Abstract:
The invention includes a method for conditioning a surface of a polishing pad after chemical-mechanical polishing of a semiconductor substrate with the pad surface. The method includes exposing the pad surface to steam, and the steam can comprise ammonium citrate. The invention also includes an apparatus for conditioning a surface of a polishing pad after chemical-mechanical polishing of a semiconductor substrate with the pad surface. The apparatus includes a conditioning stone, and a steam outlet port proximate the conditioning stone. The steam outlet port is configured to jet steam onto the pad surface during the conditioning of the pad surface.

Description:
TECHNICAL FIELD 
     The invention pertains to methods for conditioning surfaces of polishing pads after chemical-mechanical polishing, and further pertains to apparatuses for conditioning surfaces of polishing pads after chemical-mechanical polishing. 
     BACKGROUND OF THE INVENTION 
     Chemical-mechanical polishing is a process utilized for removing materials during semiconductor device fabrication. A prior art method of chemical-mechanical polishing is described diagrammatically with reference to  FIG. 1 . Specifically,  FIG. 1  illustrates a construction  10  comprising a semiconductor substrate  12 , and a polishing pad  14  provided over substrate  12 . Semiconductor substrate  12  can comprise, for example, monocrystalline silicon having one or more layers of insulative and/or conductive materials provided thereover. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. 
     Substrate  12  can comprise a conductive layer comprising, consisting essentially of, or consisting of, copper (not shown) at an upper surface, and the polishing operation shown in  FIG. 1  can be utilized to planarize such copper-containing material. Polishing pad  14  will typically comprise a porous polyurethane material. A slurry  15  is provided at an interface between pad  14  and substrate  12 . Slurry  15  comprises particulates (such as, for example, silicon dioxide and/or aluminum oxide particles) in a liquid medium. The liquid can comprise, for example, water. 
     In operation, pad  14  is displaced relative to substrate  12 , with such displacement indicated by arrow  16 . It is to be understood that pad  14  can be displaced in a linear relation relative to substrate  12  (as indicated by arrow  16 ) and/or in a rotational relation relative to substrate  12 . Also, it is to be understood that pad  14  can, in exemplary applications, be a round pad associated with a rotating platen in particular apparatuses, or can be a non-round pad associated with a web of material moved relative to substrate  12  in other apparatuses (with such other apparatusses frequently being referred to as web chemical-mechanical polishing tools). Also, it is to be understood that the displacement of pad  14  relative to substrate  12  can occur by movement of one or both of pad  14  and substrate  12 . 
     Displacement of pad  14  relative to substrate  12  causes abrasion of the upper surface of substrate  12  with the material of slurry  15 . Such abrasion polishes (typically planarizes) an upper surface of substrate  12 . More specifically, pad  14  comprises a polishing surface  18  which contacts slurry  15  and causes abrasion of an upper surface of substrate  12  with slurry  15 . 
     After polishing of the upper surface of substrate  12 , the substrate is removed from proximate pad  14 , and surface  18  is reconditioned. The reconditioning removes liquid and particles associated with slurry  15  from within pores of pad  14 . The reconditioning can also remove material displaced from the surface of substrate  12  that has lodged within the pores of polishing surface  18  of pad  14 . 
     The reconditioning of pad  14  typically comprises displacing polishing surface  18  across a conditioning stone to rub undesired materials from over surface  18 , and thereby expose a new, clean polishing surface. A typical conditioning stone will be a diamond-impregnated material, with the diamond particles being very coarse (typically, from about 100 microns to about 200 microns in average cross-sectional size). Diamond is utilized because of its superior wear characteristics relative to other materials. 
     An exemplary prior art conditioning apparatus is described with reference to  FIGS. 2 and 3 .  FIG. 2  illustrates a side-view of a conditioning apparatus  20 , and  FIG. 3  illustrates a front-view of the apparatus. Apparatus  20  comprises a pad holder  22  having a polishing pad  14  retained therein. The polishing surface  18  of pad  14  is exposed. Apparatus  20  further comprises a conditioning stone  24  retained within a conditioning stone holder  26 . The conditioning stone holder is mounted in a motor/gimbal which is configured to displace stone  24  relative to pad  14 . The displacement can be along a linear or rotating direction. Motor/gimbal assembly  28  is connected through an arm  30  to a motor  32 . Various gears and belts (not shown) can extend from motor  32  through arm  30  to motor  28 , and accordingly can drive motor/gimbal  28  to accomplish displacement of stone  24  relative to pad  14 . 
