Abstract:
Apparatus and methods are provided to polish an edge of a substrate. The invention includes a polishing head adapted to retain a backing pad having a selected contour, wherein the polishing head is adapted to press the backing pad against an edge of a substrate. Numerous other aspects are provided.

Description:
[0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/939,342, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR REMOVAL OF FILMS AND FLAKES FROM THE EDGE OF BOTH SIDES OF A SUBSTRATE USING BACKING PADS” (Attorney Docket No. 11564/L) is hereby incorporated herein by reference in its entirety for all purposes. 
       CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    The present application is related to the following commonly-assigned, co-pending U.S. Patent Applications, each of which is hereby incorporated herein by reference in its entirety for all purposes: 
         [0003]    U.S. patent application Ser. No. 11/299,295 filed on Dec. 9, 2005 and entitled “METHODS AND APPARATUS FOR PROCESSING A SUBSTRATE” (Attorney Docket No. 10121); 
         [0004]    U.S. patent application Ser. No. 11/298,555 filed on Dec. 9, 2005 and entitled “METHODS AND APPARATUS FOR PROCESSING A SUBSTRATE” (Attorney Docket No. 10414); 
         [0005]    U.S. patent application Ser. No. 11/693,695 filed on Mar. 29, 2007 and entitled “METHODS AND APPARATUS FOR POLISHING AN EDGE OF A SUBSTRATE” (Attorney Docket No. 10560); 
         [0006]    U.S. Patent Application Ser. No. 60/939,351, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE USING AN INFLATABLE POLISHING WHEEL” (Attorney Docket No. 10674/L); 
         [0007]    U.S. Patent Application Ser. No. 60/939,353, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR FINDING A SUBSTRATE NOTCH CENTER” (Attorney Docket No. 11244/L); 
         [0008]    U.S. Patent Application Ser. No. 60/939,343, filed May 21, 2007, entitled “METHODS AND APPARATUS TO CONTROL SUBSTRATE BEVEL AND EDGE POLISHING PROFILES OF EPITAXIAL FILMS” (Attorney Docket No. 11417/L); 
         [0009]    U.S. Patent Application Ser. No. 60/939,219, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE USING A SHAPED BACKING PAD” (Attorney Docket No. 11483/L); 
         [0010]    U.S. Patent Application Ser. No. 60/939,350, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR USING A BEVEL POLISHING HEAD WITH AN EFFICIENT TAPE ROUTING ARRANGEMENT” (Attorney Docket No. 11565/L); 
         [0011]    U.S. Patent Application Ser. No. 60/939,344, filed May 21, 2007 entitled “METHODS AND APPARATUS FOR USING A ROLLING BACKING PAD FOR SUBSTRATE POLISHING” (Attorney Docket No. 11566/L); 
         [0012]    U.S. Patent Application Ser. No. 60/939,333, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR SUBSTRATE EDGE POLISHING USING A POLISHING ARM” (Attorney Docket No. 11567/L); 
         [0013]    U.S. Patent Application Ser. No. 60/939,212, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR IDENTIFYING A SUBSTRATE EDGE PROFILE AND ADJUSTING THE PROCESSING OF THE SUBSTRATE ACCORDING TO THE IDENTIFIED EDGE PROFILE” (Attorney Docket No. 11695/L); 
         [0014]    U.S. Patent Application Ser. No. 60/939,337, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR HIGH PERFORMANCE SUBSTRATE BEVEL AND EDGE POLISHING IN SEMICONDUCTOR MANUFACTURE” (Attorney Docket No. 11809/L); 
         [0015]    U.S. Patent Application Ser. No. 60/939,228, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE BY SUBSTRATE VIBRATION” (Attorney Docket No. 11952/L); and 
         [0016]    U.S. Patent Application Ser. No. 60/939,209, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR CONTROLLING THE SIZE OF AN EDGE EXCLUSION ZONE OF A SUBSTRATE” (Attorney Docket No. 11987/L). 
