WO2021117834A1 - Polyurethane, polishing layer, polishing pad, and polishing method - Google Patents

Abstract

Provided are: a polyurethane for forming a polishing layer in which clogging can be suppressed, and polishing can be performed stably and with long service life with suppressed occurrence of damage; a polishing layer and polishing pad which use the polyurethane; and a polishing method.　A polyurethane having at least one structural unit derived from a compound having a carboxy group. A polishing layer and polishing pad which use the polyurethane, and a polishing method.

Description

Polyurethane, polishing layer, polishing pad and polishing method

The present invention relates to a novel polyurethane, a polishing layer using the same, a polishing pad, and a polishing method.

In recent years, semiconductor wafers and semiconductor devices are required to have high integration and multi-layer wiring, and therefore, there is an increasing demand for improvement of basic quality of these materials, for example, flatness of the surface.
Examples of the polishing method for flattening the surface of the semiconductor wafer include CMP (Chemical Mechanical Polishing). CMP is a method of polishing an object to be polished with high accuracy with a polishing pad while supplying a slurry containing abrasive grains and a reaction solution to the surface of the object to be polished. Examples of the material constituting the polishing layer of the polishing pad used in this method include polyurethane having a closed cell structure. Polyurethane having a closed cell structure is generally produced by casting foam curing using a two-component curable polyurethane (for example, Patent Documents 1 to 4).
However, with this method, it is difficult to make the reaction and foaming uniform, and there is a limit to increasing the hardness of the obtained polyurethane, so that the polishing characteristics such as the flatness of the surface to be polished and the flattening efficiency are likely to fluctuate. In addition, since the foamed structure has independent holes, polishing slurry and polishing debris used in the polishing process easily invade the voids and become clogged, resulting in problems such as a decrease in polishing speed and a shortened pad life. ..

On the other hand, examples of the polyurethane constituting the polishing layer include those in which a non-woven fabric is impregnated with a polyurethane resin and solidified (for example, Patent Documents 5 to 7). Since such a non-woven fabric type polishing pad has an uneven structure, voids, and a communication hole structure due to the structure of the non-woven fabric, it is easy to improve the polishing rate because the slurry has a good liquid pooling property at the time of polishing, and it is flexible. Since it is high, it has a feature of good contact with a wafer.

Japanese Unexamined Patent Publication No. 2000-178374 Japanese Unexamined Patent Publication No. 2000-248034 Japanese Unexamined Patent Publication No. 2001-89548 Japanese Unexamined Patent Publication No. 11-322878 Japanese Unexamined Patent Publication No. 11-99479 Japanese Unexamined Patent Publication No. 2005-212055 Japanese Unexamined Patent Publication No. 3-234475

However, in the non-woven fabric type polishing pad, the liquid accumulation property of the slurry is good due to the uneven structure of the non-woven fabric, etc., while the hardness and elastic modulus of the polyurethane change due to the clogging of the abrasive grains in the unevenness, etc. As a result, there is a problem that the wafer is easily scratched. Further, there is a problem that the stability of polishing is lowered due to a change in hardness or the like due to clogging, and the life of the polishing pad is shortened.

The present invention has been made in view of the above-mentioned conventional problems, and constitutes a polishing layer capable of stably polishing with a long life while suppressing the occurrence of scratches by suppressing clogging of the polishing layer. It is an object of the present invention to provide a polyurethane to be used, a polishing layer using the same, a polishing pad, and a polishing method.

As a result of repeated studies by the present inventors in order to solve the above problems, by using polyurethane having a carboxy group in the molecular structure for the polishing layer, the carboxy group is dissociated during polishing and the entire polishing layer becomes a negative potential. It turned out to change. As a result, it was found that clogging of the abrasive grains can be prevented by the repulsive force between the negative potential polishing layer and the negative potential abrasive grains, and that the polishing can be stably performed over a long life while suppressing scratches. The present invention has been completed.

The gist of the present invention is the following [1] to [10].
[1] Polyurethane having at least one structural unit derived from a compound having a carboxy group.
[2] The above [1] contains at least a structural unit derived from the compound having a carboxy group, a structural unit derived from a chain extender, a structural unit derived from a polymer diol, and a structural unit derived from an organic diisocyanate. Described polyurethane.
[3] The polyurethane according to the above [1] or [2], wherein the amount of the structural unit derived from the compound having a carboxy group is 3 to 30 mol% in all the structural units constituting the polyurethane.
[4] A polishing layer using the polyurethane according to any one of the above [1] to [3].
[5] The polishing layer according to the above [4], wherein the polishing layer is obtained by impregnating a non-woven fabric with the polyurethane and further solidifying the non-woven fabric.
[6] The polishing layer according to the above [4] or [5], wherein the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is -10.0 mV or less.
[7] The polishing layer according to any one of [4] to [6] above, wherein the polyurethane is a non-foaming material.
[8] The polyurethane has a storage elastic modulus of 50 to 1,200 MPa and a contact angle with water of 80 degrees or less measured at 50 ° C. after being saturated and swollen with water at 50 ° C. 4] The polishing layer according to any one of [7].
[9] A polishing pad using the polishing layer according to any one of [4] to [8] above.
[10] A polishing method using the polishing layer according to any one of [4] to [8] above.
The process of fixing the polishing pad provided with the polishing layer on the surface plate of the polishing device, and
A step of holding the object to be polished in the holder of the polishing apparatus so as to face the polished surface of the polishing layer, and
A step of polishing the object to be polished by relatively sliding the polishing pad and the object to be polished while supplying a neutral or alkaline polishing slurry between the surface to be polished and the object to be polished. When,
Polishing method with.

According to the present invention, polyurethane constituting a polishing layer capable of stably polishing with a long life while suppressing the occurrence of scratches by suppressing clogging of the polishing layer, a polishing layer using the same, and polishing. Pads, as well as polishing methods, can be provided.

FIG. 1 is a schematic diagram for explaining the carboxy group present in the molecular structure of polyurethane with respect to the polyurethane of the present invention having a structural unit derived from dimethylolpropionic acid. FIG. 2 is a schematic diagram for explaining a state in which the carboxy group is dissociated in FIG. FIG. 3 is a schematic view for explaining the polishing method of the present invention. FIG. 4 is a photograph showing the types of scratches (evaluation criteria) of the object to be polished in Examples and Comparative Examples.

[Polyurethane]
The polyurethane of the present invention has at least one structural unit derived from a compound having a carboxy group.
According to the present invention, since it has at least one structural unit derived from a compound having a carboxy group, the carboxy group is present in the molecular structure of polyurethane. When this is used as a material for the polishing layer of the polishing pad, the concavo-convex portion of the polishing layer is clogged with abrasive grains due to the repulsive force between the negative potential generated by the dissociation of the carboxy group and the negative potential of the abrasive grains. Is less likely to occur. Therefore, it is possible to suppress scratches caused by clogging and to stably polish with a long life.
In the present invention, by adjusting the amount of carboxy groups present in the molecular structure of polyurethane, it is possible to impart not only the negative potential of the polyurethane surface but also properties such as hydrophilicity.

