Patent Publication Number: US-2015065013-A1

Title: Chemical mechanical polishing pad

Description:
The present invention relates to chemical mechanical polishing pads and methods of making and using the same. More particularly, the present invention relates to a chemical mechanical polishing pad comprising a polishing layer; a rigid layer; and, a hot melt adhesive bonding the polishing layer to the rigid layer; wherein the polishing layer exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; an elongation to break of 100 to 300%; and, a unique combination of an initial hydrolytic stability and a sustained hydrolytic instability; and, wherein the polishing layer has a polishing surface adapted for polishing the substrate. 
     The production of semiconductors typically involves several chemical mechanical planarization (CMP) processes. In each CMP process, a polishing pad in combination with a polishing solution, such as an abrasive-containing polishing slurry or an abrasive-free reactive liquid, removes excess material in a manner that planarizes or maintains flatness for receipt of a subsequent layer. The stacking of these layers combines in a manner that forms an integrated circuit. The fabrication of these semiconductor devices continues to become more complex due to requirements for devices with higher operating speeds, lower leakage currents and reduced power consumption. In terms of device architecture, this translates to finer feature geometries and increased metallization levels. These increasingly stringent device design requirements are driving the adoption of copper metallization in conjunction with new dielectric materials having lower dielectric constants. The diminished physical properties, frequently associated with low k and ultra-low k materials, in combination with the devices&#39; increased complexity have led to greater demands on CMP consumables, such as polishing pads and polishing solutions. 
     In particular, low k and ultra-low k dielectrics tend to have lower mechanical strength and poorer adhesion in comparison to conventional dielectrics, rendering planarization more difficult. In addition, as integrated circuits&#39; feature sizes decrease, CMP-induced defectivity, such as, scratching becomes a greater issue. Furthermore, integrated circuits&#39; decreasing film thickness requires improvements in defectivity while simultaneously providing acceptable topography to a wafer substrate—these topography requirements demand increasingly stringent planarity, dishing and erosion specifications. 
     Polyurethane polishing pads are the primary pad chemistry used for a variety of demanding precision polishing applications. Polyurethane polishing pads are effective for polishing silicon wafers, patterned wafers, flat panel displays and magnetic storage disks. In particular, polyurethane polishing pads provide the mechanical integrity and chemical resistance for most polishing operations used to fabricate integrated circuits. For example, polyurethane polishing pads have high strength for resisting tearing; abrasion resistance for avoiding wear problems during polishing; and stability for resisting attack by strong acidic and strong caustic polishing solutions. 
     A family of polyurethane polishing layers is disclosed by Kulp in U.S. Pat. No. 8,288,448. Kulp discloses a polishing pad that includes a cast polyurethane polymeric material formed with an isocyanate-terminated reaction product formed from a prepolymer reaction of a prepolymer polyol and a polyfunctional isocyanate. The isocyanate-terminated reaction product has 4.5 to 8.7 weight percent unreacted NCO; and the isocyanate-terminated reaction product is cured with a curative agent selected from the group comprising curative polyamines, curative polyols, curative alcoholamines and mixtures thereof. 
     Notwithstanding, there is a continuing need for chemical mechanical polishing pads that exhibit an appropriate balance of properties that provides degree of planarization while minimizing defect formation. 
     The present invention provides a chemical mechanical polishing pad, comprising: a polishing layer having a polishing surface, a base surface and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface from the polishing surface to the base surface; wherein the polishing layer is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, optionally, (c) a plurality of microelements; wherein the polishing layer exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; and, an elongation to break of 100 to 300%; wherein the polishing layer exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C.; wherein the polishing layer exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by ≧1.75% following immersion in deionized water for seven days at 25° C.; a rigid layer having a top surface and a bottom surface; a hot melt adhesive interposed between the base surface of the polishing layer and the top surface of the rigid layer; wherein the hot melt adhesive bonds the polishing layer to the rigid layer; a pressure sensitive platen adhesive layer having a stack side and a platen side; wherein the stack side of the pressure sensitive platen adhesive layer is adjacent to the bottom surface of the rigid layer; and, optionally, a release liner; wherein the optional release liner is disposed on the platen side of the pressure sensitive platen adhesive layer. 
     The present invention provides a chemical mechanical polishing pad, comprising: a polishing layer having a polishing surface, a base surface and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface from the polishing surface to the base surface; wherein the polishing layer is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, optionally, (c) a plurality of microelements; wherein the curative and the isocyanate terminated prepolymer have an OH or NH 2  to unreacted NCO stoichiometric ratio of 80 to &lt;95 percent; wherein the polishing layer exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; and, an elongation to break of 100 to 300%; wherein the polishing layer exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C.; wherein the polishing layer exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by 1.75 to 3.5% following immersion in deionized water for seven days at 25° C.; a rigid layer having a top surface and a bottom surface; a hot melt adhesive interposed between the base surface of the polishing layer and the top surface of the rigid layer; wherein the hot melt adhesive bonds the polishing layer to the rigid layer; a pressure sensitive platen adhesive layer having a stack side and a platen side; wherein the stack side of the pressure sensitive platen adhesive layer is adjacent to the bottom surface of the rigid layer; and, optionally, a release liner; wherein the optional release liner is disposed on the platen side of the pressure sensitive platen adhesive layer. 
