface of the base, for example, then a polished
surface of a workpiece after it has been polished by the contact
platen tends to be scratched by buffs formed on the surface of the
base when it was cut, and the surface irregularities of the surface
of the base tend to be transferred to the polished workpiece. The
catalyst of the contact platen serves as a catalyst in the
reception of electrons between the surface of the catalyst and the
surface of the workpiece. The catalyst needs to be periodically
replaced because it is mechanically worn when the surface of the
workpiece is processed while the catalyst and the workpiece are
pressed against each other and moved relative to each other. It has
also been found that if a contact platen is constructed of a base
such as of molybdenum or the like and a catalyst such as of
platinum or the like attached to a surface of the base, then it is
necessary to replace the contact platen as a whole when the
catalyst is to be replaced, and hence the contact platen is highly
costly.
[0011] The present invention has been made in view of the above
situation. It is therefore a first object of the present invention
to provide a polishing method and a polishing apparatus which are
particularly suitable for finishing a surface of a substrate of a
compound semiconductor containing an element such as Ga or the like
to a desired level of flatness, so that a surface of a substrate of
a compound semiconductor containing an element of Ga can be
flattened with high surface accuracy within a practical processing
time.
[0012] It is a second object of the present invention to provide a
polishing method and a polishing apparatus which are capable of
polishing a surface of a substrate such as a bare substrate made of
a semiconductor alone while monitoring the progress of the
polishing process by measuring a level of damage to the surface of
the substrate at the same time that the surface of the substrate is
polished.
[0013] It is a third object of the present invention to provide a
polishing tool which is capable of producing a polished surface
that is flat and less scratched and which is made inexpensive and
durable by basically allowing only a catalyst to be replaced, and a
polishing apparatus incorporating such a polishing tool.
Solution to Problem
[0014] The present invention provides a polishing method of
polishing a surface of a substrate made of a compound semiconductor
containing either one of Ga, Al, and In by relatively moving the
surface of the substrate and a surface of a polishing pad having an
electrically conductive member in an area of the surface which is
held in contact with the substrate, while holding the surface of
the substrate and the surface of the polishing pad in contact with
each other, in the presence of weak acid water, water with air
dissolved therein, or electrolytic ion water.
[0015] The surface of the substrate, which is made of a compound
semiconductor containing an element such as Ga or the like, can
thus be finished to a high level of flatness. By combining the
finishing process with a polishing process involving the
application of light and/or the application of a bias potential,
the time required to polish the surface of the substrate, which is
made of a compound semiconductor containing an element such as Ga
or the like, can greatly be reduced.
[0016] In a preferred aspect of the present invention, the weak
acid water or the water with air dissolved therein has a pH in the
range from 3.5 to 6.0.
[0017] The weak acid water, which has a pH in the range from 3.5 to
6.0, is manufactured by dissolving a gas of CO.sub.2 into pure
water or tap water, for example, without the addition of an acid, a
pH buffer, or an oxidizer (H.sub.2O.sub.2, ozone water, persulfate,
or the like). The water with air dissolved therein which has a pH
in the range from 3.5 to 6.0 is manufactured by bringing pure water
or tap water into contact with air and dissolving CO.sub.2 in air
into the water. The water with air dissolved therein may be
manufactured by positively dissolving air with a gas dissolver or
naturally dissolving air by exposing pure water or tap water to an
air atmosphere. Preferably, the pH of the weak acid water or water
with air dissolved therein should be in the range from 3.5 to
5.5.
[0018] The present invention also provides another polishing method
of polishing a surface of a substrate at least partly made of a
compound semiconductor containing either one of Ga, Al, and In by
relatively moving the surface of the substrate and a surface of a
polishing pad having an electrically conductive member in an area
of the surface which is held in contact with the substrate, while
holding the surface of the substrate and the surface of the
polishing pad in contact with each other, in the presence of water,
water with air dissolved therein, or electrolytic ion water. The
water is preferably N.sub.2-purged water.
[0019] In a preferred aspect of the present invention, the water
with air dissolved therein comprises water with CO.sub.2 in air
being dissolved therein while the surface of the substrate is being
polished in an air atmosphere after the surface of the substrate
has started being polished by the polishing pad which is supplied
with pure water or tap water.
[0020] In a preferred aspect of the present invention, the
electrically conductive member is made of a precious metal, a
transition metal, graphite, electrically conductive resin,
electrically conductive rubber, or electrically conductive organic
matter.
[0021] The previous metal may be platinum or gold, and the
transition metal may be Ag, Fe, Ni, or Co. The electrically
conductive organic matter may be polyacetylene, polyparaphenyline,
polyaniline, polythiofuran or polyparaphenyline-vinylene.
[0022] In a preferred aspect of the present invention, the compound
semiconductor containing either one of Ga, Al, and In comprises
GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP, or InAs.
[0023] Since an oxide of GaN, GaP, GaAs, AN, AlP, AlAs, InN, InP,
or InAs is dissolvable in a weak acid or weak alkali aqueous
solution, they can be used in the polishing method according to the
present invention.
[0024] In a preferred aspect of the present invention, the
electrolytic ion water has a pH in the range from 3.5 to 6.0 or of
8.0 or higher.
[0025] In a preferred aspect of the present invention, the surface
of the substrate is polished while applying excitation light to the
surface of the substrate via through holes provided in the
polishing pad.
[0026] Alternatively, the surface of the substrate may be polished
while applying voltage between the polishing pad and the
substrate.
[0027] Preferably, the surface of the substrate is polished while
controlling at least one of the temperature of the water or
electrolytic ion water, the temperature of the substrate, and the
temperature of the polishing pad.
[0028] In a preferred aspect of the present invention, a first
polishing process for polishing the surface of the substrate while
applying excitation light to the surface of the substrate, and a
second polishing process for polishing the surface of the substrate
without applying excitation light to the surface of the substrate
are performed successively.
[0029] Alternatively, a first polishing process for polishing the
surface of the substrate while applying excitation light to the
surface of the substrate, and a second polishing process for
polishing the surface of the substrate without applying excitation
light to the surface of the substrate may be repeated
alternately.
[0030] In a preferred aspect of the present invention, a third
polishing process for polishing the surface of the substrate while
applying voltage between the substrate and the polishing pad, and a
forth polishing process for polishing the surface of the substrate
without applying voltage between the substrate and the polishing
pad are performed successively.
[0031] Alternatively, a third polishing process for polishing the
surface of the substrate while applying voltage between the
substrate and the polishing pad, and a forth polishing process for
polishing the surface of the substrate without applying voltage
between the substrate and the polishing pad are repeated
alternately.
[0032] The present invention also provides a polishing apparatus
for polishing a surface of a substrate made of a compound
semiconductor containing either one of Ga, Al, and In, comprising a
container for holding weak acid water, water with air dissolved
therein, or electrolytic ion water therein, a polishing pad having
an electrically conductive member in an area of a surface thereof
which is held in contact with the substrate, the polishing pad
being disposed in the container while being immersed in the water,
a substrate holder for holding the substrate and binging the
substrate into contact with the polishing pad while immersing the
substrate in the water in the container, and a moving mechanism for
relatively moving the polishing pad and the substrate held by the
substrate holder while holding the polishing pad and the substrate
in contact with each other.
[0033] The present invention provides another polishing apparatus
for polishing a surface of a substrate made of a compound
semiconductor containing either one of Ga, Al, and In, comprising a
polishing pad having an electrically conductive member in an area
of a surface thereof which is held in contact with the substrate, a
substrate holder for holding the substrate and binging the
substrate into contact with the polishing pad, a moving mechanism
for relatively moving the polishing pad and the substrate held by
the substrate holder while holding the polishing pad and the
substrate in contact with each other, and a water supply section
for supplying weak acid water, water with air dissolved therein, or
electrolytic ion water to a contacting region of the polishing pad
and the substrate held by the substrate holder.
[0034] In a preferred aspect of the present invention, the
polishing pad has a number of through holes, and the polishing
apparatus is configured to apply excitation light to the surface of
the substrate held by the substrate holder via the through holes of
the polishing pad.
[0035] In a preferred aspect of the present invention, the
polishing pad has a light transmission area for applying excitation
light to the surface of the substrate held by the substrate holder
via a number of the through holes and a light non-transmission
area, and the moving mechanism is configured to reciprocate the
substrate holder between the light transmission area and the light
non-transmission area on the polishing pad.
[0036] In a preferred aspect of the present invention, the
polishing apparatus further comprises a conductive wire connecting
the polishing pad and the substrate held by the substrate and
interposing therein a power source.
[0037] The present invention provides another polishing method
comprising: polishing a surface of a substrate by relatively moving
a light-permeable polishing tool and the surface of the substrate
while holding the light-permeable polishing tool and the surface of
the substrate in contact with each other in the presence of a
processing liquid; and measuring a damage level of the surface of
the substrate with at least one of damage level measuring systems
including a photocurrent-type damage level measuring system for
measuring a damage level of the surface of the substrate by
measuring the value of a current flowing through a conductive line
connecting the substrate and a metal wire on the polishing tool
when excitation light is applied to the surface of the substrate, a
photoluminescence-light-type damage level measuring system for
measuring a damage level of the surface of the substrate by
measuring photoluminescence light emitted from the surface of the
substrate when excitation light is applied to the surface of the
substrate, and a Raman-light-type damage level measuring system for
measuring a damage level of the surface of the substrate by
measuring Raman light included in reflected light from the surface
of the substrate when visible monochromatic light is applied to the
surface of the substrate, and monitoring the progress of a
polishing process based on a reduction in the damage level of the
surface of the substrate.
[0038] Since at least one of the photocurrent-type damage level
measuring system, the photoluminescence-light-type damage level
measuring system, and the Raman-light-type damage level measuring
system is used, the damage level of the surface of the substrate
can be measured at the same time that the surface of the substrate
is polished, and the progress of the polishing process can be
monitored from a reduction in the damage level of the surface of
the substrate, even if the substrate is a bare substrate, for
example, which is made of only a semiconductor with no film on its
surface.
[0039] The present invention provides still another polishing
method comprising: forming an oxide on a surface of a substrate by
applying excitation light to the surface of the substrate and
simultaneously applying a bias potential to the surface of the
substrate in the presence of a processing liquid; polishing away
the oxide formed in the surface of the substrate by relatively
moving the oxide and a polishing tool while holding the oxide and
the polishing tool in contact with each other; and measuring a
damage level of the surface of the substrate with at least one of
damage level measuring systems including a
photoluminescence-light-type damage level measuring system for
measuring a damage level of the surface of the substrate by
measuring photoluminescence light emitted from the surface of the
substrate when excitation light is applied to the surface of the
substrate, and a Raman-light-type damage level measuring system for
measuring a damage level of the surface of the substrate by
measuring Raman light included in reflected light from the surface
of the substrate when visible monochromatic light is applied to the
surface of the substrate, and monitoring the progress of a
polishing process based on a reduction in the damage level of the
surface of the substrate.
[0040] When the surface of the substrate is polished while forming
an oxide on the surface of the substrate by applying a bias
potential to the substrate, the damage level of the surface of the
substrate can be measured, while at the same time the surface of
the substrate is being polished, by at least one of the
photoluminescence-light-type damage level measuring system and the
Raman-light-type damage level measuring system, and progress of the
polishing process can be monitored based on a reduction in the
damage level of the surface of the substrate.
[0041] The present invention provides yet another polishing method
comprising: forming an oxide on a surface of a substrate by
applying excitation light to the surface of the substrate in the
presence of a processing liquid; polishing away the oxide formed on
the surface of the substrate by relatively moving the oxide and a
polishing tool while holding the oxide and the polishing tool in
contact with each other; and measuring a damage level of the
surface of the substrate with at least one of damage level
measuring systems including a photocurrent-type damage level
measuring system for measuring a damage level of the surface of the
substrate by measuring the value of a current flowing through a
conductive line connecting the substrate and a metal wire on the
polishing tool when excitation light is applied to the surface of
the substrate, a photoluminescence-light-type damage level
measuring system for measuring a damage level of the surface of the
substrate by measuring photoluminescence light emitted from the
surface of the substrate when excitation light is applied to the
surface of the substrate, and a Raman-light-type damage level
measuring system for measuring a damage level of the surface of the
substrate by measuring Raman light included in reflected light from
the surface of the substrate when visible monochromatic light is
applied to the surface of the substrate, and monitoring the
progress of a polishing process based on a reduction in the damage
level of the surface of the substrate.
