U.S. patent application number 10/875266 was filed with the patent office on 2005-01-06 for polishing composition.
Invention is credited to Fujii, Shigeo, Kitayama, Hiroaki.
Application Number | 20050003746 10/875266 |
Document ID | / |
Family ID | 32768031 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050003746 |
Kind Code |
A1 |
Fujii, Shigeo ; et
al. |
January 6, 2005 |
Polishing composition
Abstract
A polishing composition containing an .alpha.-alumina, an
intermediate alumina, an oxidizing agent and water; a method for
reducing waviness of a substrate to be polished, including the step
of applying the polishing composition to the substrate to be
polished; and a method for manufacturing a substrate, including the
step of polishing a substrate to be polished with the polishing
composition. The polishing composition is suitable for polishing
substrates for precision parts such as substrates for magnetic
recording media for magnetic discs, optical discs, opto-magnetic
discs, and the like; photomask substrates; glass for liquid
crystals; optical lenses; optical mirrors; optical prisms; and
semiconductor substrates.
Inventors: |
Fujii, Shigeo;
(Wakayama-shi, JP) ; Kitayama, Hiroaki;
(Wakayama-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
32768031 |
Appl. No.: |
10/875266 |
Filed: |
June 25, 2004 |
Current U.S.
Class: |
451/41 ;
51/309 |
Current CPC
Class: |
C09G 1/02 20130101; C09K
3/1463 20130101 |
Class at
Publication: |
451/041 ;
051/309 |
International
Class: |
B24D 003/02; B24B
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2003 |
JP |
2003-270150 |
Claims
What is claimed is:
1. A polishing composition comprising an .alpha.-alumina, an
intermediate alumina, an oxidizing agent and water.
2. The polishing composition according to claim 1, further
comprising an acid.
3. The polishing composition according to claim 1 or 2, wherein the
pH is less than 7.
4. The polishing composition according to claim 1 or 2, wherein the
weight ratio of the .alpha.-alumina to the intermediate alumina,
.alpha.-alumina/intermediate alumina, is from 99/1 to 30/70.
5. The polishing composition according to claim 3, wherein the
weight ratio of the .alpha.-alumina to the intermediate alumina,
.alpha.-alumina/intermediate alumina, is from 99/1 to 30/70.
6. The polishing composition according to claim 1 or 2, wherein the
.alpha.-alumina has a secondary average particle size of from 0.01
to 2 .mu.m and a specific surface area of from 0.1 to 50 m.sup.2/g,
and the intermediate alumina has a secondary average particle size
of from 0.01 to 5 .mu.m and a specific surface area of from 30 to
300 m.sup.2/g.
7. The polishing composition according to claim 3, wherein the
.alpha.-alumina has a secondary average particle size of from 0.01
to 2 .mu.m and a specific surface area of from 0.1 to 50 m.sup.2/g,
and the intermediate alumina has a secondary average particle size
of from 0.01 to 5 .mu.m and a specific surface area of from 30 to
300 m.sup.2/g.
8. The polishing composition according to claim 4, wherein the
.alpha.-alumina has a secondary average particle size of from 0.01
to 2 .mu.m and a specific surface area of from 0.1 to 50 m.sup.2/g,
and the intermediate alumina has a secondary average particle size
of from 0.01 to 5 .mu.m and a specific surface area of from 30 to
300 m.sup.2/g.
9. The polishing composition according to claim 2, wherein the acid
is a polyvalent acid.
10. The polishing composition according to claim 3, wherein the
acid is a polyvalent acid.
11. The polishing composition according to claim 4, wherein the
acid is a polyvalent acid.
12. The polishing composition according to claim 6, wherein the
acid is a polyvalent acid.
13. The polishing composition according to claim 2, wherein the
acid comprises an acid having a pK1 of less than 2.5 and an acid
having a pK1 of 2.5 or more.
14. The polishing composition according to claim 3, wherein the
acid comprises an acid having a pK1 of less than 2.5 and an acid
having a pK1 of 2.5 or more.
15. The polishing composition according to claim 4, wherein the
acid comprises an acid having a pK1 of less than 2.5 and an acid
having a pK1 of 2.5 or more.
16. The polishing composition according to claim 6, wherein the
acid comprises an acid having a pK1 of less than 2.5 and an acid
having a pK1 of 2.5 or more.
17. The polishing composition according to claim 9, wherein the
acid comprises an acid having a pK1 of less than 2.5 and an acid
having a pK1 of 2.5 or more.
18. A method for reducing waviness of a substrate to be polished,
comprising the step of applying the polishing composition of claim
1 or 2 to the substrate to be polished.
19. A method for manufacturing a substrate, comprising the step of
polishing a substrate to be polished with the polishing composition
of claim 1 or 2.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a polishing composition
having a high polishing rate and being capable of reducing waviness
of a substrate to be polished. Further, the present invention
relates to a method for reducing waviness of a substrate to be
polished with the polishing composition, and a method for
manufacturing a substrate with the polishing composition.