The polyurethane of the present invention can be produced, for example, by using a compound having a carboxy group in addition to the raw materials used for producing general polyurethane. Specific examples of the compound having a carboxy group include dimethylolpropionic acid and the like, and by reacting this with a raw material such as a polymer diol or isocyanate, the molecular structure shown in the schematic diagram of FIG. 1 is shown. A polyurethane having a carboxy group inside can be obtained. As described above, this carboxy group can improve the hydrophilicity of the surface of polyurethane and improve the wettability on the surface of polyurethane.

FIG. 2 is a diagram for explaining a state in which the carboxy group of polyurethane is dissociated in FIG. With respect to the polyurethane of FIG. 1, by setting the pH condition at which the carboxy group is ionized, the carboxy group ^{dissociates into −COO −} and H ^{+ as} shown in FIG. 2, so that the surface of the polyurethane is negative due to ^{−COO −.} The potential of can be imparted. Therefore, when the polyurethane of the present invention is used as the polishing layer, the carboxy group is dissociated when an alkaline slurry is used, and the zeta potential of the polishing layer becomes negative due to ^{−COO −.} As a result, the abrasive grains in the alkaline slurry and the polyurethane are repelled by the repulsive force, so that the abrasive grains are less likely to be clogged in the uneven portion of the polishing layer, and as a result, the polishing efficiency is improved.

The polyurethane of the present invention is not particularly limited as long as it has at least one structural unit derived from a compound having a carboxy group, and may be a thermoplastic polyurethane or a thermosetting polyurethane. Thermoplastic polyurethane is preferable because it can be continuously produced by melt polymerization and can be easily processed into a sheet when used as a polishing layer of a polishing pad.
The polyurethane of the present invention can be suitably used not only for the polishing layer of a polishing pad, but also for imparting hydrophilicity to the surface of polyurethane and for applications requiring modification of electrical properties and the like.

Hereinafter, the thermoplastic polyurethane will be described in detail as an example of the polyurethane of the present invention.
The thermoplastic polyurethane according to the present invention is, for example, from the viewpoint of ease of production, a structural unit derived from a compound having a carboxy group, a structural unit derived from a chain extender, a structural unit derived from a polymer diol, and an organic diisocyanate. It is preferable that the structural unit derived from the above is contained at least.

[Compound having a carboxy group]
Specific examples of the compound having a carboxy group include a diol having a carboxy group, a diamine having a carboxy group, a polymer diol having a carboxy group, and derivatives thereof. Specific examples thereof include compounds represented by the following general formulas (1) to (3).

(In formulas (1) to (3), R ¹ to R ⁶ each independently represent a hydroxyl group or an amino group, and R may each independently have a substituent and has 1 to 10 carbon atoms. Indicates a trivalent or aromatic hydrocarbon group of, and R'independently represents a divalent hydrocarbon group having 1 to 10 carbon atoms. L, m and n are integers of 1 to 10. Show.)

Examples of such a compound having a carboxy group include dimethylolpropionic acid, dimethylolbutanoic acid, tartaric acid, 2-hydroxypropionic acid, malic acid, and 4-hydroxymethylbenzoic acid from the viewpoints of excellent reactivity and availability. Examples include acid. Among these, the compound represented by the formula (1) is preferable, and among the compounds represented by the formula (1), a compound in which R is a trivalent hydrocarbon group having 1 to 6 carbon atoms is more preferable, and the rigidity of the polishing layer is improved. From the viewpoint of expressing the characteristics of the zeta potential while ensuring it, dimethylol propionic acid and dimethylol butanoic acid are more preferable.

[Chain extender]
Examples of the chain extender include compounds usually used in the production of polyurethane (excluding the compounds having a carboxy group). Specific examples thereof include low molecular weight compounds having two or more active hydrogen atoms capable of reacting with isocyanate groups and having a molecular weight of 300 or less and which do not contain dienophile or diene.
Examples of the chain extender include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,2-butanediol, 1,3. -Butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4 -Bis (β-hydroxyethoxy) benzene, 1,4-cyclohexanediamine, cyclohexanedimethylene (1,4-cyclohexanediamine, etc.), bis (β-hydroxyethyl) terephthalate, 1,9-nonandiol, m-ximethylene Hexamethylenediamine, p-xamethylenediamine, diethylene glycol, triethylene glycol and other diols; ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, un Decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 3-methylpentamethylenediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine , 1,4-Cyclohexanediamine, 1,2-diaminopropane, hydrazine, ximethylenediamine, isophoronediamine, piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, tolylenediamine, xylenediamine, adipic acid Dihydrazide, isophthalic acid dihydrazide, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-bis (3-aminophenoxy) biphenyl, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 3,4'-diaminodiphenyl ether, 4,4 '-Diaminodiphenyl sulphon, 3,4-diaminodiphenyl sulphon, 3,3'-diaminodiphenyl sulphon, 4,4'-methylene-bis (2-chloroaniline), 3,3'-dimethyl-4,4'- Diaminobiphenyl, 4,4'-diaminodiphenylsul Fide, 2,6-diaminotoluene, 2,4-diaminochlorobenzene, 1,2-diaminoanthraquinone, 1,4-diaminoanthraquinone, 3,3'-diaminobenzophenone, 3,4-diaminobenzophenone, 4,4'- Diaminobenzophenone, 4,4'-diaminobibenzyl, 2,2'-diamino-1,1'-binaphthalene, 1,3-bis (4-aminophenoxy) alkane, 1,4-bis (4-aminophenoxy) Alkanes, 1,5-bis (4-aminophenoxy) Alkanes and the like 1,n-bis (4-aminophenoxy) alkanes (n is 3 to 10), 1,2-bis [2- (4-aminophenoxy) Diamines such as ethoxy] ethane, 9,9-bis (4-aminophenyl) fluorene, and 4,4'-diaminobenzanilide can be mentioned. These may be used alone or in combination of two or more.
Among these, diols such as 1,4-butanediol and 1,5-pentanediol and diamines such as hydrazine are preferable from the viewpoint of improving the rigidity of the polishing layer.

When a chain extender is used, the ratio (mol%) of the compound having a carboxy group to the total amount of the compound having a carboxy group and the chain extender is appropriately selected depending on the intended purpose, but is preferably 5 to 5 to, for example. It is 90 mol%, more preferably 10 to 70 mol%, still more preferably 15 to 60 mol%. When the content ratio of the compound having a carboxy group is within the above range, a negative potential that sufficiently repels the negative potential of the abrasive grains can be imparted to the polyurethane.

