U.S. patent application number 13/755127 was filed with the patent office on 2013-09-19 for slurry, polishing liquid set, polishing liquid, method for polishing substrate, and substrate.
The applicant listed for this patent is Tomohiro IWANO, Takenori NARITA, Daisuke RYUZAKI. Invention is credited to Tomohiro IWANO, Takenori NARITA, Daisuke RYUZAKI.
Application Number | 20130244431 13/755127 |
Document ID | / |
Family ID | 46145883 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244431 |
Kind Code |
A1 |
IWANO; Tomohiro ; et
al. |
September 19, 2013 |
SLURRY, POLISHING LIQUID SET, POLISHING LIQUID, METHOD FOR
POLISHING SUBSTRATE, AND SUBSTRATE
Abstract
The polishing liquid according to the embodiment comprises
abrasive grains, an additive and water, wherein the abrasive grains
satisfy either or both of the following conditions (a) and (b). (a)
Producing absorbance of at least 1.50 for light with a wavelength
of 400 nm in an aqueous dispersion with a content of the abrasive
grains adjusted to 1.0 mass %, and also producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %. (b) Producing absorbance of at least 1.000
for light with a wavelength of 290 nm in an aqueous dispersion with
a content of the abrasive grains adjusted to 0.0065 mass %, and
also producing light transmittance of at least 50%/cm for light
with a wavelength of 500 nm in an aqueous dispersion with a content
of the abrasive grains adjusted to 1.0 mass %.
Inventors: |
IWANO; Tomohiro;
(Hitachi-shi, JP) ; NARITA; Takenori;
(Hitachi-shi, JP) ; RYUZAKI; Daisuke;
(Kokubunji-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IWANO; Tomohiro
NARITA; Takenori
RYUZAKI; Daisuke |
Hitachi-shi
Hitachi-shi
Kokubunji-shi |
|
JP
JP
JP |
|
|
Family ID: |
46145883 |
Appl. No.: |
13/755127 |
Filed: |
January 31, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13582969 |
Sep 5, 2012 |
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PCT/JP2011/076822 |
Nov 21, 2011 |
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13755127 |
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Current U.S.
Class: |
438/693 ;
252/79.1 |
Current CPC
Class: |
H01L 21/30625 20130101;
H01L 21/31053 20130101; B24B 37/044 20130101; C09K 3/1463 20130101;
C09G 1/02 20130101; C09K 13/12 20130101 |
Class at
Publication: |
438/693 ;
252/79.1 |
International
Class: |
C09K 13/12 20060101
C09K013/12; H01L 21/306 20060101 H01L021/306 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2010 |
JP |
2010-260036 |
Claims
1-24. (canceled)
25. A slurry comprising abrasive grains and water, the abrasive
grains including a tetravalent metal element hydroxide, and
producing absorbance of at least 1.50 for light with a wavelength
of 400 nm in an aqueous dispersion with a content of the abrasive
grains adjusted to 1.0 mass %, and producing light transmittance of
at least 50%/cm for light with a wavelength of 500 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 1.0
mass %, a mean secondary particle size of the abrasive grains being
1-200 nm.
26. The slurry according to claim 25, wherein the abrasive grains
produce absorbance of not greater than 0.010 for light with a
wavelength of 450-600 nm in an aqueous dispersion with a content of
the abrasive grains adjusted to 0.0065 mass %.
27. The slurry according to claim 25, wherein the tetravalent metal
element hydroxide is obtained by mixing a tetravalent metal element
salt and an alkali solution.
28. The slurry according to claim 25, wherein the tetravalent metal
element is tetravalent cerium.
29. A polishing liquid set comprising constituent components of a
polishing liquid separately stored as a first liquid and a second
liquid, so that the first liquid and the second liquid are mixed to
form the polishing liquid, wherein the first liquid is the slurry
according to claim 25, and the second liquid comprises an additive
and water.
30. The polishing liquid set according to claim 29, wherein the
additive is at least one selected from the group consisting of
vinyl alcohol polymers and derivatives of the vinyl alcohol
polymers.
31. The polishing liquid set according to claim 29, wherein a
content of the additive is 0.01 mass % or greater based on a total
mass of the polishing liquid.
32. A polishing liquid comprising abrasive grains, an additive and
water, the abrasive grains including a tetravalent metal element
hydroxide, and producing absorbance of at least 1.50 for light with
a wavelength of 400 nm in an aqueous dispersion with a content of
the abrasive grains adjusted to 1.0 mass %, and producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %, a mean secondary particle size of the
abrasive grains being 1-200 nm.
33. The polishing liquid according to claim 32, wherein the
abrasive grains produce absorbance of not greater than 0.010 for
light with a wavelength of 450-600 nm in an aqueous dispersion with
a content of the abrasive grains adjusted to 0.0065 mass %.
34. The polishing liquid according to claim 32, wherein the
tetravalent metal element hydroxide is obtained by mixing a
tetravalent metal element salt and an alkali solution.
35. The polishing liquid according to claim 32, wherein the
tetravalent metal element is tetravalent cerium.
36. The polishing liquid according to claim 32, wherein the
additive is at least one selected from the group consisting of
vinyl alcohol polymers and derivatives of the vinyl alcohol
polymers.
37. The polishing liquid according to claim 32, wherein a content
of the additive is 0.01 mass % or greater based on a total mass of
the polishing liquid.
38. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
supplying the slurry according to claim 25 between the abrasive pad
and the film to be polished.
39. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, a step of
mixing the first liquid and the second liquid of the polishing
liquid set according to claim 29 to obtain the polishing liquid,
and a step of polishing at least a portion of the film to be
polished while supplying the polishing liquid between the abrasive
pad and the film to be polished.
40. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
respectively supplying both the first liquid and the second liquid
of the polishing liquid set according to claim 29 between the
abrasive pad and the film to be polished.
41. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
supplying the polishing liquid according to claim 32 between the
abrasive pad and the film to be polished.
42. The polishing method according to claim 38, wherein the film to
be polished includes silicon oxide.
43. The polishing method according to claim 39, wherein the film to
be polished includes silicon oxide.
44. The polishing method according to claim 40, wherein the film to
be polished includes silicon oxide.
45. The polishing method according to claim 41, wherein the film to
be polished includes silicon oxide.
46. The polishing method according to claim 38, wherein a surface
of the film to be polished has irregularities.
47. The polishing method according to claim 39, wherein a surface
of the film to be polished has irregularities.
48. The polishing method according to claim 40, wherein a surface
of the film to be polished has irregularities.
49. The polishing method according to claim 41, wherein a surface
of the film to be polished has irregularities.
50. A slurry comprising abrasive grains and water, the abrasive
grains including a tetravalent metal element hydroxide, and
producing absorbance of at least 1.000 for light with a wavelength
of 290 nm in an aqueous dispersion with a content of the abrasive
grains adjusted to 0.0065 mass %, and producing light transmittance
of at least 50%/cm for light with a wavelength of 500 nm in an
aqueous dispersion with a content of the abrasive grains adjusted
to 1.0 mass %, a mean secondary particle size of the abrasive
grains being 1-200 nm.
51. The slurry according to claim 50, wherein the abrasive grains
produce absorbance of at least 1.50 for light with a wavelength of
400 nm in an aqueous dispersion with a content of the abrasive
grains adjusted to 1.0 mass %.
52. The slurry according to claim 50, wherein the abrasive grains
produce absorbance of not greater than 0.010 for light with a
wavelength of 450-600 nm in an aqueous dispersion with a content of
the abrasive grains adjusted to 0.0065 mass %.
53. The slurry according to claim 50, wherein the tetravalent metal
element hydroxide is obtained by mixing a tetravalent metal element
salt and an alkali solution.
54. The slurry according to claim 50, wherein the tetravalent metal
element is tetravalent cerium.
55. A polishing liquid set comprising constituent components of a
polishing liquid separately stored as a first liquid and a second
liquid, so that the first liquid and the second liquid are mixed to
form the polishing liquid, wherein the first liquid is the slurry
according to claim 50, and the second liquid comprises an additive
and water.
56. The polishing liquid set according to claim 55, wherein the
additive is at least one selected from the group consisting of
vinyl alcohol polymers and derivatives of the vinyl alcohol
polymers.
57. The polishing liquid set according to claim 55, wherein a
content of the additive is 0.01 mass % or greater based on a total
mass of the polishing liquid.
58. A polishing liquid comprising abrasive grains, an additive and
water, the abrasive grains including a tetravalent metal element
hydroxide, and producing absorbance of at least 1.000 for light
with a wavelength of 290 nm in an aqueous dispersion with a content
of the abrasive grains adjusted to 0.0065 mass %, and producing
light transmittance of at least 50%/cm for light with a wavelength
of 500 nm in an aqueous dispersion with a content of the abrasive
grains adjusted to 1.0 mass %, a mean secondary particle size of
the abrasive grains being 1-200 nm.
59. The polishing liquid according to claim 58, wherein the
abrasive grains produce absorbance of at least 1.50 for light with
a wavelength of 400 nm in an aqueous dispersion with a content of
the abrasive grains adjusted to 1.0 mass %.
60. The polishing liquid according to claim 58, wherein the
abrasive grains produce absorbance of not greater than 0.010 for
light with a wavelength of 450-600 nm in an aqueous dispersion with
a content of the abrasive grains adjusted to 0.0065 mass %.
61. The polishing liquid according to claim 58, wherein the
tetravalent metal element hydroxide is obtained by mixing a
tetravalent metal element salt and an alkali solution.
62. The polishing liquid according to claim 58, wherein the
tetravalent metal element is tetravalent cerium.
63. The polishing liquid according to claim 58, wherein the
additive is at least one selected from the group consisting of
vinyl alcohol polymers and derivatives of the vinyl alcohol
polymers.
64. The polishing liquid according to claim 58, wherein a content
of the additive is 0.01 mass % or greater based on a total mass of
the polishing liquid.
65. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
supplying the slurry according to claim 50 between the abrasive pad
and the film to be polished.
66. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, a step of
mixing the first liquid and the second liquid of the polishing
liquid set according to claim 55 to obtain the polishing liquid,
and a step of polishing at least a portion of the film to be
polished while supplying the polishing liquid between the abrasive
pad and the film to be polished.
67. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
respectively supplying both the first liquid and the second liquid
of the polishing liquid set according to claim 55 between the
abrasive pad and the film to be polished.
68. A substrate polishing method comprising: a step of placing a
film to be polished, of a substrate which has the film to be
polished on its surface, so as to face an abrasive pad, and a step
of polishing at least a portion of the film to be polished while
supplying the polishing liquid according to claim 58 between the
abrasive pad and the film to be polished.
69. The polishing method according to claim 65, wherein the film to
be polished includes silicon oxide.
70. The polishing method according to claim 66, wherein the film to
be polished includes silicon oxide.
71. The polishing method according to claim 67, wherein the film to
be polished includes silicon oxide.
72. The polishing method according to claim 68, wherein the film to
be polished includes silicon oxide.
73. The polishing method according to claim 65, wherein a surface
of the film to be polished has irregularities.
74. The polishing method according to claim 66, wherein a surface
of the film to be polished has irregularities.
75. The polishing method according to claim 67, wherein a surface
of the film to be polished has irregularities.
76. The polishing method according to claim 68, wherein a surface
of the film to be polished has irregularities.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese
Application No. JP 2010-260036, filed on Nov. 22, 2010, in the
Japanese Patent Office, the contents of which are incorporated
herein by reference. This application is a continuation of
application Ser. No. 13/582,969, filed on Sep. 5, 2012, the
contents of which are incorporated herein by reference. application
Ser. No. 13/582,969 is a 371 of International Application No.
