Abstract:
An off-line tool for breaking in pad conditioning disks used in a chemical mechanical polishing (CMP) system. The off-line tool comprises a platen having a first surface for holding a polishing pad and a motor for rotating the polishing pad. The motor is coupled to the platen via a first drive shaft. The off-line tool further comprises a mechanical drive assembly for holding a second drive shaft in a position proximate the first surface of the platen and a first break-in head removably attached to the second drive shaft. The first break-in head receives a first pad conditioning disk and the second drive shaft moves the first break-in head toward the platen, thereby pressing the first pad conditioning disk against the polishing pad on the platen.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present invention is related to that disclosed in U.S. patent application Ser. No. 10/873,557, entitled “APPARATUS AND METHOD FOR BREAKING IN MULTIPLE PAD CONDITIONING DISKS FOR USE IN A CHEMICAL MECHANICAL POLISHING SYSTEM,” filed concurrently herewith. The subject matter disclosed in patent application Ser. No. 10/873,557 is hereby incorporated by reference into the present disclosure as if fully set forth herein. 
   TECHNICAL FIELD OF THE INVENTION 
   The present invention is directed to chemical mechanical polishing (CMP) systems and, more specifically, to an off-line tool that breaks in multiple pad conditioning disks without halting operation of a CMP system. 
   BACKGROUND OF THE INVENTION 
   Chemical mechanical polishing (CMP), also called chemical mechanical planarization, is a well-known process for removing oxide and other deposits from the surface of a wafer. CMP systems are frequently used during the processing of silicon semiconductor wafers. CMP systems are made by a number of vendors, including Applied Materials, Inc., of Santa Clara, Calif. Many conventional CMP systems polish semiconductor wafers by abrading the surface of the wafer with a silica-based slurry. 
     FIG. 1  illustrates selected portions of chemical mechanical polishing (CMP) system  100  according to an exemplary embodiment of the prior art. CMP system  100  comprises support platform  101 , platen  105 , polishing pad  110 , pad conditioning disk  115 , spindle  120 , disk actuator  125 , motor  130 , and drive shaft  135 . CMP system  100  further comprises motor  140 , drive shaft  145 , polishing head  150 , motor  160 , drive shaft  165 , and slurry dispenser  170 . Applied Materials (AMAT) manufactures the AMAT Mirra™ CMP system, which houses three CMP systems similar to CMP system  100  in an enclosure. It is noted that the components of CMP system  100  depicted in  FIG. 1  are not drawn to scale. Rather, the sizes and relative positions of the components of CMP system  100  are selected for easy reference and explanation. 
   The operation of CMP system  100  is widely understood. Drive motor  140  and drive shaft  145  rotate platen  105  and polishing pad  110 . Slurry dispenser  170  dispenses onto polishing pad  110  a silica-based slurry made from de-ionized water mixed with SiO 2  (or KOH). Rotation of pad  110  carries the slurry underneath polishing head  150 . A silicon wafer (not shown) is attached to the bottom surface of polishing head  150 , which may be, for example, a Titan™ polishing head from Advanced Material, Inc. The wafer may be held in place on the bottom surface of polishing head  150  by vacuum pressure created by a membrane. 
   Motor  160  and drive shaft  165  rotate polishing head  150  and the attached wafer and press polishing head  150  and attached wafer downward onto polishing pad  110 . This downward pressure forces the exposed surface of the attached silicon wafer into firm contact with the moving slurry dispensed on rotating polishing pad  110 . The movement and pressure of the slurry abrades the exposed surface of the silicon wafer. The abrasion removes silicon oxide or other materials that are deposited on the exposed surface of the silicon wafer attached to the bottom of polishing head  150 . 
   The efficient operation of CMP system  100  requires that the surface of polishing pad  110  be continually conditioned by pad conditioning disk  115 . Polishing pad  110  may be made of polyurethane, for example. The surface of polishing pad  110  is covered by tiny grooves (e.g., depth=0.03 inch) that capture slurry particles. Pad conditioning maintains an acceptable oxide removal rate and stable performance. Pad conditioning helps maintain optimal pad roughness and porosity, thereby ensuring the even transport of slurry to the wafer surface. Without conditioning by pad conditioning disk  115 , the surface of polishing pad  110  glazes and oxide removal rates decline. 