[Polymer diol]
Specific examples of the polymer diol include polyether diols, polyester diols, polycarbonate diols, and the like. These may be used alone or in combination of two or more. Among these, a polyether diol and a polycarbonate diol are preferable, and a polyether diol is more preferable, from the viewpoint of excellent availability and reactivity.

The number average molecular weight of the polymer diol is preferably 450 to 3,000, more preferably 500 to 2,700, and even more preferably 550 to 2,400. When the number average molecular weight of the polymer diol is within the above range, it is easy to obtain a polishing layer that maintains the required characteristics such as rigidity, hardness, and hydrophilicity. The number average molecular weight of the polymer diol means the number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS K 1557-1: 2007.

(Polyesterdiol)
Specific examples of the polyether diol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly (methyltetramethylene glycol), glycerin-based polyalkylene ether glycol, and the like. These may be used alone or in combination of two or more. Among these, polyethylene glycol and polytetramethylene glycol are preferable.

(Polyester diol)
In the present invention, polyester diol can be used. The polyester diol can be obtained, for example, by directly subjecting an ester-forming derivative such as a dicarboxylic acid or an ester thereof or an anhydride to a low molecular weight diol by a transesterification reaction or a transesterification reaction.

Specific examples of the dicarboxylic acid, its ester, and its anhydride for producing a polyesterdiol include, for example, oxalic acid, succinic acid, glutaric acid, adipic acid, pimeric acid, suberic acid, azelaic acid, sebacic acid, and the like. Dodecanedicarboxylic acid, 2-methylsuccinic acid, 2-methyladiponic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecane An aliphatic dicarboxylic acid having 2 to 12 carbon atoms such as a diacid; a dimerated aliphatic dicarboxylic acid having 14 to 48 carbon atoms (dimeric acid) obtained by dimerizing an unsaturated fatty acid obtained by distilling a triglyceride, and hydrogenation thereof. Examples thereof include aliphatic dicarboxylic acids such as substances (hydrogenated dimer acid); alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and orthophthalic acid. Specific examples of the dimer acid and the hydrogenated dimer acid include, for example, the trade names "Pripole 1004", "Pripole 1006", "Pripole 1009", and "Pripole 1013" manufactured by Unichema. These may be used alone or in combination of two or more.

Specific examples of the low molecular weight diol for producing the polyester diol include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1, and so on. 4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2- Alipid diols such as methyl-1,8-octanediol, 1,9-nonanediol and 1,10-decanediol; alicyclic diols such as cyclohexanedimethanol and cyclohexanediol can be mentioned. These may be used alone or in combination of two or more.
Among these, a diol having 6 to 12 carbon atoms is preferable, and a diol having 8 to 10 carbon atoms is more preferable.

(Polycarbonate diol)
Examples of the polycarbonate diol include those obtained by reacting a low molecular weight diol with a carbonate compound such as a dialkyl carbonate, an alkylene carbonate, or a diaryl carbonate. Examples of the low molecular weight diol for producing the polycarbonate diol include the low molecular weight diols exemplified above. 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 and the like.

[Organic diisocyanate]
The organic diisocyanate is not particularly limited as long as it is an organic diisocyanate usually used for producing polyurethane. For example, ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, isophorone diisocyanate, isopropyridenebis ( 4-cyclohexylisocyanate), cyclohexylmethanediisocyanate, methylcyclohexanediisocyanate, 4,4'-dicyclohexylmethanediisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate, bis (2-isocyanatoethyl) fumarate, bis (2) -Isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis (2-isocyanatoethyl) -4-cyclohexene and other fats Group or alicyclic diisocyanate; 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylenedi isocyanate, p-phenylenedi isocyanate, m -Xylylene diisocyanate, p-xylylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3' Examples thereof include aromatic diisocyanates such as -dimethyl-4,4'-diisocyanatodiphenylmethane, chlorophenylene-2,4-diisocyanate, and tetramethylxylylene diisocyanate. These may be used alone or in combination of two or more. Among these, alicyclic diisocyanate and aromatic diisocyanate are preferable from the viewpoint of improving the abrasion resistance of the obtained polishing layer, and 4,4'-dicyclohexylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, and 2,4 are preferable. -Toluene diisocyanate and 2,6-toluene diisocyanate are more preferable, and 4,4'-diphenylmethane diisocyanate is further preferable from the viewpoint of improving the rigidity of the polishing layer.

〔Additive〕
The polyurethane of the present invention can be used as a cross-linking agent, a filler, a cross-linking accelerator, a cross-linking aid, a softening agent, a tackifier, an anti-aging agent, a foaming agent, a processing aid, an adhesion-imparting agent, and an inorganic filling. Agents, organic fillers, crystal nucleating agents, heat-resistant stabilizers, weather-resistant stabilizers, antistatic agents, colorants, lubricants, flame retardants, flame retardants (antimonium oxide, etc.), blooming inhibitors, mold release agents, thickeners , Antioxidants, conductive agents and the like may be contained.
The content ratio of the additive in the polyurethane is not particularly limited, but is preferably 50% by mass or less, more preferably 20% by mass or less, and further preferably 5% by mass or less.

[Mixing ratio]
The blending ratio of each component can be appropriately adjusted according to the desired characteristics. In the present invention, the amount of the structural unit derived from the compound having a carboxy group in all the structural units constituting the polyurethane is preferably 3 to 30 mol%, more preferably 4 to 20 mol%, and further. It is preferably 6 to 15 mol%, and even more preferably 6 to 12 mol%. When the amount of the structural unit of the compound having a carboxy group is at least the above lower limit value, the effect derived from the carboxy group can be sufficiently imparted to the obtained polyurethane. That is, since a negative potential derived from the carboxy group can be sufficiently applied to the polyurethane, by using this in the polishing layer, it is possible to repel the abrasive grains having a negative potential and suppress clogging of the polishing layer. .. Further, when the amount of the structural unit derived from the compound having a carboxy group is not more than the upper limit value, it becomes easy to adjust the physical properties such as the hardness of polyurethane within the range described later.

The amount of the isocyanate group contained in the organic diisocyanate with respect to 1 mol of the active hydroxyl group contained in the compound having a carboxy group, the polymer diol, and the chain extender is preferably 0.80 to 1.3 mol, more preferably 0. .90-1.2 mol.
When the ratio of the isocyanate group to 1 mol of the active hydroxyl group is at least the above lower limit value, the mechanical strength and abrasion resistance of the thermoplastic polyurethane tend to be improved, and the life of the polishing layer tends to be long. On the other hand, when the ratio of the isocyanate group to 1 mol of the active hydrogen atom is not more than the above upper limit value, the productivity and storage stability of the thermoplastic polyurethane are improved, and the polishing layer tends to be easily produced.