     The present invention provides a chemical mechanical polishing pad, comprising: a polishing layer having a polishing surface, a base surface and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface from the polishing surface to the base surface; wherein the polishing layer is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, optionally, (c) a plurality of microelements; wherein the polishing layer exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; and, an elongation to break of 100 to 300%; wherein the polishing layer exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C.; wherein the polishing layer exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by 1.75 to 3.5% following immersion in deionized water for seven days at 25° C.; a rigid layer having a top surface and a bottom surface; wherein the rigid layer is made of a biaxially oriented polyethylene terephthalate; wherein the rigid layer has an average thickness of 6 to 15 mils; and, wherein the rigid layer exhibits a Young&#39;s Modulus of 3,000 to 7,000 MPa; a hot melt adhesive interposed between the base surface of the polishing layer and the top surface of the rigid layer; wherein the hot melt adhesive bonds the polishing layer to the rigid layer; a pressure sensitive platen adhesive layer having a stack side and a platen side; wherein the stack side of the pressure sensitive platen adhesive layer is adjacent to the bottom surface of the rigid layer; and, optionally, a release liner; wherein the optional release liner is disposed on the platen side of the pressure sensitive platen adhesive layer. 
     The present invention provides a chemical mechanical polishing pad, comprising: a polishing layer having a polishing surface, a base surface and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface from the polishing surface to the base surface; wherein the polishing layer is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has &gt;8.7 to 9 weight percent unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereat and, optionally, (c) a plurality of microelements; wherein the polishing layer exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; and, an elongation to break of 100 to 300%; wherein the polishing layer exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C.; wherein the polishing layer exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by 1.75 to 3.5% following immersion in deionized water for seven days at 25° C.; a rigid layer having a top surface and a bottom surface; a hot melt adhesive interposed between the base surface of the polishing layer and the top surface of the rigid layer; wherein the hot melt adhesive bonds the polishing layer to the rigid layer; a pressure sensitive platen adhesive layer having a stack side and a platen side; wherein the stack side of the pressure sensitive platen adhesive layer is adjacent to the bottom surface of the rigid layer; optionally, a release liner; wherein the optional release liner is disposed on the platen side of the pressure sensitive platen adhesive layer; and, an endpoint detection window. 
     The present invention provides a method of polishing a substrate, comprising: providing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate; providing a chemical mechanical polishing pad according to the present invention; creating dynamic contact between a polishing surface of the polishing layer and the substrate to polish a surface of the substrate; and, conditioning of the polishing surface with an abrasive conditioner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a depiction of a perspective view of a chemical mechanical polishing pad of the present invention. 
         FIG. 2  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention. 
         FIG. 3  is a top plan view of a chemical mechanical polishing pad of the present invention. 
         FIG. 4  is a side perspective view of a polishing layer of the present invention. 
         FIG. 5  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention. 
         FIG. 6  is a elevational view of a plug in place window block of the present invention. 
         FIG. 7  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention with a plug in place window block. 
         FIG. 8  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention with a plug in place window block. 
         FIG. 9  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention with a plug in place window block. 
         FIG. 10  is a depiction of a cross sectional, cut away, elevational view of a chemical mechanical polishing pad of the present invention with an integral window. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional polyurethane polishing layers have been designed using polyurethane materials that exhibit both hydrolytic stability and extended hydrolytic stability. The conventional wisdom is that polyurethane materials need to remain dimensionally stable upon long term immersion in water for use in chemical mechanical polishing layers. Applicant has surprisingly found that the chemical mechanical polishing pad of the present invention having a polishing layer that exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90; an elongation to break of 100 to 300%; and, a unique combination of an initial hydrolytic stability and a sustained hydrolytic instability; provides improved planarization performance while minimizing defects, in particular, scratch defects that can lead to lower device yields. The unique balance of properties exhibited by the polishing layer of the present invention enables, for example, the effective planarization of semiconductor wafers having exposed copper features with minimal defect formation. 
     The term “average total thickness, T T-avg ” as used herein and in the appended claims in reference to a chemical mechanical polishing pad ( 10 ) having a polishing surface ( 14 ) means the average thickness, T T , of the chemical mechanical polishing pad measured in a direction normal to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the bottom surface ( 27 ) of the rigid layer ( 25 ). (See  FIGS. 1 ,  2 ,  5  and  7 - 10 ). 
     The term “initial hydrolytic stability” as used herein and in the appended claims in reference to a polishing layer means that a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C., as measured according to the procedure set forth in the Examples. 
     The term “extended hydrolytic stability” as used herein and in the appended claims in reference to a polishing layer means that a liner dimension of a sample of the polishing layer changes by &lt;1.75% following immersion in deionized water for 7 days at 25° C., as measured according to the procedure set forth in the Examples. 
