Ceramic components

Abstract

To provide a ceramic component with a low coefficient of thermal expansion, high strength, and excellent electrical properties. [Solution] A sintered body having a Si3N4 content of 88.0% by mass or more, a sintering aid content of 5.0 to 12.0% by mass, an impurity element content of 1000 ppm or less, and a number density of Si3N4 particles with a short axis diameter exceeding 1.5 μm of 1.05 particles / 100 μm 2 A ceramic component having the following characteristics: apparent porosity of less than 0.10% and pore ratio of less than 0.70%.

Description

[Technical Field]

[0001] This invention relates to ceramic members. [Background technology]

[0002] Integrated circuits are manufactured by irradiating silicon wafers with light, such as ultraviolet light, to form fine circuit patterns. When light is irradiated, the silicon wafer is held in a support called an electrostatic chuck. The electrostatic chuck is charged by applying a voltage through its electrodes, and then electrostatically attracts and holds the silicon wafer.

[0003] Patent Document 1 discloses an electrostatic checker made of a sintered body mainly composed of silicon nitride. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-220012 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, with the miniaturization and increased integration of integrated circuits, there has been a demand to form extremely fine and complex circuit patterns on silicon wafers. Therefore, when forming these circuit patterns, if the electrostatic chuck holding the silicon wafer expands and contracts due to temperature changes, it can result in misalignment of the patterns. In other words, the ceramic components used in electrostatic chucks must have a low coefficient of thermal expansion.

[0006] Furthermore, in order to electrostatically attract a silicon wafer to the electrostatic chuck, it is preferable to keep the distance between the electrode and the silicon wafer short. For this reason, the electrostatic chuck, which is placed between the electrode and the silicon wafer, is molded to be extremely thin. Even in such cases, high strength is required for the ceramic components used in the electrostatic chuck to prevent cracking or other damage.

[0007] For example, the invention described in Patent Document 1 has insufficient strength and does not take thermal expansion into consideration at all. Furthermore, the ceramic component used in the electrostatic chuck is also required to have excellent electrical properties in order to electrostatically attract silicon wafers.

[0008] The present invention aims to solve the above problems and provide a ceramic member that has a low coefficient of thermal expansion, high strength, and excellent electrical properties. [Means for solving the problem]

[0009] The present invention is essentially based on the following ceramic components.

[0010] (1) A sintered body having a Si3N4 content of 88.0% by mass or more. The sintering aid content is 5.0 to 12.0% by mass. The content of impurity elements is 1000 ppm or less. The number density of the Si3N4 particles with a minor axis diameter exceeding 1.5 μm is 1.05 particles / 100 μm 2 The following: The apparent porosity is less than 0.10%. The pore rate is less than 0.70%. Ceramic components.

[0011] (2) The bending strength is 1200 MPa or more. The ceramic member described in (1) above.

[0012] (3) The strength at which the probability of failure is 0.1% is 800 MPa or more. The ceramic member described in (1) above.

[0013] (4) The thermal expansion coefficient is 2.0×10 -6 / °C or less, the ceramic member according to (1) above.

[0014] (5) The volume resistivity at room temperature is 1.0×10 16 Ω·cm or more, the ceramic member according to (1) above.

[0015] (6) The minimum value of the volume resistivity from room temperature to 200°C is 1.0×10 15 Ω·cm or more, the ceramic member according to (1) above.

[0016] (7) The breakdown strength when an AC voltage is applied is 14.0 kV / mm or more, and the breakdown strength when a DC voltage is applied is 60.0 kV / mm or more, the ceramic member according to (1) above.

[0017] (8) The ceramic member according to (1) to (7) above, which is used as an electrostatic chuck.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a ceramic member having high strength, excellent electrical properties, and a low thermal expansion coefficient.

Embodiments for Carrying Out the Invention

[0019] Examples of the material of the ceramic member used for the electrostatic chuck include aluminum nitride, alumina, resin, etc. However, since these materials have a high thermal expansion coefficient, they are not suitable as the material of the electrostatic chuck used when forming an extremely fine and complex circuit pattern as described above. Therefore, it is conceivable to use Si3N4 having a low thermal expansion coefficient and high strength, but in the conventional ceramic member containing Si3N4, the thermal expansion coefficient, strength, and electrical properties were insufficient.

