Low density polishing pad

Abstract

Low density polishing pads and methods of fabricating low density polishing pads are described. In an example, a polishing pad for polishing a substrate includes a polishing body having a density of less than 0.5 g/cc and composed of a thermoset polyurethane material. A plurality of closed cell pores is dispersed in the thermoset polyurethane material.

What is claimed is: 
     
         1 . A polishing pad for polishing a substrate, the polishing pad comprising:
 a polishing body having a density of less than 0.5 g/cc and comprising:
 a thermoset polyurethane material; and 
 a plurality of closed cell pores dispersed in the thermoset polyurethane material. 
   
     
     
         2 . The polishing pad of  claim 1 , wherein the polishing body is a homogeneous polishing body. 
     
     
         3 . The polishing pad of  claim 1 , wherein each of the plurality of closed cell pores comprises a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         4 . The polishing pad of  claim 3 , wherein the physical shells of a first portion of the plurality of closed cell pores comprise a material different than the physical shells of a second portion of the plurality of closed cell pores. 
     
     
         5 . The polishing pad of  claim 1 , wherein each of only a portion of the plurality of closed cell pores comprises a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         6 . The polishing pad of  claim 1 , wherein each of the plurality of closed cell pores does not comprise a physical shell of a material different from the thermoset polyurethane material. 
     
     
         7 . The polishing pad of  claim 1 , wherein the plurality of closed cell pores provides a total pore volume in the thermoset polyurethane material approximately in the range of 55-80% of the total volume of the thermoset polyurethane material. 
     
     
         8 . The polishing pad of  claim 1 , wherein the polishing body further comprises:
 a first, grooved surface; and   a second, flat, surface opposite the first surface.   
     
     
         9 . The polishing pad of  claim 1 , wherein each of the plurality of closed cell pores is essentially spherical. 
     
     
         10 . The polishing pad of  claim 1 , wherein the plurality of closed cell pores has a bi-modal distribution of diameters having a first diameter mode with a first peak of size distribution and a second diameter mode with a second, different, peak of size distribution. 
     
     
         11 . The polishing pad of  claim 10 , wherein the closed cell pores of the first diameter mode each comprise a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         12 . The polishing pad of  claim 11 , wherein the closed cell pores of the second diameter mode each comprise a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         13 . The polishing pad of  claim 12 , the physical shell of each of the closed cell pores of the second diameter mode comprises a material different from the material of the physical shells of the closed cell pores of the first diameter mode. 
     
     
         14 . The polishing pad of  claim 10 , wherein the first peak of size distribution of the first diameter mode has a diameter approximately in the range of 10-50 microns, and wherein the second peak of size distribution of the second diameter mode has a diameter approximately in the range of 10-150 microns. 
     
     
         15 . The polishing pad of  claim 10 , wherein the first diameter mode overlaps with the second diameter mode. 
     
     
         16 . The polishing pad of  claim 10 , wherein the first diameter mode has essentially no overlap with the second diameter mode. 
     
     
         17 . The polishing pad of  claim 10 , wherein a total population in count number of the first diameter mode is not equal to a total population in count number of the second diameter mode. 
     
     
         18 . The polishing pad of  claim 10 , wherein a total population in count number of the first diameter mode is approximately equal to a total population in count number of the second diameter mode. 
     
     
         19 . The polishing pad of  claim 10 , wherein the bi-modal distribution of diameters is distributed essentially evenly throughout the thermoset polyurethane material. 
     
     
         20 . The polishing pad of  claim 1 , wherein the polishing body is a molded polishing body. 
     
     
         21 . The polishing pad of  claim 1 , wherein the polishing body further comprises:
 an opacifying filler distributed approximately evenly throughout the polishing body.   
     
     
         22 . The polishing pad of  claim 1 , further comprising:
 a foundation layer disposed on a back surface of the polishing body.   
     
     
         23 . The polishing pad of  claim 1 , further comprising:
 a detection region disposed in a back surface of the polishing body.   
     
     
         24 . The polishing pad of  claim 1 , further comprising:
 a sub pad disposed on a back surface of the polishing body.   
     
     
         25 . The polishing pad of  claim 1 , further comprising:
 a local area transparency (LAT) region disposed in, and covalently bonded with, the polishing body.   
     
     
         26 . A polishing pad for polishing a substrate, the polishing pad comprising:
 a polishing body having a density of less than approximately 0.6 g/cc and comprising:
 a thermoset polyurethane material; and 
 a plurality of closed cell pores dispersed in the thermoset polyurethane material, the plurality of closed cell pores having a bi-modal distribution of diameters having a first diameter mode with a first peak of size distribution and a second diameter mode with a second, different, peak of size distribution. 
   
     
     
         27 . The polishing pad of  claim 26 , wherein the polishing body is a homogeneous polishing body. 
     
     
         28 . The polishing pad of  claim 26 , wherein the closed cell pores of the first diameter mode each comprise a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         29 . The polishing pad of  claim 28 , wherein the closed cell pores of the second diameter mode each comprise a physical shell comprising a material different from the thermoset polyurethane material. 
     
     
         30 . The polishing pad of  claim 29 , the physical shell of each of the closed cell pores of the second diameter mode comprises a material different from the material of the physical shells of the closed cell pores of the first diameter mode. 
     
     
         31 . The polishing pad of  claim 26 , wherein the first peak of size distribution of the first diameter mode has a diameter approximately in the range of 10-50 microns, and wherein the second peak of size distribution of the second diameter mode has a diameter approximately in the range of 10-150 microns. 
     
     
         32 . The polishing pad of  claim 26 , wherein the first diameter mode overlaps with the second diameter mode. 
     
     
         33 . The polishing pad of  claim 26 , wherein the first diameter mode has essentially no overlap with the second diameter mode. 
     
