U.S. patent application number 10/532802 was filed with the patent office on 2005-12-29 for polishing slurry and polished substrate.
This patent application is currently assigned to Showa Denko K.K.. Invention is credited to Imai, Fumio, Ito, Katsura, Saegusa, Hiroshi.
Application Number | 20050287931 10/532802 |
Document ID | / |
Family ID | 34611350 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050287931 |
Kind Code |
A1 |
Saegusa, Hiroshi ; et
al. |
December 29, 2005 |
Polishing slurry and polished substrate
Abstract
A polishing slurry comprising an abrasive comprising as a basic
ingredient rare earth oxides containing cerium oxide, which
polishing slurry further comprises an anionic surfactant and a
nonionic surfactant and has a pH value of at least 11. The
polishing slurry is especially suitable for polishing a glass
substrate for magnetic disc, and other substrates used in
electronic field.
Inventors: |
Saegusa, Hiroshi;
(Shiojiri-shi, Nagano, JP) ; Imai, Fumio;
(Shiojiri-shi Nagano, JP) ; Ito, Katsura;
(Shiojiri-shi Nagano, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Showa Denko K.K.
13-9, Shibadaimon 1-chome
Minato-ku, Tokyo
JP
105-8518
|
Family ID: |
34611350 |
Appl. No.: |
10/532802 |
Filed: |
April 25, 2005 |
PCT Filed: |
October 24, 2003 |
PCT NO: |
PCT/JP03/13641 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60423376 |
Nov 4, 2002 |
|
|
|
Current U.S.
Class: |
451/41 ; 106/3;
51/309 |
Current CPC
Class: |
C09G 1/02 20130101; C09K
3/1463 20130101 |
Class at
Publication: |
451/041 ;
051/309; 106/003 |
International
Class: |
B24B 001/00; B24D
003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2002 |
JP |
2002-311212 |
Claims
1. A polishing slurry comprising an abrasive comprising as a basic
ingredient rare earth oxides containing cerium oxide, said
polishing slurry further comprising an anionic surfactant and a
nonionic surfactant and having a pH value of at least 11.
2. The polishing slurry according to claim 1, wherein the abrasive
comprises at least 90% by mass, based on the abrasive, of the rare
earth oxides.
3. The polishing slurry according to claim 1, wherein the rare
earth oxides contain 50% to 90% by mass, based on the rare earth
oxides, of cerium oxide.
4. The polishing slurry according to claim 1, wherein the rare
earth oxides are produced from rare earth carbonate as a starting
raw material.
5. The polishing slurry according to claim 1, wherein the abrasive
is comprised of particles having a 50% cumulative average diameter
(D50) in the range of 0.01 .mu.m to 10 .mu.m.
6. The polishing slurry according to claim 1, wherein the abrasive
is comprised of particles having a specific surface area in the
range of 1 m.sup.2/g to 50 m.sup.2/g.
7. The polishing slurry according to claim 1, wherein the anionic
surfactant is at least one surfactant selected from the group
consisting of low-molecular-weight compounds and
high-molecular-weight compounds, which are selected from carboxylic
acid salts, sulfonic acid salts, sulfuric acid ester salts and
phosphoric acid ester salts.
8. The polishing slurry according to claim 1, wherein the nonionic
surfactant is at least one surfactant selected from the group
consisting of polyoxyethylene alkyl phenyl ethers, polyoxyalkylene
alkyl ethers and polyoxyethylene fatty acid esters.
9. The polishing slurry according to claim 1, which further
comprises at least one liquid medium selected from the group
consisting of water, monohydric alcohols having 1 to 10 carbon
atoms, glycols, polyhydric alcohols having 1 to 10 carbon atoms,
dimethyl sulfoxide, dimethylformamide, tetrahydrofuran and
dioxane.
10. The polishing slurry according to claim 1, which further
comprises at least one ingredient selected from the group
consisting of phosphoric acid esters, cellulose ethers and
water-soluble high-molecular-weight compounds.