<Manufacturing method of thermoplastic polyurethane>
The thermoplastic polyurethane is obtained by polymerizing the above-mentioned raw materials by a urethanization reaction using a known prepolymer method or one-shot method. More specifically, a method of blending each of the above-mentioned components in a predetermined ratio in the absence of a solvent and performing melt polymerization while melt-mixing using a single-screw or multi-screw screw extruder. Alternatively, a method of producing by polymerization by a prepolymer method in the presence of a solvent can be mentioned. The melt polymerization may be carried out continuously.
In the present invention, it is preferable to use solution polymerization from the viewpoint of stably producing the polyurethane of the present invention. The concentration of the reaction solution is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and even more preferably 20 to 50% by mass from the viewpoint of operability due to reactivity and viscosity.

The obtained thermoplastic polyurethane is pelletized and then molded into a sheet-shaped molded product by various molding methods such as an extrusion molding method, an injection molding method, a blow molding method, and a calendar molding method. In particular, by extrusion molding using a T-die, a sheet-shaped molded product having a uniform thickness can be obtained.

[Abrasive layer]
The polishing layer of the present invention uses the polyurethane of the present invention. As described above, the polyurethane of the present invention has a carboxy group in its molecular structure, and by using this in the polishing layer, the abrasive grains are clogged due to the repulsive force between the negative potential of the carboxy group and the negative potential of the abrasive grains. Is less likely to occur, so it is possible to perform stable polishing with a long life while suppressing scratches. More specifically, the slurry used in CMP includes an alkaline slurry, and the abrasive grains contained in the alkaline slurry usually have a negative zeta potential. On the other hand, since the polishing layer of the present invention uses polyurethane having a carboxy group, the carboxy group on the surface ^{dissociates into −COO −} when it comes into contact with an alkaline slurry, so that the zeta on the surface of the polishing layer The potential becomes low, for example, to about -10 mV or less. In this case, the abrasive grains showing a negative zeta potential in alkalinity and the polishing layer show electrostatic repulsion, and as a result, the adhesion of the abrasive grains to the polishing layer is prevented, and clogging is suppressed especially in the non-woven fabric-based polishing layer. It is presumed that the occurrence of scratches and defects can be reduced.
The polishing layer may be either a polyurethane foam or a polyurethane non-foam, but is preferably a non-foam. When the polishing layer is a non-foamed polyurethane, the polishing characteristics are less likely to fluctuate and stable polishing can be realized.

<Structure of polishing layer>
The polishing layer of the present invention may be formed by molding polyurethane into a sheet shape, or may be a non-woven fabric impregnated with the polyurethane of the present invention and further solidified. By using polyurethane, abrasive grains are less likely to enter the unevenness caused by the non-woven fabric, and stable polishing is possible with a long life. Therefore, the non-woven fabric is impregnated with the polyurethane of the present invention and further solidified. A polished layer is preferred.

As a method for impregnating the non-woven fabric with polyurethane, first, an organic solution such as an N, N-dimethylformamide solution (DMF solution) having a polyurethane concentration of preferably 10 to 50% by mass, more preferably 20 to 40% by mass is prepared. To do. Next, this is preferably heated to about 27 to 40 ° C., and the non-woven fabric is allowed to stand on this for preferably about 5 to 20 minutes to allow the organic solvent to permeate. Then, the non-woven fabric is subsided in an organic solution of polyurethane for preferably 2 to 15 minutes, and then the excessively adhered organic solution is removed from the removed non-woven fabric. Then, the polyurethane is solidified by immersing the non-woven fabric in an aqueous solution having an organic solvent concentration of 5 to 30% by mass and about 27 to 40 ° C. Then, if necessary, the non-woven fabric is washed with an organic solvent, water, or the like and dried to obtain a non-woven fabric impregnated with polyurethane.
Examples of the polyurethane solution impregnated in the non-woven fabric in the present invention include water-based polyurethane and solvent-based polyurethane. Here, the water-based polyurethane means a polyurethane that can be used by being dispersed in water or an aqueous solution, and the solvent-based polyurethane means a polyurethane that can be used by being dissolved in an organic solvent. Among these, solvent-based polyurethane is more preferable from the viewpoint of improving the degree of freedom in selecting a chain extender that contributes to the development of the zeta potential.

<Non-woven fabric>
The non-woven fabric that can be used in the present invention is not particularly limited, and examples thereof include non-woven fabrics made of fibers mainly composed of polyester resins such as nylon, polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). Among these, in the case of polyester fiber, since it is difficult to absorb water during polishing, the storage elastic modulus is unlikely to fluctuate and the polishing efficiency is stable. For example, in the case of a fiber having high water absorption such as nylon fiber, the storage elastic modulus fluctuates due to the high water absorption rate during polishing, the polishing pad is easily deformed, and the polishing efficiency is likely to decrease. ..

When polyester fiber is used, its average single fiber fineness is preferably 0.01 to 5.0 dtex, more preferably 0.03 to 1.0 dtex. If the average single fiber fineness is at least the above lower limit value, the fibers are less likely to break during dressing, so that scratches due to falling off can be prevented. On the other hand, when the average single fiber fineness is not more than the upper limit value, the load on the object to be polished does not become too large, so that scratching can be prevented.

<Zeta potential>
From the viewpoint of suppressing clogging of the polishing layer and effectively suppressing scratches, the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is preferably -10.0 mV or less, more preferably -50. It is .0 to -12.0 mV, more preferably -40.0 to -15.0 mV, even more preferably -30.0 to -17.0 mV, and even more preferably -27.0 to -17.0 mV. It is -20.0 mV. When the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is equal to or less than the upper limit value, the polishing layer and the abrasive grains are electrically repelled, so that the effect of suppressing clogging is improved. On the other hand, when the zeta potential at pH 7.0 is at least the above lower limit value, the slurry held on the polishing surface does not become too small, and a good polishing rate can be maintained.
In the present specification, the zeta potential refers to the potential generated on the surface (sliding surface) of the electric double layer by counterions according to the surface charge of the substance when the substance comes into contact with the liquid. Specifically, a monitor latex (manufactured by Otsuka Electronics Co., Ltd.) dispersed in a 10 mM NaCl aqueous solution adjusted to pH 7.0 with an aqueous NaCl solution using an electrophoretic light scattering device (ELS-Z, manufactured by Otsuka Electronics Co., Ltd.) Can be measured using.

