TWI579106B - Low density polishing pad - Google Patents

Description

Low density polishing pad

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

Chemical mechanical planarization or chemical mechanical polishing (often abbreviated as CMP) is a technique used to planarize semiconductor wafers or another substrate in semiconductor fabrication.

The procedure involves the use of abrasive and corrosive chemical slurries (usually colloids) along with polishing pads and clasps that typically have larger diameters than wafers. The polishing pad and wafer are pressed together by a dynamic polishing head and held in place by a plastic retaining ring. The dynamic polishing head is rotated during polishing. This method helps to remove material and tends to flatten any irregular topography to make the wafer flat or planar. This may be necessary in order to set up the wafer for forming additional circuit components. For example, this may be necessary in order to selectively remove the entire surface within the depth of field of the photolithography system or based on its location. For the latest technology nodes below 50 nm, typical depth of field requirements are as low as E.

The material removal procedure is not just a procedure for abrasive scratching of sandpaper on wood. The chemicals in the slurry also react with and/or weaken the material to be removed. Abrasives accelerate this weakening process and the polishing pad helps to erase the reactive material from the surface. In addition to advances in slurry technology, polishing pads also play an important role in increasingly complex CMP operations.

However, additional improvements are needed in the advancement of CMP pad technology.

Embodiments of the invention include low density polishing pads and methods of making low density polishing pads.

In one embodiment, a polishing pad for polishing a substrate comprises a polishing body having a density of less than 0.5 g/cc and composed of a thermosetting polyurethane material. A plurality of closed cell pores are dispersed in the thermosetting polyurethane material.

In another embodiment, a polishing pad for polishing a substrate comprises a polishing body having a density of less than about 0.6 g/cc and comprised of a thermosetting polyurethane material. A plurality of closed cell pores are dispersed in the thermosetting polyurethane material. The plurality of closed-cell pores have a bimodal diameter distribution comprising a first diameter pattern having a first size distribution peak and a second diameter pattern having a second different size distribution peak.

In yet another embodiment, a method of making a polishing pad involves mixing a prepolymer and a chain extender or crosslinker with a plurality of trace elements to form a mixture. Each of the plurality of trace elements has an initial size. The method also involves heating the mixture in a forming mold to provide a molded polishing body comprised of a thermosetting polyurethane material and a plurality of closed cell pores dispersed in the thermosetting polyurethane material. The plurality of closed cell pores are formed by expanding each of the plurality of trace elements to a final larger size during the heating.

Section 100A‧‧‧

Section 100B‧‧‧

200‧‧‧Molding Mold/Mold

202‧‧‧Prepolymer

204‧‧‧Curing agent/chain extender or crosslinker/primary curing agent and secondary curing agent

206‧‧‧porogen

208‧‧‧ Bubbles/droplets

210‧‧‧Mixture/Polishing Pad Precursor Mixture

212‧‧‧ trace elements

214‧‧‧ trace elements

216‧‧‧ Cover

218‧‧‧Final larger size/expansion trace elements/final size/trace elements

220‧‧‧Mat material/low density polishing pad/curing material/thermosetting polyurethane material

222‧‧‧Low-density polishing pad/pad/molding polishing body/polishing body/polishing pad/impermeable Molded polished body / molded homogeneous polished body

224‧‧‧ Polished surface

226‧‧‧radial grooves

228‧‧‧Concentric circular groove

300‧‧‧Low density polishing pad/polishing pad/mat

400‧‧‧Low density polishing pad/pad/polish pad

500A‧‧‧Curve

500B‧‧‧Curve

600‧‧‧ polishing pad

601‧‧‧Homogeneous polishing body

602‧‧‧Closed pores

604‧‧‧Small diameter mode

606‧‧‧ Large diameter mode

620‧‧‧Curve

630‧‧‧Graph

700‧‧‧ polishing device

702‧‧‧ top surface

704‧‧‧ board

706‧‧‧ spindle rotation

708‧‧‧Slider oscillation

710‧‧‧sample carrier

711‧‧‧Semiconductor wafer

712‧‧‧ hanging mechanism

714‧‧‧ slurry feed

790‧‧‧Finishing unit

A-a’‧‧‧ axis

Figure 1A is a top plan view of a POLITEX polishing pad in accordance with the prior art.

Figure 1B is a cross-sectional view of a POLITEX polishing pad according to the prior art.

2A-2G illustrate cross-sectional views of the operations used in making a polishing pad in accordance with an embodiment of the present invention.

3 illustrates a cross-sectional view of a low density polishing pad comprising all of the closed cell pores based on the pore former filler in accordance with an embodiment of the present invention at 100 times and 300 times magnification.

4 illustrates a cross-sectional view of a low density polishing pad comprising closed cell pores at 100 times and 300 times magnification, in accordance with an embodiment of the present invention, one of which is based in part on a pore former filler and the closed pore pores Part of it is based on bubbles.

5A illustrates a graph of a population of broad single mode distribution versus pore diameter for a pore diameter in a low density polishing pad in accordance with an embodiment of the present invention.

5B illustrates a plot of population versus narrow pore size for a narrow single mode distribution of pore diameters in a low density polishing pad in accordance with an embodiment of the present invention.

6A illustrates a cross-sectional view of a low density polishing pad having a bimodal closed cell pore distribution of about 1:1 in accordance with an embodiment of the present invention.

6B illustrates a graph of a population of narrow distributions of pore diameters in the polishing pad of FIG. 6A as a function of pore diameter, in accordance with an embodiment of the present invention.

6C illustrates a plot of a population of broad distributions of pore diameters in the polishing pad of FIG. 6A as a function of pore diameter, in accordance with an embodiment of the present invention.

Figure 7 illustrates an isometric side view of a polishing apparatus compatible with a low density polishing pad in accordance with 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 compositions, to provide a thorough understanding of the embodiments of the invention. It will be apparent to those skilled in the art that the embodiments of the invention may be practiced without the specific details. In other instances, well-known processing techniques, such as details regarding the combination of slurry and polishing pad to perform chemical mechanical planarization (CMP) of a semiconductor substrate, are not described in detail so as not to unnecessarily obscure embodiments of the present invention. blurry. In addition, the various embodiments shown in the figures are illustrative and not necessarily to scale.

One or more embodiments set forth herein are directed to the fabrication of polishing pads having a low density of less than about 0.6 grams per cubic centimeter (g/cc) and, more specifically, less than about 0.5 g/cc. The resulting mat can be based on a polyurethane material having a closed cell pore size that provides a low density. These low density mats can be used, for example, as a buffing wheel polishing pad or as a polishing pad designed for special chemical mechanical polishing (CMP) applications such as lining/barrier removal. In some implementations In one example, the polishing pads described herein can be made to have a density as low as in the range of from 0.3 g/cc to 0.5 g/cc, such as about 0.357 g/cc. In a particular embodiment, the low density mat has a density as low as about 0.2 g/cc.

To provide context, a typical CMP pad has a density of from about 0.7 g/cc to 0.8 g/cc, and is typically at least above 0.5 g/cc. Conventionally, a typical CMP wiper pad has a "porous polymer" design that uses large holes leading to the surface. In the case of a POLITEX polishing pad, for example, a composite polyurethane skin is included on the support. Conventionally, the buffing pad is extremely soft and is made at a low density with open cell porosity (eg, fiber mats and "porous polymer" mats). These pads are often associated with two fundamental problems with CMP: short life and inconsistent performance compared to conventional closed cell polyurethane (but higher density) CMP pads. 1A and 1B are top and cross-sectional views, respectively, of a POLITEX polishing pad according to the prior art. Referring to Figure 1A, one portion 100A of a POLITEX polishing pad is shown to be magnified 300 times in a scanning electron microscope (SEM) image. Referring to FIG. 1B, one portion 100B of the POLETEX polishing pad is shown to be magnified 100 times in a scanning electron microscope (SEM) image. Referring to both Figures 1A and 1B, the aperture structure of prior art pads is readily visible.

More generally, one of the basic challenges is to make a closed cell polyurethane mat with high porosity and low density. Our own investigations in the fabrication of low density polyurethane mats by molding or casting procedures have shown that only an increased volume of pore former is added to the mat formulation mixture to ultimately provide closed pores based on the added pore former. Difficulties in the pad material. In particular, the addition of more pore formers than typical mat formulations can increase the viscosity of the formulation to a level that is difficult to manage in the casting or molding process. This situation can be particularly difficult for porogens comprising a pre-expanded porogen or a substantially same volume throughout the molding or casting process. In accordance with embodiments of the present invention, an unexpanded porogen or an increased volume of porogen throughout the molding or casting process is included in the pad formulation for final production. However, in one such embodiment, if all of the final closed cell pores are produced by an unexpanded pore former, the manageability of the viscosity of the formulation in casting or molding can be too low. As such, in one embodiment, in addition to forming a formulation to include unexpanded In addition to the pore former or the increased pore size of the pore forming agent through the molding or casting process, it also includes a pre-expansion pore former or a substantially same volume of pore former throughout the molding or casting process to achieve viscosity tuning of the pad formulation.

Thus, in one embodiment, the unexpanded porogen filler or the insufficient expansion porogen filler (both referred to as UPF) that expands above ambient temperature is used for polishing during fabrication by casting or molding. Porosity is formed in the mat. In one such embodiment, a large amount of UPF is included in the mixture formed by the polyurethane. The UPF expands during the pad casting process and forms a low density pad with closed cell pores. The above method of forming a polishing pad can have advantages over other techniques that have been used to form low density pads with apertures. For example, fabrication of the final mat porosity based solely on gas injection or entrainment may require specialized equipment and may be accompanied by difficulties in controlling the final mat density and difficulties in controlling the final pore size and distribution. In another example, only based on in situ generated gas (e.g., reaction with isocyanate portion of water (NCO) ₂ to form bubbles of CO) production of a final porosity of the mat may be accompanied by difficulties in the control of the pore size distribution.

In one aspect of the invention, a low density polishing pad can be fabricated in a molding process. For example, Figures 2A-2G illustrate cross-sectional views of the operations used in making a polishing pad in accordance with an embodiment of the present invention.

Referring to Figure 2A, a forming die 200 is provided. Referring to Figure 2B, prepolymer 202 and curing agent 204 (e.g., chain extender or crosslinker) are mixed with a plurality of trace elements to form a mixture. In one embodiment, the plurality of trace elements are a plurality of pore formers 206, such as filled or hollow microspheres. In another embodiment, the plurality of trace elements are a plurality of bubbles or droplets or both 208. In another embodiment, the plurality of trace elements are a combination of a plurality of pore formers 206 and a plurality of bubbles or droplets or both.

Referring to Figure 2C, the mixture 210 obtained from Figure 2B is shown at the base of the forming mold 200. The mixture 210 includes a first plurality of trace elements 212, each of the first plurality of trace elements having an initial size. A second plurality of trace elements 214 can also be included in the mixture 210, as set forth in more detail below.

Referring to FIG. 2D, the cover 216 of the molding die 200 is brought together with the base of the molding die 200 and the mixture 210 assumes the shape of the molding die 200. In one embodiment, the mold 200 is vented after or during the time the lid 216 of the forming mold 200 is brought together with the base such that no cavities or voids are formed within the forming mold 200. It should be understood that the embodiments set forth herein that illustrate the reduction of the lid of the forming mold need only achieve that the lid of the forming mold is attached to the base. That is, in some embodiments, the cover toward the forming mold raises the base of the forming mold, while in other embodiments the cover is lowered toward the base while the cover toward the forming mold raises the base of the forming mold.

Referring to FIG. 2E, the mixture 210 is heated in the molding die 200. Each of the plurality of trace elements 212 expands to a final larger size 218 during heating. Referring additionally to Figure 2F, the heating is used to cure the mixture 210 to provide a pad material 220 that surrounds the trace elements 218 and, if present, the partially or fully cured trace elements 214. In one such embodiment, the curing forms a crosslinked matrix based on the materials of the prepolymer and the curing agent.

Referring collectively to Figures 2E and 2F, it is understood that the order in which the trace elements 212 are expanded to the final larger size 218 and the cured mixture 210 does not necessarily occur in the order illustrated. In another embodiment, the curing of the mixture 210 occurs prior to expanding the trace elements 212 to a final larger size 218 during heating. In another embodiment, during heating, curing of the mixture 210 occurs while expanding the trace elements 212 to a final larger size 218. In yet another embodiment, two separate heating operations are performed to cure the mixture 210 and expand the trace elements 212 to a final larger size 218, respectively.

Referring to FIG. 2G, in one embodiment, the procedures set forth above are used to provide a low density polishing pad 220. The low density polishing pad 222 is comprised of a cured material 220 and comprises an expanded trace element 218 and, in one embodiment, an additional trace element 214. In one embodiment, the low density polishing pad 222 is comprised of a thermoset polyurethane material and the expanded trace element 218 provides a plurality of closed cell pores dispersed in the thermoset polyurethane material. Referring again to Figure 2G, the bottom portion of the Figure is a plan view of the upper cross-sectional view taken along the a-a' axis. As seen in the plan, in In one embodiment, the low density polishing pad 222 has a polishing surface 224 having a groove pattern therein. In a particular embodiment, as shown, the groove pattern includes a radial groove 226 and a concentric circular groove 228.

