Abstract:
A chemical mechanical polishing article can be a single contiguous layer having a polishing surface, the layer being an elongated substantially rectangular sheet having a width and a length at least four times greater than the width. Forming a polishing article can include depositing a liquid precursor on a moving belt, at least partially curing the liquid precursor while on the moving belt to form a polishing layer, and detaching the polishing layer from the belt.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of and claims priority to U.S. patent application Ser. No. 12/263,908, filed on Nov. 3, 2008, the entire contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to chemical mechanical polishing. 
       BACKGROUND 
       [0003]    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 patterned stop layer, and planarizing the filler layer until the stop layer is exposed. For example, trenches or holes in an insulative layer may be filled with a conductive 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. Planarization can also be used to provide a planar surface for photolithography. 
         [0004]    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 carrier head places the exposed surface of the substrate against a polishing pad and provides a controllable load, i.e., pressure, on the substrate. A polishing liquid, such as an abrasive slurry, is supplied to the surface of the polishing pad. 
         [0005]    In one type of polishing system, the polishing pad is a linear sheet that is incrementally advanced across a platen. 
       SUMMARY 
       [0006]    In one aspect, a chemical mechanical polishing article is a single contiguous layer having a polishing surface, the layer being an elongated substantially rectangular sheet having a width and a length at least four times greater than the width. 
         [0007]    Implementations may include one or more of the following features. The layer may be polyurethane, e.g., a porous polyurethane. The layer may have a thickness between about 30 and 50 mils. The polishing surface may include a plurality of grooves extending partially but not entirely through the polishing pad. The grooves may have a depth between about 15 and 30 mils. At least a portion of the layer may be wound in a roll. The layer may have a length between about twenty and thirty feet, and a width between about two and four feet. 
         [0008]    In another aspect, a chemical mechanical polishing article includes first and second sheet portions, and a window extending the length of and connecting the first and second sheet portions. Each sheet portion consists of a single contiguous layer having a polishing surface, and each sheet portion is an elongated substantially rectangular sheet having a width and a length at least four times greater than the width. 
         [0009]    In another aspect, a chemical mechanical polishing assembly includes a feed roller, a take-up roller, and a polishing sheet having a first end wound around the feed roller and a second end wound around the take-up roller. The polishing sheet consists of single contiguous layer having a polishing surface, the layer being an elongated substantially rectangular sheet having a width and a length at least four times greater than the width. 
         [0010]    In another aspect, a method of forming a polishing article includes depositing a liquid precursor on a moving belt, at least partially curing the liquid precursor while on the moving belt to form a polishing layer, and detaching the polishing layer from the belt. 
         [0011]    Implementations may include one or more of the following features. The liquid precursor may be deposited onto a carrier sheet, e.g., a polyethylene terephthalate polyester film, supported on the belt. The polishing layer may be removed from the carrier sheet. Top and bottom surfaces of the polishing layer may be ground. At least partially curing the liquid precursor may include heating. The polishing sheet may be fully cured after the polishing sheet is detached from the belt. The polishing sheet may be compressed, e.g., passed between pinch rollers. Grooves may be formed in the polishing sheet. Edges of the polishing sheet may be trimmed. 
         [0012]    Advantages may include the following. The polishing layer can be thicker without reducing the length of the sheet wrapped around the feed roller, thus increasing pad life. Optical transmission through a window in the polishing sheet can be improved. 
         [0013]    Other features and advantages will be apparent from the following description, including the drawings and claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a schematic exploded perspective view of a chemical mechanical polishing (CMP) apparatus. 
           [0015]      FIG. 2  is a top plan view of the CMP apparatus of  FIG. 1 . 
           [0016]      FIG. 3A  is a top plan view, cut away, of the first polishing station of the CMP apparatus of  FIG. 1 . 
           [0017]      FIG. 3B  is a schematic exploded perspective view of a rectangular platen and a polishing cartridge. 
           [0018]      FIG. 3C  is a schematic perspective view of a polishing cartridge attached to a rectangular platen. 
           [0019]      FIG. 4  is a schematic perspective view, cut away of a linear polishing sheet. 
