U.S. patent application number 13/737210 was filed with the patent office on 2013-05-23 for polishing agent and polishing method.
This patent application is currently assigned to ASAHI GLASS COMPANY, LIMITED. The applicant listed for this patent is ASAHI GLASS COMPANY, LIMITED. Invention is credited to Yuiko YOSHIDA.
Application Number | 20130130595 13/737210 |
Document ID | / |
Family ID | 45441125 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130130595 |
Kind Code |
A1 |
YOSHIDA; Yuiko |
May 23, 2013 |
POLISHING AGENT AND POLISHING METHOD
Abstract
The present invention relates to a polishing agent for polishing
a surface to be polished of an object to be polished, the polishing
agent including: first silicon oxide fine particles having an
average primary particle size of 5 to 20 nm; second silicon oxide
fine particles having an average primary particle size of 40 to 110
nm; and water, in which a ratio of the first silicon oxide fine
particles to a total amount of the first silicon oxide fine
particles and the second silicon oxide fine particles is from 0.7
to 30% by mass.
Inventors: |
YOSHIDA; Yuiko; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI GLASS COMPANY, LIMITED; |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
ASAHI GLASS COMPANY,
LIMITED
Chiyoda-ku
JP
|
Family ID: |
45441125 |
Appl. No.: |
13/737210 |
Filed: |
January 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2011/064786 |
Jun 26, 2011 |
|
|
|
13737210 |
|
|
|
|
Current U.S.
Class: |
451/36 ;
51/308 |
Current CPC
Class: |
B24B 37/044 20130101;
C09K 3/1409 20130101; H01L 33/007 20130101; H01L 21/02024
20130101 |
Class at
Publication: |
451/36 ;
51/308 |
International
Class: |
B24B 37/04 20060101
B24B037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2010 |
JP |
2010-156536 |
Claims
1. A polishing agent for polishing a surface to be polished of an
object to be polished, the polishing agent comprising: first
silicon oxide fine particles having an average primary particle
size of 5 to 20 nm; second silicon oxide fine particles having an
average primary particle size of 40 to 110 nm; and water, wherein a
ratio of the first silicon oxide fine particles to a total amount
of the first silicon oxide fine particles and the second silicon
oxide fine particles is from 0.7 to 30% by mass.
2. The polishing agent according to claim 1, wherein both the first
silicon oxide fine particles and the second silicon oxide fine
particles are colloidal silica.
3. The polishing agent according to claim 1, wherein the ratio of
the first silicon oxide fine particles to the total amount of the
first silicon oxide fine particles and the second silicon oxide
fine particles is from 1 to 10% by mass.
4. The polishing agent according to claim 1, wherein the second
silicon oxide fine particles have an average primary particle size
of 45 to 100 nm.
5. The polishing agent according to claim 1, wherein the first
silicon oxide fine particles have an average primary particle size
of 5 to 15 nm.
6. The polishing agent according to claim 1, wherein the object to
be polished is a single-crystal substrate having a revised Mohs
hardness of 10 or more.
7. A polishing method comprising: supplying the polishing agent
according to claim 1 to a polishing pad; and bringing the polishing
pad into contact with a surface to be polished of an object to be
polished to perform polishing by relative movement between the
polishing pad and the surface to be polished.
8. The polishing method according to claim 7, wherein an operation
of recovering the polishing agent supplied to the polishing pad and
used for polishing, and of supplying again the recovered polishing
agent to the polishing pad is repeated, thereby using the polishing
agent in cycles.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing agent for
polishing a surface to be polished of an object to be polished, and
a polishing method. More particularly, the invention relates to a
polishing agent which makes it possible to perform high-speed
polishing and is excellent in stability at the time when used for a
long period of time, in polishing a surface to be polished of an
object to be polished, and a polishing method using the same.