11. A process for polishing a substrate, wherein the polishing of
the substrate is carried out by using the polishing slurry as
claimed in claim 1.
12. A process for producing a polished substrate comprising a step
of polishing a substrate by the process as claimed in claim 11.
13. A polished substrate obtainable by the process as claimed in
claim 12.
14. The substrate according to claim 13, which is selected from the
group consisting of a glass substrate for optical lens, a glass
substrate for optical disc, a glass substrate for plasma display, a
glass substrate for liquid crystal, a color filter for liquid
crystal TV, a glass substrate for LSI photomask and a substrate for
magnetic disc.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is an application filed under 35 U.S.C.
.sctn. 111(a) claiming benefit pursuant to 35 U.S.C. .sctn.
119(e)(1) of the filing date of Provisional Application 60/423,376
filed Nov. 4, 2003, pursuant to 35 U.S.C. .sctn. 111(b).
TECHNICAL FIELD
[0002] This invention relates to a polishing slurry used for
precision polishing of substrates with optical and electronic
applications, such as glass substrates for optical lens, optical
disc, magnetic disc, plasma display, liquid crystal display, and
LSI photomask. This polishing slurry exhibits excellent polishing
properties, namely, has a high rate of polishing and gives a
polished surface with a reduced surface roughness and not having
surface defects such as scratches to any appreciable extent.
[0003] The invention further relates to a process for polishing a
substrate with the above-mentioned polishing slurry, a process for
producing a polished substrate, and a polished substrate.
BACKGROUND ART
[0004] In recent years, the importance of high-precision polishing
is still more rising in the field of electronics such as a glass
substrate for magnetic disc, a glass substrate for liquid crystal
display such as thin film transistor (TFT) LCD or twisted nematic
(TN) LCD, a color filter for liquid crystal TV, and a glass
substrate for LSI photomask.
[0005] Especially in the field of substrates for magnetic disc,
stiffness and other mechanical strength sufficiently high for use
as a substrate rendered thin for weight-saving or for endurance for
undulated movement of disc at high speed rotation are required.
Further, high recording density is required, and thus, minimization
of floating height of a magnetic head from a magnetic disc
substrate is required. For this requirement, it is eagerly desired
to provide a mirror-polished surface with a high flatness, an
extremely reduced surface roughness, and a minimized number of
minute scratches and minute pits. Thus, it is required to polish
surface of substrates with highly enhanced precision.
[0006] Further, improvements are also being made in chemical
composition of glass substrates and a process for making glass
substrates for satisfying the requirements for thinning, high
mechanical strength and high density recordation. For example,
glass substrates other than those made of conventional chemically
reinforced glass have been developed, which include crystallized
lithium silicate-containing glass substrates, and crystallized
glass substrates predominantly comprised of quartz crystal. These
glass substrates have very poor processability, and are difficult
to polish with conventional abrasive composition at a high
polishing rate and with good productivity.
[0007] As an abrasive composition for surface polishing of glass
substrates, rare earth oxides, especially cerium oxide is used
because rare earth oxides exhibit a very high rate of polishing as
compared with iron oxide, zirconium oxide and silicon dioxide. Rare
earth oxides are used generally as a dispersion of abrasive grains
in water or other liquid medium. For surface polishing with an
abrasive composition, both of high-precision surface polishing
performance and high rate of polishing are required.
[0008] For cerium-based abrasive compositions, various proposals
have been made to enhance the rate of polishing. For example,
polishing techniques using a cerium-based abrasive composition
having added therein colloidal silica or alumina, and a
cerium-based abrasive composition having added therein magnesium
chloride have been proposed (see Japanese Examined Patent
Publication No. S38-3643, Japanese Unexamined Patent Publication
[hereinafter abbreviated to "JP-A"] No. H3-146585). However, the
addition of different kind of sol causes an increase of scratches
or pits on a polished surface and hence high surface precision
cannot be attained.
