CN118636052A - Polishing pad with end point detection window - Google Patents

Abstract

The present application relates to a polishing pad with an endpoint detection window, comprising: a polishing layer having a top polishing surface and comprising a polishing material, a subpad layer comprising a subpad material, wherein the subpad layer is located opposite the top polishing surface, the subpad layer having a bottom subpad surface defining a bottom surface of the pad, and a window extending through the polishing pad for transmitting a signal wave through the polishing pad, wherein the window has a top portion and a bottom portion, the top portion forms a seal with the polishing layer, the top portion comprises a first window material, the bottom portion extends from an interface with the top portion of the window to the bottom surface of the pad and comprises an elastomeric material, wherein a gap exists between the side edges of the bottom portion and the subpad material. A method of polishing using the polishing pad is also provided. The polishing pad has improved endpoint detection.

Description

Polishing pad with end point detection window

Technical Field

The field of the invention is polishing pads for chemical mechanical polishing.

Background Art

Chemical mechanical planarization (CMP) is a variation of a polishing process that is widely used to planarize or flatten the construction layers of integrated circuits, or similar structures. In particular, CMP is often used to produce a flat, uniform layer of defined thickness in the manufacture of three-dimensional circuit structures built by additive stacking and planarization processes. CMP can remove excess deposited material on the surface of a substrate (e.g., a wafer) to produce an extremely flat layer of uniform thickness, the uniformity extending throughout the entire substrate (e.g., wafer) area. When the uniform thickness is throughout the entire wafer, it is referred to as global uniformity.

CMP uses a liquid (commonly referred to as a slurry) that may contain nano-sized particles. The slurry is fed onto the surface of a rotating multilayer polymer pad (sometimes referred to as a polishing sheet), which is mounted on a rotating platen. The polishing pad includes a polishing layer and may include a sub-pad. The substrate (e.g., a wafer) is mounted in a separate fixture or bracket with a separate rotating device and is pressed on the surface of the pad under a controlled load. This may result in a high relative motion rate between the substrate (e.g., a wafer) and the polishing pad, and result in a high shear rate or wear at both the substrate and pad surfaces. The shear and slurry particles captured at the pad/substrate interface wear the substrate (e.g., wafer) surface, resulting in material removal from the substrate surface. It is important to control the removal rate and the uniformity of the removal. In addition, it is useful to use metrology to determine when the polishing reaches its desired target (e.g., film thickness, expected exposure of the underlying structure, etc.).

Various types of film thickness metrology along with real-time control software can be used for endpoint detection. Endpoint detection processes periodic signals, such as collimated light waves, non-collimated light waves, or acoustic signal waves, to avoid wafer yield issues caused by both under-polishing and over-polishing. For example, one method for endpoint detection is an optical endpoint detection system that uses the transmittance of light of a desired wavelength through the polishing pad, the light is reflected from the substrate being polished, and then the reflected light signal is returned to an interferometer. This requires that at least a portion of the polishing pad is sufficiently transparent to the light source used to produce an acceptable signal-to-noise ratio. The metrology equipment can be located within the polishing equipment or within the body of the platen that holds the pad.

For certain pad structures where optical detection is used, the pad material itself may be transparent to the desired optical wavelength and or have a design that allows efficient transmission of the signal wave. Alternatively, the pad may include alternating structures to facilitate transmission of the wave. For example, a transparent polymer may be provided and an opaque material molded around it to produce a transparent window. See, e.g., U.S. 5,605,760. A third approach is to form a pad with a hole into which a transparent window material is inserted and secured in place with an adhesive. See, e.g., U.S. 5,893,796. Various versions of these pads with windows have been proposed. See, for example, U.S. 7,621,798, U.S. 8,475,228, U.S. 10,569,383, U.S. 2021/0402556, U.S. 9,475,168, US 6,045,439, US 6,716,085, and US 8,475,228.

Transmission of the signal wave through the boundary between the gap (eg, air) and the window surface may result in refraction or reflection of the signal wave, which may generate noise or degrade the signal, thereby reducing the effectiveness of endpoint detection using the signal wave.

