Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2002-08-15
2003-09-16
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C051S308000, C106S003000, C438S692000, C438S693000, C216S089000, C216S096000, C216S100000
Reexamination Certificate
active
06620216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing composition, a process for reducing fine scratches of a substrate with the polishing composition, and a method for manufacturing a substrate with the polishing composition. The polishing composition can be suitably used for final polishing memory hard disk substrates and polishing semiconductor elements.
2. Discussion of the Related Art
Recent memory hard disk drives have been demanded to have high areal density and small size. In order to increase the areal density, it has been strongly urged to lower flying height of a magnetic head and to reduce the unit area of recording. Along with this trend, the surface quality required after polishing has become severely assessed every year even in a method for manufacturing a magnetic disk substrate. In order to meet the requirement of the low flying height of the head, the disk surface is required to have reduced surface roughness, micro-waviness, roll-off, and projections. In order to meet the requirement of the reduction of the unit area of recording, sizes and depth of permitted scratches and pits have become increasingly small.
Also, in the field of semiconductors, the trends of producing thinner wiring have been progressed along with the trends of highly integrated circuits and higher speed at the operating frequencies. Even in the method for manufacturing a semiconductor device, since the focal depth becomes shallow with the trend of thinning the wiring during the exposure of a photoresist, further smoothening of a pattern-forming surface has been desired.
In order to meet such requirements, there have been proposed polishing compositions with improved surface smoothness such as surface roughness Ra and Rmax, scratches, pits and projections (Japanese Patent Laid-Open Nos. Hei 9-204657, Hei 11-167715 and Hei 11-246849). However, as a consequence of improved surface smoothness, there have been newly found fine scratches having depth of 0.1 nm or more and less than 5 nm, a width of 10 &mgr;m or more and less than 50 &mgr;m, and a length of 10 &mgr;m or more and less than 1 mm have been found. Therefore, the reduction of the generation of such fine scratches is a problem to be solved. In addition, there has been conventionally known to further add a polishing step using a colloidal silica in order to reduce scratches. However, when this polishing step is carried out, there are some defects such that the number of steps is increased, so that the polishing rate is delayed and that the productivity is lowered.
An object of the present invention is to provide a polishing composition for final polishing memory hard disk substrates and polishing semiconductor elements, which can make the surface roughness of the object to be polished after polishing small and remarkably reduce surface defects such as projections and polishing damages, especially reducing fine scratches having depth of 0.1 nm or more and less than 5 nm, a width of 10 &mgr;m or more and less than 50 &mgr;m, and a length of 10 &mgr;m or more and less than 1 mm, and can accomplish economic polishing, a process for reducing fine scratches of a substrate with the polishing composition, and a method for manufacturing a substrate with the polishing composition.
SUMMARY OF THE INVENTION
According to the present invention, there are provided:
(1) a polishing composition comprising an abrasive having an average primary particle size of 200 nm or less, an oxidizing agent, an acid having a pK1 of 2 or less and/or a salt thereof, and water, wherein the acid value (Y) of the polishing composition is 20 mg KOH/g or less and 0.2 mg KOH/g or more;
(2) a process for reducing fine scratches of a substrate, comprising polishing a substrate to be polished with the polishing composition of item (1) above; and
(3) a method for manufacturing a substrate, comprising polishing a substrate to be polished with the polishing composition of item (1) above.
DETAILED DESCRIPTION OF THE INVENTION
As mentioned above, the polishing composition of the present invention comprises an abrasive having an average primary particle size of 200 nm or less, an oxidizing agent, an acid having a pK1 of 2 or less and/or a salt thereof, and water.
As the abrasive used in the present invention, any abrasives generally employed for polishing can be used. The abrasive includes, for instance, metals; carbides of metals or metalloids, nitrides of metals or metalloids, oxides of metals or metalloids, borides of metals or metalloids; diamond, and the like. The metals or metalloids include those elements belonging to the Groups 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 7A or 8A of the Periodic Table (long period form). Concrete examples of the abrasive include aluminum oxide, silicon carbide, diamond, magnesium oxide, zinc oxide, titanium oxide, cerium oxide, zirconium oxide, silica, and the like. It is preferable that one or more of these abrasives are used, from the viewpoint of increasing the polishing rate. Among them, aluminum oxide, silica, cerium oxide, zirconium oxide, titanium oxide, and the like are suitable for polishing semiconductor wafers and semiconductor elements and substrates for precision parts such as substrates for magnetic recording media. As to the aluminum oxide, those having various crystal forms such as &agr;, &thgr; and &ggr; have been known, which can be appropriately selected and used depending upon the applications. Moreover, the silica, especially colloidal silica is suitable for an application of final polishing of a magnetic disk substrate having high recording density and an application of polishing a semiconductor device substrate, which require a higher level of smoothness.
The abrasive has an average primary particle size of 200 nm or less, and preferably 1 nm or more, more preferably 10 nm or more, still more preferably 20 nm or more, from the viewpoint of increasing the polishing rate, and is 200 nm or less, preferably 150 nm or less, more preferably 120 nm or less, especially preferably 100 nm or less, from the viewpoints of reducing the surface roughness (Ra, Rmax) and the waviness (Wa). The abrasive has an average primary particle size of preferably from 1 to 200 nm, more preferably from 1 to 150 nm, still more preferably from 10 to 120 nm, especially preferably from 20 to 100 nm. Further, when the primary particles are aggregated to form a secondary particle, the abrasive has an average secondary particle size of preferably from 50 to 3000 nm, more preferably from 100 to 1500 nm, especially preferably from 200 to 1200 nm, from the viewpoint of similarly increasing the polishing rate and from the viewpoint of reducing the surface roughness of an object to be polished. As the average primary particle size of the abrasive, a particle size at 50% counted from a smaller size side on a number base (D50) in a cumulative particle size distribution can be determined by carrying out image analysis by observation with a scanning electron microscope (magnification: preferably from 3000 to 100000 times). Here, one primary particle size is defined as an arithmetic means of major axis length and minor axis length of the particle. In addition, the average secondary particle size can be determined as a volume-average particle size by using a laser beam diffraction method.
In addition, in the present invention, it is more preferable to use silica particles as an abrasive, from the viewpoints of reducing the surface roughness (Ra, Rmax) and the waviness (Wa), and reducing the surface defects such as scratches, thereby improving the surface quality. The silica particles include colloidal silica particles, fumed silica particles, surface-modified silica particles, and the like, among which the colloidal silica particles are preferable. Here, the colloidal silica particles can be obtained by, for instance, a process comprising generating silica particles from an aqueous silicic acid.
In the present invention, by using the polishing composition comprising silica particles having the particle size distribution shown abov
Hagihara Toshiya
Oshima Yoshiaki
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Marcheschi Michael
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