[0042] Preferably, the substrate is made of a semiconductor
containing an element of Ga, and the processing liquid comprises a
pH buffer solution of a neutral pH which contains Ga ions.
[0043] The present invention provides yet another polishing method
comprising: polishing a surface of a substrate by relatively moving
the surface of the substrate and a polishing tool while holding the
surface of the substrate and the polishing tool in contact with
each other in the presence of a processing liquid; and measuring a
damage level of the surface of the substrate with a
Raman-light-type damage level measuring system for measuring a
damage level of the surface of the substrate by measuring Raman
light included in reflected light from the surface of the substrate
when visible monochromatic light is applied to the surface of the
substrate, and monitoring the progress of a polishing process based
on a reduction in the damage level of the surface of the
substrate.
[0044] Because of the relationship to the polishing rate or the
finished state of the surface such as a flatness level, there are
instances where the surface of the substrate cannot be polished
while excitation light is being applied to the surface of the
substrate or a bias potential is being applied to the surface of
the substrate. In such cases, the Raman-light-type damage level
measuring system, which does not need to apply excitation light to
the surface of the substrate or a bias potential to the surface of
the substrate, is used to measure a damage level of the surface of
the substrate while at the same time that the surface of the
substrate is polished, and the progress of a polishing process can
be monitored based on a reduction in the damage level of the
surface of the substrate.
[0045] Preferably, the processing liquid comprises weak acid water,
water with air dissolved therein, or electrolytic ion water, and an
electrically conductive member is disposed on the polishing tool in
an area which is held in contact with the surface of the
substrate.
[0046] The present invention provides still another polishing
apparatus comprising a container for holding a processing liquid
therein, a light-permeable polishing tool disposed in the container
while being immersed in the processing liquid, a substrate holder
for holding the substrate and binging the substrate into contact
with the polishing tool while immersing the substrate in the
processing liquid in the container, a moving mechanism for
relatively moving the polishing tool and the substrate held by the
substrate holder while holding the polishing pad and the substrate
in contact with each other, and at least one of damage level
measuring devices including a photocurrent-type damage level
measuring device for measuring a damage level of the surface of the
substrate by measuring the value of a current flowing through a
conductive line connecting the substrate and a metal wire on the
polishing tool when excitation light is applied to the surface of
the substrate, a photoluminescence-light-type damage level
measuring device for measuring a damage level of the surface of the
substrate by measuring photoluminescence light emitted from the
surface of the substrate when excitation light is applied to the
surface of the substrate, and a Raman-light-type damage level
measuring device for measuring a damage level of the surface of the
substrate by measuring Raman light included in reflected light from
the surface of the substrate when visible monochromatic light is
applied to the surface of the substrate.
[0047] The present invention provides yet another polishing
apparatus comprising a light-permeable polishing tool, a substrate
holder for holding the substrate and binging the substrate into
contact with the polishing tool, a moving mechanism for relatively
moving the polishing tool and the substrate held by the substrate
holder while holding the polishing pad and the substrate in contact
with each other, a processing liquid supply section for supplying a
processing liquid to a contacting region of the polishing tool and
the substrate held by the substrate holder, and at least one of
damage level measuring devices including a photocurrent-type damage
level measuring device for measuring a damage level of the surface
of the substrate by measuring the value of a current flowing
through a conductive line connecting the substrate and a metal wire
on the polishing tool when excitation light is applied to the
surface of the substrate, a photoluminescence-light-type damage
level measuring device for measuring a damage level of the surface
of the substrate by measuring photoluminescence light emitted from
the surface of the substrate when excitation light is applied to
the surface of the substrate, and a Raman-light-type damage level
measuring device for measuring a damage level of the surface of the
substrate by measuring Raman light included in reflected light from
the surface of the substrate when visible monochromatic light is
applied to the surface of the substrate.
[0048] The polishing apparatus preferably include at least one of a
light source for applying excitation light to the surface of the
substrate which is held by the substrate holder and immersed in the
processing liquid in the container and a power source for applying
a bias potential to the substrate.
[0049] The present invention provides a polishing tool comprising a
light-permeable support platen with metal wires on a surface
thereof, and a catalyst pad having a surface which includes at
least a portion held in contact with the substrate and made of a
catalyst, the catalyst pad having a plurality of holes defined
therein for passing therethrough at least one of light and an ion
current.
[0050] Since the support platen and the catalyst pad are separate
from each other and the catalyst pad has a high level of surface
flatness and does not tend to produce burrs, scratches, etc., the
polishing tool is capable of producing a flat polished surface free
of burrs, scratches, etc. The catalyst can be replaced with a new
one by replacing the catalyst pad, while allowing the support
platen to be reused. Accordingly, the polishing tool is inexpensive
and highly durable.
[0051] The metal wires are provided by embedding metal wires in
grooves defined in the surface of the support platen, forming a
metal wire pattern on the surface of the support platen, or placing
a wiring film with a metal wire pattern formed thereon on the
surface of the support platen, for example.
[0052] Alternatively, the metal wires may be formed by a metal film
pattern deposited on the surface of the support platen by vacuum
evaporation.
[0053] The support platen is preferably made of glass or
light-permeable resin.
[0054] The catalyst comprises at least one of precious metal, a
transition metal, a ceramics-based solid catalyst, a base solid
catalyst, an acid solid catalyst, graphite, electrically conductive
resin, electrically conductive rubber, and electrically conductive
organic matter, for example.
[0055] The catalyst pad is made of quartz glass, for example.
[0056] Alternatively, the catalyst pad may be formed by evaporating
a precious metal, a transition metal, an acid or base metal oxide
film, graphite, electrically conductive resin, electrically
conductive rubber, or electrically conductive organic matter on a
surface of a pad base which is made of glass, rubber,
light-permeable resin, foamable resin, or non-woven fabric.
[0057] The acid or base metal oxide film, which is evaporated on
the surface of the pad base, is not easily peeled off from the pad
base.
[0058] The present invention provides yet another polishing
apparatus comprising a container for holding a processing liquid
therein, the above-described polishing tool disposed in the
container while being immersed in the processing liquid, a
substrate holder for holding the substrate and binging the
substrate into contact with the polishing tool while immersing the
substrate in the processing liquid in the container, a moving
mechanism for relatively moving the polishing tool and the
substrate held by the substrate holder while holding the polishing
pad and the substrate in contact with each other, and at least one
of a light source for applying excitation light to the surface of
the substrate which is held by the substrate holder and immersed in
the processing liquid in the container and a power source for
applying a bias potential to the substrate.
[0059] The present invention provides yet another polishing
apparatus comprising the above-described polishing tool, a
substrate holder for holding a substrate and binging the substrate
into contact with the polishing tool, a processing liquid supply
section for supplying a processing liquid to a contacting region of
the polishing tool and the substrate held by the substrate holder,
and at least one of a light source for applying excitation light to
the surface of the substrate which is held by the substrate holder
and immersed in the processing liquid in the container and a power
source for applying a bias potential to the substrate.
[0060] The present invention provides another polishing tool
comprising an elastic base made of at least one of elastic
materials including rubber, resin, foamable resin, and non-woven
fabric, an electrically conductive member disposed on the elastic
base in an area held in contact with at least the substrate, and an
intermediate film made of carbon or chromium interposed between the
elastic base and the electrically conductive member for increasing
adhesion therebetween.
[0061] Since the elastic base of elastic material is elastically
deformable along the surface (polished surface) of the substrate,
even if the elastic base has surface irregularities, they are
prevented from being transferred to the surface of the substrate.
Inasmuch as the intermediate film made of carbon or chromium is
interposed between the elastic base and the electrically conductive
member for increasing adhesion therebetween, the adhesion between
the elastic base and the electrically conductive member is
increased by the intermediate film, so that the electrically
conductive member is less liable to be peeled off from the elastic
base.
[0062] The elastic base preferably has grooves defined in a surface
thereof for efficiently supplying the processing liquid.
[0063] The elastic base preferably has a number of through holes
for passing therethrough at least one of light and an ion
current.
[0064] The present invention provides yet another polishing
apparatus comprising a container for holding a processing liquid
therein, the above-described polishing tool disposed in the
container while being immersed in the processing liquid, a
substrate holder for holding the substrate and binging the
substrate into contact with the polishing tool while immersing the
substrate in the processing liquid in the container, and a moving
mechanism for relatively moving the polishing tool and the
substrate held by the substrate holder while holding the polishing
pad and the substrate in contact with each other.
[0065] The present invention provides a yet another polishing
apparatus comprising the above-described polishing tool, a
substrate holder for holding a substrate and binging the substrate
into contact with the polishing tool, a moving mechanism for
relatively moving the polishing tool and the substrate held by the
substrate holder while holding the polishing pad and the substrate
in contact with each other, and a processing liquid supply section
for supplying a processing liquid to a contacting region of the
polishing tool and the substrate held by the substrate holder.
Advantageous Effects of Invention
[0066] A polishing method and a polishing apparatus according to
the present invention are capable of finishing a surface of a
substrate, which is made of a compound semiconductor containing an
element such as Ga or the like, to a high level of flatness. By
combining the finishing process with a polishing process involving
the application of light and/or the application of a bias
potential, i.e., by polishing the surface of the substrate at a
high polishing rate with the application of light and/or the
application of a bias potential, and subsequently finishing the
surface of the substrate to a high level of flatness, the time
required to polish the surface of the substrate, which is made of a
compound semiconductor containing an element such as Ga or the
like, can greatly be reduced.
[0067] According to another polishing method and the polishing
apparatus of the present invention, even if the substrate is a bare
substrate, for example, which is made of only a semiconductor with
no film on its surface, a damage level of the surface of the
substrate can be measured by a photocurrent-type damage level
measuring system, a photoluminescence-light-type damage level
measuring system, or a Raman-light-type damage level measuring
system while at the same time the surface of the substrate is being
polished, and the progress of the polishing process can be
monitored.
[0068] According to a polishing toll of the present invention,
since the support platen and the catalyst pad are separate from
each other and the catalyst pad has a high level of surface
flatness and does not tend to produce burrs, scratches, etc., the
polishing tool is capable of producing a flat polished surface free
of burrs, scratches, etc. The catalyst can be replaced with a new
one by replacing the catalyst pad, while allowing the support
platen to be reused. Accordingly, the polishing tool is inexpensive
and highly durable.
[0069] Further, since the elastic base of elastic material is
elastically deformable along the surface (polished surface) of the
substrate, even if the elastic base has surface irregularities,
they are prevented from being transferred to the surface of the
substrate. Inasmuch as the intermediate film made of carbon or
chromium is interposed between the elastic base and the
electrically conductive member for increasing adhesion
therebetween, the adhesion between the elastic base and the
electrically conductive member is increased by the intermediate
film, so that the electrically conductive member is less liable to
be peeled off from the elastic base.
BRIEF DESCRIPTION OF DRAWINGS
[0070] FIG. 1 is a schematic view showing the concept of a
photocurrent-type damage level measuring system;
[0071] FIG. 2 is a band diagram showing the concept of the
photocurrent-type damage level measuring system;
[0072] FIG. 3 is a graph showing the relationship between polishing
times and photocurrent values in the photocurrent-type damage level
measuring system;
[0073] FIG. 4 is a schematic view showing the concept of a
photoluminescence-light-type damage level measuring system;
[0074] FIG. 5 is a band diagram showing the concept of the
photoluminescence-light-type damage level measuring system;
[0075] FIG. 6 is a graph showing the relationship between polishing
times and photocurrent values in the photoluminescence-light-type
damage level measuring system;
[0076] FIG. 7 is a schematic view showing the concept of a
Raman-light-type damage level measuring system;
[0077] FIG. 8 is a graph showing Rayleigh light and Raman light
before and after a polishing process in the Raman-light-type damage
level measuring system;
[0078] FIG. 9 is a plan view showing the overall construction of a
flattening system incorporating a polishing apparatus according to
an embodiment of the present invention;
[0079] FIG. 10 is a schematic cross-sectional view of the polishing
apparatus incorporated in the flattening system shown in FIG.
9;
[0080] FIG. 11 is an enlarged cross-sectional view of a substrate
holder of the polishing apparatus shown in FIG. 10;
[0081] FIG. 12 is an enlarged cross-sectional view of a polishing
tool of the polishing apparatus shown in FIG. 10;
[0082] FIG. 13 is an enlarged cross-sectional view of another
polishing tool;
[0083] FIG. 14 is a schematic cross-sectional view of the polishing
apparatus incorporated in the flattening system shown in FIG.
