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  Smoothing pad for bare semiconductor wafersUSPTO Application #: 20070015444Title: Smoothing pad for bare semiconductor wafers Abstract: One embodiment of the present invention is a smoothing pad for bare semiconductor wafers the smoothing pad for bare semiconductor wafers. The smoothing pad comprises a smoothing body having a closed-cell thermoplastic foam comprising an ethylene vinyl acetate block copolymer comprising a vinyl acetate content ranging from about 1 to about 18 wt %. The smoothing body is substantially free of particles having an average size of greater than about 1 micron. Other aspects of the invention comprise a method of preparing a bare semiconductor wafer and a method of manufacturing a pad for smoothing bare semiconductor wafers. (end of abstract)
Agent: Hitt Gaines P.C. - Richardson, TX, US Inventors: Daniel D. Marks, Anthony J. Clark, Douglas Targgart USPTO Applicaton #: 20070015444 - Class: 451041000 (USPTO) Related Patent Categories: Abrading, Abrading Process, Glass Or Stone Abrading The Patent Description & Claims data below is from USPTO Patent Application 20070015444. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 11/033,690, entitled, A THERMOPLASTIC CHEMICAL MECHANICAL POLISHING PAD AND METHOD OF MANUFACTURE, filed on Jan. 12, 2005 by Marks, et al. ("690' application"), which is currently pending. The above-listed application is commonly assigned with the present invention and is incorporated herein by reference as if reproduced herein in its entirety. TECHNICAL FIELD OF THE INVENTION [0002] The present invention is directed to semiconductor wafer smoothing pads, and methods of use and manufacture thereof. BACKGROUND OF THE INVENTION [0003] In semiconductor manufacturing, after growing a semiconductor crystal and slicing the crystal to form wafers, the wafer is subject to a preparation process. Typically, the preparation process includes one or more polishing steps to planarize the bare semiconductor wafer, followed by a smoothing step to remove scratches on the wafer's surface, and then a cleaning step to remove debris on the wafer's surface. The goals of wafer smoothing are different than the goals wafer polishing or cleaning, thereby making these separate fields of endeavor. The goal of polishing is to remove portions of the wafer itself to produce a flatter surface, while the goal of smoothing is to reduce local discontinuities on the surface of the bare wafer without removing substantial amounts of wafer material other than that needed to improve the wafer's smoothness. Unfortunately, however, the smoothing step can also inadvertently reintroduce nonplanarities or scratches into the wafer. [0004] Accordingly, what is needed is a smoothing pad and process that can provide a highly smooth wafer surface without introducing nonplanarities and minimize the introduction of scratches into the wafer. SUMMARY OF THE INVENTION [0005] To address the above-discussed deficiencies of the prior art, the present invention provides in one embodiment, a smoothing pad for bare semiconductor wafers that comprises a smoothing body. The smoothing body includes a closed-cell thermoplastic foam having an ethylene vinyl acetate block copolymer comprising a vinyl acetate content ranging from about 1 to about 18 wt %. The smoothing body is substantially free of particles having an average size of greater than about 1 micron [0006] Another embodiment is a method of preparing a bare semiconductor wafer that comprises smoothing the wafer. Smoothing the bare semiconductor wafer includes situating the above-described smoothing pad adjacent to a surface of the bare semiconductor wafer. Smoothing also includes moving the smoothing pad relative to the bare semiconductor wafer until the surface has a roughness of less than or equal to about 20 Angstroms. [0007] Still another embodiment of the present invention is a method for manufacturing a pad for smoothing bare semiconductor wafers. The method comprises placing an ethylene vinyl acetate block copolymer and a foaming agent into a container. The ethylene vinyl acetate block copolymer has a vinyl acetate content ranging from about 1 to about 18 wt %. The ethylene vinyl acetate block copolymer is substantially free of particles having an average size of about 1 micron or greater. The method also includes mixing the ethylene vinyl acetate block copolymer and the foaming agent together, and then forming closed cells throughout the ethylene vinyl acetate block copolymer to thereby produce a closed-cell thermoplastic smoothing body. [0008] The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0009] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [0010] FIG. 1 presents