JP2016525459A - Low density polishing pad - Google Patents

Abstract

Embodiments of the present invention are in the field of chemical mechanical polishing (CMP), particularly in the field of low density polishing pads and methods of manufacturing low density polishing pads. A low density polishing pad and a method of manufacturing the low density polishing pad are described. In one embodiment, a polishing pad for polishing a substrate includes a polishing body (222) having a density less than 0.5 g / cc and composed of a thermoset polyurethane material (220). A plurality of closed cell holes (214, 218) are dispersed within the thermosetting polyurethane material (220).

Description

  Embodiments of the present invention are in the field of chemical mechanical polishing (CMP), particularly in the field of low density polishing pads and methods of manufacturing low density polishing pads.

  Chemical mechanical planarization or chemical mechanical polishing, commonly abbreviated as CMP, is a technique used in semiconductor manufacturing to planarize a semiconductor wafer or other substrate.

  The process requires the use of abrasive and corrosive chemical slurries (generally colloids), typically with polishing pads and retaining rings that are larger in diameter than the wafer. The polishing pad and wafer are pressed together by the dynamic polishing head and held by a plastic retaining ring. The dynamic polishing head rotates during polishing. This approach tends to help remove material, make any irregular topography uniform, and make the wafer flat or flat. It may be necessary to condition the wafer for the formation of additional circuit elements. For example, it may be required to fit the entire surface within the depth of field of the photolithography system or to selectively remove material based on its location. Typical depth of field requirements are at the angstrom level for the latest sub-50 nanometer technology nodes.

  The material removal process is not just that of abrasive scrubbing like sanding wood. The chemicals in the slurry also react with and / or weaken the material being removed. The abrasive accelerates this weakening process, and the polishing pad helps wipe off the reacted material from the surface. In addition to advances in slurry technology, polishing pads play an important role in increasingly complex CMP operations.

  However, further improvements are required for the evolution of CMP pad technology.

  Embodiments of the present invention include a low density polishing pad and a method of manufacturing a low density polishing pad.

  In certain embodiments, a polishing pad for polishing a substrate includes a polishing body having a density of less than 0.5 g / cc and made of a thermoset polyurethane material. A plurality of closed cell pores are dispersed within the thermosetting polyurethane material.

  In another embodiment, a polishing pad for polishing a substrate includes a polishing body having a density less than approximately 0.6 g / cc and composed of a thermoset polyurethane material. A plurality of closed cell pores are dispersed within the thermosetting polyurethane material. The plurality of closed cell pores have a bimodal distribution of diameters with a first diameter mode having a first peak in the size distribution and a second diameter mode having a second different peak in the size distribution.

  In yet another embodiment, a method of manufacturing a polishing pad includes mixing a prepolymer and a chain extender or crosslinker with a plurality of microelements to form a mixture. Each of the plurality of microelements has an initial size. The method also heats the mixture in a mold to provide a molded abrasive body comprised of a thermoset polyurethane material and a plurality of closed cell pores dispersed within the thermoset polyurethane material. Including the steps of: The plurality of closed cell holes are formed by expanding each of the plurality of microelements to a final larger size during the heating step.

FIG. 1A is a top view of a POLITEX polishing pad according to the prior art. FIG. 1B is a cross-sectional photograph of a POLITEX polishing pad according to the prior art. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the invention. FIG. 3 illustrates cross-sectional photographs at 100 × and 300 × magnification of a low density polishing pad including closed cell pores all based on porogen filler, according to an embodiment of the present invention. FIG. 4 illustrates cross-sectional photographs at 100 × and 300 × magnification of a low density polishing pad, including closed cell holes, partly based on porogen filler and partly based on gas bubbles, according to an embodiment of the present invention. To do. FIG. 5A illustrates a plot of power as a function of pore diameter for a wide unimodal distribution of pore diameters within a low density polishing pad, according to an embodiment of the present invention. FIG. 5B illustrates a plot of power as a function of pore diameter for a narrow unimodal distribution of pore diameters within a low density polishing pad, according to an embodiment of the present invention. FIG. 6A illustrates a cross-section of a low density polishing pad having an approximately 1: 1 bimodal distribution of closed cell holes, according to an embodiment of the present invention. FIG. 6B illustrates a plot of power as a function of pore diameter for a narrow distribution of pore diameters within the polishing pad of FIG. 6A, according to an embodiment of the present invention. FIG. 6C illustrates a plot of power as a function of pore diameter for a wide distribution of pore diameters within the polishing pad of FIG. 6A, according to an embodiment of the present invention. FIG. 7 illustrates an isometric side view of a polishing apparatus compatible with a low density polishing pad, according to an embodiment of the present invention.

  Low density polishing pads and methods of making low density polishing pads are described herein. In the following description, numerous specific details are set forth, such as specific polishing pad designs and configurations, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other cases, well-known processing techniques, such as details regarding the combination of a slurry and a polishing pad to perform chemical mechanical planarization (CMP) of a semiconductor substrate, do not unnecessarily obscure embodiments of the present invention. Not listed. Furthermore, it should be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

  One or more embodiments described herein may have a low density below about 0.6 grams / cubic centimeter (g / cc), more specifically, a low density below about 0.5 g / cc. The present invention is directed to the manufacture of a polishing pad having The resulting pad may be based on a polyurethane material having closed cell pore pores that provide low density. The low density pad can be used as a polishing pad designed for special chemical mechanical polishing (CMP) applications such as buff polishing pads or liner / barrier removal, for example. The polishing pads described herein may be manufactured to have a density in the range of 0.3 g / cc to 0.5 g / cc, for example, as low as approximately 0.357 g / cc, in some embodiments. . In certain embodiments, the low density pad has a density as low as 0.2 g / cc.

  In context, typical CMP pads have a density of about 0.7 to 0.8 g / cc, generally at least above 0.5 g / cc. Traditionally, typical CMP buff pads have a “pomeric” design using large bubbles open on the surface. In the case of a POLITEX polishing pad, etc., a composite polyurethane skin is included on the support. Traditionally, buff pads are made of open cell pores (eg, fiber pads and “breathable” pads) and are very soft and low density. Such pads typically have two basic problems with CMP: short life and unstable performance compared to conventional closed cell polyurethane (but high density) CMP pads. Associated with FIGS. 1A and 1B are photographs of a prior art POITEX polishing pad as viewed from above and in cross-section, respectively. Referring to FIG. 1A, a POLITEX polishing pad portion 100A is shown as a scanning electron microscope (SEM) image magnified 300 times. Referring to FIG. 1B, a POLYTEX polishing pad portion 100B is shown as a scanning electron microscope (SEM) image magnified 100 times. Referring to both FIGS. 1A and 1B, the open cell structure of the prior art pad can be easily seen.

