JP2004162062A - Polishing material slurry, polishing method, substrate, and producing method of the substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing material slurry which achieves surface polishing with high surface evenness, small surface roughness and excellent precision hardly causing surface microscratches, surface micropits, or the like, and besides, achieves a high polishing speed. <P>SOLUTION: The polishing material slurry comprises a cerium oxide-containing rare earth oxide as the principal component, an anionic surfactant, and a nonionic surfactant and has a pH≥11. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an abrasive used for precision polishing of optical and electronics-related substrates such as glass substrates for optical lenses, optical disks, magnetic disks, plasma displays, liquid crystals, or LSI photomasks. In particular, the present invention relates to an abrasive slurry which has excellent polishing characteristics such as a polishing rate (polishing rate) and surface roughness and can be polished with almost no surface defects such as scratches.
The present invention further relates to a method for polishing a substrate using the above abrasive slurry, a method for manufacturing a substrate by the polishing method, and a manufactured substrate.

  In recent years, in the field of electronics-related substrates such as a glass substrate for a magnetic disk, a glass substrate for a liquid crystal such as a thin film transistor (TFT) type LCD and a twisted nematic (TN) type LCD, a color filter for a liquid crystal television, and a glass substrate for an LSI photomask, Polishing technology is becoming an increasingly important position.

  In the field of magnetic disk substrates in particular, mechanical properties such as thinning due to weight reduction and high rigidity that can withstand the undulation of the disk during high-speed rotation are required, and the demand for high recording density is increasing extremely. ing. For the purpose of achieving higher recording density, the flying height of the magnetic head with respect to the magnetic disk substrate is becoming very small, and in order to achieve this, the magnetic disk substrate is required to have a mirror-like flatness or small surface roughness. And defects such as minute scratches and minute pits on the surface are required to be as small as possible. Therefore, high-precision surface polishing is required. In addition, various improvements have been made to the chemical composition and manufacturing method of glass in order to satisfy thinness, mechanical characteristics, or high recording density. For example, as a glass substrate, in addition to the conventionally used chemically strengthened glass, a crystallized glass substrate containing lithium silicate and a crystallized glass substrate in which most of the quartz crystal is formed have been developed. However, these glass substrates are very poor in workability, and the polishing speed with conventional polishing materials is low, resulting in poor productivity.

  As an abrasive used for polishing the surface of the glass substrate, rare earth oxides, particularly cerium oxide, are used because the polishing rate is several times better than iron oxide, zirconium oxide, or silicon dioxide. Generally, abrasive grains are used by being dispersed in a liquid such as water. When performing surface polishing using an abrasive, it is required that both high-precision surface polishing performance and a high polishing rate be compatible.

  Thus, various measures have been disclosed for increasing the polishing rate when cerium oxide is used as the polishing material. For example, a polishing method in which colloidal silica, alumina, or the like is added to cerium oxide or the like, an abrasive in which magnesium chloride is added to an abrasive containing cerium oxide, and the like are disclosed (for example, Patent Documents 1 and 2). reference.). However, the addition of such a foreign particle sol leads to an increase in surface scratches or pits, and high surface accuracy cannot be achieved.

  On the other hand, in order to achieve high surface accuracy, for example, an abrasive made of alkaline cerium oxide sol containing an organic acid having two or more carboxyl groups, or coated with an anionic surfactant and a nonionic surfactant There has been disclosed a CMP polishing liquid composed of cerium oxide particles thus prepared and water in which a surfactant is dispersed (for example, see Patent Documents 3 and 4).

However, when an abrasive made of alkaline cerium oxide sol containing an organic acid having two or more carboxyl groups is used, not only does the polishing rate become extremely slow because the average particle size of the sol is as small as 2 to 200 nm. However, there has been a problem that it is difficult to increase polishing cost and achieve stable quality. Further, in the CMP polishing liquid, since the polishing material is cerium oxide, the pH of the polishing liquid does not increase, the polishing rate is low, and the surface roughness is large.
Therefore, none of the above-mentioned abrasives and polishing methods could satisfy both the highly accurate surface polishing and the polishing rate.

Japanese Patent Publication No. 38-3643 JP-A-3-146585 JP-A-8-3541 JP 2000-248263 A

  The present invention has been made in view of the above circumstances, and has achieved high surface flatness, small surface roughness, and high-precision surface polishing with little occurrence of micro scratches or micro pits on the surface. It is another object of the present invention to provide an abrasive slurry capable of achieving a high polishing rate.

