阅读说明：本技术 复合烧结体、静电卡盘部件及静电卡盘装置 (Composite sintered body, electrostatic chuck member, and electrostatic chuck device ) 是由 日高宣浩 钉本弘训 于 2018-06-28 设计创作，主要内容包括：本发明的复合烧结体为含有作为主相的氧化铝和作为副相的碳化硅的陶瓷的复合烧结体,且在氧化铝的晶粒内具有莫来石。(The composite sintered body of the present invention is a composite sintered body of a ceramic containing alumina as a main phase and silicon carbide as a secondary phase, and has mullite in the grains of the alumina.)

1. A composite sintered body of a ceramic containing alumina as a main phase and silicon carbide as a secondary phase, and

the alumina has mullite within its grains.

2. The composite sintered body according to claim 1,

no mullite is present at the grain boundaries of the alumina.

3. The composite sintered body according to claim 1 or 2,

the crystal grain of the alumina is the 1 st crystal grain,

The crystal grains containing the mullite and dispersed in the crystal grains of the 1 st crystal grain are used as the 2 nd crystal grain,

When the crystal grain of the silicon carbide existing in the grain boundary of the 1 st crystal grain is the 3 rd crystal grain,

the 1 st crystal grain has an average crystal grain diameter of 0.5 to 10 [ mu ] m,

the 2 nd crystal grain has an average crystal grain diameter smaller than that of the 3 rd crystal grain.

4. The composite sintered body according to any one of claims 1 to 3,

the crystal grain of the alumina is the 1 st crystal grain,

The crystal grains containing the mullite and dispersed in the crystal grains of the 1 st crystal grain are used as the 2 nd crystal grain,

When the crystal grain of the silicon carbide existing in the grain boundary of the 1 st crystal grain is the 3 rd crystal grain,

the ratio of the entire 2 nd crystal grains to the entire 3 rd crystal grains is 20% or more and 40% or less in an area ratio in an arbitrary cross section.

5. The composite sintered body according to any one of claims 1 to 4,

the content of mullite in the composite sintered body is 1.2% or more and 3.5% or less in an area ratio in any cross section.

6. An electrostatic chuck component, comprising:

a plate-like substrate having the composite sintered body according to any one of claims 1 to 5 as a material, and having a main surface as a mounting surface on which a plate-like sample is mounted; and

and an electrostatic adsorption electrode provided on the opposite side of the base to the mounting surface or inside the base.

7. An electrostatic chuck device comprising the electrostatic chuck member according to claim 6.

8. The composite sintered body according to claim 1, containing crystal grains of the aluminum oxide and crystal grains of the silicon carbide as 1 st crystal grains,

the silicon carbide is beta-SiC,

the grains of silicon carbide are free of mullite,

at least a part of the crystal grains of silicon carbide exist as 3 rd crystal grains at grain boundaries of the crystal grains of alumina, and the remaining crystal grains of silicon carbide exist as 4 th crystal grains within the crystal grains of alumina,

the crystal grains of alumina contain at least 1 of crystal grains formed only of the mullite and crystal grains containing the mullite and β -SiC, i.e., silicon carbide, as the 2 nd crystal grains in the interior thereof,

the amount of the beta-SiC in the composite sintered body is 4 to 15 vol%,

the content of mullite in the composite sintered body is 1.2% or more and 3.5% or less in terms of an area ratio in a cross section.

Technical Field

The invention relates to a composite sintered body, an electrostatic chuck member, and an electrostatic chuck device.

The present application claims priority based on japanese patent application No. 2017-127095, filed in japanese application at 29.6.2017, and the contents thereof are incorporated herein by reference.

Background

In a semiconductor manufacturing apparatus that performs a plasma process, an electrostatic chuck device is used that can easily mount and fix a plate-like sample (wafer) on a sample stage and can maintain the wafer at a desired temperature. The coulomb type electrostatic chuck device comprises: a substrate having a mounting surface on which a wafer is mounted; and an electrostatic adsorption electrode for generating an electrostatic force (coulomb force) between the electrostatic adsorption electrode and the wafer placed on the placing surface (for example, refer to patent document 1). The base body is made of a common ceramic sintered body.

Disclosure of Invention

Technical problem to be solved by the invention

In recent years, devices using semiconductors tend to be highly integrated. Therefore, when manufacturing a device, a microfabrication technique or a three-dimensional mounting technique of wiring is required. In implementing such a processing technique, a semiconductor manufacturing apparatus is required to reduce an in-plane temperature distribution (temperature difference) of a wafer.

In the present specification, the "degree of in-plane temperature distribution (temperature difference) of a wafer mounted on a sample stage" may be referred to as "soaking property". "high soaking property" means that the in-plane temperature distribution of the wafer is small.

In the electrostatic chuck device, the following techniques are known: in order to reduce the in-plane temperature distribution (temperature difference) of the wafer, a fine groove is provided in the sample stage, and a gas refrigerant (e.g., helium) is flowed in the groove, thereby cooling the wafer placed on the sample stage. In such an electrostatic chuck device, in order to improve heat uniformity, it is conceivable to increase the gas pressure of the refrigerant to improve cooling efficiency.

When the gas pressure of the refrigerant is increased, the electrostatic chuck device is required to have a high adsorption force so as not to detach the wafer by receiving the pressure from the refrigerant. In order to obtain a high adsorption force, the dielectric constant of the base body of the electrostatic chuck device is preferably high. However, when the dielectric constant of the base increases, the loss factor obtained from the product of the dielectric constant and the dielectric loss tangent also increases.

In a semiconductor manufacturing apparatus using an electrostatic chuck apparatus, a high frequency bias (RF) voltage is applied to generate plasma. When a substrate having a large loss factor is used in the electrostatic chuck apparatus, heat may be generated by a high-frequency electric field, and the heat uniformity may be lowered.

Further, heat uniformity is often a problem not only in the electrostatic chuck apparatus but also in various apparatuses such as a heater apparatus and a high temperature furnace using a ceramic sintered body.

The present invention has been made in view of such circumstances, and an object thereof is to provide a novel composite sintered body having high heat uniformity. It is another object of the present invention to provide an electrostatic chuck section and an electrostatic chuck apparatus using such a composite sintered body.

Means for solving the technical problem

In order to solve the above problem, a first aspect of the present invention provides a composite sintered body of a ceramic containing alumina as a main phase and silicon carbide as a secondary phase, the composite sintered body having mullite in grains of the alumina.

In one aspect of the present invention, the following may be configured: no mullite is present at the grain boundaries of the alumina.

In the first aspect of the present invention, the configuration may be such that: when the crystal grain of the alumina is the 1 st crystal grain, the crystal grain containing the mullite and dispersed in the crystal grain of the 1 st crystal grain is the 2 nd crystal grain, and the crystal grain of the silicon carbide existing in the crystal grain boundary of the 1 st crystal grain is the 3 rd crystal grain, the average crystal grain diameter of the 1 st crystal grain is more than or equal to 0.5 μm and less than or equal to 10 μm, and the average crystal grain diameter of the 2 nd crystal grain is smaller than the average crystal grain diameter of the 3 rd crystal grain.

