Alumina sintered body and electrostatic chuck

Abstract

An alumina-based sintered body, which takes aluminum oxide (Al₂O₃) as a main component, wherein the content of magnesium oxide (MgO) relative to the content of aluminum oxide satisfies 0.00 mol%<MgO≤0.20 mol%, and the density of the alumina-based sintered body is 3.96 g / cm 3 or more, and the standard deviation of the grain size of the alumina grains is less than 4.0 μm.

Description

Technical Field

[0001] This invention relates to alumina sintered bodies and electrostatic chucks. Background Technology

[0002] In recent years, there has been a growing demand for semiconductor devices with large aspect ratios, particularly in the field of flash memory (such as 3D-NAND). Manufacturing these large aspect ratio semiconductor devices requires deep etching of silicon wafers, necessitating electrostatic chucks capable of applying high power. For components used in electrostatic chucks for high-power applications, a dense structure with minimal pores and high voltage withstand capability is required.

[0003] Typically, ceramics with alumina (Al2O3) as the main component are prone to abnormal particle growth during firing, and pores (voids) easily form near the abnormally grown grains. To address this, a technique has been proposed to improve voltage resistance by adding magnesium oxide (MgO) as a particle growth inhibitor (see, for example, Patent Document 1). Additionally, a technique has been proposed to improve the density of alumina sintered bodies by adjusting the content of components other than alumina (Al2O3) (see, for example, Patent Document 2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6373212

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-69889 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] However, even with the alumina sintered body described in Patent Document 1, its voltage resistance is sometimes insufficient for high-power applications. Therefore, further improvements in the voltage resistance of alumina sintered bodies are desired. Furthermore, while Patent Document 2 describes the density of the alumina sintered body, it does not mention the number or location of the pores. It should be noted that this issue is not limited to components for electrostatic chucks but is a common problem with alumina sintered bodies used in various semiconductor manufacturing apparatus components.

[0010] This invention was made to solve the above-mentioned problems, and its purpose is to provide a technique for improving the voltage resistance of alumina sintered bodies and a technique for reducing pores (voids) in alumina sintered bodies.

[0011] Solution for solving the problem

[0012] The present invention has been made to solve at least one of the above problems and can be implemented in the following aspects.

[0013] (1) According to one aspect of the present invention, there is provided an alumina-based sintered body, which takes alumina (Al2O3) as a main component, and the content of magnesium oxide (MgO) satisfies 0.00mol% < MgO ≤ 0.20mol% relative to the content of alumina. The density of the alumina-based sintered body is 3.96g / cm 3 or more, and the standard deviation of the particle size of alumina grains is less than 4.0 μm.

[0014] According to the alumina-based sintered body of this aspect, the standard deviation of the particle size of alumina grains is less than 4.0 μm, so the fluctuation of particle size is small, and the proportion of abnormal alumina grains is low. Therefore, among alumina-based sintered bodies with the same density, compared with those in which the standard deviation of the particle size of alumina grains is 4.0 μm or more, the number of pores can be reduced. That is, the alumina-based sintered body of this aspect has high density and few pores, so the compactness can be improved. In addition, by reducing the number of pores, the voltage resistance can be improved.

[0015] (2) In the alumina-based sintered body of the above aspect, the pore content can be 0.050 pores / μm 2 or less. In this way, an alumina-based sintered body with high voltage resistance can be obtained.

[0016] (3) In the alumina-based sintered body of the above aspect, when the aforementioned pores are divided into first pores belonging to pores existing at grain boundaries and second pores belonging to pores existing inside grains, the ratio of the content of the aforementioned second pores to the content of the aforementioned pores can be 20% or more. When using such an alumina-based sintered body in which the content of pores existing at grain boundaries is reduced, leakage current flowing through grain boundaries when an electric field is applied can be suppressed, so voltage resistance can be improved.

[0017] (4) In the alumina-based sintered body of the above aspect, the dielectric breakdown voltage can be 200kV / mm or more. Such high voltage resistance can be obtained, so the alumina-based sintered body can be used for, for example, electrostatic chucks that can be applied with high power.