BACKGROUND OF THE INVENTION
[0002] In hard disks, in order to make the minimum recording area
smaller and to increase storage capacity, the flying height of the
magnetic head has been desired to be lowered. In order to lower the
flying height of the magnetic head, it is necessary to reduce both
the short-wavelength waviness (a waviness having a wavelength of
from 50 to 500 .mu.m) and the long-wavelength waviness (a waviness
having a wavelength of from 0.5 mm or more). The term "waviness" as
referred to herein means surface dents and projections having a
wavelength longer than that of the surface roughness. In order to
manufacture a substrate having reduced waviness as described above,
mechanical conditions such as control of the pore size of the
polishing pad, control of the hardness, and control of the
polishing load or rotational speed during polishing have been
studied. However, such mechanical conditions are effective but not
to a satisfactory level. On the other hand, the reduction of
waviness using the polishing compositions has been also studied.
Japanese Patent Laid-Open No. Hei 3-115383 discloses a polishing
composition containing .alpha.-alumina, a water-soluble peroxide
and boehmite, and Japanese Patent Laid-Open No. 2001-260005 (U.S.
Pat. No. 6,261,476B1) discloses a polishing composition containing
primary polishing particles, dispersible colloidal particles and an
oxidizing agent. Also, Japanese Patent Laid-Open No. 2002-327170
(US2002194789A1) discloses a polishing composition containing
colloidal silica, an oxidizing agent and an organophosphonic acid,
and Japanese Patent Laid-open No. 2003-41239 (US2003041526A1)
discloses a polishing composition containing an intermediate
alumina. However, these polishing compositions cannot be said to be
satisfactory from the viewpoint of reduction of waviness while
maintaining the necessary polishing rate.
SUMMARY OF THE INVENTION
[0003] The present invention relates to the following:
[0004] (1) a polishing composition containing an .alpha.-alumina,
an intermediate alumina, an oxidizing agent and water;
[0005] (2) a method for reducing waviness of a substrate to be
polished, including the step of applying the polishing composition
of the above (1) to the substrate to be polished; and
[0006] (3) a method for manufacturing a substrate, including the
step of polishing a substrate to be polished with the polishing
composition of the above (1).
DETAILED DESCRIPTION OF THE INVENTION
[0007] The present invention relates to a polishing composition
having a high polishing rate and being capable of reducing waviness
of a substrate to be polished; a method for reducing waviness of a
substrate to be polished with the polishing composition, and a
method for manufacturing a high-quality substrate having reduced
waviness with the polishing composition.
[0008] These and other advantages of the present invention will be
apparent from the following description.
[0009] By polishing a substrate for precision parts or the like
with the polishing composition of the present invention, an effect
such as reduction of waviness of an object to be polished at a high
polishing rate is exhibited. Especially, those composed of a
short-wavelength waviness having a wavelength of from 50 to 500
.mu.m and a long-wavelength waviness having a wavelength of from
0.5 to 5 mm are referred to microwaviness. The present invention
has an excellent effect of reducing microwaviness.
[0010] In addition, since the obtained polished object has little
deposition of stains such as polishing debris, the washing
following the polishing can be conveniently carried out, so that a
high-quality substrate having reduced waviness can be economically
manufactured.
[0011] One of the significant features of the polishing composition
of the present invention resides in the combined use of an
.alpha.-alumina and an intermediate alumina as an abrasive and the
use of an oxidizing agent as a polishing accelerator. By using the
polishing composition having the above features, a remarkable
effect is exhibited that a high polishing rate can be achieved, and
that a waviness of a substrate to be polished can be significantly
reduced.
[0012] Although not wanting to be limited by theory, the functional
mechanism for exhibiting the effects of increasing polishing rates
and reducing a waviness by using the .alpha.-alumina and the
intermediate alumina together is presumably due to the fact that
the packing property is increased because these aluminas are
composed of particles having different particle sizes and different
hardness, so that the physical polishing force effectively
functions on the surface of the object to be polished.
[0013] The polishing composition of the present invention contains
an .alpha.-alumina as an abrasive. As the .alpha.-alumina, an
alumina that is prepared by baking gibbsite, bayerite,
nordstrandite, diaspore, boehmite, pseudo-boehmite, alumino-gel,
.gamma.-alumina, .theta.-alumina or the like at a temperature of
1100.degree. C. or more according to a conventional method is
preferable. As the .alpha.-alumina, an aluminum oxide having a
purity as alumina of 95% or more, more preferably 97% or more, even
more preferably 99% or more is preferable, from the viewpoints of
reducing the waviness, reducing the surface roughness, increasing
the polishing rate, and preventing the surface defects.
[0014] The .alpha.-alumina has an average primary particle size of
preferably from 0.005 to 0.8 .mu.m, more preferably from 0.01 to
0.4 .mu.m, and an average secondary particle size of preferably
from 0.01 to 2 .mu.m, more preferably from 0.05 to 1.0 .mu.m, even
more preferably from 0.1 to 0.5 .mu.m, from the viewpoint of
reducing the waviness. The average primary particle size of the
abrasive is obtained by subjecting the abrasive to an image
analysis by observing with a scanning electron microscope
(preferably from 3000 to 30000 times) or a transmission electron
microscope (preferably from 10000 to 300000 times), and is defined
as a number-average particle size based on the arithmetic means of
major axis length and minor axis length of the particle. In
addition, the average secondary particle size can be determined as
a volume-average particle size by using a laser diffraction
method.
