JP2007154176A - Polishing liquid for polishing ito film and method for polishing substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing liquid efficiently eliminating surface unevenness of an ITO (indium-tin-oxide) film used in an organic EL or a liquid crystal panel. <P>SOLUTION: The polishing liquid for polishing the ITO film comprises water, a colloidal silica dispersed in the water and a protective film-forming agent. The pH of the polishing liquid is within the range of 2-3. The average particle diameter of the colloidal silica is 5-50 nm. A method for polishing the substrate comprises pressing the substrate having the film to be polished formed thereon to a polishing cloth of a polishing platen, pressurizing the substrate, moving the substrate and polishing platen and polishing the film while feeding the polishing liquid for polishing the ITO film between the film and the polishing cloth. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to polishing an indium tin oxide (Indium-Tin-Oxide, hereinafter also referred to as “ITO” for short) film, and in particular, a polishing liquid for polishing an ITO film suitable for planarizing the surface of the ITO film, and The present invention relates to a method for polishing a substrate using the same.

Indium tin oxide (ITO) is obtained by adding a small amount of tin oxide to indium oxide. Since it has high visible light transmittance and conductivity, an organic electroluminescence (hereinafter referred to as “EL”) panel. And used as a transparent electrode for liquid crystal panels.
FIG. 1 is a schematic cross-sectional view showing an example of the main part of the organic EL element. In many cases, a transparent electrode made of ITO is used for the anode 5 of the organic EL element. A positive hole transport layer 4, a light emitting layer 3, and an electron transport layer 2 are sandwiched between the anode 5 and the cathode 1.
The ITO manufacturing method is formed to a predetermined thickness on a transparent glass substrate by using various methods such as sputtering evaporation method, electron beam evaporation method (EB), and direct application and fusion by heating. However, the surface of ITO formed by any method is rough, and the value is an average of the surface roughness defined in the definition and display (B0601) of the surface roughness defined by the Japanese Industrial Standard (JIS). Roughness (Ra) is about several tens of millimeters.

On the other hand, since the thickness of the organic layer such as the hole transport layer 4 laminated on the anode of the organic EL element is about 500 to 2000 mm, the roughness of the ITO surface cannot be ignored.
That is, when there is a convex portion on the ITO surface, the distance between the anode and the cathode is shortened by that amount, and when a voltage in the positive direction (the direction in which the device emits light) is applied to the device, it is concentrated on that portion. A phenomenon occurs in which current flows. This is a leakage current. If a leakage current occurs during light emission of the device, not only the brightness (current-luminance characteristics) with respect to the flowing current is reduced, but also the anode and cathode of that portion are short-circuited. However, the current may not flow and the device may not emit light.
Further, in some cases, the element in the portion where the current has flowed is rapidly deteriorated so that the current cannot be passed therethrough and may appear as a non-light emitting portion (dark spot).

  Therefore, in Patent Document 1, before the step of forming the laminated structure, a step of polishing the glass substrate forming the laminated structure by a mechanical polishing method or a chemical mechanical polishing method is performed to smooth the laminated structure. In Patent Document 2, ITO on a glass substrate is smoothed by a technique such as polishing, wrapping or tape wrapping, and an organic layer or later is formed thereon.

JP-A-11-191487 Japanese Patent Laid-Open No. 9-245965

  However, in response to the recent demand for quality improvement in organic EL, it is difficult to sufficiently smooth the ITO surface with the prior art, and there has been a demand for a polishing liquid that can make the ITO surface smoother especially in polishing.

  The present invention provides a polishing liquid that can efficiently eliminate irregularities on the surface of ITO used in organic EL and liquid crystal panels while maintaining the level of the conventional polishing rate.

The present invention is a polishing liquid comprising (1) water, colloidal silica dispersed in the water, and a protective film forming agent, the pH of the polishing liquid being in the range of 2 to 3, and the colloidal silica The present invention relates to a polishing liquid for polishing an ITO film having an average particle diameter of 5 nm to 50 nm.
The present invention also relates to (2) the polishing liquid for polishing an ITO film according to (1), further comprising an organic acid.
The present invention also relates to (3) the polishing liquid for polishing an ITO film according to (2), wherein the organic acid is at least one selected from malonic acid, malic acid, tartaric acid, glycolic acid and citric acid.