           [0020]      FIG. 5A  is a schematic side view in cross-section of an implementation of the polishing sheet. 
           [0021]      FIG. 5B  is a schematic side view in cross-section of another implementation of the polishing sheet. 
           [0022]      FIG. 5C  is a schematic side view in cross-section of another implementation of the polishing sheet. 
           [0023]      FIG. 6  is a schematic side view of a feed roller of the polishing cartridge. 
           [0024]      FIG. 7  is a schematic perspective view, cut away, of another implementation of the polishing sheet. 
           [0025]      FIG. 8  is a schematic side view of a machine to manufacture the polishing sheet of  FIG. 7 . 
           [0026]      FIG. 9  is a schematic top view of an implementation of the polishing sheet. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring to  FIGS. 1 and 2 , one or more substrates  10  will be polished by a chemical mechanical polishing apparatus  20 . A description of a similar polishing apparatus may be found in U.S. Pat. No. 6,244,935, the description of which is incorporated by reference. Polishing apparatus  20  includes a machine base  22  with a table top  23  that supports a series of polishing stations, including a first polishing station  25   a , a second polishing station  25   b , and a final polishing station  25   c , and a transfer station  27 . 
         [0028]    Each polishing station includes a rotatable platen. At least one of the polishing stations, such as first station  25   a , includes a polishing cartridge  102  mounted to a rotatable, rectangular platen  100 . The polishing cartridge  102  includes a linearly advanceable sheet or belt of polishing material. The remaining polishing stations, e.g., second polishing station  25   b  and final polishing station  25   c , may include “standard” circular polishing pads  32  and  34 , respectively, each adhesively attached to a circular platen  30 . Each platen may be connected to a platen drive motor that rotates the platen. 
         [0029]    Each polishing station  25   a ,  25   b  and  25   c  also includes a slurry delivery port, a pad rinse system (which can be a combined slurry/rinse arm  52  that projects over the associated polishing surface) and a pad conditioner apparatus  40 . 
         [0030]    A rotatable multi-head carousel  60  is supported above the polishing stations by a center post  62  and is rotated about a carousel axis  64  by a carousel motor assembly (not shown). Carousel  60  can include four carrier head systems mounted on a carousel support plate  66  at equal angular intervals about carousel axis  64 . Three of the carrier head systems receive and hold substrates, and polish them by pressing them against the polishing sheet of station  25   a  and the polishing pads of stations  25   b  and  25   c . One of the carrier head systems receives a substrate from and delivers a substrate to transfer station  27 . 
         [0031]    Each carrier head system includes a carrier or carrier head  80 . A carrier drive shaft  78  connects a carrier head rotation motor  76  (shown by the removal of one quarter of the carousel cover) to carrier head  80  so that each carrier head can independently rotate about its own axis. In addition, each carrier head  80  independently laterally oscillates in a radial slot  72  formed in carousel support plate  66 . 
         [0032]    Referring to  FIGS. 3A ,  3 B, and  3 C, polishing cartridge  102  is detachably secured to rectangular platen  100  at polishing station  25   a . Polishing cartridge  102  includes a feed roller  130 , a take-up roller  132 , and a generally linear sheet  110  (which can be considered to form a polishing belt or web) of a polishing pad material. The polishing sheet (if completely unwound from the rollers) has a length significantly greater than its width. An unused or “fresh” portion  120  of the polishing sheet is wrapped around feed roller  130 , and a used portion  122  of the polishing sheet is wrapped around take-up roller  132 . A rectangular exposed portion  124  of the polishing sheet that is used to polish substrates extends between the used and unused portions  120 ,  122  over a top surface  140  of rectangular platen  100 . 
         [0033]    The rectangular platen  100  can be rotated (as shown by phantom arrow “A” in  FIG. 3A ) to rotate the exposed portion of the polishing sheet and thereby provide relative motion between the substrate and the polishing sheet during polishing. Between polishing operations, the polishing sheet can be advanced (as shown by phantom arrow “B” in  FIG. 3A ) to expose an unused portion of the polishing sheet. When the polishing material advances, polishing sheet  110  unwraps from feed roller  130 , moves across the top surface of the rectangular platen, and is taken up by take-up roller  132 . 
