STACKED POLISHING PAD FOR HIGH TEMPERATURE APPLICATIONS
BACKGROUND OF THE INVENTION
[0001] Chemical-mechanical polishing ("CMP") processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic workpieces. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting workpiece to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps. [0002] hi a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table. The process removes a desired amount of material from the wafer and ideally achieves a planar surface. [0003] CMP polishing pads often comprise two or more layers, for example a polishing layer and a bottom (e.g., subpad) layer. Multi-layer polishing pads are typically formed by laminating two or more layers of different materials. For example, a conventional two-layer polishing pad includes both a rigid polishing layer and a more compressible, softer subpad layer to improve the flatness and uniformity of the polished wafer. The bonds between the polishing pad layers can be produced by laminating the layers with an adhesive. Such a multi-layer polishing pad is disclosed, for example, in U.S. Patent 5,257,478.
[0004] Conventionally, multiple layers of the polishing pad are bonded together by a pressure-sensitive adhesive (PSA) or a hot-melt adhesive (HMA). Pressure-sensitive adhesives have relatively poor chemical resistance and can be easily weakened by high pH slurries during polishing. Failure of the adhesive can cause the layers of the polishing pad to separate, i.e., delaminate, during polishing, rendering the polishing pad useless for polishing. Although hot- melt adhesives typically have better chemical resistance, hot-melt adhesives often have low thermal resistance, resulting in delamination at higher polishing temperatures. Many CMP polishing applications involve temperatures as high as 70°C, so a relatively high thermal resistance for an adhesive utilized in a polishing pad is important.
[0005] Hot-melt adhesive materials typically comprise thermoplastic or thermoset materials selected from the group consisting of polyolefins, ethylene vinyl acetate, polyamides, polyesters, polyurethanes and polyvinyl chlorides (see, e.g., U.S. Patents 6,422,921 and 6,905,402). [0006] The bonding strength of a hot-melt adhesive can be characterized in terms of "T- peel" strength (see, e.g., U.S. Patent 4,788,798). T-peel tests can be performed according to the test set out by the American Society for Testing and Materials (ASTM), which is ASTM D 1876 (2001). This test measures the peel adhesion of the adhesive. Peel adhesion is the force per unit width required to remove a test sample from a standard test panel at a specified angle and speed. The fracture of the interface is an irreversible entropy creating process, which involves a substantial amount of energy dispersion. Standard T-peel tests increase the force applied to the sample at a constant rate, until the sample is removed from the test panel, thereby determining the force needed to peel the sample.
[0007] U.S. Patent 7,101,275 (hereinafter "the '275 patent"), assigned to Rohm & Haas Electronic Materials CMP Holdings, Inc., of Wilmington, Delaware, claims a polishing pad utilizing any one of a number of known hot-melt adhesives that exhibit a T-peel strength that is at least greater than 40 Newtons (N) at a polishing speed of 305 mm/min (col. 6, lines 1-3). While the '275 patent alleges that the polishing pad disclosed is a "more resilient polishing pad than prior art pads" (col. 4, lines 12-13) as a result of the properties of the hot-melt adhesive, the hot-melt adhesives referenced by the '275 patent are of the same general class used in the prior art, provide no advantage over those used in the prior art, and hence do not provide a polishing pad with improved resistance to delamination. For example, U.S. Patent 6,422,921 (hereinafter "the '921 patent"), discloses the same general class of hot-melt adhesives that are suitable for use in polishing pads (compare the '921 patent, col. 3, lines 22-24, with the '275 patent, col. 3,
lines 33-36). While such hot-melt adhesives, when applied to a polishing pad and tested according to the disclosure of the '275 patent, exhibit an average T-peel strength well over the minimum T-peel strength set forth in the '275 patent, the polishing pads utilizing such adhesives can delaminate during use, especially in high-temperature polishing applications. [0008] There are numerous variables that contribute to pad delamination during polishing applications. For example, the force needed to break an adhesive bond depends on the type of adhesive, the process conditions of the polishing procedure, and the temperature at which the polishing procedure is carried out. Specifically, shear and frictional stresses are induced both by the pressure on the polishing wafer during polishing as well as by the chemicals used during polishing. Shear stress can have a deleterious effect on the performance of hot-melt adhesives, and many polishing pads utilizing such adhesives undergo shear deformation during polishing. T-peel tests do not account for shear stresses, and, as such, do not always provide accurate predications of the bond strengths of hot-melt adhesives.
