Patent Publication Number: US-2018036861-A1

Title: Polishing pad, polishing apparatus and method for manufacturing polishing pad

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polishing pad, a polishing apparatus, and a method for manufacturing the polishing pad. 
     2. Description of the Related Art 
     A polishing process generally refers to a wear control for a preliminary coarse surface in a process of chemical mechanical polishing (CMP), which makes slurry containing fine particles evenly dispersed on an upper surface of a polishing pad, and at the same time places a substrate against the polishing pad and then rubs the substrate repeatedly with the polishing pad in a regular motion. The substrate may be a semiconductor, a storage medium substrate, an integrated circuit, an LCD flat-panel glass, an optical glass or a photoelectric panel. During the polishing process, a polishing pad must be used to rub the substrate, thus the quality of the polishing pad directly influences the polishing effect to the substrate. 
       FIG. 1  shows a schematic view of a polishing apparatus with a conventional polishing pad. The polishing apparatus  1  includes a pressure plate  11 , a mounting sheet  12 , a substrate  13 , a polishing plate  14 , a polishing pad  15  and slurry  16 . The pressure plate  11  is positioned opposite to the polishing plate  14 . The mounting sheet  12  is adhered to the pressure plate  11  through a backside adhesive (not shown) and is used for carrying and mounting the substrate  13 . The polishing pad  15  is mounted on the polishing plate  14  and faces the pressure plate  11  for polishing the substrate  13 . 
     The operation manner of the polishing apparatus  1  is as follows. First, the substrate  13  is mounted on the mounting sheet  12 , and then both the pressure plate  11  and the polishing plate  14  are rotated and the pressure plate  11  is simultaneously moved toward the polishing plate  14 , such that the polishing pad  15  contacts the surface of the substrate  13 . Accordingly, the substrate  13  is polished by the polishing pad  15  with the continuously supplemented slurry  16 . 
       FIG. 2  shows a cross sectional view of a conventional polishing pad. As disclosed in U.S. Pat. No. 5,578,362, the polishing pad  2  includes a plurality of pores  22  and a resin  21 . A method for manufacturing the polishing pad  2  is filling a resin composition (which is usually a foaming polymer formed by thermoplastic polyurethane) into a columnar mold. After cooling and solidifying, the polishing pad  2  is produced by cutting the cured resin composition into slices. The polishing pad  2  has an independent foam structure, which is often used in a polishing process with a higher degree of planarity. However, the biggest problem of the polishing pad  2  is that when filling the resin  21  in the columnar mold, the resin  21  cannot be uniformly distributed in the columnar mold due to the effect of surface tension. When forming, such non-uniform distribution of the resin  21  in the columnar mold results in varying sizes and uneven distribution of the pores  22 , which cannot be easily controlled. After the slicing process, the pores  22  with varying sizes can be clearly seen on a sliced surface of the polishing pad  2 . Besides, the pores  22  are not connected to each other, thus the slurry cannot easily flow therethrough. When polishing, the slurry is unable to infiltrate into the interior region of the polishing pad, thus reducing the slurry retention capacity of the surface. 
     In another aspect, R.O.C. Patent Publication 200609315 discloses a porous chemical mechanical polishing pad with component-filled pores. The polishing pad includes a polymeric material, and the pores of the polishing pad are controlled by limiting void spaces within the polymeric material matrix. At the same time, liquid, solid or a mixture thereof is added for improving polishing uniformity of the polishing pad. However, the above method cannot easily control the sizes of the pores, and small pores on a surface of the polishing pad may easily be filled by polishing powder. The polishing pad is provided with poor slurry retention capacity, which tends to cause scratches on the substrate. 
     Therefore, it is required to develop a novel polishing pad in the art field for overcoming the defect of non-uniform pore distribution and poor slurry retention capacity in the aforementioned polishing pad, thus improving its polishing performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a specific polishing layer having titanium dioxide nanowires for increasing hydrophilicity of the polishing layer. As such, slurry can adhere to the titanium dioxide nanowires, thus increasing slurry retention capacity of the polishing layer. 