[0018] (5) In the alumina-based sintered body of the above aspect, the surface roughness Sa of the surface irradiated with plasma for 40 minutes can be 50 nm or less. In this way, an alumina-based sintered body with high plasma resistance can be obtained. By applying the alumina-based sintered body with high plasma resistance to, for example, an electrostatic chuck, the reduction in air tightness and chucking force of the wafer mounting surface can be suppressed.

[0019] (6) According to another aspect of the present invention, an electrostatic chuck for holding an object is provided. The electrostatic chuck has: a plate-shaped member having a first surface for holding the object, a second surface belonging to the back surface of the first surface, and a chuck electrode formed in either the second surface or inside the first surface; and a base member disposed on the second surface side of the plate-shaped member and having a cooling function, wherein the first surface of the plate-shaped member is formed from an alumina sintered body described in technical solutions (1) to (5).

[0020] According to the electrostatic chuck of this scheme, the first surface of the plate-shaped member is formed of an alumina sintered body with few holes and high voltage resistance, thus providing an electrostatic chuck capable of applying high power.

[0021] (7) In the electrostatic chuck of the above-described scheme, the aforementioned plate-shaped member may have: a gas flow path that opens on the aforementioned first surface and introduces gas from the aforementioned second surface side; and a sealing strip that is continuously formed on the aforementioned first surface along the outer edge of the aforementioned plate-shaped member, wherein the opening of the aforementioned gas flow path is formed at a location further inward than the aforementioned sealing strip. In this way, the sealing performance of the gas (e.g., helium (He)) flowing in the gas flow path and released between the first surface of the plate-shaped member and the aforementioned object can be improved.

[0022] (8) According to another aspect of the present invention, an alumina sintered body is provided, which is mainly composed of alumina (Al2O3). The alumina sintered body has a porosity of 0.050 pores / μm. 2 In the following, when the aforementioned pores are divided into first pores belonging to pores existing at grain boundaries and second pores belonging to pores existing within grains, the ratio of the amount of the second pores to the amount of the aforementioned pores can be 20% or more. This can also reduce the number of pores (holes) and improve voltage withstand capability.

[0023] It should be noted that the present invention can be implemented in various ways, such as as a component for a semiconductor manufacturing apparatus, a semiconductor manufacturing apparatus, a holding device, an electrostatic chuck, and a device having the same, and a method for manufacturing a component for a semiconductor manufacturing apparatus. Attached Figure Description

[0024] Figure 1 A process diagram illustrating the manufacturing method of alumina sintered bodies.

[0025] Figure 2 This is an example of a cross-sectional STEM image of a sample.

[0026] Figure 3 This is an example of a cross-sectional STEM image of a sample.

[0027] Figure 4 To maintain the simplified cross-sectional diagram of the device.

[0028] Figure 5 is a top plan view of an apparatus.

[0029] Figure 6 is Figure 5 which is an enlarged schematic view of section A-A. DETAILED DESCRIPTION OF EMBODIMENTS

[0030] <First Embodiment>

[0031] The alumina sintered body according to the first embodiment of the present invention has alumina (Al₂O₃) as a main component, the content of magnesium oxide (MgO) satisfies 0.00 mol% < MgO ≤ 0.20 mol% relative to the content of alumina, and the density of the alumina sintered body is 3.96 g / cm 3 or more, and the standard deviation of the particle size of alumina grains is less than 4.0 µm. Here, "main component" refers to the component with the highest content proportion.

[0032] The content of magnesium oxide can be determined as follows. For the alumina sintered body, elemental analysis is performed by XRF (X-ray Fluorescence), and the amount of magnesium (Mg) is quantified. The magnesium amount obtained from the analysis result is converted to oxide to determine the content of magnesium oxide. Similarly, the amount of aluminum (Al) is quantified and converted to oxide, thereby determining the content of alumina. Then, the proportion of the amount (mol) of magnesium oxide relative to the amount (mol) of alumina is calculated.

[0033] In an alumina sintered body, adding magnesium oxide can inhibit abnormal grain growth of alumina grains.

[0034] The density of the alumina sintered body can be measured according to the Archimedes method (JIS R 1634).

