JP2018108612A - Polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad which allows for reduction of a scratch on a polished substrate surface.SOLUTION: The polishing pad having a polishing layer is disclosed in which a glass transition temperature Tg of the polishing layer is higher than -10°C and lower than 16°C.SELECTED DRAWING: None

Description

  The present disclosure relates to a polishing pad, a polishing method using the same, and a method for manufacturing a hard disk substrate.

  Recent memory hard disk drives are required to have a high capacity and a small diameter, and in order to increase the recording density, the flying height of the magnetic head is reduced to reduce the unit recording area. Accordingly, the surface quality required after polishing in the manufacturing process of the hard disk substrate is becoming stricter year by year. That is, it is necessary to reduce the surface roughness, micro waviness, roll-off and protrusions according to the low flying height of the head, and the allowable number of scratches per substrate surface is small according to the decrease in the unit recording area, Its size and depth are getting smaller and smaller.

  Further, in the semiconductor field, high integration and high speed are advancing. In particular, miniaturization of wiring is required for high integration. As a result, in the manufacturing process of a semiconductor substrate, the depth of focus when exposing to a photoresist becomes shallow, and further surface smoothness is desired.

  In response to such demands, various polishing pads have been proposed in order to improve the flatness of the substrate surface and reduce scratches (scratches) generated on the substrate surface after polishing (Patent Documents 1 to 6).

Japanese Patent No. 5629266 JP 2009-214275 A JP 2013-208688 A JP 2014-65119 A JP 2008-213140 A JP 2007-204651 A

  In the conventional polishing pad, if the hardness of the polishing layer is increased in order to flatten the substrate surface, scratches tend to be generated due to foreign matters (polishing waste, abrasive grains, etc.) generated during polishing. When the hardness of the polishing layer is reduced in order to suppress the occurrence of scratches, the entire polishing pad is softened, and not only the flatness of the substrate surface is deteriorated, but also the pad life tends to be shortened.

  Therefore, the present disclosure provides a polishing pad that can reduce scratches on the substrate surface after polishing.

  The present disclosure relates to a polishing pad having a polishing layer, wherein the polishing layer has a glass transition temperature Tg of more than −10 ° C. and less than 16 ° C.

  The present disclosure is a method for producing a polishing pad according to the present disclosure, comprising: a preparation step of preparing a resin-containing solution in which a resin forming a polishing layer is dissolved in a solvent; and the resin-containing solution on a substrate by a wet coagulation method. It is related with the manufacturing method of a polishing pad including the formation process formed into a film and forming the resin film used as a polishing layer.

  The present disclosure relates to a polishing method including a polishing step of polishing a substrate to be polished using the polishing pad according to the present disclosure, and the substrate to be polished is a substrate used for manufacturing a substrate for a hard disk.

  The present disclosure relates to a method for manufacturing a hard disk substrate, including a polishing step of polishing a substrate to be polished using the polishing pad according to the present disclosure.

  According to the present disclosure, it is possible to provide a polishing pad that can reduce scratches on the substrate surface after polishing. By using the polishing pad according to the present disclosure, it is possible to improve the substrate yield while maintaining the productivity of the substrate with reduced scratches.

The present disclosure is based on the finding that scratches on the substrate surface after polishing can be reduced by using a polishing pad having a polishing layer having a glass transition temperature of more than −10 ° C. and less than 16 ° C.
Generally, in the manufacture of a hard disk substrate, if the scratch can be reduced, the substrate yield tends to be improved. Therefore, according to the present disclosure, it is considered that the substrate yield can be improved while maintaining the productivity by using the polishing pad of the present disclosure in the manufacture of the substrate for the hard disk.
Conventionally, as described in paragraph [0003] of Japanese Patent Application Laid-Open No. 2014-065119 (Patent Document 4), a method of reducing scratches by reducing the hardness and elastic modulus of a molded body has been adopted. Here, the hardness of the molded body indicates the hardness of the entire pad including the pores. However, when the hardness and elastic modulus of the molded body are lowered to some extent, no clear correlation is found between the hardness (for example, Asker-C hardness) or elastic modulus (for example, storage elastic modulus) of the molded body and scratch. Therefore, it has been found that it is difficult to further reduce scratches by the conventional method. Therefore, the present disclosure has found that the scratch can be greatly reduced regardless of the storage elastic modulus and Asker-C hardness by using the glass transition temperature indicating the mobility of the resin itself as an index of the resin hardness.

