JP7137504B2 - Polishing pad, method for manufacturing polishing pad, method for polishing surface of optical material or semiconductor material, and method for evaluating polishing pad - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polishing pad, a method for manufacturing a polishing pad, a method for polishing the surface of an optical material or a semiconductor material, and a method for evaluating a polishing pad. The polishing pad of the present invention is used for polishing optical materials, semiconductor wafers, semiconductor devices, substrates for hard disks, etc., and is particularly suitable for polishing devices in which an oxide layer, a metal layer, etc. are formed on a semiconductor wafer. used for

2. Description of the Related Art In recent years, along with multi-layer wiring on the surface of a semiconductor substrate, a so-called chemical mechanical polishing (CMP) technique for polishing and flattening a semiconductor substrate has been used when manufacturing devices. CMP is a method of planarizing the surface of an object to be polished (object to be polished) such as a semiconductor substrate using a polishing composition (slurry) containing abrasive grains such as silica, an anticorrosive agent, a surfactant, and the like. The objects to be polished (objects to be polished) are silicon, polysilicon, silicon oxide films, silicon nitrides, wirings and plugs made of metal or the like.

A large amount of impurities are generated on the surface of the semiconductor substrate in the CMP process. Impurities include abrasive grains derived from the polishing composition used in CMP, organic substances such as metals, anticorrosive agents, and surfactants, silicon-containing materials to be polished, metal wiring, plugs, and the like produced by polishing. It contains silicon-containing materials, metals, and organic substances such as pad scraps generated from various pads, and remains as inorganic particles and organic residues. Contamination of the semiconductor substrate surface with these impurities can adversely affect the electrical properties of the semiconductor and reduce the reliability of the device. In particular, the low-dielectric-constant interlayer insulating film to be polished is highly hydrophobic, and impurities are likely to be adsorbed by the hydrophobic interaction. Therefore, polishing pads used in CMP are required to reduce inorganic particles and organic residues remaining on the semiconductor substrate surface by polishing.

The CMP process includes rough polishing for the purpose of adjusting the flatness and final polishing for the purpose of improving the surface roughness.

Patent Literature 1 discloses that a soft suede pad that does not easily cause scratches or other polishing damage is preferably used as a polishing pad for finishing the surface of a device.

JP 2010-149259 A

In final polishing using a finishing polishing pad as disclosed in Patent Document 1, there is a demand for a pad that does not scratch an object to be polished and that has a small variation in polishing rate during polishing. In particular, there is a great need for a pad with a small variation in polishing rate from the initial stage of polishing, and there is a demand for a finishing polishing pad that enables stable polishing immediately after the start of polishing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing pad that suppresses polishing scratches, has little variation in polishing rate during polishing, and has excellent polishing stability.

As a result of intensive research to solve the above problems, the present inventors have found that the content ratio of the crystalline phase component (Ac ₂₀ ) and the content ratio of the interfacial phase component (Ai ₂₀ ) at 20 ° C. are within specific ranges. The inventors have found that the above problems can be solved by using a layer, and have completed the present invention. Specific aspects of the present invention are as follows.

[1] A polishing pad having a polishing layer containing a polyurethane resin,
For the polishing layer, the free induction decay signal (FID) obtained by pulse NMR is subtracted in order from the component with the longer spin-spin relaxation time T2 by the least squares method, and the waveform is separated to obtain the component with the longer spin-spin relaxation time T2. When divided into three components, _i.e. , amorphous phase, interfacial phase, and crystalline phase, in order from the The polishing pad having a content (Ai ₂₀ ) of 40 to 50%.
[2] The absolute value of the difference (|Ai ₂₀ −Ai ₄₀ |) between the content ratio of the interfacial phase component at 20° C. (Ai ₂₀ ) and the content ratio of the interfacial phase component (Ai ₄₀ ) at 40° C. is 35 to 50, the polishing pad according to [1].
[3] The polishing pad according to [1] or [2], wherein the polishing layer has an A hardness of 5 to 15.
[4] The polishing pad according to any one of [1] to [3], wherein the compressibility of the polishing layer is 35 to 65%.
[5] A method for manufacturing a polishing pad according to any one of [1] to [4], comprising using a wet film-forming method.
[6] A method of polishing a surface of an optical material or a semiconductor material, comprising using the polishing pad according to any one of [1] to [4].
[7] A method for evaluating a polishing pad having a polishing layer containing a polyurethane resin, comprising:
For the polished layer, the free induction decay signal (FID) obtained by pulse NMR is subtracted in order from the component with the longer spin-spin relaxation time T2 by the least squares method, and the waveform is separated to obtain the component with the longer spin-spin relaxation time T2. When divided into three components, an _amorphous phase, an interfacial phase, and a crystalline phase, in order from The evaluation method, including the step of confirming whether the content ratio (Ai ₂₀ ) is 40 to 50%.
[8] The absolute value of the difference (|Ai ₂₀ −Ai ₄₀ |) between the content ratio of the interphase component (Ai ₂₀ ) at 20° C. and the content ratio (Ai ₄₀ ) of the interphase component at 40° C. is 35 to The evaluation method according to [7], further including the step of confirming whether or not it is 50.

The polishing pad of the present invention can suppress polishing scratches, has little variation in polishing rate during polishing, and has excellent polishing stability.

It is a figure explaining the structural-analysis method of the polishing pad by pulse NMR. FIG. 2 is a schematic view showing an example of an apparatus for carrying out coating, coagulation regeneration, washing/drying steps in the manufacturing process of the polishing pad of the present invention. It is a figure which shows sectional drawing of an example of the polishing pad of this invention. It is a figure explaining the polishing method of the to-be-polished object using the polishing pad of this invention. 4 is a graph showing the results (relaxation time of each component) of structural analysis by pulse NMR of the polishing pads obtained in Example 1 and Comparative Examples 1 to 3. FIG. 4 is a graph showing the results (content ratio of each component) of structural analysis by pulse NMR of the polishing pads obtained in Example 1 and Comparative Example 1. FIG. 4 is a graph showing the results (content ratio of each component) of structural analysis by pulse NMR of the polishing pads obtained in Comparative Examples 2 and 3. FIG. 1 is a photograph showing cross sections of polishing pads obtained in Example 1 and Comparative Example 1. FIG. 4 is a photograph showing cross sections of polishing pads obtained in Comparative Examples 2 and 3. FIG.