[0035] The particle size of alumina grains in the alumina sintered body can be measured by the intercept method. Specifically, the fracture surface of the alumina sintered body is observed using a SEM (Scanning Electron Microscope), when a straight line of length L is drawn on the obtained secondary electron image, the number n of grains intersected by the straight line is measured. It should be noted that grains with both ends of the straight line located inside are counted as 0.5. Thereafter, the average particle diameter D (µm) is calculated according to the following formula (1).

[0036] D=1.5×L / n······(1)

[0037] In this embodiment, any number of parallel lines intersecting with the number of particles n is drawn, which is more than 100, and multiple average particle sizes D are calculated. The standard deviation is then calculated using the calculated multiple average particle sizes.

[0038] In this embodiment, the alumina sintered body preferably has a porosity of 0.050 pores / μm. 2 The following describes how reducing the number of holes improves withstand voltage. Furthermore, a smaller number of holes reduces the initiation point for plasma erosion, thus improving plasma resistance.

[0039] The number of pores can be counted visually using cross-sectional STEM (Scanning Transmission Electron Microscope) images. It should be noted that fracture surface SEM images can confirm the presence of pores. While fracture surface SEM images reveal the number of pores located at grain boundaries, they do not show the number of pores within the grains. Therefore, the total number of pores calculated using fracture surface SEM images will be higher. Thus, when the number of pores is low in fracture surface SEM images, cross-sectional STEM images are preferred for confirming the presence of pores.

[0040] In the alumina sintered body of this embodiment, it is preferable that the pores are divided into first pores belonging to grain boundaries and second pores belonging to grains, with the ratio of the amount of second pores to the amount of pores being 20% ​​or more. Pores existing at grain boundaries are considered to be channels for leakage current when an electric field is applied, and are considered to be the starting point of dielectric breakdown. Therefore, if an alumina sintered body with a reduced amount of pores existing at grain boundaries is used, leakage current flowing through the grain boundaries can be suppressed, and voltage withstand capability can be further improved. The amount of pores can be counted using a cross-sectional STEM image as described above.

[0041] In the alumina sintered body of this embodiment, the dielectric breakdown voltage is preferably 200 kV / mm or higher. This provides high withstand voltage, and therefore, it can be used, for example, in electrostatic chucks capable of applying high power. The dielectric breakdown voltage was measured according to JIS C2110 when dielectric breakdown occurred.

[0042] In this embodiment, the surface roughness Sa of the surface irradiated with plasma for 40 minutes can be less than 50 nm. This results in an alumina sintered body with high plasma resistance. By using this plasma-resistant alumina sintered body, for example, in an electrostatic chuck, the hermeticity of the wafer mounting surface and the reduction in chuck force can be suppressed.

[0043] Figure 1is a process diagram illustrating a method for producing an alumina-based sintered body. In the method for producing an alumina-based sintered body according to the present embodiment, first, a powder production step is performed: a predetermined amount of Al₂O₃ raw material and a MgO raw material are mixed in ethanol by a ball mill and dried (step P1). The addition amount of the MgO raw material satisfies 0.00 mol% < MgO ≤ 0.20 mol% relative to the Al₂O₃ raw material. Next, a firing step is performed: the mixed powder obtained in the powder production step (step P1) is molded using a hot pressing apparatus, and fired at a firing temperature of 1500°C or higher and 1700°C or lower (step P2), thereby producing the alumina-based sintered body. When the firing temperature is a high temperature exceeding 1700°C, the possibility of abnormal grain growth increases, and the possibility of causing a decrease in voltage resistance increases, therefore, the firing temperature is preferably 1500°C or higher and 1700°C or lower. The pressing pressure for hot pressing can be set arbitrarily. When the pressing pressure is a low pressure lower than 10 MPa, grains are not easily crushed during hot pressing, densification cannot be promoted, and there is a high possibility that air remains as pores in crystal boundaries, therefore, the pressing pressure is preferably 10 MPa or more and 40 MPa or less. It should be noted that the content of MgO in the alumina-based sintered body can be investigated by XRF and ICP emission analysis. By applying pressure during firing, hot pressing enables firing while crushing grains compared with atmospheric firing, therefore, densification can be promoted, and pores at crystal boundaries are easily reduced. In addition, since the contact area between grains also becomes larger, the sintering step itself can be completed in a shorter time compared with atmospheric firing.

