Polishing pad

Abstract

To provide a polishing pad which has higher polishing selectivity for an insulation material than for a metal wiring, and has excellent stability of polishing rate.SOLUTION: A polishing pad includes a polyurethane sheet having a polishing surface that has a plurality of tear-shaped air bubbles and polishes an object to be polished, wherein a polyurethane resin constituting the polyurethane sheet satisfies the following condition. (1) When an unfoamed polyurethane sheet, obtained by drying a polyurethane resin solution prepared by dissolving the polyurethane resin in a solvent, is subjected to a measurement of a loss tangent tanδ in a temperature range of 20-60°C at an initial load of 10 g, a strain range of 0.1%, and a measurement frequency of 1 Hz in a compression mode and when the temperature and the loss tangent are plotted as abscissa and ordinate, respectively, a determination coefficient R2 of a linear approximate curve in a range of 20-60°C determined by a least square method is 0.9 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polishing pad, and more particularly to a polishing pad for CMP of semiconductor devices. [Background technology]

[0002] To accurately form multilayer wiring, the surface of materials such as semiconductor wafers must be flat. Chemical mechanical polishing (CMP), a free-abrasive polishing method using a polishing pad, is typically used to flatten each layer. CMP uses a polishing solution (slurry) containing abrasive particles such as silica, anticorrosive agents, surfactants, etc. to modify the surface of the workpiece while enhancing the mechanical polishing effect of the abrasive particles. In CMP, the polishing solution containing abrasive particles penetrates between the workpiece and the polishing pad, allowing the polishing pad to rotate at high speed and polish the workpiece stably.

[0003] Polishing pads for semiconductor device manufacturing require perforations on the surface to hold the polishing slurry, hardness to maintain the flatness of the workpiece, and viscoelasticity to prevent scratches on the workpiece. To meet these requirements, polishing pads with polishing surfaces made from urethane resin foam are used.

[0004] Polyurethane resin foam is usually formed by curing a prepolymer containing a urethane bond-containing polyisocyanate compound with a curing agent (dry molding method).Then, this foam is sliced ​​into sheets to form a polishing pad.In the polishing pad with a hard polishing layer produced by this dry molding method (hereinafter sometimes abbreviated as hard polishing pad), approximately spherical bubbles are formed by water foaming, hollow bead addition, mechanical foaming, chemical foaming, etc., so that the polishing surface of the polishing pad formed by slicing has openings (openings) that can hold slurry during polishing. The use of hard polishing pads can improve the flatness and polishing rate of substrates. However, due to their hardness, there is a risk of defects such as scratches occurring. In addition, with the recent trend toward finer wiring widths, more precise polishing is required, and situations where hard polishing pads are difficult to meet are becoming more common. For this reason, polishing pads with soft polishing layers manufactured by wet film deposition methods (hereinafter sometimes referred to as soft polishing pads) are being used, particularly in the finishing process. As a soft polishing pad used for the finish polishing in the CMP process, Patent Document 1 discloses a soft suede pad that is less likely to cause micro defects. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-149259 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when polishing a substrate such as a wafer having metal wiring such as copper formed on the surface, even if a conventional soft polishing pad is used, the hardness of the metal wiring is relatively small compared to the insulating material, and the metal wiring is polished more than the insulating material, so dishing or erosion may occur, and a higher polishing selectivity of the insulating material (e.g., TEOS) to the metal wiring (e.g., copper) is desired. In addition, when polishing a polished object with a conventional polishing pad, the polishing rate changes over time and may lack stability.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a polishing pad which has high selectivity for polishing insulating materials relative to metal wiring and excellent stability of the polishing rate. [Means for solving the problem]

[0008] The present invention includes the following aspects. [1] A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and a polishing surface for polishing an object to be polished, wherein the polyurethane resin constituting the polyurethane sheet satisfies the following conditions: (1) For an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent, the loss tangent tanδ was measured in the temperature range of 0°C to 100°C at a temperature rise rate of 5°C / min under an initial load of 10g, a strain range of 0.1%, a measurement frequency of 1Hz, and a compression mode. When the loss tangent tanδ was plotted with the temperature on the horizontal axis and the loss tangent on the vertical axis, the coefficient of determination R of the linear approximation curve in the range of 20 to 60°C obtained by the least squares method was 2 is 0.9 or more [2] The polishing pad according to [1], wherein the polyurethane resin constituting the polyurethane sheet further satisfies the following conditions: (2) When the loss tangent tanδ of an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent is measured in a compression mode with an initial load of 10 g, a strain range of 0.1%, a measurement frequency of 1 Hz, and a temperature rise rate of 5°C / min in a temperature range of 0°C to 100°C, and the loss modulus E″ is plotted as the horizontal axis and the loss modulus E″ as the vertical axis, the loss modulus E″ in a temperature range of 20°C to 60°C is 2.5 MPa or more. [3] The polishing pad according to [1] or [2], wherein the polyurethane resin is separated into three components, namely, an amorphous phase, an interfacial phase, and a crystalline phase, in order of the length of the spin-spin relaxation time T2, by subtracting the free induction decay signal (FID) obtained by pulse NMR in order of the length of the spin-spin relaxation time T2 by the least squares method, and the abundance ratio of the interfacial phase component at 20°C is less than 10%. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a polishing pad that has high polishing selectivity for insulating materials relative to metal wiring and excellent stability of the polishing rate. [Brief explanation of the drawings]