BACKGROUND OF THE INVENTION
[0002] Techniques for producing and processing wafers of compound
single-crystals such as sapphire (.alpha.-Al.sub.2O.sub.3), silicon
carbide (SiC) and gallium nitride (GaN), as base materials for LEDs
or power devices which are expected to greatly glow in the future,
are attracting attention. On each of these substrates, a
crystalline thin film of GaN or the like is formed to integrate a
device, so that a crystallographically less defective, high-quality
surface is regarded to be important. In order to obtain the less
defective, high smooth surface, a chemical mechanical polishing
(hereinafter also referred to as CMP) technique is drawing
attention. However, all of sapphire, SiC and GaN have very high
hardness and also have high chemical stability, so that it is
difficult to perform polishing with high efficiency while ensuring
quality, particularly in polishing in a final stage which
determines quality, and there has been a problem that a polishing
step becomes very long.
[0003] In many cases, silicon oxide fine particles have hitherto
been used for final polishing which determines quality of these
single-crystal substrates. Some attempts to increase the polishing
efficiency (removal rate) by using the silicon oxide fine particles
have hitherto been made, and it has been proposed to increase the
abrasive concentration (see Non-Patent Document 1), to mix two or
more abrasives different in particle size at a predetermined ratio
(see Patent Documents 1 and 2), to increase the polishing
pressure/rotation speed, and the like.
BACKGROUND ART
PATENT DOCUMENT
[0004] Patent Document 1: Japanese Patent No. 4231632
[0005] Patent Document 2: Japanese Patent No. 4253141
Non-Patent Document
[0006] Non-Patent Document 1: "Scratch-free Dielectric CMP Process
with Nano-colloidal Ceria Slurry", pp. 31-34, International
Conference on Planarization/CMP Technology, Nov. 19-21, 2009
SUMMARY OF THE INVENTION
Problems that the Invention is to Solve
[0007] However, in polishing of the single-crystal substrates using
the silicon oxide fine particles, the polishing agent is generally
used in cycles, and it is necessary to consider stability at the
time when used for a long period of time. When the abrasive
concentration is increased, the abrasive is aggregates by use, and
the polishing efficiency becomes liable to substantially decrease.
There is therefore a problem that the stability at the time when
the polishing agent is used for a long period of time is
deteriorated. Also in mixing of the abrasives, at mixing ratios
which have hitherto been proposed, it is cited as a problem that
not only an effect of improving the removal rate is limited, but
also the stability of the polishing agent at the time when used for
a long period of time is deteriorated. Further, when the polishing
conditions are made strict, the removal rate can be increased.
However, a problem of a wafer shape or polishing defects such as
scratches becomes liable to be induced.
[0008] The invention has been made in order to solve the
above-mentioned problems, and an object thereof is to provide a
polishing agent which polishes a surface to be polished of an
object to be polished at a higher rate and is also excellent in
stability at the time when used for a long period of time, and a
polishing method.
Means for Solving the Problems
[0009] The invention provides a polishing agent for polishing a
surface to be polished of an object to be polished, which has the
following constitutions.
[0010] [1] A polishing agent for polishing a surface to be polished
of an object to be polished, the polishing agent comprising: first
silicon oxide fine particles having an average primary particle
size of 5 to 20 nm; second silicon oxide fine particles having an
average primary particle size of 40 to 110 nm; and water, wherein a
ratio of the first silicon oxide fine particles to a total amount
of the first silicon oxide fine particles and the second silicon
oxide fine particles is from 0.7 to 30% by mass.
[0011] [2] The polishing agent according to [1], wherein both the
first silicon oxide fine particles and the second silicon oxide
fine particles are colloidal silica.
[0012] [3] The polishing agent according to [1] or [2], wherein the
ratio of the first silicon oxide fine particles to the total amount
of the first silicon oxide fine particles and the second silicon
oxide fine particles is from 1 to 10% by mass.
[0013] [4] The polishing agent according to any one of [1] to [3],
wherein the second silicon oxide fine particles have an average
primary particle size of 45 to 100 nm.
[0014] [5] The polishing agent according to any one of [1] to [4],
wherein the first silicon oxide fine particles have an average
primary particle size of 5 to 15 nm.
[0015] [6] The polishing agent according to any one of claims [1]
to [5], wherein the object to be polished is a single-crystal
substrate having a revised Mohs hardness of 10 or more.
[0016] The invention further provides a method for polishing a
surface to be polished of an object to be polished, which has the
following constitutions.
