Abstract:
An assembly for holding a substrate in a chemical mechanical planarization (CMP) apparatus is provided. The assembly includes a holder frame insertable into the chemical mechanical planarization apparatus, the holder frame having an inner wall. The assembly further includes at least one rolling mechanism rotatably mounted in the holder frame such that at least a portion of the rolling mechanism protrudes from the inner wall. The assembly also includes a wafer chuck movably mounted in the holder frame, the wafer chuck having a first side shaped to substantially conform to the inner wall and to be in continuous contact with the at least one rolling mechanism during planarization, and a second side adapted to receive a substrate for planarization. Also provided are an improved assembly for holding a substrate in a CMP apparatus and a method for reducing friction in a gimbaling mechanism of a wafer chuck in a wafer holder in a CMP apparatus during planarization.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a substrate holder for a chemical mechanical planarization (CMP) apparatus. More particularly, the present invention relates to a low friction, gimbaled wafer holder assembly for the planarization of substrates such as semiconductor wafers.  
         BACKGROUND  
         [0002]    In a CMP apparatus, a substrate holder is typically used to hold a semiconductor wafer against a polishing pad during planarization. Certain known wafer holder assemblies use a ball joint so that the wafer holder can gimbal about a point during planarization. One such wafer holder assembly is disclosed in U.S. Pat. No. 5,593,344, hereby incorporated by reference in its entirety.  
           [0003]    In one known ball joint wafer holder assembly, the wafer holder has a support frame that defines a hemispherical recess and a wafer chuck that comprises a hemispherical surface received within the hemispherical recess. Together, these two surfaces form a ball joint. One or both of the hemispherical surface and the hemispherical recess may have a fluid inlet connected to a source of fluid at a higher pressure, a fluid outlet connected to a fluid drain, and a bearing surface over which fluid flows from the source to the drain. The hemispherical surface is supported by the fluid over the bearing surface for rotation with respect to the support about a center of rotation during planarization.  
           [0004]    Wafer holder assemblies employing ball joints may experience a performance degradation due to a friction force from the hemispherical surface of the wafer chuck rubbing against the hemispherical recess of the support frame during planarization. Accordingly, there is a need to develop a substrate holder assembly that experiences less friction than a ball joint-containing assembly during planarization.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the invention, an assembly for holding a substrate in a CMP apparatus is provided. The assembly comprises a holder frame insertable into the CMP apparatus, the holder frame having an inner wall. They assembly also includes at least one rolling mechanism rotatably mounted in the holder frame such that at least a portion of the rolling mechanism protrudes from the inner wall. The assembly further comprises a wafer chuck movably mounted in the holder frame, the wafer chuck having a first side shaped to substantially conform to the inner wall and to be in continuous contact with the at least one rolling mechanism during planarization, and a second side adapted to receive a substrate for planarization.  
           [0006]    In another aspect of the invention, an assembly for holding a substrate in a CMP apparatus comprises a holder frame insertable into the CMP apparatus, the holder frame having an inner wall, the inner wall defining a substantially hemispherical recess. The assembly further includes a plurality of rolling mechanisms rotatably mounted in the holder frame such that at least a portion of each rolling mechanism protrudes from the inner wall. The assembly also includes a wafer chuck movably mounted in the holder frame, the wafer chuck having a first side shaped to substantially hemispherically and the first side being adapted to be in continuous contact each of the plurality of rolling mechanisms during planarization, and a second side adapted to receive a semiconductor wafer for planarization.  
           [0007]    In yet another aspect of the invention, an improved wafer holder in a CMP apparatus is provided. The improvement comprises a gimbaling mechanism in the holder that permits gimbaling of a wafer chuck in a wafer holder frame during planarization substantially without a friction force caused by the wafer chuck rubbing against an inner wall of the wafer holder frame by providing at least one rolling mechanism rotatably mounted with the inner wall and protruding at least partially therefrom, wherein the wafer chuck contacts the rolling mechanism as the wafer chuck gimbals during planarization.  
           [0008]    In still another aspect of the invention, a method of reducing friction in a gimbaling mechanism of a wafer chuck in a wafer holder in a CMP apparatus during planarization is provided. The method comprises (a) providing a wafer holder frame with an inner wall, the inner wall having at least one rolling mechanism rotatably mounted thereon, the rolling mechanism at least partially protruding from the inner wall; (b) movably mounting a wafer chuck in the wafer holder frame, the wafer chuck having a first side adapted to contact the at least one rolling mechanism and a second side adapted to receive a substrate for planarization; and (c) contacting the first side of the wafer chuck with the at least one rolling mechanism to provide gimbaling motion during planarization, thereby reducing the friction force cause by contacting the first side of the wafer chuck with the inner wall of the wafer holder.  
           [0009]    The present invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a cross-sectional view of a preferred substrate holder assembly for use in a CMP apparatus.  
         [0011]    [0011]FIG. 2 is a bottom view of a preferred holder frame usable in a preferred substrate holder assembly.  