  More generally, one of the basic challenges is to create a closed cell polyurethane pad with high porosity and low density. Our own research on the production of low density polyurethane pads by molding or casting process is based on the added porogen pad formulation with an increased amount of porogen to ultimately provide closed cell pores in the pad material It has proven difficult to simply add it into the mixture. In particular, adding more porogen than a typical pad formulation can increase the viscosity of the formulation to a level where the casting or molding process becomes unmanageable. It can be particularly difficult when including pre-expanded porogens or porogens that maintain essentially the same volume throughout the molding or casting process. According to embodiments of the present invention, unexpanded porogens or porogens that increase in volume throughout the molding or casting process are included in the pad formulation for ultimate production. However, in one such embodiment, if all the final closed cell pores are generated from unexpanded porogen, the viscosity of the formulation can be too low in terms of ease of handling of casting or molding. Thus, in certain embodiments, in addition to forming a formulation comprising unexpanded porogen or porogen that increases in volume throughout the molding or casting process, essentially the same volume throughout the pre-expanded porogen or molding or casting process. A porogen that maintains the viscosity is also included to allow for adjustment of the viscosity of the pad formulation.

Thus, in certain embodiments, an unexpanded or underexpanded porogen filler (both referred to as UPF) that expands at a temperature above room temperature may be produced during manufacturing by casting or molding. Used to create pores in the polishing pad. In one such embodiment, a large amount of UPF is included in the polyurethane-forming mixture. The UPF expands during the pad casting process, creating a low density pad with closed cell holes. The above approach of creating a polishing pad may have advantages over other techniques that have been used to form low density pads with open cells. For example, creating the final pad pores based solely on gas injection or entrainment may require specialized equipment and may be associated with difficult control of the final pad density and control of the final pore size and distribution. . As another example, creating the final pad pores based solely on in situ gas evolution, such as, for example, the water reaction of an isocyanate moiety (NCO) that creates CO ₂ bubbles, can control the pore size distribution. Difficulties can accompany.

In one aspect of the invention, the low density polishing pad can be manufactured by a molding process. For example, FIGS. 2A-2G illustrate a cross-section of operations used to manufacture a polishing pad, according to an embodiment of the present invention.

  Referring to FIG. 2A, a mold 200 is provided. Referring to FIG. 2B, prepolymer 202 and curing agent 204 (eg, chain extender or crosslinker) are mixed with a plurality of microelements to form a mixture. In some embodiments, the plurality of microelements are a plurality of porogens 206, such as solid or hollow microspheres. In another embodiment, the plurality of microelements are a plurality of gas bubbles and / or droplets 208. In another embodiment, the plurality of microelements is a combination of a plurality of porogens 206 and a plurality of gas bubbles or droplets 208 or both.

  Referring to FIG. 2C, the resulting mixture 210 from FIG. 2B is shown at the bottom of the mold 200. Mixture 210 includes a first plurality of microelements 212, each of the first plurality of microelements having an initial size. As described in detail below, a second plurality of microelements 214 may also be included in the mixture 210.

  Referring to FIG. 2D, the lid 216 of the mold 200 is brought together with the bottom of the mold 200 and the mixture 210 takes the shape of the mold 200. In certain embodiments, the mold 200 is degassed during or between the lid 216 and the bottom of the mold 200 so that no cavities or voids are created in the mold 210. It should be understood that the embodiments described herein that describe the mold lid as being lowered require only that the lid and the bottom of the mold be brought together. That is, in some embodiments, the bottom of the mold is raised toward the lid of the mold, while in other embodiments, the lid of the mold is at the same time as the bottom is lifted toward the lid. , Lowered toward the bottom of the mold.

  Referring to FIG. 2E, the mixture 210 is heated in the mold 200. Each of the plurality of microelements 212 is expanded to a final larger size 218 during heating. In addition, referring to FIG. 2F, heating cures mixture 210 to provide a partially or fully cured pad material 220 that surrounds microelement 218 and, if present, microelement 214. Used to make In one such embodiment, curing forms a crosslinked matrix based on the prepolymer and curing agent materials.

  Referring to FIGS. 2E and 2F together, it should be understood that the order of the steps of expanding the microelement 212 to the final larger size 218 and curing the mixture 210 is not necessarily the order shown. In another embodiment, during the heating step, the curing step of the mixture 210 occurs prior to the expansion step of the microelement 212 to the final larger size 218. In another embodiment, during the heating step, the curing step of the mixture 210 occurs simultaneously with the expansion step of the microelement 212 to the final larger size 218. In yet another embodiment, two separate heating operations are each performed to cure the mixture 210 and expand the microelement 212 to the final larger size 218.

  Referring to FIG. 2G, in some embodiments, the process described above is used to provide a low density polishing pad 220. The low density polishing pad 222 is composed of a cured material 220 and includes expanded microelements 218 along with additional microelements 214 in certain embodiments. In certain embodiments, the low density polishing pad 222 is composed of a thermoset polyurethane material and the expanded microelements 218 provide a plurality of closed cell pores dispersed within the thermoset polyurethane material. Referring again to FIG. 2G, the lower part of the figure is a top plan view taken along the a-a ′ axis. As seen in this plan view, in one embodiment, the low density polishing pad 222 has a polishing surface 228 having a groove pattern therein. In one particular embodiment as shown, the groove pattern includes radial grooves 226 and concentric grooves 228.

  Referring again to FIGS. 2D and 2E, in one embodiment, each of the plurality of microelements 212 is expanded to a final size 218 by increasing the volume of each of the plurality of microelements in a range of approximately 3 to 1000 times. The In certain embodiments, each of the plurality of microelements 212 is expanded to a final size 214 such that the final diameter of each of the plurality of microelements 218 is approximately 10-200 microns. In some embodiments, each of the plurality of microelements 212 is expanded to a final size 218 by reducing the density of each of the plurality of microelements 212 in a range of approximately 3 to 1000 times. In certain embodiments, each of the plurality of microelements 212 is expanded to a final size 218 by forming each of the plurality of final size microelements 218 in an essentially spherical shape.

In certain embodiments, the plurality of microelements 212 are additive porogens, gas bubbles, or liquid bubbles that subsequently expand to form closed cell pores in the finished polishing pad material within the pad material formulation. In some such embodiments, the plurality of closed cell pores are a plurality of larger porogens formed by expanding a corresponding smaller porogen. For example, the term “porogen” can be used to indicate a micro or nanoscale spherical or nearly spherical particle having a “hollow” center. The hollow center is not filled with solid material, but rather includes a gaseous or liquid core. In some embodiments, the plurality of closed cell pores begins as an unexpanded gas-filled or liquid-filled EXPANCEL ^™ distributed throughout the mixture. For example, an unexpanded gas-filled or liquid-filled EXPANCEL ^™ is in an expanded state during and / or during the molding of a polishing pad from the mixture by a molding process. In a specific embodiment, EXPANCEL ^™ is filled with pentane. In some embodiments, each of the plurality of closed cell pores has a diameter in the range of approximately 10-100 microns in its expanded state, eg, the final product. Thus, in some embodiments, each of the plurality of microelements having an initial size includes a physical shell, and each of the plurality of microelements having a final size includes an expanded physical shell. In another embodiment, each of the plurality of microelements 212 having an initial size is a droplet, and each of the plurality of microelements 218 having a final size is a gas bubble. In yet another embodiment, the mixing step of forming the mixture 210 to form a plurality of microelements 218 having a final size involves gassing the prepolymer and the chain extender or crosslinker, or the product formed therefrom. Injecting further. In certain such embodiments, the prepolymer is an isocyanate and the mixing step further includes adding water to the prepolymer. In any case, in some embodiments, the plurality of closed cell pores include individual pores. It is in contrast to open cell holes that can be connected to each other through a tunnel, such as in the case of pores in a typical sponge.

  Referring again to FIGS. 2C-2E, in some embodiments, the step of mixing the prepolymer 202 and the chain extender or crosslinker 204 with the plurality of microelements 212 includes forming a second plurality of microparticles to form the mixture 210. The method further includes mixing with element 214. Each of the second plurality of microelements 214 has a size. In certain such embodiments, the heating step described in connection with FIG. 2E may be such that the size of each of the second plurality of microelements 214 is essentially before and after heating, as depicted in FIG. 2E. Performed at a sufficiently low temperature to be the same. In certain such embodiments, the heating step is performed at a temperature of approximately 100 degrees Celsius or less, and the second plurality of microelements 214 has an expansion threshold greater than approximately 130 degrees Celsius. . In another embodiment, the second plurality of microelements 214 has an expansion limit that exceeds the expansion limit of the plurality of microelements 212. In certain such embodiments, the expansion limit of the second plurality of microelements 214 is approximately greater than 120 degrees Celsius, and the expansion limit of the plurality of microelements 212 is approximately less than 110 degrees Celsius. Thus, in certain embodiments, during the heating step, microelement 212 expands to provide expanded microelement 218 while microelement 214 remains essentially unchanged.

In certain embodiments, each of the second plurality of microelements 214 may be comprised of a pre-expanded, gas-filled EXPANCEL ^™ distributed throughout the polishing pad (eg, as a load element therein). . That is, any significant swelling that can occur in the microelements 214 occurs prior to inclusion in the polishing pad formation, for example, prior to inclusion in the mixture 210. In a specific embodiment, the pre-expanded EXPANCEL ^™ is filled with pentane. In certain embodiments, the microelement 214 provides a plurality of closed cell pores (represented as 214 with no or near changes during the molding process) having a diameter in the range of approximately 10-100 microns. In certain embodiments, the resulting plurality of closed cell pores include individual pores. It is in contrast to open cell holes that can be connected to each other through a tunnel, such as in the case of pores in a typical sponge.

  As mentioned above, increasing the porosity by adding more porogen than a typical pad formulation can increase the viscosity of the formulation to a level where the casting or molding process becomes unmanageable. It can be particularly difficult when including pre-expanded porogens or porogens that maintain essentially the same volume throughout the molding or casting process. On the other hand, if all the final closed cell pores are generated from unexpanded porogen, the viscosity of the formulation can be too low in terms of handling ease of casting or molding. To address such situations, according to an embodiment of the present invention, conceptually, the mixture of prepolymer 202, chain extender or crosslinker 204, and second plurality of microelements 214 is viscous. On the other hand, the prepolymer 202, the chain extender or crosslinker 204, the plurality of microelements 212 having an initial size, and the mixture of the second plurality of microelements 214 have essentially the same viscosity. That is, the inclusion of a plurality of microelements 212 having an initial (smaller) size has little or no effect on the viscosity of the mixture. In some embodiments, the viscosity described for optimal molding conditions can thus be selected based on the inclusion of a second plurality of microelements having a size that remains essentially constant throughout the molding process. In some such embodiments, therefore, the viscosity is a predetermined viscosity, and the relative amount of the second plurality of microelements 214 in the mixture 210 is selected based on the predetermined viscosity. In some embodiments, the plurality of microelements 212 has no or near effect on the viscosity of the mixture 210.

  Referring again to FIG. 2E, in one embodiment, when two different microelements are included, each of the microelements 218 having an expanded final size is expanded through a heating process, as depicted. It has substantially the same shape and size as each of the plurality of microelements 214 that are not. However, it should be understood that each of the plurality of microelements 218 having an expanded final size need not have the same shape and / or size as each of the plurality of microelements 214. In one embodiment, as will be described in detail below in connection with FIGS. 6A-6C, the resulting molded pad 222 abrasive body has a first peak with a first peak in size distribution as a closed cell hole. It includes a plurality of expanded microelements 218 having a diameter mode. Included together as a closed cell hole is a second plurality of microelements 214 having a second diameter mode with a second different peak in size distribution. In some such embodiments, the plurality of closed cell pores of microelement 218 and the second plurality of closed cell holes of microelement 214 are approximately 55 of the total volume of thermoset polyurethane material of low density polishing pad 222. Provide a total pore volume in the thermoset polyurethane material in the range of -80%.

  Referring again to FIGS. 2D-2G, in one embodiment, heating mixture 210 to provide shaped abrasive body 222 forms abrasive body 222 having a density of less than 0.5 g / cc. including. However, in certain such embodiments, mixture 210 has a density greater than 0.5 g / cc prior to the heating step. In some embodiments, prepolymer 202 is an isocyanate, chain extender or crosslinker 204 is an aromatic diamine compound, and polishing pad 222 is comprised of a thermosetting polyurethane material 220. In certain such embodiments, the step of forming the mixture 210 includes adding an opacifying filler to the prepolymer 202 and the chain extender or crosslinker 204 to provide a final opaque shaped abrasive body 222. The method further includes the step of adding. In certain such embodiments, the opacifying filler is, but not limited to, boron nitride, cerium fluoride, graphite, graphite fluoride, molybdenum sulfide, niobium sulfide, talc, tantalum sulfide, tungsten disulfide, or Teflon. (Registered trademark) and other materials. In some embodiments, as briefly mentioned above, the mixture 210 is only partially cured in the mold 200, and in some embodiments is further cured in an oven after removal from the mold 220. .

  In some embodiments, the polishing pad precursor mixture 210 is used to form a shaped homogeneous abrasive 222 composed of a thermoset, closed cell polyurethane material. In some such embodiments, the polishing pad precursor mixture 210 is used to ultimately form a hard pad and only a single type of curing agent 204 is used. In another embodiment, the polishing pad precursor mixture 210 is used to ultimately form a soft pad, using a combination of primary and secondary curing agents (together to provide 210). For example, in a specific embodiment, the prepolymer 202 includes a polyurethane precursor, the primary curing agent includes an aromatic diamine compound, and the secondary curing agent includes an ether binder. In certain embodiments, the polyurethane precursor is an isocyanate, the primary curing agent is an aromatic diamine, and the secondary curing agent includes, but is not limited to, polytetramethylene glycol, amine functionalized glycol, or amino functional Hardener such as modified polyoxypropylene. In some embodiments, the prepolymer 202, the primary curing agent, and the secondary curing agent (combined 204) are in an approximate molar ratio of 106 parts prepolymer, 85 parts primary curing agent, and 15 parts. Provide a stoichiometric composition with a secondary curing agent, ie, a prepolymer: curing agent ratio of approximately 1: 0.96. It should be understood that different ratios based on the specific properties of the polishing pad or prepolymer having different hardness values and the first and second curing agents can be used.

  Referring again to FIG. 2G, as described above, in one embodiment, heating the mold 200 includes forming a groove pattern on the polishing surface 224 of the molded abrasive body 222. The groove pattern as shown includes radial grooves and concentric circumferential grooves. It should be understood that radial or circumferential grooves can be omitted. Furthermore, the concentric circumferential grooves may instead be nested triangles, squares, pentagons, hexagons, and other polygons. Alternatively, the polishing surface can be based on protrusions instead of grooves. Furthermore, low density polishing pads can be manufactured without grooves in the polishing surface. In one such embodiment, the patternless lid of the molding apparatus is used in place of the patterned lid. Alternatively, the use of a lid during molding can be omitted. When using a lid during molding, the mixture 210 can be heated under a pressure in the range of approximately 2-12 pounds per square inch.

  In one aspect, the low density pad can be manufactured with closed cell pores. For example, in one embodiment, the polishing pad includes a polishing body having a density of less than 0.6 and made of a thermoset polyurethane material. The plurality of closed cell pores are dispersed in the thermosetting polyurethane material. In certain embodiments, the density is below 0.5 g / cc. In some embodiments, the plurality of closed cell pores provides a total pore volume in the thermosetting polyurethane material in the range of approximately 55-80% of the total volume of the thermosetting polyurethane material. In certain embodiments, each of the plurality of closed cell holes is essentially spherical. In certain embodiments, the abrasive body further includes a first grooved surface and a second flat surface opposite the first surface, as described in connection with FIG. 2G. In some embodiments, the abrasive body is a homogeneous abrasive body, as described in detail below.

  In an exemplary embodiment, each of the plurality of closed cell pores includes a physical shell composed of a material different from the thermoset polyurethane material. In such cases, closed cell pores can be created by including porogens in the mixture that is molded into the final pad manufacture, as described above.

  In another exemplary embodiment, each of the plurality of closed cell pores includes a physical shell composed of a material different from the thermoset polyurethane material. The physical shell of the first part of the plurality of closed cell holes is made of a material different from the physical shell of the second part of the plurality of closed cell holes. In such cases, closed cell pores can be created by including two types (eg, expanded and unexpanded) of porogen in the mixture that is shaped for final pad manufacture, as described above.

  In another exemplary embodiment, only a portion of the plurality of closed cell pores includes a physical shell composed of a material different from the thermoset polyurethane material. In such a case, closed cell pores may be created by including both porogen and gas bubbles or droplets in the mixture that is shaped for final pad manufacture, as described above.

  In another exemplary embodiment, each of the plurality of closed cell pores does not include a physical shell of a material different from the thermoset polyurethane material. In such cases, closed cell pores can be created by including gas bubbles or droplets, or both, in the mixture that is shaped for final pad manufacture, as described above.

  FIG. 3 illustrates cross-sectional photographs at 100 × and 300 × magnification of a low density polishing pad 300 including closed cell holes based entirely on a porogen filler, according to an embodiment of the present invention. Referring to FIG. 3, all of the pores shown are formed from porogens and therefore all contain a physical shell. Some of the pores are formed from pre-expanded Expandel porogen. Another portion is formed from an unexpanded Expandel porogen that is expanded during the molding process used to make the polishing pad 300. In some such embodiments, unexpanded Expandel expands at low temperatures by design. The temperature of the molding or casting process is above the expansion temperature, and Expandel expands rapidly during molding or casting. The density of the pad 300 is approximately 0.45, and all the pores in the pad are closed cell holes.

FIG. 4 is a cross-sectional photograph at 100 × and 300 × magnification of a low density polishing pad 400, including closed cell holes, partly based on porogen filler and partly based on gas bubbles, according to an embodiment of the present invention. Illustrated. Referring to FIG. 4, the small pores shown are formed from porogen and therefore contain a physical shell. More specifically, small pores are formed from pre-expanded Expandel porogen. Large pores are formed using gas. More specifically, large pores are formed using a small amount of water and surfactant injected into the pad formulation mixture just prior to molding or casting. During the chain extension chemical reaction, a competitive chemical reaction with the NCO of water forms CO ₂ and creates pores. It should be understood that the surfactant type and concentration, along with the catalyst type and level, controls the pore size and the ratio of closed / open cell pores. The density of the pad 400 is approximately 0.37, and most of the pores in the pad are closed cell holes.

