Polishing pad

Abstract

Provided is a polishing pad that can stably achieve a required finishing quality of an object to be polished with strict product standards. The polishing pad is formed from a foam body comprising roughly spherical air bubbles, and is characterized in that when the density of a pad constituent material is denoted by DM g / cm3, the density of the polishing pad is in the range of 0.36 to 0.70 DM, the variation (standard deviation σ1) of an opening part diameter based on the air bubbles and formed in the surface of the polishing pad is adjusted to 45 µm or less, the variation (standard deviation σ2) of a diameter, when the area of a portion surrounded by an opening based on the air bubbles and formed in the surface of the polishing pad is circularly approximated, is adjusted to 35 µm or less, and the air bubbles included in the foam body may be closed cell or open cell.

Description

[Technical Field]

[0001] The present invention relates to a polishing pad, and more particularly to a polishing pad for polishing semiconductor wafers and the like. [Background technology]

[0002] The surfaces of objects to be polished, such as semiconductor devices, hard disks, and LCD display glass, are generally polished using a polishing pad containing bubbles with a diameter of 1 μm to 5 mm (average bubble diameter 10 μm to 200 μm) and a polishing liquid (loose abrasive grains).

[0003] In polishing, not only the flatness of the object to be polished but also the finish of its surface are required. To achieve a flat finish of the object to be polished, it is effective to use a so-called hard polishing pad, but the use of a hard pad tends to increase the amount of scratches on the surface of the object to be polished, making it difficult to obtain the required surface finish.

[0004] In the prior art, a method has been proposed in which multi-stage polishing is performed by combining a polishing step that emphasizes flatness and a step that emphasizes surface finish (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 9-55362 [Patent Document 2] Patent No. 6235247 Summary of the Invention [Problem to be solved by the invention]

[0006] In multi-step polishing, if too much emphasis is placed on flatness, the surface finish will be significantly deteriorated, and steps to improve surface quality will need to be carried out for a long time.

[0007] On the other hand, steps to improve surface quality can lead to a deterioration in flatness, so improving surface quality can potentially damage the flatness achieved in the previous step. Therefore, it is necessary to balance the combination of polishing steps that emphasize flatness and steps that emphasize surface finish.

[0008] In this operation method, if there is a change in the polishing characteristics in one step, it becomes necessary to adjust the other step to ensure the final quality of the polished object.In addition, since a trade-off between processes is involved, it is difficult to simultaneously improve both flatness and surface finish.

[0009] As the final product standards for the object to be polished become stricter, the above problems become more serious, making it difficult to maintain a stable quality finish.

[0010] Polishing pads are typically made from polyurethane resin foam. An overview of a polishing pad is as follows: Polyurethane resin foam is formed by curing through the reaction of a prepolymer containing a polyurethane bond-containing isocyanate compound with a curing agent such as MOCA. Polishing pads are produced by slicing this into sheets with a slicer. Openings due to air bubbles are formed on the surface of the polishing pad (Figure 1 is a schematic cross-sectional view of a conventional polishing pad).

[0011] Polishing pads made from this polyurethane resin foam are generally polished after the polishing surface is roughened using a dresser made of electroplated diamond or the like (Figure 2). As shown in Figure 2, the surface of the polishing pad has a surface structure consisting of openings due to irregularly arranged air bubbles and a roughened polishing surface. The inventors have discovered that this surface structure causes uneven polishing results.

[0012] Such a surface structure, i.e., the polishing results caused by uneven contact, was acceptable when the standards required for the surface of the object to be polished were not strict, but as polishing standards have become stricter, it has become impossible to ignore such a surface structure.

