Compositions – Etching or brightening compositions
Reexamination Certificate
1999-01-15
2001-08-14
Mills, Gregory (Department: 1763)
Compositions
Etching or brightening compositions
C438S692000, C438S693000, C216S089000, C216S100000, C216S101000
Reexamination Certificate
active
06274063
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polishing slurries which produce very smooth surfaces on nickel- or nickel alloy-plated substrates, and methods of their preparation and use.
BACKGROUND OF THE INVENTION
Over the past several years, a significant increase in recording density in thin-film magnetic recording discs has been achieved, and there is a continuing effort to increase recording density further. Reducing the head-to-disk spacing, or the flying height, is one of the more effective ways to achieve a higher density on a magnetic rigid disk. As the read/write head is moved closer to the disk, there is less overlap of voltage signals in adjacent magnetic domains in the disk, with a corresponding increase in recording density. However, to have read/write heads flying over the disk surfaces at sub-microinch spacing, the topography of the disk surface must be very uniform. Current polishing methods for Ni/P plated disks commonly employ polishing slurries which are primarily mechanical in action, containing micron- or submicron-sized abrasive particles and a chemical accelerator, typically Al(NO
3
)
3
(aluminum nitrate). These methods have produced surfaces having roughness averages (RA) of about 0.4 nm (4 Å). However, methods of polishing such surfaces to still greater smoothness are sought.
SUMMARY OF THE INVENTION
The present invention includes, in one aspect, a composition for use in polishing a substrate having a nickel or nickel alloy surface. The composition is an aqueous slurry comprising an aqueous medium, typically deionized water, and containing the following components: (a) a soluble chemical etchant effective to convert nickel metal at the surface to a water soluble nickel salt, (b) suspended abrasive particles, and (c) a soluble oxidizer effective to convert nickel metal at the surface to nickel oxide. In a preferred embodiment, neither the etchant nor the oxidizer is capable, under normal polishing conditions, of solubilizing the nickel oxide in the aqueous medium to any significant extent. The etchant is preferably Al(NO
3
)
3
. The oxidizer is preferably a mild oxidant, such as H
2
O
2
, Fe(NO
3
)
3
, or KIO
3
. Hydrogen peroxide (H
2
O
2
) is particularly preferred.
In preferred compositions, Al(NO
3
)
3
is present in the aqueous medium at a concentration between about 0.1 and 1.0 weight percent, more preferably between about 0.1 and 0.5 weight percent, and most preferably between about 0.25 and 0.30 weight percent. Hydrogen peroxide is preferably present in the aqueous medium at a concentration between about 0.1 and 1.0 weight percent, more preferably between about 0.1 and 0.5 weight percent, and most preferably between about 0.15 and 0.30 weight percent.
The abrasive particles are generally selected from aluminum oxide particles, silicon dioxide particles, titanium dioxide particles, and a combination thereof. For first-step (coarse) polishing, the particles are typically between about 0.5 and 1.2&mgr; in diameter (d
50
); for second-step (fine or “super”) polishing, the particles are typically between about 0.1 and 0.3&mgr; in diameter (d
50
).
The composition may further contain a surfactant, for example, a polyethylene glycol-based surfactant, effective to maintain the particles dispersed in the aqueous medium. It may also contain a buffer to maintain the pH of the composition between about 2.5 and 4.5.
In another aspect, the invention provides a method of polishing a substrate having a nickel or nickel alloy surface. The method comprises applying to the substrate surface, a composition containing, in an aqueous medium, components (a)-(c) as described above, pressing a polishing pad against the substrate in the presence of the composition, and moving the pad relative to the substrate.
The invention also provides methods of preparing a polishing composition useful in polishing a substrate having a nickel or nickel alloy surface. The composition or slurry is prepared by adding to an aqueous suspension of abrasive particles, components (a) and (c) as described above, preferably in the preferred concentrations described above. Alternatively, the slurry may be prepared in more concentrated form, in which case the method of preparation further includes adding deionized water to the suspension as necessary to attain the preferred concentrations described above. Another method of preparing the polishing slurry comprises adding an oxidizer, as described above, to an aqueous medium which already contains components (a) and (b).
These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4305779 (1981-12-01), Steeves et al.
patent: 4475981 (1984-10-01), Rea
patent: 4956015 (1990-09-01), Okajima et al.
patent: 4959113 (1990-09-01), Roberts
patent: 5166006 (1992-11-01), Lal et al.
patent: 5689879 (1997-11-01), Urasaki et al.
patent: 5811355 (1998-09-01), Jordan
patent: 6068787 (2000-05-01), Grumbine et al.
Li Jiangning
Yang Ming M.
Alejandro Luz L.
Gorthey LeeAnn
HMT Technology Corporation
Mills Gregory
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