Abstract:
In one aspect, an apparatus and a method for use in substrate polishing are described wherein a conditioner head is provided for receiving an end effector for conditioning a polishing pad surface; the conditioner head is supported above the polishing pad surface to be conditioned; and the conditioner head is driven with an actuating force from a position that lies along a line that is substantially normal to the polishing pad surface to be conditioned so that an end effector attached to the conditioner head can condition the surface of the polishing pad. In another aspect, pneumatic pressure is supplied through the conditioner head support arm to apply actuating force to the conditioner head so that an end effector attached to the conditioner head can condition the surface of the polishing pad. In yet another aspect, the conditioner head support arm has a fluid channel extending therein and a fluid port, wherein the fluid channel is constructed to receive rinsing fluid and fluid port is constructed to direct rinsing fluid from the fluid channel toward the polishing pad surface to be conditioned.

Description:
This application is a con&#39;t of Ser. No. 08/890,781 filed Jul. 11, 1997, now U.S. Pat. No. 6,036,583. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to substrate polishing techniques, including chemical mechanical polishing (CMP). 
     Chemical mechanical polishing is a process by which a substrate surface is smoothed (planarized) to a uniform level by a polishing pad and an abrasive slurry. A substrate to be polished is usually mounted on a rotatable carrier head and pressed against a rotating polishing pad. The polishing pad typically consists of a disk with a roughened surface. An abrasive chemical solution (slurry) is deposited onto the polishing pad to achieve a desired substrate surface finish. Over time, the polishing process glazes the polishing pad and creates irregularities in the polishing pad surface that can adversely affect the substrate surface finish. The polishing pad surface is typically “conditioned,” whereby the polishing pad surface is deglazed and surface irregularities are removed, by scouring the polishing pad surface with an abrasive device known as an end effector. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features an apparatus and a method for use in substrate polishing according to which a conditioner head is provided for receiving an end effector; the conditioner head is supported above the polishing pad surface to be conditioned; and the conditioner head is driven with an actuating force from a position that lies along a line that is substantially normal to the polishing pad surface to be conditioned so that an end effector attached to the conditioner head can condition the surface of the polishing pad. 
     In another aspect, the invention features an apparatus and a method for use in substrate polishing according to which pneumatic pressure is supplied through the conditioner head support arm to apply actuating force to the conditioner head so that an end effector attached to the conditioner head can condition the surface of the polishing pad. 
     In yet another aspect, the invention features an apparatus and a method for use in substrate polishing according to which the conditioner head support arm has a fluid channel extending therein and a fluid port, wherein the fluid channel is constructed to receive rinsing fluid and fluid port is constructed to direct rinsing fluid from the fluid channel toward the polishing pad surface to be conditioned. 
     Embodiments may include one or more of the following features. The conditioner may be supported above the polishing pad surface by a support arm, and an actuating force may be applied to the conditioner head by a driver. The driver may apply to the conditioner head actuating force that lies along a line that is substantially normal to the polishing pad surface to be conditioned. The driver may comprise a drive shaft coupled between the conditioner head and the support arm, and the drive shaft may be linearly actuatable toward and away from the polishing pad to be conditioned along a drive shaft axis that is substantially normal to the polishing pad surface. The driver may comprise a fluid membrane coupled between the drive shaft and an interior cavity, wherein the fluid membrane seals fluid within the interior cavity of the support arm as the drive shaft is linearly actuated. The drive shaft may be constructed to rotate the conditioner head. A gimbal mechanism may be coupled between the drive shaft and the conditioner head to allow the conditioner head to rotate and to tilt at an angle relative to the drive shaft axis. The support arm may have another end coupled to a base that is constructed to move the conditioner head over the polishing pad surface to be conditioned. 
     When a driving force is applied to a conditioner head from a position that does not lie along a line that is normal to a polishing pad surface, the driving force and the responsive normal force may result in the generation of torque that tends to raise the conditioner head off the polishing pad surface; such a torque may lead to instability and thereby reduce the ability to uniformly apply force against polishing pad surface. By driving the conditioner head with an actuating force from a position that lies along a line which is substantially normal to a polishing pad surface, in accordance with one aspect of the invention, the normal force and the driving force both lie along the same line and little or no torque is generated. The invention therefore allows force to be controllably and stably applied against a polishing pad surface, improving the uniformity with which a polishing pad surface can be conditioned and thereby improving the overall polishing process. Supplying rinsing fluid to the polishing pad surface through the support arm, in accordance with another aspect of the invention, allows the overall size of the polishing apparatus to be reduced and improves the ability to control the delivery of rinsing fluid. 
