Abstract:
The present invention relates to a composite sheet for mounting a workpiece and a method for making the same. The composite sheet includes a buffer layer and an adsorption layer. The buffer layer has a plurality of continuous pores. The adsorption layer is located on the buffer layer for adsorbing a workpiece, and the compression ratio of the buffer layer is higher than that of the adsorption layer. Thereby, due to low hardness, good adsorption effect, and high compression ratio, the composite sheet of the present invention has good buffer effect.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an adsorption sheet and a method for making the same, and more particularly, to a composite adsorption sheet for mounting a workpiece and a method for making the same. 
         [0003]    2. Description of the Related Art 
         [0004]    Polishing generally refers to abrasion control of an originally rough surface in a chemical mechanical polishing (CMP) process, in which a slurry containing fine particles is uniformly distributed on an upper surface of a polishing pad, and a polishing workpiece is pressed against the polishing pad to be polished regularly in a repeated pattern. The polishing workpiece is, for example, semiconductor, storage medium substrate, integrated circuit, LCD flat panel glass, optical glass, and photoelectric panel. During the polishing, it is necessary to use a sheet to support and mount the polishing workpiece, and the quality of the sheet directly affects the polishing effect of the polishing workpiece. 
         [0005]      FIG. 1  is a schematic diagram of a polishing equipment having a conventional sheet disclosed in U.S. Pat. No. 5,871,393. The polishing equipment  1  includes a lower base plate  11 , a sheet  12 , a polishing workpiece  13 , an upper base plate  14 , a polishing pad  15 , and slurry  16 . The lower base plate  11  is opposite to the upper base plate  14 . The sheet  12  is adhered onto the lower base plate  11  with a back adhesive layer  17 , and is used to support and mount the polishing workpiece  13 . The polishing pad  15  is mounted on the upper base plate  14  and facing the lower base plate  11 , for polishing the polishing workpiece  13 . 
         [0006]    The polishing equipment  1  operates as follows. Firstly, the polishing workpiece  13  is disposed on the sheet  12 , and is adsorbed by the sheet  12 . Next, the upper base plate  14  and the lower base plate  11  are rotated in opposite directions, and meanwhile, the upper base plate  14  moves downward, so as to make the polishing pad  15  contact the surface of the polishing workpiece  13 . In this way, the polishing workpiece  13  is polished by continuously supplementing the slurry  16  together with the function of the polishing pad  15 . 
         [0007]      FIG. 2  is a schematic enlarged diagram of region A in  FIG. 1 . The region A mainly shows the sheet  12 . The sheet  12  is a single-layered structure, and the material thereof is generally polyurethane (PU) resin, which is a foam material. Furthermore, the sheet  12  has a plurality of communicating foam pores  121  inside. 
         [0008]    During the polishing process, the polishing workpiece  13  and the sheet  12  bear a downward pressure, and the compression ratio of the sheet  12  may affect the overall stress uniformity, which is also a critical factor in determining the flatness of the polishing workpiece  13  after being polished. That is, high compression ratio represents good buffer effect, such that the polishing workpiece  13  after the polishing may acquire good flatness. In general, after long-term usage, the compression ratio of the sheet  12  will gradually descend to end the life of the sheet  12 . 
         [0009]    As the sheet  12  is a single-layer structure, if the material thereof is soft, though the adsorption to the polishing workpiece  13  is strong, the compression ratio is low; while if the material thereof is hard, though the compression ratio is high, the adsorption to the polishing workpiece  13  is weak. 
         [0010]    Therefore, it is necessary to provide a composite sheet for mounting a workpiece and a method for making the same to solve the above problems. 
       SUMMARY OF THE INVENTION 
       [0011]    The objective of the present invention is to provide a composite sheet, which includes a buffer layer and an adsorption layer. The buffer layer has a plurality of continuous pores. The adsorption layer is located on the buffer layer, for adsorbing a workpiece, and the compression ratio of the buffer layer is higher than that of the adsorption layer. Thereby, a balance between the overall hardness and the compression ratio of the composite sheet is achieved. Moreover, the hardness or compression ratio can be adjusted optionally. Compared with the conventional sheet with a single-layer structure, the composite sheet of the present invention has lower hardness, thus better adsorption effect can be obtained; meanwhile, the composite sheet of the present invention has higher compression ratio, thus better buffer effect can be obtained. 