  In one aspect, the pore diameter distribution within the polishing pad is a bell curve or a unimodal distribution. For example, FIG. 5A illustrates a plot of power as a function of pore diameter for a wide unimodal distribution of pore diameters within a low density polishing pad, according to an embodiment of the present invention. Referring to plot 500A of FIG. 5A, the unimodal distribution can be relatively wide. As another example, FIG. 5B illustrates a plot of power as a function of pore diameter for a narrow unimodal distribution of pore diameters within a low density polishing pad, according to an embodiment of the present invention. Referring to plot 500B of FIG. 5B, the unimodal distribution may be narrow. In either the narrow or wide distribution, only the maximum diameter power is provided in the polishing pad, such as the maximum power at 40 microns (shown as an example).

  In another aspect, the low density polishing pad can instead be manufactured with a bimodal distribution of pore diameters. As an example, FIG. 6A illustrates a cross-section of a low density polishing pad having a bimodal distribution of approximately 1: 1 closed cell pores, according to an embodiment of the present invention.

  Referring to FIG. 6A, the polishing pad 600 includes a homogeneous polishing body 601. The homogeneous polishing body 601 is made of a thermosetting polyurethane material having a plurality of closed cell holes 602 disposed in the homogeneous polishing body 601. The plurality of closed cell holes 602 have a multimodal distribution of diameters. In certain embodiments, the multimodal distribution of diameters is a bimodal distribution of diameters including a small diameter mode 604 and a large diameter mode 606, as depicted in FIG. 6A.

  In some embodiments, the plurality of closed cell holes 602 include individual pores as depicted in FIG. 6A. It is in contrast to open cell holes that can be connected to each other through a tunnel, such as in the case of pores in a typical sponge. In some embodiments, each of the closed cell pores includes a physical shell, such as a porogen shell. However, in another embodiment, some or all of the closed cell pores do not include a physical shell. In some embodiments, the plurality of closed cell holes 602, and thus the multimodal distribution of diameters, is essentially uniform and homogeneous throughout the thermoset polyurethane material of the homogeneous abrasive 601 as depicted in FIG. 6A. Distributed.

  In some embodiments, the bimodal distribution of pore diameters of the plurality of closed cell holes 602 is approximately 1: 1, as depicted in FIG. 6A. To better illustrate the concept, FIG. 6B illustrates a plot 620 of power as a function of pore diameter for a narrow distribution of pore diameters within the polishing pad of FIG. 6A, according to an embodiment of the present invention. FIG. 6C illustrates a plot 630 of power as a function of pore diameter for a wide distribution of pore diameters within the polishing pad of FIG. 6A, according to an embodiment of the present invention.

  6A-6C, the maximum power diameter value of the large diameter mode 606 is approximately twice the maximum power diameter value of the small diameter mode 604. For example, in one embodiment, as depicted in FIGS. 6B and 6C, the maximum power diameter value for large diameter mode 606 is approximately 40 microns and the maximum power diameter value for small diameter mode 604 is approximately 20 microns. Micron. As another example, the maximum power diameter value for the large diameter mode 606 is approximately 80 microns and the maximum power diameter value for the small diameter mode 604 is approximately 40 microns.

  Referring to plot 620 in FIG. 6B, in one embodiment, the pore diameter distribution is narrow. In a specific embodiment, the power of the large diameter mode 606 has essentially no overlap with the power of the small diameter mode 604. However, referring to plot 630 in FIG. 6C, in another embodiment, the distribution of pore diameters is broad. In a specific embodiment, the power of the large diameter mode 606 overlaps the power of the small diameter mode 604. It should be understood that the bimodal distribution of pore diameters need not be 1: 1, as described in connection with FIGS. Also, the bimodal distribution of pore diameters need not be uniform. In another embodiment, the multimodal distribution of closed cell pore diameters is graded throughout the thermoset polyurethane material with a gradient from the first grooved surface to the second flat surface. In some such embodiments, the multimodal distribution of sloped diameters is a diameter of 2 including a small diameter mode proximate to the first grooved surface and a large diameter mode proximate to the second flat surface. It is a peak distribution.

  And in some embodiments, the low density polishing pad is bimodal with a first diameter mode with a first peak in the size distribution and a second diameter mode with a second different peak in the size distribution. It has a plurality of closed cell holes with sex distribution. In certain such embodiments, the first diameter mode closed cells each include a physical shell composed of a material different from the thermoset polyurethane material. In such specific embodiments, the second diameter mode closed cell pores each include a physical shell composed of a material different from the thermoset polyurethane material. In certain such embodiments, the physical shell of each of the second diameter mode closed cell pores is comprised of a different material than the material of the first diameter mode closed cell physical shell.

  In certain embodiments, the first peak of the first diameter mode size distribution has a diameter in the range of approximately 10-50 microns, and the second peak of the second diameter mode size distribution is approximately 10 It has a diameter in the range of ~ 150 microns. In certain embodiments, the first diameter mode overlaps with the second diameter mode. However, in another embodiment, the first diameter mode does not essentially overlap with the second diameter mode. In some embodiments, the total frequency count of the first diameter mode is not equal to the total frequency count of the second diameter mode. However, in another embodiment, the total frequency count of the first diameter mode is approximately equal to the total frequency count of the second diameter mode. In certain embodiments, the bimodal distribution of diameters is essentially uniformly distributed throughout the thermoset polyurethane material. However, in another embodiment, the bimodal distribution of diameters is distributed so as to be graded throughout the thermoset polyurethane material.

  In certain embodiments, the low density polishing pads described herein, such as polishing pads 222, 300, or 400, or variations thereof described above, are suitable for polishing a substrate. In some such embodiments, the polishing pad is used as a buff pad. The substrate may be one used in the semiconductor manufacturing industry, such as a silicon substrate having devices or other layers disposed thereon. However, the substrate is not limited, and may be a MEMS device, a reticle, a substrate for a solar cell module, or the like. Thus, as used herein, reference to “a polishing pad for polishing a substrate” is intended to encompass these related possibilities.

  The low density polishing pads described herein, such as polishing pads 222, 300, or 400, or variations thereof described above, can be composed of a homogeneous abrasive body of a thermosetting polyurethane material. In some embodiments, the homogeneous abrasive body is comprised of a thermoset closed cell polyurethane material. In certain embodiments, the term “homogeneous” is used to indicate that the thermoset closed cell polyurethane material is constant throughout the composition of the abrasive body. For example, in certain embodiments, the term “homogeneous” excludes polishing pads composed of, for example, multiple layers of impregnated felts or compositions (composites) of different materials. In some embodiments, the term “thermoset” is used to indicate a polymer material that cures irreversibly, such as, for example, a precursor of a material that is irreversibly transformed into an insoluble polymer network upon curing. It is done. For example, in certain embodiments, the term “thermoset” refers to, for example, a “thermoplastic” material or “thermoplastic resin”, ie, a liquid that becomes heated when heated and a very glassy when sufficiently cooled. Exclude polishing pads composed of a material consisting of a polymer that returns to state. Polishing pads made from thermoset materials are typically manufactured from lower molecular weight precursors that react to form polymers in a chemical reaction, while pads made from thermoplastic materials are typically Note that the polishing pad is manufactured by heating an existing polymer to cause a phase change so that it is formed by a physical process. Polyurethane thermosetting polymers are selected for the manufacture of the polishing pads described herein based on their stable thermal and mechanical properties, resistance to chemical environments, and wear resistance trends. obtain.

  In certain embodiments, during conditioning and / or polishing, the homogenous abrasive body has a polishing surface roughness in the range of approximately 1-5 microns in root mean square. In certain embodiments, during conditioning and / or polishing, the homogeneous abrasive has a polished surface roughness of approximately 2.35 microns in root mean square. In some embodiments, the homogeneous abrasive has a storage modulus in the range of approximately 30-120 megapascals (MPa) at 25 degrees Celsius. In another embodiment, the homogeneous abrasive has a storage modulus at 25 degrees Celsius of less than approximately 30 megapascals (MPa). In some embodiments, the homogeneous abrasive has a compression rate of approximately 2.5%.

  In certain embodiments, the low density polishing pads described herein, such as polishing pads 222, 300, or 400, or variations thereof described above, include a shaped homogeneous polishing body. The term “molded” is used to indicate that a homogeneous abrasive body has been formed in the mold, as detailed above in connection with FIGS. It should be understood that in other embodiments, a casting process can be used instead to process a low density polishing pad as described above.

  In some embodiments, the homogeneous abrasive is opaque. In certain embodiments, the term “opaque” is used to indicate a material that allows passage of visible light of approximately 10% or less. In some embodiments, the homogenous abrasive body is due in part or in full to the inclusion of an opacifying filler (eg, as an additional component) into the homogeneous thermoset, closed cell polyurethane material of the homogenous abrasive body. And opaque. In specific embodiments, the opacifying filler is, but is not limited to, boron nitride, cerium fluoride, graphite, graphite fluoride, molybdenum sulfide, niobium sulfide, talc, tantalum sulfide, tungsten disulfide, or Teflon (registered) Trademark).

  The size of the low density polishing pad, such as pads 222, 300, or 400, can vary depending on the application. Nevertheless, several parameters can be used to make a polishing pad that is compatible with conventional process equipment or even conventional chemical mechanical process operations. For example, according to embodiments of the present invention, the low density polishing pad has a thickness in the range of approximately 0.075 inches to 0.130 inches, for example, approximately 1.9 to 3.3 millimeters. In certain embodiments, the low density polishing pad ranges from approximately 20 inches to 30.3 inches, such as approximately 50 to 77 centimeters, and in some cases approximately 10 inches to 42 inches, such as approximately It has a diameter in the range of 25-107 centimeters.

  In another embodiment of the invention, the low density polishing pad described herein further comprises a locally transparent (LAT) region disposed within the polishing pad. In some embodiments, the LAT region is disposed within the polishing pad and is covalently bonded to the polishing pad. Examples of suitable LAT regions are US patent application Ser. No. 12 / 657,135 filed Jan. 13, 2010 and assigned to NexPlanar Corporation and filed Sep. 30, 2010 and assigned to NexPlanar Corporation. U.S. patent application Ser. No. 12 / 895,465. In alternative or additional embodiments, the low density polishing pad further includes an opening disposed within the polishing surface and the polishing body. The opening may accommodate, for example, a detection device included in the platen of the polishing tool. An adhesive sheet is disposed on the back surface of the polishing body. The pressure-sensitive adhesive sheet provides an impervious seal to the opening on the back surface of the abrasive body. Examples of suitable openings are described in US patent application Ser. No. 13 / 184,395, filed Jul. 15, 2011 and assigned to NexPlanar Corporation. In another embodiment, the low density polishing pad further includes a detection region used with, for example, an eddy current detection system. An example of a suitable eddy current detection region is described in US patent application Ser. No. 12 / 895,465, filed Sep. 30, 2010 and assigned to NexPlanar Corporation.

  The low density polishing pads described herein, such as polishing pads 222, 300, or 400, or variations thereof described above, can further include an underlayer disposed on the back surface of the polishing body. In some such embodiments, the result is a polishing pad having a bulk or base material that is different from the material of the polishing surface. In certain embodiments, the composite polishing pad includes a base or bulk layer made of a stable, essentially incompressible inert material on which a polishing surface layer is disposed. A harder underlayer can provide support and strength to keep the pad intact, while a softer polishing surface layer can reduce scratching and material properties of the polishing layer and the rest of the polishing pad Allows disconnection. Examples of suitable underlayers are described in US patent application Ser. No. 13 / 306,845, filed Nov. 29, 2011 and assigned to NexPlanar Corporation.

  The low density polishing pads described herein, such as polishing pads 222, 300 or 400, or variations thereof as described above, are subpads disposed on the back side of the polishing body, eg, conventional types known in the CMP art. A subpad. In certain such embodiments, the subpad is composed of a material such as, but not limited to, foam, rubber, fiber, felt, or highly porous material.

  Referring again to FIG. 2G as a descriptive basis, the individual grooves of the groove pattern formed in the low density polishing pad as described herein can have about 4 to about 4 at any point on each groove. It can be 100 mils deep. In some embodiments, the grooves are about 10 to about 50 mils deep at any point on each groove. The grooves can be of uniform depth, varying depth, or any combination thereof. In some embodiments, the grooves are all of a uniform depth. For example, the grooves in the groove pattern can all be the same depth. In some embodiments, some of the grooves in the groove pattern may have a certain uniform depth, while other grooves in the same pattern may have a different uniform depth. For example, the groove depth can increase with increasing distance from the center of the polishing pad. However, in some embodiments, the groove depth decreases with increasing distance from the center of the polishing pad. In some embodiments, the uniform depth grooves alternate with the varying depth grooves.

  The individual grooves in the groove pattern formed in the low density polishing pad as described herein can be about 2 to about 100 mils wide at any point on each groove. In some embodiments, the grooves are about 15 to about 50 mils wide at any point on each groove. The grooves can be of uniform width, varying width, or any combination thereof. In some embodiments, the grooves are all uniform in width. However, in some embodiments, some of the concentric grooves have a specific uniform width, while other grooves in the same pattern have a different uniform width. In some embodiments, the groove width increases with increasing distance from the center of the polishing pad. In some embodiments, the groove width decreases with increasing distance from the center of the polishing pad. In some embodiments, uniform width grooves alternate with varying width grooves.

  According to the depth and width dimensions described above, the individual grooves of the groove pattern described herein include a uniform volume, a varying volume, including grooves at or near the location of the polishing pad opening, Or any combination thereof. In some embodiments, the grooves are all of a uniform volume. However, in some embodiments, the groove volume increases with increasing distance from the center of the polishing pad. In some other embodiments, the groove volume decreases with increasing distance from the center of the polishing pad. In some embodiments, uniform volume grooves alternate with varying volume grooves.

  The groove pattern grooves described herein may have a pitch of about 30 to about 1000 mils. In some embodiments, the grooves have a pitch of about 125 mils. For circular polishing pads, the groove pitch is measured along the radius of the circular polishing pad. For CMP belts, the groove pitch is measured from the center of the CMP belt to the edge of the CMP belt. The grooves can be a uniform pitch, a varying pitch, or any combination thereof. In some embodiments, the grooves are all uniform pitch. However, in some embodiments, the groove pitch increases with increasing distance from the center of the polishing pad. In some other embodiments, the groove pitch decreases with increasing distance from the center of the polishing pad. In some embodiments, the pitch of the grooves in one sector changes with increasing distance from the center of the polishing pad, while the pitch of the grooves in adjacent sectors remains uniform. In some embodiments, the pitch of the grooves in one sector increases with increasing distance from the center of the polishing pad, while the pitch of the grooves in adjacent sectors increases at different rates. In some embodiments, the pitch of the grooves in one sector increases with increasing distance from the center of the polishing pad, while the pitch of the grooves in adjacent sectors increases with the distance from the center of the polishing pad. Decreases with increase. In some embodiments, uniform pitch grooves alternate with varying pitch grooves. In some embodiments, uniform pitch groove sectors alternate with varying pitch groove sectors.

  The polishing pads described herein may be suitable for use with a variety of chemical mechanical polishing equipment. As an example, FIG. 7 illustrates an isometric side view of a polishing apparatus compatible with a low density polishing pad, according to an embodiment of the present invention.

  Referring to FIG. 7, the polishing apparatus 700 includes a platen 704. The top surface 702 of the platen 704 can be used to support a low density polishing pad. Platen 704 may be configured to provide spindle rotation 706 and slider peristalsis 708. Sample carrier 710 is used, for example, to hold semiconductor wafer 711 in place during polishing of the semiconductor wafer using a polishing pad. The sample carrier 710 is further supported by a suspension mechanism 712. A slurry supply 714 is included to supply slurry to the surface of the polishing pad before and during polishing of the semiconductor wafer. A conditioning unit 790 may also be included, and in some embodiments includes a diamond tip for conditioning the polishing pad.

  Thus, a low density polishing pad and a method for manufacturing a low density polishing pad have been disclosed. According to an embodiment of the present invention, a polishing pad for polishing a substrate includes a polishing body having a density of less than 0.5 g / cc and made of a thermosetting polyurethane material. A plurality of closed cell pores are dispersed within the thermosetting polyurethane material. In some embodiments, the abrasive body is a homogeneous abrasive body.

Claims (61)