     The term “sustained hydrolytic instability” as used herein and in the appended claims in reference to a polishing layer means that a linear dimension of a sample of the polishing layer changes by ≧1.75% following immersion in deionized water for 7 days at 25° C., as measured according to the procedure set forth in the Examples. 
     The term “substantially circular cross section” as used herein and in the appended claims in reference to a chemical mechanical polishing pad ( 10 ) means that the longest radius, r, of the cross section from the central axis ( 12 ) to the outer perimeter ( 15 ) of the polishing surface ( 14 ) of the polishing layer ( 20 ) is ≦20% longer than the shortest radius, r, of the cross section from the central axis ( 12 ) to the outer perimeter ( 15 ) of the polishing surface ( 14 ). (See  FIG. 1 ). 
     The chemical mechanical polishing pad ( 10 ) of the present invention is preferably adapted for rotation about a central axis ( 12 ). (See  FIG. 1 ). Preferably, the polishing surface ( 14 ) of polishing layer ( 20 ) is in a plane ( 28 ) perpendicular to the central axis ( 12 ). The chemical mechanical polishing pad ( 10 ) is preferably adapted for rotation in a plane ( 28 ) that is at an angle, γ, of 85 to 95° to the central axis ( 12 ), preferably, of 90° to the central axis ( 12 ). Preferably, the polishing layer ( 20 ) has a polishing surface ( 14 ) that has a substantially circular cross section perpendicular to the central axis ( 12 ). Preferably, the radius, r, of the cross section of the polishing surface ( 14 ) perpendicular to the central axis ( 12 ) varies by ≦20% for the cross section, more preferably by ≦10% for the cross section. 
     The chemical mechanical polishing pad ( 10 ) of the present invention is specifically designed to facilitate the polishing of a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate. Preferably, the chemical mechanical polishing pad ( 10 ) of the present invention is designed to facilitate the polishing of a semiconductor substrate. More preferably, the chemical mechanical polishing pad ( 10 ) of the present invention is designed to facilitate the polishing of exposed copper features on the surface of a semiconductor wafer substrate. 
     The chemical mechanical polishing pad ( 10 ) of the present invention, comprises: a polishing layer ( 20 ) having a polishing surface ( 14 ), a base surface ( 17 ) and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the base surface ( 17 ); a rigid layer ( 25 ) having a top surface ( 26 ) and a bottom surface ( 27 ); a hot melt adhesive ( 23 ) interposed between the base surface ( 17 ) of the polishing layer ( 20 ) and the top surface ( 26 ) of the rigid layer ( 25 ); wherein the hot melt adhesive ( 23 ) bonds the polishing layer ( 20 ) to the rigid layer ( 25 ); optionally, a pressure sensitive platen adhesive layer ( 70 ); wherein the pressure sensitive platen adhesive layer ( 70 ) is disposed on the bottom surface ( 27 ) of the rigid layer ( 25 ) (preferably, wherein the optional pressure sensitive platen adhesive layer facilitates mounting of the chemical mechanical polishing pad on a polishing machine); optionally, a release liner ( 75 ); wherein the pressure sensitive platen adhesive layer ( 70 ) is interposed between the bottom surface ( 27 ) of the rigid layer ( 25 ) and the optional release liner ( 75 ); and, optionally, an endpoint detection window ( 30 ) (preferably, wherein the endpoint detection window facilitates in situ polishing endpoint detection); wherein the polishing layer ( 20 ) is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent (preferably, 8.65 to 9.05 wt %; more preferably, &gt;8.7 to 9 wt %) unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, (c) optionally, a plurality of microelements; wherein the polishing layer ( 20 ) exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90 (preferably, &gt;60 to 75; more preferably, 61 to 75; most preferably, &gt;65 to 70); and, an elongation to break of 100 to 300% (preferably, 100 to 200%; more preferably, 125 to 175%; most preferably, 150 to 160%); wherein the polishing layer ( 20 ) exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C. (as measured according to the method described in the Examples); wherein the polishing layer ( 20 ) exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by ≧1.75% (preferably, 1.75 to 5%; more preferably, 1.75 to 3.5%; most preferably, 2 to 3%) following immersion in deionized water for seven days at 25° C. (as measured according to the method described in the Examples). (See  FIGS. 1-10 ). 
     Preferably, the polyfunctional isocyanate used in the formation of the polishing layer ( 20 ) is selected from the group consisting of an aliphatic polyfunctional isocyanate, an aromatic polyfunctional isocyanate and a mixture thereof. Preferably, the polyfunctional isocyanate used in the formation of the polishing layer ( 20 ) contains two reactive isocyanate groups (i.e., NCO). More preferably, the polyfunctional isocyanate used in the formation of the polishing layer ( 20 ) is a diisocyanate selected from the group consisting of 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4′-diphenylmethane diisocyanate; naphthalene-1,5-diisocyanate; tolidine diisocyanate; para-phenylene diisocyanate; xylylene diisocyanate; isophorone diisocyanate; hexamethylene diisocyanate; 4,4′-dicyclohexylmethane diisocyanate; cyclohexanediisocyanate; and, mixtures thereof. Most preferably, the polyfunctional isocyanate used in the formation of the polishing layer ( 20 ) is a toluene diisocyanate (preferably, a toluene diisocyanate selected from the group consisting of 2,4-toluene diisocyanate; 2,6-toluene diisocyanate and mixtures thereof). 
     Preferably, the isocyanate terminated prepolymer used in the formation of the polishing layer ( 20 ) has a 8 to 9.5 wt % unreacted isocyanate (NCO) groups. More preferably, the isocyanate terminated prepolymer used in the formation of the polishing layer ( 20 ) has 8.65 to 9.05 wt % (most preferably &gt;8.7 to 9 wt %) unreacted isocyanate (NCO) groups. 
     Preferably, the polyether based polyol is a polypropylene glycol based polyol and has an unreacted isocyanate (NCO) concentration of 8 to 9.5 wt % (more preferably, 8.65 to 9.05 wt %; most preferably, &gt;8.7 to 9 wt %). Examples of commercially available polypropylene glycol based isocyanate terminated urethane prepolymers include Imuthane® prepolymers (available from COIM USA, Inc., such as, PPT-80A, PPT-90A, PPT-95A, PPT-65D, PPT-75D); Adiprene® prepolymers (available from Chemtura, such as, LFG 963A, LFG 964A, LFG 740D); and, Andur® prepolymers (available from Anderson Development Company, such as, 8000APLF, 9500APLF, 6500DPLF, 750IDPLF). 
     Preferably, the isocyanate terminated prepolymer used in the formation of the polishing layer ( 20 ) is a low free isocyanate terminated urethane prepolymer having less than 0.1 wt % free toluene diisocyanate (TDI) monomer content. 