[0017] [7] A polishing method comprising: supplying the polishing
agent according to any one of claims [1] to [6] to a polishing pad;
and bringing the polishing pad into contact with a surface to be
polished of an object to be polished to perform polishing by
relative movement between the polishing pad and the surface to be
polished.
[0018] [8] The polishing method according to claim [7], wherein an
operation of recovering the polishing agent supplied to the
polishing pad and used for polishing, and of supplying again the
recovered polishing agent to the polishing pad is repeated, thereby
using the polishing agent in cycles.
Advantage of the Invention
[0019] According to the polishing agent of the invention and the
polishing method using the same, the surface to be polished of the
object to be polished can be polished at a high rate, and further,
the abrasive can be stably used for a long period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a view showing an example of a polishing machine
which can be used for a polishing method of the invention.
MODE FOR CARRYING OUT THE INVENTION
[0021] Embodiments of the invention will be described below.
[Polishing Agent]
[0022] The polishing agent according to the invention is a
polishing agent for polishing a surface to be polished of an object
to be polished and contains first silicon oxide fine particles
having an average primary particle size of 5 to 20 nm, second
silicon oxide fine particles having an average primary particle
size of 40 to 110 nm and water. The ratio of the above-mentioned
first silicon oxide fine particles to the total amount of the
above-mentioned first silicon oxide fine particles and second
silicon oxide fine particles is from 0.7 to 30% by mass.
[0023] In the polishing agent of the invention, the first silicon
oxide fine particles and the second silicon oxide fine particles
are used as polishing abrasives. In the polishing agent of the
invention, the average primary particle size of the first silicon
oxide fine particles and the average primary particle size of the
second silicon oxide fine particles are adjusted to the
above-mentioned ranges, respectively. By introducing them into the
polishing agent at the above-mentioned compounding ratio, the first
silicon oxide fine particles having a smaller particle size which
are present in a small amount among the second silicon oxide fine
particles having a larger particle size which occupy a large part
thereof at the above-mentioned compounding ratio as the polishing
abrasives increases friction force between the substrate and the
abrasive. Accordingly, the high removal rate is obtained. Further,
the presence of the first silicon oxide fine particles having a
smaller particle size in a small amount as the above-mentioned
compounding ratio together with the second silicon oxide fine
particles having a larger particle size also contributes to an
improvement in dispersion stability in a dispersion medium such as
water to obtain the stability at the time of long-term use.
(1) First Silicon Oxide Fine Particles and Second Silicon Oxide
Fine Particles
[0024] In the polishing agent of the invention, the same silicon
oxide fine particles except for having different average primary
particle sizes can be used as the first silicon oxide fine
particles and the second silicon oxide fine particles, and ones
produced by various known methods can be used as both fine
particles. Examples thereof include silicon oxide fine particles
such as colloidal silica obtained by subjecting sodium silicate or
fumed silica obtained by vapor-phase synthesis of silicon
tetrachloride in flame of oxygen and hydrogen to ion exchange or
desalination after neutralization, or colloidal silica obtained by
hydrolysis of a silicon alkoxide in a liquid phase. Of these, in
the polishing agent of the invention, colloidal silica in which
sodium silicate is used as a starting material is more preferred,
from the viewpoint of the diversity of varieties.
[0025] The average primary particle size of the first silicon oxide
fine particles contained in the polishing agent of the invention is
from 5 to 20 nm, as described above. However, it is preferably from
5 to 15 nm, and more preferably from 7 to 13 nm.
[0026] There is a concern that the first silicon oxide fine
particles of less than 5 nm cannot stably exist, whereas when the
first silicon oxide fine particles exceeding 20 nm are used, there
is a possibility that the preferred removal rate is not
obtained.
[0027] Further, the average primary particle size of the second
silicon oxide fine particles contained in the polishing agent of
the invention is from 40 to 110 nm, as described above. However, it
is preferably from 45 to 100 nm. When the second silicon oxide fine
particles exceeding 100 nm are used, there is a concern that the
surface accuracy of the surface to be polished of the object to be
polished is deteriorated. When the second silicon oxide fine
particles of less than 40 nm are used, there is a possibility that
the preferred removal rate is not obtained.
[0028] Incidentally, in this specification, the average primary
particle size of the silicon oxide fine particles is one obtained
by converting the specific surface area measured by a nitrogen
adsorption BET method to the diameter of spherical particles.
[0029] Further, the compounding ratio of the above-mentioned first
silicon oxide fine particles and second silicon oxide fine
particles in the polishing agent of the invention is the
compounding ratio at which the ratio of the first silicon oxide
fine particles to the total amount of the first silicon oxide fine
particles and the second silicon oxide fine particles becomes 0.7
to 30% by mass, as described above. This compounding ratio is
preferably from 1 to 10% by mass, and more preferably from 3 to 10%
by mass.
[0030] It is preferred that the content of the first silicon oxide
fine particles and the second silicon oxide fine particles in the
polishing agent of the invention is appropriately set as the total
content of the first silicon oxide fine particles and the second
silicon oxide fine particles within the range of 10 to 50% by mass
based on the total mass of the polishing agent, in view of the
removal rate, uniformity, material selectivity, dispersion
stability and the like. When the total content of the first silicon
oxide fine particles and the second silicon oxide fine particles is
less than 10% by mass based on the total mass of the polishing
agent, the sufficient removal rate is not sometimes obtained,
whereas when it exceeds 50% by mass, an improvement of the removal
rate corresponding to an increase in abrasive concentration is not
observed, and further, the viscosity of the polishing agent
excessively increases, or gelation of the polishing agent is
enhanced, in some cases.
[0031] Further, the total content of the first silicon oxide fine
particles and the second silicon oxide fine particles in the
polishing agent of the invention is more preferably within the
range of 15 to 30% by mass based on the total mass of the polishing
agent.
(2) Water
[0032] Water contained in the polishing agent of the invention is a
medium for dispersing the above-mentioned first silicon oxide fine
particles and second silicon oxide fine particles as polishing
abrasives, and for dispersing and dissolving other optional
components added as needed. With respect to water, there is no
particular limitation. However, from influences to other
compounding components, contamination of impurities and influences
to the pH and the like, pure water or deionized water is preferred.
Water has a function of controlling fluidity of the polishing
agent, so that the content thereof can be appropriately set
according to intended polishing characteristics such as the removal
rate and smoothing characteristics.
[0033] In the polishing agent of the invention, water is preferably
contained within the range of 40 to 90% by mass based on the total
mass of the polishing agent. When the content of water is less than
40% by mass based on the total mass of the polishing agent, the
viscosity of the polishing agent increases to impair the fluidity
in some cases, whereas when it exceeds 90% by mass, the
concentration of the above-mentioned first silicon oxide fine
particles and second silicon oxide fine particles as the polishing
abrasives is sometimes decreased to fail to obtain the sufficient
removal rate.
(3) Preparation of Polishing Agent and Optional Components
[0034] The polishing agent of the invention can be prepared by
weighing the first silicon oxide fine particles and second silicon
oxide fine particles of the above (1) and water of (2) which are
contained as essential components, for example, so as to achieve
the above-mentioned compounding amount, and mixing them.
[0035] Here, when colloidal silica is used as both the first
silicon oxide fine particles and the second silicon oxide fine
particles, the polishing agent of the invention can be prepared
only by mixing colloidal silica containing the above-mentioned
first silicon oxide fine particles and colloidal silica containing
the above-mentioned second silicon oxide fine particles at a
desired ratio and appropriately diluting the mixture with water,
because colloidal silica is supplied in a state where the silicon
oxide fine particles are previously dispersed in water.
[0036] Incidentally, in addition to the essential components of the
above (1) and (2), optional components contained in normal
polishing agent for chemical mechanical polishing may be contained
in the polishing agent of the invention within the range not
impairing the above-mentioned effects of the invention.
(4) Object to be Polished
[0037] The polishing agent of the invention is a polishing agent
for polishing the surface to be polished of the object to be
polished, and the object to be polished is not particularly
limited. Specific examples thereof include glass substrates,
silicon wafers, semiconductor device wiring substrates, compound
single-crystal substrates and the like. Of these, the polishing
agent of the invention can achieve a greater effect in polishing
the compound single-crystal substrates, and particularly, effects
of higher-rate polishing and longer-term stable use can be largely
expected by use thereof for the single-crystal substrates having a
revised Mohs hardness of 10 or more.