(action)
In the present invention, the polishing layer has a crystal phase component content (Ac ₂₀ ) of 10 to 20% at 20°C and an interfacial phase component content (Ai ₂₀ ) of 40 to 50% at 20°C. use something.

The present inventors have unexpectedly found that the content of the crystalline phase component (Ac ₂₀ ) at 20°C is 10 to 20%, and the content of the interfacial phase component (Ai ₂₀ ) at 20°C is 40 to 50%. %, it is possible to obtain a polishing pad that suppresses polishing scratches, reduces fluctuations in the polishing rate during polishing, and has excellent polishing stability. Although the details of the reason why these characteristics are obtained are not clear, it is speculated as follows.

The content ratio of the crystalline phase component (Ac ₂₀ ) at 20°C corresponds to the content ratio of the crystalline phase component at room temperature (about 20°C) at the beginning of polishing, and the content ratio of the crystalline phase component is the polyurethane resin. It is thought that it means the ratio of hard segment components in In addition, the content ratio of the interfacial phase component (Ai ₂₀ ) at 20°C corresponds to the content ratio of the interfacial phase component at room temperature (about 20°C) at the initial stage of polishing. It is thought that it means a molecular chain whose movement is restrained to some extent. The polyurethane resin in the polishing pad of the present invention has a relatively low content of hard segment components and a relatively high proportion of molecular chains whose movement is constrained to some extent. As a result, it is thought that the polishing rate is less fluctuating during polishing, the polishing stability is excellent, and polishing scratches can be suppressed.

(Structural analysis by pulse NMR)
In pulse NMR, an FID signal with excellent quantification can be obtained by detecting a response signal to the pulse. Therefore, the phase separation structure of the polyurethane resin can be analyzed. The initial value of the FID signal is proportional to the number of protons in the sample to be measured, and if there are multiple components in the sample to be measured, the FID signal will be the sum of the response signals of each component. If there is a difference in the mobility of each component, the speed of attenuation of the response signal will be different and the spin-spin relaxation time T2 will be different. can. The relaxation time T2 decreases as the motility of the component decreases, and the relaxation time T2 increases as the motility increases. In other words, the shorter the relaxation time T2, the greater the crystallinity, and the longer the relaxation time T2, the greater the amorphousness.

As shown in FIG. 1, curve D shows the FID signal obtained by pulsed NMR of polyurethane resin. From the curve D, the component with the longest relaxation time T2 is subtracted in descending order by the method of least squares, and the waveform is separated. A component with a long relaxation time T2 indicated by the curve S corresponds to the amorphous phase, and a component with a short relaxation time T2 indicated by the curve H corresponds to the crystalline phase. The component indicated by curve I between curve S and curve H corresponds to the interfacial phase. In polyurethane resins, the component ratio of the amorphous phase formed by the soft segments with high mobility correlates with the compression modulus, and the component ratio of the crystalline phase formed with the hard segments with low mobility correlates with the A hardness. Therefore, if the proportion of the amorphous phase is increased, the compressive elastic modulus can be increased, and if the proportion of the crystalline phase is increased, the A hardness can be increased.

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

(polishing pad)
The polishing pad of the present invention is a polishing pad having a polishing layer containing a polyurethane resin. By subtracting the longest component in order and separating the waveform, when divided into the three components of the amorphous phase, the interfacial phase, and the crystalline phase in order from the longest spin-spin relaxation time T2, the content of the crystalline phase component at 20 ° C. The ratio (Ac ₂₀ ) is 10 to 20%, and the content ratio (Ai ₂₀ ) of the interfacial phase component at 20° C. is 40 to 50%.
Ac ₂₀ is 10-20%, preferably 10-18%, more preferably 10-17%. Ai ₂₀ is 40-50%, preferably 41-49%, more preferably 42-48%. When Ac ₂₀ and Ai ₂₀ are within the above numerical ranges, polishing scratches can be suppressed, variation in polishing rate during polishing is small, and a polishing pad with excellent polishing stability can be obtained.

A polyurethane resin (polishing layer) having an Ac ₂₀ of 10 to 20% can be obtained by reducing the 100% resin modulus (MPa) of the polyurethane resin used for the polishing layer. The 100% resin modulus of the polyurethane resin contained in the polishing layer is preferably 1.0-5.0 MPa, more preferably 1.5-4.0 MPa, most preferably 1.8-3.5 MPa. The 100% resin modulus of polyurethane resin is an indicator of the hardness of the resin, and the load applied when a non-foamed resin sheet is stretched 100% (when it is stretched to twice its original length) is expressed in terms of cross-sectional area. is the divided value. The 100% resin modulus is obtained by thinly stretching the resin solution and drying it with hot air to prepare a dry film having a thickness of about 200 μm. A sample is punched into a dumbbell shape with a thickness of 200 μm, and the measurement sample is sandwiched between the upper and lower air chucks of the universal material testing machine Tensilon (Tensilon universal testing machine "RTC-1210" manufactured by A&D Co., Ltd.), 20 ° C. (± 2 ° C.) and a humidity of 65% (±5%), pull at a pulling speed of 100 mm/min, and divide the tension at the time of 100% elongation (at the time of 2-fold elongation) by the initial cross-sectional area of the sample. The resin modulus was measured by dissolving a polyurethane foam sheet in N,N-dimethylformamide (DMF) to obtain a low-concentration polyurethane resin DMF solution, then evaporating the DMF by a casting method to obtain a non-foamed resin sheet. It can also be measured by forming.
The weight average molecular weight of the polyurethane resin contained in the polishing layer is preferably 100,000 to 200,000, more preferably 110,000 to 160,000, and most preferably 120,000 to 140,000. The weight average molecular weight of the polyurethane resin can be measured by gel permeation chromatography (GPC) described below.

