EP3887093A1

EP3887093A1 - Polishing pads and systems and methods of making and using the same

Info

Publication number: EP3887093A1
Application number: EP19890633.1A
Authority: EP
Inventors: Duy K. LEHUU; Qin Lin; David J. MURADIAN; Samad JAVID
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2018-11-27
Filing date: 2019-11-22
Publication date: 2021-10-06
Also published as: KR20210094024A; US20220023991A1; JP2022511763A; TW202033310A; KR102777772B1; JP7545968B2; WO2020109947A1; EP3887093A4

Abstract

A polishing pad includes a polishing layer having a first major surface and a second major surface opposite the first major surface. The polishing pad further includes a subpad, which is coupled to the polishing layer, and has a first major surface and a second major surface opposite the first major surface. At least 50% of the subpad, based on the total surface area of the first major surface of the subpad, is optically transparent.

Description

POLISHING PADS AND SYSTEMS AND METHODS OF MAKING AND USING

THE SAME

FIELD

The present disclosure relates to polishing pads and systems useful for the polishing of substrates, and methods of making and using such polishing pads.

SUMMARY

In some embodiments, a polishing pad is provided. The polishing pad includes a polishing layer having a first major surface and a second major surface opposite the first major surface. The polishing pad further includes a subpad, which is coupled to the polishing layer, and has a first major surface and a second major surface opposite the first major surface. At least 50% of the subpad, based on the total surface area of the first major surface of the subpad, is optically transparent.

The above summary of the present disclosure is not intended to describe each embodiment of the present disclosure. The details of one or more embodiments of the disclosure are also set forth in the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

Figure l is a schematic cross-sectional view of a polishing pad in accordance with some embodiments of the present disclosure.

Figure 2 is a schematic view of a polishing system in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

Chemical-mechanical planarization (CMP) is a process used to planarize the surface topography of a wafer in the fabrication of integrated circuits (ICs) and often employs the use a liquid or slurry and a polishing pad. During the process, the slurry chemically reacts with materials on the surface of the wafer. The reacted materials are then removed mechanically by abrasive particles in the slurry or within the pad.

Performance characteristics relevant to CMP include wafer removal rate (WRR), wafer non-uniformity (NU), and defectivity.

With respect to wafer NU, nonuniformity of the pattern layout within a layer of an IC die often contributes to nonuniform polishing across the die area

(overpolishing/dishing). Variation of the CMP process parameters (platen and wafer carrier speeds, wafer pressure, slurry transport, etc.) and process random variation contribute to increase in within-wafer and within-lot nonuniformity. To reduce the variance of polishing outputs (e.g., uniformity, overpolishing, and dishing), integration of in situ sensing and endpoint detection techniques with process optimization schemes to improve process performance are employed. Detecting the end point using optical reflectance (e.g., using reflected optical signal at either a single wave length (i.e. a laser source) or a broadband light, which travels back and forth through the polishing pad and to the wafer surface, is one of the known techniques.

The components of commercially available polishing pads (e.g., the top pad, subpad, optional foam layers, and the like) are typically non-optically transparent, e.g. opaque, and are disposed between the optical signal generator of a polishing tool and the surface of the wafer to be polished. Thus, these components prevent optical sensing directly through the pad. Consequently, to enable optical end point detection, often times an end-point detection window is fabricated within the polishing pad. This may be achieved by cutting an appropriate size aperture in the polishing pad (including the top pad and any non-optically transparent layers to be coupled to the top pad, such as the subpad and optional foam layers that overlay the polishing pad). The window is then created by inserting a solid, optically transparent (e.g., polyurethane) window into the aperture and securing the window to the pad. During the CMP process, optical signals may then be passed, via the window, though the polishing pad (including any of the coupled layers) to enable end point detection. While this practice provides adequate end point detection, accommodation of end point detection through an aperture in the polishing pad is associated with increased manufacturing complexity of the polishing pad and polishing performance issues. For example, formation of the aperture through the polishing pad results in an additional manufacturing step for each layer of the polishing pad. Additionally, the presence of apertures in the polishing pad results in non-uniform pressure and contact material to the wafer surface and, in turn, performance reliability.

Still further, end point detection through an aperture in the polishing pad limits the location of the aperture in the pad through which end point detection can occur, as the window of the pad must align with the detection system of the tool, e.g. the end point detection window of the platen the pad is mounted to. Consequently, polishing pads that do not require apertures in the various layers (or minimize the number of apertures) for end point detection are desirable, as they provide uniform pressure and contact material to the wafer surface, and/or allow for flexibility in the precise location of end point detection through the polishing pad.

Definitions

As used herein, the singular forms“a”,“an”, and“the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended embodiments, the term“or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

As used herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

“Working surface” refers to a major surface of a polishing pad that is intended to be nearest to, and at least partially contact a major surface of a substrate being polished.

“Pore” refers to a cavity in the working surface of a pad that allows a fluid, e.g. a liquid, to be contained therein. The pore enables at least some fluid to be contained within the pore and not flow out of the pore. “Precisely shaped” refers to a topographical feature, e.g. an asperity or pore, having a molded shape that is the inverse shape of a corresponding mold cavity or mold protrusion, said shape being retained after the topographical feature is removed from the mold. A pore formed through a foaming process or removal of a soluble material (e.g. a water soluble particle) from a polymer matrix, is not a precisely shaped pore.

As used herein,“major surface” refers to the surfaces of an article or layer having a greater dimension or surface area than other surfaces of the article or layer, for example, an article or layer that has an aspect ratio of greater width or diameter to height, where the surface area of the side corresponding to the article or layer height (e.g., thickness) is significantly smaller than the surface area of the width or diameter of the same article or layer.

As used herein, in some embodiments,“optically transparent” refers to an article or layer that has optical transmission value of at least 10% at wavelengths of at least 400 nm, when tested as described in the Light Transmission Test Method of the Examples. In other embodiments,“optically transparent”' refers to an article or layer that has optical transmission value of at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 80%, at wavelengths of at least 400 nm, when tested as described in the Light Transmission Test Method of the Examples. The term "optical transmission value" means the percentage of light that is not either reflected back toward the source or absorbed by the sample as a percentage of the total incident light at a wavelength of 400 ran (light emitted/light source x 100). For purposes of the present application, optically transparent articles or layers permit transmission therethrough of optical signals employed in conventional end point detection systems to an extent necessary to achieve accurate end point detection.