     
         34 . The polishing pad of  claim 26 , wherein a total population in count number of the first diameter mode is not equal to a total population in count number of the second diameter mode. 
     
     
         35 . The polishing pad of  claim 26 , wherein a total population in count number of the first diameter mode is approximately equal to a total population in count number of the second diameter mode. 
     
     
         36 . The polishing pad of  claim 26 , wherein the bi-modal distribution of diameters is distributed essentially evenly throughout the thermoset polyurethane material. 
     
     
         37 . A method of fabricating a polishing pad, the method comprising:
 mixing a pre-polymer and a chain extender or cross-linker with a plurality of microelements to form a mixture, each of the plurality of microelements having an initial size; and   heating, in a formation mold, the mixture to provide a molded polishing body comprising a thermoset polyurethane material and a plurality of closed cell pores dispersed in the thermoset polyurethane material, the plurality of closed cell pores formed by expanding each of the plurality of microelements to a final, larger, size during the heating.   
     
     
         38 . The method of  claim 37 , wherein expanding each of the plurality of microelements to the final size comprises increasing a volume of each of the plurality of microelements by a factor approximately in the range of 3-1000. 
     
     
         39 . The method of  claim 37 , wherein expanding each of the plurality of microelements to the final size comprises providing a final diameter of each of the plurality of microelements approximately in the range of 10-200 microns. 
     
     
         40 . The method of  claim 37 , wherein expanding each of the plurality of microelements to the final size comprises reducing a density of each of the plurality of microelements by a factor approximately in the range of 3-1000. 
     
     
         41 . The method of  claim 37 , wherein expanding each of the plurality of microelements to the final size comprises forming an essentially spherical shape for each of the plurality of microelements of the final size. 
     
     
         42 . The method of  claim 37 , wherein mixing the pre-polymer and the chain extender or cross-linker with the plurality of microelements further comprises mixing with a second plurality of microelements to form the mixture, each of the second plurality of microelements having a size. 
     
     
         43 . The method of  claim 42 , wherein the heating is performed at a temperature sufficiently low such that the size of each of the second plurality of microelements is essentially the same before and after the heating. 
     
     
         44 . The method of  claim 43 , wherein the heating is performed at a temperature of approximately 100 degrees Celsius or less, and wherein the second plurality of microelements has an expansion threshold of greater than approximately 130 degrees Celsius. 
     
     
         45 . The method of  claim 42 , wherein the second plurality of microelements has an expansion threshold greater than an expansion threshold of the plurality of microelements. 
     
     
         46 . The method of  claim 45 , wherein the expansion threshold of the second plurality of microelements is greater than approximately 120 degrees Celsius, and the expansion threshold of the plurality of microelements is less than approximately 110 degrees Celsius. 
     
     
         47 . The method of  claim 42 , wherein a mixture of the pre-polymer, the chain extender or cross-linker, and the second plurality of microelements has a viscosity, and the mixture of the pre-polymer, the chain extender or cross-linker, the plurality of microelements having the initial size, and the second plurality of microelements essentially has the viscosity. 
     
     
         48 . The method of  claim 47 , wherein the viscosity is a predetermined viscosity, and a relative amount of the second plurality of microelements in the mixture is selected based on the predetermined viscosity. 
     
     
         49 . The method of  claim 47 , wherein the plurality of microelements has little to no effect on the viscosity of the mixture. 
     
     
         50 . The method of  claim 42 , wherein heating provides the molded polishing body comprising the thermoset polyurethane material, the plurality of closed cell pores dispersed in the thermoset polyurethane material and formed by expanding each of the plurality of microelements to the final size having a first diameter mode with a first peak of size distribution, and a second plurality of closed cell pores dispersed in the thermoset polyurethane material and formed from the second plurality of microelements having a second diameter mode with a second, different, peak of size distribution. 
     
     
         51 . The method of  claim 50 , wherein the plurality of closed cell pores and the second plurality of closed cell pores provides a total pore volume in the thermoset polyurethane material approximately in the range of 55-80% of the total volume of the thermoset polyurethane material. 
     
     
         52 . The method of  claim 37 , wherein heating the mixture to provide the molded polishing body comprises forming the polishing body having a density of less than 0.5 g/cc. 
     
     
         53 . The method of  claim 52 , wherein the mixture has a density of greater than 0.5 g/cc prior to the heating. 
     
     
         54 . The method of  claim 37 , wherein the mixing further comprises injecting a gas into the pre-polymer and the chain extender or cross-linker, or into a product formed there from. 
     
     
         55 . The method of  claim 37 , wherein the pre-polymer is an isocyanate and the mixing further comprises adding water to the pre-polymer. 
     
     
         56 . The method of  claim 37 , wherein mixing the pre-polymer and the chain extender or cross-linker comprises mixing an isocyanate and an aromatic diamine compound, respectively. 
     
     
         57 . The method of  claim 37 , wherein the mixing further comprises adding an opacifying filler to the pre-polymer and the chain extender or cross-linker to provide an opaque molded polishing body. 
     
     
         58 . The method of  claim 37 , wherein heating the mixture comprises first partially curing in the formation mold and then further curing in an oven. 
     
     
         59 . The method of  claim 37 , wherein heating in the formation mold comprises forming a groove pattern in a polishing surface of the molded polishing body. 
     
     
         60 . The method of  claim 37 , wherein each of the plurality of microelements having the initial size comprises a physical shell, and wherein each of the plurality of microelements having the final size comprises an expanded physical shell. 
     
     
         61 . The method of  claim 37 , wherein each of the plurality of microelements having the initial size is a liquid droplet, and wherein each of the plurality of microelements having the final size is a gas bubble.