[0038] Specific examples of the above-mentioned single-crystal
substrates having a revised Mohs hardness of 10 or more include
sapphire (.alpha.-Al.sub.2O.sub.3) substrates (hardness: 12),
silicon carbide (SiC) substrates (hardness: 13), gallium nitride
(GaN) substrates (hardness: 13) and the like. Of these, the
polishing agent of the invention can be preferably used
particularly for polishing of the sapphire substrates.
[Polishing Method]
[0039] As a method for polishing the surface to be polished of the
object to be polished using the polishing agent of the invention,
preferred is a polishing method of bringing a polishing pad into
contact with the surface to be polished of the object to be
polished while supplying the polishing agent to the polishing pad
to perform polishing by relative movement between the polishing pad
and the surface to be polished.
[0040] In the above-mentioned polishing method, a conventionally
known polishing machine can be used as a polishing machine. An
example of a polishing machine which can be used in embodiments of
the invention and in which the polishing agent is used in cycles is
shown in FIG. 1 and described below. However, the polishing machine
used in the embodiments of the invention should not be construed as
being limited to one having such a structure.
[0041] This polishing machine 10 is provided with a polishing head
2 for holding an object to be polished 1, a polishing platen 3, a
polishing pad 4 stuck onto a surface of the polishing platen 3, a
tank 8 for storing an polishing agent 5 and a polishing agent
supply pipe 6 for supplying the polishing agent 5 from the tank 8
to the polishing pad 4 using an polishing agent supply pump 7. The
polishing machine 10 is constituted in such a manner that a surface
to be polished of the object to be polished 1 held by the polishing
head 2 is brought into contact with the polishing pad 4, while
supplying the polishing agent 5 from the polishing agent supply
pipe 6, and that the polishing head 2 and the polishing platen 3
are relatively rotated to perform polishing.
[0042] Using such a polishing machine 10, the surface to be
polished of the object to be polished 1 can be polished. Here, the
polishing machine 10 is a polishing machine which polishes one
surface of the object to be polished as the surface to be polished.
For example, however, it is also possible to polish the surfaces to
be polished (both surfaces) of the object to be polished, using a
double-sided simultaneous polishing machine in which the same
polishing pads as used in the polishing machine 10 are disposed on
upper and lower surfaces of the object to be polished.
[0043] The polishing head 2 may perform not only rotation movement
but also linear movement. Further, the polishing platen 3 and the
polishing pad 4 may have a size equivalent to or less than that of
the object to be polished 1. In that case, it is preferred to
relatively move the polishing head 2 and the polishing platen 3,
thereby making it possible to polish the entire surface of the
surface to be polished of the object to be polished 1. Furthermore,
the polishing platen 3 and the polishing pad 4 may not perform
rotation movement, but may move, for example, in one direction by a
belt system.
[0044] Although there is no particular limitation on polishing
conditions of such a polishing machine 10, it is also possible to
more increase the polishing pressure and to improve the removal
rate by applying a load to the polishing head 2 to press it against
the polishing pad 4. The polishing pressure is preferably from
about 10 to 50 kPa, and from the viewpoints of uniformity of the
removal rate in the surface to be polished of the object to be
polished 1, smoothing and prevention of polishing defects such as
scratches, it is more preferably from about 10 to 40 kPa. The
number of rotations of the polishing platen 3 and the polishing
head 2 is preferably from about 50 to 500 rpm, but is not limited
thereto. Further, the amount of the polishing agent 5 supplied is
appropriately adjusted and selected by a constituent material of
the surface to be polished, a composition of the polishing agent,
the above-mentioned polishing conditions and the like. However, for
example, when a wafer having a diameter of 50 mm is polished, the
amount thereof supplied is preferably from approximately 5 to 300
cm.sup.3/min.
[0045] As the polishing pad 4, there can be used one made of a
usual nonwoven fabric, a foamed polyurethane, a porous resin, a
non-porous resin or the like. Further, in order to accelerate the
supply of the polishing agent 5 to the polishing pad 4 or to allow
a certain amount of the polishing agent 5 to stay in the polishing
pad 4, lattice-shaped, concentric or helical grooves may be
processed on a surface of the polishing pad 4.
