Abstract:
In a first aspect, a first apparatus is provided for a chemical mechanical polishing (CMP) process. The first apparatus includes (1) a rotatable member; (2) an end effector adapted to receive and retain a conditioning disk; and (3) an elastic device disposed between the rotatable member and the end effector. The elastic device is (a) adapted to rotate the end effector via a torque from the rotatable member, and (b) flexibly extensible so as to impart a force to the end effector while permitting the end effector to deviate from a perpendicular alignment with the rotatable member in order for a conditioning surface of the conditioning disk to conform to an irregular polishing surface of a pad being conditioned. Numerous other aspects are provided, including methods and apparatus for using liquid or gas to deter polishing slurry or debris from entering the conditioning head.

Description:
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/514,458, filed Oct. 24, 2003, which is hereby incorporated by reference herein in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to semiconductor manufacturing, and more particularly to an apparatus for conditioning a polishing surface of a pad used for chemical mechanical polishing/planararization. 
   BACKGROUND OF THE INVENTION 
   Semiconductor device manufacturing often includes one or more polishing or planarization steps following material deposition on the device side of a substrate. For example, polishing pads are often used to polish and/or abrade a layer of deposited material in a process known as chemical mechanical polishing/planarization or CMP. The polishing surface of a polishing pad must occasionally be conditioned or ‘roughened’ in order to maintain the efficiency with which it polishes or removes deposited material from a substrate. For this purpose, apparatus have been developed and utilized which abrade the polishing surfaces of polishing pads with coarse conditioning material. For example, apparatus exist which condition polishing pads in the presence of an abrasive polishing fluid such as a microabrasive slurry (used to facilitate substrate polishing) on the polishing surface while causing a conditioning surface of a conditioning disk to press against and rotate relative to the polishing surface in a process also known as in situ pad rejuvenation or pad dressing. 
   Such conditioning apparatuses often employ conditioning heads comprising end effectors adapted to receive and retain conditioning disks. The conditioning head may be adapted to generate or at least transmit a torque to the end effector so as to rotate the end effector and the conditioning disk during pad conditioning. In addition, a down force may be generated, e.g. local to the conditioning head via pneumatic actuation, or remotely (e.g., via a mounting arm), so as to produce the desired degree of frictional interaction between the conditioning head and the polishing pad. The microabrasive slurry, however, has been known to invade such conditioning heads, e.g., in one or both of a liquid and a vapor form, doing damage to internal components such as bearings. Also, some apparatus, carefully designed to generate a desired degree of down force and/or material removal, nevertheless create manufacturing problems, such as imprecise conditioning brought about by poor rigidity, and/or scoring damage to the polishing pad&#39;s processing surface as a result of end effectors designed to reciprocate relative to their conditioning heads becoming frozen or locked-up, sometimes in cockeyed orientations not apparent until after the damage has been done. 
   Semiconductor manufacturing processes are more and more often demanding quicker pad conditioning, lower down forces, and higher rotation speeds for conditioning pads. As a result, effective methods and apparatus for reliably conditioning polishing surfaces of polishing pads, especially methods and apparatus offering good controllability and reliability, as well as high precision, are both desirable and necessary. 
   SUMMARY OF THE INVENTION 
   In a first aspect of the invention, a first apparatus is provided for a chemical mechanical polishing (CMP) process. The first apparatus includes (1) a rotatable member; (2) an end effector adapted to receive and retain a conditioning disk; and (3) an elastic device disposed between the rotatable member and the end effector. The elastic device is (a) adapted to rotate the end effector via a torque from the rotatable member, and (b) flexibly extensible so as to impart a force to the end effector while permitting the end effector to deviate from a perpendicular alignment with the rotatable member in order for a conditioning surface of the conditioning disk to conform to an irregular polishing surface of a pad being conditioned. 
   In a second aspect of the invention, a second apparatus is provided for a chemical mechanical polishing (CMP) process. The second apparatus includes (1) a rotatable member; and (2) a sealing element comprising a flexible lip disposed around the rotatable member. The flexible lip is adapted to (a) seal against the rotatable member when the rotatable member is not rotating, and (b) retract, in response to a pressure force from a gaseous media, away from the rotatable member, when the rotatable member is rotating so as to permit the gaseous media to flow past the flexible lip, along the rotatable member. 
   In a third aspect of the invention, a third apparatus is provided for a chemical mechanical polishing (CMP) process. The third apparatus includes (1) a rotatable member; and (2) a sealing element disposed around the rotatable member. The sealing element is adapted to (a) seal against the rotatable member when the rotatable member is not rotating; and (b) retract away from the rotatable member when the rotatable member is rotating. 