[0009] Further, in order to achieve high surface precision, an
abrasive composition comprised of an alkaline ceric oxide sol
containing an organic acid with at least two carboxyl groups; and a
CMP polishing liquid composition comprising cerium oxide particles
coated with an anionic surfactant and a nonionic surfactant, and an
aqueous dispersion of a surfactant have been proposed (see JP-A
H8-3541 and JP-A 2000-248263).
[0010] The alkaline ceric oxide sol containing an organic acid with
at least two carboxyl groups in the abrasive composition has a
small average particle diameter in the range of 2 nm to 200 nm, and
hence, the rate of polishing is low, the polishing cost is high,
and it is difficult to stably produce a polished substrate with
high quality. The above-mentioned CMP polishing liquid inevitably
has a low pH value because it contains ceric oxide abrasive grains,
and the rate of polishing is low and the surface roughness is
large.
[0011] Thus, it is impossible to satisfy both of high-precision
surface polishing performance and high rate of polishing with any
of the hitherto proposed polishing techniques.
SUMMARY OF THE INVENTION
[0012] In view of the foregoing, a primary object of the present
invention is to provide a polishing slurry which satisfies
high-precision surface polishing performance and provides a
polished surface with a high flatness and a small surface roughness
and having minimized number of minute scratches and minute pits,
while a high rate of polishing is attained.
[0013] In accordance with the present invention, there is provided
a polishing slurry comprising an abrasive comprising as a basic
ingredient rare earth oxides containing cerium oxide, said
polishing slurry further comprising an anionic surfactant and a
nonionic surfactant and having a pH value of at least 11. By the
term "as a basic ingredient" as used herein we mean that the
content is at least 80% by mass.
[0014] Preferable embodiments of the above-mentioned polishing
slurry are summarized as follows.
[0015] The abrasive comprises at least 90% by mass, based on the
abrasive, of the rare earth oxides.
[0016] The rare earth oxides contain 50% to 90% by mass, based on
the rare earth oxides, of cerium oxide.
[0017] The rare earth oxides are produced from rare earth carbonate
salts as a starting raw material.
[0018] The abrasive is comprised of particles having a 50%
cumulative average diameter (D50) in the range of 0.01 .mu.m to 10
.mu.m.
[0019] The abrasive is comprised of particles having a specific
surface area in the range of 1 m.sup.2/g to 50 m.sup.2/g.
[0020] The anionic surfactant is at least one kind of surfactant
selected from the group consisting of low-molecular-weight
compounds and high-molecular-weight compounds, which are selected
from carboxylic acid salts, sulfonic acid salts, sulfuric acid
ester salts and phosphoric acid ester salts.
[0021] The nonionic surfactant is at least one kind of surfactant
selected from the group consisting of polyoxyethylene alkyl phenyl
ethers, polyoxyalkylene alkyl ethers and polyoxyethylene fatty acid
esters.
[0022] The polishing slurry further comprises at least one kind of
liquid medium selected from the group consisting of water,
monohydric alcohols having 1 to 10 carbon atoms, glycols,
polyhydric alcohols having 1 to 10 carbon atoms, dimethyl
sulfoxide, dimethylformamide, tetrahydrofuran and dioxane.
[0023] The polishing slurry further comprises at least one kind of
ingredient selected from the group consisting of phosphoric acid
esters, cellulose ethers and water-soluble high-molecular-weight
compounds.
[0024] In accordance with the present invention, there is further
provided a substrate which has been polished with the
above-mentioned polishing slurry.
