JP2024047977A - Polishing pad, polishing pad manufacturing method, and method for polishing surface of optical material or of semiconductor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad that can exert a high polishing rate and is excellent in topography performance.

SOLUTION: The polishing pad has a polishing layer, where the polishing layer includes polyurethane resin and porous fine particles, and has air bubble in a nearly tear shape.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a polishing pad, a method for manufacturing a polishing pad, and a method for polishing the surface of an optical material or a semiconductor material. 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 polishing devices in which an oxide layer, metal layer, etc. are formed on a semiconductor wafer.

Polishing pads with a polishing layer made of polyurethane resin include polishing pads with a polishing layer made of hard polyurethane resin (hard polyurethane polishing pads) and polishing pads with a polishing layer made of soft polyurethane resin (soft polyurethane polishing pads). Hard polyurethane polishing pads are used for rough polishing, while soft polyurethane polishing pads are used for finish polishing. Soft polyurethane polishing pads have a texture similar to suede (brushed leather).

The wet film formation method is a common method for manufacturing soft polyurethane polishing pads, in which a resin solution in which polyurethane resin is dissolved in a polar solvent such as DMF (N,N-dimethylformamide) is applied to a substrate, which is then immersed in an aqueous coagulating liquid.
The foam obtained by the wet film-forming method is prone to have teardrop-shaped bubbles inside, which may cause the polishing rate to be unstable. Therefore, in order to obtain a uniform foam structure, mixing of hollow fine particles having a resinous outer shell has been considered. For example, Patent Documents 1 and 2 disclose a technique of mixing hollow fine particles that are poorly soluble in polar solvents such as DMF.

Patent No. 6357291 Patent No. 6587464

In recent years, semiconductor devices and other devices have required more precise levels of topography (flattening characteristics such as dishing and erosion) due to the increasing density of wiring structures. In particular, there is a demand for polishing pads that have a high polishing rate and excellent topography performance (capable of achieving flat topography).

The objective of the present invention is to provide a polishing pad that exhibits a high polishing rate and excellent topography performance.

Patent Documents 1 and 2 state that the use of non-hollow fine particles leads to a deterioration in polishing rate and topography performance. However, as a result of intensive research by the inventors to solve the above problem, they discovered that the above problem can be solved by using porous fine particles, which are a type of non-hollow fine particles, and further forming approximately teardrop-shaped bubbles, and thus completed the present invention. Specific aspects of the present invention are as follows.

[1] A polishing pad having a polishing layer,
The polishing pad, wherein the polishing layer contains a polyurethane resin and porous fine particles and has approximately teardrop-shaped bubbles.
[2] The polishing pad according to [1], wherein the specific surface area of the porous fine particles is 1 to 1000 m ² /g.
[3] The polishing pad according to [1] or [2], wherein the porous microparticles have an average particle size of 1 to 20 μm.
[4] The polishing pad according to any one of [1] to [3], wherein the pore diameter of the porous microparticles is 2 to 1000 nm.
[5] The polishing pad according to any one of [1] to [4], wherein the porous microparticles include particles of a polymer selected from the group consisting of polymethyl methacrylate, polystyrene, and mixtures thereof.
[6] The polishing pad according to any one of [1] to [5], wherein the content of the porous microparticles in the entire polishing layer is 1 to 30 mass %.
[7] The polishing pad according to any one of [1] to [6], wherein the average void diameter of the bubbles in the polishing layer is 10 to 70 μm.
[8] A method for producing a polishing pad according to any one of [1] to [7], comprising a step of using a wet film-forming method.
[9] A method for polishing a surface of an optical material or a semiconductor material, comprising a step of using the polishing pad according to any one of [1] to [7].

The polishing pad of the present invention exhibits a high polishing rate and excellent topography performance.

1 is a photograph (magnification: 100x) showing a cross section of the polishing pad obtained in Example 1. 1 is a photograph (magnification: 500x) showing a cross section of the polishing pad obtained in Example 1. 1 is a photograph (magnification: 100x) showing a cross section of the polishing pad obtained in Example 2. 1 is a photograph (magnification: 500x) showing a cross section of the polishing pad obtained in Example 2. 1 is a photograph (magnification: 100x) showing a cross section of the polishing pad obtained in Comparative Example 1. 1 is a photograph (magnification: 500x) showing a cross section of the polishing pad obtained in Comparative Example 1. 1 is a photograph (magnification: 100x) showing a cross section of the polishing pad obtained in Comparative Example 3. 1 is a photograph (magnification: 500x) showing a cross section of the polishing pad obtained in Comparative Example 3.

(Action)
The inventors have unexpectedly found that by forming an abrasive layer containing porous microparticles and having approximately teardrop-shaped bubbles, a polishing pad exhibiting a high removal rate and excellent topography performance can be obtained. Although the details of why these characteristics are obtained are not clear, it is presumed that the following occurs.

A polishing layer having approximately teardrop-shaped bubbles is relatively flexible and is capable of polishing along the unevenness of the workpiece, resulting in excellent topography performance; however, as mentioned above, it is believed that the polishing rate may not be stable.
On the other hand, the porous microparticles have a porous structure, unlike the hollow microparticles disclosed in Patent Documents 1 and 2. It is considered that the porous structure of the porous microparticles acts as minute openings, and therefore the porous microparticles can hold a larger amount of slurry and exhibit a high polishing rate.
In this way, it is believed that the improvement in topography performance due to the approximately teardrop-shaped bubbles and the improvement in polishing rate due to the porous microparticles act synergistically, resulting in a polishing pad that exhibits a high polishing rate and excellent topography performance.