         [0012]    Another objective of the present invention is to provide a method for making a composite sheet, which includes the following steps: (a) forming a resin layer on a carrier; (b) solidifying the resin layer; (c) washing the resin layer; (d) baking the resin layer, to form a buffer layer having a plurality of continuous pores; and (e) attaching an adsorption layer onto the buffer layer, to form a composite sheet, wherein the compression ratio of the buffer layer is higher than that of the adsorption layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram of a polishing equipment having a conventional sheet disclosed in U.S. Pat. No. 5,871,393; 
           [0014]      FIG. 2  is a schematic enlarged diagram of region A in  FIG. 1 ; 
           [0015]      FIG. 3  is a schematic diagram of a polishing equipment of the present invention; 
           [0016]      FIG. 4  is a schematic enlarged diagram of region B in  FIG. 3 ; 
           [0017]      FIG. 5  is a schematic flow chart of a method for making a composite sheet of the present invention; 
           [0018]      FIGS. 6 to 9  are schematic diagrams of each process in the method for making a composite sheet of the present invention; and 
           [0019]      FIG. 10  is an SEM photo of the composite sheet made according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 3  is a schematic diagram of a polishing equipment of the present invention. The polishing equipment  3  includes a lower base plate  31 , a composite sheet  32 , a polishing workpiece  33 , an upper base plate  34 , a polishing pad  35 , and a slurry  36 . The lower base plate  31  is opposite to the upper base plate  34 . The composite sheet  32  is fixed on the lower base plate  31 . In this embodiment, the composite sheet  32  is adhered to the lower base plate  31  with a back adhesive layer  37 , for supporting and mounting the polishing workpiece  33 . The polishing workpiece  33  is selected from a group consisting of semiconductor, storage medium substrate, integrated circuit, LCD flat panel glass, optical glass, and photoelectric panel. The polishing pad  35  is mounted on the upper base plate  34  and facing the lower base plate  31 , to polish the polishing workpiece  33 . 
         [0021]    The polishing equipment  3  operates as follows. Firstly, the polishing workpiece  33  is disposed on the sheet  32 , and the polishing workpiece  33  is adsorbed by the sheet  32 . Next, the upper base plate  34  and the lower base plate  31  are rotated in opposite directions, and meanwhile, the upper base plate  34  moves downward, so as to make the polishing pad  35  contact the surface of the polishing workpiece  33 . In this way, the polishing workpiece  33  is polished by continuously supplementing the slurry  36  together with the function of the polishing pad  35 . 
         [0022]      FIG. 4  is a schematic enlarged diagram of region B in  FIG. 3 . The region B mainly shows the composite sheet  32 . In the present invention, the composite sheet  32  is a double-layered structure including a buffer layer  321  and an adsorption layer  322 . The buffer layer  321  has a plurality of continuous pores  3211 , and the back adhesive  37  is formed on the lower surface of the buffer layer  321 . The adsorption layer  322  is different from the buffer layer  321 , and is located on the buffer layer  321 , for adsorbing the polishing workpiece  33 . The compression ratio of the buffer layer  321  is higher than that of the adsorption layer  322 . Preferably, the void content of the buffer layer  321  is higher than that of the adsorption layer  322 . 
         [0023]    In this embodiment, the material of the buffer layer  321  is PU resin with a void content higher than 60%; preferably, higher than 75%. The material of the adsorption layer  322  is Polyurethane (PU) resin, polyvinyl chloride (PVC) resin, polystyrene resin, polyethylene resin, polyamide resin, polypropylene resin, or ethylene-vinyl acetate resin, with a void content of 30%-60%, preferably, 40%-50%. Additionally, the compression ratio of the buffer layer  321  is higher than 30%; preferably, higher than 50%. Such compression ratio can be adjusted optionally. The compression ratio of the adsorption layer  322  is 25%-40%. 