   The bottom surface of disk  115  is coated by an abrasive layer, such as a layer of nickel in which fine diamonds are embedded. Diamond pad conditioning disks are the most widely used method of pad conditioning in wafer fabrication facilities today. Pad conditioning disk  115  refreshes (or wears) the surface of polishing pad  110  during CMP processing to thereby maintain a uniform surface on polishing pad  110 . 
   Disk actuator  125 , motor  130  and drive shaft  135  drive pad conditioning disk  115 , which is rigidly attached to spindle  120 . Disk actuator  125  and drive shaft  135  contain the necessary gearing and other drive mechanisms to rotate spindle  120 , thereby rotating disk  115 . Disk actuator  125  and drive shaft  135  also contain the necessary drive mechanisms to sweep rotating disk  115  back and forth across the surface of rotating polishing pad  110 . 
   The performance of pad conditioning disk  115  has a significant impact on the cost of operating CMP system  100 . Aggressive use of pad conditioning disk  115  gives good process performance, but rapidly wears out polishing pad  110 , thereby reducing pad life and increasing cost. A less aggressive use of pad conditioning disk  115  may not provide enough conditioning to polishing pad  110 , resulting in unstable process performance. 
   Disk flatness is an important aspect of pad conditioning disk  115 , since even wear across polishing pad  110  increases pad life and process stability. To ensure disk flatness, a new pad conditioning disk  115  must be broken in prior to use in an actual on-line CMP process. The process of breaking in a new disk  115  typically involves taking CMP system  100  off line, removing the wafer and polishing head  150 , and attaching new disk  115  to spindle  120 . Next, new disk  115  scours the surface of pad  110  for approximately 30 minutes, until the bottom surface of new disk  115  is itself evenly worn. 
   At this point, broken-in disk  115  is removed, pad  110  is replaced with a new pad, polishing head  150  is re-attached, and CMP system  100  is re-qualified. The process of re-qualifying CMP system  100  may require another two hours. The AMAT Mirra™ CMP system, which houses three CMP systems similar to CMP system  100  in a single enclosure, may break in three pad conditioning disks  115  at a time. Nonetheless, the process of breaking-in pad conditioning disk  115  may take CMP system  100  off line for two and a half hours. 
   It is important to improve process performance by increasing productivity and reducing cost of ownership. However, taking CMP system  100  off line to break in new disks  115  makes achieving these goals more difficult. Reducing off-line time has the added benefit of minimizing the frequency of tool re-qualification, resulting in higher availability and more finished wafers per month. 
   Therefore, there is a need in the art for an improved chemical mechanical polishing (CMP) system that has reduced off line time. In particular, there is a need for an improved system and method for breaking in pad conditioning disks that reduce the amount of time that a chemical mechanical polishing (CMP) system must be taken off line. 
   SUMMARY OF THE INVENTION 
   Co-pending patent application Ser. No. 10/873,557 introduced a novel multiple disk break-in head that may be used in a conventional chemical mechanical polishing (CMP) system to increase the number of pad conditioning disks that may be broken in whenever a CMP system is taken off line. The multiple disk break-in head disclosed in co-pending patent application Ser. No. 10/873,557 replaces the removed polishing head of a CMP system whenever new disks are broken in on the CMP system. 
   The present invention improves upon co-pending patent application Ser. No. 10/873,557 by introducing an off-line break-in tool that uses the multiple disk break-in head to break in new pad conditioning disks without taking the CMP system off line. The off-line break-in tool comprises a platen and polishing pad similar to a CMP system and a motor for rotating the platen and polishing pad. The off-line break-in tool also comprises an assembly that presses one or more multiple disk break-in heads downward onto the rotating polishing pad. Slurry is poured onto the rotating polishing pad by a slurry dispenser. 
   To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide an off-line tool for breaking in pad conditioning disks used in a chemical mechanical polishing (CMP) system. According to an advantageous embodiment of the present invention, the off-line tool comprises: 1) a platen having a first surface for mounting a polishing pad thereon; 2) a motor for rotating the polishing pad, wherein the motor is coupled to the platen via a first drive shaft; 3) a mechanical drive assembly capable of holding a second drive shaft in a position proximate the first surface of the platen; and 4) a first break-in head capable of being removably attached to the second drive shaft. The first break-in head is adapted to receive a first pad conditioning disk and the second drive shaft is operable to move the first break-in head toward the platen, thereby pressing the first pad conditioning disk against the polishing pad mounted on the first surface of the platen. 
