Polishing composition

Details Polishing composition Polishing composition

2000-06-29

2002-06-04

Marcheschi, Michael (Department: 1755)

Abrasive tool making process, material, or composition

With inorganic material

Clay, silica, or silicate

C106S003000, C438S692000, C438S693000, C510S165000, C510S167000, C510S397000

Reexamination Certificate

active

06398827

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing composition for polishing alumina disks, polishing substrates having silica surfaces and semiconductor wafers, comprising a stable aqueous silica sol containing moniliform colloidal silica particles having a ratio (D
1
/D
2
) of a particle diameter D
1
nm (as measured by dynamic light scattering method) to a mean particle diameter D
2
(as measured by nitrogen absorption method) of 3 or more, wherein D
1
is between 50 to 800 nm and D
2
is between 10 to 120 nm, said moniliform colloidal silica particles being composed of spherical colloidal silica particles and a metal oxide-containing silica bond which bonds these spherical colloidal silica particles together, wherein the spherical colloidal silica particles are linked together in rows in only one plane by observation through an electron microscope, and further wherein said polishing composition contains 0.5 to 50% by weight of said moniliform colloidal silica particles. Hereafter, a stable aqueous silica sol containing moniliform colloidal silica particles is referred to as a moniliform silica sol.
More particularly, the moniliform silica sol is characterized by the shape of its colloidal silica particles and the polishing method of the present invention can provide highly accurate smooth polished surface efficiently and hence it is useful as a finish polishing method. Here, polishing of an aluminum disk means polishing a surface of the substrate itself of a magnetic memory disk composed of aluminum or its alloy, or a surface of a plating layer such as Ni—P, Ni—B, etc., in particular a hard layer of non-electrolysis nickel-phosphorus (Ni—P) plating having a composition of 90 to 92% Ni and 8 to 10% P and an aluminum oxide layer provided on the substrate. Polishing of a substrate having silica on its surface means polishing a surface layer on a substrate containing 50% by weight of silica or more, for example, polishing rock crystal, quartz glass for photomasks, SiO
2
oxide layer for semiconductor devices, crystallized glass made hard disks, and aluminosilcate glass or soda lime glass reinforced glass made hard disks. Polishing semiconductor wafers means polishing semiconductor wafers made of elemental silicon, compound semiconductor wafers made of gallium arsenide, gallium phosphide, indium phosphide, etc.
Since the polishing composition of the present invention can efficiently provide highly accurate smooth polished surfaces, it is useful In precision polishing of wiring metals such as copper and aluminum in semiconductor multilayer interconnection board, of nitride layer and of carbide layer, and in finish polishing of monocrystals such as sapphire, lithium tantalate, and lithium niobate, GHR magnetic heads. etc.
2. Description of the Related Art
An aqueous silica sol generally has the property that it is converted from a state where it has a low viscosity to a gelled state through a state where it has a high viscosity. Therefore, if the SiO
2
content is the same, the lower viscosity product is evaluated as being more stable than the higher viscosity product. An aqueous silica sol shows a lower viscosity the closer the shape of colloidal silica particle contained therein is to regular sphere. For this reason, aqueous sols composed of highly stable, spherical colloidal silica particles have been conventionally used partly in finish polishing of aluminum disks, glass disks, quartz glass for photomasks, rock crystal, siliceous substrates such as SiO
2
oxide film of semiconductor devices, monocrystals such as semiconductor wafers, sapphire, lithium tantalate. lithium niobate, etc., and MR magnetic heads. etc. However, although such silica sols give highly flat polished surfaces, it has been pointed out that they have the defect of slow polishing speed. Accordingly, to increase polishing speed, efforts have been made to change the shape of colloidal silica particles. For example, JP-A-7-221059 describes use of colloidal silica particles having a lopsided shape with a longer diameter being 7 to 1,000 nm and a ratio of shorter diameter/longer diameter being 0.3 to 0.8 in polishing semiconductor wafers results in an increased polishing speed. However, no proposal has been made for improving polishing properties such as polishing speed by using of the moniliform colloidal silica sol.
As a polishing composition for aluminum disks composed of silica (silicon dioxide), water, and a polishing accelerator, U.S. Pat. No. 4,959,113 discloses a polishing method for nickel plated aluminum disks with a polishing composition comprising water, an abrasive (silicon dioxide, aluminum oxide, cerium oxide, etc.) and a salt composed of iron ion as a cation and nitrate ion or sulfate ion as an anion. U.S. Pat. No. 5,997,620 (related patent: JP-A-10-204416) discloses a polishing composition for memory hard disks, containing water and an abrasive (silicon dioxide, aluminum oxide, cerium oxide, etc.) and soluble iron compound.
SUMMARY OF THE INVENTION
The present invention is to provide a polishing composition having excellent polishing properties for aluminum disks, glass hard disks, quartz glass, rock crystal, SiO
2
oxide film of semiconductor devices, elemental silicon semiconductor wafers, and compound semiconductor wafers. Further, the present invention is to provide a polishing composition for aluminum disks having an increased polishing speed by adding to the above polishing composition of the invention one or more of iron compounds selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, and potassium iron (III) sulfate [KFe(SO
4
)
2
].
The moniliform silica sol as a constituent substance of the polishing composition of the present invention has a SiO
2
, concentration of 50% by weight or less and is stable. The shape of the colloidal silica particle dispersed in a liquid medium of the silica sol of which a particle diameter (D
1
nm) measured by dynamic light scattering method is 50 to 800 nm is featured as follows. When observed on electron microscope, the particles are composed of spherical colloidal particles and silica bounding these spherical colloidal particles, and the colloidal silica is moniliform in shape, which are linked in rows in only one plane and the degree of linking, i.e., a D
1
/D
2
value, the ratio of the above-described D
1
to a mean particle diameter D
2
(particle diameter measured by a nitrogen absorption method) is 3 or more.
The moniliform silica sol is a stable aqueous silica sol containing moniliform colloidal silica particles having a ratio (D
1
/D
2
) of a particle diameter D
1
nm (as measured by dynamic light scattering method) to a mean particle diameter D
2
(as measured by nitrogen absorption method) of 3 or more, wherein D
1
is between 50 to 800 nm and D
2
is between 10 to 120 nm, said moniliform colloidal silica particles being composed of spherical colloidal silica particles and a metal oxide-containing silica bond which bond which bonds these spherical colloidal silica particles together, wherein the spherical colloidal silica particles are linked together in rows in only one plane by observation through an electron microscope. The silica sol has 5 to 50% by weight of moniliform colloidal silica particles.
The moniliform silica sol can be efficiently obtained by a production method comprising the steps of (a), (b), (c), and (d) below:
(a) the step of adding an aqueous solution containing a water-soluble divalent (II) or trivalent (III) metal salt singly or in admixture to an aqueous colloid solution of activated silicic acid or acidic silica sol having a mean particle diameter of 3 to 8 nm, having an SiO
2
concentration of 0.5 to 10% by weight and a pH of 2 to 6, in an amount of 1 to 10% by weight of the metal oxide (MO in the case of the divalent metal (II) or M
2
O
3
in the case of the trivalent metal (III), where M represents a divalent or trivalent metal atom, and O represents an oxygen atom) based on the SiO
2
in the aqueous solution of the

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