         [0034]    Referring to  FIG. 4 , polishing sheet  110  includes a polishing layer with a polishing surface  112 , and a leader  160  and a trailer  162  that extend past the polishing layer (thus, polishing surface  112  does not extend to the ends of the polishing sheet). The leader and trailer can be formed of a material that is more flexible, and optionally less compressible, than the polishing layer. The leader  160  and trailer  162  can be attached to the feed and take-up rollers  130  and  132  by tape or a pressure sensitive adhesive on the back of the leader. A peelable liner may be placed over the tape or adhesive and removed prior to attaching the polishing sheet  110  to the rollers. 
         [0035]    The polishing layer can be a porous polyurethane, and the leader and trailer can be a thin tear-resistant material, e.g., polyethylene terephthalate. The polishing layer can be opaque, whereas the leader and trailer can be transparent. The leader  160  and trailer  162  can be printed or embossed with information, such as a part number, material type, lot number, or polishing layer length. 
         [0036]    Grooves can be formed in the polishing surface  112  running across the width and transverse to the direction of travel of the sheet The grooves can be about half the depth of the polishing layer, e.g., 18-20 mils deep. The grooves can have a uniform width and pitch, e.g., about one millimeter wide and spaced apart by about two to three millimeters. Referring to  FIG. 9 , the grooves  128  can stop short of the edge of the polishing layer. Such a groove configuration can improve resistance of the polishing pad to tearing. 
         [0037]    The backing layer  116  can be about five mils thick. The polishing layer can be between about twenty to thirty feet long, e.g., between twenty and twenty five feet long, and can be between twenty and thirty inches wide, e.g., about twenty-eight inches wide. The leader and trailer  160  and  162  have same width as the polishing layer, and can be about six feet long. 
         [0038]    Referring to  FIG. 5A , in one implementation, the polishing sheet includes a backing layer  116  and a polishing layer  114  formed on the backing layer  116 . In this implementation, the backing layer  116  can be a continuous sheet that spans the polishing layer  114 . In the transverse direction (perpendicular to the length and direction of travel of the sheet), the wide edges  164  (along the length of the sheet) of the polishing layer  114  and backing layer  116  can be aligned so that the polishing layer and backing layer  116  have the same width. In contrast, in the longitudinal direction (parallel to the length and direction of travel of the sheet), the backing layer  116  extends past the narrow edges  166  (edges across the width of the sheet) of the polishing layer  114  to provide the leader  160  and trailer  162 . In the region of the leader  160  and trailer  162 , the top surface of the backing layer  116  can be the outermost surface, i.e., there are no other layers on top of the backing layer  116 . As noted above, the leader  160  and trailer  162  can be printed or embossed with information, such as a part number, material type, lot number, or polishing layer length. 
         [0039]    The polishing layer  114  can be a porous polyurethane, and the backing layer  116  can be a thin, flexible, generally incompressible, fluid-impermeable sheet, e.g., polyethylene terephthalate. The backing layer  116  can be transparent. The polyurethane layer an be 35-40 mils thick. The polishing layer  114  can be laid down as a single continuous unbroken layer. Alternatively, the polishing layer  114  can be tiled in adjacent strips, e.g., two to four feet long. 
         [0040]    The polishing layer  114  can be secured to the top surface of the backing layer  116  by an adhesive  170 , e.g., a pressure-sensitive adhesive layer. For example, the polishing layer  114  and backing layer  116  can be fabricated separately and then adhered together. Alternatively, the polishing layer  114  can adhere to the backing layer  116  backing layer without an adhesive. For example, a liquid polishing layer precursor can be dispensed onto the backing layer  116  and cured so as to form a polishing layer  114  adhering to the backing layer  116 . 
         [0041]    Referring to  FIG. 5B , in another implementation, the polishing sheet includes a backing layer  116  and a polishing layer  114  formed on the backing layer  116 , but the leader  160  and trailer  162  are separate pieces  172  bonded to the backing layer  116 . In this implementation, the backing layer  116  can be a continuous sheet that spans and has coextensive edges with the polishing layer  114 . 
