Abstract:
A composite polishing pad for use in a linear chemical-mechanical polishing apparatus is provided. The pad comprises a hard polishing pad having a polishing surface and an attachment surface opposite the polishing surface, the attachment surface comprising a border comprising an adhesive, the border surrounding a cavity, the cavity being sized and shaped to receive a soft polishing pad. The soft polishing pad is disposed completely in the cavity and completely fills the cavity, and the soft polishing pad has a first side adhered in the cavity of the hard polishing pad, and a second side comprising an adhesive, whereby the attachment surface of the hard polishing pad and the second side of the soft polishing pad are substantially in a common plane. Other composite polishing pads are also provided, as are methods for making composite pads and methods for preventing composite pads from splitting apart into their component pads.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a composite polishing pad for use in an apparatus for the linear chemical mechanical planarization of surfaces such as semiconductor wafers.  
         BACKGROUND  
         [0002]    Chemical mechanical planarization (CMP) is a process used to planarize raw semiconductor wafers and each layer of material added to the semiconductor wafer thereafter. Conventional CMP systems often use a rotating wafer holder that brings the semiconductor wafer into contact with a polishing pad. The polishing pad moves in the plane of the semiconductor wafer surface to be polished. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad. The wafer holder then presses the semiconductor wafer against the rotating polishing pad, and polishing commences.  
           [0003]    Commercially available polishing pads come in a variety of hardnesses. Softer polishing pads have certain advantages. Softer polishing pads can more easily conform to the different features on the wafer and tend to achieve global planarity. Also, they tend to scratch the surface of the semiconductor wafer less than hard pads. Soft polishing pads also provide a better vehicle than hard polishing pads for delivering slurry to the polishing site because the slurry can soak into the soft polishing pad material. Soft polishing pads do, however, have some disadvantages. Although they achieve better global planarity, it is done at the expense of local planarity. Also, soft polishing pads tend to polish away material more slowly, given the same speed and pressure as a hard polishing pad. Harder polishing pads, although they achieve better local planarity, achieve that result at the expense of global planarity.  
           [0004]    Composite polishing pads have been created to attempt to combine the best features of soft and hard polishing pads. Two examples are “sandwich” types, which use vertical stacking of hard and soft layers (U.S. Pat. No. 5,212,910 to Breivogel, et al., hereby incorporated by reference), and “distributed” types which attach hard pieces to a soft support layer (U.S. Pat. No. 5,230,184 to Bukhman, hereby incorporated by reference).  
           [0005]    These types of composite polishing pads tend to degrade easily over time as the polishing pads wear. The soft material tends to lose its elasticity, and the composite pad becomes loaded with polish residuals and slurry. Further, in the sandwich polishing pads, the hard polishing pad layer tends to split apart from the soft polishing pad layer as a result of wear and tear. Thus, the polishing pad life is shortened.  
           [0006]    Accordingly, there remains a need for a composite polishing pad that provides uniform planarity, extended pad life, and good slurry delivery.  
         SUMMARY  
         [0007]    The composite polishing pads and the methods disclosed herein solve at least some of the problems left unsolved by conventional polishing pads.  
           [0008]    In one aspect of the invention, a composite polishing pad for use in a linear chemical-mechanical polishing apparatus is provided. The pad has a hard polishing pad having a polishing surface and an attachment surface opposite the polishing surface. The attachment surface has a border comprising an adhesive, and the border surrounds a cavity. The cavity is sized and shaped to receive a soft polishing pad. The soft polishing pad is disposed completely in the cavity and completely filling the cavity. The soft polishing pad has a first side adhered in the cavity of the hard polishing pad, and a second side comprising an adhesive, such that the attachment surface of the hard polishing pad and the second side of the soft polishing pad are substantially in a common plane.  