The polishing pad, the method for producing the polishing pad, and the method for polishing the surface of an optical material or a semiconductor material of the present invention will be described below.
In this specification and claims, when a numerical range is expressed using "A to B," the range includes both the numerical values A and B at both ends.

1. Polishing Pad The polishing pad of the present invention has a polishing layer, which contains a polyurethane resin and porous fine particles and has approximately teardrop-shaped bubbles.
By making the polishing layer contain porous fine particles and have approximately teardrop-shaped bubbles, a polishing pad that exhibits a high removal rate and is excellent in topography performance can be obtained.

(Porous Microparticles)
The porous fine particles have a porous structure, and the porous structure acts as minute openings, allowing the particles to hold a larger amount of the abrasive slurry, thereby improving the polishing rate.
A foam can be formed by mixing the porous fine particles with the components (such as polyurethane resin) that make up the polishing layer.

The average particle size of the porous microparticles is not particularly limited, but is preferably 1 to 20 μm, more preferably 4 to 15 μm, and most preferably 6 to 10 μm. By having the average particle size within the above numerical range, the average pore size on the surface of the polishing layer becomes 20 μm or less, and the polished object can be polished more precisely.
The average particle size can be determined based on the D50 (median diameter) and can be measured using a laser diffraction particle size distribution measuring device (for example, Mastersizer 2000, manufactured by Spectris Co., Ltd.).

The porous microparticles may include or consist of polymer particles, but are not particularly limited. The polymer constituting the polymer particles may include or consist of a thermoplastic resin, but are not particularly limited. The thermoplastic resin may be one or more selected from the group consisting of poly(meth)acrylic acid esters such as polymethyl methacrylate, polystyrene, polyvinylpyrrolidone, polyacrylamide, polyethylene, maleic acid copolymers, polyethylene oxide, polyvinyl acetate, polyvinyl chloride, and organic silicone resins, as well as copolymers (e.g., vinyl chloride-ethylene copolymers) in which two or more monomers constituting these resins are combined, but are not particularly limited. Of these, polymethyl methacrylate or polystyrene is preferred from the viewpoint of improving solvent resistance and the like.
The porous fine particles may be crosslinked particles of the above polymer particles (crosslinked polymer particles).
The porous microparticles may be untreated particles or may be particles that have been surface treated with an organic or inorganic compound.

The CV value (coefficient of variation) of the particle size of the porous microparticles is not particularly limited, but is preferably 5 to 30%, more preferably 5 to 20%, and most preferably 7 to 15%. When the CV value is within the above range, a uniform foam structure is obtained. The CV value of the particle size of the porous microparticles can be calculated based on the following formula.

The specific surface area of the porous fine particles is not particularly limited, but is preferably 1 to 1000 m ² /g, more preferably 1 to 500 m ² /g, and most preferably 50 to 200 m ² /g. By having the specific surface area in the above numerical range, a larger amount of slurry can be retained.
The specific surface area of the porous fine particles can be measured based on the BET method using a specific surface area pore distribution measuring device (for example, Tristar 3000 manufactured by Shimadzu Corporation).
The specific surface area of the porous fine particles refers to the surface area per unit mass.

The porous microparticles contain pores, which are minute openings, in the porous structure. The pore diameter of the porous microparticles is not particularly limited, but is preferably 2 to 1000 nm, more preferably 10 to 500 nm, and most preferably 10 to 200 nm. When the pore diameter is within the above numerical range, many minute openings are present, and the polishing rate is excellent.
The pore size of the porous fine particles can be measured based on the BJH method using a specific surface area pore distribution measuring device (for example, Tristar 3000 manufactured by Shimadzu Corporation).

Porous microparticles are not particularly limited, but can be microparticles with solvent resistance.By using porous microparticles with solvent resistance, when forming the resin film that constitutes the polishing layer by wet film forming method, the porous microparticles can be formed voids due to the porous microparticles without dissolving in the solvent (e.g., polar solvent such as DMF) used.The solvent resistance of porous microparticles can be judged, for example, based on the following criteria.
- If the resin film containing the porous microparticles that constitute the abrasive layer is placed in 100 parts by mass of DMF, left to stand overnight at room temperature, and then stirred for 30 minutes without the porous microparticles being completely dissolved, it is determined to have solvent resistance.

The solubility parameter (SP value) of the porous microparticles is not particularly limited, but is preferably 7 to 10 (cal/cm ³ ) ^1/2 , and more preferably 8.5 to 9.5 (cal/cm ³ ) ^1/2 . When the SP value of the porous microparticles is in the above numerical range, the difference with the SP value of the solvent (e.g., polar solvent such as DMF) used in the wet film-forming method or the like can be made large, thereby improving the above-mentioned solvent resistance.

The solubility parameter (SP value) is a value introduced by Hildebrand and serves as a measure of the solubility of a two-component solution of a solute and a solvent (components with similar SP values dissolve well in each other). The SP value can also be used empirically as an index of the dispersibility of particles in a solution, and components with similar SP values disperse well in each other.
The SP value can be calculated based on the following formula.

The absolute value of the difference between the SP value of the porous microparticles and the SP value of a solvent (polar solvent) described below: |(SP value of porous microparticles)-(SP value of solvent)| is not particularly limited, but is preferably 2 to 5 (cal/ ^cm3 ) ^1/2 . When the absolute value of the difference is 2 (cal/ ^cm3 ) ^1/2 or more, the solvent resistance of the porous microparticles to the solvent can be improved. Furthermore, when the absolute value of the difference is 5 (cal/ ^cm3 ) ^1/2 or less, the dispersibility of the porous microparticles in the solvent can be made appropriate, and a uniform foam structure can be obtained.