“Thickness”, when discussed in relation to a polishing pad, refers to the total average thickness of any and ail layers of the polishing pad measured in a direction normal to the working surface. “Thickness”, when discussed in relation to a layer of a polishing pad refers to the total average thickness of such layer of the polishing pad measured in a direction normal to the working surface of the polishing pad.

The present disclosure is directed to articles, systems, and methods useful for polishing substrates including, for example, semiconductor wafers. In some embodiments, as shown in FIG. 1, the present disclosure is directed to a polishing pad 10, which may be used to polish a substrate in, for example, a CMP process. The polishing pad 10 may include a polishing layer 15 (often referred to as a top pad) having a first major surface 15A (which will be referred to as the“working surface” of the polishing pad 15) and a second major surface 15B opposite the first major surface 15A. The polishing pad 10 may further include a subpad 30 that is coupled to the polishing layer 15, the subpad 30 having a first major surface 30A (nearest the polishing layer 15) and a second major surface 30B opposite the first major surface 30A (which is intended for coupling to a platen of a polishing apparatus). The polishing pad 10 may further include one or more optional layers 40 disposed between the polishing layer 15 and the subpad 30. The layers forming the polishing pad 10 may be coupled to one another via any suitable coupling mechanism know in the art. For example, adhesives, e.g. pressure sensitive adhesives (PSAs), hot melt adhesives, or cure in place adhesives may be employed. Additionally, or alternatively, lamination may be employed.

In some embodiments, the polishing layer 15 may include or be formed of a polymer. Polishing layer 15 may be fabricated from any known polymer, including thermoplastics, thermoplastic elastomers (TPEs), e.g. TPEs based on block copolymers, or thermosets, e.g. elastomers and combinations thereof. In some embodiments, the polishing layer may include or be formed of a polyurethane, polyamide, polybutadiene, or polyolefin, such as is common in commercially available polishing pads for substrate planarization.

In some embodiments, the hardness of polishing layer 15 may be predominately controlled by the polymer used to fabricate it. In some embodiments, the hardness of polishing layer 15 may be greater than about 20 Shore D, greater than about 30 Shore D, or greater than about 40 Shore D; less than about 90 Shore D, less than about 80 Shore D, or less than about 70 Shore D; between 20 and 90 Shore D, between 30 and 80 Shore D, or between 40 and 70 Shore D. In some embodiments, the hardness of polishing layer 15 may be greater than about 20 Shore A, greater than about 30 Shore A, or greater than about 40 Shore A; less than about 95 Shore A, less than about 80 Shore A or less than about 70 Shore A; or between 20 and 95 Shore A, between 30 and 80 Shore A, or between 40 and 70 Shore A. In some embodiments, the thickness of the polishing layer 15 may be greater than about 25 microns, greater than about 50 microns, greater than about 100 microns, or greater than 250 microns; less than about 20 mm, less than about 10 mm, less than about 5 mm, or less than about 2.5 mm; or between 15 microns and 20 mm, between 25 microns and 10 mm, between 50 microns and 5 mm, or between 100 microns and 2.5 mm.

In various embodiments, the polishing layer 15 may be flexible. For example, in some embodiments, the polishing layer 15 may be capable of being bent back upon itself producing a radius of curvature in the bend region of less than about 10 cm, less than about 5 cm, less than about 3 cm, or less than about 1 cm; and greater than about 0.1 mm, greater than about 0.5 mm, or greater than about 1 mm. In some embodiments, the polishing layer 15 may be capable of being bent back upon itself producing a radius of curvature in the bend region of between about 10 cm and about 0.1 mm, between about 5 cm and bout 0.5 mm, or between about 3 cm and about 1 mm.

In some embodiments, the polishing layer 15 may be a unitary sheet. For purposes of the present application, a unitary sheet refers to an article that includes only a single layer of material (i.e. it is not a multi-layer construction, or laminate) and the single layer of material has a single composition. The composition may include multiple-components, e.g. a polymer blend or a polymer-inorganic composite. Use of a unitary sheet as the polishing layer may provide cost benefits, due to minimization of the number of process steps required to form the polishing layer. A polishing layer that includes a unitary sheet may be fabricated from techniques know in the art, including, but not limited to, molding and embossing.

In some embodiments, the polishing layer 15 may be optically transparent (at least to an extent sufficient to allow for end point detection through such portion of the polishing layer 15) over at least 10%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 99% of its surface area, based on the total surface area of the working surface 15a. In such embodiments, the polishing layer 15 may not include an aperture for receiving an end point detection window. In alternative embodiments, the polishing layer 15 may not be optically transparent. In such embodiments, the polishing layer 15 may include an aperture for receiving an end point detection window.

In some embodiments, the polishing layer 15 may include a plurality of precisely shaped pores and a plurality of precisely shaped asperities on its working surface 15a, such as in the polishing pads described in U.S. Pat. App. 15/300,125, which is herein incorporated by reference in its entirety.

In some embodiments, the subpad 30, or a substantial portion of the subpad 30, may include or be formed of an optically transparent material. For example, in some embodiments, the subpad 30 may include or be formed of soft polymeric materials with glass transition below 30 °C or polymers blended with plasticizers. Other additives such as photo initiators, free radical initiators, crosslinkers, or inorganic fillers, may be added without interrupting the optical transparency.

Suitable soft polymeric materials may include elastomers, polyurethanes, polyolefins, polycarbonates, polyamides, elastomeric rubbers, styrenic polymers, polystyrenes, polymethylmethacrylates, copolymers and block copolymers thereof, and mixtures and blends thereof. In some embodiments, the subpad 30 may include or consist essentially of oligomeric acrylate or methacrylate resins.

Suitable oligomeric acrylate monomers may include epoxy oligomeric

acrylate/methacrylate, urethane oligomeric acrylate/methacrylate, polyester oligomeric acrylate/methacrylate, polyether oligomeric acrylate/methacrylate and amino

acrylate/methacrylate monomers.