Adjustment of the content ratio of the components of the interfacial phase is achieved by adjusting the composition of the thermoplastic polyurethane resin, that is, the type and molecular weight of the polymer diol, the type of diisocyanate, the amount of the chain extender and terminal blocker, or by adjusting the amount of these polymers. By adjusting the compounding molar ratio of diol, polyisocyanate, and chain extender, it is possible to produce the compound within an appropriate range. For example, by bringing the polarities of the hard segment and the soft segment closer to each other, the phase separation is less likely to proceed and the interfacial phase can be increased.

In the polishing pad of the present invention, the absolute value of the difference _{(|Ai 20 -Ai 40 |} ) is preferably 35-50, more preferably 36-48, and most preferably 37-46.
When |Ai ₂₀ -Ai ₄₀ | is within the above numerical range, it is considered that a polishing pad having the following effects can be obtained.
Regarding polishing with a polishing pad, the temperature of the polishing surface of the polishing pad at the beginning of polishing is around room temperature (approximately 20°C), but the temperature of the polishing surface during the middle and later stages of polishing is around 40°C due to frictional heat and the like. rises to It is thought that when the temperature of the polishing surface of the polishing pad rises with the progress of polishing, some of the molecular chains bound as the interfacial phase are released and become free-moving amorphous phase components. In the present invention, |Ai ₂₀ -Ai ₄₀ | is relatively large, and as the temperature rises from 20.degree. C. to 40.degree. Therefore, in a state where polishing heat is generated by polishing (approximately 40°C), the softness of the polishing pad increases, and the force of pressing the abrasive agglomerate, which consists of polishing dust, pad dust, slurry components, etc., against the object to be polished is reduced. Since it can be weakened, it is considered that the effect of suppressing polishing scratches is large for easily scratched surfaces. In addition, in the present invention, since the content of the interfacial phase at 20° C. is relatively high, the dressing performance of the polishing layer is improved when dressing is usually performed at room temperature (approximately 20° C.), and the change in polishing rate over time is reduced. considered to be suppressed.

Ai ₄₀ is preferably 1-10%, more preferably 2-8%, most preferably 3-7%.

The content of the amorphous phase component at 20° C. is preferably 25 to 60%, more preferably 30 to 50%, and most preferably 35 to 45%.
The relaxation time of the amorphous phase component at 20° C. is preferably 800-1300 μs, more preferably 900-1250 μs, and most preferably 1000-1200 μs. The relaxation time of the interphase component at 20° C. is preferably 100-300 μs, more preferably 150-280 μs, most preferably 180-250 μs. The relaxation time of the crystalline phase component at 20° C. is preferably 10-30 μs, more preferably 15-28 μs, and most preferably 18-25 μs.
The content of the amorphous phase component at 40° C. is preferably 70 to 95%, more preferably 75 to 95%, and most preferably 80 to 95%. The content of the crystalline phase component at 40° C. is preferably 1 to 10%, more preferably 2 to 8%, and most preferably 3 to 7%.
The relaxation time of the amorphous phase component at 40° C. is preferably 500-800 μs, more preferably 620-780 μs, and most preferably 650-750 μs. The relaxation time of the components of the interphase at 40° C. is preferably 10-50 μs, more preferably 15-40 μs, most preferably 20-35 μs. The relaxation time of the crystalline phase component at 40° C. is preferably 5-30 μs, more preferably 10-25 μs, and most preferably 15-20 μs.

The A hardness of the polishing layer is preferably 5-15, more preferably 6-14, and most preferably 7-13. When the A hardness is within the above numerical range, a polishing pad having a good balance between the suppression of polishing scratches and the polishing rate can be obtained.

The compressibility of the polishing layer is preferably 35-65%, more preferably 35-60%, and most preferably 35-55%. When the compressibility is within the above numerical range, the contact of the polishing pad with the object to be polished is stabilized, and good polishing characteristics are obtained.

(Polyurethane resin composition)
The polyurethane resin of the polishing pad of the present invention is obtained by reacting a polyisocyanate compound with a curing agent such as polyol or polyamine, and a chain extender can also be used. The crystalline phase (hard segment) is composed of structural units derived from isocyanate compounds and chain extenders, and the amorphous phase (soft segment) is composed of structural units derived from polyols and diamines having aliphatic organic groups with a relatively high degree of freedom. consists of

A polyisocyanate compound can be used in the form of a prepolymer obtained by previously reacting a polyisocyanate compound and a polyol to increase the molecular weight.

Examples of polyisocyanate compounds include aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, and xylylene diisocyanate: hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hydrogenated Examples include aliphatic or alicyclic diisocyanates such as tolylene diisocyanate and hydrogenated xylylene diisocyanate.

Examples of polyols (polymeric diols) include polyether diols, polyester diols, and polycarbonate diols. These polymer diols may be used alone or in combination of two or more. Among these, it is preferable to use polyether diol from the viewpoint of reducing polishing scratches.
Polyether diols include, for example, poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), poly(methyltetramethylene glycol) and the like. These polyether diols may be used alone or in combination of two or more.
The polyester diol can be produced, for example, by direct esterification reaction or transesterification reaction between a dicarboxylic acid or an ester-forming derivative thereof such as an ester or anhydride thereof and a low-molecular-weight diol.
Dicarboxylic acids constituting polyester diols include, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3- Aliphatic dicarboxylic acids having 4 to 12 carbon atoms such as methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid and 3,7-dimethyldecanedioic acid; terephthalic acid , isophthalic acid, orthophthalic acid, and other aromatic dicarboxylic acids; These dicarboxylic acids may be used alone or in combination of two or more.
Examples of low-molecular-weight diols constituting polyester diols include ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, and 1,5-pentane. Diol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decane aliphatic diols such as diols; alicyclic diols such as cyclohexanedimethanol and cyclohexanediol; and the like. These low-molecular-weight diols may be used alone or in combination of two or more. The number of carbon atoms in the low-molecular-weight diol is, for example, 6 or more and 12 or less.

Examples of chain extenders include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, saccharose, and methylene glycol. , glycerin, sorbitol and other aliphatic polyol compounds; bisphenol A, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylsulfone, hydrogenated bisphenol A, hydroquinone and other aromatic polyol Compounds, water, etc. can be used. These chain extenders may be used alone or in combination of two or more.