The amount of porous microparticles in the entire polishing layer is not particularly limited, but is preferably 1 to 30% by mass, more preferably 1 to 25% by mass, and most preferably 1 to 20% by mass. When the amount of porous microparticles is within the above range, the porous microparticles do not aggregate and a uniform foam structure is obtained.

The polishing layer may be free of hollow microparticles. In this application, "free of hollow microparticles" means that they are not intentionally added, and does not exclude the possibility of hollow microparticles being mixed in as impurities. The porous microparticles are a type of non-hollow microparticles, and are not hollow microparticles.

(Polyurethane resin)
The polyurethane resin of the polishing pad of the present invention is obtained by reacting a polyisocyanate compound with a curing agent such as a polyol or polyamine, and a chain extender may also be used.

The polyisocyanate compound can be used in the form of a prepolymer, which is a polymer that has been produced by reacting the polyisocyanate compound with a polyol in advance.

The polyisocyanate compound may include, but is not limited to, aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, 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; or a combination of two or more of these.

The polyol (polymer diol) is not particularly limited, but may include or consist of a polyether diol, a polyester diol, or a polycarbonate diol. These polymer diols may be used alone or in combination of two or more kinds.
The polyether diol may include or consist of, but is not limited to, poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), poly(methyltetramethylene glycol), etc. These polyether diols may be used alone or in combination of two or more.
The polyester diol is not particularly limited, but can be produced by subjecting a dicarboxylic acid or an ester-forming derivative thereof, such as an ester or an anhydride, to a direct esterification reaction or an ester exchange reaction with a low molecular weight diol.
Examples of dicarboxylic acids constituting the polyester diol include aliphatic dicarboxylic 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; aromatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, and orthophthalic acid; etc. These dicarboxylic acids may be used alone or in combination of two or more.
Examples of low molecular weight diols constituting polyester diols 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; alicyclic diols such as cyclohexanedimethanol and cyclohexanediol; and the like. These low molecular weight diols may be used alone or in combination of two or more. The carbon number of the low molecular weight diol may be, for example, 6 or more and 12 or less.

The chain extender is not particularly limited, but may contain or consist of aliphatic polyol compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, saccharose, 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.

(Other ingredients)
The polyurethane resin composition of the present invention may contain an additive, which is preferably selected from the group consisting of a film-forming assistant and a foaming suppressing assistant.
Examples of the film-forming aid include hydrophobic surfactants, etc. Examples of the hydrophobic surfactants include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, perfluoroalkyl ethylene oxide adducts, glycerin fatty acid esters, propylene glycol fatty acid esters, and polyether-modified silicones, and anionic surfactants such as alkyl carboxylic acids.
The foam suppressing assistant may be a hydrophilic surfactant, for example, an anionic surfactant such as a carboxylate, a sulfonate, a sulfate, or a phosphate, or a cellulose ester.
When a film-forming assistant is added as an additive, the content is preferably 0.2 to 10 mass %. When a foaming inhibitor assistant is added as an additive, the content is preferably 0.2 to 10 mass %.

The polyurethane resin can be produced by polymerizing the polyurethane resin composition described above. That is, one example of a method is to carry out a polymerization reaction in an organic solvent in the presence of a catalyst as necessary.

The solubility parameter (SP value) of the polyurethane resin is not particularly limited, but is preferably 8 to 14 (cal/cm ³ ) ^1/2 , more preferably 8 to 12 (cal/cm ³ ) ^1/2 , and most preferably 10 to 12 (cal/cm ³ ) ^1/2 . When the SP value of the polyurethane resin is within the above numerical range, the difference with the SP value of a solvent (e.g., a polar solvent such as DMF) used in a wet film-forming method or the like can be reduced, making it easier to dissolve the polyurethane resin in the solvent.

The absolute value of the difference between the SP value of the polyurethane resin and the SP value of a solvent (polar solvent) described below, |(SP value of polyurethane resin)-(SP value of solvent)|, is not particularly limited, but is preferably less than 1.5 (cal/ ^cm3 ) ^1/2 . When the absolute value of the difference is less than 1.5 (cal/ ^cm3 ) ^1/2 , the polyurethane resin becomes more easily dissolved in the solvent.

The content of polyurethane resin in the entire polishing layer is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more. The content of polyurethane resin in the entire polishing layer is not particularly limited, but can be 99% by mass or less. The above numerical ranges for the content of polyurethane resin can be combined in any way.

(Polishing layer)
The roughly teardrop-shaped bubbles in the polishing layer are anisotropic and have a vertically elongated bubble structure extending from the polishing surface to the opposite surface.

The bubbles in the polishing layer may include or consist of the above-mentioned approximately teardrop-shaped bubbles and the bubbles derived from the porous microparticles.
The teardrop-shaped bubbles are surrounded by small communicating pores that are interconnected in a three-dimensional network. The bubbles derived from the porous microparticles are independent bubbles that do not communicate with the communicating pores.
The average void diameter of the bubbles in the polishing layer (for example, the average void diameter of the bubbles including the approximately teardrop-shaped bubbles and the bubbles derived from the porous microparticles) is not particularly limited, but is preferably 10 to 70 μm, and can also be 15 to 60 μm, 20 to 50 μm, or 25 to 40 μm. When the average void diameter of the bubbles is within the above numerical range, the rigidity of the polishing layer can be maintained, and the wear resistance of the polishing layer can be improved.

The average void diameter of the air bubbles in the polishing layer can be measured according to the method and procedure described in Evaluation Method 1 in the Examples below.

The density of the polishing layer is not particularly limited, but is preferably 0.30 to 0.70 g/cm ³ , and more preferably 0.40 to 0.60 g/cm ³ .

The compression rate of the polishing layer is not particularly limited, but is preferably 0.1 to 10%, and more preferably 0.5 to 7.0%. If the compression rate is within the above numerical range, deformation of the polishing layer is suppressed and the polishing characteristics are less likely to change, improving the polishing rate.