PCT/JP2011/076822, filed on Nov. 21, 2011.
TECHNICAL FIELD
[0002] The present invention relates to a slurry, a polishing
liquid set, a polishing liquid, a substrate polishing method, and a
substrate. In particular, the invention relates to a slurry, a
polishing liquid set, a polishing liquid, a substrate polishing
method and a substrate, to be used in manufacturing steps for
semiconductor elements.
BACKGROUND ART
[0003] In recent years, machining techniques for increasing density
and micronization are becoming ever more important in manufacturing
steps for semiconductor elements. One such machining technique,
chemical mechanical polishing (CMP), has become an essential
technique in manufacturing steps for semiconductor elements, for
formation of Shallow Trench Isolation (hereunder also referred to
as "STI"), flattening of premetal dielectric layers and interlayer
dielectric films, and formation of plugs and embedded metal
wirings.
[0004] Fumed silica-based polishing liquids are commonly used in
CMP during conventional manufacturing steps for semiconductor
elements, in order to flatten the insulating films such as silicon
oxide films that are formed by methods such as CVD (Chemical Vapor
Deposition) or spin coating methods. Fumed silica-based polishing
liquids are produced by conducting grain growth of abrasive grains
by methods such as thermal decomposition with silicon
tetrachloride, and adjusting the pH. However, such silica-based
polishing liquids have the technical problem of low polishing
rate.
[0005] Incidentally, STI is used for device isolation on integrated
circuits in generation devices starting from design rules of 0.25
.mu.m. In STI formation, CMP is used to remove excess silicon oxide
films after formation on substrates. In order to halt polishing in
CMP, a stopper film with a slow polishing rate is formed under the
silicon oxide film. A silicon nitride film or polysilicon film is
used for the stopper film, preferably with a high polishing
selective ratio of the silicon oxide film with respect to the
stopper film (polishing rate ratio: polishing rate on silicon oxide
film/polishing rate on stopper film). A silica-based polishing
liquid such as a conventional colloidal silica-based polishing
liquid has a low polishing selective ratio of about 3 for the
silicon oxide film with respect to the stopper film, and it tends
not to have properties that can withstand practical use for
STI.
[0006] On the other hand, cerium oxide-based polishing liquids
comprising cerium oxide particles as abrasive grains are used as
polishing liquids for glass surfaces such as photomasks or lenses.
Cerium oxide-based polishing liquids have the advantage of faster
polishing rate compared to silica-based polishing liquids
comprising silica particles as the abrasive grains, or
alumina-based polishing liquids comprising alumina particles as the
abrasive grains. In recent years, polishing liquids for
semiconductors, employing high-purity cerium oxide particles, have
come to be used as cerium oxide-based polishing liquids (see Patent
document 1, for example).
[0007] A variety of properties are required for polishing liquids
such as cerium oxide-based polishing liquids. For example, it is
required to increase the dispersibility of the abrasive grains such
as cerium oxide particles, and to accomplish flat polishing of
substrates with irregularities. Using STI as an example, there is a
demand for improving polishing selective ratios for inorganic
insulating films (such as silicon oxide films) as films to be
polished, with respect to the polishing rates for stopper films
(such as silicon nitride films or polysilicon films). Additives are
often added to polishing liquids to meet this demand. For example,
there is known addition of additives to polishing liquids
containing cerium oxide-based particles, to control the polishing
rates of the polishing liquids and improve the global flatness (see
Patent document 2, for example).
[0008] Incidentally, as demand increases for achieving greater
micronization of wirings in recent manufacturing steps for
semiconductor elements, scratches formed during polishing are
becoming problematic. Specifically, when polishing using
conventional cerium oxide-based polishing liquids, fine scratches
have not posed problems so long as the sizes of the scratches are
smaller than conventional wiring widths, but they can be
problematic when it is attempted to achieve greater micronization
of wirings.
[0009] A solution to this problem is being sought through studying
polishing liquids that employ particles of tetravalent metal
element hydroxides (see Patent document 3, for example). Methods
for producing particles of tetravalent metal element hydroxides are
also being studied (see Patent document 4, for example). Such
techniques are aimed at reducing particle-induced scratches, by
maintaining the chemical action of the tetravalent metal element
hydroxide particles while minimizing their mechanical action.
CITATION LIST
Patent Literature
[0010] [Patent document 1] Japanese Unexamined Patent Application
Publication HEI No. 10-106994 [0011] [Patent document 2] Japanese
Unexamined Patent Application Publication HEI No. 08-022970 [0012]
[Patent Document 3] International Patent Publication No.
WO02/067309 [0013] [Patent document 4] Japanese Unexamined Patent
Application Publication No. 2006-249129
SUMMARY OF INVENTION
Technical Problem
[0014] The techniques described in Patent documents 3 and 4,
however, cannot be said to provide sufficiently high polishing
rate, despite reduction in scratches. Since polishing rate directly
affects the efficiency of the production process, polishing liquids
with higher polishing rates are desired.
[0015] When the polishing liquid contains an additive, the effect
obtained by adding the additive is often offset by reduced
polishing rate, and it has been difficult to achieve polishing rate
together with additional polishing properties.
[0016] The present invention is directed toward solving the
problems described above, and it is an object thereof to provide a
slurry that allows polishing of films at a superior polishing rate
compared to conventional polishing liquids. It is another object of
the invention to provide a slurry that can yield a polishing liquid
that allows polishing of films at a superior polishing rate
compared to conventional polishing liquids while allowing the
addition effects of additives to be maintained.
[0017] It is yet another object of the invention to provide a
polishing liquid set and polishing liquid that allow polishing of
films at a superior polishing rate compared to conventional
polishing liquids while allowing the addition effects of additives
to be maintained.
[0018] It is yet another object of the invention to provide a
polishing method using the slurry, polishing liquid set or
polishing liquid, and a substrate obtained by the method.
Solution to Problem
[0019] The present inventors have conducted diligent research on
slurries using abrasive grains comprising tetravalent metal element
hydroxides, and as a result, they have found that films can be
polished at superior polishing rates compared to conventional
polishing liquids, by using abrasive grains that can increase
photoabsorption (absorbance) for light of a specific wavelength, as
well as increase light transmittance for light of a specific
wavelength, in an aqueous dispersion comprising a specific amount
of the abrasive grains. It was also found that using a polishing
liquid obtained by adding additives to such a slurry allows
polishing of films to be accomplished at superior polishing rate
while maintaining the effects of adding the additives. The present
inventors have also found that by using such a slurry directly for
polishing without adding additives, it is possible to accomplish
polishing of films at superior polishing rate compared to
conventional polishing liquids.
[0020] Specifically, a first embodiment of the slurry of the
invention comprises abrasive grains and water, the abrasive grains
including a tetravalent metal element hydroxide, and producing
absorbance of at least 1.50 for light with a wavelength of 400 nm
in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %, and producing light transmittance of at
least 50%/cm for light with a wavelength of 500 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 1.0
mass %. An aqueous dispersion with a content of the abrasive grains
adjusted to a prescribed value is a liquid comprising the
prescribed amount of abrasive grains and water.
[0021] With a slurry according to the first embodiment, when a
polishing liquid obtained by adding an additive to the slurry is
used, it is possible to accomplish polishing of films at superior
polishing rate compared to conventional polishing liquids, while
maintaining the effects of adding the additives. In addition, it is
also possible to accomplish polishing of films with superior
polishing rate compared to conventional polishing liquids, when a
slurry according to the first embodiment is used for polishing
without addition of additives. Furthermore, with a slurry according
to the first embodiment, it is possible to inhibit formation of
scratches on polished surfaces since the abrasive grains include a
tetravalent metal element hydroxide.
[0022] A second embodiment of the slurry of the invention comprises
abrasive grains and water, the abrasive grains including a
tetravalent metal element hydroxide, and producing absorbance of at
least 1.000 for light with a wavelength of 290 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 0.0065
mass % (65 ppm), and producing light transmittance of at least
50%/cm for light with a wavelength of 500 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 1.0
mass %. Here, "ppm" represents ppm by mass, namely "parts per
million mass".
[0023] With a slurry according to the second embodiment as well,
when a polishing liquid obtained by adding an additive to the
slurry is used, it is possible to accomplish polishing of films at
superior polishing rate compared to conventional polishing liquids,
while maintaining the effect of adding the additives. In addition,
it is also possible to accomplish polishing of films with superior
polishing rate compared to conventional polishing liquids, when a
slurry according to the second embodiment is used for polishing
without addition of additives. Furthermore, with a slurry according
to the second embodiment, it is possible to inhibit formation of
scratches on polished surfaces since the abrasive grains include a
tetravalent metal element hydroxide.
[0024] In a slurry according to the second embodiment, the abrasive
grains preferably produce absorbance of at least 1.50 for light
with a wavelength of 400 nm in an aqueous dispersion with a content
of the abrasive grains adjusted to 1.0 mass %. This allows
polishing of films with even more superior polishing rate compared
to conventional polishing liquids.
[0025] In a slurry according to the invention, the abrasive grains
preferably produce absorbance of not greater than 0.010 for light
with a wavelength of 450-600 nm in an aqueous dispersion with a
content of the abrasive grains adjusted to 0.0065 mass %. This
allows polishing of films with even more superior polishing rate
compared to conventional polishing liquids.
[0026] The tetravalent metal element hydroxide is preferably
obtained by mixing a tetravalent metal element salt and an alkali
solution. This will allow particles with extremely fine particle
sizes to be obtained as abrasive grains, thus further improving the
effect of reducing scratches.
[0027] The tetravalent metal element is preferably tetravalent
cerium. This yields fine particles with high chemical activity as
abrasive grains, and therefore allows polishing of films with even
more superior polishing rate compared to conventional polishing
liquids.
[0028] In addition, the present inventors have found that in a
polishing liquid comprising additives in addition to the
constituent components of the slurry, using abrasive grains that
can increase either or both of the absorbance for light with a
wavelength of 290 nm and the absorbance for light with a wavelength
of 400 nm, and that can increase the light transmittance for light
with a wavelength of 500 nm, as mentioned above, can minimize the
reduction in the polishing rate for films that occurs when
additives are added.
[0029] Specifically, a polishing liquid set according to the
invention comprises the constituent components of a polishing
liquid separately stored as a first liquid and second liquid, so
that the first liquid and second liquid are mixed to form the
polishing liquid, the first liquid being the aforementioned slurry,
and the second liquid comprising an additive and water. With the
polishing liquid set of the invention, it is possible to accomplish
polishing of films at a superior polishing rate compared to
conventional polishing liquids, while maintaining the effects of
adding additives. The polishing liquid set of the invention can
inhibit formation of scratches.
[0030] The additive is preferably at least one selected from the
group consisting of vinyl alcohol polymers and derivatives of the
vinyl alcohol polymers. In this case, the additive will cover the
abrasive grain surfaces to inhibit adhesion of the abrasive grains
onto the surface to be polished, thereby improving the
dispersibility of the abrasive grains and improving the stability
of the polishing liquid. It can also improve the cleanability of
the polished surface.
[0031] The content of the additive is preferably 0.01 mass % or
greater based on the total mass of the polishing liquid. This will
allow polishing of films with even more superior polishing rate
compared to conventional polishing liquids, while allowing the
effect of the additives to be obtained.
[0032] The first embodiment of the polishing liquid of the
invention comprises abrasive grains, an additive and water, the
abrasive grains including a tetravalent metal element hydroxide,
and producing absorbance of at least 1.50 for light with a
wavelength of 400 nm in an aqueous dispersion with a content of the
abrasive grains adjusted to 1.0 mass %, and producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %. With the polishing liquid of the first
embodiment, it is possible to accomplish polishing of films at a
superior polishing rate compared to conventional polishing liquids,
while maintaining the effects of adding additives. Furthermore,
with a polishing liquid according to the first embodiment, it is
possible to inhibit formation of scratches on polished surfaces
since the abrasive grains include a tetravalent metal element
hydroxide.
