Abstract:
A particle cleaning module includes a housing, a substrate holder, a pad holder, an actuator and a pad conditioner. The substrate holder is disposed in the housing, is configured to retain a substrate in a substantially vertical orientation, and is rotatable on a first axis. The pad holder is disposed in the housing, has a pad retaining surface facing the substrate holder in a parallel and spaced apart relation, and is rotatable on a second axis parallel to the first axis. The actuator is operable to move the pad holder relative to the substrate holder to change a distance defined between the pad retaining surface and the substrate. The pad conditioner is disposed in the housing and has a conditioning surface oriented parallel to the pad retaining surface.

Description:
TECHNICAL FIELD 
       [0001]    A method and apparatus for cleaning and/or polishing a substrate after chemical mechanical planarizing (CMP). 
       BACKGROUND 
       [0002]    In the process of fabricating modern semiconductor integrated circuits (ICs), it is often necessary to planarize surfaces prior to depositing subsequent, e.g., to achieve tolerances for photolithography or to remove an overlying layer. One method for planarizing a layer during IC fabrication is chemical mechanical planarizing (CMP). In general, CMP involves the relative movement of the substrate held in a polishing head against a polishing material to remove surface irregularities from the substrate. In a CMP process, the polishing material is wetted with a polishing fluid that may contain at least one of an abrasive or chemical polishing composition. This process may be electrically assisted to electrochemically planarize conductive material on the substrate. 
         [0003]    Planarizing hard materials such as oxides typically requires that the polishing fluid or the polishing material itself include abrasives. As the abrasives often cling or are become partially embedded in the layer of material being polished, the substrate is processed on a buffing module to remove the abrasives from the polished layer. The buffing module removes the abrasives and polishing fluid used during the CMP process by moving the substrate which is still retained in the polishing head against a buffing material in the presence of deionized water or chemical solutions. The buffing module is substantially identical to the CMP module except for the polishing fluids utilized and the material on which the substrate is processed. 
         [0004]    Once buffed, the substrate is transferred to a series of cleaning modules that further remove any remaining abrasive particles and/or other contaminants that cling to the substrate after the planarizing and buffing process before they can harden on the substrate and create defects. The cleaning modules may include, for example, a megasonic cleaner, a scrubber or scrubbers, and a dryer. The cleaning modules that support the substrates in a vertical orientation are especially advantageous, as they also utilize gravity to enhance removal of particles during the cleaning process, and are also typically more compact. 
         [0005]    One type of cleaning module includes cylindrical rollers that are brought into contact with a surface of a substrate to remove the abrasive particles and/or other contaminants. For example, a cylindrical roller having a brush body disposed thereon can be caused to rotate and urged against a rotating substrate to clean the substrate after a CMP process. Alternatively, the cleaning module can function as a buffing module. For example, a cylindrical roller having a soft pad material disposed thereon can be caused to rotate and urged against a rotating substrate to buff the substrate. 
       SUMMARY 
       [0006]    As noted above, polishing processes tend to leave abrasives and/or contaminants (collectively debris) on the surface of the substrate. The cleaning or buffing process tends to transfer this debris onto the brush body or pad material being used for cleaning or buffing. To avoid accumulation of the debris, or to maintain the brush body or pad material in a consistent state of roughness from substrate-to-substrate, the brush body or pad material can be conditioned, e.g., abraded with a harder body. However, the conditioning process tends to wear away the brush body or pad material. 
         [0007]    A proposed cleaning or buffing module holds the substrate in a vertical orientation while a disk-shaped brush or pad is brought into contact with the substrate. In the case of a cleaning or buffing module that uses a roller, a conditioning bar can located on the side of the roller opposite the space where the substrate will be located. However, such a configuration is inappropriate for a disk-shaped brush or pad because of the conditioner needs to be located to contact the face of the disk that contacts the substrate. To address this issue, the conditioner can be located in the substrate holder or to the side of the substrate holder in a position reachable by the disk-shaped brush or pad. 
         [0008]    Because the substrate is held in a vertical orientation, gravity does not cause the substrate to rest on the brush or pad. Rather, contact between the substrate and the brush or pad is controlled by an actuator that controls the horizontal position of a support for the brush or pad. As the brush or pad wears, the compression of the brush or pad against the substrate can vary from substrate-to-substrate, resulting in variations in effectiveness of cleaning or buffing from substrate-to-substrate. To address this issue, a load cell can be installed in the module. The brush or pad can be brought into contact with the load cell and the applied pressure measured as a function of position of the support. This permits a controller to adjust the horizontal position of the support to achieve consistent compression from substrate-to-substrate. 
         [0009]    In one aspect a particle cleaning module includes a housing, a substrate holder disposed in the housing, a pad holder disposed in the housing, an actuator and a pad conditioner disposed in the housing. The substrate holder is configured to retain a substrate in a substantially vertical orientation and is rotatable on a first axis. The pad holder has a pad retaining surface facing the substrate holder in a parallel and spaced apart relation, and the pad holder is rotatable on a second axis parallel to the first axis. The actuator is operable to move the pad holder relative to the substrate holder to change a distance defined between the pad retaining surface and the substrate. The pad conditioner has a conditioning surface oriented parallel to the pad retaining surface. 
         [0010]    Implementations may include one or more of the following features. The substrate holder may be configured to hold the substrate in a plane, and the conditioning surface may be positioned on a side of the plane further from the pad holder. The pad conditioner may be mounted on and rotate with the substrate holder. The first axis of rotation may pass approximately through a center of the pad conditioner. The conditioning surface may be recessed relative to a substrate mounting surface of the substrate holder. The actuator may be operable to move the pad support along a direction parallel to the second axis. The actuator may be operable to move the pad support laterally along a direction perpendicular to the second axis to a position laterally separated from the substrate holder, and the pad conditioner may be located at the position laterally separated from the substrate holder. The pad may formed of polyurethane and the pad conditioner may include abrasive diamond particles. The pad may be formed of polyvinyl alcohol and the pad conditioner may be glass. There may be passages through the pad conditioner, and a cleaning liquid supply may inject the cleaning liquid through the passages. 
         [0011]    In another aspect, a particle cleaning module includes a housing, a substrate holder disposed in the housing, a pad holder disposed in the housing, an actuator, a pad conditioner disposed in the housing, and a pressure sensor. The substrate holder is configured to retain a substrate in a substantially vertical orientation in a first plane. The pad holder has a pad retaining surface and is configured to retain a pad in a substantially vertical orientation in a second plane parallel to the first plane. The actuator is operable to move the pad holder relative to the substrate holder along a direction normal to the first plane to change a distance between the first plane and the second plane. The actuator is configured to generate or receive a first signal representing a horizontal position of the substrate holder along the direction. The pad conditioner has a conditioning surface oriented parallel to the pad retaining surface. The pressure sensor having a contact surface and is configured to generate a second signal representing a load on the contact surface. 
         [0012]    Implementations may include one or more of the following features. A controller may be configured to receive the first signal and the second signal. The controller may be configured to cause the actuator to adjust a horizontal position of the substrate holder based on the first signal and the second signal. The controller may be configured to measure a position Z 1  of the substrate holder for a pressure P 1  prior to processing of a first substrate, and may be configured to determine a position Z 3  of the substrate holder to achieve the pressure P 1  after processing of the first substrate. The controller may be configured to position the substrate holder at a position Z 2  during processing of the first substrate, and may be configured to position the substrate holder at a position Z 4 =Z 2 +ΔZ for polishing of a subsequent second substrate, where ΔZ=Z 3 −Z 1 . The contact surface may include the conditioning surface. The pad conditioner may be mounted on the substrate holder. The pressure sensor may include a load cell positioned between the pad conditioner and a motor to rotate a drive shaft secured to the substrate holder. The contact surface may include the pad retaining surface. The substrate holder may be rotatable about a first axis and the pad holder may be rotatable about a second axis parallel to the first axis. 
         [0013]    Implementations may include one or more of the following advantages. A conditioner may be provided to condition a disk-shaped brush or pad in a module that holds a substrate in a vertical orientation. By incorporating the conditioner into the substrate hold, a conditioner may be provided without requiring additional space. The brush or pad may be brought into contact with the load cell, and the applied pressure may be measured. A controller may adjust the horizontal position of the support to achieve consistent compression from substrate-to-substrate, which may improve cleaning or buffing uniformity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    So that the manner in which the above recited embodiments of the invention are obtained and can be understood in detail, a more particular description, briefly summarized above, may be had by reference to the embodiments thereof, which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only a typical embodiment, and there may be other equally effective embodiments. 
           [0015]      FIG. 1  illustrates a top view of a semiconductor substrate chemical mechanical planarization system having a cleaning system which includes one embodiment of a particle cleaning module; 
           [0016]      FIG. 2  is a front view of cleaning system depicted in  FIG. 1 ; 
           [0017]      FIG. 3  is a cross-sectional view of the particle cleaning module depicted in  FIG. 1 ; 
           [0018]      FIG. 4  is a cross-sectional view of the particle cleaning module taken along the section line  4 - 4  of  FIG. 3 ; 
           [0019]      FIG. 5  is a cross-sectional view of the particle cleaning module taken along the section line  5 - 5  of  FIG. 3 ; 
           [0020]      FIG. 6  is a side view of a pad holder engaging a pad with a substrate retained by the substrate holder within the particle cleaning module of  FIG. 1 ; 
           [0021]      FIG. 7  is a cross-sectional view of the particle cleaning module depicted in  FIG. 3  in which the pad is moved into contact with a conditioner; 
           [0022]      FIG. 8  is a side view of a pad holder engaging a pad with a conditioner in the substrate holder within the particle cleaning module of  FIG. 1 . 
           [0023]      FIGS. 9A and 9B  are front views of a pad conditioner from the particle cleaning module of  FIG. 1 ; and 
           [0024]      FIGS. 10A and 10B  are cross-sectional views of other implementations of a particle cleaning module that includes a pressure sensor. 
       
    
    
       [0025]    To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the Figures. Additionally, elements of one embodiment may be advantageously adapted for utilization in other embodiments described herein. 
       DETAILED DESCRIPTION 
       [0026]      FIG. 1  illustrates a top view of a semiconductor substrate chemical mechanical planarization (CMP) system  100  having a cleaning system  116  that includes a particle cleaning module  182 . Although the exemplary configurations are provided for the CMP system  100  and cleaning system  116  in  FIG. 1 , it is contemplated that embodiments of the particle cleaning module  182  may be utilized alone, or with cleaning systems having alternative configurations and/or CMP systems having alternative configurations. 
         [0027]    In addition to the cleaning system  116 , the exemplary CMP system  100  generally includes a factory interface  102 , a loading robot  104 , and a planarizing module  106 . The loading robot  104  is disposed proximate the factory interface  102  and the planarizing module  106  to facilitate the transfer of substrates  122  therebetween. 
         [0028]    A controller  108  is provided to facilitate control and integration of the modules of the CMP system  100 . The controller  108  comprises a central processing unit (CPU)  110 , a memory  112  and support circuits  114 . The controller  108  is coupled to the various components of the CMP system  100  to facilitate control of, for example, the planarizing cleaning and transfer processes. 
         [0029]    The factory interface  102  generally includes an interface robot  120  and one or more substrate cassettes  118 . The interface robot  120  is employed to transfer substrates  122  between the substrate cassettes  118 , the cleaning system  116  and an input module  124 . The input module  124  is positioned to facilitate transfer of substrates  122  between the planarizing module  106  and the factory interface  102  as will be further described below. 
         [0030]    Optionally, polished substrates exiting the cleaning system  116  may be tested in a metrology system  180  disposed in the factory interface  102 . The metrology system  180  may include an optical measuring device, such as the NovaScan 420, available from Nova Measuring Instruments, Inc. located in Sunnyvale, Calif. The metrology system  180  may include a buffer station (not shown) for facilitating entry and egress of substrates from the optical measuring device or other metrology device. One such suitable buffer is described in U.S. Pat. No. 6,244,931, issued Jun. 12, 2001 to Pinson, et al., which is hereby incorporated by reference in its entirety. 
         [0031]    The planarizing module  106  includes at least one CMP station. In the embodiment depicted in  FIG. 1 , the planarizing module  106  includes a plurality of CMP stations, illustrated as a first station  128 , a second station  130  and a third station  132  disposed in an environmentally controlled enclosure  188 . The polishing stations are configured to perform an oxide or metal planarization process, e.g., utilizing an abrasive containing polishing fluid. It is contemplated that CMP processes to planarized other materials may be alternatively performed, including the use of other types of polishing fluids. As the CMP process is conventional in nature, further description thereof has been omitted for the sake of brevity. 
         [0032]    The exemplary planarizing module  106  also includes a transfer station  136  and a carousel  134  that are disposed on an upper or first side  138  of a machine base  140 . In one embodiment, the transfer station  136  includes an input buffer station  142 , an output buffer station  144 , a transfer robot  146  and a load cup assembly  148 . The loading robot  104  is configured to retrieve substrates from the input module  124  and transfer the substrates to the input buffer station  142 . The loading robot  104  is also utilized to return polished substrates from the output buffer station  144  to the input module  124 , from where the polished substrates are then advanced through the cleaning system  116  prior to being returned to the cassettes  118  coupled to the factory interface  102  by the interface robot  120 . The transfer robot  146  is utilized to move substrates between the buffer stations  142 ,  144  and the load cup assembly  148 . 
         [0033]    In one embodiment, the transfer robot  146  includes two gripper assemblies, each having pneumatic gripper fingers that hold the substrate by the substrate&#39;s edge. The transfer robot  146  may simultaneously transfer a substrate to be processed from the input buffer station  142  to the load cup assembly  148  while transferring a processed substrate from the load cup assembly  148  to the output buffer station  144 . An example of a transfer station that may be used to advantage is described in U.S. Pat. No. 6,156,124, issued Dec. 5, 2000 to Tobin, which is herein incorporated by reference in its entirety. 
         [0034]    The carousel  134  is centrally disposed on the base  140 . The carousel  134  typically includes a plurality of arms  150 , each supporting a polishing head  152 . Two of the arms  150  depicted in  FIG. 1  are shown in phantom such that a planarizing surface of a polishing pad  126  of the first station  128  and the transfer station  136  may be seen. The carousel  134  is indexable such that the polishing head assemblies  152  may be moved between the planarizing stations  128 ,  130 ,  132  and the transfer station  136 . One carousel that may be utilized to advantage is described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov, et al., which is hereby incorporated by reference in its entirety. 
         [0035]    The cleaning system  116  removes polishing debris, abrasives and/or polishing fluid from the polished substrates that remains after polishing. The cleaning system  116  includes a plurality of cleaning modules  160 , a substrate handler  166 , a dryer  162  and an output module  156 . The substrate handler  166  retrieves a processed substrate  122  returning from the planarizing module  106  from the input module  124  and transfers the substrate  122  through the plurality of cleaning modules  160  and dryer  162 . The dryer  162  dries substrates exiting the cleaning system  116  and facilitates substrate transfer between the cleaning system  116  and the factory interface  102  by the interface robot  120 . The dryer  162  may be a spin-rinse-dryer or other suitable dryer. One example of a suitable dryer  162  may be found as part of the MESA™ or Desica® Substrate Cleaners, both available from Applied Materials, Inc., of Santa Clara, Calif. 
         [0036]    In the embodiment depicted in  FIG. 1 , the cleaning modules  160  utilized in the cleaning system  116  include a megasonic clearing module  164 A, the particle cleaning module  182 , a first brush module  164 B and a second brush module  164 C. The first brush module  164 B and the second brush module  164 C can use cylindrical roller brushes. However, it is to be appreciated that the particle cleaning module  182  of the present invention may be used with cleaning systems incorporating one or more modules having one or more types of modules. For example, the megasonic cleaning module  164 A could be omitted, so that the particle cleaning module  182  is the first module and the substrate is carried in sequence from the particle cleaning module  182 , to the first brush module  164 B and then to the second brush module  164 C. Although the particle cleaning module  182  need not be the first module in the sequence, inclusion of the conditioner device in the first brush module in the sequence is advantageous in order to reduce contamination of the brushes in subsequent brush modules in the sequence. 