  That is, the present disclosure is a polishing pad having a polishing layer, wherein the polishing layer has a glass transition temperature Tg of more than −10 ° C. and less than 16 ° C. (hereinafter also referred to as “polishing pad according to the present disclosure”). Say). According to the polishing pad according to the present disclosure, an effect of reducing scratches on the substrate surface after polishing can be achieved.

  In the present disclosure, “scratch” mainly refers to defects on the substrate surface that are considered to be derived from residual abrasive grains after polishing, adhesion of abrasive grains, and abrasive sticking. The protrusion defect on the substrate surface can be evaluated by a surface defect inspection apparatus such as microscopic observation or scanning electron microscope observation of the substrate surface obtained after polishing, and can be specifically evaluated by the method described in the examples. .

[Polishing layer]
The polishing layer in the present disclosure preferably includes at least one resin selected from a polyurethane resin, a polynorbornene resin, a trans-polyisoprene resin, and a styrene-butadiene resin, and more preferably a polyurethane resin, from the viewpoint of reducing scratches. A thermoplastic polyurethane resin is more preferable.

  Examples of the thermoplastic polyurethane resin include a polyester-based polyurethane resin, a polyether-based polyurethane resin, and a polycarbonate-based polyurethane resin. These may be used alone or in combination of two or more.

  As the thermoplastic polyurethane resin, a resin having desired characteristics such as Tg may be synthesized by a known method, or a commercially available product may be used. Examples of commercially available thermoplastic polyurethane resins include “Chris Bon” (trade name, manufactured by DIC), “Samprene” (trade name, manufactured by Sanyo Chemical Industries), “Rezamin” (trade name, manufactured by Dainichi Seika Kogyo Co., Ltd.), etc. It is done. For example, a thermoplastic polyurethane resin can be obtained by reacting a polymer diol, an organic diisocyanate, and a chain extender.

  Examples of the polymer diol include polyether diol, polyester diol, and polycarbonate diol. 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 scratches.

  Examples of the polyether diol include 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 directly esterifying or transesterifying an ester-forming derivative such as dicarboxylic acid or its ester or anhydride with a low molecular weight diol.

  Examples of the dicarboxylic acid constituting the polyester diol include 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, 3,7-dimethyldecanedioic acid; terephthalic acid And aromatic dicarboxylic acids such as isophthalic acid and orthophthalic acid. These dicarboxylic acids may be used alone or in combination of two or more.

  Examples of the low-molecular diol constituting the polyester diol 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 diols may be used alone or in combination of two or more. Examples of the carbon number of the low-molecular diol include 6 or more and 12 or less.

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

  The number average molecular weight of the polymer diol is preferably 1400 to 5000, for example, from the viewpoint of suppressing scratches. In the present disclosure, the “number average molecular weight” can be calculated based on a hydroxyl value measured according to JIS K1557.

  As the organic diisocyanate, organic diisocyanates used in the production of ordinary thermoplastic polyurethanes can be used. For example, 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, Examples include isophorone diisocyanate, 1,5-naphthylene diisocyanate, and 4,4′-dicyclohexylmethane diisocyanate. These organic diisocyanates may be used alone or in combination of two or more.

  As the chain extender, a known chain extender used in the production of ordinary thermoplastic polyurethane can be used. Examples of the chain extender include low molecular weight compounds having a molecular weight of 300 or less having two or more active hydrogen atoms capable of reacting with an isocyanate group in the molecule, such as ethylene glycol, propylene glycol, and 1,4-butanediol. 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-bis (β-hydroxyethoxy) benzene, 1,4-cyclohexanediol, bis- (β-hydroxyethyl) terephthalate, And diols such as 9-nonanediol. These chain extenders may be used alone or in combination of two or more.

  The polynorbornene resin may be synthesized by a conventional method, or a commercially available product may be obtained. Examples of commercially available polynorbornene resins include “Nosolex” (trade name, manufactured by Nippon Zeon Co., Ltd.).

  The trans-polyisoprene resin may be synthesized by a conventional method, or a commercially available product may be obtained. Examples of commercially available trans-polyisoprene resins include “Kuraray TPI” (trade name, manufactured by Kuraray Co., Ltd.).

