Alumina sintered body and electrostatic chuck

Abstract

The present invention provides an alumina-based sintered body which is mainly composed of alumina (Al2O3), wherein the content of magnesia (MgO) relative to the content of alumina satisfies 0.00 mol% < MgO ≤ 0.20 mol%. This alumina-based sintered body has a density of 3.96 g / cm3 or more; and the standard deviation of the grain sizes of alumina crystal grains is less than 4.0 µm.

Description

[Technical Field]

[0001] The present invention relates to an alumina sintered body and an electrostatic chuck. [Background technology]

[0002] In recent years, there has been a growing demand for semiconductor devices, particularly flash memory devices, with large aspect ratios (e.g., 3D-NAND). To manufacture semiconductor devices with large aspect ratios, silicon wafers must be deeply etched, and the technology required for this is an electrostatic chuck capable of applying high power. Electrostatic chuck components for high-power applications require a dense structure with as few pores as possible and a voltage resistance that can withstand high electric fields.

[0003] Generally, ceramics containing alumina (Al2O3) as the main component are prone to abnormal grain growth during firing, and pores (vacancies) are likely to form near the abnormally grown crystal grains. To address this issue, a technique has been proposed for improving the withstand voltage by adding magnesia (MgO) as a grain growth inhibitor (see, for example, Patent Document 1). Another technique has also been proposed for improving the density of alumina sintered bodies by adjusting the content of components other than alumina (Al2O3) in the alumina sintered body (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6373212 [Patent Document 2] Japanese Patent Application Publication No. 2019-69889 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even in the alumina sintered body described in Patent Document 1, the withstand voltage may not be sufficient for high-power applications. Therefore, further improvement in the withstand voltage of the alumina sintered body is desired. In addition, although Patent Document 2 describes the density of the alumina sintered body, it does not mention the number and position of pores. Such problems are not limited to the members for electrostatic chucks, but are common problems for alumina sintered bodies used in various members for semiconductor manufacturing equipment.

[0006] The present invention has been made to solve the above-described problems, and an object thereof is to provide a technique for improving the withstand voltage of an alumina sintered body and a technique for reducing pores (voids) in the alumina sintered body.

Means for Solving the Problems

[0007] The present invention has been made to solve at least one of the above-described problems and can be realized in the following forms.

[0008] (1) According to one embodiment of the present invention, there is provided an alumina sintered body containing alumina (Al2O3) as a main component and having a magnesia (MgO) content of 0.00 mol% < MgO ≦ 0.20 mol% with respect to the alumina content. This alumina sintered body has a density of 3.96 g / cm 3 or more, and a standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm.

[0009] According to the alumina sintered body of this embodiment, since the standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm, the variation in particle size is small and the existence ratio of abnormal grains of alumina is small. Therefore, in an alumina sintered body having the same density, the number of voids (pores) can be reduced as compared with that having a standard deviation of the particle size of the alumina crystal grains of 4.0 μm or more. That is, the alumina sintered body of this embodiment has a large density and few pores, so that the denseness can be improved. Further, by reducing the pores, the withstand voltage can be improved.

[0010] (2) In the alumina sintered body of the above form, the number of pores is 0.050 / μm 2 In this way, an alumina sintered body with high withstand voltage can be obtained.

[0011] (3) In the alumina sintered body of the above embodiment, when the vacancies are divided into first vacancies, which are vacancies present at grain boundaries, and second vacancies, which are vacancies present within the grains, the ratio of the amount of the second vacancies to the amount of the first vacancies may be 20% or more. By using an alumina sintered body in which the amount of vacancies present at grain boundaries is reduced in this way, leakage current flowing through the grain boundaries when an electric field is applied can be suppressed, thereby improving the withstand voltage.

[0012] (4) The alumina sintered body of the above embodiment may have a breakdown voltage of 200 kV / mm or more, which allows it to have a high withstand voltage and can be used, for example, in an electrostatic chuck to which high power can be applied.