(other ingredients)
The polyurethane resin composition of the present invention can contain additives. The additive is preferably selected from the group consisting of film formation aids and foam control aids.
Examples of film-forming aids include hydrophobic activators and the like. Hydrophobic active agents include, for example, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, perfluoroalkylethylene oxide adduct, glycerin fatty acid ester, propylene glycol fatty acid ester, polyether-modified Examples include nonionic surfactants such as silicones and anionic surfactants such as alkylcarboxylic acids.
Examples of the anti-foaming aid include hydrophilic activators and the like. Hydrophilic surfactants include, for example, anionic surfactants such as carboxylates, sulfonates, sulfates, phosphates, and cellulose esters.
When a film forming aid is added as an additive, it is preferably 0.2 to 10% by mass. When a foaming inhibitor is added as an additive, it is preferably 0.2 to 10% by mass.

(Polymerization reaction of polyurethane resin composition)
A polyurethane resin can be produced by polymerizing the polyurethane resin composition described above. Namely, a method of carrying out a polymerization reaction in an organic solvent in the presence of a catalyst, if necessary, and the like can be mentioned.

(Method for manufacturing polishing pad)
A method for manufacturing a polishing pad of the present invention is the method for manufacturing a polishing pad described above, and includes a step of using a wet film-forming method.

Hereinafter, a method for manufacturing a polishing pad of the present invention will be described with reference to the drawings.
FIG. 3 shows a cross-sectional view of an example of the polishing pad of the present invention. A polishing pad 1 of the present invention has a polyurethane sheet 2 as a soft plastic foam manufactured by a wet film-forming method. The polyurethane sheet 2 is buffed on the polishing surface P side so that the thickness of the polyurethane sheet 2 (the length in the vertical direction in FIG. 3) becomes substantially uniform (details will be described later).

The polyurethane sheet 2 has the skin layer formed on the surface side by the wet film-forming method removed by buffing. A polishing surface P for polishing the object to be polished is formed by the buffing process. Inside the polyurethane sheet 2, foams 3 having a rounded cross-section and a substantially triangular shape are formed along the thickness direction of the polyurethane sheet 2. - 特許庁The spatial volume of the foam 3 is formed such that the size on the side of the polishing surface P is smaller than that on the back side of the polishing surface P. - 特許庁Microfoams having a smaller spatial volume than the foams 3 are formed in the polyurethane resin between the foams 3 . The foams 3 and the fine foams are connected to form a three-dimensional network through communicating holes.

The polishing pad 1 is formed by bonding a substrate 8 (polyethylene terephthalate resin sheet having a thickness of 188 μm) and a buffed surface of a polyurethane sheet 2 opposite to the buffed surface using an acrylic adhesive. ing. A double-sided tape for attaching the polishing pad 1 to the polishing machine is adhered to the surface of the substrate 8 opposite to the surface adhered to the polyurethane resin sheet. The double-sided tape has an adhesive layer on the other side (the side opposite to the base material 8) covered with a release paper.

A polyurethane sheet 2 is produced by a wet film-forming method, and a base material 8 is adhered to it. That is, in the wet film-forming method, a polyurethane resin solution obtained by dissolving a polyurethane resin in an organic solvent is continuously applied to a film-forming substrate, and the substrate is immersed in an aqueous coagulating liquid to coagulate and regenerate the polyurethane resin into a film. After washing and drying, a band-shaped (long-sized) polyurethane sheet 2 is produced. The order of steps will be described below.

In the preparation step, the polyurethane resin, N,N-dimethylformamide (hereinafter abbreviated as DMF), which is a water-miscible organic solvent capable of dissolving the polyurethane resin, and additives are mixed to dissolve the polyurethane resin. For example, the polyurethane resin is dissolved in DMF to a concentration of 30% by mass. In order to control the size and amount (number) of the foam 3, the additive may be a hydrophilic activator that promotes foaming and a hydrophobic activator that stabilizes the solidification and regeneration of the polyurethane resin. The resulting solution is filtered to remove aggregates and the like, and then defoamed under vacuum to obtain a polyurethane resin solution.

In the coating process, the coagulation regeneration process, and the cleaning/drying process, the polyurethane resin solution obtained in the preparation process is continuously applied to the film-forming substrate, and the polyurethane resin is coagulated and regenerated by being immersed in the water-based coagulation liquid, and then washed. After drying, a polyurethane sheet 2 is obtained. The coating process, the coagulation regeneration process, and the cleaning/drying process are continuously performed in the film forming apparatus shown in FIG. 2, for example.

As shown in FIG. 2, the film forming apparatus 60 is filled with a pretreatment liquid 15 such as water or an aqueous solution of DMF (mixture of DMF and water) for pretreating the nonwoven fabric or woven fabric of the film forming substrate. A pretreatment tank 10, a coagulation tank 20 filled with a coagulating liquid 25 mainly composed of water, which is a poor solvent for the polyurethane resin, for coagulating and regenerating the polyurethane resin, and water for washing the polyurethane resin after coagulating and regenerating. A cleaning bath 30 filled with a cleaning liquid 35 such as the above and a cylinder dryer 50 for drying the polyurethane resin are continuously provided.

On the upstream side of the pretreatment bath 10, a substrate supply roller 41 for supplying a film-forming substrate 43 is arranged. The pretreatment bath 10 has a pair of guide rollers 13 at the inner lower portion of the substantially central portion in the longitudinal direction which is the same as the conveying direction of the film forming substrate 43 . Above the pretreatment tank 10, guide rollers 11 and 12 are arranged on the side of the base material supply roller 41, and on the side of the coagulation tank 20, excess pretreatment liquid contained in the pretreated film base material 43 is disposed. A mangle roller 18 is arranged to remove 15 . On the downstream side of the mangle roller 18, a knife coater 46 is arranged to apply the polyurethane resin solution 45 to the film-forming substrate 43 substantially uniformly. A guide roller 21 is arranged downstream of the knife coater 46 and above the coagulation tank 20 .