9;
[0084] FIG. 15 is an enlarged cross-sectional view of a polishing
pad of the polishing apparatus shown in FIG. 14;
[0085] FIG. 16 is a graph showing the relationship between
polishing rates and polishing times when a GaN substrate is
polished by the polishing apparatus shown in FIG. 14.
[0086] FIG. 17 is a graph showing excitation light and
photoluminescence light before and after a polishing process in a
photoluminescence-light-type damage level measuring device
incorporated in the polishing apparatus shown in FIG. 10;
[0087] FIG. 18 is a graph showing the relationship between
polishing times and photocurrent values when a photocurrent is
measured during a polishing process by a photocurrent-type damage
level measuring device incorporated in the polishing apparatus
shown in FIG. 10;
[0088] FIG. 19A is a diagram showing an interference microscope
image of a GaN substrate surface before it is polished, and FIG.
19B is a diagram showing the relationship between distances and
heights on the substrate surface;
[0089] FIG. 20A is a diagram showing an interference microscope
image of the GaN substrate surface after it is polished in a first
stage, and FIG. 20B is a diagram showing the relationship between
distances and heights on the substrate surface;
[0090] FIG. 21A is a diagram showing an interference microscope
image of the GaN substrate surface after it is polished in a second
stage, and FIG. 21B is a diagram showing the relationship between
distances and heights on the substrate surface;
[0091] FIG. 22A is a diagram showing an interference microscope
image of the GaN substrate surface after it is polished in a third
stage, and FIG. 22B is a diagram showing the relationship between
distances and heights on the substrate surface;
[0092] FIG. 23A is a diagram showing an atomic force microscope
image of a GaN substrate surface after it is polished according to
Example 1, and FIG. 23B is a diagram showing the relationship
between distances and heights on the substrate surface;
[0093] FIG. 24A is a diagram showing an atomic force microscope
image of a GaN substrate surface after it is polished according to
Comparative Example, and FIG. 24B is a diagram showing the
relationship between distances and heights on the substrate
surface;
[0094] FIG. 25A is a diagram showing an atomic force microscope
image of a GaN substrate surface after it is polished according to
Example 2, and FIG. 25B is a diagram showing the relationship
between distances and heights on the substrate surface;
[0095] FIG. 26 is a schematic cross-sectional view of a polishing
apparatus according to another embodiment of the present
invention;
[0096] FIG. 27 is a diagram showing an atomic force microscope
image of a GaN substrate surface after it is polished by the
polishing apparatus shown in FIG. 26 while applying excitation
light to the GaN substrate surface;
[0097] FIG. 28 is a schematic cross-sectional view of a polishing
apparatus according to yet another embodiment of the present
invention;
[0098] FIG. 29 is a schematic cross-sectional view of a polishing
apparatus according to yet another embodiment of the present
invention;
[0099] FIG. 30 is an enlarged cross-sectional view of a polishing
tool of the polishing apparatus shown in FIG. 29;
[0100] FIG. 31 is an enlarged cross-sectional view of still another
polishing tool for use in the polishing apparatus shown in FIG.
10;
[0101] FIG. 32 is a plan view of the polishing tool shown in FIG.
31;
[0102] FIG. 33 is a plan view of a support platen of the polishing
tool shown in FIG. 31;
[0103] FIG. 34 is a cross-sectional view taken along line O-A of
FIG. 33;
[0104] FIG. 35 is a cross-sectional view taken along line O-B of
FIG. 33;
[0105] FIG. 36 is an enlarged cross-sectional view of yet another
polishing tool for use in the polishing apparatus shown in FIG.
10;
[0106] FIG. 37 is a plan view of a support platen of the polishing
tool shown in FIG. 36;
[0107] FIG. 38 is a plan view of another support platen;
[0108] FIG. 39 is an enlarged cross-sectional view of a still
further polishing tool for use in the polishing apparatus shown in
FIG. 10; and
[0109] FIG. 40 is an enlarged cross-sectional view of another
polishing pad for use in the polishing apparatus shown in FIG.
14.
DESCRIPTION OF EMBODIMENTS
[0110] Embodiments of the present invention will be described below
with reference to the drawings. In examples below, a surface of a
single substrate made of GaN (GaN substrate) is polished flatwise.
The present invention is applicable to a bonded substrate
(epitaxial substrate) having GaN mounted on a surface of a base of
sapphire or SiC or the like, and a p-type or n-type substrate which
is produced by introducing an impurity (dopant) into a GaN
substrate or an epitaxial substrate. The present invention is also
applicable to a substrate which is produced by forming an
interconnect pattern in a surface of the substrate after
introducing an impurity (dopant) into a GaN substrate or an
epitaxial substrate, or an activated substrate by annealing after
the formation of the interconnect pattern. Furthermore, the present
invention is also applicable to a compound semiconductor of GaP,
GaAs, AN, AlP, AlAs, InN, InP or InAs or the like other than
GaN.
[0111] The concept of a photocurrent-type damage level measuring
system for measuring a level of damage to a surface of a substrate
by measuring the value of a current which flows through a
conductive wire connecting the substrate and a metal wire provided
on a polishing tool when the surface of the substrate is irradiated
with excitation light, will be described below with reference to a
schematic view of FIG. 1 and a band diagram of FIG. 2.
[0112] As shown in FIG. 1, in the presence of a processing liquid
(not shown), a light-permeable polishing tool 10 and a surface
(surface to be polished) of a substrate W made of GaN, for example,
which is held by a substrate holder 11 are held in contact with
each other and moved relative to each other to polish the surface
(e.g., GaN surface) of the substrate W. During the polishing
process, a light source 12 applies light (excitation light) having
an energy higher than the band gap of the substrate (e.g., GaN) W
through the polishing tool 10 to the surface of the substrate W,
and an ammeter 14 measures the value of a current flowing through a
conductive wire 13 connecting the substrate W and a metal wire (not
shown) provided on the polishing tool 10.
[0113] The band gap of GaN, for example, is of 3.42 eV and the
wavelength corresponding to the band gap is of 365 nm. Therefore,
when the light source 12 applies light (excitation light) having an
energy higher than the band gap of the substrate W to the surface
of the substrate W, the light having a wavelength of 312 nm, for
example, for polishing GaN, then as shown in FIG. 2, valence band
electrons are excited to a conduction band, forming electron and
hole pairs. If the level of damage to the surface of the substrate
W is small, then some of the generated electrons move away from the
surface of the substrate W, as indicated by the arrow 1 in FIG. 2,
due to the curvature of the band on the surface of the substrate W,
and flows as a photocurrent along the conductive wire 13. If the
level of damage to the surface of the substrate W is large, on the
other hand, then the generated electrons move along a damage level
formed by the damage to the surface of the substrate W, as
indicated by the arrow 2 in FIG. 2, and disappear as they are
reunited with holes. Therefore, if the level of damage to the
surface of the substrate W is large, then the value of a
photocurrent flowing along the conductive wire 13 is small. As the
level of damage to the surface of the substrate W becomes smaller,
the value of a photocurrent flowing along the conductive wire 13
becomes greater. In the polishing process, it is thus possible to
measure the level of damage to the surface of the substrate W to
monitor the progress of the polishing process by measuring the
value of the photocurrent.
[0114] As the level of damage to the surface of the substrate W is
reduced when the polishing process is in progress, the value of the
current flowing through the ammeter 14 increases, as shown in FIG.
3. When the damage to the surface of the substrate W is removed,
the value of the current flowing through the ammeter 14 stops
increasing and becomes constant. Consequently, the value of the
photocurrent is measured during the polishing process, and the time
at which the value of the photocurrent stops increasing and becomes
constant can be regarded as an endpoint of the polishing
process.
[0115] The concept of a photoluminescence-light-type damage level
measuring system for measuring a level of damage to a surface of a
substrate by measuring photoluminescence light emitted from the
surface of the substrate when the surface of the substrate is
irradiated with excitation light, will be described below with
reference to a schematic view of FIG. 4 and a band diagram of FIG.
5.
[0116] As shown in FIG. 4, in the presence of a processing liquid
(not shown), a light-permeable polishing tool 10 and a surface
(surface to be polished) of a substrate W made of GaN, for example,
which is held by a substrate holder 11 are held in contact with
each other and moved relative to each other to polish the surface
(e.g., GaN surface) of the substrate W. During the polishing
process, a light source 12 applies light (excitation light) having
an energy higher than the band gap of the substrate (e.g., GaN) W
through the polishing tool 10 to the surface of the substrate W,
and a spectrometer 16 performs a spectral analysis on
photoluminescence light emitted from the surface of the substrate W
and monitors the intensity thereof at a wavelength corresponding to
the band gap of the substrate W, e.g., at the wavelength of 365 nm
for GaN.
[0117] When the light source 12 applies light (excitation light)
having an energy higher than the band gap of the substrate W to the
surface of the substrate W, as shown in FIG. 5, valence band
electrons are excited to a conduction band, forming electron and
hole pairs. If the level of damage to the surface of the substrate
W is small, then the excited electrons directly move to the valence
band and are reunited with holes, bringing back a state of
equilibrium, as indicated by the arrow 1 in FIG. 5. In this
process, photoluminescence light having an energy corresponding to
the band gap is observed. If the level of damage to the surface of
the substrate W is large, on the other hand, then the excited
electrons move via an energy level developed by a loss of the
crystal periodicity to the surface of the substrate W and are
reunited with holes, as indicated by the arrow 2 in FIG. 5.
[0118] In the above process, the wavelength of the observed
photoluminescence light is shifted toward a longer wavelength than
the wavelength corresponding to the band gap, or the electrons and
holes are reunited without emitting light, so that the
photoluminescence light itself will not be observed. In other
words, if the level of damage to the surface of the substrate W is
large, then the wavelength corresponding to the band gap of the
photoluminescence light is small, and as the level of damage to the
surface of the substrate W becomes smaller, the wavelength
corresponding to the band gap of the photoluminescence light
becomes greater. In the polishing process, it is thus possible to
measure the level of damage to the surface of the substrate W to
monitor the progress of the polishing process by measuring the
intensity of the photoluminescence light at the wavelength
corresponding to the band gap of the substrate W.
[0119] For example, the spectrometer 16 performs a spectral
analysis on photoluminescence light emitted from the substrate W
and monitors the intensity of the photoluminescence light at the
wavelength (e.g., 365 nm) corresponding to the band gap of the
substrate W. As the level of damage to the surface of the substrate
W is reduced when the polishing process is in progress, the
intensity of the light increases, as shown in FIG. 6. When the
damage to the surface of the substrate W is removed, the intensity
of the light stops increasing and becomes constant. Consequently,
the time at which the intensity of the light stops increasing and
becomes constant can be regarded as an endpoint of the polishing
process.
[0120] The concept of a Raman-light-type damage level measuring
system for measuring a level of damage to a surface of a substrate
by measuring Raman light included in light reflected from the
surface of the substrate, which is irradiated with a visible
monochromatic beam, will be described below with reference to a
schematic view of FIG. 7.
[0121] As shown in FIG. 7, in the presence of a processing liquid
(not shown), a light-permeable polishing tool 10 and a surface
(surface to be polished) of a substrate W made of GaN, for example,
which is held by a substrate holder 11 are held in contact with
each other and moved relative to each other to polish the surface
(e.g., GaN surface) of the substrate W. During the polishing
process, a laser beam source 17 applies a visible monochromatic
beam through the polishing tool 10 to the surface of the substrate
W, and a spectrometer 18 performs a spectral analysis on Raman
light included in the light reflected from the surface of the
substrate W.
[0122] It is known that when light having an appropriate wavelength
is applied to a semiconductor substrate, the light reflected from a
surface of the semiconductor substrate includes dispersed light
(Rayleigh light) which has the same wavelength as the applied light
and also light (Raman light) which has a wavelength slightly
shifted from the wavelength of the applied light. Since the width
of the shift depends on the periodicity of the crystal structure,
it is known that if the level of damage to the surface of the
substrate is small and the crystal structure is in order, then the
width of the wavelength shift is of a value inherent with the
material of the surface of the semiconductor substrate. If the
level of damage to the surface of the substrate is large, then the
width of the wavelength shift is varied by defects of the crystal
structure. Consequently, it is possible to measure the level of
damage to the surface of the substrate to monitor the progress of
the polishing process by measuring the spectrum of the Raman
light.