   In a fourth aspect of the invention, a fourth apparatus is provided for a chemical mechanical polishing (CMP) process. The fourth apparatus includes (1) a rotatable member; and (2) a sealing element comprising a flexible lip disposed around the rotatable member. The flexible lip is adapted to (a) seal against the rotatable member when the rotatable member is not rotating; and (b) retract away from the rotatable member when the rotatable member is rotating. 
   In a fifth aspect of the invention, a fifth apparatus is provided. The fifth apparatus includes (1) a housing; and (2) an end effector coupled to the housing. The end effector is adapted to (a) receive and retain a conditioning disk; (b) move away from the housing so as to position the conditioning disk in contact with a polishing pad; (c) urge a conditioning disk against a polishing pad and rotate relative to the housing for polishing pad conditioning; and (d) pivot relative to the housing during polishing pad conditioning so as to conform to an irregular polishing surface of a polishing pad. 
   In a sixth aspect of the invention, a sixth apparatus is provided. The sixth apparatus includes (1) a housing; (2) a rotatable member rotatably disposed within the housing, the housing and the rotatable member together defining a gap susceptible to exposure of migrating polishing slurry during pad conditioning; and (3) a duct within the housing adapted to selectively direct a flow of cleaning fluid to the gap so that the cleaning fluid flow passes along the gap, carrying polishing slurry therefrom. 
   In a seventh aspect of the invention, a first method is provided for chemical mechanical polishing (CMP). The first method includes the steps of (1) providing a pad conditioning head for a CMP process, having (a) a rotatable member; and (b) an end effector coupled to the rotatable member and adapted to receive and retain a conditioning disk; (2) imparting a force to the end effector; and (3) permitting the end effector to deviate from a perpendicular alignment with the rotatable member, and conform to an irregular polishing surface of a pad being conditioned. Numerous other inventive methods are provided, including methods of using liquid or gas to deter polishing slurry or debris from entering the conditioning head. 
   Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side cross-sectional view of a conditioning head in accordance with the present invention. 
       FIG. 2  is a side cross-sectional view of the conditioning head of  FIG. 1  wherein an elastic device of the head causes the head&#39;s end effector to assume a non-perpendicular orientation while being utilized to condition a polishing surface of a CMP polishing pad. 
       FIG. 3  is a side cross-sectional view of the conditioning head of  FIG. 1  in a cleaning mode. 
       FIG. 4  is a partial side cross-sectional view of a shaft, an end effector, and an elastic device of a conditioning head in accordance with the present invention. 
       FIG. 5  is a partial side cross-sectional view of a conditioning head including a sealing element for sealing against a shaft portion of a rotating member in accordance with the present invention. 
       FIG. 6  is a partial side cross-sectional view of a conditioning head including a sealing element adapted to retract away from a shaft portion of a rotating member in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   Multiple inventive pad conditioning heads are disclosed. According to some head embodiments, close conformance of conditioning disks to irregular polishing surfaces of a polishing pad is permitted via deviation of the head&#39;s end effector from a perpendicular orientation (e.g., vertical rotation relative to a housing of the head) via an elastic device such as a bellows, as will be explained further below. According to some other head embodiments, also described below, cleaning fluid is introduced within the conditioning head so as to rinse from the conditioning head such polishing slurry as may have migrated into the conditioning head during pad conditioning. According to still other head embodiments, a pressurized gaseous media is introduced within the conditioning head during pad conditioning so as to form a slurry-purging flow of gaseous media outward of the conditioning head, e.g. via a retracting sealing element. 
     FIG. 1  is a side cross-sectional view of a conditioning head  101  in accordance with the present invention. The conditioning head  101  may be generally circular in shape as viewed from above (not shown), and may include a pulley  103  adapted to be rotatably driven by an external source of torque, a housing  105  adapted to be secured to a means (not shown)(e.g., a rigid mounting arm) for moving the conditioning head relative to (e.g., laterally across) the polishing surface of a polishing pad ( FIG. 3 ), and an end effector  107  adapted to receive a conditioning pad  109  and to be rotated relative to the housing  105  (e.g., when the conditioning pad  109  is in contact with the polishing surface of a polishing pad during polishing pad conditioning). Applicants have observed that providing a mounting arm (not shown) having improved rigidity over arms of certain known conditioning apparatus, e.g., providing an arm comprising aluminum alloy, a width about 100 mm, and a thickness about 90 mm, improves controllability of the conditioning head  101 , e.g., by increasing a positioning precision of the end effector  107  relative to a polishing surface of a polishing pad, and by decreasing a tendency of the mounting arm to flex during application of a down-force to the polishing surface by the conditioning head  101  during polishing pad conditioning. 