The abrasive slurry of the present invention contains an abrasive mainly composed of a rare earth oxide containing cerium oxide, an anionic surfactant, and a nonionic surfactant, and has a pH of 11 or more. It is characterized by. In addition, in this specification, "main component" indicates that the content is 80% by mass or more.
Preferably, the abrasive contains at least 90% by mass of a rare earth oxide.
Further, the rare earth oxide preferably contains 50 to 90% by mass of cerium oxide.
Further, the rare earth oxide is preferably produced using a rare earth carbonate as a starting material.
Further, the 50% cumulative average diameter (D50) of the abrasive particles is preferably 0.01 to 10 μm.
Further, the specific surface area of the abrasive particles is preferably from 1 to 50 m ² / g.
Further, it is preferable that the anionic surfactant is at least one selected from the group consisting of low molecular weight compounds and high molecular weight compounds of carboxylate, sulfonate, sulfate, and phosphate.
Further, it is preferable that the nonionic surfactant is at least one selected from the group consisting of polyoxyethylene alkylphenyl ether, polyoxyalkylene alkyl ether, and polyoxyethylene fatty acid ester.
Further, the abrasive slurry is at least one selected from the group consisting of water, monohydric alcohols having 1 to 10 carbon atoms, glycols, polyhydric alcohols having 1 to 10 carbon atoms, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran and dioxane. Preferably, it contains a species of solvent.
Further, the abrasive slurry preferably contains at least one selected from the group consisting of phosphates, cellulose ethers and water-soluble polymers.
The abrasive slurry is preferably used for polishing a substrate.
Further, it is preferable that the substrate is manufactured by using the polishing method using the abrasive slurry.
The substrate is preferably selected from the group consisting of a glass substrate for an optical lens, a glass substrate for an optical disk, a glass substrate for a plasma display, a glass substrate for a liquid crystal, a color filter for a liquid crystal television, and a glass substrate for an LSI photomask. In particular, it is preferably used as a glass substrate for a magnetic disk.

  According to the present invention, in the precision polishing of electronics-related substrates, especially glass substrates for timing disks, etc., the surface flatness is high, the surface roughness is small, and there is almost no occurrence of micro scratches or micro pits on the surface. It is possible to provide an abrasive slurry capable of achieving a high polishing rate while achieving highly accurate surface polishing.

The abrasive slurry of the present invention contains an abrasive mainly composed of a rare earth oxide containing cerium oxide, an anionic surfactant, and a nonionic surfactant as essential components, and has a pH of 11 or more. It is characterized by the following. By adopting such a configuration, high surface flatness, small surface roughness, and high-precision surface polishing that hardly cause micro scratches and micro pits on the surface are achieved, and good polishing is achieved. Rate (polishing rate).
On the other hand, when the surfactant is used alone or when the pH of the slurry is less than 11, desired surface roughness and polishing rate cannot be obtained.

Hereinafter, each component of the abrasive slurry will be described.
<Abrasive>
The abrasive used in the present invention needs to contain rare earth oxides in an amount of 80% by mass or more, and preferably contains 90% by mass or more. When the amount of the rare earth oxide is less than 80% by mass, scratches are likely to occur on the surface of the object to be polished.

  The rare earth oxide preferably contains cerium oxide in a range of 50% by mass to 90% by mass. When the content of cerium oxide is less than 50% by mass, it is difficult to obtain a desired polishing rate. Conversely, when the content exceeds 90% by mass, the pH is reduced even when anionic or nonionic surfactants are contained. It is difficult to set it to 11 or more. Therefore, not only cannot a sufficient polishing rate be obtained, but also the surface roughness increases.

  The rare earth oxide may contain lanthanum oxide, praseodymium oxide, neodymium oxide, and the like, in addition to cerium oxide.

In the present invention, the abrasive particles preferably have a 50% cumulative average diameter (D50) in terms of volume of 0.01 to 10 μm, more preferably 0.05 to 5.0 μm, and particularly preferably 0.1 to 5.0 μm. 2.0 μm. If the 50% cumulative average grain size (D50) is less than 0.01 μm, it is difficult to obtain a sufficient polishing rate. Conversely, if it exceeds 10 μm, scratches and minute pits are likely to be generated on the surface of the object to be polished. There is a tendency.
Here, the 50% cumulative average diameter (D50) in terms of volume is a particle diameter that becomes 50% when integrated from the smaller particle size in the particle size distribution shown in volume.