     The invention provides a polishing pad comprising:
         a polishing layer, wherein the polishing layer comprises
           an elastomer main body; and   a plurality of titanium dioxide nanowires, wherein each of the titanium dioxide nanowires is independent and is dispersed evenly and randomly in the elastomer main body.   
               

     The invention also provides a polishing apparatus comprising:
         a polishing plate;   a substrate;   the polishing pad according to the above, which is adhered on the polishing plate for polishing the substrate; and   slurry contacting with the substrate for polishing.       

     The invention further provides a method for manufacturing the polishing pad according to the above, comprising:
         (a) providing an elastomer composition;   (b) providing the plurality of titanium dioxide nanowires;   (c) dispersing the titanium dioxide nanowires of the step (b) evenly and randomly in the elastomer composition of the step (a);   (d) providing the polishing layer by curing the elastomer composition to form the elastomer main body.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of a polishing apparatus having a conventional polishing pad. 
         FIG. 2  shows a cross sectional view of the conventional polishing pad. 
         FIG. 3  shows a cross sectional view of a polishing pad according to the present invention. 
         FIG. 4  shows a schematic view of a polishing apparatus having the polishing pad according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention provides a polishing pad comprising:
         a polishing layer, wherein the polishing layer comprises
           an elastomer main body; and   a plurality of titanium dioxide nanowires, wherein each of the titanium dioxide nanowires is independent from each other and is dispersed evenly and randomly in the elastomer main body.   
               

     The term “polishing pad” according to the present invention refers to a pad adapted for abutting against a substrate to be polished in a process of chemical mechanical polishing. The polishing pad rubs the to-be-polished substrate repeatedly in a regular motion with the cooperation of slurry containing small particles, so as to wear a preliminary coarse surface of the substrate into a smooth surface. The term “polishing layer” in the present invention refers to an element of a polishing pad, which element is adapted for contacting with and rubbing the substrate to be polished. That is, the polishing layer is the element which actually executes polishing with the cooperation of the slurry. The polishing layer can be a single sheet, or can be laminated with other elements into a sheet structure. With references to  FIG. 3 , a polishing layer  3  according to the present invention includes an elastomer main body  32  and a plurality of titanium dioxide nanowires  31 , with each of the titanium dioxide nanowires  31  being independent and distributed evenly and randomly in the elastomer main body  32 . 
     The term “elastomer main body” in the present invention refers to a main body made of an elastomer. The elastomer is a type of polymer which has rubber-like characteristics. During the polishing process, the elastomer main body provides polishing function while preventing scratches on the surface of the substrate to be polished. 
     In an embodiment of the present invention, the elastomer is provided in an elastomer composition, with said composition including a resin and a crosslinking agent. 
     The term “crosslinking agent” in the present invention refers to a reagent which undergoes a crosslinking reaction with the resin of the present invention, so as to cure the resin under appropriate conditions. The type of the crosslinking agent can be selected in accordance with the type of the resin. 
     A proper solvent for the elastomer composition includes dimethyl formamide (DMF) or water. The elastomer can optionally include an additive, such as a surfactant. A concentration of the elastomer in the elastomer composition is preferably in a range of about 2 wt % to about 60 wt %. 
     With references to  FIG. 3 , in a preferred embodiment of the present invention, the polishing layer further includes a plurality of pores  33  dispersed in the elastomer main body  32 . 
