Patent Publication Number: US-6905399-B2

Title: Conditioning mechanism for chemical mechanical polishing

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to a mechanism for conditioning a polishing surface in a chemical mechanical polishing system. 
   2. Description of the Related Art 
   Chemical mechanical polishing is one process commonly used in the manufacture of high-density integrated circuits. Chemical mechanical polishing is utilized to planarize a layer of material deposited on a semiconductor wafer by moving the substrate in contact with a polishing surface while in the presence of a polishing fluid. Material is removed from the surface of the substrate that is in contact with the polishing surface through a combination of chemical and mechanical activity. 
   In order to achieve desirable polishing results, the polishing surface must be dressed or conditioned periodically. One type of conditioning process, typically performed on polyurethane polishing pads traditionally utilized in chemical mechanical polishing, is configured to restore the fluid retention characteristics of the polishing surface and to remove embedded material from the polishing surface. Another type of conditioning process, typically performed on fixed abrasive polishing material, is configured to expose abrasive articles disposed within structures comprising the abrasive polishing material, while removing asperities from the upper surface of the polishing material and leveling the structures comprising the polishing surface to a uniform height. 
   In one embodiment, a polishing surface conditioner includes a replaceable conditioning element, such as a diamond disk, coupled to a conditioning head that is movable over the polishing surface. The diamond disk is lowered into contact with the polishing surface while being rotated. The conditioning head is generally swept across the rotating polishing surface to allow the diamond disk to condition a predefined area. 
   Conventional conditioners commonly utilize diaphragms to force the conditioning head against the polishing surface during conditioning. Typically, more force is applied near the centerline of the diaphragm, while less force applied at the perimeter of the diaphragm which is fixed to a housing. As fixed abrasive polishing material is relatively soft as compared to conventional polyurethane polishing pads, the non-uniform force applied to the polishing surface by the conditioner may result in uneven conditioning. 
   Moreover, care must be exercised while moving the conditioner over the polishing material to avoid inadvertent contact between the conditioning head and the fixed abrasive polishing material which may result in gouging or otherwise damaging the polishing material. If the vacuum applied to the diaphragm holding up the polishing head is disabled, or the diaphragm fails, the polishing head will suddenly drop, causing the conditioning head to collide with the polishing surface. Collision between the conditioning head and polishing surface generally result in damaging at least the polishing surface or the conditioning head. Once the polishing material is damaged, that section of the polishing material must be discarded (i.e., not used for polishing) thereby disadvantageously reducing the number of substrates that may be polished per unit quantity of polishing material, resulting in decreased throughput and an increased cost of consumables (e.g., the polishing material). 
   Therefore, there is a need for an improved conditioning mechanism. 
   SUMMARY OF THE INVENTION 
   Embodiments of a conditioning mechanism for a chemical mechanical polishing system have been provided. In one embodiment, a conditioning mechanism includes a rotor assembly and a conditioning element mounting assembly. A seal is disposed between the rotor assembly and conditioning element mounting assembly and bounds one surface of an expandable plenum defined between the rotor assembly and conditioning element mounting assembly. A spring is disposed between the rotor and conditioning element mounting assemblies and is adapted to bias a lower surface of the conditioning element mounting assembly towards the rotor assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that 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 top view of an illustrative chemical mechanical polishing system having one embodiment of a conditioning mechanism; 
       FIG. 2  is a sectional side view of one embodiment of the conditioning mechanism of  FIG. 1 ; 
       FIG. 3  is a sectional side view of one embodiment of a head assembly; 
       FIG. 4  is a partial sectional view of the head assembly taken along section line  4 — 4  of  FIG. 3 ; and 
       FIG. 5  is a sectional side view of the head assembly of  FIG. 3  in a retracted position. 
     To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a top view of an illustrative chemical mechanical polishing system  100  having one embodiment of a conditioning mechanism  134  of the present invention. The chemical mechanical polishing system  100  generally includes a factory interface  104 , a cleaner  106  and a polisher  108 . One polishing system  100  that may be adapted to benefit from the invention is a REFLEXION® chemical mechanical polishing system available from Applied Materials, Inc., located in Santa Clara, Calif. Another polishing system  100  that may be adapted to benefit from the invention is described in U.S. Pat. No. 6,244,935, issued Jun. 12, 2001, to Birang, et al., which is incorporated by reference in its entirety. 