[0033] The second embodiment of the polishing liquid of the
invention comprises abrasive grains, an additive and water, the
abrasive grains including a tetravalent metal element hydroxide,
and producing absorbance of at least 1.000 for light with a
wavelength of 290 nm in an aqueous dispersion with a content of the
abrasive grains adjusted to 0.0065 mass %, and producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %. With the polishing liquid of the second
embodiment, it is possible to accomplish polishing of films at a
superior polishing rate compared to conventional polishing liquids,
while maintaining the effects of adding additives. Furthermore,
with a polishing liquid according to the second embodiment, it is
possible to inhibit formation of scratches on polished surfaces
since the abrasive grains include a tetravalent metal element
hydroxide.
[0034] In a polishing liquid according to the second embodiment,
the abrasive grains preferably produce absorbance of at least 1.50
for light with a wavelength of 400 nm in an aqueous dispersion with
a content of the abrasive grains adjusted to 1.0 mass %. This
allows polishing of films with even more superior polishing rate
compared to conventional polishing liquids.
[0035] In a polishing liquid according to the invention, the
abrasive grains preferably produce absorbance of not greater than
0.010 for light with a wavelength of 450-600 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 0.0065
mass %. This allows polishing of films with even more superior
polishing rate compared to conventional polishing liquids.
[0036] The tetravalent metal element hydroxide in the polishing
liquid of the invention is preferably obtained by mixing a
tetravalent metal element salt and an alkali solution. This will
allow particles with extremely fine particle sizes to be obtained
as abrasive grains, thus a polishing liquid with an even more
excellent effect of reducing scratches can be obtained.
[0037] The tetravalent metal element in the polishing liquid of the
invention is preferably tetravalent cerium. This yields fine
particles with high chemical activity as abrasive grains, and
therefore allows polishing of films with even more superior
polishing rate compared to conventional polishing liquids.
[0038] The additive in the polishing liquid of the invention is
preferably at least one selected from the group consisting of vinyl
alcohol polymers and derivatives of the vinyl alcohol polymers. In
this case, the additive will cover the abrasive grain surfaces to
inhibit adhesion of the abrasive grains onto the surface to be
polished, thereby improving the dispersibility of the abrasive
grains and improving the stability of the polishing liquid. It can
also improve the cleanability of the polished surface.
[0039] The content of the additive in the polishing liquid of the
invention is preferably 0.01 mass % or greater based on the total
mass of the polishing liquid. This will allow polishing of films
with even more superior polishing rate compared to conventional
polishing liquids, while allowing the effect of the additive to be
obtained.
[0040] The invention further provides a substrate polishing method
using the aforementioned slurry, polishing liquid set or polishing
liquid. The polishing method allows polishing of films at a
superior polishing rate compared to conventional polishing methods.
In addition, the polishing method can inhibit formation of
scratches and yield a substrate with excellent flatness.
[0041] A first embodiment of the polishing method of the invention
is a polishing method employing the aforementioned slurry.
Specifically, the polishing method of the first embodiment
comprises a step of placing a film to be polished, of a substrate
which has the film to be polished on its surface, so as to face an
abrasive pad, and a step of polishing at least a portion of the
film to be polished while supplying the aforementioned slurry
between the abrasive pad and the film to be polished.
[0042] Second and third embodiments of the polishing method of the
invention are polishing methods using the aforementioned polishing
liquid set. These polishing methods can avoid the problems of
abrasive grain aggregation and changes in polishing properties,
which are concerns with prolonged storage after mixture of
additives.
[0043] Specifically, the polishing method of the second embodiment
comprises a step of placing a film to be polished, of a substrate
which has the film to be polished on its surface, so as to face an
abrasive pad, a step of mixing the first liquid and second liquid
of the aforementioned polishing liquid set to obtain a polishing
liquid, and a step of polishing at least a portion of the film to
be polished while supplying the polishing liquid between the
abrasive pad and the film to be polished. The substrate polishing
method of the third embodiment comprises a step of placing a film
to be polished, of a substrate which has the film to be polished on
its surface, so as to face an abrasive pad, and a step of polishing
at least a portion of the film to be polished while respectively
supplying both the first liquid and second liquid of the polishing
liquid set between the abrasive pad and the film to be
polished.
[0044] A fourth embodiment of the polishing method of the invention
is a polishing method employing the aforementioned polishing
liquid. Specifically, the polishing method of the fourth embodiment
comprises a step of placing a film to be polished, of a substrate
which has the film to be polished on its surface, so as to face an
abrasive pad, and a step of polishing at least a portion of the
film to be polished while supplying the aforementioned polishing
liquid between the abrasive pad and the film to be polished.
[0045] The film to be polished preferably includes silicon oxide.
The surface of the film to be polished preferably has
irregularities. These polishing methods allow the characteristics
of the polishing liquid to be adequately exhibited.
[0046] The substrate of the invention is one that has been polished
by the aforementioned polishing method.
Advantageous Effects of Invention
[0047] With the slurry of the invention, it is possible to
accomplish polishing of a film to be polished at a superior
polishing rate compared to a conventional polishing liquid. With
the slurry of the invention, it is also possible to obtain a
polishing liquid that allows polishing of films at a superior
polishing rate compared to conventional polishing liquids, while
maintaining the effects of adding additives. Also, with the
polishing liquid set and polishing liquid of the invention, it is
possible to accomplish polishing of films at a superior polishing
rate compared to conventional polishing liquids, while maintaining
the effects of adding additives. The polishing method of the
invention has excellent throughput since it allows polishing of
films at superior polishing rate, while permitting desired
properties (such as flatness and selectivity) to be obtained when
using additives.
BRIEF DESCRIPTION OF DRAWINGS
[0048] FIG. 1 is a schematic diagram showing the aggregated
condition of abrasive grains when an additive has been added.
[0049] FIG. 2 is a schematic diagram showing the aggregated
condition of abrasive grains when an additive has been added.
[0050] FIG. 3 is a figure showing the relationship between
absorbance for light with a wavelength of 290 nm and polishing
rate.
[0051] FIG. 4 is a figure showing the relationship between
absorbance for light with a wavelength of 400 nm and polishing
rate.
[0052] FIG. 5 is a figure showing the relationship between
absorbance for light with a wavelength of 290 nm and absorbance for
light with a wavelength of 400 nm.
DESCRIPTION OF EMBODIMENTS
[0053] Embodiments of the invention will now be explained in
detail. For this embodiment, the abrasive grains satisfy either or
both of the following conditions (a) and (b).
[0054] (a) Producing absorbance of at least 1.50 for light with a
wavelength of 400 nm in an aqueous dispersion with a content of the
abrasive grains adjusted to 1.0 mass %, and also producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %.
[0055] (b) Producing absorbance of at least 1.000 for light with a
wavelength of 290 nm in an aqueous dispersion with a content of the
abrasive grains adjusted to 0.0065 mass %, and also producing light
transmittance of at least 50%/cm for light with a wavelength of 500
nm in an aqueous dispersion with a content of the abrasive grains
adjusted to 1.0 mass %.
[0056] The present inventors, having found that increasing the
absorbance for light with a wavelength of 290 nm and/or light with
a wavelength of 400 nm is effective for improving the polishing
rate for films to be polished, have further found that increasing
the light transmittance for light with a wavelength of 500 nm,
while also increasing the aforementioned absorbance, is effective
for reliably obtaining an effect of improved polishing rate based
on absorbance as the index. Thus, the present inventors found that
using abrasive grains that satisfy the aforementioned conditions
relating to absorbance and light transmittance allows polishing of
films at a superior polishing rate compared to conventional
polishing liquids. The present inventors also found that a
polishing liquid and slurry satisfying these conditions have a
slight yellowish tint as observed visually, and that a greater
degree of yellowishness of the polishing liquid and slurry is
linked to improved polishing rate.
[0057] <Polishing Liquid>
[0058] The polishing liquid of this embodiment comprises at least
abrasive grains, an additive and water. Each of these constituent
components will now be explained.
[0059] (Abrasive Grains)
[0060] The abrasive grains include a tetravalent metal element
hydroxide. The tetravalent metal element is preferably a rare earth
element, and from the viewpoint of facilitating formation of a
hydroxide suitable for polishing, it is more preferably at least
one kind selected from the group consisting of scandium, yttrium,
lanthanum, cerium, praseodymium, neodymium, promethium, gadolinium,
terbium, dysprosium, holmium, erbium, thulium, ytterbium and
lutetium. The tetravalent metal element is even more preferably
cerium, from the viewpoint of ready availability and a more
superior polishing rate.
[0061] The abrasive grains are preferably composed of a tetravalent
metal element hydroxide, and from the viewpoint of high chemical
activity and a more superior polishing rate, they are more
preferably composed of a hydroxide of tetravalent cerium. The
polishing liquid of this embodiment may also combine other types of
abrasive grains, within ranges that do not impair the properties of
the abrasive grains including the tetravalent metal element
hydroxide. Specifically, abrasive grains of silica, alumina or
zirconia, for example, may be used.
[0062] The content of the tetravalent metal element hydroxide in
the abrasive grains is preferably 50 mass % or greater, more
preferably 60 mass % or greater, even more preferably 70 mass % or
greater, especially more preferably 80 mass % or greater and
extremely preferably 90 mass % or greater, based on the total mass
of the abrasive grains.
[0063] Of the constituent components of the polishing liquid of
this embodiment, the tetravalent metal element hydroxide is
believed to have a major effect on the polishing properties. Thus,
adjusting the content of the tetravalent metal element hydroxide
can improve chemical interaction between the abrasive grains and
surface to be polished, and further improve the polishing rate.
Specifically, the content of the tetravalent metal element
hydroxide is preferably 0.01 mass % or greater, more preferably
0.05 mass % or greater and even more preferably 0.1 mass % or
greater based on the total mass of the polishing liquid, from the
viewpoint of helping to sufficiently exhibit the function of the
tetravalent metal element hydroxide. In addition, the content of
the tetravalent metal element hydroxide is preferably not greater
than 8 mass % and more preferably not greater than 5 mass % based
on the total mass of the polishing liquid, from the viewpoint of
helping to avoid aggregation of the abrasive grains.
[0064] The abrasive grain content is not particularly restricted,
but from the viewpoint of helping to avoid aggregation of the
abrasive grains and allowing the abrasive grains to effectively act
on the surface to be polished to smoothly promote polishing, it is
preferably 0.01-10 mass % and more preferably 0.1-5 mass % based on
the total mass of the polishing liquid.
[0065] The mean secondary particle size of the abrasive grains
(hereunder referred to as "mean particle size", unless otherwise
specified) is preferably 1-200 nm from the viewpoint of obtaining a
more superior polishing rate. Since a smaller mean particle size to
some extent increases the specific surface area of the abrasive
grains that contact with the surface to be polished, and thus
allowing the polishing rate to further improved, the mean particle
size is more preferably not greater than 150 nm, even more
preferably not greater than 100 nm, especially more preferably not
greater than 80 nm and extremely preferably not greater than 50 nm.
Since a larger mean particle size to some extent tends to
facilitate increase in the polishing rate, the mean particle size
is more preferably at least 2 nm and even more preferably at least
5 nm.
