Patent Publication Number: US-2023146929-A1

Title: Platen Shield Cleaning System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 16/909,947, filed on Jun. 23, 2020, the contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to chemical mechanical polishing, and more particularly to cleaning of a shield that surrounds a platen. 
     BACKGROUND 
     An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non planar surface. In addition, planarization of the substrate surface is usually required for photolithography. 
     Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid is typically supplied to the surface of the polishing pad. 
     The polishing pad is typically supported on a rotatable platen. As the platen and polishing pad rotate, centrifugal force tends to urge the polishing liquid off the polishing pad. A platen shield can be placed around the platen to prevent the polishing liquid being thrown off the polishing pad from contaminating the work area. 
     SUMMARY 
     In one aspect, a platen shield cleaning system includes a platen shield cleaning assembly for cleaning a platen shield of a chemical mechanical polishing system. The platen shield cleaning assembly is installed on a rotatable platen in a gap between the rotatable platen and a platen shield. The assembly includes a sponge holder attached to the rotatable platen and a sponge. The sponge is held by the sponge holder such that an outer surface of the sponge is pressed against an inner surface of the platen shield. 
     Implementations may include one or more of the following features. 
     The sponge holder may include an adapter configured to be removably secured to the rotatable platen. The adapter is configured to press the sponge against the inner surface of the platen shield. The adapter may include a latch configured to be removably secured to a plug extending from a platen. The sponge may be pressed against an inner surface of the platen shield by a plurality of springs. 
     The sponge holder may include a latch and a backing piece. The latch may be configured to be removably secured to a plug extending from a platen. The backing piece is connected to the latch and having an outer surface configured to receive a sponge. The outer surface is curved so as to conform the sponge to a platen shield inner surface profile. The sponge may be attached to the outer surface of the sponge holder by a hook and loop fixture. The sponge holder may be coupled to the backing piece by multiple springs. The springs may be coupled to the backing piece and the sponge holder by a plurality of fasteners. 
     The platen shield cleaning system may include an adapter and a sponge holder. The adapter may be configured to be removably secured to a platen of a chemical mechanical polishing system. The sponge holder may be connected to the adapter and having an outer surface configured to receive a sponge and hold the sponge against an inner surface of a platen shield that surrounds the platen. The adapter may include a latch configured to be removably secured to a plug extending from a platen. The adapter may include a support flange configured to abut a top surface of the platen to prevent the adapter from rotating. 
     The platen shield cleaning system may include multiple springs interposed between the adapter and the sponge holder to urge the sponge into contact with the inner surface of the platen shield. Multiple cotter pins may hold the springs to the adapter and the sponge holder. 
     The platen shield cleaning system may include a sponge coupled to the sponge holder. The sponge may be couple to the sponge holder by a loop and hook fixture. The sponge may a dry sponge. The sponge may be a wet sponge. 
     In another aspect, a method of cleaning a platen shield includes installing a sponge and a sponge holder in a gap between a platen and a platen shield, urging the sponge into contact with the platen shield, and rotating the platen and the platen, the sponge holder, and the sponge while the sponge is in contact with the platen shield. 
     Implementations may include one or more of the following features. 
     Installing the sponge and the sponge holder may include compressing multiple spring interposed between the sponge and the sponge holder to move the sponge and the sponge holder closer to each other and releasing the spring interposed between the sponge and the sponge holder to move the sponge and the sponge holder away from each other. Installing the sponge and the sponge holder may include placing a latch on the sponge holder over a plug on the platen. Installing the sponge and sponge holder may include placing a support flange configured to abut a top surface of the platen to prevent the adapter from rotating. 
     The platen shield may be scraped with a dry sponge. The platen shield may be moistened with a wet sponge containing a cleaning solution and the platen shield may be scraped with the wet sponge. 
     Implementations may optionally include, but are not limited to, one or more of the following advantages. Polishing quality may be improved, e.g., fewer scratches and defects are created by dried abrasive particles from polishing slurry buildup detaching from the platen shield during the polishing process. Additionally, the quantity of wafers scrapped due to defects can be reduced. Maintenance down time for the polishing system may be significantly decreased. This improves productivity of the polishing system and reduces operator time because less time is devoted to the platen shield cleaning process. Switching between different modes of cleaning (i.e. dry cleaning and wet cleaning) is easier. The cleaning process can be quickly modified by adjusting tool pressure engagement with the platen shield. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  shows a schematic cross-sectional view of a chemical mechanical polishing system. 