[0123] For example, when the laser beam source 17 applies a visible
monochromatic beam to the surface of the substrate W during the
polishing process, and the spectrometer 18 performs a spectral
analysis the light reflected from the surface of the substrate,
Rayleigh light having the same wavelength and half bandwidth as the
applied light and Raman light whose wavelength is shifted toward a
longer wavelength than the applied light are measured, as shown in
FIG. 8. If the level of damage to the surface of the substrate W is
large, then the spectral intensity of the Raman light is reduced
and the half bandwidth is increased. If the level of damage to the
surface of the substrate W is small, then the spectral intensity of
the Raman light is increased and the half bandwidth is reduced. It
is possible to monitor the progress of the polishing process by
monitoring the spectrum of the Raman light during the polishing
process. The time at which the intensity or half bandwidth of the
Raman light stops changing can be regarded as an endpoint of the
polishing process.
[0124] FIG. 9 is a plan view showing the overall construction of a
flattening system incorporating a polishing apparatus according to
an embodiment of the present invention. This flattening system is
used for polishing a surface of a GaN substrate to flatten the
surface. As shown in FIG. 9, this flattening system includes a
substantially rectangular housing 1 whose interior is divided by
partition walls 1a, 1b, 1c into a loading/unloading section 2, a
polishing section 3 and a cleaning section 4. The loading/unloading
section 2, the polishing section 3 and the cleaning section 4 are
independently fabricated and independently evacuated.
[0125] The loading/unloading section 2 includes at least one (e.g.,
three as shown) front loading section 200 on which a substrate
cassette, storing a number of substrates (objects to be polished)
therein, is placed. The front loading sections 200 are arranged
side by side in the width direction (perpendicular to the long
direction) of the flattening system. Each front loading section 200
can receive thereon an open cassette, a SMIF (standard
manufacturing interface) pod or a FOUP (front opening unified pod).
The SMIF and FOUP are a hermetically sealed container which can
house a substrate cassette therein and can keep the interior
environment independent of the exterior environment by covering
with a partition.
[0126] A moving mechanism 21, extending along the line of the front
loading sections 200, is provided in the loading/unloading section
2. On the moving mechanism 21 is provided a first transfer robot 22
as a first transfer mechanism, which is movable along the direction
in which substrate cassettes are arranged. The first transfer robot
22 can reach the substrate cassettes placed in the front loading
sections 200 by moving on the moving mechanism 21. The first
transfer robot 22 has two hands, an upper hand and a lower hand,
and can use the two hands differently, for example, by using the
upper hand when returning a processed substrate to a substrate
cassette and using the lower hand when transferring an unprocessed
substrate.
[0127] The loading/unloading section 2 is an area that needs to be
kept in the cleanest environment. Accordingly, the interior of the
loading/unloading section 2 is constantly kept at a higher pressure
than any of the outside of the apparatus, the polishing section 3
and the cleaning section 4. Furthermore, a filter-fan unit (not
shown) having an air filter, such as an HEPA filter or a ULPA
filter, is provided above the moving mechanism 21 for the first
transfer robot 22. Clean air, from which particles, vapor and gas
have been removed, continually blows off downwardly through the
filter-fan unit.
[0128] The polishing section 3 is an area where polishing of a
surface (surface to be processed) of a substrate is carried out.
The polishing 3 includes two polishing apparatuses 30A, 30B which
carry out polishing at a first stage and polishing at a second
stage successively and two polishing apparatuses 30C, 30D which
carry out polishing at a third stage. The polishing apparatuses 30A
through 30D are arranged along the long direction of the flattening
system.
[0129] As shown in FIG. 10, the polishing apparatuses 30A, 30B each
includes a container 132 for holding therein a processing liquid
(polishing solution) 130 comprising a neutral pH buffer solution
containing Ga ions. Above the container 132 is disposed a
processing liquid supply nozzle 133 for supplying the processing
liquid 130 into the container 132. As the processing liquid 130 may
be used a solution which is prepared by adding Ga ions, e.g., in an
amount of not less than 10 ppm, to a phosphate buffer solution,
e.g., having a pH of 6.86 to bring Ga ions in the processing liquid
130 near to saturation. The pH of the neutral pH buffer solution
(at 25.degree. C.) is, for example, 6.0 to 8.0.
[0130] A polishing tool (polishing platen) 134 having light
permeability is mounted on the bottom of the container 132, so that
the polishing tool 134 becomes immersed in the processing liquid
130 when the container 132 is filled with the processing liquid
130. The polishing tool 134 is, for example, composed of quartz
glass which is an acid solid catalyst having excellent light
permeability. It is possible to use a basic solid catalyst for the
polishing tool 134. Further, it is possible to use one having an
acidic or basic solid catalyst layer only in a surface of the
polishing tool 134.
[0131] The container 132 is coupled to an upper end of a rotatable
rotating shaft 136. The bottom plate of the container 132 has a
ring-shaped opening 132a formed around the rotating shaft 136 and
closed by the polishing tool 134. A light source 140 for emitting
excitation light, preferably ultraviolet light, is disposed right
below the opening 132a. Thus, the excitation light, preferably
ultraviolet light, emitted from the light source 140, passes
through the opening 132a of the container 132, permeates through
the interior of the polishing tool 134 and reaches above the
polishing tool 134.
[0132] Right above the container 132 is disposed a substrate holder
144 for detachably holding a substrate 142, e.g., a GaN substrate,
with a front surface facing downwardly. The substrate holder 144 is
coupled to a lower end of a main shaft 146 that is rotatable and
vertically movable. In this embodiment, the rotating shaft 136 for
rotating the container 132 and the main shaft 146 for rotating the
substrate holder 144 constitute a movement mechanism for moving the
polishing tool 134 and the substrate (GaN substrate) 142, held by
the substrate holder 144, relative to each other. However, it is
also possible to provide only one of them.
[0133] The polishing apparatus of this embodiment is also provided
with a power source 148 for applying a voltage between the
substrate 142, held by the substrate holder 144, and the polishing
tool 134. A switch 150 is interposed in a conductive wire 152a
extending from the positive pole of the power source 148.
[0134] In this embodiment, processing of the substrate 142 is
carried out in an immersion manner: the container 132 is filled
with the processing liquid 130 and the polishing tool 134 and the
substrate 142 held by the substrate holder 144 are kept immersed in
the processing liquid 130 during processing. It is also possible to
employ a dripping manner in which the processing liquid 130 is
supplied between the substrate 142 and the polishing tool 134 by
dripping the processing liquid 130 from the processing liquid
supply nozzle 133 onto the surface of the polishing tool 134, so
that processing of the substrate 142 is carried out in the presence
of the processing liquid 130.
[0135] As shown in FIG. 11, the substrate holder 144 has a cover
160 for preventing intrusion of the processing liquid 130. Inside
the cover 160, a metal holder body 170 is coupled, via a rotation
transmission section 168 including a universal joint 164 and a
spring 166, to a drive flange 162 that is coupled to the lower end
of the main shaft 146.
[0136] A retainer ring 172 is vertically movably disposed around
the lower portion of the holder body 170. A conductive rubber 174
is mounted to a lower surface (substrate holding surface) of the
holder body 170 such that a pressure space 176 can be formed
between the lower surface of the holder body 170 and the conductive
rubber 174. An air introduction pipe 178 is connected to the
pressure space 176 via an air introduction passage extending in the
holder body 170. The flange portion of the metal holder body 170 is
provided with an extraction electrode 180 to which is connected the
conductive wire 152a extending from the positive pole of the power
source 148.
[0137] In order to prevent wear of the surface of the retainer ring
172 by making into contact with the polishing tool 134 to thereby
prevent the surface material of the retainer ring 172 from adhering
to the surface of the polishing tool 134, at least the surface
portion of the retainer ring 172, which comes into contact with the
polishing tool 134, is preferably made of a glass material, such as
quartz, sapphire or zirconia, or a ceramic material such as
alumina, zirconia or silicon carbide. The conductive rubber 174 is,
for example, a conductive chloroprene rubber, a conductive silicone
rubber or a conductive fluororubber.
[0138] When the back surface of the substrate 142 is held, e.g., by
attraction, on the lower surface (substrate holding surface) of the
holder body 170 of the substrate holder 144, the conductive rubber
174 comes into contact with the back surface of the substrate 142
to feed electricity to the back surface. While maintaining the
electricity feeding to the back surface of the substrate 142, air
can be introduced into the pressure space 176 so as to press the
substrate 142 against the polishing tool 134.
[0139] The substrate holder 144 can thus hold the substrate 142
while feeding electricity to the substrate 142 in a simple manner
at a low resistance. The substrate holder 144 is preferably
configured to be capable of filling a polar conductive grease
between the conductive rubber 174 and the substrate 142 when
bringing the substrate 142 into contact with the conductive rubber
174 upon holding of the substrate 142 on the substrate holder
144.
[0140] As shown in FIG. 12, a large number of grooves 134a are
provided in an upper surface of the polishing tool 134 in an area
corresponding to the opening 132a of the container 132.
Vapor-deposited metal films 154 comprising metal wires are formed
in bottoms of the grooves 134a. To the metal films 154 is connected
a conductive wire 152b extending from the negative pole of the
power source 148. The metal films 154 are preferably made of
platinum or gold, which is corrosion-resistant. Though the grooves
134a provided in the upper surface of the polishing tool 134 are
preferably arranged in concentric circles, it is also possible to
arrange the grooves in a spiral, radial or lattice-shaped
configuration. As shown in FIG. 13, it is also possible to provide
metal wires (metal wires) 156 of, e.g., gold or platinum in the
bottoms of the grooves 134a provided in the upper surface of the
polishing tool 134.
[0141] A heater 158 (see FIG. 10), embedded in the substrate holder
144 and extending into the main shaft 146, is provided as a
temperature control mechanism for controlling the temperature of
the substrate 142 held by the substrate holder 144. A heat
exchanger as a temperature control mechanism for controlling the
processing liquid 130 to be supplied into the container 132 at a
predetermined temperature is provided to the processing liquid
supply nozzle 133 disposed above the container 132, as necessary.
Furthermore, a fluid passage (not shown) as a temperature control
mechanism for controlling the temperature of the polishing tool 134
is provided in the interior of the polishing tool 134.
[0142] As is known by the Arrhenius equation, the higher the
reaction temperature of a chemical reaction is, the higher is the
reaction rate. Thus, by controlling at least one of the temperature
of the substrate 142, the temperature of the processing liquid 130
and the temperature of the polishing tool 134 so as to control the
reaction temperature, the processing rate can be adjusted and the
stability of the processing rate can be enhanced.
[0143] As shown in FIG. 9, the polishing apparatuses 30A, 30B are
each provided with a conditioning mechanism (conditioner) 190,
e.g., comprised of a polishing pad, for conditioning the surface
(upper surface) of the polishing tool 134 so that it has desired
flatness and appropriate roughness. The surface (upper surface) of
the polishing tool 134 is conditioned by the conditioning mechanism
(conditioner) 190 so that it has a PV (peak-to-valley) roughness of
the surface of about 0.1 to 1 .mu.m. During the conditioning of the
polishing tool 134, an abrasive-containing slurry may be supplied
to the surface of the polishing tool 134, as necessary.
[0144] As shown in FIG. 10, the polishing apparatus 30A, 30B each
includes a photocurrent-type damage level measuring device 201
having the light source 140 as a component thereof and a
photoluminescence-light-type damage level measuring device 202 also
having the light source 140 as a component thereof The
photocurrent-type damage level measuring device 201 comprises a
conductive wire 152c which connects the conductive wire 152a
extending from the power source 148 and connected to the substrate
142 held by the substrate holder 144 and the conductive wire 152b
extending from the power source 148 and connected to the metal
films (metal wires) 154 of the polishing tool 134, an ammeter 204
connected to the conductive wire 152c, and the light source 140.
The conductive wire 152c has a switch 206. The
photoluminescence-light-type damage level measuring device 202
comprises a spectrometer 208 for performing a spectral analysis on
photoluminescence light reflected from the surface of the substrate
142 to measure the intensity of the photoluminescence light having
a wavelength (e.g., 365 nm) corresponding to the band gap of the
substrate W, and the light source 140.
[0145] In this embodiment, the light source 140 for applying
excitation light to the substrate 142 to oxidize the surface of the
substrate 142 is used as respective light sources of the
photocurrent-type damage level measuring device 201 and the
photoluminescence-light-type damage level measuring device 202.
However, the photocurrent-type damage level measuring device 201
and the photoluminescence-light-type damage level measuring device
202 may have respective dedicated light sources separately from the
light source 140.
[0146] As shown in FIG. 14, the polishing apparatus 30C, 30D each
includes a rotatable turntable 230 having a flat upper surface and
a ring-shaped dam member 236 mounted on the peripheral edge of the
turntable 230 and providing a container 234 for holding water 232
therein on the upper surface of the turntable 230. The water 232
may comprise weak acid water, water with air dissolved therein, or
electrolytic ion water. The weak acid water or water with air
dissolved therein has a pH in the range from 3.5 to 6.0 or
preferably from 3.5 to 5.5. The electrolytic ion water has a pH in
the range from 3.5 to 6.0 or preferably from 3.5 to 5.5 or of 8.0
or higher.
[0147] The weak acid water, which has a pH in the range from 3.5 to
6.0, is manufactured by dissolving a CO.sub.2 gas or CO.sub.2 in
air into pure water or tap water, for example, without the addition
of an acid, a pH buffer, or an oxidizer (H.sub.2O.sub.2, ozone
water, persulfate, or the like). When the weak acid water, which
has a pH in the range from 3.5 to 6.0 that is produced without the
addition of an acid, a pH buffer, or an oxidizer, is used, the
substrate 142 can be polished at a polishing rate that is kept
against being lowered, while the surface thereof (surface to be
polished) is prevented from developing etch pits. Since this
process does not involve chemicals, such as an acid, a pH buffer,
and an oxidizer, which need to be processed by a waste liquid
treatment, the process is advantageous in that the cost of the
waste liquid treatment is dispensed with and a cleaning process
subsequent to the polishing process is simplified.
[0148] In this embodiment, a water supply line (water supply
section) 241 extending from a pure water supply source (not shown)
and having a gas dissolver 238 and a heat exchanger 240 is disposed
above the turntable 230. The gas dissolver 238 dissolves a gas of
CO.sub.2 or the like or air into pure water delivered from the pure
water supply source to produce water 232 whose pH is adjusted to
3.5 to 6.0, or preferably 3.5 to 5.5, which is introduced into the
container 234 provided by the dam member 236. If necessary, the
water 232 to be introduced into the container 234 is adjusted to a
prescribed temperature by the heat exchanger 238. In an initial
stage of the polishing process, pure water or tap water may be
introduced, and the substrate 142 may be polished in an air
atmosphere, so that CO.sub.2 in air may be dissolved into pure
water or tap water at the same time that the substrate 142 is
polished, adjusting the pH of the water to 3.5 to 6.0, or
preferably 3.5 to 5.5.
[0149] Though in this embodiment the water 232 having a pH of
3.5-6.0, preferably 3.5-5.5, by dissolving a gas of CO.sub.2 or the
like or air into pure water is used, neutral N.sub.2-purged water
that is produced by purging N.sub.2 into tap water or pure water
may be used instead of the water 232. When the neutral
N.sub.2-purged water is used, the processing rate decrease while
obtaining an equal processed surface as compared with the case
where the water 232 having a pH of 3.5-6.0, preferably 3.5-5.5, is
used.
[0150] A polishing pad 242 serving as a polishing member is mounted
on the upper surface of the turntable 230 at a position within the
container 234 whose periphery is defined by the dam member 236.
When the water 232 is introduced into the container 234, the space
above the polishing pad 242 is filled with the water 232. The
turntable 230 has a fluid passage 230a defined therein for
controlling the temperature of the turntable 230.
[0151] The substrate 142, such as a GaN substrate or the like, is
detachably held, with its surface facing downward, by a substrate
holder 244 disposed above the container 234 whose periphery is
defined by the dam member 236. The substrate holder 244 is
connected to the lower end of a main shaft 246 which is vertically
movable and rotatable about its own axis. The substrate holder 244
and the main shaft 246 are identical in structure to the substrate
holder 144 and the main shaft 146 shown in FIG. 10, and will not be
described in detail below.
[0152] As shown in FIG. 15, the polishing pad 242 comprises an
elastic base 260 made of an elastic material, e.g., having a Shure
hardness in the range from 50 to 90 and including concentric or
spiral grooves 260a defined in a surface thereof for effectively
supplying the processing liquid (water) 232, an intermediate layer
262 deposited on the surface of the elastic base 260 by vacuum
evaporation or the like, and an electrically conductive member 264
deposited on a surface of the intermediate layer 262 by vacuum
evaporation or the like. The electrically conductive member 264
that is disposed on the surface of the elastic base 260 with the
intermediate layer 262 interposed therebetween finds it easy to
follow irregularities in long/single periods on the surface
(surface to be polished) of the substrate 142. The elastic base 260
may have holes for effectively supplying the processing liquid
(water), rather than the grooves 260a.
[0153] The elastic base 260 has a thickness in the range from 0.5
to 5 mm, for example. The elastic material of the elastic base 260
may be rubber, resin, foamable resin, non-woven fabric or the like,
for example. The elastic base 260 may comprise two or more
superposed layers of elastic material which have different moduli
of elasticity.
[0154] The intermediate layer 262 has a thickness in the range from
1 to 10 nm, for example. The intermediate layer 262 is interposed
between the elastic base 260 and the electrically conductive member
264 in order to increase the adhesion between the elastic base 260
and the electrically conductive member 264, and is made of chromium
or graphite (SP2-bonded) carbon, for example, which is
characterized by better adhesion to both the elastic base 260 and
the electrically conductive member 264. When the intermediate layer
262 is formed on the surface of the elastic base 260 by vacuum
evaporation, it is preferable to employ ion sputtering deposition
in order to suppress expansion and modification of the elastic base
260 due to high temperatures. This holds true also when the
electrically conductive member 264 is formed on the surface of the
intermediate layer 262 by vacuum evaporation.
[0155] The electrically conductive member 264 has a thickness in
the range from 100 to 1000 nm, for example. If the thickness is
smaller than 100 nm, then the electrically conductive member 264
will be unduly worn when the polishing process is carried out for
about one hour, and hence is not practical. If the thickness is
greater than 1000 nm, then the surface of the electrically
conductive member 264 will tend to crack when the polishing process
is carried out. The electrically conductive member 264 is
preferably made of platinum, but may be made of any of precious
metals such as gold, transition metals (Ag, Fe, Ni, Co, etc.),
graphite, electrically conductive resin, electrically conductive
rubber, electrically conductive organic matter etc. which are
insoluble or slightly soluble (at a solving rate of 10 nm/h. or
lower) in the water 232. If the electrically conductive member is
made of a transition metal, then it is preferable to use, as the
supplied water, water (hydrogen water) in which there is dissolved
hydrogen generated at a cathode when pure water or tap water is
electrolyzed, thereby preventing the electrically conductive member
from being corroded by oxygen dissolved in the water.
[0156] As is known from the Arrhenius equation, a chemical reaction
has a higher reaction rate as the reaction temperature is higher.
Therefore, it is possible to increase the stability of the reaction
rate while varying the reaction rate, by controlling at least one
of the temperatures of the substrate 142, the water 232, and the
turntable 230 to control the reaction temperature.
[0157] As shown in FIG. 9, the polishing apparatus 30C, 30D each
includes the conditioning mechanism (conditioner) 190, which may
comprise a polishing pad, for example, for conditioning the surface
(upper surface) of the polishing tool 134 to a good level of
flatness and an appropriate level of roughness.
[0158] The polishing apparatuses 30C, 30D are each capable of
polishing the surface of the substrate 142 by holding the surface
of the substrate 142 and the electrically conductive member 264,
such as of platinum or the like, of the polishing pad 242 in
contact with each other and moving them relative to each other
while the substrate 142 held by the substrate holder 244 and the
polishing pad 242 are being immersed in the water 232. The surface
of the substrate 142 may be polished while the water 232 is being
interposed between the substrate 142 held by the substrate holder
244 and the polishing pad 242 by supplying the water 232 from the
water supply line 241 onto the upper surface of the polishing pad
242.
[0159] The mechanism of the polishing process is considered as
follows: When the surface of the substrate 142 and the electrically
conductive member 264, such as of platinum or the like, of the
polishing pad 242 are held in contact with each other and moved
relative to each other, the contacting region is strained to excite
valence band electrons to a conduction band, generating electron
and hole pairs. The electrons excited to the conduction band are
moved to the electrically conductive member 264, such as of
platinum or the like, which has a large work function, leaving
holes on the substrate surface. Off ions or H.sub.2O molecules in
the water 232 act on the left holes, resulting the oxidization of
only the contacting region. Since oxides of Ga, Al, and In are
dissolvable in a weak acid such as a carbon dioxide solution or the
like or a weak alkali, the oxides produced in the contacting region
are dissolved into the water 232 and removed from the surface of
the substrate 142.
[0160] The pressure under which the surface of the substrate 142
and the electrically conductive member 264, such as of platinum or
the like, of the polishing pad 242 are held in contact with each
other should preferably be in the range from 0.1 to 1.0
kgf/cm.sup.2, for example, and particularly should preferably be of
about 0.4 kgf/cm.sup.2, in order to eliminate any warpage of the
substrate 142 and prevent the substrate 142 from being slipped out
and the electrically conductive member 264 of the polishing pad 242
from being peeled off from the base 260.
[0161] FIG. 16 shows the relationship between polishing rates and
polishing times when a GaN substrate is polished by the polishing
apparatus shown in FIG. 14, which employs pure water with air
dissolved therein as the water 232 and a polishing pad evaporated
platinum thereon as the polishing pad 242. As can be seen from FIG.
16 that though the polishing rate is about 22 nm/h at the start of
the polishing process, the polishing rate gradually decrease as the
polishing process progresses, and the polishing rate becomes almost
0 nm/h at the end of the polishing process. In this regard, it is
conceivable that the polishing rate is high when there are large
volume of material to be removed in such a state that a surface is
roughen at the start of the polishing process, and the polishing
rate becomes lower as the surface is flatten and the material to be
removed by polishing process is decrease.
[0162] Both the elastic base 260 and the intermediate layer 262 of
the polishing pad 242 may be made of an electrically conductive
material, and, as indicated by the imaginary lines in FIG. 14, a
conductive wire 272a extending from the anode of a power source 270
and a conductive wire 272b extending from the cathode thereof may
be connected respectively to the substrate 142 held by the
substrate holder 244 and the elastic base 260 of the polishing pad
242. Then, the surface of the substrate 142 may be polished while a
voltage is being applied between the electrically conductive member
264 of the polishing pad 242 and the substrate 142 held by the
substrate holder 244. In this manner, the polishing rate can be
increased.
[0163] Returning to FIG. 9, between the polishing apparatuses 30A,
30B and the cleaning section 4 is disposed a first linear
transporter 5 as a first (translatory) transfer mechanism for
transferring a substrate between four transferring positions (a
first transferring position TP1, a second transferring position
TP2, a third transferring position TP3, and a fourth transferring
position TP4 in the order of distance from the loading/unloading
section 2) along the long direction of the flattering system. A
reversing machine 31 for reversing a substrate received from the
first transfer robot 22 is disposed above the first transferring
position TP1 of the first linear transporter 5, and a
vertically-movable lifter 32 is disposed below the reversing
machine 31. Further, a vertically-movable pusher 33 is disposed
below the second transferring position TP2, a vertically-movable
pusher 34 is disposed below the third transferring position TP3,
and a vertically-movable lifter 35 is disposed below the fourth
transferring position TP4.
[0164] Beside the polishing apparatuses 30C, 30D and adjacent to
the first linear transporter 5 is disposed a second linear
transporter 6 as a second (translatory) transfer mechanism for
transferring a substrate between three transferring positions
(fifth transferring position TP5, sixth transferring position TP6
and seventh transferring position TP7 in order of distance from the
loading/unloading section 2) along the long direction of the
flattering system. A vertically-movable lifter 36 is disposed below
the fifth transferring position TP5, a pusher 37 is disposed below
the sixth transferring position TP6, and a pusher 38 is disposed
below the seventh transferring position TP7. Further, a pure water
replacement section 192 including a tub and a pure water nozzle is
disposed between the polishing apparatus 30C and the pusher 37, and
a pure water replacement section 194 including a tub and a pure
water nozzle is also disposed between the polishing apparatus 30D
and the pusher 38.