         [0024]    In this embodiment, the adsorption layer  322  is attached to the buffer layer  321  with an adhesive layer  323 , and the material of the adhesive layer  323  is a polymer elastomer, such as pressure-sensitive adhesive, moisture curable resin, one-component resin, or two-component resin. 
         [0025]      FIG. 5  is a schematic flow chart of a method for making a composite sheet of the present invention. The method includes the following steps. Referring to  FIG. 6  and  FIG. 5 , in Step S 501 , a resin layer  71  is formed on a carrier  72 . In this embodiment, the material of the resin layer  71  is PU resin, and the resin layer  71  is formed on the carrier  72  by coating. Afterward, in Step S 502 , the resin layer  71  is solidified. In Step S 503 , the resin layer  71  is washed. And in Step S 504 , the resin layer  71  is dried or baked, so as to form a buffer layer  73 , as shown in  FIG. 7 . The buffer layer  73  has a plurality of continuous pores. 
         [0026]    Referring to  FIG. 8  and  FIG. 5 , in Step S 505 , an adsorption layer  74  is attached to the buffer layer  73 , to form a composite sheet  7 . The compression ratio of the buffer layer  73  is higher than that of the adsorption layer  74 , and the void content of the buffer layer  73  is higher than that of the adsorption layer  74 . In this embodiment, an adhesive layer  75  is formed with an attachment tool, for attaching the adsorption layer  74  onto the buffer layer  73 . The material of the adhesive layer  75  is a polymer elastomer, such as pressure-sensitive adhesive, moisture curable resin, one-component resin, or two-component resin. The attachment tool can be a coating roller, coating blade, printing roller, or transfer tool. 
         [0027]    Preferably, after the adsorption layer  74  is attached to the buffer layer  73 , these two layers are left still for a day to be cured. Meanwhile, referring to  FIG. 9 , in Step S 506 , the carrier  72  is removed, and next, in Step S 507 , a back adhesive  76  is attached to the lower surface of the buffer layer  73 , so as to form a commercialized product of the composite sheet  7 . 
         [0028]    The present invention will be described in detail with the following examples, but it does not mean that the present invention is limited to the content disclosed by the examples. 
       EXAMPLE 
       [0029]    Firstly, a carrier is provided as a coating substrate, and the carrier can be polypropylene film, polyethylene terephthalate (PET) film, polyacrylic film, polyolefm film, woven fabric, or fiber glass. Additionally, 19.9 wt % of PU resin for coating, 6.6 wt % of colorant, 2.5 wt % of interface agent, and 71 wt % of dimethylformamide (DMF) solvent are mixed uniformly to prepare a coating material. Next, the coating material is coated on the carrier to form a resin layer. Then, the resin layer is solidified in a solidifying tank having 10% of DMF. Afterward, the resin layer is washed, and the water temperature is 60° C. And then, the resin layer is baked at 100° C. to form a continuous porous buffer layer. Thereafter, an adhesive layer of a polymer elastomer is formed on the buffer layer through a printing roller, and an adsorption layer of PU material is attached to the buffer layer to form a composite adhesive sheet, as shown by an SEM photo in  FIG. 10 . In  FIG. 10 , the composite sheet includes a buffer layer  93 , an adsorption layer  94 , and an adhesive layer  95 . The void content of the buffer layer  93  is 81%, and the compression ratio thereof is 56%. The void content of the adsorption layer  94  is 37%, and the compression ratio thereof is 38%. The hardness of the composite sheet is  18  shore A, and the compression ratio thereof is 49.45%, while the hardness of the conventional sheet is above  20  shore A, and the compression ratio thereof is generally below 40%. Therefore, the composite sheet of this example has lower hardness (i.e., better adsorption effect) and higher compression ratio (i.e., better buffer effect). 
         [0030]    In the present invention, as a composite sheet is formed by compositing two different layers, a balance can be achieved between the overall hardness and the compression ratio of the composite sheet, and moreover, the hardness or compression ratio can be adjusted optionally. That is to say, compared with the conventional sheet with a single-layer structure, the composite sheet of the present invention has lower hardness, thus better adsorption effect can be obtained, and meanwhile, the composite sheet of the present invention has higher compression ratio, thus better buffer effect can be obtained. 
         [0031]    While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope defined in the appended claims.