Abstract:
A polishing pad includes a body formed of a polishing pad material and having a top polishing surface and a bottom surface; and an indicator disposed in said body and extending from an upper region of the body near the top polishing surface toward said bottom surface, for indicating wear of the polishing pad body during a life cycle of the polishing pad. An apparatus for polishing semiconductor wafers includes a polishing platen; a motor for rotating the polishing platen; and a polishing pad as described above mounted on the polishing platen. A method of polishing semiconductor wafers includes optically inspecting the indicator means to determine the wear of the body.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to the field of polishing surfaces such as glasses, semiconductors, and integrated circuits. More particularly, this invention relates to polishing pads that provide an indication during polishing and conditioning of the level of wear, uniformity of wear, and the end of the useful life thereof. The method of use allows an operator of a polishing machine, such as a chemical mechanical polishing machine for semiconductor devices, to visually inspect the level and distribution of wear during polishing and conditioning as well as detect in-line the end of useful life of the pad.  
           [0003]    2. Description of Related Art  
           [0004]    Because of the increasing density of integrated circuits, extremely small electronic devices are formed on thin, flat semiconductor wafers which results in a high degree of varying topography being created on the outer wafer surface during fabrication. Planarization of a wafer&#39;s surface is necessary to provide a substantially flat planar wafer surface. Apparatus for accomplishing such planarization are well known in the art and include chemical-mechanical (CMP) polishing.  
           [0005]    CMP is accomplished by holding a wafer with its desired coated surface to be planarized face down on a polishing pad supported on a rotating table, in the presence of an abrasive slurry. The rotating table typically includes a rotating polishing plate having a polishing pad mounted thereon and a smaller diameter rotating wafer carrier to which a wafer (or wafers) is mounted. The wafer carrier is held above the polishing pad, in either a stationary fixed position or oscillating back and forth in a predetermined path in a horizontal plane, while both polishing plate and wafer carrier are rotated about their respective central axes. A slurry of an abrasive suspension with or without an etching reagent, is fed onto the polishing pad and is fed between the polishing pad and the wafer both to polish and flush away the material removed from the wafer. Further, slurries can provide for conditioning of the polishing pad itself during polishing of a wafer so that a clean, fresh polishing pad surface results after each wafer is planarized a desired amount. However, both the CMP and conditioning of the polishing pad result in a thinning of the polishing pad itself. The thinning of a polishing pad is, in part, a result of the abrasive action of the conditioning material.  
           [0006]    Conditioning may take place during or after the polishing process. Pad conditioning or dressing is commonly used to stabilize the polishing process by roughening or refreshing the pad surface. During conditioning, the pad matrix itself or the residual materials, such as, pad debris or slurry deposits on the pad surface, will be removed. The most common method of pad conditioning is to mechanically abrade the surface of the pad, which necessarily removes a quantity of the pad&#39;s surface. That is, conditioning is a kind of destructive and irreversible approach and the profile of the pad after conditioning needs to be monitored as well, to minimize the impact of conditioning on polishing performance. The goal of conditioning is to achieve a dressed pad with uniform thickness in order to minimize the impact of conditioning on polishing performance.  
           [0007]    Heretofore, it has been virtually impossible to determine the pad profile of all commercially available pads before they reach their pad lifetime. The traditional commercial technique is to delaminate the pad from the platen after it reaches the pad lifetime followed by adhesive removal and pad cutting before the manual thickness measurement can be performed. The entire process is time consuming and laborious. An alpha step-like pad profiler is also commercially available but it can only take the measurement after polish and still cannot monitor or reveal the problem in time.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a polishing pad having a wear level indicator disposed therein for monitoring polishing pad profile and a polishing method employing the same. The use of the wear level indicator of the present invention allows for more efficient and reliable determination of pad level uniformity than prior art methods.  
           [0009]    A polishing pad, in accordance with one embodiment of the present invention, includes a pad structure and an indicator, disposed in the pad structure, indicating the uniformity of the level of wear of the pad structure, both during polishing and during conditioning, i.e., in-line.  