A guide roller 23 is arranged in the inner lower part of the coagulation tank 20 on the cleaning tank 30 side. Above the coagulation tank 20 and on the cleaning tank 30 side, a mangle roller 28 is arranged for dewatering the polyurethane resin after coagulation and regeneration. A guide roller 31 is arranged downstream of the mangle roller 28 and above the cleaning tank 30 . In the cleaning tank 30, four guide rollers 33 are arranged in the upper part and 5 guide rollers 33 in the lower part in the same longitudinal direction as the conveying direction of the film-forming base material 43 so as to be arranged vertically alternately. Above the washing tank 30 and on the side of the cylinder dryer 50, a mangle roller 38 for dehydrating the washed polyurethane resin is arranged. In the cylinder dryer 50, four cylinders having heat sources inside are arranged in four stages. A take-up roller 42 is arranged downstream of the cylinder dryer 50 to take up the dried polyurethane resin (together with the film-forming substrate 43). The mangle rollers 18, 28, 38, the cylinder dryer 50, and the take-up roller 42 are connected to a rotation drive motor (not shown). 41 to the take-up roller 42 . The conveying speed of the film-forming base material 43 is set to, for example, 2.5 m/min, preferably in the range of 1.0 to 5.0 m/min.

When non-woven fabric or woven fabric is used for the film-forming substrate 43, the film-forming substrate 43 is pulled out from the substrate supply roller 41 and continuously introduced into the pretreatment liquid 15 via the guide rollers 11 and 12. . By passing the film-forming substrate 43 between the pair of guide rollers 13 in the pre-treatment liquid 15 to perform pretreatment (filling), when the polyurethane resin solution 45 is applied, the film-forming substrate 43 will not be exposed to the inside of the film-forming substrate 43 . permeation of the polyurethane resin solution 45 is suppressed. After being pulled up from the pretreatment liquid 15 , the film-forming substrate 43 is pressed by the mangle roller 18 to squeeze out excess pretreatment liquid 15 . The film-forming substrate 43 after the pretreatment is transported toward the coagulation tank 20 . When a flexible film made of PET or the like is used as the film forming substrate 43, pretreatment is not required. The pretreatment liquid 15 may be omitted. Hereinafter, in this example, the film-forming substrate 43 will be described as a PET film.

In the application step, the polyurethane resin solution 45 prepared in the preparatory step is applied substantially uniformly to the film-forming substrate 43 by a knife coater 46 at room temperature. At this time, the coating thickness (coating amount) of the polyurethane resin solution 45 is adjusted by adjusting the gap (clearance) between the knife coater 46 and the upper surface of the film-forming substrate 43 .

In the coagulation regeneration process, the film-forming substrate 43 coated with the polyurethane resin solution 45 by the knife coater 46 is introduced into the coagulation liquid 25 from the guide roller 21 toward the guide roller 23 . In the coagulating liquid 25, first, a skin layer 4 with a thickness of several μm is formed on the surface of the polyurethane resin solution 45 applied. After that, as the replacement of the DMF in the polyurethane resin solution 45 with the coagulating liquid 25 progresses, the polyurethane resin solidifies and reproduces on one side of the film-forming substrate 43 . This coagulation regeneration of the polyurethane resin is completed before the film-forming substrate 43 coated with the polyurethane resin solution 45 enters the coagulation liquid 25 and reaches the guide roller 23 . As the DMF desolvates from the polyurethane resin solution 45, foam 3 is formed in the polyurethane resin. At this time, since the film-forming substrate 43 of the PET film does not allow water to permeate, solvent removal occurs on the surface side of the polyurethane resin solution 45, and foams 3 that are larger on the film-forming substrate 43 side than on the surface side are formed. The coagulated and regenerated polyurethane resin is pulled up from the coagulating liquid 25, and after excess coagulating liquid 25 is squeezed out by the mangle roller 28, it is conveyed to the cleaning tank 30 via the guide roller 31 and introduced into the cleaning liquid 35.

In the cleaning/drying step, the polyurethane resin introduced into the cleaning liquid 35 is alternately passed through the guide rollers 33 vertically, thereby cleaning the polyurethane resin. After washing, the polyurethane resin is pulled up from the washing liquid 35 and excess washing liquid 35 is squeezed off by the mangle roller 38 . After that, the polyurethane resin is dried by passing it alternately (in the direction of the arrow in FIG. 2) between the four cylinders of the cylinder dryer 50 along the peripheral surfaces of the cylinders. The dried polyurethane resin (polyurethane sheet 2 ) is wound around the winding roller 42 together with the film-forming substrate 43 .

In the buffing process, the skin layer side of the film-forming resin is buffed so that the thickness is uniform. The polyurethane sheet 2 wound on the winding roller 42 is formed on the PET film of the film-forming substrate 43 . Since the thickness of the polyurethane sheet 2 varies during film formation, the polishing surface P is formed with irregularities. After peeling off the film-forming substrate 43, the surface of the film-forming resin on the side opposite to the skin layer is press-contacted with the surface of a press-contact jig having a substantially flat surface, so that unevenness appears on the skin layer side. The irregularities appearing on the skin layer side are removed by buffing. In this example, since the continuously produced polyurethane sheet 2 is belt-shaped, the skin layer side is continuously buffed while the polishing surface P is pressed against the pressing jig. As a result, the polyurethane sheet 2, from which the skin layer has been removed and a flat polished surface has been formed, is uniform in thickness and has openings.

In the bonding step, the substrate 8 (polyethylene terephthalate resin sheet having a thickness of 188 μm) is bonded to the buffed surface of the polyurethane sheet 2 opposite to the buffed surface using an acrylic adhesive.

In the lamination process, a double-faced tape is attached to the surface of the substrate 8 opposite to the surface attached to the polyurethane resin sheet. After the polished surface P is embossed, it is cut into a desired shape such as a circle in a cutting/inspection process. The embossing pattern is not particularly limited as long as the slurry moves smoothly during polishing. Then, the polishing pad 1 is completed by performing an inspection such as confirming that there is no adhesion of dirt, foreign matter, or the like.

(Method for polishing surface of optical material or semiconductor material)
A method of polishing the surface of an optical or semiconductor material of the present invention includes using the polishing pad described above.