[0020] The inventors of this invention conducted a detailed investigation into the reasons why conventional ceramic components had insufficient thermal expansion coefficient, strength, and electrical properties. As a result, they found that sintering aids, which are essential components for sintering Si3N4, act as fracture initiation points, reducing the strength of the ceramic components. They also found that sintering aids increase the thermal expansion coefficient of the ceramic components and further reduce their electrical properties. This is because sintering aids often have a high thermal expansion coefficient and low volume resistivity. Furthermore, they found that when Si3N4 contains many impurity elements, the electrical properties of the ceramic components are reduced. Therefore, they found that reducing the content of sintering aids and impurity elements is effective in keeping the thermal expansion coefficient low and improving strength and electrical properties.

[0021] However, simply reducing the content of sintering aids results in insufficient sintering. This leads to ceramic components with many voids. As a result, these voids become the starting points for fracture, reducing the strength of the ceramic components. Furthermore, since Si3N4 and voids have different electrical properties, the presence of many voids degrades the electrical properties of the ceramic components.

[0022] Therefore, we further investigated methods to reduce the amount of sintering aid, reduce voids, keep the thermal expansion coefficient of the ceramic component low, and improve its strength and electrical properties. As a result, we found that reducing the particle size of the raw material, Si3N4, was effective. Specifically, we found that reducing the number of particles with a large short axis diameter was effective.

[0023] By reducing the particle size of Si3N4 particles, the surface area of ​​the Si3N4 particles increases, and the surface free energy increases. As a result, even if the amount of sintering aid is reduced, a force acts between the Si3N4 particles to reduce the surface area, causing the Si3N4 particles to aggregate and sintering to proceed more easily. In this way, by creating a dense sintered body, the thermal expansion coefficient of the ceramic component can be kept low, and the strength and electrical properties can be improved, even if the amount of sintering aid is reduced.

[0024] In this invention, "strength" refers to the bending strength and the strength when the probability of failure is 0.1%. "Electrical properties" refers to the volume resistivity and the dielectric breakdown strength.

[0025] This invention is based on the above findings. The requirements of this invention will be described in detail below. In the following description, "%" in relation to content refers to "mass%".

[0026] <Composition of ceramic components> 1. Si3N4 content In the ceramic member according to the present invention, the Si3N4 content is 88.0% or more. In the ceramic member according to the present invention, it is preferable that the total content of Si3N4 and sintering aid be 100%. Therefore, if the Si3N4 content is less than 88.0%, the content of sintering aid increases, and sufficient strength cannot be obtained as a ceramic member. In addition, the coefficient of thermal expansion increases, and the electrical properties also decrease. The Si3N4 content is preferably 90.0% or more, and more preferably 92.0% or more. Furthermore, there is no particular upper limit to the Si3N4 content, but in relation to the inclusion of 5% or more of sintering aid, the upper limit of the Si3N4 content is 95.0%.

[0027] The Si3N4 content is determined by the following method: At any point in a region of the ceramic material's surface with minimal irregularities, the amount of Si is determined using an ICP (Inductively Coupled Plasma) emission spectrometer, and this is converted to the Si3N4 content in terms of nitride content.

[0028] 2. Content of sintering aid In the ceramic member according to the present invention, the content of the sintering aid is 5.0 to 12.0%. The sintering aid has the effect of promoting the sintering of Si3N4. However, if the content of the sintering aid is excessive, grain growth is promoted and coarse grains are formed, and the number density of coarse particles, as described later, increases. Also, as mentioned above, if the content of the sintering aid is excessive, the thermal expansion coefficient of the ceramic member increases, and the strength and electrical properties decrease. For this reason, the content of the sintering aid is set to 5.0 to 12.0%. The content of the sintering aid is preferably 6.0% or more, and more preferably 7.0% or more. Furthermore, the content of the sintering aid is preferably 10.0% or less, and more preferably 8.0% or less.

[0029] Examples of sintering aids include Y2O3, Al2O3, MgO, ZrO2, TiO2, and MoO3. The "content of sintering aids" mentioned above refers to the total content of these oxides. Furthermore, the sintering aid is one or more selected from Y2O3, Al2O3, MgO, ZrO2, TiO2, and MoO3.

[0030] The content of sintering aids is measured by the following method: At any point on the surface of the ceramic member in a region with few irregularities, the amounts of Y, Al, Mg, Zr, Ti, Mo, etc. are identified using an ICP emission spectrometer, and these are converted to oxide content, representing the content of Y2O3, Al2O3, MgO, ZrO2, TiO2, and MoO3, respectively.

[0031] 3. Content of impurity elements In the ceramic member according to the present invention, the content of impurity elements is 1000 ppm or less. If the content of impurity elements exceeds 1000 ppm, the electrical properties deteriorate. The content of impurity elements is preferably 800 ppm or less, and more preferably 500 ppm or less. In this invention, impurity elements are elements other than Si, N, and elements that constitute the sintering aid.

[0032] Among the impurity elements, the Fe content is preferably less than 100 ppm. By keeping the Fe content below 100 ppm, the electrical properties can be improved. The lower the Fe content, the better; 80 ppm or less is more preferable, and 60 ppm or less is even more preferable.

[0033] Furthermore, among the impurity elements, the Ca content is preferably less than 100 ppm. By keeping the Ca content below 100 ppm, the electrical properties can be improved. The lower the Ca content, the better; 80 ppm or less is more preferable, and 60 ppm or less is even more preferable.

[0034] The content of impurity elements, Fe content, and Ca content in the ceramic component is determined by glow discharge mass spectrometry (GDMS) at any point on the surface of the ceramic component in a region with minimal irregularities.

[0035] <Number density of coarse particles> In the ceramic member according to the present invention, the number density of Si3N4 particles with a short axis diameter greater than 1.5 μm (hereinafter also referred to as "coarse particles") is 1.05 particles / 100 μm 2 The following is the reason: When the short axis diameter of Si3N4 particles exceeds 1.5 μm, it becomes the starting point for fracture. Therefore, we focus on Si3N4 particles with a short axis diameter exceeding 1.5 μm and reduce their number density. The number density of coarse particles is 1.05 particles / 100 μm. 2 In the ultra-high density, the intensity decreases. The number density of coarse particles is 0.80 particles / 100 μm 2 The following is preferable: 0.60 particles / 100 μm 2 The following are preferable.

[0036] The number of coarse particles is measured as follows. First, the surface of the ceramic member is polished until the arithmetic mean roughness Ra becomes 0.01 μm or less. The definition of the arithmetic mean roughness Ra is as described in JIS B 0601:2013. Next, using an electron microscope, a field of view of 19 μm in length × 25 μm in width (hereinafter also referred to as the "observation field of view") on the polished surface is observed at a magnification of 5000 times. Then, from the backscattered electron image, among the Si3N4 particles, particles with a minor axis diameter exceeding 1.5 μm are identified, the number of coarse particles is counted, and the number density is obtained by dividing by the area of the observation field of view. In the present invention, "the number density of coarse particles is 1.05 particles / 100 μm 2 or less" means that the number of coarse particles in the observation field of view is 5 or less.

[0037] In addition, when there are particles in the observation field of view where only a part of what seems to be coarse particles can be observed, and it can be determined that the minor axis diameter of the particle exceeds 1.5 μm, the particle is counted as 1 coarse particle. On the other hand, when it cannot be determined that the minor axis diameter of the particle exceeds 1.5 μm, the particle shall not be counted as a coarse particle.

[0038] <Apparent porosity> In the ceramic member according to the present invention, the apparent porosity is less than 0.10%. When the apparent porosity is 0.10% or more, the strength and electrical properties deteriorate. The apparent porosity is preferably 0.08% or less, more preferably 0.06% or less, and even more preferably 0.04% or less, or 0.02% or less.

[0039] The apparent porosity is measured and calculated by an apparent porosity test in accordance with JIS C 2141:1992. The apparent porosity is calculated from the dry mass m1, the underwater mass m2 of the saturated water test piece in a vacuum container, and the mass m3 of the saturated water test piece.

[0040] <Pore ratio> In the ceramic member according to the present invention, the pore ratio is less than 0.70%. If the pore ratio is 0.70% or higher, the strength and electrical properties decrease. A pore ratio of 0.60% or less is preferred, and 0.50% or less is more preferred.

[0041] The pore ratio is measured by the following method. First, the surface of the ceramic component is mirror-polished until the arithmetic mean roughness Ra is 0.01 μm or less. The definition of arithmetic mean roughness Ra is as described in JIS B 0601:2013. Next, using a microscope manufactured by Keyence Corporation, at a magnification of 500x, an area including at least 290 μm × 370 μm and 56316 μm is measured. 2 The field of view is observed. The obtained observation images are analyzed using WinROOF manufactured by Mitani Corporation. The area of ​​the parts recognized as recesses (parts displayed in black) is calculated and divided by the field of view area to determine the pore ratio.

[0042] <Bulk density> In the ceramic member according to the present invention, the bulk density is 3.20 g / cm³. 3 The above is preferable. Bulk density of 3.20 g / cm³ 3 By following these specifications, strength and dielectric breakdown strength can be ensured. The bulk density is 3.22 g / cm³. 3 The above is preferable.

[0043] Bulk density is measured and calculated by bulk density testing in accordance with JIS C 2141:1992. The bulk density is calculated from the dry mass m1, the water mass m2 of the saturated specimen in a vacuum container, and the mass m3 of the saturated specimen.

[0044] <Characteristics> 1. Bending strength In the ceramic member according to the present invention, a bending strength of 1200 MPa or more is considered to be high strength. A bending strength of 1300 MPa or more is preferable, and 1400 MPa or more is more preferable. There is no particular upper limit to the bending strength, but in a ceramic member that satisfies the requirements of the present invention, the bending strength will be 1800 MPa or less, or 1600 MPa or less.

[0045] The bending strength is measured by the following method. First, a rod-shaped test piece measuring 40 mm in length, 4 mm in width, and 3 mm in thickness is taken from the ceramic member. Then, the bending strength is measured at three points at room temperature in accordance with JIS R 1601:2008 and is used as the bending strength. In this invention, "room temperature" means 25°C.

[0046] 2. Strength when the probability of failure is 0.1% In the ceramic member according to the present invention, if the strength at which the probability of failure is 0.1% (hereinafter also referred to as "0.1% failure probability strength") is 800 MPa or higher, it is judged to be high strength. The 0.1% failure probability strength is preferably 850 MPa or higher, and more preferably 900 MPa or higher. There is no particular upper limit to the 0.1% failure probability strength, but in a ceramic member that satisfies the requirements of the present invention, the 0.1% failure probability strength will be 1100 MPa or less, or 1000 MPa or less.

[0047] The 0.1% failure probability strength is measured by the following method. First, the bending strength is measured 30 times using the method described above, and a Weibull plot is created using the saturation method according to JIS R 1625:2010 using this data. Then, the bending strength at which the failure probability is 0.1% is read from the Weibull plot and defined as the 0.1% failure probability strength.

[0048] 3. Coefficient of thermal expansion In the ceramic member according to the present invention, the coefficient of thermal expansion is 2.0 × 10 -6 If the temperature is below / ℃, it is considered that the coefficient of thermal expansion is low. The coefficient of thermal expansion is 1.8 × 10⁻⁶. -6 A temperature of 10°C or less is preferred. While there is no particular lower limit to the coefficient of thermal expansion, for ceramic members satisfying the requirements of the present invention, the coefficient of thermal expansion is 1.3 × 10°C. -6 / ℃ or higher, or 1.5 × 10 -6 The temperature will be above / ℃.

[0049] The coefficient of thermal expansion is measured by the following method: A test specimen is placed in a constant temperature bath, and the temperature of the bath is changed from room temperature to 200°C at a heating rate of 5°C / min. The change in the length of the test specimen is measured using a thermal expander. The linear expansion coefficient is then calculated using the formula in accordance with JIS R 3251:1995, and this is used as the coefficient of thermal expansion.

[0050] 4. Volume resistivity In the ceramic member according to the present invention, the volume resistivity at room temperature is 1.0 × 10⁻⁶ 16 If the resistivity is Ω·cm or higher, it is considered to have excellent electrical properties. The volume resistivity at room temperature is 2.0 × 10⁻⁶. 16 Preferably Ω·cm or larger, 3.0 × 10 16 A value of Ω·cm or higher is more preferable. The upper limit of the volume resistivity at room temperature is not particularly limited, but for a ceramic member that satisfies the requirements of the present invention, it is 6.0 × 10⁻⁶. 16 Ω·cm, or 5.0 × 10⁻⁶ 16 It becomes Ω·cm.

