JP2015165001A - Abrasive grains, manufacturing method thereof, polishing method, polishing device, and slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for polishing the surface of a material to be polished with high quality finish at a high polishing rate.SOLUTION: The surface of a material to be polished is polished by a wet polishing method. A slurry includes abrasive grains dispersed in pure water. The abrasive grains include a component having a mechanochemical function, a component reactive to the frictional heat generated in polishing of the material to be polished and the like, which are integrated into a granular form as a whole. The components retaining properties inherent to the respective materials are directly bonded to each other by mechanical alloying. Use of the slurry in lapping sapphire, silicon carbide, gallium nitride and the like allows the polishing time to be drastically reduced in comparison with a conventional method, so that the processing cost can be substantially reduced. A high quality polishing surface can be obtained. The abrasive grains can be repeatedly used in the polishing treatment. The slurry has a pH of about 3 to 9, producing no impact on the environment, with easy processing of waste liquid.

Description

  The present invention relates to abrasive grains used for polishing the surface of a material to be polished such as sapphire, silicon carbide (SiC), gallium nitride (GaN), a manufacturing method thereof, a polishing method, a polishing apparatus, and a polishing tool. Regarding slurry.

  In recent years, new semiconductor devices have been proposed one after another with the aim of increasing functionality and performance. In response to these proposals, new materials other than silicon (Si) substrates have been used. In particular, substrates such as sapphire, SiC for power devices, and GaN for light emitting diodes (LEDs) are in the spotlight. In the future, the development of new processing methods for substrates is eagerly desired in order to achieve higher performance and lower costs for mass production.

  In the manufacturing process of a semiconductor device, a polishing process is performed to flatten the surface of a substrate (Semiconductor substrate). One method conventionally employed is a method of polishing a substrate to be polished using an oily slurry containing diamond abrasive grains. The surface of the substrate of the material to be polished is mechanically scraped by diamond abrasive grains. Diamond abrasive grains are harder than silicon carbide substrates. This method has a high polishing rate and can reach a target polishing amount in a short time. However, deep and large scratches may occur on the surface of the substrate to be polished. Therefore, it is difficult to obtain a high-quality polished surface. Moreover, since the oily slurry is denatured by the heat of the polishing process, the diamond abrasive grains agglomerate. As a result, there is a problem that expensive diamond abrasive grains cannot be reused.

  In order to solve the above-mentioned problems, a technique that employs a polishing method that produces a mechanochemical effect has been introduced (Patent Document 1). In mechanochemical polishing, the surface of a material to be polished is altered and polished with softer abrasive grains than the material to be polished. Therefore, a large flaw is not generated on the surface of the material to be polished. In addition, a technique for improving the polishing rate by using an oxidizing agent as an abrasive of silicon carbide has been introduced (Patent Document 2) (Patent Document 3) (Patent Document 4).

JP 2005-81485 A Japanese Patent No. 4345746 Japanese Patent No. 4827963 WO2011136367

  The dry polishing method (Dry polishing) disclosed in Patent Document 1 generates high frictional heat between an object material and abrasive particles, thereby causing mechanochemical polishing. ) Is promoted to improve the removal rate. However, since abrasive grains and polishing debris exposed to a high temperature adhere to the inside of the polishing apparatus, it takes time to clean the apparatus. Therefore, there is a problem that productivity is poor.

  On the other hand, in the wet polishing method (Wet polishing) shown in Patent Document 2 and Patent Document 3, an oxidizing agent such as hydrogen peroxide is added to the polishing slurry to oxidize the surface of the material to be polished, thereby improving the polishing rate. I am trying. However, the slurry containing the oxidant deteriorates the working environment and increases the cost of waste liquid treatment. In addition, the oxidizer may corrode the polishing apparatus. The wet polishing method disclosed in Patent Document 4 promotes mechanochemical polishing using a strong alkaline slurry to improve the polishing rate. However, a strongly alkaline slurry having a pH of 10 to 14 deteriorates the working environment and increases the cost of waste liquid treatment. In either case, since the characteristics of the slurry are likely to change during the polishing process, there is a problem that monitoring and adjustment are indispensable and it is difficult to automate the polishing process. That is, conventionally known methods cannot polish SiC or GaN having high corrosion resistance at a high quality at a practical polishing rate.

In order to solve the above-mentioned problems, the present invention employs a wet polishing method, utilizes a polishing method that produces a mechanochemical effect, and achieves a high polishing rate with a high quality and a high polishing rate of a material to be polished. And its manufacturing method.
Furthermore, an object of the present invention is to provide a polishing method, a polishing apparatus, and a polishing slurry for wet-polishing a material to be polished using a slurry having little influence on the environment.

The following configurations are means for solving the above-described problems.
<Configuration 1>
A mechanical alloying method comprising: a particulate first abrasive that is equal to the material to be polished or has a Mohs hardness lower than the material to be polished; and a particulate second abrasive that chemically alters the material to be polished. Polishing abrasive grains that are integrated into particles by the above.

<Configuration 2>
The abrasive for polishing according to Configuration 1, wherein the first abrasive occupies 5 weight percent or more and 95 weight percent or less of the integrated particles.

<Configuration 3>
The abrasive for polishing according to Configuration 1, wherein the second abrasive occupies 5 weight percent or more and 95 weight percent or less of the integrated particles.
<Configuration 4>
4. The polishing abrasive grain according to any one of configurations 1 to 3, wherein the first abrasive and the second abrasive are integrated into particles having an average particle size of 0.05 μm to 100 μm.

<Configuration 5>
Particles for polishing the surface of a material to be polished, the particles including a plurality of types of inorganic compound components combined by mechanical alloying treatment, and each inorganic compound component is mutually connected via an amorphous layer. Abrasive grains that are bonded together.

<Configuration 6>
The polishing abrasive grain according to configuration 6, wherein the plurality of types of inorganic compound components are bonded in a state in which the properties unique to the substances of the individual components are retained.
<Configuration 7>
The plurality of types of inorganic compound components are combined in a state in which the substance-specific properties of the individual components are retained, and each inorganic compound component is partially exposed on the outer surface of the particle. Polishing abrasive.

<Configuration 8>
The abrasive for polishing according to Configuration 6 or 7, wherein any one of a plurality of inorganic compound components contains a chemically reactive abrasive that causes a mechanochemical effect on the material to be polished.
<Configuration 9>
The abrasive grains according to Configuration 8, wherein the plurality of types of inorganic compound components have the same Mohs hardness as the material to be polished or have a lower Mohs hardness than the material to be polished.

<Configuration 10>
One of the multiple types of inorganic compound components includes a chemically reactive abrasive that produces a mechanochemical effect on the material to be polished, and a component that mechanically scrapes the surface of the material that produced the mechanochemical effect. The abrasive grain for polishing according to Configuration 8.

<Configuration 11>
The abrasive for polishing according to Configuration 10, wherein the component that mechanically scrapes the surface of the material to be polished is equal to the material to be polished or has a Mohs hardness lower than that of the material to be polished.

<Configuration 12>
The chemically reactive abrasive that produces a mechanochemical effect on the object to be polished is a component that oxidizes the polishing surface of the object by reacting with frictional heat generated during the polishing process. grain.

<Configuration 13>
Chemically reactive abrasives that produce mechanochemical effects on the materials being polished include lithium, alkaline earth metal carbonates, phosphates, fluorides, boron compounds, and silver chloride, silver bromide, and silver iodide. The polishing abrasive grain according to constitution 10, which is one or two or more sparingly soluble salts selected from halogen compounds, such as halogen compounds, cryolite, or alum.

<Configuration 14>
Abrasive abrasive that mixes raw materials of multiple types of inorganic compound components, performs mechanical alloying in a dry state, and binds each inorganic compound component together through an amorphous layer to form particles Manufacturing method.

<Configuration 15>
A polishing method for polishing a material to be polished using a slurry obtained by dispersing abrasive grains according to any one of Structures 1 to 12 in pure water.
<Configuration 16>
A polishing member in which the abrasive grains according to any one of Structures 1 to 12 are dispersed and fixed on a base material.

<Configuration 17>
A polishing pad composed of any one of synthetic fibers, glass fibers, natural fibers, synthetic resins, and natural resins, and having the abrasive grains according to any one of configurations 1 to 12 dispersed and fixed on the surface;
A holding device that presses the material to be polished toward the surface of the polishing pad using elasticity,
A liquid injector for supplying pure water to the polished surface,
A polishing apparatus in which the elasticity of the holding device is set to a level that generates frictional heat above the temperature at which a chemical reaction by the reaction accelerator occurs between the polishing abrasive grains and the material to be polished.

<Configuration 18>
A suspension formed by dispersing abrasive grains according to any one of constitutions 1 to 12 in neutral water and having a pH of 4 or more and 11 or less at 25 degrees Celsius Or a slurry for polishing gallium nitride.

In the polishing abrasive grain of the present invention, a plurality of types of components are directly bonded to each other by mechanical alloying and integrated into a particle form. Since the binding energy between the components is large, the polishing abrasive grains are not decomposed during the polishing process. A mechanochemical effect is produced by a component that exerts a chemical polishing action on the material to be polished, and polishing abrasive grains having a Mohs hardness lower than that of the material to be polished can be polished at a high polishing rate. The reaction accelerator reacts with heat generated by friction between the outer surface of the abrasive grains and the material to be polished, and promotes a chemical polishing action. If the chemical polishing action is promoted, the polishing rate can be further improved.
Since a plurality of types of components are bonded together while maintaining the material-specific properties of each component, each component acts in a chain to promote polishing. Since a plurality of types of components are directly bonded to each other and integrated in the form of particles as a whole, each abrasive grain exhibits its function in a chain.
High-speed polishing is possible when a component having a relatively high hardness that exhibits a mechanical polishing action is used. When a component that exhibits a mechanical polishing action has a relatively low hardness, high-quality polishing can be achieved.
Slurries in which the above abrasive grains are dispersed in pure water are almost harmless. It does not affect the environment of the polishing workshop, and waste liquid treatment is easy. In addition, since the consumption of the components constituting the abrasive grains during polishing is small, it can be used repeatedly and is economical.
In wet polishing using a slurry such as water, heat energy is dissipated, and generally a chemical polishing action is not sufficiently exhibited. In contrast, polishing abrasive grains in which a plurality of types of components are integrated in a particulate form can sufficiently exhibit a chemical polishing action by effectively utilizing thermal energy even in wet polishing.

It is an external view which shows schematic structure of the abrasive grain for grinding | polishing of this invention. It is a schematic perspective view which shows an example of the grinding | polishing apparatus which uses the abrasive grain for grinding | polishing. It is explanatory drawing of the conventional mechanochemical polishing method. It is the microscope picture of polishing abrasive grain of this invention, and polishing operation explanatory drawing. It is the figure which compared the component of the abrasive grain before and behind a grinding | polishing process with the abrasive grain of an Example. It is a property comparison figure of the waste liquid after grind | polishing using various abrasive grains. It is a polishing rate comparison figure of SiC when the 1st ingredient is replaced. It is a polishing rate comparison figure of SiC when the 2nd ingredient is replaced. Fig. 9A is a GaN polishing rate comparison diagram, and Fig. 9B is a sapphire polishing rate comparison diagram. It is data which shows the relationship between the polishing rate when the reaction accelerator is replaced and the temperature after the polishing process. It is a comparison figure which shows the relationship between a polishing pressure and a polishing rate. It is a comparison figure which shows the relationship between the polishing rate of various abrasive grains, and surface roughness. It is a comparative figure which shows the relationship between the polishing rate of the abrasive grain of a comparative example, and surface roughness. It is a comparison figure of the polishing rate graphed. It is a comparison figure of the surface roughness after grinding which was graphed.

FIG. 1 is an external view showing a schematic structure of polishing abrasive grains of the present invention.
The polishing abrasive grain 10 of the present invention is used for polishing various materials such as sapphire, silicon carbide and gallium nitride. In the polishing abrasive grain 10 of the present invention, for example, as shown in FIG. 1A, the first component 12, the second component 13, and the reaction accelerator 14 each retain the substance-specific properties of the individual components. As is, they are directly coupled to each other by mechanical alloying. The first component 12 is a component that exerts a mechanical polishing action on the material to be polished. The second component 13 is a component that exhibits a chemical polishing action on the material to be polished. The reaction accelerator 14 is a component that accelerates the chemical polishing action in response to frictional heat generated when the material to be polished is polished. This polishing abrasive grain 10 is obtained by integrating these components into a particulate form.

  In addition to this, as shown in FIG. 1B, a polishing abrasive grain 11 composed of only the second component 13 and the third component 14 will be described later as an example. Furthermore, various combinations are possible. The chemical polishing action includes an action of causing a mechanochemical effect on the surface of the material to be polished and altering it. The chemical polishing action also includes an action of oxidizing the polished surface of the material to be polished by reacting with frictional heat generated during the polishing process. By these actions, it becomes possible to polish the surface of the material to be polished by changing it to a hardness equal to or lower than the hardness of the material to be polished in a complete state.

  A combination of the second component that reacts with the frictional heat generated during the polishing process to oxidize the polished surface of the material to be polished and the third component that promotes the oxidizing action of the polished surface with the frictional heat generated during polishing. But there is enough practicality.

  The above-described plurality of components being directly bonded means that they are not bonded using materials other than the plurality of components. It means that they are bonded without using a bonding material such as an adhesive. When a plurality of components are combined by mechanical alloying treatment, an amorphous layer 15 is formed at the boundary portion as shown in FIG. 1C. Each component is bonded together through the amorphous layer 15. Each inorganic compound component is bonded by the chemical activity of the amorphous layer 15 generated on the crystal surface by the mechanical alloying treatment. Due to this bonding force, each inorganic compound component is not easily separated before and during polishing. Therefore, the characteristics of each inorganic compound component are displayed in a chain manner in the portion of the polishing abrasive grain that is in contact with the material to be polished. In addition, as shown in FIG. 1C, the amorphous layer 15 formed in various places on the crystal surface of the second component and the third component also has an effect of enhancing these chemical polishing actions.

  Being integrated in the form of particles means that the size and shape suitable for the use as abrasive grains are selected. When the surface roughness required for lapping of a silicon carbide or gallium nitride substrate is 0.01 μm or less, the abrasive grains may be selected to have an average particle size of 10 μm or less. When used for wet polishing, the abrasive grains for polishing of the present invention are preferably produced in the form of particles having an average particle diameter of 0.05 μm or more and 100 μm or less. When this abrasive grain is used while being fixed to a polishing pad or a grindstone, one having a larger grain size can also be used. Therefore, the abrasive grains for polishing according to the present invention can meet various surface roughness requirements.

  The polishing abrasive grains only need to be an integrated lump. The outer shape of the abrasive grains for polishing may not be circular. Multiple types of components are combined by mechanical alloying. Thus, a plurality of types of components are combined in a state that retains the substance-specific properties of the individual components. The reason why the plural kinds of components are combined is to polish the material to be polished by combining the properties unique to the substances of the respective components. In any case, the polishing abrasive grain of the present invention does not use a chemical slurry containing an acid, an alkali, an oxidizing agent or the like when performing wet polishing. It has a feature that it can be used by dispersing abrasive grains in neutral water.

[Mechanical alloying treatment]
In the mechanical alloying process, first, the powder of the first component 12, the powder of the second component 13, and the powder of the reaction accelerator 14 are mixed, crushed, rubbed, compressed, pulled, hit, bent, or Repeated mechanical impacts such as impact. Any kind of impact may be applied. Multiple types of impacts may be combined. These mechanical impacts cause the powder to break up and mix evenly. Thereafter, a phenomenon occurs in which part of the powder is integrated and solidified into particles. Each component is directly bonded to each other and integrated into a particle shape while maintaining the material-specific properties of each component. Each component is bonded together through an amorphous layer.

[Operation of the first component]
The first component exhibits a mechanical polishing action on the material to be polished. The new Mohs hardness (corrected Mohs hardness) of the first component 12 is selected according to the hardness of the workpiece. For example, when the material to be polished is silicon carbide or gallium nitride, the new Mohs hardness is 7 or more and 13 or less. The reason why the new Mohs hardness is 7 or more is that the composite particles mechanically accelerate silicon carbide or gallium nitride. This is to provide the minimum hardness necessary for polishing. The reason why the new Mohs hardness is set to 13 or less is to use particles having a hardness of silicon carbide or gallium nitride or less and polish the surface of the silicon carbide or gallium nitride without damaging the surface. A silicic acid compound is suitable for the first component 12. For example, SiC, Al ₂ O ₃ , ZrSiO ₄ , ZrO ₂ , talc, or mica are suitable. Silicate compounds other than these can also be applied. In order to obtain a high polishing rate, SiC, Al ₂ O ₃ , ZrSiO ₄ or ZrO ₂ having a new Mohs hardness of 9 to 13 is suitable. On the other hand, softer talc or mica is suitable for obtaining a high-quality polished surface. That is, a silicate compound having a new Mohs hardness of less than 9 is suitable. When sapphire having a new Mohs hardness of 9 is polished, a new Mohs hardness of 7 to 9 is suitable for the abrasive grains for polishing.

  The first component 12 preferably occupies 5 weight percent or more and 95 weight percent or less when the total weight of the integrated particles is 100. If the blending ratio of the first component 12 is less than 5%, the hardness of the abrasive grains may be insufficient. On the other hand, if the blending ratio of the first component 12 exceeds 95%, the second component may be insufficient and the polishing rate may not be improved due to the chemical polishing action.