BRIEF SUMMARY OF THE INVENTION
[0009] The invention provides a polishing pad for chemical-mechanical polishing comprising (a) a polishing layer, (b) a bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer, and (c) a hot-melt adhesive, wherein the hot-melt adhesive joins together the polishing layer and the bottom layer, and the hot-melt adhesive comprises between 2 and 18 wt.% ethylene vinyl acetate or ethyl vinyl acrylate (collectively, "EVA") and is substantially resistant to delamination when the polishing layer attains a temperature of 40°C. [0010] The invention also provides a method of polishing a substrate comprising (i) providing a polishing pad for chemical-mechanical polishing comprising (a) a polishing layer, (b) a bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer, and (c) a hot-melt adhesive, wherein the hot-melt adhesive joins together the polishing layer and the bottom layer, and the hot-melt adhesive comprises between 2 and 18 wt.% EVA and is substantially resistant to delamination when the polishing layer attains a temperature of 40°C; (ii) contacting the substrate with the polishing pad and a polishing composition; and (iii) moving the polishing pad and the polishing composition relative to the substrate to abrade at least a portion of the surface of the substrate with the polishing pad to polish the substrate. [0011] The invention further provides a method of preparing a polishing pad for chemical- mechanical polishing of a substrate comprising (i) providing a polishing pad for chemical- mechanical polishing comprising (a) a polishing layer, and (b) a bottom layer, wherein the
bottom layer is substantially coextensive with the polishing layer; and (ii) laminating at least one of the polishing layer and the bottom layer with a hot-melt adhesive, wherein the hot-melt adhesive joins together the polishing layer and the bottom layer, and wherein the hot-melt adhesive comprises between 2 and 18 wt.% EVA and is substantially resistant to delamination when the polishing layer attains a temperature of 40°C.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0012] FIG. 1 is a graph of the percentage of EVA content versus the melting point and Vicat softening temperature of an EVA-based hot-melt adhesive.
[0013] FIG. 2 is a graph that illustrates the time to delamination as determined by holding power tests carried out on a comparative hot-melt adhesive and a hot-melt adhesive according to the invention. Pad lamination was carried out at approximately 165°C, both adhesives were applied to an EPIC™ DlOO pad (Cabot Microelectronics, Aurora, Illinois), and the holding power tests were carried out at 80°C.
[0014] FIG. 3 is a graph of the approximate lamination temperature versus the time to delamination determined by holding power tests carried out on a hot-melt adhesive according to the invention. The hot-melt adhesive was applied to EPIC™ DlOO pads and the holding power tests were carried out at 80°C. At a lamination temperature of approximately 175°C, no delamination was observed even when the test was stopped after 960 minutes.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The invention provides a chemical -mechanical polishing pad for polishing a substrate. The polishing pad comprises a polishing layer; a bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer; and a hot-melt adhesive. The hot- melt adhesive joins together the polishing layer and the bottom layer. The hot-melt adhesive comprises between 2 and 18 wt.% ethylene vinyl acetate or ethyl vinyl acrylate (collectively, "EVA") and is substantially resistant to delamination when the polishing layer attains a temperature of 40°C.
[0016] The polishing layer of the polishing pad can be any suitable polishing layer. Desirably, the polishing layer is substantially coextensive with the bottom layer. The polishing layer of the polishing pad optionally comprises grooves, channels, and/or perforations. Such features can facilitate the lateral transport of a polishing composition across the surface of the polishing layer. The grooves, channels, and/or perforations can be in any suitable pattern and can have any suitable depth and width. The polishing layer can have two or more different
groove patterns, for example, a combination of large grooves and small grooves as described in
U.S. Patent 5,489,233. The grooves can be in the form of linear grooves, slanted grooves, concentric grooves, spiral or circular grooves, or X-Y Crosshatch pattern, and can be continuous or non-continuous in connectivity.