  The styrene-butadiene resin may be synthesized by a conventional method, or a commercially available product may be obtained. Examples of commercially available styrene-butadiene resins include “Asmer” (trade name, manufactured by Asahi Kasei Co., Ltd.).

  The content of the resin in the polishing layer is preferably 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more with respect to the total mass of the polishing layer.

  The polishing layer in the present disclosure can further contain components other than the above-described resin. Other components include, for example, crosslinking agents, fillers, crosslinking accelerators, crosslinking aids, softeners, tackifiers, anti-aging agents, foaming agents, processing aids, adhesion promoters, inorganic fillers, organic Examples include fillers, heat stabilizers, antistatic agents, colorants, flame retardants, thickeners, antioxidants, and conductive agents.

  The glass transition temperature Tg of the polishing layer is more than −10 ° C. from the viewpoint of reducing scratches and improving the pad life, preferably −5 ° C. or higher, more preferably 0 ° C. or higher, and 5 ° C. from the viewpoint of improving the pad life. The above is more preferable, 7.6 ° C. or more is more preferable, and from the viewpoint of scratch reduction, it is less than 16 ° C., preferably less than 12 ° C., preferably less than 10 ° C., more preferably 9 ° C. or less, more preferably 8 ° C. The following is more preferable. The glass transition temperature Tg can be measured by the method described in the examples.

  In this disclosure, “pad life” refers to the durability of the polishing pad. Generally, the average opening diameter of a polishing pad tends to increase as it is used for polishing. It is known that the larger the average aperture diameter, the larger the waviness of the polishing pad surface, and the quality of the contacting substrate surface tends to deteriorate. Therefore, the durability of the polishing pad in the present disclosure can be evaluated by, for example, the number of polishings when the average hole diameter of the polishing pad is equal to or greater than a predetermined value, and can be evaluated by the method described in the examples.

  In the present disclosure, the glass transition temperature Tg can be controlled by the methods described in JP-A-2015-53420, JP-A-2014-525868, JP-A-62-502893, and examples thereof include polyols and plasticizers. It can be controlled using a drug such as Furthermore, Tg can be controlled by these agents after molding of the polishing pad. For example, the Tg of the polishing pad can be freely controlled by performing leveling polishing with an abrasive containing these chemicals at a predetermined concentration for a predetermined time. Examples of the polyol include polymer diols used for the synthesis of the above-described thermoplastic polyurethane resin. Examples of the plasticizer include paraffinic oil, phthalic acid plasticizer, adipic acid plasticizer, glycol plasticizer, and alkylamide plasticizer. Preferred examples of the alkylamide plasticizer include N-butylbenzenesulfonic acid amide.

  The Asker-C hardness of the polishing layer is preferably 60 or more, more preferably 64 or more, still more preferably 68 or more, and the same viewpoint from the viewpoints of improving pad life, improving the flatness of the substrate surface, and reducing scratches. 90 or less, more preferably 80 or less, and even more preferably 75 or less. Asker-C hardness can be measured by the method described in Examples.

  The storage elastic modulus at 25 ° C. of the polishing layer is preferably 3 MPa or less, more preferably 2.6 MPa or less, and further preferably 2.2 MPa or less from the viewpoint of reducing scratches. A storage elastic modulus can be measured by the method as described in an Example.

  The compressibility of the polishing layer is preferably 0.5% or more, more preferably 1.25% or more, further preferably 2.0% or more, from the viewpoint of reducing waviness and scratching, and from the viewpoint of improving flatness. 60% or less is preferable, 40% or less is more preferable, and 20% or less is more preferable. The compression rate can be measured by a compression tester based on, for example, the compression rate measurement method of Japanese Industrial Standard (JIS) L1096, and specifically, can be measured by the method described in the examples. The compression rate can be controlled by, for example, the pore size size on the substrate side of the polishing layer, the material of the substrate, or the like.

The density of the polishing layer, from the viewpoint of reducing scratches and pad life improvement, 0.15 g / cm ³ or more preferably, 0.3 g / cm ³ or more, and further preferably 0.45 g / cm ³ or more, and, From the viewpoint of reducing scratches and waviness, 1.0 g / cm ³ or less is preferable, 0.8 g / cm ³ or less is more preferable, and 0.6 g / cm ³ or less is more preferable. The density can be measured by the method described in the examples.