In addition, since the window is usually formed of a material different from the polishing layer, other problems may occur. In particular, since the modulus and stiffness of the solid polymer window material are usually higher than the modulus and stiffness of the surrounding composite pad, the compression difference during the polishing process causes deformation near the window. The difference in the coefficient of thermal expansion (CTE) and thermal conductivity (K) between the polishing material and the window will further exacerbate the problem. Since the upper surface of the pad and the window is heated by friction during CMP, the difference in CTE and K produces additional transient stress and deformation. This may cause the window area to protrude above the upper surface of the pad polishing area during use. The protrusion of the window may cause scratching of the polished substrate. In addition, the gap in the peripheral area around the protruding area acts as a trap for slurry, adjustment debris and other foreign contaminants, which may also cause an increase in the scratch defect rate. In addition, since the pad is adjusted during use, the adjustment wear rate is significantly higher in the raised area due to the increase in contact pressure. This differential thinning of the window may interfere with the optical signal and may eventually lead to a breakdown in the window, which is a catastrophic failure, resulting in a shortened pad life.

Therefore, there remains a need for improved polishing pads having window areas for endpoint detection.

Summary of the invention

Disclosed herein is a polishing pad for chemical mechanical polishing, comprising: a polishing layer having a top polishing surface and comprising a polishing material; a subpad layer comprising a subpad material, wherein the subpad layer is located opposite the top polishing surface, the subpad layer having a bottom subpad surface defining a bottom surface of the pad; and a window extending through the polishing pad for transmitting a signal wave through the polishing pad, wherein the window has a top portion and a bottom portion, the top portion forming a seal with the polishing layer, the top portion comprising a first window material, the bottom portion extending from an interface with the top portion of the window to the bottom surface of the pad and comprising an elastomeric material, wherein a gap exists between a side edge of the bottom portion and the subpad material.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings which are exemplary embodiments and in which like elements are numbered alike.

Figure 1A is a cross-sectional view of a portion of one example of a polishing pad as disclosed herein, not under a deforming force. Figure 1B is a cross-sectional view of the same exemplary polishing pad as in Figure 1A, under a deforming force.

Figure 2A is a cross-sectional view of a portion of one example of a polishing pad as disclosed herein, not under a deforming force. Figure 2B is a cross-sectional view of the same exemplary polishing pad as in Figure 2A, under a deforming force.

3 is a cross-sectional view of a portion of one example of a polishing pad as disclosed herein.

4 is a top view of the upper surface of an example of a pad of the present invention in which the window shape is an oval.

DETAILED DESCRIPTION

Disclosed herein is a polishing pad that can be used for chemical mechanical polishing. The polishing pad includes a window extending to the bottom of the pad, thereby avoiding refraction and reflection of the signal wave at the solid/gas interface between the bottom of the window and the area above the platen. At the same time, the polishing pad design enables the compressibility of the pad in the window area to more closely correspond to the compressibility in the rest of the pad. This design reduces stress and avoids or eliminates window protrusions above the top polishing surface, thereby reducing defects during polishing.

Specifically, the polishing pad includes a polishing layer, a subpad, and a window. The polishing layer has a top polishing surface and a thickness. The polishing layer includes a polishing material. The top surface of the window can be recessed from the top polishing surface. Alternatively, the top surface of the window can be coplanar with the top polishing surface. The subpad includes a subpad material and is located opposite the top polishing surface. The window material is transmissive to signal waves. The signal wave can be, for example, a light wave (e.g., a columnar light or a non-columnar light) or a sound wave.

The window extends through the pad. The window includes two parts. The top portion includes a first window material. The top portion can form a seal with the polishing layer. The first window material can be a material conventionally used for such windows in polishing pads. This is desirable because the adjustment rate of such conventionally used materials may have been designed to work well with the adjustment rate of the surrounding polishing material. The top portion can be relatively rigid (compared to the elastomeric bottom portion of the window) so that the top portion in the plane of the top polishing surface or in a plane parallel to the top polishing surface does not substantially deform during polishing.

The top portion of the window can include a polymer or a polymer blend as the first window material. For optical detection systems, the first window material should have sufficient transmission at the wavelength of light used for optical metrology. It may be helpful if the hardness or thermal expansion coefficient of the window material is similar to the hardness and thermal expansion coefficient of the material used in the polishing layer. Examples of window materials include polyurethanes, acrylic polymers, cyclic olefin copolymers (e.g., TOPAS 8007, etc.).