[0015] The specific surface area of the .alpha.-alumina determined
by the BET method is preferably from 0.1 to 50 m.sup.2/g, more
preferably from 1 to 40 m.sup.2/g, even more preferably from 2 to
20 m.sup.2/g, from the viewpoints of increasing the polishing rate
and reducing the waviness.
[0016] The content of the .alpha.-alumina is preferably 0.05% by
weight or more, more preferably 0.1% by weight or more, even more
preferably 0.5% by weight or more, even more preferably 1% by
weight or more, of the polishing composition, from the viewpoints
of increasing the polishing rate and reducing the waviness. Also,
the content of the .alpha.-alumina is preferably 40% by weight or
less, more preferably 30% by weight or less, even more preferably
25% by weight or less, even more preferably 20% by weight or less,
from the viewpoints of surface quality and economic advantages.
Specifically, the content of the .alpha.-alumina is preferably from
0.05 to 40% by weight, more preferably from 0.1 to 30% by weight,
even more preferably from 0.5 to 25% by weight, even more
preferably from 1 to 20% by weight, of the polishing
composition.
[0017] The polishing composition of the present invention contains
an intermediate alumina, from the viewpoints of increasing the
polishing rate and reducing the waviness. The intermediate alumina
in the present invention refers to alumina particles other than the
.alpha.-alumina particles, and concrete examples thereof include
.gamma.-alumina particles, .delta.-alumina particles,
.theta.-alumina particles, .eta.-alumina particles, .kappa.-alumina
particles, and mixtures thereof. Among them, the following
intermediate aluminas are preferable, from the viewpoints of
increasing the polishing rate and reducing the waviness. The
crystal forms thereof are preferably .gamma.-alumina,
.delta.-alumina and .theta.-alumina, and mixtures thereof, and more
preferably .gamma.-alumina and .theta.-alumina. Also, the specific
surface area as determined by the BET method is preferably from 30
to 300 m.sup.2/g, more preferably from 50 to 200 m.sup.2/g. This
average secondary particle size of the intermediate alumina is
preferably from 0.01 to 5 .mu.m, more preferably from 0.01 to 2
.mu.m, even more preferably from 0.05 to 1 .mu.m, even more
preferably from 0.1 to 0.5 .mu.m, from the viewpoint of reducing
the waviness. The average particle size can be determined as a
volume-average particle size by using a laser beam diffraction
method with, for instance, one commercially available form Horiba,
LTD. under the trade name of "LA-920."
[0018] The content of each of the alkali metal and the alkaline
earth metal in the intermediate alumina is preferably 0.1% by
weight or less, more preferably 0.05% by weight or less, even more
preferably 0.01% by weight or less. For instance, in a case where
aluminum hydroxide which has a relatively large specific surface
area and a low content of the alkali metal and the alkaline earth
metal is used as a raw material, there is little fusion of the
intermediate alumina formed so that the particle strength is small,
thereby making it effective for reducing the surface defects of the
object to be polished.
[0019] The aluminum hydroxide which can be used as the raw material
for the intermediate alumina has a specific surface area as
determined by the BET method of preferably from 10 to 500
m.sup.2/g, more preferably from 30 to 400 m.sup.2/g, even more
preferably from 50 to 300 m.sup.2/g. In addition, the content of
the alkali metal and the alkaline earth metal in the aluminum
hydroxide is preferably 0.1% by weight or less, more preferably
0.05% by weight or less, even more preferably 0.01% by weight or
less. Further, in a case where an intermediate alumina is prepared
by thermally dehydrating aluminum hydroxide, an introduction of dry
air or nitrogen gas during heating is effective in the prevention
of surface defects of the object to be polished. Here, the
above-mentioned thermal dehydration treatment can be carried out by
a conventional method. These intermediate aluminas are adjusted to
a given particle size, for instance, by wet pulverization or dry
pulverization with a pulverizer such as a ball-mill, a beads-mill,
a high-pressure homogenizer or a jet mill as occasion demands.
[0020] The aluminum hydroxide is represented by the formulas
Al(OH).sub.3, AlOOH, AlOOH.nH.sub.2O or Al.sub.2O.sub.3.nH.sub.2O,
wherein n is a number of 1 to 3, and is not particularly limited,
as long as the intermediate alumina can be prepared by thermal
dehydration. Concrete examples thereof include gibbsite, bayerite,
nordstrandite, diaspore, boehmite, pseudo-boehmite, alumino-gel,
and the like.
[0021] Although the details of the functional mechanism during
polishing with the intermediate alumina may not be certainly known,
it is considered that the increase in the physical force to the
surface of the object to be polished is exhibited because the
polishing rate is increased by mixing both the .alpha.-alumina and
the intermediate alumina as compared to a case of the
.alpha.-alumina alone, or the intermediate alumina alone.
[0022] The content of the intermediate alumina is preferably 0.05%
by weight or more, more preferably from 0.1% by weight or more,
even more preferably 0.5% by weight or more, even more preferably
1% by weight or more, of the polishing composition, from the
viewpoints of increasing the polishing rate and reducing the
waviness. Also, the content of the intermediate alumina is
preferably 40% by weight or less, more preferably 30% by weight or
less, even more preferably 25% by weight or less, even more
preferably 20% by weight or less, of the polishing composition,
from the viewpoints of surface quality and economic advantages.
Specifically, the content of the intermediate alumina is preferably
from 0.05 to 40% by weight, more preferably from 0.1 to 30% by
weight, even more preferably from 0.5 to 25% by weight, even more
preferably from 1 to 20% by weight, of the polishing
composition.
[0023] The weight ratio of the .alpha.-alumina to the intermediate
alumina, i.e. .alpha.-alumina/intermediate alumina, is preferably
from 99/1 to 30/70, more preferably from 97/3 to 40/60, even more
preferably from 95/5 to 50/50, even more preferably from 93/7 to
55/45, from the viewpoints of satisfying both increase in the
polishing rate and reduction in the waviness.
[0024] Also, the total amount of the .alpha.-alumina and the
intermediate alumina is preferably from 0.1 to 45% by weight, more
preferably from 0.2 to 35% by weight, even more preferably from 1
to 30% by weight, even more preferably from 2 to 25% by weight, in
order to efficiently satisfy both the increase in the polishing
rate and the reduction in the waviness.
[0025] The polishing composition of the present invention contains
an oxidizing agent, from the viewpoints of increasing the polishing
rate and reducing the waviness. Although the functional mechanism
for polishing may not be certainly known, it is presumably as
follows. By allowing the oxidizing agent to act on an object to be
polished, the alumina is changed to a state in which the polishing
effect can sufficiently be exhibited. The oxidizing agent usable in
the present invention includes peroxide, peroxo acid of a metal or
a salt thereof, an oxyacid or a salt thereof, a nitrate, a sulfate,
a metal salt of an acid, and the like. The oxidizing agent is
roughly classified into inorganic oxidizing agents and organic
oxidizing agents according to their structures. Concrete examples
of those oxidizing agents are as follows. As the inorganic
oxidizing agents, there can be used peroxides of alkali metal or
the alkaline earth metal, such as hydrogen peroxide, sodium
peroxide, potassium peroxide, calcium peroxide, barium peroxide and
magnesium peroxide; peroxocarbonates, such as sodium
peroxocarbonate and potassium peroxocarbonate; peroxosulfuric acids
or salts thereof, such as ammonium peroxodisulfate, sodium
peroxodisulfate, potassium peroxodisulfate and peroxomonosulfuric
acid; peroxonitric acids and salts thereof, such as peroxonitric
acid, sodium peroxonitrate and potassium peroxonitrate;
peroxophosphoric acids or salts thereof, such as sodium
peroxophosphate, potassium peroxophosphate and ammonium
peroxophosphate; peroxoborates, such as sodium peroxoborate and
potassium peroxoborate; peroxochromates, such as potassium
peroxochromate and sodium peroxochromate; permanganates, such as
potassium permanganate and sodium permanganate; halogeno-acids or
derivatives thereof, such as sodium perchlorate, potassium
perchlorate, chloric acid, sodium hypochlorite, sodium periodate,
potassium periodate, iodic acid and sodium iodate; and metal salts
of inorganic acids, such as iron (III) chloride, iron (III)
sulfate. As the organic oxidizing agents, there can be used
percarboxylic acids, such as peracetic acid, performic acid and
perbenzoic acid; peroxides, such as t-butyl peroxide and cumene
peroxide; and iron (III) citrate. Among them, the inorganic
oxidizing agent is preferable, when easy handling, such as the
increase of the polishing rate, availability, water-solubility is
compared. Moreover, in consideration of the environmental problems,
an inorganic peroxide which does not contain a heavy metal is
preferable. Furthermore, from the viewpoint of preventing the
stains on the surface of the substrate to be polished, hydrogen
peroxide, peroxosulfates, halogeno-acids or derivatives thereof are
more preferable, and hydrogen peroxide is even more preferable.
These peroxides can be used alone or in admixture of two or more
kinds.
[0026] The content of the oxidizing agent is preferably 0.002% by
weight or more, more preferably from 0.005% by weight or more, even
more preferably 0.007% by weight or more, even more preferably
0.01% by weight or more, of the polishing composition, from the
viewpoints of increasing the polishing rate and reducing the
waviness. Also, the content of the oxidizing agent is preferably
20% by weight or less, more preferably 15% by weight or less, even
more preferably 10% by weight or less, even more preferably 5% by
weight or less, of the polishing composition, from the viewpoints
of surface quality and economic advantages. Specifically, the
content of the oxidizing agent is preferably from 0.002 to 20% by
weight, more preferably from 0.005 to 15% by weight, even more
preferably from 0.007 to 10% by weight, even more preferably from
0.01 to 5% by weight, of the polishing composition.
[0027] It is preferable that the polishing composition of the
present invention further contains an acid, from the viewpoints of
increasing the polishing rate and reducing the waviness.
[0028] The acid usable in the present invention has a pK1 of
preferably 7 or less, more preferably 5 or less, even more
preferably 3 or less, even more preferably 2 or less, from the
viewpoints of increasing the polishing rate and reducing the
waviness. Here, the pK1 refers to a logarithmic value of an inverse
of a first acid dissociation constant, when a logarithmic value of
an inverse of an acid dissociation constant at 25.degree. C. is
expressed as pKa. The pK1 of each compound is listed in, for
instance, in Kagaku Binran (Kiso-hen) II, Fourth Revision, pp.
316-325 (Edit. by Nippon Kagakukai), and the like.
[0029] Concrete examples of acids usable in the present invention
are as follows. Inorganic compounds include monovalent mineral
acids, such as nitric acid, hydrochloric acid, perchloric acid, and
amide sulfuric acid; and polyvalent mineral acids, such as sulfuric
acid, sulfurous acid, phosphoric acid, pyrophosphoric acid,
polyphosphoric acid, phosphonic acid, and phosphinic acid. Also,
organic compounds include monocarboxylic acids, such as formic
acid, acetic acid, glycolic acid, lactic acid, propanoic acid,
hydroxypropanoic acid, butyric acid, benzoic acid, and glycine; and
polycarboxylic acids, such as oxalic acid, succinic acid, glutaric
acid, adipic acid, maleic acid, fumaric acid, itaconic acid, malic
acid, tartaric acid, citric acid, isocitric acid, phthalic acid,
nitrilotriacetic acid and ethylenediaminetetraacetic acid;
alkylsulfonic acids, such as methanesulfonic acid and
paratoluenesulfonic acid; alkylphosphoric acids, such as
ethylphosphoric acid and butylphosphoric acid; organic phosphonic
acids, such as phosphonohydroxyacetic acid, hydroxyethylidene
diphosphonic acid, phosphonobutane tricarboxylic acid and
ethylenediaminetetramethylene phosphonic acid; and the like. Among
them, the polyvalent acids are preferable, more preferably
polyvalent mineral acids, organic polycarboxylic acids and organic
polyphosphonic acids, even more preferably polyvalent mineral acids
and organic polycarboxylic acids, from the viewpoints of increasing
the polishing rate and reducing the waviness. Here, the polyvalent
acid refers to an acid having two or more hydrogen atoms in its
molecule, which is capable of generating hydrogen ions. In
addition, nitric acid, sulfuric acid, the sulfonic acids and the
carboxylic acids are preferable, from the viewpoint of preventing
the surface stains of the object to be polished.
[0030] Although the above-mentioned acids can be used alone, it is
preferable to use the acids in admixture of two or more kinds.
Especially in the case of polishing a metal surface such as a
Ni--P-plated substrate, a metal ion of the object to be polished is
eluted during polishing, thereby increasing the pH of the polishing
composition, so that a high polishing rate cannot be achieved. In
such case, it is preferable to use a combination of an acid having
a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more,
more preferably to use a combination of an acid having a pK1 of 1.5
or less and an acid having a pK1 of 2.5 or more, in order to make
the pH change smaller. When the polishing composition contains the
two or more kinds of the acids as mentioned above, among the acids
having a pK1 of less than 2.5, it is preferable to use mineral
acids, such as nitric acid, sulfuric acid, phosphoric acid and
polyphosphoric acid, or organic phosphonic acid in considerations
of increase in the polishing rate, reduction in the waviness and
availability of the acid. On the other hand, among the acids having
a pK1 of 2.5 or more, organic carboxylic acids, such as acetic
acid, succinic acid, malic acid, tartaric acid and citric acid are
preferable from the same viewpoints.
[0031] The total content of the above-mentioned acids is preferably
0.002% by weight or more, more preferably 0.005% by weight or more,
even more preferably 0.007% or more, even more preferably 0.01% by
weight or more, of the polishing composition, from the viewpoints
of increasing the polishing rate and reducing the waviness. Also,
the total content of the acids is preferably 20% by weight or less,
more preferably 15% by weight or less, even more preferably 10% by
weight or less, even more preferably 5% by weight or less, from the
viewpoints of surface quality and economic advantages.
Specifically, the total content of the acids is preferably from
0.002 to 20% by weight, more preferably from 0.005 to 15% by
weight, even more preferably from 0.007 to 10% by weight, even more
preferably from 0.01 to 5% by weight, of the polishing composition.
The weight ratio of the acid having a pK1 of less than 2.5 to the
acid having a pK1 of 2.5 or more, i.e. the acid having a pK1 of
less than 2.5/the acid having a pK1 of 2.5 or more, is preferably
from 9/1 to 1/9, more preferably from 7/1 to 1/7, even more
preferably from 5/1 to 1/5, from the viewpoint of increasing the
polishing rate.
[0032] Water in the polishing composition of the present invention
is used as a medium. The content of water is preferably from 50 to
99% by weight, more preferably from 60 to 97% by weight, even more
preferably from 70 to 95% by weight, from the viewpoint of
effectively polishing the object to be polished.
[0033] In addition, there can be added other components to the
polishing composition of the present invention, in accordance with
the purpose of increasing the polishing rate, reducing the waviness
and other purposes. For instance, other components include
inorganic salts, thickeners, anticorrosive agents, basic
substances, and the like. Examples of the inorganic salt include
ammonium nitrate, ammonium sulfate, potassium sulfate, nickel
sulfate, aluminum nitrate, aluminum sulfate, ammonium sulfaminate,
and the like. These other components can be used alone or in
admixture of two or more kinds. Also, the content of the other
components is preferably from 0.05 to 20% by weight, more
preferably from 0.05 to 10% by weight, even more preferably from
0.05 to 5% by weight, of the polishing composition, from the
viewpoint of economic advantages.
[0034] In addition, there can be added other components, such as
disinfectants and antibacterial agents, as occasion demands. The
content of the disinfectant and the antibacterial agent is
preferably from 0.0001 to 0.1% by weight, more preferably from
0.001 to 0.05% by weight, even more preferably from 0.002 to 0.02%
by weight, of the polishing composition, from the viewpoint of
exhibiting the function of the agents and from the viewpoints of
the influence on polishing performance, and economic
advantages.