   According to one embodiment of the present invention, the mechanical drive assembly is capable of holding a third drive shaft in a position proximate the first surface of the platen. 
   According to another embodiment of the present invention, the off-line break in tool further comprises a second break-in head capable of being removably attached to the third drive shaft, wherein the second break-in head is adapted to receive a second pad conditioning disk, and wherein the third drive shaft is operable to move the second break-in head toward the platen, thereby pressing the second pad conditioning disk against the polishing pad. 
   According to still another embodiment of the present invention, the mechanical drive assembly is capable of rotating the second and third drive shafts. 
   According to yet another embodiment of the present invention, the mechanical drive assembly couples the first drive shaft to the second and third drive shafts such that rotation of the first drive shaft causes rotation of the second and third drive shafts. 
   According to a further embodiment of the present invention, the first break-in head comprises a first drive mechanism capable of rotating the first pad conditioning disk. 
   According to a still further embodiment of the present invention, the first drive mechanism is coupled to the second drive shaft and rotates the first pad conditioning disk by translating a rotating motion of the second drive shaft into a rotating motion of the first pad conditioning disk. 
   According to a yet further embodiment of the present invention, the first drive mechanism comprises a first gear assembly coupled to the second drive shaft and to a first spindle connected to the first pad conditioning disk. 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
       FIG. 1  illustrates selected portions of a chemical mechanical polishing (CMP) system according to an exemplary embodiment of the prior art; 
       FIG. 2  illustrates a side view of selected portions of a multiple disk break-in head; 
       FIG. 3  illustrates a top view of selected portions of a multiple disk break-in head; 
       FIG. 4  illustrates a top view of selected portions of a multiple disk break-in head according to an alternate embodiment; 
       FIG. 5  illustrates a side view of selected portions of an off-line break-in tool that uses a multiple disk break-in head according to an exemplary embodiment of the present invention; and 
       FIG. 6  illustrates a top view of selected portions of an off-line break-in tool that uses a multiple disk break-in head according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 2 through 6 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged chemical mechanical polishing (CMP) system. 
     FIG. 2  illustrates a side view of selected portions of multiple disk break-in head  200  according to an exemplary embodiment of the present invention. When CMP system  100  is taken off line, polishing head  150  is removed and break-in head  200  is installed in CMP system  100  in place of polishing head  150 . The exemplary embodiment of break-in head  200  holds four pad conditioning disks  115 , namely disk  115   a , disk  115   b , disk  115   c  and disk  115   d  (not visible in  FIG. 1 ). In alternate embodiments of the present invention, break-in head  200  may hold more than four disks  115  or less than four disks  115 . 
   Multiple disk break-in head  200  comprises coupling  205 , circular housing  210 , drive shaft  215 , and drive mechanism  250  (shown by dotted outline). Coupling  205  is used to attach break-in head to drive shaft  165  in CMP system  100 . Drive shaft  215  transfers the rotation of drive shaft  165  to drive mechanism  250 . 
   Break-in head  200  further comprises four spindles  120 , namely spindle  120   a , spindle  120   b , spindle  120   c  and spindle  120   d  (not visible in  FIG. 2 ). Disk  115   a  is removably coupled to spindle  120   a , disk  115   b  is removably coupled to spindle  120   b , disk  115   c  is removably coupled to spindle  120   c , and disk  115   d  is removably coupled to spindle  120   d.    
   Break-in head  200  also comprises four drive shafts  220 , including drive shaft  220   a , drive shaft  220   b , drive shaft  220   c , and drive shaft  220   d  (not visible in  FIG. 2 ). Spindles  120  are coupled to drive shafts  220  by retaining rings  225 , springs  230 , and retaining rings  235 . For example, retaining ring  235   a  is rigidly attached to spindle  120   a  and to drive shaft  220   a . Retaining ring  225   a  is rigidly attached to the body of housing  210  and is slidably coupled to drive shaft  220 . Drive shaft  220  is slidably attached to a drive gear in drive mechanism  250 . 
   When break-in head  200  is pressed down on pad  110 , spindle  120   a  and retaining ring  235   a  press upward on spring  230   a . Drive shaft  220   a  also is pressed upward by retaining ring  230   a . The upward movement of drive shaft  220   a  is accommodated by the slidable coupling to the gears in drive mechanism  250 . Retaining ring  225   a  is rigidly attached to housing  210  and resists the upward movement of spring  230   a . Thus, the pressure of disk  115   a  against the surface of pad  110  is determined by the characteristics of spring  230   a.    
   Disks  115   b ,  115   c  and  115   d  are connected to drive shafts  220   b ,  220   c  and  220   d  by similar assemblies of retaining rings, spindles, and springs. The operation of these other assemblies are similar to the operation of ring  225   a , ring  235   a , and spring  230   a  and need not be explained separately. To avoid redundancy, such separate explanations are omitted. 
     FIG. 3  illustrates a top view of selected portions of multiple disk break-in head  200  according to an exemplary embodiment of the present invention. Exemplary drive mechanism  250  is enclosed by a dotted line. Exemplary drive mechanism  250  comprises central gear  310 , transfer gears  311 – 314  and drive gears  321 – 324 . Disks  115   a – 115   d  are positioned below break-in head  200  and are shown in partial dotted outlines. 
   Central gear  310  is coupled to, and rotated by, drive shaft  215 . Transfer gear  311  transfers the rotation of central gear  310  to drive gear  321 , which in turn causes the rotation of disk  115   a . Transfer gear  312  transfers the rotation of central gear  310  to drive gear  322 , which in turn causes the rotation of disk  115   b . Transfer gear  313  transfers the rotation of central gear  310  to drive gear  323 , which in turn causes the rotation of disk  115   c . Transfer gear  314  transfers the rotation of central gear  310  to drive gear  324 , which in turn causes the rotation of disk  115   d.    
   In this manner, the rotation of drive shaft  165  in CMP system  100  causes the individual rotations of each of disks  115   a ,  115   b ,  115   c  and  115   d . The relative sizes of central gear  310 , transfer gears  311 – 314 , and drive gears  321 – 324  determine the speed of rotation of disks  115   a – 115   d.    
   The exemplary arrangement of the gears in drive mechanism  250  is by way of example only and should not be construed to limit the scope of the present invention. Those skilled in the art will readily understand that many other types of mechanical drive systems may be used to rotate pad conditioning disks  115   a – 115   d . For example, in an alternate embodiment, a single large central gear  310  may directly couple to drive gears  321 – 324  without the use of intermediate transfer gears. In still other embodiments, belts or chains may be used to rotate disks  115   a – 115   d.    
     FIG. 4  illustrates a top view of selected portions of multiple disk break-in head  200  according to an alternate exemplary embodiment of the present invention. In  FIG. 4 , drive mechanism  250  has been removed entirely, so that disks  115   a – 115   d  are not driven by drive shafts  165  and  215 . Nonetheless, pad conditioning disks  115   a – 115   d  rotate when pressed down upon pad  110  due to the speed differences between different points on the surface of pad  110 . Surface points near the outer diameter of pad  110  must move at a faster speed than surface points near the center of rotation of pad  110  in order to complete one rotation in the same time period. Thus, a first point on the bottom surface of disk  115  that is closer to the center of pad  110  contacts a slower moving portion of the surface of pad  110  than a second point on the bottom surface of disk  115  that is further from the center of pad  110 . Thus, there is a greater amount of friction at the second point. 
   Spindle  120  is at the center of rotation of disk  115 . Collectively, the combined friction of all of the points on the bottom surface of disk  115  that are located to the side of spindle  120  closer to the center of pad  110  is less than the combined friction of all of the points on the bottom surface of disk  115  that are located to the side of spindle  120  that is further from the center of pad  110 . The friction difference causes disk  115  to rotate about spindle  120 , even in the absence of drive mechanism  250 . 
   The multiple disk break-in head described above overcomes the shortcomings of conventional chemical mechanical polishing (CMP) systems by greatly increasing the number of pad conditioning disks that may be broken in whenever a CMP system is taken off line. Instead of mounting only one new disk  115  on spindle  120  in  FIG. 1 , multiple (e.g., 4) other new disks  115  are mounted on other spindles  120  on break-in head  200  (which replaced polishing head  150 ) and are broken-in at the same time. 
   However, the process of breaking-in new pad conditioning disks may be further improved by means of an off-line tool that completely eliminates the need to halt CMP system  100  in order to break in new disks. The new off-line tool uses one or more of the multiple disk break-in heads  200  described above to break in pad conditioning disks while CMP system continues to polish semiconductor wafers. 