   In one embodiment, the factory interface  104  includes a first or interface robot  110  adapted to transfer substrates from one or more substrate storage cassettes.  112  to a first transfer station  114 . A second robot  116  is positioned between the factory interface  104  and the polisher  108  and is configured to transfer substrates between the first transfer station  114  of the factory interface  104  and a second transfer station  118  disposed on the polisher  108 . The cleaner  106  is typically disposed in or adjacent to the factory interface  104  and is adapted to clean and dry substrates returning from the polisher  108  before being returned to the substrate storage cassettes by the interface robot  110 . 
   The polisher  108  includes at least one polishing station  126  and a transfer device  120  disposed on a base  140 . In the embodiment depicted in  FIG. 1 , the polisher  108  includes three polishing stations  126 , each having a platen  130  that supports a polishing material  128  on which the substrate is processed. 
   The transfer device  120  supports at least one polishing head  124  that retains the substrate during processing. In the embodiment depicted in  FIG. 1 , the transfer device  120  is a carousel supporting one polishing head  124  on each of four arms  122 . One arm  122  of the transfer devices is cutaway to show the second transfer station  118 . The transfer device  120  facilitates moving substrates retained in each polishing head  124  between the second transfer station  118  and the polishing stations  126  where substrates are processed. The polishing head  124  is configured to retain a substrate while polishing. The polishing head  124  is coupled to a transport mechanism that is configured to move the substrate retained in the polishing head  124  between the transfer station  118  and the polishing stations  126 . One polishing head  124  that may be adapted to benefit from the invention is a TITAN HEAD™ substrate carrier, available from Applied Materials, Inc. 
   The second transfer station  118  includes a load cup  142 , an input buffer  144 , an output buffer  146  and a transfer station robot  148 . The input buffer  144  accepts a substrate being transferred to the polisher  108  from the second robot  116 . The transfer station robot  148  transfers the substrate from the input buffer  144  to the load cup  142 . The load cup  142  transfers the substrate vertically to the polishing head  124 , which retains the substrate during processing. Polished substrates are transferred from the polishing head  124  to the load cup  142 , and then moved by the transfer station robot  148  to the output buffer  146 . From the output buffer  146 , polished substrates are transferred to the first transfer station  114  by the second robot  118  and then transferred through the cleaner  106 . One second transfer station  118  that may be adapted to benefit from the invention is described in U.S. Pat. No. 6,156,124, issued Dec. 5, 2000, to Tobin, which is incorporated by reference in its entirety. 
   A polishing fluid delivery system  102  includes at least one polishing fluid supply  150  coupled to at least one polishing fluid delivery arm assembly  152 . Generally, each polishing station  126  is equipped with a respective delivery arm assembly  152  positioned proximate to a respective platen  130  to provide polishing fluid thereto during polishing. In the embodiment depicted in  FIG. 1 , the three polishing stations  126  each have one delivery arm assembly  152  associated therewith. 
   The platen  130  of each polishing station  126  supports a polishing material  128 . During processing, the substrate is held against the polishing material  128  by the polishing head  124  in the presence of polishing fluid provided by the delivery system  102 . The platen  130  rotates to provide at least a portion of the polishing motion imparted between the substrate and the polishing material  128 . Alternatively, the polishing motion may be imparted by moving at least one of the polishing head  124  or polishing material  128  in a linear, orbital, random, rotary or other motion. 
   The polishing material  128  may be comprised of a foamed polymer, such as polyurethane, or may be a fixed abrasive material. Fixed abrasive material generally includes a plurality of abrasive elements disposed on a flexible backing. In one embodiment, the abrasive elements are comprised of geometric shapes formed from abrasive particles suspended in a polymer binder. The polishing material  128  may be in either pad or web form. 
   One conditioning mechanism  134  is disposed proximate each polishing station  126  and is adapted to dress or condition the polishing material  128  disposed on each platen  130 . Each conditioning mechanism  134  is adapted to move between a position clear of the polishing material  128  and platen  130  as shown in  FIG. 1 , and a conditioning position over the polishing material  128 . In the conditioning position, the conditioning mechanism  134  engages the polishing material  128  to work the surface of the polishing material  128  to a state that produces desirable polishing results. 
