Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-08-27
2003-09-30
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C428S313500, C428S317900, C521S130000, C521S137000, C521S155000, C521S163000, C521S170000
Reexamination Certificate
active
06627671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to method for making urethane molded products for polishing pad which are provided for polishing articles to be polished such as semiconductor devices, and also to urethane molded products for polishing pad.
2. Description of the Prior Art
Polishing pads used for semiconductor devices and glasses are known, including those pads of the porous non-woven fabric type obtained by applying a polyurethane solution to a non-woven fabric as set out in Japanese Laid-open Patent No. 64-58475 and of the foamed polyurethane type which is obtained by wet molding of a polyurethane solution. Both types of pads have a structure which is provided with cellular holes on the surface thereof, and thus, are a good property of holding an article to be polished at the time of polishing and are able to favorably retain a supplied grain solution (polishing slurry) therein. However, these pads are disadvantageous in that they are too soft to cause compressive deformation on use, poor in flatness of the surface of a polished article obtained by polishing, and short in life of the polishing pad.
In recent years, as semiconductor devices are highly integrated, an interconnection pattern on a substrate is more densified, under which there is a strong demand for flatness on a substrate surface as influencing the transfer of a pattern. In order to provide a more flattened wafer surface of a semiconductor substrate, there has been adopted a chemical mechanical polishing process (abbreviated as CMP process) wherein a chemical function and a mechanical function are combined. It has been demanded to develop a polishing pad which is suitably applicable to such the CMP process.
For instance, Japanese Laid-open Patent No. Hei 8-500622 discloses a polishing pad which comprises a plurality of polymeric fine elements, such as expanded microballoons, in a polyurethane matrix. The pad has a high surface hardness, so that it is more unlikely to cause compressive deformation than such a non-woven or foamed polyurethane-type polishing pad as mentioned above, thereby ensuring a high polishing rate and a good flatness. However, only one type of the expanded microballoons are mentioned as the polymeric fine elements used. When used as a polishing pad, the cells derived from the microballoons are allowed to open at the surface of the polishing pad, and abrasive grains are held at the opened cells. Nevertheless, the holding or retaining property of abrasive grains or the like with the cells alone is not satisfactory. Accordingly, there is a demand for a polishing pad which is improved in the retaining property and ensures improved polishing rate and flatness.
Further, once expanded microballoons have the drawback that they are small in specific gravity and have a great difference in specific gravity with an isocyanate-terminated urethane prepolymer, so that when mixed, they are liable to separate from each other, resulting in a poor dispersion of high viscosity, and that when such microballoons are mixed with an amine compound under agitation, air-mixing is caused. Moreover, when a microballoon-incorporated isocyanate-terminated urethane prepolymer and an amine compound are subjected to cast molding in a mold, the expanded microballoons are floated during a time before curing of the polyurethane resin, thus presenting the problem that a uniformly dispersed polishing pad cannot be obtained.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide the urethane molded products for use as a polishing pad, which comprises two types of cells of different sizes, created by expanded microballoons and water, in the urethane molded products, so that a polishing pad obtained by slicing the resultant urethane molded products into pieces is improved in polishing characteristics, with a reduced variation in the polishing characteristics among polishing pads.
A further object of the invention is to provide the urethane molded products for use as a polishing pad wherein two different sizes of cells are formed in the urethane molded products, including one type of cells formed by expanding non-expanded, thermally expandable microspheres and the other type of cells having a larger size than the former cells and formed with water.
According to one embodiment of the invention, there is provided a method for making urethane molded products for polishing pad which comprises mixing a mixture of expanded microballoons (A1), an isocyanate-terminated urethane prepolymer (B), and an active hydrogen-containing compound (C) with 0.005 to 0.5 wt %, based on the mixture, of water (D), and forming cells created by the action of the water (D) along with cells derived from the expanded microballoons (A1) in the resultant molded products wherein the expanded microballoons (A1) are pre-mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C) . It is preferred that the expanded microballoons are present in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the total of the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C). The urethane molded products for polishing pad obtained according to this embodiment comprises expanded microballoons (A1) and cells formed by means of water (D) therein.
According to another embodiment of the invention, there is also provided a method for making urethane molded products for polishing pad which comprises mixing a mixture of non-expanded, thermally expandable microspheres (A2), an isocyanate-terminated urethane prepolymer (B), and an active hydrogen-containing compound (C) with 0.005 to 0.5 wt %, based on the mixture, of water (D), and expanding the non-expanded, thermally expandable microspheres (A2) by application of heat of reaction and heat from outside and also forming cells created by the action of the water (D) wherein the non-expanded, thermally expandable microspheres (A2) are pre-mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C) . Preferably, the non-expanded, thermally expandable microspheres are present in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the total of the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C). The urethane molded products for polishing pad obtained according to this second embodiment of the invention comprises microballoons (A1) expanded by application of heat at the time of urethane molding and cells formed by means of water (D) therein.
In this invention, the active hydrogen-containing compound should preferably consist of a diamine compound (C1) or a mixture of the diamine compound (C1) and a low molecular weight diol (C2) having a molecular weight of 500 to 1000.
DETAILED DESCRIPTION OF THE INVENTION
As disclosed in Japanese Laid-open Patent No. Sho 57-137323 and the like, the expanded microballoons (A1) used in the present invention are obtained by thermal expansion of non-expanded, thermally expandable microspheres which individually have a low boiling hydrocarbon, such as, for example, isobutane, pentane, isopentane, petroleum ether or the like, at a center thereof and a shell encapsulating the hydrocarbon therein and made of a thermoplastic resin such as, for example, an acrylonitrile-vinylidene chloride copolymer, an acrylonitrile-methyl methacrylate copolymer, a vinyl chloride-ethylene copolymer or the like. When heated, the low boiling hydrocarbon existing at the center of each microspheres is vaporized and gasified to cause the shell portion to be softened thereby providing microballoons (A1) having a gas encapsulated therein. The expanded microballoons (A1) preferably have a size of 10 to 100 &mgr;m. If the size of the expanded microballoons (A1) is smaller than 10 &mgr;m, an appreciable polishing effect may not be expected. On the contrary, when the size is larger than 100 &mgr;m, the resultant urethane molded products for polishing pad u
Kihara Katushi
Mochizuki Yoshimi
Cooney Jr. John M.
Fuji Spinning Co., Ltd.
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