Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1999-11-23
2001-06-12
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S066200, C428S066500, C451S041000, C451S063000, C451S287000, C451S539000
Reexamination Certificate
active
06245406
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to an abrasive shaped article used for polishing a substrate material such as a silicon wafer and an oxide substrate, and an optical material; an abrasive disc comprising the abrasive shaped article; and a polishing method. More particularly it relates to an abrasive shaped article made by shaping an ultrafine silica powder into a shaped article, and sintering the shaped article; an abrasive disc comprising the abrasive shaped silica article and a supporting auxiliary; and a polishing method using the abrasive shaped silica article.
(2) Description of the Related Art
In a process for polishing a substrate material such as a silicon wafer or an oxide substrate, a loose abrasive polishing procedure has heretofore been employed wherein the substrate material is polished with a polishing pad made of nonwoven fabric or suede cloth, while a polishing liquid comprising a loose abrasive grain such as colloidal silica or cerium oxide, and a chemical such as potassium hydroxide is continuously supplied onto the substrate material. For example, it is described in Japanese Unexamined Patent Publication (abbreviated to “JP-A”) 5-154760 and JP-A 7-326597 that a silicon wafer is polished with a polishing cloth and a loose abrasive grain. In the conventional loose grain polishing procedures using a loose grain-containing polishing liquid, a salient amount of a waste polishing liquid containing a loose grain is produced during polishing, and therefore, the efficiency of the polishing procedure, equipment for waste disposal and environmental pollution with the waste polishing liquid must be considered. The polishing pad such as polishing cloth is liable to be clogged and the polishing performance is deteriorated, and thus the polishing pad must be often renewed and the polishing efficiency is decreased.
Further, the conventional polishing procedure using a polishing pad has a problem such that the surface of the polishing pad is pliable and therefore the entire surface of a material to be polished is not uniformly abraded, i.e., the corner portions of the material surface are excessively abraded upon polishing.
To sum up, the conventional polishing procedure using a polishing pad and a loose abrasive grain bears problems in the disposal of waste polishing liquid, the working efficiency of polishing, and the uniformity in abrasion of the entire material surface to be polished.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an abrasive shaped article which is used for polishing a material such as a substrate material, for example, a substrate for a semiconductor device, such as a silicon wafer, and an oxide substrate, and an optical material for which a precision working is required; and which has advantages such that the problem of waste disposal can be mitigated or avoided, a polished surface with precision of the same degree as or higher degree than that achieved by the conventional polishing procedure using a polishing pad and a loose abrasive grain can be obtained, the material can be polished with enhanced efficiency, the abrasive shaped article has an improved durability and economics of the polishing working can be achieved.
Another object of the present invention is to provide an abrasive disc and a polishing process, which have the above-mentioned advantages.
As the result of research for achieving the above objects, the inventors have found that when an abrasive shaped article composed of ultrafine silica particles is used as an abrasive, the following advantages can be obtained.
(1) The hard and fine abrasive surfaces of silica particles are brought into direct contact with a material to be polished, and, therefore, a polishing liquid which does not contain loose abrasive grains such as colloidal silica or cerium oxide can be used. The silica particles fall off only to a very minor amount from the abrasive shaped article, and, therefore, the problem of waste liquid disposal can be mitigated or avoided.
(2) The abrasive shaped article composed of ultrafine silica particles has a high tenacity and an enhanced durability. Therefore, the polishing operation can be continued for a long period without renewal of the abrasive shaped article.
(3) The smooth finish and the rate of polishing achieved with the abrasive shaped article are of the same levels as or higher than those of the conventional polishing procedure using a polishing pad and a loose abrasive grain. The smooth finish and the rate of polishing are not decreased with a lapse of polishing time.
(4) If an abrasive loose grain is used in combination with the abrasive shaped article of the invention, a more enhanced rate of polishing can be achieved with a polishing liquid containing the abrasive loose grain at a lower concentration.
The present invention has been completed based on the above-listed findings.
In one aspect of the present invention, there is provided an abrasive shaped article comprising at least 90% by weight of silica (namely, silicon dioxide) and having a bulk density of 0.2 g/cm
3
to 1.5 g/cm
3
, a BET specific surface area of 10 m
2
/g to 400 m
2
/g and an average particle diameter of 0.001 &mgr;m to 0.5 &mgr;m.
In another aspect of the present invention, there is provided an abrasive disc comprising one or more of the above-mentioned abrasive shaped article and a supporting auxiliary, said abrasive shaped article or articles being fitted to the supporting auxiliary.
In still another aspect of the present invention, there is provided a process for polishing a material by using the above-mentioned abrasive disc.
REFERENCES:
patent: 3857123 (1974-12-01), Walsh
patent: 4544604 (1985-10-01), Usui et al.
patent: 5401568 (1995-03-01), Hähn et al.
patent: 5418043 (1995-05-01), Ogawa et al.
patent: 261546 (1988-11-01), None
patent: 1715133 (1995-08-01), None
Kubota Yoshitaka
Kuramochi Hideto
Ahmad Nasser
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tosoh Corporation
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