The compressive elastic modulus of the polishing layer is not particularly limited, but is preferably 70 to 100%, and more preferably 80 to 95%. If the compressive elastic modulus is within the above numerical range, the polishing layer has appropriate elasticity and improves topography performance.

The Shore A hardness of the polishing layer is not particularly limited, but is preferably 35 to 70°, and more preferably 40 to 60°. If the Shore A hardness is within the above numerical range, the polishing characteristics are less likely to change as polishing progresses, and the polishing rate improves.

The tensile strength of the polishing layer is not particularly limited, but is preferably 0.1 to 1 kg/mm ^2. When the tensile strength is within the above numerical range, the abrasion resistance of the polishing layer is improved.

The elongation of the polishing layer is not particularly limited, but is preferably 200 to 600%, and more preferably 300 to 500%. If the elongation is within the above numerical range, the polishing layer becomes appropriately flexible, improving its ability to conform to the workpiece being polished and improving topography performance.

The tear strength of the polishing layer is not particularly limited, but is preferably 0.5 to 3.0 kg/mm, and more preferably 0.5 to 2.0 kg/mm. If the tear strength is within the above numerical range, the abrasion resistance of the polishing layer is improved, and the product life can be improved.

The density, compressibility, compressive modulus, Shore A hardness, tensile strength, elongation, and tear strength of the polishing layer can be measured according to the method and procedure described in Evaluation Method 1 in the Examples below.

The polishing rate of the polishing pad is not particularly limited, but is preferably 520 Å or more, more preferably 530 Å or more, and most preferably 540 Å or more. The polishing rate is also not particularly limited, but can be 1000 Å or less, 800 Å or less, or 700 Å or less. The above numerical ranges regarding the polishing rate can be combined arbitrarily.
The polishing rate of the polishing layer can be measured based on the method and procedure described in <Evaluation Method 2> in the Examples below.

The polishing pad may have one type of support member selected from flexible films such as polyethylene terephthalate (hereinafter abbreviated as PET), nonwoven fabrics, and woven fabrics on the side (lower side) opposite the polishing surface of the polishing layer. A double-sided tape is attached to the lower side of the support member, which has release paper on the other side (lowest side) for mounting the polishing pad to the polishing table.

2. Method for Producing a Polishing Pad The method for producing a polishing pad of the present invention is the method for producing the above-mentioned polishing pad, and includes a step of using a wet film-forming method.
The components of the polishing pad in the method for producing the polishing pad can be the same as those described in "1. Polishing pad" above.

The polishing pad can be manufactured by a wet film-forming method, for example, a method including a step of preparing a polyurethane resin solution in which a polyurethane resin, a polar solvent, and porous fine particles are mixed and dispersed, a step of applying the polyurethane resin solution to a substrate, and a step of coagulating and regenerating the polyurethane resin by immersing the substrate to which the polyurethane resin solution has been applied in a coagulating liquid.

(1) Step of preparing a polyurethane resin solution As the polyurethane resin, the polyurethane resin described above in "1. Polishing pad" can be used.
The concentration of the polyurethane resin in the polyurethane resin solution is, for example, 10 to 50% by mass, preferably 20 to 40% by mass. Within this concentration range, the sheet density can be adjusted to an appropriate range, and a desired foam structure can be formed.

The polar solvent is not particularly limited, but may contain or consist of DMF, DMAc, THF, DMSO, NMP, acetone, or a mixture of two or more of these. Among these, DMF is preferred from the viewpoint of excellent solubility of polyurethane resin.
The SP value of the polar solvent is not particularly limited, but is preferably 9 to 13 (cal/cm ³ ) ^1/2 , and more preferably 10 to 13 (cal/cm ³ ) ^1/2 . When the SP value of the polar solvent is in the above numerical range, the difference with the SP value of the polyurethane resin or the SP value of the porous microparticles can be controlled within an appropriate range.
When DMF is used, DMF, which is a good solvent for polyurethane resin, can be mixed with water at any ratio, so that the replacement speed with the coagulation liquid (water) is fast, and the DMF on the lower layer (substrate side) side of the polyurethane resin solution moves quickly to the upper layer (surface layer) side, and relatively large bubbles (bubbles elongated in the sheet thickness direction) are easily formed on the lower layer side. This allows the formation of approximately teardrop-shaped bubbles in the polishing layer.

The porous microparticles to be mixed and dispersed in the polyurethane resin can be the porous microparticles described in "1. Polishing pad" above.

The absolute value of the difference between the SP value of the polyurethane resin and the SP value of the solvent (polar solvent), and the absolute value of the difference between the SP value of the porous microparticles and the SP value of the solvent (polar solvent) can be within the numerical ranges described above in "1. Polishing pad."

The polyurethane resin solution may further contain additives as necessary. The additives are not particularly limited, but from the viewpoint of adjusting the coagulation speed of the polyurethane resin to form the desired foam shape in the coagulation regeneration process of the polyurethane resin, pigments such as carbon black, hydrophobic activators, and hydrophilic activators are preferred. These additives can be used alone or in combination of two or more. The amount of additives is not particularly limited, and is, for example, 30 parts by mass or less, preferably 20 parts by mass or less (for example, 1 to 15 parts by mass) per 100 parts by mass of the urethane resin-containing solution. However, it is preferable not to use additives such as carbon black, which may cause defects.

(2) Polyurethane Resin Solution Coating Process The substrate used in the polyurethane resin solution coating process may be any flexible material, and examples thereof include plastic films (e.g., polyester films, polyolefin films, etc.), nonwoven fabrics, etc. The method for coating the substrate with the polyurethane resin-containing solution is not particularly limited, and examples thereof include coating methods using a conventional coater (knife coater, reverse coater, roll coater, etc.). The coating thickness is, for example, 0.5 to 2.5 mm, preferably 1.0 to 2.0 mm, and more preferably 1.2 to 1.8 mm, from the viewpoint of forming a predetermined foam structure.

(3) Polyurethane Resin Coagulation Regeneration Process In the polyurethane resin coagulation regeneration process, the coagulation liquid in which the substrate coated with the polyurethane resin solution is immersed is mainly composed of a poor solvent for polyurethane resin (water, etc.). Examples of the coagulation liquid include water and a mixed solution of water and a polar solvent (e.g., DMF, DMAc, THF, DMSO, NMP, acetone, etc.). The concentration of the polar solvent in the mixed solution is preferably 0.5 to 30 mass%.

The polyurethane resin coagulation and regeneration process results in a polyurethane foam sheet coagulated on the substrate. The method for producing a polishing pad of the present invention may further include a process of peeling the polyurethane foam sheet obtained by coagulation on the substrate from the substrate, if necessary, and then washing and drying the polyurethane foam sheet.

(4) Washing and drying process of polyurethane resin By washing and drying, the polar solvent and coagulation liquid (water) remaining in the polyurethane resin are removed. Water is usually used as the washing liquid for washing. Drying is usually performed at 80 to 150°C for about 5 to 60 minutes.

The manufacturing method of the polishing pad of the present invention may further include grinding the front surface or the front surface and back surface, and may also include surface treatments such as groove processing by cutting or embossing, if necessary.

The method of grinding (buffing) is not particularly limited, and examples include a method using sandpaper. The surfaces to be ground (buffed) may be either the polished surface (surface on the surface layer side) or the non-polished surface (surface on the side to which the platen is attached), or both. The amount of grinding (buffing) is, for example, 0.05 to 0.3 mm, preferably 0.1 to 0.2 mm, depending on the desired surface shape. This forms openings due to polyurethane foam and openings due to air bubbles in the porous microparticles in the surface layer of the polishing pad, and also makes the thickness of the sheet uniform.

In groove processing and embossing, the processing temperature and processing pressure are not particularly limited, but the processing temperature is, for example, 100 to 200°C, preferably 120 to 180°C, and the processing pressure is, for example, 3 to 6 MPa, preferably 4 to 5 MPa. The processing time is also not particularly limited, but is, for example, 30 to 300 seconds, preferably 60 to 180 seconds.

The recesses formed by groove processing or embossing may be formed randomly, or may be formed regularly (e.g., in a lattice, concentric, radial, or honeycomb pattern). The width of the recesses is, for example, 0.3 to 3.0 mm, preferably 0.5 to 1.5 mm, and more preferably 0.8 to 1.2 mm. The average center-to-center distance between adjacent recesses is, for example, 1 to 100 mm, and preferably 2 to 20 mm. This can promote the supply and discharge of slurry to and from the surface layer side of the polishing pad.

The polishing layer obtained as described above can be attached to the opposite side (lower side) of the polishing surface with the support member described above to produce a polishing pad.

3. Method for polishing a surface of an optical material or a semiconductor material The method for polishing a surface of an optical material or a semiconductor material of the present invention includes a step of using the polishing pad described above.
The respective components of the polishing pad in the above polishing method can be the same as those described in "1. Polishing pad" above.

The optical material or semiconductor material to be polished is not particularly limited, but a device having an oxide layer, metal layer, etc. formed on a semiconductor wafer is particularly preferred.
The step of using the polishing pad described above may further include a step of finish polishing an optical material or a semiconductor material.

The above-mentioned step of using polishing pad can further include the step of using polishing slurry (slurry).When using polishing slurry, the part of the porous structure in the porous microparticles acts as minute openings, so it can hold more slurry and show high polishing rate.
The polishing slurry preferably contains an abrasive component. The liquid component contained in the polishing slurry is not particularly limited, but includes water, acid, alkali, organic solvent, etc., and is selected according to the material of the object to be polished and the desired polishing conditions. The abrasive component contained in the polishing slurry is not particularly limited, but includes silica, zirconium silicate, cerium oxide, aluminum oxide, manganese oxide, etc. The polishing slurry may contain other components such as organic matter soluble in the liquid component and pH adjuster.

The present invention will be described experimentally by the following examples, but the following description is not intended to limit the scope of the present invention to the following examples.

(material)
The materials used in Examples 1 to 3 and Comparative Examples 1 to 3 described below are listed below.

・Polyurethane resin:
Polyurethane resin (1)...ester-based polyurethane resin (manufactured by DIC Corporation, product name "UW-2", solid content concentration 30 mass%, SP value: 10 to 12 (cal/cm ³ ) ^1/2 , 100% resin modulus: 6 MPa)

·solvent:
DMF...N,N-dimethylformamide (SP value: 12.1 (cal/cm ³ ) ^1/2 )

・Fine particles:
Porous microparticles (1)...Techpolymer (registered trademark) manufactured by Sekisui Plastics Co., Ltd. (composition: cross-linked polymethyl methacrylate, structure: porous, SP value: 9.0-9.5 (cal/cm ³ ) ^1/2 , specific surface area: 85 m ² /g, average particle size: 6-10 μm, pore size: 100 nm, CV value: 15%)
Porous microparticles (2)...Techpolymer (registered trademark) manufactured by Sekisui Plastics Co., Ltd. (composition: cross-linked polystyrene, structure: porous, SP value: 8.5 to 9.0 (cal/cm ³ ) ^1/2 , specific surface area: 85 m ² /g, average particle size: 6 to 10 μm, pore size: 100 nm, CV value: 20%)
Hollow microparticles (1)...Expancel (registered trademark) 461DU20 (manufactured by Nippon Phillite Co., Ltd.) (shell composition: acrylonitrile-vinylidene chloride copolymer, structure: hollow, SP value: 12 to 12.5 (cal/cm ³ ) ^1/2 , average particle size in unexpanded state: 6 to 9 μm)
Hollow microparticles (2)...Techpolymer (registered trademark) manufactured by Sekisui Plastics Co., Ltd. (shell composition: cross-linked polymethyl methacrylate, structure: hollow, SP value: 9.0 to 9.5 (cal/cm ³ ) ^1/2 , specific surface area: 0.8 m ² /g, average particle size: 6 to 10 μm)

