Patent Publication Number: US-8968055-B2

Title: Methods and apparatus for pre-chemical mechanical planarization buffing module

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to chemical mechanical planarization (CMP) systems, and more particularly is directed to methods and apparatus for buffing a substrate before performing a CMP process. 
     BACKGROUND OF THE INVENTION 
     Existing chemical mechanical planarization (CMP) systems may sometimes receive substrates for processing that have relatively large debris particles stuck to the surface of the substrates. Frequently pre-CMP rinse systems are unable to effectively remove these larger particles and when the substrate is polished using a conventional CMP system, the particles can cause deep scratches in the surface of the substrates. To address this problem using a conventional CMP system, substrates are sometimes polished twice using different membrane pressures. This solution however, has the drawback of slowing down throughput. Thus, what is needed are methods and apparatus that enable removal of the large debris particles without slowing down CMP processing throughput. 
     SUMMARY OF THE INVENTION 
     Inventive methods and apparatus are provided for a pre-CMP buffing module for a CMP system. In some embodiments, the buffing module includes a polishing pad assembly adapted to be rotated against a major surface of a substrate; a chuck adapted to hold the substrate and to rotate the substrate against the polishing pad assembly as the polishing pad assembly is rotated; and a lateral motion motor adapted to oscillate the polishing pad assembly laterally across the major surface of the substrate while the polishing pad assembly is rotated against the rotating substrate. 
     In some embodiments, the invention provides a method of substrate buffing. The method includes rotating a polishing pad assembly against a major surface of a substrate; rotating a chuck holding the substrate to rotate the substrate against the polishing pad assembly as the polishing pad assembly is rotated; and oscillating the polishing pad assembly laterally across the major surface of the substrate while the polishing pad assembly is rotated against the rotating substrate. 
     In yet other embodiments, the invention provides a method of using a buffing module. The method includes providing a buffing module; loading a substrate into the buffing module; applying a down force on the substrate with a polishing pad assembly of the buffing module; and buffing the substrate by concurrently rotating the polishing pad assembly, rotating the substrate, and oscillating the polishing pad assembly laterally. 
     Numerous other aspects are provided. Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram depicting an example pre-CMP buffing module for a CMP system according to some embodiments of the present invention. 
         FIG. 2  is flowchart depicting an example method of buffing a substrate using a pre-CMP buffing module according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides improved methods and apparatus for pre-treating semiconductor substrates to remove large debris particles from the surface of the substrate before CMP processing. The invention includes a pre-CMP semiconductor substrate buffing module which includes a rotating polishing pad assembly suspended from a motorized gantry that allows the polishing pad assembly to be moved laterally across the surface of a substrate while the substrate is buffed by the rotating polishing pad assembly. The substrate is supported on a rotating substrate chuck which securely holds and rotates the substrate during buffing. The module is contained in a tank and a cleaning/polishing slurry may be applied to the surface of the substrate through the polishing pad assembly. Both the motor for rotating the polishing pad assembly and the motor for rotating the substrate chuck may be hollow shaft motors. The slurry may be applied to the back of the polishing pad assembly via the hollow shaft of the motor for rotating the polishing pad assembly. The used slurry may be drained from the tank via the hollow shaft of the motor for rotating the substrate chuck. 
     In some embodiments, the pre-CMP buffing module may be part of a CMP system wherein substrates to be CMP processed are first buffed in the pre-CMP buffing module. The buffing module may include a substrate holder adapted to lift the substrate off the substrate chuck to facilitate loading and unloading of the module using an end effector. In addition, the buffing module may include a polishing pad lifting actuator to raise the gantry to better enable (e.g., provide more clearance for a robot) loading and unloading of the substrate. 