Hereinafter, the polishing method using the polishing pad of the present invention will be described with reference to the drawings.
When polishing the object to be polished, for example, as shown in FIG. 4, a single-sided polisher 70 is used. The single-sided polisher 70 has a press platen 72 for pressing the object to be polished on the upper side, and a rotatable rotary platen 71 on the lower side. Both the lower surface of the pressing surface plate 72 and the upper surface of the rotating surface plate 71 are formed flat. A back pad 75 is attached to the lower surface of the pressure platen 72 , and a polishing pad 1 for polishing an object to be polished is attached to the upper surface of the rotary platen 71 . By soaking the back pad 75 with an appropriate amount of water and pressing the object 78 to be polished, the object 78 to be polished is held on the back pad 75 by the surface tension of water and the adhesiveness of the polyurethane resin. By rotating the rotating surface plate 71 while pressing the object 78 to be polished with the pressure plate 72 , the lower surface (surface to be processed) of the object 78 to be polished is polished with the polishing pad 1 .

(Evaluation method of polishing pad)
The method for evaluating a polishing pad of the present invention is a method for evaluating a polishing pad having a polishing layer containing a polyurethane resin. -By subtracting the component with the longer spin relaxation time T2 in descending order and separating the waveform, when divided into the three components of the amorphous phase, the interfacial phase, and the crystalline phase in order from the longer spin-spin relaxation time T2, at 20 ° C. A step of confirming whether the content of the crystalline phase component (Ac ₂₀ ) is 10 to 20% and the content of the interfacial phase component (Ai ₂₀ ) at 20° C. is 40 to 50%.

The evaluation method of the polishing pad of the present invention is based on the absolute value of the difference ₍ | _{Ai 20} − Ai ₄₀ |) can further include the step of checking whether it is 35-50.

In the evaluation method of the polishing pad of the present invention, the numerical ranges of Ac ₂₀ , Ai ₂₀ , |Ai ₂₀ −Ai ₄₀ |, and Ai ₄₀ may be those described for the polishing pad.

The present invention will be experimentally illustrated by the following examples, but the following descriptions are not intended to be construed as limiting the scope of the present invention to the following examples.

(Example 1)
To 100 parts by mass of a polyurethane DMF solution containing 30% by mass of a polyester polyurethane resin having a 100% resin modulus of 4.0 MPa and a weight average molecular weight of 132,800, 50 parts by mass of DMF, 5 parts by mass of polyether-modified silicone as an additive, acetyl A resin-containing solution was obtained by adding and mixing 1 part by mass of butyl cellulose, 1 part by mass of nonionic surfactant, and 1 part by mass of cellulose ester. The polyester-based polyurethane resin includes a polyester diol obtained by reacting adipic acid with a polyol having 1,4-butanediol as a constituent unit, and a chain of 1,4-butanediol/ethylene glycol=9/1 molar ratio. A product obtained by condensing an extender with 4,4'-diphenylmethane diisocyanate (MDI) was used.
In this example, the 100% resin modulus means the value obtained by dividing the load applied when a non-foamed resin sheet is stretched 100% (when stretched to twice its original length) by the cross-sectional area. . The 100% resin modulus is obtained by thinly stretching the resin solution and drying it with hot air to prepare a dry film having a thickness of about 200 μm. A sample is punched into a dumbbell shape with a thickness of 200 μm, and the measurement sample is sandwiched between the upper and lower air chucks of the universal material testing machine Tensilon (Tensilon universal testing machine "RTC-1210" manufactured by A&D Co., Ltd.), 20 ° C. (± 2 ° C.) and a humidity of 65% (±5%), the tensile strength was obtained by dividing the tension at the time of 100% elongation (at the time of 2-fold elongation) by the initial cross-sectional area of the sample.
Moreover, in the present Examples, the weight average molecular weight means that measured by GPC under the measurement conditions described later.

Next, a PET film is prepared as a substrate for film formation, and the resin-containing solution is applied thereon with a knife coater to a thickness of 1.0 mm, and immersed in a coagulation bath (coagulation liquid: water), After the resin-containing solution was solidified, it was washed and dried, and then peeled off from the PET film to obtain a resin film (thickness: 1.0 mm). The skin layer formed on the surface of the obtained resin film was subjected to a grinding treatment (amount of grinding: 200 μm). Thereafter, a portion of the resin film was embossed with a grid-like mold to obtain a polishing pad.

(Comparative example 1)
Instead of the polyurethane-DMF solution of Example 1, a polyurethane-DMF solution containing a polyester-based polyurethane resin having a 100% resin modulus of 7.0 MPa and a weight-average molecular weight of 104,300 and a concentration of 30 mass % was prepared. 32 parts of DMF and 5 parts of water were mixed with 100 parts by mass of this polyurethane DMF solution to obtain a resin-containing solution. The polyester-based polyurethane resin includes a polyester diol obtained by reacting adipic acid with a polyol having 1,4-butanediol as a structural unit, and 1,4-butanediol/1,6-hexanediol=9/1. The one obtained by condensing a molar ratio of chain extender and 4,4'-diphenylmethane diisocyanate (MDI) was used.
Thereafter, a resin film was produced in the same manner as in Example 1 to obtain a polishing pad.

(Comparative example 2)
Instead of the polyurethane-DMF solution of Example 1, a polyurethane-DMF solution containing a polyester-based polyurethane resin having a 100% resin modulus of 8.5 MPa and a weight-average molecular weight of 137,700 and a concentration of 30 mass % was prepared. 56 parts of DMF, 2 parts of polyether-modified silicone, and 3 parts of cellulose ester were mixed with 100 parts by mass of this polyurethane-DMF solution to obtain a resin-containing solution. The polyester-based polyurethane resin includes a polyester diol obtained by reacting adipic acid with a polyol having 1,4-butanediol as a structural unit, and 1,4-butanediol/1,6-hexanediol=9/1. The one obtained by condensing a molar ratio of chain extender and 4,4'-diphenylmethane diisocyanate (MDI) was used.
Thereafter, a resin film was produced in the same manner as in Example 1 to obtain a polishing pad.