[0044] According to the production method of the present embodiment, an alumina-based sintered body with fewer impurities and high voltage resistance can be obtained compared with the case where the alumina-based sintered body is produced by gel casting.

[0045] The alumina-based sintered body of the present embodiment can be used for components for semiconductor manufacturing apparatuses, semiconductor manufacturing apparatuses, holding devices, electrostatic chucks, and apparatuses provided with any of the above, etc.

[0046] Examples

[0047] The present invention will be further specifically described with reference to examples.

[0048] Samples 1 to 9 of alumina-based sintered bodies were used to evaluate voltage resistance and plasma resistance. Samples 1 to 5 and 8 are examples of the alumina-based sintered bodies according to the above embodiment, and samples 6, 7 and 9 are comparative examples of alumina-based sintered bodies.

[0049] Table 1 is a table showing specifications and evaluation results of samples 1 to 9. The evaluation method is described later.

[0050] [Table 1]

[0051]

[0052] 1. Sample preparation

[0053] Samples 1-5 and 8 were manufactured using the manufacturing method described in the above embodiments. Sample 6 was sintered at atmospheric pressure without hot pressing, but otherwise manufactured in the same manner as described in the above embodiments. Sample 7 was hot-pressed at a temperature exceeding 1700°C, but otherwise manufactured in the same manner as described in the above embodiments. Sample 9 was obtained by subjecting sample 6, sintered at atmospheric pressure, to HIP (Hot Isostatic Pressing) treatment at a pressure below 200 MPa. Even with HIP treatment, pores, especially grain boundary pores, can be reduced, thus improving voltage withstand capability.

[0054] Of samples 1 to 9, those with a purity of 99.9% or higher were used as alumina raw materials.

[0055] Magnesium oxide was added to the alumina raw material in the proportions listed in Table 1. Specifically, 0.10 mol% was added to samples 1-3, 5, and 7; 0.20 mol% was added to sample 4; 0.13 mol% was added to samples 6 and 8; and 0.3 mol% was added to sample 9. Magnesium oxide, as described later, can inhibit abnormal grain growth in alumina.

[0056] In samples 1-5 and 7, yttrium oxide (Y₂O₃) was added to the alumina raw material at a specified ratio (0-0.05 mol%). If the amount of yttrium oxide added exceeds 0.05 mol%, yttrium oxide, as a secondary phase, becomes more prone to segregation. Segregation of the secondary phase increases the likelihood of a decrease in withstand voltage; therefore, the suitable amount of yttrium oxide added is 0-0.05 mol%. In samples 6, 8, and 9, no yttrium oxide was added. Yttrium oxide was added as a sintering aid.

[0057] In these samples, the amount of sintering aid added was trace to 0~0.05 mol%, and the amount of magnesium oxide added was roughly the same as the magnesium oxide content in the alumina sintered body.

[0058] By varying the amounts of magnesium oxide and yttrium oxide added, the firing methods (hot pressing, atmospheric pressure), the firing atmosphere (argon (Ar), atmosphere, vacuum), and the firing temperature, the density, standard deviation of particle size, number of pores, and ratio of pores at grain boundaries in the alumina sintered bodies differ among samples 1-9. Samples 1-9 contain no impurities other than magnesium oxide and yttrium oxide. Here, "no impurities" means that "processing impurities such as Si, Ca, and Fe are below 10 ppm."

[0059] The density of the alumina sintered body was determined according to the Archimedes method (JIS R 1634).

[0060] The standard deviation of the alumina grain size in the alumina sintered body was calculated as described above using the grain size determined by the intercept method.

[0061] The number of pores and the pore presence ratio were determined using cross-sectional STEM images (magnification: 5000x) as described above. Specifically, at least three fields of view containing four or more pores were captured, and their average was taken as the pore presence. For sample 4, the use of cross-sectional STEM images was not confirmed; unfortunately, the number of pores determined using fracture surface SEM was recorded as a reference. It should be noted that the pore presence ratio in Table 1 is relative to the total number of pores present within the grains, which includes both pores present at grain boundaries and pores present within the grains.