[0066] The mean particle size of the abrasive grains can be
measured with a particle size distribution meter based on the
photon correlation method, and specifically, it may be measured
using a Zetasizer 3000HS by Malvern Instruments Ltd. or an N5 by
Beckman Coulter, Inc., for example. Specifically, in a measuring
method using a Zetasizer 3000HS, for example, an aqueous dispersion
with the content of the abrasive grains adjusted to 0.2 mass % is
prepared, and approximately 4 mL (where L represents "liters", same
hereunder) of the aqueous dispersion is poured into a 1 cm-square
cell, and the cell is placed in the apparatus. Measurement is
conducted at 25.degree. C. with a dispersing medium refractive
index of 1.33 and a viscosity of 0.887 mPas, and the value
represented as Z-average Size is read as the mean particle size of
the abrasive grains.
[0067] [Absorbance]
[0068] In regard to condition (a), it is not necessarily fully
understood why an effect of improving polishing rate is obtained by
using abrasive grains that produce absorbance of at least 1.50 for
light with a wavelength of 400 nm in an aqueous dispersion with a
content of the abrasive grains adjusted to 1.0 mass %, but the
present inventors conjecture as follows. Specifically, depending on
the conditions for production of the tetravalent metal element
hydroxide (M(OH).sub.4), it is believed that particles of
M(OH).sub.3X, composed of a tetravalent metal (M.sup.4+), 3
hydroxyl groups (OH.sup.-) and one anion (X.sup.-), are produced
for some of the abrasive grains. In M(OH).sub.3X, the
electron-withdrawing anion (X.sup.-) acts to improve the reactivity
of the hydroxyl groups, and an increasing abundance of M(OH).sub.3X
is thought to lead to improved polishing rate. Also, since the
M(OH).sub.3X particles absorb light with a wavelength of 400 nm,
presumably an increased abundance of M(OH).sub.3X causes increased
absorbance for light with a wavelength of 400 nm, and improves the
polishing rate.
[0069] The absorption peak of M(OH).sub.3X at a wavelength of 400
nm has been confirmed to be much lower than the absorption peak at
a wavelength of 290 nm. In this regard, as a result of studying
degrees of absorbance using aqueous dispersions with relatively
high abrasive grain contents of 1.0 mass %, which allow absorbance
to be easily detected as high absorbance, the present inventors
have found that the effect of improving polishing rate is superior
when using abrasive grains that produce absorbance of at least 1.50
for light with a wavelength of 400 nm in the aqueous dispersion.
Incidentally, since it is thought that the absorbance for light
with a wavelength of 400 nm derives from the abrasive grains, as
explained above, naturally it would not be possible to polish a
film at a superior polishing rate with a polishing liquid
comprising a substance (such as a pigment component exhibiting a
yellow color) that produces absorbance of at least 1.50 for light
with a wavelength of 400 nm, instead of abrasive grains that
produce absorbance of at least 1.50 for light with a wavelength of
400 nm.
[0070] The absorbance for light with a wavelength of 400 nm is
preferably at least 2.00, more preferably at least 2.50 and even
more preferably at least 3.00, from the viewpoint of allowing
polishing of films at an even more superior polishing rate. The
upper limit for the absorbance for light with a wavelength of 400
nm is not particularly restricted, but is preferably 10.0, for
example.
[0071] In regard to condition (b), it is not necessarily fully
understood why an effect of improving polishing rate is obtained by
using abrasive grains that produce absorbance of at least 1.000 for
light with a wavelength of 290 nm in an aqueous dispersion with a
content of the abrasive grains adjusted to 0.0065 mass %, but the
present inventors conjecture as follows. Specifically, particles of
M(OH).sub.3X that are produced depending on the production
conditions for the tetravalent metal element hydroxide
(M(OH).sub.4) have a calculated absorption peak at a wavelength of
about 290 nm, and for example, particles composed of
Ce.sup.4+(OH.sup.-).sub.3NO.sub.3.sup.- have an absorption peak at
a wavelength of 290 nm Consequently, it is believed that the
polishing rate is improved in accordance with the increase in
absorbance for light with a wavelength of 290 nm due to the
increase in the abundance of M(OH).sub.3X.
[0072] The absorbance for light with a wavelength of about 290 nm
tends to be detected to a greater degree as the measuring limit is
exceeded. In this regard, as a result of studying degrees of
absorbance using aqueous dispersions with relatively low abrasive
grain contents of 0.0065 mass %, which allow absorbance to be
easily detected as low absorbance, the present inventors have found
that the effect of improving polishing rate is superior when using
abrasive grains that produce absorbance of at least 1.000 for light
with a wavelength of 290 nm in the aqueous dispersion. The present
inventors have also found that, apart from light with a wavelength
of about 400 nm, which when absorbed by an absorbing substance
tends to cause the absorbing substance to exhibit a yellow color,
higher absorbance of abrasive grains for light with a wavelength of
about 290 nm produces deeper yellowishness in a polishing liquid or
slurry employing such abrasive grains. Specifically, the present
inventors found that the absorbance for light with a wavelength of
290 nm in an aqueous dispersion with an abrasive grain content of
0.0065 mass % and the absorbance for light with a wavelength of 400
nm in an aqueous dispersion with an abrasive grain content of 1.0
mass % are very well correlated, as shown in FIG. 5 described
below.
[0073] The absorbance for light with a wavelength of 290 nm is
preferably at least 1.050, more preferably at least 1.100, even
more preferably at least 1.200 and especially preferably at least
1.300, from the viewpoint of allowing polishing of films at an even
more superior polishing rate. The upper limit for the absorbance
for light with a wavelength of 290 nm is not particularly
restricted, but is preferably 10.00, for example.
[0074] From the viewpoint of polishing of films at an even more
superior polishing rate with a polishing liquid of this embodiment,
the abrasive grains are preferably ones that produce absorbance of
at least 1.50 for light with a wavelength of 400 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 1.0
mass %, while also producing absorbance of at least 1.000 for light
with a wavelength of 290 nm in an aqueous dispersion with a content
of the abrasive grains adjusted to 0.0065 mass %.
[0075] Also, the aforementioned metal hydroxides (M(OH).sub.4 and
M(OH).sub.3X) tend not to exhibit absorption for light with
wavelengths of 450 nm and greater, and especially for light with
wavelengths of 450-600 nm. Therefore, from the viewpoint of
minimizing adverse effects on polishing by the presence of
impurities, the abrasive grains preferably produce absorbance of
not greater than 0.010 for light with a wavelength of 450-600 nm in
an aqueous dispersion with a content of the abrasive grains
adjusted to 0.0065 mass % (65 ppm). Specifically, the absorbance
preferably does not exceed 0.010 for all light within a wavelength
range of 450-600 nm in an aqueous dispersion with a content of the
abrasive grains adjusted to 0.0065 mass %. The absorbance for light
with a wavelength of 450-600 nm is more preferably not greater than
0.005 and even more preferably not greater than 0.001. The lower
limit for the absorbance for light with a wavelength of 450-600 nm
is preferably 0.
[0076] The absorbance in an aqueous dispersion can be measured, for
example, using a spectrophotometer (model name: U3310) by Hitachi,
Ltd. Specifically, an aqueous dispersion with a content of the
abrasive grains adjusted to 0.0065 mass % or 1.0 mass % is prepared
as a measuring sample. Approximately 4 mL of the measuring sample
is placed in a 1 cm-square cell, and the cell is set in the
apparatus. Spectrophotometry is then conducted in a wavelength
range of 200-600 nm, and the absorbance is judged from the obtained
chart.
[0077] If absorbance of at least 1.000 is exhibited when the
absorbance for light with a wavelength of 290 nm is measured with
excessive dilution so that the abrasive grain content in the
measuring sample is lower than 0.0065 mass %, it is clear that the
absorbance will also be at least 1.000 when the abrasive grain
content is 0.0065 mass %. Thus, the absorbance may be screened by
measuring the absorbance using an aqueous dispersion excessively
diluted so that the abrasive grain content is lower than 0.0065
mass %.
[0078] Screening of the absorbance may also be accomplished by
assuming that if absorbance of at least 1.50 is exhibited when the
absorbance for light with a wavelength of 400 nm is measured with
excessive dilution so that the abrasive grain content is lower than
1.0 mass %, the absorbance will also be at least 1.50 when the
abrasive grain content is 1.0 mass %. Also, screening of the
absorbance may be accomplished by assuming that if absorbance of
not greater than 0.010 is exhibited when the absorbance for light
with a wavelength of 450-600 nm is measured with dilution so that
the abrasive grain content is greater than 0.0065 mass %, the
absorbance will also be not greater than 0.010 when the abrasive
grain content is 0.0065 mass %.
[0079] [Light Transmittance]
[0080] The polishing liquid of this embodiment has high
transparency for visible light (it is visually transparent or
nearly transparent). Specifically, the abrasive grains of the
polishing liquid of this embodiment produce light transmittance of
at least 50%/cm for light with a wavelength of 500 nm in an aqueous
dispersion with a content of the abrasive grains adjusted to 1.0
mass %. This makes it possible to reliably obtain an effect of
improving the polishing rate based on absorbance as the index, and
since reduction in polishing rate by addition of additives can be
inhibited, it becomes easier to obtain other properties while
maintaining polishing rate. From this viewpoint, the light
transmittance is preferably at least 60%/cm, more preferably at
least 70%/cm, even more preferably at least 80%/cm and especially
preferably at least 90%/cm. The upper limit for the light
transmittance is 100%/cm.
[0081] Although the reason for which reduction in polishing rate
can be inhibited by adjusting the light transmittance of the
abrasive grains is not thoroughly understood, the present inventors
conjecture as follows. The action exhibited as abrasive grains by
the tetravalent metal element hydroxide particles, such as cerium
hydroxide particles, is thought to depend more on chemical action
than on mechanical action. Therefore, the number of abrasive grains
is believed to contribute to the polishing rate more than the sizes
of the abrasive grains.
[0082] In the case of low light transmittance in an aqueous
dispersion having an abrasive grain content of 1.0 mass %, the
abrasive grains present in the aqueous dispersion presumably have
relatively more particles with large particle sizes (hereunder
referred to as "coarse particles"). When an additive (such as
polyvinyl alcohol (PVA)) is added to a polishing liquid comprising
such abrasive grains, other particles aggregate around the coarse
particles as nuclei, as shown in FIG. 1. As a result, the number of
abrasive grains acting on the surface to be polished per unit area
(the effective abrasive grain number) is reduced and the specific
surface area of the abrasive grains contacting with the surface to
be polished is reduced, whereby presumably reduction in the
polishing rate occur.
[0083] Conversely, in the case of high light transmittance in an
aqueous dispersion having an abrasive grain content of 1.0 mass %,
the abrasive grains present in the aqueous dispersion presumably
are in the state of fewer "coarse particles". In such cases with a
low abundance of coarse particles, few coarse particles are
available as nuclei for aggregation, and therefore aggregation
between abrasive grains is inhibited or the sizes of the aggregated
particles are smaller than the aggregated particles shown in FIG.
1, even when an additive (such as polyvinyl alcohol) is added to
the polishing liquid, as shown in FIG. 2. As a result, the number
of abrasive grains acting on the surface to be polished per unit
area (the effective abrasive grain number) is maintained and the
specific surface area of the abrasive grains contacting with the
surface to be polished is maintained, whereby presumably reduction
in the polishing rate does not easily occur.
[0084] According to research by the present inventors, it was found
that even among polishing liquids having identical particle sizes
to each other as measured with a common particle size measuring
apparatus, some may be visually transparent (high light
transmittance) and some visually turbid (low light transmittance).
This suggests that coarse particles, which produce the action
described above, contribute to reduced polishing rate even in
slight amounts that cannot be detected with common particle size
measuring apparatuses.