[0025] The above-mentioned polished substrate is preferably used as
a glass substrate for optical lens, a glass substrate for optical
disc, a glass substrate for plasma display, a glass substrate for
liquid crystal, a color filter for liquid crystal TV, a glass
substrate for LSI photomask and a glass substrate for magnetic
disc. Of these, a glass substrate for magnetic disc is especially
preferable.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] The polishing slurry of the present invention comprises (i)
an abrasive comprising as a basic ingredient rare earth oxides
containing cerium oxide, (ii) an anionic surfactant and (iii) a
nonionic surfactant, and has a pH value of at least 11. By this
constitution, the polishing slurry exhibits excellent polishing
performance, namely, it gives a polished surface with a highly
enhanced flatness, a reduced surface roughness and not having, to
any appreciable extent, surface defects such as minute scratches
and minute pits, while a high rate of polishing is attained.
[0027] If only one of the anionic surfactant and the nonionic
surfactant is contained in the slurry, or the slurry has a pH value
of lower than 11, at least one of the high-precision surface
polishing performance and the high rate of polishing cannot be
attained.
[0028] The ingredients constituting the polishing slurry of the
present invention will be described below.
[0029] Abrasive
[0030] The abrasive used in the present invention comprises at
least 80% by mass, preferably at least 90% by mass, based on the
abrasive, of rare earth oxides. If the content of rare earth oxides
is smaller than 80% by mass, scratches tend to occur on a polished
surface.
[0031] The rare earth oxides preferably contain 50% to 90% by mass,
based on the rare earth oxides, of cerium oxide. With a cerium
content of smaller than50%by mass, the desired high rate of
polishing is difficult to attain. In contrast, with a cerium
content of larger than 90% by mass, a pH value of at least 11 is
difficult to obtain even when an anionic surfactant and a nonionic
surfactant are incorporated, with the results that the desired high
rate of polishing is difficult to attain and a polished surface is
liable to have a large surface roughness.
[0032] The rare earth oxides may contain, in addition to cerium
oxide, lanthanum oxide, praseodymium oxide, neodymium oxide and
other rare earth oxides.
[0033] The abrasive is preferably comprised of particles having a
50% accumulative average particle diameter (D50), as expressed in
terms of volume, in the range of 0.01 .mu.m to 10 .mu.m, more
preferably 0.05 .mu.m to 5 .mu.m and especially preferably 0.1
.mu.m to 2.0 .mu.m. When the 50% accumulative average particle
diameter (D50) is smaller than 0.01 .mu.m, the desired high rate of
polishing is difficult to attain. In contrast, when the 50%
accumulative average particle diameter (D50) is larger than 10
.mu.m, a polished surface is liable to have minute scratches and
minute pits.
[0034] The term "50% accumulative average particle diameter (D50)
as expressed in terms of volume" as used herein we mean a particle
diameter when the integral of particle diameters reaches 50% as
calculated from the smallest diameter to the larger diameter in the
particle distribution as expressed in terms of volume.
[0035] The rare earth oxides used in the present invention are
preferably produced from rare earth carbonate as a starting raw
material. The rare earth carbonate used as a starting material is
prepared by a process wherein a rare earth concentrate containing
large amounts of naturally occurring cerium, lanthanum,
praseodymium, neodymium and other rare earth elements is crushed;
ingredients other than the rare earth elements, such as alkali
metals, alkaline earth metals and radioactive substances, are
chemically separated for removal from the crushed product; and
ammonium bicarbonate or oxalic acid was added to the rare
earth-containing residue to give rare earth carbonate.
[0036] The rare earth carbonate is baked at a temperature of about
500.degree. C. to about 1,200.degree. C. in an electric oven, and
the baked product is pulverized whereby a rare earth oxide-based
abrasive is obtained. An abrasive having a desired particle
distribution can be obtained by appropriately selecting the baking
conditions and pulverizing conditions.
[0037] The state of baking can be evaluated by the specific surface
area of abrasive particles. The specific surface area is preferably
in the range of 1 m.sup.2/g to 50 m.sup.2/g, more preferably 2
m.sup.2/g to 20 m.sup.2/g. When the specific surface area is
smaller than 1 m.sup.2/g, minute scratches and minute pits are
liable to occur on a polished surface. In contrast, when the
specific surface area is larger than 50 m.sup.2/g, the rate of
polishing is reduced.