an cross-sectional view of a portion of an example smoothing pad of the present invention; [0011] FIG. 2 illustrates, by flow diagram, an example method of preparing a bare semiconductor wafer according to the principles of the present invention; and [0012] FIG. 3 illustrates, by flow diagram, an example method of manufacturing a pad for smoothing bare semiconductor wafers according to the principles of the present invention. DETAILED DESCRIPTION [0013] As part of the present invention it was discovered that an exceptionally smooth bare semiconductor wafer surface can be prepared by using a pad having a smoothing body that comprises a certain type of thermoplastic foam that is substantially free of particles having an average size of about 1 micron or greater. The combination of the thermoplastic foam and the absence of particles are important to producing a smooth surface while not introducing nonplanarities or scratches into the wafer during smoothing. [0014] FIG. 1 presents a cross-sectional view of a portion of an exemplary smoothing pad 100 for smoothing bare semiconductor wafers 110, and in particular smoothing a surface 112 of the wafer 110. The term bare semiconductor wafer as used herein refer to a semiconductor wafer with no integrated circuit components, including sacrificial structures, formed thereon. Example bare semiconductor wafers 110 include silicon, silicon carbide or gallium arsenide wafers. [0015] The smoothing pad 100 comprises a smoothing body 115 that has a closed-cell thermoplastic foam 120. The closed cell foam 120 comprises an ethylene vinyl acetate (EVA) block copolymer 125 comprising a vinyl acetate content ranging from about 1 to about 18 weight percent (wt %) and that is substantially free of particles having an average size of about 1 micron or greater. In some preferred embodiments, the smoothing body 115 consists essentially of the closed-cell thermoplastic foam 120, which in turn, consists essentially of the above-described ethylene vinyl acetate (EVA) block copolymer 125. The thermoplastic foam 120 can also comprise trace amounts (e.g., about 1 to 2 wt %) of foaming agents, cross-linking agents, reaction products of the cross-linking or foaming agent, or catalysts to activate the cross-linking agent or foaming agent. [0016] The term substantially free of particles, as used herein, is defined as a particle content of about 1 wt % or less, where the particles have an average size of 1 micron or greater. While not limiting the scope of the invention by theory, it is believed that hard particles projecting from the surface of the smoothing body 115 could cause substantial material losses from the bare semiconductor wafer 110, thereby increasing the potential for scratches to be introduced into the wafer's surface 112 during smoothing. In particular, it is desirable for the smoothing body 115 to be free of particles having a hardness of about 5 mohs or greater. Examples of such particles include inorganic oxides such as silica, alumina, ceria, titania, or zirconia. [0017] In some embodiments, however, the smoothing body 115 can include sub-micron sized particles 130. E.g., some embodiments of the smoothing body 115 include about 4.5 wt % of titania particles 130 added as a colorant, the titania particles 130 having an average size of about 0.3 microns. In some embodiments, to further facilitate the production of a smooth surface 112 and to reduce pad manufacturing costs, it is desirable for the smoothing body 115 to also be substantially free (e.g., less than about 1 wt %) of the submicron particles 130, including colorant particles having an average size of about 0.3 microns or greater. [0018] The term smoothing pad 100, as used herein, refers to a material, or composition of materials, that is configured to smooth the wafer's surface 112 while not substantially removing material from the wafer 110. E.g., while smoothing the bare semiconductor wafer 110 with the smoothing pad 115, no more than about 1 to 2 microns per minute of a thickness 135 of the bare semiconductor wafer 110 is removed from the surface 112. This is in contrast to a conventional wafer polishing pad, which is configured to remove substantially greater amounts of material from the wafer's surface 112 (e.g., about 30 microns or more per minute of the wafer polishing). This is also in contrast to a conventional cleaning pad, which is configured to remove debris on the wafer's surface 112. Continue reading... Full patent description for Smoothing pad for bare semiconductor wafers Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Smoothing pad for bare semiconductor wafers patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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