           [0010]    The pad structure may, for example, include colored or dyed and shaped portions inserted into the top surface of the pad, to facilitate pad profile monitoring and pad end-of-life determination, in-line, without waiting for a predetermined period until pad change-out. The wear level indicated may, for example, be a loss of a critical thickness of the polishing pad surface which indicates the end of the pad&#39;s lifetime or the need to change the polishing process. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a polishing pad having shaped portions inserted into the top surface thereof.  
         [0012]    [0012]FIG. 2 shows a cross-sectional view of an insertion with a variable width to show degree of wear during use.  
         [0013]    FIGS.  3 A-B show cross-sectional views of an insertion with a variable width, but with less depth than the polishing pad depth, to indicate in-line both degree of wear during use and end-of-life of the polishing pad; in both instances end-of-life is indicated by visual absence of the insert.  
         [0014]    [0014]FIG. 4A shows a cross-section of a polishing pad with a wedge-shaped groove in its top surface that is filled with high contrast material.  
         [0015]    [0015]FIG. 4B shows a top view of a polishing pad with a groove filled with high contrast material, the groove being situated along a diameter of the top surface of a circular polishing pad.  
         [0016]    [0016]FIG. 4C shows a cross-section of a polishing pad with a plurality of periodically placed inverted cone-shaped or pyramid-shaped inserts filled with high contrast material.  
         [0017]    [0017]FIG. 4D show a top view of a polishing pad with a plurality of periodically placed inverted cone-shaped inserts filled with high contrast material, the periodical placement lying along a diameter of a circular polishing pad.  
         [0018]    [0018]FIG. 5 is a partial cross-sectional view of a CMP polishing device for polishing semiconductor wafers, according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    In a preferred embodiment of the present invention, a colored or dyed and shaped portion is inserted into the top surface of a polishing pad  1  to enable monitoring of the pad uniformity profile and pad lifetime in-line without waiting for the expiration of a predetermined pad lifetime.  
         [0020]    Referring to FIG. 1, the insert in a preferred embodiment can be of various forms  12   a - 12   d , either continuous pieces  10  or discrete pieces  11 , but must cover a sufficient amount of the pad surface to indicate the uniformity of wear of the entire pad surface, e.g., a diameter of a circular pad.  
         [0021]    As shown in FIG. 1, the insert can be a continuous piece  10  or can be periodically discrete pieces  11 . The shape of the insert can be any shape  12   a - 12   d  that provides a size variation resulting from polishing and conditioning that can be detected in-line, preferably via optical detection. That is, the shape of the insert  12   a - 12   d  must be such that a decrease thereof when the polishing pad wears in the thickness direction of the polishing pad will result in exposing a smaller cross-section of the insert that will be optically detectable by an observer.  
         [0022]    In a preferred embodiment illustrated in the side view of FIG. 2, the top dimension  20  and bottom dimension  21  of a high contrast insert are designed to be of different widths so that they will indirectly indicate the removal of thickness of the pad by polishing and conditioning, across the entire surface of the pad. Then, with a top down optical scan at a given time, it will be possible to know the actual distribution of wear or removal thickness of a pad according to the width variation data obtained from the insert(s).  
         [0023]    FIGS.  3 A-B illustrate embodiments in which a colored or dyed insert extends from a region at or near the top surface  22  of a pad to a position  30  above the bottom surface  23 , which position  30  indicates pad end-of-life, with the width of the insert varying from thickest to thinnest (FIG. 3A) and vice versa (FIG. 3B), respectively, from top  22  to position  30  in such a way as to be able in-line to optically indicate a percentage removal of a pad&#39;s surface resulting from both polishing and conditioning.  
         [0024]    In an alternative embodiment, an insert with a fixed thickness from top to bottom can also serve as an indicator of the pad&#39;s end-of-life, in combination with variable thickness indicators such as a color variation of the insert from top to bottom of the pad.  
         [0025]    The inserted piece or pieces should have the same properties as the pad itself to avoid material incompatibility during the conditioning process and to achieve uniform material and structure on a top polishing surface.  