Further, the zeta potential of the polyurethane forming the polishing layer at pH 5.0 is preferably −5.0 mV or less, more preferably -40.0 to -12.0 mV, and further preferably from the same viewpoint as described above. Is -35.0 to -15.0 mV, and even more preferably -30.0 to -17.0 mV.
Further, the zeta potential of the polyurethane forming the polishing layer at pH 8.0 is preferably -15.0 mV or less, more preferably -60.0 to -20.0 mV, still more preferably, from the same viewpoint as described above. Is -50.0 to -25.0 mV, and even more preferably -40.0 to -30.0 mV.

<Storage modulus>
After the polyurethane constituting the polishing layer is saturated and swollen with water at 50 ° C., the storage elastic modulus measured at 50 ° C. is preferably 50 to 1,200 MPa, more preferably 100 to 1,100 MPa, and further. It is preferably 200 to 1,000 MPa, and even more preferably 400 to 1,000 MPa. When the storage elastic modulus at 50 ° C. is at least the lower limit value, the polishing layer has appropriate softness, so that the polishing rate becomes good. On the other hand, when the storage elastic modulus is not more than the upper limit value, the scratches on the surface to be polished of the object to be polished tend to be reduced.
The storage elastic modulus can be measured by the method described in Examples.
The polyurethane satisfying the storage elastic modulus can be obtained, for example, by adjusting the content of nitrogen atoms derived from the isocyanate group in the polyurethane. Specifically, the content of nitrogen atoms derived from isocyanate groups in polyurethane is preferably 4.5 to 7.6% by mass, more preferably 5.0 to 7.4% by mass, and even more preferably. It is 5.2 to 7.3% by mass.

<Contact angle with water>
The contact angle of the polyurethane constituting the polishing layer with water is preferably 80 degrees or less, more preferably 70 degrees or less, still more preferably 60 degrees or less, still more preferably 49 degrees or less. When the contact angle of polyurethane with water is not more than the above upper limit value, the hydrophilicity of the polished surface is improved, so that scratches during polishing can be reduced.
The contact angle of polyurethane with water can be measured according to the method described in Examples.

The polyurethane constituting the polishing layer of the present invention preferably has the storage elastic modulus within the above range and the contact angle with water within the above range. Specifically, the polyurethane constituting the polishing layer is saturated and swollen with water at 50 ° C., and then the storage elastic modulus measured at 50 ° C. is preferably 50 to 1,200 MPa, more preferably 100 to 1, It is 100 MPa, more preferably 200 to 1,000 MPa, and the contact angle of the polyurethane constituting the polishing layer with water is preferably 80 degrees or less, more preferably 70 degrees or less, still more preferable. Is 60 degrees or less, and more preferably 50 degrees or less.
When both the storage elastic modulus and the contact angle with water are within the above ranges, polishing uniformity and polishing stability are further improved.

<Density>
In the present invention, the non-woven fabric may be impregnated with polyurethane and solidified, or may be made of a molded sheet of polyurethane, but the density of polyurethane when made of a molded sheet is preferably 1.0 g. It is / cm ³ or more, more preferably 1.1 g / cm ³ or more, and further preferably 1.2 g / cm ³ or more. When the density of the molded product of the thermoplastic polyurethane is at least the above lower limit value, the polishing layer has appropriate flexibility. Further, as the thermoplastic polyurethane, non-foamed thermoplastic polyurethane is particularly preferable because it is excellent in polishing stability due to its high rigidity and material homogeneity.

<Thickness of polishing layer>
The shape of the polishing layer of the present invention can be appropriately adjusted by cutting, slicing, punching, or the like, for example, a sheet-shaped molded body of thermoplastic polyurethane. The thickness of the polishing layer is not particularly limited, but is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.0 mm, and even more preferably 1.2 to 2.0 mm. When the thickness of the polishing layer is within the above range, productivity and handleability are improved, and stability of polishing performance is also improved.

<Hardness of polishing layer>
The hardness of the polishing layer is preferably 60 or more, more preferably 65 or more, and preferably 95 or less, more preferably 90 or less, as measured by JIS K 6253-3: 2012. When the hardness is at least the above lower limit value, the followability of the polishing pad to the surface to be polished becomes low, and the flatness is improved. On the other hand, when the hardness is not more than the upper limit value, scratches are less likely to occur, which is preferable.

<Shape of polishing layer>
It is preferable that the polished surface of the polishing layer is formed with recesses such as grooves and holes in a predetermined concentric, lattice-like, spiral-like, and radial patterns by grinding or laser processing. Such recesses are useful for uniformly and sufficiently supplying the slurry to the polished surface, discharging polishing debris that causes scratches, and preventing wafer damage due to adsorption of the polishing layer. For example, when the grooves are formed concentrically, the distance between the grooves is preferably 1.0 to 50 mm, more preferably 1.5 to 30 mm, and further preferably 2.0 to 15 mm. The width of the groove is preferably 0.1 to 3.0 mm, more preferably 0.2 to 2.0 mm. The depth of the groove is less than the thickness of the polishing layer, preferably 0.2 to 1.8 mm, and more preferably 0.4 to 1.5 mm. Further, as the cross-sectional shape of the groove, for example, a shape such as a rectangle, a trapezoid, a triangle, or a semicircle is appropriately selected according to an object.

[Polishing pad]
The polishing pad of the present invention uses the polishing layer of the present invention. The polishing pad of the present invention may be composed of only the polishing layer of the present invention, or may be a laminated body in which a cushion layer is laminated on a surface of the polishing layer that is not the polishing surface.
The cushion layer is preferably a layer having a hardness lower than the hardness of the polishing layer. When the hardness of the cushion layer is lower than the hardness of the polishing layer, the hard polishing layer follows the local unevenness of the surface to be polished, and the cushion layer responds to the warp and waviness of the entire substrate to be polished. In order to follow, it is possible to perform polishing with an excellent balance between global flatness (a state in which irregularities with a large period of the wafer substrate are reduced) and local flatness (a state in which local irregularities are reduced).

Specific examples of the material used as the cushion layer include a composite in which a non-woven fabric is impregnated with polyurethane (for example, "Suba400" (manufactured by Nitta Haas Co., Ltd.)); natural rubber, nitrile rubber, polybutadiene rubber, silicone rubber, etc. Rubber; thermoplastic elastomers such as polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers; foamed plastics; polyurethane and the like. Among these, polyurethane having a foamed structure is particularly preferable because it is easy to obtain preferable flexibility as a cushion layer.

The thickness of the cushion layer is not particularly limited, but is preferably about 0.5 to 5 mm, for example. If the cushion layer is too thin, the effect of following the entire warp or waviness of the surface to be polished tends to decrease, and the global flatness tends to decrease. On the other hand, if the cushion layer is too thick, the entire polishing pad tends to be soft and stable polishing tends to be difficult. When the cushion layer is laminated on the polishing layer, the thickness of the polishing pad is preferably about 0.3 to 5 mm.

