JP2007091898A - Foamed resin and polishing pad using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad which has a homogeneous foam structure and can improve the smoothness and the smoothing efficiency for a surface to be polished, wherein the change of hardness during a polishing work is small (particularly the change of hardness according to the change of the temperature during the polishing work is small). <P>SOLUTION: The foamed resin comprises mainly thermoplastic polyurethane which is obtained by reacting a polymer diol, an organic diisocyanate and a chain extender at a ratio of mass parts of the polymer diol/(the total mass parts of the organic diisocyanate and the chain extender) of 10/90-35/65. The polymer diol has a number average molecular weight of 400-2,000, 50 mol% or more of the polymer diol is a dimer diol having a carbon number of 30-42, 50 mol% or more of the chain extender is 1,4-cyclohexane dimethanol, and the nitrogen atom content originated from the organic diisocyanate of the thermoplastic polyurethane is 5-7 mass%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a resin foam having a highly uniform foam structure and a polishing pad made of the foam. The polishing pad of the present invention is particularly useful for applications in which a semiconductor wafer or the like is polished with high accuracy and high efficiency.

  As a polishing pad used for mirror processing of a semiconductor wafer used as a base material for forming an integrated circuit, a fiber-resin composite material such as velor tone or suede tone, or a thermoplastic polyurethane resin is generally used. A relatively flexible sheet having a large compressive deformation characteristic, which is impregnated into a nonwoven fabric and wet-solidified, has been frequently used.

  In recent years, semiconductor wafers have been increasingly demanded for lower prices in addition to higher quality such as higher integration of semiconductor elements (devices) and higher flatness accompanying multilayer wiring. Along with this, there is a demand for higher functionality, such as enabling flattening more than ever for polishing pads for polishing semiconductor wafers. Furthermore, it must be usable for a long time.

  Conventional non-woven type polishing pads with relatively high flexibility have good contact properties with semiconductor wafers and good retention of polishing slurries. Cannot be achieved. In addition, polishing slurry and polishing scraps clog the voids in the nonwoven fabric, which tends to damage the wafer surface. In addition, the polishing slurry and polishing scraps are easily clogged, and if they penetrate deeply into the gap, it is difficult to clean them, and there is a problem that the usage time of the polishing pad is short.

  On the other hand, polishing pads using polymer foam are also known, and since they are more rigid than non-woven type polishing pads, they are often used for applications that require surface flattening such as polishing of semiconductor wafers. Yes. In addition, since the polishing pad using the polymer foam has a closed cell structure, the polishing slurry and polishing debris do not penetrate into the back of the gap unlike the nonwoven type polishing pad, so that the polishing pad can be cleaned relatively easily. It can withstand long-term use. As the polymer foam, foamed polyurethane is often used because it is particularly excellent in wear resistance.

  This polishing pad is usually manufactured by appropriately grinding or slicing foamed polyurethane. Also, foamed polyurethane for polishing pads has been conventionally produced by cast foam curing using a two-component curable polyurethane (see Patent Documents 1 to 4 below). However, in this method, it is difficult to make the reaction and foam uniform, and there is a limit to increasing the hardness of the resulting polyurethane foam. In addition, with conventional foamed polyurethane polishing pads, the polishing characteristics such as the flatness and planarization efficiency of the surface to be polished may fluctuate. This is due to variations in the foamed structure of the original polyurethane foam. It is thought to be the cause. Recently, as described in Non-Patent Document 1, for example, a polishing pad with higher hardness is desired in order to increase planarization efficiency.

  Made of a specific polyurethane using 1,4-cyclohexanedimethanol as a chain extender as a polishing pad that can improve the flatness of the surface to be polished, flattening efficiency, etc. A polishing pad using a polyurethane foam is known (see Patent Document 5 below). When polishing with a polishing pad, clogging of the fine holes on the polishing pad surface and deformation or wear of the polishing pad that occur during the polishing operation deteriorate the polishing rate, flatness and uniformity of the surface to be polished, etc. A process called dressing is performed constantly or periodically. The “dressing” is an operation of scraping the surface of the polishing pad using a diamond grindstone, and the dressing process ensures the polishing ability and maintains the reproducible polishing characteristics. However, the surface formed on the surface of the polishing pad by this dressing treatment is not necessarily in the initial state of polishing, and foam holes are deformed or crushed, resulting in lack of stability of polishing characteristics. Existing polishing pads are required to have higher performance such as stability of such polishing characteristics and improvement of in-plane uniformity of the surface to be polished when the number of polishing is repeated.

JP 2000-178374 A JP 2000-248034 A JP 2001-89548 A Japanese Patent Laid-Open No. 11-322878 JP 2004-35669 A U.S. Pat. No. 4,473,665 JP-A-6-322168 JP-A-8-11190 Japanese Patent Laid-Open No. 10-36547 JP 2000-169615 A JP 2000-248101 A Masahiro Kusunoki et al., “CMP Science”, Science Forum, Inc., August 20, 1997, p.113-119

  The present invention has been made in view of the above circumstances, and has a uniform foamed structure, and when applied to a polishing pad, can improve the flatness and planarization efficiency of the surface to be polished. The object is to provide a foam. It is another object of the present invention to provide a resin foam capable of providing a polishing pad with a small change in hardness during the polishing operation, particularly a polishing pad with a small change in hardness against temperature fluctuations during the polishing operation. It is another object of the present invention to provide a polishing pad that does not adversely affect polishing performance (polishing rate, flatness) during polishing.

  As a result of repeated studies to achieve the above object, the present inventors have found that the above problems can be solved by a resin foam mainly composed of a specific polyurethane, and have completed the present invention.

That is, the present invention
(1) A resin foam mainly composed of thermoplastic polyurethane, having a density of 0.4 to 0.95 g / cm ³ and a cell size of 1 to 100 μm,
The thermoplastic polyurethane reacts with a polymer diol, an organic diisocyanate, and a chain extender at a ratio of mass of polymer diol / (total mass of organic diisocyanate and chain extender) of 10/90 to 35/65. Is obtained by
The number average molecular weight of the polymer diol is 400 to 2000,
50 mol% or more of the polymer diol is a dimer diol having 30 to 42 carbon atoms,
More than 50 mol% of the chain extender is 1,4-cyclohexanedimethanol,
The present invention relates to a resin foam having a nitrogen atom content of 5 to 7% by mass derived from the organic diisocyanate of the thermoplastic polyurethane.

The present invention also provides:
(2) The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane is 2 × 10 ⁸ Pa to 2 × 10 ⁹ Pa, and the storage elastic modulus at 30 ° C. of the thermoplastic polyurethane (E ′ ₃₀ ) and the storage elastic modulus (E ′ ₈₀ ) at 80 ° C. (E ′ ₃₀ / E ′ ₈₀ ) is 1 to 4 and relates to the resin foam described in (1) above.

The present invention also provides:
(3) The resin foam according to (1) or (2) above, wherein the dimer diol has 36 carbon atoms.

The present invention also provides:
(4) The above-mentioned (3), wherein the dimer diol is obtained by reducing dimer acid obtained by heat-polymerizing at least one selected from the group consisting of oleic acid, linoleic acid and linolenic acid. The resin foam described in 1. above.

The present invention also provides:
(5) A non-reactive gas is dissolved in a polyurethane resin composition composed of thermoplastic polyurethane or mainly thermoplastic polyurethane under heating and pressure conditions, then cooled to 50 ° C. or lower, and then the pressure is released. In any one of the above (1) to (4), a polyurethane resin composition comprising a thermoplastic polyurethane in which a non-reactive gas is dissolved or mainly a thermoplastic polyurethane is obtained and then heated and foamed. Resin foam.

The present invention also provides:
(6) The resin foam according to (5), wherein the non-reactive gas is carbon dioxide or nitrogen.

The present invention also provides:
(7) It is related with the polishing pad containing the resin foam in any one of said (1) thru | or (6).

  According to a preferred aspect of the present invention, it is possible to provide a resin foam having a uniform foam structure, high hardness, and low hardness temperature dependence, and a polishing pad having the resin foam. The polishing pad according to a preferred embodiment of the present invention is useful for chemical mechanical polishing (hereinafter sometimes abbreviated as CMP), and can polish a semiconductor wafer or the like with high accuracy and high efficiency. In particular, the polishing pad according to the preferred embodiment of the present invention can improve the flatness and flattening efficiency of the surface to be polished as compared with the prior art, and can extend the use time as compared with the conventional one.

Hereinafter, the present invention will be described in more detail.
The resin foam of the present invention is mainly composed of thermoplastic polyurethane. And the density of the resin foam of this invention is 0.4-0.95 g / cm < ³ >, and bubble size is 1-100 micrometers.

  The thermoplastic polyurethane used in the present invention has a polymer diol, an organic diisocyanate, and a chain extender, and the mass of the polymer diol / (total mass of the organic diisocyanate and the chain extender) is 10/90 to 35/65. It is obtained by reacting at a ratio. The number average molecular weight of the polymer diol is 400 to 2000, 50 mol% or more of the polymer diol is a dimer diol having 30 to 42 carbon atoms, and 50 mol% or more of the chain extender is 1,4-cyclohexanediol, and the content of nitrogen atoms derived from the organic diisocyanate in the thermoplastic polyurethane is 5 to 7% by mass.

  The thermoplastic polyurethane can be obtained by reacting a polymer diol, an organic diisocyanate and a chain extender.

  The polymer diol used in the production of the thermoplastic polyurethane used in the present invention is a dimer diol having 30 to 42 carbon atoms in 50 mol% or more. When the polymer diol contains 50 mol% or more of the dimer diol having 30 to 42 carbon atoms, the temperature dependency of the hardness of the obtained thermoplastic polyurethane is reduced, and the hardness of the resin foam is also less temperature dependent. It is difficult for the flatness of the surface to be polished and the polishing efficiency to decrease during work. In addition, the thermoplastic polyurethane obtained has improved water resistance, acid resistance, alkali resistance, etc., and even in resin foam, the water resistance, acid resistance, alkali resistance, etc. are improved due to the influence of the slurry during polishing work. Since properties such as elastic modulus do not change, the flatness of the surface to be polished and the polishing efficiency are unlikely to occur. The proportion of the dimer diol having 30 to 42 carbon atoms in the polymer diol is preferably 80 mol% or more, and more preferably 90 mol% or more.

  The dimer diol that can be used as the polymer diol can be obtained by reducing a dimer acid having 30 to 42 carbon atoms. Dimer acid is a general term for dicarboxylic acids obtained by heat-polymerizing two molecules of unsaturated aliphatic monocarboxylic acid having a double bond. The dimer diol thus obtained may contain unreacted substances and trimers. Such unreacted substances and trimers prevent the polymerization degree of the thermoplastic polyurethane from being lowered. From the viewpoint of preventing the generation of gelled products, the content is preferably 5% by mass or less, more preferably 1% by mass or less, based on the total mass of the polymer diol used. The dimer diol used in the present invention is not particularly limited as long as the carbon number of the obtained dimer diol is 30 to 42. For example, unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, tall oil, cottonseed oil In general, a dimer diol obtained by reducing dimer acid produced by heat-polymerizing two molecules of dry oil fatty acid or semi-dry oil fatty acid obtained from soybean oil or the like is generally used. In addition, what is generally marketed (for example, the product made by Toa Gosei Co., Ltd., Pespol HP1000 etc.) can be used as dimer diol. As carbon number of dimer diol, Preferably it is 34-38, More preferably, it is 36. Among the dimer diols having 36 carbon atoms, those obtained by reducing dimer acid obtained by heat-polymerizing at least one selected from the group consisting of oleic acid, linoleic acid and linolenic acid are preferable.

  If high molecular diol is 50 mol% or less, other high molecular diols other than said C30-42 dimer diol may be included. Examples of such other polymer diols include polyether diols, polyester diols, and polycarbonate diols. Moreover, dimer diols other than those having 30 to 42 carbon atoms may be included. These other polymer diols and dimer diols other than those having 30 to 42 carbon atoms may be used alone or in combination of two or more. Among these, it is preferable to use polyether diol.

  Examples of the polyether diol include poly (ethylene glycol), poly (propylene glycol), poly (tetramethylene glycol), poly (methyltetramethylene glycol), glycerin-based polyalkylene ether glycol, and the like. These polyether diols may be used alone or in combination of two or more. Among these, it is preferable to use poly (tetramethylene glycol).

  Examples of the polyester diol include those that can be produced by direct esterification or transesterification of an ester-forming derivative such as dicarboxylic acid or its ester or acid anhydride and a low molecular diol according to a conventional method. These polyester diols may be used alone or in combination of two or more.

  Examples of the dicarboxylic acid constituting the polyester diol include oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 2-methylsuccinic acid, and 2-methyladipic acid. Aliphatic dicarboxylic acids having 4 to 12 carbon atoms, such as 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid Aliphatic dicarboxylic acids such as dimerized aliphatic dicarboxylic acids having 14 to 48 carbon atoms (dimer acid) obtained by dimerization of unsaturated fatty acids obtained by fractionation of triglycerides and hydrogenated products thereof (hydrogenated dimer acid); Alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; terephthalic acid, isophthalic acid, orthophthalic acid How and aromatic dicarboxylic acids. These dicarboxylic acids may be used alone or in combination of two or more. As the dimer acid and hydrogenated dimer acid, trade names “Pripol 1004”, “Plipol 1006”, “Plipol 1009”, “Plipol 1013” and the like manufactured by Unikema Corporation can be used.

  Examples of the low molecular diol constituting the polyester diol include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, Neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-methyl-1,8 -Aliphatic diols such as octanediol, 1,9-nonanediol, 1,10-decanediol; and alicyclic diols such as cyclohexanedimethanol and cyclohexanediol. These low molecular diols may be used alone or in combination of two or more. Among these, the diol preferably used is a diol having 6 to 12 carbon atoms, more preferably a diol having 8 to 10 carbon atoms, and still more preferably a diol having 9 carbon atoms.

  As polycarbonate diol, what is obtained by reaction with carbonate compounds, such as low molecular diol, dialkyl carbonate, alkylene carbonate, diaryl carbonate, can be used. As the low molecular weight diol constituting the polycarbonate diol, the low molecular weight diol exemplified above as a constituent component of the polyester diol can be used. Examples of the dialkyl carbonate include dimethyl carbonate and diethyl carbonate. Further, examples of the alkylene carbonate include ethylene carbonate. Examples of the diaryl carbonate include diphenyl carbonate.

  The number average molecular weight of the polymer diol is in the range of 400 to 2000, preferably in the range of 500 to 1500, and more preferably in the range of 500 to 1200. By using a polymer diol having a number average molecular weight within this range, a high-hardness thermoplastic polyurethane can be favorably obtained. When the number average molecular weight of the polymer diol exceeds 2000, when molding by extrusion molding or injection molding, a thickening phenomenon occurs in the molding machine, an insoluble material is generated, the molding operation is interrupted, and the inside is washed. There are things you have to do. Furthermore, after dissolving the non-reactive gas under heating / pressurizing conditions and then cooling and cooling the resulting product, giant bubbles are likely to be produced, making it difficult to obtain a uniform foam. is there. On the other hand, when the number average molecular weight of the polymer diol is less than 400, the wear resistance of the resulting polyurethane foam tends to decrease. The number average molecular weight of the polymer diol referred to in this specification means the number average molecular weight calculated based on the hydroxyl value measured according to JIS K1557.

  As the organic diisocyanate used in the production of the thermoplastic polyurethane used in the present invention, any of the organic diisocyanates conventionally used in the production of ordinary thermoplastic polyurethanes may be used. For example, ethylene diisocyanate, tetra Methylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, isophorone diisocyanate, isopropylidenebis (4-cyclohexylisocyanate), cyclohexylmethane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate, (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, cyclohexylene diisocyanate, bis (2-isocyanatoethyl)- Aliphatic or cycloaliphatic diisocyanates such as 4-cyclohexene; 2,4′- or 4,4′-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, m- or p-phenylene diisocyanate, m- or p-xylylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl -4,4'-diisocyanatodiphenylmethane, chlorophenylene-2 4-diisocyanate, and aromatic diisocyanates such as tetramethylxylylene diisocyanate and the like. These organic diisocyanates may be used alone or in combination of two or more. Among these, 4,4'-diphenylmethane diisocyanate is preferable from the viewpoint of wear resistance of the obtained resin foam.

  As for the chain extender used for manufacture of the thermoplastic polyurethane used in this invention, the 50 mol% or more is 1, 4- cyclohexane dimethanol. When the chain extender contains 1,4-cyclohexanediol in an amount of 50 mol% or more, the temperature dependency of the hardness of the obtained thermoplastic polyurethane or the resin foam using the thermoplastic polyurethane is reduced, and the surface to be polished during the polishing operation is reduced. Flatness and reduction in polishing efficiency can be prevented. The content of 1,4-cyclohexanedimethanol in the chain extender is preferably 70 mol% or more, and more preferably 80 mol% or more.

  The chain extender may contain other compounds than 1,4-cyclohexanedimethanol as long as it is 50 mol% or less. As such other compounds, compounds conventionally used as chain extenders in the production of ordinary thermoplastic polyurethanes can be used, but active hydrogen atoms capable of reacting with isocyanate groups are added in the molecule. It is preferable to use a low molecular weight compound having a molecular weight of 300 or less, for example, ethylene glycol, diethylene glycol, propylene glycol, 2,2-diethyl-1,3-propanediol, 1,2-, 1,3-, 2,3- or 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-bis (β-hydroxy Ethoxy) benzene, 1,4-cyclohexanediol, bis- (β-hydroxyethyl) terephthalate Diols such as 1,9-nonanediol, m- or p-xylylene glycol. These other compounds may be used alone or in combination of two or more.

  The thermoplastic polyurethane used in the present invention comprises a polymer diol, an organic diisocyanate, and a chain extender, wherein the mass of the polymer diol / (total mass of the organic diisocyanate and the chain extender) is 10/90 to 35/65. It is obtained by reacting at a ratio. By making the mass of the polymer diol react with the total mass of the organic diisocyanate and the chain extender within this range, the polishing pad containing the resulting resin foam improves the flatness and planarization efficiency of the surface to be polished. In addition, a polishing pad with little change in altitude with respect to a change in temperature during polishing work is obtained. Further, poor polishing such as scratches is less likely to occur. The mass of the polymer diol / (total mass of the organic diisocyanate and the chain extender) is preferably in the range of 15/85 to 35/65, and more preferably in the range of 20/80 to 30/70. preferable.

  In producing the thermoplastic polyurethane used in the present invention, the above-mentioned polymer diol, organic diisocyanate and chain extender can be melt-mixed at a predetermined ratio. The mixing ratio of each component is appropriately determined in consideration of physical properties to be imparted to the thermoplastic polyurethane, abrasion resistance, etc., but with respect to 1 mol of active hydrogen atoms contained in the polymer diol and the chain extender, It is preferable to use each component in such a ratio that the isocyanate group contained in the organic diisocyanate is 0.95 to 1.3 mol. When the ratio of isocyanate groups is lower than 0.95 mol, the mechanical strength and abrasion resistance of the resulting resin foam are lowered, and when it is higher than 1.3 mol, productivity and storage stability of thermoplastic polyurethane are reduced. Tends to decrease. From these viewpoints, it is more preferable that the isocyanate group contained in the organic diisocyanate is in the range of 0.96 to 1.10 with respect to 1 mol of active hydrogen atoms contained in the polymer diol and the chain extender. More preferably, it is in the range of 97 to 1.05.

  The method for producing the thermoplastic polyurethane used in the present invention is not particularly limited, but a prepolymer method using the above three components (polymer diol, organic diisocyanate and chain extender) and utilizing a known urethanization reaction. Or you may manufacture by any method of a one shot method. The thermoplastic polyurethane is preferably produced by a method of melt polymerization substantially in the absence of a solvent, and more preferably produced by a method of continuous melt polymerization using a multi-screw extruder.

The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane used in the present invention is preferably 2 × 10 ⁸ Pa or more. When the storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane is 2 × 10 ⁸ Pa or more, it becomes a resin foam with less change in hardness with respect to temperature fluctuation, and the polishing pad obtained therefrom is to be polished. A decrease in the planarization efficiency of the surface is suppressed. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane is more preferably 4 × 10 ⁸ Pa or more. However, if the storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane exceeds 2 × 10 ⁹ Pa, the foaming holes generated on the surface of the dressing process and the polishing pad are likely to be deformed and crushed, resulting in polishing characteristics. It may not be possible to obtain a foam having good stability. Therefore, it is preferable that the storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane is 2 × 10 ⁹ Pa or less. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of the thermoplastic polyurethane is more preferably 1 × 10 ⁹ Pa or less.

Further, it is preferable that a storage modulus at 30 ° C. of the thermoplastic polyurethane ratio of (E _'30) and a storage modulus at _{80 ℃ (E' 80) (} E '30 / E' 80) is from 1 to 4 . Thermoplastic polyurethane that satisfies these conditions has a small temperature dependency of its hardness, so the temperature dependency of the hardness of the resin foam is small, and when used as a polishing pad, the flatness of the surface to be polished during the polishing operation is reduced. It is possible to suppress a decrease and a decrease in planarization efficiency. The ratio (E ′ ₃₀ / E ′ ₈₀ ) is more preferably 1 to 3.

The resin foam of the present invention is mainly composed of the thermoplastic polyurethane described above. The ratio of the thermoplastic polyurethane to the total mass of the resin foam (excluding the mass of the bubble part) is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, and 98 to 98%. More preferably, it is 100 mass%.
The resin foam of the present invention may contain components other than the thermoplastic polyurethane as long as the effects of the present invention are not impaired. Examples of the other components include commonly used additives.

The density of the resin foam of the present invention is in the range of 0.4 to 0.95 g / cm ³ . For example, when used as a polishing pad, if the density of the resin foam is less than 0.4 g / cm ³ , the resulting resin foam becomes too soft, so that the flatness of the surface to be polished and the polishing efficiency are lowered. On the other hand, when the density of the resin foam is larger than 0.95 g / cm ³ , the polishing efficiency is lowered. The density of the resin foam is preferably in the range of 0.50 to 0.85 g / cm ³ , for example, from the viewpoint of flatness of the surface to be polished, and in the range of 0.55 to 0.80 g / cm ³ . It is more preferable that In addition, the density of the resin foam in this specification is the value measured based on A method (underwater substitution method) of JISK7112.

  The cell size of the resin foam of the present invention is in the range of 1 to 100 μm. For example, when used as a polishing pad, if the bubble size is smaller than 1 μm, the abrasive (abrasive grains) is likely to be clogged with bubbles, the polishing efficiency is reduced, and polishing defects such as scratches are liable to occur. When it is larger than 100 μm, the surface smoothness of the resin foam is deteriorated, and the polishing agent (abrasive grains) is localized, and poor polishing such as scratches and orange peel scratches is likely to occur. The cell size of the resin foam is preferably in the range of 5 to 80 μm, and more preferably in the range of 10 to 60 μm, for example, from the viewpoint of retention of the abrasive (abrasive grains). The bubble size of the resin foam in the present specification is calculated from the density of the resin foam and the number of bubbles obtained by scanning electron microscope (SEM) photography, as will be described later in Examples. Value.

The resin foam having the above-described density and cell size can be obtained by setting the content of nitrogen atoms derived from the organic diisocyanate in the thermoplastic polyurethane to be used to 5 to 7% by mass. The nitrogen atom content is preferably in the range of 5.2 to 6.5% by mass, for example, from the viewpoint of the hardness and abrasion resistance of the obtained resin foam. More preferably, it is in the range of mass%. When the nitrogen atom content is less than 5% by mass, the hardness of the thermoplastic polyurethane itself becomes too low, resulting in a resin foam having a large temperature dependency of the hardness, and when used as a polishing pad, polishing occurs during polishing. Performance (polishing rate, flatness) is likely to decrease. On the other hand, when the content of the nitrogen atom exceeds 7% by mass, the resulting resin has a large change in melt viscosity over time, the sheet formability is inferior, the softening temperature becomes too high, and the desired foam is obtained. There is a problem that it becomes difficult to obtain. In addition, the content rate of the nitrogen atom derived from the organic diisocyanate in a thermoplastic polyurethane can be adjusted by selecting suitably the usage-amounts, such as a chain extender to be used, organic diisocyanate, and a chain extender.
In order to improve the polishing efficiency of the polishing pad containing the resin foam, it is better that the number of bubbles present on the surface of the resin foam is larger. Generally, if the number of bubbles is increased, the density of the resin foam decreases, and the resin Since the hardness of the foam is too low, the polishing efficiency tends to decrease. In the present invention, by increasing the hardness of the thermoplastic polyurethane constituting the resin foam, a decrease in the hardness of the resin foam when the number of bubbles is increased is prevented, thereby improving the polishing efficiency.

  The resin foam of the present invention is produced by foaming the above-described thermoplastic polyurethane or a polyurethane resin composition mainly composed of the thermoplastic polyurethane (hereinafter sometimes simply referred to as “polyurethane resin composition”). be able to. In foaming, it is preferable to use a non-reactive gas as a foaming agent. The non-reactive gas means a gas that does not react with a thermoplastic polyurethane or a component for producing the thermoplastic polyurethane. Specific examples of the non-reactive gas include nitrogen, carbon dioxide, argon, helium and the like. Among these, carbon dioxide or nitrogen is preferable from the viewpoint of solubility in thermoplastic polyurethane and production cost.

  When a sheet-like molded product is used as the shape of the thermoplastic polyurethane or polyurethane resin composition when dissolving the non-reactive gas, it is easy to produce a resin foam having a uniform foam structure, and a polishing pad is obtained. This is advantageous in that the process can be simplified. As this sheet-like molded object, what shape | molded the thermoplastic polyurethane and the polyurethane resin composition using extrusion molding machines, such as a uniaxial extrusion molding machine and a biaxial extrusion molding machine, or an injection molding machine is preferable. The thickness of the sheet-like molded body is preferably in the range of 0.8 to 5 mm, for example, from the viewpoint of ease of production of the resin foam and the time required for dissolving the non-reactive gas. More preferably, it is in the range of ˜4 mm.

  A method for producing a foamed article by dissolving a gas in a thermoplastic resin or a molded body thereof and then reducing the pressure is disclosed in U.S. Pat. No. 4,473,665, JP-A-6-322168, JP-A-8- No. 11190, JP-A-10-36547, JP-A 2000-169615, JP-A 2000-248101 (see the above-mentioned Patent Documents 6 to 11) and the like. An example applied to the production of the specific resin foam described above is not known.

The dissolution of the non-reactive gas is preferably performed in a pressure resistant vessel adjusted to have a pressure in the range of 3 to 15 MPa and a temperature in the range of 50 to 150 ° C. When the pressure at the time of dissolving the reactive gas is less than 3 MPa, it takes a long time to dissolve the saturated amount of the non-reactive gas. On the other hand, when the pressure at the time of dissolving the non-reactive gas exceeds 15 MPa, the time required for dissolving the non-reactive gas is shortened, but the amount of gas to be dissolved becomes larger than necessary, and the size of the generated bubbles is reduced. . The pressure during dissolution of the non-reactive gas is more preferably within a range of 5 to 14 MPa, and further preferably within a range of 7 to 13 MPa. Moreover, when the temperature at the time of non-reactive gas melt | dissolution is less than 50 degreeC, it takes a long time to melt | dissolve non-reactive gas in saturation amount. On the other hand, when the temperature at the time of non-reactive gas dissolution exceeds 150 ° C., the molded body is deformed, or the dissolved amount of the non-reactive gas becomes small and the size of the generated bubbles becomes too large. The temperature during dissolution of the non-reactive gas is more preferably within the range of 70 to 150 ° C, further preferably within the range of 80 to 140 ° C, and particularly preferably within the range of 90 to 130 ° C. preferable.
Here, the dissolution amount of the non-reactive gas is preferably 98% or more of the saturation amount under dissolution conditions, for example, from the viewpoint of obtaining a resin foam having a uniform foam structure, and is 99% or more of the saturation amount. More preferably, it is more preferably a saturated amount. In addition, it can discriminate | determine that the non-reactive gas melt | dissolved in the saturated amount by measuring the relationship between melt | dissolution time and the mass of the thermoplastic polyurethane and polyurethane resin composition after melt | dissolution.

  The thermoplastic polyurethane or polyurethane resin in which the non-reactive gas is dissolved in the thermoplastic polyurethane or polyurethane resin composition as described above, then cooled to 50 ° C. or lower, and then the pressure is released to dissolve the non-reactive gas. After obtaining the composition, the resin foam of the present invention can be obtained by heating and foaming the composition.

  If the temperature when the pressure is released after the non-reactive gas is dissolved in the thermoplastic polyurethane or polyurethane resin composition exceeds 50 ° C., the dissolved non-reactive gas is degassed from the resin and the desired cell size May not be obtained or the skin layer (non-foamed layer) may increase. The temperature at the time of releasing the pressure is more preferably 40 ° C. or less, and further preferably 30 ° C. or less, from the viewpoint of, for example, maintaining dissolved non-reactive gas.

  When the heating temperature at the time of heating and foaming is too low, the formation and growth of bubbles will be insufficient, so when the softening point of the thermoplastic polyurethane or polyurethane resin composition is T ° C, (T-10) to ( It is preferably in the range of T + 40) ° C, more preferably in the range of (T-5) ° C to (T + 40) ° C, and further in the range of (T) ° C to (T + 30) ° C. preferable. Although there is no restriction | limiting in particular in the method of heating foaming, The method of applying a heat | fever uniformly to the molded object which melt | dissolved non-reactive gas is preferable at the point of ensuring the uniformity of a foam structure. Examples of the heating and foaming method include a method of passing through a heat medium such as hot water, a hot oil bath, hot air, and water vapor, a method of heating with an external heating device such as a high-frequency press heating facility and an infrared heater.

  The polishing pad of the present invention contains the above-described resin foam of the present invention. The polishing pad of the present invention can be produced by grinding or slicing the resin foam produced as described above so that bubbles are exposed on the surface thereof. Further, the obtained polishing pad can be further processed into a predetermined shape, subjected to surface processing, or laminated with a material to be a cushion layer.

  The polishing pad of the present invention can be used for CMP together with a polishing slurry known per se. The polishing slurry contains components such as a liquid medium such as water and oil; an abrasive such as aluminum oxide, cerium oxide, zirconium oxide, and silicon carbide; a base, an acid, and a surfactant. Moreover, when performing CMP, you may use lubricating oil, a coolant, etc. together with polishing slurry as needed.

  CMP can be performed by using a known CMP apparatus and bringing the surface to be polished and the polishing pad into contact with each other through a polishing slurry at a constant speed for a certain period of time under pressure. The article to be polished is not particularly limited, and examples thereof include quartz, silicon, glass, an optical substrate, an electronic circuit substrate, a multilayer wiring substrate, and a hard disk.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In addition, the physical property of the thermoplastic polyurethane described in the Example and the resin foam was evaluated by the following method.

Density of thermoplastic polyurethane and resin foam Measured according to JIS K 7112, Method A (submersion method).

Bubble size of resin foam Photograph a cross section of the resin foam with a scanning electron microscope (SEM), count the number of bubbles present in a certain area, and calculate the number of bubbles per unit volume (number density of bubbles) did. From the value, the density of the resin foam, and the density of the thermoplastic polyurethane, the average cell size when the cells were assumed to be true spherical was calculated to obtain the cell size of the resin foam.

A dynamic viscoelasticity measuring device [DVE-V4 Leo was prepared using a test piece obtained by preparing a 2 mm-thick injection sheet using thermoplastic polyurethane using storage elastic modulus and softening temperature , and heat-treating the sheet at 90 ° C. for 8 hours. Storage modulus (E ′ ₃₀ and E ′ ₈₀ ) was determined by measuring dynamic viscoelasticity at 30 ° C. and 80 ° C. at a frequency of 11 Hz using Spectra: manufactured by Rheology Co., Ltd. . The temperature at which the storage elastic modulus (E ′) reached 1 × 10 ⁷ Pa was defined as the softening temperature (T). Furthermore, from these values, the ratio (E ′ ₃₀ / E ′ ₈₀ ) between the storage elastic modulus at 30 ° C. and the storage elastic modulus at 80 ° C. was determined.

<Reference Example 1>
Dimerdiol (abbreviation: DD) [Pespol HP1000 manufactured by Toa Gosei Co., Ltd.], 4,4′-diphenylmethane diisocyanate (abbreviation: MDI) and 1,4-cyclohexanedimethanol (abbreviation: CHDM) [chain extender] : MDI: CHDM molar ratio is 1: 4.4: 3.4 (nitrogen atom content: 5.8% by mass), and the total feed rate is 300 g / min. In this way, a thermoplastic polyurethane is obtained by continuously supplying to a twin-screw extruder (30 mmφ, L / D = 36, cylinder temperature: 75 to 260 ° C.) rotated coaxially by a metering pump to perform continuous melt polymerization. Manufactured. The resulting thermoplastic polyurethane melt is continuously extruded into water in the form of strands, then chopped into pellets with a pelletizer, and the pellets are dehumidified and dried at 70 ° C. for 5 hours and further at 90 ° C. for 5 hours. A thermoplastic polyurethane having a softening temperature of 104 ° C. (hereinafter abbreviated as PU-1) was produced. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-1 was 1.16 × 10 ⁹ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.6 × 10 ⁹ Pa. The ratio between the two (E ′ ₃₀ / E ′ ₈₀ ) was 1.4 (see Table 1).

<Reference Example 2>
Dimer diol (DD) [Pespol HP1000 manufactured by Toa Gosei Co., Ltd.], 4,4′-diphenylmethane diisocyanate (MDI), 1,4-cyclohexanedimethanol (CHDM) [chain extender] and 1,4-butanediol (abbreviation) : BD) [chain extender], the molar ratio of DD: MDI: CHDM: BD is 1: 4.1: 2.5: 0.6 (the ratio of CHDM in the chain extender: 80 mol%, A thermoplastic polyurethane having a softening temperature of 101 ° C. (hereinafter referred to as “PU-2”) in the same manner as in Reference Example 1 except that the nitrogen atom content is 5.8% by mass. Abbreviated). The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-2 was 7.0 × 10 ⁸ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.5 × 10 ⁹ Pa. The ratio between the two (E ′ ₃₀ / E ′ ₈₀ ) was 2.1 (see Table 1).

<Reference Example 3>
Dimerdiol (DD) [Pespol HP1000 manufactured by Toa Gosei Co., Ltd.], 4,4′-diphenylmethane diisocyanate (MDI), 1,4-cyclohexanedimethanol (CHDM) [chain extender] and 1,4-butanediol (BD) ) [Chain extender], the molar ratio of DD: MDI: CHDM: BD is 1: 3.3: 0.5: 1.8 (CHDM ratio in the chain extender: 20 mol%, nitrogen atom) In the same manner as in Reference Example 1 except that it was used at a ratio such that the content was 5.8% by mass), a thermoplastic polyurethane having a softening temperature of 88 ° C. (hereinafter abbreviated as PU-3). ) Was manufactured. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-3 was 1.8 × 10 ⁸ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.3 × 10 ⁹ Pa. The ratio of both (E ′ ₃₀ / E ′ ₈₀ ) was 7.2 (see Table 2).

<Reference Example 4>
Using dimer diol (DD) [Pespol HP1000 manufactured by Toa Gosei Co., Ltd.], 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD) [chain extender], DD: MDI: BD The softening temperature was 84 ° C. in the same manner as in Reference Example 1, except that the molar ratio of 1: 3.1: 2.1 (the nitrogen atom content: 5.8% by mass) was used. A thermoplastic polyurethane (hereinafter abbreviated as PU-4) was produced. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-4 was 1.17 × 10 ⁸ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.22 × 10 ⁹ Pa. The ratio of both (E ′ ₃₀ / E ′ ₈₀ ) was 10.4 (see Table 2).

<Reference Example 5>
Poly (3-methylpentanediol adipate) diol (abbreviation: PMPA) having a number average molecular weight of 1,500, 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) [chain extender], Except that the molar ratio of PMPA: MDI: BD was 1: 5.5: 4.5 (nitrogen atom content: 4.7% by mass), the same as in Reference Example 1, A thermoplastic polyurethane having a softening temperature of 150 ° C. (hereinafter abbreviated as PU-5) was produced. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-5 was 3.23 × 10 ⁷ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.85 × 10 ⁸ Pa. The ratio between the two (E ′ ₃₀ / E ′ ₈₀ ) was 5.7 (see Table 2).

<Reference Example 6>
Poly (tetramethylene glycol) having a number average molecular weight of 1,400 [abbreviation: PTMG], 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-cyclohexanedimethanol (CHDM) [chain extender] were converted to PTMG: MDI. : CHDM molar ratio is 1: 9.6: 8.6 (nitrogen atom content: 5.3 mass%), and the total supply amount thereof is 300 g / min. Then, it was continuously supplied to a twin-screw extruder (30 mmφ, L / D = 36, cylinder temperature: 75 to 260 ° C.) rotated coaxially by a metering pump, and continuous melt polymerization was performed to produce polyurethane. The resulting polyurethane melt is continuously extruded into water as a strand, then chopped into pellets with a pelletizer, and the pellets are dehumidified and dried at 70 ° C. for 5 hours and further at 80 ° C. for 5 hours to soften. A thermoplastic polyurethane having a temperature of 99 ° C. (hereinafter, abbreviated as PU-6) was produced. The storage elastic modulus (E ′ ₈₀ ) at 80 ° C. of PU-6 was 1.13 × 10 ⁸ Pa, and the storage elastic modulus (E ′ ₃₀ ) at 30 ° C. was 1.47 × 10 ⁹ Pa. The ratio between the two (E ′ ₃₀ / E ′ ₈₀ ) was 13.0 (see Table 2).

<Example 1>
A gap between the thermoplastic polyurethane (PU-1) and a single screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 215 to 230 ° C. and a die temperature of 230 ° C., and adjusted to 60 ° C. 1. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet is put into a pressure vessel, and carbon dioxide is dissolved for 5 hours under the conditions of a temperature of 110 ° C. and a pressure of 7 MPa to obtain a gas dissolving sheet containing 1.6% by mass (saturated amount) of carbon dioxide. It was. After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the obtained gas-dissolved sheet was immersed in 115 ° C. silicone oil for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.70 g / cm ³ and the bubble size was 48 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The polishing characteristics of the 4-inch thermal oxide film of this polishing pad were evaluated with a polishing apparatus (MAT-BC15 manufactured by MTT). Conditioner manufactured by Applied Materials Co., Ltd. (# 100—coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. The in-plane film thickness of 49 points of the thermal oxide film at this time was measured, and the in-plane uniformity was determined by the following formula (1). The smaller the value of in-plane uniformity, the better the uniformity. The results are summarized in Table 1.

In-plane uniformity (%) = {(maximum polishing thickness−minimum film thickness) / (2 × average film thickness)} × 100
... Formula (1)

<Example 2>
1. Gap spacing 1. Thermoplastic polyurethane (PU-2) was charged into a single screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 215 to 230 ° C. and a die temperature of 230 ° C., and adjusted to 60 ° C. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet was put into a pressure vessel, and carbon dioxide was dissolved for 5 hours under conditions of a temperature of 110 ° C. and a pressure of 8 MPa to obtain a gas-dissolved sheet containing 2% by mass (saturated amount) of carbon dioxide. . After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the resulting gas-dissolved sheet was immersed in silicon oil at 130 ° C. for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.80 g / cm ³ and the bubble size was 42 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The polishing characteristics of the 4-inch thermal oxide film of this polishing pad were evaluated with a polishing apparatus (MAT-BC15 manufactured by MTT). Conditioner manufactured by Applied Materials Co., Ltd. (# 100—coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. The in-plane film thickness of 49 points of the thermal oxide film at this time was measured, and the in-plane uniformity was determined by the above formula (1). The results are summarized in Table 1.

<Comparative Example 1>
1. Gap spacing 1. Thermoplastic polyurethane (PU-3) was charged into a single screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 215 to 230 ° C and a die temperature of 230 ° C, and adjusted to 60 ° C. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet is put into a pressure vessel, carbon dioxide is dissolved for 5 hours under conditions of a temperature of 120 ° C. and a pressure of 7 MPa, and a gas dissolving sheet containing 1.8% by mass (saturated amount) of carbon dioxide is obtained. Obtained. After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the obtained gas-dissolved sheet was immersed in silicon oil at 110 ° C. for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.68 g / cm ³ and the bubble size was 45 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The polishing characteristics of the 4-inch thermal oxide film of this polishing pad were evaluated with a polishing apparatus (MAT-BC15 manufactured by MTT). Conditioner manufactured by Applied Materials Co., Ltd. (# 100—coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. The in-plane film thickness of 49 points of the thermal oxide film at this time was measured, and the in-plane uniformity was determined by the above formula (1). The results are summarized in Table 2.

<Comparative example 2>
A thermoplastic polyurethane (PU-4) was charged into a single-screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 215 to 230 ° C and a die temperature of 230 ° C, and adjusted to 60 ° C. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet is put in a pressure vessel, carbon dioxide is dissolved for 5 hours under conditions of a temperature of 120 ° C. and a pressure of 7 MPa, and a gas dissolving sheet containing 1.9% by mass (saturated amount) of carbon dioxide is obtained. Obtained. After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the obtained gas-dissolved sheet was dipped in silicon oil at 100 ° C. for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.68 g / cm ³ and the bubble size was 41 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The polishing characteristics of the 4-inch thermal oxide film of this polishing pad were evaluated with a polishing apparatus (MAT-BC15 manufactured by MTT). Conditioner manufactured by Applied Materials Co., Ltd. (# 100-coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. The in-plane film thickness of 49 points of the thermal oxide film at this time was measured, and the in-plane uniformity was determined by the above formula (1). The results are summarized in Table 2.

<Comparative Example 3>
1. Gap spacing 1. Thermoplastic polyurethane (PU-5) was charged into a single screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 180 to 210 ° C. and a die temperature of 210 ° C., and adjusted to 60 ° C. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet is put into a pressure vessel, carbon dioxide is dissolved for 5 hours under conditions of a temperature of 80 ° C. and a pressure of 5 MPa, and a gas dissolving sheet containing 2.8% by mass (saturated amount) of carbon dioxide is obtained. Obtained. After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the obtained gas-dissolved sheet was immersed in 160 ° C. silicon oil for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.70 g / cm ³ and the bubble size was 28 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The pad was evaluated for the polishing characteristics of a 4-inch thermal oxide film with a polishing apparatus (MAT-BC15 manufactured by MG Corporation). Conditioner manufactured by Applied Materials Co., Ltd. (# 100—coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. At this time, the film thickness of 49 points of the in-plane thermal oxide film was measured, and the in-plane uniformity was determined by the above formula (1). The results are summarized in Table 2.

<Comparative example 4>
1. Gap spacing 1. Thermoplastic polyurethane (PU-6) was charged into a single screw extruder (65 mmφ), extruded from a T-die at a cylinder temperature of 210 to 225 ° C and a die temperature of 220 ° C, and adjusted to 60 ° C. An 8 mm roll was passed through to form a sheet having a thickness of 2 mm. Next, the obtained sheet is put into a pressure resistant container, carbon dioxide is dissolved for 10 hours under conditions of a temperature of 110 ° C. and a pressure of 8 MPa, and a gas dissolving sheet containing 3.5% by mass (saturated amount) of carbon dioxide is obtained. Obtained. After cooling to room temperature, the pressure was set to normal pressure, and the gas-dissolving sheet was taken out from the pressure vessel. Next, the obtained gas-dissolved sheet was immersed in 115 ° C. silicone oil for 3 minutes and then taken out and cooled to room temperature to obtain a resin foam. The density of the obtained resin foam was 0.82 g / cm ³ and the bubble size was 32 μm.
The surface of the obtained resin foam (sheet-like material) is ground to expose the bubbles on the surface to produce a circular polishing pad having a thickness of 1.3 mm and a diameter of 38 cm. The surface has a width of 0.8 mm, XY groove processing (lattice-shaped grooves) having a depth of 0.8 mm and a pitch of 6 mm was performed. The polishing characteristics of the 4-inch thermal oxide film of this polishing pad were evaluated with a polishing apparatus (MAT-BC15 manufactured by MTT). Conditioner manufactured by Applied Materials Co., Ltd. (# 100—coverage 80%, diameter 10 cm, load 1 kg) as a conditioner at this time, silica slurry as slurry (Cabot's SS25 diluted to 1/2 with distilled water) Was run at a polishing pressure of 2 psi, a platen rotation speed of 60 rpm, and a head rotation speed of 59 rpm. As the polishing characteristics, the polishing rate and flatness (in-plane uniformity) when 50, 100, and 500 thermal oxide films were polished were evaluated. At this time, the film thickness of 49 points of the in-plane thermal oxide film was measured, and the in-plane uniformity was determined by the above formula (1). The results are summarized in Table 2.

  From the above results, it can be seen that in Examples 1 and 2 satisfying the constituent requirements of the present invention, a polishing pad exhibiting stable polishing performance can be obtained. On the other hand, Comparative Example 1 using a thermoplastic polyurethane with a low content of 1,4-cyclohexanedimethanol in the chain extender, without using 1,4-cyclohexanedimethanol as the chain extender, and the mass ratio of the polymer diol Comparative Example 2 using a large amount of thermoplastic polyurethane, and Comparative Example 3 using a thermoplastic polyurethane having a nitrogen atom content of less than 5% by mass derived from organic diisocyanate without using dimer diol as a polymer diol. Then, the stability of the polishing rate was poor, and the flatness (in-plane uniformity) of the polished surface deteriorated as the number of polishing operations increased. Also in Comparative Example 4 using thermoplastic polyurethane using poly (tetramethylene glycol) as the polymer diol, the polishing rate is poor in stability, and the flatness of the polished surface (in-plane uniformity) as the number of polishing increases. ) Worsened.

  According to the present invention, a resin foam having a uniform foam structure and a polishing pad containing the resin foam are provided. The polishing pad of the present invention is useful for CMP, and can polish a semiconductor wafer or the like with high accuracy and high efficiency. In particular, the polishing pad of the present invention can improve the flatness and flattening efficiency of the surface to be polished, and has less change in hardness with respect to temperature fluctuations during the polishing operation than conventional ones.

Claims (7)

A resin foam mainly composed of thermoplastic polyurethane, having a density of 0.4 to 0.95 g / cm ³ and a cell size of 1 to 100 μm,
The thermoplastic polyurethane reacts with a polymer diol, an organic diisocyanate, and a chain extender at a ratio of mass of polymer diol / (total mass of organic diisocyanate and chain extender) of 10/90 to 35/65. Is obtained by
The number average molecular weight of the polymer diol is 400 to 2000,
50 mol% or more of the polymer diol is a dimer diol having 30 to 42 carbon atoms,
More than 50 mol% of the chain extender is 1,4-cyclohexanedimethanol,
The resin foam whose content rate of the nitrogen atom derived from the organic diisocyanate of this thermoplastic polyurethane is 5-7 mass%. The storage elastic modulus (E ′ ₈₀ ) of the thermoplastic polyurethane at 80 ° C. is 2 × 10 ⁸ Pa to 2 × 10 ⁹ Pa, and the storage elastic modulus (E ′ ₃₀ ) of the thermoplastic polyurethane at 30 ° C. 'ratio of ₍₈₀ (E storage modulus E)' at ₈₀ ℃ ₃₀ / E '80) is 1 to 4, a resin foam according to claim 1.   The resin foam according to claim 1 or 2, wherein the dimer diol has 36 carbon atoms.   The resin according to claim 3, wherein the dimer diol is obtained by reducing dimer acid obtained by heat-polymerizing at least one selected from the group consisting of oleic acid, linoleic acid and linolenic acid. Foam.   A non-reactive gas is dissolved in a polyurethane resin composition made of thermoplastic polyurethane or mainly thermoplastic polyurethane under heating and pressure conditions, then cooled to 50 ° C. or lower, and then the pressure is released to make it unreacted. The resin foam according to any one of claims 1 to 4, which is obtained by heating and foaming a polyurethane resin composition comprising a thermoplastic polyurethane having a soluble gas dissolved therein or mainly a thermoplastic polyurethane.   The resin foam according to claim 5, wherein the non-reactive gas is carbon dioxide or nitrogen.   A polishing pad containing the resin foam according to claim 1.