In some embodiments, suitable monomers have a single ethylenically unsaturated group. The monomers may include or consist essentially of alkyl (meth)acrylate. The alkyl group can be linear, branched, cyclic, bicyclic, tricylic, adamantly or a combination thereof. Suitable alkyl (meth)acrylates include methyl (meth)acrylate, ethyl

(meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, 4- methyl-2-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-methylhexyl

(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-octyl (meth)acrylate, isononyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, isobomyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate, 2-octyldecyl

(meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, dicyclopentenloxyethy (meth)acrylate, dicyclopentanyl acrylate, 1- adamantly (meth) acrylate, 2-adamantly (meth)acrylate and heptadecanyl (meth)acrylate. Some suitable branched alkyl (meth)acrylates include (meth)acrylic acid esters of Guerbet alcohols having 12 to 32 carbon atoms as described in U.S. Patent No. 8,137,807 (Clapper et al.). The alkyl monomers can be a single isomer or an isomer blend such as those described in U.S.

Patent No. 9,102,774 (Clapper et al.). Other monomers with a single ethylenically unsaturated group that can be used are heteroalkyl (meth)acrylates. The heteroalkyl group can be linear, branched, cyclic, bicyclic, or a combination thereof. The heteroatom is often oxygen (-0-) but can be sulfur (-S-) or nitrogen (-NH-). The heteroalkyl often has 2 to 12 carbon atoms and 1 to 4 heteroatom or 4 to 10 carbon atoms and 1 to 3 heteroatoms.

Suitable heteroalkyl (meth)acrylates include alkoxylated alkyl (meth)acrylates such as 2- (2-ethoxyethoxy)ethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylates. Still other monomers with a single ethylenically unsaturated group can include a urethane linkage (-NH-(CO)-O-). One example is 2-

[[(butylamino)carbonyl]oxy]ethyl acrylate, which is commercially available under the trade designation GENOMER G1122 from Rahn USA Corp. (Aurora, IL, USA).

In some embodiments, suitable plasticizers can be small molecular, oligomeric or polymeric compounds, which are compatible with the resin/soft polymer system, and thus significantly lowering the glass transition temperature for the plastic and making it softer. For example, plasticizers may include sebacates, adipates terephalate, dibenzoate, gluterate, phthalates, azelates, other ester compounds or any other organic chemicals, such as sulfonamides, organophosphates, polyethers and polybutene compatible with the resin. Additional examples include benzyl butyl phthalate, bis[2-(2-butoxyethoxy)ethyl] adipate, bis(2-ethylhexyl) adipate, bis(2-ethylhexyl) maleate, bis(2-ethylhexyl) sebacate, dibasic ester mixture( mixture of dimethyl adipate and dimethyl glutarate), dibasic ester mixture (mixture of dimethyl glutarate and dimethyl succinate), dimethyl glutarate, dibutyl adipate, dibutyl itaconate, dibutyl sebacate, dicyclohexyl phthalate, diethyl adipate, diethyl azelate, di(ethylene glycol) dibenzoate, diethyl sebacate, diethyl succinate, diheptyl phthalate, diisobutyl adipate, diisobutyl fumarate, diisobutyl phthalate, diisodecyl adipate, diisononyl phthalate, dimethyl adipate, dimethyl azelate, dimethyl phthalate, di(propylene glycol) dibenzoate, dipropyl phthalate, ethyl 4-acetylbutyrate, 2-(2-ethylhexyloxy)ethanol, isooctyl tallate, neopentyl glycol dimethylsulfate, polyethylene glycol) bis(2- ethylhexanoate), poly(ethylene glycol) dibenzoate, poly(ethylene glycol) dioleate, poly(ethylene glycol) monolaurate, poly(ethylene glycol) monooleate, sucrose benzoate, trioctyl trimellitate, trimethyl trimellitate, tri-(2-ethylhexyl) trimellitate, tri-(heptyl,nonyl) trimellitate, N-ethyl toluene sulfonamide, N-(2-hydroxypropyl) benzene sulfonamide, N- (n-butyl) benzene sulfonamide. Plasticizers can also be bio-based materials , acetylated monoglycerides, triethyl citrate, tributyl citrate, acetyltributyl citrate, trioctyl citrate, acetyl trioctyl citrate, trihexyl citrate, acetyl trihexyl citrate, butyryl trihexyl citrate, trimethyl citrate, methyl ricinoleate, epoxidized soybean oil, or epoxidized vegetable oil.

In some embodiments, the acrylate/methacrylate can be polymerized and crosslinked by photoinitiators/ or thermal initiators. In some embodiments, inorganic filler such fume silica, calcium carbonate, kaolin, alumina trihydrate, calcium sulfate or titanium oxide can be added to modify the mechanical performances.

In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 99%, or 100% of the subpad 30, based on the total surface area of the first major surface 30A of the subpad 30, may be optically transparent. In embodiments in which the polishing layer 15 (or at least a portion of the polishing layer 15) is optically transparent, at least 10%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 99%, or 100% of the of the optically transparent region of the subpad 30 may overlay an optically transparent region of the polishing layer 15. In such embodiments, the polishing pad 10 (including the polishing layer 15, subpad 30, and any intervening layers) may be optically transparent (in a direction normal to the working surface) at least in the overlay region of subpad 30 and the polishing layer 15. For purposes of the present application, it is to be appreciated that overlaid layers of the polishing pad 10 may refer to directly overlaid layers (i.e., layers that are in physical contact) or indirectly overlaid layers (i.e, layers that are not in physical contact due to, for example, one or more intervening layers) but that overlap with one another when one layer is superimposed on the other layer. Overlaying optically transparent regions of the polishing layer 15 and subpad 30 in this fashion facilitates increased flexibility in selecting the position through which end point detection can occur within the polishing pad 10. Moreover, it eliminates the need for the inclusion of a pad window (and the associated apertures in the polishing layer and subpad) which, in turn, facilitates uniform pressure and contact material from the polishing pad to the substrate to be polished.

In some embodiments, the thickness of the subpad 30 may be greater than about 25 microns, greater than about 50 microns, greater than about 100 microns, or greater than 250 microns; less than about 20 mm, less than about 10 mm, less than about 5 mm, or less than about 2.5 mm; or between 25 microns and 20 mm, between 50 microns and 10 mm, or between 100 microns and 5 mm.