[0085] It was also found that even repeated filtration to reduce
the amount of coarse particles does not significantly improve the
phenomenon of reduced polishing rate with addition of additives,
and in some cases the aforementioned effect of improving polishing
rate due to absorbance is not adequately exhibited. The present
inventors found that this problem can be overcome by using abrasive
grains with high light transmittance in aqueous dispersion, by
modifying the method for producing the abrasive grains, for
example.
[0086] The light transmittance is the transmittance for light with
a wavelength of 500 nm. The light transmittance is measured with a
spectrophotometer, and specifically, it is measured with an U3310
Spectrophotometer (apparatus name) by Hitachi, Ltd., for
example.
[0087] As a more specific measuring method, an aqueous dispersion
with a content of the abrasive grains adjusted to 1.0 mass % is
prepared as a measuring sample. Approximately 4 mL of the measuring
sample is placed in a 1 cm-square cell, the cell is set in the
apparatus, and measurement is conducted. If the light transmittance
is at least 50%/cm in an aqueous dispersion having an abrasive
grain content of greater than 1.0 mass %, it is clear that the
light transmittance will also be at least 50%/cm when the measuring
sample is diluted to 1.0 mass %. Therefore, using an aqueous
dispersion with an abrasive grain content of greater than 1.0 mass
% allows screening of the light transmittance by a convenient
method.
[0088] [Method for Production of Abrasive Grains]
[0089] The tetravalent metal element hydroxide is preferably
produced by mixing a tetravalent metal element salt (metal salt)
and an alkali solution. This will allow particles with extremely
fine particle sizes to be obtained, whereby a polishing liquid with
an even more excellent effect of reducing scratches can be
obtained. This method is disclosed in Patent document 4, for
example. The tetravalent metal element hydroxide may be obtained by
mixing an aqueous solution of a tetravalent metal element salt and
an alkali solution. Examples of tetravalent metal element salts
include M(SO.sub.4).sub.2, M(NH.sub.4).sub.2(NO.sub.3).sub.6 and
M(NH.sub.4).sub.4(SO.sub.4).sub.4, where M is the metal.
[0090] The means for adjusting the absorbance or light
transmittance may be optimization of the method for producing the
tetravalent metal element hydroxide. The method of altering the
absorbance for light with a wavelength of 400 nm or a wavelength of
290 nm may be, specifically, selecting the base in the alkali
solution, adjusting the starting concentrations of the metal salt
aqueous solution and the alkali solution, or adjusting the mixing
rate of the metal salt aqueous solution and the alkali solution.
The method of altering the light transmittance for light with a
wavelength of 500 nm may be, specifically, adjusting the starting
concentrations of the metal salt aqueous solution and the alkali
solution, adjusting the mixing rate of the metal salt aqueous
solution and the alkali solution, adjusting the stirring speed for
mixing, or adjusting the liquid temperature during mixing.
[0091] In order to increase the absorbance for light with a
wavelength of 400 nm or a wavelength of 290 nm, and to increase the
light transmittance for light with a wavelength of 500 nm, the
method for producing the tetravalent metal element hydroxide is
preferably more "moderate". A method of controlling the absorbance
and light transmittance will now be explained in greater
detail.
[0092] {Alkali Solution}
[0093] The base to be used as an alkaline source in the alkali
solution (such as an aqueous alkali solution) is not particularly
restricted, but specific examples include organic bases such as
ammonia, triethylamine, pyridine, piperidine, pyrrolidine,
imidazole and chitosan and inorganic bases such as potassium
hydroxide and sodium hydroxide. These bases may be used alone or in
combinations of two or more.
[0094] From the viewpoint of further inhibiting rapid reaction and
further increasing the absorbance for light with a wavelength of
400 nm and a wavelength of 290 nm, the alkali solution used is
preferably an alkali solution exhibiting weak basicity. Of the
bases mentioned above, nitrogen-containing heterocyclic organic
bases are preferred, pyridine, piperidine, pyrrolidine and
imidazole are more preferred, and pyridine and imidazole are even
more preferred.
[0095] {Concentration}
[0096] The absorbance for light with a wavelength of 400 nm or a
wavelength of 290 nm, and the light transmittance for light with a
wavelength of 500 nm, can be altered by controlling the starting
concentrations of the metal salt aqueous solution and the alkali
solution. Specifically, the absorbance and light transmittance tend
to be higher with reduced progression of the reaction between the
acid and alkali per unit time, and for example, the absorbance and
light transmittance tend to be higher with increased concentration
of the metal salt aqueous solution, while the absorbance and light
transmittance tend to be higher with reduced concentration of the
alkali solution. When a nitrogen-containing heterocyclic organic
base or the like exhibiting weak basicity is used as the base, the
alkali solution concentration is preferably higher than when
ammonia is used, from the viewpoint of productivity.
[0097] From the viewpoint of a gentler rise in pH, the metal salt
concentration of the tetravalent metal element salt in the metal
salt aqueous solution is preferably 0.010 mol/L or greater, more
preferably 0.020 mol/L or greater and even more preferably 0.030
mol/L or greater, based on the total metal salt aqueous solution.
There is no particular restriction on the upper limit for the metal
salt concentration of the tetravalent metal element, but for easier
manageability, it is preferably not greater than 1.000 mol/L based
on the total metal salt aqueous solution.
[0098] From the viewpoint of a gentler rise in pH, the alkaline
concentration of the alkali solution is preferably not greater than
15.0 mol/L, more preferably not greater than 12.0 mol/L and even
more preferably not greater than 10.0 mol/L or greater, based on
the total alkali solution. There is no particular restriction on
the lower limit for the alkali solution, but from the viewpoint of
productivity, it is preferably at least 0.001 mol/L based on the
total alkali solution.
[0099] The alkaline concentration of the alkali solution is
preferably adjusted as appropriate depending on the type of alkali
selected. For example, for an alkali with a pKa in the range of 20
or greater, the alkaline concentration is preferably not greater
than 0.1 mol/L, more preferably not greater than 0.05 mol/L and
even more preferably not greater than 0.01 mol/L based on the total
alkali solution, from the viewpoint of a gentler rise in pH. There
is no particular restriction on the lower limit for the alkali
solution, but from the viewpoint of productivity, it is preferably
at least 0.001 mol/L based on the total alkali solution.
[0100] For an alkali with a pKa in the range of 12 or greater and
less than 20, the alkaline concentration is preferably not greater
than 1.0 mol/L, more preferably not greater than 0.5 mol/L and even
more preferably not greater than 0.1 mol/L based on the total
alkali solution, from the viewpoint of a gentler rise in pH. There
is no particular restriction on the lower limit for the alkali
solution, but from the viewpoint of productivity, it is preferably
at least 0.01 mol/L based on the total alkali solution.
[0101] For an alkali with a pKa in the range of less than 12, the
alkaline concentration is preferably not greater than 15.0 mol/L,
more preferably not greater than 10.0 mol/L and even more
preferably not greater than 5.0 mol/L based on the total alkali
solution, from the viewpoint of a gentler rise in pH. There is no
particular restriction on the lower limit for the alkali solution,
but from the viewpoint of productivity, it is preferably at least
0.1 mol/L based on the total alkali solution.
[0102] Specific examples of alkalis with pKa values in these ranges
include 1,8-diazabicyclo[5.4.0]undec-7-ene (pKa: 25) as an alkali
with a pKa of 20 or greater, potassium hydroxide (pKa: 16) and
sodium hydroxide (pKa: 13) as alkalis with a pKa of 12 or greater
and less than 20, and ammonia (pKa: 9) and imidazole (pKa: 7) as
alkalis with a pKa of less than 12. The pKa value of the alkali
used is restricted by adjustment to an appropriate concentration,
without being particularly limited thereto.
[0103] {Mixing Rate}
[0104] The absorbance for light with a wavelength of 400 nm or a
wavelength of 290 nm, and the light transmittance for light with a
wavelength of 500 nm, can be altered by controlling the mixing rate
of the metal salt aqueous solution and the alkali solution.
Specifically, the absorbance tends to be higher when the mixing
rate is increased, while the absorbance tends to be lower when the
mixing rate is decreased. Also, the light transmittance for light
with a wavelength of 500 nm tends to be higher when the mixing rate
is increased, while the light transmittance tends to be lower when
the mixing rate is decreased.
[0105] From the viewpoint of absorbance and light transmittance,
there is no particular restriction on the lower limit for the
mixing rate, but it is preferably at least 0.1 ml/min from the
viewpoint of shortening the mixing time to increase efficiency. The
upper limit for the mixing rate is preferably not greater than 100
ml/min, from the viewpoint of minimizing rapid reaction. However,
the mixing rate is preferably determined according to the starting
concentrations, and specifically, the mixing rate is preferably
decreased when the starting concentrations are high, for
example.
[0106] {Stirring Speed}
[0107] By controlling the stirring speed for mixing of the metal
salt aqueous solution and the alkali solution, it is possible to
alter the light transmittance for light with a wavelength of 500
nm. Specifically, the light transmittance tends to be higher when
the stirring speed is increased, while the light transmittance
tends to be lower when the stirring speed is decreased.
[0108] As the stirring speed, for example, in the case of a mixing
scale in which a stirring blade with a total length of 5 cm is used
for stirring of a 2 L solution, the rotational speed of the
stirring blade is preferably 50-1000 rpm. The upper limit for the
rotational speed is preferably not greater than 1000 rpm, more
preferably not greater than 800 rpm and even more preferably not
greater than 500 rpm, from the viewpoint of preventing excessive
increase in the liquid level. In the case of modifying (for
example, enlarging) the mixing scale, the optimal stirring speed
will be changed, but so long as it is within the range of about
50-1000 rpm, it is possible to obtain a polishing liquid with
satisfactory light transmittance.
[0109] {Liquid Temperature (Synthesis Temperature)}
[0110] By controlling the liquid temperature for mixing of the
metal salt aqueous solution and the alkali solution, it is possible
to alter the light transmittance for light with a wavelength of 500
nm. Specifically, the light transmittance tends to be higher when
the liquid temperature is reduced, while the light transmittance
tends to be lower when the liquid temperature is increased.
[0111] The liquid temperature is preferably within the range of
0-60.degree. C., as the temperature in the reaction system read
upon placing a thermometer in the reaction system. The upper limit
for the liquid temperature is preferably not higher than 60.degree.
C., more preferably not higher than 50.degree. C., even more
preferably not higher than 40.degree. C., especially preferably not
higher than 30.degree. C. and especially preferably not higher than
25.degree. C., from the viewpoint of preventing rapid reaction.
From the viewpoint of facilitating progression of the reaction, the
lower limit for the liquid temperature is preferably 0.degree. C.
or higher, more preferably 5.degree. C. or higher, even more
preferably 10.degree. C. or higher, especially more preferably
15.degree. C. or higher and extremely preferably 20.degree. C. or
higher.
[0112] The tetravalent metal element salt in the metal salt aqueous
solution and the base of the alkali solution are preferably reacted
at a fixed synthesis temperature T (for example, in a temperature
range of synthesis temperature T.+-.3.degree. C.). The method of
adjusting the synthesis temperature is not particularly restricted,
and for example, it may be a method in which a container holding
either the metal salt aqueous solution or the alkali solution is
placed in a water tank filled with water, and the metal salt
aqueous solution and alkali solution are mixed while adjusting the
water temperature of the water tank using a Coolnics Circulator
(product name: Cooling Thermopump CTP 101 by Eyela) as the external
circulation apparatus.
[0113] The tetravalent metal element hydroxide prepared as
described above may include impurities, but the impurities can be
removed, for example, by a method of repeating solid-liquid
separation by centrifugal separation or the like. This can adjust
the absorbance for light with a wavelength of 450-600 nm.