(Comparative Example 3)
Instead of the polyurethane-DMF solution of Example 1, a polyurethane-DMF solution containing a 30% by weight polyester polyurethane resin having a 100% resin modulus of 7.5 MPa and a weight-average molecular weight of 120,000 was prepared. 31.8 parts of DMF, 1 part of polyether-modified silicone and 1 part of cellulose ester were mixed with 100 parts by mass of this polyurethane-DMF solution to obtain a resin-containing solution. Polyester-based polyurethane resins include a polyester diol obtained by reacting adipic acid with a polyol having 1,4-butanediol as a structural unit, and 1,4-butanediol/3-methyl-1,5-pentanediol. =9/1 molar ratio of a chain extender and 4,4'-diphenylmethane diisocyanate (MDI) were used.
Thereafter, a resin film was produced in the same manner as in Example 1 to obtain a polishing pad.

(Evaluation method)
The polishing pads of Example 1 and Comparative Examples 1 to 3 were subjected to the following GPC measurement, pulse NMR, A hardness, and D hardness measurements. Further, the polishing pads of Example 1 and Comparative Examples 1 to 3 were subjected to a polishing test to evaluate the polishing rate variability, polishing stability, and polishing scratches.

(GPC measurement)
From the polishing pads obtained in Example 1 and Comparative Examples 1 to 3, 0.05 g of the polyurethane resin of the polishing layer was cut off and dissolved in 4.95 g of DMF to prepare a 1% polyurethane DMF solution. Shake at 50° C. for 14 hours with a mixer. After shaking, 0.5 g of the supernatant was weighed and mixed with 2 g of DMF to form a 0.2% polyurethane DMF solution, which was then filtered through a 0.45 μm filter to obtain a measurement sample. The resulting measurement sample was subjected to gel permeation chromatography (GPC) measurement under the following conditions to determine the weight average molecular weight. A standard curve was prepared using polyethylene glycol oxide (EasiVial PEG/PEO manufactured by Agilent Technologies) as a standard sample.
(Measurement condition)
Column: Ohpak KB-805HQ (exclusion limit 2000000)
Mobile phase: 5mM LiBr/DMF
Flow rate: 0.75ml/min (21kg/cm ² )
Oven: 60℃
Detector: RI
Sample volume: 30 μl

(Pulse NMR)
Structural analysis was performed on the polishing pads of Example 1 and Comparative Examples 1 to 3 by pulse NMR under the following conditions.

Using the above equipment and conditions, the land portion of the embossed polishing pad obtained was cut out with a cutter, and a sample piece of about 1 to 3 mm square was filled in a 10 mmφ sample tube to a height of 1 to 2 cm, and subjected to pulse NMR. An attenuation curve was obtained by measuring Analysis was performed by the method of least squares using the Lorenz function (straight line portion) and Gaussian function (curved portion) so that the obtained attenuation curve and the fitting curve were in agreement. The ratio (abundance ratio (%)) and relaxation time (T2) were obtained. For fitting and analysis, the software attached to the measuring device was used.

(A hardness)
The A hardness of the polishing layer was measured by cutting out a urethane foam sheet sample piece (10 cm × 10 cm) from the polishing pad and stacking a plurality of the sample pieces so that the thickness is 4.5 mm or more. It was measured using a hardness meter.

(compression rate)
The compressibility of the polishing layer was determined according to JIS L 1021 using a Shopper-type thickness gauge (pressure surface: circle with a diameter of 1 cm). Specifically, at room temperature (about 20 ° C.), the thickness _t0 after applying an initial load for 30 seconds from an unloaded state is measured, and then the final pressure is measured from the thickness _t0 state. The thickness t ₁ after standing for 1 minute under the same load was measured. From these, the compression rate was calculated by the following formula. The initial load was 300 g/cm ² and the final pressure was 1800 g/cm ² .

(Polishing rate variability, polishing stability)
Using the polishing pads of Example 1 and Comparative Examples 1 to 3, 50 silicon wafers each with a TEOS (Tetro Ethyl Ortho Silicate) film and 50 silicon wafers with a Cu film were repeatedly polished under the following conditions. rice field.
<Polishing conditions>
Polishing machine used: Ebara Corporation, trade name "F-REX300"
Polishing speed (surface plate rotation speed): 70 rpm
Dresser: 3M diamond dresser, model number "A188"
Pad break: 30N 30min
Conditioning: Ex-situ, 30N, 4 scans Processing pressure: 176 g/cm ²
Slurry: colloidal silica slurry (pH: 11.5)
Slurry flow rate: 200mL/min
Polishing time: 60 seconds Object to be polished: Silicon wafer with TEOS or silicon wafer with Cu film

Then, for each of the silicon wafers with the TEOS film and the silicon wafers with the Cu film, the respective polishing rates for 1 to 50 polished wafers were obtained as follows.
First, for the TEOS film or Cu film on the wafer before and after the polishing test, 121 points were randomly selected over the entire wafer, and the thicknesses of those points before and after the polishing test were measured. Based on the measured thickness, calculate the average value of the thickness before the polishing test and the average value of the thickness after the polishing test, and calculate the average value of the polished thickness by taking the difference between these average values. did. Then, the polishing rate (Å/min) was obtained by dividing the obtained average value of the polished thickness by the polishing time. The thickness was measured in the DBS mode of an optical film thickness and film quality measuring device (KLA-Tencor, Model No. "ASET-F5x"). The maximum value, the minimum value, the average value, and the standard deviation of the polishing rate were determined for 50 polishing rates, and the polishing rate variability and the polishing stability were calculated by the following equations.
In the evaluation of the polishing rate variability and polishing stability, the evaluation includes polishing of 1 to 4 wafers, which corresponds to the initial stage of polishing where the polishing rate tends to fluctuate, so 5 to 50 wafers are polished. This means that the polishing rate variability and the polishing stability are evaluated more strictly than the evaluation for processing.

A lower polishing rate variability (%) value indicates a smaller polishing rate fluctuation in the initial stage of polishing. When the polishing rate variability (%) is 25% or less for the silicon wafer with the TEOS film and 5% or less for the silicon wafer with the Cu film, it can be said that the fluctuation of the polishing rate is sufficiently small.
Also, the lower the numerical value of the polishing stability (%), the smaller the dispersion of the polishing rate value, indicating that the polishing rate is more stable. When the polishing stability (%) is 10% or less for the silicon wafer with the TEOS film and 2.0% or less for the silicon wafer with the Cu film, it can be said that the polishing rate is sufficiently stable.