[0062] Figure 2 , Figure 3 This is an example of a cross-sectional STEM image showing the alumina sintered body 10 of samples 1-3. Separately... Figure 2 (A) represents the STEM image of sample 1. Figure 2 (B) represents the STEM image of sample 2. Figure 2 (C) represents the STEM image of sample 3. Figure 3 (D) represents the STEM image of sample 8 (magnification: 5000x). Figure 2 In the figure, the pores (pores 10P) existing in the alumina sintered body 10 are represented by solid lines, the pores (first pores 11) existing in the grain boundaries are surrounded by solid lines, and the pores (second pores 12) existing in the grains are surrounded by dashed lines.

[0063] 2. Evaluation Methods

[0064] (1) Withstand voltage

[0065] Withstand voltage is evaluated using the dielectric breakdown voltage. A higher dielectric breakdown voltage indicates a higher withstand voltage. The dielectric breakdown voltage is calculated as follows: Test pieces with a rectangular plate of 20 mm on each side and a thickness of 0.15 mm were formed from samples 1-9. The voltage at which dielectric breakdown occurred was measured according to JIS C2110. The values ​​shown in Table 1 are the average of four measurements.

[0066] (2) Plasma resistance

[0067] Each sample was irradiated with plasma, and the surface roughness Sa of the plasma-irradiated surface was measured. The surface roughness Sa was measured using an apparatus according to ISO 25178. This apparatus utilizes a vertical scanning type low-coherence interferometry method to measure the surface roughness Sa.

[0068] The plasma durability evaluation conditions are as follows.

[0069] Apparatus: NLD (Neutral Loop Discharge) plasma device

[0070] Antenna RF power: 1kW

[0071] • Bias voltage: 0.3kW

[0072] CF4 = 90 sccm, O2 = 10 sccm

[0073] • Exposure time: 40 minutes

[0074] 3. Evaluation Results

[0075] The alumina sintered bodies of samples 1-5 and 8 (examples) meet all the conditions described below [1]-[5].

[0076] [1] The content of magnesium oxide (MgO) is 0.00 mol%. <MgO≤0.20mol%。

[0077] [2] The density is 3.96 g / cm³. 3 above.

[0078] [3] The standard deviation of the alumina grain size is less than 4.0 μm.

[0079] [4] The number of pores present is 0.050 per μm. 2 the following.

[0080] [5] When the pores are divided into first pores that belong to the pores existing at the grain boundaries and second pores that belong to the pores existing within the grains, the ratio of the amount of second pores to the amount of pores is more than 20%.

[0081] In contrast, while Sample 6 (Comparative Example) satisfies conditions [1] and [3] above, it does not satisfy conditions [2], [4], and [5]. That is, compared to the Example, Sample 6 (Comparative Example) has a lower density, a greater number of pores, and a higher proportion of pores present at grain boundaries. Furthermore, while Sample 7 (Comparative Example) satisfies conditions [1] and [2] above, it does not satisfy condition [3]. The density of Sample 7 (Comparative Example) is the same as that of the Example, but compared to the Example, the standard deviation of the alumina grains is larger, therefore it is considered to have greater particle size fluctuation, a higher proportion of anomalous alumina particles, and a greater number of pores. While Sample 9 (Comparative Example) satisfies conditions [2] to [4] above, it does not satisfy condition [1]. That is, compared to the Example, Sample 9 (Comparative Example) has a higher magnesium oxide (MgO) content.

[0082] Compared to samples 6, 7, and 9 (comparative examples), the alumina sintered bodies of samples 1-5 and 8 (Examples) exhibit higher voltage resistance and plasma resistance in at least one of the following:

[0083] Samples 1-5 and 8 of the comparative examples will be described in further detail.

[0084] Compared to sample 1, sample 2 shows a significant reduction in the number of pores. Therefore, sample 2 demonstrates improved voltage withstand capability compared to sample 1.

[0085] Compared to sample 2, sample 3 shows a significant reduction in the proportion of pores present at grain boundaries. Therefore, sample 3, compared to sample 1, can further improve voltage withstand capability.