In the first aspect of the present invention, the configuration may be such that: when the crystal grain of the alumina is the 1 st crystal grain, the crystal grain containing the mullite and dispersed in the crystal grain of the 1 st crystal grain is the 2 nd crystal grain, and the crystal grain of the silicon carbide existing in the crystal grain boundary of the 1 st crystal grain is the 3 rd crystal grain, the proportion of the whole 2 nd crystal grain to the whole 3 rd crystal grain is 20% to 40% in terms of the area ratio in any cross section.

In the first aspect of the present invention, the configuration may be such that: the content of mullite in the composite sintered body is 1.2% or more and 3.5% or less in an area ratio in any cross section.

The features described above are also preferably combined with each other. The combination may be arbitrarily selected, and 2 features arbitrarily selected may be combined, or 3 or more features may be combined.

A second aspect of the present invention provides an electrostatic chuck component comprising: a plate-like substrate having the composite sintered body as a forming material and having one main surface as a mounting surface on which a plate-like sample is mounted; and an electrostatic adsorption electrode provided on the opposite side of the substrate from the mounting surface or inside the substrate.

A third aspect of the present invention provides an electrostatic chuck device including the electrostatic chuck member.

Effects of the invention

According to the present invention, a novel composite sintered body having high heat uniformity can be provided. Further, an electrostatic chuck section and an electrostatic chuck apparatus using such a composite sintered body can be provided.

Drawings

Fig. 1 is a schematic cross-sectional view showing a preferred example of the electrostatic chuck device of the present embodiment.

Fig. 2 is a schematic view showing an example of the composite sintered body according to the present invention.

Fig. 3 is a graph showing a relationship between the pH of the slurry in the slurry and the zeta potential of the particles.

Fig. 4 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

Fig. 5 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

Fig. 6 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

Fig. 7 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

Fig. 8 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

Fig. 9 is a schematic explanatory view for explaining a preferred method for producing the composite sintered body of the present invention.

FIG. 10 is a BF-STEM photograph of the composite sintered body obtained in example 1.

Fig. 11 is EDX measurement results of the composite sintered body obtained in example 1.

Fig. 12 is EDX measurement results of the composite sintered body obtained in example 1.

Detailed Description

Preferred examples of the electrostatic chuck apparatus and preferred examples of the composite sintered body and the electrostatic chuck member according to the present embodiment will be described below with reference to fig. 1 and the like. In all the drawings described below, the dimensions, ratios, and the like of the respective constituent elements are sometimes changed as appropriate for easy viewing of the drawings. In the following examples, preferred examples are specifically described to better understand the gist of the present invention, and the present invention is not limited to these examples unless otherwise specified. Omission, addition, replacement, and other changes in the number, quantity, position, size, proportion, and components may be made without departing from the spirit of the present invention.

[ Electrostatic chuck device ]

Fig. 1 is a sectional view showing an electrostatic chuck device according to the present embodiment. The electrostatic chuck device 1 of the present embodiment preferably includes a disk-shaped electrostatic chuck section 2 in a plan view having one main surface (upper surface) side as a mounting surface, and a disk-shaped temperature adjustment base section 3 in a plan view, which is provided below the electrostatic chuck section 2, adjusts the electrostatic chuck section 2 to a desired temperature, and has a thickness. The electrostatic chuck section 2 and the temperature adjustment base section 3 are bonded to each other via an adhesive layer 8 provided between the electrostatic chuck section 2 and the temperature adjustment base section 3.

The following description will be made in order.

(Electrostatic chuck part)

The electrostatic chuck section 2 includes a mounting plate 11 having an upper surface serving as a mounting surface 11a on which a plate-like sample W such as a semiconductor wafer is mounted, a support plate 12 integrated with the mounting plate 11 and supporting a bottom side of the mounting plate 11, an electrostatic attraction electrode 13 provided between the mounting plate 11 and the support plate 12, and an insulating material layer 14 insulating a periphery of the electrostatic attraction electrode 13. The mounting plate 11 and the support plate 12 correspond to a "base" in the present invention.

The mounting plate 11 and the support plate 12 are preferably disk-shaped members having the same shape of the surfaces to be overlapped. The mounting plate 11 and the support plate 12 are preferably formed of a ceramic sintered body having mechanical strength and durability against corrosive gas and plasma thereof. The materials for forming the mounting plate 11 and the support plate 12 will be described in detail later.

A plurality of projections 11b having a diameter smaller than the thickness of the plate-like sample are formed at predetermined intervals on the mounting surface 11a of the mounting plate 11, and the projections 11b support the plate-like sample W.

The thickness of the entire structure including the mounting plate 11, the support plate 12, the electrostatic-adsorption electrode 13, and the insulating material layer 14, that is, the thickness of the electrostatic chuck section 2 can be arbitrarily selected, and is, for example, 0.7mm to 5.0 mm.

For example, if the thickness of the electrostatic chuck section 2 is less than 0.7mm, it may be difficult to ensure the mechanical strength of the electrostatic chuck section 2. If the thickness of the electrostatic chuck section 2 is larger than 5.0mm, the thermal capacity of the electrostatic chuck section 2 may increase, and the thermal responsiveness of the plate-like sample W placed on the electrostatic chuck section may deteriorate, and it may be difficult to maintain the in-plane temperature of the plate-like sample W in a desired temperature field (temperature pattern) due to an increase in the heat transfer in the lateral direction of the electrostatic chuck section. The thickness of each portion described herein is an example, and is not limited to the above range. The conditions may be changed as desired.

The electrostatic adsorption electrode 13 is used as an electrostatic chuck electrode for generating electric charges and fixing the plate-like sample W by electrostatic adsorption force. The shape or size thereof may be appropriately adjusted according to the purpose thereof.

The electrostatic adsorption electrode 13 can be formed using an arbitrarily selected material. The electrostatic adsorption electrode 13 is preferably made of oxygen, for exampleAluminum-tantalum carbide (Al)₂O₃-Ta₄C₅) Conductive composite sintered body, alumina-tungsten (Al)₂O₃-W) conductive composite sintered body, alumina-silicon carbide (Al)₂O₃-SiC) conductive composite sintered body, aluminum nitride-tungsten (AlN-W) conductive composite sintered body, aluminum nitride-tantalum (AlN-Ta) conductive composite sintered body, yttrium oxide-molybdenum (Y)₂O₃-Mo) a conductive ceramic such as a conductive composite sintered body, or a high melting point metal such as tungsten (W), tantalum (Ta), molybdenum (Mo).

The thickness of the electrostatic adsorption electrode 13 is not particularly limited, and can be arbitrarily selected. The thickness of the electrostatic attraction electrode 13 can be selected, for example, from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm, and still more preferably from 5 μm to 20 μm.