In the present invention, it is desirable to use a rare earth oxide produced using a rare earth carbonate as a starting material. Here, the rare earth carbonate as a starting material is obtained by pulverizing a rare earth concentrate containing a large amount of naturally occurring cerium, lanthanum, praseodymium, and neodymium, and then crushing the alkali metal, alkaline earth metal, radioactive material, etc. It is obtained by chemically separating and removing components other than rare earths and converting them into carbonates with ammonium bicarbonate, oxalic acid or the like.
After sintering the rare earth carbonate at about 500 ° C. to about 1200 ° C. in an electric furnace or the like, the sintering powder is pulverized to produce an abrasive mainly composed of a rare earth oxide. Note that an abrasive having a desired particle size distribution can be obtained by appropriately selecting firing conditions, grinding conditions, and the like.

The firing of the state can be determined in numerical values of the specific surface area of the abrasive particles, it is preferred that the specific surface area is in the range of 1 to 50 m 2 / ^g, more range of 2 to 20 m 2 / ^g Is particularly preferred. When the specific surface area is less than 1 m ² / g, scratches and minute pits tend to be generated on the surface of the object to be polished, and when the specific surface area exceeds 50 m ² / g, the polishing rate decreases.

<Anionic surfactant>
Examples of the anionic surfactant used in the present invention include known carboxylate (soap, N-acylamino acid salt, alkyl ether carboxylate, acylated peptide, etc.), sulfonate (alkane sulfonate (alkylbenzene) Sulfonates), alkyl naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, N-acyl sulfonates, etc.), sulfates (sulfated oils, alkyl sulfates, alkyl ether sulfates, Selected from alkyl allyl ether sulfates, alkyl amide sulfates, and the like, and phosphoric acid ester salts (alkyl phosphates, alkyl ether phosphates, alkyl allyl ether phosphates, etc.), and include low molecular weight compounds and high molecular weight compounds. Here, the salt is selected from at least one of Li salt, Na salt, K salt, Rb salt, Cs salt, ammonium salt, and H type.

  For example, soap is a fatty acid salt having a carbon number of C12 to C18. Generally, the fatty acid group includes lauric acid, myristic acid, palmitic acid, and stearic acid. And C12-C18 N-acyl-N-methylglycine salts and N-acylglutamate salts. Examples of the alkyl ether carboxylate include compounds having C6 to C18, and examples of the acylated peptide include compounds having C12 to C18. Examples of the sulfonic acid salt include the compounds having C6 to C18. For example, in the case of alkanesulfonic acid, laurylsulfonic acid, dioctylsuccinsulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, myristylsulfonic acid, kerylsulfonic acid Benzenesulfonic acid, stearylsulfonic acid and the like can be mentioned. Examples of the sulfate ester salt include the compounds having a carbon number of C6 to C18. For example, alkyl sulfates such as lauryl sulfate, dioctylsuccisulfate, myristyl sulfate, and stearyl sulfate; and phosphate ester salts include a carbon number of C8 to C18. And the aforementioned compounds of C18. Examples of the surfactant which is a polymer compound include a special polycarboxylic acid type compound (Kao Corporation, trade name: Demol EP).

  In the present invention, the content of the anionic surfactant is preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass, based on the abrasive.

<Nonionic surfactant>
Examples of the nonionic surfactant used in the present invention include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, and polyoxyalkylene alkyl ether.

  In the present invention, the content of the nonionic surfactant is preferably 0.0001 to 10% by mass, more preferably 0.001 to 1.0% by mass, based on the abrasive.

As a method for producing an abrasive slurry, for example, when producing an abrasive, a method in which fired powder obtained by firing in advance is dispersed in water or a water-soluble organic solvent, and then wet pulverization may be used, Alternatively, a method in which the fired powder is dry-pulverized and then the obtained powder is wet-dispersed in water may be used. However, in the present invention, it is desirable to go through a wet pulverization process using, for example, a ball mill.

  Examples of the water-soluble organic solvent include monohydric alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, isopropanol, and butanol; polyhydric alcohols having 3 to 10 carbon atoms, such as ethylene glycol and glycerin; Sulfoxide (DMSO), dimethylformamide (DMF), tetrahydrofuran, dioxane and the like can be mentioned. Among them, water, alcohol or glycols are preferred. These are used alone or in combination of two or more.

  Furthermore, in the abrasive slurry of the present invention, in order to prevent sedimentation of the slurry or improve stability, a polymer dispersant such as tripolyphosphate, a phosphate such as hexametaphosphate, methylcellulose, if necessary. Additives such as cellulose ethers such as carboxymethyl cellulose and water-soluble polymers such as polyvinyl alcohol can also be added. The amount of these additives is generally preferably in the range of 0.05 to 20% by mass, and particularly preferably in the range of 0.1 to 10% by mass, based on the abrasive.

  The abrasive concentration (slurry concentration) of the abrasive slurry thus prepared is 1 to 50% by mass, preferably 5 to 40% by mass, and more preferably 10 to 30% by mass. If the abrasive concentration is less than 1% by mass, it is difficult to exhibit sufficient polishing performance, and if it exceeds 50% by mass, the viscosity of the slurry increases and the fluidity becomes low, so that a production problem is likely to occur. In addition, it is uneconomical because excessive abrasive is used.

  The polishing object to which the abrasive slurry of the present invention is applied is not particularly limited, but is preferably a glass substrate for an optical lens, a glass substrate for an optical disk or a magnetic disk, a glass substrate for a plasma display, a thin film transistor (TFT) type LCD, Used for various types of optics such as glass substrates for liquid crystals such as twisted nematic (TN) LCDs, color filters for liquid crystal televisions, glass substrates for LSI photomasks, etc., glass materials for electronics, and final polishing of general glass products. . Among these, it is particularly suitable for a glass substrate for a magnetic disk.

Glass substrates for magnetic disks are attracting attention as substrates that take advantage of the advantages of high rigidity and thinness and high impact resistance.The glass materials for the substrates are chemically strengthened glass and crystallized glass. Are roughly divided into Each of these materials has been subjected to a strengthening treatment to overcome the disadvantage of glass being brittle. Usually, the presence of a scratch on the glass surface greatly impairs the mechanical strength, and therefore, a chemical strengthening treatment by ion exchange is performed from the viewpoint of improving disk reliability. That is, a glass substrate (original sheet) is immersed in an alkali molten salt, and exchanges alkali ions on the glass surface with larger ions in the molten salt, thereby forming a compressive stress-strain layer on the surface layer of the glass and breaking the glass. The strength is greatly increased. The alkali leaching from the inside of the glass is suppressed in the glass substrate thus chemically strengthened, and the abrasive slurry of the present invention is excellent even for such a chemically strengthened magnetic disk (HD) substrate material. Polishing performance (polishing speed, substrate surface roughness, suppression of surface defects such as scratches, etc.) can be obtained. HD glass substrates preferably used include an aluminosilicate glass substrate containing Li ⁺ and Na ⁺ , a soda lime glass substrate containing K ⁺ and Na ^+, and crystallized glass.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
Using 4 kg of commercially available coarse rare earth carbonate powder (ignition loss: 55.8%), firing was performed in a box-type electric furnace. The firing conditions were as follows: a heating rate of 1.7 ° C./min, a firing temperature of 900 ° C., and a holding time of 2 hours. Analysis of the elements contained in the powder after firing revealed that the content of the rare earth oxide was 99% by mass and the concentration of cerium oxide contained in the rare earth oxide was 60% by mass. Further, the specific surface area of the obtained calcined powder was determined by a specific surface area measuring device by a BET method, and was found to be 10 m ² / g.
1.7 kg of the calcined powder obtained by calcining is put into 2.5 kg of pure water and stirred, and then a special carboxylic acid type polymer surfactant (trade name “Demol EP”, Kao ( 68 g (corresponding to 4% by mass with respect to the calcined powder) and 0.17 g (based on the calcined powder) of polyoxyalkylene alkyl ether (trade name "Emulgen MS-110", manufactured by Kao Corporation) (Corresponding to 0.01% by mass), and the mixture was stirred to prepare a slurry.
The obtained slurry was wet-milled for 2.5 hours while circulating through a wet mill, and then pure water was added to the slurry to obtain 8 kg of an abrasive slurry having a concentration of 20% by mass. The pH of the obtained abrasive slurry was 12.0.
When a part of the obtained abrasive slurry was measured by a laser diffraction type particle size distribution analyzer (“HR850”, manufactured by CILAS), the 50% cumulative average particle size (D50) in terms of volume was 0.1%. It was 55 μm.

(Examples 2 to 7)
An abrasive slurry was produced in the same manner as in Example 1, except that the addition amounts of the carboxylate and the polyoxyalkylene alkyl ether were changed to the addition amounts shown in Table 1, respectively.

(Comparative Examples 1-2)
In Example 1, the abrasive slurry was prepared in the same manner as in Example 1 except that the addition amounts of the carboxylate and the polyoxyalkylene alkyl ether were appropriately adjusted and changed so as to be the addition amounts shown in Table 1, respectively. Manufactured.

(Comparative Example 3)
In Example 1, except that the starting raw material was changed from commercially available coarse rare earth carbonate powder to high-purity cerium carbonate, and the addition amounts of the carboxylate and the polyoxyalkylene alkyl ether were changed to the addition amounts shown in Table 1. Produced an abrasive slurry in the same manner as in Example 1.