[0035] The concentration of each component of the polishing
composition in the present invention is the concentration which is
preferable for polishing, and may be the concentration during the
preparation of the composition. In many cases, the composition is
usually prepared as a concentrate, which is diluted before use or
upon use.
[0036] The polishing composition can be prepared by adding or
mixing the intended components by an optional method.
[0037] It is preferable that the pH of the polishing composition is
appropriately determined depending upon the kinds of the object to
be polished and the required properties. For instance, the pH of
the polishing composition is preferably less than 7, more
preferably from 0.1 to 6, even more preferably from 0.5 to 5, even
more preferably from 1 to 4, even more preferably from 1 to 3, from
the viewpoints of increase in the polishing rate and reduction in
the waviness, and from the viewpoints of prevention of the
corrosion of the processing machine and operator safety. The pH can
be adjusted by properly adding an inorganic acid, such as nitric
acid or sulfuric acid; an organic acid, such as a hydroxycarboxylic
acid, a polycarboxylic acid, an aminopolycarboxylic acid, an amino
acid, or a metal salt or an ammonium salt thereof; or a basic
substance, such as an aqueous ammonia, potassium hydroxide, sodium
hydroxide or an amine, in a desired amount.
[0038] The method for manufacturing a substrate of the present
invention includes the step of polishing a substrate to be polished
with the above-mentioned polishing composition.
[0039] The material for the object to be polished represented by
the substrate for the present invention includes, for instance,
metals or metalloids such as silicon, aluminum, nickel, tungsten,
copper, tantalum and titanium and alloys which contains these
metals as the main components; glassy substances such as glass,
glassy carbon and amorphous carbons; ceramic materials such as
alumina, silicon dioxide, silicon nitride, tantalum nitride, and
titanium nitride; resins such as polyimide resins; and the like.
Among them, it is preferable that an object to be polished is made
of a metal such as aluminum, nickel, tungsten or copper, or made of
an alloy containing these metals as the main components; or an
object to be polished is a semiconductor substrate made of
semiconductor elements containing these metals. Especially, when
the polishing composition of the present invention is applied to a
substrate made of an aluminum alloy plated with Ni--P, it is
preferable because the waviness can remarkably be reduced. The
shape for the object to be polished is not particularly limited.
For instance, those having shapes containing planar portions such
as discs, plates, slabs and prisms, or shapes containing curved
portions such as lenses can be subjects for polishing with the
polishing composition of the present invention. Among them, those
having the disc-shaped objects to be polished are especially
preferable in polishing.
[0040] The present invention also relates to a method for reducing
waviness of the above-mentioned substrate to be polished. In the
method for reducing waviness of the substrate to be polished with
the polishing composition of the present invention, the waviness
can be remarkably reduced by polishing the above-mentioned
substrate with the polishing composition of the present invention.
For instance, a high-quality substrate having reduced waviness can
be manufactured by the method including the steps of clamping a
substrate with polishing platens to which a polishing cloth made of
a porous organic polymer and the like is pasted; feeding the
polishing composition of the present invention to a surface to be
polished; and moving the polishing platens or the substrate, while
applying pressure.
[0041] The polishing composition of the present invention can be
preferably used in polishing a substrate for precision parts. For
instance, the polishing composition is suitable for polishing
substrates for magnetic recording media, such as magnetic disks,
optical disks, opto-magnetic disks, and photomask substrates,
optical lenses, optical mirrors, optical prisms and semiconductor
substrates, and the like. The polishing of a semiconductor
substrate includes, for instance, the steps of polishing a silicon
wafer (bare wafer), forming a film for shallow trench isolation,
subjecting an interlayer dielectric to planarization, forming an
embedded metal line, and forming an embedded capacitor, and the
like. The polishing composition is especially effective in the
polishing step, and the polishing composition can be similarly
applied to polishing steps other than these, for instance, lapping
step, and the like. The polishing composition of the present
invention is especially suitable for polishing a magnetic disk
substrate.
EXAMPLES
[0042] The following examples further describe and demonstrate
embodiments of the present invention. The examples are given solely
for the purposes of illustration and are not to be construed as
limitations of the present invention.
Examples 1 to 17, Comparative Examples 1 to 5
[0043] [Method for Formulating Polishing Composition]
[0044] There were mixed together given amounts of .alpha.-alumina
(average primary particle size: 0.07 .mu.m, average secondary
particle size: 0.3 .mu.m, specific surface area: 15 m.sup.2/g,
purity: 99.9%), .theta.-alumina (average secondary particle size:
0.2 .mu.m, specific surface area: 120 m.sup.2/g, purity: 99.9%), an
oxidizing agent, an acid and other additives as listed in Tables 1
to 3, and balance ion-exchanged water, while stirring, and
pH-adjusted with an aqueous ammonia, to give a polishing
composition.