         [0026]    A polishing pad  1 , according to preferred embodiments illustrated in FIGS.  4 A-D, is a unitary pad having a top surface  22  and a bottom surface  23 . The top surface is made to include a wedge or V-shaped grove  41 , as illustrated in FIG. 4A, extending across a diameter  13  of a circular polishing pad  1 , as illustrated in FIG. 4B. In an alternative preferred embodiment, illustrated in FIG. 4C, cone-shaped or pyramid-shaped inserts  42  are inverted and inserted pointed end down into comparably shaped holes  43  extending from at or near the top surface  22  to the bottom surface  23  of a polishing pad  1  and periodically spaced along a diameter of a circular polishing pad  1 , as illustrated in FIG. 4D. The polishing pad  1  can be made, for example, of any suitable polishing pad material such as urethane or urethane impregnated cloth or polymeric materials. A groove  41  and holes  43  can be formed by cutting, molding, or embossing the desired pattern into the top surface  22  of the pad. The particular method of forming the groove  41  and holes  43  is determined by the desired result, i.e., shape, depth, size, and the like.  
         [0027]    In some embodiments, a high contrast dye is included in the material  43  which fills the groove  41  or the holes  43 , so that pad wear can be optically judged, assessed, or determined by its visible appearance, that is, by the brightness or brightness uniformity of the high contrast material in the groove  41  or holes  43  as viewed from the top surface  22  of the polishing pad  1 .  
         [0028]    As shown in the cross-section of FIG. 4A, as the polishing pad  1  wears thinner during use and conditioning, less and less of the high contrast material  40  will remain visible. That is, as the polishing pad  1  wears, the high contrast material  40  in the groove  41  or holes  43  will become visibly duller (or, alternatively, less noticeable) when being viewed from the top surface  22  of the polishing pad  1 . If the polishing pad  1  is worn in a non-uniform manner, then the color brightness of the high contrast material  40  in the groove  41  or holes  43  will vary across the diameter  13  of the polishing pad  1  when viewed from above the top surface  22 . Similarly, an end-of-life for the polishing pad  1  can also be determined by the complete absence of the high contrast color  40  when viewed from the top surface  22  of the polishing pad  1 .  
         [0029]    [0029]FIG. 5 shows a CMP polishing device  50  for polishing semiconductor wafers, including a polishing platen  51 , a motor M for rotating the polishing platen  51 , and a polishing pad  53  mounted on the polishing platen  51 . The polishing pad  53  comprises a body formed of a polishing pad material and having a top polishing surface  53 A and a bottom surface  53 B and an indicator insert  55  disposed therein, which insert may be formed according to any of the several embodiments as described above.  
         [0030]    The present wear indicating polishing pad, as disclosed herein, provides a simple indicator of polishing pad wear and wear uniformity and can be fabricated to indicate pad end-of-life. The present wear indicator can be applied to a wide range of polishing pad configurations, other than the circular configuration illustrated in the figures as a non-limiting example. For example, belt type polishers can benefit from pads with periodically placed cross-wise indicators according to the present invention. The polishing pad wear indicator, as discussed herein, utilizes modifications to the top surface of a polishing pad for providing wear, wear uniformity and end-of-life indications, when viewed from the top surface of the polishing pad, and can be employed in a wide variety of polishing applications.  
         [0031]    The modifications to the top surface of the polishing pad thus provide an advantageous polishing effect in particular for CMP processes and apparatus, as well as in general, extending to other applications which can benefit from in-line determination of polishing pad wear and wear uniformity as well as end-of-life.  
         [0032]    From the foregoing, it will be apparent to those skilled in the art that, although the present invention has been fully described by way of examples with reference to the accompanying drawings, numerous modifications, substitutions and variations, as well as rearrangements and combinations, of the preceding illustrative embodiments can be made without departing from the spirit and scope of the novel aspects of the present invention. It is to be understood that no limitation of the scope of the present invention with respect to the specific embodiments illustrated is intended or should be inferred, but the scope of the present invention is to be defined solely by the attached claims.