A polishing pad for polishing a substrate, the polishing pad comprising:
A polishing body having a density of less than 0.5 g / cc,
A thermosetting polyurethane material;
A polishing pad comprising: a polishing body comprising: a plurality of closed cell holes dispersed in the thermosetting polyurethane material.   The polishing pad according to claim 1, wherein the polishing body is a homogeneous polishing body.   The polishing pad according to claim 1, wherein each of the plurality of closed cell holes includes a physical shell including a material different from the thermosetting polyurethane material.   The polishing pad according to claim 3, wherein the physical shell of the first part of the plurality of closed cell holes comprises a material different from the physical shell of the second part of the plurality of closed cell holes.   The polishing pad according to claim 1, wherein each of a part of the plurality of closed cell holes includes a physical shell including a material different from the thermosetting polyurethane material.   The polishing pad according to claim 1, wherein each of the plurality of closed cell holes does not include a physical shell of a material different from the thermosetting polyurethane material.   The polishing of claim 1, wherein the plurality of closed cell pores provide a total cell pore volume in the thermosetting polyurethane material in a range of approximately 55-80% of the total volume of the thermosetting polyurethane material. pad. The abrasive is
A first grooved surface;
The polishing pad according to claim 1, further comprising: a second flat surface opposite the first surface.   The polishing pad according to claim 1, wherein each of the plurality of closed cell holes is essentially spherical.   The plurality of closed cell pores have a bimodal 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. The polishing pad according to claim 1.   The polishing pad of claim 10, wherein each of the closed cell pores in the first diameter mode includes a physical shell comprising a material different from the thermoset polyurethane material.   The polishing pad of claim 11, wherein each of the closed cell holes in the second diameter mode includes a physical shell comprising a material different from the thermosetting polyurethane material.   The polishing pad of claim 12, wherein the physical shell of each closed cell hole in the second diameter mode comprises a material different from the material of the physical shell of the closed cell hole in the first diameter mode. .   The first peak of the first diameter mode size distribution has a diameter in the range of approximately 10-50 microns, and the second peak of the second diameter mode size distribution is approximately 10-150 microns. The polishing pad of claim 10, having a diameter in the range.   The polishing pad according to claim 10, wherein the first diameter mode overlaps with the second diameter mode.   The polishing pad of claim 10, wherein the first diameter mode has essentially no overlap with the second diameter mode.   The polishing pad according to claim 10, wherein the total frequency count of the first diameter mode is not equal to the total frequency count of the second diameter mode.   The polishing pad according to claim 10, wherein the total frequency count of the first diameter mode is approximately equal to the total frequency count of the second diameter mode.   The polishing pad of claim 10, wherein the bimodal distribution of diameters is essentially uniformly distributed throughout the thermoset polyurethane material.   The polishing pad according to claim 1, wherein the polishing body is a molded polishing body.   The polishing pad according to claim 1, wherein the polishing body further comprises an opacifying filler distributed substantially uniformly throughout the polishing body.   The polishing pad according to claim 1, further comprising an underlayer disposed on a back surface of the polishing body.   The polishing pad according to claim 1, further comprising a detection region disposed in a back surface of the polishing body.   The polishing pad according to claim 1, further comprising a subpad disposed on a back surface of the polishing body.   The polishing pad of claim 1, further comprising a locally transparent (LAT) region disposed within and covalently bonded to the polishing body. A polishing pad for polishing a substrate,
The polishing pad is
A polishing body having a density of less than about 0.6 g / cc,
A thermosetting polyurethane material;
A polishing body comprising a plurality of closed cell pores dispersed in the thermosetting polyurethane material,
The plurality of closed cell pores have a bimodal 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. ,
Polishing pad.   The polishing pad according to claim 26, wherein the polishing body is a homogeneous polishing body.   27. The polishing pad of claim 26, wherein each of the closed cell holes in the first diameter mode comprises a physical shell comprising a material different from the thermosetting polyurethane material.   29. A polishing pad according to claim 28, wherein each of the closed cell holes in the second diameter mode includes a physical shell comprising a material different from the thermosetting polyurethane material.   30. The polishing pad of claim 29, wherein the physical shell of each closed cell hole in the second diameter mode comprises a material different from the material of the physical shell of the closed cell hole in the first diameter mode. .   The first peak of the first diameter mode size distribution has a diameter in the range of approximately 10-50 microns, and the second peak of the second diameter mode size distribution is approximately 10-150 microns. 27. The polishing pad of claim 26, having a diameter in the range of   27. A polishing pad according to claim 26, wherein the first diameter mode overlaps with the second diameter mode.   27. The polishing pad of claim 26, wherein the first diameter mode has essentially no overlap with the second diameter mode.   27. The polishing pad of claim 26, wherein the total frequency count in the first diameter mode is not equal to the total frequency count in the second diameter mode.   27. The polishing pad of claim 26, wherein the total frequency count of the first diameter mode is approximately equal to the total frequency count of the second diameter mode.   27. The polishing pad of claim 26, wherein the bimodal distribution of diameters is essentially uniformly distributed throughout the thermoset polyurethane material. A method for manufacturing a polishing pad, comprising:
The method
Mixing a prepolymer and a chain extender or crosslinker with a plurality of microelements to form a mixture, each of the plurality of microelements having an initial size;
Heating the mixture in a mold to provide a molded abrasive body comprising a thermosetting polyurethane material and a plurality of closed cell pores dispersed within the thermosetting polyurethane material;
The plurality of closed cell holes are formed by expanding each of the plurality of microelements to a final larger size during the heating step.   38. The method of claim 37, wherein expanding each of the plurality of microelements to a final size includes increasing the volume of each of the plurality of microelements in a range of approximately 3 to 1000 times.   38. The method of claim 37, wherein expanding each of the plurality of microelements to a final size comprises providing a final diameter of each of the plurality of microelements in the range of approximately 10-200 microns.   38. The method of claim 37, wherein expanding each of the plurality of microelements to a final size includes decreasing the density of each of the plurality of microelements in a range of approximately 3 to 1000 times.   38. The method of claim 37, wherein expanding each of the plurality of microelements to a final size includes forming an essentially spherical shape for each of the plurality of microelements of the final size.   Mixing the prepolymer and chain extender, or crosslinker with the plurality of microelements further comprises mixing with the second plurality of microelements to form the mixture, the second plurality of microelements. 38. The method of claim 37, wherein each microelement has a size.   43. The method of claim 42, wherein the heating step is performed at a sufficiently low temperature so that the size of each of the second plurality of microelements is essentially the same before and after the heating step.   44. The method of claim 43, wherein the heating step is performed at a temperature of approximately 100 degrees Celsius or less, and the second plurality of microelements has an expansion limit of approximately greater than 130 degrees Celsius.   43. The method of claim 42, wherein the second plurality of microelements has an expansion limit that exceeds an expansion limit of the plurality of microelements.   46. The method of claim 45, wherein the expansion limit of the second plurality of microelements is approximately greater than 120 degrees Celsius, and the expansion limit of the plurality of microelements is approximately less than 110 degrees Celsius.   The mixture of prepolymers, the chain extender or crosslinker, and the second plurality of microelements are viscous and the prepolymer, the chain extender or crosslinker, the plurality of the initial size. 43. The method of claim 42, wherein the microelements and the mixture of the second plurality of microelements have essentially 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.   48. The method of claim 47, wherein the plurality of microelements have no or near effect on the viscosity of the mixture.   The heating step comprises the thermosetting polyurethane material and a final size having a first diameter mode dispersed within the thermosetting polyurethane material, each of the plurality of microelements having a first peak of a size distribution. The plurality of closed cell pores formed by expansion and the second plurality of second modes having a second diameter mode dispersed within the thermosetting polyurethane material and having a second different peak in size distribution. 43. The method of claim 42, wherein said shaped abrasive body is provided comprising a second plurality of closed cell pores formed from microelements.   The plurality of closed cell holes and the second plurality of closed cell holes provide a total cell volume in the thermosetting polyurethane material in a range of approximately 55-80% of the total volume of the thermosetting polyurethane material. 51. The method of claim 50.   38. The method of claim 37, wherein heating the mixture to provide the shaped abrasive body comprises forming an abrasive body having a density less than 0.5 g / cc.   53. The method of claim 52, wherein the mixture has a density greater than 0.5 g / cc prior to the heating step.   38. The method of claim 37, wherein the mixing step further comprises injecting a gas into the prepolymer and the chain extender or crosslinker, or into a product formed therefrom.   38. The method of claim 37, wherein the prepolymer is an isocyanate and the mixing step further comprises adding water to the prepolymer.   38. The method of claim 37, wherein mixing the prepolymer and the chain extender or crosslinker includes mixing an isocyanate and an aromatic diamine compound, respectively.   38. The method of claim 37, wherein the mixing step further comprises adding an opacifying filler to the prepolymer and the chain extender or cross-linking agent to provide an opaque shaped abrasive body.   38. The method of claim 37, wherein heating the mixture includes first first curing in the mold and then further curing in an oven.   38. The method of claim 37, wherein heating in the mold includes forming a groove pattern on a polished surface of the molded abrasive body.   38. The method of claim 37, wherein each of the plurality of microelements having the initial size includes a physical shell, and each of the plurality of microelements having a final size includes an expanded physical shell. 38. The method of claim 37, wherein each of the plurality of microelements having the initial size is a droplet and each of the plurality of microelements having a final size is a gas bubble.

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