US20130316621A1

US20130316621A1 - Chemical mechanical polishing pad and chemical mechanical polishing method using same

Info

Publication number: US20130316621A1
Application number: US13/992,554
Authority: US
Inventors: Ayako Maekawa; Satoshi Kamo; Naoki Nishiguchi; Hirotaka Shida; Takahiro Okamoto; Kotaro Kubo
Original assignee: JSR Corp
Current assignee: JSR Corp
Priority date: 2010-12-07
Filing date: 2011-12-02
Publication date: 2013-11-28
Also published as: KR20130124331A; WO2012077592A1; TW201235153A; JPWO2012077592A1

Abstract

A chemical mechanical polishing pad includes a polishing layer that is formed of a composition that includes a polyurethane, the polishing layer having a specific gravity of 1.1 to 1.3 and a thermal conductivity of 0.2 W/m·K or more.

Description

TECHNICAL FIELD

The present invention relates to a chemical mechanical polishing pad and a chemical mechanical polishing method using the chemical mechanical polishing pad.

BACKGROUND ART

A porous nonwoven fabric obtained by impregnating a nonwoven fabric with a polyurethane solution, or a polyurethane molded product has been used as a polishing pad for polishing glass or a semiconductor material. The following polyurethane polishing pads have been studied as a chemical mechanical polishing pad suitable for chemical mechanical polishing (hereinafter may be referred to as “CMP”) that planarizes the surface of a semiconductor substrate.
JP-T-8-500622 discloses a polishing pad wherein a filler-like component is dispersed in a polyurethane, and JP-A-2000-17252 and Japanese Patent No. 3956364 disclose a polishing pad formed using a polyurethane foam, for example.
When performing CMP using such a polishing pad, friction may produce heat when the polishing target surface (e.g., the surface of a wafer) and the surface of the polishing pad rub against each other, and the temperature of the surface of the polishing pad may increase locally. Since the polishing performance of the polishing pad changes due to a local increase in temperature of the surface of the polishing pad, the planarity of the polishing target surface may become worse, or polishing defects (scratches) or the like may be caused. Moreover, the polishing performance of the entire polishing pad may change when frictional heat that is produced during CMP performed over a long time is accumulated in the polishing pad, and an increase in temperature of the polishing pad continuously occurs. In order to solve the problems caused by frictional heat, JP-A-7-142432 and JP-A-2003-197586 disclose a CMP system in which a cooling mechanism (e.g., coolant circulation system) is incorporated in a platen that holds the polishing pad.

SUMMARY OF THE INVENTION

Technical Problem

However, since a related-art chemical mechanical polishing pad has insufficient thermal conductivity, an improvement achieved by improving a CMP system (e.g., cooling mechanism) has been limited. In particular, a polyurethane foam that is widely used as a material for the polishing pad has a low thermal conductivity due to its foamed structure, and is used as a residential insulation. A polishing pad composed of a polyurethane foam having such properties has problems such as (1) a local increase in temperature of the surface of the polishing pad occurs due to frictional heat, and the polishing performance deteriorates, and (2) the temperature of the entire polishing pad increases due to CMP performed for a long time, and the polishing performance changes since frictional heat is not easily dissipated.
Several aspects of the invention may solve the above problems, and may provide a chemical mechanical polishing pad that can improve the Planarity of the polishing target surface, suppress occurrence of polishing defects (scratches), and maintain stable polishing performance during CMP performed for a long time, and a chemical mechanical polishing method that utilizes the chemical mechanical polishing pad.

Solution to Problem

The invention was conceived in order to solve at least some of the above problems, and may be implemented as the following aspects or application examples.

Application Example 1

According to one aspect of the invention, a chemical mechanical polishing pad includes a polishing layer that is formed of a composition that includes a polyurethane, the polishing layer having a specific gravity of 1.1 to 1.3 and a thermal conductivity of 0.2 W/m·K or more.

Application Example 2

The chemical mechanical polishing pad according to Application Example 1 may include a laminate that includes the polishing layer and a support layer that is formed on one side of the polishing layer, the laminate having a thermal conductivity of 0.2 W/m·K or more.

Application Example 3

In the chemical mechanical polishing pad according to Application Example 1 or 2, the polishing layer may have a residual strain of 2 to 10% when applying tension to the polishing layer.

Application Example 4

In the chemical mechanical polishing pad according to any one of Application Examples 1 to 3, the polishing layer may have a volume change ratio of 0.8 to 5.0% when immersed in water at 23° C. for 24 hours.

Application Example 5

In the chemical mechanical polishing pad according to Application Example 2, the support layer may have a compressibility of 5% or more.

Application Example 6

In the chemical mechanical polishing pad according to any one of Application Examples 1 to 5, the polyurethane may be a thermoplastic polyurethane.

Application Example 7

In the chemical mechanical polishing pad according to any one of Application Examples 1 to 6, the composition may further include water-soluble particles.

Application Example 8

According to another aspect of the invention, a chemical mechanical polishing method includes chemically and mechanically polishing a polishing target using the chemical mechanical polishing pad according to any one of Application Examples 1 to 7.

Advantageous Effects of the Invention

Since the chemical mechanical polishing pad according to one aspect of the invention includes the polishing layer that has a specific gravity and a thermal conductivity within the specific ranges, it is possible to improve the planarity of the polishing target surface, suppress occurrence of polishing defects (scratches), and maintain stable polishing performance during CMP performed for a long time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating the concept of the residual strain of a polishing layer when applying tension to the polishing layer.

FIG. 2A is an enlarged view of an area I illustrated in FIG. 1.

FIG. 2B is an enlarged view of an area I illustrated in FIG. 1.

FIG. 2C is an enlarged view of an area I illustrated in FIG. 1.

FIG. 2D is an enlarged view of an area I illustrated in FIG. 1.

FIG. 2E is an enlarged view of an area I illustrated in FIG. 1.

FIG. 3A is a schematic view illustrating the concept of the volume change ratio of a polishing layer.

FIG. 3B is a schematic view illustrating the concept of the volume change ratio of a polishing layer.

FIG. 4A is a schematic view illustrating the concept of the durometer D hardness of a polishing layer.

FIG. 4B is a schematic view illustrating the concept of the durometer D hardness of a polishing layer.

FIG. 5A is a schematic view illustrating the concept of the surface hardness of a polishing layer.

FIG. 5B is a schematic view illustrating the concept of the surface hardness of a polishing layer.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the invention are described in detail below. Note that the term “wet state” used herein refers to the state of the polishing layer that has been immersed in water at 23° C. for 4 hours or more. The term “hardness” used herein refers to durometer D hardness, and the term “surface hardness” used herein refers to universal hardness (HU: N/mm²). Note that the surface hardness of the polishing layer in the wet state is indicated by universal hardness (HU: N/mm²) measured when applying a constant pressure to the polishing layer (see the examples).

1. CHEMICAL MECHANICAL POLISHING PAD

A chemical mechanical polishing pad according to one embodiment of the invention includes a polishing layer that forms at least one side of the chemical mechanical polishing pad. The polishing layer has a specific gravity of 1.1 to 1.3 and a thermal conductivity of 0.2 W/m·K or more. The details of the chemical mechanical polishing pad according to one embodiment of the invention are described below.

1.1. Polishing Layer

The polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention is formed by the following production method using a composition that includes a polyurethane (hereinafter may be referred to as “composition”). The structure and the type of the polyurethane included in the composition are not particularly limited as long as the polishing layer has a specific gravity and a thermal conductivity within the above ranges. An optimum polyurethane may be appropriately selected taking account of the material of the polishing target, affinity to the slurry used for polishing, and the like. Note that the term “polishing layer” used herein refers to a single layer having a surface that comes in contact with the polishing target during chemical mechanical polishing (hereinafter referred to as “polishing surface”). The chemical mechanical polishing pad may include an additional layer that does not have a polishing surface between the polishing layer and a support layer. Such an additional layer does not fall under the term “polishing layer”.
A polyurethane-containing polishing layer is normally classified into a foamed polishing layer and a non-foamed polishing layer. Since the non-foamed polishing layer that is widely used at present has a specific gravity and a hardness higher than those of the foamed polishing layer due to its structure, the non-foamed polishing layer is elastically deformed to a small extent when coming in contact with roughness of the polishing target surface (e.g., the surface of a wafer). Therefore, the polishing target surface is sufficiently planarized. However, since the non-foamed polishing layer has higher hardness than the foamed polishing layer, polishing defects (e.g., scratches) may increase due to polishing waste or pad waste present between the polishing target surface and the polishing layer.
The foamed polishing layer tends to have a low specific gravity and low hardness due to its structure. Therefore, since polishing waste or pad waste that present between the polishing target surface (e.g., the surface of a wafer) and the polishing layer is captured by the soft surface of the polishing layer, and is not strongly pressed against the polishing target surface, occurrence of polishing defects can be suppressed. However, since the foamed polishing layer is elastically deformed to a large extent so as to follow roughness of the polishing target surface, the polishing target surface may not be sufficiently planarized. Accordingly, it has been considered that it is difficult to improve the planarity of the polishing target surface (e.g., the surface of a wafer) while suppressing occurrence of polishing defects (e.g., scratches).
The inventors of the invention found that it is possible to improve the planarity of the polishing target surface (e.g., the surface of a wafer) while suppressing occurrence of polishing defects (e.g., scratches), and achieve stable polishing performance even during CMP performed over a long time by forming the polishing layer using a composition that includes a polyurethane while controlling the specific gravity and the thermal conductivity of the polishing layer.