[0045] [Polishing Method]
[0046] A substrate surface made of a Ni--P plated aluminum alloy,
the substrate surface having an average deviation, of all points
from plane fit to test part surface Ra of 0.2 .mu.m, as determined
by Talystep commercially available from Rank Taylor-Hobson Limited
(size of tip end of profilometer: 25 .mu.m.times.25 .mu.m, by-pass
filter: 80 .mu.m, measurement length: 0.64 mm), a thickness of 1.27
mm and a diameter of 3.5 inches (diameter of 95.0 mm) was polished
with a double-sided processing machine under Set Conditions for
Double-Sided Processing Machine given below, to give a polished
Ni--P plated, aluminum alloy substrate usable for a substrate for
magnetic recording media.
[0047] Set Conditions for Double-Sided Processing Machine are as
follows.
[0048] <Set Conditions for Double-Sided Processing
Machine>
[0049] Double-sided processing machine: double-sided processing
machine, Model 9B, manufactured by SPEEDFAM CO., LTD.
[0050] Processing pressure: 9.8 kPa
[0051] Polishing Pad: "H9900S" (manufactured by FUJIBO Co.,
Ltd.).
[0052] Rotational speed of platen: 50 r/min
[0053] Feeding flow rate for a polishing composition: 100
ml/min
[0054] Polishing time period: 5 minutes
[0055] Number of substrates introduced: 10
[0056] [Polishing Rate]
[0057] Weights of each substrate before and after polishing were
measured using a device commercially available from Sartorius under
the trade name of "BP-210S." Change in weight of each substrate was
obtained, and an average of 10 substrates is defined as an amount
reduced, and a value obtained by dividing the amount reduced by the
polishing time is referred to as a rate of weight reduced. The rate
of weight reduced is introduced into the following equation and
converted to a polishing rate (.mu.m/min). A relative value
(relative polishing rate) of each Example or Comparative Example
was calculated based on the polishing rate of the polishing
composition in Comparative Example 1 as a standard value of 1.
Rate of Weight Reduction (g/min.)=[Weight Before Polishing
(g)-Weight After Polishing (g)]/Polishing Time (min.)
Polishing Rate (.mu.m/min.)=Rate of Weight Reduction (g/min.)/Area
of One Side of Substrate (mm.sup.2)/Ni--P Plating Density
(g/cm.sup.3).times.10.sup.6
[0058] [Waviness]
[0059] Each of the polished substrates was determined for
short-wavelength waviness and long-wavelength waviness at two
points of 180.degree. intervals (total of 4 points) under the
conditions given below.
1 Equipment: "Zygo New View 200" Object Lens: Magnification, 2.5
times, Michelson Zooming Ratio: 0.5 Remove: Cylinder Filter: FFT
Fixed Band Pass
[0060] Wavelength Determined:
2 Short-Wavelength Waviness: Filter High Wavelength 50 .mu.m Filter
Low Wavelength 500 .mu.m Long-Wavelength Waviness: Filter High
Wavelength 0.5 mm Filter Low Wavelength 5 mm Area: 4.33 mm .times.
5.77 mm
[0061] [Stains on Substrate Surface]
[0062] Each of the polished substrate was subjected to washing with
a liquid detergent using a PVA (polyvinyl acetate) pad in a
sheet-fed cleaning machine, and then subjected to washing with
ion-exchanged water. Thereafter, the washed substrate was observed
with a polarization microscope at a magnification of 300, and the
stains on the substrate surface was evaluated based on the 4
criteria as follows.
[0063] .circleincircle.: Alumina residue and polishing debris are
not observed on the surface at all.
[0064] .largecircle.: Hardly any alumina residue and polishing
debris are observed on the surface.
[0065] .DELTA.: Some alumina residue and polishing debris are
observed on certain locations on the surface.
[0066] .times.: Much alumina residue and polishing debris are
observed on the surface.
[0067] The results are shown in Tables 1 and 2. The values for the
polishing rates and waviness for each Example and each Comparative
Example is expressed as a relative value based on the value of
Comparative Example 1 as a standard value of 1. It is seen that the
polishing compositions obtained in Examples 1 to 12 containing
.alpha.-alumina, intermediate alumina and an oxidizing agent are
remarkably excellent in both the increase in polishing rates and
reduction in waviness, as compared to those of the comparative
examples. Especially when an acid is added, such an effect is
outstandingly excellent. In addition, it is seen that the polishing
compositions obtained in Examples 1 to 12 have excellent
stain-preventing effects for a substrate to be polished.