[Operation of the second component]
The second component 13 causes a mechanochemical effect on the material to be polished. To create a mechanochemical effect on the material to be polished means that at least the surface molecules and atoms on the surface of the material to be polished are broken or oxidized, and some molecules and atoms are exchanged with other molecules and atoms. It means to act to replace. By chemically changing the surface of the material to be polished in this way, it is possible to peel off the changed portion with abrasive grains equivalent to or softer than the material to be polished. Thereby, the surface of the material to be polished is flattened. Since only the portion close to the surface of the material to be polished is peeled off, no deep and large scratches are generated on the surface of the material to be polished. By the action of the second component, it becomes possible to perform polishing at a high polishing rate (removal rate per unit time) that has not been obtained so far.

When silicon carbide or gallium nitride is the material to be polished, the second component 13 is Cr ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , ZnO, NiO, SnO ₂ , Sb ₂ O ₃ , CuO, Co _3. It is preferable to select and use one or more oxides selected from the group consisting of O ₄ , CeO ₂ , Pr ₆ O ₁₁ and MnO ₂ . The second component is an oxide or a double oxide of a transition metal element or a group 12 element (zinc group element) on the periodic table that exists between group 3 and group 11 on the periodic table excluding Zr. is there. The multiple oxide is a solid solution of any two or more of these oxides.

The material selected as the second component 13 includes a substance that easily oxidizes silicon carbide or gallium nitride at a high temperature. All of the second components 13 listed in the above examples are oxides. Particularly, MnO ₂ is well known as a solid oxidizing agent, and highly active manganese dioxide produced by an electrolytic method is suitable. Manganese dioxide reacts with frictional heat generated during the polishing process to oxidize the C surface of silicon carbide, and reacts with the Si surface in a solid phase. The oxidized polished surface can be mechanically removed efficiently with a Mohs hardness component equal to or less than that of silicon carbide.

When sapphire is used as the material to be polished, a material that is likely to undergo isomorphous substitution with sapphire aluminum ions (Al ₃ ⁺ ) is preferable. This material is a substance whose ion radius approximates that of aluminum (Al). On the other hand, silica (SiO ₂ ) causes substitution that occurs during dehydration of siloxane. By this chemical reaction, the surface of the material to be polished (sapphire) is denatured, and it becomes possible to efficiently polish with the first abrasive having a hardness equal to or lower than that of the material to be polished. The second component 13 preferably occupies 5 weight percent or more and 95 weight percent or less when the total weight of the integrated particles is 100. If the blending ratio of the second component 13 is less than 5%, the chemical polishing action may be insufficient and a sufficiently high polishing rate may not be maintained. On the other hand, if the blending ratio of the second component 13 exceeds 95%, the hardness of the abrasive grains as a whole may be insufficient.

[Action of reaction accelerator]
The reaction accelerator 14 is hardly soluble in pure water used as a slurry, and is made of an alkali metal salt or an alkaline earth metal salt. The reaction accelerator 14 is not a liquid but a solid. If the reaction accelerator 14 is solid, it can be integrated with the first component 12 and the second component 13 by mechanical energy to obtain abrasive grains for polishing. On the other hand, when the reaction accelerator 14 is a liquid or a material that is easily dissolved in water, the abrasive grains are decomposed in the slurry. Furthermore, the waste liquid has an adverse effect on the environment.

The reaction accelerator 14 is a kind selected from the group of CaCO ₃ , SrCO ₃ , MgCO ₃ , BaCO ₃ , LiCO ₃ , Ca ₃ (PO ₄ ) ₂ , Li ₃ PO ₄ , AlK (SO ₄ ) _2. Or it is preferable that they are 2 or more types of materials. Alkali metal salts or alkaline earth metal salts are suitable because they are hardly soluble in pure water. Any material can promote the polishing function of the second component 13 by frictional heat generated during polishing. In addition, inorganic compounds that are hardly soluble in pure water stable in the air, such as CaF ₂ , Na ₃ AlF ₆ , Na ₂ B ₄ O ₇ , AgCl, AgBr, and Ag1, are suitable.

Specifically, the material selected as the reaction accelerator 14 has a solubility in pure water of 0.1 or less except for LiCO ₃ and AlK (SO ₄ ) ₂ . That is, the amount dissolved in 100 grams of pure water at 25 degrees Celsius is 0.1 grams or less. On the other hand, the solubility of LiCO ₃ in pure water is 1.33, and the solubility of AlK (SO ₄ ) ₂ is 6.74, which is larger than other materials. However, when used as polishing abrasive grains, none of them are separated during polishing and dissolved in a large amount in pure water. That is, by integrating by mechanical login processing, the reaction accelerator is made difficult to dissolve in pure water. Therefore, polishing abrasive grains were circulated with the slurry and could be used repeatedly for polishing. In the present invention, poorly soluble means that the amount dissolved in 100 grams of pure water at 25 degrees Celsius is 7 grams or less.

  The reaction accelerator 14 preferably accounts for 5 to 95 percent when the total weight of the integrated particles is 100. If the blending ratio of the reaction accelerator 14 is less than 5 weight percent, the effect of promoting the polishing function of the second component 13 may be insufficient. If the blending ratio of the reaction accelerator 14 exceeds 95 weight percent, the amount of the second component 13 may be insufficient.

  For example, consider the case where lithium carbonate or alkaline earth carbonate is selected as the reaction accelerator. When wet polishing is performed with the polishing abrasive grains of the present invention, the polishing abrasive grains are rubbed against the material to be polished, and frictional heat is locally generated. As a result, carbon dioxide is released from lithium carbonate and alkaline earth carbonate. The lithium oxide or alkaline earth oxide generated here reacts with moisture instantaneously to generate high heat of hydration, and lithium hydroxide and alkaline earth hydroxide, which are strongly alkaline substances, are generated.

  This phenomenon occurs in a minute region on the surface of the material to be polished that is in contact with the abrasive grains for polishing. Because it contains a component that produces a mechanochemical effect on the abrasive grains for polishing and a component that exerts a mechanical polishing action on the material to be polished, the mechanochemical effect is promoted in a chain and the part is efficient. It is scraped off.

  When alum, that is, AlK (SO4) 2, is selected as the reaction accelerator, an acidic region is formed near the surface of the material to be polished by the action of frictional heat to promote the mechanochemical effect.

When a fluorine compound or a halogen compound is selected as the reaction accelerator, it is considered that the following reaction occurs.
In the vicinity of the surface of the Si-based material to be polished, the atoms lose their covalent bonds and are in a state called dangling bonds. Electrons on dangling bonds are chemically active because they are unstable. When polishing abrasive grains are rubbed against the surface of the material to be polished, fluorine ions are generated by frictional heat. As a result, dangling bonds and fluorine are bonded. Fluorine atoms having strong electronegativity distort the crystal structure of the surface of the material to be polished. Thereby, the mechanochemical effect on the surface of the material to be polished is promoted.

[Polishing equipment]
FIG. 2 is a schematic perspective view showing an example of a polishing apparatus using the polishing abrasive grain of the present invention.
The polishing surface plate 20 is driven to rotate in the direction of the arrow 32. The upper surface of the polishing surface plate 20 is covered with a polishing pad 22. The holding device 24 is a device for pressing and supporting the material to be polished 26 (silicon carbide substrate or gallium nitride substrate) against the polishing pad 22. In the present invention, abrasive grains are supplied together with the slurry from the liquid injector 28 in the direction of the arrow 30. The material to be polished 26 pressed against the surface of the polishing pad 22 is polished in contact with the polishing abrasive grains. The slurry and abrasive grains are continuously supplied in a fixed amount during the polishing process.

  The polishing abrasive grains of the present invention can be used, for example, in a polishing process for sapphire substrates and silicon carbide or gallium nitride substrates for power devices. The sapphire substrate has a new Mohs hardness of 9. The silicon carbide substrate and the gallium nitride substrate have a new Mohs hardness of 13. In the polishing process, for example, polishing is performed until the surface roughness of the silicon carbide or gallium nitride substrate reaches 0.010 μm or less. A suspension obtained by dispersing abrasive grains in pure water can be supplied to the polishing surface for polishing treatment. Neutral water can be used for the slurry. A surfactant or chelating agent may be added to this water in order to disperse the abrasive grains for polishing. The suspension formed by dispersing the abrasive grains of the present invention in neutral water has a pH of 4 or more and 11 or less at 25 degrees Celsius, as will be described later. That is, the slurry can be within a weakly acidic or weakly alkaline range.

  In general, the above-mentioned various substrates are first polished on both sides so as to adjust the shape. This is called roughing. Thereafter, intermediate processing is performed to reduce scratches caused by rough processing. Finally, a finishing process is performed to polish the surface to an atomic level flatness. Conventionally, diamond abrasive grains are used for polishing a silicon carbide or gallium nitride substrate in a roughing process. However, since the diamond abrasive grains have a Vickers hardness higher than that of the silicon carbide or gallium nitride substrate, damage that reaches a deep portion from the surface, called a “saw mark”, is caused. In order to repair this polishing mark, long-term intermediate processing was required thereafter. The reason why diamond abrasive grains are used for roughing is to improve the polishing rate as much as possible.