[0046] Furthermore, a pad conditioner may be brought into contact
with the surface of the polishing pad 4 to perform polishing while
conditioning the surface of the polishing pad 4, as needed.
[0047] In addition, the polishing machine 10 shown in FIG. 1 is
constituted in such a manner that it has a recovery unit (not
shown) for recovering the polishing agent 5 used for polishing from
the polishing pad 4, and that the polishing agent 5 recovered is
transferred to the tank 8. The polishing agent 5 which has returned
to the tank 8 is supplied again to the polishing pad 4 through the
polishing agent supply pipe 6 using the polishing agent supply pump
7. In this way, the polishing agent 5 is used in cycles.
[0048] Incidentally, in the polishing method of the invention, the
polishing agent supplied to the polishing pad is recovered in the
same manner as described above after used for polishing. However,
it is also possible to use a polishing machine having a so-called
no-return constitution in which the abrasive is discarded for every
polishing use.
[0049] The polishing method in which the polishing agent is used in
cycles is preferred as compared to the polishing method in which
the polishing agent is discarded for every polishing use, because
the consumption thereof can be reduced. However, with the progress
of polishing, the polishing agent is contaminated with components
of the material to be polished by polishing, so that there has been
a problem that the conventional polishing agent is liable to bring
about aggregation or gelation of polishing abrasives, which induces
clogging of the pad to gradually decrease the removal rate.
According to the polishing agent of the invention, the gelation or
the aggregation due to the contamination of the components of the
polished material, which are generated by the above-mentioned
polishing, is difficult to occur, and the decrease in the removal
rate at the time of cyclic use is suppressed.
[0050] That is to say, the polishing agent of the invention is
characterized in that the initial removal rate is high, and that
the decrease in the removal rate at the time of use in a cyclic
system is suppressed. Thereby, not only the efficiency of the
polishing step is improved, but also the downtime is shortened by a
reduction in the consumption of the polishing agent or a decrease
in dressing or flashing frequency of the pad. Further, this also
leads to a reduction in the consumption of the pad, and the
polishing step can be efficiently performed. It can therefore be
said that the significance of the invention to improvement in mass
production of various devices is very large.
EXAMPLES
[0051] The invention will be described below with reference to
examples, but the invention should not be construed as being
limited to the following description. Examples 1 to 6 are working
examples of the invention, and Examples 7 to 12 are comparative
examples.
Example 1
[0052] Colloidal silica having an average primary particle size of
10 nm (an aqueous dispersion of first silicon oxide fine particles
having a solid concentration of 40% by mass) as first silicon oxide
fine particles and colloidal silica having an average primary
particle size of 80 nm (an aqueous dispersion of second silicon
oxide fine particles having a solid concentration of 40% by mass)
as second silicon oxide fine particles are mixed at such a ratio
that the compounding ratio of the first silicon oxide fine
particles to the total amount of the first silicon oxide fine
particles and the second silicon oxide fine particles becomes 1% by
mass, followed by thorough stirring. Ion-exchange water was added
to a resulting mixed liquid in such a manner that the total amount
of the first silicon oxide fine particles and the second silicon
oxide fine particles based on the total mass of the polishing agent
to be finally obtained, namely based on the total mass of the total
amount of the first silicon oxide fine particles and the second
silicon oxide fine particles and water, becomes 20% by mass, to
prepare a polishing agent. In the resulting polishing agent, the
first silicon oxide fine particles and the second silicon oxide
fine particles are abrasive components.
[0053] With respect to the abrasive components composed of the
first silicon oxide fine particles and the second silicon oxide
fine particles, respectively, in the polishing agent obtained in
Example 1 described above, the average primary particle size and
the compounding ratio of the respective silicon oxide fine
particles are shown in Table 1. In Example 1 and all Examples (2 to
12) shown below, the existing ratio of abrasive components:water in
polishing agents is 20:80 (mass ratio).
[0054] Incidentally, the average primary particle size of the
silicon oxide fine particles compounded in the polishing agent is a
value obtained by measuring the specific surface area by the
nitrogen adsorption BET method. All the average primary particle
sizes of the silicon oxide fine particles used in Examples 2 to 12
described below are values obtained by performing the measurement
in the same manner.