In some embodiments, the subpad 30 may be intended to provide the polishing pad 10 with sufficient compliance to mitigate pressure variation at the surface of the substrate to be polished by the polishing pad 10. The pressure nonuniformity might be caused by variation in the engagement of slurry abrasive particles into the substrate surface due to, for example, variation in the size of the abrasive particles, thickness variation in any layer of the polishing pad 10, existence of debris in the contact area between the substrate surface and the major surface 15 A of the polishing pad 10, or topology variation in the substrate surface. The pressure variation at the surface of the substrate exposing to the polishing pad causes undesired polishing variation on the substrate surface and thus need to be moderated. In this regard, in some embodiments, the subpad 30 may have a Young’s Modulus of less than about 4000 kPa, less than about 3000 kPa, or less than about 2000 kPa; greater than about 100 kPa, greater than about 200 kPa, or greater than about 300 kPa; or between 4000 kPa and 100 kPa, between 3000 kPa and 200 kPa, or between 2000 and 300 kPa. In some embodiments, the subpad 30 may be composed of a material selected according to hardness. In this regard, in some embodiments, subpad 30 may have a Shore A hardness (measured in accordance with ASTM D2240) of less than about 70, less than about 60, or less than about 50; greater than about 5, greater than about 10, or greater than about 15; or between 70 and 5, between 60 and 10, or between 50 and 15. In some embodiments, the subpad 30 may be composed of a material selected according to elastic deformation. Elastic deformation may represent an ability of a material to recover to its original state after being deformed. The material of subpad 30 may be elastically deformable, e.g., being capable of substantially 100% (e.g., 99% or more, 99.5% or more, or 99.9% or more) recovering to its original state after being deformed. In some embodiments, the subpad 30 may be composed of a material selected according to relaxation modulus. Relaxation modulus may represent a measure of a time-dependent viscoelastic property. In this disclosure, relaxation modulus is measured according to the Relaxation Test described herein. In this regard, in some embodiments, subpad 30 may have a relaxation modulus of less than 40%, less than 35%, or less than 30% measured according to the Relaxation Test. In some embodiments, subpad 30 or at least a portion of that may contain cavities or voids, or may be expanded, engraved, or perforated to provide more compliance to the polishing pad 10. The voids and cavities may be distributed sporadic or patterned regularly at least in a portion of subpad 30. The volume percentage of voids and cavities may be less than about 50, less than about 30, or less than about 20 vol. %, based on the total volume of the subpad 30. The voids can be defects during fabrication or can be fabricated by, but not limited to, casting on mold or machined by different methods, such as mechanical drilling, or laser blasting. The voids can have a variety of shapes such as rectangular column, pyramid, cone, sphere, hemisphere, or others. The voids can pass through the whole subpad layer 30, or terminate mid-layer, or a combination thereof. The average size (in terms of longest dimension) of the voids may be less than 5 mm, less than 3 mm, or less than 2 mm. The voids can be arranged in different patterns or densities. In any case, the cavities or voids do not meaningfully interrupt the optical transparency of subpad 30.

In some embodiments, the subpad 30 may have a compressibility at 25% deflection, measured according to ASTM D1056, of less than 1000 kPa, less than 750 kPa, or less than 500 kPa; greater than about 25 kPa, greater than about 50 kPa, or greater than about 75 kPa; or between 1000 kPa and 25 kPa, between 750 kPa and 50 kPa, or between 500 and 75 kPa. In some embodiments, the subpad 30 may have a Poisson’s ratio of less than 0.5, less than 0.4, less than 0.3, less than about 0.2, or a negative Poisson’s ratio.

In some embodiments, the subpad may include multiple layers, e.g. may include two or more layers of material. In some embodiments, the subpad may include a rigid layer, e.g. a high modulus material such as a thermoplastic, and a compliant layer, e.g. a low modulus material as previously described above. A polishing pad that includes a multiple layer subpad, having at least one rigid layer and at least one compliant layer, may enable the planarization characteristic of the polishing pad to be adjusted and thus provide the ability to optimize the polishing pads polishing performance to the wafer topography being polished.

In some embodiments, the polishing pad 10 may include one or more layers that are disposed between the polishing layer 15 and the subpad 30. For example, as shown in FIG. 1, the polishing pad may include a foam layer 40 that is interposed between the polishing layer 15 and the subpad 30. In some embodiments, the foam layer 40 may be open-cell or closed-cell including or be formed of list suitable materials for foam layer, for example, synthetic or natural foams, thermoformed foams, polyurethanes, polyesters, polyethers, filled or grafted polyethers, viscoelastic foams, melamine foam, polyethylenes, cross-linked polyethylenes, polypropylenes, silicone, or ionomeric foams.

In some embodiments, the thickness of the foam layer 40 may be greater than 25 microns, greater than 50 microns, greater than 100 microns, or greater than 250 microns; less than 20 mm, less than 10 mm, less than 5 mm, or less than 2.5 mm.

In some embodiments, the foam layer 40 may be optically transparent (at least to an extent sufficient to allow for end point detection through such portion of the foam layer 40) over at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 99% of its surface area, based on the total surface area one of its major surfaces. In such embodiments, the foam layer 40 may not include an aperture for receiving an end point detection window. In alternative embodiments, the foam layer 40 may not be optically transparent. In such embodiments, the foam layer 40 may include an aperture for receiving an end point detection window.

In some embodiments, the foam layer 40 may have a durometer from between about 20 Shore D to about 90 Shore D and/or between about 20 Shore A to about 90 Shore A.

In some embodiments, in addition to, or as an alternative to the foam layer 40, layers disposed between the polishing layer 15 and the subpad 30 may include one or more stiff polymer layers such as polycarbonate, polymethyl methacrylate, polyethylene, polyethylene terephthalate, polyethylene terephthalate-glycol modified, polypropylene, polyvinylchloride, acrylonitrile-butadiene-styrene. Adhesive layers can also be present including acrylic adhesives, urethane adhesives, or other epoxy adhesives.