Referring again to FIGS. 2D and 2E, in one embodiment, each of the plurality of trace elements 212 increases the volume of each of the plurality of trace elements by between about 3 and 1000. Expand to a final size of 218 in multiples. In one embodiment, each of the plurality of trace elements 212 is expanded to a final size 218 to provide a final diameter of each of the plurality of trace elements 218 in a range from about 10 microns to 200 microns. In one embodiment, each of the plurality of trace elements 212 expands to a final size 218 by reducing the density of each of the plurality of trace elements 212 by a factor in the range of from about 3 to about 1000. . In one embodiment, each of the plurality of trace elements 212 expands to a final size 218 by forming a substantially spherical shape for each of the plurality of trace elements 218 of the final size.

In one embodiment, the plurality of trace elements 212 are subsequently expanded within the pad material formulation to form a porogen, bubble or liquid foam in the closed pores of the finished polishing pad material. In one such embodiment, the plurality of closed cell pores are a plurality of larger pore formers formed by expanding corresponding smaller pore formers. For example, the term "porogen" can be used to indicate micron or nanoscale spherical or slightly spherical particles having a "hollow" center. The hollow center is not filled with solid material, but may contain a gas or liquid core. In one embodiment, the plurality of closed porosity distributed in the unexpanded throughout the mixture or filled with a gas filling liquids as EXPANCEL ^TM starts. After the (e.g.) formed by molding a mixture of a polishing pad procedure and / or during the filling gas or unexpanded EXPANCEL ^TM becomes filled with the liquid expander. In a particular embodiment, the EXPANCEL ^{(TM) is} filled with pentane. In one embodiment, each of the plurality of closed cell pores has a diameter in the expanded state (eg, in the final product) that is in the range of from about 10 microns to about 100 microns. Thus, in one embodiment, each of the plurality of trace elements having an initial size comprises a solid outer shell, and each of the plurality of trace elements having a final size comprises an expanded solid outer shell. In another embodiment, each of the plurality of trace elements 212 having an initial size is a droplet, and each of the plurality of trace elements 218 having a final size is a bubble. In yet another embodiment, for forming a plurality of trace elements 218 having a final size, the mixing used to form the mixture 210 further involves injecting a gas into the prepolymer and the chain extender or crosslinker, or injecting thereto In the product formed. In certain such embodiments, the prepolymer is an isocyanate and the mixing further involves adding water to the prepolymer. In either case, in one embodiment, the plurality of closed cell pores comprise discrete pores from each other. This is in contrast to the apertures of the apertures that are permeable to each other, such as those in conventional sponges.

Referring again to FIGS. 2C-2E, in one embodiment, mixing the prepolymer 202 and the chain extender or crosslinker 204 with the plurality of trace elements 212 further involves mixing with the second plurality of trace elements 214 to form the mixture 210. Each of the second plurality of trace elements 214 has a size. In one such embodiment, the heating set forth in association with FIG. 2E is performed at a temperature sufficiently low that the size of each of the second plurality of trace elements 214 is substantially the same before and after heating, As shown in Figure 2E. In certain such embodiments, the heating is performed at a temperature of about 100 degrees Celsius or less, and the second plurality of trace elements 214 have an expansion threshold greater than about 130 degrees Celsius. In another embodiment, the second plurality of trace elements 214 have an expansion threshold greater than the expansion threshold of the plurality of trace elements 212. In a particular such embodiment, the expansion threshold of the second plurality of trace elements 214 is greater than about 120 degrees Celsius, and the expansion threshold of the plurality of trace elements 212 is less than about 110 degrees Celsius. As such, in one embodiment, during heating, the trace elements 212 expand to provide an expanded trace element 218, while the trace elements 214 remain substantially unchanged.

In one embodiment, each of the second plurality of trace elements 214 throughout the polishing pad (e.g., in the polishing pad as an additional component) filled with a pre-expansion and distribution of gas constitutes EXPANCEL ^TM. That is, any significant expansion that may occur with respect to the trace elements 214 is performed prior to its inclusion in the polishing pad formation (eg, prior to inclusion in the mixture 210). In a particular embodiment, the pre-expanded EXPANCEL ^{(TM) is} filled with pentane. In one embodiment, the trace elements 214 provide a plurality of closed cell pores (shown again as 214 with little change during the molding process) having a diameter in the range of from about 10 microns to about 100 microns. In one embodiment, the resulting plurality of closed cell pores comprise discrete pores from one another. This is in contrast to the apertures of the apertures that are permeable to each other, such as those in conventional sponges.

As noted above, increasing the porosity by adding more pore former than typical mat formulations can increase the viscosity of the formulation to a level that is difficult to manage in the casting or molding process. This situation can be particularly difficult for porogens comprising a pre-expanded porogen or a substantially same volume throughout the molding or casting process. On the other hand, if all of the final closed cell pores are produced by an unexpanded pore former, the manageability of the viscosity of the formulation in casting or molding can be too low. In order to address such circumstances, in accordance with an embodiment of the present invention, a mixture of prepolymer 202, chain extender or crosslinker 204 and second plurality of trace elements 214 is conceptually having a viscosity. At the same time, the mixture of prepolymer 202, chain extender or crosslinker 204, a plurality of trace elements 212 having an initial size, and a second plurality of trace elements 214 have substantially the same viscosity. That is, the inclusion of a plurality of trace elements 212 having an initial (smaller) size has little effect on the viscosity of the mixture. In one embodiment, the viscosity of the preferred molding conditions can then be selected based on a second plurality of trace elements comprising a size that remains substantially constant throughout the molding process. In one such embodiment, then the viscosity is a predetermined viscosity and the relative amount of the second plurality of trace elements 214 in the mixture 210 is selected based on the predetermined viscosity. Moreover, in one embodiment, the plurality of trace elements 212 have little effect on the viscosity of the mixture 210.

Referring again to FIG. 2E, in one embodiment, in the case where two different plurality of trace elements are included, each of the plurality of trace elements 218 having the expanded final size has a plurality of unexpanded throughout the heating sequence. Each of the trace elements 214 is large About the same shape and size, as shown. However, it should be understood that each of the plurality of trace elements 218 having the expanded final size need not have the same shape and/or size as each of the plurality of trace elements 214. In one embodiment, as described in more detail below in association with Figures 6A-6C, the resulting molded polishing body of pad 222 includes a plurality of expanded microelements 218 as closed cell pores, and a plurality of expanded microelements 218 comprising A first diameter pattern having a peak of a first size distribution. Moreover, a second plurality of trace elements 214 are also included as closed-cell pores, and a second plurality of trace elements 214 comprise a second diameter pattern having a second peak of different size distribution. In one such embodiment, the plurality of closed cell pores of trace element 218 and the second plurality of closed cell pores of trace element 214 provide a thermoset polyurethane material in the thermoset polyurethane material about between low density polishing pad 222. The total pore volume in the range of 55% to 80% of the total volume.

Referring again to FIGS. 2D-2G, in one embodiment, heating the mixture 210 to provide a molded polishing body 222 involves forming a polishing body 222 having a density of less than 0.5 g/cc. However, in one such embodiment, the mixture 210 has a density greater than 0.5 g/cc prior to heating. In one embodiment, the prepolymer 202 is an isocyanate and the chain extender or crosslinker 204 is an aromatic bisamine compound, and the polishing pad 222 is comprised of a thermoset polyurethane material 220. In one such embodiment, forming the mixture 210 further involves adding a devitrified filler to the prepolymer 202 and chain extender or crosslinker 204 to ultimately provide an opaque molded polishing body 222. In certain such embodiments, the devitrification filler is such as, but not limited to, boron nitride, barium fluoride, graphite, graphite fluoride, molybdenum sulfide, barium sulfide, talc, barium sulfide, tungsten disulfide or Teflon. Material. In an embodiment, as briefly mentioned above, the mixture 210 is only partially cured in the mold 200, and in one embodiment, is further cured in the furnace after removal from the forming mold 200.

In one embodiment, the polishing pad precursor mixture 210 is used to ultimately form a molded homogeneous polishing body 222 comprised of a thermoset closed cell polyurethane material. In one such embodiment, the polishing pad precursor mixture 210 is used to ultimately form a hard mat and only a single type is used Curing agent 204. In another embodiment, the polishing pad precursor mixture 210 is used to ultimately form a cushion and a combination of primary and secondary curing agents (provided together 210) is used. For example, in a particular embodiment, the prepolymer 202 comprises a polyurethane precursor, the primary curing agent comprises an aromatic bisamine compound, and the secondary curing agent comprises an ether linkage. In a particular embodiment, the polyurethane pre-system isocyanate, the primary curing agent is an aromatic diamine, and the secondary curing agent is such as, but not limited to, polytetramethylene glycol, amine functional diol or amine functional A curing agent for polyoxypropylene. In one embodiment, the prepolymer 202, the primary curing agent, and the secondary curing agent (together 204) have an approximate molar ratio of 106 parts prepolymer, 85 parts primary curing agent, and 15 secondary curing agents, ie, To provide a prepolymer of about 1:0.96: stoichiometry of the curing agent. It will be appreciated that polishing pads having varying hardness values can be provided using variations in ratios or based on the specific properties of the prepolymer and the first and second curing agents.

Referring again to FIG. 2G, as explained above, in one embodiment, heating in the forming mold 200 involves forming a groove pattern in the polishing surface 224 of the molded polishing body 222. The groove pattern as shown includes a radial groove and a concentric circular circumferential groove. It should be understood that radial or circumferential grooves may be omitted. Further, the concentric circumferential grooves may alternatively be polygonal, such as a nested triangle, a square, a pentagon, a hexagon, or the like. Alternatively, the polishing surface can alternatively be based on a protrusion rather than a groove. In addition, a low density polishing pad can be fabricated without a recess in the polishing surface. In one such example, an unpatterned lid of the molding device is used instead of a patterned lid. Alternatively, another option may omit the use of the cover during molding. In the case where a lid is used during molding, the mixture 210 can be heated at a pressure in the range of from about 2 pounds per square inch to 12 pounds per square inch.

In one aspect, a low density mat having closed cell pores can be fabricated. For example, in one embodiment, the polishing pad comprises a polishing body having a density of less than 0.6 and composed of a thermosetting polyurethane material. A plurality of closed cell pores are dispersed in the thermosetting polyurethane material. In a particular embodiment, the density is less than 0.5 g/cc. In one embodiment, the plurality of closed cell pores provide about a total volume of the thermosetting polyurethane material in the thermoset polyurethane material. The total pore volume in the range of 55% to 80%. In one embodiment, each of the plurality of closed cell apertures is substantially spherical. In an embodiment, the polishing body further includes a first channel-shaped surface; and a second planar surface opposite the first surface, as set forth in association with FIG. 2G. In one embodiment, the polishing master system homogenizes the body, as explained in more detail below.

In an exemplary embodiment, each of the plurality of closed cell pores comprises a physical outer shell comprised of a material different from the thermoset polyurethane material. In this case, the closed cell pores can be made by including a pore former in the mixture molded for final pad fabrication, as set forth above.

In another exemplary embodiment, each of the plurality of closed cell pores comprises a physical outer shell comprised of a material different from the thermoset polyurethane material. The physical outer casing of the first portion of the plurality of closed-cell apertures is constructed of a material different from the physical outer casing of the second portion of the plurality of closed-cell apertures. In this case, the closed cell pores can be made by including two types of pore formers (e.g., expanded and unexpanded) in the mixture molded for final pad fabrication, as set forth above.

In another exemplary embodiment, each of only a portion of the plurality of closed cell apertures comprises a physical outer shell comprised of a material different from the thermoset polyurethane material. In this case, the closed cell pores can be made by including both a pore former and a bubble or droplet in the mixture molded for final pad fabrication, as set forth above.

In another exemplary embodiment, each of the plurality of closed cell pores does not comprise a physical outer shell of a material other than the thermoset polyurethane material. In this case, the closed cell pores can be made by including bubbles or droplets or both in the mixture molded for final pad fabrication, as set forth above.

3 illustrates a cross-sectional view of a low density polishing pad 300 comprising all of the closed cell pores based on the pore former filler in accordance with an embodiment of the present invention at 100 times and 300 times magnification. Referring to Figure 3, all of the pores shown are formed from a pore former, and as such, all pores contain Body shell. One portion of the pores is formed by a pre-expanded Expancel porogen. The other portion is formed from an unexpanded Expancel porogen that expands during the molding process used to make the polishing pad 300. In one such embodiment, the unexpanded Expancel is designed to expand at low temperatures. The molding or casting process temperature is above the expansion temperature and Expancel rapidly expands during molding or casting. Pad 300 has a density of about 0.45 and all of the pores in the mat are closed cell pores.

4 illustrates a cross-sectional view of a low density polishing pad 400 comprising closed cell voids at 100 times and 300 times magnification, in accordance with an embodiment of the present invention, one of which is based in part on a pore former filler and the closed cells One of the pores is based in part on the bubbles. Referring to Figure 4, the small pores shown are formed of a pore former and, as such, comprise a solid outer shell. More specifically, the small pores are formed by a pre-expanded Expancel porogen. Large pores are formed using a gas. More specifically, the macropores are formed using a small amount of water and a surfactant that is injected into the pad formulation mixture prior to molding or casting. During the chemical reaction of the chain extension, there are competing chemical reaction of water with NCO to form CO ₂ and the hole is formed. It should be understood that the type and concentration of surfactant and the type and amount of catalyst control pore size and closed/open pore ratio. The density of the pad 400 is approximately 0.37 and the majority of the apertures in the pad are closed cell pores.

In one aspect, the pore diameter distribution in the polishing pad can have a bell curve or a single mode distribution. For example, Figure 5A illustrates a plot of population versus pore diameter for a broad monomodal pore diameter distribution in a low density polishing pad in accordance with an embodiment of the present invention. Referring to graph 500A of Figure 5A, the single mode distribution can be relatively wide. As another example, FIG. 5B illustrates a plot of population versus narrow pore size for a narrow single mode distribution of pore diameters in a low density polishing pad in accordance with an embodiment of the present invention. Referring to graph 500B of Figure 5B, the single mode distribution can be relatively narrow. In a narrow distribution or a broad distribution, only one largest diameter population (such as the largest population of 40 microns) (as shown by way of example) is provided in the polishing pad.

In another aspect, a low density polishing pad can alternatively be fabricated with a bimodal pore diameter distribution. As an example, FIG. 6A illustrates having approximately 1:1 in accordance with an embodiment of the present invention. A cross-sectional view of a low density polishing pad of a bimodal closed cell pore distribution.

Referring to FIG. 6A, polishing pad 600 includes a homogeneous polishing body 601. The homogeneous polishing body 601 is composed of a thermosetting polyurethane material in which a plurality of closed cell apertures 602 are disposed in the homogeneous polishing body 601. A plurality of closed cell apertures 602 have a multimodal diameter distribution. In one embodiment, the multimodal diameter distribution includes a bimodal diameter distribution of the small diameter mode 604 and the large diameter mode 606, as depicted in Figure 6A.

In one embodiment, the plurality of closed cell apertures 602 comprise discrete apertures from each other, as depicted in Figure 6A. This is in contrast to the open pores that are permeable to each other through channels, such as those in conventional sponges. In one embodiment, each of the closed cell pores comprises a solid outer shell, such as a shell of a porogen. However, in another embodiment, some or all of the closed cell pores in the closed cell pores do not comprise a solid outer shell. In one embodiment, the plurality of closed cell apertures 602 and thus the thermoset polyurethane material having a multimodal diameter distribution throughout the homogeneous polishing body 601 are substantially equally and uniformly distributed, as depicted in Figure 6A.

In one embodiment, the bimodal pore diameter distribution of the plurality of closed cell pores 602 can be about 1:1, as depicted in Figure 6A. To illustrate this concept for a better map, FIG. 6B illustrates a graph 620 of a population of narrow pore diameter distributions in the polishing pad of FIG. 6A as a function of pore diameter, in accordance with an embodiment of the present invention. Figure 6C is a graph 630 of a population of broad pore diameter distributions in the polishing pad of Figure 6A as a function of pore diameter, in accordance with an embodiment of the present invention.

Referring to Figures 6A-6C, the diameter of the largest population of large diameter modes 606 is approximately twice the diameter of the largest population of small diameter modes 604. For example, in one embodiment, the largest population of large diameter modes 606 has a diameter value of about 40 microns and the largest population of small diameter modes 604 has a diameter value of about 20 microns, as depicted in Figures 6B and 6C. Show. As another example, the largest population of large diameter modes 606 has a diameter value of about 80 microns and the largest population of small diameter modes 604 has a diameter value of about 40 microns.

Referring to the graph 620 of FIG. 6B, in one embodiment, the pore diameter distribution is narrow of. In a particular embodiment, the population of large diameter patterns 606 does not substantially overlap with the population of small diameter patterns 604. However, in another embodiment, referring to graph 630 of Figure 6C, the pore diameter distribution is broad. In a particular embodiment, the population of large diameter patterns 606 overlaps with the population of small diameter patterns 604. It should be understood that the bimodal pore diameter distribution need not be 1:1 as explained above in association with Figures 6A-6C. Furthermore, the bimodal pore diameter distribution does not have to be uniform. In another embodiment, the multimodal diameter distribution of the closed cell pores is gradient across the thermoset polyurethane material with a gradient from the first trough surface to the second flat surface. In one such embodiment, the gradient multimodal diameter distribution is a bimodal diameter distribution comprising a small diameter pattern proximate to the first trough surface and a large diameter pattern proximate to the second flat surface.

In one embodiment, the low density polishing pad then comprises a plurality of closed cell pores having a bimodal diameter distribution comprising a first diameter pattern having a first size distribution peak and having a second different size The second diameter mode of the distribution peak. In one such embodiment, the first diameter mode closed cell pores each comprise a solid outer shell comprised of a material different from the thermoset polyurethane material. In certain such embodiments, the second diameter mode closed cell pores each comprise a solid outer shell comprised of a material different from the thermoset polyurethane material. In certain such embodiments, the physical outer shell of each of the closed-cell apertures of the second diameter mode is constructed of a material that is different from the material of the solid outer shell of the first diameter mode closed-cell aperture.

In an embodiment, the first size distribution peak of the first diameter mode has a diameter in a range of approximately 10 microns to 50 microns, and the second size distribution peak of the second diameter pattern has a range of approximately 10 microns to 150 The diameter in the range of microns. In an embodiment, the first diameter mode overlaps the second diameter mode. However, in another embodiment, the first diameter mode and the second diameter mode have substantially no overlap. In an embodiment, the total population of the number of counts of the first diameter mode is not equal to the total population of the number of counts of the second diameter mode. However, in another embodiment, the total population of the number of counts of the first diameter mode is approximately A total population equal to the number of counts of the second diameter mode. In one embodiment, the bimodal diameter distribution is substantially equally distributed throughout the thermoset polyurethane material. However, in another embodiment, the bimodal diameter distribution is distributed over the thermosetting polyurethane material in a gradient manner.