In this embodiment, the 100% resin modulus means the value obtained by dividing the load applied when a non-foamed resin sheet is stretched 100% (stretched twice its original length) by the cross-sectional area. The 100% resin modulus was obtained by thinly spreading the resin solution and drying it with hot air to produce a dry film with a thickness of about 200 μm, and then curing the film for a while. After that, a sample was punched out into a dumbbell shape with a total length of 90 mm, width at both ends of 20 mm, distance between grippers of 50 mm, parallel width of 10 mm, and thickness of 200 μm. The measurement sample was clamped between the upper and lower air chucks of a universal material testing machine Tensilon (Tensilon universal testing machine "RTC-1210" manufactured by A&D Co., Ltd.) and pulled at a pulling speed of 100 mm/min in an atmosphere of 20°C (±2°C) and humidity of 65% (±5%), and the tension at 100% elongation (when stretched twice) was divided by the initial cross-sectional area of the sample.

Example 1
A resin-containing solution containing 100 parts by mass of the polyurethane resin (1), 3.4 parts by mass of the porous fine particles (1), and 20 parts by mass of a solvent (DMF) was obtained.

Next, prepare a PET film as a film-forming substrate, apply the above-mentioned resin-containing solution to a thickness of 1.0 mm using a knife coater, immerse in a coagulation bath (coagulation liquid: water), coagulate the above-mentioned resin-containing solution, wash and dry it, and then peel it off from the PET film to obtain a resin film (thickness 1.0 mm). Grind the skin layer side formed on the surface of the obtained resin film (grinding amount: 200 μm). Then, emboss a part of the resin film with a lattice-shaped mold, and attach a double-sided adhesive tape to the back side of the resin film (polishing layer) to obtain a polishing pad.
In the resulting polishing pad, the contents of the polyurethane resin (solid content) and the fine particles in the polishing layer were calculated to be 90% by mass and 10% by mass, respectively.

Example 2
A resin-containing solution was obtained in the same manner as in Example 1, except that the amount of the porous fine particles (1) in Example 1 was changed from 3.4 parts by mass to 7.5 parts by mass. Then, using the resin-containing solution, the formation of a resin film, grinding treatment, and embossing were performed in the same manner as in Example 1, to obtain a polishing pad of Example 2.
In the resulting polishing pad, the contents of the polyurethane resin (solid content) and the fine particles in the polishing layer were calculated to be 80% by mass and 20% by mass, respectively.

Example 3
A resin-containing solution was obtained in the same manner as in Example 1, except that 3.4 parts by mass of the porous fine particles (2) were used instead of 3.4 parts by mass of the porous fine particles (1) in Example 1. Then, using the resin-containing solution, resin film formation, grinding treatment, and embossing were performed in the same manner as in Example 1, to obtain a polishing pad of Example 3.
In the resulting polishing pad, the contents of the polyurethane resin (solid content) and the fine particles in the polishing layer were calculated to be 90% by mass and 10% by mass, respectively.

(Comparative Example 1)
A resin-containing solution was obtained in the same manner as in Example 1, except that 3.4 parts by mass of the porous fine particles (1) of Example 1 was not added and fine particles were not used. Then, using the resin-containing solution, the formation of a resin film, grinding treatment, and embossing were performed in the same manner as in Example 1, to obtain a polishing pad of Comparative Example 1.

(Comparative Example 2)
A resin-containing solution was obtained in the same manner as in Example 1, except that 3.4 parts by mass of the hollow fine particles (1) were used instead of 3.4 parts by mass of the porous fine particles (1) in Example 1. Then, using the resin-containing solution, resin film formation, grinding treatment, and embossing were performed in the same manner as in Example 1, to obtain a polishing pad of Comparative Example 2.

(Comparative Example 3)
A resin-containing solution was obtained in the same manner as in Example 1, except that 3.4 parts by mass of the hollow fine particles (2) were used instead of 3.4 parts by mass of the porous fine particles (1) in Example 1. Then, using the resin-containing solution, resin film formation, grinding treatment, and embossing were performed in the same manner as in Example 1, to obtain a polishing pad of Comparative Example 3.
In the resulting polishing pad, the contents of the polyurethane resin (solid content) and the fine particles in the polishing layer were calculated to be 90% by mass and 10% by mass, respectively.

Cross-sectional photographs of the polishing pads obtained in Examples 1 and 2 and Comparative Examples 1 and 3 taken with a scanning electron microscope (JSM-5000LV, manufactured by JEOL Ltd.) are shown in FIGS.
Figures 1 and 2 are cross-sectional photographs of the polishing pad of Example 1 measured at magnifications of 100 and 500 times, respectively. Figures 3 and 4 are cross-sectional photographs of the polishing pad of Example 2 measured at magnifications of 100 and 500 times, respectively. Figures 5 and 6 are cross-sectional photographs of the polishing pad of Comparative Example 1 measured at magnifications of 100 and 500 times, respectively. Figures 7 and 8 are cross-sectional photographs of the polishing pad of Comparative Example 3 measured at magnifications of 100 and 500 times, respectively.