[Polishing method]
The polishing method of the present invention uses the polishing layer of the present invention, and includes a step of fixing a polishing pad provided with the polishing layer on a surface plate of a polishing apparatus.
A step of holding the object to be polished in the holder of the polishing apparatus so as to face the polished surface of the polishing layer, and
A step of polishing the object to be polished by relatively sliding the polishing pad and the object to be polished while supplying a neutral or alkaline polishing slurry between the surface to be polished and the object to be polished. When,
It is a polishing method having.
According to the polishing method of the present invention, when CMP is performed using an alkaline slurry, clogging of the abrasive grains can be suppressed by improving the repulsive force between the abrasive grains in the slurry and the polishing pad. This makes it possible to extend the life of the polishing pad.

An embodiment in the case where the polishing method of the present invention is performed by CMP will be described with reference to FIG.
In CMP, a CMP apparatus 10 including a circular rotary surface plate 2 shown in FIG. 3, a slurry supply nozzle 3, a holder 4, and a pad conditioner 6 is used. A polishing pad 1 having the above-mentioned polishing layer is attached to the surface of the rotary surface plate 2 with double-sided tape or the like. Further, the holder 4 supports the object to be polished 5.

In the CMP device 10, the rotary surface plate 2 is rotated in the direction indicated by the arrow by the motor shown in the figure. Further, the holder 4 is rotated in the plane of the rotary surface plate 2 by a motor (not shown) in the direction indicated by, for example, an arrow. The pad conditioner 6 is also rotated in the plane of the rotary surface plate 2 by a motor (not shown) in the direction indicated by an arrow, for example.

First, while flowing distilled water on the polishing surface of the rotating polishing pad 1 fixed to the rotary surface plate 2, for example, a pad conditioner 6 for CMP in which diamond particles are fixed to the carrier surface by nickel electrodeposition or the like is pressed against it. Then, the polished surface of the polishing pad 1 is conditioned. Conditioning adjusts the polished surface to a surface roughness suitable for polishing the surface to be polished. Next, the slurry 7 is supplied from the slurry supply nozzle 3 to the polished surface of the rotating polishing pad 1. Further, when performing CMP, if necessary, a lubricating oil, a coolant, or the like may be used in combination with the slurry.

Here, the slurry includes an acidic slurry, an alkaline slurry, and a slurry in the vicinity of neutrality. For example, a liquid medium such as water or oil; abrasive grains such as silica, alumina, cerium oxide, zirconium oxide, and silicon carbide. A slurry used for CMP containing a base, an acid, a surfactant, an oxidizing agent such as a hydrogen peroxide solution, a reducing agent, a chelating agent, etc. is preferably used.
When the polishing layer of the present invention is used, the CMP is adjusted to alkaline using a neutral or alkaline slurry, and CMP is preferably prepared using a slurry having a pH of 5.0 to 12.0, more preferably a pH of 6.0 to 10.0. This is preferable in that the repulsive force between the abrasive grains and the polishing layer is maintained.

Then, the rotating object 5 fixed to the holder 4 is pressed against the polishing pad 1 in which the slurry 7 is evenly distributed on the polishing surface of the polishing layer. Then, the polishing process is continued until a predetermined flatness is obtained. Finishing quality is affected by adjusting the pressing force applied during polishing and the speed of relative movement between the rotary surface plate 2 and the holder 4.

The polishing conditions are not particularly limited, but in order to perform efficient polishing, it is preferable that the rotation speeds of the rotary surface plate and the holder are as low as 300 rpm or less, and the pressure applied to the object to be polished causes scratches after polishing. It is preferably 150 kPa or less so as not to prevent it. During polishing, it is preferable to continuously supply the slurry to the polished surface by a pump or the like. The amount of the slurry supplied is not particularly limited, but it is preferable to supply the slurry so that the polished surface is always covered with the slurry.

Then, it is preferable that the object to be polished after polishing is thoroughly washed with running water, and then water droplets adhering to the object to be polished are wiped off and dried using a spin dryer or the like. By polishing the surface to be polished with the slurry in this way, a smooth surface can be obtained over the entire surface to be polished. The above-mentioned CMP can be suitably used for polishing various semiconductor materials such as silicon wafers.

An example of the present invention will be described below by way of examples. The scope of the present invention is not limited to the following examples.

[Example 1]
Polytetramethylene glycol (PTG850) having a number average molecular weight of 850, dimethylolpropionic acid (DMP), which is a compound having a carboxy group, 1,4-butanediol (BD), and 4,4'-diphenylmethane diisocyanate (MDI). , PTG850: DMP: BD: MDI mass ratio of 19.9: 6.0: 16.0: 58.1 (molar ratio of DMP to BD is 20/80) for solution polymerization. To produce a thermoplastic polyurethane having a carboxy group. The produced thermoplastic polyurethane solution was made into a cast film and then dehumidified and dried at 80 ° C. for 20 hours to obtain a thermoplastic polyurethane.
The obtained thermoplastic polyurethane was evaluated as described later. The results are shown in Table 1.

[Examples 2 to 10, Comparative Examples 1 to 3]
Polyurethanes of Examples 2 to 10 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1 except that the formulations shown in Table 1 were used. The obtained thermoplastic polyurethane was evaluated as described later. The results are shown in Table 1.

The raw materials listed in Table 1 are as follows.
BD: 1,4-butanediol PD: 1,5-pentanediol DMP: Dimethylolpropionic acid (2,2-bis (hydroxymethyl) propionic acid)
DMB: Dimethylolbutanoic acid (2,2-bis (hydroxymethyl) butyric acid)
MPD: 3-Methyl-1,5-pentanediol PTG850: Polytetramethylene glycol with a number average molecular weight of 850 PEG600: Polyethylene glycol with a number average molecular weight of 600 PD1000: Polycarbonate diol with a number average molecular weight of 1000 MDI: 4,4'-diphenylmethane diisocyanate

[Evaluation method]
Each evaluation was performed on the thermoplastic polyurethanes obtained in Examples and Comparative Examples according to the method described later.

<Measurement of zeta potential>
Pellets (5 to 14 g) of each thermoplastic polyurethane produced in Examples and Comparative Examples are sandwiched between Teflon (registered trademark) sheets and then pressed at 200 to 230 ° C. using a hot press to form the molded product. A molded sheet of thermoplastic polyurethane having a thickness of 0.3 to 0.5 mm was obtained.
Next, the obtained molded sheet was cut into a size of 30 mm × 60 mm, and the surface thereof was washed. Then, using an electrophoretic light scattering device (ELS-Z, manufactured by Otsuka Electronics Co., Ltd.), the sample was attached to the plate measurement cell. Next, the zeta potential was measured using a monitor latex (manufactured by Otsuka Electronics Co., Ltd.) dispersed in a 10 mM NaCl aqueous solution adjusted to pH 5.0, pH 7.0, and pH 8.0 with an aqueous NaOH solution.

<Contact angle with water>
For each thermoplastic polyurethane produced in Examples and Comparative Examples, a film having a thickness of 300 μm was prepared by a heat pressing method. Next, the obtained film was left to stand under the conditions of 20 ° C. and 65% RH for 3 days, and 15 minutes after dropping water on the surface, a contact angle with water using DropMaster 500 manufactured by Kyowa Interface Science Co., Ltd. was used. Was measured.

<Storage modulus at 50 ° C after saturated swelling with water at 50 ° C>
For each thermoplastic polyurethane produced in Examples and Comparative Examples, injection-molded sheets having a width of 5 mm, a length of 30 mm, and a thickness of 2 mm were produced. Then, the injection molded sheet was immersed in water at 50 ° C. for 3 days. Next, after wiping the water on the surface of the injection-molded sheet taken out from the water, the dynamic viscoelasticity at 50 ° C. using a dynamic viscoelasticity measuring device (“DVE Leospectler”, manufactured by Rheology Co., Ltd.). Was measured at a frequency of 11 Hz to determine the storage elastic modulus.

<Evaluation of polishing pad>
Polishing pads were manufactured and evaluated using the polyurethanes obtained in Examples and Comparative Examples.

[Manufacture of raw fabric containing PET non-woven fabric and non-porous polyurethane]
A strand of 25 islands of sea-island type composite fiber containing polyethylene terephthalate (PET) as an island component and water-soluble thermoplastic PVA as a sea component and having a mass ratio of sea component / island component of 25/75 is melted at 265 ° C. A sea-island type composite fiber was spun by discharging from a mouthpiece for composite spinning and cooling while stretching and thinning. Then, a long fiber web was obtained by continuously collecting and pressing. Next, the long fiber webs were overlapped and needle punching treatment was performed alternately on both sides, and the long fiber webs were entangled with each other to obtain a three-dimensional entangled body.
Next, as a non-porous polymer elastic body, an aqueous emulsion of polyurethane for raw material was impregnated into a three-dimensional entangled body to impregnate it and dried. Then, the three-dimensional entangled fabric is dipped in hot water to dissolve and remove the water-soluble thermoplastic PVA of the island component from the sea-island type composite fiber, and dried to obtain PET fiber having 25 bundles of single fiber (average single fiber). A raw fabric containing a non-woven fabric (thickness 1.8 mm) having a fineness of 0.05 dtex) and non-porous polyurethane was obtained.

[Impression of thermoplastic polyurethane of Examples and Comparative Examples]
The obtained raw fabric was cut out to a size of 380 mm × 380 mm. Next, the cut out raw fabric was impregnated with the thermoplastic polyurethanes obtained in Examples and Comparative Examples, respectively.
The impregnation was applied as follows. A DMF solution having a concentration of 25% by mass of each thermoplastic polyurethane was heated to 30 ° C., and the raw fabric was allowed to stand on it for 10 minutes to allow the DMF solution to permeate. Next, the raw fabric was subsided in the DMF solution for 5 minutes, the raw fabric was taken out and placed on a glass plate, and the surface of the raw fabric was traced with a doctor knife to remove the adhered DMF solution. The same operation was performed on the back surface.

Next, an aqueous solution having a DMF concentration of 10% by mass was maintained at 30 ° C., and the raw fabric was immersed therein. The thermoplastic polyurethanes of Examples and Comparative Examples were solidified by leaving this for 30 minutes, and then the raw fabric impregnated with the thermoplastic polyurethane was immersed in hot water at 70 to 95 ° C. Next, the raw fabric impregnated with the thermoplastic polyurethane was sandwiched between metal rolls, water was squeezed out, and then the fabric was immersed in hot water again and washed with water. This operation was repeated until the DMF concentration of the squeezed water became 0.3% by mass or less. The concentration of DMF was measured with an Abbe refractometer 1T (Atago Co., Ltd.).
Next, the raw fabric washed with water was placed in a hot air dryer (device name: Safety Oven SPH-202 / ESPEC CO., LTD.) And dried at 100 ° C. for 40 minutes. In this way, the original fabric of the polishing pad was obtained.

[Flatration and grooving of the original fabric of the polishing pad]
After buffing the surface of the original fabric of the polishing pad with sandpaper (count # 180) to eliminate thickness unevenness and adjusting it to a flat surface, a flattening groove processing machine is used to make the polishing surface of the polishing pad a groove width of 2.0 mm and a groove depth. A lattice groove having a size of 0.5 mm and a pitch of 15 mm was formed. Then, the polishing pad having the lattice groove formed was cut out into a circle having a diameter of 370 mm to obtain a polishing pad with a groove having a thickness of 1.5 mm (a polishing pad composed of only a polishing layer).

Then, the obtained polishing pad was polished according to the polishing method of the present invention. Specifically, the obtained polishing pad was attached to a polishing device "MAT-BC15" manufactured by MAT Co., Ltd. Then, using a diamond dresser (# 100-coverage 80%, diameter 19 cm, mass 1 kg) manufactured by A.L.M. Co., Ltd., while flowing distilled water at a speed of 150 mL / min, the dresser rotation speed is 140 rpm and the platen rotation speed is 100 rpm. The pad surface was conditioned under the condition of 15 minutes. Next, a slurry having a pH of 7.0 to 11 was prepared by diluting the slurry (colloidal silica, slurry concentration 1%) 20 times. Then, under the conditions of a platen rotation speed of 100 rpm, a head rotation speed of 99 rpm, and a polishing pressure of 55.1 kPa, a diameter having a silicon oxide film having a thickness of 1000 nm on the surface while supplying the slurry to the polishing surface of the polishing pad at a rate of 200 mL / min. A 4-inch silicon wafer was polished for 60 seconds. Then, after polishing for 60 seconds, the polishing pad was conditioned for 30 seconds. Then, another silicon wafer was polished again and further conditioned for 30 seconds. In this way, 10 silicon wafers were polished.
Then, the speed was calculated from the weight change before and after polishing the 10th silicon wafer, and the average value was taken as the polishing speed.

<Amount of change in polishing rate (nm / min), stability of polishing rate (%)>
A 6-hour long-run test was carried out using each polishing layer, and the change in polishing rate in the latter stage of polishing (after polishing for 5 hours) was based on the value of the polishing rate when the polishing rate became stable (after polishing for 1 hour). The amount was defined as "amount of change in polishing rate (nm / min)". Further, the rate of change after polishing for 5 hours with respect to that after polishing for 1 hour was defined as "polishing rate stability (%)".