Using the abrasive slurries obtained in the examples and comparative examples, the following workpiece (polished body) was polished. A 4-way type double-side polishing machine ("USP-5B", manufactured by Fujikoshi Machinery Co., Ltd.) was used as a polishing machine, and a suede type pad ("Polytex DG", manufactured by Rodale) was used as a polishing pad. Polishing was performed at a slurry supply speed of 60 ml / min, a lower platen rotation speed of 90 rpm, a processing pressure of 75 g / cm ² , and a polishing time of 10 min. After polishing, the glass substrate was taken out of the polishing machine, subjected to ultrasonic cleaning using pure water, and then dried and evaluated as follows. Table 2 shows the results.
The workpiece is a 2.5 inch φ aluminosilicate for a magnetic disk which has been polished with a commercially available cerium oxide abrasive (“SHOROX H-1”, manufactured by Tohoku Metal Chemical Co., Ltd.) in advance. Was used as the main component (surface roughness Ra = 9 °).

Workpiece evaluation:
(1) Surface roughness (Ra)
The surface roughness (Ra) of the glass substrate surface was measured using an atomic force microscope (AFM).

(2) Surface Defects The surface of the glass substrate was observed using a differential interference microscope, and the adhesion state of the surface, the presence or absence of pits and scratches, and the like were examined. The evaluation of scratches is indicated by the number of scratches generated on the surface of the glass substrate, and the evaluation of surface defects is performed by a relative evaluation of three stages. "B" indicates that pits are slightly generated and is a practical problem, and "C" indicates that the surface condition is extremely poor.

(3) Polishing Rate The polishing rate (μm / min) was determined from the change in weight of the glass substrate before and after polishing.

As is clear from Table 2, when the polishing was performed using the abrasive slurries of Examples 1 to 7, the polishing rate was high, the surface roughness was small, and a good polished surface free from scratches and surface defects was realized. We were able to.
On the other hand, since the abrasive slurry of Comparative Example 1 did not contain a nonionic surfactant, when polished using the same, the polishing rate was low and the surface roughness was large.
The polishing slurry of Comparative Example 2 did not contain an anionic surfactant and had a pH of less than 11, so when polished using this, the polishing rate was low and the surface roughness was large, It was found that scratches and surface defects occurred, and were not suitable for precision polishing.
Although the abrasive slurry of Comparative Example 3 contained an anionic surfactant and a nonionic surfactant but had a pH of less than 11, the polishing rate was low and the polishing rate was low even when polishing was performed using this. The roughness was great.

Claims (14)

An abrasive slurry containing an abrasive mainly composed of a rare earth oxide containing cerium oxide, an anionic surfactant, and a nonionic surfactant, and having a pH of 11 or more. The abrasive slurry according to claim 1, wherein the abrasive contains at least 90% by mass of a rare earth oxide. The abrasive slurry according to claim 1, wherein the rare earth oxide contains 50 to 90% by mass of cerium oxide. The abrasive slurry according to any one of claims 1 to 3, wherein the rare earth oxide is manufactured using a rare earth carbonate as a starting material. The abrasive slurry according to any one of claims 1 to 4, wherein the 50% cumulative average diameter (D50) of the abrasive particles is 0.01 to 10 m. The specific surface area of the abrasive particles, the abrasive slurry according to claim 1, characterized in that a 1 to 50 m 2 / ^g. The anionic surfactant is at least one selected from the group consisting of low molecular weight compounds and high molecular weight compounds of carboxylate, sulfonate, sulfate, and phosphate. 7. The abrasive slurry according to any one of 6. The nonionic surfactant is at least one selected from the group consisting of polyoxyethylene alkylphenyl ether, polyoxyalkylene alkyl ether, and polyoxyethylene fatty acid ester, according to any one of claims 1 to 7, wherein An abrasive slurry as described in the above. Contains at least one solvent selected from the group consisting of water, monohydric alcohols having 1 to 10 carbon atoms, glycols, polyhydric alcohols having 1 to 10 carbon atoms, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran and dioxane. The abrasive slurry according to any one of claims 1 to 8, wherein The abrasive slurry according to any one of claims 1 to 9, comprising at least one selected from the group consisting of phosphates, cellulose ethers and water-soluble polymers. A method for polishing a substrate, comprising polishing using the abrasive slurry according to claim 1. A method for manufacturing a substrate, comprising using the polishing method according to claim 11. A substrate manufactured by using the method for manufacturing a substrate according to claim 12. It is selected from the group consisting of glass substrates for optical lenses, glass substrates for optical disks, glass substrates for plasma displays, glass substrates for liquid crystals, color filters for liquid crystal televisions, glass substrates for LSI photomasks, and glass substrates for magnetic disks. The substrate according to claim 13, wherein: