Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-12-17
2002-03-26
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S526000, C451S539000, C051S308000
Reexamination Certificate
active
06361403
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This Invention relates to a silica-based abrasive member, an abrasive disc provided with the abrasive member, and a process for polishing a material to be polished by using the abrasive disc.
The abrasive disc of the invention is useful for polishing or chemicomechanically polishing substrate materials such as a silicon wafer, oxide substrate materials such as lithium niobate and lithium tantalate, compound semiconductor substrates and glass substrates; and metals, silica glass and stone.
(2) Description of the Related Art
In conventional processes for polishing substrate materials, such as silicon wafer, oxide substrates, compound semiconductor substrates and a glass substrate, a loose abrasive polishing process has heretofore been employed wherein the substrate materials are polished with a polishing pad made of nonwoven fabric or suede cloth, while a polishing liquid comprising a loose grain such as colloidal silica and a chemical agent such as potassium hydroxide is continuously applied onto the polishing surface. For example, a process for polishing a silicon wafer by using a polishing cloth and a loose abrasive grain is described in Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) H5-154760 and JP-A H7-326597. In the conventional loose grain polishing process, a polishing liquid containing a large amount of a loose grain is used, and thus, a certain amount of a waste polishing liquid containing a loose grain is produced during polishing. Therefore, the efficiency of the polishing process, equipment for the waste disposal and the environmental pollution with the waste polishing liquid must be considered. The polishing pad such as polishing cloth tends to be clogged and the polishing performance is deteriorated, and thus, the polishing pad must be exchanged with considerable frequency and the polishing efficiency is decreased.
To solve the above problems, a proposal has been made in JP-A H6-39732 wherein a grinding stone for first polishing is used which is made by curing a slurry of an abrasive grain in a mixed liquid of a liquid phenolic resin and a liquid melamine resin. However, a problem of clogging still arises because the resins are not removed and are made present on the polished surface of a substrate material during polishing.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems, the inventors have conducted research to utilize an abrasive silica molding in a polishing process as suggested in, for example, JP-A H10-1376, and made the following findings.
(1) An abrasive silica molding has a rough surface due to finely divided silica particles, and the silica particles are placed in direct contact with a substrate material to be polished, and thus, polishing can be effected by using a polishing liquid containing no loose grain such as colloidal silica. Further, the silica particles fall off from the abrasive silica molding only to a minimized extent, and thus, the problem of waste disposal can be mitigated.
(2) An abrasive silica molding has a relatively high tenacity and thus exhibits a relatively good durability. Therefore, polishing can be continued over a long period without exchange of the abrasive molding. In addition, the polishing can be carried out under a high pressure leading to shortening of polishing time.
(3) A surface finish equal to or better than those of the conventional polishing processes can be obtained. At a polishing rate equal to or higher than those of the conventional processes, a surface finish of the same quality can be obtained. Further, decrease of the polishing performance with time is minor.
(4) Even when a polishing liquid comprising a loose abrasive grain is used, a high polishing rate can be employed at an abrasive grain concentration lower than that in the conventional polishing processes.
However, an abrasive molding with which a more efficient polishing process can be employed and which exhibits an enhanced duration of life is still desired.
In view of the foregoing, an object of the present invention is to provide an abrasive member made of a silica molding, an abrasive disc having the abrasive member, and a polishing process using the abrasive disc, which are characterized by using a specific silica molding which is not easily damaged during polishing, abrasion of which is reduced, and by which the problem of waste disposal is mitigated.
In one aspect of the present invention, there is provided an abrasive member made of a silica molding predominantly comprised of silica, and having a bulk density of 0.2 to 1.5 g/cm
3
, a BET specific surface area of 10 to 400 m
2
/g, an average particle diameter of 0.001 to 0.5 &mgr;m, and a multiplicity of interconnecting minute pores which are open to the exterior; said abrasive member containing a solid within the minute pores of the silica molding, which solid is soluble in a polishing liquid.
In another aspect of the present invention, there is provided an abrasive disc comprising the above-mentioned abrasive member and a supporting auxiliary, to which the abrasive member is fixed.
In still another aspect of the present invention, there is provided a process for polishing a material to be polished, which comprises rubbing the material to be polished with an abrasive disc while at least one of the abrasive disc and the material to be polished is moved and while a polishing liquid is applied to the abrasive disc, wherein an abrasive disc having the above-mentioned abrasive member is used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The abrasive member of the invention is made of a silica molding predominantly comprised of silica, and having a bulk density of 0.2 to 1.5 g/cm
3
, a BET specific surface area of 10 to 400 m
2
/g, an average particle diameter of 0.001 to 0.5 &mgr;m, and a multiplicity of interconnecting minute pores which are open to the exterior. The abrasive member contains a solid within the minute pores of the silica molding, which solid is soluble in a polishing liquid (said solid is hereinafter referred to as “soluble solid” for brevity).
Silica Molding
By the term “predominantly” used herein, we mean that the silica molding comprises at least 90% by weight of silica based on the weight of the silica molding. The content of silica can be expressed as a silica content as measured on a silica material which has been prepared by heat-treating a silica raw material such as a silica powder or soot at a temperature of 105° C. for 2 hours. The heat-treated silica material comprises silica, impurities and an ignition loss. Usually the content of silica in the silica raw material for the preparation of the silica molding used in the invention is at least about 97% by weight based on the sum of silica and impurities. If the content of silica in the silica molding is not larger than 90% by weight, problems arise in that the material to be polished tends to be contaminated with impurities to a significant degree and deteriorated during polishing.
The silica molding predominantly comprised of silica is made, for example, by molding a silica powder which is a wet process silica (i.e., precipitated silica) powder prepared from sodium silicate, or a dry process silica prepared by vapor phase thermal decomposition of silicon tetrachloride, or by piling a fine silica powder directly into a molded form (usually called as soot), which powder is as-prepared by vapor phase thermal decomposition of silicon tetrachloride.
The bulk density of the silica molding is in the range of 0.2 to 1.5 g/cm
3
. If the bulk density is too small, the abrasive member has poor durability and poor shape retention, and is abraded to an undesirably great extent during polishing. In contrast, if the bulk density is too large, the polished material has surface defects and the surface has a poor smoothness.
The BET specific surface area of the silica molding is in the range of 10 to 400 m
2
/g. If the BET specific surface area is too large, the abrasive member has poor shape retention. In contrast, if the BET specific
Kubota Yoshitaka
Kuramochi Hideto
Shakeri Hadi
Sughrue & Mion, PLLC
Tosoh Corporation
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