The present invention also relates to (4) the polishing liquid for polishing an ITO film according to any one of (1) to (3), wherein the protective film forming agent is at least one selected from benzotriazole and derivatives thereof.
The present invention also relates to (5) the polishing liquid for polishing an ITO film according to any one of (1) to (4), wherein the ITO film is used as a transparent electrode for an organic electroluminescence panel or a liquid crystal panel.

  Further, in the present invention, (6) a substrate on which a film to be polished is formed is pressed against a polishing cloth of a polishing surface plate and pressed, and the ITO film polishing polishing liquid according to any one of (1) to (5) is used as a film. The present invention relates to a method for polishing a substrate in which a film is polished by moving a substrate and a polishing surface plate while being supplied between the polishing cloths.

  According to the present invention, the smoothness of the ITO film surface can be greatly improved by polishing while maintaining the level of the conventional polishing rate. For this reason, it is possible to prevent the occurrence of leakage current, non-light emitting portion, etc., and contribute to the improvement of the quality of the organic EL panel and the liquid crystal panel.

Hereinafter, the best mode for carrying out the invention will be described in more detail.
In the present invention, colloidal silica is used as the abrasive. Colloidal silica is excellent in smoothing the ITO surface. When generally used fumed silica, cerium oxide, alumina or the like is used, sufficient smoothness cannot be obtained.

  The average particle size of the colloidal silica used in the present invention is in the range of 5 to 50 nm, preferably in the range of 8 to 45 nm. If the particle size is too small, a sufficient polishing rate for the ITO film cannot be obtained, and the particle size is large. If it is too large, the smoothness of the polished ITO film surface cannot be obtained. When colloidal silica is prepared by hydrolysis of tetraethoxysilane in an ammonia solution, the average particle size is adjusted by adjusting the mass ratio of water to ethanol and the concentration of ammonia among tetraethoxysilane, water, ethanol and ammonia. You can control it.

In the present invention, the average particle size of the abrasive grains was determined by centrifuging the polishing liquid at 8000 min ⁻¹ for 10 minutes, and measuring the supernatant liquid with a laser diffraction particle size distribution meter (median diameter of volume distribution, cumulative center). Value). For example, it can be measured with Malvern particle size distribution meter trade name Zeta Sizer 3000HS.

In the present invention, the pH of the ITO film polishing polishing liquid (hereinafter also referred to as “polishing liquid”) is in the range of 2-3, preferably in the range of 2.2-2.8. The piping system of the apparatus may be damaged. If the pH is too high, the storage stability of the polishing liquid may be impaired.
In the present invention, the pH of the polishing solution is a pH meter (for example, model number PH81 manufactured by Yokogawa Electric Corporation), a standard buffer solution (phthalate pH buffer solution pH 4.21 (25 ° C.), neutral phosphoric acid. After calibrating two points using a salt pH buffer solution (pH 6.86 (25 ° C.)), the electrode is placed in the polishing solution, and the value after 2 minutes or more has been stabilized is measured. The pH can be adjusted by the amount of organic acid added, and can also be adjusted by alkali components such as ammonia and other acids.

  The polishing liquid of the present invention preferably contains an organic acid. When adding an organic acid, formic acid, acetic acid, propionic acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, Preferred are phthalic acid, malic acid, tartaric acid, citric acid and the like, and salts of these organic acids such as ammonium salts. Further, sulfuric acid, nitric acid, ammonia, ammonium salts such as ammonium persulfate, ammonium nitrate, ammonium chloride, chromic acid, or a mixture thereof can be further added. Among these, at least one selected from malonic acid, malic acid, tartaric acid, glycolic acid and citric acid is preferable in that a practical polishing rate and smoothness can be obtained.