     FIG. 2  is a sectional view of one embodiment of a conditioning mechanism  134 . The conditioning mechanism  134  generally includes a head assembly  202  coupled to a support member  204  by an arm  206 . The support member  204  is disposed through the base  140  of the polisher  108 . Bearings  212  are provided between the base  140  and the support member  204  to facilitate rotation of the support member  204 . An actuator  210  is coupled between the base  140  and the support member  204  to control the rotational orientation of the support member  204 . The actuator  210 , such as a pneumatic cylinder, AC servo motor, motorized ball screw, harmonic drive or other motion control device that is adapted to control the rotational orientation of the support member  204 , allows the arm  206  extending from to the support member  204  to be rotated about the support member  204 , thus laterally positioning the head assembly  202  relative to the polishing station  126 . A conditioning element  208  is coupled to the bottom of the head assembly  202  and may be selectively pressed against the platen  130  while rotating to condition the polishing material  128 . 
   The support member  204  houses a drive shaft  214  coupling a motor  216  disposed below the base  140  to a pulley  218  disposed adjacent a first end  220  of the arm  206 . A belt  222  is disposed in the arm  206  and operably couples the pulley  218  and the head assembly  202 , thereby allowing the motor  216  to selectively rotate the conditioning element  208 . The belt  222  is contemplated as any member adapted to transfer rotational motion between two rotatable bodies. 
   A control fluid conduit  224  from a fluid control system  226  is routed through the support member  204  and arm  206 , and is couple to the head assembly  202 . The fluid control system  226  includes a gas supply and various control devices (i.e., valves, regulators and the like) that facilitate the application and/or removal of fluid pressure to the motion of the head assembly  202 . In one embodiment, the fluid control system  226  provides air or nitrogen to control the elevation of the conditioning element  208  relative to the platen  130 , and to control the pressure applied by the conditioning element  208  against the polishing material  128  during conditioning. 
     FIG. 3  is a sectional view of the head assembly  202 . The head assembly  202  includes a rotor assembly  330 , a housing  332  and a conditioning element mounting assembly  334 . A seal  344  is disposed between the rotor assembly  330  and the conditioning element mounting assembly  334 . The seal  344  provides a portion of the boundary of an expandable plenum  346  defined between the rotor assembly  330  and the conditioning element mounting assembly  334 . The plenum  346  is coupled by the control fluid conduit  224  to the fluid control system  226  and may be pressurized to urge the conditioning element mounting assembly  334  away from the rotor assembly  330  to engage the polishing material  128 . 
   The housing  332  is coupled to a second end  336  of the arm  206 . The housing  332  is generally an annular member having an inner diameter  340  configured to fit the rotor assembly  330  concentrically therein. A bearing assembly  338  is disposed between the inner diameter  340  of the housing  332  and an outer diameter  342  of the rotor assembly  330  to facilitate smooth concentric rotation of the rotor assembly  330  within the housing  332 . 
   The rotor assembly  330  includes a sheave  350 , a clamp ring  352 , a stem  354  and a rotor body  356 . The rotor body  356  is bounded by the bearing assembly  338  and has a generally hollow cylindrical form. The clamp ring  352  is coupled to the upper portion of the rotor body  356  by a plurality of fasteners  358 . The fasteners  358  urge a lower surface of the clamp ring  352  against the rotor body  356 , thereby sealingly clamping a first end  360  of the seal  344  between the rotor body  356  and clamp ring  352 . An upper surface of the clamp ring  352  is coupled to the sheave  350  by fasteners  302 . The sheave  350  includes a pulley  362  oriented parallel to the base  140 . The sheave is coupled to the stem  354  extending therefrom downward along a central axis  306 . The pulley  362  is driven by the belt  222  and transfers its rotational motion through the rotor assembly  330  to the conditioning element mounting assembly  334 . The pulley  362  has a first port  366  formed therein concentric to the central axis  306 . The first port  366  is coupled to a passage  364  extending through the pulley  362  and downward into the stem  354 . The passage  364  exits the stem  354  at a second port  368 . The second port  368  is positioned on the stem  354  to allow fluid to be introduced and removed from the expandable plenum  346 , thereby imparting vertical motion to the conditioning element mounting assembly  334  relative to the rotor assembly  330 . A rotary union  370  is coupled between the first port  366  and the control fluid conduit  224  to allow passage of fluid through the passage  364  while the rotor assembly  330  is rotating. 