The window is advantageously made of a material containing an aliphatic polyisocyanate ("prepolymer"). The prepolymer is the reaction product of an aliphatic polyisocyanate (e.g., a diisocyanate) and a hydroxyl-containing material. The prepolymer is then cured with a curing agent. Preferred aliphatic polyisocyanates include, but are not limited to, methylenebis-4,4'cyclohexyl isocyanate, cyclohexyl diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, tetramethylene-1,4-diisocyanate, 1,6-hexamethylene diisocyanate, dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, methylcyclohexene diisocyanate, triisocyanate of hexamethylene diisocyanate, triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate, uretdione of hexamethylene diisocyanate, ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate and mixtures thereof. Preferred aliphatic polyisocyanates have less than 10 wt% of unreacted isocyanate groups.

Advantageously, the curing agent is a polydiamine. Preferred polydiamines include, but are not limited to, diethyltoluenediamine ("DETDA"), 3,5-dimethylthio-2,4-toluenediamine and its isomers, 3,5-diethyltoluene-2,4-diamine and its isomers such as 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"), polytetramethylene oxide-di-p-aminobenzoate, N,N'-dialkyldiaminodiphenyl Methane, p,p'-methylenedianiline ("MDA"), m-phenylenediamine ("MPDA"), methylene-bis-2-chloroaniline ("MBOCA"), 4,4'-methylene-bis-(2-chloroaniline) ("MOCA"), 4,4'-methylene-bis-(2,6-diethylaniline) ("MDEA"), 4,4'-methylene-bis-(2,3-dichloroaniline) ("MDCA"), 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, 2,2',3,3'-tetrachlorodiaminodiphenylmethane, trimethylene glycol di-p-aminobenzoate and mixtures thereof. Preferably, the curing agent of the present invention includes 3,5-dimethylthio-2,4-toluenediamine and isomers thereof. Suitable polyamine curing agents include both primary and secondary amines.

In addition, other curing agents, such as diols, triols, tetraols or hydroxyl terminated curing agents can be added to the above polyurethane composition. Suitable diol, triol and tetraol groups include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, lower molecular weight polytetramethylene ether glycol, 1,3-bis(2-hydroxyethoxy)benzene, 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene, 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, resorcinol-bis-(β-hydroxyethyl)ether, hydroquinone-bis-(β-hydroxyethyl)ether, and mixtures thereof. Preferred hydroxyl-terminated curing agents include 1,3-bis(2-hydroxyethoxy)benzene, 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene, 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene, 1,4-butanediol, and mixtures thereof. Both hydroxyl-terminated curing agents and amine curing agents may contain one or more saturated, unsaturated, aromatic, and cyclic groups. In addition, hydroxyl-terminated curing agents and amine curing agents may contain one or more halogen groups. The polyurethane composition may be formed with a blend or mixture of curing agents. However, if desired, the polyurethane composition may be formed with a single curing agent.

The bottom portion comprises an elastomeric material. As used herein, "elastomeric material" means a material that deforms when subjected to a force but substantially returns to its original original form when the force is removed. There is a gap between at least a portion of the elastomeric material and at least a portion of the subpad material. When the pad is under a downward pressure, the gap allows the elastomeric material of the bottom portion of the window to deform into the gap (but substantially return to its original shape when the downward pressure is removed). In particular, the thickness of the bottom portion will decrease under the downward pressure, but the circumference can expand in a direction perpendicular to the downward pressure. This compression reduces the deformation forces in the polishing layer, particularly at the polishing surface. The compression rate of the bottom portion can be selected to substantially match the compression rate of the surrounding subpad material, the surrounding polishing material, or both. Because the window extends to the bottom edge of the pad, reflection and refraction of the signal wave at the solid/gas or solid/vacuum interface are avoided.

The elastic modulus of elastomeric material is lower than the elastic modulus of the first window material. Desirably, the elastomeric material can have a refractive index and optical transmittance similar to the upper window layer. Various transparent elastomers can be used, such as polyurethane, polyolefin, polyamide, polyacrylate, styrene block copolymer and silicone elastomer. Preferred material family is silicone elastomer. It is desirable that the elastomeric material that can be easily cast or molded into a suitable shape.

CMP pads are produced with a variety of top and bottom layer thicknesses and moduli. For example, a CMP pad may have a polishing layer with a tensile storage modulus of 300 to 400 MPa, while a subpad tensile storage modulus may be 5 to 30 MPa. The overall compressibility of the composite material is greatly affected by the relative layer thicknesses. The design of the pad of the present invention allows for a simple method for selecting the appropriate lower window layer material. For example, a standard compressibility test method can be used on a test sample of a pad stack and a window stack to allow for rapid compressibility matching prior to any pad manufacturing.

In one example, the top surface of the window (the top surface of the top portion) can be recessed below the top polishing surface. Recessing the top window surface below the top polish avoids protrusions of the window material above the top polishing surface (which can cause defects or scratches). For example, the recessed top window surface avoids or prevents direct pressure transfer between the window between substrates (e.g., silicon wafers). In addition, such recessing can avoid problems caused by differences in the conditioned wear rate between the polishing layer material and the first window material. Stress relief can be further enhanced by including a peripheral portion of the polishing material around the window that is also recessed below the top polishing surface. The recessed area can provide enhanced flexibility, which can be particularly helpful in alleviating stresses caused by differences in thermal expansion effects between the polishing layer and the top portion of the window.

Figures 1A and 1B, 2A and 2B, and 3 show cross-sections of three examples of a portion of a polishing pad 100 as disclosed herein. Figures 1A, 2A, and 3 show an exemplary pad in an undeformed state. Figures 1B and 2B show the exemplary pads of Figures 1A and 2A, respectively, under a down pressure, as would occur during use for polishing.

The polishing pad 100 has a polishing layer 101 and a top polishing surface 110. The polishing layer 101 includes a polishing material. FIG3 shows an optional macrotexture 112 on the polishing layer 101. The macrotexture may be grooves, protrusions, or raised features to enhance polishing and management of slurry liquids and removed materials.

The polishing pad 100 includes a subpad 102 opposite a top polishing surface 110. The subpad has a bottom surface 102b.

The window 103 extends through the pad. The window includes a top portion 103t and a bottom portion 103b. The top portion 103t forms a seal with the polishing layer 101. The bottom portion 103b extends from an interface 103i with the top portion to a bottom edge 103bb that is coplanar with the bottom edge 102b of the subpad 102. There is a gap 105 between the bottom portion 103t and the subpad material 102. The top portion 103t is joined to the bottom portion 103b at the interface 103i. As shown in Figures 1A and 1B, the interface 103i is coplanar with the bottom edge of the polishing layer 101. However, the interface can be located at a higher or lower position than the bottom edge of the polishing layer 101. For example, as shown in Figure 2A, the interface 103i is located above the lower edge of the polishing layer, so that the bottom portion 103b of the window and the gap 105 extend into the thickness of the polishing layer. As another example, in FIG. 3 , the interface 103 i is located below the lower edge of the polishing layer 101 , such that the top portion 103 t of the window extends into the thickness of the subpad 102 .

When a down force is applied during polishing, the pad 100 compresses. As shown in Figures 1B and 2B, when under this force, the elastomeric material of the bottom portion 103b of the window compresses vertically, but expands laterally into the gap 105, thereby relieving or reducing the force that would otherwise create stress in the polishing layer 101 and at the interface of the polishing layer 101 with the top portion 103t of the window. After the force is removed, the pad returns to the configuration shown in Figures 1A and 2A, respectively.

Optionally, the pad 100 may include a pressure sensitive adhesive 106 extending on the bottom of the subpad 102, the bottom of the bottom portion 103b of the window, or both, for adhering the pad to the platform when in use. The use of such a pressure sensitive adhesive on the bottom of the bottom portion 103b can be used to ensure that there is no air gap between the platform and the area and window where the signal wave is provided.

4 shows a top view of an example of a polishing pad 100 as disclosed herein, where 110 is a top polishing layer, 112 is an optional groove, and 103 is a window.

FIG. 3 shows an exemplary embodiment in which the top surface 103tt of the window 103 can be recessed a distance c from the polishing surface 110. Optionally, a protrusion 101e having, for example, a width d can be formed adjacent to the recessed top portion 103t. The recessing of the window area can extend the pad life. The depth of the window area recess (e.g., 113) can be adjusted to accommodate the properties of the material used in the pad (e.g., polishing material, window material), thereby providing the desired flexibility without excessive, harmful deformation during use. Extending the window substantially to the bottom of the subpad avoids additional interfaces that may disrupt the transmission of signal waves through the pad to the substrate to be polished. For example, a window having a bottom surface that is recessed above the bottom of the subpad can produce a reflective surface that can generate noise and interfere with wave transmission. Note that due to the presence of slurry in the recess 113 during the use of the pad, the disruption of the wave signal in this area is reduced. In particular, for optical systems, a translucent slurry can be used.