[0114] (Additives)
[0115] The polishing liquid of this embodiment is suitable for use
in polishing of substrates with inorganic insulating films because
it allows an especially superior polishing rate to be obtained for
inorganic insulating films (for example, silicon oxide films), but
appropriate selection of additives will allow high levels to be
achieved for both the polishing rate and the polishing properties
other than polishing rate.
[0116] An additive used may be a known additive without any
particular restrictions, such as a dispersing agent that increases
the dispersibility of the abrasive grains, a polishing rate
improver that improves the polishing rate, a flattening agent (a
flattening agent that reduces irregularities on the polished
surface after polishing, or a global flattening agent that improves
the global flatness of the substrate after polishing), or a
selection ratio improver that improves the polishing selective
ratio of the inorganic insulating film with respect to stopper
films such as silicon nitride films or polysilicon films.
[0117] Examples of dispersing agents include vinyl alcohol polymers
and their derivatives, betaine, lauryl betaine, lauryldimethylamine
oxide, and the like. Examples of polishing rate improvers include
.beta.-alanine betaine, stearyl betaine, and the like. Examples of
flattening agents that reduce irregularities on polished surfaces
include ammonium lauryl sulfate, triethanolamine polyoxyethylene
alkyl ether sulfate, and the like. Examples of global flattening
agents include polyvinylpyrrolidone, polyacrolein, and the like.
Examples of selection ratio improvers include polyethyleneimine,
polyallylamine, chitosan, and the like. These may be used alone or
in combinations of two or more.
[0118] The polishing liquid of this embodiment preferably comprises
a vinyl alcohol polymer or a derivative thereof as an additive.
However, vinyl alcohol, which is a monomer of polyvinyl alcohol,
generally tends not to exist alone as stable compounds. Therefore,
polyvinyl alcohol is usually obtained by polymerization of a vinyl
carboxylate monomer such as vinyl acetate monomer to obtain
poly(vinyl carboxylate), followed by saponification (hydrolysis).
Thus, a vinyl alcohol polymer obtained using vinyl acetate monomer
as the starting material, for example, has --OCOCH.sub.3 and
hydrolyzed --OH groups as functional groups in the molecule, and
the proportion of --OH groups is defined as the saponification
degree. That is, a vinyl alcohol polymer whose saponification
degree is not 100% has a structure which is essentially a copolymer
of vinyl acetate and vinyl alcohol. It may also be one in which a
vinyl carboxylate monomer such as vinyl acetate monomer and another
vinyl group-containing monomer (for example, ethylene, propylene,
styrene or vinyl chloride) are copolymerized, and all or some of
the portions derived from the vinyl carboxylate monomer are
saponified. In the invention, all of these are collectively
referred to as "vinyl alcohol polymers", and a "vinyl alcohol
polymer" is ideally a polymer having the following structural
formula.
##STR00001##
(wherein n represents a positive integer)
[0119] A "derivative" of a vinyl alcohol polymer is defined as a
term including a derivative of a homopolymer of vinyl alcohol (that
is, a polymer with a saponification degree of 100%), and
derivatives of copolymers of vinyl alcohol monomer and other vinyl
group-containing monomers (for example, ethylene, propylene,
styrene, vinyl chloride or the like).
[0120] Examples of the aforementioned derivatives include polymers
having a portion of the hydroxyl groups substituted with amino,
carboxyl, ester groups or the like, and polymers having a portion
of the hydroxyl groups modified. Examples of such derivatives
include reactive polyvinyl alcohols (for example, GOHSEFIMER
(registered trademark) Z by Nippon Synthetic Chemical Industry Co.,
Ltd.), cationized polyvinyl alcohols (for example, GOHSEFIMER
(registered trademark) K by Nippon Synthetic Chemical Industry Co.,
Ltd.), anionized polyvinyl alcohols (for example, GOHSERAN
(registered trademark) L and GOHSENOL (registered trademark) T by
Nippon Synthetic Chemical Industry Co., Ltd.), and hydrophilic
group-modified polyvinyl alcohols (for example, ECOMATI by Nippon
Synthetic Chemical Industry Co., Ltd.).
[0121] As mentioned above, vinyl alcohol polymers and their
derivatives function as abrasive grain dispersing agents, and have
effects of improving polishing liquid stability. It is believed
that interaction between the hydroxyl group of the vinyl alcohol
polymer or its derivative and tetravalent metal element hydroxide
particles can inhibit aggregation of the abrasive grains and
minimize changes in particle size of the abrasive grains in the
polishing liquid, thereby improving stability. Also, by using the
vinyl alcohol polymer or its derivative in combination with
tetravalent metal element hydroxide particles, it is possible to
increase the polishing selective ratio for inorganic insulating
films (for example, silicon oxide films) with respect to stopper
films (for example, silicon nitride films and polysilicon films)
(i.e., polishing rate for inorganic insulating films/polishing rate
for stopper films). In addition, a vinyl alcohol polymer and its
derivative can also improve the flatness of the polished surface
after polishing, and can prevent adhesion of abrasive grains on the
polished surface (cleanability improver).
[0122] The saponification degree of the vinyl alcohol polymer is
preferably not greater than 95 mol % from the viewpoint of further
increasing the polishing selective ratio for inorganic insulating
films with respect to stopper films. From the same viewpoint, the
saponification degree is more preferably not greater than 90 mol %,
even more preferably not greater than 88 mol %, especially
preferably not greater than 85 mol %, extremely preferably not
greater than 83 mol % and very preferably not greater than 80 mol
%.
[0123] There are no particular restrictions on the lower limit for
the saponification degree, but from the viewpoint of excellent
solubility in water, it is preferably at least 50 mol %, more
preferably at least 60 mol % and even more preferably at least 70
mol %. The saponification degree of the vinyl alcohol polymer can
be measured according to JIS K 6726 (Polyvinyl alcohol test
method).
[0124] There are no particular restrictions on the upper limit for
the mean polymerization degree (weight-average molecular weight) of
the vinyl alcohol polymer, but from the viewpoint of further
inhibiting reduction in polishing rate for inorganic insulating
films (for example, silicon oxide films), it is preferably not
greater than 3000, more preferably not greater than 2000 and even
more preferably not greater than 1000.
[0125] From the viewpoint of further increasing the polishing
selective ratio for inorganic insulating films with respect to
stopper films, the lower limit for the mean polymerization degree
is preferably at least 50, more preferably at least 100 and even
more preferably at least 150. The mean polymerization degree of the
vinyl alcohol polymer can be measured according to JIS K 6726
(Polyvinyl alcohol test method).
[0126] In order to adjust the polishing selective ratio for
inorganic insulating films with respect to stopper films, and the
flatness of polished substrates, a combination of multiple polymers
with different saponification degrees or mean polymerization
degrees may be used as the vinyl alcohol polymer or its derivative.
In such cases, preferably the saponification degree of at least one
vinyl alcohol polymer and its derivative is not greater than 95 mol
%, and from the viewpoint of further improving the polishing
selective ratio, the average saponification degree calculated from
each saponification degree and the mixing ratio is preferably not
greater than 95 mol %. The preferred range for these saponification
degrees is the same range specified above.
[0127] From the viewpoint of more efficiently obtaining the effects
of additives, the additive content is preferably 0.01 mass % or
greater, more preferably 0.1 mass % or greater and even more
preferably 1.0 mass % or greater, based on the total mass of the
polishing liquid. From the viewpoint of further inhibiting
reduction in the polishing rate for inorganic insulating films, the
additive content is preferably not greater than 10 mass %, more
preferably not greater than 5.0 mass % and even more preferably not
greater than 3.0 mass % based on the total mass of the polishing
liquid.
[0128] (Water)
[0129] There are no particular restrictions on the water used in
the polishing liquid of this embodiment, but deionized water or
ultrapure water is preferred. The water content is not particularly
restricted and may be the remaining portion of the polishing liquid
excluding the other constituent components.
[0130] The method of dispersing the abrasive grains in water is not
particularly restricted, and specifically, a dispersion method
employing stirring, a homogenizer, an ultrasonic disperser or a wet
ball mill may be used.
[0131] [Polishing Liquid Properties]
[0132] The pH of the polishing liquid is preferably 2.0-9.0, for a
satisfactory relationship of the surface potential of the abrasive
grains with respect to the surface potential of the surface to be
polished, to facilitate action of the abrasive grains on the
surface to be polished, and thereby obtaining a more superior
polishing rate. From the viewpoint of stabilizing the pH of the
polishing liquid and minimizing problems such as aggregation of the
abrasive grains due to addition of a pH stabilizer, the lower limit
for the pH is preferably at least 2.0, more preferably at least 4.0
and even more preferably at least 5.0. Also, from the viewpoint of
excellent dispersibility of the abrasive grains and obtaining a
more superior polishing rate, the upper limit for the pH is
preferably not greater than 9.0, more preferably not greater than
7.5 and even more preferably not greater than 6.5.
[0133] The pH of the polishing liquid can be measured with a pH
meter (for example, a Model PH81 by Yokogawa Electric Corp.). The
pH is measured by placing an electrode in the polishing liquid
after 2-point calibration using standard buffer (phthalate pH
buffer: pH 4.01 (25.degree. C.), neutral phosphate pH buffer: pH
6.86 (25.degree. C.)), and then measuring the value upon
stabilization after an elapse of 2 minutes or more.
[0134] Any known pH regulator may be used to adjust the pH of the
polishing liquid, without any particular restrictions, and
specifically, there may be used inorganic acids such as phosphoric
acid, sulfuric acid or nitric acid, organic acids such as formic
acid, acetic acid, propionic acid, maleic acid, phthalic acid,
citric acid or succinic acid, amines such as ethylenediamine,
toluidine, piperazine, histidine or aniline, and
nitrogen-containing heterocyclic compounds such as pyridine,
imidazole, triazole or pyrazole.
[0135] A pH stabilizer is an additive for adjustment to a
prescribed pH, and it is preferably a buffer component. The buffer
component is preferably a compound with a pKa in the range of
.+-.1.5, and more preferably a compound with a pKa in the range of
.+-.1.0, relative to the prescribed pH. Such compounds include
amino acids such as glycine, arginine, lysine, asparagine, aspartic
acid and glutamic acid, amines such as ethylenediamine,
2-aminopyridine, 3-aminopyridine, picolinic acid, histidine,
piperazine, morpholine, piperidine, hydroxylamine and aniline,
nitrogen-containing heterocyclic compounds such as pyridine,
imidazole, benzimidazole, pyrazole, triazole and benzotriazole, and
carboxylic acids such as formic acid, acetic acid, propionic acid,
malonic acid, succinic acid, glutaric acid, adipic acid, maleic
acid, fumaric acid, phthalic acid, citric acid, lactic acid and
benzoic acid.
[0136] <Slurry>
[0137] The slurry of this embodiment may be used directly for
polishing, or it may be used as a slurry in a "two-pack type
polishing liquid", having the constituent components of the
polishing liquid separated into a slurry and an additive solution.
According to this embodiment, the polishing liquid and the slurry
differ in the presence or absence of additives, and the polishing
liquid is obtained by adding the additives to the slurry.
[0138] The slurry of this embodiment comprises at least the same
abrasive grains as the polishing liquid of this embodiment, and
water. For example, the abrasive grains include a tetravalent metal
element hydroxide, and the mean secondary particle size of the
abrasive grains is the same as the abrasive grains used in the
polishing liquid of this embodiment.
[0139] In the slurry of this embodiment, the abrasive grains
satisfy either or both of conditions (a) and (b) relating to the
absorbance and light transmittance. Also, the abrasive grains
preferably produce absorbance of not greater than 0.010 for light
with a wavelength of 450-600 nm in an aqueous dispersion with a
content of the abrasive grains adjusted to 0.0065 mass %. These
preferred ranges and measuring methods for the absorbance and light
transmittance are the same as for the polishing liquid of this
embodiment.