         FIG.  1 B  shows a schematic cross-sectional view of a platen shield cleaning system installed on the chemical mechanical polishing system of  FIG.  1   . 
         FIG.  2    shows a perspective view of the platen shield cleaning system of  FIG.  2    installed on the chemical mechanical polishing system of  FIG.  1   . 
         FIG.  3    shows an exploded front perspective view of the platen shield cleaning system of  FIG.  2   . 
         FIG.  4    shows an exploded rear perspective view of the platen shield cleaning system of  FIG.  2   . 
         FIG.  5    shows a method of cleaning a platen shield. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     During chemical mechanical polishing, a polishing liquid, e.g., an abrasive polishing slurry, is supplied to the surface of the polishing pad. As the platen and polishing pad are rotated, the abrasive polishing, the polishing liquid is thrown off the platen. A platen shield placed around the platen can serve as a barrier to block the polishing liquid from contaminating the surrounding regions of the polishing system. 
     Although some of the polishing liquid will flow off the shield and can be collected in a basin, some of the polishing liquid can dry and build up on the platen shield. The build up of dried polishing liquid on the platen shield over time has multiple deleterious effects. For example, abrasive particles in the polishing liquid can form agglomerates which can be dislodged and return to the polishing surface, thus creating the danger of scratching and defects. A significant amount of non-productive time is required to clean the platen shield to prevent build-up of the dried polishing liquid. 
     A platen shield cleaning tool that can be easily attached to the platen and that does not require equipment dis-assembly can alleviate these deleterious effects. 
       FIG.  1 A  shows a polishing system  20  operable to polish a substrate  10 . The polishing system  20  includes a rotatable platen  24 , on which a main polishing pad  30  is situated and a platen shield  26  surrounding the rotatable platen  24  and separated from the platen  24  by an annular gap  22 . As shown in  FIG.  1 B , a platen shield cleaning system  50  can be mechanically coupled to the rotatable platen  24  and interposed in between the rotatable platen  24  and the platen shield  26 . The platen shield is circular and surrounds the rotatable platen  26 . The platen shield can include a vertical cylindrical portion  26   a , and the top of the platen shield can be curved inward to form a lip  26   b . The lip  26   b  can be positioned above the vertical plane of the surface of the platen  24 . 
     The rotatable platen  24  is operable to rotate about an axis  28 . For example, a motor  30  can turn a drive shaft  32  to rotate the rotatable platen  24 . 
     The polishing system  20  includes a carrier head  70  operable to hold the substrate  10  against the polishing pad  30 . The carrier head  70  is suspended from a support structure  72 , for example, a carousel or track, and is connected by a carrier drive shaft  74  to a carrier head rotation motor  76  so that the carrier head can rotate about an axis  71 . In addition, the carrier head  70  can oscillate laterally across the polishing pad  30 , e.g., by moving in a radial slot in the carousel  72  as driven by an actuator, by rotation of the carousel as driven by a motor, or movement back and forth along the track as driven by an actuator. In operation, the platen  24  is rotated about its central axis  25 , and the carrier head is rotated about its central axis  71  and translated laterally across the top surface of the polishing pad  30 . 
     The polishing system  20  can include a polishing liquid delivery arm  34 . During polishing, the arm  34  is operable to dispense a polishing liquid  36 . The polishing liquid  36  can be a slurry with abrasive particles. The polishing liquid  36  can be referred to by multiple names, e.g., abrasive polishing slurry, abrasive polishing liquid, or polishing slurry. Alternatively, the polishing system  20  can include a port in the platen  24  operable to dispense the polishing liquid  36  onto the main polishing pad  30 . As the platen  24  is rotated, the abrasive polishing, the polishing liquid  36  is thrown off the platen  24 . The platen shield  26  placed around the platen  24  can serve as a barrier to block the polishing liquid  36  from contaminating the surrounding regions of the polishing system  20 . Although some of the polishing liquid  36  will flow off the platen shield  26  and can be collected below the polishing system  20 , some of the polishing liquid  36  can build up on the platen shield  26 . Subsequent polishing operations will continue to deposit polishing liquid  36  on the platen shield  26 , and the polishing liquid  36  can dry and further accumulate on the platen shield  26 . 