[0165] As will be understood from the use of a slurry or the like
during polishing, the polishing section 3 is the dirtiest area. In
this system, therefore, discharge of air is performed around a
removal processing site, such as a platen, so as to prevent
particles in the polishing section 3 from flying to the outside.
Further, the internal pressure of the polishing section 3 is made
lower than the external pressure of the system and the internal
pressures of the neighboring cleaning section 4 and
loading/unloading section 2, thereby preventing particles from
flying out. An exhaust duct (not shown) and a filter (not shown)
are usually provided respectively below and above a removal
processing site, such as a platen, so as to create a downward flow
of cleaned air.
[0166] The cleaning section 4 is an area for cleaning a substrate.
The cleaning section 4 includes a second transfer robot 40, a
reversing machine 41 for reversing a substrate received from the
second transfer robot 40, three cleaning units 42-44 each for
cleaning the substrate, a drying unit 45 for rinsing the cleaned
substrate with pure water and then spin-drying the substrate, and a
movable third transfer robot 46 for transferring the substrate
between the reversing machine 41, the cleaning units 42-44 and the
drying unit 45. The second transfer robot 40, the reversing machine
41, the cleaning units 42-44 and the drying unit 45 are arranged in
a line along the long direction of the flattering system, and the
third transfer robot 46 is movably disposed between the first
linear transporter 5 and the line of the second transfer robot 40,
the reversing machine 41, the cleaning units 42-44 and the drying
unit 45. A filter-fan unit (not shown) having an air filter is
provided above the cleaning units 42-44 and the drying unit 45, and
clean air, from which particles have been removed by the filter-fan
unit, continually blows downward. The interior of the cleaning
section 4 is constantly kept at a higher pressure than the
polishing section 3 to prevent inflow of particles from the
polishing section 3.
[0167] A shutter 50, located between the reversing machine 31 and
the first transfer robot 22, is provided in the partition wall 1 a
surrounding the polishing section 3. The shutter 50 is opened when
transferring a substrate between the first transfer robot 22 and
the reversing machine 31.
[0168] Further, a shutter 53 located at a position facing the
polishing apparatus 30B and a shutter 54 located at a position
facing the polishing apparatus 30C are respectively provided in the
partition wall lb surrounding the polishing section 3.
[0169] Processing for flattening a surface of a substrate by the
flattening system having the above construction will now be
described.
[0170] The first transfer robot 22 carries a substrate out of the
substrate cassette placed in the front loading section 200 and
transfers the substrate to the reversing machine 31. The reversing
machine 31 reverses the substrate through 180.degree. and then
places the reversed substrate on the lifter 32 at the first
transferring position TP1. The first linear transporter 5 moves to
transfer the substrate on the lifter 32 to the first transferring
position TP1 or the third transferring position TP3. The substrate
holder 144 of the polishing apparatus 30A receives the substrate
from the pusher 32 or the substrate holder 144 of the polishing
apparatus 30B receives the substrate from the pusher 34. Then, the
polishing apparatus 30A or 30B polishes the surface of the
substrate in a first stage and a second stage.
[0171] Specifically, in the polishing apparatus 30A, the substrate
holder 144 which is holding the substrate 142 such as a GaN
substrate or the like with its surface (surface to be processed)
facing downward is moved to a position above the container 132, and
then is lowered to immerse the substrate 142 in the processing
liquid 130 held in the container 132. While the processing liquid
130 is present between the substrate 142 and the polishing tool
134, the light source 140 applies excitation light, preferably
ultraviolet light, to the surface (lower surface) of the substrate
142. If the substrate 142 comprises a GaN substrate, then since the
band gap of GaN is of 3.42 eV, the excitation light should
preferably have a wavelength equal to or lower than the wavelength
corresponding to the band gap of the workpiece, i.e., equal to or
lower than 365 nm, e.g., should preferably have a wavelength of 312
nm. When the GaN substrate is machined, therefore, GaN is oxidized
to form a Ga oxide (Ga.sub.2O.sub.3) on the surface of the GaN
substrate.
[0172] The substrate 142 may be polished while the processing
liquid 130 is being supplied through the processing liquid supply
nozzle 133 between the substrate 142 and the polishing tool
134.
[0173] At this time, the switch 150 of the power source 148 is
turned on to apply a voltage between the polishing tool 134 and the
substrate 142 held by the substrate holder 144 such that the
polishing tool 134 serves as a cathode. When the GaN substrate is
processed, therefore, the formation of the Ga oxide
(Ga.sub.2O.sub.3) on the surface of the GaN substrate is
promoted.
[0174] Then, while the light source 140 is emitting the excitation
light, preferably ultraviolet light, and also while the voltage is
being applied between the polishing tool 134 and the substrate 142,
the rotating shaft 136 is rotated to rotate the polishing tool 134,
and at the same time that the substrate holder 144 is rotated to
rotate the substrate 142, the substrate 142 is lowered to cause the
surface of the polishing tool 134 to contact the surface of the
substrate 142 under a surface pressure preferably in the range from
0.1 to 1.0 kgf/cm.sup.2. If the surface pressure is lower than 0.1
kgf/cm.sup.2, then any warpage of the substrate 142 may not
possibly be corrected and the substrate 142 may not possibly be
polished uniformly in its entirety. If the surface pressure is
higher than 1.0 kgf/cm.sup.2, then the surface of the substrate 142
may possibly develop mechanical defects. In this manner, the
surface of the substrate 142, such as a GaN substrate, is polished
in the first stage for selectively removing regions of an Ga oxide
formed on the surface of the substrate 142 which are held in
contact with the polishing tool 134, i.e., for selectively removing
the Ga oxide formed on the tip ends of convex regions the surface
of the substrate 142 which has surface irregularities, primarily
for removing damage to the surface of the substrate 142. The
surface of the substrate 142 is polished in the first stage at a
polishing rate up to about 1000 nm/h., for a machining time of
about 5 minutes, for example.
[0175] While the surface of the substrate 142 is being polished in
the first stage, the spectrometer 208 of the
photoluminescence-light-type damage level measuring device 202
performs a spectral analysis on photoluminescence light emitted
from the surface of the substrate 142 and monitors the intensity of
the photoluminescence light at a wavelength corresponding to the
band gap of the substrate 142, e.g., at the wavelength of 365 nm
for GaN. As shown in FIG. 17, as the polishing process progresses,
the intensity of the photoluminescence light at the wavelength of
365 nm increases. An endpoint of the polishing process in the first
stage is detected by detecting when the intensity of the
photoluminescence light at the wavelength of 365 nm reaches a
predetermined value or becomes constant.
[0176] When the polishing process in the first stage is ended, the
switch 150 is turned off to stop applying the voltage between the
polishing tool 134 and the substrate 142 while the excitation
light, preferably ultraviolet light, is being continuously applied
from the light source 140, thereby polishing the surface of the
substrate 142 in the second stage for improving the surface
roughness of the substrate 142. The surface of the substrate 142 is
polished in the second stage at a polishing rate up to about 200
nm/h., for a machining time of about 30 minutes, for example. While
the surface of the substrate 142 is being polished in the second
stage, the switch 206 is turned on to enable the ammeter 204 of the
photocurrent-type damage level measuring device 201 to measure a
current flowing along the conductive wire 152c which connects the
substrate 142 and the metal films (metal wires) 154 of the
polishing tool 134. As shown in FIG. 18, as the polishing process
progresses, the value of the current flowing through the ammeter
204 gradually increases until it becomes substantially constant in
time. An endpoint of the polishing process in the second stage is
detected by measuring the value of the current flowing through the
ammeter 204 and detecting when the value of the current reaches a
predetermined value or becomes constant.
[0177] After the polishing process in the second stage is ended,
the excitation light, preferably the ultraviolet radiation, applied
from the light source 140 is stopped, and the substrate holder 144
is raised, after which the rotation of the substrate 142 is
stopped. If necessary, the surface of the substrate 142 is rinsed
with pure water, and then the substrate 142 is transferred to the
pusher 33 at the second transferring position TP2. The first linear
transporter 5 transfers the substrate 142 on the pusher 33 to the
lifter 35. The polishing apparatus 30B similarly receives the
substrate 142 from the pusher 34 with the substrate holder 144, and
polishes the substrate 142 in the first stage and the second stage.
Thereafter, the polished substrate 142 is transferred to the lifter
35 at the fourth transferring position TP4.
[0178] The second transfer robot 40 receives the substrate 142 from
the lifter 35 and places the substrate 142 onto the lifter 36 at
the fifth transferring position TP5. The second linear transporter
6 moves to transfer the substrate 142 on the lifter 36 to the sixth
transferring position TP6 or the seventh transferring position
TP7.
[0179] The polishing apparatus 30C receives the substrate 142 from
the pusher 37 with the substrate holder 244, and polishes the
substrate 142 in the third stage. Specifically, the substrate
holder 244, which is holding the substrate 142, such as a GaN
substrate or the like, with its surface (surface to be processed)
facing downwardly, is moved to a position above the container 234,
and then is rotated and lowered to immerse the substrate 142 in the
water 232 held in the container 234. The substrate holder 244 is
further lowered to bring the surface of the substrate 142 into
contact with the electrically conductive member 264, such as of
platinum, of the polishing pad 242, which is being rotated, under a
contact pressure (pressure force) in the range from 100 to 1000 hPa
(from 0.1 to 1.0 kgf/cm.sup.2), for example, preferably under a
contact pressure of 400 hPa (0.4 kgf/cm.sup.2). In this manner, the
polishing process in the third stage is performed for finishing the
surface of the substrate 142 by relatively moving the surface of
the substrate 142 and the electrically conductive member 264 such
as of platinum of the polishing pad 242 while holding them in
contact with each other. The polishing process in the third stage
may be performed while the water 232 is being supplied between the
surface of the substrate 142 and the electrically conductive member
264, such as of platinum, of the polishing pad 242.
[0180] After the polishing process in the third stage is ended, the
water 232 left on the surface of the substrate 142 is replaced with
pure water by the pure water replacement section 192, and then the
substrate 142 is returned to the sixth transferring position TP6.
The polishing apparatus 30D similarly receives the substrate 142
from the pusher 38 with the substrate holder 244 and polishes
(finishes) the surface of the substrate 142 in the third stage. The
water 232 left on the surface of the substrate 142 after the
polishing process is replaced with pure water by the pure water
replacement section 194, and then the substrate 142 is returned to
the seventh transferring position TP7. Thereafter, the second
linear transporter 6 moves to move the substrate 142, on which the
water 232 has been replaced with the pure water, to the fifth
transferring position TP5.
[0181] The second transfer robot 40 takes the substrate out of the
fifth transferring position TP5 and transfers the substrate to the
reversing machine 41. The reversing machine 41 reverses the
substrate through 180.degree. and then transfers it to the first
cleaning unit 42, where the substrate is cleaned. The third
transfer robot 46 transfers the substrate from the first cleaning
unit 42 to the second cleaning unit 43, where the substrate is
cleaned.
[0182] The third transfer robot 46 transfers the substrate after
cleaning to the third cleaning unit 44, where the substrate is
cleaned with pure water. The third transfer robot 46 transfers the
substrate after pure water cleaning to the drying unit 45, where
the substrate is rinsed with pure water and then rotated at a high
speed to spin-dry the substrate. The first transfer robot 22
receives the substrate after spin-drying from the drying unit 45
and returns the substrate to the substrate cassette mounted in the
front loading section 200.
[0183] An interference microscope image of a GaN substrate surface
before it is polished is shown in FIG. 19A, and the relationship
between distances and heights on the substrate surface is shown in
FIG. 19B. An interference microscope image of the GaN substrate
surface after it is polished in the first stage wherein the GaN
substrate surface is polished at a polishing rate up to 1000 nm/h
for 5 minutes with the excitation light and the voltage being
applied is shown in FIG. 20A, and the relationship between
distances and heights on the substrate surface is shown in FIG.
20B. An interference microscope image of the GaN substrate surface
after it is polished in the second stage wherein the GaN substrate
surface is polished at a polishing rate up to 200 nm/h for 30
minutes with only the excitation light being applied, after the
polishing process in the first stage, is shown in FIG. 21A, and the
relationship between distances and heights on the substrate surface
is shown in FIG. 21B. An interference microscope image of the GaN
substrate surface after it is polished in the third stage wherein
the GaN substrate surface is polished at a polishing rate up to 10
nm/h for 180 minutes using platinum as the electrically conductive
member and water with its pH adjusted to 5.5 by dissolving CO.sub.2
in pure water, after the polishing process in the first stage and
the polishing process in the second stage, is shown in FIG. 22A,
and the relationship between distances and heights on the substrate
surface is shown in FIG. 22B.
[0184] It can be seen from FIGS. 19 through 22B that the surface
roughness Ra of the GaN substrate improved from Ra: 5.271 .mu.m to
Ra: 4.17 .mu.m when it was polished in the first stage for 5
minutes, then improved to Ra: 0.363 .mu.m when it was polished in
the second stage for 30 minutes, and further improved to Ra: 0.083
.mu.m when it was polished in the third stage for 180 minutes. It
can thus be seen that a substrate having a sufficient level surface
flatness can be obtained by polishing it for about 215 minutes.
Example 1
[0185] A GaN substrate was prepared by polishing a substrate
surface in the first stage by applying excitation light and a
voltage and then polishing the substrate surface in the second
stage by applying only excitation light. The surface of the GaN
substrate was polished (finished) in the third stage by the
polishing apparatus shown in FIG. 14. In the polishing apparatus
shown in FIG. 14, the electrically conductive member 264 was made
of platinum, and water 232 with its pH adjusted to 5.5 by
dissolving CO.sub.2 in pure water with the gas dissolver 238 was
poured into the container 234 provided by the dam member 236. The
surface of the GaN substrate was polished for 3 hours by rotating
the turntable 230 at a rotational speed of 10 rpm and holding the
substrate surface and the electrically conductive member (platinum)
264 in contact with each other under a contact pressure (pressing
force) of 0.4 kgf/cm.sup.2.
[0186] An atomic force microscope (AFM) image of the GaN substrate
surface after it is polished is shown in FIG. 23A, the relationship
between distances and heights on the substrate surface is shown in
FIG. 23B. Any etch pits depending on crystal defects are not
observed from FIG. 23A, and a clear terrace-step structure is
observed from FIG. 23B, indicating that the GaN substrate surface
was polished in an atomic level to a flat damageless finish.
Comparative Example 1
[0187] A GaN substrate surface was polished under the same
conditions as Example 1 except that an HF-dissolved solution was
used instead of the water 232 with its pH adjusted to 5.5 by
dissolving CO.sub.2 in pure water with the gas dissolver 238.
[0188] An atomic force microscope (AFM) image of the GaN substrate
surface after it is polished is shown in FIG. 24A, the relationship
between distances and heights on the substrate surface is shown in
FIG. 24B. Although a clear terrace-step structure is observed from
FIG. 24B, strips of etch pits having a depth of 0.5 nm are observed
on the terrace from FIG. 24A. The etch pits are considered to
result from selective etching of crystal defects, etc. with highly
corrosive HF.
Example 2
[0189] A GaN substrate surface was polished under the same
conditions as Example 1 except that a bonded substrate (epitaxial
substrate) with GaN mounted on a surface of a sapphire substrate
was used instead of the GaN substrate made of only GaN.
[0190] An atomic force microscope (AFM) image of the substrate
surface after it is polished is shown in FIG. 25A, the relationship
between distances and heights on the substrate surface is shown in
FIG. 25B. Any etch pits depending on crystal defects are not
observed from FIG. 25A, and a clear terrace-step structure is
observed from FIG. 25B, indicating that the substrate surface was
polished in an atomic level to a flat damageless finish.
[0191] In this Example 2, the bonded substrate with GaN mounted on
the surface of the sapphire substrate. It is also possible to
polish a bonded substrate with GaN mounted on a surface of a SiC
substrate, a bonded substrate with GaN mounted on a surface of a Si
substrate, or a bonded substrate with GaN mounted on a surface of a
GaAs substrate.
[0192] In the above embodiment, the polishing process in the first
stage and the polishing process in the second stage are performed
by the same polishing apparatus. However, the polishing process in
the first stage and the polishing process in the second stage may
be performed by separate polishing apparatus. Though the third
polishing process is performed on a substrate which has been
polished in the first stage and the second stage in the above
embodiment, the third polishing process ma be performed on a
substrate which has been polished in the first stage or the second
stage.
[0193] Furthermore, a substrate after it has been processed by CMP,
ion implantation, activation annealing, or RIE may be finished
(polished in the third stage) by the polishing apparatus shown in
FIG. 14.
[0194] FIG. 26 is a schematic cross-sectional view of a polishing
apparatus 30E according to another embodiment of the present
invention. The polishing apparatus 30E is replaced with at least
one of the polishing apparatuses 30C, 30D shown in FIG. 9, for
example, and used for polishing process in the third stage.
[0195] As shown in FIG. 26, the polishing apparatus 30E includes a
container 132 for holding therein water 232. Weak acid water, water
with air dissolved therein, or electrolytic ion water is used as
the water 232. A turntable 302 having light permeability is mounted
on the bottom of the container 300, and a polishing pad 304 is
mounted on an upper surface of the turntable 302, so that the
polishing pad 304 becomes immersed in the water 232 when the
container 300 is filled with the water 232. An electrically
conductive member, for example, composed of platinum, is formed on
at least a surface (upper surface) of the polishing pad 304 by
vacuum evaporation or the like.
[0196] The container 300 is coupled to an upper end of a rotatable
rotating shaft 306. The bottom plate of the container 300 has a
ring-shaped opening 300a formed around the rotating shaft 306 and
closed by the turntable 302. A light source 308 for emitting
excitation light, preferably ultraviolet light, is disposed right
below the opening 300a. The polishing pad 304 has a number of
through holes 304 defined therein in a region corresponding the
light source 308. Thus, the excitation light, preferably
ultraviolet light, emitted from the light source 308, passes
through the opening 300a of the container 300 and the through holes
304a of the polishing pad 304, and reaches above the polishing pad
304.
[0197] Right above the container 300 is disposed a substrate holder
310 for detachably holding a substrate 142, e.g., a GaN substrate,
with a front surface facing downwardly. The substrate holder 310 is
coupled to a lower end of a main shaft 312 that is rotatable and
vertically movable. The substrate holder 310 and the main shaft 312
are identical in structure to the substrate holder 144 and the main
shaft 146 shown in FIG. 10, and will not be described in detail
below.
[0198] The polishing apparatus 30E of this embodiment is also
provided with a power source 314 for applying voltage between the
substrate 142 held by the substrate holder 310 and the polishing
pad 304. An ammeter 318 is interposed in a conductive wire 316a
extending from the positive pole of the power source 314. The
conductive wire 316a extending from the positive pole of the power
source 314 is connected to the substrate 142 held by the substrate
holder 310, and a conductive wire 316b extending from the negative
pole of the power source 314 is connected to the polishing pad
304.
[0199] When a substrate having deep scratches locally is polished,
a large amount of shavings should be removed for removing the
scratches. Since the polishing rate is lowered when most of a
substrate is flattened as the polishing process progresses, it
takes a long time to polish a substrate until the deep scratches
locally present in the substrate are removed. In this case, the
surface of the substrate 142 is polished by the polishing apparatus
30E shown in FIG. 26 while applying excitation light to the surface
of the substrate 142 and voltage, as necessary, between the
substrate 142 and the polishing pad 304. By thus polishing the
substrate 142, the surface of the substrate 142 is polished while
minute etch pits (1-2 nm) are being formed on the surface of the
substrate 142 because of the influence of the excitation light, as
shown in FIG. 27. The surface of the substrate 142 is polished at
the polishing rate equal to the polishing rate when the surface
having surface roughness is polished because of the present of the
etch pits, and therefore a large amount of shavings can be removed
without lowering the polishing rate. By performing finish polishing
process after the application of the excitation light and the
voltage are stopped, the etch pits formed on the surface of the
substrate can be removed.
[0200] If the substrate comprises a GaN substrate, then since the
band gap of GaN is of 3.42 eV, the excitation light should
preferably have a wavelength equal to or lower than the wavelength
corresponding to the band gap of the workpiece, i.e., equal to or
lower than 365 nm, e.g., should preferably have a wavelength of 312
nm.
[0201] For example, as described above, the polishing apparatus 30A
or 30B performs the polishing process in the first stage for five
minutes while applying the excitation light, preferably ultraviolet
light, from the light source 140 and the voltage between the
polishing tool 134 and the substrate 142. The polishing apparatus
30A or 30B performs the polishing process in the second stage for
25 minutes successively while applying the voltage between the
polishing tool 134 and the substrate 142 is stopped and the
excitation light, preferably ultraviolet light, is being
continuously applied from the light source 140.
[0202] Next, the polishing apparatus 30E shown in FIG. 26 performs
a first step polishing process in the third stage for 15 minutes
while applying the excitation light, preferably ultraviolet light,
from the light source 308 and the voltage between the polishing pad
304 and the substrate 142. Then, the polishing apparatus 30E
performs a second step polishing process in the third stage for 25
minutes while applying the excitation light from the light source
408 and the voltage between the polishing pad 304 and the substrate
142 are stopped.
[0203] By thus dividing the polishing process in the third stage
into two polishing step and performing the polishing process, a
substrate, e.g., having deep scratches locally can be polished
effectively.
[0204] In the above embodiment, the surface of the substrate 142 is
polished while applying the excitation light to the surface of the
substrate 142, and then finishing the surface of the substrate 142
without applying the excitation light to the surface of the
substrate 142. A polishing process for polishing the surface of the
substrate 142 while applying excitation light to the surface of the
substrate 142, and a polishing process for polishing the surface of
the substrate 142 without applying excitation light to the surface
of the substrate 142 may be repeated alternately. In this case, the
surface of the substrate 142 is finally polished for finishing
without applying excitation light to the surface of the substrate
142.
[0205] In the above embodiment, the substrate 142 is polished while
applying the excitation light to the surface of the substrate 142
and the voltage, if necessary, between the substrate 142 and the
polishing pad 304. The substrate 142 may be polished while applying
the voltage between the substrate 142 and the polishing pad 304
without applying the excitation light to the surface of the
substrate 142. This can form etch pits on the surface of the
substrate 142 and enhance the polishing rate.
[0206] FIG. 28 is a schematic cross-sectional view of a polishing
apparatus 30F according to yet another embodiment of the present
invention. The polishing apparatus 30F shown in FIG. 28 is
different from the polishing apparatus 30E shown in FIG. 26 is
that: a polishing pad 320 comprising a light transmission area E1
having through holes 320a and a light non-transmission area E2 is
used instead of the polishing pad 304; and the substrate holder 320
is configured to reciprocate between the light transmission area E1
and the light non-transmission area E2 on the polishing pad
320.
[0207] According to this embodiment, the application of the
excitation light to the substrate 142 held by the substrate holder
310 can be stopped by moving the substrate holder 310 from the
light transmission area El to the light non-transmission area E2 on
the polishing pad 320 while applying the excitation from the light
source 308.
[0208] FIG. 29 is a schematic cross-sectional view of a polishing
apparatus 30G according to yet another embodiment of the present
invention. The polishing apparatus 30G is replaced with at least
one of the polishing apparatuses 30C, 30D shown in FIG. 9, for
example, and used for polishing in the third stage.
[0209] As shown in FIG. 29, the polishing apparatus 30G has a
container 290 for holding therein water 232 such as weak acid
water, water with air dissolved therein, or electrolytic ion water.
A polishing pad 242a made of a light-permeable material is attached
to the bottom of the container 290. The polishing pad 242a is
connected to an upper end of a rotatable rotating shaft 292. The
polishing apparatus 30G also includes a Raman-light-type damage
level measuring device 218 which comprises a laser beam source 214
for applying a visible monochromatic beam to a surface of a
substrate 142 which is held by the substrate holder 244 and a
spectrometer 216 for performing a spectral analysis on reflected
light from the surface of the substrate 142 and measuring the
intensity of Raman light. The other structural details are
identical to those of the polishing apparatus shown in FIG. 14.
[0210] As shown in FIG. 30, the polishing pad 242a comprises a base
250 made of transparent glass or the like, for example, an elastic
body 252 having a Shure hardness in the range from 50 to 90
disposed on a surface of the base 250, the elastic body 252 having
light-permeable through holes 252a defined therein at grid pattern
positions for contact with the substrate, an intermediate layer 254
deposited on a surface of the elastic body 252 by vacuum
evaporation or the like, and an electrically conductive member 256
deposited on a surface of the intermediate layer 254 by vacuum
evaporation or the like. The electrically conductive member 256
that is disposed on the surface of the elastic body 252 with the
intermediate layer 254 interposed therebetween finds it easy to
follow irregularities in long/single periods on the surface
(surface to be polished) of the substrate 142.
[0211] The elastic body 252 may be made of rubber, resin, foamable
resin, non-woven fabric or the like, for example, and has a
thickness in the range from 0.5 to 5 mm. The elastic body 252 may
comprise two or more superposed layers of elastic material which
have different modulus of elasticity.
[0212] The intermediate layer 254 has a thickness in the range from
1 to 10 nm, for example. The intermediate layer 254 is interposed
between the elastic body 252 and the electrically conductive member
256 in order to increase the adhesion between the elastic body 252
and the electrically conductive member 256, and is made of chromium
or graphite (SP2-bonded) carbon, for example, which have good
adhesion to both the elastic body 252 and the electrically
conductive member 256. When the intermediate layer 254 is formed on
the surface of the elastic body 252 by vacuum evaporation, it is
preferable to employ ion sputtering deposition in order to suppress
expansion and modification of the elastic body 252 due to high
temperatures. This holds true also when the electrically conductive
member 256 is formed on the surface of the intermediate layer 254
by vacuum evaporation.
[0213] The electrically conductive member 256 has a thickness in
the range from 100 to 1000 nm, for example. If the thickness is
smaller than 100 nm, then the electrically conductive member 256
will be unduly worn when the polishing process is carried out for
about one hour, and hence is not practical. If the thickness is
greater than 1000 nm, then the surface of the electrically
conductive member 256 will tend to crack when the polishing process
is carried out. The electrically conductive member 256 is
preferably made of platinum, but may be made of any of precious
metals such as gold, transition metals (Ag, Fe, Ni, Co, etc.),
graphite, electrically conductive resin, electrically conductive
rubber, electrically conductive organic matter etc. which are
insoluble or slightly soluble (at a solving rate of 10 nm/h. or
lower) in the water 232.
[0214] When the polishing apparatus 30G shown in FIG. 29 performs
the polishing process in the third stage, the laser beam source 214
of the Raman-light-type damage level measuring device 218 applies a
visible monochromatic beam to the surface of the substrate 142 held
by the substrate holder 244 through the base 250 and the
light-permeable through holes 252a in the elastic body 252 of the
polishing pad 242a, and the spectrometer 216 performs a spectral
analysis on the reflected light from the surface of the substrate
142 and measures the intensity of Raman light. As described above,
as the polishing process progresses, the intensity of the Raman
light increases, as shown in FIG. 8. Therefore, an endpoint of the
polishing process in the third stage is detected by detecting when
the intensity of the Raman light reaches a predetermined value or
becomes constant.
[0215] In the above embodiment, the endpoint of the polishing
process in the first stage is detected by the
photoluminescence-light-type damage level measuring device 202.
However, the endpoint of the polishing process in the first stage
may be detected by the Raman-light-type damage level measuring
device 218 shown in FIG. 29. Alternatively, the endpoint of the
polishing process in the first stage may be detected by a
combination of the photoluminescence-light-type damage level
measuring device 202 and the Raman-light-type damage level
measuring apparatus 218 based on an average value of their output
signals.
[0216] Though the endpoint of the polishing process in the second
stage is detected by the photocurrent-type damage level measuring
device 201, it may be detected by the photoluminescence-light-type
damage level measuring device 202 or the Raman-light-type damage
level measuring apparatus 218 shown in FIG. 29, or two or more
damage level measuring apparatus based on an average value of their
output signals. The polishing process in the first stage and the
polishing process in the second stage are performed using a pH
buffer solution of a neutral pH which contains Ga ions. However,
the detection of the endpoints is not limited to these polishing
processes.
[0217] Since SiC and GaN are permeable to visible light and
infrared rays, visible light or infrared rays may be applied to a
substrate, and the thickness of the substrate may be measured based
on light reflected from the face and reverse sides of the
substrate. A film thickness measuring device based on such a light
interference process and the above processes of monitoring the
progress of the polishing process may be combined and used
complementarily.
[0218] FIG. 31 is a cross-sectional of still another polishing tool
134b for use in the polishing apparatuses 30A, 30B shown in FIG.
10, and FIG. 32 is a plan view of the polishing tool 134b shown in
FIG. 31. As shown in FIGS. 31 and 32, the polishing tool 134b
comprises a support platen 400 having a number of concentric
grooves 400a defined therein in a region corresponding to the
opening 132a of the container 132 and metal lines 402 disposed as
metal wires in the grooves 400a, and a catalyst pad 408 including a
pad base 404 disposed on the support platen 400 and having a
plurality of through holes 404a defined therein in a scattered
pattern for passing therethrough at least one of light and an ion
current and a catalyst layer 406 deposited on the pad base 404 by
vacuum evaporation or the like in areas except the through holes
404a.
[0219] As shown in FIG. 33, the metal lines 402 extend fully
diametrically across the substrate 142 which is held by the
substrate holder 144. As shown in FIG. 32, the through holes 404a
are positioned in a region where the metal lines 402 are
disposed.
[0220] The catalyst pad 408 is of a diameter which is substantially
the same (same shape) as the diameter of the support platen 400 or
smaller (small shape) than the diameter of the support platen 400.
The catalyst pad 408 is detachably mounted on the support platen
400 by screws or double-faced adhesive tapes at its outer
circumferential edge. The polishing tool 134b itself is also
detachably mounted on the bottom plate of the container 132 by
mechanical fasteners such as screws or the like.
[0221] Since the support platen 400 and the catalyst pad 408 are
separate from each other and the catalyst pad 408 has a high level
of surface flatness and does not tend to produce burrs, scratches,
etc., the polishing tool 134b is capable of producing a flat
polished surface free of burrs, scratches, etc. Further, when the
catalyst layer 406 is worn, the polishing tool 134b is replaced
with a new one as follows: The polishing tool 134b is removed from
the bottom plate of the container 132, and then the catalyst pad
408 is detached from the support platen 400. A new catalyst pad 408
is mounted on the support platen 400, and the polishing tool 134b
with the new catalyst pad 408 is mounted on the bottom plate of the
container 132. As the support platen 400 can be reused, the
polishing tool 134b is inexpensive and highly durable.
[0222] The support platen 400 is made of a light-permeable material
such as glass such as synthetic quartz or the like or
light-permeable resin such as acrylic resin or the like. The metal
lines 402 as metal wires are made of platinum, gold, silver,
copper, aluminum, or the like. The pad base 404 is made of glass,
rubber, light-permeable resin, foamable resin, or non-woven
fabric.
[0223] The catalyst pad 408 is constructed of the catalyst layer
406 and the pad base 404. The catalyst layer 406 is made of one or
more of a precious metal, a transition metal, a ceramics-based
solid catalyst, a base solid catalyst, and an acid solid catalyst,
for example. The precious metal comprises one of platinum, gold,
and silver or a combination thereof. The transition metal comprises
at least one of Fe, Ni, Co, Cu, Cr, i, molybdenum, and a compound
thereof, or a combination thereof The base solid catalyst or the
acid solid catalyst comprises one of non-woven fabric, resin, and
metal, an acid or base metal oxide, and glass with an ion exchange
function or a combination thereof.
[0224] In this embodiment, the catalyst layer 406 is formed on the
surface of the pad base 404 by depositing one of the
above-described materials or a combination thereof by the way of
vacuum evaporation. The catalyst layer 406 can be formed uniformly
to a desired thickness on the surface of the pad base 404 by vacuum
evaporation.
[0225] The catalyst pad 408 may be made of only quartz glass. If
the catalyst pad 408 is made of quartz glass, it can be separate
from and detachably mounted on the support platen 400, so that the
metal lines (metal wires) 402 in the support platen 400 can be
reused.
[0226] The pad base 404 should preferably is made of an elastic
material such as rubber or the like. In this case, since the pad
base 404 is elastically deformable along the surface (surface to be
processed) of the substrate 142, even if the catalyst pad 408 has
surface irregularities, they are prevented from being transferred
to the surface of the substrate 142. For example, if the pad base
404 is made of resin and the adhesion between the pad base 404 of
resin and the catalyst layer 406 is weak, then carbon is evaporated
on the surface of the pad base 404 of resin, and the catalyst layer
406 is formed on the carbon by evaporation, so that the adhesion
between the pad base 404 of resin and the catalyst layer 406 is
increased by the carbon. The catalyst pad 408 with increased
adhesion as a whole can thus be produced.
[0227] In this embodiment, as shown in FIG. 35, the support platen
400 has a plurality of through holes 406b defined therein, and the
metal wires 402 extend through the through holes 400b to the
surface of the support platen 400. The metal lines (metal wires)
402 are disposed along the grooves 400a defined concentrically in
the surface of the support platen 400, and the conductive wire 152b
extending from the cathode of the power source 148 is connected to
the metal lines 402.
[0228] FIGS. 36 and 37 show yet another polishing tool 134c for use
in the polishing apparatuses 30A, 30B shown in FIG. 10. The
polishing tool 134c is different from the polishing tool 134b shown
in FIGS. 31 and 32 in that metal films 412 serving as metal wires
are deposited on a flat surface of a support platen 410 by vacuum
evaporation. The catalyst pad 408, which is identical to the
catalyst pad 408 described above, is detachably mounted on the
surface of the support platen 410 by screws, double-faced adhesive
tapes, or the like. The metal films (metal wires) 412 comprise a
plurality of concentric metal films 412a and at least one straight
connecting metal film 412b which connects the concentric metal
films 412a. The connecting metal film 412b has an electrode 412c at
a proximal end thereof to which the conductive wire 152b extending
from the cathode of the power source 148 is connected.
[0229] In this embodiment, as shown in FIG. 37, the concentric
metal films 412a extend fully diametrically across the substrate
142 which is held by the substrate holder 144. The retainer ring
172 has opposite sides slightly projecting from the region where
the concentric metal films 412a are disposed.
[0230] As shown in FIG. 38, the support platen 410 may be divided
into a plurality of zones (five zones in FIG. 38), and concentric
metal films 412a disposed in the respective zones may be connected
individually to a plurality of connecting metal films 412b. The
connecting metal films 412b may have respective electrodes 412c
connected individually to a plurality of conductive lines extending
respectively from the cathodes of a plurality of power sources for
controlling polishing rates in the respective zones.
[0231] FIG. 39 shows a still further polishing tool 134d for use in
the polishing apparatuses 30A, 30B shown in FIG. 10. The polishing
tool 134d is different from the polishing tool 134b shown in
[0232] FIGS. 31 and 32 in that a light-permeable wiring film 416
made of fluororesin, acrylic resin, or the like and having a
thickness in the range from 10 to 500 .mu.m, for example, is
interposed between a flat surface of a support platen 410 and the
catalyst pad 408. A wiring pattern 418 serving as metal wires is
evaporated on an upper surface of the wiring film 416. The wiring
pattern (metal wires) 418 comprises a plurality of concentric metal
films as shown in FIG. 37, for example. The concentric metal films
may be divided into a plurality of zones as shown in FIG. 38.
[0233] FIG. 40 shows another polishing pad 242b for use in the
polishing apparatuses 30C, 30D shown in FIG. 14. The polishing pad
242b is different from the polishing pad 242 shown in FIG. 15 in
that it includes a support platen 280 made of a light-permeable
material such as glass such as synthetic quartz or the like or
light-permeable resin such as acrylic resin or the like, an elastic
base 282 made of an elastic material and having a number of through
holes 282a defined therein, the elastic base 282 being disposed on
an upper surface of the support platen 280, an intermediate layer
284 deposited on a surface of the elastic base 282 in areas except
the through holes 282a by vacuum evaporation or the like, and an
electrically conductive member 286 deposited on an upper surface of
the intermediate layer 284 by vacuum evaporation or the like.
INDUSTRIAL APPLICABILITY
[0234] The polishing method and the polishing apparatus according
to the present invention are used to polish flatwise a surface
(surface to be processed) of a substrate such as a single substrate
made of a compound semiconductor (e.g., GaN) containing an element
such as Ga, Al, In, or the like, or a bonded substrate (epitaxial
substrate) on which a compound semiconductor containing an element
such as Ga, Al, In, or the like is mounted.
* * * * *