   The conditioning head  101  may also include a rotatable member  111  which may comprise an axis  113  about which the rotatable member  111  may be rotated, and which may be fixedly coupled to the pulley  103  so as to permit a torque from the pulley  103  to rotate the rotatable member  111  relative to the housing  105 . The rotatable member  111  may comprise an extended cylindrical portion  114 , which may be in the form of a torque-transmitting shaft, coupled to the pulley  103  and spanning a distance from the pulley  103 , into the housing  105 , and to and/or beyond a lower portion of the housing  105 , where the rotatable member  111  may terminate in a flanged portion  115  of the rotatable member  111 . The flanged portion  115  may be attached to the extended cylindrical portion  114 , e.g., fixedly attached, or the rotatable member  111  comprising the extended cylindrical portion  114  and the flanged portion  115  may be of unitary construction, e.g., a machined piece of stainless steel. The flanged portion  115  may be adapted to participate in an interface between the rotatable member  111  and the end effector  107 , as described further below, or an additional assembly component, e.g., another flange-type component (not shown), specifically designed for the purpose and/or comprising a different material, may be attached to the flanged portion  115  for that purpose. 
   The conditioning head  101  may also include a bearing  117  disposed within the housing  105  and around the extended cylindrical portion  114  of the rotatable member  111 . The bearing  117  may be any one of a number of conventional bearing types. For example, a sealed and lubricated double row angular-contact ball bearing has been observed to provide a good result and to have wide applicability, in particular with respect to future pad conditioning applications expected to require rotation speeds of 200 RPM or more. The bearing  117  may be adapted to essentially fix a lateral position of the axis  113  of the rotatable member  111  within and relative to the housing  105  (e.g., so as to provide a rigid vertical orientation within the housing  105 ), while permitting the rotatable member  111  to freely rotate about its axis  113  within and relative to the housing  105 . 
   Movement of the End Effector  107  Relative to the Flanged Portion  115  of the Rotatable Member  111   
   The conditioning head  101  may also comprise an elastic device  119  coupled between the flanged portion  115  of the rotatable member  111  and the end effector  107  and having important features and functions adapted to provide improved pad conditioning. For example, and as shown in the side cross-sectional view of the conditioning head  101  illustrated in  FIG. 2 , in operation, the elastic device  119  may be adapted via elastic extension to permit the end effector  107  to move relative to the flanged portion  115  of the rotatable member  111  in a direction aligned with the axis  113  of the rotatable member  111 , e.g., so as to extend away from the flanged portion  115  of the rotatable member  111  and establish contact between the conditioning pad  109  and the polishing surface of a polishing pad P, and/or to retract away from the polishing pad P and toward the flanged portion  115  of the rotatable member  111  (e.g., to enable the conditioning head  101  and/or a polishing pad to be moved toward or away from a conditioning position). The elastic device  119  may also be adapted to generate and/or apply a force (e.g., a down force) to the end effector  107 , e.g., a down force sufficient for pad conditioning. The elastic device  119  may be further adapted to permit torque to be transmitted from the rotatable member  111  to the end effector  107  for rotation of the end effector  107 , e.g., while the conditioning pad  109  is in contact with the polishing surface of the polishing pad P, so as to condition the polishing pad P in combination with the down force. 
   During polishing pad conditioning, and as also shown in  FIG. 2 , the elastic device  119  may be adapted to permit the end effector  107  to deviate from a perpendicular orientation with respect to the axis  113  of the rotatable member  111  (e.g., as necessary in response to irregular pad surfaces). Also, where the elastic device  119  may be adapted to permit non-perpendicular positions of the end effector  107  during pad conditioning, the elastic device  119  may also be adapted to prevent the end effector  107  from becoming stuck in non-perpendicular and extended positions during or after pad conditioning, e.g., so as to protect the conditioning head  101  and/or the polishing surface of the polishing pad from the risk of damage associated with the end effector  107  being frozen in an extended and/or cockeyed position/orientation. 
   Protection of the Bearing  117  from Polishing Slurry During Pad Conditioning 
   Applicants have observed that sensitive and/or precision components disposed within the housings of conditioning heads may be prematurely degraded (e.g., wherein a period of useful life is shortened) and/or entirely disabled by the invasion of polishing slurry, e.g., via the effects of corrosion and/or abrasion. For example, and as shown in  FIG. 2 , while the rotatable member  111  and the end effector  107  are rotating, and while the conditioning pad  109  is being used to condition the polishing surface of a polishing pad P in the presence of a polishing slurry (not shown), a risk exists that polishing slurry, such as liquid or particulate polishing slurry, or polishing slurry in vapor form, will migrate into the conditioning head  101 , e.g., via a gap  121  between the housing  105  and the flanged portion  115  of the rotatable member  111 , and ultimately enter a cavity  123  within the housing  105  containing sensitive and/or precision components, such as the bearing  117 . 