     A plug  60  is installed in a recess  42  in a cylindrical outside surface  44  of the platen  24 . The plug  60  is removable from the recess  42 . The plug  60  extends from the outside surface  44  into the gap  22 . The plug can be a plastic or a metal. The plug  60  is configured to mechanically couple to the platen shield cleaning system  50  (shown in  FIG.  2   ). 
       FIG.  1 B  shows a platen shield cleaning system  50  installed in the polishing system  20 . The platen shield cleaning system  50  includes a sponge holder  52  and a sponge  54 . The sponge holder  52  biases the sponge  54  against inside surface  38  of the platen shield  26  to clean the platen shield  26 . The sponge  54  has an outer surface  56  that cleans the inside surface  38  of the platen shield  26 . 
     The sponge  54  is made of a soft, porous, absorbent material. The sponge  54  can be made of a naturally occurring material or a synthetic material. For example, the sponge  54  can formed from naturally occurring material, such as vegetal cellulose, an animal sea sponge, hemp, or wood fiber. Alternatively, the sponge  54  can be formed from a synthetic material, such as polyester or polyurethane. 
     The sponge holder  52  is removably attached to the platen  24  and situated in the gap  22  between the platen  24  and the platen shield  26 . The sponge  54  is removably attached to the sponge holder, e.g., by a weak adhesive layer coated on one surface of the sponge or by mechanical fasteners. 
     The sponge  54  is held by the sponge holder  52  such that an outer surface  56  of the sponge  54  is pressed against an inner surface  38  of the platen shield  24 . In operation, the rotatable platen  24  and the platen shield cleaning system  50  rotate about the axis  28  with the sponge  54  engaging the inner surface  38  of the platen shield  26 . The circular sweep of the sponge  54  around the inner surface  38  of the platen shield  26  can scrape off buildup of the polishing liquid  36 . 
     A cleaning chemical can be applied to the sponge  54  to facilitate cleaning of the platen shield  26 . A chemical can be applied to the sponge  54  to further prevent subsequent polishing liquid  36  buildup on the inner surface  38  of the platen shield  26 . For example, de-ionized water, isopropyl alcohol, or potassium hydroxide can be applied to the sponge. 
       FIG.  2    shows a perspective view of a platen shield cleaning system  50  installed in chemical mechanical polishing system  20 . The platen shield cleaning system  50  is mechanically coupled to the rotatable platen  24  and interposed in between the rotatable platen  24  and the platen shield  26 . 
       FIG.  3    shows an exploded perspective view of the platen shield cleaning system  50  of  FIG.  1   .  FIG.  4    shows a rear exploded perspective view of the platen shield cleaning system  50 . Referring to  FIGS.  1 ,  3  and  4   , the platen shield cleaning system  50  includes an adapter  66  configured to be removably secured to the platen  24 , and a sponge holder  52  with a backing piece  62  connected to the adapter  66  and having an outer surface  64  configured to receive the sponge  54 . 
     The outer surface  64  of the backing piece  62  is curved so as to conform the sponge  54  to an inner surface  38  of the platen shield  26 . The backing piece  62  can have a vertical section  84 , an angled section  86 , and a curved section  88  connecting the vertical section  84  to the angled section  86 . This configuration conforms the sponge  54  to the vertical section  26   a  and inwardly curving lip  26   b  of the platen shield  26 . 
     The sponge holder  52  includes a latching mechanism  58  to removably secure the sponge holder to the plug  60 . For example, the rear face  100  of the adapter  66  adjacent the platen  24  can include a recess  92  into which the plug  60  can fit. 
     The adapter  66  includes a generally vertical main body  90  that will rest against the cylindrical outer surface of the platen, and a support flange  68  extending horizontally from a top edge of the main body  90  and configured to abut a top surface  40  of the pad or platen  24 . The support flange  68  can prevent the adapter  66  from rotating under the effect of torque from the friction of the sponge against the platen shield. The adapter  66  has a rear face  100  with a recess  92 . The recess  92  is configured to accommodate the plug  60 . The recess  92  has a ridge  102  configured to latch onto the plug  60 . The plug  60  slides vertically in the recess  92  until constrained by the ridge  102 . Alternatively, the clamp could grab the platen  26  and the adapter  66  then secured to the clamp. 
     The main body  90  has voids  104  connected to the recesses  96 . The voids  104  are sized to accommodate fastener  82 . 
     The sponge holder  52  includes compression pins  94  protruding vertically from the rear surface  106 . The compression pins  94  compress springs  80  into recesses  96  in the front face  102  of the adapter  66 . The compression pins  94  can have vertical slits  98  that extend through the compression pins  94 . The vertical slits  98  are sized to accommodate a fastener  82 . 
     The sponge holder can made of a metal or a plastic. For example, the sponge holder can be steel, aluminum, high density polyethylene, or a composite. 
     The sponge  54  can be removably attached to the sponge holder  52  by a hook and loop fixture. One half of the hook and loop fixture is attached to the outer surface  64  by an adhesive. The other half of the hook and loop fixture is attached to the sponge  54  by an adhesive. The sponge  54  can be a dry sponge or a wet sponge. A dry sponge does not have any fluid chemicals added to the sponge. A wet sponge has a fluid added to the sponge. A wet sponge can be used to can be used to scrape off dry polishing liquid  36  buildup, soften and loosen dry polishing liquid  36  buildup, or to apply a chemical to the platen shield. For example, a chemical can be applied to the platen shield to reduce or prevent further dry polishing liquid  36  buildup. For example, a cleaning fluid can be added to the sponge. 
     The platen shield cleaning system  50  includes springs  80  interposed between the adapter  66  and the sponge holder  52  to urge the sponge  54  into contact with the inner surface  38  of the platen shield  26 . The springs  80  fit into recesses  96  on the adapter  66 . The springs  80  couple to the sponge holder  52  and are compressed by the compression pins  94 . The springs  80  can be permanently attached or removably secured. The springs  80  can be permanently attached by welding or gluing, for example. The springs  80  can be removably secured by fasteners  82  like pins. For example, the fasteners  82  can be cotter pins. The platen shield cleaning system  50  can include fasteners  82  to hold the springs  80  to the adapter  66  and the sponge holder  52 . The springs  80  are placed in the recesses  96  of the adapter  66 . The sponge holder  54  compression pins  94  are coupled to the springs  80 . A force is applied to the sponge holder  54  to compress the springs  80  into the recesses  96 . The vertical slits  98  of the compression pins  94  are aligned with the voids  104  of the adapter  66 . The cotter pins  82  are placed through the voids  104  and the vertical slits  98 , capturing the springs  80 . 
     In particular, to attach the adapter  66  to the platen  24 , the plug  60  is aligned and placed inside the recess  42  in the cylindrical outside surface  44  of the platen  24 . Then, the rear face  100  of the adapter  66  is aligned to the outside surface  44  of the platen  24 . The adapter recess  92  is aligned to the plug  60 . The adapter recess  92  is coupled to the recess  92 . The adapter  66  vertically slides constrained by the plug  60  and the recess  92 . The plug  60  contacts the ridge  102  of the latch mechanism  58 . The adapter  66  is movement is constrained. The sponge holder  54  is released. The sponge holder  54  moves to a fully extended position. 
       FIG.  5    shows a method  500  of cleaning a platen shield. At  502 , a plurality of springs interposed between a sponge and a sponge holder compress to move the sponge and the sponge holder closer to each other. At  504 , the sponge and the sponge holder are installed in a gap between a platen and a platen shield. At  506 , a latch on the sponge holder is placed over a plug on the platen. At  508 , a support flange configured to abut a top surface of the platen to prevent the adapter from rotating is placed on the top surface of the platen. At  510 , the plurality of spring interposed between the sponge and the sponge holder release to move the sponge and the sponge holder away from each other. At  512 , the sponge is urged into contact with the platen shield. At  514 , the platen and the platen, the sponge holder, with the sponge rotate in contact with the platen shield. The sponge can be a dry sponge or a wet sponge moistened with a liquid. The liquid can be a cleaning solution or a buildup prevention solution. 
     Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims.