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  Polyurethane urea polishing padUSPTO Application #: 20060089095Title: Polyurethane urea polishing pad Abstract: The present invention relates to an article for altering a surface of a workpiece, or a polishing pad having a window. In particular, the polishing pad includes a polyurethane urea material wherein the polyurethane urea material contains cells which are at least partially filled with gas. The polyurethane urea material can be prepared by combining polyisocyanate and/or polyurethane prepolymer, hydroxyl-containing material, amine-containing material and blowing agent. The polishing pad according to the present invention is useful for polishing articles, and is especially useful for chemical mechanical polishing or planarization of microelectronic and optical electronic devices such as but not limited to semiconductor wafers. The window of the polishing pad is at least partially transparent and thus, can be particularly useful with polishing or planarizing tools that are equipped with through-the-platen wafer metrology. (end of abstract)
Agent: Ppg Industries, Inc. Law Department - Intellectual Property - Pittsburgh, PA, US Inventors: Robert G. Swisher, Alan E. Wang, William C. Allison USPTO Applicaton #: 20060089095 - Class: 451533000 (USPTO) Related Patent Categories: Abrading, Flexible-member Tool, Per Se, Laminate The Patent Description & Claims data below is from USPTO Patent Application 20060089095. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to an article for altering a surface of a workpiece. In particular, the present invention is directed to a polishing pad having a window. More particularly, the polishing pad can include a polyurethane urea material wherein cells at least partially filled with gas are substantially uniformly distributed throughout the material and/or pad. The polyurethane urea material can be prepared by combining polyisocyanate and/or polyurethane prepolymer; hydroxyl-containing material; amine-containing material and blowing agent. The polishing pad according to the present invention is useful for polishing articles, and is especially useful for chemical mechanical polishing or planarization of microelectronic and optical electronic devices such as but not limited to semiconductor wafers. The window of the polishing pad is at least partially transparent and thus, can be particularly useful with polishing or planarizing tools that are equipped with through-the-platen wafer metrology. [0002] The polishing or planarization of a rough surface of an article such as a microelectronic device, to a substantially smooth surface generally involves rubbing the rough surface with the work surface of a polishing pad using a controlled and repetitive motion. A polishing fluid can be interposed between the rough surface of the article that is to be polished and the work surface of the polishing pad. [0003] The fabrication of a microelectronic device can comprise the formation of a plurality of integrated circuits on a semiconductor substrate. The composition of the substrate can include silicon or gallium arsenide. The integrated circuits generally can be formed by a series of process steps in which patterned layers of materials, such as conductive, insulating and semi-conducting materials, are formed on the substrate. In order to maximize the density of integrated circuits per wafer, it is desirable to have a planar polished substrate at various stages throughout the production process. As such, production of a microelectronic device typically involves at least one polishing step and can often involve a plurality of polishing steps, which can result in the use of more than one polishing pad. [0004] The polishing step can include rotating the polishing pad and the semiconductor substrate against each other in the presence of a polishing fluid. The polishing fluid can be mildly alkaline and can optionally contain an abrasive particulate material such as but not limited to particulate cerium oxide, particulate alumina, or particulate silica. The polishing fluid can facilitate the removal and transport of abraded material off and away from the rough surface of the article. [0005] Polishing pad characteristics such as pore volume and pore size can vary from pad-to-pad and throughout the operating lifetime of a particular pad. Variations in the polishing characteristics of the pads can result in inadequately polished and planarized substrates which can be unsuitable for fabricating semiconductor wafers. Thus, it is desirable to develop a polishing pad that exhibits reduced pad-to-pad variation in polishing and planarization characteristics. It is further desirable to develop a polishing pad that exhibits reduced variations in polishing and planarization characteristics throughout the operating lifetime of the pad. [0006] Planarizing tools having the ability to measure the progress of the planarization process while the wafer is held in the tool and in contact with the pad are known in the art. Measuring the progress of planarizing a microelectronic device during the planarizing process can be referred to in the art as "in-situ metrology". U.S. Pat. Nos. 5,964,643 and 6,159,073; and European Patent 1,108,501 describe polishing or planarizing tools and in-situ metrology systems. In general, in-situ metrology can include directing a beam of light through an at least partially transparent window located in the platen of the tool; the beam of light can be reflected off the surface of the wafer, back through the platen window, and into a detector. The polishing pad can include a window that is at least partially transparent to the wavelengths used in the metrology system, and essentially aligned with the planten window. [0007] Thus, it is desirable to develop a polishing pad that comprises a window area useful for in-situ metrology. It is further desirable that the window provides suitable transparency throughout the operating life of the pad. [0008] One disadvantage with known pads having windows which are coplanar with the polishing surface, can include wearing of the window portion at a slower rate than the pad surface. A further disadvantage with known pads having a coplanar window can include scratching of the window as a result of its contact with abrasive particles in the slurry during the polishing or planarization process. A scratched window can generally reduce the transparency of the window and can cause an attenuation of the metrology signal. [0009] For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. [0010] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. [0011] The present invention includes a pad having an at least partially transparent cast-in-place window adapted to polish a microelectronic substrate. The pad of the present invention comprises polyurethane urea material. At least a portion of the polyurethane urea contains cells that are at least partially filled with gas, and at least a portion of the at least partially gas-filled cells is formed by an in-situ reaction. [0012] In a non-limiting embodiment, the cells can be substantially uniformly distributed throughout the material and/or pad. In another non-limiting embodiment, the polyurethane urea can be prepared by combining polyisocyanate, hydroxyl-containing material, amine-containing material and blowing agent. In another non-limiting embodiment, the polyurethane urea can be formed by condensation polymerization of polyisocyanate functional polyurethane prepolymer with polyamine and blowing agent. In a further non-limiting embodiment, the polyurethane urea can be formed by combining polyisocyanate and polyurethane prepolymer, optional hydroxyl-containing material, amine-containing material and blowing agent. In a non-limiting embodiment, at least a portion of the pad can comprise a window which is at least partially transparent to wavelengths used by the metrology instrumentation of polishing tools. [0013] In alternate non-limiting embodiments, the amount of polyisocyanate, hydroxyl-containing material and amine-containing material can be selected such that the equivalent ratio of (NCO+NCS):(NH+OH) can be greater than 0.95, or at least 1.0, or at least 1.05, or less than 1.3, or less than 1.2, or less than 1.1. [0014] Polyisocyanates useful in the preparation of the polyurethane urea of the present invention are numerous and widely varied. Suitable polyisocyanates can include but are not limited to polymeric and C.sub.2-C.sub.20 linear, branched, cyclic and aromatic polyisocyanates. Non-limiting examples can include polyisocyanates having backbone linkages chosen from urethane linkages (--NH--C(O)--O--). [0015] The molecular weight of the polyisocyanate can vary widely. In alternate non-limiting embodiments, the number average molecular weight (Mn) can be at least 100 grams/mole, or at least 150 grams/mole, or less than 15,000 grams/mole, or less than 5000 grams/mole. The number average molecular weight can be determined using known methods. The number average molecular weight values recited herein and the claims were determined by gel permeation chromatography (GPC) using polystyrene standards. [0016] Non-limiting examples of suitable polyisocyanates can include but are not limited to polyisocyanates having at least two isocyanate groups. [0017] Non-limiting examples of polyisocyanates can include but are not limited to aliphatic polyisocyanates, cycloaliphatic polyisocyanates wherein one or more of the isocyanato groups are attached directly to the cycloaliphatic ring, cycloaliphatic polyisocyanates wherein one or more of the isocyanato groups are not attached directly to the cycloaliphatic ring, aromatic polyisocyanates wherein one or more of the isocyanato groups are attached directly to the aromatic ring, and aromatic polyisocyanates wherein one or more of the isocyanato groups are not attached directly to the aromatic ring. [0018] In a non-limiting embodiment of the present invention, the polyisocyanate can include but is not limited to aliphatic or cycloaliphatic diisocyanates, aromatic diisocyanates, cyclic dimers and cyclic trimers thereof, and mixtures thereof. Non-limiting examples of suitable polyisocyanates can include but are not limited to Desmodur N 3300A (hexamethylene diisocyanate trimer) which is commercially available from Bayer; Desmodur N 3400 (60% hexamethylene diisocyanate dimer and 40% hexamethylene diisocyanate trimer). [0019] In a non-limiting embodiment, the polyisocyanate can include dicyclohexylmethane diisocyanate and isomeric mixtures thereof. As used herein and the claims, the term "isomeric mixtures" refers to a mixture of the cis-cis, trans-trans, and cis-trans isomers of the polyisocyanate. Non-limiting examples of isomeric mixtures for use in the present invention can include the trans-trans isomer of 4,4''-methylenebis(cyclohexyl isocyanate), hereinafter referred to as "PICM" (paraisocyanato cyclohexylmethane), the cis-trans isomer of PICM, the cis-cis isomer of PICM, and mixtures thereof. [0020] In one non-limiting embodiment, the PICM used in this invention can be prepared by phosgenating the 4,4'-methylenebis(cyclohexyl amine) (PACM) by procedures well known in the art such as the procedures disclosed in U.S. Pat. Nos. 2,644,007 and 2,680,127 which are incorporated herein by reference. The PACM isomer mixtures, upon phosgenation, can produce PICM in a liquid phase, a partially liquid phase, or a solid phase at room temperature. The PACM isomer mixtures can be obtained by the hydrogenation of methylenedianiline and/or by fractional crystallization of PACM isomer mixtures in the presence of water and alcohols such as methanol and ethanol. [0021] In a non-limiting embodiment, the isomeric mixture can contain from 10-100 percent of the trans,trans isomer of 4,4'-methylenebis(cyclohexyl isocyanate) (PICM). [0022] In a non-limiting embodiment, the polyisocyanate can include 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate and mixtures of these isomers ("TDI"). [0023] Additional aliphatic and cycloaliphatic diisocyanates that can be used in alternate non-limiting embodiments of the present invention include 3-isocyanato-methyl-3,5,5-trimethyl cyclohexyl-isocyanate ("IPDI") which is commercially available from Arco Chemical, and meta-tetramethylxylene diisocyanate (1,3-bis(1-isocyanato-1-methylethyl)-benzene) which is commercially available from Cytec Industries Inc. under the tradename TMXDI.RTM. (Meta) Aliphatic Isocyanate. [0024] As used herein and the claims, the terms aliphatic and cycloaliphatic diisocyanates refer to 6 to 100 carbon atoms linked in a straight chain or cyclized having two diisocyanate reactive end groups. In a non-limiting embodiment of the present invention, the aliphatic and cycloaliphatic diisocyanates for use in the present invention can include TMXDI and compounds of the formula R--(NCO).sub.2 wherein R represents an aliphatic group or a cycloaliphatic group. Continue reading... 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