1.1.1. Composition

1.1.1.1. Polyurethane

The structure and the type of the polyurethane included in the composition are not particularly limited. When the polishing target is a semiconductor wafer on which wirings are formed, it is preferable to use a thermoplastic polyurethane in order to improve the planarity of the polishing target surface while suppressing occurrence of polishing defects (scratches). It is more preferable to use a thermoplastic polyurethane that includes a repeating unit derived from at least one compound selected from an alicyclic isocyanate and an aromatic isocyanate. A polishing layer that exhibits excellent flexibility can be formed when the composition includes a thermoplastic polyurethane having such a chemical structure. In this case, since polishing waste or pad waste present between the polishing target surface and the polishing layer is captured by the soft surface of the polishing layer, and is not strongly pressed against the polishing target surface, occurrence of polishing defects can be suppressed. When the polishing layer is formed using a polyurethane obtained by crosslinking a thermally crosslinkable polyurethane (thermosetting polyurethane), it is difficult to provide the polishing layer with sufficient flexibility. This makes it difficult to suppress occurrence of polishing defects.
A polishing layer formed using a polyurethane which is obtained by crosslinking a thermally crosslinkable polyurethane and in which the molecular chains are strongly bonded, swells to only a small extent even when coming in contact with water (i.e., surface hardness does not decrease in the wet state) as compared with a polishing layer formed using a thermoplastic polyurethane. Therefore, when the polishing layer includes a crosslinked polyurethane, polishing waste or pad waste present between the polishing target surface and the polishing layer is captured by the surface of the polishing layer having high surface hardness, and is strongly pressed against the polishing target surface. This makes it difficult to suppress occurrence of polishing defects.
When forming the polishing layer using the composition that includes a thermoplastic polyurethane that includes a repeating unit derived from at least one compound selected from an alicyclic isocyanate and an aromatic isocyanate, it is possible to easily control the specific gravity, the hardness, and the like of the polishing layer since the crystallinity of the polyurethane can be easily controlled.
Examples of the alicyclic isocyanate include isophorone diisocyanate (IPDI), norbornene diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate (hydrogenated MDI), and the like. These alicyclic isocyanates may be used either alone or in combination.
Examples of the aromatic isocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, naphthalene diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylene diisocyanate, and the like. Among these, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4′-diphenylmethane diisocyanate are preferable since a reaction with a hydroxyl group can be easily controlled. These aromatic isocyanates may be used either alone or in combination.
The thermoplastic polyurethane included in the composition may include a repeating unit derived from the alicyclic isocyanate and a repeating unit derived from the aromatic isocyanate, or may further include a repeating unit derived from an additional isocyanate other than the alicyclic isocyanate and the aromatic isocyanate. Examples of the additional isocyanate include aliphatic diisocyanates such as ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate.
It is preferable that the thermoplastic polyurethane included in the composition include a repeating unit derived from an alicyclic isocyanate. When the thermoplastic polyurethane includes a repeating unit derived from an alicyclic isocyanate, the thermoplastic polyurethane exhibits appropriate hardness. Moreover, it is possible to more appropriately control the surface hardness of the polishing layer in the wet state, and provide the polishing layer with higher flexibility.
It is preferable that the thermoplastic polyurethane included in the composition further include a repeating unit derived from at least one compound selected from a polyether polyol, a polyester polyol, a polycarbonate polyol, and a polyolefin polyol. When the thermoplastic polyurethane includes a repeating unit derived from at least one compound selected from these polyols, the thermoplastic polyurethane tends to exhibit improved water resistance.
The thermoplastic polyurethane included in the composition may include a repeating unit derived from a chain extender. Examples of the chain extender include low-molecular-weight dihydric alcohols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and 1,4-bis(2-hydroxyethoxy)benzene. Among these, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butylene glycol, 1,4-butanediot, 1,5-pentanediol, and 1,6-hexanediol are preferable, and 1,4-butanediol is more preferable, since a reaction with an isocyanate group can be easily controlled.
The content of a repeating unit derived from at least one compound selected from an alicyclic isocyanate and an aromatic isocyanate in the thermoplastic polyurethane included in the composition is preferably 2 to 60 mass %, and more preferably 3 to 55 mass %. When the content of a repeating unit derived from at least one compound selected from an alicyclic isocyanate and an aromatic isocyanate in the thermoplastic polyurethane is within the above range, the thermoplastic polyurethane exhibits appropriate hardness. Moreover, it is possible to appropriately control the surface hardness of the polishing layer in the wet state, and provide the polishing layer with higher flexibility.
The thermoplastic polyurethane included in the composition may be produced by an arbitrary common polyurethane production method (e.g., known batch method or prepolymer method).

1.1.1.2. Water-Absorbing Polymer Compound

The composition may further include an additional polymer compound other than the thermoplastic polyurethane. The additional polymer compound that may be included in the composition is preferably a polymer compound that has a water absorption of 3 to 3000% (hereinafter may be referred to as “water-absorbing polymer compound”). When the composition includes the water-absorbing polymer compound, the polishing layer exhibits moderate water-absorbing properties, and it is possible to easily control a change in volume of the polishing layer that may occur when the polishing layer swells due to absorption of water.
The additional polymer compound is more preferably a water-absorbing polymer compound that includes at least one bond selected from an ether bond, an ester bond, and an amide bond.
Examples of the water-absorbing polymer compound that includes an ether bond include polyoxyethylene, a polyoxyethylene alkyl ether, a polyoxyethylene alkylphenol ether, a poly(ether ester amide), a poly(ether amide imide), polypropylene glycol, polyoxypropylene butyl ether, polyoxypropylene glyceryl ether, polyoxypropylene sorbitol, an oxyethylene-epichlorohydrin copolymer, a methoxypolyethylene glycol (meth)acrylate copolymer, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene oleyl cetyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxypropylene butyl ether, polyoxyethylene polyoxypropylene hexylene glycol ether, polyoxyethylene polyoxypropylene trimethylolpropane, polyoxyethylene polyoxypropylene glyceryl ether, a copolymer of an olefin and a monomer that includes an ether bond, a chlorine-containing polyether, a polyacetal resin, an alkyl glucoside, a polyoxyethylene fatty acid amine, and the like.
Examples of the water-absorbing polymer compound that includes an ester bond include a polyoxyethylene fatty acid ester, a sucrose fatty acid ester, a sorbitan fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a glycerol fatty acid ester, an acrylate copolymer (acrylic rubber), and the like. Examples of the polyoxyethylene fatty acid ester include polyethylene glycol monostearate, polyethylene glycol laurate, polyethylene glycol monooleate, polyethylene glycol distearate, and the like.
Examples of the water-absorbing polymer compound that includes an amide bond include a fatty acid alkanolamide, a modified polyamide resin, and the like.
The polystyrene-reduced weight average molecular weight of the water-absorbing polymer compound determined by gel permeation chromatography is preferably 500 to 1,000,000, and more preferably 5000 to 500,000.
The water absorption of the water-absorbing polymer compound may be determined in accordance with JIS K 6258 (see below). Specifically, the water-absorbing polymer compound is formed into a sheet having a thickness of 2 mm. The sheet is cut to dimensions of 2×2 cm, and immersed in water at 23T for 24 hours. The mass (M1) of the sheet in air before immersion and the mass (M3) of the sheet in air after immersion are measured, and the mass change ratio is calculated by the following expression (1), and taken as the water absorption.
Water absorption (%)=((M3−M1)/M1)×100 (1)
The content of the water-absorbing polymer compound in the composition is preferably 1 to 20 mass %, more preferably 3 to 15 mass %, and particularly preferably 5 to 10 mass %, based on the total content (=100 mass %) of the thermoplastic polyurethane and the water-absorbing polymer compound. When the content of the water-absorbing polymer compound in the composition is within the above range, the volume change ratio of the polishing layer in the wet state can be easily controlled to 0.8 to 5.0%. When the volume change ratio of the polishing layer is within the above range, the surface of the polishing layer is moderately softened when the polishing layer absorbs water. Therefore, the polishing target surface can be sufficiently planarized, and occurrence of polishing defects (scratches) can be suppressed.