[0038] Anionic Surfactant
[0039] The anionic surfactant used in the present invention
includes, for example, publicly known carboxylic acid salts such as
soaps, N-acylamino acid salts, alkylethercarboxylic acid salts and
acylated peptides; sulfonic acid salts such as alkanesulfonic acid
salts (including alkylbenzenesulfonic acid salts),
alkylnaphthalenesulfonic acid salts, sulfosuccinic acid salts,
.alpha.-olefinsulfonic acid salts and N-acylsulfonic acid salts;
sulfuric acid ester salts such as sulfated oil, alkylsulfuric acid
salts, alkylethersulfuric acid salts, alkylarylethersulfuric acid
salts and alkylamidesulfuric acid salts; and phosphoric acid ester
salts such as alkylphosphoric acid salts, alkyletherphosphoric acid
salts and alkylaryletherphosphoric acid salts. These anionic
surfactants may span from low-molecular-weight compounds to
high-molecular weight compounds. The salts as herein used are at
least one kind of salt selected from Li salts, Na salts, K salts,
Rb salts, Cs salts, ammonium salts, and H-type salts.
[0040] More specifically, the soaps include fatty acid salts having
12 to 18 carbon atoms, and, as specific examples of the fatty acid
groups, there can be mentioned lauric acid, myristic acid, palmitic
acid and stearic acid. The N-acylamino acid salts include those
which have 12 to 18 carbon atoms, and, as specific examples
thereof, there can be mentioned N-acyl-N-methylglycine salts and
N-acylglutamic acid salts. The alkylethercarboxylic acid salts
include those which have 6 to 18 carbon atoms. The acylated
peptides include those which have 12 to 18 carbon atoms. The
sulfonic acid salts include those which have 6 to 12 carbon atoms,
such as recited above, and, as specific examples of alkanesulfonic
acid salts, there can be mentioned laurylsulfonic acid salts,
dioctylsuccinosulfonic acid salts, benzenesulfonic acid salts,
dodecylbenzenesulfonic acid salts, myristilsulfonic acid salts,
kerylbenzenesulfonic acid salts and stearylsulfonic acid salts. The
sulfuric acid ester salts include those which have 6 to 18 carbon
atoms, such as recited above, and, as specific examples of the
alkylsulfuric acid ester salts, there can be mentioned
laurylsurfuric acid salts, dioctylsuccinosulfuric acid salts,
myristilsurfuric acid salts and stearyl surfuric acid salts. The
phosphoric acid ester salts include those which have 8 to 18 carbon
atoms, such as recited above. High-molecular-weight surfactants
include specific polycarboxylic acid type compounds such as "DEMOL
EP" (trademark) available from Kao Corporation.
[0041] The amount of anionic surfactant is preferably in the range
of 0.05% to 20% by mass, more preferably 0.1% to 10% by mass, based
on the abrasive.
[0042] Nonionic Surfactant
[0043] The nonionic surfactant used in the present invention
includes, for example, polyoxyethylenealkyl phenyl ethers,
polyoxyethylenealkyl ethers, polyoxyethylene fatty acid esters and
polyoxyalkylene-alkyl-ether.
[0044] The amount of nonionic surfactant is preferably in the range
of 0.0001% to 10% by mass, more preferably 0.001% to 1.0% by mass,
based on the abrasive.
[0045] The polishing slurry of the present invention can be
produced by a process wherein a rare earth oxide-based abrasive, as
obtained by baking rare earth carbonate, followed by crushing, is
dispersed in a liquid medium such as water or a water-soluble
organic solvent, and then, the thus-obtained aqueous slurry is
subjected to wet grinding; or a process wherein a rare earth
oxide-based abrasive composition, as obtained by baking rare earth
carbonate, followed by crushing, is subjected to dry grinding, and
then, the thus-obtained powdered abrasive is dispersed in water or
a water-soluble organic solvent. However, the former process is
preferable wherein the dispersed rare earth oxide-based abrasive is
subjected to wet grinding using, for example, a ball mill.