     Preferably, the curative agent used in the formation of the polishing layer ( 20 ) is selected from the group consisting of polyamines, curative polyols, curative alcoholamines and mixtures thereof. More preferably, the curative agent used in the formation of the polishing layer ( 20 ) is selected from polyols and polyamines. Still more preferably, the curative agent used in the formation of the polishing layer ( 20 ) is a difunctional curative selected from the group consisting of primary amines and secondary amines. More preferably, the difunctional curative is selected from the group consisting of diethyltoluenediamine (DETDA); 3,5-dimethylthio-2,4-toluenediamine and isomers thereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof (e.g., 3,5-diethyltoluene-2,6-diamine); 4,4′-bis-(sec-butylamino)-diphenylmethane; 1,4-bis-(sec-butylamino)-benzene; 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) (MCDEA); polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline (MDA); m-phenylenediamine (MPDA); 4,4′-methylene-bis-(2-chloroaniline) (MBOCA); 4,4′-methylene-bis-(2,6-diethylaniline) (MDEA); 4,4′-methylene-bis-(2,3-dichloroaniline) (MDCA); 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane, 2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycol di-p-aminobenzoate; isomers thereof; and, mixtures thereof. Most preferably, the curative agent is 4,4′-methylene-bis-(2-chloroaniline) (MBOCA). 
     Preferably, the stoichiometric ratio of the reactive hydrogen groups (i.e., the sum of the amine (NH 2 ) groups and the hydroxyl (OH) groups) in the curative agent to the unreacted isocyanate (NCO) groups in the isocyanate terminated prepolymer is 80 to &lt;95 percent (more preferably, 85 to &lt;95 percent; still more preferably, 87 to 94 percent; most preferably, 89 to 92 percent). 
     The polishing layer ( 20 ) optionally further comprises a plurality of microelements. Preferably, the plurality of microelements are uniformly dispersed throughout the polishing layer ( 20 ). Preferably, the plurality of microelements is selected from entrapped gas bubbles, hollow core polymeric materials, liquid filled hollow core polymeric materials, water soluble materials, an insoluble phase material (e.g., mineral oil) and a combination thereof. More preferably, the plurality of microelements is selected from entrapped gas bubbles and hollow core polymeric materials uniformly distributed throughout the polishing layer ( 20 ). Preferably, the plurality of microelements has a weight average diameter of less than 150 μm (more preferably of less than 50 μm; most preferably of 10 to 50 μm). Preferably, the plurality of microelements comprise polymeric microballoons with shell walls of either polyacrylonitrile or a polyacrylonitrile copolymer (e.g., Expancel® from Akzo Nobel). Preferably, the plurality of microelements are incorporated into the polishing layer ( 20 ) at 0 to 35 vol % porosity (more preferably 10 to 25 vol % porosity). 
     The polishing layer ( 20 ) can be provided in both porous and nonporous (i.e., unfilled) configurations. Preferably, the polishing layer ( 20 ) exhibits a specific gravity of greater than 0.6 as measured according to ASTM D1622. More preferably, the polishing layer ( 20 ) exhibits a specific gravity of 0.6 to 1.5 (still more preferably 0.7 to 1.2; most preferably 0.95 to 1.2) as measured according to ASTM D1622. 
     Preferably, the polishing layer ( 20 ) exhibits a Shore D hardness of 60 to 90 as measured according to ASTM D2240. More preferably, the polishing layer ( 20 ) exhibits a Shore D hardness of &gt;60 to 75 (more preferably, 61 to 75; most preferably, &gt;65 to 70) as measured according to ASTM D2240. 
     Preferably, the polishing layer ( 20 ) exhibits an elongation to break of 100 to 300% as measured according to ASTM D412. Preferably, the polishing layer ( 20 ) exhibits an elongation to break of 100 to 200% (still more preferably 125 to 175%; most preferably 150 to 160%) as measured according to ASTM D412. 
     One of ordinary skill in the art will understand to select a polishing layer ( 20 ) having a thickness, T P , suitable for use in a chemical mechanical polishing pad ( 10 ) for a given polishing operation. Preferably, the polishing layer ( 20 ) exhibits an average thickness, T P-avg , along an axis (A) perpendicular to a plane ( 28 ) of the polishing surface ( 14 ). More preferably, the average thickness, T P-avg , is 20 to 150 mils (more preferably 30 to 130 mils; most preferably 70 to 90 mils). (See  FIGS. 2 ,  5  and  7 - 10 ). 
     Preferably, the polishing surface ( 14 ) of the polishing layer ( 20 ) is adapted for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate (more preferably, a semiconductor substrate; still more preferably, a semiconductor wafer; most preferably, a semiconductor wafer having a surface with exposed copper features). The polishing surface ( 14 ) of the polishing layer ( 20 ) exhibits at least one of macrotexture and microtexture to facilitate polishing the substrate. Preferably, the polishing surface ( 14 ) exhibits macrotexture, wherein the macrotexture is designed to do at least one of (i) alleviate at least one of hydroplaning; (ii) influence polishing medium flow; (iii) modify the stiffness of the polishing layer; (iv) reduce edge effects; and, (v) facilitate the transfer of polishing debris away from the area between the polishing surface ( 14 ) and the substrate being polished. 
     The polishing surface ( 14 ) preferably exhibits macrotexture selected from at least one of perforations and grooves. Preferably, the perforations can extend from the polishing surface ( 14 ) part way or all of the way through the thickness of the polishing layer ( 20 ). Preferably, the grooves are arranged on the polishing surface ( 14 ) such that upon rotation of the pad ( 10 ) during polishing, at least one groove sweeps over the substrate. Preferably, the grooves are selected from curved grooves, linear grooves and combinations thereof. The grooves exhibit a depth of ≧10 mils (preferably, 10 to 120 mils). Preferably, the grooves form a groove pattern that comprises at least two grooves having a combination of a depth selected from ≧10 mils, ≧15 mils and 15 to 120 mils; a width selected from ≧10 mils and 10 to 100 mils; and a pitch selected from ≧30 mils, ≧50 mils, 50 to 200 mils, 70 to 200 mils, and 90 to 200 mils. 
     Preferably, the polishing layer ( 20 ) contains &lt;1 ppm abrasive particles incorporated therein. 
     Preferably, the rigid layer ( 25 ) is made of a material selected from the group consisting of a polymer, a metal, a reinforced polymer and combinations thereof. More preferably, the rigid layer ( 25 ) is made of a polymer. Most preferably, the rigid layer ( 25 ) is made of a polymer selected from the group consisting of a polyester, a nylon, an epoxy, a fiberglass reinforced epoxy; and, a polycarbonate (more preferably, a polyester; still more preferably, a polyethylene terephthalate polyester; most preferably, a biaxially oriented polyethylene terephthalate polyester). 