     In operation, stone  24  has a surface  25  which contacts polishing surface  18 , and abrades surface  18  to remove contaminants from the surface. The removal of the contaminants ultimately exposes a clean surface of pad  14 . Typically, stone  24  removes a portion of pad  14  associated with surface  18  to remove contaminants and expose a fresh polishing surface of the pad. 
     Various difficulties can occur during the reconditioning of polishing pads with conditioning stones. For instance, some contaminants can be difficult to remove from a polishing pad during reconditioning, with particular difficult contaminants including metals, such as, for example, copper. Accordingly, it would be desirable to develop improved methods for reconditioning polishing pads. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention encompasses a method for conditioning a surface of a polishing pad after chemical-mechanical polishing of a semiconductor substrate with the pad surface. The method includes exposing the pad surface to steam. In particular aspects, the steam can comprise ammonium citrate. 
     In another aspect, the invention encompasses an apparatus for conditioning a surface of a polishing pad after chemical-mechanical polishing of a semiconductor substrate with the pad surface. The apparatus includes a conditioning stone, and a steam outlet port proximate the conditioning stone. The steam outlet port is configured to jet steam onto the pad surface during the conditioning of the pad surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
         FIG. 1  is a diagrammatic, cross-sectional view of a polishing pad juxtaposed relative to a semiconductor wafer during a prior art polishing operation. 
         FIG. 2  is a diagrammatic side view of a prior art apparatus utilized for reconditioning a polishing pad. 
         FIG. 3  is a diagrammatic front view of the  FIG. 2  apparatus. 
         FIG. 4  is a diagrammatic side view of a polishing pad reconditioning apparatus constructed in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagrammatic front view of the  FIG. 4  apparatus. 
         FIG. 6  is a diagrammatic front view of a second embodiment apparatus that can be utilized in various aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  is a diagrammatic view of an apparatus  50  which can be utilized in according to methodology of the present invention for reconditioning a polishing pad. In referring to  FIG. 4 , similar numbering will be utilized as was used above in describing the prior art structures of  FIGS. 1–3 , where appropriate. 
     Apparatus  50  comprises a polishing pad holder  22  which retains a polishing pad  14  having a polishing pad surface  18  which is to be reconditioned. Apparatus  50  further comprises a conditioning stone  24 , retained within a conditioning stone holder  26 . Stone holder  26  is mounted to a motor/gimbal apparatus  28 . Motor/gimbal apparatus  28  is joined through a conditioning arm  30  to a motor  32 . The structures  14 ,  22 ,  24 ,  26 ,  28 ,  30  and  32  can be identical to those structures described above having the same numbers in the prior art apparatuses of  FIGS. 2 and 3 . Apparatus  50  differs from the prior art in having a steam conditioning head  52  mounted relative to conditioning stone holder  26  through mounting structures (not shown). Steam conditioning head  52  comprises an end which terminates in a port  54 . 
     Steam conditioning head  52  is mounted to a conduit  56  which is in fluid communication with a steam source  60 . Source  60  can comprise, for example, a steam generator; and the steam can be generated from, for example, deionized water. 
     In operation, steam is transferred from source  60  through conduit  56  and into conditioning head  52 . The steam then jets out of head  52  (indicated by downwardly extending arrows exiting from port  54 ) and impacts polishing surface  18 . The exposure of surface  18  to the steam can force contaminants out of pores associated with surface  18 , and can thereby assist in cleaning surface  18 . Further, steam  60  can have cleaning agents provided therein which assist in removing contaminating materials from polishing surface  18 . For instance, if a contaminating material comprises copper, or other metals, various metal-solubilizing agents can be included within the steam. An exemplary solubilizing agent for solubilizing copper is ammonium, and such agent can be provided within the steam as, for example, ammonium citrate. In embodiments in which ammonium citrate is provided within the steam, the concentration of ammonium citrate can be, for example, from about 3% to about 10% (by volume). 
     The steam preferably impacts surface  18  with a pressure from about 10 psig (pounds per square inch gauge) to about 20 psig, which can effectively displace particulates from within pores associated with surface  18 . The steam preferably has a temperature of at least about 200° F. at a pressure of at least about 10 psig, and preferably has a temperature of from about 200° F. to about 300° F. as it exits port  54 . The heated steam can beneficially reduce a temperature range of a thermal-cycle that pad  14  is exposed to in going from polishing operations to reconditioning operations. Specifically, pad  14  will typically be heated by friction during a polishing operation, and it can be advantageous to keep pad  14  relatively heated during a reconditioning operation to avoid thermal stresses which could otherwise contribute to wear of the pad. 
       FIG. 5  shows a front view of a portion of apparatus  50 , and illustrates an exemplary shape of conditioning head  52 .  FIG. 5  also illustrates steam exiting from head  52  (downwardly extending arrows) and impacting surface  18  of pad  14 . 
     In the shown embodiment, head  52  covers only a portion of pad  14 , and head  52  is preferably displaced relative to pad  14  during a cleaning operation so that an entirety of surface  18  is exposed to steam. It is to be understood, however, that the invention encompasses other embodiments (not shown) wherein head  52  is configured to be large enough to have a port  54  which entirely covers surface  18  of pad  14 . Accordingly, the entire surface of pad  18  can be exposed to steam without displacing head  52  relative to the pad. The displacement of head  52  relative to pad  14  can comprise movement of either head  52  (while holding pad  14  stationery); pad  14  (while holding head  52  stationery); or both pad  14  and head  52 . 
     In the shown embodiment, the displacement of head  52  relative to pad  14  preferably also displaces surface  18  relative to stone  24  to cause stone  24  to rub against surface  18  to further recondition the surface. Surface  18  is shown separated from stone  24  by a space for illustrative purposes. It is to be understood, however, that in actual operation surface  18  would preferably contact a conditioning surface  25  of stone  24  during a reconditioning operation. 
     The polishing pad  14  cleaned by methodology of the present invention can comprise any suitable geometry; including round and non-round geometries. Regardless of the geometry, pad  14  is preferably exposed to a pressurized spray of steam during cleaning of the pad. 
     Although the shown embodiment exposes polishing surface  18  to a conditioning stone during the cleaning of surface  18  with steam, it is to be understood that the invention encompasses other embodiments (not shown) wherein conditioning stone  24  is eliminated, and wherein steam is utilized as the sole cleaning source for reconditioning surface  18  of pad  14 . 
     Pad  14  can be rubbed against a surface of conditioning stone  24  either during exposure of various portions of surface  18  to steam, prior to exposure of the surfaces of surface  18  to steam, or after exposure of various portions of surface  18  to steam. Preferably, surface  18  is exposed to conditioning stone  24  prior to exposure to steam to enable the steam to remove particulates from the surface that may have been left behind after the exposure of the surface to the reconditioning stone. In a most preferred embodiment of the present invention, the conditioning of surface  18  comprises reconditioning with both a stone and steam, and the reconditioning with the stone is completed prior to the last exposure of the surface to steam. By having the reconditioning with the stone completed prior to a final exposure to steam, the steam can be utilized to remove particulates that would otherwise be left behind after exposure to the abrasive stone surface. Such particulates can include abraded portions of pad  14 , as well as particulates from the stone. In particular aspects of the invention, pad  14  can be removed from contact with stone  24  prior to a final exposure of the pad  14  to steam. The final exposure to steam can be the only exposure of the pad to steam, or alternatively can be in addition to previous exposures which had occurred prior to, or during, the period that the pad was in contact with the reconditioning stone. 
       FIG. 6  illustrates a front view of a portion of a second embodiment apparatus  70 , and illustrates a second embodiment exemplary shape of a conditioning head. The conditioning head of  FIG. 6  comprises conduits  72 ,  24  and  76  terminating in nozzles  78 ,  80  and  82 , respectively. The nozzles can alternatively be referred to as outlet ports. 
       FIG. 6  illustrates steam exiting from the nozzles (downwardly extending arrows) and impacting surface  18  of pad  14 . The steam exits the nozzles in overlapping fans  84 ,  86  and  88 . The steam from the fans impacts a surface of conditioning pad  14  at angles from about 0° to about 45°, and the total spray angle of each fan can be from about 105° to about 145°. Suitable nozzles can be stainless steel nozzles capable of flow rate from 0.014 gallons per minute to 235 gallons per minute, and capable of spraying a flat fan spray pattern. The nozzles can direct the spray pattern directly at a surface of pad  14 , and can tilt the spray pattern by, for example, about 75° relative to an inlet axis extending into the nozzles. The outlets of the nozzles can be circular, and can have diameters of from about 70 thousandths of an inch to about 110 thousandths of an inch. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.