<Appearance test (scratch amount)>
The appearance of the object to be polished after polishing was observed using a high-intensity halogen lighting device. The presence and number of scratches, scratches, stains, and unpolished parts were evaluated according to the following evaluation criteria. Note that FIG. 4 is a diagram showing each of a state with scratches, a state with scratches, and a state with stains and unpolished residue, and corresponds to "3" to "4" in the following evaluations.
<Evaluation criteria>
[1: Very good]
There are no scratches, scratches, stains, or unpolished residue on 90% or more of the evaluated silicon wafers [2: Good]
There are no scratches, scratches, stains, or unpolished residue on 70% or more and less than 90% of the evaluated silicon wafers [3: Bad]
There are scratches, scratches, stains, and unpolished residue on 50% or more and less than 70% of the evaluated silicon wafers [4: Very bad]
There are scratches, scratches, stains, unpolished residue, or large scratches on 70% or more of the evaluated silicon wafers.

<Clogged (%)>
After polishing for 6 hours, a photograph of a cross section of the polishing pad was taken, and the proportion of the portion where the brown-colored abrasive grains were clogged was defined as the amount of clogging.

As is clear from the results in Table 1, according to the present invention, it is possible to provide a polishing pad capable of suppressing clogging, suppressing the occurrence of scratches, and stably polishing with a long life. I understand.
Further, as is clear from the comparison between Examples 1 to 9 and Example 10 in Table 1, it is more preferable to use a polyether diol as the polymer diol from the viewpoint of excellent stability and clogging suppression.

[Example 11]
[Manufacture of raw fabric containing PET non-woven fabric and non-porous polyurethane]
A strand of 25 islands of sea-island type composite fiber containing polyethylene terephthalate (PET) as an island component and water-soluble thermoplastic PVA as a sea component and having a mass ratio of sea component / island component of 25/75 is melted at 265 ° C. A sea-island type composite fiber was spun by discharging from a mouthpiece for composite spinning and cooling while stretching and thinning. Then, a long fiber web was obtained by continuously collecting and pressing. Next, the long fiber webs were overlapped and needle punching treatment was performed alternately on both sides, and the long fiber webs were entangled with each other to obtain a three-dimensional entangled body.
Next, as a non-porous polymer elastic body, an aqueous emulsion of polyurethane for raw material was impregnated into a three-dimensional entangled body to impregnate it and dried. Then, the three-dimensional entangled fabric is dipped in hot water to dissolve and remove the water-soluble thermoplastic PVA of the island component from the sea-island type composite fiber, and dried to obtain PET fiber having 25 bundles of single fiber (average single fiber). A raw fabric containing a non-woven fabric (thickness 1.8 mm) having a fineness of 0.05 dtex) and non-porous polyurethane was obtained.

[Impression of thermoplastic polyurethane of Examples and Comparative Examples]
Next, the obtained non-woven fabric was impregnated with an aqueous dispersion of the crosslinked polyurethane elastic body A adjusted to have a solid content concentration of 25% by mass.
The aqueous dispersion of the crosslinked polyurethane elastic body A contains 95% by mass of an amorphous polycarbonate-based polyol which is a copolymerized polyol of hexamethylene carbonate and pentamethylene carbonate, and 2,2-bis (hydroxymethyl) propionic acid 5. A polyisocyanate compound composed of a polyol component consisting of mass%, a chain extender composed of dimethylolpropionic acid (a diol having a carboxy group), 4,4'-dicyclohexylmethanediisocyanate, and an amine-based chain extension composed of hydrazine. This is obtained by adding 3 parts by mass of a carbodiimide-based cross-linking agent to 100 parts by mass of an aqueous dispersion of polyurethane obtained by blending and polymerizing the agent.
The component ratio of the polyol component, the polyisocyanate component, and the chain extender forming the polyurethane was blended in the ratio of polyol component: polyisocyanate component: chain extender = 55: 40: 5.

In the impregnation, the solid content of the aqueous dispersion was 15% by mass with respect to the mass of the non-woven fabric. Then, the non-woven fabric impregnated with the aqueous dispersion was heat-treated at 90 ° C. in a 50% RH atmosphere to solidify the polyurethane. Then, the crosslinked structure was formed by further heat-treating at 150 ° C. Then, by further heat pressing at 150 ° C., the original fabric of the polishing pad was obtained.

[Flatration and grooving of the original fabric of the polishing pad]
After buffing the surface of the original fabric of the polishing pad with sandpaper (count # 180) to eliminate thickness unevenness and adjusting it to a flat surface, a flattening groove processing machine is used to make the polishing surface of the polishing pad a groove width of 2.0 mm and a groove depth. A lattice groove having a size of 0.5 mm and a pitch of 15 mm was formed. Then, the polishing pad having the lattice groove formed was cut out into a circle having a diameter of 370 mm to obtain a polishing pad with a groove having a thickness of 1.5 mm (a polishing pad composed of only a polishing layer).
The obtained polishing pads were evaluated in the same manner as in Examples 1 to 10. The results are shown in Table 2.

As is clear from the results in Table 2, according to the present invention, even with water-based polyurethane, polyurethane that can be stably polished for a long life while suppressing the occurrence of scratches can be obtained as in the case of solvent-based polyurethane. It turns out that it can be done.

Claims (10)

1. Polyurethane having at least one structural unit derived from a compound having a carboxy group.
2. The polyurethane according to claim 1, further comprising at least a structural unit derived from the compound having a carboxy group, a structural unit derived from a chain extender, a structural unit derived from a polymer diol, and a structural unit derived from an organic diisocyanate.
3. The polyurethane according to claim 1 or 2, wherein the amount of the structural unit derived from the compound having a carboxy group is 3 to 30 mol% in all the structural units constituting the polyurethane.
4. A polishing layer using the polyurethane according to any one of claims 1 to 3.
5. The polishing layer according to claim 4, wherein the polishing layer is a non-woven fabric impregnated with the polyurethane and further solidified.
6. The polishing layer according to claim 4 or 5, wherein the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is -10.0 mV or less.
7. The polishing layer according to any one of claims 4 to 6, wherein the polyurethane is a non-foaming material.
8. Claims 4 to 7 wherein the polyurethane is saturated and swollen with water at 50 ° C., and then has a storage elastic modulus of 50 to 1,200 MPa and a contact angle with water of 80 degrees or less measured at 50 ° C. The polishing layer according to any one of.
9. A polishing pad using the polishing layer according to any one of claims 4 to 8.
10. A polishing method using the polishing layer according to any one of claims 4 to 8.
    The process of fixing the polishing pad provided with the polishing layer on the surface plate of the polishing device, and
    A step of holding the object to be polished in the holder of the polishing device so as to face the polished surface of the polishing layer, and
    A step of polishing the object to be polished by relatively sliding the polishing pad and the object to be polished while supplying a neutral or alkaline polishing slurry between the surface to be polished and the object to be polished. When,
    Polishing method with.

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