Patent Publication Number: US-6666755-B1

Title: Belt wiper for a chemical mechanical planarization system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to chemical mechanical planarization (CMP) methods and systems, and more particularly, to a belt wiper for removing fluid and particulate material that can interfere with a CMP process. 
     2. Description of the Related Art 
     In the fabrication of semiconductor devices, planarization operations on silicon wafers, which can include planarizing, polishing, buffing, and cleaning, are often performed. Typically, integrated circuit devices are in the form of multi-level structures on silicon substrate wafers. At the substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. Patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric and metal layers increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. 
     Planarizing metallization layers is becoming more important due to replacement of aluminum with copper as the metal of choice for metallization processes. One method for achieving semiconductor wafer planarization is the chemical mechanical planarization (CMP) technique. Further applications include planarization of dielectric films deposited prior to the metallization process, such as dielectrics used for shallow trench isolation or for poly-metal insulation. CMP systems typically implement a rotary, an orbital, or a linear pad system in which a preparation surface of a polishing pad is used to polish one side of a wafer. In general, the CMP process involves applying a controlled pressure to a typically rotating wafer that is in contact with a moving polishing pad coupled with a slurry containing a mixture of abrasive materials and chemicals to facilitate the planarization process. Slurry is most usually introduced onto a moving preparation surface and distributed over the preparation surface as well as the surface of the semiconductor wafer being prepared by the CMP process. The distribution of the slurry is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the fluid dynamics between the semiconductor wafer and the preparation surface. 
     FIG. 1 shows a conventional linear belt-type CMP system  100 . The conventional linear belt-type CMP system  100  includes a polishing head  108 , also known as a wafer carrier, which secures and holds a wafer  104  in place during CMP processing. A belt pad  102 , also known as a linear polishing belt, is disposed in the form of a band around rotating drums  112 . The belt pad  102  is composed of materials that provide structural integrity and facilitate the planarization/polishing of the CMP process. The belt pad  102  moves in a direction  106  at a speed of up to approximately 1000 feet per minute; however, this speed may vary depending upon the specific CMP process. As the belt pad  102  moves, the polishing head  108  rotates and lowers the wafer  104  onto the top surface (i.e., the preparation surface) of the belt pad  102 . The wafer  104  is applied to the belt pad  102  with a force  118  sufficient to facilitate the CMP process. 
     A fluid bearing platen manifold assembly  110  supports the belt pad  102  during the CMP process. Typically, the fluid bearing platen manifold assembly  110  utilizes a pressurized gas bearing. The pressurized gas bearing, typically composed of clean dry air, is provided by a gas source  114  and is input through the fluid bearing platen manifold assembly  110  via several independently controlled dispersion holes. The pressurized gas bearing provides upward force on the belt pad  102  to control the profile of the belt pad  102 . 
     A slurry  122  is delivered to the belt pad  102  by a slurry manifold  120  including many nozzles. The slurry manifold  120  dispenses the slurry  122  on the top surface of the belt pad  102 . Movement of the belt pad  102  in the direction  106  transports slurry  122  underneath the wafer  104 . The slurry manifold  120  is typically aligned in a position relative to the wafer  104  such as center on the wafer  104 . However, the position of the slurry manifold  120  can be adjusted to somewhat optimize the uniformity of the removal of material from the surface of the wafer  104 . 
     A pre-wet manifold  124  containing a number of dispersion holes  126  is positioned at a leading edge of a platen assembly  135 , where the leading edge is defined relative to the belt pad  102  movement direction  106 . A fluid, typically deionized water, flows through the dispersion holes  126  of the pre-wet manifold  124  to provide both rinsing and lubrication of the underside of the belt pad  102  and the fluid bearing platen manifold assembly  110 . Prior to reaching the pre-wet manifold  124 , the edge of the belt pad  102  passes by a belt-tracking sensor  128 . The belt-tracking sensor  128  is used to sense the position of the belt pad  102  edge so that the belt pad  102  can be steered accurately while traveling around the rotating drums  112  in the direction  106 . 
     FIG. 2 shows a top view of the platen assembly  135 . The platen assembly  135  includes the fluid bearing platen manifold assembly  110 . Pressurized gas flows out of a number of dispersion holes  136  to provide support and lubrication to the belt pad  102  as it traverses the platen assembly  135 . Also, a platen optics window  130  is located at the center of the fluid bearing platen manifold assembly  110 . The platen optics window  130  is a component of an endpoint detection system which measures a wafer film thickness and signals when the CMP process is finished. The pre-wet manifold  124  containing the number of dispersion holes  126  is also shown attached to the leading edge of the platen assembly  135  with respect to the belt pad  102  direction  106 . 
     FIG. 3 shows a top view of the belt pad  102  traversing the pre-wet manifold  124  and the platen assembly  135  in the direction  106 . The belt pad  102  contains a belt window  132  which passes over the platen optics window  130  as the belt pad  102  traverses the platen assembly  135 . The belt-tracking sensor  128  is also shown in relation to the belt pad  102  edge and platen assembly  135 . By monitoring a distance across a region  134  between the belt-tracking sensor  128  and the belt pad  102  edge, the belt pad  102  can be accurately steered as it travels around the rotating drums  112 . 
     The belt-tracking sensor  128  operates based on sound wave propagation and detection. The belt-tracking sensor  128  generates and directs sound waves toward the belt pad  102  edge. The sound waves are reflected back from the belt pad  102  edge to the belt-tracking sensor  128  where they are detected. A propagation time required for the sound waves to travel to the edge of the belt pad  102  and return to the belt-tracking sensor  128  is used to accurately determine the position of the belt pad  102  edge. The sound wave propagation time can be affected by variations in the region  134  through which the sound wave travels. Normally, the belt pad  102  edge position is determined using the sound wave propagation time and assumptions regarding the prevailing characteristics of the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge. During a CMP process, air from the fluid bearing platen manifold assembly  110  blows through both the fluid provided by the pre-wet manifold  124  and any excess slurry  122  on the underside of the belt pad  102  resulting in a disturbance of the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge. The air, fluid, and slurry  122  disturbance causes a change in the density of the region  134  resulting in a corresponding change in sound wave propagation velocity within the region  134 . Therefore, the assumptions regarding the prevailing characteristics of the region  134  combined with the actual sound wave propagation time as measured by the belt-tracking sensor  128  will result in an erroneous determination of the belt pad  102  position. An inability to correctly determine the position of the belt pad  102  prohibits effective belt pad  102  steering. Thus, a problem with the prior art is belt pad  102  steering inaccuracies caused by the intrusion of air, pre-wet fluid, and slurry  122  into the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge. 
     As previously discussed, the platen optics window  130  and belt window  132  are components of the endpoint detection system used to determine when a CMIP process is completed. Completion of a CMP process is determined by performing an active interrogation of the wafer  104  surface to determine if the desired wafer  104  surface condition has been achieved. The active interrogation in performed using an optical method wherein light is pulsed from an optical device in the platen optics window  130  toward the surface of the wafer  104 . The light pulse reflects off the wafer  104  toward the platen optics window  130 . The characteristics of the reflected light are used to determine the condition of the wafer  104  surface. When the wafer  104  surface condition achieves the desired results the CMP process is terminated. The belt window  132  allows the light pulse to travel from the platen optics window  130  to the wafer  104  surface and back to the platen optics window  130  to be analyzed. A problem with the prior art is that during the CMP process, slurry  122  and fluid cause both the platen optics window  130  and belt window  132  to become obscured such that the intensity of the light pulse used for endpoint detection is adversely affected. 
     In view of the foregoing, there is a need for an apparatus and method that can be implemented in a CMP process to prevent belt pad  102  steering inaccuracies caused by the intrusion of air, fluid, and slurry  122  into the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge. Furthermore, there is a need for an apparatus and method that can be implemented in a CMP process to prevent the platen optics window  130  and belt window  132  from becoming obscured by slurry  122  and fluid such that optical endpoint detection is not adversely affected. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing apparatuses and methods for a belt wiper that can be used in a linear belt-type chemical mechanical planarization (CMP) system to maintain a belt pad in a manner that preserves the functionality of both a belt pad steering system and an endpoint detection system. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below. 
     In one embodiment, a linear belt-type CMIP system is disclosed. The linear belt-type CMP system includes a first drum and a second drum. A belt pad having a width, a preparation surface, and an undersurface is configured around the first drum and the second drum. As the first drum and second drum rotate, the belt pad moves linearly. A platen provides support at a wafer preparation location where a wafer contacts the belt pad preparation surface during a CMIP process. More specifically, the wafer preparation location is located between a first platen side and a second platen side. The belt pad is configured to traverse over the wafer preparation location in a direction from the first platen side to the second platen side. The first platen side contains a plurality of delivery holes through which a gas is delivered to condition the undersurface of the belt pad prior to traversing the platen. The second platen side contains a plurality of delivery holes through which a liquid is delivered to condition the undersurface of the belt pad after traversing the platen. A wiper blade is positioned between the first drum and the second drum and inside of the belt pad. The wiper blade is configured to extend across width of the belt pad and to be in contact with the undersurface of the belt pad. In this configuration, the wiper blade is capable of removing fluid and particulate material from the underside of the belt pad. The wiper blade is generally configured to remove fluid and particulate material from the undersurface of the belt pad at a position next to the wafer preparation location. In a preferred embodiment, the wiper blade is attached to the first platen side. However, in other embodiments a plurality of wiper blades may be utilized and configured to contact the undersurface of the belt pad at an arbitrary number of positions between the first drum and second drum and inside the belt pad. The wiper blade can be configured to contact the undersurface of the belt pad in either a perpendicular or non-perpendicular manner. The wiper blade further includes a gutter that is configured to flow fluid and direct particulate material removed by the wiper blade toward each of the gutter ends. The gutter ends are formed to direct a flow of fluid and particulate material away from the gutter and away from the belt pad. 
     In another embodiment, a belt wiper assembly for use in a CMP system is disclosed, wherein the CMP system includes a linear polishing belt having a preparation surface and an undersurface. The belt wiper assembly includes a support body disposed within the linear polishing belt, a bracket attached to the support body, and a blade attached to the bracket. The bracket includes a gutter that is configured to extend across the width of the linear polishing belt. The ends of the gutter can be notched if necessary to direct a flow of fluid and particulate material. The blade is configured to contact the undersurface of the linear polishing belt in either a perpendicular or non-perpendicular manner. The blade contacting the undersurface of the linear polishing belt is flexible and can be shaped to enhance removal of fluid and particulate material. 
     In yet another embodiment, a method for maintaining an underside of a linear polishing belt of a CMP system is disclosed. Generally speaking, the method includes moving the linear polishing belt while wiping the underside of the linear polishing belt. More specifically, a wiping operation is performed prior to movement of the linear polishing belt over a wafer preparation location. Following the wiping operation, a drying of the underside of the linear polishing belt is performed prior to movement of the linear polishing belt over the wafer preparation location. Once the linear polishing belt moves over the wafer preparation location, a wetting of the underside of the linear polishing belt occurs. In alternate embodiments, numerous wiping operations are implemented using a plurality of wiper blades configured to contact the undersurface of the linear polishing belt at an arbitrary number of locations. 
     The advantages of the present invention are numerous. Most notably, the use of the belt wiper in the CMP system as disclosed in the present invention avoids the problems of the prior art by providing a device and method for preventing belt pad steering inaccuracies caused by the intrusion of air, fluid, and slurry into the region between the belt-tracking sensor and the belt pad edge. Furthermore, the use of the belt wiper in the CMP system provides a device and method that prevents the platen optics window and belt window from becoming obscured by slurry and fluid such that optical endpoint detection is adversely affected. 
     Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an illustration showing a prior art conventional linear belt-type CMP system; 
     FIG. 2 is an illustration showing a top view of a prior art platen assembly; 
     FIG. 3 is an illustration showing a top view of a prior art belt pad traversing the pre-wet manifold and the platen assembly; 
     FIG. 4 is an illustration showing a belt wiper assembly incorporated into a CMP system in accordance with a preferred embodiment of the present invention; 
     FIG. 5 is an illustration showing a side view of a belt wiper assembly incorporated into a CMP system in accordance with a preferred embodiment of the present invention; 
     FIG. 6 is an illustration showing a front view of the belt wiper assembly in relation to the belt pad in accordance with one embodiment of the present invention; 
     FIG. 7 is an illustration showing a top view of the belt wiper assembly attached to the platen assembly in accordance with one embodiment of the present invention; 
     FIG. 8 is an illustration showing the belt window traversing over the wiper blade in accordance with one embodiment of the present invention; 
     FIG. 9 is an illustration showing a belt wiper assembly configured to contact the belt pad in a perpendicular manner in accordance with an alternate embodiment of the present invention; 
     FIG. 10 is an illustration showing the belt wiper assembly incorporated into a CMP system that uses a pre-wet fluid in accordance with an alternate embodiment of the present invention; and 
     FIG. 11 is an illustration showing a side view of a plurality of wiper blade assemblies incorporated into a CMP system in accordance with an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention is disclosed for a belt wiper that can be used in a linear belt-type chemical mechanical planarization (CMP) system to maintain a belt pad. The belt wiper of the present invention mitigates disturbances within a detection region important to a belt pad steering system. Also, the belt wiper mitigates the obscuring of optical components important to operation of an endpoint detection system. Thus, the belt wiper of the present invention eliminates problems of the prior art by preserving the functionality of both the belt pad steering system and the endpoint detection system. 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIG. 4 shows a belt wiper assembly  201  incorporated into a CMP system in accordance with a preferred embodiment of the present invention. The belt wiper assembly  201  includes a wiper blade  200  configured between a locking bar  204  and a gutter  202 . The locking bar  204 , wiper blade  200 , and gutter  202  are held together by a plurality of fasteners  206 . Each of the gutter  202  ends are formed with a notch  208  to direct a flow of fluid and particulate material away from the gutter  202 . The gutter  202  is supported underneath by a bracket  210  wherein the gutter  202  and bracket  210  are held together with a plurality of fasteners  218  (see FIG.  5 ). The bracket  210  is attached to a support body using a plurality of fasteners  212 . In a preferred embodiment, the support body is the platen assembly  135 . Of course, other support mechanisms will also work, so long as the wiper blade  200  is supported. 
     A plurality of delivery holes  126  are configured at a leading edge of the platen assembly  135  to deliver clean dry air (CDA)  214  (see FIGS. 4 and 5) against the undersurface of the belt pad  102 . The platen assembly  135  further comprises the fluid bearing platen manifold assembly  110  which provides an air bearing  216  (see FIGS. 4 and 5) composed of CDA to support the belt pad  102  as it moves in direction  106  over the platen assembly  135 . Additionally, a plurality of post-wet delivery holes  222  (see FIG. 7) are positioned at a trailing edge of the platen assembly  135  to provide a post-wet fluid  220  (see FIG. 5) to the undersurface of the belt pad  102 . The wafer  104  contacts the belt pad  102  at a wafer preparation location  203  (see FIG. 5) located directly above the fluid bearing platen manifold assembly  110 . 
     In a preferred embodiment, the belt wiper assembly  201  is positioned between the belt-tracking sensor  128  and the platen assembly  135 . The wiper blade  200  is configured to contact the belt pad  102  undersurface in a substantially non-perpendicular manner. The wiper blade  200  is composed of a flexible material that will adjust to the contours of the belt pad  102  undersurface as the belt pad  102  travels over the wiper blade  200  in direction  106 . Also, the wiper blade  200  edge contacting the undersurface of the belt pad  102  can be shaped in wedged manner as required for removal of particular types of slurry  122 , fluid, and particulate material. In addition to being flexible, the wiper blade  200  material is preferably non-abrading and chemically inert. In a preferred embodiment, the wiper blade  200  is made of polyurethane. However, the wiper blade  200  can be made of any other material that affords sufficient flexible, non-abrading, and chemically inert characteristics. As the belt pad  102  moves in direction  106 , the wiper blade  200  removes fluid and particulate material from the undersurface of the belt pad  102 . The fluid and particulate material moves down the wiper blade  200 , over the locking bar  204 , and into the gutter  202 . Once in the gutter  202  the fluid and particulate material move toward the ends of the gutter  202  where they are directed downward through the notch  208 . The fluid and particulate material removed from the belt pad  102  by the wiper blade  200  of the present invention can be in the form of a fluid only, a particulate material only, or a combination of fluid and particulate material (e.g., slurry  122 ). The combination of fluid and particulate material typically behaves as a fluid and is simply referred to as a fluid. 
     FIG. 5 shows a side view of the belt wiper assembly  201  incorporated into a CMP system in accordance with a preferred embodiment of the present invention. A distance D 103  is shown between the wiper blade  200  and the platen assembly  135 . In a preferred embodiment, the distance D 103  may vary within a range from about 1 inch to about 3 inches. However, the distance D 103  is not a critical characteristic affecting the belt wiper performance. Thus, values for distance D 103  falling outside the 1 inch to 3 inch range are acceptable in other embodiments. A distance D 105  is shown between the belt pad  102  and the platen assembly  135 . In a preferred embodiment, the distance D 105  generally varies within a range from about 0.001 inch to about 0.013 inch. However, the distance D 105  is not a critical characteristic affecting the belt wiper performance so long as the wiper blade  200  remains in contact with the belt pad  102  undersurface as the belt pad  102  travels in direction  106 . Thus, the distance D 105  may vary outside of the range from 0.001 inch to 0.013 inch as required by the CMP process. Also, the wiper blade  200  is shown having a thickness D 101 . In a preferred embodiment, the thickness D 101  is approximately 0.060 inch. However, the thickness D 101  of the wiper blade  200  can be arbitrarily chosen as long as the wiper blade  200  remains flexible and capable of conforming to the contours of the belt pad  102  undersurface. 
     FIG. 6 shows a front view of the belt wiper assembly  201  in relation to the belt pad  102  in accordance with one embodiment of the present invention. The wiper blade  200  can have a width W1 greater than or equal to a width W2 of the belt pad  102 . In a preferred embodiment, the wiper blade  200  width W1 is slightly greater than the belt pad  102  width W2 to accommodate changes in the belt pad  102  position as it is steered around the rotating drums  112 . 
     During the CMP process, air from the region between the platen assembly  135  and belt pad  102  is directed outward due to the forces applied at the wafer preparation location  203 . As the air flows outward, slurry  122 , fluid, and particulate material become entrained in the air flow. When either air, slurry  122 , fluid, or particulate material travel into the region  134  between the belt-tracking sensor  128  and belt pad  102  edge, the belt pad  102  steering accuracy can be adversely affected. As previously mentioned, a preferred embodiment has the belt wiper assembly  201  positioned between the belt-tracking sensor  128  and the platen assembly  135  such that the wiper blade  200  is contacting the belt pad  102  in a non-perpendicular manner as shown in FIG.  4 . The belt wiper assembly  201  configured in this manner substantially shields the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge from projected air, slurry  122 , fluid, and particulate material. Therefore, the belt wiper assembly  201  configured between the belt-tracking sensor  128  and platen assembly  135  provides an apparatus and method to prevent belt pad  102  steering inaccuracies caused by the intrusion of air, slurry  122 , fluid, or particulate material into the region  134  between the belt-tracking sensor  128  and the belt pad  102  edge. 
     FIG. 7 shows a top view of the belt wiper assembly  201  attached to the platen assembly  135  in accordance with one embodiment of the present invention. The platen assembly  135  is shown including the platen optics window  130 . As the belt pad  102  travels over the platen assembly  135  the belt window  132  passes over the platen optics window  130 . The endpoint detection system depends on the transmission of a light pulse through the platen optics window  130  and belt window  132  when they eclipse one another. If slurry  122  or other fluid and particulate material obscure either the platen optics window  130  or the belt window  132 , the light pulse intensity will be diminished such that the endpoint detection system will not function properly. Positioning the belt wiper assembly  201  to allow the undersurface of the belt pad  102  to be wiped prior to passing over the platen optics window  130  will prevent slurry  122 , fluid, and particulate material from obscuring the platen optics window  130  and belt window  132 . 
     FIG. 8 shows the belt window  132  traversing over the wiper blade  200  in the direction  106  in accordance with one embodiment of the present invention. A Frame  1 , a Frame  2 , a Frame  3 , and a Frame  4  show the belt pad  102  and belt window  132  at different positions relative to the wiper blade  200  as the belt pad  102  traverses over the wiper blade  200 . For ease of illustration, multiple instances of the wiper blade  200  are shown. However, the wiper blade  200  remains stationary as the belt pad  102  moves in the direction  106 . The belt pad  102  includes a belt window  132  that contains a window insert  224  appropriate for the CMP process. The belt pad  102  shown in FIG. 8 uses a “shaped” window insert  224 . However, many different window insert  224  configurations may be used in conjunction with the belt wiper assembly  201  of the present invention. Frame  1  shows the belt window  132  approaching the wiper blade  200 . Frame  2  shows the belt window  132  passing over the wiper blade  200 . As the belt window  132  passes over the wiper blade  200 , the wiper blade  200  flexes to follow the contour of the window insert  224 . Frame  3  shows the undersurface of the belt pad  102  approaching the wiper blade  200 . Frame  4  shows the undersurface of the belt pad  102  passing over the wiper blade  200 . As the undersurface of the belt pad  102  passes over the wiper blade  200 , the wiper blade  200  flexes to follow the contour of the undersurface of the belt pad  102 . In the aforementioned manner, the wiper blade  200  wipes slurry  122  or other fluid and particulate material from the window insert  224 . Therefore, the belt wiper assembly  201  provides an apparatus and method to prevent the platen optics window  130  and belt window  132  from becoming obscured by slurry  122  and other fluid and particulate material such that optical endpoint detection is not adversely affected. 
     In addition to the preferred embodiment, the present invention may be implemented in a number of useful alternate embodiments. FIG. 9 shows an alternate embodiment of a belt wiper assembly  231  configured to contact the belt pad  102  in a perpendicular manner. The belt wiper assembly  231  uses a bracket  234  designed to direct the wiper blade  200  in a direction perpendicular to the undersurface of the belt pad  102 . The perpendicular characteristic of the belt wiper assembly  231  can be useful for increasing the rate of movement of slurry, fluid, and particulate material away from the undersurface of the belt pad  102 . 
     FIG. 10 shows the belt wiper assembly  201  incorporated into a CMP system that uses a pre-wet fluid  236  in accordance with an alternate embodiment of the present invention. The pre-wet fluid  236  can be useful in some CMP processes wherein the undersurface of the belt pad  102  benefits from a rinsing operation prior to traversing the platen assembly  135 . 
     FIG. 11 shows a side view of a CMP system incorporating a plurality of belt wiper assemblies in accordance with an alternate embodiment of the present invention. 
     The belt wiper assembly  201  corresponds to the preferred embodiment of the present invention as previously discussed. A belt wiper assembly  201   a  corresponds to an alternate embodiment of the present invention wherein the belt wiper assembly  201   a  is configured to contact the undersurface of the belt pad  102  between a trailing edge of the platen assembly  135  and the second rotating drum  112 . The belt wiper assembly  201   a  is useful for removing slurry  122 , fluid, and particulate material from the undersurface of the belt pad  102  immediately after the belt pad  102  traverses the wafer preparation location  203 . A belt wiper assembly  201   b  and a belt wiper assembly  201   c  correspond to an alternate embodiment of the present invention wherein the belt wiper assemblies  201   b  and  201   c  are configured to contact the undersurface of the belt pad  102  while being attached to the bottom of a platen housing  238 . The belt wiper assemblies  201   b  and  201   c  may be configured to cross the belt pad  102  width W2 at an angle to enhance the removal of the slurry  122 , fluid, and particulate material. The belt wiper assemblies  201   b  and  201   c  are useful for removing slurry  122 , fluid, and particulate material that may fall from the belt wiper assemblies  201  and  201   a.    
     While this invention has been described in terms of several preferred embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. It is therefore intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the claimed invention.