   In accordance with the present invention, the conditioning head  101  is adapted to block the polishing slurry, whether in liquid, particulate, or vapor form, from entering the cavity  123 , e.g., while the conditioning head  101  is in use conditioning a polishing pad, and to do so without requiring frictional sealing contact (e.g., which may tend be a source of contamination via particle generation) with the rotatable member  111 . For example, and as shown in  FIG. 2 , during polishing pad conditioning (e.g., while the rotatable member  111  and the end effector  107  are being rotated), the conditioning head  101  may be adapted to direct a flow  125  of pressurized gas away from the cavity  123 , along the gap  121 , and outward of the housing  105  of the conditioning head  101 . Applicants have observed that positive pressure gas applied in this way will reduce and/or minimize, if not essentially prevent, the problem of polishing slurry entering the housing  105  and invading the cavity  123  via the gap  121  in liquid, particle, or vapor form. In addition, and as also shown in  FIG. 2 , where the conditioning head  101  comprises a sealing element  127  adapted to achieve sealing contact (see  FIG. 1 ) against the rotatable member  111  (e.g., for sealing the cavity  123  (e.g., during periods when the rotatable member  111  is not rotating relative to the housing  105  of the conditioning head  101 ), the sealing element  127  may be further adapted to break and/or extend away from such sealing contact (see  FIG. 2 ) during rotation of the rotatable member  111  so as to reduce and/or preclude potentially particle-generating friction, and to permit the slurry-purging flow  125  of pressurized gas away from the cavity  123  and outward of the conditioning head  101 . 
   Preventing Polishing Slurry From Accumulating Within the Conditioning Head  101   
   The conditioning head  101  is further adapted to prevent any potentially damaging polishing slurry which may (e.g., despite the action of the flow  125  ( FIG. 2 ) of pressurized gas) enter the conditioning head  101  via the gap  121  during polishing pad conditioning from accumulating therein over time and/or as a result of repeated use of the conditioning head  101  for conditioning multiple pads. For example, and as shown in the side cross section view of the conditioning head  101  illustrated in  FIG. 3 , the conditioning head  101  may be adapted (e.g., between pad conditioning sessions) to direct a flow  129  of cleaning fluid, e.g., an aqueous cleaning fluid adapted to dissolve a buildup of polishing slurry, outward along the gap  121  from within the conditioning head  101 , e.g., so as to rinse the affected surfaces of the flanged portion  115  of the rotatable member  111  and of the housing  105 . 
   Applicants have observed that given a sufficient time and volume of flow of the cleaning/rinsing fluid, an operator may be assured that any polishing slurry which may have accumulated in the gap  121  during polishing pad conditioning will have been rinsed off the affected surfaces and subsequently flushed out of the conditioning head  101 , and that the next polishing session may be commenced, e.g., without risk of the gap  121  remaining clogged with a residue of polishing slurry such as may inhibit a relative rotation of the rotatable member  111  relative to the housing  105  or as may partially or completely block a flow  125  ( FIG. 2 ) of slurry-purging pressurized gas from within the conditioning head  101 . 
   EXEMPLARY EMBODIMENT OF AN  INVENTIVE ELASTIC DEVICE  119   
     FIG. 4  is a partial side cross-sectional view of a subset of the components of a conditioning head  101   a , similar to the conditioning head  101  of  FIGS. 1-3  but including specific embodiments of the above-discussed components, including a shaft  111   a , an end effector  107   a , and an elastic device  119   a . The rotatable member  111   a , the end effector  107   a  and the elastic device  119   a  may be similar to the rotatable member  111 , the end effector  107 , and the elastic device  119  discussed above, and may include additional features and aspects as discussed below. 
   The elastic device  119   a  may include an elastic element adapted to be selectively extended (e.g. via inflation/pressurization) and/or retracted (e.g., via deflation/depressurization), and which may provide a reciprocating motion of the end effector  107 . For example, based on a predetermined degree of inflation and/or internal pressure, the elastic device  119   a  may be adapted to produce a desired position of the end effector  107  relative to the flanged portion  115  of the rotatable member  111  and/or relative to a polishing surface of a polishing pad (see the polishing pad P of  FIG. 2 ). Also, the same element of the elastic device  119   a  may permit a desired and/or predetermined amount of force (e.g., down force) to be applied to the end effector  107  while the conditioning pad  109  contacts a polishing surface of a polishing pad ( FIG. 2 ), and may be further adapted to transmit torque from the rotatable member  111   a  to the end effector  107   a  so as to provide pad conditioning. 