     Other features and advantages will become apparent from the following description, including the drawings and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective view of a polishing apparatus. 
     FIG. 1B is an exploded view of the polishing apparatus of FIG.  1 . 
     FIGS. 2A and 2B are diagrammatic top views of a substrate being polished and a polishing pad being conditioned by the polishing apparatus of FIG.  1 . 
     FIG. 3A is a diagrammatic view of a driver applying force to a conditioner head from a position that does not lie along a line that is normal to a polishing pad surface. 
     FIG. 3B is a diagrammatic view of a driver applying force to a conditioner head from a position that lies along a line that is normal to a polishing pad surface. 
     FIG. 4A is a diagrammatic side view of a polishing pad conditioner which includes a carrier head in an extended position. 
     FIG. 4B is a diagrammatic side view of a portion of the polishing pad conditioner of FIG. 4A with the carrier head in a retracted position. 
     FIG. 4C is a diagrammatic side view of the carrier head of the polishing pad conditioner of FIG.  4 A. 
     FIG. 4D is diagrammatic side view of gimbal mechanism coupling the carrier head to a conditioner drive shaft in the polishing pad conditioner of FIG.  4 A. 
     FIG. 4E is a diagrammatic side view of the base of the polishing pad conditioner of FIG.  4 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1A and 1B, a polishing apparatus  10  includes a housing  12  that contains three independently-operated polishing stations  14 , a substrate transfer station  16 , and a rotatable carousel  18  which choreographs the operation of four independently rotatable carrier heads  20 . Attached to one side of housing  12  is a substrate loading apparatus  22  that includes a tub  24  that contains a liquid bath  26  in which cassettes  28  of substrates  30  are immersed before polishing. An arm  32  rides along a linear track  34  and supports a wrist assembly  36 , which includes a cassette claw  38  for moving cassettes  28  from a holding station  39  into tub  24  and a substrate blade  40  for transferring substrates from tub  24  to transfer station  16 . 
     Carousel  18  has a support plate  42  with slots  44  through which shafts  46  of carrier heads  20  extend. Carrier heads  20  can independently rotate and oscillate back-and-forth in slots  44  to achieve a uniformly polished substrate surface. Carrier heads  20  are rotated by respective motors  48 , which are normally hidden behind removable sidewalls  50  of carousel  18 . In operation, a substrate is loaded from tub  24  to transfer station  16 , from which the substrate is transferred to a carrier head  20 ; carousel  18  then transfers the substrate through a series of one or more polishing stations  14  and finally returns the polished substrate to transfer station  16 . 
     Each polishing station  14  includes a rotatable platen  52 , which supports a polishing pad  54 , and a pad conditioner  56 ; platen  52  and conditioner  56  are both mounted to a tabletop  57  inside polishing apparatus  10 . Each pad conditioner  56  includes a conditioner head  60 , an arm  62 , and a base  64  for positioning conditioner head  60  over the surface of a polishing pad  54  to be conditioned. Each polishing station  14  also includes a cup  66 , which contains a fluid for rinsing conditioner head  60 . 
     Referring to FIGS. 2A and 2B, in one mode of operation, polishing pad  54  is conditioned by pad conditioner  56  while polishing pad  54  polishes a substrate which is mounted on carrier head  20 . Conditioner head  60  sweeps across polishing pad  54  with a motion that is synchronized with the motion of carrier head  20  across polishing pad  54 . For example, a carrier head  20  with a substrate to be polished may be positioned in the center of polishing pad  54  and conditioner head  60  may be immersed in a rinsing fluid contained within cup  66 . During polishing, cup  66  may pivot out of the way as shown by arrow  69 , and conditioner head  60  carrying a substrate may be swept back-and-forth across polishing pad  54  as shown by arrows  70  and  72 , respectively. Three water jets  71 ,  73 , and  75  may direct streams of water toward polishing pad  54  to rinse slurry from the pad surface. 
     For further details regarding the general features and operation of polishing apparatus  10 , please refer to co-pending application Ser. No. 08/549,336, filed, Oct. 27, 1995, by Perlov et al., entitled “Continuous Processing System for Chemical Mechanical Polishing,” and assigned to the assignee of the present invention, which is herein incorporated by reference. 