[0140] In the slurry of this embodiment, the abrasive grain content
is not particularly restricted, but it is preferably not greater
than 15 mass % based on the total mass of the slurry, from the
viewpoint of helping to avoid aggregation of the abrasive grains.
The abrasive grain content is preferably 0.01 mass % or greater
based on the total mass of the slurry, from the viewpoint of
allowing the mechanical effect of the abrasive grains to be easily
obtained.
[0141] Of the constituent components of the slurry of this
embodiment, the tetravalent metal element hydroxide is believed to
have a major effect on the polishing properties. The tetravalent
metal element hydroxide content is preferably not greater than 10
mass % based on the total mass of the slurry, from the viewpoint of
helping to avoid aggregation of the abrasive grains, as well as
achieving satisfactory chemical interaction with the surface to be
polished and thereby allowing further improvement in the polishing
rate. The tetravalent metal element hydroxide content is preferably
0.01 mass % or greater based on the total mass of the slurry, from
the viewpoint of allowing the function of the tetravalent metal
element hydroxide to be adequately exhibited.
[0142] The pH of the slurry of this embodiment is preferably
2.0-9.0, for a satisfactory surface potential of the abrasive
grains with respect to the surface potential of the surface to be
polished, to facilitate action of the abrasive grains on the
surface to be polished, and thereby obtaining a more superior
polishing rate. Also, from the viewpoint of stabilizing the pH of
the slurry and minimizing problems such as aggregation of the
abrasive grains due to addition of a pH stabilizer, the lower limit
for the pH is preferably at least 2.0, more preferably at least 2.5
and even more preferably at least 3.0. Furthermore, from the
viewpoint of excellent dispersibility of the abrasive grains and
obtaining a more superior polishing rate, the upper limit for the
pH is preferably not greater than 9.0, more preferably not greater
than 7.0 and even more preferably not greater than 5.0. The pH of
the slurry can be measured by the same method as for the pH of the
polishing liquid of this embodiment.
[0143] <Polishing Liquid Set>
[0144] In the polishing liquid set of this embodiment, the
constituent components of the polishing liquid are separately
stored as a slurry and an additive solution, so that the slurry
(first liquid) and additive solution (second liquid) are mixed to
form the polishing liquid. The slurry used may be the slurry
according to this embodiment. The additive solution used may be a
solution having the additive dissolved in water. The polishing
liquid set is used as a polishing liquid by mixing the slurry and
additive solution at the time of polishing. By thus separately
storing the constituent components of the polishing liquid into at
least two liquids, it is possible to obtain a polishing liquid with
excellent storage stability.
[0145] The additives used in the additive solution may be the same
additives as described for the polishing liquid. The content of
additives in the additive solution is preferably 0.01-20 mass % and
more preferably 0.02-20 mass %, based on the total mass of the
additive solution, from the viewpoint of inhibiting excessive
reduction in the polishing rate when the additive solution and
slurry are mixed to form the polishing liquid.
[0146] There are no particular restrictions on the water for the
additive solution, but deionized water or ultrapure water is
preferred. The water content is not particularly restricted and may
be the content of the remainder excluding the other constituent
components.
[0147] <Substrate Polishing Method and Substrate>
[0148] A substrate polishing method using the aforementioned
polishing liquid, slurry or polishing liquid set, and a substrate
obtained by the method, will now be described. When the polishing
liquid or slurry is to be used, it will be a polishing method using
a one-pack type polishing liquid, and when the polishing liquid set
is to be used, it will be a polishing method using a two-pack type
polishing liquid or a three-pack or greater type polishing
liquid.
[0149] In the substrate polishing method of this embodiment,
polishing is performed on a substrate having a film to be polished
on its surface. In the substrate polishing method of this
embodiment, the film to be polished may be polished using a stopper
film formed under the film to be polished. The substrate polishing
method of this embodiment comprises at least a substrate
positioning step and a polishing step. In the substrate positioning
step, a film to be polished, of a substrate which has the film to
be polished on its surface, is placed so as to face an abrasive
pad.
[0150] The film to be polished is preferably an inorganic
insulating film, such as a silicon oxide film. The silicon oxide
film can be obtained by low-pressure CVD method, plasma CVD, or the
like. The silicon oxide film may be doped with an element such as
phosphorus or boron. The inorganic insulating film may be a Low-k
film or the like. The surface of the film to be polished (surface
to be polished) preferably has irregularities. In the substrate
polishing method of this embodiment, the convexities of the
irregularities of the film to be polished are preferentially
polished, to obtain a substrate with a flattened surface.
[0151] In the polishing step, when a one-pack type polishing liquid
is to be used, in the state that the film to be polished of the
substrate is pressed against the abrasive pad of the polishing
platen, at least a portion of the film to be polished is polished
by relatively moving the substrate and the polishing platen while
supplying the polishing liquid or slurry between the abrasive pad
and the film to be polished. Here, the polishing liquid and slurry
may be supplied onto the abrasive pad directly as a polishing
liquid with the prescribed water content.
[0152] From the viewpoint of minimizing costs for preservation,
transport and storage, the polishing liquid and slurry of this
embodiment can be stored as a storage solution for a polishing
liquid or a storage solution for a slurry to be used, for example,
in a two-fold or greater dilution with a liquid medium such as
water at the time of use. The storage solution may be diluted with
the liquid medium immediately before polishing, or the storage
solution and liquid medium may be supplied onto the abrasive pad
for dilution on the abrasive pad.
[0153] Since a greater dilution factor of the storage solution
results in a greater effect of minimizing cost for preservation,
transport and storage, it is preferably two-fold or greater and
more preferably 3-fold or greater. There are no particular
restrictions on the upper limit, but a greater dilution factor
requires a greater amount of components in the storage solution (a
higher concentration), which tend to lower the stability during
storage, and therefore it is preferably not greater than 500-fold,
more preferably not greater than 200-fold, even more preferably not
greater than 100-fold and especially preferably not greater than
50-fold. The same is applied for a polishing liquid with the
constituent components divided into 3 or more liquids.
[0154] When a two-pack type polishing liquid is to be used, the
method may include a polishing liquid preparation step in which the
slurry and additive solution are mixed before the polishing step to
obtain a polishing liquid. In this case, in the polishing step, the
film to be polished is polished using the polishing liquid obtained
from the polishing liquid preparation step. In the polishing liquid
preparation step of this polishing method, the slurry and additive
solution are conveyed through separate tubings, and the tubings are
merged just before the supply tubing outlet to obtain the polishing
liquid. Alternatively, the polishing liquid may be supplied onto
the abrasive pad directly as a polishing liquid with the prescribed
water content. The same is applied for a polishing liquid with the
constituent components divided into 3 or more liquids.
[0155] In the polishing step, when a two-pack type of polishing
liquid is to be used, at least a portion of the film to be polished
may be polished using the polishing liquid obtained by mixing the
slurry and additive solution while respectively supplying the
slurry and additive solution. In this polishing method, the slurry
and additive solution may be supplied onto the abrasive pad through
separate liquid conveyance systems. The slurry may be diluted on
the abrasive pad after being supplied onto the abrasive pad as the
aforementioned slurry storage solution, and the additive solution
may be diluted on the abrasive pad after being supplied onto the
abrasive pad as a storage solution with a low water content. The
same is applied for a polishing liquid with the constituent
components divided into 3 or more liquids.
[0156] The polishing apparatus to be used in the polishing method
of this embodiment may be, for example, a common polishing
apparatus comprising a holder to hold the substrate with the film
to be polished, and a polishing platen that mounts a motor having a
variable rotational speed and allows attachment of an abrasive pad.
Examples of such polishing apparatuses include a polishing
apparatus by Ebara Corp. (Model EPO-111), and polishing apparatuses
by Applied Materials (trade names: Mirra3400 and Reflection
Polishing Machine).
[0157] There are no particular restrictions on the abrasive pad,
and a common nonwoven fabric, foamed polyurethane, porous fluorine
resin or the like may be used. The abrasive pad is preferably
furrowed to allow accumulation of the polishing liquid.
[0158] The polishing conditions are not particularly restricted,
but from the viewpoint of minimizing fly off of the semiconductor
substrate, the rotational speed of the polishing platen is
preferably a low speed of not greater than 200 rpm. The pressure
(machining load) on the semiconductor substrate is preferably not
greater than 100 kPa, from the viewpoint of further minimizing
formation of scratches after polishing. The polishing liquid is
preferably continuously supplied to the surface of the abrasive pad
with a pump or the like during polishing. The amount supplied is
not particularly restricted, but the surface of the abrasive pad is
preferably covered by the polishing liquid at all times.
Preferably, the polished semiconductor substrate is thoroughly
rinsed in running water, and is then dried after removing off the
water droplets adhering to the semiconductor substrate using a spin
dryer or the like.
[0159] According to this embodiment, there is provided the use of
the aforementioned polishing liquid, slurry and polishing liquid
set for polishing of a film to be polished (for example, a silicon
oxide film). Also according to this embodiment, there is provided
the use of the aforementioned polishing liquid, slurry and
polishing liquid set for polishing of a film to be polished (for
example, a silicon oxide film) using a stopper film (for example, a
silicon nitride film or polysilicon film).
EXAMPLES
[0160] The present invention will now be described in greater
detail by examples, with the understanding that the invention is
not limited to these examples.
Examples 1 to 17, Comparative Examples 1 to 3
Preparation of Tetravalent Metal Element Hydroxides
[0161] Tetravalent metal element hydroxides were prepared by the
following procedure. The values indicated as A to G throughout the
explanation below are the values shown in Table 1.
[0162] After placing A [g] of water into a container, B [g] of
cerium ammonium nitrate aqueous solution (general formula:
Ce(NH.sub.4).sub.2(NO.sub.3).sub.6, formula weight: 548.2 g/mol) at
a concentration of 50 mass % was added and mixed therewith, and the
liquid temperature was adjusted to C [.degree. C.] to obtain a
metal salt aqueous solution. The metal salt concentration of the
metal salt aqueous solution was as shown in Table 1.
[0163] Next, the alkali shown in Table 1 was dissolved in water to
prepare E [g] of an aqueous solution at a concentration of D
[mol/L], and the liquid temperature was adjusted to a temperature
of C [.degree. C.] to obtain an alkali solution.
[0164] The container holding the metal salt aqueous solution was
placed in a water tank filled with water and the water temperature
of the water tank was adjusted to the temperature indicated by C
[.degree. C.] in Table 1 using an external-circulating Coolnics
Circulator (product name: Cooling Thermopump CTP 101 by Eyela). The
alkali solution was added into the container at a mixing rate of G
[mL/min] while keeping the water temperature at C [.degree. C.] and
stirring the metal salt aqueous solution at the rotational speed
indicated by F [rpm] in Table 1, to obtain slurry precursor 1
comprising abrasive grains of tetravalent cerium hydroxide. The pH
of slurry precursor 1 was as indicated by "final pH" in Table 1. In
Example 11, a 4-blade pitched paddle with a total blade length of
17 cm was used for stirring of the metal salt aqueous solution,
while in the other examples and the comparative examples, an
ordinary stirring blade with a total blade length of 5 cm was used
for stirring of the metal salt aqueous solution.
[0165] Slurry precursor 1 was centrifuged and subjected to
solid-liquid separation by decantation to remove the liquid. The
procedure of adding a suitable amount of water to the obtained
resultant solid, thoroughly stirring and conducting solid-liquid
separation by decantation was carried out an additional 3
times.
