JP2015174985A - Polishing material and method of polishing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing material that is specialized in an electric field application polishing technique and that can realize a high electric field application effect, and to provide a method of polishing.SOLUTION: A polishing material is provided that is to be fed between a polishing surface table and a member to be polished and to which electric voltage is applied, the polishing material including abrasive grain and a dispersant drawn between the polishing surface table and the member to be polished by the electric field generated by the voltage. The polishing material is a composite polishing material in which a core material having a higher dielectric constant than the dispersant is coated with a shell material having a higher polishing amount (polishing rate) per unit time with respect to the member to be polished than the core material. The core material is a titanium metal complex oxide and SrTiOand/or BaTiO, and the shell material is at least one material selected from an oxide, carbide, nitride, boride, and diamond.

Description

  The present invention relates to an abrasive used for polishing a member to be polished and a polishing method.

  Today, precision polishing of hard and brittle materials is an important basic technology in various industries. With regard to improvement in polishing efficiency and polishing quality in precision polishing, for example, development of auxiliary materials for polishing such as abrasive grains, solvents, pads, etc., and technical development aimed at improving polishing technology are active (see Patent Document 1 below) ).

  In such a flow, a technique for improving the polishing efficiency by applying an external electric field during polishing to control the slurry flow has been developed. By applying an external electric field during polishing, for example, if the slurry is oil-based, an electric field is applied to the abrasive grains, and if the slurry is water-based, the electric field mainly acts on the dispersion medium.

JP 2012-81529 A

However, in precision polishing using a slurry, when the polishing efficiency is improved by applying an external electric field, the dielectric constant of the abrasive grains and the dispersion medium constituting the slurry is an important factor. For example, in the case of a water-based slurry, since the dielectric constant of water is about 80, the dielectric constant of abrasive grains (eg, silica, ceria, diamond, etc.) is often lower than that of water. Therefore, when a water-based slurry is used, it is difficult to positively apply an electric field to abrasive grains even when an external electric field is applied. On the other hand, a material having a dielectric constant higher than that of water (for example, SrTiO ₃ , BaTiO _3, etc.) has a low polishing rate (polishing removal amount per unit time), and thus is difficult to use as abrasive grains.

  The present invention has been proposed in view of the above circumstances. That is, it is an abrasive specialized in electric field application polishing technology, and an object thereof is to provide an abrasive and a polishing method capable of realizing a high electric field application effect regardless of the type of dispersion medium.

  In order to achieve the above object, a polishing material according to the present invention is supplied between a polishing surface plate and a member to be polished and a voltage is applied thereto, and the polishing platen and the object to be polished are generated by an electric field generated by the voltage. In an abrasive containing abrasive grains and a dispersion medium brought close to a member, the abrasive grains are composed of a core material and a shell material covering the core material, and the dielectric constant of the abrasive grains is The shell material has a higher polishing amount per unit time than the dispersion medium, and the shell material is higher than the core material.

  The abrasive according to the present invention is characterized in that the core material has a dielectric constant higher than that of the dispersion medium.

  The abrasive according to the present invention is characterized in that the core material is a titanium metal composite oxide.

The abrasive according to the present invention is characterized in that the core material includes one or more selected from SrTiO ₃ and BaTiO ₃ .

  The abrasive according to the present invention is characterized in that the shell material is one or more materials selected from oxides, carbides, nitrides, borides, and diamonds.

In the abrasive according to the present invention, the shell material includes one or more selected from iron oxide, manganese oxide, silica, ceria, diamond, alumina, titania, zirconia, cBN, SiC, and B ₄ C. It is characterized by that.

  In the polishing method according to the present invention, an abrasive is supplied between a polishing surface plate and a member to be polished, and an electric field generated by applying a voltage causes the polishing between the polishing surface plate and the member to be polished. It is characterized by controlling the arrangement of grains.

  The abrasive and the polishing method according to the present invention have the above-described configuration. With this configuration, since the dielectric constant of the abrasive grains is higher than that of the dispersion medium, an electric field acts on the abrasive grains, and the arrangement of the abrasive grains is controlled between the polishing surface plate and the member to be polished. Further, since the polishing rate of the shell material with respect to the member to be polished is higher than that of the core material, the member to be polished is efficiently polished. Therefore, by covering the core material having a dielectric constant higher than that of the dispersion medium with a shell material whose polishing rate for the member to be polished is higher than that of the core material, a high response to an external electric field and excellent polishing characteristics are combined, A high electric field application effect can be realized in the electric field application polishing technique.