     Referring to FIG. 3A, it has been realized that when a driving force (F driver ) is applied to a conditioner head  75  from a position that does not lie along a line that is normal to a polishing pad surface  76 , the driving force and the responsive normal force (F normal ) result in a counterclockwise torque (T′) that tends to raise conditioner head  75  off polishing pad surface  76 . Such torque generation may lead to instability and thereby reduce the ability to controllably apply force against polishing pad surface  76 . As shown in FIG. 3B, when, in accordance with one aspect of the invention, actuating force is applied to conditioner head  60  from a position that lies along a line  82  which is substantially normal to polishing pad surface  76 , the normal force and the driving force both lie along the same line  82  and little or no torque is generated. The invention therefore allows force to be controllably and stably applied against polishing pad surface  76 , improving the uniformity with which a polishing pad surface can be conditioned and thereby improving the overall polishing process. 
     Referring to FIGS. 4A and 4B, support and  62  of pad conditioner  56  has one end coupled to conditioner head  60  and another end coupled to base  64 , which sweeps conditioner head  60  across a polishing pad surface. A driver  84  couples conditioner head  60  to arm  62  and drives conditioner head  60  between an extended position (FIG. 4A) and a retracted position (FIG.  4 B). As explained above, driver  84  applies an actuating force to conditioner head  60  from a position that lies along a line that is substantially normal to the polishing pad surface to be conditioned, so as to significantly reduce the amount of torque generated in polishing pad conditioner  56 . 
     Referring to FIG. 4C, driver  84  includes a housing  86  that defines an interior portion of a fluid cavity  88 . Fluid cavity  88  is further defined by a face plate  90  and a fluid membrane  92 , which is made of neoprene rubber with, for example, a hardness of about 40 durometer and a thickness of about 0.03 inch. Fluid membrane  92  has one end  93  that is attached to housing  86  by an annular clamp  94  and another end  96  that is attached to face plate  90  by an annular clamp  98  which is coupled to face plate  90  by bolts  100 ,  102 . A flange  104  couples face plate  90  to a spline shaft  106  which is, in turn, coupled to a flange  108  of conditioner head  60  by a bolt  110 . In operation, fluid cavity  88  receives pressurized air through fluid channels  112  and  114  defined in driver housing  86  and through a fluid channel  116  which extends through and  62  and through base  64  to an inlet port  117  (FIG.  4 A). The build-up of air pressure inside fluid cavity  88  drives face plate  90 , spline shaft  106 , and conditioner head  60  in the direction indicated by arrow  118 . As air is evacuated from fluid cavity  88 , the reduction in air pressure in fluid cavity  88  causes face plate  90 , spline shaft  106 , and conditioner head  60  to retract in the direction indicated by arrow  120 . 
     Fluid channel  116  includes separate tubes for respectively receiving air and a rinsing solution, such as water. The rinsing solution tube is coupled to waterjets  71 ,  73 , and  75  located along aim  62  (see FIGS. 2A,  2 B, and  4 A). The rinsing solution may be used to rinse a polishing pad surface before, during, or after polishing to prevent the build-up of slurry deposits. 
     Driver  84  also includes a toothed sheave  122  which is coupled to a spline nut  124 . Toothed sheave  122  and spline nut  124  are rotated by a toothed drive belt (not shown) which is driven by a motor in base  64  (discussed in detail below). Spline nut  124  engages spline shaft  106  and thereby causes spline shaft  106  and conditioner head  60  to rotate when driven by the drive belt. A pair of annular bearings  126 ,  128  are held in place between arm  62  and spline nut  124  by an upper collars  130 ,  131  and a lower collar  132 ; annular bearings  126 ,  128  are spaced apart by an annular spacer  134 . Annular bearings  126 ,  128  allow spline nut  124  to rotate freely with respect to an  62 . A pair of bearings  136 ,  138  allow spline nut  124  and spline shaft  106  to rotate freely with respect to face plate  90 . 
     Conditioner head  60  includes a face plate  140  which has an annular magnet  142  for holding in place an end effector (not shown) which is used to condition a surface of a polishing pad; pins  144  are used to engage and thereby transfer torque to an end effector held to face plate  140 . Face plate  140  and flange  108  are coupled together by a gimbal mechanism which includes a plurality of ball bearings  146 ,  148  seated within holes in an annular cage  150  and positioned between an upper annular race  152  and a lower annular race  154 . Ball bearings  146 ,  148  and springs  147 ,  149  allow face plate  140  to mutate with respect to spline shaft  106 . The degree of nutation is limited by three torque transfer pins  156  which are mounted to flange  108  (only one torque transfer pin is shown in FIG.  4 B). Torque transfer pins  156  have protrusions  158  which extend into recesses  160  in face plate  140  and transfer rotational forces from flange  108  to face plate  140 . Each protrusion  158  includes an o-ring  162  with a hardness of about 40 durometer that limits the degree of nutation between face plate  140  and flange  108 . Although limited, this nutation allows face plate  140  to accommodate small features on the surface of a polishing pad so that one side of face plate  140  does not polish with greater force than another. 