[0010] [Figure 1] The polyurethane resins used in the manufacture of the polishing pads of the Examples and Comparative Examples were measured by dynamic viscoelasticity measurement, and the results are plotted with temperature on the horizontal axis and loss tangent (tan δ) on the vertical axis. [Figure 2] The polyurethane resins used in the manufacture of the polishing pads of the Examples and Comparative Examples were measured by dynamic viscoelasticity measurement, and the results are plotted with temperature on the horizontal axis and loss modulus (E'') on the vertical axis. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. <Polishing pad> The polishing pad of the present invention is a polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and a polishing surface for polishing an object to be polished, wherein the polyurethane resin constituting the polyurethane sheet satisfies the following conditions: (1) For an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent, the loss tangent tanδ is measured in a temperature range of 0°C to 100°C under an initial load of 10g, a strain range of 0.1%, a measurement frequency of 1Hz, and a compression mode. When the loss tangent tanδ is plotted with the temperature on the horizontal axis and the loss tangent on the vertical axis, the coefficient of determination R of a linear approximation curve in the range of 20 to 60°C obtained by the least squares method is 2 is 0.9 or more

[0012] (Polyurethane sheet) The polyurethane sheet included in the polishing pad of the present invention has multiple teardrop-shaped bubbles. The term "teardrop-shaped bubbles" refers to bubbles formed within the polyurethane sheet by a wet film-forming method (anisotropic bubbles with a diameter increasing from the top of the resin sheet (the side in contact with the substrate)) and is distinct from the roughly spherical bubbles found in polishing pads formed by dry molding. Therefore, the polyurethane sheet can be rephrased as a polyurethane sheet formed by a wet film-forming method. The wet film-forming method involves dissolving the resin to be used for film formation in an organic solvent, applying the resin solution to a sheet-like substrate, and then passing the solution through a coagulation liquid that dissolves the organic solvent but not the resin, replacing the organic solvent with the coagulation liquid. The polyurethane sheet is then solidified and dried to form a foamed layer. Typically, when a polyurethane sheet is produced by a wet film-forming method, the escape route for the organic solvent inside the polyurethane sheet to escape into the coagulation liquid becomes hollow, resulting in the formation of multiple roughly teardrop-shaped macrobubbles (teardrop-shaped bubbles). In the present invention, a polyurethane sheet refers to a sheet whose main component is polyurethane resin (50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more), and is clearly distinguished from sheets whose main component is another resin (such as silicone resin).

[0013] (Polyurethane resin) The polyurethane resin constituting the polyurethane sheet contained in the polishing pad of the present invention is an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution in which the polyurethane resin is dissolved in a solvent. When the loss tangent tanδ is measured in a temperature range of 0°C to 100°C at a temperature rise rate of 5°C / min under an initial load of 10g, a strain range of 0.1%, a measurement frequency of 1Hz, and a compression mode, and the temperature is plotted on the horizontal axis and the loss tangent on the vertical axis, the coefficient of determination R of the linear approximation curve in the range of 20 to 60°C obtained by the least squares method is 2 The loss tangent tanδ is 0.9 or more. The definition and measurement method of the loss tangent tanδ will be described later. The coefficient of determination R 2When tan δ is 0.9 or higher, the rate of change of tan δ with temperature is approximately constant, resulting in an excellent balance between the elasticity and viscosity of the polyurethane resin. The applicant discovered that by using a polyurethane resin with an excellent balance of elasticity and viscosity, a polishing pad can be obtained that exhibits high selectivity for polishing insulating materials relative to metal wiring and excellent polishing rate stability. While the mechanism behind this is unclear, it is thought to be as follows: The viscoelasticity of a material can be considered as a combination of the storage modulus (E'), which reflects elasticity, and the loss modulus (E''), which reflects viscosity. tan δ = loss modulus (E'') / storage modulus (E') is a parameter that reflects the balance between the two. Generally, a larger tan δ indicates a more viscous material, while a smaller tan δ indicates a more elastic material. Conventional polyurethane resin polishing layers tend to exhibit a nonlinear (e.g., exponential) decrease in tan δ as the temperature rises from 0°C to 60°C, and this change tends to be rapid. However, the inventors of the present invention found that the value of tan δ of the polishing layer at room temperature (near 20°C) was larger than that of conventional polishing pads, and that the change in tan δ of the polishing layer with temperature was small within the polishing temperature range of 20°C to 60°C, making it highly viscous and less likely to damage the workpiece even at relatively low temperatures around 20°C, while not becoming too viscous even at relatively high temperatures around 60°C, allowing the initial polishing rate to be maintained and contributing to the stability of the polishing rate. Generally, when the value of tan δ of the polishing layer is high, it is expected that the contribution of elasticity will be small and the polishing rate will be low. However, in the present invention, because the value of tan δ is less likely to change with temperature, when evaluated throughout the entire polishing process from start to finish, the unexpected result of fewer defects and a higher polishing rate for insulating material relative to metal wiring was obtained.