  The average pore diameter of the polishing layer is preferably 1 μm or more, more preferably 2 μm or more, more preferably 3 μm or more, from the viewpoint of securing the polishing rate and scratch reduction, and from the viewpoint of reducing waviness and scratching, 70 μm or less. Preferably, 65 μm or less is more preferable, 50 μm or less is further preferable, 30 μm or less is more preferable, and from the viewpoint of ensuring the pad life, it is preferably less than 65 μm, more preferably 50 μm or less, further preferably 40 μm or less, and further preferably 30 μm or less. . The average pore diameter can be controlled, for example, by adding additives such as a hydrophilic active agent that promotes foaming and a hydrophobic active agent that stabilizes the wet coagulation of thermoplastic polyurethane. In the present disclosure, the average pore diameter is a value at the time of starting use of the polishing pad for polishing (during polishing), and can be measured by, for example, the method described in the examples.

  The thickness of the polishing layer is preferably 0.5 mm or more, more preferably 0.7 mm or more, further preferably 0.9 mm or more from the viewpoint of reducing scratches and waviness, and 1.5 mm from the viewpoint of improving flatness. The following is preferable, 1.2 mm or less is more preferable, and 0.9 mm or less is further preferable.

  As the polishing layer, a continuous foaming type is preferably used from the viewpoint of discharging of polishing scraps. Examples of the continuous firing type polishing layer include a layer having bubbles formed by a normal wet coagulation method, for example, a polishing layer having spindle-shaped pores substantially perpendicular to the substrate of the polishing pad, Specifically, a polyurethane resin foam is mentioned. For example, the polishing pad according to the present disclosure includes a suede type polishing pad having a base material and a polishing layer having spindle-shaped pores substantially perpendicular to the base material. As a base material, the base material normally used in the said technical field can be used, For example, a polyester film, a polyolefin film, etc. are mentioned.

  The polishing pad according to the present disclosure may have a single-layer structure including only a polishing layer, or may have a multilayer structure in which another layer is bonded to a surface opposite to the polishing surface of the polishing layer. . As the other layer, a layer harder than the polishing layer is preferable from the viewpoint of avoiding minute unevenness of the polishing platen from affecting the shape of the polishing surface and improving the flatness of the substrate to be polished.

  When the polishing pad according to the present disclosure has a multilayer structure, a plurality of layers may be bonded to each other using a double-sided tape, an adhesive, or the like while applying pressure as necessary. It does not specifically limit as a double-sided tape and an adhesive agent, For example, the well-known double-sided tape and adhesive agent used in the said technical field are mentioned.

  The polishing layer in the present disclosure can contain abrasive grains, but preferably does not contain abrasive grains from the viewpoint of reducing scratches, in particular, reducing scratches on hard disk substrates.

[Production method of polishing pad]
In the present disclosure, a preparation step of preparing a resin-containing solution in which a resin (for example, a thermoplastic polyurethane resin) forming a polishing layer is dissolved in a solvent, and the resin-containing solution is formed on a substrate by a wet coagulation method. The present invention relates to a polishing pad manufacturing method (hereinafter also referred to as “a polishing pad manufacturing method according to the present disclosure”) including a forming step of forming a resin film (polishing layer).

  Examples of the solvent that dissolves the resin that forms the polishing layer include a mixed solution of water and an organic solvent. The organic solvent may be any resin that can dissolve the resin forming the polishing layer and is miscible with water. For example, N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), Tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetone and the like can be mentioned.

  The forming step includes, for example, an application step of applying a resin-containing solution onto a substrate, and a coagulation step of immersing the substrate on which the resin-containing solution is applied in a coagulating liquid to coagulate the resin-containing solution to obtain a resin film. And a washing and drying step of washing and drying the resin film. Examples of the coagulation liquid include water, a mixed solution of water and the organic solvent described above, and the like. Water is mentioned as a washing | cleaning liquid used for the washing | cleaning of a washing | cleaning drying process.

  The polishing pad manufacturing method according to the present disclosure may further include a step of adjusting the glass transition temperature Tg of the polishing layer to more than −10 ° C. and less than 16 ° C. after the forming step. Examples of the adjustment include the aforementioned drugs.

  The polishing pad manufacturing method according to the present disclosure may further include a step of performing grooving or embossing on the surface.