If the thickness of the electrostatic adsorption electrode 13 is less than 0.1 μm, it may be difficult to ensure sufficient conductivity. If the thickness of the electrostatic attraction electrode 13 exceeds 100 μm, cracks may easily occur at the joint interface between the electrostatic attraction electrode 13 and the mounting plate 11 and the support plate 12 due to the difference in thermal expansion coefficient between the electrostatic attraction electrode 13 and the mounting plate 11 and the support plate 12.

The electrostatic attraction electrode 13 having such a thickness can be easily formed by a film formation method such as a sputtering method or a deposition method, or an application method such as a screen printing method.

The insulating material layer 14 surrounds the electrostatic attraction electrode 13 to protect the electrostatic attraction electrode 13 from the corrosive gas and the plasma thereof, and integrally bonds the boundary portion between the mounting plate 11 and the support plate 12, that is, the outer peripheral region excluding the electrostatic attraction electrode 13. The insulating material layer 14 is made of an insulating material having the same composition or the same main component as the material constituting the carriage plate 11 and the support plate 12.

(base for temperature adjustment)

The temperature adjustment base portion 3 is a disk-shaped member having a thickness for adjusting the electrostatic chuck portion 2 to a desired temperature. As the temperature adjustment base section 3, for example, a liquid cooling base or the like in which a flow path 3A for circulating a refrigerant is formed can be preferably used.

The material constituting the temperature adjustment base portion 3 is not particularly limited as long as it is a metal having excellent thermal conductivity, electrical conductivity, and workability, or a composite material containing these metals. For example, aluminum (Al), aluminum alloy, copper (Cu), copper alloy, stainless steel (SUS), or the like is preferably used. At least the surface of the temperature adjustment base portion 3 exposed to plasma is preferably subjected to alumite (alumite) treatment or an insulating film such as alumina is formed.

An insulating plate 7 is bonded to the upper surface side of the temperature adjustment base portion 3 via an adhesive layer 6. The adhesive layer 6 is formed of an arbitrarily selected material, and is preferably formed of a sheet-like or film-like adhesive resin having heat resistance and insulation properties, such as polyimide resin, silicone resin, and epoxy resin. The thickness of the adhesive layer can be arbitrarily selected, and is, for example, about 5 to 100 μm. The insulating plate 7 is preferably formed of a sheet, or a film of a heat-resistant resin such as polyimide resin, epoxy resin, or acrylic resin.

Instead of the resin sheet, the insulating plate 7 may be an insulating ceramic plate or may be a thermally sprayed film having insulating properties such as alumina.

(Focus ring)

The focus ring 10 is an annular member in plan view that is placed on the peripheral portion of the temperature adjustment base portion 3. The focus ring 10 can be formed of any selected material, but is preferably formed of a material having conductivity equivalent to that of a wafer placed on the placement surface, for example. By disposing the focus ring 10, the electrical environment for plasma can be made substantially equal to the wafer at the peripheral portion of the wafer, and a difference or variation in plasma processing between the central portion and the peripheral portion of the wafer can be made less likely to occur.

(other Components)

A power supply terminal 15 for applying a dc voltage to the electrostatic attraction electrode 13 is connected to the electrostatic attraction electrode 13. The power supply terminal 15 is inserted into a through hole 16 penetrating the temperature adjustment base portion 3, the adhesive layer 8, and the support plate 12 in the thickness direction. An insulator 15a having an insulating property is provided on the outer peripheral side of the power feeding terminal 15. The power supply terminal 15 is insulated from the metallic temperature adjustment base portion 3 by the insulator 15 a.

In fig. 1, the power supply terminal 15 is shown as an integral member, but the power supply terminal 15 may be configured by electrically connecting a plurality of members. The power supply terminal 15 is inserted into the temperature adjustment base portion 3 and the support plate 12 having different thermal expansion coefficients. Therefore, for example, it is also preferable that the portions of the temperature adjustment base portion 3 and the power supply terminal 15 of the support plate 12 to be inserted are made of different materials.

The material of the power supply terminal 15 is not particularly limited as long as it is a conductive material having excellent heat resistance, as a portion (extraction electrode) connected to the electrostatic adsorption electrode 13 and inserted into the support plate 12. For example, the thermal expansion coefficient of the material of the portion is preferably similar to that of the electrostatic adsorption electrode 13 and the support plate 12. For example, Al is also preferable₂O₃-TaC or the like conductive ceramic material.

In the power supply terminal 15, a portion inserted into the temperature adjustment base portion 3 is preferably formed of a metal material such as tungsten (W), tantalum (Ta), molybdenum (Mo), niobium (Nb), or Kovar (Kovar) alloy.

The two members are preferably connected by a silicon-based conductive adhesive having flexibility and electric resistance.

A heating element 5 is provided on the lower surface side of the electrostatic chuck section 2. Conditions such as the material and thickness of the heating element 5 can be arbitrarily selected. As an example of a preferable heating element 5, a non-magnetic metal thin plate (for example, a thin plate selected from a titanium (Ti) thin plate, a tungsten (W) thin plate, a molybdenum (Mo) thin plate, and the like) having a thickness of 0.2mm or less (preferably, a constant thickness of about 0.1 mm) is processed into a desired heater shape (for example, the entire contour of a strip-shaped conductive thin plate is processed into a circular ring shape) by photolithography or laser processing, whereby a preferable heating element is obtained.

Such a heating element 5 may be provided by machining the surface of the electrostatic chuck section 2 after bonding a non-magnetic metal thin plate to the electrostatic chuck section 2. Alternatively, the heating element 5 may be provided by being formed by machining at a position different from the electrostatic chuck section 2 and then transferred to the surface of the electrostatic chuck section 2.

The heating element 5 is bonded and fixed to the bottom surface of the support plate 12 by an adhesive layer 4 made of a sheet-like or film-like silicone resin or acrylic resin having heat resistance and insulation properties and having a uniform thickness.

A power supply terminal 17 for supplying power to the heating element 5 is connected to the heating element 5. As a material constituting the power feeding terminal 17, a material similar to the material constituting the power feeding terminal 15 can be used. The power supply terminals 17 are provided so as to penetrate through-holes 3b formed in the temperature adjustment base portion 3.

A temperature sensor 20 is provided on the lower surface side of the heating element 5. In the electrostatic chuck apparatus 1 according to the present embodiment, the installation hole 21 is formed so as to penetrate the temperature adjustment base portion 3 and the insulating plate 7 in the thickness direction, and the temperature sensor 20 is provided at the uppermost portion of the installation hole 21. In addition, it is preferable that the temperature sensor 20 is disposed as close to the heating element 5 as possible. Therefore, the temperature sensor 20 and the heating element 5 may be configured to be brought close to each other by forming the installation hole 21 to extend from the configuration shown in fig. 1 to the adhesive layer 8 side.

The temperature sensor 20 can be arbitrarily selected, and is preferably a fluorescent light-emitting temperature sensor in which a phosphor layer is formed on the upper surface side of a rectangular parallelepiped light-transmitting body made of quartz glass or the like, for example. The temperature sensor 20 having the above-described structure is bonded to the lower surface of the heating element 5 with a silicone adhesive or the like having light transmittance and heat resistance.

The phosphor layer is formed of a material that generates fluorescence in accordance with heat input from the heating element 5. As a material for forming the phosphor layer, any material that generates fluorescence by heat generation may be used, and various types of phosphor materials can be arbitrarily selected. As preferable examples, the material for forming the phosphor layer may include a phosphor material to which a rare earth element having an energy level suitable for light emission is added, a semiconductor material such as AlGaAs, a metal oxide such as magnesium oxide, and a mineral such as ruby or sapphire, and these materials can be appropriately selected and used.

The temperature sensors 20 corresponding to the heating elements 5 are provided at arbitrary positions in the circumferential direction of the lower surface of the heating element 5 that do not interfere with the power supply terminals and the like of the heating elements.

The type and structure of the temperature measuring unit 22 for measuring the temperature of the heating element 5 from the fluorescence of the temperature sensor 20 can be arbitrarily selected. As an example, in fig. 1, the temperature measuring section 22 is constituted by an excitation section 23 that irradiates the phosphor layer with excitation light outside (below) the installation hole 21 of the temperature adjustment base section 3, a fluorescence detector 24 that detects fluorescence emitted from the phosphor layer, and a control section 25 that controls the excitation section 23 and the fluorescence detector 24 and calculates the temperature of the main heater from the fluorescence.

The electrostatic chuck apparatus 1 further includes an air hole 28 provided to penetrate from the temperature adjustment base portion 3 to the mounting plate 11 in the thickness direction. The inner periphery of the air hole 28 is preferably provided with a cylindrical insulator 29.

A gas supply device (cooling mechanism) is connected to the gas hole 28. The cooling gas (heat conductive gas) for cooling the plate-like sample W is supplied from the gas supply device through the gas hole 28. The cooling gas is supplied through the gas holes to the grooves 19 formed between the plurality of projections 11b on the upper surface of the mounting plate 11, thereby cooling the plate-like sample W.

The electrostatic chuck apparatus 1 preferably has pin insertion holes, not shown, provided so as to penetrate from the temperature adjustment base portion 3 to the mounting plate 11 in the thickness direction. The pin insertion hole can be configured similar to the air hole 28, for example. A plate-like sample detachment lift pin is inserted into the pin insertion hole.

The electrostatic chucking device 1 has the structure described above.

(composite sintered body)

Next, the base (the mounting plate 11 and the support plate 12) of the present embodiment will be described in detail. Fig. 2 is a schematic view showing an example of a composite sintered body according to the present invention, which is a preferable material for forming a base body.

Preferred examples of the composite sintered body according to the present invention that can be preferably used for the base body will be described below.

The composite sintered body 100 is formed of a composite sintered body of ceramics containing alumina as a main phase and silicon carbide as a secondary phase. The composite sintered body 100 has Mullite (Mullite) in the grains of alumina. The main phase refers to a region having an area ratio or a volume ratio of more than 50% of the entire region, and the sub-phase may be considered as a region other than the main phase. The main phase also preferably has an area ratio or a volume ratio of more than 75% or more than 80%. More specifically, for example, the main phase preferably has 85 to 96 vol%, and still more preferably 87 to 95 vol%.

In such a composite sintered body 100, the thermal conductivity is reduced as compared with a sintered body in which mullite is not present. This reduces the influence of a heater provided in the electrostatic chuck device or a heat source such as plasma in the use environment, thereby improving the heat uniformity of the entire substrate.

In addition, mullite has low durability when exposed to plasma compared to silicon carbide or alumina. Therefore, when mullite exists at the grain boundaries of alumina, the mullite at the grain boundaries is easily consumed when the composite sintered body 100 is used in a plasma environment. This makes it easy for the composite sintered body having mullite at the grain boundary to change its physical properties in the plasma environment. Consider that: when the amount of mullite present in the grain boundary is large, the physical properties are also greatly changed.

In contrast, in the composite sintered body 100 used for the base body of the present embodiment, mullite exists in the grains of alumina. No mullite or very little mullite is present in the grain boundaries. Therefore, the physical properties are not easily changed even when used in a plasma environment, and therefore, the plasma processing method is preferable.

Herein, "mullite" is an aluminum silicate compound that is stable at high temperatures. The mullite may have a chemical composition of 3Al₂O₃·2SiO₂-2Al₂O₃SiO₂The range of (1). The Al/Si ratio of mullite can vary between 3 and 4. The "mullite" in the present invention may be composed of 3Al₂O₃·2SiO₂A compound represented by or Al₆O₁₃Si₂The compound shown in the specification.

The composite sintered body 100 shown in fig. 2 has the 1 st crystal grain 110 as a crystal grain of alumina, the 2 nd crystal grain 120 as a crystal grain containing mullite, and the 3 rd crystal grain 130 as a crystal grain of silicon carbide. In addition, the 3 rd crystal grain 130 does not contain mullite.

The plurality of 2 nd crystal grains 120 are dispersed in the grains of the 1 st crystal grains 110 in the main phase constituted by sintering the plurality of 1 st crystal grains 110. Also, a plurality of the 3 rd crystal grains 130 exist at the grain boundary 110a of the 1 st crystal grain 110.

Further, the composite sintered body 100 has the 4 th crystal grain 140 which is a crystal grain of silicon carbide. The 4 th crystal grain is dispersed in the 1 st crystal grain 110. The 4 th grain 140 also does not contain mullite. Among the silicon carbide crystal grains, the 3 rd crystal grain 130 exists at the grain boundary, and the 4 th crystal grain 140 is dispersed in the 1 st crystal grain. The average crystal grain size of the 4 th crystal grain can be arbitrarily selected, but is preferably 0.04 to 0.8 μm, more preferably 0.1 to 0.3. mu.m. The 4 th crystal grain 140 preferably has an average grain size smaller than that of the 3 rd crystal grain 130.

The 2 nd crystal grain 120 containing mullite can be confirmed by, for example, performing elemental analysis on an arbitrary cross section of the composite sintered body 100 by energy dispersive X-ray analysis (EDX). Can be judged as: among the "sites where no carbon atom is detected" in the "sites where silicon atoms are detected by EDX", silicon carbide reacts with alumina to produce mullite. The crystal grain including such a site for producing mullite is specified as the 2 nd crystal grain 120.

The average crystal grain size of the 1 st crystal grain 110 may be arbitrarily selected, but is preferably 0.5 μm or more and 10 μm or less, and more preferably 0.8 μm or more and 1.6 μm or less. If the average crystal grain size of the 1 st crystal grain 110 is 0.5 μm or more, the number of grain boundaries is not too large, and a decrease in thermal conductivity can be suppressed. Therefore, the composite sintered body 100 is easily adapted to a temperature change when heated or cooled. As will be described later, the average crystal grain size of the 1 st crystal grain can be determined as the average crystal grain size by taking an electron micrograph and calculating the major axis diameter of 200 or more crystal grains of the 1 st crystal grain.