[0051] In the ceramic member according to the present invention, the minimum value of the volume resistivity from room temperature to 200°C is 1.0 × 10⁻⁶. 15 A value of Ω·cm or higher indicates excellent electrical properties. The minimum volume resistivity from room temperature to 200°C is 2.0 × 10⁻⁶. 15 Preferably Ω·cm or larger, 3.0 × 10 15 A value of Ω·cm or higher is more preferable. The upper limit of the minimum volume resistivity from room temperature to 200°C is not particularly limited, but for a ceramic member that satisfies the requirements of the present invention, it is 6.0 × 10⁻⁶. 15 Ω·cm, or 5.0 × 10⁻⁶ 15 It becomes Ω·cm.

[0052] Volume resistivity is measured by the following method: Based on JIS C 2141:1992, the test specimen is placed in an electric furnace, and the temperature inside the furnace is increased from room temperature to 200°C at a rate of 5°C / min while the volume resistance is measured using a high insulation resistance meter. Then, the volume resistivity at each temperature is determined using the formula in accordance with JIS C 2141:1992.

[0053] 5. Dielectric breakdown strength In the ceramic member according to the present invention, if the dielectric breakdown strength when an AC voltage is applied is 14.0 kV / mm or more, and the dielectric breakdown strength when a DC voltage is applied is 60.0 kV / mm or more, it is determined that the member has excellent electrical properties.

[0054] The dielectric breakdown strength is measured by the following methods: The dielectric breakdown strength due to AC voltage application is measured by a short-time test in accordance with JIS C 2110-1:2016. The voltage boosting rate is 1 kV / s, and the dimensions of the test specimen are 50 mm x 50 mm with a thickness of 1.0 mm. The dielectric breakdown strength due to DC voltage application is measured by a short-time test in accordance with JIS C 2110-2:2016. The voltage boosting rate is 1 kV / s, and the dimensions of the test specimen are 50 mm x 50 mm with a thickness of 1.0 mm.

[0055] <Application> The ceramic member according to the present invention is suitable for applications such as electrostatic chucks and probe guide components because it has excellent thermal expansion coefficient, strength, and electrical properties. In particular, the ceramic member according to the present invention is suitable for use as a Coulomb force type electrostatic chuck.

[0056] <Shape and dimensions of ceramic components> The shape of the ceramic member according to the present invention is not particularly limited. When used as an electrostatic chuck or probe guide component, it is preferable to have a plate shape. Furthermore, the dimensions of the ceramic member according to the present invention are not particularly limited. When used as an electrostatic chuck or probe guide component, the plate thickness is preferably 0.1 to 1.0 mm.

[0057] <Manufacturing method> The ceramic component according to the present invention can be stably manufactured by the following method.

[0058] 1. Granulation process Si3N4, a sintering aid, and a solvent are mixed using a known method such as a ball mill. Specifically, the Si3N4, sintering aid, and solvent are mixed in a container with grinding balls to form a slurry. At this time, the slurry is prepared so that when the total mass of Si3N4 and sintering aid is taken as 100%, the Si3N4 content is 88.0% or more and the sintering aid content is 12.0% or less. Water or alcohol can be used as the solvent. Furthermore, additives such as dispersants and binders may be used as needed.

[0059] As for Si3N4, we use Si3N4 produced by the imide decomposition method and in which 95% or more is α phase. Si3N4 contains both α and β phases, and when Si3N4 containing a large amount of β phase is used for sintering, grain growth is easily achieved with the β phase as seed crystals. Furthermore, grain growth makes densification difficult, resulting in many voids in the ceramic component. For this reason, the proportion of α phase in Si3N4 is set to 95% or more. In addition, while methods for producing Si3N4 include the imide decomposition method, direct nitriding, and reductive nitriding, this invention uses Si3N4 produced by the imide decomposition method. This is because the imide decomposition method can reduce the content of impurity elements compared to other production methods. Also, compared to other production methods, Si3N4 produced by the imide decomposition method has the least amount of β phase, which suppresses grain growth during the sintering process.

[0060] Examples of sintering aids include Y2O3, Al2O3, MgO, ZrO2, TiO2, and H2MoO4. Examples of dispersants include quaternary ammonium salts. Examples of binders include polyvinyl alcohol (PVA).

[0061] The type of ball used for grinding shall be made of zirconia. Using zirconia balls may result in the incorporation of ZrO2 into the ceramic component, potentially reducing its purity. Therefore, balls made of nylon, silicon nitride, or alumina are typically used in the manufacture of ceramic components. However, these balls have weak grinding power and cannot sufficiently finely pulverize Si3N4 and reduce the number density of coarse particles as required by this invention. Furthermore, when using the ceramic component of this invention for the aforementioned applications, the presence of ZrO2 as an impurity is not a problem, and even if present, the amount is so small that it is unlikely to degrade the properties of the ceramic component of this invention. Moreover, by preparing the slurry using zirconia balls, the sintering aid can also be finely and uniformly dispersed, allowing for a dense sintered body even with a reduced sintering aid content. For this reason, zirconia balls are used as the grinding balls.