  In order to suppress the generation of the above-mentioned polishing marks, there is a method using fine diamond abrasive grains. However, when performing mechanical polishing, the polishing rate decreases as the abrasive grain size decreases, and the cost of using diamond abrasive grains increases as the abrasive grain size decreases. There is. Therefore, a method for increasing the speed of the polishing process and preventing the occurrence of damage has not been established yet.

  The polishing abrasive grains of the present invention solve this problem. When the polishing abrasive grain of the present invention is used, a sufficiently high polishing rate can be obtained, so that rough processing and intermediate processing can be performed at once. The polishing abrasive grains of the present invention are polished using a component 3 that is comparable to or softer than a silicon carbide or gallium nitride substrate.

In the above polishing process, for example, a polishing slurry in which the abrasive grains of the present invention are dispersed in a concentration of 15 weight percent in 100 ml of pure water is used. The pH of the slurry at 25 degrees Celsius is 4 or more and 11 or less. According to the experiment, the waste liquid after polishing for 4 hours was about pH 8. The pH of the waste liquid is most preferably 5 or more and 9 or less, and was within this range when a material other than LiCO ₃ and Ca ₃ (PO ₄ ) ₂ was used. When LiCO ₃ and Ca ₃ (PO ₄ ) ₂ were used as reaction accelerators, the pH was about 10 to 11. Both are in the range of weak acidity to weak alkalinity, and the adverse effect on the work environment can be suppressed. At the same time, waste liquid treatment is simplified.

  The above slurry contains 5 weight percent or more of abrasive grains with respect to pure water 100, and the apparent specific volume (static method) of the abrasive grains is 0.5 ml / g or more and 200 ml / g or less. It is preferable to adjust so that it becomes. If the apparent specific volume (stationary method) is less than 0.5 ml / g, each component of the abrasive grains for polishing is separated. Even if the apparent specific volume (static method) exceeds 200 ml / g, the polishing rate is not improved, and the abrasive grains for polishing become excessive in the slurry, resulting in severe sedimentation.

  In the apparatus shown in FIG. 2, when the material to be polished 26 is pressed against the surface of the polishing pad 22 by using elasticity, the material between the polishing abrasive grains dispersed on the surface of the polishing pad 22 and the material to be polished 26 is used. Frictional heat is likely to occur. Therefore, for example, it is preferable to configure the holding device 24 with a resilient rubber plate or the like. The polishing pad 22 is preferably made of synthetic fiber, glass fiber, natural fiber, synthetic resin, natural resin, or the like. When the holding device 24 gives an appropriate elasticity to the material to be polished 26, it is possible to effectively generate frictional heat and realize a high polishing rate. It is preferable to generate frictional heat between the polishing abrasive and the material to be polished above the temperature at which a chemical reaction by the reaction accelerator occurs.

  In addition, since the frictional heat does not accumulate at the beginning of starting the polishing apparatus, the temperature rise of the polishing surface of the material to be polished 26 becomes insufficient. Therefore, the polishing rate is lowered. In this case, a device for adjusting the temperature of the slurry to an appropriate temperature may be provided. Further, the polishing abrasive grain of the present invention can also be used for dry polishing. For example, when the substrate is a polishing pad, the abrasive grains are dispersed and fixed at an appropriate density on the surface of the pad to obtain a polishing member. What fixed and disperse | distributed the composite abrasive grain to resin and fiber can be used. When the substrate is a plastic molded product, the abrasive grains and the plastic before solidification are mixed and then cured by a predetermined method to obtain an abrasive member. Further, it may be dispersed and fixed on a tape-like base material. This polishing member is suitable for dry polishing, but can also be wet polished by supplying pure water to the polishing surface during the polishing process.

[Comparison with conventional technology]
FIG. 3 is an explanatory view of a conventional mechanochemical polishing method.
These are all listed as comparative examples. The abrasive grains shown in FIG. 3A are a mixture of a plurality of types of abrasives. The A abrasive 16 and the B abrasive 18 are mixed and supplied to the polishing apparatus together with the slurry. The B abrasive 18 has a function of promoting the polishing action of the A abrasive 16. In this case, in general, the specific gravity of the A abrasive 16 and the B abrasive 18 are different from each other, so that they are separated in the slurry as shown in FIG. 3B.

  FIG. 3C shows an example in which a slurry 17 that promotes the polishing action of the A abrasive 16 is used. Since this method solves the above problems, it has been widely adopted in recent years. However, the slurry 17 uses a strongly alkaline material, an oxidizer, or the like, resulting in a highly corrosive solution, which deteriorates the working environment. Furthermore, the cost of processing the waste liquid after the polishing process is large.

  FIG. 3D shows an example in which the A abrasive 16 is fixed to the surface of the polymer material 19. It is difficult to obtain abrasive grains having an average particle size suitable for a lapping process for hard and brittle materials. That is, only a large size can be obtained. Moreover, specific gravity becomes light as a whole, and it will be pushed away from a grinding | polishing apparatus. Since the polishing abrasive grain of the present invention has a high specific gravity, it stays long on the upper surface of the pad of the polishing apparatus and improves the polishing rate.

[Structure and action of abrasive grains for polishing]
Fig. 4 Fig. 4A and Fig. 4B are micrographs of the abrasive grains of the present invention, and Fig. 4A and below are explanatory diagrams of the polishing action.
FIG. 4A is a photomicrograph showing the polishing abrasive grains of Example 1. This is immediately after the integration process, and abrasive grains of various sizes are mixed. Those having an average particle diameter of 5 to 6 μm and a particle diameter of about 1 μm are also mixed. Fig. 4B is a partially enlarged view. This is a photograph of one abrasive grain having an outer diameter of about 6 μm. Three types of pre-ground components are mixed and strongly connected and integrated with each other. All three types of components are integrated in the form of particles while maintaining the inherent physical and chemical properties. The polishing abrasive grains of the examples are integrated with a force that does not separate even after being used in the polishing process. For example, the surface state of polishing abrasive grains collected after polishing a silicon carbide substrate for 4 hours was also indistinguishable from this photograph.

The polishing abrasive grain of Example 1 is obtained by integrating aluminum oxide (Al ₂ O ₃ ), manganese dioxide (MnO ₂ ), and calcium carbonate (CaCO ₃ ). These were mixed at a ratio of 50 parts by weight, 37.5 parts by weight and 12.5 parts by weight, respectively. These were pulverized to a powder having an outer diameter of 1 μm or less by a ball milling method, and further subjected to mechanical impact for about 0.5 hours to obtain abrasive grains for polishing. Among them, abrasive grains having an average particle size of 1 μm were selected and used. The abrasive grains obtained by the above method were supplied to the apparatus shown in FIG. 2 together with pure water, and the silicon carbide substrate was polished for 4 hours. The slurry containing the abrasive grains for polishing is supplied onto the polishing pad 22 during the polishing process and sequentially discharged. The discharged slurry was recovered again and supplied onto the polishing pad 22 so that it could be used repeatedly.

For sapphire polishing, aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ) and calcium carbonate (CaCO ₃ ) are mixed at a ratio of 50 parts by weight, 37.5 parts by weight and 12.5 parts by weight, respectively. Thus, an integrated product was produced by a ball milling method. Polishing abrasive grains having an average particle size of 2 μm were obtained. The composite abrasive grains taken out of the slurry after polishing the sapphire substrate for 4 hours also obtained the same result as above.

  For example, a method of bonding a plurality of inorganic compound components using an adhesive such as a resin is known. However, the bonding force by an adhesive such as a resin cannot prevent a plurality of inorganic compound components from being separated from each other by an external force received during polishing. In addition, a method of sintering and integrating the components can be considered. However, when sintering is performed, the inorganic compound components mix with each other, and the inherent properties of the individual inorganic compound components are largely lost. Therefore, the function like the abrasive grains for polishing of the present invention cannot be exhibited effectively. That is, a sufficiently efficient polishing rate cannot be realized. Moreover, the components are altered or decomposed by the heat of about 1000 degrees Celsius received during the sintering process. In the mechanical alloying process, heat that alters or decomposes each component is not applied.

  As shown in FIG. 4C, in the polishing abrasive grains of this example, each component is uniformly mixed, and therefore all of the components are partially exposed on the outer surface of the polishing abrasive grains. The abrasive grains are in direct and continuous contact with the material to be polished so as to roll. The abrasive grains themselves generate heat due to frictional heat, and the chemically reactive abrasive is directly heated by the frictional heat, causing a mechanochemical effect on the surface of the material to be polished. Further, when the state shown in FIG. 4C is changed to the state shown in FIG. 4D, the component that mechanically scrapes the surface of the polishing material of the abrasive grains immediately contacts the portion where the mechanochemical effect occurs. As a result, a portion where the mechanochemical effect of the material to be polished is generated is removed.

  The abrasive grains move so as to roll on the surface of the material to be polished. At this time, the chemically reactive polishing material and the component having a function of mechanically cutting the polishing material are alternately and repeatedly brought into contact with the surface of the polishing material. In addition, before the frictional heat diffuses into the slurry, they come into contact with each other without a time interval, so that the polishing process efficiently proceeds in a chain. In addition, the whole abrasive grain can also be coated with any component. In this case, other components are not exposed on the outer surface of the abrasive grains. However, if the coating breaks during the polishing process and all components are exposed on the surface, the above effects occur. Further, for example, as long as the coating has a thickness that does not interfere with the action of other components, all the components may not be exposed on the surface of the abrasive grains for polishing.

  When a chemically reactive abrasive and an inorganic compound component that has a mechanical cutting function are dispersed in the slurry, it has a function to mechanically cut that part of the polishing material where the mechanochemical effect occurs. The probability that the inorganic compound component is in direct contact is very low. Therefore, the polishing process must be continued for a long time.

  Any part may be mechanically cut as long as a mechanochemical effect is uniformly produced on the entire surface. Therefore, a method in which a mechanochemical effect is produced on the entire surface of the material to be polished by using a strong alkaline solution slurry has been conventionally adopted as the most practical method. However, this method has a problem of waste liquid treatment. This has already been explained.

  FIG. 4E is a cross-sectional view of the vicinity of the surface of the material to be polished when the material to be polished is polished with the abrasive grains of the example. Only the hatched portion near the surface of the material to be polished 26 is scraped off. FIG. 4F is a cross-sectional view of the vicinity of the surface of the material to be polished when the surface of the material to be polished 26 is polished with diamond abrasive grains 36. In this case, a deep polishing mark 38 is generated on the surface of the material 26 to be polished. This has been the most problematic in the past.

[Analysis of abrasive grains after polishing]
FIG. 5A is a diagram comparing the components of abrasive grains before and after polishing a silicon carbide substrate for 4 hours.
The upper part of Fig. 5A shows the ratio of each component to the abrasive grains before polishing. A lower stage shows the ratio which each component accounts for the abrasive grain for grinding | polishing after grinding | polishing processing. As shown in this figure, the polishing abrasive grains of the examples have no significant change in the component ratio before and after the polishing treatment. The polishing abrasive grains of the present invention have high mechanical strength and can be used repeatedly because they are not destroyed by polishing treatment. That is, it was found that most of the mixed material was present in its original form from the appearance and analysis results of the abrasive grains taken out from the slurry after polishing the silicon carbide substrate for 4 hours. It was also found that about 3% of the total weight was consumed by the above chemical reaction.

FIG. 5B is a diagram comparing the components of the composite abrasive before and after polishing the sapphire substrate for 4 hours.
Prior to polishing, the proportions of aluminum (Al), silicon (Si), and calcium (Ca) in the total were 38.2 wt%, 43.8 wt%, and 17.9 wt%, respectively. After the polishing treatment, they were 41.2 wt%, 42.3 wt%, and 16.5 wt%. The ratio of the components other than the aluminum component to the whole was not substantially changed. The cause of the increase in the proportion of the aluminum component is considered to be that polishing scraps obtained by polishing sapphire were newly included.

  The residue discharged together with the slurry after polishing was separated and analyzed. As a result, a residue containing aluminum (Al), silicon (Si) and calcium (Ca) in the proportions of 52%, 33% and 0.5%, respectively, was obtained. As a result of component analysis, mullite was included.

  During the polishing process, it was examined whether the composite abrasive grains were mechanically or thermally decomposed to produce mullite or other causes. The amount of mullite produced was proportional to the polishing time. Moreover, an amount of mullite was generated that sufficiently exceeded the consumption of the composite abrasive before and after the polishing treatment. That is, it was found that the composite abrasive was polished while chemically altering the surface of the material to be polished, and the residue was mullite. Using any of the conventional wet polishing methods, this amount of mullite was not generated after 4 hours of polishing. Therefore, it was proved that the above reaction accelerator functions effectively during polishing.

Mullite is a compound of aluminum oxide and silicon dioxide. The chemical formula is represented by 3Al ₂ O ₃ .2SiO _{2 to} 2Al ₂ O ₃ .SiO ₂ , or Al ₆ O ₁₃ Si ₂ . Friction heat of several hundred degrees Celsius is locally generated by friction between the composite abrasive grains and the material to be polished. Although this heat is diffused by the slurry, the micro area where the composite abrasive grains and the material to be polished are in contact with each other becomes high temperature. It can be determined that calcium carbonate has generated mullite as a result of promoting the reaction between the material to be polished and aluminum oxide.

FIG. 6 is a property comparison diagram of waste liquid as a result of polishing using various abrasive grains.
As shown in Fig. 6A, the temperature of the slurry discharged after the polishing treatment was measured, and as a result, the temperature rose from room temperature to about 30 to 40 degrees Celsius by the polishing treatment, so the influence of the reaction accelerator could be confirmed. . The residue excluding the pure water of the slurry discharged after the polishing treatment is shavings of the silicon carbide or gallium nitride substrate. The residue is a solid component and can be removed from the waste liquid by a filter. Although there is a difference depending on the type of reaction accelerator, most of the waste liquid had a pH of about 7.5. The wastewater is neutral and easy to treat, and there is no problem of environmental pollution. Further, the pH is 11.2 at the maximum and can be processed without any problem.

When the sapphire was polished with polishing abrasive grains in which Al ₂ O ₃ , SiO ₂ and CaCO ₃ were integrated, a high polishing rate of 0.7 to 1.0 μm per minute was realized. As shown in FIG. 6B, when a material other than LiCO ₃ and Ca ₃ (PO ₄ ) ₂ is used as a reaction accelerator, the measured value before polishing is pH 4.63 8.0, and the measured value after polishing is pH 4. It was in the range of 2 to 8.2. When LiCO ₃ and Ca ₃ (PO ₄ ) ₂ are used as reaction accelerators, the measured values before polishing are pH 10.1 and 9.0, and the measured values after polishing are pH 11.2 and 9.6, respectively. there were. Both are in the range of weak acidity to weak alkalinity, and the adverse effect on the work environment can be suppressed. Moreover, the waste liquid treatment becomes simple. It was found that since the region of high alkali atmosphere at high temperature is a very small region, the pH of the slurry is not greatly affected.

[Verify the action of the first component]
FIG. 7 is a comparison diagram of polishing rates when the first component is replaced and SiC is polished.
The portion indicated as Sample 1-1 shows the result of using polishing abrasive grains in which Al ₂ O ₃ , MnO ₂ and CaCO ₃ are integrated for polishing silicon carbide.

In this embodiment, the operating conditions of the polishing apparatus are that the rotation speed of the polishing surface plate 20 is 50 rotations per minute (rpm), the rotation speed of the holding apparatus 24 is 100 rotations per minute, and the holding apparatus 24 polishes the material 26 to be polished. The polishing pressure pressed in the direction of the surface plate 20 was 160 grams (g / cm ² ) per square centimeter. Polishing abrasive grains are mixed in 15% by weight in pure water. The slurry thus adjusted was supplied onto the polishing pad 22 from the liquid injector 28 at a rate of 10 milliliters per minute (ml / min).

The portion indicated as Sample 2-1 shows the result of using polishing abrasive grains in which ZrO ₂ , MnO ₂ and CaCO ₃ are integrated for polishing silicon carbide. In Sample 2-2, the first component is ZrSiO ₄ , in Sample 2-3, the first component is mica, and in Sample 2-4, the first component is talc. The first component does not have a mechanochemical effect. The first component ZrO _{2 has} a new Mohs hardness of 11. The new Mohs hardness of silicon carbide is 13. Silicon carbide cannot be polished with the first component alone.

However, the abrasive grains in which the first component ZrO ₂ , the second component MnO ₂ and the reaction accelerator CaCO are integrated show the highest polishing rate as shown in the figure. The polishing rate of the conventional diamond abrasive shown in Comparative Example 6 in FIG. 8 is 0.26 (μm / min), whereas the polishing rate of Sample 1-1 is about 2 0.8 times 0.72 (μm / min). The effect of the first component on gallium nitride is substantially the same. Therefore, this experimental example is not shown for gallium nitride.

[Verify the action of the second component]
FIG. 8 is a comparison diagram of polishing rates when the second component is replaced and SiC is polished.
The portion indicated as Sample 1-1 shows the result of using polishing abrasive grains in which Al ₂ O ₃ , MnO ₂ and CaCO ₃ are integrated for polishing silicon carbide. The example of FIG. 8 shows an example in which the first component and the reaction accelerator are the same, and the second component is sequentially replaced. Sample 3-1 has a second component of TiO ₂ , Sample 3-2 has a second component of ZnO, Sample 3-3 has a second component of NiO, Sample 3-4 has a second component of SnO ₂ , In sample 3-5, the second component is Sb ₂ O ₃ , sample 3-6 is the second component CuO, sample 3-7 is the second component Co ₃ O ₄ , and sample 3-8 is the second component The component is CeO ₂ , Sample 3-9 is the second component Pr ₆ O ₁₁ , and Sample 3-10 is the second component Ti—Cr—Sb, which is a double oxide.

Samples 3-11 and 3-12 are two-component polishing abrasive grains. Sample 3-11 shows the result of using abrasive grains in which aluminum oxide (Al ₂ O ₃ ) and manganese dioxide (MnO ₂ ) are mechanically bonded and integrated in the same manner as in the present invention. Sample 3-12 shows the result of using abrasive grains in which calcium carbonate (CaCO ₃ ) and manganese dioxide (MnO ₂ ) are mechanically bonded and integrated in the same manner as in the present invention. Even with two components, it was possible to obtain a polishing rate equivalent to that obtained when conventional diamond abrasive grains were used.

Comparative Example 1 shows the result of using abrasive grains in which aluminum oxide (Al ₂ O ₃ ) and calcium carbonate (CaCO ₃ ) are mechanically bonded and integrated in the same manner as in the present invention. Comparative Example 2 shows the result of using a simple mixture (not integrated) of aluminum oxide (Al ₂ O ₃ ), manganese dioxide (MnO ₂ ), and calcium carbonate (CaCO ₃ ) mixed in the slurry. Comparative Example 3 shows the result of using only manganese dioxide (MnO ₂ ) as abrasive grains. Comparative Example 4 shows the result of using only aluminum oxide (Al ₂ O ₃ ) as abrasive grains. Comparative Example 5 shows the result of using only calcium carbonate (CaCO ₃ ) as abrasive grains.

  In each of the above examples, a resin pad was used in the polishing apparatus, and a slurry in which abrasive grains were mixed in pure water was used. On the other hand, Comparative Example 6 shows the result of using diamond abrasive grains having an average particle diameter of 1 to 3 μm, using a metal surface plate for the polishing apparatus, and using an oily slurry.

  Here, when the polishing rates of all these examples were compared, when using the abrasive grains of sample 1, it was 0.72 μm per minute, whereas in the examples of Comparative Examples 1 to 5, Neither could be polished. Even in Comparative Example 6 using diamond abrasive grains, the polishing rate is a low value of 0.26 per minute. Moreover, when diamond abrasive grains are used, there is a problem of polishing marks.

  The sample 1-1 shown in FIG. 8 shows a very high polishing rate, and can be said to be sufficiently effective in polishing SiC. It can be said that Sample 3-11 and Sample 3-12 also have a higher polishing rate than the conventional one and are sufficiently practical. Other samples have the following polishing rates when diamond abrasive grains are used. However, these samples have the advantage that no harmful waste liquid is produced and the quality of the polished surface is extremely high, and can be said to be superior to conventional methods. That is, since the second abrasive grains are integrated with the abrasive grains for polishing, it is difficult to elute into the slurry and the slurry is not greatly contaminated.

  All samples use a slurry using pure water as a dispersion medium, which does not deteriorate the working environment and can be easily treated as a waste liquid. The surface of the metal surface plate used for polishing must be as flat as required for a polished surface of silicon carbide or gallium nitride. However, it is not easy to maintain the flatness. On the other hand, the resin pad merely applies pressure for pressing the abrasive grains against the polished surface of silicon carbide or gallium nitride. Therefore, a highly accurate structure is not required. Resin pads are inexpensive and easy to maintain.

(In the case of gallium nitride)
FIG. 9 is a comparison diagram of the polishing rate of gallium nitride GaN when the second component is replaced.
The abrasive grains of Samples 1-1 and 3-1 to 3-11 have the same structure as the abrasive grains having the same sample name in FIG. When gallium nitride was polished, Sample 1-1 showed a very high polishing rate. Samples 3-9 and 3-10 also showed a high polishing rate. Samples 3-2, 3-3-3-4, and 3-6 also showed a high polishing rate comparable to that of Comparative Example 8. Although the other samples have a low polishing rate, they do not emit harmful waste liquid and have the advantage that the polished surface has a very high quality, which is the same as in the case of FIG. That is, even when the first component has a low New Mohs hardness such as talc or mica, a polishing rate comparable to or higher than that of diamond abrasive grains can be realized. Moreover, an extremely high quality polished surface can be obtained, which is very effective.

(In the case of safar)
Fig. 9B is a comparative diagram of the results of polishing sapphire using various abrasive grains.
The part indicated as Sample 1 shows the result of using composite abrasive grains in which Al ₂ O ₃ , SiO ₂ and CaCO ₃ are integrated for polishing sapphire. The part indicated as sample 2 shows the result of using composite abrasive grains in which Al ₂ O ₃ , Fe ₂ O ₃ and CaCO ₃ are integrated for polishing sapphire. The part indicated as Sample 3 shows the result of using composite abrasive grains in which Al ₂ O ₃ , Cr ₂ O ₃ and CaCO ₃ are integrated for polishing sapphire.

In this example, the sapphire wafer was polished with GC (green carbonite) having an average particle size of # 325, and a surface roughness Ra = 0.22 μm was used as the polishing target. The operating conditions of the polishing apparatus are: the rotation speed of the polishing surface plate 20 is 50 rotations per minute (rpm), the rotation speed of the holding device 24 is 100 rotations per minute, and the holding device 24 moves the material 26 to be polished in the direction of the polishing surface plate 20. The polishing pressure to be pressed against the surface was 160 grams per square centimeter (g / cm ² ). The composite abrasive is mixed in 15% by weight in pure water. The slurry thus adjusted was supplied onto the polishing pad 22 from the liquid injector 28 at 1 milliliter per minute (ml / min).

The following is a comparative example. ref1 shows the result of using only aluminum oxide (Al ₂ O ₃ ) as abrasive grains. ref2 shows the result of using only silicon oxide (SiO ₂ ) as abrasive grains. ref3 shows the result of using only calcium carbonate (CaCO ₃ ) as abrasive grains.

ref4 shows the result of using composite abrasive grains in which aluminum oxide (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ) are mechanically bonded and integrated in the same manner as in the present invention. ref5 shows the result of using composite abrasive grains in which aluminum oxide (Al ₂ O ₃ ) and calcium carbonate (CaCO ₃ ) are mechanically bonded and integrated in the same manner as in the present invention.

ref6 shows the result of using composite abrasive grains in which silicon oxide (SiO ₂ ) and calcium carbonate (CaCO ₃ ) are mechanically bonded and integrated in the same manner as in the present invention. ref7 shows the result of using a simple mixture (not integrated) of aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ) and calcium carbonate (CaCO ₃ ) mixed in the slurry. ref8 shows the result of using diamond abrasive grains having an average particle diameter of 1 to 3 μm. In each of the above examples, a resin pad was used as a polishing pad, and a slurry in which abrasive grains were mixed in pure water was used. On the other hand, ref9 indicates the result of using diamond abrasive grains having an average particle diameter of 1 to 3 μm, using a metal surface plate in the polishing apparatus, and using an oily slurry.

  Here, when the polishing rates of all these examples are compared, when the composite abrasive grain of sample 1 is used, it is 1 μm per minute, whereas in the examples of ref1 to ref8, all are about It cannot exceed 0.3 μm. Even in the case of ref9, the polishing rate is 0.8 μm per minute, which is not equal to the polishing rate of the present invention. An example of ref9 is a method that is said to have the highest known polishing rate.

  Samples 1 and 2 were able to achieve a higher polishing rate than any known method. In the case of sample 3, a polishing rate comparable to that of ref9 was achieved. All samples use a slurry using pure water as a dispersion medium, which does not deteriorate the working environment and can be easily treated as a waste liquid. In addition, when a metal surface plate is used, its surface must be as flat as required for the polished surface of sapphire. However, it is not easy to maintain the flatness. On the other hand, the resin pad is for applying pressure to press the composite abrasive grains against the polished surface of sapphire. Therefore, a highly accurate structure is not required. Resin pads are inexpensive and easy to maintain. Since the present invention can use a soft polishing pad such as a resin pad, it is more advantageous than using a metal surface plate.

[Demonstration of action of reaction accelerator]
FIG. 10 is data showing the relationship between the SiC polishing rate and the temperature after polishing when the reaction accelerator is replaced.
Comparative Example 1 is an example using abrasive grains that do not contain a reaction accelerator. Samples 11 to 18 are the results of experiments using polishing abrasive grains in which Al ₂ O ₃ is used as the first component and MnO ₂ is used as the _second component and different reaction accelerators are used. The results of measuring the polishing rate and the temperature of the slurry after polishing silicon carbide for 4 hours are displayed.

Sample 19 is an example in which a polishing abrasive in which only a reaction accelerator (CaCO ₃ ) and a second component MnO ₂ are integrated is used. Sample 20 is an example in which polishing abrasive grains in which only a reaction accelerator (CaCO ₃ ) and a first component Al ₂ O ₃ are integrated are used.

  As shown in FIG. 10A, except for Comparative Example 1, the temperature of the slurry after polishing was 30 degrees Celsius or higher. This means that the slurry was heated by the heat generated by the reaction accelerator. It can also be seen that the higher the slurry temperature after polishing, the higher the polishing rate. That is, the more the chemical reaction of the reaction accelerator is caused by frictional heat, the higher the polishing rate.

  In the case of Comparative Example 1, the polishing rate was 0.31 μm / min, and the temperature of the slurry after polishing was 27 degrees Celsius. Comparing this example with other examples, it can be seen that not only the frictional heat generated during polishing but also the heat generated by the chemical reaction of the reaction accelerator increases the temperature of the slurry. Furthermore, it was proved that the abrasive grains combining the first component, the second component, and the reaction accelerator as in Samples 11 to 18 dramatically increase the polishing rate. The action of the reaction accelerator is not illustrated because it is the same for polishing gallium nitride.

FIG. 10B is a table showing the relationship between the temperature of the slurry after polishing and the polishing rate. Experimental Examples 1 to 8 are experimental results using composite abrasive grains in which Al ₂ O ₃ is used as the first abrasive, SiO ₂ is used as the _second abrasive, and different reaction accelerators are used. It is. Each of these composite abrasive grains comprises 50% by weight of the first abrasive, 37.5% by weight of the second abrasive, and 12.5% by weight of the reaction accelerator. ing. The polishing conditions are all the same. The material to be polished is one having a surface roughness Ra−0.22 μm after the sapphire wafer is polished with GC (green carbonite) having an average particle size # 325. The temperature of the slurry before polishing was 25 degrees Celsius. The temperature of the slurry after polishing sapphire for 1 hour was measured. The polishing rate is obtained by measuring the thickness of the polished material after polishing and calculating the polishing amount per minute (min).

ref1 is a comparative example using abrasive grains that do not use a reaction accelerator. ref2 is a comparative example using only the reaction accelerator (CaCO ₃ ) and the second abrasive SiO ₂ . ref3 is a comparative example using only the reaction accelerator (CaCO ₃ ) and the first abrasive Al ₂ O ₃ .

  From the results of Experimental Examples 1 to 8, the temperature of the slurry after polishing was 30 degrees Celsius or higher. This means that the slurry was heated not only by heat generated by friction between the material to be polished and the abrasive but also by a chemical reaction of the reaction accelerator. It can also be seen that the higher the temperature of the slurry after polishing, the higher the polishing rate. That is, it has been found that the more the chemical reaction of the reaction accelerator is caused by frictional heat, the faster the polishing rate becomes.

  In the case of ref1, the polishing rate was 0.40 μm / min, and the temperature of the slurry after polishing was 27 degrees Celsius. Further, it was found that the slurry was heated to 41 degrees Celsius due to the heat generated by the reaction accelerator in ref2 (without the first abrasive) and ref3 (without the second abrasive). However, the polishing rate is not so high. Thereby, it was proved that only the composite abrasive grains of the present invention in which the first abrasive, the second abrasive and the reaction accelerator are combined sufficiently increase the polishing rate.

[Reason for improving polishing rate]
Here, the reason for the remarkable improvement in the polishing rate by the abrasive grains of the present invention will be described in an organized manner.
(1) When the first component having a new Mohs hardness of 13 or less is included in the polishing abrasive grains The particles having a new Mohs hardness of 13 or less are ZrSiO ₄ , Al ₂ O ₃ , ZrO _2, and SiC. These components serve to form a plastic deformation layer (amorphous layer) by applying a physical force to silicon carbide or gallium nitride. Further, the second component having the property of causing a mechanochemical effect is used to mechanically peel off the plastic deformation layer after the plastic alteration layer has been altered. When the plastic deformation layer is formed on the material to be polished with the first component, the mechanochemical effect due to the second component is likely to occur because the crystal structure of the portion is destroyed. When the plastically altered layer is altered, it can be peeled off by the first abrasive grains having a hardness lower than that of the material to be polished. This effect is the same when the material to be polished is sapphire.

Al ₂ O ₃ has a new Mohs hardness of 9. ZrSiO ₄ and ZrO ₂ have a new Mohs hardness of 8. Since none of the particles has a new Mohs hardness higher than that of silicon carbide or gallium nitride, generation of polishing marks is suppressed. Since Al ₂ O ₃ is harder than the ZrSiO _4, than abrasive grains using ZrSiO _4, a high polishing rate towards the abrasive grains using Al ₂ O _3.

(2) In the case where an abrasive that causes a mechanochemical effect is included in the abrasive grains for polishing The mechanochemical abrasive is Cr ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , ZnO, NiO, SnO ₂ , Sb ₂ O _3. CuO, Co ₃ O ₄ , CeO ₂ , Pr ₆ O ₁₁ , and MnO ₂ . In either case, an oxidation reaction is likely to occur with silicon carbide or gallium nitride in a high temperature atmosphere. Moreover, it is easy to cause a solid phase reaction. This chemical reaction is thought to alter the polished surface of silicon carbide or gallium nitride. This is as introduced in the prior art document.

The mechanochemical abrasive for sapphire is Cr ₂ O ₃ , Fe ₂ O ₃ or SiO ₂ . These abrasives are susceptible to isomorphous substitution with sapphire (Al ₂ O ₃ ). Isomorphous substitution is a phenomenon in which ions having similar ionic radii are replaced with each other when pressure or heat is applied from the outside.

Substances with an ionic radius close to that of sapphire six-coordination Al ₃ ⁺ (ionic radius 0.54 Å) are Fe ₂ O ₃ hexacoordinated Fe ₃ ⁺ (ionic radius 0.55 Å) and , Cr ₂ O ₃ hexacoordinate Cr ₃ ⁺ (ion radius 0.62 Å). These ion groups cause isomorphous substitution. This chemical reaction is thought to alter the polished surface of sapphire.

On the other hand, SiO ₂ undergoes the following chemical reaction. When SiO ₄ tetrahedrons having silanol groups (≡Si—OH) are linked by a dehydration condensation reaction, Al ₃ ⁺ is added to the dehydration condensation reaction in the form of Al (OH) ₃ . The SiO ₄ connector is incorporated into the crystal structure of sapphire. Inside the SiO ₄ linked body, hexacoordinate Si ₄ ⁺ (ionic radius 0.40Å) is replaced by four-coordinate Al ₃ ⁺ (ionic radius 0.39Å). It is thought that the chemical reaction due to this isomorphous substitution alters the polished surface of sapphire.

(3) When a reaction accelerator is included in the abrasive grains The chemical reaction when calcium carbonate (CaCO ₃ ) is used as the reaction accelerator will be described. Calcium carbonate is decomposed into CaO and CO ₂ by frictional heat generated by friction between the abrasive grains for polishing and the polished surface of silicon carbide or gallium nitride. Further, when heat of several hundred degrees Celsius is generated by frictional heat, calcium oxide CaO reacts with water to generate heat, and calcium hydroxide (Ca (OH ₂ )) is generated. This reaction occurs only in a very narrow region where the silicon carbide or gallium nitride contacts the polishing abrasive. This reaction alters silicon carbide and gallium nitride. At the same time, it is considered that the chemical reaction of the abrasive that causes a mechanochemical effect is accelerated in a high-temperature strong alkali atmosphere.

  As described above, the abrasive grains form a plastic deformation layer on the polished surface of silicon carbide or gallium nitride, and cause a mechanochemical effect in the portion where the high temperature and strong alkali atmosphere is formed by the reaction accelerator. Polish silicon and gallium nitride. Due to this heat generation, the slurry after polishing became 30 to 40 degrees Celsius. The strong alkali atmosphere is generated in a very narrow region around the abrasive grains for polishing, and thus does not greatly affect the pH of the entire slurry.

The same reaction occurs with SrCO ₃ , MgCO ₃ , BaCO _{3 and the} like. The above reactions occur very locally. The pH of the slurry after polishing is only slightly higher than neutral 7. Further, even if the surface of silicon carbide or gallium nitride is altered by the second component, the polishing rate is not improved unless the first component is in exact contact with the location. Therefore, even if the abrasive and the reaction accelerator are separated and contained in the slurry as in the prior art, a high polishing rate cannot be obtained. In the abrasive grains for polishing of the present invention, the first component or the second component and the friction-dissipating agent are integrally bonded, and thus the above-described effect is obtained. That is, it has become possible to obtain a high-quality polished surface by polishing silicon carbide or gallium nitride at a sufficiently high polishing rate by wet polishing.

FIG. 11 is data showing the relationship between the polishing pressure and the polishing rate of Samples 1 to 3.
This example is for confirming the change in the polishing rate due to the change in the polishing pressure. In this figure, the holding device 24 presses the workpiece 26 in the direction of the polishing platen 20 with three polishing pressures of 500 g per square centimeter (g / cm ² ), 750 g / cm ² , and 1000 g / cm ² . The experimental results are shown. The platen rotation speed was 50 rotations per minute, the carrier rotation speed was 100 rotations per minute, the slurry concentration was 15%, and the slurry supply amount was 10 milliliters per minute.

According to this result, when the polishing pressure is increased, the polishing rate of the SiC substrate is improved. For example, in the case of Sample 1, when the polishing pressure is 500 g / cm ² , the polishing rate is 0.72 micrometer per minute (μm / min), whereas when the polishing pressure is 1000 g / cm ² . As a result, a polishing rate of 1.39 μm / min was obtained. The polishing rate has been doubled. Moreover, even when the polishing pressure was 1000 g / cm ² , the surface roughness after polishing of the silicon carbide substrate could be 0.003 μm without any polishing marks.

  By increasing the polishing pressure, more frictional heat is generated, and at the same time, it was proved by this example that the abrasive grains efficiently scrape the polished surface of the material to be polished. Any of the abrasive grains of Samples 1 to 3 can polish the material to be polished at a higher speed than any conventional method.

FIG. 12 is a comparative diagram showing the relationship between the polishing rate and surface roughness of various composite abrasive grains.
This example shows the polishing rate of various abrasive grains and the surface roughness (Surface roughness = Ra) of the polished material after polishing when pure water is used for the slurry. For comparison, an example using SiO ₂ , MnO ₂ , CeO ₂ , TiO ₂ alone and diamond abrasive grains was included. Abrasive grains other than diamond abrasive grains have a very low polishing rate for SiC polishing and are not practical. The polishing abrasive grains of the present invention all show a higher polishing rate than diamond abrasive grains even when pure water is used as a slurry. Moreover, the surface roughness of the SiC substrate after polishing is significantly smaller than that of diamond abrasive grains. That is, a high-quality polished surface can be obtained.

FIG. 13 is a comparative diagram showing the relationship between the polishing rate and the surface roughness of the abrasive grains of the comparative example.
Here, the result of polishing a SiC substrate by including SiO ₂ , MnO ₂ , CeO ₂ , TiO ₂ and H ₂ O ₂ as an oxidizing agent in the slurry is shown. Compared to the example of FIG. 12, it can be seen that the polishing is slightly possible. However, at this polishing rate, it takes too much polishing time and is not practical.

FIG. 14 is a comparative diagram of the graphed polishing rates. FIG. 15 is a comparative view of the surface roughness after polishing that is graphed.
The results of FIGS. 12 and 13 are displayed graphically in FIGS. 14 and 15. As shown in FIG. 14, the polishing abrasive grains of the present invention can realize a polishing rate equivalent to or higher than that of diamond abrasive grains. At the same time, as shown in FIG. 15, an overwhelmingly high quality polished surface can be obtained as compared with the roughness of the polished surface by diamond abrasive grains.

  As described above, the region where the reaction accelerator generates frictional heat and the region where manganese dioxide exerts an oxidizing action are extremely narrow. Moreover, the time when the effect appears is very short. The oxidation action by the second component is promoted by the frictional heat, and the first component immediately contacts the corresponding surface in this state, thereby enabling effective polishing by the interaction. Even when the reaction accelerator, the oxidizing agent, and the mechanical polishing agent alternately and irregularly contact with the surface of the polishing target at irregular intervals, sufficient interaction does not appear. That is, there is a significant difference between the case where these particles are dispersed in the slurry and the case of the abrasive grains integrated as in the present invention. This is the reason why the polishing abrasive grains of the present invention have dramatically improved the polishing rate.

  According to the above invention, the intermediate step of polishing the material to be polished is compressed in a short time and a polished surface with high flatness is generated, so that the finishing process can be greatly shortened. Therefore, it is possible to greatly contribute to the cost reduction of the polishing process that greatly affects the production cost of this type of substrate. In addition, since the abrasive grains are dispersed in neutral water without using a strong acidic or alkaline aqueous solution, the waste liquid is weakly acidic or weakly alkaline and does not adversely affect the environment.

  In the above-described embodiment, sapphire, silicon carbide, or gallium nitride is exemplified as the material to be polished. However, the polishing abrasive of the present invention enables high-quality and high-speed polishing even with other materials. In the above-described embodiment, an example in which a two-component or three-component inorganic compound is bonded is shown. However, polishing abrasive grains in which four or more kinds of inorganic compound components are integrally bonded to each other via an amorphous layer also have the same function. The mixing ratio and the combination of components may be freely selected according to the type of material to be polished.

  Further, in the above-described embodiment, an example has been described in which one type of the first component and the second component are combined, or one type of the first component, the second component, and the third component are combined. However, for example, a plurality of types of components may be combined and combined, such as one type of first component and two types of second component. .

The polishing abrasive grains of the present invention can be widely used in polishing steps of sapphire, silicon carbide or gallium nitride used for power device substrates, other electronic component materials, electrical insulating materials and the like. Furthermore, the abrasive grains of the present invention can be used for high-quality polishing of metal, ceramics, or biomaterials such as artificial bones. It can also be used for polishing hard materials such as tungsten. Compared to conventional polishing methods, the polishing time can be greatly shortened, and the cost of the product can be greatly reduced.

10 Abrasive grains for polishing (3 components)
11 Abrasive grains for polishing (2 components)
12 First component 13 Second component 14 Reaction accelerator 15 Amorphous layer 16 A abrasive 18 B abrasive 17 Slurry 19 Polymer material 20 Polishing surface plate 22 Polishing pad 24 Holding device 26 Polishing material 28 Injection liquid 30 arrows 32 arrows 33 arrows

Claims (18)

  A mechanical alloying method comprising: a particulate first abrasive that is equal to the material to be polished or has a Mohs hardness lower than the material to be polished; and a particulate second abrasive that chemically alters the material to be polished. Polishing abrasive grains that are integrated into particles by the above.   The polishing abrasive according to claim 1, wherein the first abrasive accounts for 5 to 95 weight percent of the integrated particles.   The polishing abrasive according to claim 1, wherein the second abrasive accounts for 5 to 95 weight percent of the integrated particles.   The polishing abrasive grain according to any one of claims 1 to 3, wherein the first abrasive and the second abrasive are integrated into particles having an average particle diameter of 0.05 µm to 100 µm.   Particles for polishing the surface of a material to be polished, the particles including a plurality of types of inorganic compound components combined by mechanical alloying treatment, and each inorganic compound component is mutually connected via an amorphous layer. Abrasive grains that are bonded together.   The abrasive grains according to claim 6, wherein the plurality of types of inorganic compound components are bonded in a state in which the properties inherent to the substances of the individual components are retained.   The plurality of types of inorganic compound components are combined in a state in which the individual properties of the individual components are retained, and each of the inorganic compound components is partially exposed on the outer surface of the particle. Abrasive grains for polishing.   The abrasive grain according to claim 6 or 7, wherein any one of a plurality of kinds of inorganic compound components contains a chemically reactive abrasive that causes a mechanochemical effect on the material to be polished.   The abrasive grains according to claim 8, wherein each of the plurality of types of inorganic compound components has the same Mohs hardness as the material to be polished or has a lower Mohs hardness than the material to be polished.   One of the multiple types of inorganic compound components includes a chemically reactive abrasive that produces a mechanochemical effect on the material to be polished, and a component that mechanically scrapes the surface of the material that produced the mechanochemical effect. The abrasive grain for polishing according to claim 8.   The abrasive for polishing according to claim 10, wherein the component that mechanically scrapes the surface of the material to be polished is equal to the material to be polished or has a Mohs hardness lower than that of the material to be polished.   11. The polishing material according to claim 10, wherein the chemically reactive polishing material that causes a mechanochemical effect on the material to be polished is a component that reacts with frictional heat generated during the polishing process to oxidize the polishing surface of the material to be polished. Abrasive grain.   Chemically reactive abrasives that produce mechanochemical effects on the materials being polished include lithium, alkaline earth metal carbonates, phosphates, fluorides, boron compounds, and silver chloride, silver bromide, and silver iodide. The abrasive grain according to claim 10, which is one or two or more sparingly soluble salts selected from among halogen compounds such as, for example, cryolite, or alum.   Abrasive abrasive that mixes raw materials of multiple types of inorganic compound components, performs mechanical alloying in a dry state, and binds each inorganic compound component together through an amorphous layer to form particles Manufacturing method.   A polishing method for polishing a material to be polished using a slurry in which the abrasive grains according to any one of claims 1 to 12 are dispersed in pure water.   A polishing member in which the abrasive grains according to any one of claims 1 to 12 are dispersed and fixed on a base material. A polishing pad composed of any one of synthetic fiber, glass fiber, natural fiber, synthetic resin, and natural resin, wherein the polishing abrasive grains according to any one of claims 1 to 12 are dispersed and fixed on the surface;
A holding device that presses the material to be polished toward the surface of the polishing pad using elasticity,
A liquid injector for supplying pure water to the polished surface,
A polishing apparatus in which the elasticity of the holding device is set to a level that generates frictional heat above the temperature at which a chemical reaction by the reaction accelerator occurs between the polishing abrasive grains and the material to be polished.   A suspension produced by dispersing the abrasive grains according to any one of claims 1 to 12 in neutral water, and having a pH of 4 to 11 at 25 degrees Celsius. Slurry for polishing silicon or gallium nitride.

Images