When the average crystal grain size of the 1 st crystal grain 110 is 10 μm or less, the number of grain boundaries is not too small, and an increase in thermal conductivity can be suppressed. Therefore, the heat uniformity of the composite sintered body 100 is easily ensured.

The 2 nd crystal grain 120 contains mullite produced by reacting silicon carbide, which is a raw material of the composite sintered body 100, with alumina. When focusing on the 1 nd crystal grain 120, the 2 nd crystal grain 120 may contain a part of mullite and the remainder of silicon carbide, or may be composed of only mullite. In the case where a part of mullite is contained, the ratio of mullite in the 2 nd crystal grain can be set as needed.

The 2 nd crystal grain 120 preferably has an average crystal grain size smaller than that of the 3 rd crystal grain 130. The average crystal grain size of the 2 nd crystal grains 120 can be arbitrarily selected. For example, in the composite sintered body of the present embodiment, the average crystal grain size of the 2 nd crystal grains 120 is preferably 0.03 μm or more and 0.2 μm or less.

The average crystal grain diameter of the 2 nd crystal grain 120 is 0.03 μm or more, whereby the 2 nd crystal grain 120 can sufficiently affect the thermal conductivity of the composite sintered body 100. Further, the 2 nd crystal grains 120 have an average grain size of 0.2 μm or less, and thus mullite can be suitably formed.

The average crystal grain size of the 3 rd crystal grains 130 can be arbitrarily selected, but is preferably 0.9 μm or less. Since the average crystal grain size of the 3 rd crystal grains 130 is 0.9 μm or less, the electric field applied to the composite sintered body 100 is less likely to be attenuated in the 3 rd crystal grains, and the loss factor is less likely to be deteriorated. The lower limit of the average crystal grain size of the 3 rd crystal grains 130 can be arbitrarily selected.

The 2 nd crystal grain 120 is preferably smaller than the 3 rd crystal grain 130 of the grain boundary. The smaller the size of the 2 nd crystal grain 120, the more mullite is easily obtained and desired physical properties are easily obtained. In addition, mullite means that crystals containing mullite are formed.

In any cross section of the composite sintered body 100, the ratio of the whole 2 nd crystal grain 120 to the whole 3 rd crystal grain 130 can be arbitrarily selected, but is preferably 20% or more and 40% or less in terms of area ratio. The ratio may be 25% or more in terms of area ratio. The ratio may be 35% or less by area.

In the composite sintered body, when the ratio of the whole 2 nd crystal grains 120 to the whole 3 rd crystal grains 130 is 20% or more and 40% or less in terms of area ratio, the mullite content is easily set to a desired value as described later. Furthermore, desired physical properties can be easily obtained.

In the present invention, the "proportion of the entire 2 nd crystal grain 120" in the composite sintered body 100 is calculated from a scanning electron micrograph of an arbitrarily selected field of view of the composite sintered body.

That is, an electron micrograph is taken at a magnification of 10000 times at a randomly selected field of view, and the total area of crystal grains of silicon carbide existing at grain boundaries (3 rd crystal grains 130) taken in the electron micrograph is defined as the area of "the entire 3 rd crystal grains 130". On the other hand, in the electron micrograph, the "2 nd crystal grain 120" is identified by the above method, and the area of the "entire 2 nd crystal grain 120" is determined. From the area thus obtained, the ratio of "the whole of the 2 nd crystal grain 120" to "the whole of the 3 rd crystal grain 130" is obtained as an area ratio.

The same treatment was performed on the other part of the composite sintered body 100, evaluation was performed on an electron micrograph of 2 fields, and the average value was obtained as an area ratio indicating "the ratio of the entire 2 nd crystal grain 120 to the entire 3 rd crystal grain 130".

In addition, in addition to the 3 rd crystal grain 130, the same mullite-containing crystal grain as the 2 nd crystal grain 120 may exist in the grain boundary 110 a. However, it is preferable that mullite is not present in the grain boundary 110 a. In addition, the mullite-containing grains located at the grain boundary 110a are not judged as the 2 nd grains 120.

The area ratio of the 2 nd crystal grain 120 to the mullite-containing crystal grain located at the grain boundary 110a can be arbitrarily selected. The area ratio of the No. 2 crystal grain 120 to the mullite-containing crystal grain located at the grain boundary 110a may be, for example, 100 to 90:0 to 10, 100 to 95:0 to 5, or 100 to 99:0 to 1.

In the composite sintered body of the present embodiment, the average crystal grain size of the crystal grains of silicon carbide contained in the composite sintered body 100, that is, the average crystal grain size of the crystal grains of silicon carbide that join the 3 rd crystal grain 130 and the 4 th crystal grain 140, can be arbitrarily selected, but is preferably 0.2 μm or more and 0.8 μm or less.

The crystal grains of silicon carbide having a large crystal grain size tend to move along the grain boundary of alumina when the alumina crystal grains grow, and the positions of the crystal grains are likely to change according to the growth of the alumina crystal grains. Therefore, the silicon carbide crystal grains having a large crystal grain size are not taken into the inside of the alumina in which the crystal grains grow and are repelled, and are likely to be located in the grain boundary of the sintered body.

On the other hand, as described above, silicon carbide having an average crystal grain size of 0.2 μm or more and 0.8 μm or less is less likely to follow grain boundary movement of alumina during the growth of alumina crystal grains. Therefore, the crystal grains of silicon carbide having a small crystal grain size are easily taken into the inside of the alumina in which the crystal grains grow.

As a result, the crystal grain size of silicon carbide existing in the alumina grains tends to be smaller than the crystal grain size of silicon carbide existing in the grain boundaries.

In addition, the area ratio of the 3 rd crystal grain 130 to the 4 th crystal grain 140 can be arbitrarily selected.

In the composite sintered body of the present embodiment, the content of mullite in the composite sintered body 100 can be arbitrarily selected, but it is preferable that the area ratio in an arbitrarily selected cross section is 1.2% or more and 3.5% or less. The content of mullite is 1.2% or more in terms of area ratio, and thus sufficient thermal conductivity can be ensured. The content of mullite is 3.5% or less, so that the thermal conductivity is not excessively lowered, and the temperature increase/cooling rate is easily brought into a desired state when the composite sintered body 100 is used as a base body of an electrostatic chuck device. The area ratio may be 1.5% or more, 2.0% or more, or 2.5% or more. The area ratio may be 3.0% or less, 2.5% or less, or 2.0% or less.

The composite sintered body 100, which is a material for forming the mounting plate 11 and the support plate 12, has the above-described structure, and thus has high heat uniformity.