[0062] The obtained slurry is granulated by spray drying with a spray dryer, or powdered by drying with a vacuum evaporator. The resulting granules or powder are hereinafter referred to as mixed powder.

[0063] 2. Sintering process If a dispersant and / or binder is used, the mixed powder may be degreased. The degreasing step is performed to remove organic binders contained in the mixed powder and can be carried out by known methods, such as heating the mixed powder. For example, the degreasing step of the mixed powder is preferably carried out in air, vacuum, or in an inert gas atmosphere. Vacuum means that the pressure is in the range of 0 Pa to 1000 Pa. Examples of an inert gas atmosphere include a nitrogen gas atmosphere or a noble gas atmosphere such as helium, neon, or argon.

[0064] The temperature for degreasing the mixed powder should be set according to the type and amount of organic binder contained in the mixed powder, for example, 300°C or higher, 500°C or higher, or 600°C or higher. Alternatively, the temperature for degreasing the mixed powder should usually be 1000°C or lower, or 900°C or lower. The holding time at the above temperature should be, for example, 12 hours or more, 24 hours or more, or 36 hours or more. Alternatively, the holding time at the above temperature should be 84 hours or less, 72 hours or less, or 60 hours or less.

[0065] A mixed powder is filled into a jig of the desired shape and sintered by a hot press method under high temperature and pressure to obtain a ceramic component. Sintering by methods other than the hot press method, such as atmospheric pressure firing, results in many voids and grain growth. Sintering by the hot press method allows for the production of a dense sintered body. Sintering is performed in a nitrogen atmosphere, and the firing temperature is in the range of 1400 to 1800°C. If the firing temperature is below 1400°C, the mixed powder cannot be sufficiently sintered. On the other hand, if the sintering temperature exceeds 1800°C, Si3N4 grains grow, and the number density of coarse particles increases. Furthermore, the problem of oxide components leaching out and the liquid phase adhering to jigs, equipment, etc., can be suppressed. If the pressing force is less than 10 MPa or the pressing duration exceeds 5 hours, Si3N4 grains grow, and the number density of coarse particles increases. Therefore, the pressing force should be 10 MPa or more, and the pressing duration should be 5 hours or less. Furthermore, the lower limit of the applied pressure duration should be at least one hour to ensure sufficient sintering of the mixed powder. While there is no specific upper limit to the applied pressure, it should be kept below 50 MPa.

[0066] In this way, the ceramic member according to the present invention can be obtained. Furthermore, when used as an electrostatic chuck or probe guide component, the ceramic member may be subjected to cutting, grinding, polishing, or other processing.

[0067] The ceramic members according to the present invention will be described in more detail below with reference to examples, but the embodiments are not limited to these examples. [Examples]

[0068] Si3N4 produced by the manufacturing method shown in Table 1 and a sintering aid were mixed together with zirconia balls, and the resulting slurry was spray-dried with a spray dryer to form granules. After degreasing by a known method, the obtained granules were filled into a graphite die, and hot press sintering was performed at 1750 °C and 30 MPa in a nitrogen atmosphere to obtain plate-shaped test specimens (Test Nos. A1 to A6 and B1 to B6) with a length of 250 mm × width of 250 mm × thickness of 30 mm.

[0069] Here, the Si3N4 produced by the imide decomposition method had an α-phase content of 95% or more. Also, the Si3N4 produced by the direct nitridation method had an α-phase content of less than 95%. In Test No. B2, a high purity grade Si3N4 with an α-phase content of less than 95% produced by the direct nitridation method was used.

[0070] In Test No. B1, it was produced by the atmospheric pressure sintering method, and in Test No. B3, the hot press sintering temperature was 1850 °C and the applied pressure was 5 MPa.

[0071] Using the obtained test specimens, the content of Si3N4, the content of the sintering aid, and the content of impurity elements were measured as follows.

[0072] <Content of Si3N4> The content of Si3N4 was specified by the following method. At an arbitrary point in a region with few irregularities on the surface of the test specimen, the amount of Si was specified using an ICP emission spectroscopic analyzer, and the content of Si3N4 was obtained by converting it to nitride.

[0073] <Content of sintering aid> The content of the sintering aid was measured by the following method. At an arbitrary point in a region with few irregularities on the surface of the test specimen, the amounts of Y, Al, Mg, Zr, Ti, Mo, etc. were specified using an ICP emission spectroscopic analyzer, and the contents of Y2O3, Al2O3, MgO, ZrO2, TiO2, and MoO3 were obtained by converting them to oxides.

[0074] <Content of impurity elements> The content of impurity elements, Fe content, and Ca content in the test material was determined by GDMS at an arbitrary point on the surface of the test material in a region with minimal irregularities.

[0075] Table 1 shows the measurement results for the Si3N4 content, sintering aid content, and impurity element content of each test material.

[0076] [Table 1]

[0077] Furthermore, the number density, pore ratio, apparent porosity, bulk density, flexural strength, 0.1% fracture probability strength, volume resistivity, dielectric breakdown strength, and thermal expansion coefficient of the coarse particles were measured as follows.

[0078] <Number density of coarse particles> The number of coarse particles was measured as follows. First, the surface of the test material was polished until the arithmetic mean roughness Ra was 0.01 μm or less. The definition of arithmetic mean roughness Ra is as described in JIS B 0601:2013. Next, an electron microscope was used to observe a 19 μm x 25 μm field of view on the polished surface at a magnification of 5000x. Then, from the backscattered electron image, particles with a short axis diameter greater than 1.5 μm among the Si3N4 particles were identified, the number of coarse particles was counted, and the number density was calculated by dividing by the area of ​​the observation field of view.

[0079] Furthermore, if only a portion of what appeared to be a coarse particle was observed within the field of view, and it was determined that the short axis diameter of that particle was greater than 1.5 μm, then that particle was counted as one coarse particle. On the other hand, if it was not determined that the short axis diameter of that particle was greater than 1.5 μm, then that particle was not counted as a coarse particle.

[0080] <Pore rate> The pore ratio was measured using the following method. First, the surface of the test material was mirror-polished until the arithmetic mean roughness Ra was 0.01 μm or less. The definition of arithmetic mean roughness Ra is as described in JIS B 0601:2013. Next, using a microscope manufactured by Keyence Corporation, the surface was measured at 500x magnification, including an area of ​​290 μm × 370 μm and 56316 μm. 2 The field of view was observed. The obtained observation images were analyzed using WinROOF manufactured by Mitani Corporation. The area of ​​the parts recognized as recesses (parts displayed in black) was calculated and the pore ratio was determined by dividing it by the field of view area.

[0081] <Apparent porosity> The apparent porosity was measured and calculated by an apparent porosity test in accordance with JIS C 2141:1992. The apparent porosity was calculated from the dry mass m1, the water mass m2 of the saturated specimen in a vacuum container, and the mass m3 of the saturated specimen.

[0082] <Bulk density> The bulk density was measured and calculated by a bulk density test in accordance with JIS C 2141:1992. The bulk density was calculated from the dry mass m1, the water mass m2 of the saturated test specimen in a vacuum container, and the mass m3 of the saturated test specimen.

[0083] <Bending strength> The bending strength was measured using the following method. First, a rod-shaped test specimen measuring 40 mm in length, 4 mm in width, and 3 mm in thickness was taken from the test material. Then, the bending strength was measured at three points at room temperature according to JIS R 1601:2008 and was used as the bending strength.

[0084] <0.1% probability of failure intensity> The 0.1% fracture probability strength was measured using the following method. First, the bending strength was measured 30 times using the method described above. Using this data, a Weibull plot was created using the saturation method in accordance with JIS R 1625:2010. Then, the bending strength at which the fracture probability was 0.1% was read from the Weibull plot and defined as the 0.1% fracture probability strength.

[0085] <Volume resistivity> The volume resistivity was measured using the following method. Based on JIS C 2141:1992, a test specimen was placed in an electric furnace, and the temperature inside the furnace was increased from room temperature to 200°C at a rate of 5°C / min. The volume resistivity was then measured using a high-insulation resistance meter. The volume resistivity at each temperature was then determined based on JIS C 2141:1992.