  In the present invention, the protective film forming agent is preferably selected from benzotriazole (BTA), BTA derivatives, naphthotriazoles, naphthotriazole derivatives or a mixture containing these. BTA derivatives include, for example, tolyltriazole, which is one hydrogen atom of the benzene ring of BTA, substituted with a methyl group, benzotriazole 4-carboxylic acid, which is substituted with a carboxyl group, methyl, ethyl, propyl, butyl And octyl esters. At least one selected from benzotriazole and derivatives thereof is preferable.

  The addition amount of the abrasive grains in the polishing liquid for polishing an ITO film of the present invention is preferably in the range of 0.01% by mass to 10% by mass with respect to the total mass, and in the range of 0.05% by mass to 5% by mass. It is more preferable that If the blending amount is less than 0.01% by mass, there is no significant difference from the polishing rate when no abrasive grains are contained, and if it exceeds 10% by mass, the polishing rate is not improved even if it is added more.

  The compounding amount of the organic acid in the polishing liquid of the present invention is preferably 0.0001 to 0.05 mol, and more preferably 0.001 to 0.01 mol, with respect to 100 g of the total mass. If this amount exceeds 0.05 mol, the smoothness of the ITO film after polishing tends to deteriorate.

  The blending amount of the protective film forming agent in the polishing liquid of the present invention is preferably 0.0001 to 0.01 mol, and more preferably 0.0005 to 0.005 mol, with respect to 100 g of the total mass. If the amount is less than 0.0001 mol, the smoothness of the ITO film after polishing may not be sufficient. On the other hand, if it exceeds 0.01 mol, the polishing rate tends to decrease.

  In the substrate polishing method of the present invention, a substrate on which a film to be polished is formed is pressed against a polishing cloth on a polishing platen and pressed, and the ITO film polishing polishing liquid of the present invention is supplied between the film and the polishing cloth. However, the film is polished by relatively moving the substrate and the polishing platen. In the substrate polishing method of the present invention, as a polishing apparatus that can be used, a holder for holding the substrate, a motor or the like that can change the number of rotations, and a surface plate on which a polishing cloth (pad) can be attached are provided. A general polishing apparatus may be used without any particular limitation.

Further, the polishing cloth is not particularly limited, such as a general nonwoven fabric, foamed polyurethane, porous fluororesin, etc., but it is preferable that the polishing cloth is subjected to a groove processing so that the polishing slurry for ITO film polishing is accumulated.
Furthermore, although there are no restrictions on the polishing conditions, the rotation speed of the surface plate is preferably a low rotation of 200 min ⁻¹ or less so that the substrate does not pop out, and the pressure applied to the substrate causes polishing scratches on the polishing surface of the substrate. It is preferable to make it 9.8 × 10 ⁴ Pa or less (1 kgf / cm ² or less).

The method of supplying the polishing liquid of the present invention to the polishing apparatus is not particularly limited as long as the polishing liquid can be continuously supplied to the polishing cloth with a pump or the like during polishing. Furthermore, although there is no restriction | limiting in this supply amount, it is preferable that the surface of polishing cloth is always covered with polishing liquid.
The substrate after polishing is preferably washed in running water, and then dried after removing water droplets adhering to the substrate using a spin dryer or the like.

In the present invention, the flatness of the ITO film surface after polishing is evaluated by the surface roughness Ra, and Ra is measured by an AFM (atomic force microscope). The range of Ra is preferably 3.0 mm or less, more preferably 2.5 mm or less.
The polishing rate is obtained by converting the film thickness difference before and after polishing from the electric resistance value.

  The polishing solution for polishing an ITO film of the present invention is particularly suitable for polishing an ITO film used as a transparent electrode for an organic EL panel or a liquid crystal panel, and for other uses such as a resistive film type touch panel and a solar cell. It can also be used for polishing an ITO film used for an electrode of a blue light emitting diode.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. The present invention is not limited by these examples.
Example 1
A polishing solution was prepared by adding water to 0.4 parts by mass of malic acid, 5 parts by mass of colloidal silica having an average particle diameter of 20 nm and 20 parts by mass of colloidal silica and 0.2% by mass of BTA. The prepared polishing liquid had a pH of 2.50. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution. The average particle size of colloidal silica was controlled by adjusting the mass ratio of water to ethanol and the concentration of ammonia among tetraethoxysilane, water, ethanol and ammonia.
While dripping the polishing liquid onto the pad attached to the surface plate, CMP treatment was performed under the following substrate and polishing conditions, and the following evaluation was performed. Table 1 shows the polishing composition, pH, and evaluation results.
As a result of the evaluation, the polishing amount of ITO was 50 mm, and the surface roughness Ra was 1.7 mm, indicating good smoothness.

(Polishing conditions)
Polishing machine: Nanofactor Co., Ltd. polishing system FACT-200
Polishing pad: Polyurethane resin with closed cells Polishing pressure: 25 kPa / cm ² (250 gf / cm ² )
Rotation speed of polishing surface plate: 50 min ⁻¹
Polishing fluid flow rate: 15 cc / min
Polishing time: 2 minutes

(Substrate used)
A glass substrate (2 cm square) with an ITO film with a thickness of 0.1 μm
Unpolished Ra: 20 mm

(Evaluation items and evaluation methods)
Polishing rate by CMP: The difference in film thickness before and after polishing the substrate was calculated from the change in sheet resistance.
Surface roughness (Ra): A value obtained by measuring the surface roughness of the ITO film after polishing with an AFM (atomic force microscope) under the following conditions was employed. That is, the surface of the ITO film was measured with a scanning probe microscope (model number SPI3800N / SPA500 manufactured by Seiko Instruments Inc.) in a measurement region of 5 microns □.

Example 2
A polishing liquid was prepared by adding water to 0.4 parts by mass of malic acid, 5 parts by mass of colloidal silica having an average particle size of 25 nm and 20 parts by mass of colloidal silica and 0.2% by mass of BTA. The prepared polishing liquid had a pH of 2.50. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polished amount of ITO was 56 mm, and the surface roughness Ra was 1.9 mm, indicating good smoothness.

Example 3
Water was added to and dissolved in 0.4% by mass of malic acid, 1 part by mass of colloidal silica having an average particle diameter of 40 nm and 0.2% by mass of BTA to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.52. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polished amount of ITO was 58 Å and the surface roughness Ra was 2.4 、, which showed good smoothness.

Example 4
Water was added to and dissolved in 0.4% by mass of glycolic acid, 1 part by mass of colloidal silica having an average particle diameter of 20 nm and 0.2% by mass of BTA to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.58. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polishing amount of ITO was 47 mm, and the surface roughness Ra was 2.0 mm, indicating good smoothness.

Example 5
Water was added to 0.4% by mass of malonic acid, 1 part by mass of colloidal silica having an average particle diameter of 20 nm, and 0.2% by mass of BTA to dissolve it to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.46. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polished amount of ITO was 47 mm, and the surface roughness Ra was 2.1 mm, which showed good smoothness.

Example 6
Water was added to and dissolved in 0.4 mass% of citric acid, 5 mass parts of colloidal silica having an average particle diameter of 20 nm and 20 wt% colloidal silica, and 0.2 mass% of BTA to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.40. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polishing amount of ITO was 47 mm, and the surface roughness Ra was 2.2 mm, indicating good smoothness.

Example 7
Water was added to and dissolved in 0.4% by mass of malonic acid, 1 part by mass of colloidal silica having an average particle size of 40 nm and 0.2% by mass of BTA to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.46. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polishing amount of ITO was 52 mm, and the surface roughness Ra was 2.1 mm, which showed good smoothness.

Example 8
Water was added to 0.4 parts by mass of citric acid, 20 parts by weight of colloidal silica having an average particle size of 40 nm and 5 parts by weight of BTA and 0.2 parts by weight of BTA to dissolve them to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.40. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polished amount of ITO was 60 mm, and the surface roughness Ra was 2.3 mm, which showed good smoothness.