   For example, and as shown in the particular embodiment of the elastic device  119   a  shown in  FIG. 4 , the elastic device  119   a  may comprise a bellows  131  (shown in a cutaway view) which may be caused to flexibly span a selectively adjustable distance between an downward-facing surface of the flanged portion  115  of the rotatable member  111   a  and an upward-facing surface of the end effector  107   a . For example, applicants observe that providing a bellows  131  that may extend, e.g., from a free length of 0.2 inches to an extended length of 0.4 inches provides a good result. The bellows  131  may further be of such a construction and be comprised of any suitable materials so that it may further be adapted to perform reliably during and after numerous reciprocation cycles, e.g., one million reciprocation cycles, wherein a reciprocation cycle may consist of a pressurized inflation followed by a deflation in which pressure is relaxed. For example, the bellows  131  may comprised of INCo 625, 0.004 inches thick in a two-ply construction, welded so as to comprise 5 convolutions, reaching an extended length via a 3 PSID internal pressure, and exerting an additional 7 pounds of load with each additional 1 PSID of internal pressure. 
   The bellows  131  may also be suitably flexible in an extended state (e.g., during pad conditioning) to permit various non-perpendicular positions of the end effector  107  as described above with reference to  FIG. 2 . For example, the above-described embodiment of the bellows  131  readily permits the end effector  107  to diverge on the order of from 0 to 5 degrees or more from a perpendicular orientation with respect to the flanged portion  115  of the rotatable member  111 , e.g., for close conformance to a polishing surface during polishing pad conditioning. Also, the extended bellows  131  may comprise a suitably strong spring force so as to promptly retrieve the end effector  107  from such positions when the cause of the misaligned condition is removed, e.g., such as when the conditioning head  101  is moved during pad conditioning from an irregular (e.g., angled, bumpy, curved) region of the polishing surface to a region that is relatively horizontal and/or flat, and/or when being employed to retract the end effector  107  from the polishing surface and toward the flanged portion  115  of the rotatable member  111   a.    
   The bellows  131  may comprise an internal volume  133  that may be caused to increase, e.g., via inflation from an external source (not shown) of elevated pressure and/or caused to decrease, e.g., via deflation as determined by the same source of elevated pressure (e.g., such that the source of pressure is adapted to vary the pressure applied) and/or by an external source of vacuum pressure. For example, Applicants have observed that at least briefly applying subatmospheric levels of pressure to the internal volume  133  of the bellows  131  for purposes of deflation may afford a greater range and/or a more precise degree of control over the motion of the end effector  107   a  and/or the position of the end effector  107   a  relative to the flanged portion  115  of the rotatable member  111   a  at any given time. 
   Where an external source of pressure and/or vacuum is desired to inflate and/or deflate the bellows  131 , the rotatable member  111   a  may comprise a pressure duct  135 , e.g., leading from the internal volume  133 , through the flanged portion  115  and the extended cylindrical portion  114  of the rotatable member  111   a , to an upper end of the rotatable member  111   a . The pressure duct  135  may be aligned with the axis  113  ( FIG. 1 ) of the rotatable member  111   a , and a rotary pressure fitting  137  may be coupled to the rotatable member  111   a  where the pressure duct  135  emerges from the upper end of the rotatable member  111   a , such that pressure and/or vacuum may be applied to the bellows  131  while the rotatable member  111   a  is rotating during pad conditioning. 
   It may also be desired to shield the bellows  131  of the elastic device  119   a  from exposure to polishing slurry. For example, where a particular construction and/or material composition of the bellows  131  may be preferable from a mechanical/functional standpoint, the same bellows  131  (e.g., which may comprise a metal or a metal alloy) may be somewhat or particularly susceptible to damage and/or deterioration from effects of exposure to polishing slurry, e.g., corrosion and/or abrasion. As such, the elastic device  119   a  may further comprise a boot  139  adapted to be disposed around the bellows  131  and coupled between the flanged portion  115  of the rotatable member  111   a  and the end effector  107   a , e.g., via retaining rings  141 , so as to seal outward-facing surfaces of the bellows  131  and substantially prevent polishing slurry in any form from contacting the same. For example, the boot  139  may be of a flexible length so as to be adapted to extend and retract to the same extent as bellows  131  while remaining firmly affixed to the flanged portion  115  of the rotatable member  111   a  and the end effector  107   a , e.g. so as to maintain an airtight seal against the same. As such, the boot  139  may comprise any inert material of suitable toughness, flexibility (e.g., EPDM Rubber). 