     Preferably, the rigid layer ( 25 ) has an average thickness, T R-avg , of &gt;5 to 60 mils (more preferably, 6 to 15 mils; most preferably, 6 to 8 mils). 
     Preferably, the top surface ( 26 ) and the bottom surface ( 27 ) of the rigid layer ( 25 ) are both ungrooved. More preferably, the top surface ( 26 ) and the bottom surface ( 27 ) are both smooth. Most preferably, the top surface ( 26 ) and the bottom surface ( 27 ) have a roughness, Ra, of 1 to 500 nm (preferably, 1 to 100 nm; more preferably, 10 to 50 nm; most preferably 20 to 40 nm) as determined using an optical profilometer. 
     Preferably, the top surface ( 26 ) of the rigid layer ( 25 ) is treated with an adhesion promoter to improve adhesion between the rigid layer ( 25 ) and the reactive hot melt adhesive ( 23 ). One of ordinary skill in the art will know how to select an appropriate adhesion promoter given the material of construction of the rigid layer ( 25 ) and the composition of the hot melt adhesive ( 23 ). 
     Preferably, the rigid layer ( 25 ) exhibits a Young&#39;s Modulus, measured according to ASTM D882-12, of ≧100 MPa (more preferably, 1,000 to 10,000 MPa; still more preferably, 2,500 to 7,500 MPa; most preferably, 3,000 to 7,000 MPa). 
     Preferably, the rigid layer ( 25 ) exhibits a void fraction of &lt;0.1 vol % (more preferably, &lt;0.01 vol %). 
     Preferably, the rigid layer ( 25 ) is made of a biaxially oriented polyethylene terephthalate having an average thickness of 6 to 15 mils; and, a Young&#39;s Modulus, measured according to ASTM D882-12, of 2,500 to 7,500 MPa (most preferably, 3,000 to 7,000 MPa). 
     One of ordinary skill in the art will know how to select an appropriate hot melt adhesive ( 23 ) for use in the chemical mechanical polishing pad ( 10 ). Preferably, the hot melt adhesive ( 23 ) is a cured reactive hot melt adhesive. More preferably, the hot melt adhesive ( 23 ) is a cured reactive hot melt adhesive that exhibits a melting temperature in its uncured state of 50 to 150° C., preferably of 115 to 135° C. and exhibits a pot life of ≦90 minutes after melting. Most preferably, the hot melt adhesive ( 23 ) in its uncured state comprises a polyurethane resin (e.g., Mor-Melt™ R5003 available from Rohm and Haas). 
     The chemical mechanical polishing pad ( 10 ) is preferably adapted to be interfaced with a platen of a polishing machine. Preferably, the chemical mechanical polishing pad ( 10 ) is adapted to be affixed to the platen of a polishing machine. The chemical mechanical polishing pad ( 10 ) can be affixed to the platen using at least one of a pressure sensitive adhesive and vacuum. 
     Preferably, the chemical mechanical polishing pad ( 10 ) includes a pressure sensitive platen adhesive layer ( 70 ) applied to the bottom surface ( 27 ) of the rigid layer ( 25 ). One of ordinary skill in the art will know how to select an appropriate pressure sensitive adhesive for use as the pressure sensitive platen adhesive layer ( 70 ). Preferably, the chemical mechanical polishing pad ( 10 ) will also include a release liner ( 75 ) applied over the pressure sensitive platen adhesive layer ( 70 ), wherein the pressure sensitive platen adhesive layer ( 70 ) is interposed between the bottom surface ( 27 ) of the rigid layer ( 25 ) and the release liner ( 75 ). (See FIGS.  2  and  7 - 10 ). 
     An important step in substrate polishing operations is determining an endpoint to the process. One popular in situ method for endpoint detection involves providing a polishing pad with a window, which is transparent to select wavelengths of light. During polishing, a light beam is directed through the window to the wafer surface, where it reflects and passes back through the window to a detector (e.g., a spectrophotometer). Based on the return signal, properties of the substrate surface (e.g., the thickness of films thereon) can be determined for endpoint detection. To facilitate such light based endpoint methods, the chemical mechanical polishing pad ( 10 ) of the present invention, optionally further comprises an endpoint detection window ( 30 ). Preferably, the endpoint detection window is selected from an integral window ( 34 ) incorporated into the polishing layer ( 20 ); and, a plug in place window block ( 32 ) incorporated into the chemical mechanical polishing pad ( 10 ). (See  FIGS. 1-10 ). One of ordinary skill in the art will know to select an appropriate material of construction for the endpoint detection window for use in the intended polishing process. 
     Preferably, the endpoint detection window used in the chemical mechanical polishing pad ( 10 ) of the present invention is an integral window ( 34 ) incorporated into the polishing layer ( 20 ). Preferably, the chemical mechanical polishing pad ( 10 ) containing the integral window ( 34 ), comprises: a polishing layer ( 20 ) having a polishing surface ( 14 ), a base surface ( 17 ) and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the base surface ( 17 ); a rigid layer ( 25 ) having a top surface ( 26 ) and a bottom surface ( 27 ); a hot melt adhesive ( 23 ) interposed between the base surface ( 17 ) of the polishing layer ( 20 ) and the top surface ( 26 ) of the rigid layer ( 25 ); wherein the hot melt adhesive ( 23 ) bonds the polishing layer ( 20 ) to the rigid layer ( 25 ); a pressure sensitive platen adhesive ( 70 ); a release liner ( 75 ); wherein the pressure sensitive platen adhesive ( 70 ) is interposed between the bottom surface ( 27 ) of the rigid layer ( 25 ) and the release liner ( 75 ); and, the integral window ( 34 ) incorporated into the polishing layer ( 20 ); wherein the polishing layer ( 20 ) is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (1) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent (more preferably, 8.65 to 9.05 wt %; most preferably, &gt;8.7 to 9 wt %) unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, (c) optionally, a plurality of microelements; wherein the polishing layer ( 20 ) exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90 (preferably, &gt;60 to 75; more preferably, 61 to 75; most preferably, &gt;65 to 70); and, an elongation to break of 100 to 300% (preferably, 100 to 200%; more preferably, 125 to 175%; most preferably, 150 to 160%); wherein the polishing layer ( 20 ) exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C. (as measured according to the method described in the Examples); wherein the polishing layer ( 20 ) exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by ≧1.75% (preferably, 1.75 to 5%; more preferably, 1.75 to 3.5%; most preferably, 2 to 3%) following immersion in deionized water for seven days at 25° C. (as measured according to the method described in the Examples); wherein the polishing layer ( 20 ) has a polishing surface ( 14 ) adapted for polishing a substrate. The integral window ( 34 ) preferably has a thickness, T W , measured along an axis, B, perpendicular to the plane ( 28 ) of the polishing surface ( 14 ). (See  FIG. 10 ). Preferably, the integral window ( 34 ) has an average thickness, T W-avg , along an axis (B) perpendicular to the plane ( 28 ) of the polishing surface ( 25 ), wherein the average window thickness, T W-avg , is equal to the average thickness, T P-avg , of the polishing layer ( 20 ). (See  FIG. 10 ). 