         [0042]    The polishing layer  114  can be a porous polyurethane. The backing layer  116  can be either softer or less compressible than the polishing layer and can be transparent or opaque. For example, the backing layer can be a soft subpad such as a urethane-impregnated fibrous mat, or a generally incompressible layer such as polyethylene terephthalate. The separate pieces  172  can be thin, flexible, tear-resistant, generally incompressible, fluid-impermeable sheets, e.g., polyethylene terephthalate. 
         [0043]    As discussed above, the polishing layer  114  can be secured to the backing layer with or without an adhesive. The leader and trailer pieces  172  can be secured to the backing layer  116  with a butt joint and a thin tape  174  on the underside of the polishing sheet. 
         [0044]    Referring to  FIG. 5C , in another implementation, the polishing sheet includes a polishing layer  114  without any backing layer, and the leader  160  and trailer  162  are separate pieces bonded to the polishing layer  114 . The polishing layer  114  can be a porous polyurethane. The tensile strength of the polishing layer  114  can be about 22 MPa (&gt;3000 psi), which should exceed the average stresses applied while vacuum chucking the web onto the platen (˜14 psi) or while advancing the web (˜100 psi). 
         [0045]    The separate pieces  172  can be thin, flexible, tear-resistant, generally incompressible, fluid-impermeable sheets, e.g., polyethylene terephthalate. The leader and trailer pieces  172  can be bonded to the polishing layer  114  by a thin tape  174  on the underside of the polishing sheet. 
         [0046]    In each of the above implementations, since the polishing layer does not extend to the edges of the polishing sheet, the polishing sheet can be fabricated using less polishing layer material, and thus at lower cost in comparison to a polishing sheet having the polishing layer across the entire length. 
         [0047]    Referring to  FIGS. 3B and 6 , feed and take-up rollers  130  and  132  should be slightly longer than the width of polishing sheet  110 . The rollers  130 ,  132  may be plastic or metal cylinders slightly longer than the width of the polishing sheet and about 2″ in diameter. The opposing end faces  134  of feed roller  130  (only the feed roller is shown in  FIG. 6 , but the take-up roller would be constructed similarly) can each include a recess  136  which will engage support and drive mechanisms on the platen. For example, one end face can include keyed slot into which an alignment pin will fit, and the other end face can include a keyed star pattern into which a drive gear will fit. In addition, both ends of each roller can include a circular flange  138  that projects above the surface of the roller to hold the polishing sheet in place and prevents it from sliding off either side of the roller. 
         [0048]    Because the leader and trailer can be more flexible than the polishing layer, they can be easier to manipulate and thus easier to install on the rollers. In addition, because the leader and trailer can be more flexible than the polishing layer, the leader and trailer can be wound more tightly on the roller. This permits the diameter of the roller to be decreased, thus either reducing the volume required by the cartridge or permitting more polishing material to be stored in the cartridge. 
         [0049]    Referring to  FIG. 7 , in another implementation, the polishing sheet is a single layer, specifically a polishing layer  114  with a polishing surface  112  but without any backing layer or carrier film, and without a leader or trailer. The polishing layer  114  is a contiguous and monolithic layer; the entire length of the polishing layer between the feed and take-up roller is an uninterrupted seamless part, e.g., there is no adhesive connection between separate pieces, and the entire polishing layer  114  is generally of uniform composition. In some implementations, the polishing layer is formed without heat-based molding of separate pieces (such molding should generate regions of slightly different consistency where the molding occurs, and the polishing layer  114  can be sufficiently homogeneous to lack such regions). The polishing layer  114  has sufficient cohesive strength and mechanical integrity to avoid tearing under the mechanical forces applied in typical CMP process conditions. The polishing layer  114  can be a porous polyurethane. The length of the polishing layer  114  can be at least six times greater than the width. For example, the polishing layer  114  can be about two to three feet wide, e.g., 2.5 feet wide, and thirty to forty feet long. Although illustrated in  FIG. 7  in a flat state, in use the end portions of the polishing sheet  114  would be wound in a roll around take-up and feed rollers, e.g., as shown in  FIG. 3B . A ration of length to width of the polishing sheet can be at least 4:1, e.g., 12:1. 