In an exemplary embodiment with a recessed window, the recessed depth c can be, for example, greater than 0.1, greater than 0.2, or at least 0.3 millimeters (mm), up to 1.1, up to 1, up to 0.8, up to 0.6 mm, or up to 0.4 mm. Having a thinner polishing material in the peripheral portion of the polishing layer relative to the entire polishing layer thickness can enable flexibility during use. Similarly, the width of the peripheral portion can be adjusted to provide a desired mechanical response for the pad material and design. The width d of the peripheral region can be, for example, at least 0.05, at least 0.1, at least 0.2, or at least 0.3 millimeters (mm), up to 1.1, up to 1, up to 0.8, up to 0.6 mm, or up to 0.4 mm.

The top portion 103t of the window can have a major dimension e in a direction parallel to the top polishing surface 110, which can be the size of a window commonly used in a CMP pad. For example, the dimension of the window in a direction parallel to the top polishing surface 100 is about 6 to 20 mm.

The bottom portion 103b can have a dimension f parallel to dimension e that is smaller than e to provide a gap 105. For example, dimension f can be about 5 to 18 mm. The dimension of the bottom portion 103b in a plane parallel to the top polishing surface can be about the size of the platen detector window, for example, it can be 8 to 18 mm. The gap 105 around the bottom portion can be about 2% to 10%, 3% to 8%, or 4% to 6% of the dimension of the bottom portion 103b in a direction parallel to the top polishing surface 110 (e.g., dimension f). For example, the gap can be from 0.1, from 0.2, from 0.3, from 0.4, or from 0.5 mm up to 2, up to 1.8, up to 1.6, up to 1.4, up to 1.2, or up to 1 mm.

The total thickness of the polishing pad (e.g., polishing layer plus subpad) is preferably no greater than 4 mm. For example, the total thickness of the polishing pad can be from 1 to 4 mm, from 1.5 to 4 mm, from 1.7 to 3.5 mm, or from 2 to 3 mm. The thickness of the polishing layer can be from 0.5 to 3, from 0.7 to 2.5, from 1.2 to 2.2, or from 1 to 2 mm. The thickness of the subpad can be from 0.5 to 3, from 0.7 to 2.5, from 1 to 2 mm. The thickness of the top portion of the window can have a thickness of, for example, from 0.3 to 3.2, from 0.4 to 2.7, from 0.8 to 2.2, or from 1 to 1 mm, while the thickness of the bottom portion of the window can be from 0.3 to 3.2, from 0.4 to 2.7, from 0.8 to 2.2, or from 1 to 1 mm, provided that the total thickness of the window does not exceed the total thickness of the pad.