     Preferably, the endpoint detection window used in the chemical mechanical polishing pad ( 10 ) of the present invention is a plug in place window block ( 32 ). Preferably, the chemical mechanical polishing pad ( 10 ) containing the plug in place window block ( 32 ), comprises: a polishing layer ( 20 ) having a polishing surface ( 14 ), a base surface ( 17 ) and an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the base surface ( 17 ); a rigid layer ( 25 ) having a top surface ( 26 ) and a bottom surface ( 27 ); a hot melt adhesive ( 23 ) interposed between the base surface ( 17 ) of the polishing layer ( 20 ) and the top surface ( 26 ) of the rigid layer ( 25 ); wherein the hot melt adhesive ( 23 ) bonds the polishing layer ( 20 ) to the rigid layer ( 25 ); a pressure sensitive platen adhesive ( 70 ); a release liner ( 75 ); wherein the pressure sensitive platen adhesive ( 70 ) is interposed between the bottom surface ( 27 ) of the rigid layer ( 25 ) and the release liner ( 75 ); and, a plug in place window ( 32 ) incorporated into the chemical mechanical polishing pad ( 10 ); wherein the polishing layer ( 20 ) is a cast polyurethane, wherein the cast polyurethane is a reaction product of ingredients, comprising: (a) an isocyanate terminated prepolymer obtained by reaction of: (i) a polyfunctional isocyanate; and, (ii) a polyether based polyol; wherein the isocyanate terminated prepolymer has 8 to 9.5 weight percent (preferably, 8.65 to 9.05 wt %; more preferably, &gt;8.7 to 9.00 wt %) unreacted NCO; (b) a curative agent, wherein the curative agent is selected from the group consisting of curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and, (c) optionally, a plurality of microelements; wherein the polishing layer ( 20 ) exhibits a specific gravity of greater than 0.6; a Shore D hardness of 60 to 90 (preferably, &gt;60 to 75; more preferably, 61 to 75; most preferably, &gt;65 to 70); and, an elongation to break of 100 to 300% (preferably, 100 to 200%; more preferably, 125 to 175%; most preferably, 150 to 160%); wherein the polishing layer ( 20 ) exhibits an initial hydrolytic stability, wherein a linear dimension of a sample of the polishing layer changes by &lt;1% following immersion in deionized water for 24 hours at 25° C. (as measured according to the method described in the Examples); wherein the polishing layer ( 20 ) exhibits a sustained hydrolytic instability, wherein the linear dimension of the sample of the polishing layer changes by ≧1.75% (preferably, 1.75 to 5%; more preferably, 1.75 to 3.5%; most preferably, 2 to 3%) following immersion in deionized water for seven days at 25° C. (as measured according to the method described in the Examples); wherein the polishing layer ( 20 ) has a polishing surface ( 14 ) adapted for polishing a substrate; wherein the chemical mechanical polishing pad ( 10 ) has a through opening ( 35 ) that extends through the chemical mechanical polishing pad ( 10 ) from the polishing surface ( 14 ) of the polishing layer ( 20 ) through to the bottom surface ( 27 ) of the rigid layer ( 25 ); wherein the plug in place window block ( 30 ) is disposed within the through opening ( 35 ); and, wherein the plug in place window block ( 30 ) is secured to the pressure sensitive platen adhesive ( 70 ). The plug in place window block ( 30 ) has a thickness, T W , measured along an axis, B, perpendicular to the plane ( 28 ) of the polishing surface ( 14 ). (See  FIGS. 5-7 ). Preferably, the plug in place window block ( 30 ) has an average window thickness, T W-avg , along an axis (B) perpendicular to the plane ( 28 ) of the polishing surface ( 25 ), wherein the average window thickness, T W-avg , is 5 mils to the average total thickness, T T-avg , of the chemical mechanical polishing pad ( 10 ). (See  FIG. 7 ). More preferably, wherein the plug in place window block ( 30 ) has an average window thickness, T W-avg , of 5 mils to &lt;T T-avg . Still more preferably, wherein the plug in place window block ( 30 ) has an average window thickness, T W-avg , of 5 mils to 75 mils (yet still more preferably, 15 to 50 mils; most preferably 20 to 40 mils). (See  FIGS. 5-7 ). 
     Preferably, the endpoint detection window used in the chemical mechanical polishing pad ( 10 ) of the present invention is a plug in place window block ( 32 ). Preferably, the chemical mechanical polishing pad ( 10 ) containing the plug in place window block ( 32 ), comprises: a polishing layer ( 20 ) having a polishing surface ( 14 ), a base surface ( 17 ), an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the base surface ( 17 ), and a counterbore opening ( 40 ) that enlarges a through passage ( 35 ) that extends through the thickness, T P , of the polishing layer ( 20 ), wherein the counterbore opening ( 40 ) opens on the polishing surface ( 14 ) and forms a ledge ( 45 ) at an interface between the counterbore opening ( 40 ) and the through passage ( 35 ) at a depth, D O , along an axis, B, parallel with an axis, A, and perpendicular to the plane ( 28 ) of the polishing surface ( 14 ). (See  FIGS. 1 ,  4 ,  6  and  8 ). Preferably, the ledge ( 45 ) is parallel with the polishing surface ( 14 ). Preferably, the counterbore opening defines a cylindrical volume with an axis that is parallel to axis (A). Preferably, the counterbore opening defines a non-cylindrical volume. Preferably, the plug in place window block ( 32 ) is disposed within the counterbore opening ( 40 ). Preferably, the plug in place window block ( 32 ) is disposed within the counterbore opening ( 40 ) and adhered to the polishing layer ( 20 ). Preferably, the plug in place window block ( 32 ) is adhered to the polishing layer ( 20 ) using at least one of ultrasonic welding and an adhesive. Preferably, the average depth of the counterbore opening, D O-avg , along an axis, B, parallel with an axis, A, and perpendicular to the plane ( 28 ) of the polishing surface ( 14 ) is 5 to 75 mils (preferably 10 to 60 mils; more preferably 15 to 50 mils; most preferably, 20 to 40 mils). Preferably, the average depth of the counterbore opening, D O-avg , is ≦the average thickness, T W-avg , of the plug in place window block ( 32 ). (See  FIGS. 6 and 8 ). More preferably, the average depth of the counterbore opening, D O-avg , satisfies the following expression 