     In a preferred embodiment of the present invention, the elastomer main body and the plurality of pores can be provided by a foaming resin simultaneously. The term “foaming resin” in the present invention refers to a material containing a thermoplastic resin and a thermodecomposing foaming agent. Preferably, the resin includes at least one selected from a group consisting of polyurethane, polyolefin, polycarbonate, polyvinyl alcohol, nylon, elastic rubber, polystyrene, poly aromatic molecules, fluorine-containing polymer, polyimide, crosslinked polyurethane, crosslinked polyolefin, polyether, polyester, polyacrylate, elastic polyethylene, polytetrafluoroethene, poly (ethylene terephthalate), poly aromatic amide, polyarylalkene, polymethyl methacrylate, a copolymer thereof, a block copolymer thereof, a mixture thereof, and a blend thereof. 
     A manner of foaming the resin according to the present invention can be chemically foaming or physically foaming, wherein the chemically foaming manner uses an agent capable of conducting a chemical reaction to yield gas, with the gas evenly distributed in the resin composition. In another aspect, the physically foaming manner includes infiltrating gas into the resin composition, and making the gas evenly distributed in the resin composition by stirring. In another preferred embodiment of the present invention, the plurality of pores is provided by disposing a plurality of hollow polymeric micropheres in the elastomer. Particular examples of the hollow micropheres are Expancel® 551DE40d42 (weight average diameter of 30 to 50 μm, produced by Akzo Nobel N.V.) or Expancel® 551DE20d60 (weight average diameter of 15 to 25 μm, produced by Akzo Nobel N.V.). 
     The plurality of pores according to the present invention can be continuous pores or independent pores. The term “continuous pores” in the present invention refers to at least two pores connecting to each other to form a pore system similar to an ant nest, which is beneficial to flow of the slurry, distribution of the polishing particles and removal of polishing residues. The term “independent pores” in the present invention refers to pores which are independent without connecting to each other. Generally, the independent pores have cross sections of circle shape or oval shape, and are ball-shaped or egg-shaped pores. The independent pores provide greater hardness and higher removal rate. 
     Preferably, as shown in  FIG. 3 , each of the pores  33  is independent and is not connected to each other. Further, the plurality of pores  33  is preferably ball-shaped or egg-shaped. In another aspect, according to a preferred embodiment of the present invention, the plurality of pores has a pore diameter of about 2 μm to about 250 μm, preferably about 10 μm to about 150 μm, and more preferably about 20 μm to about 80 μm. 
     In another embodiment of the present invention, the polishing layer further includes a nonwoven fabric. The nonwoven fabric can be arranged above or below the elastomer main body, or can be immersed in the elastomer composition to form the polishing layer. 
     The term “nonwoven fabric” used in the present invention refers to a sheet, web or bat manufactured by directionally or randomly oriented fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper or products which are woven, knitted, tufted stitch bonded incorporating binding yarns or filaments, or felted by wet milling, whether or not additionally needled. The fibers may be of natural or man-made origin. They may be staple or continuous filaments or may be formed in situ. Depending on the method for forming the web, the nonwoven fabric usually includes a composite nonwoven fabric, a needle-punched nonwoven fabric, a melt-blown nonwoven fabric, a spun bonded nonwoven fabric, a dry-laid nonwoven fabric, a wet-laid nonwoven fabric, a stitch-bonded nonwoven fabric, or a spun lace nonwoven fabric. Compared with a woven fabric, a nonwoven fabric has a better material property. 
     Ordinarily skilled artisans can choose suitable kinds of fibers according to the disclosure of the specification. The term “fibers” in the present invention refers to single fibers or composite fibers, preferably composite fibers. Preferably, the fibers are made of at least one material selected from the group consisting of polyamide, terephthalamide, polyester, polymethyl methacrylate, polyethylene terephthalate, polyacrylonitrile, and a mixture thereof. 
     In an embodiment of the present invention, the plurality of pores of the polishing pad is the void spaces between the fibers of the nonwoven fabric. In still another embodiment of the present invention, the plurality of pores is constructed by the elastomer main body and the fibers jointly. 