It is the figure which showed the graph which compared the polishing rate at the time of grind | polishing a to-be-polished member using the abrasive | polishing material which concerns on the Example of this invention with the abrasive | polishing material comprised only by a core material. It is the figure which showed the grinding | polishing speed-frequency graph at the time of grind | polishing a to-be-polished member using the abrasive | polishing material which concerns on the Example of this invention. It is the figure which showed the graph which compared the polishing rate at the time of grind | polishing a to-be-polished member using the abrasive | polishing material which concerns on the Example of this invention with the comparative example.

  Hereinafter, an abrasive and a polishing method according to embodiments of the present invention will be described.

  The abrasive according to the present embodiment is arranged when the member to be polished is disposed between an upper surface plate and a lower surface plate (not shown) as a polishing surface plate, and the member to be polished is polished while applying an electric field. Supplied between both surface plates and the member to be polished. Examples of the member to be polished include glass, sapphire, silicon carbide (SiC), gallium nitride (GaN), and diamond.

The abrasive is a slurry containing abrasive grains and a dispersion medium. In the abrasive grains, the core material is coated with a shell material in order to realize a high dielectric constant and a high polishing rate. The dielectric constant of the core material is higher than that of the dispersion medium. If the dispersion medium is, for example, water or oil, the core material is, for example, a titanium metal composite oxide, and is selected from strontium titanate (SrTiO ₃ ), barium titanate (BaTiO ₃ ), and the like.

The shell material has a higher polishing rate for the member to be polished than the core material. Examples of the shell material include metal oxides, carbides, nitrides, borides, and diamonds, and iron oxide, manganese oxide, silicon dioxide (silica, SiO ₂ ), cerium oxide (ceria), diamond (C), and aluminum oxide. (Alumina, Al ₂ O ₃ ), titanium oxide (titania, TiO ₂ ), zirconium oxide (zirconia, ZrO ₂ ), boron carbide (B ₄ C), cubic boron nitride (cBN), silicon carbide (SiC), etc. Selected.

  The polishing rate depends on the chemical characteristics and mechanical characteristics of the abrasive grains. For example, if the member to be polished is sapphire, silica-based abrasive grains have a high polishing rate because the chemical characteristics and mechanical characteristics of sapphire are balanced. On the other hand, strontium titanate and barium titanate have a low polishing rate because the chemical and mechanical properties of sapphire are not balanced. Therefore, the shell material is appropriately selected according to the member to be polished from the viewpoint of the chemical characteristics and mechanical properties of the member to be polished. For example, if the member to be polished is glass, the shell material is preferably ceria.

  Next, the effect of this embodiment will be described.

  As described above, according to this embodiment, since the dielectric constant of strontium titanate or barium titanate that is the core material is higher than that of water or oil that is the dispersion medium, the electric field acts on the core material, and the abrasive grains It is brought between the polishing board and sapphire which is a member to be polished. Moreover, since the polishing rate with respect to sapphire which is a member to be polished is higher than that of strontium titanate or barium titanate, silica or the like which is a shell material is efficiently polished. Therefore, by covering the core material having a dielectric constant higher than that of the dispersion medium with a shell material whose polishing rate for the member to be polished is higher than that of the core material, a high response to an external electric field and excellent polishing characteristics are combined, A high electric field application effect can be realized in the electric field application polishing technique.

  Next, examples of the present invention will be described.

As an example, an abrasive (SiO ₂ -coated SrTiO ₃ abrasive grains) was produced by coating strontium titanate with silica. In this embodiment, SrTiO ₃ synthesized by the spray pyrolysis method is synthesized as the core material and SiO ₂ as the shell material is synthesized by the sol-gel method. However, the method for synthesizing the abrasive grains is not particularly limited to this method.

The comparative example uses uncoated SrTiO ₃ abrasive grains in the evaluation of the basic polishing characteristics of the abrasive grains, and silica abrasive grains synthesized using a thermal decomposition synthesis method. In the electropolishing evaluation, sapphire for an LED substrate is used. Aqueous solvent colloidal silica abrasive grains (manufactured by Nitta Haas Co., Ltd .: MS-2000) generally used in precision polishing of substrates were used. In the basic polishing characteristic evaluation, the polishing rate of each abrasive grain was verified. On the other hand, in the electropolishing evaluation, the polishing characteristics when the sapphire substrate was polished were verified using the SiO ₂ coated SrTiO ₃ abrasive grains of the example and the silica abrasive grains (MS-2000) of the comparative example.

  When polishing is performed while applying an external electric field using silica abrasive grains (MS-2000), since the dielectric constant of silica is 2, the electric field acts on water as a dispersion medium. On the other hand, in the present invention, since strontium titanate particles are coated with silica, strontium titanate particles having a dielectric constant higher than that of water realize high response to an electric field, and polishing a sapphire substrate with silica. Excellent polishing characteristics can be realized. The following is verified.

<Synthesis of strontium titanate particles by spray pyrolysis method>
Dissolve strontium nitrate and titanium peroxo ammonium citrate in water and adjust to pH 8.5 with citric acid and aqueous ammonia. While flowing 0.25 mol / L of the raw material solution at a carrier gas (air) of 3 L / min, it passes through the tubular path installed in the order of different heating temperatures (200 ° C.-400 ° C.-800 ° C.-1000 ° C.) Perform a decomposition reaction. The particles passing through the tubular passage and trapped on the filter were calcined at 800 ° C. for 4 hours to obtain strontium titanate particles.

<SilTiO ₃ particles coated with silica by the sol-gel method>
After dispersing 20 g of strontium titanate particles obtained by the spray pyrolysis method in 2000 ml of alcohol (econol) such as ethanol, ultrasonic treatment was further performed for 30 minutes to disperse the particles. Thereafter, 120 ml of 25% aqueous ammonia was added while stirring at room temperature, and the mixture was stirred for 45 minutes. Thereafter, 60 ml of tetraethyl orthosilicate (TEOS) was added and stirred for 24 hours. After standing, the supernatant was removed and dried at 65 ° C. The thickness of the shell material depends on the particle size of the core material, but is 0.5% or more, preferably 5% or more, more preferably 15% or more, and 80% or less, preferably 60% of the particle radius of the core material. % Or less, more preferably 50% or less.

<SiO ₂ coated SrTiO ₃ abrasive grain basic characteristics polishing conditions>
The polishing machine used was a polishing machine owned by the Fine Ceramics Center. The specifications of the polishing machine are as follows. Upper surface plate diameter: φ150 mm, lower surface plate diameter: φ300 mm, upper surface plate rotation speed range: 150 rpm, lower surface plate rotation speed range: 40 to 600 rpm, polishing load (polishing pressure) application method: air cylinder pressurization method, polishing load range 1 kgf to 10 kgf, slurry flow rate range: 30 to 280 ml / min.

Polishing was performed at an upper surface plate and a lower surface plate at a rotation speed of 150 rpm, a slurry supply speed of 100 mL / min, and a polishing pressure of 314 gcm ⁻² .

The polishing rate characteristics using the SiO ₂ -coated SrTiO ₃ abrasive grains of the examples, the SrTiO ₃ abrasive grains and the silica abrasive grains of the comparative examples are shown in FIG. The polishing rate in each abrasive grain was measured.

SrTiO ₃ abrasive grains have a polishing rate of about 0.03 μmh ^−1, while SiO ₂ coated SrTiO ₃ abrasive grains are 0.52 μmh ⁻¹ , an increase of about 17 times, and a polishing rate equivalent to that of SiO ₂ abrasive grains. It was.

This result shows that CMP is manifested by the fact that SrTiO _{3 as the} core material is appropriately coated with SiO _{2 as the} shell material by the sol-gel method, and that SiO ₂ and the sapphire substrate come into contact with each other in the polishing field in the composite particles. It shows that you are doing.

<Electric field polishing conditions>
As the polishing machine, a polishing machine owned by Akita Industrial Technology Center was used. The specifications of the polishing machine are as follows. Upper surface plate diameter: φ80 mm, lower surface plate diameter: φ160 mm, upper surface plate rotation speed range: 0 to 800 rpm, lower surface plate rotation speed range: 0 to 120 rpm, polishing load (polishing pressure) application method: air cylinder pressurization method, polishing Load range: 1 kgf to 14 kgf, slurry flow rate range: 0 to 70 ml / min. Here, pH adjustment for the abrasive, addition of a dispersant, an additive, and the like may be appropriately performed.

Polishing was performed at an upper surface plate and a lower surface plate at a rotation speed of 100 rpm, a slurry supply speed of 5 mL / min, and a polishing pressure of 100 to 300 gcm ⁻² . The waveform of the applied voltage is a rectangular wave, and the voltage is from 0 kV to 3 kV.

FIG. 2 shows the frequency dependence on the polishing rate at each polishing pressure using SiO ₂ -coated SrTiO ₃ abrasive grains. The polishing rate was measured while changing the polishing pressure.

For electroless, with an increase in polishing pressure, the polishing rate 0.20μmh ^-1, 0.28μmh ^-1, increased to 0.47μmh ^-1.

When the frequency was changed, when the polishing pressure was 100 gcm ⁻² , 2 Hz: 0.21 μmh ⁻¹ , 5 Hz: 0.20 μmh ⁻¹ , 10 Hz: 0.19 μmh ⁻¹ , 32 Hz: 0.22 μmh ⁻¹ It was. Compared to the case of no electric field, the polishing rate was improved by 10.1% at maximum.