       0.90* T   W-avg   ≦D   O-avg   ≦T   W-avg . 
     More preferably, the average depth of the counterbore opening, D O-avg , satisfies the following expression 
       0.95* T   W-avg   ≦D   O-avg   ≦T   W-avg . 
     Preferably, the endpoint detection window used in the chemical mechanical polishing pad ( 10 ) of the present invention is a plug in place window block ( 32 ). Preferably, the chemical mechanical polishing pad ( 10 ) containing the plug in place window block ( 32 ), comprises: a polishing layer ( 20 ) having a polishing surface ( 14 ), a base surface ( 17 ), an average thickness, T P-avg , measured in a direction perpendicular to the polishing surface ( 14 ) from the polishing surface ( 14 ) to the base surface ( 17 ), and a polishing layer opening ( 37 ) that enlarges a through passage ( 35 ) that extends through the total thickness, T T , of the chemical mechanical polishing pad ( 10 ), wherein the polishing layer opening ( 37 ) opens on the polishing surface ( 14 ) and forms a shelf ( 55 ) on the top surface ( 26 ) of the rigid layer ( 25 ) at an interface between the polishing layer opening ( 37 ) and the through passage ( 35 ) at a depth, D O , along an axis, B, parallel with an axis, A, and perpendicular to the plane ( 28 ) of the polishing surface ( 14 ). (See  FIGS. 1 ,  4 ,  6  and  9 ). Preferably, the shelf ( 55 ) is parallel with the polishing surface ( 14 ). Preferably, the polishing layer opening ( 37 ) defines a cylindrical volume with an axis that is parallel to axis (A). Preferably, the polishing layer opening ( 37 ) defines a non-cylindrical volume. Preferably, the plug in place window block ( 32 ) is disposed within the polishing layer opening ( 37 ). Preferably, the plug in place window block ( 32 ) is disposed within the polishing layer opening ( 37 ) and adhered to the top surface ( 26 ) of the rigid layer ( 25 ). Preferably, the plug in place window block ( 32 ) is adhered to the top surface ( 26 ) of the rigid layer ( 25 ) using at least one of ultrasonic welding and an adhesive. Preferably, the average depth of the counterbore opening, D O-avg , along an axis, B, parallel with an axis, A, and perpendicular to the plane ( 28 ) of the polishing surface ( 14 ) is 5 to 75 mils (preferably 10 to 60 mils; more preferably 15 to 50 mils; most preferably, 20 to 40 mils). Preferably, the average depth of the counterbore opening, D O-avg , is ≦the average thickness, T W-avg , of the plug in place window block ( 32 ). (See  FIGS. 6 and 9 ). More preferably, the average depth of the counterbore opening, D O-avg , satisfies the following expression 
       0.90* T   W-avg   ≦D   O-avg   ≦T   W-avg . 
     More preferably, the average depth of the counterbore opening, D O-avg , satisfies the following expression 
       0.95* T   W-avg   ≦D   O-avg   ≦T   W-avg . 
     Some embodiments of the present invention will now be described in detail in the following Examples. 
     Example 1 
     Preparation of Polishing Layer 
     A cast polyurethane cake was prepared by the controlled mixing of (a) an isocyanate terminated prepolymer at 51° C. obtained by the reaction of a polyfunctional isocyanate (i.e., toluene diisocyanate) and a polyether based polyol (i.e., Adiprene® LFG740D commercially available from Chemtura Corporation); (b) a curative agent at 116° C. (i.e., 4,4′-methylene-bis-(2-chloroaniline)); and, (c) 0.3 wt % of a plurality of microelements (i.e., 551DE40d42 Expancel® microspheres commercially available from Akzo Nobel). The ratio of the isocyanate terminated prepolymer and the curative agent was set such that the stoichiometry, as defined by the ratio of active hydrogen groups (i.e., the sum of the —OH groups and —NH 2  groups) in the curative agent to the unreacted isocyanate (NCO) groups in the isocyanate terminated prepolymer, was 91 percent. The plurality of microelements was mixed into the isocyanate terminated prepolymer prior to the addition of the curative agent. The isocyanate terminated prepolymer with the incorporated plurality of microelements and the curative agent were then mixed together using a high shear mix head. After exiting the mix head, the combination was dispensed over a period of 5 minutes into a 86.4 cm (34 inch) diameter circular mold to give a total pour thickness of approximately 8 cm (3 inches). The dispensed combination was allowed to gel for 15 minutes before placing the mold in a curing oven. The mold was then cured in the curing oven using the following cycle: 30 minutes ramp of the oven set point temperature from ambient temperature to 104° C., then hold for 15.5 hours with an oven set point temperature of 104° C., and then 2 hour ramp of the oven set point temperature from 104° C. down to 21° C. 
     The cured polyurethane cakes were then removed from the mold and skived (cut using a moving blade) at a temperature of 30 to 80° C. into multiple polishing layers having an average thickness, T P-avg , of 2.0 mm (80 mil). Skiving was initiated from the top of each cake. 
     Analysis of Polishing Layer Properties 
     The ungrooved, polishing layer material prepared according to Example 1 was analyzed to determine its physical properties as reported in T ABLE  1. Note that the specific gravity reported was determined relative to pure water according to ASTM D1622, the Shore D hardness reported was determined according to ASTM D2240. 
     The tensile properties of the polishing layer (i.e., median tensile strength, median elongation to break, median modulus, toughness) were measured according to ASTM D412 using an Alliance RT/5 mechanical tester available from MTS Systems Corporation as a crosshead speed of 50.8 cm/min. All testing was performed in a temperature and humidity controlled laboratory set at 23° C. and a relative humidity of 50%. All of the test samples were conditioned under the noted laboratory conditions for 5 days before performing the testing. The reported median tensile strength (MPa) and median elongation to break (%) for the polishing layer material was determined from stress-strain curves of five replicate samples. 
     The storage modulus, G′, and loss modulus, G″, of the polishing layer material was measured according to ASTM D5279-08 using a TA Instruments ARES Rheometer with torsion fixtures. Liquid nitrogen that was connected to the instrument was used for sub-ambient temperature control. The linear viscoelastic response of the samples was measured at a test frequency of 10 rad/sec (1.59 Hz) with a temperature ramp of 3° C./min from −100° C. to 200° C. The test samples were stamped out of the polishing layer using a 47.5 mm×7 mm die on an Indusco hydraulic swing arm cutting machine and then cut down to approximately 35 mm in length using scissors. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Polishing layer Property 
                 Ex. 1 polishing layer material 
               