         [0050]    The polishing layer  114  can be about 30 to 50 mils thick. Because the backing layer and adhesive that would hold the backing layer to the polishing layer are eliminated, the polishing layer can be made thicker and yet the same length of polishing sheet can be wound around a spindle without increasing the diameter of the polishing magazine. Since the polishing layer  114  is thicker, the number of substrates polished per unit length of the polishing sheet can increase, and thus the pad life can increase. For example, in comparison to a polishing sheet with a 40 mil thick polishing layer, a 5 mil thick backing layer and a 5 mil thick adhesive, a polishing sheet 50 mil thick polishing layer (but no backing layer or adhesive) should have about a 20-33% increase in capacity. Grooves extending partially but not entirely through the polishing layer pad, e.g., having a depth between about 15 and 30 mils, e.g., about half the thickness of the polishing layer, can be formed in the polishing surface  112  of the polishing layer  114 . 
         [0051]    Where a window stripe is formed in the polishing sheet, the two portions on either side of the stripe can each be a single contiguous layer. The sides of the window can be molded to the sides of the polishing layer portions. 
         [0052]    Referring to  FIG. 8 , a method of producing such a monolithic polishing sheet is to deposit a liquid precursor  200  onto a moving belt  210 . The layer of liquid precursor on the belt  210  can be subjected to a first curing process, e.g., the belt and layer can pass through an oven  212  or other heat source, to at least partially cure the precursor into a semi-solid sheet  202 . The semi-solid sheet  202  can then be detached from belt and pass between pinch-rollers  214 ,  216  that compress the sheet to a desired thickness. In addition, protrusions on one of the pinch rollers  216  can imprint grooves into the surface of the semi-solid sheet  202 . Then the sheet  202  can be subjected to a second curing process, e.g., additional heat, such as from the second over  220  to be cured to a final desired rigidity. Edges of the sheet  202  can be trimmed to provide a polishing sheet of uniform width, and if necessary the polishing sheet can be smoothed and/or thinned, e.g., with a grinder or by passing between blades that will skive off top and bottom portions of the sheet, to remove burrs or other defects. A similar process can be used to produce the polishing layer  114  for the implementation of  FIG. 5C . 
         [0053]    In some implementations, a polishing sheet can be formed by casting the polyurethane precursor material on a carrier sheet (e.g., with the carrier sheet on the moving belt or supported on spaced-apart rollers so that the carrier sheet provides a moving belt-like surface), and subjecting the precursor to the first curing step. The carrier sheet can peeled off either before or after the final cure step. Both sides of the polish sheet can then be skived, ground and/or sanded to adjust pad thickness and remove any cured crust layer. 
         [0054]    Grooves can be formed on the cured polishing sheet using a cutting tool such as a knife blade. If the grooves are formed by imprinting with patterned rollers and a subsequent cure step, by selecting an appropriate degree of compression, the grooves could be formed with a smooth or non-porous surface layer in the grooves (in contrast, the polishing surface itself can be porous, and grooves formed in a porous pad with a knife have porous walls and bottoms). If so, waste products or polishing debris can be less likely to remain trapped in the grooves, thus reducing the potential for defects, e.g., scratches. 
         [0055]    Returning to  FIGS. 3A ,  3 B and  3 C, rectangular platen  100  includes a generally planar rectangular top surface  140  bounded by a feed edge  142 , a take-up edge  144 , and two parallel lateral edges  146 . A groove  150  (shown in phantom in  FIGS. 3A and 3C ) is formed in top surface  140 . The groove  150  can be a generally-rectangular pattern that extends along edges  142 ,  144 ,  146  of top surface  140 . Alternatively, vacuum groove  150  can be circular and about 29″ in diameter, and the polish area described by the motion of the head and platen contained within area described by the dashed lines  150  in  FIG. 3A . 