   Where the seals formed between the boot  139  and the flanged portion  115  of the rotatable member  111   a  and between the boot  139  and the end effector  107   a  are intended to be, and to remain, air tight, it may be desirable to prevent the creation of, and or minimize the potential for, a pressure cycle within a volume  142  between the boot  139  and an outward-facing surface of the bellows  131 . For example, as the bellows  131  undergoes an inflation/deflation cycle via regulation of an internal pressure such that the internal volume  133  increases or decreases, and if there is no provision for introducing and/or removing air from the volume  142 , the volume  142  may be subject to cyclical increases and/or decreases in pressure. Such pressure cycles may, e.g., break integrity of the seal between the boot  139  and the end effector  107   a  and infuse the surrounding slurry into the volume  142 , which may in turn reduce a useful life of the bellows  131  and/or the elastic device  119   a.    
   The conditioning head  101   a  a may be adapted to prevent and/or minimize the potential for such undesired pressure cycles in the volume  142  between the boot  139  and the bellows  131 . For example, and as shown in  FIG. 4 , the end effector  107   a  may comprise a pressure relief duct  143  leading inward from the volume  142 . The rotatable member  111   a  may also comprise a pressure relief duct  145  which, similar to the pressure duct  135 , may lead from the internal volume  133 , through the flanged portion  115  and the extended cylindrical portion  114  of the rotatable member  111   a , to an upper end of the rotatable member  111   a , and which (as opposed to the pressure duct  135 ) may be permitted to communicate with the atmosphere. A coupling apparatus  146  may be provided within the end effector  107   a  and/or within the internal volume  133  of the bellows  131  so as to connect the pressure relief duct  143  of the end effector  107   a  and the pressure relief duct  145  of the rotatable member  111   a  and to form a ventilation path from the volume  142  to atmosphere. A rotationally symmetrical arrangement of such ducts and connection apparatus, or of other (e.g., similar) ducts and connection apparatus adapted to perform the same function, may be provided such that any resulting imbalance in the rotating portions of the conditioning head  101   a  may be substantially eliminated, or at least substantially reduced and/or minimized. For example, such an arrangement may be of particular importance as pad rotation speeds in the multiple hundreds of RPM become common. 
   EXEMPLARY EMBODIMENTS OF APPARATUS AND METHODS FOR PREVENTING POLISHING SLURRY FROM DAMAGING INTERNAL COMPONENTS OF A CONDITIONING HEAD 
   Embodiments of the present invention provide methods and apparatus for preventing (and/or reducing an amount of) polishing slurry from migrating into a conditioning head and risking damage to precise and/or sensitive components disposed therein. For example,  FIG. 5  is a partial side cross sectional view of a conditioning head  101   b  similar to the conditioning head  101  shown in  FIG. 1  and having additional features and functions as described below. 
   Referring to  FIG. 5 , the conditioning head  101   b  may comprise a sealing element  127   a  similar to the sealing element  127  described above and having additional features and functions as described below. The sealing element  127   a  may be adapted to assume a fixed non-rotating position within the housing  105  above the gap  121  (e.g., the conditioning head  101  may comprise an insert (not shown) adapted to provide a receptacle for receipt of the sealing element  127   a ) and may comprise one or more circular lips  147  adapted to form a water-tight seal about a circumference of the rotatable member  111 . For example, a lower lip  147   a  of a relatively thin gage may be provided which extends from a main seal body  149  inward and downward toward the extended cylindrical portion  114  of the rotatable member  111 , so that the integrity of the seal formed between the lower lip  147   a  and the rotatable member  111  is adapted to generally increase (e.g., the seal will become tighter) should the lower lip  147   a  be acted on by forces tending to urge the lower lip  147   a  upward. As discussed generally with regard to  FIG. 3 , and as more specifically described here with regard to  FIG. 5 , should the conditioning head  101  be subjected to irrigation by a flow  129  of cleaning fluid directed into the housing  105  for subsequent diversion outward of the housing  105  along the gap  121 , the lower lip  147   a  of the sealing element  127   a  may provide a water-tight seal against the rotatable member  111  that may prevent cleaning fluid from entering the cavity  123  of the housing  105  that contains the bearing  117 . Moreover, the lower lip  147   a  may form a surface adapted to absorb pressure forces associated with the flow  129  of cleaning fluid in a manner which increases seal integrity and diverts the flow  129  of cleaning fluid into the gap  121  so as to rinse a build-up of polishing slurry from the adjacent surfaces of the housing  105  and of the flanged portion  115  of the rotatable member  111 . 
   As also shown in  FIG. 5 , the housing  105  may comprise a utility interface surface  151 , which may be perimetrically disposed about the housing  105 , and which may feature one or more apertures. For example, the utility interface surface  151  may comprise a cleaning fluid inlet  153 , and the housing  105  may include a cleaning fluid duct  155  adapted to direct the flow  129  of cleaning fluid into a space  157  beneath the sealing element  127   a  and near the lower lip  147   a . The space  157  may be the deepest and highest location within the housing  105  at which polishing slurry may be expected to accumulate, and so to direct the flow  129  of cleaning fluid toward such a location may be the most effective method of ensuring that it and all downstream locations are rinsed clean of polishing slurry deposits. 
   In operation, the end effector  107  ( FIG. 2 ) of the conditioning head  101   b  may be retracted from a polishing surface of a polishing pad P ( FIG. 2 ) and the conditioning head  101   b  may be moved to a stand-by position, e.g., separate from a pad conditioning station, where an internal rinse may be performed to eliminate polishing slurry deposits. The rotatable member  111  may be caused to cease rotation, and the sealing element  127   a  may be caused to seal against the extended cylindrical portion  114  of the rotatable member  111 . Specifically, the lower lip  147   a  of the sealing element  127   a  may be caused to press against the extended cylindrical portion  114  of the rotatable member  111  for sealing the cavity  123  against entry of cleaning fluid and/or polishing slurry as a result of the rinse. Once the necessary seal is achieved, the flow  129  of cleaning fluid may be introduced to the housing  105  via an appropriate fitting (not shown) attached to the utility interface surface  151  at the cleaning fluid inlet  153 , and the flow  129  may be allowed to flow along the cleaning fluid duct  155  and into the space  157  for rinsing and/or cleaning of polishing slurry deposits as described above. A time and volume of the flow  129  may be predetermined and may be adapted to permit the rinse to be accomplished during the time necessary to swap a conditioned polishing pad for a polishing pad requiring conditioning. 
     FIG. 6  is a partial side cross sectional view of a conditioning head  101   c  similar to the conditioning head  101  shown in  FIG. 1  and having additional features and functions as described as follows. Referring to  FIG. 6 , the conditioning head  101   c  may comprise the sealing element  127   a  described above with reference to  FIG. 5 , and the sealing element  127   a  may be adapted to break or retract away from sealing contact with the rotatable member  111  (see  FIG. 2  and relevant description above) during rotation of the rotatable member  111  and the flow  125  of pressurized gas used to block polishing slurry from entering the cavity  123  of the housing  105  that contains the bearing  117 . The sealing element  127   a  may comprise both a lower lip  147   a  and an upper lip  147   b , with the upper lip  147   b  having structure and function that may be similar to the lower lip  147   a  except in that the upper lip  147   a  is adapted to extend inward and upward (i.e., from the main seal body  149 ) toward the rotatable member  111 . As discussed generally with regard to  FIG. 2 , and as more specifically described here with regard to  FIG. 6 , just prior to the conditioning head  101   c  being employed to condition a polishing surface of a polishing pad (e.g., before the rotatable member  111  of the conditioning head  101   c  has begun rotating), the conditioning head  101   c  may direct the flow  125  of pressurized gas to the main seal body  149  of the sealing element  127   a , and the main seal body  149  of the sealing element  127   a  may direct the flow  125  into a gap  159  between the upper and lower lips  147   a ,  147   b . Pressure within the gap  159  caused by the flow  125  of pressurized gas may cause the lower lip  147   a  to break sealing contact with the rotatable member  111  and/or flex away from the rotatable member  111 , permitting at least a portion of the flow  125  of pressurized gas to flow (e.g., downward) along the rotatable member  111  (e.g., away from the cavity  123  and the bearing  117 ) and outward of the housing  105  along the gap  121 . Once such a flow of slurry-purging pressurized gas has been established, and the lower lip  147   a  (along with the upper lip  147   b  as described below) has retracted away from the extended cylindrical portion  114  of the rotatable member  111 , the rotatable member  111  may begin rotating and pad conditioning may begin, and the flow  125  of pressurized gas may act to protect sensitive components of the conditioning head  101   c  (e.g., the bearing  117 ) from damage from migrating polishing slurry. 
   As also shown in  FIG. 6 , the utility interface surface  151  of the housing  105  may comprise a pressurized gas inlet  161 , and the housing  105  may include a pressurized gas duct  163  adapted to direct the flow  125  of pressurized gas to the main seal body  149  of the sealing element  127   a , after which the flow  125  of pressurized gas will flow to the gap  159  between the lips  147   a ,  147   b  as described above. The gap  159  may be an advantageous location at which to apply the flow  125  of pressurized gas since it is below the bearing  117  and immediately upstream of the space  157  ( FIG. 5 ) at which the flow  129  ( FIG. 5 ) of the cleaning fluid is applied and redirected downstream along the gap  121 . 