1.1.1.3. Water-Soluble Particles

The composition may further include water-soluble particles. It is preferable that the water-soluble particles be uniformly dispersed in the composition. In this case, a polishing layer in which the water-soluble particles are uniformly dispersed can be obtained.
When the polishing layer that includes the water-soluble particles comes in contact with a polishing aqueous dispersion that includes abrasive grains and chemicals (hereinafter may be referred to as “slurry”), the water-soluble particles are removed from the surface of the polishing layer, so that pores that retain the slurry are formed. In this case, the slurry can be sufficiently retained in the pores that are formed in the surface of the polishing layer by utilizing the water-soluble particles instead of using a polyurethane foam having a cell structure. It is also possible to control the surface hardness of the polishing layer in the wet state by utilizing the pores formed in of the polishing layer. Moreover, the specific gravity of the polishing layer can be increased by utilizing particles having a high specific gravity as the water-soluble particles.
When the composition that includes the thermoplastic polyurethane includes the water-soluble particles, the following advantages (1) to (3) can be obtained. (1) Since the water-soluble particles serve as a reinforcing agent (e.g., filler), elastic deformation of the polishing layer can be reduced, and the planarity of the polishing target surface can be improved. (2) Since a non-foamed polishing layer is formed, the polishing layer exhibits excellent mechanical strength. (3) Since it is unnecessary to uniformly control a foamed cell structure, productivity can be improved.
Examples of the water-soluble particles include, but are not limited to, organic water-soluble particles and inorganic water-soluble particles. Specific examples of the water-soluble particles include a substance that is dissolved in water (e.g., water-soluble polymer), and a substance that swells or gels when coming in contact with water and is removed from the surface of the polishing layer (e.g., water-absorbing resin).
Examples of a material for forming the organic water-soluble particles include a saccharide (e.g., polysaccharide (e.g., starch, dextrin, and cyclodextrin), lactose, and mannitol), a cellulose (e.g., hydroxypropyl cellulose and methyl cellulose), a protein, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyethylene oxide, sulfonated polyisoprene, a sulfonated isoprene copolymer, and the like.
Examples of a material for forming the inorganic water-soluble particles include potassium acetate, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, potassium bromide, potassium phosphate, potassium sulfate, magnesium sulfate, calcium nitrate, and the like.
These materials may be used either alone or in combination when forming the organic water-soluble particles or the inorganic water-soluble particles. It is preferable that the water-soluble particles be solid from the viewpoint of adjusting the mechanical strength (e.g., hardness) of the polishing layer to an appropriate value.
The composition preferably includes the water-soluble particles in an amount of 3 to 150 parts by mass based on 100 parts by mass of the thermoplastic polyurethane. When the amount of the water-soluble particles is within the above range, it is possible to form a polishing layer that achieves a high polishing rate during chemical mechanical polishing, and exhibits appropriate mechanical strength (e.g., hardness).
It is preferable that the water-soluble particles have an average particle size of 0.5 to 200 micrometers. The size of the pores formed when the water-soluble particles are removed from the surface of the polishing layer of the chemical mechanical polishing pad is preferably 0.1 to 500 micrometers, and more preferably 0.5 to 200 micrometers. When the average particle size of the water-soluble particles is within the above range, it is possible to produce a chemical mechanical polishing pad that includes a polishing layer that achieves a high polishing rate and exhibits excellent mechanical strength.

1.1.2. Specific Gravity

The polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention has a specific gravity of 1.1 to 1.3, and preferably 1.15 to 1.27. When the specific gravity of the polishing layer is within the above range, the polishing target surface can be sufficiently planarized since the polishing layer exhibits appropriate hardness. Moreover, it is possible to suppress occurrence of polishing defects (scratches) since the polishing layer exhibits moderate elastic deformation (i.e., followability) along elevations and depressions of the polishing target surface. If the specific gravity of the polishing layer is less than the above range, the hardness of the polishing layer may decrease to a large extent, and the polishing target surface may not be sufficiently planarized. If the specific gravity of the polishing layer exceeds the above range, the hardness of the polishing layer may increase to a large extent, and the number of polishing defects (scratches) may increase.
The upper limit of the specific gravity of the polishing layer is set to 1.30 taking account of the balance between the specific gravity of a polyurethane and the hardness of the polishing layer. It is necessary to use a material having a high specific gravity together with a urethane in order to produce a polishing layer having a specific gravity of more than 1.30. For example, a polishing layer having a specific gravity of more than 1.30 may be formed by mixing a urethane with a material having a high specific gravity (e.g., silica or alumina) as a filler. In this case, however, the resulting polishing layer exhibits high hardness due to the filler, and the polishing target surface may be scratched to a large extent. Therefore, it is impossible to achieve the advantageous effects of the polishing layer used in connection with the embodiments of the invention.
The specific gravity of the polishing layer may be measured in accordance with JIS Z 8807. Specifically, a Le Chatelier specific gravity bottle containing water is charged with a sample having a known mass, and the volume of the sample is determined from an increase in liquid level. The specific gravity of the sample is calculated from the mass and the volume of the sample.
It is preferable that the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention be a non-foamed polishing layer in order to adjust the specific gravity of the polishing layer within the above range. Note that the term “non-foamed polishing layer” used herein refers to a polishing layer that substantially does not include bubbles. The specific gravity of a commercially available urethane pad that includes a foamed polishing layer (e.g., “IC 1000” manufactured by Rohm & Haas) is about 0.40 to about 0.90.

1.1.3. Thermal Conductivity

The polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention has a thermal conductivity of 0.2 W/m·K or more, and preferably 0.3 W/m·K or more. When the polishing layer has a thermal conductivity of 0.2 W/m·K or more, frictional heat that is produced when the polishing target surface and the surface of the polishing pad rub against each other can be promptly diffused in the polishing layer, and a local increase in temperature of the surface of the polishing pad can be reduced. Moreover, the durability of the polishing layer can be improved by suppressing a situation in which frictional heat that is produced during CMP performed over a long time is accumulated in the polishing layer.
The thermal conductivity of the polishing layer is preferably 0.2 W/m·K or more from the viewpoint of the technical idea of the invention. The upper limit of thermal conductivity of a general-purpose engineering plastic (e.g., polyvinyl alcohol, polyvinyl chloride, epoxy resin, polyurethane, polyacrylic resin, and polyester resin) currently known in the art is 0.6 W/m·K. Note that a polymer composition having a higher thermal conductivity can be obtained by mixing a thermally conductive filler or the like into a general-purpose engineering plastic. It is considered that a novel polyurethane having a higher thermal conductivity may be developed in the future. Accordingly, the technical idea of the invention is not limited to the above thermal conductivity upper limit.
The thermal conductivity of the polishing layer is calculated from the thermal diffusivity, specific heat, and specific gravity. More specifically, a specimen is placed on a sensor, and covered with a jig equipped with a microheater, and a weight (50 g) is placed over the specimen. The thermal diffusivity D is measured from amplitude attenuation and a phase delay that occur when thermal waves generated from the surface of the microheater diffuse in the thickness direction and reach the back side of the specimen. The thermal conductivity (W/m·K) is calculated by the following expression (2) using the thermal diffusivity D, the specific heat rho and the specific gravity Cp of the specimen.
Thermal conductivity (W/m·K)=D/(rho×Cp) (2)
It is preferable that the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention be a non-foamed polishing layer in order to obtain a thermal conductivity within the above range. It is preferable that the polishing layer include a filler that exhibits high thermal conductivity. For example, the polishing layer may include water-soluble particles (see above) or the like as the filler. Note that the thermal conductivity of the polishing layer of a commercially available urethane pad that includes a foamed polishing layer (e.g., “IC 1000” manufactured by Rohm & Haas) is about 0.05 to about 0.10 W/m·K.
When the chemical mechanical polishing pad according to one embodiment of the invention includes a laminate that includes the polishing layer and a support layer (described later), or includes a laminate that includes the polishing layer, a support layer, and an additional layer that is provided between the polishing layer and the support layer, it is preferable that the laminate have a thermal conductivity of 0.2 W/m·K or more, and preferably 0.3 W/m·K or more. When the laminate has a thermal conductivity of 0.2 W/m·K or more, frictional heat that occurs when the polishing target surface and the surface of the polishing pad rub against each other can be efficiently diffused to a platen that holds the polishing pad through the additional layer and/or the support layer.
The thermal conductivity of the laminate is calculated from the thickness and the thermal conductivity of each layer. For example, when the chemical mechanical polishing pad includes the polishing layer (thickness: d1, thermal conductivity: lambda1), a support layer (thickness: d3, thermal conductivity: lambda3), and an additional layer (thickness: d2, thermal conductivity: lambda2) that is provided between the polishing layer and the support layer, the thermal conductivity is calculated by the following expression (3). When the chemical mechanical polishing pad does not include the additional layer, the thermal conductivity is calculated by the expression (3) provided that the values d2 and d2/lambda2 are 0.
Thermal conductivity (W/m·K)=(d1+d2+d3)/((d1/lambda1)+(d2/lambda2)+(d3/lambda3)) (3)
Note that the thermal conductivity of a commercially available urethane pad that includes a foamed polishing layer (e.g., “IC 1000” manufactured by Rohm & Haas) is about 0.02 to about 0.10 W/m·K.
Note that it is preferable to provide a cooling mechanism that controls temperature to a platen that holds the chemical mechanical polishing pad. This makes it possible to efficiently reduce an increase in temperature of the polishing layer, and easily allow the entire chemical mechanical polishing pad to have a constant temperature.
1.1.4. Residual Strain when Applying Tension
The residual strain of the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention when applying tension to the polishing layer is preferably 2 to 10%, and more preferably 2 to 9%.
Small pores and/or depressions are normally formed in the surface of the polishing layer, and are gradually filled (clogged) with polishing waste or pad waste, whereby a deterioration in polishing performance occurs. In this case, the surface of the polishing layer is ground by dressing using a diamond grinding wheel (hereinafter may be referred to as “diamond conditioning”) so that a surface under the initial conditions is obtained. The surface of the polishing layer may be roughened, or pad waste may occur during diamond conditioning.
FIG. 1 is a schematic view illustrating the concept of the residual strain of the polishing layer when applying tension to the polishing layer. FIGS. 2A to 2E are enlarged views of an area I in FIG. 1 that illustrate the concept of the residual strain of the polishing layer when applying tension to the polishing layer. As illustrated in FIG. 1, the surface of a polishing layer 10 is ground during diamond conditioning by rotating a dresser 20 in the direction indicated by the arrow. As illustrated in FIGS. 2A and 2B, part of the surface of the polishing layer 10 is pulled by the dresser 20 when dressing the polishing layer 10. As illustrated in FIG. 2C, part of the surface of the polishing layer 10 is removed (cut) to produce pad waste 10 a. As illustrated in FIG. 2D, an elongated portion 10 b of the polishing layer 10 shrinks so as to return to the original state due to the elasticity of the polishing layer. In this case, a roughened portion 10 b′ (see FIG. 2E) is formed due to the residual strain of the polishing layer. Therefore, the residual strain of the polishing layer when applying tension to the polishing layer is an index that indicates the degree of roughness of the surface of the polishing layer during diamond conditioning.
When the residual strain of the polishing layer when applying tension to the polishing layer is within the above range, occurrence of pad waste and roughening of the surface of the polishing layer during diamond conditioning are suppressed. It is also possible to suppress deformation of the polishing layer due to elevations and depressions of the polishing target surface (e.g., the surface of a wafer). This makes it possible to improve the planarity of the polishing target surface while suppressing occurrence of polishing defects. If the residual strain of the polishing layer when applying tension to the polishing layer is less than 2%, the amount of pad waste that occurs when subjecting the surface of the polishing layer to diamond conditioning may increase, and the number of polishing defects may increase due to entrance of the pad waste in the polishing step. If the residual strain of the polishing layer when applying tension to the polishing layer exceeds 10%, the surface of the polishing layer may be roughened to a large extent when subjecting the surface of the polishing layer to diamond conditioning, and the polishing layer may be deformed to a large extent along elevations and depressions of the polishing target surface. As a result, the polishing target surface may not be sufficiently planarized.
The residual strain of the polishing layer when applying tension to the polishing layer may be measured in accordance with JIS K 6270 (see below). A residual strain tester includes a plurality of fixed clamps that hold one end of a specimen, a plurality of reciprocating clamps that hold the other end of the specimen, a driver device that reciprocates the reciprocating clamps at a given frequency and a given amplitude, a counter that displays the number of reciprocations of the reciprocating clamps, and the like. Two dumbbell-shaped specimens are held by the clamps. After reciprocating the reciprocating clamps 1×10³times, the operation of the tester is stopped so that no stress is applied to one of the specimens. When 1 minute has elapsed, the bench mark distance of the specimen is measured. After reciprocating the reciprocating clamps 100 times, the bench mark distance of the other specimen is measured in the same manner as described above. The test is normally performed at a frequency of 1 to 5 Hz. The residual strain (%) when applying tension to the specimen is calculated by the following expression (4) using the bench mark distance (I₀) measured before the test and the bench mark distance (I_n) measured after the test in a state in which tension is not applied to the specimen.
Residual strain (%) when applying tension=((I _n −I ₀)/I ₀)×100 (4)
The temperature and the humidity during the measurement are set in accordance with “6.1 Standard temperature in test room” and “6.2 Standard humidity in test room” defined in JIS K 6250. Specifically, the standard temperature in the test room is set to 23° C. (allowance: +2° C.). The standard humidity (relative humidity) in the test room is set to 50% (allowance: ±10%).

1.1.5. Volume Change Ratio

The volume change ratio of the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention when immersing the polishing layer in water at 23° C. for 24 hours is preferably 0.8 to 5%, and more preferably 1 to 3%.
FIGS. 3A and 3B are schematic views illustrating the concept of the volume change ratio of the polishing layer. The chemical mechanical polishing pad is always exposed to the slurry during polishing. As illustrated in FIG. 3A, a depression 30 is formed in the polishing layer 10 to have given dimensions and a given shape. As illustrated in FIG. 3B, the depression 30 may change in dimensions, shape, degree of roughening, or the like when the polishing layer 10 swells due to absorption of water. When the volume change ratio of the polishing layer when immersing the polishing layer in water is within the above range, the surface of the polishing layer is moderately softened when the polishing layer swells due to absorption of water, so that occurrence of scratches can be suppressed. If the volume change ratio of the polishing layer is less than the above range, the surface of the polishing layer may not be sufficiently softened since the polishing layer may swell to only a small extent due to absorption of water, and occurrence of scratches may not be sufficiently suppressed. If the volume change ratio of the polishing layer exceeds the above range, the polishing layer may swell to a large extent due to absorption of water, and the polishing target surface may not be sufficiently planarized although occurrence of scratches may be suppressed. When a depression pattern is formed in the polishing surface of the polishing layer, the shape or the dimensions of the depression pattern may change depending on the polishing time if the polishing layer swells to a large extent due to absorption of water. As a result, stable polishing properties may not be achieved. Therefore, it is preferable to prevent a situation in which the polishing layer swells to a large extent in order to prevent deformation of the polishing surface.
The volume change ratio of the polishing layer may be determined in accordance with JIS K 6258 (see below). A polishing layer having a thickness of 2.8 mm is cut to obtain a specimen having dimensions of 2×2 cm, and the specimen is immersed in water at 23° C. for 24 hours. The mass (M1) of the specimen in air before immersion, the mass (M2) of the specimen in water before immersion, the mass (M3) of the specimen in air after immersion, and the mass (M4) of the specimen in water after immersion are measured, and the volume change ratio is calculated by the following expression (5),
Volume change ratio (%)=(((M3−M4)−(M1−M2))/(M1−M2))×100 (5)

1.1.6. Durometer D Hardness

The durometer D hardness of the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention is preferably 50 to 80, more preferably 55 to 75, and particularly preferably 60 to 70.
FIGS. 4A and 4B are schematic views illustrating the concept of the durometer D hardness of the polishing layer. When a load is applied to the polishing layer 10 from above (in the same manner as in the polishing step) as illustrated in FIG. 4A, the polishing layer 10 warps as illustrated in FIG. 4B. The durometer D hardness is an index of the degree of macroscopic warping of the polishing layer 10 when a load is applied to the polishing layer 10 in the polishing step. This can be understood from the measurement method described below. When the durometer D hardness of the polishing layer is within the above range, the polishing target surface can be sufficiently planarized, and occurrence of polishing defects (scratches) can be suppressed since the polishing layer exhibits moderate elastic deformation (i.e., followability) along elevations and depressions of the polishing target surface. If the durometer D hardness of the polishing layer is less than the above range, the polishing target may not be sufficiently planarized. If the durometer D hardness of the polishing layer exceeds the above range, the number of polishing defects (scratches) may increase.
The durometer D hardness of the polishing layer may be measured in accordance with JIS K 6253 (see below). A specimen is placed on a flat and rigid surface. A type D durometer is held so that the pressure plate of the type D durometer is parallel to the surface of the specimen, and the indenter is perpendicular to the surface of the specimen. The pressure plate is then brought into contact with the specimen without applying an impact to the specimen. Note that the measurement point (at which the end of the indenter comes in contact with the specimen) is apart from the edge of the specimen by 12 mm or more. When 15 seconds has elapsed after bringing the pressure plate into contact with the specimen, the hardness of the specimen is measured. The hardness of the specimen is measured five times at measurement points that are apart from each other by 6 mm or more. The average value of the measured values is taken as the durometer D hardness.

