Abrasive tool making process – material – or composition – With inorganic material – Clay – silica – or silicate
Reexamination Certificate
2002-10-28
2004-04-13
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Clay, silica, or silicate
C106S003000
Reexamination Certificate
active
06719819
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Art
The present invention relates to a polishing composition for aluminum disks having a SiO
2
concentration of 0.5 to 50% by weight containing colloidal silica particle groups having different monomodal numerical particle size distribution therein or substrates having silica on the surface thereof, in order to obtain a polished surface having a smaller mean waviness.
Here, the polishing of aluminum disks referred to herein means polishing the surface of the substrate itself of a magnetic memory disk composed of aluminum or its alloy, or polishing the surface of the nickel-phosphorus (Ni—P) or nickel-boron (Ni—B) plating, especially a hard layer of non-electrolysis nickel-phosphorus (Ni—P) plating composing of 90 to 92% of Ni and 8 to 10% of P, and aluminum oxide layer on the substrate.
Polishing of the substrate with silica on the surface thereof means polishing the surface layer on the substrate containing 50% or more by weight of silica. Examples of such polishing include polishing rock crystal, quartz glass for photomasks, silicon oxide films on semiconductor devices, crystallized glass-made hard disks, and either aluminosilicate glass- or soda lime glass-made hard disks.
Since the polishing composition of the present invention can efficiently give smooth polished surfaces with high precision, it is also useful for the precision polishing of semiconductor wafers made of silicon alone, semiconductors wafers made of chemical compounds such as gallium arsenide, gallium phosphide or indium phosphide, and interconnecting metals such as copper and aluminum for semiconductor multi level interconnection substrates, nitride films and carbide films and the like, as well as for final polishing of single crystals of sapphire, lithium tantalate, lithium niobate and the like, and GMR magnetic head among others.
2. Description of the Related Art
Sols composed of highly stable colloidal silica particles as the silica sol have been used in part or under consideration for use in the final polishing of aluminum disks, glass disks, quartz glass for photomasks, rock crystal, siliceous substrate such as silicon oxide films for semiconductor devices, semiconductor wafers, single crystals such as sapphire, lithium tantalate and lithium niobate, MR magnetic head and the like. However, it has been pointed out that silica sol has a shortcoming in low removal rate in spite of attaining highly satisfactory polished surface having a good mean surface roughness.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a polishing composition for aluminum disks and glass-made disks, quartz glass, rock crystal as well as silicon oxide films for semiconductor devices in view of solving low removal rate and giving polished surface of excellent quality. In particular, the disk is likely to be rotated at an increased rotation speed with the decreased gap between the disk and the magnetic head in order to meet the increase in the density of memory capacity in the case of aluminum disks and glass-made hard disks, and furthermore, disks with less mean waviness are being desired in recent days.
In particular, more rigorous requirements for mean waviness are being asked for aluminum disks and glass-made hard disks in order to meet the increase in the density of memory capacity leading to faster rotation of the disk with the decreased gap between the disk and the magnetic head. Recently, disks having a mean waviness of less than 3 Å are being desired.
Here, the present invention was accomplished in making a polishing composition containing colloidal silica particles with a SiO
2
concentration of 0.5 to 50% by weight by the use of a water dispersed stable silica sol containing colloidal silica particle groups having two or three types of different monomodal numerical particle size distributions with the ratio of the mean particle size (particle size measured with the nitrogen adsorption method) being 0.15 to 0.80 mixed with SiO
2
with the weight ratio of 1:0.05 to 9.0, and in obtaining an aluminum disk or a substrate having silica on the surface thereof of good quality.
The measured particle size of colloidal silica particle group determined with the nitrogen adsorption method can be obtained according to the formula D=2720/S (nm) from the specific surface area S (m
2
/g) measured with the nitrogen adsorption method.
More specifically, the first embodiment of the instant invention relates to a polishing composition for an aluminum disk comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 80 to 120 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
a
(particle size measured with the nitrogen adsorption method) in the range of 65 to 100 nm (referred as colloidal silica particle group (a) hereinafter), and
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 20 to 40 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
c
(particle size measured with the nitrogen adsorption method) in the range of 15 to 25 nm (referred as colloidal silica particle group (c) hereinafter),
wherein said composition has the ratio of D
c
/D
a
of 0.15 to 0.38, contains a water dispersed stable silica sol mixed as SiO
2
with the weight ratio of said colloidal silica particle group (a) to said colloidal silica particle group (c) of W(a):W(c)=1:0.05 to 9.0, and contains colloidal silica particles with the SiO
2
concentration of 0.5 to 50% by weight.
The second embodiment of the instant invention relates to a polishing composition for an aluminum disk containing silica sol comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 80 to 120 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
a
(particle size measured with the nitrogen adsorption method) in the range of 65 to 100 nm (referred as colloidal silica particle group (a) hereinafter),
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 20 to 40 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
c
(particle size measured with the nitrogen adsorption method) in the range of 15 to 25 nm (referred to as colloidal silica particle group (c) hereinafter), and
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 5 to 15 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
d
(particle size measured with the nitrogen adsorption method) in the range of 8 to 12 nm (referred as colloidal silica particle group (d) hereinafter),
wherein said composition has the ratio of D
c
/D
a
of 0.15 to 0.38 and the ratio of D
d
/D
c
of 0.26 to 0.80, contains a water dispersed stable silica sol mixed as SiO
2
with the weight ratio of said colloidal silica particle group (a), said colloidal silica particle group (c) and said colloidal particle group (d) being W(a):W(c):W(d)=1:0.05 to 9.0:0.01 to 1.4, and contains colloidal silica particles with the SiO
2
concentration of 0.5 to 50% by weight.
The third embodiment of the instant invention relates to a polishing composition for an aluminum disk containing silica sol comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 40 to 70 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size D
b
(particle size measured with the nitrogen adsorption method)
Nishimura Tohru
Ota Isao
Yamada Gen
Marcheschi Michael
Nissan Chemical Industries Ltd.
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