[0017] The bottom layer of the polishing pad, i.e., subpad, can be any suitable bottom layer.
Desirably, the bottom layer is substantially coextensive with the polishing layer.
[0018] The polishing pad optionally further comprises one or more middle layers disposed between the polishing layer and the bottom layer. Optionally, the polishing pad comprises three or more (e.g., four or more, six or more, or eight or more) layers disposed between the polishing layer and the bottom layer. Typically, the polishing pad comprises ten or less (e.g., eight or less, or six or less) layers disposed between the polishing layer and the bottom layer.
[0019] The middle layer or middle layers of the polishing pad can be any suitable layer or layers. Desirably, each of the middle layer or middle layers is substantially coextensive with the polishing layer and the bottom layer. Each of the polishing layer, bottom layer, and the middle layer or middle layers preferably is joined together with the hot-melt adhesive.
[0020] The advantage of such multi-layer polishing pads is that each of the layers can have different physical or chemical properties. For example, in some applications it may be desirable for each of the layers to have the same chemical composition but have different physical properties such as hardness, density, porosity, compressibility, rigidity, tensile modulus, bulk modulus, rheology, creep, glass transition temperature, melt temperature, viscosity, or transparency. In other applications, it may be desirable for the polishing pad layers to have similar physical properties but different chemical properties (e.g., different chemical compositions). Of course, the polishing pad layers can have different chemical properties as well as different physical properties.
[0021] The layers of the polishing pad can be any suitable layers. Each of the layers of the polishing pad can be hydrophilic, hydrophobic, or a combination thereof. Each of the layers of the polishing pad optionally contains particles, e.g., particles that are incorporated into the layer.
The particles can be abrasive particles, polymer particles, composite particles (e.g., encapsulated particles), organic particles, inorganic particles, clarifying particles, water-soluble particles, and mixtures thereof. Suitable particles are described, for example, in U.S. Patents 6,884,156 and
7,059,936.
[0022] Each of the layers of the polishing pad can have any suitable hardness (e.g., 30-50 Shore A or 25-80 Shore D). Similarly, each of the layers can have any suitable density and/or porosity. For example, each of the layers can be non-porous (e.g., solid), nearly solid (e.g., having less than 10% void volume), or porous, and/or can have a density of 0.3 g/cm3 or higher (e.g., 0.5 g/cm3 or higher, or 0.7 g/cm3 or higher) or even 0.9 g/cm3 or higher (e.g., 1.1 g/cm3or higher, or up to 99% of the theoretical density of the material). For some applications, it may be desirable for one or more layers of the polishing pad material (e.g., a polishing layer) to be hard, dense, and/or have low porosity, while one or more of the other layers is soft, highly porous, and/or has low density.
[0023] Each of the layers of the polishing pad can have any suitable thickness. Preferably, each layer has a thickness that is at least 10% or more (e.g., 20% or more, or 30% or more) of the total thickness of the polishing pad. The thickness of each layer will depend in part on the total number of polishing pad layers. Moreover, two or more (e.g., all) of the polishing pad layers can have the same thickness, or the layers can each have a different thickness. [0024] Each of the layers of the polishing pad optionally further comprises an optical endpoint detection port. Desirably, each layer of the multi-layer polishing pad comprises an optical endpoint detection port, and the optical endpoint detection ports are substantially aligned. The optical endpoint detection port can be one or more apertures, transparent regions, or translucent regions, e.g., windows as described in U.S. Patent 5,893,796. The inclusion of such apertures or translucent regions, i.e., optically transmissive regions, is desirable when the polishing pad is to be used in conjunction with an in situ CMP process monitoring technique. Techniques for inspecting and monitoring the polishing process by analyzing light or other radiation reflected from a surface of the workpiece are known in the art. Such methods are described, for example, in U.S. Patents 5,196,353, 5,433,651, 5,609,511, 5,643,046, 5,658,183, 5,730,642, 5,838,447, 5,893,796, 5,949,927, and 5,964,643. Desirably, the inspection or monitoring of the progress of the polishing process with respect to a workpiece being polished enables the determination of the polishing end-point, i.e., the determination of when to terminate the polishing process with respect to a particular workpiece.
[0025] The aperture can have any suitable shape and can be used in combination with drainage channels for minimizing or eliminating excess polishing composition on the polishing surface. The optically transmissive region or window can be any suitable window, many of which are known in the art. For example, the optically transmissive region can comprise a glass
or polymer-based plug that is inserted in an aperture of the polishing pad or can comprise the same polymeric material used in the remainder of the polishing pad. Typically, the optically transmissive region has a light transmittance of 10% or more, e.g., 20% or more, or 30% or more, at one or more wavelengths between from 190 run to 10,000 nm, e.g., from 190 run to 3500 nm, from 200 nm to 1000 nm, or from 200 nm to 780 nm.
[0026] The optically transmissive region can have any suitable structure, e.g., crystallinity, density, and porosity. For example, the optically transmissive region can be solid or porous, e.g., microporous or nanoporous. Preferably, the optically transmissive region is solid or is nearly solid, e.g., has a void volume of 3% or less. The optically transmissive region optionally further comprises particles selected from polymer particles, inorganic particles, and combinations thereof. The optically transmissive region optionally contains pores. [0027] The optically transmissive region optionally further comprises a dye, which enables the polishing pad substrate material to selectively transmit light of a particular wavelength(s). The dye acts to filter out undesired wavelengths of light, e.g., background light, and thus improves the signal to noise ratio of detection. The optically transmissive region can comprise any suitable dye or may comprise a combination of dyes. Suitable dyes include polymethine dyes, di- and tri-arylmethine dyes, aza analogues of diarylmethine dyes, aza (18) annulene dyes, natural dyes, nitro dyes, nitroso dyes, azo dyes, anthraquinone dyes, sulfur dyes, and the like. Desirably, the transmission spectrum of the dye matches or overlaps with the wavelength of light \ιsed for in situ endpoint detection. For example, when the light source for the endpoint detection (EPD) system is a HeNe laser, which produces visible light having a wavelength of 633 nm, the dye preferably is a red dye, which is capable of transmitting light having a wavelength of 633 nm.
[0028] The hot-melt adhesive can be any suitable hot-melt adhesive. The hot-melt adhesive comprises between 2 and 18 wt.% ethylene vinyl acetate or ethyl vinyl acrylate (collectively, "EVA")- In particular, the EVA can be present in the hot-melt adhesive in an amount of 18 wt.% or less, e.g., 16 wt.% or less, 15 wt.% or less, 12 wt.% or less, 11 wt.% or less, 10 wt.% or less, 8 wt.% or less, 5 wt.% or less, or 3 wt.% or less. Alternatively, or in addition, the EVA can be present in the hot-melt adhesive in an amount of 2 wt.% or more, e.g., 3 wt.% or more, 5 wt.% or more, 8 wt.% or more, 10 wt.% or more, 12 wt.% or more, or 15 wt.% or more. For example, the EVA can be present in the hot-melt adhesive in an amount of 3-15 wt.%, 5-11 wt.%, 8-10 wt.%, or 12-16 wt.%.
[0029] It has been unexpectedly found that hot-melt adhesives comprising between 2 and 18 wt.% EVA exhibit high chemical and thermal resistance during CMP and thus resist delamination. Desirably, the hot-melt adhesive layer is substantially resistant to delamination when the polishing layer attains a temperature of 40°C, e.g., 45°C, 50°C, 55°C, 60°C, 650C, 70°C, 75°C, 800C, 85°C, 90°C, 95°C, or 1000C.
[0030] The thermal resistance of a hot-melt adhesive according to the invention can be measured by a shear adhesion or holding power test. Holding power provides an accurate prediction of adhesive strength at elevated temperatures and under shear conditions. As used herein, holding power is the time required, under specified test conditions, to slide a standard area of sample on a standard flat surface in a direction parallel to that surface. Holding power is a constant load creep test that measures millimeters (mm) of sample moved at a specified load after a specified amount of time.
[0031] The relatively high holding power of a hot-melt adhesive utilized in the context of the invention demonstrates the thermal resistance of the adhesive at polishing temperatures as high as 1000C. At 400C, and under the stress of a 1 kg load for one hour, for example, the hot- melt adhesive moves 0.2 mm or less, e.g., 0.15 mm or less, 0.1 mm or less, 0.05 mm or less, or 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves 0.5 mm or less, e.g., 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0 mm. At 600C, and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves 0.2 mm or less, e.g., 0.15 mm or less, 0.1 mm or less, 0.05 mm or less, or 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves 0.5 mm or less, e.g., 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0 mm. At 800C and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves 0.5 mm or less, e.g., 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves 1.0 mm or less, e.g., 0.8 mm or less, 0.5 mm or less, 0.3 mm or less, 0.1 mm or less, or 0 mm. At 1000C and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves 0.5 mm or less, e.g., 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves 1.5 mm or less, e.g., 1.2 mm or less, 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, 0.3 mm or less 0.1 mm or less, or 0 mm.
[0032] The melt flow index of a hot-melt adhesive can be determined according to the test described in ASTM D1238 (2004). Melt flow index measures the rate of extrusion of thermoplastics through an orifice at a specified temperature and load. It provides a method of measuring the flow of a melted material that can be used to differentiate grades of that material. Specifically, in the context of polishing pad applications, the melt flow index characterizes the rate at which the adhesive fills any divots or pinholes that may be present on the surface on the layer in contact with the adhesive.
[0033] The melt flow index of the hot-melt adhesive can be any suitable value. For example, the melt flow index can be 400 g/10 min or less, e.g., 200 g/10 min or less, 100 g/10 min or less, 75 g/10 min or less, 65 g/10 min or less, 50 g/10 min or less, 35 g/10 min or less, 25 g/10 min or less, 15 g/10 min or less, 10 g/10 min or less, or 5 g/10 min or less. Alternatively, or in addition, the melt flow index can be 4 g/10 min or more, e.g., 10 g/10 min or more, 25 g/10 min or more, 50 g/10 or more, 75 g/10 min or more, 100 g/10 min or more, 200 g/10 min or more, or 300 g/10 min or more. The melt flow index of the hot-melt adhesive is desirably between 4 g/10 min and 400 g/10 min.
[0034] The Vicat softening temperature of a hot-melt adhesive can be determined according to the test described in ASTM D 1525 (2006). The Vicat softening temperature is the temperature at which a 1 mm2 flat-ended needle penetrates a sample to a 1 mm depth under a specific load at a specific heating rate. The Vicat softening temperature can be used to predict at what point an adhesive will soften when applied to a polishing pad or when used in a high temperature application.
[0035] The invention also provides a method of polishing a substrate comprising (i) providing the aforementioned polishing pad for chemical-mechanical polishing, (ii) contacting the substrate with the polishing pad and a polishing composition, and (iii) moving the polishing pad and the polishing composition relative to the substrate to abrade at least a portion of the surface of the substrate with the polishing pad to polish the substrate.
[0036] In particular, the invention provides a method of polishing a substrate comprising (i) providing a polishing pad for chemical-mechanical polishing comprising (a) a polishing layer, (b) a bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer, and (c) a hot-melt adhesive, wherein the hot-melt adhesive joins together the polishing layer and the bottom layer, and the hot-melt adhesive comprises between 2 and 18 wt.% EVA and is substantially resistant to delamination when the polishing layer attains a temperature of
400C; (ii) contacting the substrate with the polishing pad and a polishing composition; and (iii) moving the polishing pad and the polishing composition relative to the substrate to abrade at least a portion of the surface of the substrate with the polishing pad to polish the substrate. [0037] The polishing composition can be any suitable polishing composition. The polishing composition typically comprises an aqueous carrier, a pH adjustor, and optionally an abrasive. Depending on the type of workpiece being polished, the polishing composition optionally can further comprise oxidizing agents, organic acids, complexing agent, pH buffers, surfactants, corrosion inhibitors, anti-foaming agents, and the like.
[0038] The invention further provides a method of preparing a polishing pad for chemical- mechanical polishing of a substrate comprising (i) providing a polishing pad for chemical- mechanical polishing comprising (a) a polishing layer, and (b) a bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer; and (ii) laminating at least one of the polishing layer and the bottom layer with a hot-melt adhesive, wherein the hot-melt adhesive joins together the polishing layer and the bottom layer, and the hot-melt adhesive comprises between 2 and 18 wt.% EVA and is substantially resistant to delamination when the polishing layer attains a temperature of 4O0C.
[0039] Lamination can be achieved by any suitable lamination method. Typically, lamination is achieved by use of a standard laminator roll to apply the adhesive to the layer(s) of the polishing pad. In a polishing pad comprising a polishing layer and a bottom layer, for example, the hot-melt adhesive is applied to at least one of the polishing layer and the bottom layer, which then are contacted together. Optionally, the hot-melt adhesive is applied to both the polishing layer and the bottom layer, which are then contacted together. In a polishing pad comprising one or more middle layers disposed between the polishing layer and the bottom layer, the hot-melt adhesive also can be applied to at least one of the middle layers in addition to or as an alternative to the polishing layer and/or the bottom layer, which are then contacted together at the same time or at a different time. Desirably, the hot-melt adhesive joins each of the layers and, therefore, is applied to the side of at least one of each pair of layers in contact which each other such that there is adhesive between the pair of layers. [0040] Lamination can be carried out at any suitable lamination temperature and pressure. Desirably, lamination is carried out at a temperature sufficient to heat the layer to a temperature that is equal to or greater than the activation temperature of the hot-melt adhesive. Layers laminated at or above the adhesive activation temperature maintain holding power and resist
delamination even at relatively high polishing temperatures. The activation temperature of an EVA-based hot-melt adhesive is typically between 80°C and 120°C, e.g., between 8O0C and 11O0C, between 80°C and 1000C, between 800C and 900C, between 900C and 1200C, between 900C and 11O0C, between 900C and 1000C, between 1000C and 1200C, between 1000C and 1100C, or between 1100C and 1200C. Desirably, lamination is carried out at temperatures sufficient to heat the layer to a temperature between 1100C and 1200C, e.g., 112°C, 115°C, or 118°C.
[0041] The temperature actually achieved by the layer can be significantly lower than the lamination temperature set on a typical lamination device. Specifically, the temperature achieved by the layer can be 500C to 700C lower than the set lamination temperature. The lamination temperature can be set on the lamination device to any suitable temperature to achieve the desired temperature of the layer. For example, the lamination temperature can be set to a temperature in the range of 15O0C to 2000C, e.g., 15O0C to 1900C, 15O0C to 1800C, 1500C to 17O0C, 1500C to 1600C, 1600C to 2000C, 1600C to 1900C, 1600C to 1800C, 16O0C to 1700C, 1700C to 2000C, 1700C to 1900C, 1700C to 180°C, 1800C to 2000C, 1800C to 1900C, or 1900C to 2000C. Typically, the lamination temperature is set to a temperature in the range of 1700C to 1900C, e.g., 175°C, 1800C, or 185°C.
[0042] Lamination can be carried out at any suitable speed. For example, the layer can be run through the laminator roll at any suitable speed and can be exposed to the laminator roll for any suitable residence time. Desirably, the laminator roll speed can be decreased to increase the residence time of the layer, thereby causing the surface temperature of the layer to more closely approach the lamination temperature set on the lamination device. [0043] It has been unexpectedly found that polishing pads laminated with a hot-melt adhesive at a temperature sufficient to heat the surface of the pad to a temperature that is equal to or greater than the activation temperature of the hot-melt adhesive exhibit improved resistance to delamination in high-temperature polishing applications. Specifically, polishing pads laminated with a hot-melt adhesive comprising between 2 and 18 wt.% EVA at a temperature in the range of 1500C to 2000C exhibit high chemical and thermal resistance during CMP and thus resist delamination. Specifically, the hot-melt adhesive is substantially resistant to delamination when the polishing layer attains a temperature of 400C or higher, e.g., 400C, 45°C, 5O0C, 55°C, 600C, 65°C, 700C, 75°C, 800C, 850C, 9O0C, 95°C, or 1000C.
EXAMPLES
[0044] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.
EXAMPLE 1
[0045] This example demonstrates the thermal stability and melt flow of EVA-based hot-melt adhesives as a function of EVA content.
[0046] The melting point, Vicat softening point, and melt flow index were determined for twelve different hot-melt adhesives, i.e., Adhesives 1A-1L, containing varying amounts of EVA. The melt flow index was determined according to ASTM D 1238 (2004) to determine the flow of the various hot-melt adhesives. The Vicat softening point was determined according to ASTM D 1525 (2006) to determine the thermal stability of the hot-melt adhesives. Table 1: Hot-Melt Adhesive Properties as a Function of EVA Content
[0047] These results demonstrate that hot-melt adhesives comprising between 2 and 18 wt.% EVA have relatively low melt flow indices as compared to hot-melt adhesives comprising other amounts of EVA or no EVA.
EXAMPLE 2
[0048] This example demonstrates the holding power of hot-melt adhesives according to the invention at high temperatures.
[0049] The holding power of three different adhesives, i.e., Adhesives 2A-2C, was determined at various temperatures. Adhesive 2A (comparative) is a hot-melt adhesive. Adhesive 2B (comparative) is a pressure-sensitive adhesive. Adhesive 2C (inventive) is an EVA-based hot-melt adhesive comprising between 2 and 18 wt.% EVA. Adhesives 2B and 2C were tested twice.
[0050] Laminated samples were prepared for testing. The laminated samples were approximately four inches long. Each laminated sample contained a release layer, an adhesive layer (usually used to affix the pad assembly to the platen for polishing), a subpad, an adhesive affixing the subpad to the top pad, and a top pad. The release liners were removed from the samples, and the samples were affixed to aluminum plates that were approximately 10.16 cm (four inches) long, 2.54 cm (one inch) wide, and 0.64 cm (0.25 inch) thick. The laminated sample was allowed 15-30 minutes to fully adhere to the aluminum plate. [0051] Each aluminum plate included a hole that was approximately 0.64 cm (0.25 inch) in diameter, so that each plate could be hung from a hook in an oven. Further, a hole was punched into each laminated sample so that a 1 kg weight could be hung from the sample. The holding power tests were conducted in a temperature-controlled oven that was heated to different temperatures (approximately 400C, 600C, 800C, and 1000C). The aluminum plates, including the laminated samples and hanging weights, were placed into the heated oven. A timer was started once the sample and oven temperature stabilized. The extent of delamination between the adhesive and the pad layers was recorded after 1 hour and after 24 hours. A "drop" indicates that the sample completely delaminated, i.e., the adhesive was completely debonded from the pad layer. The results are summarized in Table 2.
Table 2: Adhesive Holding Power as a Function of Time and Temperature
[0052] These results demonstrate that the type of adhesive used, i.e., pressure sensitive adhesive or hot-melt adhesive, as well as the particular chemical makeup of the adhesive, i.e., weight percent of EVA, has a significant impact on the holding power of the adhesive at various temperatures. Hot-melt adhesives according to the invention exhibit a greater holding power, i.e., a lesser extent of delamination, even at temperatures as high as 800C or 1000C.
EXAMPLE 3
[0053] This example demonstrates the effect of lamination temperature on the holding power of hot-melt adhesives according to the invention.
[0054] Twenty-seven polishing pads, i.e., Polishing Pads 3AA-3BA, were laminated with an EVA-based hot-melt adhesive according to the invention at various lamination temperatures. Samples of the laminated pads were prepared according to Example 2, and holding power tests were conducted at 700C and 800C. The polishing pads were observed for up to 16 hours (960 minutes), and the time to any observed delamination was recorded. The results are summarized in Table 3.
Table 3: Delamination of Hot-Melt Adhesive as a Function of Lamination Temperature
[0055] These results demonstrate that a polishing pad laminated with a hot-melt adhesive in accordance with the invention at a temperature at or in excess of the activation temperature of the hot-melt adhesive exhibits increased holding power and is resistant to delamination at high temperature.
EXAMPLE 4
[0056] This example compares the properties of a polishing pad prepared with a hot-melt adhesive in accordance with the present invention with the properties of a polishing pad prepared with a hot-melt adhesive discussed in U.S. Patent 6,422,921 and of the same general class recited in U.S. Patent 7,101,275.
[0057] UAF-420 hot-melt adhesive was obtained from Adhesive Films of Pine Brook, New Jersey. Four EPIC™ DlOO pads (Cabot Microelectronics, Aurora, Illinois), i.e., Polishing Pads 4A-4D, were laminated with the UAF-420 hot-melt adhesive at a lamination temperature between 90°C and 95 °C for a residence time of 1 minute. The laminator roll pressure was set to 8.6 kPa (1.25 psi) and the actual pressure applied to the pad was 550 kPa (80 psi). The T-peel strength of each laminated pad was determined at a speed of 305 mm/min. [0058] These test parameters were in accordance with U.S. Patent 7, 101,275. Specifically, the '275 patent provides that the lamination temperature can be from 500C to 1500C (col. 5, lines 4-5) and that the T-peel strength is determined at a speed of 305 mm/min (see, e.g., col. 3, lines 62-63). The '275 patent discloses that polyurethane hot-melt adhesives are included within the "invention" (col. 3, lines 33-36), and U.S. Patent 6,422,921 discloses that UAF-420 is such a polyurethane hot-melt adhesive (col. 3, lines 25-27). The T-peel results for the UAF-420 hot- melt adhesive are summarized in Table 4A.
Table 4 A: T-Peel Stren th of Prior Art Hot-Melt Adhesive
[0059] These results demonstrate that polishing pads prepared with the general class of hot- melt adhesives disclosed in the prior art exhibit the same T-peel strength of the polishing pads subsequently claimed in the '275 patent.
[0060] Five additional EPIC™ DlOO pads, i.e., Polishing Pads 4E-4I, were laminated with the UAF-420 hot-melt adhesive at a lamination temperature of 1700C. The laminator roll pressure was set to 8.6 kPa (1.25 psi) and the actual pressure applied to the pad was 550 kPa (80 psi). Samples of the laminated pads were prepared according to Example 2, and holding power tests were conducted at 800C. The polishing pads were observed, and the time to any observed delamination was recorded. Each delamination was a complete delamination or "drop," i.e., the adhesive was completely debonded from the pad layer. The results are summarized in Table 4B.
Table 4B: Holding Power of Prior Art Hot-Melt Adhesive
[0061] These results demonstrate that while the UAF-420 prior art hot-melt adhesive exhibited a T-peel strength sufficient to meet the claims of U.S. Patent 7,101,275, it did not exhibit a holding power comparable to that exhibited by the EVA-based hot-melt adhesives utilized in the context of the invention at high temperatures. In particular, when polishing pads were laminated at approximately 1700C with an EVA-based hot-melt adhesive according to the invention, and subjected to holding power tests at an oven temperature of 800C, no delamination was observed even after 960 minutes (see Example 3, Laminated Polishing Pads 3AW, 3AX, 3AY, 3AZ, and 3BA). To contrast, complete delamination of UAF-420 adhesive was observed after an average of only 12.4 minutes under the same test conditions.
[0062] These results further demonstrate that the T-peel test is an insufficient indicator of adhesive strength at elevated temperatures and under shear conditions. While the UAF-420 prior art hot-melt adhesive exhibited a T-peel strength sufficient to meet the claims of U.S. Patent 7,101,275, the results of the holding power test demonstrate that it did not withstand shear force at elevated temperatures. The T-peel strength of an adhesive does not alone indicate that a polishing pad laminated with that adhesive will resist delamination during high temperature polishing applications. The holding power test disclosed herein provides a more accurate representation of adhesive strengths at elevated temperatures and under shear conditions.