Silicon carbide (SiC) is known to have a plurality of crystal structures, and examples thereof include silicon carbide having a 3C-type (sphalerite-type) crystal structure in a cubic system, silicon carbide having a wurtzite-type crystal structure in a hexagonal system such as 4H-type and 6H-type, and silicon carbide having a 15R-type crystal structure in a rhombohedral system. Among them, silicon carbide having a 3C type crystal structure is referred to as "β -SiC". All silicon carbide having a crystal structure other than this is referred to as "α -SiC". Any silicon carbide can be used, and β -SiC can be particularly preferably contained in the composite sintered body.

In the mounting plate 11 and the support plate 12 of the present embodiment, SiC contained in the composite sintered body is preferably β -SiC. In the sintered body, it is preferable that the β -SiC crystal grains are dispersed and present in a state surrounded by the metal oxide crystal grains as the matrix material. The volume ratio of β -SiC in the sintered body can be arbitrarily selected. SiC (preferably β -SiC) is preferably 4% by volume or more and 15% by volume or less, more preferably 5% by volume or more and 13% by volume or less of the entire sintered body.

If the volume fraction of SiC (preferably β -SiC) is less than 4 vol%, the SiC particles may exert little effect on electron conductivity. If the volume ratio of β -SiC is greater than 15 vol%, the SiC particles may come into contact with each other, and the resistance value via the SiC particles may decrease.

In the composite sintered body of the present embodiment, the content of metal impurities other than aluminum and silicon is preferably 100ppm or less. The content of metal impurities is preferably 50ppm or less, more preferably 25ppm or less.

[ method for producing composite sintered body ]

The composite sintered body according to the present embodiment can be preferably produced by mixing and sintering alumina particles and silicon carbide particles. In this case, the composite sintered body can be preferably produced by controlling (i) the amount of silicon carbide particles to be increased and (ii) the particle diameter of the silicon carbide particles to be decreased, as described below, with respect to the silicon carbide particles to be introduced into the plurality of alumina particles and sintered. The composite sintered body of the present invention can be obtained by the present production method.

(i) When a plurality of alumina particles are sintered to form the 1 st crystal grain 110, if the number of silicon carbide particles taken into the inside increases, the alumina particles and the silicon carbide particles are likely to react with each other. As a result, mullite is easily formed in the grains of the 1 st crystal grain 110.

(ii) When the particle diameter of the silicon carbide particles taken into the inside is small when a plurality of alumina particles are sintered to form the 1 st crystal grain 110, the reactivity of the silicon carbide particles is improved, and the alumina particles and the silicon carbide particles are likely to react with each other kinetically. As a result, mullite is easily formed in the grains of the 1 st crystal grain 110.

For example, the composite sintered body of the present invention and the composite sintered body according to the present embodiment can be suitably produced by the following method.

The method for producing a composite sintered body of the present embodiment includes:

(a) a step of spraying alumina particles and silicon carbide particles at a high speed, respectively, and mixing them while making them collide with each other;

(b) adjusting the pH of the slurry obtained in the mixing step to a range in which the surface charge of the alumina particles in the slurry becomes a positive value and the surface charge of the silicon carbide particles in the slurry becomes a negative value;

(c) a step of forming a molded body after adjusting the pH and removing the dispersion medium from the slurry; and

(d) and a step of compacting the obtained molded body in a non-oxidizing atmosphere at a pressure of 25MPa or more and heating the compacted body to 1600 ℃ or more to perform pressure sintering.

In the method for producing a composite sintered body according to the present embodiment, the alumina content of the alumina particles used is preferably 99.99% or more. Such high purity alumina particles can be adjusted by using the alum method. The alumina particles adjusted using the alum method can greatly reduce the content of sodium atoms as metal impurities, compared to, for example, the alumina particles adjusted using the bayer method (bayer). Further, as long as alumina particles having a desired purity can be obtained, various methods can be employed.

The above-described steps will be described below.

(a step of mixing)

In the mixing step, alumina particles and silicon carbide particles (dispersion liquid) dispersed in a dispersion medium are prepared. It is preferable that the dispersion liquid is pressurized by using a two-flow particle collision type pulverizing and mixing device and is sprayed at a high speed to mix the particles while colliding with each other. Thereby, the alumina particles and the silicon carbide particles are pulverized, and a dispersion liquid containing these pulverized particles is obtained. In this step, the slurries ejected at high speeds may collide with each other. The speed at which the slurry collides can also be chosen arbitrarily.

When the alumina particles and the silicon carbide particles collide with each other, the kinetic energy of the large particles at the time of collision is large, and the particles are easily crushed. On the other hand, small particles have small kinetic energy at the time of collision, and are not easily pulverized. Therefore, the alumina particles and the silicon carbide particles obtained by the above-mentioned pulverizing and mixing device have a narrow particle size distribution width with a small number of coarse particles or over-pulverized particles. Therefore, if the mixed particles obtained by pulverizing and mixing the particles by the dual-flow particle collision type pulverizing and mixing apparatus are used, abnormal grain growth with coarse particles as nuclei can be suppressed in the sintering step.

In addition, in the case of performing the pulverizing and mixing using such a pulverizing and mixing device, it is possible to suppress the mixing of impurities due to the breakage of each medium, as compared with a method of performing the pulverizing and mixing using a medium such as a ball mill or a bead mill.

In the method of manufacturing a composite sintered body according to the present embodiment, it is preferable that the method further includes a step of previously subjecting the silicon carbide particles to heat treatment in an oxidizing atmosphere to thereby oxidize the surfaces of the silicon carbide particles. Hereinafter, the oxidation treatment is referred to as "pre-oxidation".

The temperature condition for the pre-oxidation can be arbitrarily selected, but is preferably 300 ℃ to 500 ℃ inclusive, for example. When the pre-oxidation temperature is 300 ℃ or higher, the surface of the silicon carbide particles can be oxidized. When the pre-oxidation temperature is 500 ℃ or lower, the surface of the silicon carbide particles is not excessively oxidized. For example, when the oxidation temperature is set to 600 ℃ or higher, the oxidation of the surface of the silicon carbide particles proceeds too much, and as a result, the silicon carbide particles may be bonded to each other through the oxide film on the particle surface and coarsened.

The time for the pre-oxidation can be arbitrarily selected, but is preferably 10 hours or more. In the case where the time for the pre-oxidation is less than 10 hours, the oxidation hardly proceeds sufficiently. The time for the pre-oxidation may be long (for example, 50 hours), but the amount of the oxide film hardly changes after a certain amount of the oxide film is formed. Therefore, the time for the pre-oxidation is preferably 10 hours or more and 20 hours or less, for example.

The hydrophilicity of the silicon carbide particles can be improved by subjecting the silicon carbide particles to a pre-oxidation treatment. This improves the dispersibility of the silicon carbide particles in the slurry.

The type of the dispersion medium can be arbitrarily selected, and for example, distilled water or the like can be preferably used.

The ratio of the alumina particles and the silicon carbide particles to be mixed can be arbitrarily selected, but is preferably 85 to 96/4 to 15, more preferably 87 to 95/5 to 13 in terms of volume ratio.