(polishing scratches)
Regarding polishing scratches, the 10th, 25th, and 50th silicon wafers with a TEOS film and the silicon wafers with a Cu film obtained by polishing in the above (polishing rate variability, polishing stability) were polished. The wafer was measured in a high-sensitivity measurement mode of a surface inspection device (Surfscan SP2XP, manufactured by KLA-Tencor), the number of polishing scratches on the substrate surface was observed, and the total was obtained.
When the number of polishing scratches is 5 or less for the silicon wafer with the TEOS film, and 30 or less for the silicon wafer with the Cu film, it can be said that the number of polishing scratches is small and good.

The results are shown in Table 2 below, as well as Figures 5-6B. Also, cross-sectional photographs of the polishing pads obtained in Example 1 and Comparative Examples 1 to 3 are shown in FIGS. 7A and 7B.

From the results in Table 2, the content of the crystalline phase component (Ac ₂₀ ) at 20°C is 10 to 20%, and the content of the interfacial phase component (Ai ₂₀ ) at 20°C is 40 to 50%. The polishing pad of Example 1 has little variation in polishing rate during polishing for both silicon wafers with a TEOS film and silicon wafers with a Cu film, has excellent polishing stability, and can suppress the occurrence of polishing scratches. I found out.

On the other hand, the polishing pad of Comparative Example 1, which has an Ac ₂₀ of more than 20% and an Ai ₂₀ of less than 40%, is superior to the polishing pad of Example 1 for both the silicon wafer with the TEOS film and the silicon wafer with the Cu film. Also, the polishing rate fluctuated greatly during polishing, and the polishing stability was poor. This is probably because the Ai ₂₀ of the polishing pad of Comparative Example 1 was small.
Further, the polishing pad of Comparative Example 1 caused more polishing scratches on the silicon wafer with the Cu film than the polishing pad of Example 1.

Compared to the polishing pad of Example 1, the polishing pad of Comparative Example 2, in which Ac ₂₀ greatly exceeds 20% and Ai ₂₀ is less than 40%, is superior to the polishing pad of Example 1 for both silicon wafers with a TEOS film and silicon wafers with a Cu film. The polishing rate fluctuated greatly during polishing, and the polishing stability of the silicon wafer with the TEOS film was poor.
In addition, the polishing pad of Comparative Example 2, as compared with the polishing pad of Example 1, had an extremely large number of polishing scratches on both the silicon wafer with the TEOS film and the silicon wafer with the Cu film. A possible reason for the large number of polishing scratches is that the Ac ₂₀ in the polishing pad of Comparative Example 2 was considerably large.

Although Ai ₂₀ is 40 to 50%, Ac ₂₀ exceeds ₂₀ %. ₄₀ ) and the absolute value of the difference (|Ai ₂₀ −Ai ₄₀ |) is less than 35, compared to the polishing pad of Example 1, the silicon wafer with the TEOS film and the silicon wafer with the Cu film In both cases, the polishing rate fluctuated greatly during polishing, and the polishing stability was poor. This is because in the polishing pad of Comparative Example 3, although the content ratio of the interfacial phase component at 20°C is high, the value does not decrease significantly even at 40°C. ) was too high, the amount of wear of the pad was excessive, the opening of the polishing surface was enlarged, and the fluctuation of the polishing surface area became large.
In addition, the polishing pad of Comparative Example 3, as compared with the polishing pad of Example 1, had an extremely large number of polishing scratches on both the silicon wafer with the TEOS film and the silicon wafer with the Cu film.

From the above results, the content of the crystalline phase component (Ac ₂₀ ) at 20° C. is 10 to 20%, and the content of the interfacial phase component (Ai ₂₀ ) at 20° C. is 40 to 50%. However, it was confirmed that polishing scratches were suppressed, fluctuations in the polishing rate during polishing were small, and polishing stability was excellent.

Further, according to the present invention, the content of the crystalline phase component (Ac ₂₀ ) at 20° C. is 10 to 20%, and the content of the interfacial phase component (Ai ₂₀ ) at 20° C. is 40 to 50%. It has been found that by confirming whether or not there is, it is possible to evaluate the performance of the polishing pad, such as suppression of polishing scratches, suppression of variation in polishing rate during polishing, and excellent polishing stability.

Claims (8)

A polishing pad having a polishing layer containing a polyurethane resin,
For the polishing layer, the free induction decay signal (FID) obtained by pulse NMR is subtracted in order from the component with the longer spin-spin relaxation time T2 by the least squares method, and the waveform is separated to obtain the component with the longer spin-spin relaxation time T2. When divided into three components, _i.e. , amorphous phase, interfacial phase, and crystalline phase, in order from the The polishing pad having a content (Ai ₂₀ ) of 40 to 50%. The absolute value of the difference (|Ai ₂₀ -Ai ₄₀ |) between the content ratio of the interphase component at 20°C (Ai ₂₀ ) and the content ratio of the interphase component at 40°C (Ai ₄₀ ) is 35 to 50. The polishing pad of claim 1. 3. The polishing pad according to claim 1, wherein the polishing layer has an A hardness of 5 to 15. The polishing pad according to any one of claims 1 to 3, wherein said polishing layer has a compressibility of 35 to 65%. A method of manufacturing a polishing pad according to any one of claims 1 to 4, comprising using a wet deposition method. A method of polishing the surface of an optical or semiconductor material, said method comprising using a polishing pad according to any one of claims 1-4. A method for evaluating a polishing pad having a polishing layer containing a polyurethane resin, comprising:
For the polished layer, the free induction decay signal (FID) obtained by pulse NMR is subtracted in order from the component with the longer spin-spin relaxation time T2 by the least squares method, and the waveform is separated to obtain the component with the longer spin-spin relaxation time T2. When divided into three components, an _amorphous phase, an interfacial phase, and a crystalline phase, in order from The evaluation method, including the step of confirming whether the content ratio (Ai ₂₀ ) is 40 to 50%. The absolute value of the difference (|Ai ₂₀ -Ai ₄₀ |) between the content ratio of the interphase component at 20°C (Ai ₂₀ ) and the content ratio of the interphase component at 40°C (Ai ₄₀ ) is 35 to 50. 8. The evaluation method according to claim 7, further comprising a step of confirming whether or not.

Images