[0013] The present invention has been made to solve these problems, and has as its object to simultaneously improve both the flatness and surface finish of the object to be polished. Another object of the present invention is to provide a polishing pad that makes it possible to stably achieve the required finish quality of polished objects, for which product standards have become stricter. A further object of the present invention is to provide a polishing pad that has a uniform contact surface distribution with the object to be polished. A further object of the present invention is to provide a polishing pad that can suppress the occurrence of scratches on an object to be polished even if it has a high hardness. A further object of the present invention is to provide a polishing pad which does not deteriorate the flatness of an object to be polished even if it has a low hardness. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a polishing pad made of a foam containing approximately spherical cells, and the density of the pad constituent material is DMg / cm 3 In this case, the density of this polishing pad is in the range of 0.36 DM or more and 0.70 DM or less, the variation in diameter of the openings due to the bubbles formed on the surface of the polishing pad (standard deviation σ1) is adjusted to 45 μm or less, and the variation in diameter when the area surrounded by the openings due to the bubbles formed on the surface of the polishing pad is approximated as a circle (standard deviation σ2) is adjusted to 35 μm or less.

[0015] When the hardness of the polishing pad is increased to improve the flatness of the object to be polished, the number density of air bubbles in the polishing pad decreases, and the resin part between the bubbles changes from a shape divided by the air bubbles to a continuous shape. As a result, the variation in diameter (standard deviation σ2) increases when the area surrounded by the openings due to the air bubbles is approximated as a circle. Furthermore, if the hardness of the polishing pad is reduced to improve the finish, the number density of bubbles in the polishing pad increases, the bubbles become connected to each other, and the variation in the opening diameter due to the bubbles (standard deviation σ1) increases. To simultaneously improve both the flatness and surface finish of the polished object, the density of the pad material should be set to DMg / cm 3 If this is the case, by setting the density of the polishing pad in the range of 0.36 DM or more and 0.70 DM or less, it is possible to set σ1 to 45 μm or less and σ2 to 35 μm or less.

[0016] The material of the polishing pad is not particularly limited, and examples thereof include polyurethane resin, polyester resin, polyamide resin, polyimide resin, acrylic resin, polycarbonate resin, halogen-based resin (polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, etc.), polystyrene, olefin-based resin (polyethylene, polypropylene, etc.), epoxy resin, and photosensitive resin. Among these, polyurethane resin is particularly preferred as a material for the polishing pad because it has excellent abrasion resistance and can be adjusted to have desired physical properties by changing the raw material composition.

[0017] In the case of a polyurethane resin foam, which is one form of polishing pad, the preferred density is 0.40 to 0.60 g / cm 3 is in the range.

[0018] The polyurethane resin foam contains cells with an average diameter of 130 μm or less, and is composed of independent cells and cells where adjacent cells join at their contact points to form openings, i.e., so-called open cells.

[0019] The urethane resin foam preferably has a Shore A hardness in the range of 70 to 95. [Effects of the Invention]

[0020] The polishing pad of the present invention can stably achieve the required finish quality of the object to be polished, which has become increasingly strict in product standards. Furthermore, the polishing pad of the present invention has a uniform contact area distribution with the object to be polished on the polishing surface, and even if the hardness is made high corresponding to the object to be polished, it can suppress the occurrence of scratches on the object to be polished. Conversely, even if the hardness is made low, it does not deteriorate the flatness of the object to be polished. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the cross-sectional structure of a conventional polishing pad. [Figure 2] FIG. 2 is a schematic cross-sectional view of a conventional polishing pad after diamond dressing. [Figure 3] FIG. 3 is an SEM photograph showing the surface structure of a conventional polishing pad. [Figure 4] FIG. 4 is an SEM photograph showing the surface structure of the polishing pad of the present invention. [Figure 5] FIG. 5 is a table showing the main physical properties of conventional polishing pad A and polishing pad B of the present invention. [Figure 6] FIG. 6 is a histogram showing the diameter distribution of the openings in conventional polishing pad A. [Figure 7] FIG. 7 is a histogram showing the diameter distribution of the openings in polishing pad B of the present invention. [Figure 8] FIG. 8 is a histogram showing the diameter distribution when the area surrounded by the openings of conventional polishing pad A is approximated as a circle. [Figure 9] FIG. 9 is a histogram showing the diameter distribution when the area surrounded by the openings of polishing pad B of the present invention is approximated as a circle. [Figure 10]FIG. 10 is a graph showing a comparison of the number of defects when 18 wafers are polished with a conventional polishing pad A and a polishing pad B of the present invention. [Figure 11] FIG. 11 is a graph showing a comparison of surface roughness Ra when 18 wafers are polished with conventional polishing pad A and polishing pad B of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] A polishing pad according to one embodiment of the present invention is made of a polyurethane resin foam containing substantially spherical cells, which is produced by the method described below. The density of the polyurethane resin foam is preferably 0.40 to 0.60 g / cm. 3 is in the range. The polyurethane resin foam of one embodiment of the present invention contains cells that are independent of each other and cells in which adjacent cells join at their contact points to form openings, i.e., so-called open cells. The variation in diameter of the openings formed on the surface of the polishing pad due to the cells (standard deviation σ1) is adjusted to 45 μm or less, and the variation in diameter of the area surrounded by the openings formed on the surface of the polishing pad due to the cells, when approximated as a circle (standard deviation σ2), is adjusted to 35 μm or less. The Shore A hardness of the urethane foam is preferably in the range of 70 to 95.

[0023] As described below, it is essential that the variations in opening diameter due to the cells in the foam polishing pad of the present invention be precisely controlled.

[0024] An SEM photograph showing the surface structure of conventional polishing pad A is shown in Figure 3. An SEM photograph showing the surface structure of polishing pad B of the present invention is shown in Figure 4. As shown in the figure (SEM photograph), the openings present in the surface of conventional polishing pad A have a larger variation in diameter than the openings present in the surface of polishing pad B of the present invention.

[0025] 6 shows a histogram illustrating the opening diameter distribution of conventional polishing pad A. The variation in opening diameter (standard deviation σ1) is 61 μm. 7 shows a histogram showing the opening diameter distribution of the polishing pad B of the present invention. The variation in the opening diameter (standard deviation σ1) is 43 μm.

[0026] Furthermore, as shown in the figure (SEM photograph), the area of ​​the portion surrounded by the openings on the surface of conventional polishing pad A varies more than the area of ​​the portion surrounded by the openings on the surface of polishing pad B of the present invention.

[0027] Specifically, Figure 8 shows a histogram showing the diameter distribution when the area surrounded by the openings of conventional polishing pad A is approximated as a circle. The variation in diameter (standard deviation σ2) when the area surrounded by the openings is approximated as a circle is 36 μm. 7 shows a histogram showing the diameter distribution when the area surrounded by the openings of polishing pad B of the present invention is approximated as a circle. The variation in diameter (standard deviation σ2) when the area surrounded by the openings is approximated as a circle is 29 μm. The variation in the diameter of the opening (standard deviation σ1) and the variation in the diameter when the area enclosed by the opening is approximated as a circle (standard deviation σ2) were calculated using commercially available image analysis software from data obtained with a scanning electron microscope.

[0028] Generally, during the production process of a foam polishing pad, bubbles coalesce, ultimately resulting in a foam with bubbles of various sizes. By adjusting the dispersion liquid containing the foaming agent, foam stabilizer, and catalyst used, it is possible to control the reaction by which the bubbles coalesce, and as a result, it is possible to produce a foam polishing pad composed of almost uniform bubbles, such as the polishing pad of the present invention.

[0029] Therefore, the surface of the polishing pad of the present invention can be understood as having an orderly arrangement of approximately spherical bubbles, and the areas formed between the bubbles, i.e., the contact surface, are uniformly distributed, as shown in Figure 4. When the polishing pad is pressed against the workpiece for polishing, the uniformly distributed contact surface distributes the pressure evenly, eliminating any contact surface with locally high pressure, thereby suppressing the occurrence of scratches on the workpiece. Therefore, when polishing is performed with a high-hardness polishing pad, it is possible to achieve flatness while suppressing the occurrence of scratches.

[0030] Furthermore, since the diameter variation (standard deviation σ1) of the polishing pad of the present invention is kept small, the compressibility of the polishing pad is also uniform. Therefore, when polishing is performed with a polishing pad having low hardness, the required finishing precision can be achieved without impairing the flatness of the polished object.

[0031] The polishing pad of the present invention is produced as follows. Polishing pads are manufactured using a conventional in-line mixing device, which continuously mixes raw materials and pours them into a mold.

[0032] As a preliminary preparation, a polyisocyanate compound, a polyol compound, a dispersion liquid in which a blowing agent (water) and a silicone-based foam stabilizer are dispersed and diluted in the polyol compound, and a low-molecular-weight (molecular-weight 62 to 350) polyamine compound or a low-molecular-weight polyol compound is prepared as a curing agent.

[0033] The polyisocyanate compound has two or more isocyanate groups in the molecule. For example, diisocyanate compounds having two isocyanate groups in the molecule include m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate (2,6-TDI), 2,4-tolylene diisocyanate (2,4-TDI), naphthalene-1,5-diisocyanate, diphenylmethane-4, 4'-diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, diphenylpropane-4,4'-diisocyanate, trimethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, cyclohexylmethane-4,4'-diisocyanate, etc. These can be used alone or in combination of two or more.

[0034] Examples of polyol compounds include diol compounds, triol compounds, and the like, and include low-molecular-weight polyol compounds such as ethylene glycol and butylene glycol, high-molecular-weight (number-average molecular weight 500 to 7000) polyether polyol compounds such as polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG), polyester polyol compounds such as reaction products of ethylene glycol and adipic acid and reaction products of butylene glycol and adipic acid, polycarbonate polyol compounds, polycaprolactone polyol compounds, and the like. These may be used alone or in combination of two or more.

[0035] The polyisocyanate compound and the polyol compound are reacted in advance to produce an isocyanate group-containing compound, i.e., an isocyanate-terminated urethane prepolymer (hereinafter referred to as "prepolymer"). This prepolymer is used as a base component to obtain a polyurethane foam by mixing it with a curing agent such as a polyamine and a dispersion containing a blowing agent.

[0036] The prepolymer in a fluid state is charged into a tank, and the viscosity is preferably set in the range of 50 to 20,000 mPa·s at a temperature of 20 to 60° C. The prepolymer is preferably degassed using a vacuum pump to remove dissolved gases.

[0037] The dispersion containing the blowing agent is prepared by dispersing water, a foam stabilizer, a catalyst, and other additives added as needed in a polyol compound that is not involved in foaming. By using this dispersion to foam the prepolymer, it is possible to reduce the occurrence of uneven mixing that tends to occur when the blowing agent is mixed alone with the prepolymer.

[0038] The polyol compound used in this dispersion may be, for example, a low molecular weight polyol compound such as ethylene glycol or butylene glycol, or a high molecular weight polyol compound such as PTMG, PPG or polyethylene glycol (PEG).

[0039] The foaming agent may be, but is not limited to, water, and it is preferable to use distilled water to avoid contamination with impurities.

[0040] A surfactant is used as a foam stabilizer, but in order to prevent bubbles from coalescing and form closed bubbles, a silicone-based foam stabilizer such as polydimethylsiloxane modified with a polyoxyalkylene chain can be used.

[0041] The amount of this silicone foam stabilizer used is adjusted by the amount of water used, but is preferably 6.5 to 8.5 parts by weight, more preferably 7.0 to 8.0 parts by weight, per 1.0 part by weight of water.

[0042] Known catalysts can be used. Examples include amine catalysts such as tertiary amines, alcohol amines, and ether amines, acetates (potassium, calcium), and organometallic catalysts. In this example, the tertiary amine DABCO33LV (EVONIK) is used as the catalyst, but the effects of the present invention are not limited to the use of this catalyst. The amount of catalyst is not particularly limited, but is preferably 0.01 to 0.5 parts by mass, and more preferably 0.05 to 0.3 parts by mass, per 100 parts by mass of prepolymer.

[0043] By using this dispersion, the dispersibility of water in the polyurethane resin is excellent, and the foam shape and distribution become uniform.

[0044] In the preliminary preparation, a polyamine compound may be further mixed in. The polyamine compound reacts with the isocyanate group of the isocyanate group-containing compound.

[0045] The polyamine compound may be an aliphatic or aromatic polyamine compound, such as ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4'-diamine, 3,3'-dichloro-4,4'-diaminodiphenylmethane (hereinafter abbreviated as "MOCA"), diethylmethylbenzenediamine, dimethylthiotoluenediamine, 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 1,3-propanediol-bis-(4-aminobenzoate), etc. The polyamine compound may also have a hydroxyl group, and examples of such amine compounds include methyldiethanolamine, di-(2-hydroxyethyl)ethylenediamine, di-(2-hydroxyethyl)propylenediamine, and di(2-hydroxyethyl)aniline. These may be used alone or in combination. In this embodiment, an example will be described in which MOCA is heated to about 120° C. and used in a molten state.

[0046] Although water has been described as the foaming agent, it is not limited to this. For example, bubbles can be formed by a water-soluble substance that retains water, or by gas generated by the decomposition of a chemical foaming agent or the evaporation of an organic compound. Foam can also be formed by a method (mechanical foaming method) in which air, nitrogen, oxygen, carbon dioxide, or an inert gas such as helium or argon is mechanically stirred and mixed, or a combination of the above-mentioned foam-forming methods can be used.

[0047] The chemical foaming agent may be, for example, at least one selected from the group consisting of N,N'-dinitrosopentamethylenetetramine, azodicarbonamide, 4,4'-oxybisbenzenesulfonylhydrazide, and hydrazodicarbonamide. When the thermal decomposition temperature of the chemical foaming agent is 100°C or higher, premature decomposition during the formation of the polyurethane foam is further suppressed, resulting in more uniform and homogeneous dispersion of the bubbles.

[0048] Examples of water-soluble substances that retain water include water-soluble polysaccharides and derivatives thereof, such as carboxymethyl cellulose, hydroxypropyl cellulose, carboxymethyl chitin, dextrin, and cyclodextrin; oligosaccharides and monosaccharides, such as chitooligosaccharides, fructooligosaccharides, sucrose, and glucose; cationic surfactants, such as aliphatic amine salts and aliphatic ammonium salts; anionic surfactants, such as alkylbenzene sulfonates, sulfonates, alkyl ether sulfates, and phosphate ester salts; nonionic surfactants, such as ether-type, ether ester-type, and ester-type surfactants; amino acids; proteins; polyvinyl alcohol; polyvinylpyrrolidone; polyvinyl sulfonic acid; and poly(meth)acrylic acid. These may be used alone or in combination. These water-soluble substances readily retain water, and therefore, during the formation of a polyurethane molded body, the water retained in the water-soluble substance reacts with an isocyanate group-containing compound to generate gas and form bubbles.

[0049] The mixture is quickly poured into a mold, and the isocyanate group-containing compound and the active hydrogen compound in the mixture are reacted and cured in the mold, while a blowing agent is used to form multiple cells, yielding a block-shaped polyurethane foam. At this time, the isocyanate group-containing compound cures through a reaction (polymerization or crosslinking) with the active hydrogen compound, forming a polyurethane resin foam with a matrix resin.

[0050] The content ratio of the isocyanate group-containing compound in the mixed solution is not particularly limited, but from the viewpoint of more effectively and reliably achieving the effects of the present invention, it is 0.9 to 1.2, and preferably 0.95 to 1.1, in terms of molar ratio (equivalent ratio) to the active hydrogen compound.

[0051] The resulting polyurethane foam is sliced ​​to a desired thickness and cut into a desired shape, such as a circle, to form a sheet-like foam pad. Grooves of a desired shape may be formed in consideration of the supply of slurry during polishing and the discharge of polishing debris.

[0052] When using this polishing pad, a pressure-sensitive adhesive tape is attached to the back of the pad. The pad can be attached to the platen of a polishing machine via the adhesive tape and used as a polishing pad.

[0053] (Comparative Example) Each of the 18 wafers was polished using a polishing pad A according to the prior art having the following configuration: The base material was a prepolymer composed of 30 parts by weight of tolylene diisocyanate (TDI) and 48 parts by weight of polytetramethylene glycol (PTMG). 1.0 part by weight of polydimethylsiloxane-based silicone was used as a foam stabilizer, and 1.0 part by weight of water was used as a blowing agent. After mixing the above materials under specified conditions, 20 parts by weight of dichlorodiaminodiphenylmethane (MOCA) was added as a curing agent. After continuing mixing for a certain period of time, the mixture was poured into a mold and allowed to harden. The mixture was then placed in a constant temperature oven for a specified period of time to complete the reaction, resulting in a solid polyurethane cake. This solid polyurethane cake was then cut into the specified thickness using a slicer to produce polishing pads. The main physical properties of the conventional polishing pad A as a comparative example and the polishing pad B of the present invention are shown in FIG.

[0054] (Example) Each of the 18 wafers was polished using the polishing pad B of the present invention having the following composition. The base prepolymer used was the same as in the comparative example. However, in this example, the prepolymer was degassed in a sealed container for a predetermined period of time as a preliminary preparation. In addition, a dispersion was prepared by pre-dispersing 1.0 parts by weight of foam stabilizer, 1.0 parts by weight of water, and 0.1 parts by weight of catalyst in 1.0 parts by weight of PTMG. DABCO33LV was used as the catalyst. Once these preparations were complete, the components were stirred and mixed so that the foam stabilizer, water, and curing agent to prepolymer ratio was the same as in the comparative example, and then immediately poured into a mold and cured. The polishing pad was then manufactured using the same process as the conventional polishing pad A.

[0055] As shown in FIG. 5, conventional polishing pad A and polishing pad B of the present invention have similar physical property values ​​except for the average pore diameter.

[0056] Using a SpeedFam 50B single-sided polishing machine, 6-inch silicon wafers were polished using two types of polishing pads: conventional polishing pad A and polishing pad B of the present invention. In order to directly compare the performance of the pads, the usual finish polishing was not performed. After polishing, the silicon wafers were subjected to RCA cleaning, and the number of defects on the wafer surface was counted using a laser particle counter (Topcon WM-7S). The measurement results for the number of coarse particles of 0.25 μm or larger are shown in Figure 10. The surface roughness was also measured using an optical interference microscope. The measurement results of surface roughness Ra are shown in Figure 11.

[0057] As shown in FIGS. 10 and 11, it was confirmed that the polishing pad B of the present invention was improved over the conventional polishing pad A in both the total number of defects and the surface roughness Ra. As shown in Figure 5, conventional polishing pad A and polishing pad B of the present invention are made from the same raw materials and are manufactured to approximately the same density, so their physical properties other than the average pore diameter are similar to each other. As a result, the flatness results, which were not specifically disclosed, were also similar. Therefore, the polishing pad B of the present invention was able to improve the surface finish compared to the conventional polishing pad A while maintaining flatness.

[0058] In this embodiment, a polishing pad using foamed polyurethane is described, but the material of the polishing pad is not limited to polyurethane. [Industrial Applicability]

[0059] The present invention has been described using polishing of a semiconductor (silicon) wafer as an example of the object to be polished, but the object to be polished is not limited to a semiconductor (silicon) wafer, and it can also be used for polishing, for example, glass, sapphire, various ceramics, metals, etc.

Claims

1. A polishing pad made of a foam containing approximately spherical bubbles, The density of the pad material is DMg / cm 3 In this case, the density of the polishing pad is in the range of 0.36 DM or more and 0.70 DM or less, and the variation (standard deviation σ) of the opening diameter due to the bubbles formed on the surface of the polishing pad is adjusted to 45 μm or less, The variation in diameter (standard deviation σ) of the area of ​​the portion surrounded by the openings due to the bubbles formed on the surface of the polishing pad when the area is approximated as a circle is adjusted to 35 μm or less. A polishing pad characterized by:

2. A polishing pad made of a foam containing approximately spherical bubbles, The density of the pad material is DMg / cm 3 In this case, the density of the polishing pad is in the range of 0.36 DM or more and 0.70 DM or less, and the diameter variation (standard deviation σ) of the area of ​​the portion surrounded by the openings due to the bubbles formed on the surface of the polishing pad when the area is approximated as a circle is adjusted to 35 μm or less. A polishing pad characterized by:

3. 3. The polishing pad of claim 1, wherein the foam is made of polyurethane foam.

4. 4. The polishing pad of claim 3, wherein the polyurethane foam has an average cell diameter not exceeding 150 μm.

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