     
    
     FIELD OF THE INVENTION 
       [0017]    The present invention relates generally to substrate processing, and more particularly to methods and apparatus for cleaning an edge of a substrate. 
       BACKGROUND OF THE INVENTION 
       [0018]    Substrates are used in semiconductor device manufacturing. During processing, a film and/or flakes may be deposited on the surface of the substrate. However, it may be undesirable to have this film and/or flakes on the edge of the substrate, as it may negatively affect the semiconductor devices. Conventional systems, which contact a substrate edge with an abrasive tape to clean the edge, may not thoroughly clean the edge. For example, the abrasive tape may not sufficiently contact both bevels of the edge during cleaning. The inability to sufficiently clean the substrate may affect semiconductor device manufacturing throughput. Accordingly improved methods and apparatus for cleaning an edge of a substrate are desired. 
       SUMMARY OF THE INVENTION 
       [0019]    In aspects of the invention, an apparatus is provided for polishing an edge of a substrate. The apparatus comprises a backing pad coupled to a polishing head, wherein the backing pad has a selected contour, and wherein the polishing head is adapted to press the backing pad against an edge of a substrate. 
         [0020]    In other aspects of the invention, a system is provided for polishing an edge of a substrate. The system comprises a substrate support adapted to rotate a substrate; a backing pad coupled to a polishing head, wherein the backing pad has a selected contour, and wherein the polishing head is adapted to press the backing pad against an edge of the substrate; and a controller adapted to operate the rotation of the substrate and the polishing head. 
         [0021]    In yet other aspects of the invention, a method is provided for polishing an edge of a substrate. The method comprises rotating a substrate; contacting an edge of a substrate with polishing tape, wherein the polishing tape is contacted by the polishing strip section of the backing pad via a polishing head; and determining that a pre-set amount of film has been removed from the substrate edge. 
         [0022]    Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]      FIG. 1  is a schematic illustration of a cross-section of a portion of a substrate. 
           [0024]      FIG. 2  is a schematic illustration of an example embodiment of a polishing head adapted to polish the edge of a substrate according to the present invention. 
           [0025]      FIG. 3  is a perspective view depicting an example embodiment of a film polishing system according to the present invention. 
           [0026]      FIGS. 4A ,  4 B and  4 C are example embodiments of a backing pad according to the present invention. 
           [0027]      FIGS. 5A and 5B  are an example embodiment of a backing pad according to the present invention. 
           [0028]      FIGS. 6A and 6B  are an example embodiment of a backing pad according to the present invention. 
           [0029]      FIG. 7  is an example embodiment of a backing pad according to the present invention. 
           [0030]      FIG. 8  is a flowchart depicting an example application of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The present invention provides improved methods and apparatus for cleaning and/or polishing the edge of a substrate. The edge of a substrate may be polished by application of an abrasive polishing pad or abrasive polishing tape contacting the substrate edge via a polishing head, for example, as the substrate is rotated or otherwise moved (e.g., oscillated). In some embodiments, the backing pad may contact a non-abrasive side of the polishing tape, such that the polishing tape contacts and polishes the substrate. According to the present invention, the surface of the polishing or backing pad may have contours which may be mapped onto, or correspond to, locations on the substrate where film removal is desired. In other words, the surface shape of the backing pad may be angled, for example, such that when the backing pad contacts the substrate edge (in some instances via the polishing tape), the backing pad (through the polishing tape) may impose its own shape onto the substrate  100  and may remove a corresponding profile or area of film from the substrate edge. With reference to  FIG. 1 , a substrate  100  may include two major surfaces  102 ,  102 ′, and an edge  104 . Each major surface  102 ,  102 ′ of the substrate  100  may include a device region  106 ,  106 ′ and an exclusion region  108 ,  108 ′. (Typically however, only one of the two major surfaces  102 ,  102 ′ will include a device region and an exclusion region.) The exclusion regions  108 ,  108 ′ may serve as buffers between the device regions  106 ,  106 ′ and the edge  104 . The edge  104  of a substrate  100  may include an outer edge  110  and bevels  112 ,  114 . The bevels  112 ,  114  may be located between the outer edge  110  and the exclusion regions  108 ,  108 ′ of the two major surfaces  102 ,  102 ′. The present invention is adapted to clean and/or polish all or part of the exclusion regions  108 ,  108 ′, the outer edge  110 , and at least one bevel  112 ,  114  of a substrate  100  without affecting the device regions  106 ,  106 ′. 
         [0032]    Turning to  FIG. 2 , a schematic illustration of an example embodiment of a polishing head apparatus  200 , including a polishing head  201 , adapted to polish the exclusion regions  108 ,  108 ′ and the edge  104  of the substrate  100  is depicted. The substrate  100  may be held and rotated, for example, by a vacuum chuck  208 . Other substrate rotation means may be used (e.g., driver rollers and guide rollers, etc.). The polishing head  201  may include a backing pad  204 . In some embodiments, the backing pad  204  may be inflatable. In either case, the backing pad  204  and/or inflatable pad may be soft and/or include, or develop, contours to conform to the shape of the substrate edge  104 . The backing pad  204  may be used to polish the substrate exclusion regions  108 ,  108 ′ and the edge  104 . Additionally or alternatively, the backing pad  204  may be pressed against a polishing tape  206 , used to polish the substrate exclusion regions  108 ,  108 ′ and the edge  104 . As the substrate  100  rotates, the backing pad  204  may be pushed by an actuator (e.g., a pneumatic slide, hydraulic ram, servo motor driven pusher, etc.) (not shown), such that the backing pad  204 , and hence the polishing tape  206 , may be pressed against the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). Alternatively or additionally, the actuator may be adjustable, and may be used to also push the entire head  201  toward the substrate  100 . Alternatively, a biasing device (e.g., a spring) may be employed to mount the pad  204  to the head  201  to provide flexible/dynamic counter pressure to the pad  204 . The substrate  100  may contact the polishing tape  206  for about 15 to 150 seconds depending on the type of tape used, the grit of the tape, the rate of rotation, the amount of polishing required, etc. More or less time may be used. The contact between the backing pad  204  (and abrasive or polishing tape  206 ) and the substrate exclusion regions  108 ,  108 ′ and the edge  104 , combined with the particular rotation speed of the substrate  100 , may provide relative movement between the abrasive tape  206  and the substrate exclusion regions  108 ,  108 ′ and edge  104 , resulting in the substrate exclusion regions  108 ,  108 ′ and the edge  104  being polished. Depending on the amount of force applied by the actuator, the resiliency of the pad selected, the amount of inflation of an inflatable pad, and/or the amount of tension on the polishing tape, a controlled amount of pressure may be applied to polish the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). Thus, the present invention provides precise control of an edge polish process, which may be used to compensate for different edge geometries and changes in the substrate  100  as material is removed from the edge  104 . 
         [0033]    The pad  204  may be made of material such as, for example, an acetal resin (e.g., Delrin® manufactured by DuPont Corporation), PVDF, polyurethane closed cell foam, silicon rubber, PTFE, PEEK, ceramics, stainless steel etc. Other materials may be used. Such materials may have resilience or an ability to conform that is a function of the thickness or density of the pad. The material may be selected based upon its resilience. The desired resilience may be selected based upon the type of polishing required. 
         [0034]    In some embodiments, the pad  204  may have an adjustable amount of ability to conform to the substrate&#39;s edge  104  (and edge exclusion zones  108 ,  108 ′), or other areas to be polished. For example the pad  204  may be, or include an inflatable bladder, inflatable by air, liquid or other fluid. 
         [0035]    The substrate  100  may be rotated in a horizontal plane. The substrate edge  104  may be aligned with, or normal to, the polishing tape  206 , pad  204  and/or polishing head  201 . In additional or alternative embodiments, the substrate  100  may be rotated in a vertical plane, other non-horizontal plane, and/or be moved between different planes of rotation. 
         [0036]    In the embodiment described herein, as the substrate  100  rotates, the polishing head  201  may rock around the substrate exclusion regions  108 ,  108 ′ and the edge  104  to polish the entire exclusion regions  108 ,  108 ′ and the edge  104  as indicated by the curved arc  203  in  FIG. 1 . The selected angle of rocking along the arc  203 , may include, for example, plus or minus 90 degrees. Other rocking angles may be used. In operation, the polishing head  201  may be “rocked” by angularly translating the head  201 , and consequently, the backing pad  204  and polishing tape  206  in contact with and contoured to the exclusion regions  108 ,  108 ′ and edge  104  of a substrate  100 , around an axis that is tangential to the outer edge  110  of the substrate  100  as it is rotated. In some embodiments, the head  201  may be adapted to continuously or intermittently oscillate between the various positions. The head  201  may be moved by drivers (not shown) under the direction of a programmed or user operated controller. Alternatively, the head  201  may be fixed and/or only adjusted while the substrate  100  is not being rotated. In yet other embodiments, the substrate  100  may be held fixed while the head  201  is oscillated (as described above) as well as rotated circumferentially around the substrate  100 . The key parameters to control the edge polishing area may be the angle of rocking, the center of rotation for rocking, and the contour of the backing pad. 
         [0037]    In some embodiments, fluids used to aid in the polishing or washing away of accumulated particles, may be delivered to the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). The chemicals may be sprayed directly onto the substrate  100 , at the substrate/abrasive tape interface, and/or may be applied to and/or through the tape and/or the pad  204 . A fluid channel (not shown) may be provided to drip or spray the fluid on or into the pads  204 . Alternatively, an inflatable pad  204  may include a bladder (not shown) with a semi-permeable membrane that allows fluid to be slowly released and transmitted to the polishing tape  206  (e.g., through the pad). In such embodiments, the pad  204  may be covered by, made of, and/or include material that absorbs and/or retains the fluids used (e.g., polyvinyl alcohol (PVA), etc.). Additionally, the present invention may employ gravity or suction to cause the runoff not to contaminate or contact other parts of the substrate  100  or apparatus of the invention. Further, energy (e.g., megasonic energy) may be applied to the substrate edge  104  (and edge exclusion zones  108 ,  108 ′) via fluid carrying such energy. 
         [0038]    As described above, in some embodiments, a controller  304  (shown in  FIG. 3 ) (e.g., a programmed computer, a programmed processor, a gate array, a logic circuit, an operator directed valve system, an embedded real time processor, etc.) may control the driver(s) used to rotate the substrate  100 , and the actuator used to push the pad  204  against the exclusion regions  108 ,  108 ′ and substrate edge  104 . Note that the controller  304  may be coupled (e.g., electrically, mechanically, pneumatically, hydraulically, etc.) to each of a plurality of actuators. Likewise, operation of the fluid channels may also be under the direction of the controller  304 . Under direction of the controller  304 , various fluids may be selectively delivered to the pads  204  and/or the substrate exclusion regions  108 ,  108 ′ and edge  104  via the fluid channels. The controller  304  may be adapted to receive feedback signals from the driver and/or actuator that indicate the amount of energy being exerted to drive the substrate  100  (e.g., rotate a vacuum chuck holding the substrate  100 ) and/or actuate the actuator to push the pad, respectively. These feedback signals may be employed to determine when a particular selected layer of film has been removed and/or whether a sufficient or selected amount of polishing has occurred. 
         [0039]      FIG. 3  is a perspective view depicting an example embodiment of a substrate polishing system  300  according to the present invention.  FIG. 3  depicts a substrate polishing system  300  including three heads  302 . As suggested by  FIGS. 2 and 3 , any number and type of heads  302  may be used in any practicable combination. In addition, in such multi-head embodiments, each head  302  may use a differently selected contoured backing plate or pad (e.g., different contours of the strip-like feature  404 , shown in  FIG. 4A , for example, etc.). Any number of heads  302  may be used concurrently, individually, and/or in a sequence. The heads  302  may be disposed in different positions, and in different orientations (e.g., aligned with the substrate edge  104 , normal to the substrate edge  104 , angled relative to the substrate edge  104 , etc.) to allow the polishing pad strip (described below) to polish different portions of the rotating substrate edge  104  (and edge exclusion zones  108 ,  108 ′). The heads  302  may be adapted to be oscillated or moved (e.g., angularly translated about a tangential axis of the substrate  100  and/or circumferentially relative to the substrate  100 ) around or along the substrate edge  104  by the frame so as to polish different portions of the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). Different heads  302  may be used for different substrates  100 , different types of substrates  100 , or different polishing processes. Substrate polishing may be performed using one or more polishing apparatuses. In one or more embodiments, a plurality of polishing apparatuses may be employed, in which each polishing apparatus may have similar or different characteristics and/or mechanisms. In the latter case, particular polishing apparatuses may be employed for specific operations. For example, one or more of a plurality of polishing apparatuses may be adapted to perform relatively rough/coarse polishing and/or adjustments, while another one or more of the plurality of polishing apparatus may be adapted to perform relatively smooth/fine polishing and/or adjustments. Polishing apparatuses may be used in sequence so that, for example, a rough polishing procedure may be performed initially and a fine polishing procedure may be employed subsequently to make adjustments to a relatively rough polish as needed or according to a polishing recipe. The plurality of polishing apparatuses may be located in a single chamber or module, or alternatively, one or more polishing apparatuses may be located in separate chambers or modules. Where multiple chambers are employed, a robot or another type of transfer mechanism may be employed to move substrates between the chambers so that polishing apparatuses in the separate chambers may be used in series or otherwise. 
         [0040]    Turning to  FIGS. 4A and 4B , an example embodiment of a backing pad  400  according to the present invention is depicted. In  FIG. 4A , a curved top surface  402  of the backing pad  400  has symmetrical contours  401  in perpendicular directions from a central location, providing a strip-like feature  404  on the top surface  402 . In the example embodiment shown herein, the center of rotation (R), shown in cross-section  FIG. 4B , may act as the central location. Other central locations may be used. In some embodiments, the strip  404  may be the only region of the backing pad  400  that contacts a smooth backside of the polishing tape  206 , whose abrasive side in turn polishes the substrate exclusion regions  108 ,  108 ′ and the substrate edge  104 , as described above with respect to  FIG. 2 . The symmetrical contours  401  of the strip  404 , may provide symmetrical controlled removal of film from the exclusion regions  108 ,  108 ′, the top and bottom bevels  112 ,  114 , as well as the outer edge  110  of the substrate  100 . Based on the shape of symmetrical contours  401 , the width of the strip  404  may be optimized for best removal rate and performance. In addition, variations in removal area may be achieved by changing the rocking angles of the head  201 , for example, the conformity/resilience of the pad, the contours of the strip  404 , etc. 
         [0041]      FIG. 4B  is a cross-section taken along line  4 B- 4 B of  FIG. 4A . As shown herein, an axis of rotation (R) is centered, such that, for example, the centered axis is 7.75 mm from each of a first and second edge  406 ,  408  of the backing pad  400 . Other measurements may be used. In some embodiments the axis of rotation (R) may be selected by a user, and may be based on a particular polishing procedure. 
         [0042]    In alternate embodiments, the backing pad  400  may have a semi-spherical or convex shape, such as the roller backing pad  400  shown in  FIG. 4C . The roller backing pad  400  may include the same contours  401  and polishing strip  404  as the backing pad shown in  FIGS. 4A and 4B . In some embodiments, the radius of the convex contour may range from approximately 25 mm to approximately 50 mm. Other dimensions may be used. The dimensions of the convex contour may affect the contact of the polishing tape  206  against the substrate  100 , and may therefore impact the rate of removal of the film. The roller backing pad  400  may rotate as the polishing strip  404  is pressed against the polishing tape  206 , which may in turn be pressed against the substrate edge  104  (including the edge exclusion zone  108 ,  108 ′ in some embodiments). In some embodiments, the polishing strip  404  may range from 7 to 8 mm, for example. Other polishing strip  404  widths may be used. In some embodiments, the rotation of the substrate may apply a perpendicular force to the polishing tape  206 , which may cause the polishing tape  206  to slip, in the same direction as the perpendicular force, from a flat surface (not shown) of the backing pad  400 , for example. In some embodiments, the combination of the perpendicular force, the flat surface and a misalignment of the backing pad  400  and the polishing tape  206  may cause the polishing tape  206  to slip off of the backing pad  400 . However, the convex contour, and in particular the polishing strip  404 , on the roller backing pad  400  may help prevent or minimize the polishing tape  206  from slipping off of the roller backing pad  400  during the polishing process. The rotation of the roller backing pad  400  with the polishing tape  206  may create less friction therebetween than with the non-rotating backing pad  400  shown in  FIGS. 4A and 4B , for example, which may drag the polishing tape  206 . The decreased friction may result in less wear and tear on the polishing tape  206 , for example, thereby increasing the usable life of the polishing tape  206 . Additionally, the decreased friction may result in a decrease of particle formation, as particle formation may be undesirable due to its ability to interfere with the polishing system components and substrate production. The roller backing pad  400  may also have a greater usable lifespan than the non-rotating backing pad  400  shown in  FIGS. 4A and 4B , for example. This may be because the substrate, rotating at a particular speed and pressure, may be pressed into a single fixed location against the polishing tape  206  and in turn the non-rotating backing pad  400  shown in  FIGS. 4A and 4B , for example, and may create a groove in the non-rotating backing pad  400 , which in turn may impact the process performance. 
         [0043]    The material used to form the backing pad  400  may be firm enough, as described further below, to cause a good contact between the polishing tape  206  and the substrate  100 . The material may also have a low coefficient of friction and a high wear resistance. Alternatively, as described above, the backing pad  400  may have an adjustable amount of ability to conform to the substrate edge  104  (and edge exclusion zones  108 ,  108 ′), or other areas being polished. Backing pads  400  with the ability to conform to the substrate edge  104  (and edge exclusion zones  108 ,  108 ′), for example, may still cause a good contact between the polishing tape  206  and the substrate  100 . In some embodiments, the softer the material, the more conformable the material may be to the substrate edge  104  (and edge exclusion zones  108 ,  108 ′), which in turn may better distribute the contact pressure and improve the contact between the backing pads  400  and the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). Additionally, the softer the material, the more the force from the backing pad  400  may be spread on the substrate  100 , which may avoid damage or scratches on the substrate, for example. Materials that may be used to form the backing pad  400  may include, for example, PTFE, PEEK, Delrin, stainless steel or ceramics. Other suitable materials may be used. In some embodiments, the hardness of the backing pads  400  may range from approximately 60 to approximately 90 Shore A Durometers. Other hardnesses may be used. 