[0013] (5) In the alumina sintered body of the above embodiment, the surface roughness Sa of the surface irradiated with plasma for 40 minutes may be 50 nm or less. In this way, an alumina sintered body with high plasma resistance can be obtained. By using the alumina sintered body with high plasma resistance in, for example, an electrostatic chuck, it is possible to suppress a decrease in the gas sealing property and chucking force of the wafer mounting surface.

[0014] (6) According to another aspect of the present invention, there is provided an electrostatic chuck for holding an object, the electrostatic chuck including a plate-shaped member having a first surface for holding the object, a second surface opposite to the first surface, and a chuck electrode formed on either the second surface or an interior thereof, and a base member having a cooling function and disposed on the second surface side of the plate-shaped member, wherein the first surface of the plate-shaped member is formed from the alumina sintered body according to any one of claims 1 to 5.

[0015] According to this form of electrostatic chuck, the first surface of the plate-shaped portion is formed from an alumina sintered body with few pores and high withstand voltage, so that an electrostatic chuck to which high power can be applied can be provided.

[0016] (7) In the electrostatic chuck of the above aspect, the plate-shaped member may have a gas flow path that opens on the first surface and through which gas is introduced from the second surface side, and a seal band portion that is continuously formed on the first surface along the outer edge of the plate-shaped member, and the opening of the gas flow path may be formed inside the seal band portion. In this way, it is possible to improve the sealing performance of gas (e.g., helium (He) gas) that flows through the gas flow path and is released between the first surface of the plate-shaped member and the object.

[0017] (8) According to another aspect of the present invention, there is provided an alumina sintered body containing alumina (Al2O3) as a main component. This alumina sintered body has a pore density of 0.050 pores / μm 2 When the pores are divided into first pores that are pores present at grain boundaries and second pores that are pores present within crystal grains, the ratio of the amount of the second pores to the amount of the first pores may be 20% or more. In this way, the number of pores can be reduced and the withstand voltage can be improved.

[0018] The present invention can be realized in various forms, for example, in the form of a semiconductor manufacturing equipment component, a semiconductor manufacturing equipment, a holding device, an electrostatic chuck, an apparatus including these, and a method for manufacturing a semiconductor manufacturing equipment component. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a process diagram showing a method for producing an alumina sintered body. FIG. [Figure 2] FIG. 1 shows an example of a cross-sectional STEM image of a sample. [Figure 3] FIG. 1 shows an example of a cross-sectional STEM image of a sample. [Figure 4]It is a schematic cross-sectional view of the holding device. [Figure 5] It is a schematic top view of the holding device. [Figure 6] It is an enlarged schematic view of the A-A cross-section in FIG. 5.

Embodiments for Carrying Out the Invention

[0020] <First Embodiment> The alumina-based sintered body as the first embodiment of the present invention contains alumina (Al2O3) as the main component, and the content of magnesia (MgO) with respect to the content of alumina is 0.00 mol% < MgO ≤ 0.20 mol%. It is an alumina-based sintered body with a density of 3.96 g / cm 3 or more, and the standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm. Here, the "main component" means the component with the highest content ratio.

[0021] The content of magnesia can be determined as follows. For the alumina-based sintered body, elemental analysis by XRF (X-ray Fluorescence) is performed to quantify the amount of magnesium (Mg). The amount of magnesium in the analysis result is converted to an oxide to obtain the content of magnesia. Similarly, the amount of aluminum (Al) is quantified and converted to an oxide to obtain the content of alumina. Then, the ratio of the amount of magnesia (mol) to the amount of alumina (mol) is calculated.

[0022] In the alumina-based sintered body, by adding magnesia, abnormal grain growth of the alumina crystal grains can be suppressed.

[0023] The density of the alumina-based sintered body can be measured by the Archimedes method (JIS R 1634).

[0024] The grain size of alumina crystal grains in an alumina sintered body can be measured by the intercept method. Specifically, the fracture surface of the alumina sintered body is observed using a scanning electron microscope (SEM), and when a line of length L is drawn on the obtained secondary electron image, the number n of grains that the line crosses is measured. Note that grains with both ends of the line inside are counted as 0.5 grains. Then, the average grain size D (μm) is calculated using the following formula (1): D = 1.5 × L / n (1) In this embodiment, an arbitrary number of lines intersecting with the number n of particles of 100 or more are drawn in parallel to determine a plurality of average particle diameters D, and the standard deviation is calculated using the determined plurality of average particle diameters.

[0025] The alumina sintered body of this embodiment has a pore density of 0.050 pores / μm 2 It is preferable that the pore count is less than 1 / 2. By reducing the number of pores, the withstand voltage can be improved. Furthermore, since the number of pores is small, the starting points for plasma erosion are reduced, and plasma resistance can be improved.

[0026] The number of pores present can be counted visually using a cross-sectional STEM (Scanning Transmission Electron Microscope) image. The presence of pores can also be confirmed using a fractured surface SEM image. Although a fractured surface SEM image can determine the number of pores at the grain boundaries, it cannot determine the number of pores present within the grains. Therefore, the total number of pores found using a fractured surface SEM image will be greater than the number of pores present. Therefore, when the number of pores is small in a fractured surface SEM image, it is preferable to confirm the number of pores present using a cross-sectional STEM image.

[0027] In the alumina sintered body of this embodiment, when pores are divided into first pores, which are pores present at grain boundaries, and second pores, which are pores present within crystal grains, the ratio of the number of second pores to the number of pores is preferably 20% or more. Pores present at grain boundaries are thought to serve as paths for leakage current when an electric field is applied, and are thought to be the starting points for dielectric breakdown. Therefore, using an alumina sintered body with a reduced number of pores present at grain boundaries can suppress leakage current flowing through the grain boundaries and further improve the withstand voltage. The number of pores can be counted using cross-sectional STEM images, as described above.

[0028] In the alumina sintered body of this embodiment, it is preferable that the breakdown voltage is 200 kV / mm or more. This allows a high withstand voltage to be obtained, and therefore the body can be used, for example, in an electrostatic chuck to which high power can be applied. The breakdown voltage is measured according to JIS C2110, and is the voltage at which breakdown occurs.

[0029] In the alumina sintered body of this embodiment, the surface roughness Sa of the surface irradiated with plasma for 40 minutes may be 50 nm or less. In this way, an alumina sintered body with high plasma resistance can be obtained. By using the alumina sintered body with high plasma resistance in, for example, an electrostatic chuck, it is possible to suppress a decrease in the gas sealing property and chucking force of the wafer mounting surface.

[0030] FIG. 1 is a process diagram showing a method for manufacturing an alumina sintered body. In the method for manufacturing an alumina sintered body of the present embodiment, first, a powder preparation step is performed in which a previously measured amount of an Al2O3 raw material and a MgO raw material are mixed by ball milling in ethanol and dried (step P1). The addition amount of the MgO raw material is 0.00 mol% < MgO ≦ 0.20 mol% with respect to the Al2O3 raw material. Next, a firing step is performed in which the mixed powder obtained in the powder preparation step (step P1) is molded by a hot press device and fired at a firing temperature of 1500°C or higher and 1700°C or lower (step P2), and an alumina sintered body is manufactured. When the firing temperature is as high as exceeding 1700°C, abnormal grain growth of particles is likely to occur, and the possibility of a decrease in breakdown voltage increases. Therefore, the firing temperature is preferably 1500°C or higher and 1700°C or lower. The press pressure of the hot press can be arbitrarily set. When the press pressure is as low as less than 10 MPa, particles are difficult to be crushed during hot pressing, densification cannot be promoted, and air is likely to remain as pores at grain boundaries. Therefore, the press pressure is preferably 10 MPa or higher and 40 MPa or lower. The content of MgO in the alumina sintered body can be examined by XRF or ICP emission analysis. Since hot pressing can apply pressure during firing, compared with atmospheric firing, it can fire while crushing particles, so densification can be promoted, and pores at grain boundaries are likely to be reduced. Also, since the contact area between particles increases, the sintering process itself can be completed in a shorter time compared with atmospheric firing.