[0086] Sample 4 was prepared under the same firing conditions as Sample 2, but with a higher content of magnesium oxide. Compared to Sample 2, Sample 4 showed an increased number of pores and a decreased voltage withstand capability. This is because an increased amount of magnesium oxide makes it easier to form secondary phases such as MgAl₂O₄. Although Sample 4 showed a lower voltage withstand capability compared to Sample 2, it still achieved a voltage withstand capability equivalent to Sample 1. Sample 9 (Comparative Example) had 0.3 mol% more magnesium oxide than the examples, resulting in a lower voltage withstand capability. Therefore, the appropriate magnesium oxide (MgO) content is 0.00 mol%. <MgO≤0.20mol%。

[0087] Compared to other examples, Sample 5, although having a larger standard deviation in particle size, has fewer pores and virtually no pores present at grain boundaries, resulting in high voltage resistance and high plasma resistance. In Sample 7 (Comparative Example), the standard deviation in particle size is 4.0 μm, and the voltage resistance is low. Therefore, by having a standard deviation in particle size of less than 4.0 μm, high plasma resistance can be achieved.

[0088] Although Sample 8 has more pores than Sample 2, its pore ratio is higher, achieving the same level of voltage withstand and plasma resistance. This result indicates that the pore ratio has a significant impact on voltage withstand. It is believed that when voltage is applied, grain boundaries are more likely to become current pathways than intragranular pores. Grain boundary pores present in these current pathways are more likely to become the starting point for dielectric breakdown than intragranular pores. Therefore, reducing grain boundary pores can improve voltage withstand.

[0089] <Second Implementation>

[0090] Figure 4 This is a simplified cross-sectional view of a holding device 100 using the alumina sintered body 10 of the first embodiment. The holding device 100 is part of a semiconductor manufacturing apparatus that performs plasma etching, ion implantation, electron beam exposure, etc. The holding device 100 performs tasks such as fixing, flatness correction, and transporting of semiconductor wafers W (hereinafter also simply referred to as "wafer W"), and is used as an electrostatic chuck for cooling the wafer W. Figure 4 In this document, the XYZ axes, which are orthogonal to each other, are shown for a specific orientation. For convenience, the positive direction of the Z-axis is referred to as the stacking direction in this specification.

[0091] Figure 4 In the diagram, the wafer W held by the holding device 100 is shown with dashed lines. Figure 4 As shown, the holding device 100 includes: a plate-shaped member 20 for holding a wafer W, which is the object; and a base member 30 bonded to the plate-shaped member 20 and having a cooling function. The plate-shaped member 20 includes: a first surface 23 for holding the wafer W, a second surface 24 belonging to the back surface of the first surface 23, and a chuck electrode 21 formed inside the plate-shaped member 20. As shown, the base member 30 is bonded to the second surface 24 of the plate-shaped member 20 by means of a bonding layer 40. It should be noted that the first surface 23 of the plate-shaped member 20 for holding the wafer W is... Figure 4 The diagram is simplified, but it forms the sealing strip 26 and multiple embossed sections 27, which will be described later.

[0092] The plate-shaped member 20 is an alumina sintered body with alumina (Al2O3) as the main component, and at least satisfies the conditions shown in the first embodiment [1] to [3]. A plurality of chuck electrodes 21, which serve as conductors, are embedded inside the plate-shaped member 20. When the wafer W is placed on the first surface 23, an electrostatic force is generated when a voltage is applied to the chuck electrodes 21, and the wafer W is fixed to the first surface 23.

[0093] A gas flow path 22 is provided inside the plate-shaped member 20, which is a through hole that extends along the stacking direction between the second surface 24 and the first surface 23 of the plate-shaped member 20. The gas flow path 22 supplies an inactive gas (e.g., helium) for cooling the wafer W, supplied from the gas supply hole 32 of the substrate member 30 (described later), to the first surface 23. Figure 4 As shown, the gas flow path 22 opens on the first surface 23.

[0094] The base member 30 is formed of a metal such as aluminum or stainless steel. A gas supply hole 32 is formed inside the base member 30, extending through the lamination direction. Inert gas supplied by a pump or similar device is supplied to the gas flow path 22 of the plate-shaped member 20 via the gas supply hole 32.

