Polishing pad and method of manufacturing the same

Abstract

To provide a polishing pad excellent in wear resistance, and a method for manufacturing the same.SOLUTION: The polishing pad includes a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet does not contain a nonionic surfactant containing a polyalkylene oxide unit and contains a water repellent.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a polishing pad used for polishing semiconductor devices, etc. The present invention particularly relates to a polishing pad having excellent wear resistance. [Background technology]

[0002] Since flatness is required for the surfaces of materials such as silicon, hard disk substrates, mother glass for thin LCD displays, semiconductor wafers, and semiconductor devices, a free abrasive method using a polishing pad is used for polishing. The free abrasive method is a method of polishing the processed surface of an object by supplying a slurry containing abrasive particles (polishing liquid, polishing slurry) between the polishing pad and the object to be polished.

[0003] Chemical mechanical polishing (CMP) is a commonly used method for planarizing the surfaces of semiconductor devices and the like. Polishing pads for semiconductor devices require pores on the surface to hold polishing slurry, hardness to maintain the flatness of the semiconductor device surface, and elasticity to prevent scratches on the semiconductor device surface. To meet these requirements, polishing pads with polishing layers made of polyurethane 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 a polishing pad with a hard polishing layer produced by this dry molding method (hereinafter sometimes abbreviated as a hard polishing pad), relatively small, approximately spherical bubbles are formed inside the foam during the curing molding of the polyurethane resin, 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 an example of a polishing pad having a soft polishing layer, Patent Document 1 describes a soft suede pad that is less likely to cause minute defects (scratches). [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, conventional soft polishing pads have insufficient wear resistance when polished by the CMP method, and suffer from wear degradation during polishing of the workpiece, resulting in a short product life. The present invention has been made in view of the above-mentioned problems, and aims to provide a polishing pad with excellent wear resistance and a method for manufacturing the same. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have found that the wear resistance of a polishing pad can be improved by using a polishing pad that does not contain a nonionic surfactant containing a polyalkylene oxide unit and that includes a polyurethane sheet containing a water repellent agent, and have arrived at the present invention. The present invention includes the following aspects. [1] A polishing pad having a polishing layer with a polyurethane sheet containing a plurality of teardrop-shaped bubbles, The polishing pad, wherein the polyurethane sheet does not contain a nonionic surfactant containing a polyalkylene oxide unit and contains a water repellent agent. [2] The polishing pad according to [1], wherein the polyurethane sheet does not contain a nonionic surfactant having an oxygen atom derived from an ether bond. [3] The polishing pad according to [1] or [2], which contains an ionic surfactant. [4] The polishing pad according to [3], wherein the ionic surfactant is an anionic surfactant. [5] The polishing pad according to [4], wherein the anionic surfactant is a sodium salt of an alkyl sulfosuccinate. [6] The polishing pad according to any one of [1] to [5], wherein the water repellent is a fluorine-based water repellent. [7] A method for producing a polishing pad according to any one of [1] to [6], comprising the steps of: preparing a solution containing a polyurethane resin and a water repellent agent, the solution not containing a nonionic surfactant containing a polyalkylene oxide unit; applying the solution to a film-forming substrate; and immersing the film-forming substrate to which the solution has been applied in a coagulation liquid to coagulate the polyurethane resin and obtain a polyurethane sheet. [Effects of the Invention]

[0008] The polishing pad of the present invention has excellent wear resistance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the zeta potential of each polishing pad of Example 1, Comparative Example 1, and Reference Example 1 at various pH values. [Figure 2] 2 is a cross-sectional SEM image taken by cutting the polishing pad in the thickness direction of Example 1. The white parts are the Si components. [Figure 3] 3 is a cross-sectional SEM image taken by cutting the polishing pad of Comparative Example 1 in the thickness direction. The white parts are the Si components. [Figure 4]4 is a cross-sectional SEM image taken by cutting the polishing pad of Reference Example 1 in the thickness direction. The white parts are the Si components. [Figure 5] FIG. 5 is a photograph of the surface of a Cu pattern wafer when the Cu pattern wafer was polished using the polishing pads of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described. <<Polishing pads>> The polishing pad of the present invention is a polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet does not contain a nonionic surfactant containing a polyalkylene oxide unit and contains a water repellent agent.

[0011] The polyurethane sheet has multiple teardrop-shaped bubbles. The term teardrop-shaped bubbles refers to bubbles formed within the polyurethane sheet by a wet film-forming method (bubbles that are anisotropic and have a diameter that increases from the top (the side in contact with the polished object) of the resin sheet to the bottom), and is used to distinguish them from roughly spherical bubbles formed by a dry molding method. Therefore, the polyurethane sheet of the present invention having multiple teardrop-shaped bubbles can be rephrased as a polyurethane sheet formed by a wet film-forming method. The wet film-forming method refers to a method in which a resin to be formed into a film is dissolved in an organic solvent, the resin-containing solution is applied to a sheet-like substrate, and the organic solvent is replaced by a coagulation liquid that dissolves the organic solvent but not the resin, followed by coagulation and drying to form a foamed layer. Typically, when a polyurethane sheet is produced by a wet film-forming method, multiple roughly teardrop-shaped macrobubbles (teardrop-shaped bubbles) are generated within the polyurethane sheet (see Figures 2 to 4). Furthermore, when a polyurethane sheet is produced by a wet film-forming method, in addition to macrobubbles, a large number of bubbles that are much finer than macrobubbles (microbubbles, minute bubbles) are usually formed (see FIGS. 2 to 4). In this specification and claims, polyurethane sheet means a sheet whose main component is polyurethane resin (50% by mass or more of the total resin constituting the polyurethane sheet, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more is polyurethane resin, and polyurethane resin may be 100% by mass), and is clearly distinguished from sheets whose main component is another resin (such as silicone resin). In this specification and claims, the term "polishing layer" refers to a layer having a surface (polishing surface) that comes into contact with an object to be polished when polishing the object, such as a semiconductor device. The polishing pad of the present invention may have another layer, such as a cushion layer, on the side opposite the polishing layer.