     One technical feature of the present invention is to provide the plurality of titanium dioxide nanowires, which is independent from each other, and is dispersed evenly and randomly in the elastomer main body. Through the addition of the plurality of titanium dioxide nanowires, the polishing pad of the present invention can provide improved slurry retention capacity. While not wishing to be limited to any particular theory, it is believed that since the titanium dioxide nanowires have extremely high hydrophilicity (superhydrophilicity), the slurry can be continuously adhered to the titanium dioxide nanowires during the polishing process, thus dramatically increasing slurry retention capacity of the polishing pad. As such, polishing efficiency can be improved while preventing scratches on the substrate to be polished. In another aspect, since the titanium dioxide nanowires possess extremely high hydrophilicity, surface tension of the elastomer composition dispersed with the titanium dioxide nanowires can be reduced. When filling in a mold, the elastomer composition dispersed with the titanium dioxide nanowires has a small contact angle to a wall of the mold, and the surface of the elastomer composition lowers to serve as nucleation sites for the pores. The titanium dioxide nanowires are dispersed on surfaces of the pores, thus enlarging contact area with the slurry and overcoming the defect of varying sizes of the pores. 
     In a preferred embodiment of the present invention, a length of the plurality of titanium dioxide nanowires is about 0.1 nm to about 100 nm, preferably about 0.5 nm to about 40 nm, and more preferably about 1 nm to about 20 nm. 
     In another aspect, a diameter of the plurality of titanium dioxide nanowires is about 0.1 nm to about 50 nm, preferably about 0.5 nm to about 20 nm, and more preferably about 1 nm to about 10 nm. 
     Preferably, a ratio of the plurality of titanium dioxide nanowires in the polishing layer is about 0.1% to about 20% by weight, preferably about 0.5% to about 10% by weight, and more preferably about 1% to about 5% by weight. 
     In an embodiment of the present invention, preparation of the plurality of titanium dioxide nanowires includes a hydrothermal method which comprises growing a lot of titanium dioxide nanowires on a titanium dioxide substrate, sonicating the plurality of titanium dioxide nanowires into an aqueous solution with a supersonic apparatus, and then removing water by heating, thus providing the plurality of titanium dioxide nanowires required in the present invention. 
     In a preferred embodiment of the present invention, a portion of the plurality of titanium dioxide nanowires is exposed on a surface of the polishing layer. 
     In another preferred embodiment of the present invention, a portion of the plurality of titanium dioxide nanowires is disposed in the plurality of pores. 
     In a preferred embodiment of the present invention, the polishing layer includes a plurality of polishing particles. The plurality of polishing particles is evenly distributed in the elastomer main body, as well as disposed in the plurality of pores. Preferably, the plurality of polishing particles is made of cerium dioxide, silicon dioxide, aluminum oxide, yttrium oxide, or ferric oxide. In another aspect, a particle size of the plurality of polishing particles is between about 0.01 μm to about 10 μm. 
     In a preferred embodiment of the present invention, the polishing pad further includes a buffer layer on a surface of the polishing layer. The term “buffer layer” as used in the present invention refers to a thin layer located between the polishing layer and a polishing apparatus. The buffer layer withstands the pressure in various directions from a pressure plate and a polishing plate during the polishing process, so as to prevent scratches on the substrate to be polished. The buffer layer according to the present invention includes fibers which can be the same as those fibers of the nonwoven fabric described above, and are not repeated again. 