     Turning to  FIG. 1 , an example embodiment of a pre-CMP buffing module  100  is illustrated. A rotating polishing pad assembly  102  is suspended from a motorized gantry  104 . The polishing pad assembly  102  may include a polishing pad  103 , a fluid distribution manifold  105 , and a carriage adapted to securely, but releasably, hold the polishing pad  103 . In some embodiments, an air pressure controlled pneumatic clamping mechanism in the carriage may be used to releasably hold the polishing pad  103 . The motorized gantry  104  allows the polishing pad assembly  102  to be moved laterally across the surface of a substrate  106 . This lateral oscillating motion of the rotating polishing pad assembly  102  while the substrate  106  is buffed by the assembly  102  enhances the consistency of the buffing of the substrate  106  and ensures that the entire surface of the substrate  106  is buffed. In some embodiments, the polishing pad assembly  102  has a pad diameter smaller than the diameter of the substrate  106 . The substrate  106  is supported on a rotating substrate chuck  108 . The rotating substrate chuck  108  securely, but releasably, holds and rotates the substrate  106  during buffing. 
     In some embodiments, the module  100  may be contained in a tank  110  and slurry, deionized (DI) water, pressurized nitrogen gas (N 2 ), pressurized clean dry air (CDA), other cleaning fluids, other chemicals, etc. from a supply may be applied to the surface of the substrate  106  during buffing. The slurry and other fluids may be distributed over the polishing pad  103  via the manifold  105  and dispensed onto the substrate  106  through the polishing pad assembly  102 . In some embodiments, the motor  112  for rotating the polishing pad assembly  102  may be a hollow shaft motor adapted to allow various channels carrying slurry and other fluids to be piped through the hollow shaft  113  to the manifold  105 . Thus, in some embodiments, slurry and/or other fluids may be applied through the back (top) of the polishing pad assembly  102  via the hollow shaft  113  of the motor  112  for rotating the polishing pad assembly. Note that a rotary union may be coupled to the motor shaft  113  to facilitate coupling various supply lines to the moving parts of the buffing module  100 . In some embodiments, the pressurized CDA channeled to the manifold  105  may be coupled to and used to operate the pneumatic clamping mechanism in the carriage used to releasably hold the polishing pad  103 . 
     The motor  114  for rotating the substrate chuck  108  may also be a hollow shaft motor adapted to allow channels carrying used slurry and other fluids to be piped through the hollow shaft  115 . Thus, the used fluids may be drained from the tank  110  via the hollow shaft  115  of the motor  114  for rotating the substrate chuck. Note that some of the channels in the hollow shaft  115  may allow fluids to be brought into the tank  110  to the substrate  106 . For example, purging gas (e.g., N 2 ) may be channeled through the hollow shaft  115  to a distribution manifold  117  for purging and/or drying the substrate  106  before or during unloading of the substrate  106  after processing in the buffing module  100  is complete. In addition, vacuum pressure lines may be extended to the manifold  117  in the chuck  108  via the shaft  115  to provide vacuum pressure to operate the substrate holding function of the chuck  108 . Again, a rotary union may be coupled to the motor  114  to allow supply and drainage lines to be coupled to moving parts of the buffing module  100 . 
     The buffing module  100  may include a substrate holder  116  adapted to lift the substrate  106  off the substrate chuck  108  to facilitate loading and unloading of the module  100  using an end effector. A substrate holder lift actuator  118  may be provided to raise and lower the substrate holder  116 . In addition, the buffing module  100  may include a polishing pad lifting actuator  120 , for example, built into one of the gantry upright supports  122 . The polishing pad lifting actuator  120  may be adapted to raise the gantry  104  to better enable loading and unloading of the substrate  106  from the module  100 . The gantry upright supports  122 , the motor  114  for rotating the substrate chuck, and the substrate holder lift actuator  118  may all be coupled to a base plate  124 . 
     In operation, the pre-CMP buffing module  100  raises the gantry  104  and the substrate holder  116  using the polishing pad lifting actuator  120  and the substrate holder lift actuator  118 , respectively. A substrate  106  is loaded onto the substrate chuck  108  (e.g., a vacuum chuck or any other practicable type of chuck). The gantry  104  and the substrate holder  116  are lowered by the polishing pad lifting actuator  120  and the substrate holder lift actuator  118 , respectively. 