[0012] <Polyurethane resin> The polyurethane sheet contains a polyurethane resin. There are no particular limitations on the type of polyurethane resin, and it may be selected from various polyurethane resins depending on the intended use. For example, polyester-based, polyether-based, or polycarbonate-based polyurethane resins may be used. Examples of polyester resins include polymers of polyester polyols such as ethylene glycol or butylene glycol with adipic acid and diisocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polyether resins include polymers of polyether polyols such as polytetramethylene ether glycol and polypropylene glycol with isocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polycarbonate resins include polymers of polycarbonate polyol and isocyanates such as diphenylmethane-4,4'-diisocyanate. These resins may be commercially available resins such as those manufactured by DIC under the trade name "Crisvon," those manufactured by Sanyo Chemical Industries, Ltd. under the trade name "Sunprene," and those manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. under the trade name "Rezamin," or resins having the desired properties may be manufactured by the manufacturer.

[0013] (modulus) Modulus is an index that indicates the hardness of a resin, and is the value obtained by dividing the load applied when an unfoamed resin sheet is stretched 100% (stretched to twice its original length) by the cross-sectional area (hereinafter referred to as 100% modulus). The higher this value, the harder the resin. The polyurethane resin preferably has a 100% modulus of 1 to 10 MPa, more preferably 3 to 8 MPa. When the 100% modulus is within the above range, it is suitable for use in polishing wafers having metal wiring, since defects can be reduced.

[0014] <Nonionic surfactants> In the polishing pad of the present invention, the polyurethane sheet does not contain a nonionic surfactant containing a polyalkylene oxide unit. By not containing a nonionic surfactant containing a polyalkylene oxide unit, wear resistance can be improved. The polyalkylene oxide includes polyalkylene oxides such as polyethylene oxide and polypropylene oxide. The nonionic surfactants containing polyalkylene oxide units are (-CR 1 R 2 -CR 3 R 4 -O-) n This can be rephrased as a nonionic surfactant having the structure (R 1 ~R 4 are each independently a hydrogen atom or an organic group, and n is an integer of 2 or more. 1 ~R 4 may each independently be an alkyl group). In addition, in the polishing pad of the present invention, it is more preferable that the polyurethane sheet does not contain a nonionic surfactant containing an alkylene oxide unit. The nonionic surfactant containing an alkylene oxide unit is (-CR 1 R 2 -CR 3 R 4 -O-) nThis can be rephrased as a nonionic surfactant having the structure (R 1 ~R 4 are each independently a hydrogen atom or an organic group, and n is an integer of 1 or more. 1 ~R 4 may each independently be a hydrogen atom or an alkyl group). Nonionic surfactants containing polyalkylene oxide units have multiple oxygen atoms derived from ether bonds, and are therefore classified as nonionic surfactants having multiple oxygen atoms derived from ether bonds. In the polishing pad of the present invention, the polyurethane sheet preferably does not contain a nonionic surfactant having multiple oxygen atoms derived from ether bonds, and more preferably does not contain a nonionic surfactant having one or more oxygen atoms derived from ether bonds. Examples of nonionic surfactants containing polyalkylene oxide units include polyether-modified silicones having a polyoxyalkylene chain as the hydrophilic group and a methylpolysiloxane as the hydrophobic group. Specific examples include polyoxyethylene-methylpolysiloxane copolymers, poly(oxyethylene-oxypropylene)methylpolysiloxane copolymers, polyoxyethylene alkylpolysiloxane-polyoxypropylene alkylpolysiloxane-dimethylpolysiloxane copolymers, and methylpolysiloxane-alkylmethylpolysiloxane-poly(oxyethylene-oxypropylene)methylpolysiloxane copolymers. The polyurethane sheet may or may not contain a nonionic surfactant other than a nonionic surfactant containing a polyalkylene oxide unit, but preferably does not contain one. If a nonionic surfactant other than a nonionic surfactant containing a polyalkylene oxide unit is contained, the amount is preferably 5% by mass or less, more preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, based on the polyurethane sheet. The polyurethane sheet may or may not contain a nonionic surfactant other than a nonionic surfactant containing multiple oxygen atoms derived from an ether bond, but preferably does not contain one. If a nonionic surfactant other than a nonionic surfactant containing multiple oxygen atoms derived from an ether bond is contained, the amount is preferably 5% by mass or less, more preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, based on the polyurethane sheet. The polyurethane sheet may or may not contain a nonionic surfactant having an oxygen atom other than that derived from an ether bond (for example, an oxygen atom derived from an ester bond), but it is preferable that the polyurethane sheet does not contain a nonionic surfactant.

[0015] <Water repellent> In the polishing pad of the present invention, the polyurethane sheet contains a water repellent. The inclusion of the water repellent improves abrasion resistance and suppresses corrosion when polishing metal pattern wafers or barrier metals. Examples of water repellents include fluorine-based water repellents, silicone-based water repellents, hydrocarbon-based water repellents, etc. Among these, fluorine-based water repellents (water repellents containing fluorine atoms) are preferred, and fluorine-based water repellents having a polyfluoroalkyl group are more preferred. A polyfluoroalkyl group (hereinafter sometimes referred to as an Rf group) is a group in which two or more hydrogen atoms of an alkyl group have been substituted with fluorine atoms. The Rf group preferably has 1 to 20 carbon atoms, more preferably 2 to 16, and even more preferably 4 to 8. The Rf group may be linear or branched, but is preferably linear. The Rf group is preferably a perfluoroalkyl group (hereinafter sometimes referred to as an Rf group) in which all hydrogen atoms of the alkyl group have been substituted with fluorine atoms. The Rf group preferably has 1 to 20 carbon atoms, more preferably 2 to 16, and even more preferably 4 to 8. The Rf group may be linear or branched, but is preferably linear. Examples of fluorine-based water repellents having a polyfluoroalkyl group include fluorine-containing polymers having a perfluoroalkyl group, such as fluorine-containing poly(meth)acrylate resins and fluorine-containing polyurethane resins, and fluorine-containing polyurethane resins are preferred. Examples of fluorine-containing polyurethane resins include polyurethane resins disclosed in Japanese Patent Nos. 2699538, 2699539, 4682981, and 5846118. There are no particular restrictions on the amount of water repellent agent contained in the polyurethane sheet, but it is preferably 0.01 to 5 mass % relative to the polyurethane sheet, more preferably 0.02 to 1 mass %, and even more preferably 0.05 to 0.5 mass %.

[0016] <Effect of not containing a nonionic surfactant and containing a water repellent agent> The polishing pad of the present invention does not contain a nonionic surfactant containing a polyalkylene oxide unit, and contains a water repellent agent, thereby improving wear resistance. The reason for this is not clear, but is presumed to be as follows. When a polyurethane sheet contains a nonionic surfactant containing polyalkylene oxide units, hydrogen bonds form between the multiple oxygen atoms derived from the polyalkylene oxide and the hydroxyl (OH) groups present on the surface of the abrasive grains (e.g., colloidal silica) contained in the slurry, causing the abrasive grains to adhere to the nonionic surfactant portion of the polyurethane sheet. The surfactant portion with the adsorbed abrasive grains acts as a nucleus for the abrasive grains to aggregate and accumulate, forming large aggregates inside the teardrop-shaped cells. As the abrasive grains aggregate and accumulate within the polyurethane sheet, the polyurethane sheet gradually hardens and loses its elasticity. This causes the polyurethane sheet to lose its elongation, becoming embrittled, which accelerates wear degradation and reduces its wear resistance. In contrast, the polishing pad of the present invention does not contain a nonionic surfactant containing a polyalkylene oxide unit in the polyurethane sheet, which prevents adhesion and aggregation of abrasive grains to the polyurethane sheet via hydrogen bonds, and is therefore thought to improve wear resistance. In addition, wet polishing pads contain many microscopic bubbles in addition to the teardrop-shaped bubbles, and abrasive particles enter and accumulate in these microscopic bubbles during polishing. Therefore, even if aggregation due to hydrogen bonding can be suppressed, as the number of abrasive particles entering these microscopic bubbles increases, the polyurethane sheet will harden and its wear resistance will decrease. In contrast, the polishing pad of the present invention contains a water repellent agent, which makes it difficult for abrasive grains to enter the micro-cells in the polyurethane sheet, thereby suppressing not only aggregation due to hydrogen bonding but also accumulation of abrasive grains in the micro-cells. As a result, it is believed that the polishing pad of the present invention can greatly improve its wear resistance.

[0017] <Ionic surfactants> In the polishing pad of the present invention, the polyurethane sheet preferably contains an ionic surfactant, more preferably an ionic surfactant that does not have a polyalkylene oxide unit. The inclusion of an ionic surfactant can improve film-forming properties and stably form teardrop-shaped bubbles while suppressing the aggregation problem that can occur when the nonionic surfactant is included. Examples of ionic surfactants include cationic surfactants and anionic surfactants. Among these, anionic surfactants are particularly preferred. By including an anionic surfactant, wear resistance can be further improved, particularly under acidic slurry conditions. Examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Among these, sulfonates and sulfates are preferred, and sulfonates are more preferred. Examples of sulfonates include sodium sulfosuccinate alkyl esters, specifically dihexyl sulfosuccinate sodium salt, dipentyl sulfosuccinate sodium salt, and di-2-ethylhexyl sulfosuccinate sodium salt, with di-2-ethylhexyl sulfosuccinate sodium salt being particularly preferred.

[0018] The amount of ionic surfactant contained in the polyurethane sheet is not particularly limited, but is preferably 0.001 to 1.5 mass %, more preferably 0.01 to 1.2 mass %, and even more preferably 0.05 to 0.5 mass %, relative to the polyurethane sheet. The amount of the anionic surfactant contained in the polyurethane sheet is preferably 0.001 to 1.5% by mass, more preferably 0.01 to 1.2% by mass, and even more preferably 0.05 to 0.5% by mass, based on the polyurethane sheet.

[0019] The reason why the polishing pad of the present invention can further improve its wear resistance, particularly under acidic slurry conditions, by containing an anionic surfactant is not clear, but is presumed to be as follows. In general, the zeta potential of polyurethane resins that make up polyurethane sheets tends to be positive under acidic conditions and negative under alkaline conditions (see the results of Comparative Example 1 in Figure 1). The zeta potential of silica, which is contained as an abrasive in polishing slurries, has a large negative value under alkaline conditions, and is often adjusted to have a negative potential under acidic conditions to prevent silica from agglomerating. Therefore, under acidic slurry conditions, the polyurethane sheet, which has a positive potential, is attracted to the silica, which has a negative potential, and silica is adsorbed onto the foam surface of the polyurethane sheet, which is thought to make aggregation and accumulation of silica within the foam more likely to occur than under alkaline slurry conditions. In contrast, the polishing pad of the present invention, because the polyurethane sheet contains an anionic surfactant, can maintain a negative zeta potential of the polyurethane sheet even under acidic conditions (see the results of Example 1 in Figure 1). This is thought to result in the polyurethane sheet, which has a negative zeta potential, repelling silica, which also has a negative zeta potential, and preventing the aggregation and accumulation of silica within the foam of the polyurethane sheet, even under acidic slurry conditions, just as under alkaline slurry conditions.

[0020] <Micropore adjuster> In the polishing pad of the present invention, the polyurethane sheet may contain a micropore-regulating agent, provided that if the micropore-regulating agent can also be a nonionic surfactant containing a polyalkylene oxide unit, the micropore-regulating agent is not contained in the polyurethane sheet. The micropore adjuster is an agent that promotes the formation of microbubbles during the formation of a polyurethane sheet, imparting a uniform, fine microcellular structure. The use of the micropore adjuster increases the number of openings for retaining abrasive grains. The more openings a polishing pad has, the more abrasive grains are retained on the polishing surface, improving the polishing rate. Examples of the micropore adjuster include cellulose derivatives and polyols. Cellulose derivatives are preferred, and ester-based cellulose derivatives are more preferred. Examples of ester-based cellulose derivatives include acetyl cellulose, triacetyl cellulose, acetyl butyl cellulose, diacetyl cellulose, acetyl propyl cellulose, ethyl cellulose, cellulose propionate, cellulose butyrate, nitrocellulose, cellulose sulfate, cellulose phosphate, cellulose acetate butyrate, cellulose nitrate acetate, and cellulose acetate propionate. The amount of micropore-regulating agent contained in the polyurethane sheet is not particularly limited, but is preferably 0.1 to 10% by mass, more preferably 0.2 to 8% by mass, and even more preferably 0.5 to 5% by mass relative to the polyurethane sheet. By containing the micropore-regulating agent in this range, a sufficient microcellular structure can be formed when the polyurethane resin-containing solution applied to the film-forming substrate is wet-coagulated. In addition, the brittleness of the polishing pad is less likely to increase, and physical properties such as elongation are less likely to deteriorate.

[0021] <Other ingredients> In the polishing pad of the present invention, the polyurethane sheet may contain components other than those described above, such as fillers such as carbon black, as long as the effects of the present invention are not impaired.

[0022] (Thickness) There are no particular restrictions on the thickness of the polyurethane sheet in the polishing pad of the present invention, but it can be used in the range of, for example, 0.3 to 3.0 mm, preferably 0.5 to 2.0 mm, and more preferably 0.7 to 1.5 mm.

[0023] (other layers) The polishing pad of the present invention is designed on the premise that the surface (polishing surface) of the polyurethane sheet will come into contact with the object to be polished, and therefore no other resin layer exists on the polishing surface of the polyurethane sheet. On the other hand, in the polishing pad of the present invention, another resin layer (lower layer, support layer) may be attached to the surface of the polyurethane sheet opposite to the surface (polishing surface) used to polish the object to be polished, or no other resin layer may be attached. The properties of the other resin layer are not particularly limited, but it is preferable that a layer harder than the polyurethane sheet (high hardness such as Shore A hardness or Shore D hardness) is attached. By providing a layer harder than the polyurethane sheet, it is possible to prevent minute irregularities on the polishing table from affecting the shape of the polishing surface, further improving polishing flatness. In addition, by increasing the rigidity of the polishing pad overall, it is possible to suppress the occurrence of wrinkles when attaching the polishing pad to the polishing table, thereby improving workability.

[0024] (Application) The polishing pad of the present invention can be suitably used as a polishing pad for polishing (chemical mechanical polishing (CMP)) objects such as semiconductor devices, semiconductor wafers, silicon, and glass. Among these, the polishing pad of the present invention can be suitably used as a polishing pad for semiconductor devices. Furthermore, the polishing pad of the present invention can be suitably used as a polishing pad for polishing metal pattern wafers such as copper, and as a polishing pad for polishing barrier metals. The polishing pad of the present invention can be suitably used for chemical mechanical polishing of an object to be polished using a polishing slurry, and can also be suitably used for chemical mechanical polishing using either an acidic slurry or an alkaline slurry.

[0025] The polishing pad of the present invention can be produced, for example, by the following method.

[0026] <<Polishing pad manufacturing method>> The manufacturing method of the present invention includes the steps of preparing a solution containing a polyurethane resin and a water repellent agent, but not containing a nonionic surfactant containing a polyalkylene oxide unit (hereinafter sometimes referred to as a polyurethane resin-containing solution), applying the solution to a film-forming substrate, and immersing the film-forming substrate to which the solution has been applied in a coagulation liquid to coagulate the polyurethane resin and obtain a polyurethane sheet. Each step will be described below.

[0027] <Step of preparing a solution containing a polyurethane resin and a water repellent agent> In the step of preparing a solution containing a polyurethane resin and a water repellent, a solution containing a polyurethane resin and a water repellent, but not containing a nonionic surfactant containing a polyalkylene oxide unit, is prepared.

[0028] (Polyurethane resin) The polyurethane resin-containing solution contains a polyurethane resin, which is a material for the polyurethane polishing sheet. As the polyurethane resin, the polyurethane resins mentioned in the description of the polishing pad can be used.

[0029] (Water repellent) The polyurethane resin-containing solution contains a water repellent, and the water repellent mentioned in the description of the polishing pad can be used as the water repellent. The amount of the water repellent agent is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the polyurethane resin.

[0030] (nonionic surfactant) The polyurethane resin-containing solution does not contain a nonionic surfactant containing a polyalkylene oxide unit. As the nonionic surfactant containing a polyalkylene oxide unit, the nonionic surfactants mentioned in the description of the polishing pad can be used.

[0031] (ionic surfactants) The polyurethane resin-containing solution may contain an ionic surfactant. As the ionic surfactant, the ionic surfactants mentioned in the description of the polishing pad can be used. As the ionic surfactant, an anionic surfactant is preferred. The ionic surfactant is preferably contained in the polyurethane resin-containing solution in an amount of 0.1 to 10 parts by mass per 100 parts by mass of polyurethane resin, more preferably 0.2 to 8 parts by mass, even more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass. The anionic surfactant is preferably contained in the polyurethane resin-containing solution in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the polyurethane resin, more preferably 0.2 to 8 parts by mass, even more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass.

[0032] (organic solvent) The organic solvent can be any solvent that can dissolve the polyurethane resin and is miscible with water. Examples include N,N-dimethylformamide (DMF), methyl ethyl ketone, N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and acetone. Among these, DMF and DMAc are preferably used. The organic solvent is preferably contained in the polyurethane resin-containing solution in an amount such that the solids concentration in the polyurethane resin-containing solution is preferably 10 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 30 mass %. If the concentration is within the above range, the polyurethane resin-containing solution has appropriate fluidity and can be uniformly applied onto the film-forming substrate in the subsequent coating step.

[0033] (micropore adjuster) The polyurethane resin-containing solution may contain a micropore adjusting agent in addition to the above components. As the micropore adjusting agent, the micropore adjusting agents mentioned in the description of the polishing pad can be used. The micropore regulator is preferably contained in the polyurethane resin-containing solution in an amount of 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the polyurethane resin.

[0034] (Other ingredients) The polyurethane resin-containing solution may further contain other components in addition to the above components, as long as the effects of the present invention are not impaired. As the other components, the other components listed in the description of the polishing pad can be used.

[0035] <Coating process> The polyurethane resin-containing solution obtained above is continuously applied to the film-forming substrate so as to be substantially uniform, for example, using a knife coater, a reverse coater, or the like. The film-forming substrate can be any substrate commonly used in this technical field without any particular limitations. Examples of the film-forming substrate include flexible polymer films such as polyester films and polyolefin films, and nonwoven fabrics impregnated with elastic resins, among which polyester films are preferably used.

[0036] <Coagulation process> The film-forming substrate coated with the polyurethane resin-containing solution is immersed in a coagulation liquid containing water, which is a poor solvent for polyurethane resin, as its main component. The coagulation liquid may be water or a mixed solution of water and a polar solvent such as DMF. Examples of the polar solvent include the water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, and acetone. The concentration of the polar solvent in the mixed solvent is preferably 0.5 to 30% by mass. There are no particular limitations on the temperature of the coagulation liquid or the immersion time, and immersion at 5 to 80° C. for 5 to 60 minutes may be sufficient, for example.

[0037] <Washing and drying> The sheet-like polyurethane resin obtained by coagulation in the coagulation bath is washed and dried after or without being peeled off from the film-forming substrate. The washing treatment removes the organic solvent remaining in the polyurethane resin. The washing liquid used for washing includes water. After washing, the polyurethane resin is dried by a conventional method, for example, by drying in a dryer at 80 to 150°C for about 5 to 60 minutes. A polyurethane sheet can be obtained through the above steps.

[0038] In the method for producing a 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) as necessary. The polishing surface of the polyurethane sheet may be grooved, embossed, and / or perforated (punched), or a substrate may be bonded to the polyurethane sheet. Furthermore, a light-transmitting portion may be provided on the polyurethane sheet and / or the polishing pad. There are no particular limitations on the grinding method, and grinding can be performed by a known method, specifically, grinding with sandpaper. There are no particular limitations on the shape of the grooves and embossing, and examples thereof include lattice, concentric circle, and radial shapes. When substrates are bonded together to form a multilayer structure, the layers may 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 may be selected and used.

[0039] Then, double-sided tape is applied to the surface of the polyurethane sheet opposite the polishing surface, or to the surface of the substrate opposite the surface bonded to the polyurethane sheet, and the sheet is cut into a predetermined shape, preferably a disk, to complete the polishing pad of the present invention. There are no particular restrictions on the double-sided tape, and any double-sided tape known in the art can be selected and used.

[0040] <Polishing method> The polishing method of the present invention is a method for polishing an object to be polished, which comprises a step of polishing the object to be polished with a polishing pad. During polishing, the object to be polished may be polished with the polishing pad while being held by a holding pad. When using the polishing pad of the present invention, the polishing pad is attached to the polishing platen of a polishing machine with the polishing surface of the polyurethane sheet facing the workpiece, and the polishing platen is rotated while supplying abrasive slurry to polish the work surface of the workpiece. Examples of the object to be polished (held object) include semiconductor devices, semiconductor wafers, silicon, glass, etc. Among these, semiconductor devices are preferred as the object to be polished. Materials for semiconductor devices include silicon, polysilicon, silicon oxide film, silicon nitride, and metals such as Cu, W, Al, Ta, and TiN. The polishing pad of the present invention can also be suitably used as a polishing pad for polishing metal pattern wafers such as copper, or as a polishing pad for polishing barrier metals. As a method for polishing an object to be polished, for example, a method of polishing the surface of the object to be polished using a polishing liquid (polishing slurry) can be mentioned. Examples of polishing slurries include slurries for barrier metals, slurries for oxide films, slurries for Cu, etc. The slurries may contain abrasive grains, oxidizing agents, components for protecting the object to be polished, etching agents, chelating agents, etc. Examples of abrasives (abrasive grains) in polishing slurries include silica (SiO2), alumina (Al2O3), and ceria (CeO2). Among these, silica is preferred, and colloidal silica is more preferred. Examples of components for protecting the polished object include triazole compounds, pyrazole compounds, pyramidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, and tetrazole compounds, which act as metal corrosion inhibitors. The polishing slurry may be acidic or alkaline, and the polishing slurry may be adjusted by adding, to the above-mentioned slurry as needed, an acidic component such as sulfuric acid or phosphoric acid, an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, rubidium hydroxide, or cesium hydroxide, an organic alkali compound such as tetramethylammonium hydroxide or choline, or an alkaline component such as ammonia. [Example]

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0042] In Example 1, Comparative Example 1, and Reference Example 1, "parts" means "parts by mass" unless otherwise specified.

[0043] Example 1 A polyurethane resin-containing solution was obtained by mixing 100 parts of an ester-based polyurethane resin solution (solids concentration 30% by mass) with a 100% modulus of 5.4 MPa with 55 parts of DMF, 0.35 parts of sodium di-2-ethylhexyl sulfosuccinate (anionic surfactant), 1.2 parts of cellulose acetate propionate (micropore adjuster), and 0.05 parts of a fluorine-containing polyurethane resin having a carbon number 6 RF group (water repellent (CRISBON ASISTOR SD-38, manufactured by DIC Corporation)). Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied to it using a knife coater. The film was then immersed in a coagulation bath (coagulation liquid: water) at 35°C for 30 minutes to coagulate the polyurethane resin-containing solution. The film-forming substrate was then peeled off, washed, and dried to obtain a polyurethane sheet. The skin layer was then buffed to open the surface, a polyethylene terephthalate (PET) sheet was attached to the side of the polyurethane sheet opposite the buffed side, and the buffed side of the polyurethane sheet was embossed with a grid-shaped mold to obtain the polishing pad of Example 1.

[0044] <Comparative Example 1> A polyurethane resin-containing solution was obtained by mixing 100 parts of an ester-based polyurethane resin solution (solid content concentration 30% by mass) with 55 parts of DMF and 2 parts of a polyether-modified silicone (nonionic surfactant containing polyalkylene oxide units (Crisbon Assister SD-7, manufactured by DIC Corporation)). Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied thereto using a knife coater. The film-forming substrate was then immersed in a coagulation bath (coagulation liquid: water) at 35 ° C for 30 minutes to coagulate the polyurethane resin-containing solution. The film-forming substrate was then peeled off, washed, and dried to obtain a polyurethane sheet. The skin layer was then buffed to open the surface, and a polyethylene terephthalate (PET) sheet was attached to the side opposite the buffed surface of the polyurethane sheet. The buffed surface of the polyurethane sheet was embossed with a lattice-shaped mold to obtain the polishing pad of Comparative Example 1.

[0045] <Reference example 1> A polyurethane resin-containing solution was obtained by mixing 100 parts of an ester-based polyurethane resin solution (solid content concentration 30% by mass) with 100 parts of a 100% modulus 5.4 MPa, 55 parts of DMF, 0.35 parts of di-2-ethylhexyl sulfosuccinate sodium salt (anionic surfactant), and 1.2 parts of cellulose acetate propionate (micropore adjuster). Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied thereto using a knife coater. The film-forming substrate was then immersed in a coagulation bath (coagulation liquid: water) at 35 ° C for 30 minutes to coagulate the polyurethane resin-containing solution. The film-forming substrate was then peeled off, washed, and dried to obtain a polyurethane sheet. The skin layer was then buffed to open the surface, and a polyethylene terephthalate (PET) sheet was attached to the side opposite the buffed surface of the polyurethane sheet. The buffed surface of the polyurethane sheet was embossed with a lattice-shaped mold to obtain the polishing pad of Reference Example 1.

[0046] <Physical property testing> The zeta potential at various pH levels was measured in a 1 mM KCl aqueous solution by a streaming potential method for each of the polishing pads of Example 1, Comparative Example 1, and Reference Example 1. Aqueous HCl solutions and aqueous KOH solutions were used to adjust the pH. The results are shown in Figure 1.

[0047] <Evaluation test> An abrasive grain aggregation test, a wear resistance test, and a corrosion evaluation test were carried out on each of the polishing pads of Example 1, Comparative Example 1, and Reference Example 1. The respective evaluation methods were as follows.

[0048] (Abrasive grain agglomeration test) Using a small polishing machine, the polishing pads of Example 1, Comparative Example 1, and Reference Example 1 were rotated for 10 minutes under acidic slurry conditions with a 50 mm diameter polishing pad attached to the polishing head and a PET film attached to the surface plate. The test conditions were as follows: Rotation speed: (surface plate) 40 rpm, (head) 24 rpm Weight: 3kg Surface pressure: 152.8g / cm 2 Acidic slurry: Colloidal silica slurry (pH 2.7) containing 0.5% by mass of H2O2 Slurry flow rate: 30 mL / min Polishing time: 10 minutes

[0049] After rotating for 10 minutes, the cross section of the polishing pad (cross section in the thickness direction of the polishing pad) was evaluated for aggregation and adhesion of the abrasive silicon component using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDX). The amount of silicon component adhesion was evaluated by energy dispersive X-ray analysis of the area of ​​the SEM image of the polishing pad cross section. The results are shown in Table 1 and FIGS.

[0050] As a result of the abrasive grain aggregation test, in Comparative Example 1, agglomerates of Si components about several tens of μm in size remained inside the teardrop-shaped bubbles. In Reference Example 1, which did not use a nonionic surfactant, no adhesion of large agglomerates inside the teardrop-shaped bubbles was observed, but many fine bubbles with accumulated Si components were observed. In the polishing pad of Example 1, which did not contain a nonionic surfactant but contained a water repellent, no adhesion of large agglomerates of Si components was observed inside the teardrop-shaped bubbles, and almost no accumulation of Si components was observed inside the fine bubbles.

[0051] (Wear resistance test) Using a small polishing machine, a wear resistance test was conducted under acidic and alkaline slurry conditions for the polishing pads of Example 1, in which suppression of abrasive agglomeration was confirmed in the abrasive agglomeration test, and Comparative Example 1, in which the occurrence of abrasive agglomeration was confirmed. Specifically, a Φ100 mm retainer ring was attached to the polishing head, and a polishing pad was attached to the surface plate, and the pads were rotated for 3 hours under acidic and alkaline slurry conditions. The test conditions were as follows: Rotation speed: (Surface plate) 90 rpm, (Head) 24 rpm Weight: 9kg Surface pressure: 212.9g / cm 2 Acidic slurry: Colloidal silica slurry (pH 2.7) containing 0.5% by mass of H2O2 Alkaline slurry: Colloidal silica slurry (pH 11) containing 0.8% by mass of H2O2 Slurry flow rate: 200 mL / min Polishing time: 3 hours

[0052] The cross section of the polishing pad was observed by SEM before and after polishing, and the thickness of the polishing layer was measured to determine the amount of polishing pad wear under both acidic and alkaline slurry conditions. In addition, the Si content of the polishing pad cross section under acidic and alkaline slurry conditions was measured using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDX). Specifically, energy dispersive X-ray analysis was performed on the SEM image of the cross section. Furthermore, for the polishing pad after the wear test, compressive stress was measured by the following method with respect to the hardening before and after the test, and a stress-strain curve was obtained. Using the obtained stress-strain curve, the Young's modulus during compression was evaluated by the following method. The compressive stress measurement was carried out by cutting the polishing pad to be measured into a rectangular piece of 8 mm x 12 mm to form a sheet-like test piece, and compressing the test piece with a micro strength evaluation tester (Shimadzu Corporation, Micro Autograph MST-I). The point where a load of 8.0 g was applied with a circular pressure plate (flat plate) of 20 mm in diameter was set as the origin, and a load was applied in the thickness direction at a rate of 0.1 mm / min until the compressive stress (Stress) reached 1000 g / cm. 2 The pressure was increased until The Young's modulus during compression was determined by measuring the compressive stress within a range of up to 5% compression relative to the thickness in the natural state without pressure, and calculating the coefficient when linearly approximating the stress using the least squares method. The results are shown in Table 1.

[0053] The results of the wear resistance test showed that the polishing pad of Example 1 had a smaller amount of wear under both acidic and alkaline slurry conditions than the polishing pad of Comparative Example 1, demonstrating superior wear resistance. Furthermore, compared to the polishing pad of Comparative Example 1, the polishing pad of Example 1 had a smaller amount of detected Si components under both acidic and alkaline slurry conditions, resulting in a smaller amount of abrasive grain adhesion. Furthermore, as a result of evaluating Young's modulus, the polishing pad of Comparative Example 1 showed an increase in value after polishing under both conditions, whereas the polishing pad of Example 1 showed little increase in value after polishing under both conditions. From the above, it is believed that the polishing pad of Comparative Example 1 hardened due to the aggregation and accumulation of abrasive grains in the polyurethane sheet, resulting in a loss of elasticity. This caused the polyurethane sheet to lose its elongation, becoming embrittled and leading to a decrease in wear resistance. In contrast, the polishing pad of Example 1 prevented the aggregation and accumulation of abrasive grains, thereby preventing hardening of the polishing pad and resulting in improved wear resistance.

[0054] Next, the polishing pad of Comparative Example 1 showed particularly large wear under acidic slurry conditions, while the polishing pad of Example 1 showed small wear under both acidic and alkaline slurry conditions, and had good wear resistance. Furthermore, the polishing pad of Comparative Example 1 showed a larger amount of detected Si components under acidic slurry conditions than under alkaline slurry conditions, and the Young's modulus after polishing also increased, while the polishing pad of Example 1 showed a small amount of detected Si under both conditions, and the Young's modulus after polishing did not increase significantly. From the above, it is believed that the polishing pad of Comparative Example 1 showed increased abrasive particle aggregation and accumulation, particularly under acidic slurry conditions, which significantly impaired the elasticity of the polishing pad, leading to a significant decrease in wear resistance. In contrast, the polishing pad of Example 1 was able to suppress abrasive particle aggregation even under acidic slurry conditions, which is thought to have prevented the polishing pad from hardening and improved wear resistance.

[0055] (Corrosion evaluation test) Using each polishing pad of Example 1 and Comparative Example 1, a Cu pattern wafer was repeatedly polished under the following conditions, and the presence of corrosion in the pattern wafer wiring portion (line 100 μm, space 100 μm) after polishing was visually confirmed using a defect review SEM (eDR5210, manufactured by KLA-Tencor Corporation). The results are shown in Table 1 and Figure 5. Grinding machine: Ebara Corporation, F-REX300 Polishing speed: (platen) 70 rpm, (top ring) 71 rpm Dresser: 3M, A188 Pad break: 30N, 30min Conditioning: Ex-situ, 30N, 16sec Processing pressure: 176g / cm 2 Acidic slurry: Colloidal silica slurry (pH 2.7) containing 0.5% by mass of H2O2 Slurry flow rate: 200 mL / min Polishing time: Approximately 45 seconds Polished object: Cu pattern wafer

[0056] The corrosion evaluation test results showed that the polishing pad of Comparative Example 1 exhibited roughness (unevenness) on the pattern wafer surface, indicating the occurrence of corrosion. In contrast, the roughness (unevenness) on the pattern wafer surface of Example 1 was reduced, confirming that corrosion was improved. The reason for this is unclear, but it is presumed to be as follows: When the polished object protective component (protective component against corrosion) typically contained in the slurry is absorbed into the polyurethane sheet, the amount of the polished object protective component in contact with the polished object is reduced, preventing its full effectiveness. It is presumed that the polishing pad of Example 1 contains a water repellent, which makes the polyurethane sheet itself hydrophobic, making it difficult for the polished object protective component to be absorbed into the polyurethane sheet and less likely to interfere with contact between the polished object protective component and the polished object. This allows the protective component to fully exert its effect, protecting the polished object from corrosion.

[0057] [Table 1]

[0058] <Result> As can be seen from the results in Table 1, the polishing pad of Comparative Example 1, which was equipped with a polyurethane sheet containing a nonionic surfactant containing a polyalkylene oxide unit, exhibited a large amount of wear when polishing a workpiece. This tendency was particularly pronounced under acidic slurry conditions. In contrast, the polishing pad of Example 1 exhibited a small amount of wear when polishing a workpiece, regardless of whether the slurry was alkaline or acidic, and exhibited excellent wear resistance. Furthermore, as a result of the corrosion evaluation test, when the polishing pad of Comparative Example 1 was used to polish the workpiece, corrosion occurred in the wiring portion of the patterned wafer. In contrast, the polishing pad of Example 1 exhibited reduced corrosion, demonstrating its corrosion-inhibiting effect. Therefore, it can be said that the polishing pad of Example 1 can be suitably used for polishing metal patterned wafers and barrier metals. [Industrial Applicability]

[0059] The polishing pad of the present invention has excellent wear resistance. Therefore, the polishing pad of the present invention and the method for producing the same have industrial applicability.

Claims

1. 1. A polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped cells, The polishing pad, wherein the polyurethane sheet does not contain a nonionic surfactant containing a polyalkylene oxide unit and contains a water repellent agent.

2. 2. The polishing pad according to claim 1, wherein the polyurethane sheet does not contain a nonionic surfactant having an oxygen atom derived from an ether bond.

3. 3. The polishing pad of claim 1, further comprising an ionic surfactant.

4. The polishing pad of claim 3 , wherein the ionic surfactant is an anionic surfactant.

5. 5. The polishing pad of claim 4, wherein the anionic surfactant is a sodium salt of an alkyl sulfosuccinate ester.

6. 6. The polishing pad according to claim 1, wherein the water repellent is a fluorine-based water repellent.

7. A method for manufacturing a polishing pad according to any one of claims 1 to 6, comprising the steps of: preparing a solution containing a polyurethane resin and a water repellent, the solution not containing a nonionic surfactant containing a polyalkylene oxide unit; applying the solution onto a film-forming substrate; and immersing the film-forming substrate to which the solution has been applied in a coagulation liquid to coagulate the polyurethane resin and obtain a polyurethane sheet.

Images