               
                   
                   
               
             
            
               
                   
                 Hardness Shore D 15 Sec. 
                 66.0  
               
               
                   
                 G′ @ 30° C. 
                 241.0 MPa  
               
               
                   
                 G′ @ 40° C. 
                 210.6 MPa  
               
               
                   
                 G″ @ 40° C. 
                 15.9 MPa 
               
               
                   
                 G′ @ 30° C./G′ @ 90° C. 
                 2.5 
               
               
                   
                 G′ @ 90° C. 
                 95.5 MPa 
               
               
                   
                 Median Tensile Strength 
                 33.2 MPa 
               
               
                   
                 Median elongation to break 
                 155.3%     
               
               
                   
                 Median Modulus 
                 391.0 MPa  
               
               
                   
                 Toughness 
                 44.5 MPa 
               
               
                   
                 Specific gravity 
                  1.072 
               
               
                   
                   
               
            
           
         
       
     
     Hydrolytic Stability Analysis 
     The ungrooved, polishing layer material prepared according to Example 1 was then analyzed to determine whether it exhibited an initial hydrolytic stability and a sustained hydrolytic instability. Three commercially available polishing layer materials were also analyzed (i.e., IC1000™ polishing layer material; VisionPad™ 3100 polishing layer material and VisionPad™ polishing layer material all available from Rohm and Haas Electronic Materials CMP Inc.). Commercial pad specifications for the commercial polishing layer materials are provided in T ABLE  2. Specifically, 1.5″×1.5″ samples of each of the 2 mm thick polishing layer materials were initially measured along both 1.5″ dimensions (i.e., x and y dimension) using a calipers. The samples were then immersed in deionized water at 25° C. The samples were again measured along both the x and y dimension using calipers after 24 hours of immersion and seven days of immersion. The results of these measurements are provided in T ABLE  3. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Commercial Pad Specification 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pad 
                 Average SG    
                   
                 Shore D Hardness 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Material 
                 LSL    
                 USL £   
                 LSL    
                 USL £   
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 IC1000 ™ A2 
                 0.74 
                 0.85 
                 52 
                 62 
               
               
                   
                 VP3100 ™ 
                 0.76 
                 0.84 
                 42.5 
                 49.5 
               
               
                   
                 VP5200 ™ 
                 0.64 
                 0.70 
                 44 
                 60 
               
               
                   
                   
               
               
                   
                     “SG” means specific gravity 
               
               
                   
                     “LSL” means lower specification limit 
               
               
                   
                   £ “USL” means upper specification limit 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Linear measurement (in inches) 
                 24 hr 
                 7 day 
               
            
           
           
               
               
               
               
               
               
            
               
                 Material 
                 Initial 
                 24 hrs 
                 7 Days 
                 % Δ 
                 % Δ 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ex. 1 (x) 
                 1.52 
                 1.53 
                 1.56 
                 0.66 
                 2.63 
               
               
                 Ex. 1 (y) 
                 1.51 
                 1.52 
                 1.55 
                 0.66 
                 2.65 
               
               
                 IC1000 ™ A2 (x) 
                 1.52 
                 1.52 
                 1.53 
                 0 
                 0.66 
               
               
                 IC1000 ™ A2 (y) 
                 1.51 
                 1.52 
                 1.52 
                 0.66 
                 0.66 
               
               
                 VP3100 ™ (x) 
                 1.51 
                 1.52 
                 1.52 
                 0.66 
                 0.66 
               
               
                 VP3100 ™ (y) 
                 1.52 
                 1.52 
                 1.52 
                 0 
                 0 
               
               
                 VP5200 ™ (x) 
                 1.52 
                 1.52 
                 1.53 
                 0 
                 0.66 
               
               
                 VP5200 ™ (y) 
                 1.52 
                 1.52 
                 1.53 
                 0 
                 0.66