     FIG. 5  illustrates a side view of selected portions of off-line break-in tool  500 , which uses multiple disk break-in heads  200   a  and  200   b , according to an exemplary embodiment of the present invention. Off-line break-in tool  500  comprises basin  501 , platen  505 , polishing pad  510 , head drive assembly  520 , support  530 , drive shaft  535 , motor  540 , drive shaft  545 , drive shaft  555  and drive shaft  565 . Off-line break-in tool  500  further comprises gears  521   526 , drive chains (or belts)  527 – 529 , weight  560 , weight  570 , and a slurry dispenser  610  (not visible in  FIG. 5 ). It is noted that the components of break-in tool  500  depicted in  FIG. 5  are not drawn to scale. The sizes and relative positions of the components of break-in tool  500  are selected for easy reference and explanation. 
   Basin  501  catches excess slurry that overflows polishing pad  510  and provides a support platform for the other components of break-in tool  500 . Support  530  and drive shaft  535  support head drive assembly  520  in position above platen  505 . Motor  540  rotates drive shaft  545 , which in turn rotates platen  505  and gear  525 . Drive chain (or belt)  520  transfers the rotation of gear  525  to gear  526 , which is attached to drive shaft  535 . The rotation of gear  526  rotates drive shaft  535 , which in turn rotates gear  524 . 
   Drive chain (or belt)  528  transfers the rotation of gear  524  to gear  523 , which is attached to drive shaft  565 . The rotation of gear  523  rotates drive shaft  565 , which in turn rotates gear  522 . Drive chain (or belt)  527  transfers the rotation of gear  522  to gear  521 , which is attached to drive shaft  555 . The rotation of gear  521  rotates drive shaft  555 . Thus, the rotation of motor  540  rotates all of drive shafts  535 ,  545 ,  555  and  565  via gears  521 – 526  and drive chains  527 – 529 . 
   Moreover, the rotation of drive shaft  555  rotates the pad conditioning disks on the bottom surface of multiple disk break-in head  200   a  in the manner described above in  FIGS. 2 and 3 . Similarly, the rotation of drive shaft  565  rotates the pad conditioning disks on the bottom surface of multiple disk break-in head  200   b  in the manner described above in  FIGS. 2 and 3 . Thus, motor  540  powers the operation of all parts of off-line break-in tool  500 . 
   Drive shaft  555  is slidably attached to gear  521 , so that drive shaft  555  may slide vertically within gear  521 . A spring or a similar mechanism (not shown) pushes upward on drive shaft  555 , so that when multiple disk break-in head  200   a  is attached to drive shaft  555 , multiple disk break-in head  200   a  is held in a raised (or UP) position in which the pad conditioning disks of multiple disk break-in head  200   a  do not touch polishing pad  510 . However, when weight  560  is attached to drive shaft  555 , drive shaft  555  slides downward and multiple disk break-in head  200   a  is pressed downward to a lowered (or DOWN) position in which the pad conditioning disks of break-in head  200   a  do make contact with polishing pad  510 . 
   Similarly, drive shaft  565  is slidably attached to gears  522  and  523 , so that drive shaft  565  may slide vertically within gears  522  and  523 . A spring or a similar mechanism (not shown) pushes upward on drive shaft  565 , so that when multiple disk break-in head  200   b  is attached to drive shaft  565 , multiple disk break-in head  200   b  is held in a raised (or UP) position in which the pad conditioning disks of multiple disk break-in head  200   b  do not touch polishing pad  510 . However, when weight  570  is attached to drive shaft  565 , drive shaft  565  slides downward and multiple disk break-in head  200   b  is pressed downward to a lowered (or DOWN) position in which the pad conditioning disks of break-in head  200   b  do make contact with polishing pad  510 . 
     FIG. 6  illustrates a top view of selected portions of off-line break-in tool  500  according to an exemplary embodiment of the present invention. In  FIG. 6 , slurry dispenser  610  is visible, but weights  560  and  570  are not visible. Support  530 , gear  521 , gear  522 , gear  524 , and belts  527  and  528  are visible within head drive assembly  520 . 
   Advantageously, the off-line break-in tool according to the principles of the present invention may also be used to break in, or condition, polishing head  150  prior to being used to polish semiconductor wafers. The lower surfaces of many conventional polishing heads, such as Titan™ polishing heads, must be smoothed prior to use to remove irregularities. 
   Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.