The particle size of the alumina particles dispersed in the dispersion medium can be arbitrarily selected, but is preferably 0.1 to 0.3 μm, more preferably 0.15 to 0.25 μm.

The particle diameter of the silicon carbide particles in the dispersion medium before ejection can be arbitrarily selected, but is preferably 10 to 150nm, more preferably 30 to 100 nm.

The proportion of the alumina particles in the dispersion medium before ejection can be arbitrarily selected, but is, for example, preferably 85 to 96 vol%, and preferably 87 to 95 vol%.

The proportion of the silicon carbide particles in the dispersion medium before ejection can be arbitrarily selected, but is, for example, preferably 4 to 15 vol%, and preferably 5 to 13 vol%.

The ratio of the total amount of the silicon carbide particles and the alumina particles in the dispersion medium before ejection to the amount of the dispersion medium can be arbitrarily selected. Examples of the lower limit value include 10 mass% or more, 20 mass% or more, 30 mass% or more, or 40 mass% or more. Examples of the upper limit value include 90% by mass or less, 80% by mass or less, and 70% by mass or less.

The method of preparing the alumina particles and the silicon carbide particles dispersed in the dispersion medium for pulverization and mixing can be arbitrarily selected. For example, alumina particles and silicon carbide particles may be added to the dispersion medium either continuously or simultaneously. Alternatively, the alumina particles may be dispersed in a dispersion medium, and the silicon carbide particles may be dispersed in a separately prepared same dispersion medium. These two dispersions may be used in combination or may be sprayed separately.

The dispersant may be added to any amount of the dispersion medium in advance and used. The dispersant can be arbitrarily selected.

(b) Process for adjusting pH)

The pH of the obtained mixed solution (slurry) was adjusted. In this step, the pH is adjusted in consideration of the surface charges of the alumina particles and the silicon carbide particles contained in the slurry. The slurry obtained in the mixing step (slurry before pH adjustment) usually exhibits alkalinity of about pH 11.

Fig. 3 is a graph showing a relationship between the pH of the slurry and the zeta potential of the particles for alumina particles and silicon carbide particles in the slurry. In the figure, the horizontal axis represents the pH of the slurry, and the vertical axis represents the zeta potential (unit: mV) of each particle. Here, the solvent of the slurry before the pH adjustment was 0.1N NH₄NO₃。

As shown in the figure, when the pH of the system was on the acidic side (pH < 7), the zeta potential of the alumina particles became positive. This is because, when the pH of the system is on the acidic side, the hydroxyl groups on the surface of the alumina particles are protonated (H)⁺) And the surface is positively charged.

On the other hand, when the pH of the system is on the alkaline side (pH > 7), the zeta potential of the alumina particles becomes negative. This is because, when the pH of the system is on the alkaline side, protons are dissociated from hydroxyl groups on the surface of the alumina particles, and the surface is negatively charged.

On the other hand, the behavior of the zeta potential of the silicon carbide particles is different. As shown in the figure, the zeta potential of the silicon carbide particles is 0 at around pH2 to 3, and is negative in a wide range from an acidic region to a basic region at around pH 3.

In the case where 2 particles having such a relationship coexist in the same slurry, when the pH of the system is in the range of "the surface charge of the alumina particles in the slurry becomes a positive value" and "the surface charge of the silicon carbide particles in the slurry becomes a negative value", so-called heterogeneous aggregation in which two particles aggregate occurs.

In this case, it is preferable to add a dispersant to the slurry as appropriate so as not to precipitate the alumina particles and the silicon carbide particles.

The pH of the system is preferably 3 or more and 7 or less, more preferably 5 or more and 7 or less, and further preferably 6 or more and 7 or less. When the zeta potentials of the two particles after pH adjustment are compared with each other, heterogeneous aggregation is more likely to occur as the absolute values of the zeta potentials are closer to each other, and a desired aggregated state is obtained.

The adjustment of the pH in the above range can be performed by adding an acid to the slurry. Examples of the acid that can be used include inorganic acids such as nitric acid, phosphoric acid, hydrochloric acid, and sulfuric acid, and organic acids such as acetic acid. Among them, hydrochloric acid, sulfuric acid, and the like may cause deterioration of the apparatus by generating chlorine or sulfur in the apparatus in a sintering step described later. Therefore, nitric acid, phosphoric acid, organic acids, and the like are preferably used for adjusting the pH.

(c) Process for Forming the molded article)

In the step of forming a molded article, first, the dispersion (slurry) after pH adjustment is spray-dried. Thus, dry particles composed of mixed particles of alumina particles and silicon carbide particles were obtained.

Next, the obtained particles are molded, for example, uniaxially molded (uniaxial press molding) according to the shape of the target sintered body.

Next, the obtained molded body is heated at an arbitrarily selected temperature under normal pressure (without pressurization) in an inert gas atmosphere. For example, heating to 500 ℃ to remove impurities such as moisture and a dispersion medium contained in the molded article. As the inert gas, nitrogen or argon can be used. In this operation, if the dope can be removed from the molded body without modifying the molded body, the heating temperature is not limited to 500 ℃. Examples thereof include 350 to 600 ℃, and more preferably 450 to 550 ℃.

Preferably, the method for producing the composite sintered body further includes an oxidation step of heating the formed body from which the dopant has been removed at a temperature selected as necessary, for example, 400 ℃ in the air, and oxidizing the mixed particles constituting the formed body. According to this operation, in the oxidation treatment, an oxide film is formed on the surface of the silicon carbide particles contained in the mixed particles. The metal impurities contained in the mixed particles are easily eluted in the oxide film. Therefore, the metal impurities contained in the mixed particles are present while being biased toward the particle surface. This is preferable because the metal impurities can be easily removed in the step of pressure sintering described later. The temperature of the oxidation treatment is not limited to 400 ℃, and examples thereof include 250 to 500 ℃ and more preferably 300 to 450 ℃ as required. The time of the oxidation treatment can be arbitrarily selected, but examples thereof include 6 to 48 hours, and more preferably 12 to 24 hours.

(d) Process for pressure sintering

In the step of performing pressure sintering, first, the molded body obtained in the above step is heated (preheated) at a temperature lower than 1600 ℃ and at normal pressure (without pressurization) in a vacuum atmosphere (1 st non-oxidizing atmosphere). According to this operation, by appropriately setting the temperature at the time of preheating, it is possible to evaporate metal impurities such as alkali metals contained in the mixed particles and easily remove the metal impurities. Therefore, according to such an operation, the purity of the mixed particles can be easily improved, and the volume resistance value of the matrix can be easily controlled. As the temperature lower than 1600 ℃, it can be selected as needed.

In the step of forming the molded article, when the molded article from which the dopant is removed as described above is subjected to oxidation treatment, the oxide film formed on the particle surface in the present step is volatilized by preheating in a vacuum atmosphere. At the same time, metal impurities contained in the oxide film are evaporated. Therefore, the metal impurities can be easily removed from the molded body. Therefore, according to such an operation, the purity of the mixed particles can be easily improved, and the volume resistance value of the matrix can be easily controlled.