Comparative Example 1
A polishing liquid was prepared by adding water to 0.4 parts by weight of malic acid, 5 parts by weight of colloidal silica having an average particle size of 80 nm and 20 parts by weight of colloidal silica and 0.2% by weight of BTA. The prepared polishing liquid had a pH of 2.50. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed and evaluated in the same manner as in Example 1 except that the polishing time was set to 1.5 minutes using the above polishing liquid. As a result of the evaluation, the polishing amount of ITO was 63 Å and the surface roughness Ra was 5.3 平滑, and the smoothness deteriorated as compared with the Examples.

Comparative Example 2
Water was added to and dissolved in 0.4 mass% of glycolic acid, 20 mass parts of 5 wt% α-alumina suspension having an average particle size of 240 nm and 0.2 mass% of BTA to obtain a polishing liquid. The prepared polishing liquid had a pH of 2.58. The α-alumina suspension was prepared by suspending α-alumina powder having a purity of 99.9% in pure water, ultrasonically dispersing, and removing coarse particles by classification.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polishing amount of ITO was 60 mm and the surface roughness Ra was 3.6 mm, and the smoothness was worse than that of the example.

Comparative Example 3
A polishing solution was prepared by adding water to 0.4 parts by mass of malic acid, 1 part by mass of a fumed silica suspension having an average particle diameter of 160 nm and 1 part by mass of fumed silica, and 0.2% by mass of BTA. The prepared polishing liquid had a pH of 2.53. The fumed silica suspension was prepared by suspending Aerosil 200 (trade name of Nippon Aerosil Co., Ltd.) in pure water and ultrasonically dispersing it.
Polishing was performed and evaluated in the same manner as in Example 1 except that the polishing time was set to 10 minutes using the above polishing liquid. As a result of the evaluation, the polishing amount of ITO was 40 mm and the surface roughness Ra was 15 mm, and the smoothness deteriorated as compared with the examples.

Comparative Example 4
After adding water to 5 parts by mass of malic acid 0.4% by mass, an average particle size of 25 nm, 20% by weight colloidal silica and 0.2% by mass of BTA, the pH is adjusted to 4.02 with ammonia, did. The abrasive grains were prepared by hydrolysis of tetraethoxysilane in an ammonia solution.
Polishing was performed in the same manner as in Example 1 using the above polishing liquid, and evaluation was performed. As a result of the evaluation, the polishing amount of ITO was 42 Å and the surface roughness Ra was 5.0 Å, and the smoothness deteriorated as compared with the examples.

It is a schematic sectional drawing which shows an example of the principal part of an organic EL element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cathode 2 Electron transport layer 3 Light emitting layer 4 Hole transport layer 5 Anode (ITO)
6 Glass substrate

Claims (6)

  A polishing liquid comprising water, colloidal silica dispersed in the water, and a protective film forming agent, wherein the pH of the polishing liquid is in the range of 2 to 3, and the average particle diameter of the colloidal silica is 5 nm to 50 nm. A polishing liquid for polishing an ITO film.   The polishing liquid for polishing an ITO film according to claim 1, further comprising an organic acid.   The polishing liquid for polishing an ITO film according to claim 2, wherein the organic acid is at least one selected from malonic acid, malic acid, tartaric acid, glycolic acid and citric acid.   The polishing liquid for polishing an ITO film according to claim 1, wherein the protective film forming agent is at least one selected from benzotriazole and derivatives thereof.   The polishing liquid for polishing an ITO film according to any one of claims 1 to 4, wherein the ITO film is used as a transparent electrode for an organic electroluminescence panel or a liquid crystal panel.   While pressing the substrate on which the film to be polished is pressed against the polishing cloth of the polishing platen and supplying the polishing liquid for ITO film polishing according to any one of claims 1 to 5 between the film and the polishing cloth, A substrate polishing method in which a film is polished by moving a substrate and a polishing surface plate.

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