3 TABLE 1 Polishing Waviness .alpha.- .theta.- Rate (Relative
Value) Alumina Alumina Oxidizing Agent Acid (Relative Short- Long-
Stain on (%) (%) (%) (%) pH Value) wavelength wavelength Substrate
Ex. 1 3 1 Hydrogen Peroxide 0.6 -- -- 4.1 2.5 0.59 0.77
.largecircle. Ex. 2 3.5 0.5 Hydrogen Peroxide 0.6 Citric Acid 3.0
2.0 29 0.24 0.43 .circleincircle. Ex. 3 2 2 Hydrogen Peroxide 0.6
Citric Acid 3.0 2.0 28 0.23 0.38 .circleincircle. Ex. 4 1 3
Hydrogen Peroxide 0.6 Citric Acid 3.0 2.0 20 0.21 0.34
.circleincircle. Ex. 5 3 1 Hydrogen Peroxide 0.6 Citric Acid 3.0
2.0 42 0.26 0.25 .circleincircle. Ex. 6 3 1 Hydrogen Peroxide 0.6
Nitric Acid 1.1 0.8 36 0.27 0.42 .circleincircle. Ex. 7 3 1
Hydrogen Peroxide 0.6 Sulfuric Acid 1.7 0.8 53 0.26 0.21
.circleincircle. Ex. 8 3 1 Hydrogen Peroxide 1.8 Sulfuric Acid 5.1
0.5 63 0.25 0.19 .circleincircle. Ex. 9 3 1 Hydrogen Peroxide 0.6
Methanesulfonic 1.7 0.8 41 0.26 0.30 .circleincircle. Acid Ex. 10 3
1 Hydrogen Peroxide 0.6 Phosphoric Acid 1.7 1.4 34 0.27 0.35
.largecircle. Ex. 11 3 1 Hydrogen Peroxide 0.6 Hydroxyethylidene
1.8 1.2 44 0.26 0.22 .largecircle. Diphosphonic Acid Ex. 12 3 1
Hydrogen Peroxide 0.6 Polyphosphoric 1.4 1.4 37 0.25 0.27
.largecircle. Acid Comp. 3 1 -- -- -- -- 4.1 1 1 1 X Ex. 1 In the
table, "%" means % by weight.
[0068]
4 TABLE 2 Polishing Waviness .alpha.- .theta.- Acid and Other Rate
(Relative Value) Alumina Alumina Oxidizing Agent Additives
(Relative Short- Long- Stain on (%) (%) (%) (%) pH Value)
wavelength wavelength Substrate Comp. 3 1 -- -- -- -- 4.1 1 1 1 X
Ex. 1 Comp. 3 0 Hydrogen 0.6 Boehmite 1.0 4.1 1.1 0.91 0.92
.largecircle. Ex. 2 Peroxide Comp. 3 0 Aluminum 0.6 Colloidal
Silica*.sup.) 1.0 4.1 2.0 0.59 0.77 .DELTA. Ex. 3 Nitrate Comp. 3 1
-- -- Citric Acid 0.5 3.0 2.3 0.72 0.85 .DELTA. Ex. 4 Comp. 0 0
Hydrogen 0.6 Colloidal Silica*.sup.) 4.0 1.2 1.5 0.27 0.92
.largecircle. Ex. 5 Peroxide Hydroxyethylidene 1.8 Diphosphonic
Acid In the table, "%" means % by weight. *.sup.)Average particle
size: 0.05 .mu.m, purity: 99.9%
[0069] Table 3 shows the results of cases where the pH is higher
than those of Table 1, in consideration of safety to human bodies
and corrosiveness to machines. It is seen that the polishing
compositions obtained in Examples 13 to 17 are both excellent in
the increase in polishing rate and reduction in waviness as
compared to those of Comparative Example 1. In addition, it is seen
that as in the cases of Examples 15 to 17 where two kinds of acids,
such as a carboxylic acid and sulfuric acid, which is a mineral
acid, are used together, the effects of an increase in polishing
rate and reduction in waviness are further enhanced, as compared to
the cases where an acid is used alone (Examples 13 and 14). Also,
it is seen that all of the polishing compositions obtained in
Examples 13 to 17 have excellent stain-preventing effects for a
substrate to be polished.
[0070] In addition, since the waviness evaluated in Examples 1 to
17 is microwaviness, it is seen that all of the polishing
compositions obtained in Examples 1 to 17 are excellent for
reducing microwaviness.
5 TABLE 3 Polishing Waviness .alpha.- .theta.- Rate (Relative
Value) Alumina Alumina Oxidizing Agent Acid*.sup.) (Relative Short-
Long- Stain on (%) (%) (%) (%) (%) pH Value) wavelength wavelength
Substrate Ex. 13 3 1 Hydrogen 0.6 Citric 1.0 -- -- 2.2 35 0.29 0.37
.circleincircle. Peroxide Acid Ex. 14 3 1 Hydrogen 0.6 -- --
Sulfuric 1.1 2.1 20 0.29 0.40 .largecircle. Peroxide Acid Ex. 15 3
1 Hydrogen 0.6 Citric 1.0 Sulfuric 1.1 2.1 49 0.25 0.19
.circleincircle. Peroxide Acid Acid Ex. 16 3 1 Hydrogen 0.6
Tartaric 1.0 Sulfuric 1.1 2.1 40 0.27 0.22 .circleincircle.
Peroxide Acid Acid Ex. 17 3 1 Hydrogen 0.6 Citric 1.0 Sulfuric 1.1
2.1 41 0.26 0.20 .circleincircle. Peroxide Acid Acid Comp. 3 1 --
-- -- -- -- -- 4.1 1 1 1 X Ex. 1 In the table, "%" means % by
weight. *.sup.)Citric acid: pK1 = 2.9, tartaric acid: pK1 = 2.8,
acetic acid: pK1 = 4.6, sulfuric acid: pK1 < 0
[0071] The polishing composition of the present invention is
suitable for polishing substrates for precision parts such as
substrates for magnetic recording media for magnetic discs, optical
discs, opto-magnetic discs, and the like; photomask substrates;
glass for liquid crystals; optical lenses; optical mirrors; optical
prisms; and semiconductor substrates.
[0072] The present invention being thus described, it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the invention, and all such modifications as would be obvious to
one skilled in the art are intended to be included within the scope
of the following claims.
* * * * *