In the present embodiment, "vacuum" refers to a state in which the space is filled with a gas having a pressure lower than atmospheric pressure, and is defined as a pressure that can be industrially used under JIS standard. In the present embodiment, the vacuum atmosphere may be a low vacuum (100Pa or more), but is preferably a medium vacuum (0.1Pa to 100Pa), and more preferably a high vacuum (10 Pa)^-5Pa～0.1Pa)。

In the method for producing a composite sintered body according to the present embodiment, after preheating at 1200 ℃ for 4 hours or more in a vacuum atmosphere, for example, the gas pressure is preferably returned to atmospheric pressure with an inert gas such as argon.

Next, the preheated molded body is compacted under an inert gas atmosphere, for example, an argon atmosphere (2 nd non-oxidizing atmosphere) at a pressure of 5MPa or more and heated to 1600 ℃ or more to perform pressure sintering. By this operation, the alumina particles or the silicon carbide particles contained in the compact are sintered, and a dense sintered body having few pores is obtained. Temperatures above 1600 c can be selected as desired. The pressure can also be chosen arbitrarily.

In the method for producing a composite sintered body according to the present embodiment, for example, sintering can be performed in an argon atmosphere at 1600 ℃ to 1850 ℃ and at a sintering pressure in a range of 25MPa to 50 MPa.

The sintered body obtained by this method has a reduced content of metal impurities and a high purity. In the case where the content of the metal impurities does not reach the target value, it is preferable to increase the time of preheating or increase the temperature of preheating.

Fig. 4 to 9 are explanatory views for explaining a method for producing the composite sintered body according to the present embodiment. Fig. 4 to 6 schematically show the state of the particles at each stage when the pH of the slurry is adjusted to about pH11, and fig. 7 to 9 schematically show the state of the particles at each stage when the pH of the slurry is adjusted to about pH 6.5. These figures are explained below.

First, a step of not adjusting pH will be described.

Fig. 4 is a schematic diagram showing the state of particles in a slurry having a pH of about 11, for example. Fig. 5 is a schematic view showing a state of particles when the dispersion medium is removed from the slurry shown in fig. 4. Fig. 6 is a schematic view showing a composite sintered body produced using the particles shown in fig. 5.

In fig. 6, each hexagon represents a crystal grain of alumina as a main phase. In fig. 6, each black circle indicates a crystal grain of silicon carbide as a secondary phase, and the size of the black circle indicates the size of the crystal grain of silicon carbide.

In fig. 4, reference symbol a denotes alumina particles, and reference symbol B denotes silicon carbide particles. As shown in fig. 3, in the slurry having a pH of about 11, the surfaces of both the alumina particles and the silicon carbide particles are negatively charged (the zeta potential is negative), and therefore they repel each other in the slurry system.

As a result, as shown in fig. 5, when the dispersion medium is removed in the step (c) of forming the molded article, different types of particles are difficult to be uniformly mixed with each other and the same type of particles are likely to aggregate with each other.

As a result, in the step (d) of sintering, the alumina particles are easily sintered so as to exclude the silicon carbide particles from each other.

Therefore, as shown in fig. 6, in the obtained composite sintered body, many of the crystal grains of silicon carbide exist in the grain boundary so as to be excluded from the crystal grains of alumina. Further, the crystal grains of silicon carbide existing in the crystal grains of alumina tend to grow large, and the number of particles also tends to decrease.

Next, a step of adjusting pH will be described.

On the other hand, fig. 7 is a schematic view showing a state after the slurry of fig. 4 is adjusted from pH11 to pH about 6.5, for example. FIGS. 7 to 9 are views corresponding to FIGS. 4 to 6, respectively.

As shown in fig. 7, in the slurry having a ph of about 6.5, the surfaces of the alumina particles were positively charged (the zeta potential was a positive value), and the surfaces of the silicon carbide particles were negatively charged (the zeta potential was a negative value).

Therefore, the silicon carbide particles, which are relatively small particles, are heterogeneously aggregated in the slurry system, and the surfaces of the alumina particles, which are relatively large particles, are attached.

On the other hand, in the method for producing a composite sintered body according to the present embodiment, when the zeta potential of the silicon carbide particles is reduced by adjusting the pH of the slurry to about 6.5, the possibility of the silicon carbide particles agglomerating with each other (homogeneous agglomeration) also increases.

In contrast, as described above, when the silicon carbide particles to be used are pre-oxidized, the dispersibility of the silicon carbide particles is improved. Therefore, when the silicon carbide particles subjected to the pre-oxidation treatment are used, homogeneous aggregation of the silicon carbide particles can be suppressed, and the heterogeneous aggregation can be preferentially promoted. Thereby, a desired aggregated state is easily obtained.

As shown in fig. 8, when the dispersion medium is removed in the step (c) of forming a molded body, alumina having silicon carbide attached to the surface thereof is aggregated, and thus different types of particles are easily and uniformly mixed with each other. As a result, in the step (d) of sintering, the alumina particles are easily sintered together while being taken into the silicon carbide particles.

Therefore, as shown in fig. 9, in the obtained composite sintered body, alumina grows while taking in a large amount of crystal grains of silicon carbide. Therefore, the amount of crystal grains of silicon carbide present in the grain boundaries of alumina is reduced. In addition, in the alumina crystal grains, the crystal grains of silicon carbide are also likely to be small, and the number of particles is also likely to increase.

When the crystal grains of the alumina particles during sintering grow, the silicon carbide having relatively large crystal grains also moves along with the movement of the alumina particles (grain boundaries). With this movement, the probability of the silicon carbide having large crystal grains coming into contact with the crystal grains of another silicon carbide increases, and the crystal grains are likely to grow.

On the other hand, even if the alumina particles move, it is difficult for silicon carbide having relatively small crystal grains to follow the movement. Therefore, silicon carbide having small crystal grains is easily taken into the grain boundary of alumina while maintaining the small crystal grains.

As a result, the 2 nd crystal grains existing in the grains are often smaller than the 3 rd crystal grains 130 existing in the grain boundaries.

In this manner, the composite sintered body of the present embodiment can be manufactured.

The obtained composite sintered body can be formed into a desired base body by grinding in a subsequent step. The projections formed on the mounting surface of the base can be formed by a known method.

The composite sintered body as described above has excellent soaking properties.

Further, the electrostatic chuck section and the electrostatic chuck apparatus using the composite sintered body have high performance that are excellent in heat uniformity and can realize high processing accuracy when applied to a processing apparatus.

While the preferred embodiments of the present invention have been described above with reference to the drawings, it goes without saying that the present invention is not limited to these examples. The various shapes, combinations, and the like of the respective constituent members shown in the above examples are examples, and various modifications can be made in accordance with design requirements and the like without departing from the spirit of the present invention.