[0046] As specific examples of the water-soluble organic solvent,
there can be mentioned monohydric alcohols having 1 to 10 carbon
atoms such as methanol, ethanol, propanol, isopropanol and butanol;
polyhydric alcohols having 3 to 10 carbon atoms such as ethylene
glycol and glycerine; and dimethyl sulfoxide (DMSO),
dimethylformamide (DMF), tetrahydrofuran and dioxane. Water, and
organic solvents such as alcohols and glycols are preferable. These
liquid mediums may be used either alone or as a combination of at
least two thereof.
[0047] According to the need, to prevent precipitation of the
abrasive in the slurry or improve stability of the slurry, a
polymeric dispersant such as tripolyphosphate, a phosphoric acid
salt such as hexametaphosphate, cellulose ether such as
carboxymethyl cellulose, and a water-soluble high-molecular-weight
compound such as polyvinyl alcohol can be added in the polishing
slurry. These additive substances may be used either alone or as a
combination of at least two thereof. The amount of these substances
is preferably in the range of 0.05% to 20% by mass, more preferably
0.1% to 10% by mass, based on the abrasive.
[0048] The concentration of abrasive in the thus-prepared polishing
slurry is preferably in the range of 1% to 50% by mass, more
preferably 5% to 40% by mass and especially preferably 10% to 30%
by mass, based on the polishing slurry. When the concentration of
abrasive is smaller than 1% by mass, a sufficient polishing
performance cannot be obtained. In contrast, when the concentration
of abrasive is larger than 50% by mass, the polishing slurry has a
high viscosity and its fluidity is lowered, and thus, an excessive
amount of abrasive composition is inevitably used for polishing
with the result of an increase in polishing cost.
[0049] The material or member to be polished with the polishing
slurry of the present invention is not particularly limited, but,
as examples thereof, there can be mentioned various optical glass
materials or members and electronic glass materials or members,
such as a glass substrate for optical lens, a glass substrate for
optical disc or magnetic disc, a glass substrate for plasma
display, a glass substrate for liquid crystal display such as thin
film transistor (TFT) LCD or twisted nematic (TN) LCD, a color
filter for liquid crystal TV, and a glass substrate for LSI
photomask; and general glass articles. The polishing slurry is
especially suitable for polishing a glass substrate for magnetic
disc.
[0050] A glass substrate for magnetic disc has a high stiffness and
is capable of being rendered thin, and has a high impact strength.
Because of these characteristics, this substrate attracts
widespread attention. Glass material of the glass substrate is
classified into chemically reinforced glass and crystallized glass.
Both of these glass materials have been reinforced to remedy
brittleness,which is a defect in herently possessed by glass. Flaws
on a glass surface greatly influences the mechanical strength of
glass, and therefore, to enhance the reliability of glass, glass is
generally chemically reinforced by ion exchange. More specifically,
a glass substrate (i.e., original sheet) is immersed in amolten
alkali salt to exchange an alkali ion on the glass surface with an
ion of larger size in the molten alkali salt whereby a compression
stress-resistant layer is formed on the surface and the breaking
strength is greatly enhanced. Elution of an alkali from the inside
of glass is suppressed in the chemically reinforced glass. The
polishing slurry of the present invention can be used even for
polishing the chemically reinforced glass substrate for magnetic
disc (HD) with enhanced polishing performance in high polishing
rate, reduced roughness of polished surface, and minimized
occurrence of minute scratches and other surface defects. As
preferable examples of the glass substrate for magnetic disc (HD),
there can be mentioned an aluminosilicate glass substrate
containing Li.sup.+ and Na.sup.+, a soda lime glass substrate
containing K.sup.+ and Na.sup.+, and a crystallized glass
substrate.
EXAMPLES
[0051] The invention will now be described specifically by the
following examples that by no means limit the scope of the
invention.