         [0037]    Each of the modules  160  is configured to process a vertically oriented substrate, i.e., one in which the polished surface is in a substantially vertical plane. The vertical plane is represented by the Y-axis, which is perpendicular to the X-axis and Z-axis shown in  FIG. 1 . The particle cleaning module  182  will be discussed in detail further below with reference to  FIG. 3 . 
         [0038]    In operation, the CMP system  100  is initiated with the substrate  122  being transferred from one of the cassettes  118  to the input module  124  by the interface robot  120 . The loading robot  104  then moves the substrate from the input module  124  to the transfer station  136  of the planarizing module  106 . The substrate  122  is loaded into the polishing head  152  moved over and polished against the polishing pad  126  while in a horizontal orientation. Once the substrate is polished, polishing substrates  122  are returned to the transfer station  136  from where the robot  104  may transfer the substrate  122  from the planarizing module  106  to the input module  124  while rotating the substrate to a vertical orientation. The substrate handler  166  then retrieves the substrate from the input module  124  transfers the substrate through the cleaning modules  160  of the cleaning system  116 . Each of the modules  160  is adapted to support a substrate in a vertical orientation throughout the cleaning process. Once cleaned, the cleaned substrate  122  is transferred to the output module  156 . The cleaned substrate  122  is returned to one of the cassettes  118  by the interface robot  120  while returning the cleaned substrate  122  to a horizontal orientation. Optionally, the interface robot  120  may transfer the cleaned substrate to the metrology system  180  prior to the substrate&#39;s return to the cassette  118 . 
         [0039]    Although any suitable substrate handler may be utilized, the substrate handler  166  depicted in  FIG. 1  includes a robot  168  having at least one gripper (two grippers  174 ,  176  are shown) that is configured to transfer substrates between the input module  124 , the cleaning modules  160  and the dryer  162 . Optionally, the substrate handler  166  may include a second robot  170  configured to transfer the substrate between the last cleaning module  160  and the dryer  162  to reduce cross contamination. 
         [0040]    In the embodiment depicted in  FIG. 1 , the substrate handler  166  includes a rail  172  coupled to a partition  158  separating the cassettes  118  and interface robot  120  from the cleaning system  116 . The robot  168  is configured to move laterally along the rail  172  to facilitate access to the cleaning modules  160 , dryer  162  and the input and output modules  124 ,  156 . 
         [0041]      FIG. 2  depicts a front view of the substrate handler  166  according to one embodiment of the invention. The robot  168  of the substrate handler  166  includes a carriage  202 , a mounting plate  204  and the substrate grippers  174 ,  176 . The carriage  202  is slideably mounted on the rail  172  and is driven horizontally by an actuator  206  along a first axis of motion A 1  defined by the rail  172  which is parallel to the Z-axis. The actuator  206  includes a motor  208  coupled to a belt  210 . The carriage  202  is attached to the belt  210 . As the motor  208  advances the belt  210  around the sheave  212  positioned at one end of the cleaning system  116 , the carriage  202  moves along the rail  172  to selectively position the robot  168 . The motor  208  may include an encoder (not shown) to assist in accurately positioning the robot  168  over the input and output modules  124 ,  156  and the various cleaning modules  160 . Alternatively, the actuator  206  may be any form of a rotary or linear actuator capable of controlling the position of the carriage  202  along the rail  172 . In one embodiment, the carriage  202  is driven by a linear actuator having a belt drive, such as the GL15B linear actuator commercially available from THK Co., Ltd. located in Tokyo, Japan. 
         [0042]    The mounting plate  204  is coupled to the carriage first  202 . The mounting plate  204  includes at least two parallel tracks  216 A-B along which the positions of the grippers  174 ,  176  are independently actuated along a second and third axes of motion A 2 , A 3 . The second and third axes of motion A 2 , A 3  are oriented perpendicular to the first axis A 1  and are parallel to the Y-axis. 
         [0043]      FIG. 3  depicts a cross-sectional view of the particle cleaning module  182  of  FIG. 1 . The particle cleaning module  182  includes a housing  302 , a substrate rotation assembly  304 , a pad actuation assembly  306  that includes a pad  344 , and a pad conditioner  410 . The pad  344  may be fabricated from a polymer material. If the particle cleaning module is functioning primarily as a buffing module, then the pad  344  can be a soft polishing pad typically used for buffing. Such as soft polishing pad can be polyurethane and the like, for example, a POLYTEX™ pad available from Rodel, Inc. of Newark, Del. If the particle cleaning module is functioning primarily as a cleaning module rather than a buffing module, then the pad  344  can be a brush pad. Such a brush pad can be rubber, e.g., polyvinyl alcohol (PVA). 
         [0044]    The housing  302  includes an opening  308  at a top of the housing and a substrate receiver  310  at a bottom  318  of the housing. A drain  368  is formed through the bottom  318  of the housing  302  to allow fluids to be removed from the housing  302 . The opening  308  allows the robot  168  (not shown in  FIG. 3 ) to vertically transfer the substrate to an internal volume  312  defined within the housing  302 . The housing  302  may optionally include a lid  330  that can open and close to allow the robot  168  in and out of the housing  302 . 
         [0045]    The substrate receiver  310  has a substrate receiving slot  332  facing upwards parallel to the Y-axis. The receiving slot  332  is sized to accept the perimeter of the substrate  122 , thereby allowing the one of the grippers  174 ,  176  of the substrate handler  166  to place the substrate  122  in the receiving slot  322  in a substantially vertical orientation. The substrate receiver  310  is coupled to an Z-Y actuator  311 . The Z-Y actuator  311  may be actuated to move the substrate receiver  310  upwards in the Y-axis to align a centerline of the substrate  122  disposed in the substrate receiver  310  with a centerline of the substrate rotation assembly  304 . Once the centerline of the substrate  122  is aligned with the centerline of the substrate rotation assembly  304 , the Z-Y actuator  311  may be actuated to move the substrate receiver  310  in the Z-axis to contact the substrate  122  against the substrate rotation assembly  304 , which then actuates to chuck the substrate  122  to the substrate rotation assembly  304 . After the substrate  122  has been chucked to the substrate rotation assembly  304 , the Z-Y actuator  311  may be actuated to move the substrate receiver  310  in the Y-axis clear of the substrate  122  and the substrate rotation assembly  304  so that the substrate  122  held by the substrate rotation assembly  304  may be rotated without contacting the substrate receiver  310 . 
         [0046]    The substrate rotation assembly  304  is disposed in the housing  302  and includes a substrate holder  314  coupled to a substrate rotation mechanism  316 . The substrate holder  314  may be an electrostatic chuck, a vacuum chuck, a mechanical gripper or any other suitable mechanism for securely holding the substrate  122  while the substrate is rotated during processing within the particle cleaning module  182 . The substrate holder  314  can include a pad conditioner  410 , which will be described further below. 
         [0047]      FIG. 4  is a cross-sectional view of the particle cleaning module  182  taken along the section line  4 - 4  of  FIG. 3  thus illustrating a face  404  of the substrate holder  314 . Referring to both  FIG. 3  and  FIG. 4 , the face  404  of the substrate holder  314  includes one or more apertures  402  fluidly coupled to a vacuum source  380 . The vacuum source  380  is operable to apply a vacuum between the substrate  122  and the substrate holder  314 , thereby securing the substrate  122  and the substrate holder  314 . Once the substrate  122  is held by the substrate holder  314 , the substrate receiver  310  moves downward in a vertical direction parallel to the Y-axis towards the bottom  318  of the housing  318  to be clear of the substrate, as seen in  FIG. 4 . The substrate receiver  310  may move in a horizontal direction towards an edge of the housing  302  to be further clear of the substrate. 
         [0048]    The substrate holder  314  is coupled to the substrate rotation mechanism  316  by a first shaft  323  that extends through a hole  324  formed through the housing  302 . The hole  324  may optionally include sealing members  326  to provide a seal between the first shaft  323  and the housing  302 . The substrate holder  314  is controllably rotated by the substrate rotation mechanism  316 . The substrate rotation mechanism  316  may be an electrical motor, an air motor, or any other motor suitable for rotating the substrate holder  314  and substrate  122  chucked thereto. The substrate rotation mechanism  316  is coupled to the controller  108 . In operation, the substrate rotation mechanism  316  rotates the first shaft  323 , which rotates the substrate holder  314  and the substrate  122  secured thereto. In one embodiment the substrate rotation mechanism  316  rotates the substrate holder  314  (and substrate  122 ) at a rate of at least 500 revolutions per minute (rpm). 
         [0049]    The pad actuation assembly  306  includes a pad rotation mechanism  336 , a pad cleaning head  338 , and a lateral actuator mechanism  342 . The pad cleaning head  338  is located in the internal volume  312  of the housing  302  and includes a pad holder  334  that holds a pad  344  and a fluid delivery nozzle  350 . The fluid delivery nozzle  350  is coupled to a fluid delivery source  382  that provides deionized water, a chemical solution or any other suitable fluid to the pad  344  during cleaning the substrate  122 . The lid  330  may be moved to a position that closes the opening  308  of the housing  302  above the fluid delivery nozzle  350  to prevent fluids from being spun out of the housing  302  during processing. 
         [0050]    A centerline of the pad holder  334  may be aligned with the centerline of the substrate holder  314 . The pad holder  334  (and pad  344 ) has a diameter much less than that of the substrate  122 , for example at least less than half the diameter of the substrate or even as much as less than about one eighth the diameter of the substrate. In one embodiment, the pad holder  334  (and pad  344 ) may has a diameter of less than about 25 mm. The pad holder  334  may holds the pad  344  utilizing clamps, vacuum, adhesive or other suitable technique that allows for the pad  344  to periodically be replaced as the pad  344  becomes worn after cleaning a number of substrates  122 . 
         [0051]    The pad holder  334  is coupled to the pad rotation mechanism  336  by a second shaft  346 . The second shaft  346  is oriented parallel to the Z-axis and extends from the internal volume  312  through an elongated slit formed through the housing  302  to the pad rotation mechanism  336 . The pad rotation mechanism  336  may be an electrical motor, an air motor, or any other suitable motor for rotating the pad holder  334  and pad  344  against the substrate. The pad rotation mechanism  336  is coupled to the controller  108 . In one embodiment, the pad rotation mechanism  336  rotates the pad holder  334  (and pad  344 ) at a rate of at least about 1000 rpm. 
         [0052]    The pad rotation mechanism  336  is coupled to bracket  354  by an axial actuator  340  carriage. The axial actuator  340  is coupled to the controller  108  or other suitable controller, and is operable to move the pad holder  334  along the Z-axis to move the pad  344  against and clear of the substrate  122  held by the substrate holder  314 . The axial actuator  340  may be a pancake cylinder, linear actuator or any other suitable mechanism for moving the pad holder  334  in a direction parallel to the Z-axis. In operation, after the substrate holder  314  is in contact with and holding the substrate, the axial actuator  340  drives the pad holder  334  in a z-direction to make contact with the substrate. 
         [0053]    The bracket  354  is coupled to a base  370  by the lateral actuator mechanism  342  by a carriage  352  and rail  358  that allows the pad cleaning head  338  to move laterally in a direction parallel to the X-axis, as depicted in  FIG. 5 . The carriage  352  is slideably mounted on the rail  358  and is driven horizontally by the lateral actuator mechanism  342  to scan the pad  344  across the substrate  122 . The lateral actuator mechanism  342  may be a lead screw, a linear actuator or any other suitable mechanism for moving the cleaning head  338  horizontally. The lateral actuator mechanism  342  is coupled to controller  108  or other suitable controller. 
         [0054]    Scanning the polymer pad  344  across the substrate  122  in the particle cleaning module  182  has effectively demonstrated the ability to effectively remove particles, such as abrasives from the polishing fluid, from the surface of the substrate  122 . Accordingly, the need for a dedicated buffing station on the polishing module is substantially eliminated. 
         [0055]      FIG. 6  is a side view of the pad holder  334  engaging the pad  344  with the substrate  122  retained by the substrate holder  314 . In operation, the axial actuator  340  urges the pad  344  against the substrate  122  rotated by the substrate rotation mechanism  316  while the pad rotation mechanism  336  spins the pad  344 . The lateral actuator mechanism  342  moves the pad holder  334  and pad  344  in a horizontal direction across the surface of the substrate  122 . While the pad  344  is in contact with the substrate  122 , the fluid delivery nozzle  350  provides at least one of deionized water, a chemical solution or any other suitable fluid to the surface of the substrate  122  being processed by the pad  344 . Accordingly, the pad  344  cleans the entire surface of the substrate with minimal movement. One advantage of the invention is the relatively small size of the pad  344  compared to the size of the substrate  122 . Conventional systems use large pads positioned on the polishing module to clean smaller substrates, where the substrate is in 100 percent contact with the pad. Large pads are prone to trapping abrasives and particulates which often cause scratches and defects in the substrate. However, the smaller pad of the present invention is significantly less prone to abrasive and particulate trapping, which advantageously results in a cleaner pad and substrates with less scratches and defects. Additionally, the smaller pad of the present invention significantly reduces the cost of consumables, both in the amount of fluid utilized during processing and the cost of replacement pads. Furthermore, the smaller pad of the present invention significantly allows the pad to be easily removed or replaced. 
         [0056]    Referring back to  FIG. 5 , once the substrate is cleaned the pad actuation assembly  306  retracts the pad holder  334  and pad  344  away from the substrate  122  (shown in phantom) and moves the pad holder  334  and pad  344  linearly in a direction parallel to the X-axis away from the substrate and out of the internal volume  312  of the housing  302  into a pocket  504  coupled to the housing  302 . Positioning the pad holder  334  and pad  344  in the pocket  504  as shown in phantom in  FIG. 5  and out of the internal volume  312  of the housing  302  advantageously provides more space for the robot  168  to enter the housing  302  and transfer the substrate without risk of damaging either the pad  344  or the substrate  122 , while allowing the housing  302  to be smaller and less expensive. 
         [0057]    Substrate transfer begins after cleaning and moving the pad holder  334  and pad  344  in the pocket  504  by having the substrate receiver  310  move upward in a direction parallel to the Y-axis to engage the substrate  122  in the receiving slot  332 . Once the substrate is disposed in the substrate receiving slot  332 , the substrate holder  314  releases the substrate  122  by turning off the vacuum provided by the vacuum source  380 , and optionally providing a gas through the apertures  402  of the substrate holder  314  to separate the substrate from the substrate holder  314 . The substrate receiver  310  with the substrate  122  disposed in the receiving slot  332  is then moved laterally away from the substrate holder  314  in a direction parallel to the Z-axis to clear the substrate  122  from the substrate holder  314 . One of the grippers  174 ,  176  of the robot  168  retrieves the substrate  122  from the substrate receiver  310  and removes the substrate  122  from the housing  302 . An optional top spray bar  364  and bottom spray bar  366  are positioned across the internal volume  312  may spray the substrate  122  with deionized water or any other suitable fluid to clean the substrate  122  as the substrate  122  is removed from the particle cleaning module  182  by the robot  168 . At least one of the spray bars  364 ,  366  may be utilized to wet the substrate  122  prior to chucking against the substrate receiver  310  to remove particles that may potentially scratch the backside of the substrate and/or to improve chucking by the substrate receiver  310 . The spray bars  364 ,  366  may be coupled to different fluid sources  388 ,  390  so that different fluids may be provided to each of the spray bars  364 ,  366 , or both spray bars  364 ,  366  may be coupled to a single fluid delivery source. 
         [0058]    Referring to  FIGS. 7 and 8 , the particle cleaning module  182  includes a pad conditioner  410 . The pad conditioner  410  can be a disk formed of a material that is more rigid than the pad  344 . For example, if the pad  344  is a brush pad, e.g., PVA, then the pad conditioner  410  can be glass. As another example, if the pad  344  is a buffing pad, e.g., a polyurethane pad, then the pad conditioner  410  can be a body coated with abrasive diamond grit. 
         [0059]    In the implementation illustrated in  FIGS. 7 and 8 , the pad conditioner  410  is attached to the substrate holder  314 . The pad conditioner  410  is oriented vertically, with an outer surface  412  facing toward the pad  344 . The outer surface  412  of the pad conditioner  410  is parallel to the face  424  of the substrate holder  314  that contacts the substrate. The pad conditioner  410  can be inset into a recess in the face  424  of the substrate holder  314 . Optionally, the outer surface  412  can be slightly recessed relative to the face  424  so that the abrasive outer surface  412  does not contact the substrate  122  when the substrate is held by the substrate holder  314 . This can prevent damage or contamination of the substrate  122 . The pad conditioner  410  can be located at the center of the substrate holder  314 , e.g., the axis of rotation of the pad holder  314  can pass through the approximate center of the pad conditioner  410 . 
         [0060]    Pad conditioning can begin once the substrate  122  no longer blocks access of the pad  344  to the pad conditioner  410 , e.g., after the substrate  122  is removed from the particle cleaning module  182 . In operation, the axial actuator  340  urges the pad  344  against the pad conditioner  410 . Relative motion between the pad  344  and the conditioner  410  is generated, e.g., by rotating the pad conditioner  410  with the substrate rotation mechanism  316  and/or rotating the pad  344  with the pad rotation mechanism  336 . If the pad conditioner is large enough, then optionally the lateral actuator mechanism  342  moves the pad holder  334  and pad  344  in an oscillating horizontal motion across the surface of the conditioner  410 . While the pad  344  is in contact with the substrate  122 , the fluid delivery nozzle  350  can provide a cleaning liquid, e.g., at least one of deionized water, a chemical solution or another suitable fluid to the interface between the pad conditioner  410  and the pad  344 . 
         [0061]    Although  FIGS. 7 and 8  illustrate the pad conditioner  410  attached to the substrate holder  314 , other locations are possible for the pad conditioner. For example, as shown in  FIG. 5 , the pad conditioner  410  can instead be located to the side of the substrate holder  314 , e.g., in the pocket  504  of the housing  302 . An additional conditioner rotation mechanism could be included to provide rotation of the pad conditioner  410 . The conditioner rotation mechanism can be constructed in a manner similar to the substrate rotation mechanism, with a drive shaft passing through the wall of the particle cleaning module  182  to a motor. 
         [0062]    Referring to  FIG. 8 , in some implementations, both the pad conditioner  410  and the pad  344  rotate. For example, for a conditioning operation, the pad conditioner  410  can rotate at about 200-2000 rpm, e.g., about 1000 rpm, and the pad  344  can also rotate at about 200-2000 rpm, e.g., 800 rpm. The pad  344  and pad conditioner  410  can be rotated in the same direction at different speeds, or in opposite directions. The pad  344  can be pressed against the pad conditioner with a pressure of about 0.5-2 psi, e.g., 1 psi. 
         [0063]    An advantage of placing the pad conditioner  410  on the substrate holder  314  is the conditioner does not occupy extra space and that extra mechanical components to provide rotation of the pad conditioner  410  are not needed. An advantage of placing the pad conditioner in the pocket  504  is that the pad  344  can be conditioned while the substrate  122  is positioned on the substrate holder  314 . 
         [0064]    Referring to  FIG. 9A , in some implementations, the pad conditioner  410  can include a plurality of passages  430  that exit on the outer surface  412 . While the pad  344  is in contact with the substrate  122 , a cleaning liquid, e.g., at least one of deionized water, a chemical solution or another suitable fluid, can be delivered through the passages  430  to the interface between the pad conditioner  410  and the pad  344 . 
         [0065]    Referring to  FIG. 9B , in some implementations, which can optionally be combined with the passage of  FIG. 9A , a plurality of grooves  432  are formed on the outer surface of the pad conditioner  432 . The grooves  432  can carry away debris dislodged from the pad  344 . Although illustrated as parallel grooves in  FIG. 9B , the grooves can be extend radially outward from the center of the pad conditioner  410 , or be concentric circles, or be some other pattern or combination of patterns. 
         [0066]    Returning to  FIG. 7 , the particle cleaning module  182  can also include a pressure sensor  430 . The pressure sensor can includes a vertical contact surface. The module  182  is configured such that the axial actuator  340  can move the pad  344  into contact with the contact surface, and the pressure sensor  430  is configured to generate a signal representing an applied pressure of the pad  344  pressed against the contact surface. The signal can be sent to the controller  108  on a data line  432 . 
         [0067]    In some implementations, the pressure sensor  430  measures the pressure of the pad  344  against the pad conditioner  410 . That is, the contact surface can be the outer surface  412  of the pad conditioner  410 . The pressure sensor can be a load cell, and can be positioned between the pad conditioner and a rigid component of the pad rotation mechanism  336 . For example, in the implementation shown in  FIG. 7 , the load cell  430  can be positioned between the substrate holder  314  and the draft shaft that extends from the substrate rotation mechanism  316 . However, in other implementations, the load cell  430  could be positioned between the pad conditioner  410  and the substrate holder  314 , or between two axially separated portions of the drive shaft. 
         [0068]    In some implementations, the pressure sensor  430  measures the pressure of the pad  344  against a surface other than the pad conditioner. For example, if the pad conditioner  410  is positioned on the substrate support  314 , then as shown in  FIG. 10A , the contact surface could be the surface of a body  434  located in the pocket  504 . In this case, the load cell  430  can be located between the body  434  and another rigid part, e.g., the wall  436  of the particle cleaning module  186 . Conversely, if the pad conditioner  410  is located in the pocket, the contact surface could be the surface  424  of the substrate holder  314 . In this case, as shown in  FIG. 10B , the load cell  430  can be positioned between the substrate holder  314  and the draft shaft that extends from the substrate rotation mechanism  316  or between two axially separated portions of the drive shaft. 
         [0069]    Either the axial actuator  340  or a controller that controls the axial actuator  340 , e.g., controller  108 , is configured to generate a signal representing the horizontal position of the pad holder  334 . For example, the axial actuator can include a linear encoder that measures linear translation of a component of the pad actuation assembly  306 , e.g., the second shaft  346 . The linear encoder can send the signal to the controller  108 . Alternatively or in addition, the controller  108  could monitor a voltage level used to control the axial actuator  340 . 
         [0070]    As noted above, the pad  344  wears over time. If the pad actuation assembly were to position the pad holder  346  at the same axial position for each substrate, then the compression of the pad  344  against the substrate would vary from substrate-to-substrate, resulting in variations in effectiveness of cleaning or buffing from substrate-to-substrate. However, by using a pressure sensor  430  to measure the pressure applied by the pad  344  as a function of the axial position of the pad holder, a controller can adjust the axial position of the pad support to improve consistency of compression from substrate-to-substrate. 
         [0071]    In operation, at some time a “fresh” pad  344 , e.g., a pad that has not be used for buffing or cleaning yet, is installed on the pad support  346 . The pad actuator assembly  306  moves the pad holder  334  to a position Z 1  at which the pad  344  abuts the contact surface of the pressure sensor. The load on the load cell  430  is measured for the pad holder at the position Z 1 . The position Z 1  could be a preset position, or the axial actuator  340  could advance the pad holder  344  horizontally until the load on the load cell  430  reaches a preset load value. Assuming that the load cell  430  is integrated with the substrate holder  314 , the pad  344  is moved along the Z-axis away from the substrate holder  314  so that a substrate can be lowered into the particle cleaning module  186  as described above. 
         [0072]    One or more substrates are processed in the particle cleaning module  186 . To perform this processing, the axial actuator  340  advances the pad holder to a position Z 2  in which the pad  344  contacts the substrate  10 . 
         [0073]    After cleaning or buffing of one or more substrates in the particle cleaning module  186 , the pad actuator assembly  306  returns the pad  344  into contact with the contact surface of the pressure sensor  430 . In some implementations, the axial actuator  340  advances the pad holder  334  horizontally along the Z-axis until the load cell  430  reaches the same preset load value. The position Z 3  of the pad holder which generates this load value is determined from the signal representing the horizontal position of the pad holder  334 . The controller can determine a difference ΔZ from Z 3 -Z 1 . 
         [0074]    For processing of a subsequent substrate  10 , when the pad  334  is returned into contact with a substrate  10 , the axial actuator  340  advances the pad holder  334  by an additional amount based on the difference, e.g., to a position Z 4 =Z 3 +ΔZ. Consequently, even though the pad wears, the pressure applied by the pad  344  during processing should be more consistent from substrate-to-substrate, thereby improving substrate-to-substrate uniformity. 
         [0075]    The controller  108  can receive the signal representing the pressure of the pad  344  against the contact surface, can receive the signal representing the horizontal position of the pad holder  334 , can store and/or calculate the preset pressure value and the position values Z 1 , Z 2 , Z 3 , Z 4 . 
         [0076]    Referring back to the planarizing module  106  of  FIG. 1 , both of the second and third station  130 ,  132  may be used to perform CMP process as the particle cleaning module  182  substantially eliminates the need for a buffing pad disposed in one of the stations  130 ,  132  as required in conventional systems. Since the second and third station,  130 ,  132  to be used for CMP processes, the use of the particle cleaning module  182  advantageously increases the throughput of the CMP system  100 . The vertical substrate orientation of the particle cleaning module  182  is also beneficial, as it removes particles in a more compact footprint as compared to traditional horizontal designs utilized on the polishing module. 
         [0077]    Furthermore, the particle cleaning module  182  effectively cleans the substrate and decreases the loading of particulate on the brushes of the first brush module  164 B and second brush module  164 C. Therefore, the lifespan of the brushes in the first brush module  164 B and second brush module  164 C are advantageously increased. Thus, the particle cleaning module removes particularly difficult to remove polishing fluids without requiring a buffing station in the polishing module and simultaneously frees the second and or third station for additional CMP stations to increase throughput of the planarizing system. 
         [0078]    It is contemplated that the CMP station may be configured as an electrochemical mechanical planarizing station. 
         [0079]    While the foregoing is directed to some embodiments, other and further embodiments of the invention may be devised without departing from the scope of the claims.