         [0012]    [0012]FIG. 3 is a bottom view of another preferred holder frame usable in a preferred substrate holder assembly.  
         [0013]    [0013]FIG. 4 is a bottom view of still another preferred holder frame usable in a preferred substrate holder assembly.  
         [0014]    [0014]FIG. 5 is a bottom view of a preferred holder frame usable in a preferred substrate holder assembly.  
         [0015]    [0015]FIG. 6 is a bottom view of another preferred holder frame usable in a preferred substrate holder assembly.  
         [0016]    [0016]FIG. 7 is a cross-sectional view of a preferred substrate holder assembly for use in a CMP apparatus.  
         [0017]    [0017]FIG. 8 is a cross-sectional view of a rolling mechanism mounted in a preferred holder frame.  
         [0018]    [0018]FIG. 9 is a cross-sectional view of a rolling mechanism mounted in a preferred holder frame. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Referring to FIG. 1, a preferred substrate holding assembly  10  is shown. Substrate holding assembly  10  is adapted for use in a CMP apparatus, including linear polishing systems such as the TERES CMP system, available from Lam Research Corporation of Fremont, Calif.; rotary polishing systems such as the MIRRA CMP system, available from Applied Materials of Santa Clara, Calif.; and other suitable CMP systems known to those who are skilled in the art. The substrate holding assembly can be used to planarize semiconductor wafers W as well as silicon-on-insulator (SOI) surfaces, silicon-on-sapphire (SOS) surfaces and other surfaces that are fabricated on non-conductive carriers.  
         [0020]    Substrate holding assembly  10  comprises a holder frame  17 . Holder frame  17  can comprise any material typically used in semiconductor wafer holding frames in CMP apparatuses. Preferably, the holder frame  17  comprises Stainless Steel of Thermoplastic B19/20 Series. Holder frame  17  has an inner wall  20 . In FIG. 1, the inner wall  20  defines a substantially hemispherical recess. However, the inner wall  20  can have any shape so long as the inner wall  20  substantially conforms to the shape of a first side of a wafer chuck  27 .  
         [0021]    A second side of the wafer chuck  27  is adapted to receive a substrate for planarization. Thus, the second side of the wafer chuck  27  is flat. Preferably, the second side of the wafer chuck  27  is shaped substantially like a disc. Optionally, the second side of wafer chuck  27  may have a carrier film  25 .  
         [0022]    The purpose of the carrier film  25  is to prevent the substrate to be planarized from moving around during planarization. The carrier film  25  can be any standard film used in semiconductor manufacturing and processing that is suitable for contacting the substrate to be planarized. Carrier films are typically made of polymeric material and commercially available from manufacturers of CMP auxiliary equipment, such as RODEL in Newark, Del. Preferably, the carrier film  25  is an oxide. The carrier film  25  may contain tungsten, copper, or aluminum. Carrier films and the process for attaching the carrier films to wafer chucks are described in U.S. Pat. No. 5,769,696, which is hereby incorporated by reference in its entirety.  
         [0023]    Wafer chuck  27  may comprise any material typically used to make wafer chucks in CMP apparatuses. Preferably, the wafer chuck  27  comprises hardened stainless steel, which is commercially available through Rocklin Precision Machining of Rocklin, Calif.  
         [0024]    Wafer chuck  27  may be supported in the holder frame  17  using any method known in the art, preferably a vacuum force. In FIG. 1, the holder frame  17  has fluid inlets  21   a  and  21   c  and fluid outlets  21   b  and  21   d . The fluid inlets  21   a  and  21   c  are connected to a source of fluid at a higher pressure. The fluid outlets  21   b  and  21   d  are connected to a fluid drain at a lower pressure. Fluid flows from the source to the drain creating a bearing surface to minimize any friction force between the wafer chuck  27  and the inner wall  20  during planarization.  
         [0025]    To further minimize any friction force between the first side of the wafer chuck  27  and the inner wall  20 , as the wafer chuck  27  gimbals during planarization of the substrate, the first side of the wafer chuck  27  does not constantly rub a substantial portion of its entire surface against the inner wall  20 . Instead, as the wafer chuck  27  gimbals, the first side of the wafer chuck  27  is in contact with at least one rolling mechanism that is mounted in the inner wall  20  rather than the inner wall  20  itself.  
         [0026]    If there is more than one rolling mechanism mounted in the inner wall  20 , the force of the wafer chuck  27  acting on the rolling mechanisms during planarization is preferably distributed evenly among each of the rolling mechanisms. This way, the first side of the wafer chuck  27  is in constant contact with only a few discrete rolling mechanisms, creating much less friction than if the entire surface of the first side of the wafer chuck  27  were in constant contact with almost the entire surface of the inner wall  20 .  
         [0027]    In FIG. 1, the inner wall  20  has rolling mechanisms  5 ,  7 , and  9  mounted therein such that the rolling mechanisms  5 ,  7 , and  9  protrude at least partially from the inner wall  20 . In one preferred embodiment, rolling mechanisms  5 ,  7 , and  9  are ball bearings that are supported in the inner wall  20 . As shown in FIG. 7, ball bearings  605 ,  607 , and  609  are supported in the inner wall  620  using holes that are formed into the inner wall  620 , the holes being sized and shaped so that the ball bearings  605 ,  607 , and  609  can protrude, at least partially, from the holes, but cannot fall from the holes. Preferred ball bearings are made of hardened stainless steel and are commercially available through King Bearing of San Jose, Calif.  
         [0028]    In another preferred embodiment, rolling mechanisms  5 ,  7 , and  9  are rollers supported in the inner wall  20  that protrude, at least partially, from the inner wall  20 . As shown in FIGS. 8 and 9, rollers  705  and  805  are supported in the inner wall  720  and  820  using arms  706  and  806 , respectively. They protrude at least partially from inner walls  720  and  820 , respectively. The rollers  705  and  805  may rotate freely about their longitudinal axes. Preferred rollers  705  and  805  are commercially available through Bearing Engineers, Inc. of Redwood City, Calif.  
         [0029]    Referring to FIG. 2, the rolling mechanisms in the holder frame  117  are rollers  105 ,  107 , and  107 . The rollers are mounted in inner wall  120 , and protruding at least partially therefrom. Rollers  105 , 107 , and  107  are arranged end-to-end to outline the shape of a triangle. This way, the first side of the wafer chuck is in constant contact with rollers  105 ,  106 , and  107  during planarization, and the wafer chuck is free to gimbal during planarization. Moreover, the force of the wafer chuck acting against the rollers is distributed evenly across each of rollers  105 , 107 , and  109 . Importantly, the first side of the wafer chuck is not in constant contact with inner wall  120  as the wafer chuck gimbals during planarization, which reduces the amount of friction in the substrate holder assembly  110 .  
         [0030]    Referring to FIG. 3, the rolling mechanisms in the holder frame  217  are rollers  205 ,  207 ,  209  and  211 . The rollers are mounted in inner wall  220 , and protruding at least partially therefrom. Rollers  205 ,  207 ,  209  and  211  are arranged end-to-end to outline the shape of a square. This way, the first side of the wafer chuck is in constant contact with rollers  205 ,  207 ,  209  and  211  during planarization, and the wafer chuck is free to gimbal during planarization. Moreover, the force of the wafer chuck acting against the rollers is distributed evenly across each of rollers  205 ,  207 ,  209  and  211 . Importantly, the first side of the wafer chuck is not in constant contact with inner wall  220  as the wafer chuck gimbals during planarization, which reduces the amount of friction in the substrate holder assembly  210 .  
         [0031]    Referring to FIG. 4, the rolling mechanisms in the holder frame  317  are rollers  305 ,  307 ,  309 ,  311 , and  313 . The rollers are mounted in inner wall  220 , and protruding at least partially therefrom. Rollers  305 ,  307 ,  309 ,  311 , and  313  are arranged end-to-end to outline the shape of a pentagon. This way, the first side of the wafer chuck is in constant contact with rollers  305 ,  307 ,  309 ,  311 , and  313  during planarization, and the wafer chuck is free to gimbal during planarization. Moreover, the force of the wafer chuck acting against the rollers is distributed evenly across each of rollers  305 ,  307 ,  309 ,  311 , and  313 . Importantly, the first side of the wafer chuck is not in constant contact with inner wall  320  as the wafer chuck gimbals during planarization, which reduces the amount of friction in the substrate holder assembly  310 .  
         [0032]    Referring to FIG. 5, the rolling mechanism in the holder frame  417  is a single ball bearing  405 . The ball bearing  405  is mounted in the frame so that it protrudes from the inner wall  420 . This way, the first side of the wafer chuck is in constant contact with ball bearing  405  during planarization, and the wafer chuck is free to gimbal during planarization. Importantly, the first side of the wafer chuck is not in constant contact with inner wall  420  as the wafer chuck gimbals during planarization, which reduces the amount of friction in the substrate holder assembly  410 .  
         [0033]    Referring to FIG. 6, the rolling mechanisms in the holder frame  517  are ball bearings  505 ,  507 , and  509 . The ball bearings  505 ,  507 , and  509  are mounted in the frame so that they protrude from the inner wall  520 . This way, the first side of the wafer chuck is in constant contact with ball bearings  505 ,  507 , and  509  during planarization, and the wafer chuck is free to gimbal during planarization. Moreover, the force of the wafer chuck acting against the ball bearings is distributed evenly across each of ball bearings  505 ,  507 , and  509 . Importantly, the first side of the wafer chuck is not in constant contact with inner wall  520  as the wafer chuck gimbals during planarization, which reduces the amount of friction in the substrate holder assembly  510 .  
         [0034]    Of course, it should be understood that a wide range of changes and modifications could be made to the preferred embodiments described above. For example, other fluids including gasses can be used in place of water. If desired the fluid bearings can be formed on the platen rather than the support, and the fluid inlet and outlet may be formed on different components. The hemispherical surfaces described above may depart from a true hemisphere to some extent, for example to provide self-centering forces. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the scope of this invention.