In some embodiments, the thickness of the polishing pad 10 is not particularly limited. For example, the thickness of the polishing pad 10 may coincide with the required thickness to enable polishing on the appropriate polishing tool. In some embodiments, the thickness of the polishing pad may be greater than 25 microns, greater than 50 microns, greater than 100 microns, or greater than 250 microns; less than 20 mm, less than 10 mm, less than 5 mm, or less than 2.5 mm; or between 25 microns and 20 mm, between 50 microns and 10 mm, or between 50 microns and 5 mm. The shape of the polishing pad 10 (when viewed from a direction normal to the working surface) is not particularly limited. In some embodiments, the polishing pads 10 may be fabricated such that the pad shape coincides with the shape of the corresponding platen of the polishing tool the pad will be attached to during use. Pad shapes, such as circular, square, hexagonal and the like may be used. A maximum dimension of the pad in a direction parallel to the working surface (i.e. the diameter for a circular shaped pad) is not particularly limited. In some embodiments, such maximum dimension of the polishing pad 10 may be greater than 10 cm, greater than 20 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 60 cm; less than 2.0 meters, less than 1.5 meters, or less than 1.0 meter.

In some embodiments, the present disclosure relates to a polishing system, the polishing system including any one of the previously discussed polishing pads 10 and a polishing solution. The polishing solutions used are not particularly limited and may be any of those known in the art. The polishing solutions may be aqueous or non-aqueous.

An aqueous polishing solution is defined as a polishing solution having a liquid phase (does not include particles, if the polishing solution is a slurry) that is at least 50% by weight water. A non-aqueous solution is defined as a polishing solution having a liquid phase that is less than 50% by weight water. In some embodiments, the polishing solution is a slurry, i.e. a liquid that contains organic or inorganic abrasive particles or

combinations thereof. The concentration of organic or inorganic abrasive particles or combination thereof in the polishing solution is not particularly limited. The concentration of organic or inorganic abrasive particles or combinations thereof in the polishing solution may be, greater than 0.5%, greater than 1%, greater than 2%, greater than 3%, greater than 4% or even greater than 5% by weight; may be less than 30%, less than 20% less than 15%, or less than 10% by weight. In some embodiments, the polishing solution is substantially free of organic or inorganic abrasive particles. By“substantially free of organic or inorganic abrasive particles” it is meant that the polishing solution contains less than 0.5%, less than 0.25%, less than 0.1% or less than 0.05% by weight of organic or inorganic abrasive particles. In one embodiment, the polishing solution may contain no organic or inorganic abrasive particles. The polishing system may include polishing solutions, e.g. slurries, used for silicon oxide CMP, including, but not limited to shallow trench isolation CMP; polishing solutions, e.g. slurries, used for metal CMP, including, but not limited to, tungsten CMP, copper CMP and aluminum CMP; polishing solutions, e.g. slurries, used for barrier CMP, including but not limited to tantalum and tantalum nitride CMP and polishing solutions, e.g. slurries, used for polishing hard substrates, such as, sapphire. The polishing system may further include a substrate to be polished or abraded.

FIG. 2 is a schematic illustration of a polishing system 100 for utilizing the polishing pads and methods in accordance with some embodiments of the present disclosure. As shown, the system 100 may include a polishing pad 150 (such as any one of the above described polishing pads) and a polishing solution 160. The system may further include a substrate 110 to be polished or abraded, a platen 140, and a carrier assembly 130. An adhesive layer 170 may be used to attach the polishing pad 150 to platen 140 and may be part of the polishing system. Polishing solution 160 may be a layer of solution disposed about a major surface of the polishing pad 150. The polishing solution is typically disposed on the working surface of the polishing layer of the polishing pad. The polishing solution may also be at the interface between substrate 110 and polishing pad 150. During operation of the polishing system 100, a drive assembly 145 may rotate (arrow A) the platen 140 to move the polishing pad 150 to carry out a polishing operation. The polishing pad 150 and the polishing solution 160 may separately, or in combination, define a polishing environment that mechanically and/or chemically removes material from or polishes a major surface of a substrate 110. To polish the major surface of the substrate 110 with the polishing system 100, the carrier assembly 130 may urge substrate 110 against a working surface, i.e. a polishing surface, of the polishing pad 150 in the presence of the polishing solution 160. The platen 140 (and thus the polishing pad 150) and/or the carrier assembly 130 then move relative to one another to translate the substrate 110 across the polishing surface of the polishing pad 150. The carrier assembly 130 may rotate (arrow B) and optionally traverse laterally (arrow C). As a result, the polishing layer of polishing pad 150 removes material from the surface of the substrate 110. In some embodiments, inorganic abrasive material, e.g. inorganic abrasive particles, may be included in the polishing layer to facilitate material removal from the surface of the substrate. In other embodiments, the polishing layer is substantially free of any inorganic abrasive material and the polishing solution may be substantially free of organic or inorganic abrasive particle or may contain organic or inorganic abrasive particles or combination thereof. It is to be appreciated that the polishing system 100 of FIG. 2 is only one example of a polishing system that may be employed in connection with the polishing pads and methods of the present disclosure, and that other conventional polishing systems may be employed without deviating from the scope of the present disclosure.

In another embodiment, the present disclosure relates to a method of polishing a substrate, the method of polishing including: providing a polishing pad according to any one of the previously discussed polishing pads, providing a substrate, contacting the working surface of the polishing pad with the substrate surface, and moving the polishing pad and the substrate relative to one another while maintaining contact between the working surface of the polishing pad and the substrate surface. Such polishing operation may be conducted in the presence of a polishing solution. In some embodiments, the polishing solution is a slurry and may include any of the previously discussed slurries. In some embodiments, the substrate is a semiconductor wafer. The materials comprising the semiconductor wafer surface to be polished, i.e. in contact with the working surface of the polishing pad, may include, but are not limited to, at least one of a dielectric material, an electrically conductive material, a barrier/adhesion material and a cap material. The dielectric material may include at least one of an inorganic dielectric material, e.g. silicone oxide and other glasses, and an organic dielectric material. The metal material may include, but is not limited to, at least one of copper, tungsten, aluminum, silver and the like. The cap material may include, but is not limited to, at least one of silicon carbide and silicon nitride. The barrier/adhesion material may include, but is not limited to, at least one of tantalum and tantalum nitride. The method of polishing may also include a pad conditioning or cleaning step, which may be conducted in-situ, i.e. during polishing. Pad conditioning may use any pad conditioner or brush known in the art, e.g. 3M CMP PAD CONDITIONER BRUSH PB33A, 4.25 in diameter available from the 3M

Company, St. Paul, Minnesota. Cleaning may employ a brush, e.g. 3M CMP PAD CONDITIONER BRUSH PB33 A, 4.25 in diameter available from the 3M Company, and/or a water or solvent rinse of the polishing pad.

Embodiments

1 ) A poll shing pad compri sing :

a polishing layer having a first major surface and a second major surface opposite the first major surface; a subpad having a first major surface and a second major surface opposite the first major surface,

wherein the subpad is coupled to the polishing layer; and

wherein at least 50% of the subpad, based on the total surface area of the first major surface of the subpad, is optically transparent.

2) The polishing pad of embodiment 1, wherein at least 50% of the polishing layer, based on the total surface area of the first major surface of the polishing pad, is optically transparent.

3) The polishing pad of embodiment 2, wherein at least 50% of the optically transparent region of the subpad overlays the optically transparent region of the polishing pad.

4) The polishing pad of embodiment 3, wherein the polishing pad is optically transparent in the region of the subpad that overlays the optically transparent region of the polishing pad.

5) The polishing pad of any one of the previous embodiments, wherein the subpad has a Young’s Modulus of between 4000 kPa and 100 kPa, between 3000 kPa and 200 kPa, or between 300 and 2000 kPa.

6) The polishing pad of any one of the previous embodiments, wherein the subpad has a Shore A hardness of between 5 and 70.

7) The polishing pad of any one of the previous embodiments, wherein the subpad is elasctically deformable.

8) The polishing pad of any one of the previous embodiments, wherein the subpad has a relaxation modulus of less than 40%. 9) The polishing pad of any one of the previous embodiments, wherein the subpad comprises cavities or voids.

10) The polishing pad of embodiment 9, wherein a volume percentage of the voids and cavities is less than about 50.

11) The polishing pad of any one of the previous embodiments, wherein the subpad has a compressibility at 25% deflection of between 25 and 1000 kPa. 12) The polishing pad of any one of the previous embodiments, wherein the subpad comprises a polymer having a glass transition below room temperature.

13) The polishing pad of any one of the previous embodiments, wherein the subpad comprises a polymer and a plasticizer.

14) The polishing pad of any one of the previous embodiments, wherein the subpad comprises an acrylate or methacrylate resin.

15) The polishing pad of any one of the previous embodiments, wherein the polishing layer comprises pores and asperities.

16) A method of polishing a substrate, the method comprising:

providing a polishing pad according to any one of embodiments 1-15;

providing a substrate;

contacting the first major surface of the polishing pad with the substrate;

moving the polishing pad and the substrate relative to one another while maintaining contact between the first major surface of the polishing pad and the substrate. EXAMPLES

Test Methods:

Glass Transition Temperature Test Method

The glass transition temperature (Tg, °C) of the prepared subpads was defined as the location of the peak of tan delta value as determined from a dynamic mechanical analysis (DMA) test. DMA was conducted using a dynamic mechanical analyzer, model DMA Q800, available from TA Instrument, New Castle, Delaware. Subpad samples, having a length of 13 mm and a width of 5.5 mm, were tested in a tensile mode at a frequency of 1 Hz over a temperature range from -60 °C to 120 °C at a scan rate of 5 °C/min. Testing results are shown in Table 1.

Light Transmission Test Method

Light transmission of the prepared subpads and several examples was measured using a benchtop spectrophotometer, model Color i7 from X-Rite, Inc., Grand Rapids, Michigan. Data was collected at 10 nm intervals from 800 nm to 350 nm. The sample thickness was about 53 mils (1.34 mm). Testing results are shown in Table 2.

Stress Relaxation Test Method

Stress relaxation characteristics of the prepared subpads were measured following ASTM D6048. Cylindrical subpad samples, 1.25 in (3.18 cm) diameter x 53 mils (1.35 mm) thickness, were loaded in a MTS INSIGHT Electromechanical System, from MTS Systems Corp., Eden Prairie, Minnesota and held under a constant compressive strain (e.g. as change in the sample thickness divided by its original, non-deformed thickness). The force applied by the sample to the testing machine platens was measured and recorded continuously along with the corresponding elapsed time. The stress, s, modulus at a given time, E(t), and the relaxation modulus (%) were calculated as described below.

Stress (s) was calculated from the recorded force using the following equation: s(ΐ) = Force (t) / Sample’s cross section area

Modulus (E) was calculated by dividing stress (s) by the constant strain (e_e), using the following equation:

E (t) = s(ΐ) / E_C Relaxation Modulus (%) was calculated using the following equation:

Relaxation Modulus (%) = [(Eo - E2) / Eo] * 100 where Eo is the instantaneous modulus and E2 is the modulus after two minutes of relaxation of the sample material under constant compressive strain. The instantaneous modulus is defined as the modulus of the sample material immediately after starting the test. Testing results are shown in Table 1.

An MTS INSIGHT Electromechanical System, from MTS Systems Corp., Eden Prairie, Minnesota, was used to conduct compression cycle testing on subpad samples. A 1.25 in (3.18 cm) diameter sample was placed between 2 in (51 cm) diameter platens. The sample was then put through repeated compression cycles of 0 psi (0 kPa) to 12 psi (83 KPa) for 60 cycles at a frequency of approximately 1 Hz. This was followed by a 15 second break The series of 60 compressions at about 1 Hz followed by a 15 second break was repeated 299 times. A total of 18,000 compression cycles were run on each sample. Compression values, i.e. the difference between the thickness of the sample when measured at 0 psi and 12 psi, was measured over the time range of 500 to 700 seconds and then averaged to obtain an initial compression value. Similarly, compression values were measured over the last 200 seconds of the test and averaged to obtain a final compression value. The difference between the two averages is compared to estimate sample fatigue. Testing results are shown in Table 1.