[0095] Figure 5is a top schematic view of the holding apparatus 100. Figure 6 is Figure 5 an enlarged schematic view of the A-A cross-section in. As shown in Figure 5 , the plate-like member 20 and the base member 30 are generally disc-shaped centered on the center O. A plurality of outlets (openings) of gas flow paths 22 are formed on the first surface 23 of the plate-like member 20. Further, as shown in Figure 5 and Figure 6 , the first surface 23 includes: a flat surface 25, a convex sealing strip portion 26 continuously formed along the outer edge of the flat surface 25, and a plurality of cylindrical embossments 27 protruding from the flat surface 25 inside the sealing strip portion 26. When a wafer W is held by the plate-like member 20, it is adsorbed on the surfaces of the sealing strip portion 26 and the embossments 27.

[0096] When the alumina-based sintered body 10 is used for the plate-like member 20, the mixed powder as the raw material of the alumina-based sintered body 10 is pre-compacted and formed in advance. In a state where the metal mesh or metal foil for the chuck electrode 21 of the plate-like member 20 is arranged, the pre-compacted mixed powder is arranged between the press-molded bodies, and fired by hot pressing. After firing, processing is performed by grinding to manufacture the plate-like member 20 formed with the sealing strip portion 26 and the embossments 27. That is, the surfaces of the sealing strip portion 26 and the embossments 27 are formed of the alumina-based sintered body 10.

[0097] As described above, the holding apparatus 100 includes: a plate-like member 20 and a base member 30 joined to the plate-like member 20. The plate-like member 20 has: a chuck electrode 21 formed inside, and a sealing strip portion 26 continuously formed along the outer edge of the first surface 23. The surface of the first surface 23 that holds the wafer W is formed of a surface of an alumina-based sintered body, the alumina-based sintered body takes aluminum oxide (Al2O3) as a main component, the content of magnesium oxide (MgO) satisfies 0.00 mol% < MgO ≤ 0.20 mol% relative to the content of aluminum oxide, the density of the alumina-based sintered body is 3.96 g / cm 3 or more, and the standard deviation of the particle size of alumina crystal grains is less than 4.0 μm. That is, the surface of the first surface 23 holding the wafer W is formed of an alumina-based sintered body with fewer pores and high voltage resistance, so that high power can be applied. Therefore, if the holding apparatus 100 of the present embodiment is used, the wafer W can be etched deeper.

[0098] In addition, in the holding apparatus 100, the plate-like member 20 has the gas flow paths 22 and the sealing strip portion 26, and the openings of the gas flow paths 22 are formed further inside than the sealing strip portion 26, therefore, circulation in the gas flow paths 22 can improve the sealing performance of the gas (for example, helium (He)) released between the first surface 23 of the plate-like member 20 and the wafer W.

[0099] <Modification of the Present Embodiment>

[0100] The present invention is not limited to the above-described embodiments, and can be implemented in various ways without departing from the gist thereof. For example, the following modifications can also be made.

[0101] • The method for producing an alumina-based sintered body is not limited to the above embodiment. By appropriately changing the type of sintering aid, the addition amount of the sintering aid, the firing method, the firing atmosphere, the firing temperature, the hot pressing pressure, etc., it is possible to produce an alumina-based sintered body wherein the content of magnesium oxide (MgO) relative to the content of alumina satisfies 0.00mol%<MgO≤0.20mol%, the density is 3.96g / cm 3 or more, and the standard deviation of the particle size of alumina crystal grains is less than 4.0μm. In addition, the alumina-based sintered body can also be produced by other known methods such as gel casting.

[0102] • In the above embodiment, an alumina-based sintered body that does not contain impurities other than magnesium oxide and yttrium oxide is exemplified, but the sintered body may also contain other impurities. However, when no other impurities are contained, the voltage resistance can be further improved, which is preferable.

[0103] • In the above embodiment, an alumina-based sintered body wherein the content of magnesium oxide (MgO) relative to the content of alumina satisfies 0.00mol%<MgO≤0.20mol%, the density is 3.96g / cm 3 or more, and the standard deviation of the particle size of alumina crystal grains is less than 4.0μm is exemplified, but the content of magnesium oxide, the density, and the standard deviation of the particle size of alumina crystal grains are not limited to the above embodiment. For example, the sintered body may also contain no magnesium oxide. The alumina-based sintered body having aluminum oxide (Al2O3) as a main component may also satisfy the following: the existing amount of pores is 0.050 pores / μm 2 or less; when pores are divided into first pores existing at grain boundaries and second pores existing inside crystal grains, the ratio of the existing amount of the second pores to the existing amount of all pores is 20% or more. When a voltage is applied, grain boundaries are more likely to become current paths than the inside of crystal grains, and grain boundary pores existing on current paths are more likely to become starting points of dielectric breakdown than intragranular pores. Therefore, reducing grain boundary pores can improve voltage resistance, and thus voltage resistance can also be improved in this case.

[0104] • In the second embodiment described above, an example is shown in which the plate-shaped member 20 of the holding device 100 includes the gas flow path 22, the seal tape portion 26 and the embossment 27, but the holding device may not include at least one of these.

[0105] In the second embodiment described above, the entire plate-shaped member 20 is formed of an alumina sintered body 10, but the surface of the first surface 23 of the wafer W is at least covered with an alumina sintered body 10. For example, the surface of the first surface 23 is formed of an alumina sintered body 10, while the second surface 24 can be formed of an alumina sintered body other than the alumina sintered body 10. Furthermore, different components (e.g., alumina sintered bodies other than the alumina sintered body 10) can be disposed or joined between the plate-shaped member 20 and the substrate member 30.

[0106] • In the above embodiments, an electrostatic chuck is exemplified as a holding device, but the holding device is not limited to an electrostatic chuck. It can be composed of various holding devices such as heater devices, bases, and stage for vacuum devices such as CVD (chemical vapor deposition), PVD (physical vapor deposition), and PLD (pulsed laser deposition).

[0107] The present invention has been described above based on embodiments, examples, and modifications. However, the embodiments described above are for the purpose of facilitating understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved without departing from its spirit and claims, and the present invention includes equivalents. Furthermore, technical features that are not described as essential features in this specification can be appropriately deleted.

[0108] Explanation of reference numerals in the attached figures

[0109] 10…alumina sintered body

[0110] 10P…pores

[0111] 11…First pore

[0112] 12…Second pore

[0113] 20…plate-shaped members

[0114] 21…Chuck electrode

[0115] 22…Gas Flow Path

[0116] 23… Page 1

[0117] 24… Page 2

[0118] 25…plane

[0119] 26…Sealing strip section

[0120] 27… Embossing

[0121] 30…base components

[0122] 32…Gas supply port

[0123] 40… Bonding layer

[0124] 100…holding device

[0125] W… wafer

Claims

1. An alumina sintered body, characterized in that, The main component is aluminum oxide (Al₂O₃), and the content of magnesium oxide (MgO) relative to the aluminum oxide content is 0.10 mol% ≤ MgO ≤ 0.20 mol%. The density of the alumina sintered body is 3.96 g / cm³. 3 The above conditions apply, and the standard deviation of the alumina grain size is less than 4.0 μm. The content of yttrium oxide (Y₂O₃) relative to the content of aluminum oxide is 0. <Y2O3≤0.05mol%, The number of pores present is 0.050 per μm. 2 the following, When the pores are divided into first pores (belonging to grain boundaries) and second pores (belonging to grains), the ratio of the amount of second pores to the amount of pores is 20% or more. The dielectric breakdown voltage of the alumina sintered body is above 200 kV / mm.

2. The alumina sintered body according to claim 1, characterized in that, The surface roughness Sa of the surface irradiated with plasma for 40 minutes is less than 50 nm.

3. An electrostatic chuck, characterized in that, It is an electrostatic chuck for holding objects. The electrostatic chuck has the following features: A plate-shaped member having a first surface for holding the object, a second surface belonging to the back of the first surface, and a chuck electrode formed in or within the second surface; and, A base member, disposed on the second surface side of the plate-shaped member, and having a cooling function. The first surface of the plate-shaped member is formed from the alumina sintered body as described in claim 1 or 2.

4. The electrostatic chuck according to claim 3, characterized in that, The plate-shaped member has: A gas flow path that opens on the first surface and introduces gas from the second surface side; and, A sealing strip is formed continuously along the outer edge of the plate-like member on the first surface. The opening of the gas flow path is formed further inside than the sealing strip.

Images