When the polishing pressure was 300 gcm ⁻² , 3 Hz: 0.47 μmh ⁻¹ , 10 Hz: 0.53 μmh ⁻¹ , 32 Hz: 0.49 μmh ⁻¹ . Compared to the case of no electric field, the polishing rate was improved by 13.5% at the maximum.

When the polishing pressure was 200 gcm ⁻² , the polishing rate increased by 27% compared to the case of no electric field.

From the above results, it was found that the SiO ₂ coated SrTiO ₃ abrasive grains of the example responded to the electric field, and the frequency value at which the polishing rate was highest differs depending on the polishing pressure. The polishing rate increased most as compared with the case of no electric field when the polishing pressure was 200 gcm ⁻² and the frequency was 32 Hz. At this time, the comparison of the polishing rate between the SiO ₂ -coated SrTiO ₃ abrasive grains and the silica abrasive grains (MS-2000) of the comparative example was carried out separately depending on the presence or absence of an electric field.

FIG. 3 shows changes in the polishing rate of the comparative silica abrasive grains (MS-2000) and the SiO ₂ coated SrTiO ₃ abrasive grains of the examples with respect to the electric field. When polishing was performed at an applied voltage of 1-3 kV and a frequency of 32 Hz, the polishing rate changed from 0.28 μmh ⁻¹ to 0.15 μmh ⁻¹ , and the polishing rate was reduced by about 45% compared to the case of no electric field. On the other hand, when polishing was performed at an applied voltage of 0-3 kV and a frequency of 32 Hz, the polishing rate changed from 0.28 μmh ⁻¹ to 0.35 μmh ⁻¹ , and the polishing rate increased by about 27% compared to the case of no electric field. .

  In a system where a non-uniform electric field is applied, such as a polishing field, when the dielectric constant of the dispersoid (abrasive grain) is larger than that of the dispersion medium, the migration force acts on the strong electric field side, and the dispersoid is fixed near the electrode. . This phenomenon is known as dielectrophoresis and the results are similar to this phenomenon. When the applied voltage is 1-3 kV, the abrasive grains stay in the polishing field and deteriorate, leading to a reduction in the polishing rate. On the other hand, when the applied voltage is 0-3 kV, used abrasive grains and processing waste are released from the polishing field when the applied voltage is 0 kV. In addition, it is considered that the polishing rate was increased because an electric field was applied and new abrasive slurry flowed into the polishing field.

Silica abrasive grains in Comparative Example (MS-2000) is the applied voltage 0-3KV, when performing polishing at a frequency 32 Hz, it varies from 0.23Myumh ^-1 to 0.25Myumh ^-1, compared with the case of no electric field As a result, the polishing rate increased by about 11%.

As a result, it was found that the SiO ₂ -coated SrTiO ₃ abrasive grains of the examples responded more remarkably to the electric field and increased the polishing rate than the silica abrasive grains (MS-2000) of the comparative example. That is, it was found that the SiO ₂ coated SrTiO ₃ abrasive grains have high responsiveness to an external electric field and excellent polishing characteristics, and can realize a high electric field application effect in the electric field application polishing technique.

  As mentioned above, although embodiment of this invention was explained in full detail, this invention is not limited to the said embodiment. The present invention can be modified in various ways without departing from the scope of the claims.

Claims (7)

A voltage is applied between the polishing platen and the member to be polished, and abrasive grains and a dispersion medium brought between the polishing platen and the member to be polished by an electric field generated by the voltage are included. In abrasives,
The abrasive is composed of a core material and a shell material covering the core material,
The abrasive has a higher dielectric constant than the dispersion medium,
The amount of polishing per unit time for the member to be polished is higher in the shell material than in the core material,
An abrasive characterized by the above. The dielectric constant of the core material is higher than that of the dispersion medium,
The abrasive according to claim 1. The core material is a titanium metal composite oxide;
The abrasive according to claim 1 or 2, characterized in that The core material includes one or more selected from SrTiO ₃ and BaTiO ₃ ,
The abrasive according to any one of claims 1 to 3, wherein: The shell material is one or more materials selected from oxides, carbides, nitrides, borides, and diamonds.
The abrasive according to any one of claims 1 to 4, wherein: The shell material includes one or more selected from iron oxide, manganese oxide, silica, ceria, diamond, alumina, titania, zirconia, cBN, SiC, and B ₄ C.
The abrasive according to any one of claims 1 to 5, wherein: The abrasive according to any one of claims 1 to 6 is supplied between a polishing platen and a member to be polished, and an electric field generated by applying a voltage to the polishing platen and the substrate. The arrangement control of the abrasive grains is performed with the polishing member.
A polishing method characterized by the above.