Thermal Oxide Wafer (300 mm diameter) Removal Rate Test Method

Substrate removal rates for the following Examples were calculated by

determining the change in thickness of the layer being polished from the initial (i.e before polishing) thickness and the final (i.e. after polishing) thickness and dividing this difference by the polishing time. Thickness measurements are made using a non- contacting, film analysis system NovaScan 3090Next available from Nova Measuring Instruments Ltd., Rehovot, Israel Fifty-three points diameter scans with 2 mm edge exclusion were employed. Wafer Non-1 nlformils Determination

Percent wafer non-uniformity was determined by calculating the standard deviation of the change in thickness of the layer being polished at points on the surface of the wafer (as obtained from the above Removal Rate Test Methods), dividing the standard deviation by the average of the changes in thickness of the layer being polished, and multiplying the value obtained by 100, results were therefore reported as a percentage.

300 mm Thermal Oxide Wafer Polishing Test Method

Wafers were polished using a CMP polisher available under the trade designation REFLEXION polisher from Applied Materials, Inc. of Santa Clara, CA. The polisher was fitted with a 300 mm CONTOUR head for holding 300 mm diameter wafers. A 30.5 in (77.5 cm) diameter pad was laminated to the platen of the polishing tool with a layer of PSA. There was no break-in procedure. During this polish, the pressures applied to the CONTOUR head’s zones, zone 1, zone 2, zone 3, zone 4, zone 5 and retaining ring were 3.0 psi (20.7 kPa), 1.4 psi (9.7 kPa), 1.3 psi (9.0 kPa), 1.1 psi (7.6 kPa), 1. 1 psi (7.6 kPa) and 3 7 psi (25.5 kPa), respectively. The platen speed was 53 rprn and the head speed was 47 rpm. A brush type pad conditioner, available under the trade designation 3M CMP PAD CONDITIONER BRUSH PB33A, 4.25 in diameter available from the 3M

Company, St. Paul, Minnesota was mounted on the conditioning arm and used at a speed of 81 rpm with a 3 lbf downforce. The pad conditioner was swept across the surface of the pad via a sinusoidal sweep, with 100% in-situ conditioning. The polishing solution was a slurry', available under the trade designation WIN W7300 A34 and WIN W7300 B34 from Cabot Microelectronics Corporation, Aurora, Illinois. Prior to use, the WIN W7300 A34 and WIN W7300 B34 is mixed in a ratio of 4: 1 and 30% hydrogen peroxide was added such that the final volume ratios of A34+B34/30% H2Q2 were 98/2. Polishing was conducted at a solution flow rate of 100 mL/min. Fifty thermal oxide monitor wafers were polished for 1 minute and subsequently measured. 300 rnm diameter Thermal Oxide monitor v/afers were obtained from Advantiv Technologies Inc., Freemont, California.

The wafer stack was as follows: 300 mm prime Si substrate + thermal oxide 20KA. 300 mm

The copper wafer polishing method used the same 300 mm REFLEXION equipment and brush as the 300 mm thermal oxide wafer polishing. During this polish, the pressures applied to the CONTOUR head’s zones, zone 1, zone 2, zone 3, zone 4, zone 5 and retaining ring were 4.6 psi (31.7 kPa), 2.2 psi (15.2 kPa), 2.1 psi (14.5 kPa), 2.0 psi (13.8 kPa), 2.0 psi (13.8 kPa) and 5.3 psi (36.5 kPa), respectively. The polish recipe was run with the ISRM software enabled. The polishing solution was a slurry, available under the trade designation CSL 9044c from Planar Solutions LLC, Adrian, Michigan, USA. Prior to use, CSL 9044c was diluted with DI water and 30% hydrogen peroxide was added such that the final volume ratios of 9044c/DI water/ H2O2 were 9/88/3. Polishing was conducted at a solution flow rate of 150 mL/min. The polish process began with running ten dummy thermal oxide wafers followed by a Cu wafer. 300 mm diameter Cu monitor wafers were obtained from Advantiv Technologies Inc., Freemont, California. The wafer stack was as follows: 300 mm prime Si substrate + thermal oxide 3KA + TaN 250A + PVD Cu 1KA + e-Cu 15KA + anneal. Thickness measurements of the Cu were not taken as the goal of this test was to observe the ISRM signal for a change when the wafer is completely cleared of Cu. At the times indicated in Table 5, the ISRM signal was recorded. The wafer polished until a change in signal was observed and an appropriate amount of overpolish completed.

97.6 lbs (44.3 kg) CN973H85, 48.0 lbs (21.8 kg) SR-506C, 14.4 lbs (6.53 kg) SR- 256 and 0.32 lbs (145 g) Irgacure 651 were mixed at room temperature under vacuum to degas. The obtained mixture was cast between two layers of 43543 Liner and cured via exposure under UV light with a dose of 2,000 mJ/cm². After removal of the liners, the thickness of the obtained 38 inch (0.965 m) wide cured film was 53 ± 1 mils (1.34 ± 0.025 mm).

106.7 lbs (48.4 kg) CN973H85, 53.3 lbs (24.2 kg) SR-506C and 0.32 lbs (145 g) Irgacure 651 were mixed at room temperature under vacuum to degas. The obtained mixture was cast between two layers of 43543 Liner and cured via exposure under UV light with a dose of 2,000 mJ/cm². After removal of the liners, the thickness of the obtained 36 inch (0.914 mm) wide cured film was 53 ± 1 mils (1.34 ± 0.025 mm).

Subpad 3

100 g CN9071, 120 g Uniplex 155 and 0.44 g Irgacure 651 were mixed at room temperature under vacuum to degas. The obtained mixture was cast between two layers of 43543 Liner, and cured via exposure under UV light with a dose of 2,500 mJ/cm². After removal of the liners, the thickness of the obtained 8 in (20.3 cm) wide cured film was 53 ± 1 mils (1.34 ± 0.025 mm).

Subpad 4

100 g CN9021, 40 g Uniplex 155 and 0.30 g Irgacure 651 were mixed at room temperature under vacuum to degas. After removal of the liners, the obtained mixture was cast between two layers of 43543 Liner and cured via exposure under UV light with a dose of 2,500 mJ/cm². The thickness of the obtained 8 in (20.3 cm) wide cured film was 53 ± 1 mils (1.34 ± 0.025 mm).

