Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-02-13
2004-03-02
Sanders, Kriellion (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S612000, C524S803000, C051S298000, C051S297000, C433S166000, C451S533000, C451S540000
Reexamination Certificate
active
06699920
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to reaction molding and to polishing pads for use in manufacturing semiconductor devices such as wafers or memory disc substrates.
BACKGROUND OF THE INVENTION
Many industries require the ability to efficiently polish highly finished surfaces used in the semiconductor and disc industry. Specific articles having highly finished surfaces include, but are not limited to, semiconductor/silicon wafers and memory disc substrates. Presently, the method of polishing silicon wafers utilizes polishing pads made from felts saturated with urethanes, which have been polymerized to form a rigid surface. Although these devices are highly useful and efficient in polishing highly finished surfaces, they are difficult to manufacture and it is difficult to control their quality during the manufacturing process. The variations that exist from pad to pad are systemic to the saturation process and it is very difficult to produce large numbers of polishing pads with predictable quality and performance characteristics.
Thus, there is a need for new and improved methods of manufacturing polishing pads that are inexpensive, highly efficient, and that produce durable compositions having extremely predictable quality and performance characteristics.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above purposes and others realized in reaction molding processes for manufacturing polishing pad substrates. A reaction molding process of the invention includes disposing a reaction mixture into a reaction mold and then applying pressure and temperature to the reaction mixture sufficient to cause polymerization and substrate formation. In accordance with the principle of the invention, the reaction mixture consists of polyvinyl alcohol and a dibasic acid with a suitable catalytic cross-linking agent. In another embodiment, the reaction mixture consists of polyvinyl alcohol and an amine with a suitable catalytic cross-linking agent. In yet another embodiment, the reaction mixture consists of mixtures of both dibasic acids and amines with polyvinyl alcohol and a suitable catalytic cross-linking agent. The reaction pressure preferably falls within a range of 10,000-20,000 pounds per square inch (PSI) and the reaction temperature preferably falls within a range of 100-200° C. A polishing pad substrate formed by the reaction molding process of the invention is mildly hard with a typical durometer reading between 90 and 55 Shore D scale and exhibits a mildly waxy surface and, in accordance with the invention, is useful for polishing highly finished surfaces. Prior to the reaction, the reaction mixture is capable of being fortified with one or more polishing agents, one or more fillers for controlling modulus and/or coefficient of expansion of the reaction process, and/or a selected quantity of one or more hydroxylated polymers and/or one or more catalytic cross-linking agents. The reagents of the reaction mixture can be layered in order to produce useful zones of reaction, depending upon the polishing performance characteristics desired of the substrate.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Reacting a dibasic acid, such as adipic acid, with an alcohol or other hydroxylated polymer under a pressure in a range of 10,000-20,000 pounds per square inch (PSI) and a temperature in a range of 100-200° C., in the presence of a suitable catalyst, produces a polymer having the following structure:
Prosecuting the foregoing reaction with the additional reactant polyvinyl alcohol (PVA), produces a polymer, which exhibits a mildly hard and waxy surface which is useful as a polishing pad for producing highly finished surfaces. The characteristics of the polymer are capable of being altered by the addition of one or more polishing agents such as aluminum oxide, silica, cerium oxide or combinations of several agents, to produce characteristics required to polish substrates to a highly finished surface. These polishing agents can be classified as polyesters.
Reacting a polybasic acid with urea in the presence of a hydroxylated polymer such as PVA produces a mixture of polymers consisting of polyester/polyamides having structures as described above, in addition to the formation of urethanized polymers having the following structure:
Depending on the particular dibasic acid being used, the amine, and hydroxylated polymer, the resulting hardness of the polishing pad substrate is capable of being varied in order to meet specific polishing needs. Other such dibasic acids are, for example, azelaic acid, malonic acid, succinic acid and certain lactones. Primary and secondary amines can also be used to change the polishing characteristics when urethanization takes place upon the hydroxylated polymer, for example with PVA.
In accordance with the invention, a quantity of dibasic acid, a quantity of PVA and a quantity of urea are mixed together with a suitable catalyst to form a reaction mixture, which is disposed into a reaction mold. To the reaction mixture are added various polishing agents, if desired. The mold is closed and the reaction mixture subjected to high pressure and temperature causing polymerization to take place. These physical conditions cause polymerization to take place forming a polishing substrate. The various components of the reaction mixture can be laid down in layers in the mold, in accordance with an embodiment of the invention. An example of this is disposing a mounting layer of PVA and a cross-linking catalyst on the bottom of the mold and mounting on the mounting layer a polishing layer consisting of the remaining reactants of the reaction mixture including the polishing agents and catalyst in addition to, if desired, a plasticizer, polyethylene glycol, ethylene glycol, etc., in addition to other various polishing agents such as cerium oxide, feldspar, silica, etc. A surfactant can also be used in the polishing layer for facilitating distribution of the polishing layer as it is cross-linked during the molding process. At this point, the mold is closed and the layered substrate subjected to high pressure and temperature. These physical conditions cause polymerization to take place in all the layers with specific polymers grown in zones. This growth zone polymerization forms the basic polishing pad substrate. The zones are chemically attached to one another producing inseparable zones, each having unique chemical and physical characteristics. In a typical example, the polishing layer can consist of 2-5% by weight of a plasticizer, 25-60% by weight of a polishing agent, 1-2% by weight of a surfactant, 35-55% by weight of PVA, and 9-10% by weight of a cross-linking agent. The mounting layer can consist of 90% by weight of PVA and 10% by weight of the cross linking agent.
Just as the shape of the mold defines the form of the product being molded during conventional molding, various geometric inscriptions incorporated into the mold produce various geometric surfaces upon the surface of the pad substrate, enhancing the ability of the substrate to polish highly finished surfaces. A pattern placed onto the surface of various polishing pads imparts specific polishing characteristics when polishing silicon wafer substrates.
Each of the reaction mixtures of the invention is capable of being fortified with additives prior to reaction molding for affecting the physical characteristics of the resulting substrate. For instance, selected quantities cutting and polishing agents such as aluminum oxide, cerium oxide, carborundum, silicon dioxide and the like can be added, either individually or in selected combinations, for producing substrates having desired polishing characteristics. In order to increase modulus and/or reduce the coefficient of expansion, selected quantities of one or more other fillers can be incorporated into the reaction mixture such as microfibers, mineral fillers, etc. Other suitable fillers include, but are not limited to, various inorganic compounds such as silicon carbides, boron derivatives, dry-type slurry
Goltry Michael W.
Parson&Goltry
Parsons Robert A.
Sanders Kriellion
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