         [0044]    Turning to  FIGS. 5A and 5B , an example embodiment of a backing pad  500  according to the present invention is depicted. Similarly to the backing pad  400  in  FIG. 4A , the backing pad  500  shown in  FIG. 5A  has a curved top surface  502  contoured in perpendicular directions  501  from a central location, and forming a strip  504 . In the example embodiment shown herein, the center of rotation (R) (shown in cross-section  FIG. 5B ) may act as the central location. Other central locations may be used. However, unlike the strip  402  in  FIG. 4 , the strip  504  in  FIGS. 5A and 5B , is asymmetrically contoured. As shown in  FIG. 5B , which is a cross section taken along line  5 B- 5 B in  FIG. 5A , the strip  504  herein includes two different radii ( 506 , 508 ), each corresponding to the top and bottom exclusion region  108 , 108 ′, and edge  104  of the substrate  100 . In other words, the contour  501  (or downward angle) of the polishing strip  504  from a first edge  503  of the polishing pad  500  to a center of rotation (R) is different (in this case smaller) than the top contour  501  (or downward angle) of the polishing strip  504  from a second edge  505  of the polishing pad  500  to the center of rotation (R). The backing pad  500  shown in  FIGS. 5A and 5B  may provide a well-defined film edge on the top exclusion zone  108 , bevel  112  and outer edge  110  of the substrate  100 , by using the small radius, and a less defined edge on the bottom exclusion zone  108 ′, bevel  114 , and outer edge  110  of the substrate  100 , using the larger radius. In some embodiments, by providing a less defined edge, the rate of polishing may increase. As the bottom exclusion zone  108 ′, bevel  114 , and outer edge  110  of the substrate  100  may not receive electronics, the bottom exclusion zone  108 ′, bevel  114  and outer edge  110  of the substrate  100  may not need a clear defined film edge. 
         [0045]    Additionally, as the regions on the surface  502  of the backing pad  500  may be directly mapped to corresponding regions on the substrate  100 , as described above, the mapping may be used to add flexibility in the design of the backing pad  500  to perform at different parameters as required by the process. 
         [0046]    Turning to  FIGS. 6A and 6B , an example embodiment of a backing pad  600  according to the present invention is depicted. Similarly to the backing pads  400  and  500  shown in  FIGS. 4A ,  4 B,  5 A and  5 B, respectively, the backing pad  600  shown in  FIG. 6A  has a curved top surface  602  contoured  601  in perpendicular directions from a central location, and forming a polishing strip  604 . As also described above, the contour  601  along the polishing strip  604  may be modified for different requirements. For example, from a first polishing pad edge  606  to a center of the polishing strip  604 , the contour  601  of the curved top surface  602  is not the same as the contour  601  of the curved top surface  602  from the center of the polishing strip  604  to a second polishing pad edge  608 . As shown in  FIG. 6B , which is a cross section taken along line  6 B- 6 B in  FIG. 6A , the axis of rotation (R) is not centered. For example, as described above, the centered axis of rotation in  FIGS. 4A ,  4 B and  FIGS. 5A ,  5 B is 7.75 units from each of the first and second edge  406 ,  408 ,  503 ,  505  in FIGS.  4 A/ 4 B and FIGS.  5 A/ 5 B, respectively. However, in  FIG. 6 , the off-centered axis of rotation (R) is 6.25 units from the first polishing pad edge  606  and 9.25 units from the second polishing pad edge  608 . Other measurements may be used. This off-centered design may allow different areas on the top and bottom exclusion region  108 , 108 ′, and edge  104  of the substrate  100  to be polished. The off-centered design may be determined based on process requirements. 
         [0047]    Turning to  FIG. 7 , an example embodiment of a backing pad  700  according to the present invention is depicted. The backing pad  700  of  FIG. 7  is shaped as a roller, similar to the roller embodiment shown in  FIG. 4C , and may incorporate the features of backing pads  400 ,  500  and  600 . In other words, as described above, the roller backing pad  700  may, via the polishing tape  206 , symmetrically remove film from both the top and bottom exclusion regions  108 , 108 ′, and edge  104  of the substrate  100  similarly to the backing pad  400  shown in  FIGS. 4A and 4B . The roller backing pad  700 , via the polishing tape  206 , may remove film from the top and bottom exclusion regions  108 , 108 ′, and edge  104  of the substrate  100  in an asymmetric manner (i.e., a different amount from the top exclusion region  108  and bevel  112  and top edge  110  compared to the bottom exclusion region  108 ′, bevel  114  and bottom edge  110 ). The asymmetric removal of film may be achieved via different selected rocker angles for the top exclusion region  108 , bevel  112  and top edge  110  compared to the bottom exclusion region  108 ′, bevel  114  and bottom edge  110 . Additionally, the roller backing pad  700  may be mounted off-center within the polishing head  201 . The off-center mounting may also allow the roller backing pad  700  to remove film from the top and bottom exclusion regions  108 , 108 ′, and edge  104  of the substrate  100  in an asymmetric manner. In other words, for the same selected angle of rotation, a different amount of film may be removed from the top exclusion region  108 , bevel  112  and top edge  110  compared to the bottom exclusion region  108 ′, bevel  114  and bottom edge  110 , which may achieve similar results as the off-centered backing pad  600  described in  FIG. 6 . In some embodiments, when a large amount of film is selected to be removed from the top exclusion region  108 , top bevel  112 , and edge  110 , compared to the bottom exclusion region  108 ′, bottom bevel  114  and edge  110 , the off-centered roller  700  may be more efficient than selecting different rocking angles for the top exclusion region  108  and top bevel  112 , and edge  110 , compared to the bottom exclusion region  108 ′, and bottom bevel  114  and edge  110 . In some embodiments, the roller backing pad  700  may have contours on the cylindrical surface, which may distribute the contact forces on the substrate edge  103 . The shape of the contour may be different based on the type of polishing application or the area of the substrate being polished, for example. Additionally, the different pads  400 ,  500 ,  600 , and  700  may be modular or easily replaceable, such that pads  400 ,  500 ,  600 , and  700  with different contours may be selected depending on the type of polishing application being performed. 
         [0048]    Additionally, as described above, the use of a roller backing pad  700  may decrease the frictional forces acting on the motion of the polishing tape  206 , shown in  FIG. 2 , and therefore may enhance the performance of the roller backing pad  700 . The decreased frictional force may also reduce the wear of the backing pad  700 , as well as the polishing tape  206 . 
         [0049]      FIG. 8  is a flowchart depicting an example application  800  of the present invention. In step S 802 , a backing pad  400  for a symmetrical polishing on the edge  104  (and edge exclusion zones  108 ,  108 ′) of a substrate  100  is selected. The backing pad may be selected based on the contour of the backing pad used for a particular polishing application. The backing pad  400  is inserted into the polishing head  200  in step S 804 . In step S 806 , the substrate  100  is rotated via a vacuum chuck, for example. In step S 808 , the backing or polishing pad  400  contacts the polishing tape  206 , which in turn contacts the edge  104  (and edge exclusion zones  108 ,  108 ′) of the substrate  100  The backing pad may rock about the edge  104  (and edge exclusion zones  108 ,  108 ′) of the substrate  100 . The rocking motion may allow the contours of the backing pad  400  to appropriately contact and polish the substrate edge  104  (and edge exclusion zones  108 ,  108 ′). A selected amount of film is removed from the substrate  100  in step S 810 . In some embodiments, for example, sensors may be used to determine that a pre-set or selected amount of film has been removed. Alternatively, for example, the rocking motion may continue for a pre-set or selected amount of time, whereby it has previously been determined that rocking the polishing pad for the selected amount of time removes a particular amount of film from the substrate. Other suitable methods may be used to determine a selected amount of film has been removed from the substrate. 
         [0050]    It should be understood that the inventive edge polishing apparatus described herein may be employed in apparatuses other than those adapted for bevel and edge polishing and/or removal of films on substrates. Further, as will be apparent to those of ordinary skill in the art, the apparatus described herein may be employed to polish and/or remove films on an edge of a substrate supported in any orientation (e.g., horizontal, vertical, diagonal, etc). 
         [0051]    Further, it should be understood that although only examples of cleaning a round substrate are disclosed, the present invention could be modified to clean substrates having other shapes (e.g., a glass or polymer plate for flat panel displays). Further, although processing of a single substrate by the apparatus is shown above, in some embodiments, the apparatus may process a plurality of substrates concurrently. 
         [0052]    The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.