Subpad 5

100 lbs (45.4 kg) CN973H85, 40 lbs (18.1 kg) PL-1104 and 0.28 lbs (127 g) Irgacure 651 were mixed at room temperature under vacuum to degas. The obtained mixture was cast between a layer of PET-EVA film and a layer of 43543 Liner and cured via exposure under UV light with a dose of 2,000 mJ/cm². The 43543 Liner was removed, while the PET- EVA film remained attached to the cured film. The thickness of the obtained 38 in (0.965 m) wide cured film with PET-EVA film was 58 ± 1 mil (1.47 ± 0.025 mm) and.

Subpad 6

Subpad 6 is a perforated film with squared through holes, made from the film of Subpad 5. The through holes were fabricated on the film using an Epilog Laser Engraver, model Fusion 40 laser, from Epilog Corp. (Golden, Colorado). The holes are arranged in a square grid array with a hole width of 1 mm and a hole pitch of 5 mm. Subpad 7

Subpad 7 was prepared similarly to Subpad 6, except the square grid array had a pitch of 2.5 mm.

Subpad 8

Subpad 8 was prepared from the film of Subpad 5. Square blind holes at a depth of 0.1 mm were ablated in the film using the Epilog Laser Engraver. The holes are arranged in a squared grid array with hole width of 1 mm and hole pitch of 5 mm.

Subpad 9

Subpad 9 was prepared similarly to Subpad 6, except the hole width was 2 mm.

Example 1

A polishing pad according to FIG. 1 was prepared with the following procedure. The polishing layer was prepared with the procedure described in U.S. Patent Pat. No. 6,285,001. More specifically, the polishing layer included a plurality of precisely shaped asperities and a plurality of precisely shaped pores, the asperities being tapered cylinders of height 18 pm, diameter 50 pm, pitch 90 pm with bearing area of 24%. The pores were generally hemispherical shaped with depth 30 pm, diameter 60 pm, and pitch 90 pm. Both the plurality of precisely shaped asperities and the plurality of precisely shaped pores were configured in a square array pattern.

The polymeric material used in the embossing process to form the polishing layer was a thermoplastic polyurethane, available under the trade designation Estane 58277 resin from Lubrizol Corporation (Wickliffe, Ohio). The polyurethane had a durometer of about 92 Shore A and the polishing layer had thickness of about 22 mils (0.559

mm). During the embossing process, a 2.96 mil (0.0752 mm) PET film was brought into contact and adhered to the back surface the polishing layer.

The polishing pad was formed through multiple lamination steps, using an AGL 4400 laminator from Advanced Greig Laminators, Inc (Deforest, Wisconsin). The first step was lamination of a subpad (Subpad 1, after removing the 43543 Liners) to a 32 in (81 cm) x 32 in (81 cm) x 10 mil (0.25 mm) PET sheet prelaminated with an adhesive available under the trade designation 3M ADHESIVE TRANSFER TAPE 468MP (from the 3M Company, St. Paul, Minnesota) on the side to be laminated to the polishing layer. The second step was lamination of a rubber-based adhesive on the opposite side of Subpad 1, which was used to laminate the polishing pad to the platen of a polishing tool during polishing testing. The third step was the lamination of another layer of 3M ADHESIVE TRANSFER TAPE 468MP to the exposed surface of the PET sheet that had previously been laminated to Subpad 1 in the first lamination step. The fourth step was the lamination of the polishing layer to the exposed surface of 3M ADHESIVE TRANSFER TAPE 468MP of the third 3, yielding Example 1. A 30.5 in (76.2 cm) diameter pad was die cut using conventional techniques, forming the final polishing pad.

Example 2

A polishing pad was prepared similarly to Example 1, except Subpad 1 was replaced by Subpad 2, yielding Example 2. Comparative Example 3

Comparative Example 3 was prepared similarly to Example 1, except Subpad 1 was replaced by a sheet of Poron Foam, yielding Comparative Example 3 (CE-3).

Table 1.

* Sample was too soft to be measured by DMA. Table 2.

Table 3. Example 1 Thermal Oxide Polishing Results

Table 4. Example 2 Thermal Oxide Polishing Results Table 5. Example 1 Copper Polishing ISRM Signal Results

For CE-3, as the transmission is zero (Table 2), the ISRM signal is expected to be zero and use of visible light endpoint detection is not possible.

Claims

What is claimed is:

1) A polishing pad comprising:

a polishing layer having a first major surface and a second major surface opposite the first major surface;

a subpad having a first major surface and a second major surface opposite the first major surface,

wherein the subpad is coupled to the polishing layer; and

2) The polishing pad of claim 1, wherein at least 50% of the polishing layer, based on the total surface area of the first major surface of the polishing pad, is optically

transparent.

3) The polishing pad of claim 2, wherein at least 50% of the optically transparent region of the subpad overlays the optically transparent region of the polishing pad.

4) The polishing pad of claim 3, wherein the polishing pad is optically transparent in the region of the subpad that overlays the optically transparent region of the polishing pad.

5) The polishing pad of claim 4, wherein the subpad has a Young’s Modulus of between 4000 kPa and 100 kPa, between 3000 kPa and 200 kPa, or between 300 and 2000 kPa.

6) The polishing pad of claim 4, wherein the subpad has a Shore A hardness of between 5 and 70.

7) The polishing pad of claim 4, wherein the subpad is elasctically deformable.

8) The polishing pad of claim 4, wherein the subpad has a relaxation modulus of less than 40%. 9) The polishing pad of claim 1, wherein the subpad comprises cavities or voids.

10) The polishing pad of claim 9, wherein a volume percentage of the voids and cavities is less than about 50.

11) The polishing pad of claim 4, wherein the subpad has a compressibility at 25% deflection of between 25 and 1000 kPa.

12) The polishing pad of claim 4, wherein the subpad comprises a polymer having a glass transition below room temperature.

13) The polishing pad of claim 4, wherein the subpad comprises a polymer and a plasticizer. 14) The polishing pad of claim 4, wherein the subpad comprises an acrylate or methacrylate resin.

15) The polishing pad of claim 4, wherein the polishing layer comprises pores and asperities.

16) A method of polishing a substrate, the method comprising:

providing the polishing pad of claim 4;

providing a substrate;

contacting the first major surface of the polishing pad with the substrate;

moving the polishing pad and the substrate relative to one another while maintaining contact between the first major surface of the polishing pad and the substrate.