Example 1
[0052] 4 kg of a commercially available unrefined rare earth
carbonate powder (ignition loss: 55.8%) was baked in a box oven.
That is, the powder was heated to 900.degree. C. at a temperature
elevation rate of 1.7.degree. C./minute and maintained at
900.degree. C. for 2 hours. The elementary analysis of the baked
powder revealed that the content of rare earth oxides was 99% by
mass, and the content of cerium oxide was 60% by mass based on the
rare earth oxides. The baked powder had a specific surface area of
10 m.sup.2/g as measured by the BET method. 1.7 kg of the baked
powder was put into 2.5 kg of pure water with stirring. Then, 68 g
(4% by mass based on the baked powder) of a specific carboxylic
acid-type surfactant (tradename "DEMOL EP" available from Kao
Corporation) as a carboxylic acid salt (anionic surfactant), and
0.17 g (0.01% by mass based on the baked poeder) of polyoxyalkylene
alkyl ether (tradename "EMULGEN MS-110" available from Kao
Corporation) (nonionic surfactant) were added with stirring to
prepare a slurry.
[0053] The slurry was subjected to wet grinding while being
circulated through a wet mill for 2.5 hours. Then pure water was
added to the slurry to give 8 kg of a polishing slurry having an
abrasive content of 20% by mass. The polishing slurry had a pH
value of 12.0.
[0054] Particle size distribution was determined on a part of the
polishing slurry by a laser diffraction particle size distribution
analyzer (HR 850, available from CILAS Co.). The 50% accumulative
average particle diameter (D50) as expressed in terms of volume was
0.55 .mu.m.
Examples 2 to 7
[0055] Polishing slurries were prepared by the same procedures as
described in Example 1 except that the amounts of the carboxylic
acid salt (anionic surfactant) and polyoxyalkylene alkyl ether
(nonionic surfactant) were varied as shown in Table 1. All other
conditions remained the same. The pH values of the slurries are
shown in Table 1.
Comparative Examples 1 and 2
[0056] Polishing slurries were prepared by the same procedures as
described in Example 1 except that the amounts of the carboxylic
acid salt (anionic surfactant) and polyoxyalkylene alkyl ether
(nonionic surfactant) were varied as shown in Table 1. All other
conditions remained the same. The pH values of the slurries are
shown in Table 1.
Comparative Example 3
[0057] Polishing slurry was prepared by the same procedures as
described in Example 1 except that the starting raw material was
changed from the commercially available unrefined rare earth
carbonate powder to high-purity cerium carbonate, and the amounts
of the carboxylic acid salt (anionic surfactant) and
polyoxyalkylene alkyl ether (nonionic surfactant) were varied as
shown in Table 1. All other conditions remained the same. The pH
value of the slurry is shown in Table 1.
1 TABLE 1 Amount of Amount of anionic nonionic surfactant
surfactant pH of Raw material (mass %)*1 (mass %)*1 slurry Example
1 Rare earth carbonate 4.0 0.01 12.0 Example 2 " 4.0 0.001 11.6
Example 3 " 4.0 0.005 11.7 Example 4 " 4.0 0.05 11.5 Example 5 "
4.0 0.1 12.0 Example 6 " 3.0 0.01 11.2 Example 7 " 10.0 0.01 12.5
Comp. Ex. 1 " 4.0 0 11.7 Comp. Ex. 2 " 0 1.0 10.1 Comp. Ex. 3
High-purity 10.0 0.01 9.6 cerium carbonate Note, *1% by mass based
on the baked powder
[0058] Polishing Test
[0059] Using each of the polishing slurries prepared in the above
examples and comparative examples, a glass substrate was polished
under the following conditions.
[0060] Polishing machine: 4 way-type both side polisher "USP-5B"
available from Fujikoshi Machinery Industries Co.
[0061] Polishing pad: Suede-type pad "Polytex DG" available from
Rodel Co.