1.1.7. Surface Hardness in Wet State

The surface hardness of the polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention in the wet state is preferably 2 to 10 N/mm², more preferably 3 to 9 N/mm², and particularly preferably 4 to 8 N/mm². The surface hardness of the polishing layer in the wet state is an index that indicates the surface hardness of the polishing layer during CMP. FIGS. 5A and 5B are schematic views illustrating the concept of the surface hardness of the polishing layer. As illustrated in FIG. 5A, a minute probe 40 is pressed against the surface of the polishing layer 10. As illustrated in FIG. 5B, the polishing layer 10 is deformed (pushed out) by the probe 40 in an area directly under the probe 40. The surface hardness thus indicates the degree of deformation or warping of the uppermost surface of the polishing layer. More specifically, while data that indicates the macroscopic hardness of the entire polishing layer is obtained by measuring the durometer D hardness (i.e., hardness on millimeter scale) (see FIGS. 4A and 4B), data that indicates the microscopic hardness of the uppermost surface of the polishing layer is obtained by measuring the surface hardness of the polishing layer in the wet state (see FIGS. 5A and 5B). The polishing layer is depressed to a depth of 5 to 50 micrometers during CMP. Therefore, it is preferable to determine the flexibility of the uppermost surface of the polishing layer during CMP based on the surface hardness of the polishing layer in the wet state. When the surface hardness of the polishing layer in the wet state is within the above range, the uppermost surface of the polishing layer exhibits moderate flexibility, and occurrence of polishing defects (scratches) can be suppressed. If the surface hardness of the polishing layer in the wet state is less than the above range, the polishing target surface may not be sufficiently planarized. If the surface hardness of the polishing layer in the wet state exceeds the above range, the number of polishing defects (scratches) may increase. Note that the surface hardness of the polishing layer in the wet state is indicated by the universal hardness (HU) measured when pressing the polishing layer that has been immersed in water at 23° C. for 4 hours at 300 mN using a nanoindenter (“HM2000” manufactured by FISCHER).

1.1.8. Shape of Polishing Layer and Depressions

The planar shape of the polishing layer is not particularly limited. For example, the polishing layer may have a circular planar shape. When the polishing layer has a circular planar shape, the diameter of the polishing layer is preferably 150 to 1200 mm, and more preferably 500 to 1000 mm. The thickness of the polishing layer is preferably 0.5 to 5.0 mm, more preferably 1.0 to 4.0 mm, and particularly preferably 1.5 to 3.5 mm.
A plurality of depressions may be formed in the polishing surface of the polishing layer. The depressions serve as a path that retains the slurry supplied during CMP, uniformly distributes the slurry over the polishing surface, temporarily stores waste (e.g., polishing waste, pad waste, or spent slurry), and discharges the waste to the outside.
The depth of the depressions is preferably 0.1 mm or more, more preferably 0.1 to 2.5 mm, and particularly preferably 0.2 to 2.0 mm. The width of the depressions is preferably 0.1 mm or more, more preferably 0.1 to 5.0 mm, and particularly preferably 0.2 to 3.0 mm. The interval between the adjacent depressions is preferably 0.05 mm or more, more preferably 0.05 to 100 mm, and particularly preferably 0.1 to 10 mm. The pitch (i.e., the sum of the width of the depression and the distance between adjacent depressions) is preferably 0.15 mm or more, more preferably 0.15 to 105 mm, and particularly preferably 0.6 to 13 mm. The depressions may be formed at constant intervals within the above range. It is possible to easily produce a chemical mechanical polishing pad that achieves an excellent effect of suppressing occurrence of scratches on the polishing target surface and has a long lifetime by forming the depressions as described above.
The above preferable ranges may be arbitrarily combined. For example, it is preferable that the depressions have a depth of 0.1 mm or more, a width of 0.1 mm or more, and an interval of 0.05 mm or more. It is more preferable that the depressions have a depth of 0.1 to 2.5 mm, a width of 0.1 to 5.0 mm, and an interval of 0.05 to 100 mm. It is particularly preferable that the depressions have a depth of 0.2 to 2.0 mm, a width of 0.2 to 3.0 mm, and an interval of 0.1 to 10 mm.
The depressions may be formed using a multi-blade tool having the shape disclosed in JP-A-2006-167811, JP-A-2001-18164, JP-A-2008-183657, or the like. The cutting blades of the tool may be provided with a coating layer formed using diamond, or at least one metal element selected from Group 4, 5, and 6 metals (e.g., Ti, Cr, Zr, and V) and at least one non-metal element selected from nitrogen, carbon, and oxygen. The cutting blades may be provided with a plurality of coating layers that differ in material. The thickness of the coating layer is preferably 0.1 to 5 micrometers, and more preferably 1.5 to 4 micrometers. The coating layer may be formed by an appropriate known technique (e.g., technique using an arc ion plating apparatus) depending on the material of the tool, the material of the coating layer, and the like.

1.1.9. Production Method

The polishing layer included in the chemical mechanical polishing pad according to one embodiment of the invention is obtained by molding the composition that includes the polyurethane. The composition may be kneaded using a known mixer or the like. Examples of the mixer include a roller, a kneader, a Banbury mixer, an extruder (single-screw extruder or multi-screw extruder), and the like. For example, the composition that has been plasticized at 120 to 230° C. may be molded by press molding, extrusion molding, or injection molding, and plasticized/sheeted to obtain a polishing layer. The specific gravity and the hardness of the polishing layer may be controlled by appropriately adjusting the molding conditions.
Depressions may be formed in the polishing surface of the polishing layer by cutting. The depressions may be formed when forming the polishing layer by molding the composition using a mold provided with a depression pattern.

1.2. Support Layer

The chemical mechanical polishing pad according to one embodiment of the invention may include only the polishing layer, or may further include a support layer that is provided on the surface of the polishing layer opposite to the polishing surface.
The support layer included in the chemical mechanical polishing pad is used to support the polishing layer on a platen of a polishing system. The support layer may be an adhesive layer, or may be a cushion layer that has an adhesive layer on each side. The adhesive layer may be a pressure-sensitive adhesive sheet, for example.
The thickness of the pressure-sensitive adhesive sheet is preferably 50 to 250 micrometers. When the pressure-sensitive adhesive sheet has a thickness of 50 micrometers or more, it is possible to sufficiently reduce the pressure applied to the polishing surface of the polishing layer. When the pressure-sensitive adhesive sheet has a thickness of 250 micrometers or less, it is possible to obtain a chemical mechanical polishing pad having a uniform thickness so that the polishing performance is not affected by elevations or depressions of the polishing target surface.
A material for forming the pressure-sensitive adhesive sheet is not particularly limited as long as the polishing layer can be secured on the platen of the polishing system. The material for forming the pressure-sensitive adhesive sheet is preferably an acrylic material or a rubber material that has a modulus of elasticity lower than that of the polishing layer.
The adhesive strength of the pressure-sensitive adhesive sheet is not particularly limited as long as the chemical mechanical polishing pad can be secured on the platen of the polishing system. The adhesive strength of the pressure-sensitive adhesive sheet measured in accordance with JIS Z 0237 is preferably 3 N/25 mm or more, more preferably 4 N/25 mm or more, and particularly preferably 10 N/25 mm or more.
A material for forming the cushion layer is not particularly limited as long as the material has a hardness lower than that of the polishing layer. The cushion layer may be formed of a porous body (foam) or a non-porous body. Examples of the cushion layer include a layer obtained by molding a polyurethane foam or the like. The thickness of the cushion layer is preferably 0.1 to 5.0 mm, and more preferably 0.5 to 2.0 mm.
It is preferable that the support layer have a thermal conductivity of 0.2 W/m·K or more, and more preferably 0.3 W/m·K or more. When the support layer has a thermal conductivity of 0.2 W/m·K or more, frictional heat that is produced when the polishing target surface and the surface of the polishing pad rub against each other can be efficiently diffused to the platen through the support layer. As a result, frictional heat that has been produced in the polishing layer can be efficiently removed, so that an increase in temperature of the polishing layer can be reduced, and stable polishing performance can be maintained even when performing CMP for a long time.
The thermal conductivity of the support layer is measured in the same manner as in the case of measuring the thermal conductivity of the polishing layer. Note that the thermal conductivity of the support layer of a commercially available urethane pad that includes a foamed polishing layer (e.g., “IC 1000” manufactured by Rohm & Haas) is about 0.01 to about 0.10 W/m·K.
The compressibility of the support layer is preferably 5% or more, and more preferably 6% or more. When polishing the polishing target (e.g., silicon wafer), pressure applied to the polishing target per unit area differs between the center area and the peripheral area of the polishing target (i.e., pressure applied to the peripheral area of the polishing target tends to increase). In this case, since the polishing rate differs to a large extent between the center area and the peripheral area of the polishing target, it is difficult to polish the polishing target surface at a uniform polishing rate. When the compressibility of the support layer is within the above range, the support layer is effectively deformed so that an increase in pressure applied to the peripheral area of the polishing target can be reduced. Therefore, it is possible to polish the entire polishing target surface at a uniform polishing rate. If the compressibility of the polishing layer is within the above range, the polishing rate may decrease to a large extent, and the planarity of the polishing target surface may be impaired due to a decrease in pressure applied to the polishing target. Accordingly, it is desirable that the compressibility of the support layer be within the above range in order to achieve the object of the invention.

2. CHEMICAL MECHANICAL POLISHING METHOD

A chemical mechanical polishing method according to one embodiment of the invention includes chemically and mechanically polishing a polishing target using the chemical mechanical polishing pad according to one embodiment of the invention. The chemical mechanical polishing pad includes the polishing layer that is formed using the composition that includes the polyurethane, and has a specific gravity and a thermal conductivity within the specific ranges. Therefore, the chemical mechanical polishing method according to one embodiment of the invention can improve the planarity of the polishing target surface, suppress occurrence of polishing defects (scratches), and maintain stable polishing performance during CMP performed for a long time.
The chemical mechanical polishing method according to one embodiment of the invention may be implemented using a commercially available chemical mechanical polishing system. Examples of a commercially available chemical mechanical polishing system include EPO-112 and EPO-222 (manufactured by Ebara Corporation); LGP-510 and LGP-552 (manufactured by Lapmaster SFT); Mirra and Reflexion LK (manufactured by Applied Materials); and the like.
An optimum slurry may be appropriately selected depending on the polishing target (e.g., copper film, insulating film, or low-dielectric-constant insulating film).

3. EXAMPLES

The invention is further described below by way of examples. Note that the invention is not limited to the following examples.

3.1. Production of Chemical Mechanical Polishing Pad

3.1.1. Example 1

100 parts by mass of a non-alicyclic thermoplastic polyurethane (“Elastollan 1174D” manufactured by BASF, hardness: 70D) and 29 parts by mass of beta-cyclodextrin (“Dexy Pearl beta-100” manufactured by Ensuiko Sugar Refining Co., Ltd., average particle size: 20 micrometers) (water-soluble particles) were kneaded using an extruder heated at 200° C. to prepare a thermoplastic polyurethane composition. The thermoplastic polyurethane composition was compression-molded at 180° C. in a press mold to obtain a cylindrical molded product (diameter: 845 mm, thickness: 3.2 mm). The surface of the molded product was ground using sandpaper to adjust the thickness. A plurality of concentric depressions (width: 0.5 mm, depth: 1.0 mm, pitch: 1.5 mm) were formed in the surface of the molded product using a cutting machine (manufactured by Kato Machine Corporate), and the periphery of the molded product was cut to obtain a polishing layer (diameter: 600 mm, thickness: 2.5 mm). The surface of the polishing layer in which the depressions were not formed was laminated with a double-sided tape “#422JA” (manufactured by 3M) to produce a chemical mechanical polishing pad.

3.1.2. Example 2

A polishing layer was obtained in the same manner a in Example 1. The surface of the polishing layer in which the depressions were not formed was laminated with a double-sided tape “#550PS5” (manufactured by Sekisui Chemical Co., Ltd.). A sheet-like urethane (“Nippalay EXY” manufactured by NHK Spring Co., Ltd.) (support layer) was bonded to the tape, and laminated with a double-sided tape “#442JA” (manufactured by 3M) to produce a chemical mechanical polishing pad.

3.1.3. Examples 3 and 4

A chemical mechanical polishing pad was produced in the same manner as in Example 1, except that the type and the amount of each component of the composition were changed as shown in Table 1.

3.1.4. Example 5

A polishing layer was obtained in the same manner as in Example 1. The surface of the polishing layer in which the depressions were not formed was laminated with a double-sided tape “#550PS5” (manufactured by Sekisui Chemical Co., Ltd.). A support layer having the compressibility and the thermal conductivity shown in Table 1 was bonded to the tape, and laminated with a double-sided tape “#442JA” (manufactured by 3M) to produce a chemical mechanical polishing pad. Note that the support layer having the compressibility and the thermal conductivity shown in Table 1 was produced by adding an appropriate amount of spheroidal graphite (“WF-15C” manufactured by Chuetsu Graphite Works Co., Ltd.) to a hydrogenated ethylene-butylene block copolymer (“DYNARON” manufactured by JSR Corporation) so that the compressibility and the thermal conductivity shown in Table 1 were obtained, kneading the mixture using a kneader, and forming the mixture into a sheet.

3.1.5. Example 6

A chemical mechanical polishing pad was produced in the same manner as in Example 5. Note that the support layer having the compressibility and the thermal conductivity shown in Table 1 was produced by adding an appropriate amount of spheroidal alumina (“DAM-70” manufactured by Denki Kagaku Kogyo Kabushiki Kaisha) to a hydrogenated ethylene-butylene block copolymer (“DYNARON” manufactured by JSR Corporation) so that the compressibility and the thermal conductivity shown in Table 1 were obtained, kneading the mixture using a kneader, and forming the mixture into a sheet.

3.1.6. Example 7

A chemical mechanical polishing pad was produced in the same manner as in Example 2, except that a flame-retardant polycarbonate insulating sheet “SunMorfee” (manufactured by SunDelta Corporation) was used as the support layer.

3.1.7. Comparative Example 1

A commercially available chemical mechanical polishing pad (“IC 1000” manufactured by Rohm & Haas, wherein the polishing layer is formed of a thermally crosslinkable polyurethane) was used. The specific gravity and the thermal conductivity of the polishing layer measured by the following methods were 0.81 and 0.05 W/m·K, respectively.

3.1.8. Comparative Example 2

100 parts by mass of 1,2-polybutadiene (“RB830” manufactured by JSR Corporation, hardness: 47D) and 38 parts by mass of beta-cyclodextrin (“Dexy Pearl beta-100” manufactured by Ensuiko Sugar Refining Co., Ltd, average particle size: 20 micrometers) (water-soluble particles) were mixed to prepare a composition. After the addition of 1 part by mass of an organic peroxide (“Percumyl D-40” manufactured by NOF Corporation) to 100 parts by mass of the composition, the mixture was kneaded. A polishing layer formed of a water-soluble particle-containing thermally crosslinked polybutadiene resin was obtained in the same manner as in Example 1. The surface of the polishing layer in which the depressions were not formed was laminated with a double-sided tape “#550PS5” (manufactured by Sekisui Chemical Co., Ltd.). A high-density sheet-like hydrogenated ethylene-butylene block copolymer (“DAYNARON” manufactured by JSR Corporation) (support layer) was bonded to the tape, and laminated with a double-sided tape “#442JA” (manufactured by 3M) to produce a chemical mechanical polishing pad.
The abbreviation of each component shown in Table 1 has the following meaning.
“PU1-1”: non-alicyclic thermoplastic polyurethane (“Elastollan 1174D” manufactured by BASF, hardness: 70D)
“PU2-1”: alicyclic thermoplastic polyurethane (“Elastollan NY 1197A” manufactured by BASF, hardness: 61D)
“beta-CD”: beta-cyclodextrin (“Dexy Pearl beta-100” manufactured by Ensuiko Sugar Refining Co., Ltd., average particle size: 20 micrometers)
“Thermally crosslinked polybutadiene resin”: 1,2-polybutadiene (“RB830”manufactured by JSR Corporation, hardness: 47D)
“Organic peroxide”: dicumyl peroxide (“Percumyl D-40” manufactured by NOF Corporation, crosslinking agent)

3.2. Measurement of Properties of Polishing Layer

3.2.1. Specific gravity

The specific gravity of the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” was measured. The specific gravity was measured in accordance with JIS Z 8807. The results are shown in Table 1.