The polishing material of the polishing layer 101 may comprise a polymer. The polishing material at the thickness of the polishing layer 101 may be opaque. The porosity may be provided, for example, by adding a hollow flexible polymer element (e.g., hollow microspheres), a foaming agent, a blowing agent, or supercritical carbon dioxide. Examples of polymeric materials for the polishing layer include: polyurethane, polycarbonate, polysulfone, nylon, polyether, polyester, polystyrene, acrylic polymer, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, polybutadiene, polyethyleneimine, polyethersulfone, polyamide, polyetherimide, polyketone, epoxy resin, silicone, their copolymers (e.g., polyether-polyester copolymers), and combinations or blends thereof. The polishing layer may include a polymer that is a polyurethane formed by the reaction of one or more polyfunctional isocyanates and one or more polyols. For example, a polyisocyanate-terminated urethane prepolymer may be used. The polyfunctional isocyanate used to form the polishing layer of the chemical mechanical polishing pad of the present invention may be selected from the group consisting of: aliphatic polyfunctional isocyanates, aromatic polyfunctional isocyanates, and mixtures thereof. For example, the polyfunctional isocyanate used to form the polishing layer of the chemical mechanical polishing pad of the present invention can be a diisocyanate selected from the group consisting of: 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4'-diphenylmethane diisocyanate; naphthalene-1,5-diisocyanate; toluidine diisocyanate; p-phenylene diisocyanate; xylylene diisocyanate; isophorone diisocyanate; hexamethylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate; cyclohexane diisocyanate; and mixtures thereof. The polyfunctional isocyanate can be an isocyanate-terminated urethane prepolymer formed by reacting a diisocyanate with a prepolymer polyol. The isocyanate-terminated urethane prepolymer can have 2 wt% to 12 wt%, 2 wt% to 10 wt%, 4 wt% to 8 wt%, or 5 wt% to 7 wt% of unreacted isocyanate (NCO) groups. The prepolymer polyol used to form the polyfunctional isocyanate-terminated urethane prepolymer can be selected from the group consisting of diols, polyols, polyol diols, copolymers thereof, and mixtures thereof. For example, the prepolymer polyol can be selected from the group consisting of polyether polyols (e.g., poly(oxytetramethylene) glycol, poly(oxypropylene) glycol, and mixtures thereof); polycarbonate polyols; polyester polyols; polycaprolactone polyols; mixtures thereof; and mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butylene glycol; 1,3-butylene glycol; 2-methyl-1,3-propanediol; 1,4-butylene glycol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; and tripropylene glycol. For example, the prepolymer polyol can be selected from the group consisting of: polytetramethylene ether glycol (PTMEG); ester-based polyols (such as ethylene glycol adipate, butylene adipate); polypropylene ether glycol (PPG); polycaprolactone polyols; copolymers thereof; and mixtures thereof. For example, the prepolymer polyol can be selected from the group consisting of: PTMEG and PPG. When the prepolymer polyol is PTMEG, the unreacted isocyanate (NCO) concentration of the isocyanate-terminated urethane prepolymer can be 2 to 10 wt% (more preferably 4 to 8 wt%; most preferably 6 to 7 wt%). Examples of commercially available PTMEG-based isocyanate-terminated urethane prepolymers include Prepolymers (available from COIM USA, Inc., such as PET-80A, PET-85A, PET-90A, PET-93A, PET-95A, PET-60D, PET-70D, PET-75D); prepolymers (available from Chemtura, such as LF 800A, LF 900A, LF 910A, LF 930A, LF 931A, LF 939A, LF 950A, LF952A, LF 600D, LF 601D, LF 650D, LF 667, LF 700D, LF750D, LF751D, LF752D, LF753D, and L325); Prepolymers (available from Anderson Development Company, such as 70APLF, 80APLF, 85APLF, 90APLF, 95APLF, 60DPLF, 70APLF, 75APLF). When the prepolymer polyol is PPG, the unreacted isocyanate (NCO) concentration of the isocyanate-terminated urethane prepolymer can be 3 to 9 wt% (more preferably 4 to 8 wt%; most preferably 5 to 6 wt%). Examples of commercially available PPG-based isocyanate-terminated urethane prepolymers include Prepolymer (available from American Keyi Company, such as PPT-80A, PPT-90A, PPT-95A, PPT-65D, PPT-75D); Prepolymers (available from Chemtura, such as LFG 963A, LFG 964A, LFG 740D); and Prepolymer (available from Anderson Development Company, such as 8000APLF, 9500APLF, 6500DPLF, 7501DPLF). The isocyanate-terminated urethane prepolymer can be a low-free isocyanate-terminated urethane prepolymer having a free toluene diisocyanate (TDI) monomer content of less than 0.1 wt%. Non-TDI-based isocyanate-terminated urethane prepolymers can also be used. For example, isocyanate-terminated urethane prepolymers include those formed by reacting 4,4'-diphenylmethane diisocyanate (MDI) with a polyol such as polytetramethylene glycol (PTMEG) with an optional diol such as 1,4-butanediol (BDO). When such an isocyanate-terminated urethane prepolymer is used, the concentration of unreacted isocyanate (NCO) is preferably 4 to 10 wt% (more preferably 4 to 10 wt%, most preferably 5 to 10 wt%). Examples of commercially available isocyanate-terminated urethane prepolymers in this category include Prepolymer (available from American Ke Yi Company, such as 27-85A, 27-90A, 27-95A); Prepolymers (available from Anderson Development as IE75AP, IE80AP, IE 85AP, IE90AP, IE95AP, IE98AP); and Prepolymer (available from Chemtura, such as B625, B635, B821).

Subpad 102 may include a polymeric material. The subpad material may be more compliant (or more resilient) than the polishing material. Subpad 102 may include a porous layer. Examples of polymeric materials for one or more subpad layers include polyurethane, polycarbonate, polysulfone, nylon, epoxy resin, polyether, polyester, polystyrene, acrylic polymer, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, polybutadiene, polyethyleneimine, polyethersulfone, polyamide, polyetherimide, polyketone, silicone, copolymers thereof (e.g., polyether-polyester copolymers), and combinations or blends thereof.

Polishing pads as disclosed herein can be prepared by a variety of processes including inserting a discrete window assembly into a pad having a matching opening, adding a lower window component to a pad that already has an upper window component cast in place in an upper pad layer, or inserting the window assembly into a mesh mold used to prepare a top pad layer blank followed by lamination of a subpad and application of an optional pressure sensitive adhesive 106.

For example, a plug of material including the top portion on the window can be placed in a mold, and the polishing material can be molded into a block or cake around the plug. The block or cake can then be cut into layers having the desired polishing layer thickness. The bottom portion of the window can be applied to the surface of the top portion of the window. For example, a preformed bottom portion can be adhered, or the bottom portion can be cast or molded. The subpad can be laminated or cast onto the bottom surface of the polishing layer.

A window assembly having a top portion and a bottom portion as described herein may be placed in a mold and a polishing layer formed around the relevant portions. A subpad may then be applied by lamination.

As another example, a polishing pad as disclosed herein can be made by providing a window assembly with a recess in a mold to secure at least a portion of a bottom portion of the window, and molding a polishing layer around the portion of the window that protrudes into the mold cavity. This forms a polishing layer with an embedded plug, wherein a portion of the plug protrudes beyond the polishing layer. To form a subpad portion of the pad, the subpad can be molded in a second molding step in a separate mold, provided that the mold includes a spacer to provide a gap.

Where desired, depressions of the window areas 113 are cut into the top surface of the pad. The polishing layer 101 may also be cut to provide a macrotexture 112. Cutting to form the depressions may be performed, for example, by milling. A commercially available example of a milling machine that may be used may be a CNC milling machine.

A method of using a polishing pad as disclosed herein, comprising: providing a substrate to be polished, providing a polishing pad as disclosed herein, optionally providing a slurry on the polishing pad, contacting the polishing pad with the substrate and moving the substrate and the polishing pad relative to each other (e.g., in a rotational motion), and transmitting a signal wave through a window and detecting the signal wave reflected from the substrate through the window to determine when polishing is complete. When optical detection is used, it is preferred to use a translucent slurry.

The present disclosure further encompasses the following aspects.

Aspect 1: A polishing pad for chemical mechanical polishing of a substrate (e.g., a semiconductor wafer), comprising: a polishing layer having a top polishing surface and comprising a polishing material; a subpad layer comprising a subpad material, wherein the subpad layer is located opposite the top polishing surface, the subpad layer having a bottom subpad surface defining a bottom surface of the pad; and a window extending through the polishing pad for transmitting a signal wave through the polishing pad, wherein the window has a top portion and a bottom portion, the top portion forming a seal with the polishing layer, the top portion comprising a first window material, the bottom portion extending from an interface with the top portion of the window to the bottom surface of the pad and comprising an elastomeric material, wherein a gap exists between a side edge of the bottom portion and the subpad material.

Aspect 2: The polishing pad according to aspect 1, wherein a portion of the polishing layer in contact with the side edge of the top portion of the window forms a peripheral region recessed from the top polishing surface.

Aspect 3: A polishing pad as described in Aspect 1 or 2, wherein the bottom portion of the window has a dimension in a plane parallel to the top polishing surface, and the size of the gap is 2% to 10%, preferably 3% to 8%, and more preferably 4% to 6% of the dimension of the bottom portion of the window in a plane parallel to the top polishing surface.

Aspect 4: The polishing pad of any of the preceding aspects, wherein the size of the gap is 0.1 to 2, preferably 0.2 to 1.8, more preferably 0.3 to 1.6, even more preferably 0.3 to 1.4, still more preferably 0.4 to 1.2, and most preferably 0.5 to 1 mm.

Aspect 5: The polishing pad of any of the preceding aspects, wherein the interface of the bottom portion and the top portion is above a plane defined by a bottom edge of the polishing layer.

Aspect 6: The polishing pad of any of Aspects 1 to 4, wherein the interface of the bottom portion and the top portion is coplanar with a plane defined by a bottom edge of the polishing layer.

Aspect 7: The polishing pad according to any of the preceding aspects, wherein the elastomeric material is selected from the group consisting of polyurethanes, polyolefins, polyamides, polyacrylates, styrene block copolymers and silicone elastomers, preferably silicone elastomers.

Aspect 8: The polishing pad of any of the preceding aspects, wherein the polishing layer comprises a polymer matrix having closed porosity.

Aspect 9: The polishing pad of any of the preceding aspects, wherein the top portion and the bottom portion are optically transparent.

Aspect 10: The polishing pad of any of the preceding aspects, further comprising a pressure sensitive adhesive on the bottom surface of the pad.

Aspect 11. A polishing method, comprising providing a substrate to be polished, providing a polishing pad as described in any of the preceding aspects, providing a polishing pad between the polishing pad and the substrate, moving the substrate relative to the polishing pad, transmitting a signal wave through the window material and the slurry, and detecting the signal wave reflected back from the substrate through the window and the slurry to determine when polishing is completed.

Aspect 12: The method according to Aspect 11, wherein the signal wave comprises a cylindrical light wave, a non-cylindrical light wave or a sound wave.

Aspect 13: The method of aspect 11, wherein the signal wave comprises a cylindrical light wave or a non-cylindrical light wave, and the top portion and the bottom portion are transparent to the corresponding cylindrical light wave or the non-cylindrical light wave.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., the range of "up to 25 wt %, or more specifically 5 wt % to 20 wt %" includes the endpoint and all intermediate values within the range of "5 wt % to 25 wt %, etc.). In addition, the upper and lower limits can be combined to form ranges (e.g., "at least 1 or at least 2 weight percent" and "up to 10 or 5 weight percent" can be combined into the ranges "1 to 10 weight percent", or "1 to 5 weight percent", or "2 to 10 weight percent", or "2 to 5 weight percent").

The present disclosure may alternatively include, consist of, or consist essentially of any suitable component disclosed herein. The present disclosure may additionally or alternatively be formulated so as to be free of, or substantially free of, any component, material, ingredient, adjuvant, or substance that is used in prior art compositions or that is otherwise not necessary to achieve the functions or objectives of the present disclosure.

All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

Unless stated to the contrary herein, all test standards are the most current standards in effect as of the filing date of the present application or, if priority is claimed, as of the filing date of the earliest priority application in which the test standards appear.

Claims (10)

1. A polishing pad for chemical mechanical polishing, comprising: a polishing layer having a top polishing surface and comprising a polishing material, a subpad layer comprising a subpad material, wherein the subpad layer is located opposite the top polishing surface, the subpad layer having a bottom subpad surface defining a bottom surface of the pad, and A window extending through the polishing pad for transmitting signal waves through the polishing pad, wherein the window has a top portion and a bottom portion, the top portion forming a seal with the polishing layer, the top portion comprising a first window material, and the bottom portion extending from an interface with the top portion of the window to the bottom surface of the pad and comprising an elastomeric material, wherein a gap exists between a side edge of the bottom portion and the subpad material. 2. The polishing pad of claim 1, wherein a portion of the polishing layer in contact with the side edge of the top portion of the window forms a peripheral region recessed from the top polishing surface. 3. The polishing pad of claim 1 , wherein the bottom portion of the window has a dimension in a plane parallel to the top polishing surface, and the size of the gap is 4% to 6% of the dimension of the bottom portion of the window in a plane parallel to the top polishing surface. 4. The polishing pad of claim 1, wherein the interface of the bottom portion and the top portion is coplanar with a bottom edge of the polishing layer. 5. The polishing pad of claim 1, wherein the interface of the bottom portion and the top portion is above a plane defined by a bottom edge of the polishing layer. 6. The polishing pad of claim 1, wherein the elastomeric material is selected from the group consisting of polyurethanes, polyolefins, polyamides, polyacrylates, styrene block copolymers, and silicone elastomers. 7. The polishing pad of claim 1, wherein the polishing layer comprises a polymer matrix having closed porosity. 8. The polishing pad of claim 1, wherein the top portion and the bottom portion are optically transparent. 9. The polishing pad of claim 1 further comprising a pressure sensitive adhesive on the bottom surface of the pad. 10. A polishing method comprising Providing a substrate to be polished Provide a polishing pad as claimed in claim 1 providing a slurry on the polishing pad, moving the substrate relative to the polishing pad, A signal wave is transmitted through the window material and the signal wave is detected after being reflected from the substrate through the window and slurry to determine when polishing is complete.