     Referring to FIG. 4D, the gimbal mechanism is constructed so as to substantially reduce non-uniform conditioning of a surface of polishing pad  54 . The ball-and-socket joint created by ball bearings  146 ,  148  and upper and lower races  152 ,  154  is constructed so that the spherical center of symmetry  168  coincides with the center of frictional torque (F′) generated between an end effector  170  attached to conditioner head  60  and a polishing pad. The effective rotational center  168  is the point around which, when the compression and varying lateral consistency of the polishing pad and the end effector are taken into account, the rotational frictional forces between the polishing pad and the end effector produce substantially no net torque in the vertical direction relative to center point  168 . That is, the gimbal mechanism is constructed so that the resultant force (R′) needed to drag conditioner head  60  across a polishing pad appears in the plane at the interface between conditioner head  60  and the polishing pad; this is the same plane that contains the resultant frictional force (F′) between conditioner head  60  and the polishing pad. The resulting net torque generated between conditioner head  60  and the polishing pad is thereby substantially reduced because the resultant dragging force (R′) and the resultant frictional force (F′) lie in substantially the same plane, with little or no moment arm separating these resultant forces. This construction substantially reduces the tendency of the conditioner head to rotate which would otherwise cause conditioner head  60  to apply polishing pressure nonuniformly across polishing pad  54 . 
     Referring to FIG. 4E, base  64  includes a pivot support plate  180 , which is attached to arm  62 , and a motor bracket  182 , which is mounted onto tabletop surface  57 . Motor bracket  182  is attached to a harmonic drive  184  (e.g., a harmonic drive available from Harmonic Drive Technologies, Teijin Seiki Boston, Inc. of Peabody, Mass.). The high-speed, low-torque side of harmonic drive  184  is fixed to motor bracket  182 , and the low-speed, high-torque side is fixed by flanges  186 ,  188  to pivot support plate  180  and arm  62 . A drive sweep motor  190  is mounted to motor bracket  182  underneath tabletop  57 . Drive sweep motor  190  has a drive shaft  192  which is coupled by a clamp  194  to a gear  196  that engages with a rim drive gear  198  of harmonic drive  184 . In operation, drive sweep motor  190  drives harmonic drive  184  which, in turn, rotates pivot support plate  180 , thereby sweeping arm  62  back-and-forth across a surface of a polishing pad. Bearings  199  allow pivot support plate  180  to rotate freely with respect to motor bracket  182 . 
     As mentioned above with respect to FIG. 4C, conditioner head  60  is rotated by driving spline shaft  106  and spline nut  124  with a toothed sheave  122  that engages with a toothed drive belt at one end of arm  62 . At the other end of arm  62 , shown in FIG. 4D, the toothed drive belt (not shown) engages with a corresponding toothed sheave  200  which is coupled to one end of a drive shaft  202 . The other end of drive shaft  202  has a gear  204 , which engages with a gear  206  coupled by a clamp  208  to a motor drive shaft  210  of a conditioner motor  212 . Gears  204 ,  206  are contained within a gear housing  214  that is fixed to tabletop  57 . Rotation of motor drive shaft  210  drives shaft  202  which, in turn, rotates toothed sheave  122  and thereby rotates conditioner head  60 . Bearings  216 ,  218  enable drive shaft  202  to rotate freely with respect to pivot support plate  180  and motor bracket  182 . 
     Air is introduced into and evacuated from pad conditioner  56  through a pneumatic input  117  that is coupled to an inner tube  222  which extends through drive shaft  202  and connects with fluid channel  116 . Fluid, such as water, used to rinse an end effector attached to conditioner head  60  is introduced into pad conditioner  56  through a fluid input  224  which is coupled to an annular channel defined between the outer surface of inner tube  222  and the interior surface of an outer tube  226 . 
     Polishing pad conditioner  56  can be used in a number of different ways. For example, pad conditioner  56  may be controlled by a software program running on a computer. A polishing pad can be conditioned before, during or after a substrate is polished. A variety of end effectors may also be used. In general, an end effector includes an abrasive surface, such as a diamond-impregnated surface, that is pressed against a polishing pad to deglaze the pad and remove any surface irregularities. The abrasive surface may have teeth or recesses depending upon the desired substrate surface finish. An end effector may have an adhesive surface for attaching the end effector to the conditioner head. 
     Other embodiments are within the scope of the claims.