     In a preferred embodiment of the present invention, the polishing pad further includes a binder layer for binding the polishing layer and the buffer layer together. Preferably, a material of the binder layer is selected from a group consisting of pressure-sensitive adhesive, one-part adhesive, two-part adhesive, polyol curing-type PU paste, acrylic resin, and epoxy resin. The pressure-sensitive adhesive generally includes a supporting film which can be, for instance, a polyester film. A fluidic adhesive agent is coated on upper and lower sides of the supporting film. The one-part adhesive refers to an adhesive agent which utilizes an elastomer with high molecular weight for providing adhesion function, preferably includes polyurethane. The one-part adhesive includes oil-modified paste and moisture-curing paste. The oil-modified paste is formed by reacting natural oil-modified or diglyceride-modified polyols with toluene diisocyanate (TDI). The moisture-curing paste includes hydroxyl-containing polyesters and polyethers, with excess NCO groups (NCO/OH&gt;1) reacting with hydroxyl groups of toluene diisocyanate, diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), etc., to form isocyanate-terminated prepolymers. Such isocyanate groups can react with moisture in the air to produce amines, which undergoes further reactions to form urea linkage and biuret, thus forming a cured film. The two-part adhesive refers to an adhesive agent including two components which react or crosslink with each other to provide adhesion function; preferably includes an elastomer and polyisocyanate. The two-part adhesive may be of catalyst-curing type, which is cured by reacting a mono-diglyceride mixture transesterified by polyethylene glycol, polypropylene glycol or polyol with a catalyst, such as tertiary amines or metal salts. The polyolcuring-type PU paste may be formed by reacting isocyanate prepolymers and a hydroxyl group of polyol-esters or polyethers or polyols, such as hydroxyl-containing acrylic resins. The acrylic resin may be cold curing type or dry-heat curing type. The cold curing-type acrylic resin, which can be cured under room temperature, is essentially composed of acrylic resin monomers. The heat-dry curing-type acrylic resin includes acrylic resin polymers as the basic structure, with active reacting groups introduced therein. When heated, said resin alone or with a resin containing reacting groups and crosslinking agent undergo a reaction to form a 3D network structure. The epoxy resin can form 3D network structure with the addition of the crosslinking agent. 
     In an embodiment of the present invention, the polishing layer and the buffer layer are produced separately, and then bound together by the binder layer. Means for binding the polishing layer with the buffer layer can be varied according to the forms of the binder layer. The binder layer for binding the polishing layer and the buffer layer is preferably applied on a surface of the buffer layer or the polishing layer by coating, transferring, printing or scraping, more preferably by coating on a surface of the buffer layer or the polishing layer. 
     In another preferred embodiment of the present invention, the polishing layer further includes a polishing surface, and the polishing surface includes a groove. A proper processing for forming the groove on the polishing surface may be chosen by ordinarily skilled artisans based on the disclosure of the specification. For instance, laser processing can be used. The groove assists slurry flow during the polishing process. Preferably, the ratio of the groove interval and the groove width is from about 1 to about 0.05. 
     In another preferred embodiment of the present invention, the polishing pad further includes an adhesive layer on a surface of the polishing layer, which is adapted for fixing the polishing pad on a polishing plate. A material of the adhesive layer can be the same as that of the binder layer, thus is not repeated again. 
     The present invention also provides a polishing apparatus, including:
         a polishing plate;   a substrate;   a polishing pad adhered on the polishing plate for polishing the substrate; and   slurry contacting with the substrate for polishing.       

     Preferably, the polishing apparatus further includes:
         a pressure plate positioned opposite to the polishing plate; and   a mounting sheet adhered on the pressure plate for carring and mounting the substrate.       

       FIG. 4  shows a schematic view of a polishing apparatus according to the polishing pad of the invention. The polishing apparatus  4  includes a pressure plate  41 , a mounting sheet  42 , a substrate  43 , a polishing plate  44 , a polishing pad  45  and slurry  46 . The pressure plate  41  is positioned opposite to the polishing plate  44 . The mounting sheet  42  is adhered to the pressure plate  41  through a backside adhesive (not shown) and is used for carrying and mounting the substrate  43 . The polishing pad  45  is mounted on the polishing plate  44  and faces the pressure plate  41  for polishing the substrate  43 . 
     The operation manner of the polishing apparatus  4  is as follows. First, the substrate  43  is mounted on the mounting sheet  42 , and then both the pressure plate  41  and the polishing plate  44  are rotated and the pressure plate  41  is simultaneously moved toward the polishing plate  44 , such that the polishing pad  45  contacts the surface of the substrate  43 . Accordingly, the substrate  43  can be polished by the polishing pad  45  with the continuously supplemented slurry  46 . 