[0166] After again adding water to the obtained resultant solid to
adjust the liquid volume to 2.0 L, ultrasonic dispersion treatment
was carried out for 180 minutes to obtain slurry precursor 2. A
suitable amount of the obtained slurry precursor 2 was sampled, and
the mass after drying (the nonvolatile component mass) was measured
to calculate the content of tetravalent cerium hydroxide abrasive
grains in the slurry precursor 2.
TABLE-US-00001 TABLE 1 Metal salt solution 50 mass % metal salt
Alkali solution Synthesis conditions Water solution Alkali solution
Mixing Stirring Synthesis amount amount Concentration Concentration
amount speed speed temp. A [g] B [g] [mol/L] Alkali type D [mol/L]
E [g] G [mL/min] F [rpm] C [.degree. C.] Final pH Example 1 1840
76.8 0.037 Ammonia 8.8 29 10 200 25 5.2 Example 2 1840 76.8 0.037
Ammonia 2.9 88 5 200 25 5.2 Example 3 1200 40.0 0.029 Pyridine 2.5
52 5 200 25 5.2 Example 4 1656 69.1 0.037 Imidazole 1.5 148 10 500
25 3.2 Example 5 1656 69.1 0.037 Imidazole 1.5 157 10 500 25 5.2
Example 6 1656 69.1 0.037 Imidazole 1.5 152 10 500 25 4.5 Example 7
1656 69.1 0.037 Imidazole 1.5 152 10 500 10 5.2 Example 8 1656 69.1
0.037 Imidazole 1.5 152 10 500 15 4.8 Example 9 1656 69.1 0.037
Imidazole 1.5 152 5 500 10 5.2 Example 10 1656 69.1 0.037 Imidazole
1.5 152 10 500 5 5.3 Example 11 165600 6912 0.037 Imidazole 1.5
15200 80 100 15 5.2 Example 12 1656 69.1 0.037 Imidazole 1.5 152 2
500 10 5.2 Example 13 9200 384.0 0.037 Ammonia 14.7 87 5 300 25 5.2
Example 14 1472 61.4 0.037 Ammonia 8.8 24 3 500 25 5.2 Example 15
1472 61.4 0.037 Ammonia 5.9 36 3 500 25 5.2 Example 16 1472 61.4
0.037 Ammonia 2.9 70 3 500 25 5.2 Example 17 1840 76.8 0.037
Imidazole 0.29 173 3 500 20 5.2 Comp. Ex. 1 1840 76.8 0.037 Ammonia
14.7 17 25 200 25 5.2 Comp. Ex. 2 2500 40.0 0.014 Potassium 1.8 70
10 500 25 5.2 hydroxide Comp. Ex. 3 1840 76.8 0.037 Ammonia 14.7 17
10 500 25 5.2
Comparative Example 4
[0167] Slurry precursor 2 obtained in Example 4 and slurry
precursor 2 obtained in Comparative Example 1 were mixed in a
proportion of 3:1 (mass ratio) to obtain slurry precursor 2 for
Comparative Example 4.
[0168] (Measurement of Absorbance and Light Transmittance)
[0169] A suitable amount of slurry precursor 2 was sampled and
diluted with water to an abrasive grain content of 0.0065 mass %
(65 ppm) to obtain a measuring sample (aqueous dispersion).
Approximately 4 mL of the measuring sample was placed in a 1
cm-square cell, and the cell was set in a spectrophotometer
(apparatus name: U3310) by Hitachi, Ltd. Spectrophotometry was
performed in a wavelength range of 200-600 nm to determine the
absorbance at a wavelength of 290 nm and the absorbance at a
wavelength of 450-600 nm. The results are shown in Table 2.
[0170] A suitable amount of slurry precursor 2 was also sampled and
diluted with water to an abrasive grain content of 1.0 mass % to
obtain a measuring sample (aqueous dispersion). Approximately 4 mL
of the measuring sample was placed in a 1 cm-square cell, and the
cell was set in a spectrophotometer (apparatus name: U3310) by
Hitachi, Ltd. Spectrophotometry was performed in a wavelength range
of 200-600 nm to measure the absorbance for light with a wavelength
of 400 nm and the light transmittance for light with a wavelength
of 500 mm. The results are shown in Table 2.
[0171] (Measurement of Mean Secondary Particle Size)
[0172] A suitable amount of slurry precursor 2 was sampled and
diluted with water to an abrasive grain content of 0.2 mass % to
obtain a measuring sample. Approximately 4 mL of the measuring
sample was placed in a 1 cm-square cell, and the cell was set in a
Zetasizer 3000HS, an apparatus name by Malvern Instruments Ltd.
Measurement was conducted at 25.degree. C. with a dispersing medium
refractive index of 1.33 and a viscosity of 0.887 mPas, and the
value represented by Z-average Size was read as the mean secondary
particle size. The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Light Mean Absorbance Absorbance Absorbance
transmittance secondary [290 nm] [450-600 nm] [400 nm] [500 nm]
[%/cm] particle size Abrasive grain content: 65 ppm Abrasive grain
content: 1.0 mass % [nm] Example 1 1.112 <0.010 1.57 62 74
Example 2 1.039 <0.010 1.71 92 52 Example 3 1.124 <0.010 1.91
91 61 Example 4 1.272 <0.010 2.32 >99 22 Example 5 1.036
<0.010 1.57 >99 25 Example 6 1.230 <0.010 2.04 >99 22
Example 7 1.140 <0.010 1.83 >99 21 Example 8 1.153 <0.010
1.78 >99 19 Example 9 1.238 <0.010 2.28 >99 24 Example 10
1.133 <0.010 1.98 >99 23 Example 11 1.312 <0.010 3.02
>99 18 Example 12 1.232 <0.010 2.68 >99 20 Example 13
1.091 <0.010 1.81 95 33 Example 14 1.152 <0.010 1.89 81 78
Example 15 1.101 <0.010 1.69 89 53 Example 16 1.023 <0.010
1.51 98 42 Example 17 1.056 <0.010 1.77 >99 49 Comp. Ex. 1
1.256 <0.010 2.70 41 95 Comp. Ex. 2 1.239 <0.010 2.22 46 91
Comp. Ex. 3 1.246 <0.010 2.69 43 101 Comp. Ex. 4 1.265 <0.010
2.58 49 85
[0173] (Preparation of Polishing Liquids)
[0174] Water was added to slurry precursor 2 for adjustment to an
abrasive grain content of 1 mass % to obtain a storage solution for
a slurry. The results of observing the outer appearance of each
storage solution for a slurry are shown in Table 3.
[0175] Purified water was added to 60 g of the storage solution for
a slurry to obtain a slurry. Also, a 5 mass % polyvinyl alcohol
aqueous solution was prepared as an additive solution. After adding
60 g of the additive solution to the slurry, the mixture was mixed
and stirred to obtain a polishing liquid with an abrasive grain
content of 0.2 mass %. The amount of purified water added was
calculated to be for a final abrasive grain content of 0.2 mass %.
The saponification degree of polyvinyl alcohol in the polyvinyl
alcohol aqueous solution was 80 mol %, and the mean polymerization
degree was 300. The polyvinyl alcohol content in the polishing
liquid was 1.0 mass %. The pH (25.degree. C.) values of the slurry
and polishing liquid, as measured using a Model PH81 by Yokogawa
Electric Corp., were 3.6 and 6.0.
[0176] (Polishing of Insulating Film)
[0177] A .phi.200 mm silicon wafer, with a silicon oxide insulating
film formed thereon, was set in the holder of a polishing
apparatus, mounting an adsorption pad for substrate attachment. The
holder was placed on a porous urethane resin pad-attached platen,
with the insulating film facing the pad. The substrate was pressed
onto the pad at a polishing load of 20 kPa while supplying the
obtained polishing liquid onto the pad at a feed rate of 200
cc/min. Polishing was performed for 1 minute of rotation of the
platen at 78 rpm and the holder at 98 rpm. The polished wafer was
thoroughly washed with purified water and dried. A
light-interference film thickness meter was used to measure the
change in film thickness before and after polishing, and the
polishing rate was calculated. The results are shown in Table
3.
[0178] Evaluation of the absorbance, light transmittance and
polishing rate were all conducted within 24 hours after preparing
slurry precursor 2.
[0179] The relationship between absorbance for light with a
wavelength of 290 nm and polishing rate is shown in FIG. 3, and the
relationship between absorbance for light with a wavelength of 400
nm and polishing rate is shown in FIG. 4. Also, the relationship
between absorbance for light with a wavelength of 290 nm and
absorbance for light with a wavelength of 400 nm is shown in FIG.
5. In FIGS. 3 to 5, a case with a light transmittance of 90%/cm or
greater is indicated by a circle, a case with a light transmittance
of at least 50%/cm and less than 90%/cm is indicated by a triangle,
and a case with a light transmittance of less than 50%/cm is
indicated by a diamond.
[0180] As clearly seen in FIGS. 3 to 5, a higher light
transmittance value resulted in increased polishing rate, and with
a light transmittance of 50%/cm or greater (especially 90%/cm or
greater), the polishing rate was improved as the absorbance for
light of 290 nm or 400 nm increased. Also, FIG. 5 shows a good
correlation between absorbance for light with a wavelength of 290
nm and absorbance for light with a wavelength of 400 nm
TABLE-US-00003 TABLE 3 Outer appearance of Polishing rate storage
solution for slurry (nm/min) Example 1 Slightly turbid, faint
yellow 280 Example 2 Transparent, faint yellow 320 Example 3
Transparent, faint yellow 340 Example 4 Transparent, faint yellow
380 Example 5 Transparent, faint yellow 327 Example 6 Transparent,
faint yellow 376 Example 7 Transparent, faint yellow 350 Example 8
Transparent, faint yellow 355 Example 9 Transparent, faint yellow
377 Example 10 Transparent, faint yellow 368 Example 11
Transparent, faint yellow 405 Example 12 Transparent, faint yellow
389 Example 13 Transparent, faint yellow 320 Example 14 Very
slightly turbid, faint yellow 255 Example 15 Very slightly turbid,
faint yellow 285 Example 16 Transparent, faint yellow 305 Example
17 Transparent, faint yellow 335 Comp. Ex. 1 Turbid, white 170
Comp. Ex. 2 Turbid, white 190 Comp. Ex. 3 Turbid, white 175 Comp.
Ex. 4 Turbid, faint yellow 220
[0181] Next, using a polishing liquid obtained using the slurry of
Example 7 and a polishing liquid obtained using the slurry of
Comparative Example 1, the relationship between polyvinyl alcohol
(PVA) content of the polishing liquid and polishing rate was
examined. Specifically, the polishing rates for silicon oxide films
were examined in the same manner as Example 1, with polyvinyl
alcohol contents of 3.0 mass %, 2.0 mass %, 1.0 mass %, 0.5 mass %
and 0.1 mass % in the polishing liquid. The results are shown in
Table 4.
TABLE-US-00004 TABLE 4 PVA content (mass %) 3.0 2.0 1.0 0.5 0.1
Polishing rate Comp. Ex. 1 90 135 170 225 232 (nm/min) Example 7
253 312 350 375 384
[0182] As is clear by the results in Table 4, the polishing rate in
Example 7, which had a light transmittance of at least 50%/cm for
light with a wavelength of 500 nm, was higher than in Comparative
Example 1 with addition of additives in the same amount, and
therefore a wide margin exists for further addition of additives,
in addition to polyvinyl alcohol. This suggests that the effective
number of abrasive grains on the surface to be polished was
maintained by increased light transmittance for inhibited formation
of coarse aggregated particles, and that increased absorbance
allowed the polishing rate to be maintained at a higher value than
Comparative Example 1. This indicates that in Example 7 it is
possible to impart further properties by adding more additives,
compared to Comparative Example 1.
* * * * *