   The conditioning element mounting assembly  334  includes a sleeve  372  and a mounting flange  374 . The sleeve  372  and mounting flange  374  are coupled by a gimbal  396  that allows the angular orientation of the mounting flange  374  to align with the polishing material  128  during conditioning. The mounting flange  374  extends radially outward from one end of the sleeve  372  and is configured to accept the conditioning element  208 . The conditioning element  208  may be clamped, adhered or otherwise removably coupled to the lower surface of the mounting flange  374  that faces the platen  130 . 
   The sleeve  372  extends through an aperture  376  defined by a flange  378  extending radially inward from the lower edge of the inner diameter  308  of the rotor body  356 . The sleeve  372  is generally hollow is configured to slide axially over the stem  354  along the axis  306 . The sleeve  372  and stem  354  may be keyed or have other geometry that facilitates axial translation of the sleeve relative to the stem, while preventing relative rotational motion therebetween. 
   In the embodiment depicted in the sectional view of  FIG. 4 , the stem  354  includes a key  402  that engages a slot  404  formed in the sleeve  372 . The key  402  and slot  404  interface to allow linear motion in an axial direction while preventing rotation. A separate key other interlocking or engaging geometries that prevent relative rotation are also contemplated. Alternatively, guide pins parallel to the axis  306  may be disposed between the rotor assembly  330  and mounting assembly  334 . 
   Returning to  FIG. 3 , a spring  382  is disposed concentrically around the sleeve  372  and is adapted to bias the mounting flange  374  towards the housing  332  and rotor body  336 . The spring  382  is generally selected to support the rotor assembly  330  in a retracted position (e.g., a position that maintains the conditioning element  208  and the upper surface of the polishing material  128  in a spaced-apart relation as depicted in FIG.  5 ), thereby avoiding inadvertent contact therebetween that may result in damage to the polishing material  128 . Moreover, the bias provided by the spring  382  urging the rotor assembly  330  away from the polishing material  128  additionally provides fail-safe operation, preventing contact during electrical or pneumatic failure of the system. The counter force provided by the spring  382  against the weight of the rotor assembly  330  also allows for a lower net down force against the polishing material  128  while using higher and more easily regulated control pressure for better control and resolution of the force of the conditioning element  208  against the polishing material  128   
   A cap  386  extends radially outwardly from a distal end of the sleeve  372  opposite the mounting flange  374 . The cap  386  may be a nut engaged with a threaded portion of the sleeve  372 . A cage  380  is secured by means not shown to at least one of the cap  386  or sleeve  372 , sealingly clamping a second end  384  of the seal  344  therebetween. The cage  380  additionally includes a cylindrical section  388  having a diameter greater than the aperture  376  of the rotor body  356  that bounds the outer diameter of the spring  382 . The cylindrical section  388  may have a height selected to control the stroke (e.g., downward movement) of the conditioning element mounting assembly  334  as the cage  380  is squeezed between the cap  386  and flange  378  when the pressure is applied to the plenum  346  to actuate the conditioning element mounting assembly  334  downward. 
   The cage  380  also includes a flange  394  that extend radially inward from the upper end of the cylindrical section  388 . A lip  392  extends downward from the inner edge of the flange  394  to capture one end of the spring  382  between the flange  394  and the cylindrical section  388 . The second end of the spring  382  is retained between the cylindrical section  388  of the cage  380  and a lip  390  extending upwardly from the flange  378  of the housing  332 . 
   In one embodiment, the seal  344  is a rolling diaphragm. The inner diameter  308  of rotor body  356  provides an outer support surface for the rolling diaphragm as the conditioning element mounting assembly  334  moves downward. The cylindrical body  388  of the cage  380  provides an inner support surface for the rolling diaphragm as the conditioning element mounting assembly  334  is retracted by the spring  382 . Thus, the seal  344  configured as a rolling diaphragm provides uniform pressure in a direction defined by the central axis  376  across the width of the conditioning element  208  and mounting flange  374  as the plenum  346  is pressurized without a lateral force component, thereby enhancing conditioning uniformity. 
   Thus, a conditioning mechanism has been provided that is mechanically biased away from a polishing surface, thus advantageously reducing the potential incidence of inadvertent contact with a polishing material disposed on the polishing surface, thereby preventing damage to the polishing surface which prolongs the life of the polishing material and reduces substrate defects. Moreover, in one embodiment, the inclusion of a rolling diaphragm enhances the uniform application of pressure to the polishing surface during conditioning, advantageously enhancing conditioning uniformity and substrate polishing performance. 
   While the foregoing is directed to the preferred embodiment 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.