3.2.2. Thermal Conductivity

The thermal conductivity of the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” was measured. The thermal conductivity was measured as described below. A specimen was placed on a sensor, and covered with a jig equipped with a microheater, and a weight (50 g) was placed over the specimen. The thermal diffusivity D was measured from an amplitude attenuation and a phase delay that occurred when thermal waves generated from the surface of the microheater diffused in the thickness direction and reached the back side of the specimen. The thermal conductivity (W/m·K) was calculated by the following expression (2) using the thermal diffusivity D, the specific heat rho and the specific gravity Cp of the specimen. The results are shown in Table 1.
Thermal conductivity (W/m·K)=D/(rho×Cp) (2)

3.2.3. Residual Strain when Applying Tension

A specimen was prepared from the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” in an area in which the depressions were not formed, and the residual strain when applying tension was measured. The residual strain when applying tension was measured in accordance with JIS K 6270. The temperature and the humidity (relative humidity) during the measurement were respectively 23° C. and 50%. The results are shown in Table 1.

3.2.4. Volume Change Ratio

The volume change ratio of the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” was measured. The volume change ratio of the polishing layer was measured in accordance with JIS K 6258 (see below). The polishing layer having a thickness of 2.8 mm was cut into a square measurement specimen (2×2 cm). The measurement specimen was immersed in water at 23° C. for 24 hours. The mass (M1) of the measurement specimen in air before immersion, the mass (M2) of the measurement specimen in water before immersion, the mass (M3) of the measurement specimen in air after immersion, and the mass (M4) of the measurement specimen in water after immersion were measured using an electronic balance (“JP-300” manufactured by Cho Balance Co., Ltd.), and the volume change ratio was calculated by the following expression (5). The results are shown in Table 1.
Volume change ratio (%)=(((M3−M4)−(M1−M2))/(M1−M2))×100 (5)

3.2.5. Durometer D Hardness

The durometer D hardness of the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” was measured. The durometer D hardness of the polishing layer was measured in accordance with JIS K 6253. The results are shown in Table 1.

3.2.6. Surface Hardness in Wet State

The surface hardness of the polishing layer produced in the section “3.1. Production of chemical mechanical polishing pad” and the polishing layer of the pad “IC 1000” in the wet state was measured. The universal hardness (HU) measured when pressing a nanoindenter (“HM2000” manufactured by FISCHER) against the polishing layer (that had been immersed in water at 23° C. for 4 hours) at 300 mN was taken as the surface hardness of the polishing layer in the wet state. The results are shown in Table 1.

3.3. Measurement of Properties of Support Layer

3.3.1. Compressibility

The support layer used in the section “3.1. Production of chemical mechanical polishing pad” and the support layer removed from the pad “IC 1000” were cut into a square small piece (2×2 cm). The small piece was placed on the probe of a measurement system “Compressive Elasticity Tester Model. SE-15” (manufactured by Intec Co., Ltd.). A load of 10 gf or 600 gf was applied to the small piece, and the small piece was allowed to stand for 1 minute while applying a constant load. The thickness of the small piece was then measured, and taken as a temporary thickness of the small piece. The thickness in a blank state (i.e., a state in which the small piece was not placed on the probe) was also measured. The compressibility was calculated by the following expression (6) using the measurement results.
|Temporary thickness of small piece at 10 gf−thickness in blank state at 10 gf|=thickness of support layer at 10 gf
|Temporary thickness of small piece at 600 gf−thickness in blank state at 600 gf|=thickness of support layer at 600 gf
(Thickness of support layer at 10 gf−thickness of support layer at 600 gf)/thickness of support layer at 10 gf×100=compressibility (%) (6)

3.4. Evaluation of Chemical Mechanical Polishing

The chemical mechanical polishing pad produced in the section “3.1. Production of chemical mechanical polishing pad” was installed in a chemical mechanical polishing system (“EPO-112” manufactured by Ebara Corporation), and dressed for 30 minutes using a dresser (“#325-63R” manufactured by A.L.M.T. Corp.) at a table rotational speed of 20 rpm, a dressing rotational speed of 19 rpm, and a dressing load of 5.1 kgf. The polishing target was chemically mechanically polished using the dressed chemical mechanical polishing pad under the following conditions, and the polishing performance was evaluated as described below.
Head rotational speed: 60 rpm
Head load: 3 psi (20.6 kPa)
Table rotational speed: 61 rpm
Slurry supply rate: 300 cm³/min
Slurry: CMS8401/CMS8452 (manufactured by JSR Corporation)

3.4.1. Evaluation of Flatness

A polishing target (test substrate) was prepared by depositing a PETEOS film (thickness: 5000 angstroms) on a silicon substrate, forming a mask pattern (“SEMATECH 854”), and sequentially depositing a tantalum nitride film (thickness: 250 angstroms), a copper seed film (thickness: 1000 angstroms), and a copper film (thickness: 10,000 angstroms) over the mask pattern.
The polishing target was chemically and mechanically polished for 1 minute under the conditions described in the section “3.4. Evaluation of chemical mechanical polishing”. The thickness of the polishing target was measured before and after chemical mechanical polishing using an electric conduction-type thickness measurement system (“OmniMap RS75” manufactured by KLA-Tencor), and the polishing rate was calculated from the thickness of the polishing target before chemical mechanical polishing, the thickness of the polishing target after chemical mechanical polishing, and the polishing time. An end point detection time at which Cu had been completely removed (i.e., Cu clear) was calculated from the time from the start of polishing to the end point detected based on a change in table torque current. The polishing target (patterned wafer) was polished for a time 1.2 times the end point detection time, and the amount of dishing of a copper interconnect (width: 100 micrometers) was measured (in an area in which a pattern in which a copper interconnect area (width: 100 micrometers) and an insulating area (width: 100 micrometers) were alternately provided, was continuously formed to a length of 3.0 mm in the direction perpendicular to the longitudinal direction) using a precision step meter (“HRP-240” manufactured by KLA-Tencor Corporation). The planarity of the polishing target surface was evaluated based on the amount of dishing. The results are shown in Table 1. The amount of dishing is preferably less than 400 angstroms, more preferably less than 300 angstroms, and particularly preferably less than 200 angstroms.

3.4.2. Evaluation of Scratches

The number of scratches that occurred on the polishing target surface of the polishing target (patterned wafer) due to polishing was counted using a wafer defect inspection system (“KLA 2351” manufactured by KLA-Tencor Corporation). The results are shown in Table 1. The number of scratches is preferably less than 50, more preferably less than 30, and particularly preferably less than 20.

3.4.3. Evaluation of Polishing Rate

A polishing target (8-inch wafer on which a PETEOS film (thickness: 1000 nm) was formed) was chemically and mechanically polished under the conditions described in the section “3.4. Evaluation of chemical mechanical polishing”. Note that the PETEOS film is a silicon oxide film formed by plasma-enhanced chemical vapor deposition using tetraethylorthosilicate (TEOS) as a raw material.
The thickness of the PETEOS film of the polishing target was measured (at 33 points situated at equal intervals in the diametrical direction excluding the range of 5 mm from each end) before and after chemical mechanical polishing using an optical interference-type thickness meter (“Nano Spec 6100” manufactured by Nanometrics Japan Ltd.). The polishing rate was calculated by the following expressions (7) and (8) using the measurement results.
Amount of polishing (nm)=thickness (nm) before polishing−thickness (nm) after polishing (7)
Polishing rate (nm/min)=average amount of polishing (nm) at 33 points/polishing time (min) (8)
The polishing rate evaluation results are shown in Table 1. The polishing performance was evaluated as acceptable when the polishing rate was 200 nm/min or more, and evaluated as unacceptable when the polishing rate was less than 200 nm/min.

3.4.4. Evaluation of Durability

The polishing rate change ratio when continuously polishing the wafer based on the method described in the section “3.4.3. Evaluation of polishing rate” was calculated by the following expression (9) to evaluate the durability of the polishing layer. More specifically, the dresser and the pad were set to a frictional state for 10 hours by dressing in order to reproduce a state in which the wafer is continuously polished, and the change ratio was calculated by the expression (9) using the polishing rate before and after dressing. The durability was evaluated as “Acceptable” when the polishing rate change ratio was less than 5%, evaluated as “Fair” when the polishing rate change ratio was 5% or more and less than 10%, and evaluated as “Unacceptable” when the polishing rate change ratio was 10% or more (see Table 1).
Polishing rate change ratio (%)=((polishing rate after 10 hours of dressing−initial polishing rate)/initial polishing rate)×100 (9)

3.4.5. Evaluation of Polishing Rate Change Ratio in Edge Area

A polishing target (8-inch wafer on which a PETEOS film (thickness: 1000 nm) was formed) was chemically and mechanically polished under the conditions described in the section “3.4. Evaluation of chemical mechanical polishing”. The thickness of the PETEOS film of the polishing target was measured (at 0 mm, 4 mm, 8 mm, and 98 mm from the center of the wafer in the diametrical direction) before and after chemical mechanical polishing using an optical interference-type thickness meter (“Nano Spec 6100” manufactured by Nanometrics Japan Ltd.). The polishing rate change ratio in the edge area RR was calculated by the following expressions using the measurement results.
Amount of polishing (nm)=thickness (nm) before polishing−thickness (nm) after polishing
Amount of polishing (nm) in center area=average amount of polishing (nm) at 0 mm, 4 mm, and 8 mm from center
Polishing rate (nm/min) in center area=amount of polishing (nm) in center area/polishing time (min)
Amount of polishing (nm) in edge area=average amount of polishing (nm) at 98 mm from center
Polishing rate (nm/min) in edge area=amount of polishing (nm) in edge area/polishing time (min)
Polishing rate change ratio in edge area=|(polishing rate in edge area−polishing rate in center area)/polishing rate in center area|
It is preferable that the polishing rate change ratio in the edge area be as small as possible. It is determined that the polishing rate change ratio is practical when the polishing rate change ratio is 30% or less. The evaluation results for the polishing rate change ratio in the edge area are shown in Table 1.

TABLE 1

							Compar-	Compar-
Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	ative	ative
ple 1	ple 2	ple 3	ple 4	ple 5	ple 6	ple 7	Example 1	Example 2

Composi-	Thermo-	PU1-1	100	100	70	50	100	100	100	IC1000
tion	plastic	(parts by mass)								(commercially
	poly-	PU2-1			30	50				available
	urethane	(parts by mass)								pad)
	Other	Thermally									100
		crosslinked
		polybutadiene
		resin
		(parts by mass)
		beta-CD	29	29	29		29	29	29		38
		(parts by mass)
		Organic peroxide									1.38
		(parts by mass)

Properties	Specific gravity	1.23	1.23	1.21	1.13	1.23	1.23	1.23	0.81	1.03
of polishing	Thermal conductivity	0.27	0.27	0.32	0.20	0.27	0.27	0.27	0.10	0.24
layer	(W/m · k)
	Residual strain (%) when	2.6	2.6	3.8	13.7	2.6	2.6	2.6	8.0	7.0
	applying tension
	Volume change ratio (%)	1.4	1.4	0.7	0.8	1.4	1.4	1.4	0.2	0.1
	Durometer D hardness	79D	79D	72D	64D	79D	79D	79D	63D	67D
	Surface hardness (N/mm²)	6.7	6.5	4.4	4.0	6.7	6.7	6.7	14.5	8.9
Properties	Compressibility (%)	—	3.5	—	—	13.0	6.5	3.0	12.0	2.0
of support	Thermal conductivity	—	0.08	—	—	0.55	0.80	1.45	0.03	0.18
layer	(W/m · k)
Properties	Thermal conductivity	0.27	0.12	0.32	0.24	0.34	0.37	0.34	0.05	0.47
of laminate	(W/m · k)
Chemical	Number of scratches	45	49	33	12	48	47	46	125	130
mechanical	Amount of dishing (angstroms)	220	231	145	380	225	228	215	310	350
polishing	Polishing rate (angstroms/min)	610	810	591	700	710	600	650	730	450
evaluation	Durability	Accept-	Fair	Accept-	Accept-	Accept-	Accept-	Accept-	Unaccept-	Unaccept-
results		able		able	able	able	able	able	able	able
	Polishing rate change ratio	30	15	28	30	9	12	25	28	25
	(%) in edge area

3.5. Chemical Mechanical Polishing Pad Evaluation Results

As shown in Table 1, since the polishing layer of the chemical mechanical polishing pads of Examples 1 to 7 had a thermal conductivity of 0.2 W/m·K or more, frictional heat that occurred when the polishing target surface and the polishing pad rubbed against each other could be reduced. It is considered that the polishing layer of the chemical mechanical polishing pads of Examples 1 to 7 showed excellent durability due to the above effect. The chemical mechanical polishing pads of Examples 1 to 7 showed excellent results for planarity and scratches.
In contrast, the chemical mechanical polishing pads of Comparative Examples 1 and 2 showed poor results for one or more polishing performance items.
The polishing layer of the chemical mechanical polishing pad of Comparative Example 1 was formed of the thermally crosslinked polyurethane having a foamed structure, and had a thermal conductivity of 0.10 W/m·K. In this case, frictional heat tends to be accumulated in the polishing layer. As a result, the polishing layer of the chemical mechanical polishing pad of Comparative Example 1 exhibited poor durability. The chemical mechanical polishing pad of Comparative Example 1 was a laminate of the polishing layer and the support layer. Since the laminate had a thermal conductivity of 0.05 W/m·K, it was difficult to diffuse frictional heat.
The polishing layer of the chemical mechanical polishing pad of Comparative Example 2 was formed of polybutadiene, and had a sufficiently high thermal conductivity of 0.24 W/m·K. However, since the surface of the polishing layer had poor hydrophilicity, and transfer of heat to the slurry on the surface of the polishing layer was insufficient, the polishing layer exhibited poor durability. The chemical mechanical polishing pad also exhibited poor scratch resistance.
As is clear from the results obtained in the examples and the comparative examples, the chemical mechanical polishing pad according to the embodiments of invention achieved excellent flatness and exhibited excellent scratch resistance and excellent durability as a result of specifying the balance between the specific gravity and the thermal conductivity of the polishing layer formed of a polyurethane.
The invention is not limited to the above embodiments. Various modifications and variations may be made of the above embodiments. For example, the invention includes various other configurations substantially the same as the configurations described in connection with the above embodiments (e.g., a configuration having the same function, method, and results, or a configuration having the same objective and results). The invention also includes a configuration in which an unsubstantial part (element) described in connection with the above embodiments is replaced with another part (element). The invention also includes a configuration having the same effects as those of the configurations described in connection with the above embodiments, or a configuration capable of achieving the same objective as that of the configurations described in connection with the above embodiments. The invention further includes a configuration in which a known technique is added to the configurations described in connection with the above embodiments.

REFERENCE SIGNS LIST

10: polishing layer, 10 a: pad waste, 10 b: elongated portion, 10 b′: roughened portion, 20: dresser, 30: depression, 40: probe

Claims

1. A chemical mechanical polishing pad comprising a polishing layer that is formed of a composition comprising a polyurethane,

wherein the polishing layer has a specific gravity of from 1.1 to 1.3 and a thermal conductivity of 0.2 W/m·K or more.

2. The chemical mechanical polishing pad according to claim 1, further comprising a laminate which comprises the polishing layer and a support layer that is formed on one side of the polishing layer,

wherein the laminate has a thermal conductivity of 0.2 W/m·K or more.

3. The chemical mechanical polishing pad according to claim 1,

wherein the polishing layer has a residual strain of from 2 to 10% when applying tension to the polishing layer.

4. The chemical mechanical polishing pad according to claim 1,

wherein the polishing layer has a volume change ratio of from 0.8 to 5.0% when immersed in water at 23° C. for 24 hours.

5. The chemical mechanical polishing pad according to claim 2,

wherein the support layer has a compressibility of 5% or more.

6. The chemical mechanical polishing pad according to claim 1,

wherein the polyurethane is a thermoplastic polyurethane.

7. The chemical mechanical polishing pad according to claim 1,

wherein the composition further comprises water-soluble particles.

8. A chemical mechanical polishing method comprising chemically and mechanically polishing a polishing target with the chemical mechanical polishing pad according to claim 1.

9. The chemical mechanical polishing pad according to claim 2,

10. The chemical mechanical polishing pad according to claim 2,

11. The chemical mechanical polishing pad according to claim 3,

12. The chemical mechanical polishing pad according to claim 2, wherein the polyurethane is a thermoplastic polyurethane.

13. The chemical mechanical polishing pad according to claim 3, wherein the polyurethane is a thermoplastic polyurethane.

14. The chemical mechanical polishing pad according to claim 4, wherein the polyurethane is a thermoplastic polyurethane.

15. The chemical mechanical polishing pad according to claim 5, wherein the polyurethane is a thermoplastic polyurethane.

16. The chemical mechanical polishing pad according to claim 2, wherein the composition further comprises water-soluble particles.

17. The chemical mechanical polishing pad according to claim 3, wherein the composition further comprises water-soluble particles.

18. The chemical mechanical polishing pad according to claim 4, wherein the composition further comprises water-soluble particles.

19. The chemical mechanical polishing pad according to claim 5, wherein the composition further comprises water-soluble particles.

20. The chemical mechanical polishing pad according to claim 6, wherein the composition further comprises water-soluble particles.