<Evaluation Method 1>
The resin film (polishing layer) contained in each of the polishing pads of Examples 1 to 3 and Comparative Examples 1 to 3 obtained as described above was measured for the following: density, compressibility, compressive modulus, Shore A hardness, tensile strength, elongation, tear strength, and average void diameter of the bubbles and microparticle bubbles due to foaming of polyurethane, and the results in Table 1 were obtained.

(density)
The density was measured by cutting a resin film sample (10 cm×10 cm) from the resin film constituting the polishing pad, measuring the mass of the sample using an automatic balance, and then calculating the mass using the following formula:
Density (g/cm ³ )=mass (g)/(10 (cm)×10 (cm)×thickness of sample piece (cm))
The calculation was carried out as follows.

(Compressibility), (Compressive elastic modulus)
The compressibility and compressive elastic modulus were determined in accordance with JIS L 1021. Specifically, a resin film sample piece (10 cm x 10 cm) was cut out from the resin film constituting the polishing pad, and the thickness t ₀ was measured after applying an initial load for 30 seconds from a no-load state at room temperature, and then the thickness t ₁ was measured after applying a final load for 5 minutes from the thickness t ₀ state. Next, all loads were removed from the thickness t ₁ state, and after leaving it for 5 minutes (to make it a no-load state), the thickness t _{0 '} was measured after applying the initial load again for 30 seconds.
The compression ratio was calculated by the formula: Compression ratio (%) = 100 × (t ₀ - _{t 1} ) / t ₀ , and the compression modulus was calculated by the formula: Compression modulus (%) = 100 × (t _0' - t ₁ ) / (t ₀ - t ₁ ). At this time, the initial load was 100 g/cm ² , and the final pressure was 1120 g/cm ² .

(Shore A hardness)
The Shore A hardness was measured by cutting a resin film sample (10 cm x 10 cm) from the resin film constituting the polishing pad, stacking multiple sample pieces to a thickness of 4.5 mm or more, and using a type A hardness tester (Japanese Industrial Standards, JIS K7311).

(Tensile strength), (Elongation)
A dumbbell shape (length 9 cm, width 2 cm, width of constricted part 1 cm) was punched out from the resin film constituting the polishing pad, the measurement sample was clamped between the upper and lower air chucks of the measuring machine, the measurement was started at a pulling speed of 100 mm/min and an initial gripping distance of 50 mm, and the value at which the measured value reached a peak (break) was taken as the strength (maximum load). The elongation at which the measurement sample broke (fractured) was taken as the elongation.
The above measurements were carried out twice, and the breaking strength was calculated from the formula: breaking strength (kgf/ ^mm2 ) = strength (maximum load) kgf/(thickness (mm) x sample width (10 mm)), and the breaking strength (tensile strength) was calculated from the average value. The elongation was also calculated as an average value. The sample thickness was measured using a thickness gauge when the measurement sample was attached to the chuck, and calculated using the dimension table.
The tensile strength and elongation were measured using a Tensilon universal testing machine RTC manufactured by A&D Co., Ltd. according to the method of Japanese Industrial Standards (JIS K6550).

(Tear strength)
A resin film sample (100 mm x 25 mm) was cut out from the resin film constituting the polishing pad. A 70 mm cut was made from the longitudinal end in the width direction center of the obtained sample, and two points 25 mm along the cut from the end of the cut in the sample were clamped and fixed with a jig, and the two points were pulled in opposite directions along the cut (one of the two points was rotated 180 degrees relative to the other) with a universal material testing machine Tensilon (manufactured by A&D Co., Ltd., Tensilon type universal testing machine RTC-1210), and the measurement was performed until the sample broke, and the strength (maximum load) kg at which the measured value peaked was obtained. Then, the following formula:
Tear strength (kg/mm) = strength (maximum load) kg/thickness (mm)
The tear strength was determined by the following.

(Average void diameter of bubbles produced by foaming polyurethane and bubbles produced by fine particles)
The average void diameter of the bubbles due to foaming of polyurethane and the bubbles of fine particles was observed at 9 points by enlarging the cross section of a resin film sample piece (10 cm x 10 cm) obtained in the same manner as above (Shore A hardness) by 500 times with a scanning electron microscope (JSM-5000LV, manufactured by JEOL Ltd.) in an area of about 5 mm square. The image was binarized using image processing software (Image Analyzer V20LAB Ver.1.3, manufactured by Nikon Corporation) to confirm the total number of voids (bubbles including bubbles due to foaming of polyurethane and bubbles of fine particles) present in the sample, and the circle equivalent diameter and its average value were calculated as the average void diameter from the void area of each void. Note that for parts where fine particles could not be identified by the binarization process, correction can be made with a freehand tool so that the outline of the fine particles can be identified. In the measurement of the void diameter, the cutoff value (lower limit) of the void diameter was set to 4 μm, and noise components were excluded. The voids referred to here include both bubbles formed by foaming of polyurethane and bubbles formed by fine particles.

<Evaluation Method 2>
In addition, the polishing pads of Examples 1 to 3 and Comparative Examples 1 to 3 obtained as described above were polished under the following polishing conditions, and the polishing rate and topography performance (polishing uniformity) were measured and evaluated, and the results shown in Table 1 were obtained. When using the polishing pad, the polishing pad was attached to the polishing platen of the polishing machine so that the polishing surface of the polishing layer faces the object to be polished. Then, while supplying slurry to the polishing surface of the polishing pad, the polishing platen was rotated to polish the processed surface of the object to be polished.

The workpiece to be polished was a 12-inch silicon wafer with an insulating film formed by CVD of tetraethoxysilane to a thickness of 1 μm (uniformity (CV%): 13%). 25 substrates were polished in sequence.