In one embodiment, the low density polishing pads (such as polishing pads 222, 300 or 400 or variations thereof set forth herein) as set forth herein are suitable for polishing substrates. In one such embodiment, the polishing pad is used as a wiper pad. The substrate can be a substrate used in the semiconductor manufacturing industry, such as a germanium substrate on which devices or other layers are disposed. However, the substrate can be, for example, but not limited to, a substrate for a MEMS device, a photomask, or a solar module. Thus, as used herein, reference to "a polishing pad for polishing a substrate" is intended to encompass such and related possibilities.

The low density polishing pads (such as polishing pads 222, 300 or 400 or variations thereof set forth herein) as set forth herein may be comprised of a homogeneous polishing body of thermoset polyurethane material. In one embodiment, the homogeneous polishing body is comprised of a thermoset closed cell polyurethane material. In one embodiment, the term "homogeneous" is used to indicate that the composition of the thermoset closed cell polyurethane material is consistent throughout the entire composition of the polishing body. For example, in one embodiment, the term "homogeneous" excludes polishing pads composed of, for example, impregnated felt or a combination of multiple layers of different materials (composites). In one embodiment, the term "thermosetting" is used to indicate an irreversibly solidified polymeric material, such as a polymer web that is irreversibly rendered infusible and insoluble by curing. For example, in one embodiment, the term "thermosetting" excludes polishing pads composed of, for example, "thermoplastic" materials or "thermoplastics" - which become liquid when heated and return to the pole when sufficiently cooled Composition of a glassy polymer. It should be noted that polishing pads made from thermoset materials are typically made from lower molecular weight precursors that react in a chemical reaction to form a polymer, while pads made from thermoplastic materials are typically made by heating pre-existing The polymer causes a phase change to form a polishing pad in a physical process. Polyurethane thermoset polymers can be selected for use in making the throws described herein based on their tendency to stabilize thermal and mechanical properties, chemical environmental tolerance and abrasion resistance. Light pad.

In one embodiment, the homogeneous polishing body has a polished surface roughness in the range of about 1 micron to 5 micron root mean square after trimming and/or polishing. In one embodiment, the homogeneous polishing body has a polished surface roughness of about 2.35 microns root mean square after trimming and/or polishing. In one embodiment, the homogeneous polishing body has a storage modulus in the range of from about 30 megapascals (MPa) to about 120 megapascals at 25 degrees Celsius. In another embodiment, the homogeneous polishing body has a storage modulus of less than about 30 megapascals (MPa) at 25 degrees Celsius. In one embodiment, the homogeneously polished body has a compression ratio of about 2.5%.

In an embodiment, the low density polishing pad (such as polishing pad 222, 300 or 400 or variations thereof as set forth above) as set forth herein comprises a molded homogeneous polishing body. The term "molded" is used to indicate that a homogeneous polishing body is formed in a forming mold, as explained in more detail above in association with Figures 2A-2G. It should be understood that in other embodiments, casting procedures may alternatively be used to make low density polishing pads, such as the low density polishing pads described above.

In one embodiment, the homogeneous polishing master system is opaque. In one embodiment, the term "opaque" is used to indicate a material that allows about 10% or less of visible light to pass through. In one embodiment, the homogeneous polishing body is largely or completely opaque because the homogeneous thermoset closed cell polyurethane material throughout the homogeneous polishing body comprises a devitrified filler (eg, as an additional component thereof). In a particular embodiment, the devitrification filler is a material such as, but not limited to, boron nitride, barium fluoride, graphite, graphite fluoride, molybdenum sulfide, barium sulfide, talc, barium sulfide, tungsten disulfide or Teflon. .

The size of the low density polishing pad, such as pad 222, 300 or 400, can vary depending on the application. However, specific parameters can be used to make polishing pads that are compatible with conventional processing equipment or even with conventional chemical mechanical processing operations. For example, in accordance with an embodiment of the present invention, the low density polishing pad has a thickness in the range of from about 0.075 inches to 0.130 inches (eg, in the range of from about 1.9 mm to 3.3 mm). In one embodiment, a low density polishing pad Having a range of between about 20 inches and 30.3 inches (eg, between about 50 centimeters and 77 centimeters) and possibly between about 10 inches and 42 inches (eg, about 25 centimeters) The diameter to the extent of 107 cm).

In another embodiment of the invention, the low density polishing pad described herein further comprises a localized transparent (LAT) region disposed in the polishing pad. In an embodiment, the LAT region is disposed in the polishing pad and is covalently bonded to the polishing pad. U.S. Patent Application Serial No. 12/657,135, filed on Jan. 13, 2010, to the entire entire entire entire entire entire entire entire content An example. In an alternative or additional embodiment, the low density polishing pad further includes an aperture disposed in the polishing surface and in the polishing body. The aperture can house, for example, a detection device contained in a platen of the polishing tool. The adhesive sheet is placed on the rear surface of the polishing body. The adhesive sheet provides a watertight seal to the orifice at the surface behind the polishing body. An example of a suitable orifice is set forth in U.S. Patent Application Serial No. 13/184,395, filed on Jan. 15, 2011. In another embodiment, the low density polishing pad further includes a detection area for use with, for example, an eddy current detection system. An example suitable for an eddy current detection zone is set forth in U.S. Patent Application Serial No. 12/895,465, filed on Sep. 30, 2010.

The low density polishing pad (such as polishing pad 222, 300 or 400 or variations thereof as set forth above) as set forth herein may further comprise a base layer disposed on the rear surface of the polishing body. In one such embodiment, the result is a polishing pad having a block or base material that is different from the material of the polishing surface. In one embodiment, the composite polishing pad comprises a base or block layer of a stable, substantially incompressible inert material to which the polishing surface layer is disposed. The harder base layer provides support and strength to the pad integrity, while the softer polished surface layer reduces scratches, thereby achieving the disengagement of the material properties of the polishing layer from the remainder of the polishing pad. Examples of suitable base layers are set forth in U.S. Patent Application Serial No. 13/306,845, filed on Nov. 29, 2011.

The low density polishing pad (such as polishing pad 222, 300 or 400 or variations thereof as set forth above) as set forth herein may further comprise a subpad disposed on the rear surface of the polishing body, for example, as is known in the art of CMP. pad. In one such embodiment, the subpad is constructed from materials such as, but not limited to, foam, rubber, fiber, felt, or high porosity materials.

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

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

The individual grooves of the groove pattern (including at or near one of the orifices in the polishing pad) as described herein may have a uniform volume, a variable volume, or any combination thereof, depending on the depth and width dimensions previously set forth. . In some embodiments, the grooves all have a uniform volume. However, in some embodiments, the groove volume increases as the distance from the center of the polishing pad increases. In certain other embodiments, the groove volume decreases as the distance from the center of the polishing pad increases. In some embodiments, the grooves of uniform volume alternate with the grooves of variable volume.

The grooves of the groove pattern set forth herein may have a spacing of from about 30 mils to about 1000 mils. In some embodiments, the grooves have a spacing of about 125 mils. For a circular polishing pad, the groove spacing is measured along the radius of the circular polishing pad. In the CMP tape, the groove pitch is measured from the center of the CMP tape to the edge of the CMP tape. The grooves can have a uniform pitch, a variable pitch, or any combination thereof. In some embodiments, the grooves all have a uniform spacing. However, in some embodiments, the groove pitch increases as the distance from the center of the polishing pad increases. In certain other embodiments, the groove pitch decreases as the distance from the center of the polishing pad increases. In some embodiments, the distance between the grooves in one sector varies with increasing distance from the center of the polishing pad, while the spacing between the grooves in adjacent sectors remains uniform. In some embodiments, the distance between the grooves in one sector increases with increasing distance from the center of the polishing pad, while the spacing between grooves in adjacent sectors increases at different rates. In some embodiments, the distance between the grooves in one sector increases as the distance from the center of the polishing pad increases, and the distance between the grooves in the adjacent sectors increases with distance from the center of the polishing pad. Reduced. In some embodiments, the uniformly spaced grooves alternate with the variable pitch grooves. In some embodiments, the sectors of the uniformly spaced grooves alternate with the sectors of the variable pitch grooves.

The polishing pads described herein can be adapted for use with a variety of chemical mechanical polishing devices. As an example, Figure 7 illustrates an isometric side view of a polishing apparatus compatible with a low density polishing pad in accordance with an embodiment of the present invention.

Referring to Figure 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. The platen 704 can be configured to provide a mandrel rotation 706 and a slider oscillation 708. During polishing of the semiconductor wafer using the polishing pad, the sample carrier 710 is used to hold, for example, the semiconductor wafer 711 in place. The sample carrier 710 is further supported by a suspension mechanism 712. A slurry feed 714 is included to provide a slurry for the surface of the polishing pad before and during polishing of the semiconductor wafer. A trim unit 790 can also be included, and in one embodiment, the trim unit 1090 includes a diamond tip for trimming the polishing pad.

Thus, low density polishing pads and methods of making low density polishing pads have been disclosed. In accordance with an embodiment of the present invention, a polishing pad for polishing a substrate comprises a polishing body having a density of less than 0.5 g/cc and composed of a thermosetting polyurethane material. A plurality of closed cell pores are dispersed in the thermosetting polyurethane material. In one embodiment, the polishing master system homogenizes the body.

214‧‧‧ trace elements

218‧‧‧Final larger size/expansion trace elements/final size/trace elements

220‧‧‧Mat material/low density polishing pad/curing material/thermosetting polyurethane material

222‧‧‧Low-density polishing pad/pad/molding polishing body/polishing body/polishing pad/opaque molding polishing body/molding homogeneous polishing body

224‧‧‧ Polished surface

226‧‧‧radial grooves

228‧‧‧Concentric circular groove

A-a’‧‧‧ axis

Claims (60)

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 thermosetting polyurethane material; and a plurality of closed cell pores dispersed in the thermosetting polyurethane material, wherein The plurality of closed-cell pores have a bimodal diameter distribution comprising a first diameter pattern having a first size distribution peak and a second diameter pattern having a second different size distribution peak. A polishing pad according to claim 1, wherein the polishing main system homogenizes the polishing body. The polishing pad of claim 1, wherein each of the plurality of closed cell apertures comprises a physical outer casing comprising a material different from the thermoset polyurethane material. The polishing pad of claim 3, wherein the physical shells of the first portion of the plurality of closed-cell apertures comprise materials of the physical shells that are different from the second portion of the plurality of closed-cell apertures. The polishing pad of claim 1, wherein each of only a portion of the plurality of closed cell apertures comprises a physical outer casing comprising a material different from the thermoset polyurethane material. The polishing pad of claim 1, wherein each of the plurality of closed cell pores does not comprise a physical outer shell having a material different from the thermoset polyurethane material. The polishing pad of claim 1, wherein the plurality of closed cell pores provide a total pore volume in the thermosetting polyurethane material in a range from about 55% to about 80% of the total volume of the thermosetting polyurethane material. The polishing pad of claim 1, wherein the polishing body further comprises: a first surface having a groove shape; and a second surface opposite the first surface, the second surface being flat. The polishing pad of claim 1, wherein each of the plurality of closed cell apertures is substantially spherical. The polishing pad of claim 1, wherein the closed pore apertures of the first diameter mode each comprise a solid outer shell comprising a material different from the thermoset polyurethane material. The polishing pad of claim 10, wherein the closed cell apertures of the second diameter mode each comprise a solid outer shell comprising a material different from the thermoset polyurethane material. The polishing pad of claim 11, wherein the physical outer casing of each of the closed-cell apertures of the second diameter mode comprises the material of the physical outer casings of the closed-cell apertures of the first diameter mode Material. The polishing pad of claim 1, wherein the first size distribution peak of the first diameter mode has a diameter in a range of approximately 10 microns to 50 microns, and wherein the second size distribution peak of the second diameter pattern It has a diameter in the range of approximately 10 microns to 150 microns. The polishing pad of claim 1, wherein the first diameter pattern overlaps the second diameter pattern. The polishing pad of claim 1, wherein the first diameter mode has substantially no overlap with the second diameter mode. The polishing pad of claim 1, wherein the total population of the number of counts of the first diameter mode is not equal to the total population of the number of counts of the second diameter mode. The polishing pad of claim 1, wherein the total population of the number of counts of the first diameter pattern is approximately equal to a total population of the number of counts of the second diameter pattern. A polishing pad according to claim 1, wherein the bimodal diameter distribution is substantially equally distributed throughout the thermosetting polyurethane material. A polishing pad according to claim 1, wherein the polishing master system molds the polishing body. The polishing pad of claim 1, wherein the polishing body further comprises: a devitrified filler distributed approximately equally throughout the polishing body. A polishing pad according to claim 1, further comprising: a base layer disposed on a rear surface of the polishing body. The polishing pad of claim 1, further comprising: a detection area disposed in a rear surface of the polishing body. The polishing pad of claim 1, further comprising: a subpad disposed on a rear surface of the polishing body. The polishing pad of claim 1, further comprising: a localized transparent (LAT) region disposed in the polishing body and covalently bonded to the polishing body. A polishing pad for polishing a substrate, the polishing pad comprising: a polishing body having a density of less than about 0.6 g/cc and comprising: a thermosetting polyurethane material; and a plurality of closed cell pores dispersed in the thermosetting polyurethane material, The plurality of closed-cell pores have a bimodal diameter distribution comprising a first diameter pattern having a first size distribution peak and a second diameter pattern having a second different size distribution peak. A polishing pad according to claim 25, wherein the polishing main system homogenizes the polishing body. The polishing pad of claim 25, wherein the closed cell apertures of the first diameter mode each comprise a solid outer shell comprising a material different from the thermoset polyurethane material. The polishing pad of claim 27, wherein the closed cell apertures of the second diameter mode each comprise a solid outer shell comprising a material different from the thermoset polyurethane material. a polishing pad of claim 28, each of the closed pores of the second diameter mode The physical outer casing of one of the materials includes the material of the material of the physical outer casings of the closed pores of the first diameter mode. The polishing pad of claim 25, wherein the first size distribution peak of the first diameter mode has a diameter in a range from about 10 microns to 50 microns, and wherein the second size distribution peak of the second diameter pattern It has a diameter in the range of approximately 10 microns to 150 microns. The polishing pad of claim 25, wherein the first diameter pattern overlaps the second diameter pattern. The polishing pad of claim 25, wherein the first diameter mode has substantially no overlap with the second diameter mode. The polishing pad of claim 25, wherein the total population of the number of counts of the first diameter pattern is not equal to the total population of the number of counts of the second diameter pattern. A polishing pad according to claim 25, wherein the total population of the number of counts of the first diameter pattern is approximately equal to a total population of the number of counts of the second diameter pattern. A polishing pad according to claim 25, wherein the bimodal diameter distribution is substantially equally distributed throughout the thermosetting polyurethane material. A method of making a polishing pad, the method comprising: mixing a prepolymer and a chain extender or a crosslinking agent with a plurality of trace elements to form a mixture, each of the plurality of trace elements having an initial size; and in a molding die Heating the mixture to provide a molded polishing body, the molded polishing body comprising a thermosetting polyurethane material and a plurality of closed cell pores dispersed in the thermosetting polyurethane material, the plurality of closed cell pores being made by the plural during the heating Each of the trace elements is expanded to a final larger size to form. The method of claim 36, wherein expanding each of the plurality of trace elements to the final size comprises increasing a volume of each of the plurality of trace elements by a factor of between about 3 and 1000 . The method of claim 36, wherein expanding each of the plurality of trace elements to the final size comprises providing a final diameter of each of the plurality of trace elements to between about 10 microns and 200 microns Within the scope. The method of claim 36, wherein expanding each of the plurality of trace elements to the final size comprises reducing a density of each of the plurality of trace elements by between about 3 and 1000 multiple. The method of claim 36, wherein expanding each of the plurality of trace elements to the final size comprises forming a substantially spherical shape for each of the plurality of trace elements of the final size. The method of claim 36, wherein mixing the prepolymer and the chain extender or crosslinker with the plurality of trace elements further comprises mixing with the second plurality of trace elements to form the mixture, the second plurality of traces Each of the elements has a size. The method of claim 41, wherein the heating is performed sufficiently low that the size of each of the second plurality of trace elements is performed at substantially the same temperature prior to the heating and after the heating. The method of claim 42, wherein the heating is performed at a temperature of about 100 degrees Celsius or less, and wherein the second plurality of trace elements have an expansion threshold greater than about 130 degrees Celsius. The method of claim 41, wherein the second plurality of trace elements have an expansion threshold greater than an expansion threshold of the plurality of trace elements. The method of claim 44, wherein the expansion threshold of the second plurality of trace elements is greater than about 120 degrees Celsius, and the expansion threshold of the plurality of trace elements is less than about 110 degrees Celsius. The method of claim 41, wherein the prepolymer, the chain extender or crosslinker, and the second plurality of trace elements have a viscosity, and the prepolymer, The chain extender or crosslinker, the mixture of the plurality of trace elements has the initial size, and the second plurality of trace elements have substantially the viscosity. The method of claim 46, wherein the viscosity is a predetermined viscosity and the relative amount of the second plurality of trace elements in the mixture is selected based on the predetermined viscosity. The method of claim 46, wherein the plurality of trace elements have little effect on the viscosity of the mixture. The method of claim 41, wherein the heating provides the molded polishing body, the molded polishing body comprising the thermosetting polyurethane material, the plurality of closed pore pores being dispersed in the thermosetting polyurethane material and by making the plurality of trace elements Each of which is formed by expanding to a final size comprising a first diameter pattern having a peak of a first size distribution, and a second plurality of closed cell pores are dispersed in the thermoset polyurethane material and comprising a peak having a second different size distribution The second plurality of trace elements of the second diameter mode are formed. The method of claim 49, wherein the plurality of closed cell pores and the second plurality of closed cell pores provide about 55% to 80% of the total volume of the thermosetting polyurethane material in the thermosetting polyurethane material The total pore volume. The method of claim 36, 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. The method of claim 51, wherein the mixture has a density greater than 0.5 g/cc prior to the heating. The method of claim 36, wherein the mixing further comprises injecting a gas into the prepolymer and the chain extender or crosslinker, or into a product formed therefrom. The method of claim 36, wherein the prepolymer is an isocyanate and the mixing further comprises adding water to the prepolymer. The method of claim 36, wherein the prepolymer and the chain extender or crosslink are mixed The agent includes a mixture of an isocyanate and an aromatic bisamine compound, respectively. The method of claim 36, wherein the mixing further comprises adding a devitrified filler to the prepolymer and the chain extender or crosslinker to provide an opaque molded polishing body. The method of claim 36, wherein heating the mixture comprises first partially curing in the forming mold and then further curing in the furnace. The method of claim 36, wherein heating in the forming mold comprises forming a groove pattern in the polishing surface of the molded polishing body. The method of claim 36, wherein each of the plurality of trace elements having the initial size comprises a solid outer shell, and wherein each of the plurality of trace elements having the final size comprises an expanded solid outer shell. The method of claim 36, wherein each of the plurality of trace elements having the initial size is a droplet, and wherein each of the plurality of trace elements having the final size is a bubble.