[0062] Feed rate of slurry: 60 ml/min
[0063] Revolution of base disc: 90 rpm
[0064] Polishing pressure: 75 g/cm.sup.2
[0065] Polishing time: 10 min
[0066] After polishing, the glass substrate was taken and washed by
ultrasonic washing with pure water, and then dried to give a test
specimen.
[0067] The glass substrate was an aluminosilicate-based glass
substrate for magnetic disc with a diameter of 2.5 inches having a
surface roughness Ra of 9 .ANG., which was prepared by previously
abrading with a commercially available cerium oxide abrasive
compound "SHOROX H-1", tradename, available from Tohoku Kinzoku
Kagaku K.K.
[0068] Evaluation of Polished Substrate
[0069] (1) Surface roughness (Ra)
[0070] Surface roughness (Ra) of a glass substrate surface was
measured by an atomic force microscope (AFM).
[0071] (2) Surface Defect
[0072] A glass substrate surface was observed by a differential
interference microscope to examine the adhered state on the
surface, and occurrence of pits and scratches. Evaluation result of
scratches was expressed by the relative number of scratches.
Evaluation of surface defects was expressed according to the
following three ratings.
[0073] A: occurrence of pits was not observed to any appreciable
extent and the surface state was good.
[0074] B: pits were observed to some extent and the polished
substrate was not practically acceptable.
[0075] C: surface state was very bad.
[0076] (3) Rate of Polishing
[0077] Rate of polishing (.mu.m/min) was calculated from the weight
change of glass substrate as measured before and after
polishing.
[0078] The evaluation results are shown in Table 2.
2 TABLE 2 Rate of Surface Relative polishing roughness number of
Surface (.mu.m/min) Ra (.ANG.) scratches defect Example 1 0.89 2.3
18 A Example 2 0.79 2.4 30 A Example 3 0.90 2.3 34 A Example 4 0.91
2.5 27 A Example 5 0.81 2.1 33 A Example 6 0.77 2.6 32 A Example 7
0.95 2.2 22 A Comp. Ex. 1 0.47 3.2 39 A Comp. Ex. 2 0.28 4.1 120 C
Comp. Ex. 3 0.45 4.2 32 A
[0079] As seen from Table 2, when polishing was carried out by
using the polishing slurries prepared in Examples 1 to 7, the rate
of polishing was high, the surface roughness was small, and a good
polished surface with no scratches nor surface defects was
obtained.
[0080] In contrast, when polishing was carried out by using the
polishing slurry prepared in Comparative Example 1, which did not
contain a nonionic surfactant, the rate of polishing was low and
the surface roughness was large.
[0081] When polishing was carried out by using the polishing slurry
prepared in Comparative Example 2, which did not contain an anionic
surfactant and had a pH value smaller than 11, the rate of
polishing was low, the surface roughness was large, and scratches
and surface defects occurred. This polishing slurry was not
suitable for precision polishing.
[0082] When polishing was carried out by using the polishing slurry
prepared in Comparative Example 3, which contained an anionic
surfactant and a nonionic surfactant, but had a pH smaller than 11,
the rate of polishing was low, and the surface roughness was
large.
INDUSTRIAL APPLICABILITY
[0083] The polishing slurry of the present invention can be used
for polishing various optical glass materials or members and
electronic glass materials or members, such as a glass substrate
for optical lens, a glass substrate for optical disc or magnetic
disc, a glass substrate for plasma display, a glass substrate for
liquid crystal display such as thin film transistor (TFT) LCD or
twisted nematic (TN) LCD, a color filter for liquid crystal TV, and
a glass substrate for LSI photomask; and general glass
articles.
[0084] The polishing slurry is especially suitable for polishing a
glass substrate for magnetic disc, and other substrates used in
electronic field. Using the polishing slurry, a highly flat surface
with small surface roughness and not having minute scratches and
minute pits to any appreciable extent can be obtained at a high
polishing rate.
* * * * *