[0014] The coefficient of determination is preferably 0.92 or more, more preferably 0.94 or more, and even more preferably 0.96 or more. 2 The upper limit of is not particularly limited, but may be less than 1.00 or less than 0.99.

[0015] In the present invention, the storage modulus (E') and loss modulus (E'') are the storage modulus and loss modulus, respectively, measured in accordance with JIS K7244-4 at a predetermined temperature, under an initial load of 10 g, a strain range of 0.1%, a measurement frequency of 1 Hz, and in a compression mode. In the present invention, the loss tangent (tan δ) is the ratio of the loss modulus to the storage modulus, and is defined as follows: tanδ=E'' / E' Tan δ is an index of viscoelasticity under certain temperature conditions. Storage modulus is a measure of the energy stored and fully recovered per cycle when a sinusoidally varying stress is applied. On the other hand, loss modulus refers to the magnitude of the stress component that is π / 2 out of phase with the strain when a sinusoidal strain of a characteristic frequency is applied. E' and E'' can be measured by dynamic viscoelastic testing (DMA). The unfoamed polyurethane sheet used in measuring tan δ is preferably one obtained by forming a polyurethane resin solution dissolved in a solvent into an (unfoamed) sheet without immersing it in a coagulation bath, and then drying it. The concentration of the polyurethane resin solution is not particularly limited and may be 10 to 30 mass %. The drying conditions are also not particularly limited and may be, for example, a temperature range of 80 to 150°C for 5 to 120 minutes. Examples of solvents for dissolving polyurethane resins include dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), etc. Among these, DMF is preferred.

[0016] The linear approximation can be obtained by linear approximation (least squares method) using the spreadsheet software "Microsoft (registered trademark) Excel (registered trademark)."

[0017] (Pulsed NMR) Pulse NMR can be measured at 20°C using a pulse NMR measurement device (JNM-MU25, 25 MHz, manufactured by JEOL Ltd.) by the solid echo method. The solid echo method is already well known, so we will not go into detail here; however, it is primarily used to measure samples with short relaxation times, such as glassy and crystalline polymers. A method that seemingly eliminates dead time is the 90°x-τ-90°y pulse method, in which two 90° pulses are applied with a 90° phase difference. When a 90° pulse is applied in the x-axis direction, a free induction decay (FID) signal is observed after the dead time. If a second 90° pulse is applied in the y-axis direction at time τ, when the FID signal does not decay, the magnetization orientation aligns and an echo appears at time t = 2τ. The resulting echo can be approximated to the FID signal after a 90° pulse. Methods for analyzing the relationship between physical properties, phase-separated structure, and composition from the results of pulsed NMR analysis are already well known. The free induction decay (FID) signal obtained by pulsed NMR can be separated into three components by subtracting the component with the longest spin-spin relaxation time T2 using the least-squares method and waveform separation. The component with the longest relaxation time is defined as the amorphous phase, with high mobility; the component with the shortest relaxation time is defined as the crystalline phase, with low mobility; and the intermediate component is defined as the interfacial phase (if it is difficult to separate the interfacial phase and the amorphous phase, it is analyzed as the interfacial phase). The amount of each component can be calculated using a formula using Gaussian and Lorentzian functions (see, for example, "Analysis of the Phase-Separated Structure of Polyurethane Resin by Solid-State NMR (High-Resolution NMR and Pulsed NMR)" (DIC Technical Review No. 12, pp. 7-12, 2006)).

[0018] The pulsed NMR measurement is described in detail below. First, a 1-cm-diameter glass tube is filled with a sample approximately 1–3 mm square, packed to a height of 1–2 cm, and placed in a magnetic field. After a high-frequency pulsed magnetic field is applied, the relaxation behavior of the macroscopic magnetization is measured, yielding a free induction decay (FID) signal (horizontal axis: time (μsec), vertical axis: free induction decay signal). The initial value of the FID signal is proportional to the number of protons in the sample. If the sample contains three components, the FID signal appears as the sum of the response signals of the three components. However, because the components in the sample have different mobilities, the decay rates of the response signals differ between the components, resulting in different spin-spin relaxation times, T2. Therefore, the sample can be separated into three components using the least-squares method. The components with the longest spin-spin relaxation times, T2, are the amorphous phase, the interface phase, and the crystalline phase, respectively. The amorphous phase is a component with high molecular mobility, the crystalline phase is a component with low molecular mobility, and the intermediate component is the interface phase. For the above-mentioned pulse NMR, solid echo method, and spin-spin relaxation time T2, reference can be made to Japanese Patent Application Laid-Open No. 2007-238783 (particularly paragraphs

[0028] to

[0033] ).

[0019] To achieve a coefficient of determination of 0.9 or greater, for example, by subtracting the free induction decay signal (FID) obtained by pulsed NMR from the component with the longest spin-spin relaxation time T2 by the least squares method and performing waveform separation to separate the signal into three components: amorphous phase, interfacial phase, and crystalline phase, in descending order of spin-spin relaxation time T2, it is preferable to use a polyurethane resin in which the abundance ratio of the interfacial phase component at 20°C is less than 10%. Polyurethane resins typically exhibit increased molecular mobility with increasing temperature, resulting in the transition of the interfacial phase component to the amorphous phase component, which tends to increase the rate of change of tan δ with temperature. On the other hand, by using a polyurethane resin with a low interfacial phase component, the rate of change of the amorphous and crystalline phases is small even with increasing temperature, thereby maintaining a substantially constant rate of change of tan δ with temperature, thereby achieving a coefficient of determination of 0.9 or greater.

[0020] The interphase is the interface between the hard and soft segments. A low interphase fraction indicates a clear interface between the hard and soft segments and low compatibility between the hard and soft segments. There are no particular limitations on the means for reducing the abundance ratio of interphase components in a polyurethane resin at 20°C to less than 10%, and examples include increasing the difference in polarity between the hard and soft segments of the polyurethane resin to facilitate separation. To increase the difference in polarity between the hard and soft segments, the materials, blending ratios, molecular weights, etc. of the polyol component, polyisocyanate component, and chain extender used can be appropriately adjusted. Specifically, for example, when a polyester polyol obtained by dehydration condensation of a diol and a dibasic acid is used as the polyol component, the longer the diol chain (the greater the number of carbon atoms between hydroxyl groups), the lower the polarity, and the more easily the polyisocyanate component separates from the highly polar hard segment. Furthermore, the higher the blending ratio of the polyisocyanate component (especially MDI), the higher the polarity of the hard segment, facilitating separation from the soft segment. Furthermore, by using a diol with a small number of carbon atoms as a chain extender, the polarity of the hard segment increases, making it easier to separate from the soft segment. The polyurethane resins may be used alone or in combination of two or more, but it is preferable to use one type alone.

[0021] Furthermore, the polyurethane resin preferably has a loss modulus E'' of 2.5 MPa or more in a temperature range of 20 to 60°C when an unfoamed polyurethane sheet is obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent, under an initial load of 10 g, a strain range of 0.1%, a measurement frequency of 1 Hz, and compression mode. If the loss modulus is 2.5 MPa or more, the polyurethane resin has high viscosity and excellent adhesion, reducing convex defects and suppressing the occurrence of defects in the object to be polished. The loss modulus of the polyurethane resin in a temperature range of 20 to 60°C is preferably 2.6 MPa or more, more preferably 2.7 MPa or more, and even more preferably 2.8 MPa or more. In the present invention, defects refer to convex and concave defects found on the polished object after polishing. Convex defects include organic residues, particles, pad debris, watermarks, etc. Concave defects include scratches, voids, etc.

[0022] The polyol component is not particularly limited, and various polyol components can be used, such as polyether diol, polyester diol, polycarbonate diol, etc., with polyester diol being preferred. One type of polyol component may be used alone, or two or more types may be used in combination.

[0023] The polyether diol is not particularly limited, and various polyether diols can be used. Preferred examples of polyether polyols include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol). One type of polyether polyol may be used alone, or two or more types may be used in combination.

[0024] The polyester diol is not particularly limited, and various polyester diols can be used. Examples of preferred polyester diols include polyester diols obtained by directly esterifying or transesterifying a dicarboxylic acid or an ester-forming derivative thereof, such as an ester or anhydride, with a low-molecular-weight diol. Examples of the dicarboxylic acid include aliphatic carboxylic acids having 4 to 12 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, and 3,7-dimethyldecanedioic acid; and aromatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, and orthophthalic acid. Examples of the low molecular weight diol include aliphatic diols such as ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; and alicyclic diols such as cyclohexanedimethanol and cyclohexanediol. The carbon number of the low molecular weight diol is preferably 2 to 12. One type of polyester diol may be used alone, or two or more types may be used in combination.

[0025] When a polyester diol is used as a polyol component, it is preferable to reduce the content of low-molecular-weight diol contained in the polyester diol from the viewpoint of reducing interfacial phase components in the polyurethane resin. During the polymerization of an ester-forming derivative such as a dicarboxylic acid with a low-molecular-weight diol, a significant amount of low-molecular-weight diol is contained as a by-product of an equilibrium reaction. Because this low-molecular-weight diol behaves as a hard segment in the polyurethane resin, the hard segment is dispersed among the soft segment. As a result, the interface (interfacial phase components) between the hard segment and the soft segment increases. From the viewpoint of reducing interfacial phase components in the polyurethane resin, the number average molecular weight of the polyol component is preferably in the range of 700 to 10,000, more preferably in the range of 800 to 7,500, and even more preferably in the range of 1,000 to 5,000. When the number average molecular weight is within the above range, clear separation of the hard segment and the soft segment is likely to occur, and the interfacial phase components are likely to be reduced.

[0026] (Polyisocyanate component) The polyisocyanate component is not particularly limited, and various polyisocyanate components can be used. Examples of the polyisocyanate component include aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate (MDI), phenylene diisocyanate, and xylylene diisocyanate; aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate; and prepolymers obtained by reacting a polyisocyanate component with a polyol component in advance to obtain a high molecular weight. Among these, aromatic diisocyanates are preferred, and 4,4'-diphenylmethane diisocyanate is more preferred.

[0027] From the viewpoint of reducing the interfacial phase components of polyurethane resins, the polyisocyanate component is preferably 4,4'-diphenylmethane diisocyanate with a reduced oligomer content. 4,4'-Diphenylmethane diisocyanate (MDI) is commercially available and easily available, but it is highly reactive and begins to gradually produce oligomers by self-polymerization immediately after production, so commercially available products generally contain a certain amount of oligomers. If MDI containing oligomers is used as a raw material in the production of polyurethane resins, the aggregation of hard segments is inhibited, making it difficult to reduce the interfacial phase components. The oligomer content in MDI is not particularly limited, but it is preferably, for example, 0.5% by mass or less. The method for reducing the content of oligomers in MDI is not particularly limited, and known purification methods can be used. Examples include distillation, recrystallization, reprecipitation, and filtration, with filtration being preferred from the viewpoint of efficiency.

[0028] (Chain extender) The chain extender is not particularly limited, and various chain extenders can be used. Examples of the chain extender include propylene glycol, 1-ethyl-1,2-ethanediol, 1,2-dimethyl-1,2-ethanediol, 1-methyl-2-ethyl-1,2-ethanediol, 1-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-dimethyl-1,2-propanediol, 1,3-dimethyl-1,3-propanediol, 2,2-dimethyl-1, 3-Propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 1-methyl-1,4-butanediol, 2-methyl-1,4-butanediol, 2,3-dimethyl-1,4-butanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,5-pentanediol, 3-ethyl-1,5-pentanediol Examples of suitable chain extenders include aliphatic polyol compounds such as pentanediol, 2,4-dimethyl-1,5-pentanediol, 3-methyl-1,6-hexanediol, 2-methyl-1,8-octanediol, 2,7-dimethyl-1,8-octanediol, 2-methyl-1,9-nonanediol, 2,8-dimethyl-1,9-nonanediol, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, sucrose, methylene glycol, glycerin, and sorbitol; aromatic polyol compounds such as bisphenol A, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, hydrogenated bisphenol A, and hydroquinone; and water. These chain extenders may be used alone or in combination of two or more. From the viewpoint of reducing interfacial phase components in the polyurethane resin, the chain extender preferably contains 50 to 100% by weight of a linear, short-chain chain extender having a number average molecular weight of 250 or less. The chain extender is preferably a low-molecular-weight diol having 2 to 6 carbon atoms, more preferably ethylene glycol or 1,4-butanediol. These chain extenders can increase the cohesive force of the hard segments, which tends to reduce interfacial phase components.

[0029] (Other ingredients) The polyurethane resin may or may not contain, in addition to the above components, inorganic fillers such as carbon black, film-forming stabilizers, surfactants, etc., as long as the effects of the present invention are not impaired. While inorganic fillers such as carbon black improve the polishing rate, they also cause polishing defects, so it is preferable that the polyurethane sheet contains a small amount of inorganic filler, more preferably 5% by mass or less (preferably 3% by mass or less, more preferably 1% by mass or less), and even more preferably no inorganic filler is contained. Furthermore, it is preferable that the polyurethane sheet contains a small amount of carbon black, and it is more preferable that the amount of carbon black is 5% by mass or less (preferably 3% by mass or less, and more preferably 1% by mass or less), and it is even more preferable that the polyurethane sheet does not contain any carbon black.

[0030] The polyurethane sheet in the polishing pad of the present invention has a polishing surface for polishing an object to be polished. In the polishing pad of the present invention, the polishing surface and / or the surface opposite to the polishing surface of the polyurethane sheet may be ground (buffed) or not, but it is preferable that the polishing surface of the polyurethane sheet be ground, which results in the presence of many openings originating from microbubbles on the polishing surface, and the openings can hold the slurry, thereby improving the polishing rate. The polishing pad of the present invention may have grooves, embossing, and / or holes (punching) on ​​the polishing surface of the polyurethane sheet. The polishing pad of the present invention may have a light-transmitting portion. The polishing pad of the present invention may have a single-layer structure consisting of only a polyurethane sheet, or may have a multi-layer structure in which a substrate is attached to the surface of the polyurethane sheet opposite the polishing surface. Examples of the substrate include substrates made of nonwoven fabric, PET, and vinyl chloride. While there are no particular limitations on the properties of the substrate, it is preferable that the substrate is harder than the polyurethane sheet (for example, has a higher A hardness or D hardness). By providing a layer harder than the polyurethane sheet, the polishing pad made from the polyurethane sheet can be prevented from expanding, contracting, or bending when polishing an object to be polished.

[0031] The polishing pad of the present invention is used for polishing optical materials, semiconductor devices, glass substrates for hard disks, etc., and is particularly suitable for chemical mechanical polishing (CMP) of devices in which an oxide layer or barrier metal layer and a metal layer such as copper are formed on a semiconductor wafer. The polishing pad of the present invention can be obtained, for example, by the following production method.

[0032] <Polishing Pad Manufacturing Method> The polishing pad of the present invention can be manufactured by a method for manufacturing a polishing pad, which includes, for example, a step of preparing a resin solution containing a polyurethane resin, a step of applying the resin solution to a film-forming substrate, and a step of immersing the film-forming substrate to which the solution has been applied in a coagulation liquid to coagulate the solution. Each step will be described below.

[0033] (Step of preparing a resin solution) In this step, a polyurethane resin is dissolved in a water-miscible organic solvent to prepare a resin solution containing the polyurethane resin. As the polyurethane resin, those mentioned above can be used. Examples of the organic solvent include N,N-dimethylformamide (DMF), methyl ethyl ketone, N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetone, and 1,3-dimethyl-2-imidazolidinone (DMI). One or more of the organic solvents may be used. Among these, DMF or DMAc is preferred. The solid content of the resin solution is not particularly limited, but is preferably 15 to 50 mass %, more preferably 15 to 40 mass %, and even more preferably 20 to 35 mass %. When the solid content is within the above range, the resin solution has appropriate fluidity, making it easy to apply the resin solution uniformly to the film-forming substrate. The resin solution may contain components other than the above components as long as the effects of the present invention are not impaired.

[0034] (Process for applying a resin solution to a film-forming substrate) The resin solution obtained above is continuously applied to the film-forming substrate so as to be approximately uniform using a coating machine such as a knife coater, a reverse coater, etc. At this time, the thickness of the coating film can be adjusted by adjusting the gap (clearance) between the film-forming substrate and the die or knife of the coating machine. The film-forming substrate can be any substrate commonly used in this technical field without any particular limitation, and examples thereof include flexible polymer films such as polyester films and polyolefin films, nonwoven fabrics impregnated with elastic resins, etc. Among these, polyester films are preferably used.

[0035] (Process for solidifying the resin solution) The substrate coated with the resin solution is immersed in a coagulation liquid (coagulation bath) whose main component is water, which is a poor solvent for polyurethane resin, to coagulate and regenerate the polyurethane resin. The coagulation liquid may be water or a mixed solvent of water and a polar organic solvent such as DMF. Examples of the polar organic solvent include the water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, acetone, and DMI. The concentration of the polar organic solvent in the mixed solvent is preferably 0 to 20% by mass, more preferably 1 to 20% by mass, and even more preferably 5 to 15% by mass. The coagulation liquid is preferably water or a mixed solvent of water and DMF, and more preferably a mixed solvent of water and DMF. There are no particular limitations on the temperature of the coagulation liquid or the immersion time, and it is preferable that the temperature be 10 to 60°C, preferably 15 to 50°C, for example, and that the time be 5 to 120 minutes. In the coagulation liquid, a dense skin layer is first formed at the interface between the applied resin solution and the coagulation liquid. Then, solvent substitution between the organic solvent in the resin solution and the coagulation liquid proceeds through the skin layer, and the polyurethane resin is coagulated and regenerated in a sheet form on the film-forming substrate, resulting in a resin sheet with a film-forming substrate having multiple teardrop-shaped bubbles formed therein.

[0036] Thereafter, the coagulated and regenerated polyurethane sheet is peeled off from the resin sheet, or is washed and dried without being peeled off. The washing treatment removes the organic solvent remaining in the polyurethane sheet. The washing liquid used for washing includes water. After washing, the polyurethane sheet is dried by a conventional method, for example, by drying in a dryer at 80 to 150°C for about 5 to 60 minutes.

[0037] If necessary, the polished surface and / or the surface opposite to the polished surface of the polyurethane sheet may be ground (buffed). The polished surface of the polyurethane sheet may be grooved, embossed, and / or perforated (punched), and a substrate may be attached to the surface opposite to the polished surface. There are no particular limitations on the grinding method, and known methods such as grinding using sandpaper, grinding using a buffing machine or a slicing machine can be used. Among these, using a buffing machine or a slicing machine is preferred because it allows for obtaining a polyurethane sheet with a substantially uniform thickness. There are no particular limitations on the shape of the grooves and embossing, and examples thereof include lattice, concentric circle, and radial shapes. When a substrate is attached to a polyurethane sheet to form a multilayer structure, the multiple layers can be bonded and fixed together using double-sided tape, adhesive, etc., while applying pressure as necessary. There are no particular restrictions on the double-sided tape or adhesive used in this case, and any double-sided tape or adhesive known in the art can be selected and used. [Example]

[0038] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0039] (polishing pad manufacturing) Example 1 A polyurethane resin-containing solution was obtained by adding 55 parts by weight of DMF and 2 parts by weight of a nonionic surfactant consisting of a polyether resin / silicone resin mixture (7 / 3 by weight, product name: CRISBON ASISTOR SD-7, manufactured by DIC Corporation) to 100 parts by weight of a DMF solution containing a 30% solids concentration of polyester-based polyurethane resin with a 100% modulus of 7.2 MPa. The mixture was then stirred to obtain a polyester-based polyurethane resin. The polyester-based polyurethane resin was obtained by condensing a polyester polyol obtained by dehydration condensation of ethylene glycol, propylene glycol, and adipic acid, followed by vacuum distillation at 120°C to 140°C for several hours to adjust the content of low-molecular-weight diol components of 160 or less to 1.3 mol%, with a chain extender of 1,4-butanediol / trimethylolpropane in a molar ratio of 97 / 3, and 4,4'-diphenylmethane diisocyanate (MDI). Next, a PET film was prepared as a substrate for film formation. The resin-containing solution was applied to the film using a knife coater, and the film was immersed in a coagulation bath containing DMF and water in a 95:5 mass ratio at 18°C ​​for 60 minutes to coagulate the resin-containing solution. The film was then washed and dried to obtain a resin film. The skin layer formed on the surface of the resulting resin film was subjected to a 12 μm buffing treatment to obtain a 0.80 mm thick polyurethane sheet. Double-sided tape was then attached to the back of the buffed surface, and the buffed surface was embossed with a grid-shaped mold to obtain a polishing pad.

[0040] Comparative Example 1 A polyurethane resin-containing solution was obtained by adding 55 parts by weight of DMF and 2 parts by weight of a nonionic surfactant consisting of a polyether resin / silicone resin mixture (7 / 3 by weight, product name: CRISBON ASISTOR SD-7, manufactured by DIC Corporation) to 100 parts by weight of a DMF solution containing a 30% solids concentration of polyester-based polyurethane resin with a 100% modulus of 5.4 MPa. The polyester-based polyurethane resin was obtained by condensing a polyester polyol (used without distillation, containing 12.9 mol% low-molecular-weight diol components with a molecular weight of 160 or less) obtained by dehydration condensation of 1,4-butanediol and adipic acid with a chain extender of 1,4-butanediol / trimethylolpropane in a 60 / 40 molar ratio with 4,4'-diphenylmethane diisocyanate (MDI). Next, a PET film was prepared as a substrate for film formation. The resin-containing solution was applied to the film using a knife coater, and the film was immersed in a coagulation bath of water at 18°C ​​for 60 minutes to coagulate the resin-containing solution. The film was then washed and dried to obtain a resin film. The skin layer formed on the surface of the resulting resin film was subjected to a 10 μm buffing treatment to obtain a 0.98 mm thick polyurethane sheet. Double-sided tape was then attached to the back of the buffed surface, and the buffed surface was embossed with a grid-shaped mold to obtain a polishing pad.

[0041] (Pulse NMR measurement) The resulting polishing pad was subjected to pulse NMR measurement under the following conditions. Specifically, sample pieces of approximately 1 to 3 mm square were cut out from the land portion of the ground polishing pad with a cutter, filled into a 10 mm diameter sample tube to a height of 1 to 2 cm, and pulse NMR measurement was performed to obtain an attenuation curve. To ensure that the obtained attenuation curve and the fitting curve matched, analysis was performed by the least squares method using a Lorentz function (linear portion) and a Gaussian function (curved portion), and the proportions (abundance ratios (mass%)) of the amorphous phase, interface phase, and crystalline phase in the polishing layer were determined. The fitting and analysis were performed using the software attached to the measurement device described below. [Measurement conditions] Equipment: JNM-MU25 manufactured by JEOL Ltd. Measurement magnetic field strength: 0.58T Observation frequency: 25MHz Observed nucleus: 1H Measurement: Spin-spin relaxation (T2) Measurement method: Solid Echo method Pulse width: 2.2 μs Pulse interval: 13.0 μs Pulse repetition time: 4.0 seconds Accumulation count: 16 times Measurement temperature: 20℃

[0042] (Dynamic viscoelasticity measurement) Dynamic viscoelasticity measurements of the polyurethane resin used in the manufacture of polishing pads were carried out under the following conditions. The measurement sample was prepared by dissolving the polyurethane resin in the solvent DMF to a concentration of 25% by mass, coating the resulting solution, and drying with hot air (80°C, 120 minutes) to prepare a polyurethane film approximately 0.1 mm thick. This was then cut into a piece measuring 5 mm long and 20 mm wide. The loss tangent (tanδ) was measured in the temperature range of 0°C to 100°C by dynamic viscoelasticity measurements, and the temperature was plotted on the horizontal axis and the loss tangent on the vertical axis. A linear approximation curve was obtained in the range of 20 to 60°C by the least squares method, and the coefficient of determination (R 2 ) was calculated by linear approximation (least squares method) using the spreadsheet software "Microsoft® Excel®." The minimum value of the loss modulus (E'') was also measured in the temperature range of 20 to 60°C. The loss tangent data was obtained by plotting 104 points in the temperature range of 0 to 100°C. [Measurement conditions] Device: RSA3 (TA Instruments) Test piece size: 5mm x 20mm x 0.1mm Frequency: 1Hz Distortion range: 0.1% Initial load: 10g Test mode: Compression Temperature range: 0~100℃ Heating rate: 5°C / min

[0043] (Polishing test) Using the obtained polishing pad, 51 silicon wafers with a TEOS (tetraethoxysilane) film, 51 wafers with a BDII (Black Diamond II (registered trademark): silicon oxide carbide (SiOC), a low-k material manufactured by Applied Materials, Inc.) film, and 51 silicon wafers with a Cu film were polished under the following conditions, and the polishing rate, polishing selectivity, polishing rate stability, and defects were evaluated.

[0044] [Polishing conditions] Polishing machine used: Ebara Corporation, product name "F-REX300X" Grinding pressure: 2.5psi Abrasive: CuBM slurry Abrasive temperature: room temperature Dresser: 3M diamond dresser, model number "A188" Polished object: 300mmφ TEOS coated silicon wafer, BDII coated wafer and Cu coated wafer Pad break: 9N x 30 min, diamond dresser 54 rpm, surface plate rotation speed 80 rpm, ultrapure water 200 mL / min Polishing: Platen rotation speed 70 rpm, head rotation speed 71 rpm, slurry flow rate 200 mL / min, polishing time 60 seconds

[0045] (removal rate and removal selectivity) For each wafer with TEOS film, BDII film, and Cu film, the thickness was measured at 121 points before and after polishing, and the average value was calculated. The thickness measured at each point was then divided by the polishing time to calculate the polishing rate (Å / min). The thickness measurements were performed using an optical film thickness and quality analyzer (KLA-Tencor Corporation, product name "ASET-F5x", measurement: DBS mode). Of the 51 film-coated wafers polished, the 1st, 5th, 10th, 15th, 20th, 25th, 35th, 50th, and 51st wafers were selected, and the polishing rates for each were determined to calculate the average polishing rate.The average TEOS polishing rate relative to the average Cu polishing rate (TEOS / Cu) and the average BDII polishing rate relative to the average Cu polishing rate (BDII / Cu) were calculated to compare polishing selectivity.The larger the TEOS / Cu and BDII / Cu values, the higher the polishing selectivity of TEOS or BDII (insulator) relative to Cu (metal wiring).

[0046] (Stability of polishing rate) The average value and standard deviation of each polishing rate calculated above were determined, and the polishing rate non-uniformity was calculated using the following formula: The lower the polishing rate non-uniformity value, the higher the stability of the polishing rate was evaluated. Polishing rate non-uniformity (%) = (standard deviation of polishing rate / average polishing rate) x 100

[0047] (Defect rating) After polishing, defects were detected and counted on the Cu surface of nine Cu-filmed wafers using a surface inspection device (KLA-Tencor Corporation, Surfscan SP5, detection limit 130 nm), and the average value was calculated. The defects evaluated here are the total of defects such as particles, organic matter thought to be derived from pad debris, organic residue, scratches, voids derived from the film, watermarks, etc. The results are shown in Table 1 and Figures 1 and 2.

[0048] [Table 1]

[0049] As can be seen from Table 1, by using a polyurethane resin with a small interphase component, when the temperature is plotted on the horizontal axis and the loss tangent on the vertical axis, the coefficient of determination R of the linear approximation curve obtained by the least squares method in the range of 20 to 60°C is 2The polishing rate of copper is 0.9 or more, and when a wafer is polished with the polishing pad thus obtained, the polishing rate of copper can be suppressed compared to that of TEOS or silicon oxide carbide (SiOC) (i.e., the polishing selectivity of insulating material relative to metal wiring can be increased), and the stability of the polishing rate can be improved. Furthermore, the polishing pad of the present invention can also suppress the occurrence of defects because the polyurethane resin used has a loss modulus E" of 2.5 MPa or more in the temperature range of 20°C to 60°C. [Industrial Applicability]

[0050] The polishing pad of the present invention has high selectivity for polishing insulating materials relative to metal wiring and excellent stability of polishing rate, and therefore has industrial applicability.

Claims

1. A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished, wherein the polyurethane resin constituting the polyurethane sheet satisfies the following conditions: (1) For an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent, the loss tangent tanδ was measured in a temperature range of 0°C to 100°C at a temperature rise rate of 5°C / min under an initial load of 10g, a strain range of 0.1%, a measurement frequency of 1Hz, and a compression mode. When the loss tangent tanδ was plotted with the temperature on the horizontal axis and the loss tangent on the vertical axis, the coefficient of determination R of a linear approximation curve in the range of 20 to 60°C obtained by the least squares method was 2 is equal to or greater than 0.96 and less than 0.99; (2) When the loss tangent tanδ of an unfoamed polyurethane sheet obtained by drying a polyurethane resin solution obtained by dissolving the polyurethane resin in a solvent is measured in a compression mode under an initial load of 10 g, a strain range of 0.1%, a measurement frequency of 1 Hz, and a temperature rise rate of 5°C / min in a temperature range of 0°C to 100°C, and the plot is made with temperature as the horizontal axis and loss modulus E'' as the vertical axis, the loss modulus E'' in a temperature range of 20°C to 60°C is 2.5 MPa or more. (3) When the polyurethane resin is separated into three components, namely, an amorphous phase, an interface phase, and a crystalline phase, in order of decreasing spin-spin relaxation time T2, by subtracting the free induction decay signal (FID) obtained by pulse NMR in order of decreasing spin-spin relaxation time T2 by the least squares method and performing waveform separation, the abundance ratio of the interface phase component at 20°C is less than 10%. Meet the polishing pad.

2. 2. The polishing pad according to claim 1, wherein (2) the loss modulus E'' of the polyurethane resin constituting the polyurethane sheet is 2.8 MPa or more.

3. A polishing pad as described in claim 1 or 2, wherein the presence ratio of interfacial phase components in the polyurethane resin at 20°C is 3% or less.

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