[0031] According to the manufacturing method of the present embodiment, compared with the case of manufacturing an alumina sintered body by the gel-casting method, an alumina sintered body with fewer impurities and higher breakdown voltage can be obtained.

[0032] The alumina sintered body of the present embodiment can be used for parts for semiconductor manufacturing equipment, semiconductor manufacturing equipment, holding devices, electrostatic chucks, and devices equipped with these.

Example

[0033] The present invention will be described more specifically by way of examples. The voltage resistance and plasma resistance were evaluated using alumina sintered body samples 1 to 9. Samples 1 to 5 and 8 are examples of the alumina sintered body of the above embodiment, and samples 6, 7 and 9 are comparative examples.

[0034] Table 1 shows the specifications and evaluation results of Samples 1 to 9. The evaluation method will be described later.

[0035] [Table 1]

[0036] 1. Sample Preparation Samples 1 to 5 and 8 were manufactured by the manufacturing method of the above embodiment. Sample 6 was manufactured in the same manner as the manufacturing method of the above embodiment, except that it was fired at atmospheric pressure without hot pressing. Sample 7 was manufactured in the same manner as the manufacturing method of the above embodiment, except that it was hot pressed at a temperature exceeding 1700°C. Sample 8 was obtained by subjecting Sample 6, which had been fired at atmospheric pressure, to a HIP (Hot Isostatic Pressing) treatment at a pressure of 200 MPa or less. The HIP treatment can also reduce pores, especially grain boundary pores, and improve the withstand voltage.

[0037] In Samples 1 to 9, the alumina raw material used has a purity of 99.9% or higher. The magnesia raw material is added to the alumina raw material in the ratio shown in Table 1. Specifically, 0.10 mol % is added to Samples 1 to 3, 5, and 7, 0.20 mol % to Sample 4, 0.13 mol % to Samples 6 and 8, and 0.3 mol to Sample 9. As will be described later, magnesia can suppress abnormal grain growth of alumina crystal grains.

[0038] In samples 1 to 5, and 7, yttria (yttrium oxide: Y2O3) is added to the alumina raw material at a specified ratio (0 to 0.05 mol%). If the amount of yttria added exceeds 0.05 mol%, yttria is likely to segregate as a secondary phase. If segregation of the secondary phase occurs, there is a high possibility that it will cause a decrease in withstand voltage, so the amount of yttria added is preferably 0 to 0.05 mol%. In samples 6, 8, and 9, yttria is not added. Yttria is added as a sintering aid.

[0039] In these samples, the amount of sintering aid added was a minute amount of 0 to 0.05 mol %, and the amount of magnesia added was approximately equal to the magnesia content in the alumina sintered body.

[0040] By varying the amount of magnesia added, the amount of yttria added, the firing method (hot press, atmospheric pressure), the firing atmosphere (argon (Ar), air, vacuum), and the firing temperature, the density of the alumina sintered body, the standard deviation of the grain size, the number of pores, and the proportion of pores present at the grain boundaries were varied among Samples 1 to 9. Samples 1 to 9 do not contain impurities other than magnesia and yttria. Here, "does not contain impurities" means that "process impurities such as Si, Ca, and Fe are 10 ppm or less."

[0041] The density of the alumina sintered body was measured by the Archimedes method (JIS R 1634).

[0042] The standard deviation of the particle size of the alumina crystal particles in the alumina sintered body was calculated using the particle sizes measured by the intercept method as described above.

[0043] The number of pores and the proportion of pores present were determined using cross-sectional STEM images (magnification: 5000x) as described above. Specifically, images of three or more fields of view containing four or more pores were taken, and the average was used as the amount of pores present. For sample 4, confirmation using cross-sectional STEM images was not performed, so the number of pores determined using fracture surface SEM is listed for reference. Note that the proportion of pores present in Table 1 is the number of pores present within crystal grains relative to the total number of pores, which is the sum of the number of pores present at grain boundaries and the number of pores present within crystal grains.

[0044] 2 and 3 are diagrams showing examples of cross-sectional STEM images of the alumina sintered bodies 10 of Samples 1 to 3. Fig. 2(A) shows a STEM image (magnification: 5000x) of Sample 1, Fig. 2(B) shows a STEM image of Sample 2, Fig. 2(C) shows a STEM image of Sample 3, and Fig. 3(D) shows a STEM image (magnification: 5000x) of Sample 8. In Fig. 2, of the pores (voids 10P) present in the alumina sintered body 10, pores present at the grain boundaries (first voids 11) are surrounded by solid lines, and pores present within the crystal grains (second voids 12) are surrounded by dashed lines.

[0045] 2. Evaluation Method (1) Withstand voltage The withstand voltage was evaluated using the dielectric breakdown voltage. The higher the dielectric breakdown voltage, the higher the withstand voltage. The dielectric breakdown voltage was determined as follows. Test pieces with a rectangular plate measuring 20 mm on a side and a thickness of 0.15 mm were formed from Samples 1 to 9, and the voltage at which dielectric breakdown occurred was measured according to JIS C2110. The values ​​shown in Table 1 are the average values ​​of four measurements.

[0046] (2) Plasma resistance 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 conforming to the ISO 25178 standard. The apparatus measures the surface roughness Sa using vertical scanning low-coherence interferometry. The plasma durability evaluation conditions are as follows. Device: NLD (Neutral Loop Discharge) plasma device Antenna RF power: 1kW Bias: 0.3kW CF4=90sccm, O2=10sccm ·Exposure time 40 minutes

[0047] 3. Evaluation Results The alumina sintered bodies of Samples 1 to 5 and 8 (Examples) satisfy all of the following requirements [1] to [5]. [1] Magnesia (MgO) content is 0.00 mol% <MgO≦0.20mol%である。 [2] Density is 3.96 g / cm 3 That's all. [3] The standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm. [4] The number of voids is 0.050 / μm 2 The following is the result. [5] When vacancies are divided into primary vacancies, which are vacancies existing at grain boundaries, and secondary vacancies, which are vacancies existing within grains, the ratio of the amount of secondary vacancies to the amount of vacancies is 20% or more.

[0048] In contrast, Sample 6 (Comparative Example) satisfies the requirements [1] and [3] above, but does not satisfy the requirements [2], [4], and [5] above. That is, Sample 6 (Comparative Example) has a lower density, a larger number of pores, and a higher proportion of pores at the grain boundaries compared to the Examples. Furthermore, Sample 7 (Comparative Example) satisfies the requirements [1] and [2] above, but does not satisfy the requirement [3] above. Although Sample 7 (Comparative Example) has a density equivalent to that of the Examples, the standard deviation of the alumina crystal grains is larger than that of the Examples, which is thought to result in greater variation in particle size, a higher proportion of abnormal alumina grains, and a larger number of pores. Sample 9 (Comparative Example) satisfies the requirements [2] to [4] above, but does not satisfy the requirement [1] above. That is, Sample 9 (Comparative Example) has a higher magnesia (MgO) content compared to the Examples.

[0049] The alumina sintered bodies of Samples 1 to 5 and 8 (Examples) have at least one of higher withstand voltage and plasma resistance compared to Samples 6, 7, and 9 (Comparative Examples). The alumina sintered bodies of the Examples have a reduced number of pores, high density, and a reduced proportion of pores present at grain boundaries. Therefore, the leakage current flowing through the grain boundaries can be suppressed, and the withstand voltage can be improved. Also, since the Examples have fewer pores than the Comparative Examples, the starting points of plasma erosion are reduced, and the surface roughness after plasma irradiation is lowered.

[0050] Samples 1 to 5 and 8 of the Examples will be described in more detail by comparison. Sample 2 has a significantly reduced number of pores compared to Sample 1. As a result, Sample 2 was able to improve the withstand voltage compared to Sample 1.

[0051] Sample 3 has a significantly reduced proportion of pores present at grain boundaries compared to Sample 2. As a result, Sample 3 was able to further improve the withstand voltage compared to Sample 1.

[0052] Sample 4 has more magnesia added than Sample 2 but is fabricated under the same firing conditions as Sample 2. Sample 4 has an increased number of pores and a decreased withstand voltage compared to Sample 2. This is because when the addition amount of magnesia increases, secondary phases such as MgAl2O4 are likely to occur. Although Sample 4 has a lower withstand voltage than Sample 2, it can obtain a withstand voltage equivalent to that of Sample 1. Sample 9 (Comparative Example) has a high magnesia addition amount of 0.3 mol% compared to the Examples and has a low withstand voltage. Therefore, a suitable content of magnesia (MgO) is 0.00 mol% < MgO ≦ 0.20 mol%.

[0053] Although sample 5 had a larger standard deviation of grain size compared to the other examples, the number of pores was small and there were almost no pores at the grain boundaries, resulting in high withstand voltage and high plasma resistance.Sample 7 (comparative example) had a standard deviation of grain size of 4.0 μm and low withstand voltage, so by making the standard deviation of grain size smaller than 4.0 μm, high plasma resistance could be obtained.

[0054] Although Sample 8 had a larger number of pores than Sample 2, the proportion of pores present was also higher than Sample 2, and it was able to achieve the same level of withstand voltage and plasma resistance as Sample 2. From these results, it can be said that the proportion of pores present has a large effect on withstand voltage. When voltage is applied, grain boundaries are more likely to become paths for current than intragranular pores, and grain boundary pores present on the current path are more likely to become the starting point of dielectric breakdown than intragranular pores, so it is thought that withstand voltage can be improved by reducing grain boundary pores.

[0055] Second Embodiment FIG. 4 is a schematic 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 fixes, corrects flatness, transports, etc., of a semiconductor wafer W (hereinafter simply referred to as "wafer W"), and is used as an electrostatic chuck for cooling the wafer W. In FIG. 4, mutually orthogonal X, Y, and Z axes are shown to identify directions. For convenience, the positive direction of the Z axis is referred to as the stacking direction in this specification.

[0056] In FIG. 4, the wafer W held by the holding device 100 is illustrated by a dashed line. As shown in FIG. 4, the holding device 100 includes a plate-shaped member 20 on which the wafer W, which is an object, is held, 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 on which the wafer W is held, a second surface 24 that is the backside of the first surface 23, and a chuck electrode 21 formed inside the plate-shaped member 20. As shown in the figure, the base member 30 is bonded to the second surface 24 of the plate-shaped member 20 via a bonding layer 40. Note that, although the first surface 23 of the plate-shaped member 20 that holds the wafer W is shown simply in FIG. 4, it is formed with a seal band portion 26 and multiple embossments 27, which will be described later.

[0057] The plate-shaped member 20 is an alumina sintered body whose main component is alumina (Al2O3), and satisfies at least the requirements [1] to [3] described in the first embodiment. A plurality of chuck electrodes 21 serving as conductors are embedded inside the plate-shaped member 20. When a voltage is applied to the chuck electrodes 21 with the wafer W placed on the first surface 23, an electrostatic force is generated, and the wafer W is fixed to the first surface 23.

[0058] A gas flow path 22, which is a through-hole that penetrates the second surface 24 and the first surface 23 of the plate-shaped member 20 in the stacking direction, is provided inside the plate-shaped member 20. The gas flow path 22 supplies an inert gas (e.g., helium gas) for cooling the wafer W, which is supplied from a gas supply hole 32 of the base member 30 (described later), onto the first surface 23. As shown in FIG. 4 , the gas flow path 22 opens onto the first surface 23.

[0059] The base member 30 is made of a metal such as aluminum or stainless steel. Gas supply holes 32 are formed inside the base member 30 so as to penetrate in the stacking direction. An inert gas is supplied from a device such as a pump through the gas supply holes 32 into the gas flow paths 22 of the plate-like member 20.

[0060] FIG. 5 is a schematic top view of the holding device 100. FIG. 6 is an enlarged schematic view of the A-A cross section in FIG. 5. As shown in FIG. 5, the shapes of the plate-like member 20 and the base member 30 are substantially disk-shaped centered on the center O. On the first surface 23 of the plate-like member 20, outlets (openings) of a plurality of gas flow paths 22 are formed. Further, as shown in FIGS. 5 and 6, the first surface 23 includes a flat surface 25, a convex seal band portion 26 continuously formed along the outer edge of the flat surface 25, and a plurality of columnar embosses 27 protruding from the flat surface 25 inside the seal band portion 26. When the wafer W is held by the plate-like member 20, it is adsorbed to the surfaces of the seal band portion 26 and the emboss 27.

[0061] When the alumina sintered body 10 is used for the plate-like member 20, the mixed powder that is the raw material of the alumina sintered body 10 is preformed by pre-pressing in advance. With the metal mesh or metal foil for the chuck electrode 21 of the plate-like member 20 disposed, the mixed powder pre-pressed between the press-molded bodies is disposed and fired by hot pressing. After firing, it is processed by grinding to produce the plate-like member 20 in which the seal band portion 26 and the emboss 27 are formed. That is, the surfaces of the seal band portion 26 and the emboss 27 are formed of the alumina sintered body 10.

[0062] As described above, the holding device 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 seal band 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 an alumina sintered body mainly composed of alumina (Al2O3), in which the content of magnesia (MgO) with respect to the content of alumina is 0.00 mol% <MgO ≦ 0.20 mol%, and the density is 3.96 g / cm 3It is formed on the surface of the alumina sintered body which has the above properties and the standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm. That is, since the surface of the first surface 23 that holds the wafer W is formed of an alumina sintered body with few pores and high breakdown voltage, high power can be applied. Therefore, by using the holding device 100 of the present embodiment, the wafer W can be etched deeply.

[0063] Further, in the holding device 100, the plate-like member 20 has the gas flow path 22 and the seal band portion 26, and the opening of the gas flow path 22 is formed inside the seal band portion 26. Therefore, the sealing property of the gas (for example, helium (He) gas) flowing through the gas flow path 22 and discharged between the first surface 23 of the plate-like member 20 and the wafer W can be improved.

[0064] <Modification Example of the Present Embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various aspects without departing from the gist thereof. For example, the following modifications are possible.

[0065] · The method for manufacturing the alumina 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 press pressure, etc., the content of magnesia (MgO) with respect to the content of alumina is 0.00 mol% <MgO ≤ 0.20 mol%, and the density is 3.96 g / cm 3 It is possible to manufacture an alumina sintered body which has the above properties and the standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm. Further, it may be manufactured by other known methods such as the gel-casting method.

[0066] · In the above embodiment, an alumina sintered body containing no impurities other than magnesia and yttria was exemplified, but it may contain other impurities. However, it is preferable not to contain other impurities because the breakdown voltage can be further improved.

[0067] ·In the above embodiment, the content of magnesia (MgO) with respect to the content of alumina is 0.00 mol% < MgO ≤ 0.20 mol%, and the density is 3.96 g / cm 3 or more, and an alumina sintered body having a standard deviation of the particle size of alumina crystal particles smaller than 4.0 μm was exemplified. However, the content of magnesia, the density, and the standard deviation of the particle size of alumina crystal particles are not limited to the above embodiment. For example, it may not contain magnesia. An alumina sintered body mainly composed of alumina (Al2O3) has an abundance of pores of 0.050 pieces / μm 2 or less. When the pores are divided into first pores existing at grain boundaries and second pores existing within grains, the ratio of the abundance of the second pores to the abundance of the pores may be 20% or more. When a voltage is applied, the grain boundary is more likely to be a current path than the grain interior, and grain boundary pores existing on the current path are more likely to be the starting point of dielectric breakdown than intragranular pores. Therefore, the dielectric breakdown voltage can be improved by reducing grain boundary pores. Even in this case, the dielectric breakdown voltage can be improved.

[0068] ·In the above second embodiment, an example in which the plate-like member 20 of the holding device 100 has a gas flow path 22, a seal band portion 26, and an emboss 27 was shown. However, the holding device may not include at least one of them.

[0069] ·In the above second embodiment, the entire plate-like member 20 is made of the alumina sintered body 10. However, it is sufficient that at least the surface of the first surface 23 that holds the wafer W is applied with the alumina sintered body 10. For example, the surface of the first surface 23 may be formed of the alumina sintered body 10, and the second surface 24 may be formed of another alumina sintered body different from the alumina sintered body 10. Also, a different member (for example, another alumina sintered body different from the alumina sintered body 10) may be disposed or joined between the plate-like member 20 and the base member 30.

[0070] In the above embodiment, an electrostatic chuck is used as an example of the holding device. However, the holding device is not limited to an electrostatic chuck and may be configured as various holding devices such as a heater device for a vacuum device such as CVD (chemical vapor deposition), PVD (physical vapor deposition), or PLD (pulsed laser deposition), a susceptor, or a mounting table.

[0071] The present invention has been described above based on embodiments, examples, and modifications. However, the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0072] 10...Alumina sintered body 10P…Vacancy 11...First hole 12...Second hole 20...Plate-shaped member 21...Chuck electrode 22...Gas flow path 23...First side 24...Second Side 25…Plane 26...Seal band part 27...Emboss 30...Base member 32...Gas supply hole 40...Joining layer 100...Holding device W...wafer

Claims

1. Alumina (Al 2 O 3 ) as a main component, and the content of magnesia (MgO) relative to the content of alumina is 0.00 mol% < MgO ≦ 0.20 mol%, Density is 3.96 g / cm 3 or more, and the standard deviation of the particle size of the alumina crystal particles is less than 4.0 μm, The breakdown voltage is 186 kV / mm or more, The ratio of yttria (Y) to the alumina content 2 O 3 ) content is 0 mol% < Y 2 O 3 ≦0.05 mol %, The number of pores present is 0.050 pores / μm 2 or less, When the vacancies are divided into first vacancies which are vacancies existing at grain boundaries and second vacancies which are vacancies existing within crystal grains, the ratio of the amount of the second vacancies to the amount of the vacancies is 20% or more. Alumina sintered body.

2. The alumina sintered body according to claim 1, An alumina sintered body, characterized in that the pores have a diameter of 1.0 μm or less.

3. The alumina sintered body according to claim 1 or 2, The surface roughness Sa of the surface irradiated with plasma for 40 minutes is 50 nm or less. Alumina sintered body.

4. An electrostatic chuck for holding an object, a plate-like member having a first surface on which the object is held, a second surface opposite to the first surface, and a chuck electrode formed on either the second surface or inside the plate-like member; a base member having a cooling function, the base member being disposed on the second surface side of the plate-like member; The first surface of the plate-like member is formed from the alumina sintered body according to any one of claims 1 to 3. Electrostatic chuck.

5. The electrostatic chuck of claim 4, The plate-like member is a gas flow path that opens to the first surface and into which gas is introduced from the second surface side; a seal band portion formed continuously along the outer edge of the plate-like member on the first surface, The opening of the gas flow path is formed inside the seal band portion. Electrostatic chuck.

6. Alumina (Al 2 O 3 An alumina sintered body having as its main component The content of magnesia (MgO) relative to the content of alumina is 0.00 mol% < MgO ≦ 0.20 mol%, The breakdown voltage is 186 kV / mm or more, The number of voids is 0.050 / μm 2 is as follows: When the vacancies are divided into first vacancies which are vacancies existing at grain boundaries and second vacancies which are vacancies existing within crystal grains, the ratio of the amount of the second pores to the amount of the pores is 20% or more; An alumina sintered body, characterized in that the pores have a diameter of 1.0 μm or less.

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