  The polishing pad manufacturing method according to the present disclosure may include a step of grinding the polishing surface and / or the back surface of the polishing layer. The grinding treatment is not particularly limited, and grinding can be performed by a known method, and examples thereof include sandpaper grinding.

  The polishing pad manufacturing method according to the present disclosure can include a step of bonding a base material and / or an adhesive layer or the like to the polishing layer.

[Polished substrate]
Examples of the substrate to be polished by the polishing pad according to the present disclosure include a substrate used for manufacturing a hard disk substrate. Examples of the hard disk substrate include a Ni—P plated aluminum alloy substrate, a glass substrate, and the like. From the viewpoint of exhibiting the effects of the present disclosure, a Ni—P plated aluminum alloy substrate is preferable.

[Method of manufacturing hard disk substrate]
The present disclosure includes a method for manufacturing a substrate for a hard disk (hereinafter referred to as “the present disclosure”) including a polishing step (hereinafter, also referred to as “a polishing step according to the present disclosure”) for polishing a substrate to be polished using the polishing pad according to the present disclosure. It is also referred to as a “substrate manufacturing method”. According to the manufacturing method of the present disclosure, an effect that a hard disk substrate with reduced scratches can be manufactured with high substrate yield and high productivity can be achieved. The substrate described above can be used as the substrate to be polished.

  Generally, a hard disk substrate can be manufactured by a base material that is a base of a hard disk substrate being subjected to a shape processing step, a rough grinding step, a fine grinding step, a rough polishing step, a final polishing step, and the like. Then, the hard disk substrate can be a magnetic hard disk, for example, through a recording part forming step. The polishing pad according to the present disclosure can be suitably used for polishing in the final polishing step.

  In the polishing step according to the present disclosure, when using a polishing pad, for example, the polishing pad is placed on a polishing surface plate of a polishing machine so that the polishing surface of the polishing layer faces the substrate to be polished, and the polishing composition is applied. Supplying the polishing target surface of the polishing substrate, bringing the polishing pad according to the present disclosure into contact with the polishing target surface, and polishing the polishing target surface by moving at least one of the polishing pad and the substrate to be polished. it can. Examples of the abrasive grains in the polishing composition include silica, alumina, cerium oxide, zirconium oxide, silicon carbide, and the like. When the polishing process according to the present disclosure is a final polishing process, the substrate surface flatness, scratches, etc. From the viewpoint of reduction, silica is preferable.

[Polishing method]
The present disclosure relates to a polishing method (hereinafter, also referred to as “polishing method according to the present disclosure”) including a polishing step according to the present disclosure. By using the polishing method of the present disclosure, an effect that a hard disk substrate with reduced scratches can be manufactured with high substrate yield and high productivity can be achieved.

  Hereinafter, the present disclosure will be described in more detail by way of examples. However, these examples are illustrative, and the present disclosure is not limited to these examples.

1. Polishing pad Thermoplastic polyurethane resin: 30% by mass and organic solvent (DMF): 70% by mass were mixed to prepare a resin-containing solution. The prepared resin-containing solution was applied on a substrate (polyester film, thickness: 0.2 mm). Then, the substrate coated with the resin-containing solution was immersed in a coagulation liquid (water) to coagulate the resin-containing solution, and then washed and dried. Thereby, a polishing pad having a resin film (polishing layer) formed on the substrate was obtained.
Tg of the pads of Examples 1 to 5, 7 and Comparative Examples 1 to 4 was adjusted by changing the composition of the thermoplastic polyurethane resin.
The polishing pads of Examples 6 and 8 were prepared by polishing the polishing pads of Comparative Examples 2 and 4 each containing a plasticizer (N-butylbenzenesulfonic acid amide, 300 ppm) in a polishing composition for finishing polishing described later. It was used as a liquid and obtained by polishing 12 times (leveling polishing) under the polishing conditions for finish polishing described later.

2. Physical properties
[Compression rate]
The resin film 10 cm × 10 cm, which is the polishing layer of the polishing pad, is pressed at 100 g / cm ² for 30 seconds, and the thickness A0 is measured. Then, it pressurizes for 5 minutes at 1100 g / cm < ² >, and measures thickness A1. Then, the compression rate is calculated by the following formula. The calculation results are shown in Table 1.
Compression rate (%) = (A0−A1) / A0 × 100

[Compressive modulus]
After measuring the compression rate of the resin film (10 cm × 10 cm) which is the polishing layer of the polishing pad, the pressure is released. Five minutes after the release of the pressurization, pressurization is performed at 100 g / cm ² for 30 seconds, and the thickness A2 is measured. Then, the compression elastic modulus is calculated by the following formula. The calculation results are shown in Table 1.
Compression modulus (%) = (A2−A1) / (A0−A1) × 100

[Asker-C hardness]
A test piece was obtained by stacking three resin films as polishing layers of the polishing pad, measured at five locations, and the average value was calculated as Asker-C hardness. The push needle was made to be perpendicular to the test piece measurement surface, contacted with a load of 1000 g, and the value of the memory after 3 seconds was measured. The measurement results are shown in Table 1.
<Measurement conditions>
Asker-C hardness meter: push needle type (Asker rubber hardness meter C type manufactured by Kobunshi Keiki Co., Ltd.)
Needle shape: hemispherical, diameter 5.08mm

[Glass transition temperature Tg and storage modulus G ′]
The resin film as the polishing layer of the polishing pad was punched into a disk shape having a diameter of 24 mm, washed twice with ion exchange water (10 seconds), dried, and then determined by dynamic viscoelasticity measurement. The measurement results are shown in Table 1.
<Measurement conditions>
DMS measuring device: ARES-G2 (TA Instrument Japan Inc.)
DMS measurement conditions: Strain: 0.01%
Frequency: 10Hz
Modulation temperature range: -100 ° C to 200 ° C
Tg was a peak value of tan δ, and G ′ was a value at 25 ° C.

[Average hole diameter]
First, the surface of the polishing pad was dressed by using a diamond dresser (SPIN-32, manufactured by KINIK Co., Ltd.), adjusting the time so as to obtain a predetermined average opening diameter at a dresser load of 50 g / cm ² and a rotation speed of 27 rpm. However, in Comparative Example 4, the polishing pad before the dressing process of Comparative Example 2 was used, and the dressing process was performed using “SPD-02” manufactured by KINIK instead of “SPD-32” as the diamond dresser. . Then, the surface of the polishing pad after the dressing treatment was observed with a scanning electron microscope, the pore diameter was measured at 20 points, and the average value was taken as the average pore diameter. The measurement results are shown in Table 1.

3. Polishing Test Using the polishing pads of Examples 1 to 8 and Comparative Examples 1 to 4, the substrate to be polished was subjected to final polishing under the following polishing conditions, and washed with pure water for 15 seconds to obtain an evaluation substrate.

[Polished substrate]
As the substrate to be polished, a substrate obtained by rough polishing an aluminum alloy substrate plated with Ni-P in advance with a polishing composition containing alumina abrasive grains was used. The substrate to be polished has a thickness of 1.27 mm, an outer diameter of 95 mm, and an inner diameter of 25 mm. The center line average roughness Ra measured by AFM (Digital Instrument Nanoscope IIIa Multi Mode AFM) is 1 nm, and a long wavelength undulation ( The amplitude of the wavelength 0.4-2 mm was 2 nm, and the amplitude of the short wavelength waviness (wavelength 50-400 μm) was 2 nm.

[Preparation of polishing composition used for finish polishing]
Polishing liquid composition used for final polishing by mixing and stirring abrasive grains (colloidal silica), acid (sulfuric acid or phosphoric acid), hydrogen peroxide solution (concentration: 35% by mass) and water (ion exchange water) ( pH 1.5) was prepared. The pH was measured using a pH meter (manufactured by TOA DK Corporation). The numerical value after 2 minutes after the electrode was immersed in the polishing composition was adopted.
As the colloidal silica, spherical silica particles having an average particle diameter of 22 nm were used. The content of each component in each polishing composition is 5% by weight of abrasive grains, 0.5% by weight when the acid is sulfuric acid, 1.0% by weight when the acid is phosphoric acid, and hydrogen peroxide solution. : 0.4% by mass.

[Polishing conditions (finish polishing)]
Polishing tester: Double-sided polishing machine (“Surface Fam Co.,“ Double-sided 9B polishing machine ”)
Polishing pad: Suede type (Examples 1-8 and Comparative Examples 1-4)
Polishing liquid: Polishing liquid composition for finish polishing Abrasive liquid composition supply amount: 100 mL / min (supply rate per 1 cm ^{2 of} substrate to be polished: 0.076 mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 11.8kPa
Polishing time: Number of substrates loaded for 5 minutes: 10

4). Evaluation method [Measurement and evaluation of the number of scratches]
Measuring instrument: “OSA7100” manufactured by Candela Instruments
Evaluation: Four substrates were randomly selected from the substrates put into the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure scratches. The total number of scratches (both) on each of the four substrates was divided by 8 to calculate the number of scratches per substrate surface. The results are shown in Table 1 as relative values with Comparative Example 2 taken as 100. However, Example 8 and Comparative Example 4 having an average aperture diameter of 65 μm are relative values with the number of scratches of Comparative Example 4 being 100.
<Evaluation criteria>
Number of scratches (relative value): Evaluation Less than 95: Generation is extremely suppressed and improvement in substrate yield can be expected 95 to less than 110: Real production possible 110 to less than 125: Improvement required for actual production 125 or more: Substrate yield Is significantly reduced

[Measurement and evaluation of pad life]
Evaluation: In the above polishing test, the average pore diameter after polishing of the polishing pad was calculated every time 50 polishings were performed under the above polishing conditions. Here, the surface of the polishing pad used for polishing was observed with a scanning electron microscope, the aperture diameter was measured at 20 points, and the average value was calculated as the average aperture diameter after polishing. And the frequency | count of grinding | polishing when the average hole diameter after grinding | polishing of a polishing pad became 40 micrometers or more was evaluated by the following reference | standard as a pad life. The polishing time was 5 minutes per time.
<Evaluation criteria>
Polishing frequency: Evaluation Less than 100 times: High cost, unsuitable for actual production 100 times or more and less than 500 times: Real production possible 500 times or more: Good actual productivity

5. result

  As shown in Table 1, when the polishing pads of Examples 1 to 8 in which the Tg of the polishing layer is more than −10 ° C. and less than 16 ° C. are used, the polishing of Comparative Examples 1 to 4 in which the Tg of the polishing layer is 16 ° C. or more. Compared with the case where a pad was used, scratches on the surface of the substrate after polishing could be reduced. Moreover, the polishing pad of Examples 1-7 was restrained in the range which can reduce a pad life actually.

  Since the polishing pad according to the present disclosure can reduce scratches on the substrate surface after polishing, the substrate yield can be improved while maintaining the productivity of the hard disk substrate. The present disclosure can be suitably used for manufacturing a hard disk substrate.

Claims (12)

A polishing pad having a polishing layer,
The polishing pad whose glass transition temperature Tg of the said polishing layer is more than -10 degreeC and less than 16 degreeC.   The polishing pad according to claim 1, wherein the polishing layer contains a polyurethane resin.   The polishing pad according to claim 1 or 2, wherein the polishing layer has an Asker-C hardness of 60 or more and 90 or less.   The polishing pad according to any one of claims 1 to 3, wherein the storage elastic modulus of the polishing layer at 25 ° C is 3 MPa or less.   The polishing pad according to any one of claims 1 to 4, wherein the compressibility of the polishing layer is 1% or more and 20% or less. The polishing pad according to claim 1, wherein the density of the polishing layer is 0.2 g / cm ³ or more and 1.0 g / cm ³ or less.   The polishing pad according to any one of claims 1 to 6, wherein an average pore diameter of the polishing layer is 1 µm or more and 70 µm or less. A method for producing a polishing pad according to any one of claims 1 to 7,
A preparation step of preparing a resin-containing solution in which a resin forming the polishing layer is dissolved in a solvent;
A method for producing a polishing pad, comprising a forming step of forming the resin-containing solution on a substrate by a wet coagulation method to form a resin film to be a polishing layer.   The manufacturing method of the polishing pad of Claim 8 including the process of adjusting the glass transition temperature Tg of the said polishing layer to more than -10 degreeC and less than 16 degreeC after the said formation process. A polishing step of polishing the substrate to be polished using the polishing pad according to claim 1;
The polishing method, wherein the substrate to be polished is a substrate used for manufacturing a substrate for a hard disk.   A method for manufacturing a hard disk substrate, comprising a polishing step of polishing a substrate to be polished using the polishing pad according to claim 1.   The manufacturing method according to claim 11, wherein the polishing step is a finish polishing step.