     The present invention further provides a method for manufacturing the polishing pad according to claim  1 , comprising:
         (a) providing an elastomer composition;   (b) providing the plurality of titanium dioxide nanowires;   (c) dispersing the titanium dioxide nanowires of the step (b) evenly and randomly in the elastomer composition of the step (a);   (d) providing the polishing layer by curing the elastomer composition to form the elastomer main body.       

     In a preferred embodiment of the present invention, definition of the elastomer composition is the same as described above, thus is not repeated again. 
     In an embodiment of the present invention, the method further includes coating the elastomer composition randomly dispersed with the plurality of titanium dioxide nanowires of the step (c) on a carrier before the step (d). 
     The term “carrier” in the present invention refers to an element which allows the elastomer composition to be formed thereon and to be easily removed therefrom after cured. Preferably, the carrier is a sheet; in another aspect, the carrier is a release liner. The term “release liner” in the present invention refers to a material which does not react with the elastomer composition during the polishing pad manufacturing process, and the cured elastomer composition can be easily removed from such material. Preferably, the release liner is “a film with low permeability.” The term “film with low permeability” in the present invention refers to a film or a thin membrane which substantially prevents the elastomer composition on an upper surface thereof from permeating to a lower surface thereof. In a preferred embodiment of the invention, the film with low permeability can be formed on a base material, such as paper. Preferably, the carrier includes a polyethylene glycol terephthalate film, a polypropylene film, a polycarbonate film, a polyethylene film, a polyethylene terephthalate film, releasing paper or a releasing fabric. Additionally, the preferable polypropylene is oriented polypropylene. 
     Preferably, the carrier is continuously provided, such as a release liner roll. The release liner roll can be used in a roll-to-roll manner Comparing to the conventional manufacture process related to molding or casting a single polishing pad, the method according to the invention improves batch uniformity. 
     In an embodiment of the present invention, the method further includes filling the elastomer composition randomly dispersed with the plurality of titanium dioxide nanowires of the step (c) in a cavity of a mold before the step (d). Particular means of the method can be readily performed by ordinarily skilled artisans. For instance, the plurality of titanium dioxide nanowires can be mixed or stirred with the components of the elastomer composition, so as to prepare the elastomer composition and disperse the titanium dioxide nanowires evenly and randomly in the elastomer composition at the same time. 
     In an embodiment of the present invention, the method further includes immersing a nonwoven fabric in the elastomer composition randomly dispersed with the plurality of titanium dioxide nanowires of the step (c) before the step (d), which is performed by a common method for immersing a fabric in an elastomer liquid. The immersing conditions can be readily understood by ordinarily skilled artisans. 
     According to the method in the present invention, the step (d) cures the elastomer composition of the step (c). Particular means for the curing step can be determined ordinarily skilled artisans based on the types of the resin and the optional crosslinking agent. In a preferred embodiment of the present invention, the curing step includes curing the elastomer composition at about 60° C. to about 130° C. after the elastomer composition is dried under a high temperature. 
     Preferably, the method according to the present invention further includes a slicing step of cutting the elastomer cured in the mold into slices as the polishing pads. Particular means for the slicing step can be readily understood by ordinarily skilled artisans. 
     In a preferred embodiment of the present invention, the method further includes a step of removing the carrier. Preferably, the step of removing the carrier can be performed right after the manufacture process, removing the polishing pad from the manufacturing equipment. Alternatively, the carrier-removing step can be performed just before the polishing process, removing the carrier from the polishing pad. Particular means for the carrier-removing step can be choosen based on the type of the carrier, such as a teering process. 
     While embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by persons skilled in the art. It is intended that the present invention is not limited to the particular forms as illustrated, and that all modifications not departing from the spirit and scope of the present invention are within the scope as defined in the following claims.