Patent Application
20080274674
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.
In 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.
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. Pat. No. 5,257,478.
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.
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. Pat. Nos. 6,422,921 and 6,905,402).
The bonding strength of a hot-melt adhesive can be characterized in terms of “T-peel” strength (see, e.g., U.S. Pat. No. 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 D1876 (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.
U.S. Pat. No. 7,101,275 (hereinafter “the '275 patent”), assigned to Rohm & Haas Electronic Materials CMP Holdings, Inc., of Wilmington, Del., 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. Pat. No. 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.
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.
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 about 2 and about 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 about 40° C.
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 about 2 and about 18 wt. % EVA and is substantially resistant to delamination when the polishing layer attains a temperature of about 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.
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 about 2 and about 18 wt. % EVA and is substantially resistant to delamination when the polishing layer attains a temperature of about 40° C.
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 about 2 and about 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 about 40° C.
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. Pat. No. 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.
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.
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.
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.
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.
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. Pat. Nos. 6,884,156 and 7,059,936.
Each of the layers of the polishing pad can have any suitable hardness (e.g., about 30-50 Shore A or about 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 about 10% void volume), or porous, and/or can have a density of about 0.3 g/cm3 or higher (e.g., about 0.5 g/cm3 or higher, or about 0.7 g/cm3 or higher) or even about 0.9 g/cm3 or higher (e.g., about 1.1 g/cm3 or higher, or up to about 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.
Each of the layers of the polishing pad can have any suitable thickness. Preferably, each layer has a thickness that is at least about 10% or more (e.g., about 20% or more, or about 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.
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. Pat. No. 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. Pat. Nos. 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.
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 about 10% or more, e.g., about 20% or more, or about 30% or more, at one or more wavelengths between from about 190 nm to about 10,000 nm, e.g., from about 190 nm to about 3500 nm, from about 200 nm to about 1000 nm, or from about 200 nm to about 780 nm.
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 about 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.
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 used 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 about 633 nm, the dye preferably is a red dye, which is capable of transmitting light having a wavelength of about 633 nm.
The hot-melt adhesive can be any suitable hot-melt adhesive. The hot-melt adhesive comprises between about 2 and about 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 about 18 wt. % or less, e.g., about 16 wt. % or less, about 15 wt. % or less, about 12 wt. % or less, about 11 wt. % or less, about 10 wt. % or less, about 8 wt. % or less, about 5 wt. % or less, or about 3 wt. % or less. Alternatively, or in addition, the EVA can be present in the hot-melt adhesive in an amount of about 2 wt. % or more, e.g., about 3 wt. % or more, about 5 wt. % or more, about 8 wt. % or more, about 10 wt. % or more, about 12 wt. % or more, or about 15 wt. % or more. For example, the EVA can be present in the hot-melt adhesive in an amount of about 3-15 wt. %, about 5-11 wt. %, about 8-10 wt. %, or about 12-16 wt. %.
It has been unexpectedly found that hot-melt adhesives comprising between about 2 and about 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 about 40° C., e.g., about 45° C., about 50° C., about 55° C., about 60° C., about 65° C., about 70° C., about 75° C., about 80° C., about 85° C., about 90° C., about 95° C., or about 100° C.
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.
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 100° C. At 40° C., and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves about 0.2 mm or less, e.g., about 0.15 mm or less, about 0.1 mm or less, about 0.05 mm or less, or about 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves about 0.5 mm or less, e.g., about 0.4 mm or less, about 0.3 mm or less, about 0.2 mm or less, about 0.1 mm or less, or about 0 mm. At 60° C., and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves about 0.2 mm or less, e.g., about 0.15 mm or less, about 0.1 mm or less, about 0.05 mm or less, or about 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves about 0.5 mm or less, e.g., about 0.4 mm or less, about 0.3 mm or less, about 0.2 mm or less, about 0.1 mm or less, or about 0 mm. At 80° C. and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves about 0.5 mm or less, e.g., about 0.4 mm or less, about 0.3 mm or less, about 0.2 mm or less, about 0.1 mm or less, or about 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves about 1.0 mm or less, e.g., about 0.8 mm or less, about 0.5 mm or less, about 0.3 mm or less, about 0.1 mm or less, or about 0 mm. At 100° C. and under the stress of a 1 kg load for one hour, for example, the hot-melt adhesive moves about 0.5 mm or less, e.g., about 0.4 mm or less, about 0.3 mm or less, about 0.2 mm or less, about 0.1 mm or less, or about 0 mm. After 24 hours at the same temperature and under the same stress, the hot-melt adhesive moves about 1.5 mm or less, e.g., about 1.2 mm or less, about 1.0 mm or less, about 0.8 mm or less, about 0.5 mm or less, about 0.3 mm or less about 0.1 mm or less, or about 0 mm.
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.
The melt flow index of the hot-melt adhesive can be any suitable value. For example, the melt flow index can be about 400 g/10 min or less, e.g., about 200 g/10 min or less, about 100 g/10 min or less, about 75 g/10 min or less, about 65 g/10 min or less, about 50 g/10 min or less, about 35 g/10 min or less, about 25 g/10 min or less, about 15 g/10 min or less, about 10 g/10 min or less, or about 5 g/10 min or less. Alternatively, or in addition, the melt flow index can be about 4 g/10 min or more, e.g., about 10 g/10 min or more, about 25 g/10 min or more, about 50 g/10 or more, about 75 g/10 min or more, about 100 g/10 min or more, about 200 g/10 min or more, or about 300 g/10 min or more. The melt flow index of the hot-melt adhesive is desirably between about 4 g/10 min and about 400 g/10 min.
The Vicat softening temperature of a hot-melt adhesive can be determined according to the test described in ASTM D1525 (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.
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.
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 about 2 and about 18 wt. % EVA and is substantially resistant to delamination when the polishing layer attains a temperature of about 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.
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.
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 about 2 and about 18 wt. % EVA and is substantially resistant to delamination when the polishing layer attains a temperature of about 40° C.
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.
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 about 80° C. and about 120° C., e.g., between about 80° C. and about 110° C., between about 80° C. and about 100° C., between about 80° C. and about 90° C., between about 90° C. and about 120° C., between about 90° C. and about 110° C., between about 90° C. and about 100° C., between about 100° C. and about 120° C., between about 100° C. and about 110° C., or between about 110° C. and about 120° C. Desirably, lamination is carried out at temperatures sufficient to heat the layer to a temperature between about 110° C. and about 120° C., e.g., about 112° C., about 115° C., or about 118° C.
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 about 50° C. to about 70° C. 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 about 150° C. to about 200° C., e.g., about 150° C. to about 190° C., about 150° C. to about 180° C., about 150° C. to about 170° C., about 150° C. to about 160° C., about 160° C. to about 200° C., about 160° C. to about 190° C., about 160° C. to about 180° C., about 160° C. to about 170° C., about 170° C. to about 200° C., about 170° C. to about 190° C., about 170° C. to about 180° C., about 180° C. to about 200° C., about 180° C. to about 190° C., or about 190° C. to about 200° C. Typically, the lamination temperature is set to a temperature in the range of about 170° C. to about 190° C., e.g., about 175° C., about 180° C., or about 185° C.
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.
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 about 2 and about 18 wt. % EVA at a temperature in the range of about 150° C. to about 200° C. 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 about 40° C. or higher, e.g., about 40° C., about 45° C., about 50° C., about 55° C., about 60° C., about 65° C., about 70° C., about 75° C., about 80° C., about 85° C., about 90° C., about 95° C., or about 100° C.
The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.
This example demonstrates the thermal stability and melt flow of EVA-based hot-melt adhesives as a function of EVA content.
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 D1238 (2004) to determine the flow of the various hot-melt adhesives. The Vicat softening point was determined according to ASTM D1525 (2006) to determine the thermal stability of the hot-melt adhesives.
These results demonstrate that hot-melt adhesives comprising between about 2 and about 18 wt. % EVA have relatively low melt flow indices as compared to hot-melt adhesives comprising other amounts of EVA or no EVA.
This example demonstrates the holding power of hot-melt adhesives according to the invention at high temperatures.
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 about 2 and about 18 wt. % EVA. Adhesives 2B and 2C were tested twice.
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.
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 40° C., 60° C., 80° C., and 100° C.). 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.
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 80° C. or 100° C.
This example demonstrates the effect of lamination temperature on the holding power of hot-melt adhesives according to the invention.
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 70° C. and 80° C. 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.
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.
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. Pat. No. 6,422,921 and of the same general class recited in U.S. Pat. No. 7,101,275.
UAF-420 hot-melt adhesive was obtained from Adhesive Films of Pine Brook, N.J. Four EPIC™ D100 pads (Cabot Microelectronics, Aurora, Ill.), i.e., Polishing Pads 4A-4D, were laminated with the UAF-420 hot-melt adhesive at a lamination temperature between about 90° C. and about 95° C. for a residence time of about 1 minute. The laminator roll pressure was set to about 8.6 kPa (about 1.25 psi) and the actual pressure applied to the pad was about 550 kPa (about 80 psi). The T-peel strength of each laminated pad was determined at a speed of 305 mm/min.
These test parameters were in accordance with U.S. Pat. No. 7,101,275. Specifically, the '275 patent provides that the lamination temperature can be from about 50° C. to about 150° C. (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. Pat. No. 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.
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.
Five additional EPIC™ D100 pads, i.e., Polishing Pads 4E-4I, were laminated with the UAF-420 hot-melt adhesive at a lamination temperature of about 170° C. The laminator roll pressure was set to about 8.6 kPa (about 1.25 psi) and the actual pressure applied to the pad was about 550 kPa (about 80 psi). Samples of the laminated pads were prepared according to Example 2, and holding power tests were conducted at 80° C. 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.
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. Pat. No. 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 170° C. with an EVA-based hot-melt adhesive according to the invention, and subjected to holding power tests at an oven temperature of 80° C., 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.
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. Pat. No. 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.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