           [0009]    In another aspect of the invention, a composite polishing pad includes a hard polishing pad having a polishing surface and an attachment surface opposite the polishing surface, the attachment surface comprising a border comprising an adhesive, the border surrounding a cavity. The cavity is adapted to receive a soft polishing pad; the soft polishing pad disposed completely in the cavity and completely filling the cavity. The soft polishing pad has a first side adhered in the cavity of the hard polishing pad and a second side comprising an adhesive, whereby the attachment surface of the hard polishing pad and the second side of the soft polishing pad are substantially in a common plane. The composite polishing pad is adhered to a belt in the linear chemical-mechanical polishing apparatus.  
           [0010]    In still another aspect of the invention, a composite polishing pad includes a hard polishing pad of a certain length having a polishing surface and an attachment surface opposite the polishing surface, the attachment surface comprising an adhesive; a soft polishing pad of a length less than the length of the hard polishing pad, the soft polishing pad having a first side adhered to a first portion of the attachment surface of the hard polishing pad, and the soft polishing pad having a second side comprising an adhesive; and a steel belt in the linear chemical-mechanical polishing apparatus adhered to the second side of the soft polishing pad and to a second portion the attachment surface of the hard polishing pad.  
           [0011]    In still another aspect of the invention, a method of making a composite polishing pad is provided. The method comprises (a) providing a hard polishing pad having a polishing side and an attachment side opposite the polishing side, the attachment side comprising an adhesive; (b) shaping the attachment side to form a border surrounding a cavity that is adapted to receive a soft polishing pad therein; (c) inserting the soft polishing pad into the cavity, the soft polishing pad being completely within the cavity and filling the cavity; and (d) adhering the soft polishing pad in the cavity.  
           [0012]    In still another aspect of the invention, another method if making a composite polishing pad comprises: (a) providing a hard polishing pad of a predetermined length having a polishing side and having an attachment side opposite the polishing side, the attachment side comprising an adhesive; (b) providing a soft polishing pad of a length shorter than the length of the hard polishing pad, the soft polishing pad having a first side comprising an adhesive and a second side comprising an adhesive; (c) providing a belt in a linear apparatus for chemical-mechanical polishing; (d) adhering the second side of the soft polishing pad to the belt; (e) adhering a first portion of the attachment side of the hard polishing pad to the soft polishing pad; and (f) adhering a second portion of the attachment side of the hard polishing pad to the belt.  
           [0013]    In yet another aspect of the invention, a method of preventing a composite polishing pad from splitting apart is provided. The method comprises: (a) providing a hard polishing pad having a polishing side and an attachment side opposite the polishing side, the attachment side comprising an adhesive; (b) shaping the attachment side to form a border surrounding a cavity that is adapted to receive a soft polishing pad therein; (c) inserting the soft polishing pad into the cavity, the soft polishing pad being completely within the cavity and filling the cavity; (d) adhering the soft polishing pad in the cavity to form a composite pad; and (e) adhering the composite pad to a belt in a linear chemical-mechanical polishing apparatus such that the border adheres to the belt and the soft polishing pad adheres to the belt.  
           [0014]    The present invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a top view of a preferred composite polishing pad.  
         [0016]    [0016]FIG. 2 is a bottom view of the composite polishing pad of FIG. 1.  
         [0017]    [0017]FIG. 3 is a cut-away end view of the composite polishing pad of FIG. 1.  
         [0018]    [0018]FIG. 4 is a cut-away end view of a second preferred embodiment of a composite polishing pad.  
         [0019]    [0019]FIG. 5 is a linearCMP apparatus comprising a plurality of composite polishing pads aligned along a continuous linear belt. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     DEFINITIONS  
       [0020]    “Hard polishing pad,” as used herein, means a polishing pad having a hardness of about 40 durometers or greater on a Shore D scale. Preferably the hardness is from about 40 durometers to about 70 durometers, more preferably from about 50 durometers to about 60 durometers. Many materials may be used to manufacture a hard polishing pad, but preferably, a hard polishing pad comprises a rigid, microporous polyurethane material. Although many different hard polishing pads can be used with the present invention, particularly preferred hard polishing pads are the RODEL IC1000 pad or the FREUDENBERG FX9 hard pad, which are commercially available from RODEL in Newark, Del. and from FREUDENBERG in Lowell, Mass., respectively.  
         [0021]    “Soft polishing pad,” as used herein, means a polishing pad having a hardness of less than about 40 durometers on a Shore D scale. A soft polishing may comprise any suitable soft material, but it preferably comprises a polyurethane impregnated polyester felt pad such as SUBA. Although many different soft polishing pads can be used with the present invention, a particularly preferred soft polishing pad is the THOMAS WEST TW817 pad, which is commercially available from THOMAS WEST, in Sunnyvale, Calif.  
       FIGURES ILLUSTRATING PREFERRED EMBODIMENTS  
       [0022]    Referring to FIG. 1, a top view of a preferred composite polishing pad  2  is shown. The composite polishing pad  2  is for use in a linear chemical-mechanical polishing (CMP) apparatus, for the polishing of semiconductor wafers, silicon-on-insulator surfaces, silicon-on-sapphire surfaces, and the like. Although the composite polishing pad  2  is intended for use with any suitable linear CMP apparatus, the TERES CMP system, available from LAM RESEARCH CORPORATION of Fremont, Calif. is preferred. A single composite polishing pad  2  is shown on a stiff support surface  3 , preferably a linear belt  3 , for use in a CMP apparatus.  
         [0023]    Referring to FIG. 1, only the polishing surface of the composite polishing pad  2  is shown. Preferably, the polishing surface has longitudinal grooves  4  or slanted grooves  4 , though grooves  4  are not necessary. The polishing surface may also be perforated, though perforations are not necessary. The polishing surface in the composite polishing pad  2  comprises a hard polishing pad, as defined above.  
         [0024]    Referring to FIG. 2, a bottom view of the composite polishing pad  2  is shown with the continuous linear belt  3  stripped away. A hard polishing pad  6  forms a border  8  around the soft polishing pad  10 . In FIG. 2, the border  8  is generally rectangular, but it can be shaped like a parallelogram, or other geometric shapes. The border  8  has two longitudinal edges 8L and two ends 8W.  
         [0025]    The width of border edges 8L is preferably constant. A width for border edges 8L should be chosen so that the hardness of the portion of the composite polishing pad  2  that contacts the surface to be polished is uniform. For example, assume a semiconductor wafer to be polished has a diameter of four inches and the linear belt  3  is six inches wide. Then, the width of each border edge 8L should be no greater than one inch. This way, the composite polishing pad  2  has a uniform hardness in the area that polishes the wafer—the four inches between the border edges 8L.  
         [0026]    Optimal widths for 8L vary according to the width of the surface to be polished and the width of the continuous linear belt  3  in a particular CMP apparatus. In a standard TERES CMP apparatus, it is preferable that the border 8L be about 1 inch wide, though many other widths may be acceptable, such as 1.5 inches and 0.5 inches.  
         [0027]    Similarly, the width of the border ends 8W are preferably constant. The width of border ends 8W is preferably small, to minimize any non-uniformities that might result from the composite polishing pad  2  being harder along its border ends 8W (which comprise only hard polishing pad  6 ) than in its central area (which comprises a hard polishing pad  6  and a soft polishing pad  10 ). Preferably, the border ends 8W are about one inch wide, more preferably about one-half inch wide.  
         [0028]    To minimize inconsistencies that might result due to the composite polishing pad  2  being harder along its border ends 8W than in its central area, it is preferable to minimize the number of composite polishing pads  2  that are adhered to a given linear belt  3 . This is done by adjusting the length of the composite polishing pads  2 .  
         [0029]    The length of the composite polishing pad  2  can equal to or less than the length of the continuous linear belt  3 . If multiple composite polishing pads  2  are used on the single continuous linear belt  3 , it is preferred that each of the multiple composite polishing pads  2  be equal in length.  
         [0030]    For example, referring to FIG. 5, composite polishing pads  202 ,  302 ,  402 , and  502  are equal in length and are aligned in a head-to-toe arrangement around the continuous linear belt  203  in the linear CMP apparatus  201 . The central, longitudinal region extending through all four pads (the region of the pads that contacts the surface to be polished) has generally the same hardness throughout, except in areas A, B, C, and D. Areas A, B, C, and D represent the areas where the individual pads meet. Thus, each of areas A, B, C, and D is twice the width of border end 8W, and comprises only hard polishing pad. Accordingly, the areas A, B, C, and D diverge from the preferred uniform hardness of the single composite pad.  
         [0031]    Because of the size and shape of commercially available hard polishing pads and commercially available soft polishing pads, it is presently preferred to align four, equally sized composite pads around a linear belt as shown in FIG. 5. Smaller composite polishing pads have the advantage of being easier to align evenly along the linear belt  203 .  
         [0032]    However, for improved uniformity, it may be advantageous to use only three composite polishing pads, two composite polishing pads, or even a single composite polishing pad around a continuous linear belt  203  to minimize any non-uniformities that might result from the individual composite polishing pads being harder along their border ends than in their central regions.  
         [0033]    Referring again to FIG. 2, the width of the composite polishing pad  2  can be no longer than the width of the linear belt  3 . The width of the composite polishing pad  2  can be no shorter than the diameter of the surface to be polished. Within those limits, the composite polishing pad can be any length. Preferably, the width of the composite polishing pad  2  is less than the width of the linear belt  3  by about 2 inches or by about 1 inch. The composite polishing pad  2  can be centered in the linear belt  3 .  
         [0034]    Referring to FIG. 3, a cut-away end view of the composite polishing pad  2  adhered to the linear belt  3  is shown. The hard polishing pad  6  has a polishing surface  7  and another surface  9  opposite the polishing surface  7 . The polishing surface  7  is preferably as described above for FIG. 1.  
         [0035]    The surface  9  comprises an adhesive so that a portion of the hard polishing pad  6  adheres directly to the linear belt  3 . The adhesive can be any adhesive known in the art. Preferably, the adhesive is the standard adhesive that comes with the RODEL IC1000 CMP pads.  
         [0036]    The surface  9  that is opposite the polishing surface  7  has preferably been shaped during manufacture to have a cavity therein or cut or milled after manufacture to have a cavity therein. The cavity should be shaped and sized so that the soft polishing pad  10  fits entirely within the cavity and fills the cavity. Specialized milling, machining, and manufacturing vendors to make the cavity in the surface  9  of the hard polishing pad  6  to precise specifications are commercially available through the companies that provide and manipulate polishing pads, such as RODEL and THOMAS WEST.  
         [0037]    The cavity is surrounded by the border  8 , which has the dimensions 8L and 8W as described above. The depth of the cavity depends upon the particular soft polishing pad  10  being used. The depth of the cavity should equal the thickness of the soft polishing pad  10 , including adhesive layer  11 . Adhesive layer  11  can be part of the hard polishing pad  6 , part of the soft polishing pad  10 , or a separately packaged adhesive that can be applied to either or both the hard polishing pad  6  or the soft polishing pad  10 . Preferably the adhesive layer  11  is the standard adhesive supplied with the soft polishing pad  10 , such as the adhesive provided with the THOMAS WEST TW817 polishing pads.  
         [0038]    An adhesive layer  13  should be in substantially the same plane as the adhesive on surface  9  so that both the adhesive layer  13  and the adhesive on surface  9  may adhere to the linear belt  3 . The adhesive in adhesive layer  13  can be any adhesive known in the art. Preferably, the adhesive is the standard adhesive that comes with the THOMAS WEST TW817 polishing pads.  
         [0039]    Advantageously, each of the component pads of the composite polishing pad  2  is independently adhered to the linear belt  3 . The soft polishing pad  10  is preferably fully encapsulated between the hard polishing pad  6  and the linear belt  3 , so that the seam between the hard polishing pad  6  and the soft polishing pad  10  is not exposed. Because the seam is not exposed and because the soft polishing pad  10  and the hard polishing pad  6  are independently adhered to the linear belt  3 , the composite pad  2  is less likely to split apart prematurely.  
         [0040]    The composite polishing pad  2  can be manufactured any number of ways. Assuming the hard polishing pad  6  has been provided with a cavity as described above, the soft polishing pad  10  (which is commercially available with adhesive layers  11  and  13 ) can be inserted into the cavity and adhered to the hard polishing pad  6  to form the composite polishing pad  2 . Optionally, adhesive can manually be added between the soft polishing pad  10  and the hard polishing pad  6 . Then when the composite polishing pad  2  is formed, it can be aligned on and adhered to a linear belt  3  with the adhesives that came with the commercially available hard polishing pads and soft polishing pads. Optionally, adhesive can be manually added between the composite polishing pad  2  and the linear belt  3 .  
         [0041]    Alternatively, the soft polishing pad  10  can be aligned to the linear belt  3  and adhered to the linear belt  3  as a first step. The next step would call for fitting the cavity of the hard polishing pad  6  over the soft polishing pad  10 , and adhering the hard polishing pad  6  to the soft polishing pad  10  and the linear belt  3  at roughly the same time. A heated environment may optionally be used during any of the adhesion steps, according to procedures that are well known in the art.  
         [0042]    Referring to FIG. 4, another preferred composite polishing pad  102  is shown. In this embodiment, a hard polishing pad  106  has a polishing surface  107  and a second surface  109  opposite the polishing surface  107 . The second surface  109  comprises an adhesive that adheres to the linear belt  103  and to an adhesive layer  111  of a soft polishing pad  110 . The soft polishing pad  110  has a second adhesive layer  113  that adheres directly to the linear belt  103 .  
         [0043]    In this embodiment, the second surface  109  does not comprise a cavity into which the polishing pad  110  can be inserted. Instead, the hard polishing pad  106  lies upon the soft polishing pad  110 , completely encapsulating the soft polishing pad  110  between the hard polishing pad  106  and the linear belt  103 . For complete encapsulation, the hard polishing pad  106  must be longer and wider than the soft polishing pad  110 . Then, the seam between the soft polishing pad  110  between the hard polishing pad  106  is not exposed, and both pads are independently adhered to the linear belt  103 , making it more difficult for the composite polishing pad  102  to split apart prematurely.  
         [0044]    This embodiment has the advantage of being less expensive to manufacture because it is not necessary to cut, machine, mill, or otherwise manipulate the hard polishing pad  106  to include a cavity therein. FIG. 4 shows, however, that composite polishing pad  102  does not have a constant flat polishing surface  107 . Since uniform flatness is desirable in a polishing pad, it is preferable to minimize the number of composite polishing pads  102  that fit around a given linear belt. Because of the length of commercially available pads makes it convenient, presently four equally long composite polishing pads  102  can be fitted around a linear belt. It may be desirable to cover a linear belt with only one, two, or three composite polishing pads  102 .  
         [0045]    The composite polishing pad  102  can be manufactured any number of ways. The soft polishing pad  110  can be adhered to adhesive side of the hard polishing pad  106  before the entire composite polishing pad  102  is adhered to the linear belt  103 . The adhesion can comprise adhesives that come with the commercially available pads, and they can also be enhanced the through the manual application of additional adhesive.  
         [0046]    Alternatively, the soft polishing pad  110  can be aligned to the linear belt  103  and adhered to the linear belt  103  as a first step. The second step would call for laying the hard polishing pad  106  over the soft polishing pad  110 , and adhering the hard polishing pad  106  to the soft polishing pad  110  and the linear belt  103  at roughly the same time. A heated environment may optionally be used during any of the adhesion steps, according to well-known procedures.  
         [0047]    It should be appreciated that the apparatus of the present invention is capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described above. The invention may be embodied in other forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is therefore indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are embraced to be within their scope.