   As is also shown in  FIG. 6 , the housing  105  may also comprise a pressurized gas ventilation duct  165 , and pressure from the flow  125  of pressurized gas within the gap  159  between the lips  147  may also force the upper lip  147   a  to break sealing contact with the rotatable member  111  and/or flex outward, permitting a portion of the flow  125  of pressurized gas to flow into the cavity  123 , past the bearing  117 , and outward of the housing  105  through the pressurized gas ventilation duct  165 . Such an arrangement may be utilized so as to exhaust any contamination which may have accumulated in the cavity  123  of the housing  105  (e.g., by expelling particles generated by operation of the bearing  117  and/or any slurry particles or other types contamination which may have entered the cavity  123  from below despite the combined cleaning action of the flow  125  of the pressurized gas and the flow  129  of cleaning fluid. It should be noted that the upper lip  147   b  may be of the same rigidity as the lower lip  147   a  for the creation of an air bearing between said lips  147   a - b  and the rotatable member  111 . Such an arrangement would both eliminate the possibility of seal abrasion and reduce the operating torque. 
   In operation, the flow  125  of pressurized gas may be introduced to the housing  105  via an appropriate fitting (not shown) attached to the utility interface surface  151  at the pressurized gas inlet  161 , the flow  125  may be allowed to flow along the pressurized gas duct  163  and into the gap  159 , the sealing element  127   a  may be caused to retract (e.g., via the pressure from the flow  125  of pressurized gas) from the rotatable member  111 , and the flow  125  of pressurized gas may then be used to purge, e.g., in the manner described above, any polishing slurry, e.g., slurry in particulate, liquid, or vapor form, that may tend to migrate into the housing  105  along the gap  121  during upcoming pad conditioning. As also described above, a portion of the flow  125  of pressurized gas may be directed through the cavity  123  of the housing  105  so as to exhaust contamination from the cavity  123  and eject the same from the housing  105  through the pressurized gas ventilation duct  165 . Once the purging flow  125  of pressurized gas has been established and is flowing, the end effector  107  ( FIG. 1 ) of the conditioning head  101   c  may be extended away from the flanged portion  115  of the rotatable member  111  and into contact with a polishing surface of a polishing pad P ( FIG. 2 ) so as to rotate relative to the same in the presence of polishing slurry during pad conditioning. A continuous flow  129  of pressurized gas may be maintained throughout the period of pad conditioning so as to provide continuous protection against slurry migration into the housing  105  of the conditioning head  101   c.    
   TESTING OF AN EMBODIMENT OF AN INVENTIVE CONDITIONING HEAD 
   A conditioning head  101  ( FIG. 1 ) comprising a sealing element  127   a  ( FIG. 5 ) as described above, a flow  125  of pressurized gas applied throughout pad conditioning, a rotatable member  111  having a extended cylindrical portion  114  of 20 mm, and a bearing  117  comprising a 20 mm ID ball bearing manufactured by Koyo Corporation (part number 5204), was placed in contact with polishing pads and operated in a pad conditioning mode. The rotatable member  111  of the conditioning head  101  was rotated at 1600 RPM for 10 hours during testing in pad polishing conditions (e.g., in the presence of polishing slurry). Applicants observed no signs of degradation of the bearing  117  or the sealing element  127   a . Since conventional conditioning pad rotation speeds typically range from 90-120 RPM, and with new pad conditioning applications being predicted to require rotation speeds of 400-500 RPM, conditioning heads in accordance with the present invention would appear well suited for use either in any compatible pad conditioning apparatus which are either presently available or are being developed for such future applications. 
   The foregoing description discloses only particular embodiments of the invention; modifications of the above disclosed methods and apparatus which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, although specific embodiments of the inventive conditioning heads described herein are configured for use with an aqueous cleaning fluid for dissolving/removing deposits of polishing slurry, non-aqueous cleaning fluids, or even a flow of deposit-purging gas may be substituted for the aqueous cleaning fluid in certain applications, if desired. Further, it will be understood that the specific configuration of the rotating member, bearing, housing, sealing element, elastic device, and end effector, etc., may vary and still fall within the scope of the invention. The housing may include multiple cleaning fluid ducts and/or pressurized gas ducts, e.g., radially-arrayed around the head, and/or one or more annular ducts (i.e., passing into the paper of  FIG. 5  or  6  and concentric with the axis of rotation of the rotating member) as desired, e.g., so as to provide a plurality of perimetrically-spaced locations from which to direct a pressurized gas purge or a flow of irrigating/cleaning fluid outward from the center of the head. The rotating member need not comprise a shaft portion of a smaller diameter than a flange portion. The seal need not necessarily include an upper lip, whether flexible or not, and an additional duct for gas purging near the bearing may be omitted. The elastic device may comprise any manner of device which, like the bellows disclosed herein, provides torque and down-force transmission while permitting various non-perpendicular orientations of the end effector and conditioning pad. Accordingly, while the present invention has been disclosed in connection with specific embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.