(Polishing conditions)
Grinding machine: EBARA F-REX300
Polishing head: GII
Slurry: Planar Slurry (colloidal silica, pH: 9.7)
Workpiece to be polished: 300mmφSIO2 (TEOS)
Pad diameter: 740mmφ
Pad break: 9N x 30 min, diamond dresser 54 rpm, platen rotation speed 80 rpm
Polishing pressure: 175 hPa
Ultrapure water: 200ml/min
Polishing: Platen rotation speed 70 rpm, head rotation speed 71 rpm, slurry flow rate 200 ml/min, polishing time 60 seconds

(Polishing rate)
The polishing rate is the amount of polishing per minute expressed in thickness (Å). For the 25 polished substrates, the insulating film of each substrate was measured at 17 locations before and after polishing, and the average value for all 25 substrates was calculated. The thickness was measured using an optical film thickness and film quality measuring instrument (KLA Tencor Corporation, ASET-F5x) in DBS mode.

(Topography Performance)
Using a step, surface roughness, and micro-shape measuring device (KLA Tencor Corporation, P-16+), the step between the metal wiring and the oxide film wiring on the polished substrate was measured, and the topography performance was evaluated according to the criteria of "good: ◯, poor: ×". If the topography performance is evaluated as good, a flat topography has been achieved.

From the results in Table 1, it was found that the polishing pads of Examples 1 to 3 had high polishing rates and excellent topography performance. Also, from Figures 1 to 4, it was confirmed that in the polishing layers of the polishing pads of Examples 1 and 2, both bubbles (approximately teardrop-shaped bubbles, large black parts in Figures 1 to 4) due to foaming of polyurethane in the wet film-forming method and bubbles of porous microparticles (small black parts in Figures 1 to 4) were formed. Furthermore, from a comparison of Figures 1 and 2 for Example 1 with Figures 3 and 4 for Example 2, it was confirmed that the number of bubbles of the porous microparticles increased when the amount of the porous microparticles added was increased.
The porous microparticles used in Examples 1 to 3 have a porous structure and have a larger surface area than the hollow microparticles used in Comparative Examples 2 and 3. It is presumed that the porous structure of such porous microparticles acts as minute openings on the surface (polishing surface) of the polishing layer, allowing more slurry to be held, and therefore the polishing pads of Examples 1 to 3 using the porous microparticles exhibited high polishing performance.

On the other hand, the polishing pads of Comparative Examples 1 to 3 were found to have a low polishing rate and poor topography performance.

5 and 6, it was confirmed that in the polishing layer of the polishing pad of Comparative Example 1, which does not contain microparticles, bubbles are formed due to foaming of polyurethane in the wet film-forming method, but no bubbles are formed due to the microparticles.
The polishing pad of Comparative Example 1, unlike the polishing pads of Examples 1 to 3, does not have voids in the porous microparticles, and therefore the amount of slurry that can be held on the surface (polishing surface) of the polishing layer is small, which is thought to result in inferior polishing performance.
5 and 6, a number of small bubbles are present among the teardrop-shaped bubbles, but these bubbles are also formed by the wet film-forming method and are hollow voids. The voids are interconnected pores, and therefore the slurry retention is low.

Furthermore, it was confirmed that in the polishing layer of the polishing pad of Comparative Example 2, bubbles were formed due to foaming of polyurethane in the wet film-forming method, but bubbles of hollow fine particles were not formed.
In Comparative Example 2, the difference between the SP value of the solvent (DMF) used in wet film-forming method and the SP value of hollow fine particles is small.Therefore, in Comparative Example 2, hollow fine particles are dissolved in the solvent and do not remain in the polishing layer, so it is considered that the bubbles of hollow fine particles are not formed.In this way, in Comparative Example 2, the bubbles of hollow fine particles are not formed, so it is considered that the polishing performance is inferior.

7 and 8, it was confirmed that in the polishing layer of the polishing pad of Comparative Example 3, both bubbles due to foaming of polyurethane in the wet film-forming method and bubbles of hollow fine particles were formed.
The hollow fine particles used in Comparative Example 3 do not have a porous structure, unlike the porous fine particles used in Examples 1 to 3. Therefore, the amount of slurry that can be held on the surface of the hollow fine particles is small, and it is considered that the polishing performance of the polishing pad of Comparative Example 3 was inferior.

These results confirm that polishing pads that contain polyurethane resin and porous microparticles and have a polishing layer with roughly teardrop-shaped bubbles have a high polishing rate and excellent topography performance.

Claims (9)

A polishing pad having a polishing layer,
The polishing pad, wherein the polishing layer contains a polyurethane resin and porous fine particles and has approximately teardrop-shaped bubbles. 2. The polishing pad according to claim 1, wherein the porous fine particles have a specific surface area of 1 to 1000 m ² /g. The polishing pad according to claim 1 or 2, wherein the porous microparticles have an average particle size of 1 to 20 μm. The polishing pad according to claim 1 or 2, wherein the pore diameter of the porous microparticles is 2 to 1000 nm. The polishing pad according to claim 1 or 2, wherein the porous microparticles include particles of a polymer selected from the group consisting of polymethylmethacrylate, polystyrene, and mixtures thereof. The polishing pad according to claim 1 or 2, wherein the content of the porous microparticles in the entire polishing layer is 1 to 30 mass %. The polishing pad according to claim 1 or 2, wherein the average void diameter of the bubbles in the polishing layer is 10 to 70 μm. A method for producing the polishing pad according to claim 1 or 2, comprising a step of using a wet film forming method. A method for polishing a surface of an optical material or a semiconductor material, the method comprising a step of using the polishing pad according to claim 1 or 2.