[0086] <Dielectric breakdown strength> The dielectric breakdown strength was measured using the following methods. The dielectric breakdown strength under AC voltage application was measured by a short-time test in accordance with JIS C 2110-1:2016. The voltage boosting rate was 1 kV / s, and the test specimen dimensions were 50 mm × 50 mm with a thickness of 1.0 mm. The dielectric breakdown strength under DC voltage application was measured by a short-time test in accordance with JIS C 2110-2:2016. The voltage boosting rate was 1 kV / s, and the test specimen dimensions were 50 mm × 50 mm with a thickness of 1.0 mm.

[0087] <Coefficient of thermal expansion> The coefficient of thermal expansion was measured using the following method: A test specimen was placed in a constant temperature bath, and the temperature of the bath was increased from room temperature to 200°C at a heating rate of 5°C / min. The change in the length of the test specimen was measured using a thermal expander. The linear coefficient of thermal expansion was then calculated using the formula in accordance with JIS R 3251:1995, and this was used as the coefficient of thermal expansion.

[0088] Table 2 shows the measured results for the number density of coarse particles, pore ratio, apparent porosity, bulk density, flexural strength, 0.1% fracture probability strength, volume resistivity, dielectric breakdown strength, and thermal expansion coefficient of each test specimen.

[0089] [Table 2]

[0090] As shown in Table 2, in Tests A1 to A6, which satisfied all the provisions of the present invention, low thermal expansion coefficient, high strength, and excellent electrical properties were obtained. In contrast, in Test No. B1, since Si3N4 manufactured by direct nitriding was used, the content of impurity elements was high and it contained a large amount of β phase which is prone to grain growth. In addition, because it was sintered by atmospheric pressure firing, the number density of coarse particles and the pore ratio were high. As a result, the strength and electrical properties deteriorated. In Test No. B2, although the Fe content was within a favorable range because it was a high-purity grade Si3N4, the total content of impurity elements was high because Si3N4 manufactured by direct nitriding was used. In addition, because it contained a large amount of β phase which is prone to grain growth, the number density of coarse particles and the pore ratio were high. As a result, the strength and electrical properties deteriorated.

[0091] In Test No. B3, the hot-press firing conditions exceeded the preferred range, resulting in a high number density of coarse particles. Consequently, the strength decreased. In Test No. B4, Si3N4 manufactured by direct nitriding was used, resulting in a high content of impurity elements. Therefore, the electrical properties deteriorated. In addition, because it contained a large amount of the β phase, which is prone to grain growth, the number density of coarse particles and the pore ratio increased. As a result, the strength and electrical properties deteriorated.

[0092] In test No. B5, the Si3N4 content was low and the sintering aid content was high. As a result, the number density of coarse particles was high, leading to insufficient strength, electrical properties, and thermal expansion coefficient. In test No. B6, the sintering aid content was low, resulting in high pore ratio and apparent porosity. As a result, strength and electrical properties deteriorated. [Industrial applicability]

[0093] According to the present invention, a ceramic member with a low coefficient of thermal expansion, high strength, and excellent electrical properties can be obtained.

Claims

1. Si ３ N ４ A sintered body having a content of 88.0% by mass or more, The sintering aid content is 5.0 to 12.0% by mass. The content of impurity elements is 1000 ppm or less. The Si having a minor axis diameter exceeding 1.5 μm ３ N ４ The number density of particles is 1.05 particles / 100 μm ２ The following: The apparent porosity is less than 0.10%. The pore rate is less than 0.70%. Ceramic components.

2. The bending strength is 1200 MPa or more. The ceramic member according to claim 1.

3. The strength at which the probability of failure is 0.1% is 800 MPa or higher. The ceramic member according to claim 1.

4. The coefficient of thermal expansion is 2.0 × 10⁻⁶. －６ It is below / ℃. The ceramic member according to claim 1.

5. The volume resistivity at room temperature is 1.0 × 10⁻⁶. １６ It is greater than or equal to Ω·cm. The ceramic member according to claim 1.

6. The minimum volume resistivity from room temperature to 200°C is 1.0 × 10⁻⁶. １５ It is greater than or equal to Ω·cm. The ceramic member according to claim 1.

7. The dielectric breakdown strength when an AC voltage is applied is 14.0 kV / mm or higher, and the dielectric breakdown strength when a DC voltage is applied is 60.0 kV / mm or higher. The ceramic member according to claim 1.

8. A ceramic member according to any one of claims 1 to 7, used as an electrostatic chuck.

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