     A predetermined amount of downward pressure is applied to the substrate  106  by the polishing pad assembly  102 . To insure the polishing pad assembly  102  remains parallel with the major surface of the substrate  106 , a flexible linkage  126  (e.g., a gimbal, ball joint, etc.) may be used between the motor  112  and the polishing pad assembly  102 . Thus, even if the gantry  104  is not level or parallel with the substrate  106 , the polishing pad  103  remains substantially parallel with the substrate  106 . In some embodiments, the shaft  113  through the motor  112  may extend down past the lateral motion motor  130  and through the flexible linkage  126  to allow fluid supply channels to reach the fluid distribution manifold  105 . Thus, the flexible linkage  126  may include a hollow shaft. In some embodiments, a hard stop  128  may be provided to limit the downward pressure of the polishing pad assembly  102  on the substrate  106 . 
     Slurry and/or other fluids are applied to the polishing pad assembly  102  via the hollow shaft  113  of the motor  112  for rotating the polishing pad assembly  102 . The polishing pad assembly motor  112  rotates the polishing pad assembly  102  and the substrate chuck motor  114  rotates the substrate  106 , concurrently. In addition, a lateral motion motor  130  mounted on the gantry  104  also moves the polishing pad assembly  102  laterally oscillating back and forth across the substrate  106 . The buffing continues for a predefined period of time or until a desired endpoint is reached (e.g., torque measurement sensors may be coupled to the motors and an end point may be identified based upon a detected change in the applied torque). The used slurry flows out of the tank  110  via a channel though the hollow shaft  114  of the substrate chuck motor  114 . 
     Upon buffing completion, the pre-CMP buffing module  100  stops the motors  112 ,  114 ,  130  and raises the gantry  104  and the substrate holder  116  using the polishing pad lifting actuator  120  and the substrate holder lift actuator  118 , respectively. The substrate  106  is purged with N 2 , removed from the chuck  108 , and transferred to a CMP polisher for CMP processing. In some embodiments, a controller  132  (e.g., a computer) adapted to execute a program is electronically coupled to each of the motors  112 ,  114 ,  130 , actuators  118 ,  120 , valves in the manifolds  105 ,  117 , and any other controllable components (e.g., fluid supply valves and pumps, vacuum pressure supplies, drainage valves and pumps, purge valves, etc.). In addition, the controller  132  may be connected to any number of meters and sensors (e.g., a current measurement meter on the motor  112  that drives the polishing pad assembly, a fluid supply valve status sensor on the slurry supply channel, etc.) used to monitor operation and status of the buffing module  100  and associated components. The control program is adapted to perform the methods and operate the pre-CMP buffing module  100  of the present invention by causing the controller  132  to send signals to, and receive signals from, the components. 
     Turning now to  FIG. 2 , a flow chart depicting an example method  200  of pre-CMP buffing a substrate is provided. In Step  202 , a pre-CMP buffing module  100  is provided. In Step  204 , a substrate  106  is loaded into the pre-CMP buffing module  100 . In Step  206 , the polishing pad assembly  102  is lowered onto the substrate  106  to apply a down force on the substrate  106 . In Step  208 , the substrate  106  is buffed by applying slurry (and/or other fluids) via the polishing pad assembly  102 , rotating the polishing pad assembly  102 , rotating the substrate  106  (i.e., against the polishing pad assembly  102 ), and moving the polishing pad assembly  102  back and forth laterally. All of this is may be done concurrently. The rate and direction of the rotation of the polishing pad assembly  102  and the substrate  106  may be varied to optimize the buffing and to ensure debris particles are removed. The frequency with which the polishing pad assembly  102  is moved laterally to repeatedly sweep across the substrate  106  and the rate slurry or other fluids are flowed onto the substrate may also be optimized to enhance the buffing and to ensure debris particles are removed. 
     In Step  210 , the controller  132  monitors the buffing progress and determines if an end point or end time is reached. In Step  212 , the motors  112 ,  114 ,  130  are stopped, the tank is drained, and the substrate is purged, released from the chuck, lifted off the chuck, and unloaded. 
     Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.