Abstract:
A method for cleaning a polishing pad is disclosed. In CMP and ECMP, a polishing pad must be conditioned to obtain good and predictable polishing results. During conditioning, debris is generated that must be removed to prevent processing defects. An effective method to clean a polishing pad is disclosed herein. In one embodiment, a washing fluid is directed at the pad to clean debris from the while a second fluid is utilized to remove the washing fluid. In another embodiment, the washing fluid is provided by a high pressure water jet while the second fluid is provided by an air knife.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention relate to a method and apparatus for cleaning a pad used in chemical mechanical polishing (CMP) or electrochemical mechanical polishing (ECMP). 
     2. Description of the Related Art 
     ECMP is one method of planarizing a surface of a substrate. ECMP removes conductive materials from a substrate surface by electrochemical dissolution while polishing the substrate with a reduced mechanical abrasion compared to conventional CMP processes, which may require a high relative down force on a substrate to remove materials, such as metals and metal containing layers, from the substrate. 
     The polishing pad is one of the most critical parts for CMP or ECMP. The success or failure of the polishing process largely depends upon the pad. The pad has taken on a greater importance in recent years in ECMP wherein the pad provides two equally important functions, providing electrical contact to the substrate and providing surface abrasion. The pad to substrate contact area is what determines the pad performance in a polishing process, so it is critical to have a pad cleaning process that provides the best possible pad surface properties. 
     The surface of the pad is periodically conditioned to restore polishing performance. Conditioning is typically an abrasive process that may leave particles or other contaminants on the pad surface. To remove these contaminants, the pad is cleaned during and/or after conditioning. 
     One method for cleaning a pad includes rinsing the pad with a high pressure jet of liquid. Although high pressure rinsing may be suitable for cleaning conventional dielectric pads, the cleaning efficiency of a simple high pressure rinse is insufficient for ECMP processes due to the nature of the conductive pads utilized for ECMP processes. For example, debris located deep inside perforations in the conductive pad may be moved to the pad&#39;s surface during high pressure rinsing. Once at the pad&#39;s surface, the contaminants may stay on the surface or within scratches that are present on the surface of the pad. 
     There is a need in the art to provide an effective method and apparatus for cleaning polishing pads. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a method for cleaning a polishing pad. In one embodiment, the method for cleaning a polishing pad comprises spraying the polishing pad with a washing fluid, and directing the washing fluid off of the pad. The washing fluid may be applied to the pad with a high pressure water jet (HPWJ). The washing fluid may be directed off of the polishing pad with a downstream director. The downstream director may be at least one of a fluid stream or spray, a vacuum, wiper or other object or device suitable for directing the washing fluid from the pad. 
     In another embodiment, the method for cleaning a polishing pad comprises directing polishing fluid off of the pad to create a fluid free zone, and spraying the fluid free zone of the polishing pad with a washing fluid. The washing fluid may be applied to the pad with a HPWJ. Fluids, such as polishing fluid, may be directed off of the polishing pad with an upstream director so that the washing fluid from the HPWJ is delivered directly to the pad without energy loss due to residual polishing fluid being disposed on the pad. The upstream director may be at least one of a gas stream or spray, a vacuum, wiper or other object or device suitable for directing the polishing fluid from the pad. 
     In another embodiment, the method for cleaning a polishing pad comprises rotating the polishing pad, spraying water from a HPWJ onto the polishing pad, and directing the water away from the polishing pad with air. The HPWJ and the air source may be positioned over the polishing pad using separate arms. 
     In yet another embodiment, an apparatus for cleaning a polishing pad is disclosed. The apparatus comprises a rotatable platen, a polishing pad disposed on the platen, an air jet mounted on a first delivery arm pivotable over said polishing pad, and an HPWJ mounted on a second delivery arm positioned over said polishing pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a side view of an ECMP station having one embodiment of the pad cleaning assembly of the invention. 
         FIG. 2  is a top view of the ECMP pad station of  FIG. 1 . 
         FIG. 3  is a partial side view of a high pressure water jet assembly of the invention. 
         FIGS. 4A-B  are partial side views of various embodiments of a downstream director of the invention. 
         FIG. 5  is a plan view of another ECMP station having another embodiment of the pad cleaning assembly of the invention. 
         FIG. 6  is a partial side view of the ECMP station of  FIG. 5  taken along section lines  6 - 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a method and apparatus for cleaning a polishing pad. While the invention will be described in the context of a conductive polishing pad, it should be understood that the method for cleaning a pad could be practiced on a dielectric polishing pad, and on a web polishing material, both conductive and dielectric. While the particular apparatus in which the present invention can be practiced is not limited, it is particularly beneficial to practice the invention in a REFLEXION LK ECMP™ system or MIRRA MESA® system sold by Applied Materials, Inc., Santa Clara, Calif. Additionally, apparatus described in U.S. patent application Ser. No. 10/941,060 filed Sep. 14, 2004, U.S. Pat. No. 5,738,574, and U.S. Pat. No. 6,244,935, which are hereby incorporated by reference in their entirety, can also be used to practice the invention. 
       FIG. 1  depicts a sectional view of an ECMP station  102  having a planarizing head assembly  152  positioned over a platen assembly  230 . The planarizing head assembly  152  comprises a drive system  202  coupled to a carrier head  204  held by an arm  138 . The drive system  202  provides at least rotational motion to the carrier head  204 . The carrier head  204  additionally may be actuated toward the platen assembly  230  such that the substrate  114 , retained in the carrier head  204 , may be disposed against a contact surface of the ECMP station  102  during processing. The head assembly  152  may also oscillate during processing. 
     In one embodiment, the carrier head  204  may be a TITAN HEAD™ or TITAN PROFILER™ wafer carrier manufactured by Applied Materials, Inc. The carrier head  204  comprises a housing  214  and a retaining ring  216  that defines a center recess in which the substrate  114  is retained. The retaining ring  216  may circumscribe the substrate  114  disposed within the carrier head  204  to prevent the substrate  114  from slipping out from under the carrier head  204  during processing. The retaining ring  216  can be made of plastic materials such as PPS, PEEK, and the like, or conductive materials such as stainless steel, Cu, Au, Pd, and the like, or some combination thereof. It is further contemplated that a conductive retaining ring may be electrically biased to control the electric field during the ECMP process or an electrochemical plating process. It is also contemplated that other planarizing or carrier heads may be utilized. 
     The ECMP station  102  includes a platen assembly  230  that is rotationally disposed on a base  108 . The platen assembly  230  is supported above the base  108  by a bearing  238  so that the platen assembly  230  may be rotated relative to the base  108 . The platen assembly  230  is coupled to a motor  232  that provides the rotational motion to the platen assembly  230 . The motor  232  is coupled to a controller that provides a signal for controlling for the rotational speed and direction of the platen assembly  230 . The motor received its power from a power source  244 , and a vacuum can be drawn from a vacuum source  246 . The platen assembly  230  is fabricated from a rigid material, such as aluminum, rigid plastic, or other suitable material. 
     An area of the base  108  circumscribed by the bearing  238  is open and provides a conduit for the electrical, mechanical, pneumatic, control signals and connections communicating with the platen assembly  230 . Conventional bearings, rotary unions and slip rings, collectively referred to as rotary coupler  276 , are provided such that electrical, mechanical, fluid, pneumatic, control signals and connections may be coupled between the base  108  and the rotating platen assembly  230  through a hollow drive shaft  212 . 
     A pad assembly  222  is disposed on an upper surface of the platen assembly  230 . The pad assembly  222  may be held to the surface of the platen assembly  230  by magnetic attraction, static attraction, vacuum, adhesives, or the like. The pad assembly  222  depicted in  FIG. 1  includes a contact layer  208  defining an upper surface of the pad assembly  222 , a sub pad  215 , and an electrode  292 . The electrode  292  may be a single electrode, or may comprise multiple independently biasable electrode zones isolated from each other. Zoned electrodes are discussed in United States Patent Publication No. 2004/0082289, which is hereby incorporated by reference. 
     The upper surface of the contact layer  208  is adapted to contact a feature side  115  of the substrate  114  during processing. The contact layer  208  may be fabricated from polymeric materials compatible with the process chemistry. The polymeric materials may be dielectric or, alternatively, conductive. The contact layer  208  may be smooth or patterned to facilitate distribution of the polishing solution over the surface of the pad assembly  222 . The pad assembly  222  may further include perforations  218  which expose the electrode  292  to process (e.g., polishing) fluids disposed on the upper surface of the contact layer  208  during processing. 
     The plurality of perforations  218  may be formed uniformly distributed pattern and has a percent open area of from about 10% to about 90% (i.e., the area of the perforations  218  open to the electrode as a percentage of the total surface area of the polishing layer). The location and open area percentage of the perforations  218  in the pad assembly  222  controls the quantity and distribution of polishing fluid contacting the electrode  292  and substrate  114  during processing, thereby controlling the rate of removal of material from the feature side  115  of the substrate  114  in a polishing operation, or the rate of deposition in a plating operation. 
     In another embodiment, the pad assembly  222  may include conductive contact elements adapted to extend above the contact layer  208 . Examples of polishing pad assemblies having contact elements that may be utilized are described in United States Patent Publication No. 2002/0119286, United States Patent Publication No. 2004/0163946, and United States Patent Publication No. 2005/0000801, which are hereby incorporated by reference. 
     Polishing pad assemblies may be conditioned at three separate times. The first time that the polishing pad is conditioned is at break-in. Break-in is the procedure used to condition a new polishing pad before its first use. Polishing pads are broken-in to ensure uniform and predictable pad to pad processing results. 
     The second time that the polishing pad is conditioned is in-situ processing. In-situ conditioning occurs during processing of the substrate on the pad. In-situ maintains a substantially constant pad surface condition so that process variation is minimized between the beginning to end of a substrate polishing process. 
     The third time for polishing pad conditioning is ex-situ conditioning. Ex-situ conditioning occurs between polishing of substrates. Ex-situ conditioning may occur between each substrate processed, between batches of substrates, or on an as needed basis. 
     The method and apparatus for pad conditioning may be utilized with most conditioning processes. One conditioning process includes pressing a rotating disk against the pad assembly. The rotating disk is located at the end of an arm  420  that is supported on a support structure  415 . The arm  420  is rotated to sweep the rotating disk  413  across the pad surface. One example of a pad conditioning process can be found in U.S. patent application Ser. No. 11/209,167, filed Aug. 22, 2005, which is hereby incorporated by reference in its entirety. 
     During polishing, a polishing fluid is provided from a polishing fluid supply  248  to the polishing pad assembly  222  through a polishing fluid delivery nozzle  306 . The polishing fluid delivery nozzle  306  is located on a separate arm  304  from the arm  420  on which the conditioning pad assembly  413  is attached. The polishing fluid delivery nozzle  306  is positioned at the end of the arm  304 . The arm  304  is coupled to a support structure  315  which allows the arm  304  to selectively position the delivery nozzle  306  over desired locations above the polishing pad assembly  222 . 
     A washing fluid is provided to the polishing pad assembly  222  to remove debris that may collect on the surface of the polishing pad assembly  222  and within the perforations  218 . The washing fluid is removed from the surface of the pad assembly by a downstream director  120  to prevent debris removed from the perforations from settling out of the washing fluid on the surface of the pad assembly and rotated into contact with the substrate  114  being polished on the polishing pad assembly  222 . In one embodiment, the washing fluid is provided by a high pressure water jet (HPWJ). However it is to be understood that the washing fluid can be provided by other high pressure delivery devices and to the surface of polishing pad assembly  222 . 
     In the embodiment depicted in  FIG. 1 , the downstream director  120  provides a second fluid to the polishing pad assembly  222  at an angle and velocity that moves the washing fluid out of an area of the polishing pad assembly  222  that will be swept under the substrate  114  during polishing. One suitable downstream director  120  is an air knife  320 . While the second fluid is described as being provided from an air knife  320 , it is to be understood that any fluid, gas or liquid that can be directed against the pad assembly to sweep the washing fluid wake and debris off of the polishing pad assembly  222  may be provided by other devices. Moreover, it is contemplate that the air knife  320  may be replaced by one or more fluid streams or sprays. 
     A washing fluid supply  405  provides the washing fluid that will be used to clean the polishing pad. The washing fluid is fed from the washing fluid supply  405  through a supply line  410  to one or more nozzles  412  that spray the washing fluid to the polishing pad  222 . The nozzles  412  may be positioned on the same arm  420  as the conditioning pad assembly  413 . In one embodiment, the washing fluid supply  405  is a HPWJ water supply, and the nozzle  412  is a HPWJ. In another embodiment, the washing fluid is water or deionized water. The nozzle  412  may be selectively positioned laterally along the arm  420 . 
       FIG. 3  depicts a side view of the nozzle  412  mounted to the arm  420 . The nozzle  412  is attached to a guide  403  that runs along a rail  401  mounted to the arm  420 . The nozzle  412  may be dynamically positioned along the rail  401  using an actuator (not shown) or be locked in place using a clamp, detent or set screw  402 . 
     To remove the washing fluid and any entrained debris prior to interfacing with the substrate, the downstream director  120 , shown in this embodiment as an air knife  320 , has a second nozzle that is provided to direct the second fluid against the pad assembly between the nozzle  412  and the carrier head  204  (as referenced by the pad rotation). The second fluid source is provided from a fluid source  305  and travels within the supply line  310  to the second nozzle, shown in  FIG. 1  as an air knife  320 . The air knife  320  provides the fluid to the polishing pad assembly  222  in a sheet that is oriented substantially radially across the pad. Thus, as the washing fluid disposed on the pad assembly rotates towards the carrier head  204 , the sheet of second fluid creates a barrier that drives the washing fluid radially off the polishing pad assembly thereby substantially preventing the washing fluid from contacting the substrate. It is contemplated that the sheet may be alternatively formed by a plurality of nozzles. The air knife  320  may be coupled to the same arm  304  as the polishing fluid delivery nozzle  306 . 
     In one embodiment, the second fluid is air. It is to be understood that the second fluid may be any gas or fluid that does not adversely effect processing of the substrate. The second fluid is delivered from the air knife  320  with sufficient force to remove the washing fluid. In one embodiment, the second fluid is delivered from an air knife to impinge the pad assembly over a linear span of at least 200 mm, and in another embodiment, at least 300 mm. 
       FIGS. 4A-B  depict alternative embodiments of downstream directors that may be utilized in the ECMP stations described therein. In the embodiment depicted in  FIG. 4A , a downstream director  600  includes a body  602  having one or more suction ports  604  one a side of the body  602  facing the polishing pad assembly  222 . The suction port  604  is coupled to an exit port  606  formed in the body  602 . The exit port  606  is coupled to a vacuum source  610 . The vacuum source  610  pulls a vacuum though the suction port  604  that, when the body  602  is placed in close proximity to the polishing pad assembly  222 , the washing fluid is removed from the surface of the pad assembly  222  through the director  600 . The downstream director  600  may be coupled to the polishing fluid delivery arm  304  (not shown in  FIG. 4B ), or supported by another suitable member. 
     In the embodiment depicted in  FIG. 4B , a downstream director  700  includes a body  702  having lip  704  extending from a side of the body  702  facing the polishing pad assembly  222 . The lip  704  may be made from a material that does not damage the surface of the pad assembly  222  if placed in contact therewith. In one embodiment, the lip  704  is a polymer, such as an elastomer or plastic. The lip material is selected to be compatible with the fluids disposed on the pad assembly  222 . When the body  702  is placed in close proximity to, or in contact with, the polishing pad assembly  222 , the lip  704  of the director  700  wipes the washing fluid from the surface of the pad assembly  222 . The downstream director  700  may be coupled to the polishing fluid delivery arm  304  (not shown in  FIG. 4B ), or supported by another suitable member. 
       FIG. 2  is a simplified top view of an ECMP station. The nozzle  412  is mounted on the arm  420  so that the nozzle  412  may be rotated relative to the pad  222 . Further, the height of the nozzle  412  relative to the upper surface of the pad  222  may also be adjustable. The arm  420  is shown with its center line  375  at an angle relative to a radial centerline  370  of the pad  222  for convenience. It is to be understood that the arm  420  can pivot about its axis P so that the nozzle  412  can reach any point between the center C of the polishing pad  222  and the periphery. Arrow  380  denotes the direction of rotation of the pad  222 . 
     The air knife  320  is mounted on the arm  304  so that the air knife  320  may be rotated relative to the pad  222 . Further, the height of the air knife  320  relative to the upper surface of the pad  222  may also be adjustable. The arm  304  is shown with its center line  475  at an angle relative to a radial centerline  370  of the pad  222  for convenience. It is to be understood that the arm  304  can pivot about its axis Q so that the air knife  320  oriented across the polishing pad  222 . Arrows  381  and  382  denote the path of the second fluid as it is directed off the polishing pad  222  by the air knife  320 . 
     In operation, the washing fluid is sprayed onto the polishing pad at high pressure during and/or after conditioning. The washing fluid wake, along with any debris loosened from the polishing pad surface, is directed away from the polishing pad by the second fluid delivered to the pad surface by the air knife. In one embodiment, the washing fluid is directed to the polishing pad at about 1500 psi to about 2000 psi. In one embodiment, the washing fluid is directed to the polishing pad at about 1650 to about 1900 psi. In yet another embodiment, the washing fluid is directed to the polishing pad at about 1800 to about 1850 psi. During the cleaning, the washing fluid is swept across the surface of the polishing pad by pivoting the arm  420  about its axis P. Optionally, the nozzle  412  may be moved along the arm. 
     The polishing pad is rotated during the cleaning so that all areas of the polishing pad will be sprayed with the washing fluid. The polishing pad may be rotated at about 10 to about 100 rpm during the cleaning process. In another embodiment, the polishing pad to rotate at about 30 to about 60 RPM during the cleaning process. In another embodiment, the polishing pad rotated at about 40 to about 50 RPM during the cleaning process. 
     The washing fluid will clean debris from substantially all surfaces of the polishing pad, including the perforations. The spray of washing fluid may be directed towards the edge of the polishing pad so that any debris collected within the wake of the washing fluid will be swept away. The second fluid provided by the air knife will sweep away the washing fluid wake, as well as any debris collected by the washing fluid wake. The arm  304  may be pivoted about its axis if desired. 
     The second fluid and the washing fluid can be provided to the polishing pad simultaneously. It is also contemplated by the present invention for the second fluid to be provided before the washing fluid so that loose debris can be removed from the polishing pad surface. Additionally, it is contemplated that the washing fluid can be provided to the polishing pad before the second fluid. 
     Rotating the polishing pad during the cleaning is beneficial to the cleaning process. If the polishing pad is not rotated, then the washing fluid will be provided at a high pressure to only the area that the arm  420  holding the nozzles  412  can cover when rotated about its axis. The other areas of the polishing pad would only receive the washing fluid wake. 
       FIG. 5  is a plan view of another ECMP station  800  having another embodiment of the pad cleaning assembly of the invention. The ECMP station  800  generally includes a rotating disk  413  for conditioning a pad assembly  222 , a polishing fluid delivery nozzle  306  and optionally, a downstream director  120 . The ECMP station  800  also includes an upstream director  802  for directing polishing fluid  806  (after passing by or polishing the substrate  114 ) off of the pad assembly  222 , as shown by arrows  820  to create a fluid free zone  804 . The fluid free zone  804  is generally defined between the upstream director  802  and the HPWJ nozzle  412 . The fluid free zone  804  has substantially no polishing fluid  806  disposed therein as compared to an area of the pad assembly  222  immediately upstream (via pad rotation) of the upstream director  802 , as illustrated in the partial side view of the ECMP station  800  depicted in  FIG. 6 . Washing fluid  808  is sprayed the fluid free zone  804  of the polishing pad assembly  222 . As substantially all of the polishing fluid has been removed from the surface of the pad assembly by the upstream director  802 , the washing fluid may more energetically impinge upon the pad surface, thereby more effectively removing debris from the apertures of the pad assembly  222 . The upstream director  802  may be at least one of a gas stream or spray, a vacuum, wiper or other object or device suitable for directing the polishing fluid from the pad, and may be constructed similar to as described with reference to the downstream director  120 . 
     In embodiment wherein the downstream director  120  is present, the washing fluid  808  is moved off the pad assembly  222 , as shown by arrows  381 ,  382 , prior to dispensing the polishing fluid  806  on the pad assembly  222 . Thus, the downstream director  120  substantially prevents intermixing of the washing and polishing fluids  806 ,  808  directly in front of the substrate  114 . 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.