         [0056]    A passage through platen  100  connects groove  150  to a vacuum source. When passage is evacuated, exposed portion  124  of polishing sheet  110  is vacuum-chucked to top surface  140  of platen  100 . This vacuum-chucking helps ensure that lateral forces caused by friction between the substrate and the polishing sheet during polishing do not force the polishing sheet off the platen. Optionally, a central region  148  of top surface  140  can be free from grooves to prevent potential deflection of the polishing sheet into the grooves from interfering with the polishing uniformity. 
         [0057]    An unillustrated compressible backing pad can be placed on the top surface of the platen to cushion the impact of the substrate against the polishing sheet. In addition, platen  100  may include an unillustrated shim plate. Shim plates of differing thickness may be attached to the platen to adjust the vertical position of the top surface of the platen. The compressible backing pad can be attached to the shim plate. 
         [0058]    In some implementations, the rectangular platen  100  also includes four retaining flanges  156  that hold feed and take-up rollers  130  and  132  at feed and take-up edges  142  and  144 , respectively. Each retaining flange  156  includes a projection or detent that can engage the corresponding feature on the end of the rollers  130  or  132 . 
         [0059]    The rollers  130  and  132  can be positioned sufficiently below top surface  140  so that the polishing sheet stays in contact with the feed and take-up edges  142  and  144  of the platen when the entire polishing sheet is wound around either roller. This assists in the creation of a seal between the polishing sheet and the rectangular platen when vacuum is applied to the passage to vacuum-chuck the polishing sheet to the platen. Furthermore, feed edge  142  and take-up edge  144  of the platen are rounded to prevent abrasion of the underside of the polishing sheet as it moves across the platen. 
         [0060]    A transparent strip  118  can be formed along the length of polishing sheet  110 . The transparent strip may be positioned at the center of the sheet, and may be about 0.6 inches wide. With respect to  FIGS. 5A and 5B , transparent strip  118  may be formed by removing the upper layer  114  from this region of the transparent backing layer  116 . With respect to  FIG. 5C , a transparent strip  118  may be formed by molding a window into the polishing layer  114 . The transparent strip  118  can be aligned with an aperture or transparent window  154  in rectangular platen  100  to provide optical monitoring of the substrate surface for end point detection. 
         [0061]    Referring again to  FIGS. 3A ,  3 B and  3 C, in operation, exposed portion  124  of polishing sheet  110  is vacuum-chucked to rectangular platen  100  by applying a vacuum to the passage. A substrate is lowered into contact with polishing sheet  110  by carrier head  80 , and both platen  100  and carrier head  80  rotate to polish the exposed surface of the substrate. After polishing, the substrate is lifted off the polishing pad by the carrier head. The vacuum on passage  152  is removed. The polishing sheet is advanced to expose a fresh segment of the polishing sheet. The polishing sheet is then vacuum-chucked to the rectangular platen, and a new substrate is lowered into contact with the polishing sheet. Thus, between each polishing operation, the polishing sheet may be advanced incrementally. If the polishing station includes a cleaning apparatus the polishing sheet may be washed between each polishing operation. 
         [0062]    The amount that the sheet may be advanced will depend on the desired polishing uniformity and the properties of the polishing sheet, but should be on the order of 0.05 to 1.0 inches, e.g., 0.4 inch, per polishing operation. Assuming that the exposed portion  124  of polishing sheet is 20 inches long and the polishing sheet advances 0.4 inches after each polishing operation, the entire exposed portion of the polishing sheet will be replaced after about fifty polishing operations. 
         [0063]    In another embodiment, a polishing sheet can be fabricated with a polishing layer disposed on a carrier layer, e.g., a polyethylene terephthalate polyester film, e.g. a Mylar sheet. In some implementations, the polishing sheet can be formed by casting the polyurethane precursor material on a carrier layer as discussed above (e.g., with the carrier layer on the moving belt). However, rather than removing the carrier layer, the polishing layer remains on the carrier layer to form the final polishing sheet. In this case, grinding and surface finishing operations to adjust the polishing layer thickness or roughness would take place only on the top surface. In some implementations, the initial carrier layer is removed, grinding and surface finishing operations are performed, and the polishing layer can then be attached to a new carrier layer for the final polishing sheet 
         [0064]    The invention is not limited to the embodiment depicted and described. Rather, the scope of the invention is defined by the appended claims.