Examples 2 to 12
[0055] In the same manner as in Example 1, first silicon oxide fine
particles and second silicon oxide fine particles each having an
average primary particle size shown in Table 1 were compounded as
abrasive components so as to give a composition shown in Table 1,
and further, water was added thereto in such a manner that the
total amount of the first silicon oxide fine particles and the
second silicon oxide fine particles based on the total mass of the
polishing agent, namely the compounding amount of the abrasive
components, becomes 20% by mass. Thus, polishing agents of Examples
2 to 12 were prepared. Incidentally, all the silicon oxide fine
particles used were colloidal silica.
[Evaluation]
[0056] Polishing characteristics of the polishing agents of
Examples 1 to 12 obtained above were evaluated by the following
methods.
[0057] As the evaluation of the polishing characteristics, there
were performed (1) evaluation of the removal rate at the time when
the polishing agent was used in the no-return system, and (2)
evaluation of continuity of the removal rate at the time when the
polishing agent was used in the cyclic system.
<Material to be Polished>
[0058] In both evaluation (1) and evaluation (2), a 2-inch wafer of
a single-crystal sapphire substrate (manufactured by Shinkosha Co.,
Ltd., (0001) plane, the thickness of the substrate: 420 .mu.m) was
used as a material to be polished.
<Polishing Method>
[0059] As a polishing machine, there was used a bench polishing
machine manufactured by Speedfam Co., Ltd. As polishing pads, there
were used (1) K-groove of single layer IC 1000 (no-return use) and
(2) SUBA 800-XY-groove (cyclic use) (both manufactured by Nitta
Haas Incorporated). Before the test, conditioning was performed
using MEC100-PH3.5L (manufactured by Mitsubishi Material
Corporation) and a brush.
[0060] The polishing was performed under conditions where the
supply rate of the polishing agent was (1) 10 cm.sup.3/min
(no-return use) and (2) 100 cm.sup.3/min (cyclic use), the number
of rotations of a polishing platen was 100 rpm, the polishing
pressure was 5 psi, namely 34.5 kPa, and the polishing time was (1)
30 minutes (no-return use) and (2) 60 minutes (cyclic use).
Further, when the polishing agent was used in cycles, the
above-mentioned sapphire substrate was changed every 60 minutes,
and the polishing was continuously performed without conducting any
pad conditioning in the course thereof.
<Removal Rate>
[0061] The removal rate was evaluated by the amount of change in
thickness of the substrate per unit time (.mu.m/hr). Specifically,
with respect to each of the single-crystal sapphire substrates used
for the evaluation of the above (1) and (2), the mass of the
unpolished substrate having a known thickness and the mass of the
substrate after polished for each period of time were measured, and
the mass change was determined from the difference therebetween.
Further, the change in thickness of the substrate per period of
time determined from the mass change was calculated using the
following formulas.
(Calculation Formulas of Removal Rate (V))
[0062] .DELTA.m=m0-m1
V=.DELTA.m/m0.times.T0.times.60/t
(in the formula, .DELTA.m (g) represents the mass change between
before and after polishing, m(0) (g) represents the initial mass of
the unpolished substrate, m1(g) represents the mass of the
substrate after polished, V represents the removal rate (.mu.m/hr),
T0 represents the substrate thickness (.mu.m) of the unpolished
substrate, and t represents the polishing time (min).
<Initial Removal Rate>
[0063] First, with respect to the polishing agents of Examples 1 to
12, the removal rate under no-return (non-cyclic use) polishing
agent conditions was measured and calculated as the initial removal
rate according to the above-mentioned polishing method (1).
Incidentally, when the initial removal rate of the polishing agent
prepared in Example 7, in which only the second silicon oxide fine
particles having an average primary particle size of 80 nm was used
as the abrasive, was taken as 1.00, the ratio at that time was
determined, and the initial removal rate was represented thereby.
The results thereof are shown in Table 1.
TABLE-US-00001 TABLE 1 Abrasive Component Composition First
Colloidal Silica Second Colloidal Silica compounding compounding
Evaluation Average Primary Amount Average Primary Amount Initial
Example Particle Size [nm] [mass %] Particle Size [nm] [mass %]
Removal Rate* Example 1 10 1 80 99 1.12 Example 2 10 5 80 95 1.27
Example 3 10 10 80 90 1.24 Example 4 10 25 80 75 1.20 Example 5 17
5 80 95 1.18 Example 6 10 5 54 95 1.15 Example 7 (Comparative
Example) 10 0 80 100 1.00 Example 8 (Comparative Example) 10 0.5 80
99.5 1.02 Example 9 (Comparative Example) 10 50 80 50 1.07 Example
10 (Comparative Example) 10 100 80 0 0.94 Example 11 (Comparative
Example) 27 10 80 90 1.01 Example 12 (Comparative Example) 10 5 120
95 0.68 *Ratio of the removal rate at the time when the removal
rate of Example 7 was taken as 1.00
<Continuity of Removal Rate>
[0064] Then, continuity of the removal rate at the time when the
polishing agent was used in cycles was evaluated by the following
method. The polishing method was a method according to the above
(2). The continuity of the polishing agent at the time of cyclic
use was evaluated by the accumulated removal amount of the sapphire
substrate at the time when the polishing was performed until the
removal rate measured and calculated every 60 minutes was decreased
by 15% compared to the initial removal rate (removal rate for 60
minutes from the initiation of the polishing). Taking the
accumulated removal amount with the polishing agent of Example 7 as
1.00, the continuity of the abrasive was represented by the ratio
thereof. When the value is larger than 1.00, it shows that
maintenance of the removal rate is better than that of the
polishing agent of Example 7.
[0065] The term "gel" as used herein is a kind of dispersion system
and a colloid of a liquid dispersion medium such as a sol, but
means a state where it has high viscosity due to a network of a
dispersed material to lose fluidity, resulting in becoming solid as
the entire system, different from the sol.
TABLE-US-00002 TABLE 2 Abrasive Component Composition First
Colloidal Silica Second Colloidal Silica compounding compounding
Evaluation Average Primary Amount Average Primary Amount Removal
Rate Example Particle Size [nm] [mass %] Particle Size [nm] [mass
%] Continuity** Example 1 10 1 80 99 1.09 Example 2 10 5 80 95 1.42
Example 3 10 10 80 90 1.20 Example 4 10 25 80 75 1.08 Example 7
(Comparative Example) 10 0 80 100 1.00 Example 8 (Comparative
Example) 10 0.5 80 99.5 1.00 Example 9 (Comparative Example) 10 50
80 50 Gelled Example 10 (Comparative Example) 10 100 80 0 Gelled
**Ratio of the accumulated removal amount at the time when the
accumulated removal amount of Example 7 was taken as 1.00
[0066] As will be seen from Tables 1 and 2, the polishing agents
each containing the first silicon oxide fine particles and the
second silicon oxide fine particles each having an average primary
particle size defined by the invention at a compounding ratio
defined by the invention have a higher removal rate and good
continuity of the removal rate during use, namely excellent
long-term use stability, compared to the polishing agents of
Comparative Examples.
[0067] While the invention has been described in detail with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
[0068] Incidentally, the present application is based on Japanese
Patent Application No. 2010-156536 filed on Jul. 9, 2010, and the
contents are incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0069] According to the invention, it becomes possible to perform
high-speed polishing of object to be polished which is polished,
particularly surface to be polished of compound single-crystal
substrates having high hardness, such as sapphire
(.alpha.-Al.sub.2O.sub.3) substrates, silicon carbide (SiC)
substrates and gallium nitride (GaN) substrates, and it becomes
possible to improve long-term use stability of the polishing agent.
Thereby, the invention can contribute to improvement in
productivity of these substrates.
Description of Reference Numerals and Signs
[0070] 1 . . . Object to be polished,
[0071] 2 . . . Polishing head,
[0072] 3 . . . Polishing platen,
[0073] 4 . . . Polishing pad,
[0074] 5 . . . Polishing agent,
[0075] 6 . . . Polishing agent supply pipe,
[0076] 7 . . . Polishing agent supply pump,
[0077] 8 . . . Tank,
[0078] 10 . . . Polishing machine
* * * * *