Holding device

Abstract

To provide a retainer that solve a problem of an overheat under a high plasma environment and a problem caused by a difference of a thermal expansion coefficient between a plate-like member and a base part, and suppresses a deterioration of a processability of the base part.SOLUTION: A retainer for holding an object, comprises: a plate-like member formed in a plate like; and a base part that is bonded to the plate-like member, and is constructed by an ultra hard alloy, in which a value of a saturation magnetization in a room temperature is 5×10-7 Tm3 / kg or less, and a difference of a means linear thermal expansion coefficient from -70°C to 200°C with the plate-like member is 1 ppm / K or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a holding device. [Background technology]

[0002] Conventionally, in semiconductor manufacturing equipment such as etching equipment, CVD equipment, and PVD equipment, holding devices such as electrostatic chucks have been used to hold wafers within the equipment. Generally, a holding device comprises a plate-shaped member that attracts and holds the semiconductor wafer by generating electrostatic attraction, and a base part joined to the plate-shaped member. When such a holding device is used in a high-power plasma environment, the temperature of the holding device can rise significantly, so in order to suppress the problem of overheating, it is necessary to improve the heat dissipation of the holding device. For this reason, for example, a base part made of aluminum, which has a relatively high thermal conductivity, has been selected as the base part of the holding device. However, aluminum has a relatively large coefficient of thermal expansion, which leads to the problem of a large difference in thermal conductivity between it and the plate-shaped member formed of alumina or the like. To solve this problem, a configuration has been proposed in which a ceramic composite material containing, for example, silicon carbide (SiC) or titanium silicide (TiS2) is used as the constituent material of the base part to reduce the difference in thermal conductivity between it and the plate-shaped member (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6182082 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, ceramic materials are generally brittle, and the ceramic composite materials mentioned above, in particular, contain silicon carbide (SiC), which is difficult to process, making it difficult to process them into desired dimensions and shapes. Specifically, for example, it may become difficult to meet the requirement for larger holding devices. Therefore, there has been a need for a technology that suppresses the problem of overheating in high-plasma environments and problems caused by the difference in thermal expansion coefficients between the plate-like member and the base, while also suppressing the decrease in the processability of the base. [Means for solving the problem]

[0005] This disclosure can be implemented in the following forms: (1) According to one embodiment of the present disclosure, a holding device for holding an object is provided. The holding device comprises a plate-shaped plate member and a cemented carbide bonded to the plate member, the cemented carbide having a saturation magnetization value of 5 × 10 at room temperature. -7 Tm 3 The device comprises a base portion having a coefficient of thermal expansion of 1 ppm / K or less, and a difference of 1 ppm / K or less in the average linear thermal expansion coefficient between it and the plate-like member from -70°C to 200°C. This type of holding device has the effect of suppressing heat generation in the base even under relatively high-power plasma irradiation by suppressing the value of saturation magnetization, suppressing stress generated between the base and the plate-shaped member by suppressing the difference in thermal expansion coefficient between the base and the plate-shaped member, and ensuring workability in the base, thereby improving the performance of the holding device. (2) In the above-described form of the holding device, the main component of the plate-shaped member may be alumina. With this configuration, since alumina has a relatively high volume resistivity, the stable performance of the holding device can be maintained even in a high-power plasma environment, for example. (3) In the above-described holding device, the cemented carbide may comprise a hard phase mainly composed of tungsten carbide (WC) and a binder phase mainly composed of nickel (Ni), wherein the nickel content in the cemented carbide is 18 to 27% by mass. This configuration helps to suppress the decrease in workability of the base due to the low nickel content, and the decrease in thermal conductivity of the base due to the high nickel content. (4) In the above-described holding device, the average linear thermal expansion coefficient of the base portion from -70°C to 200°C may be 4.61 to 6.61 ppm / K. With such a configuration, when the main component of the plate-shaped member is alumina, it becomes easy to make the difference in the average linear thermal expansion coefficient between the base portion and the plate-shaped member from -70°C to 200°C 1 ppm / K or less. (5) In the above-described form of the holding device, the average thermal conductivity of the base portion at temperatures from 50°C to 200°C may be 50 W / mK or higher. With such a configuration, even when the holding device is used in a relatively high and wide temperature range of 50°C to 200°C, it becomes easier to ensure heat dissipation from the plate-shaped member via the base portion. (6) In the above-described form of the holding device, a connecting portion made of a metal material may be provided to connect the plate-shaped member and the base portion. With such a configuration, the thermal conductivity of the connecting portion can be increased, thereby improving the heat dissipation from the plate-shaped member in the holding device. In addition, the heat resistance of the connecting portion can be increased, making it possible to use the holding device under higher temperature conditions. This disclosure can be implemented in various forms other than those described above, for example, in the form of a semiconductor manufacturing apparatus including a holding device, or a method for manufacturing a holding device. [Brief explanation of the drawing]

[0006] [Figure 1] A perspective view showing a schematic representation of the appearance of the electrostatic chuck according to the embodiment. [Figure 2] A schematic cross-sectional view showing the configuration of an electrostatic chuck. [Figure 3] An explanatory diagram summarizing the composition, manufacturing conditions, and evaluation results of each sample. [Figure 4] An explanatory diagram showing the progression of the firing temperature of sample S1. [Modes for carrying out the invention]

[0007] A. Overall configuration of the electrostatic chuck: Figure 1 is a perspective view showing a schematic appearance of the electrostatic chuck 10 as an embodiment of the present disclosure. Figure 2 is a cross-sectional view schematically showing the configuration of the electrostatic chuck 10. In Figure 1, a part of the electrostatic chuck 10 is shown in a cutaway. Figures 1 and 2 also show mutually orthogonal XYZ axes to specify the direction. The X, Y, and Z axes shown in each figure represent the same direction. In this specification, the Z axis represents the vertical direction, and the X and Y axes represent the horizontal direction. Note that the above figures schematically represent the arrangement of each part and do not accurately represent the ratio of the dimensions of each part.

[0008] The electrostatic chuck 10 is a device that attracts and holds an object by electrostatic attraction, and is used, for example, to fix a wafer W, which is the object, in a vacuum chamber of a semiconductor manufacturing apparatus. The electrostatic chuck 10 comprises a ceramic part 20, a base part 30, and a connecting part 40. These are stacked in the order of ceramic part 20, connecting part 40, and base part 30 in the direction of the -Z axis (vertically downward). The electrostatic chuck 10 in this embodiment is also called a "holding device".

[0009] The ceramic part 20 is a roughly circular "plate-like member" and is formed mainly of ceramic. In this specification, "main component" of a specific component means that the content of that specific component is 50% by mass or more. The ceramic that is the main component of the ceramic part 20 can be, for example, aluminum oxide (alumina: Al2O3) or aluminum nitride (AlN). In particular, aluminum oxide is desirable because it has a relatively high volume resistivity, which allows for stable performance of the electrostatic chuck 10 even in a high-power plasma environment.

[0010] For example, if the volume resistivity of the ceramic part 20 is relatively low, only a Johnson-Rahbek force type electrostatic chuck can be obtained. In this case, there is a possibility that the wafer W may be damaged in order to allow a minute current to flow between the dielectric layer of the ceramic part 20 and the wafer W. Also, even when the voltage applied to the internal electrode (adsorption electrode 22 described later) of the ceramic part 20 is turned off, there may occur a problem that de-chucking is difficult (it takes time for de-chucking). On the other hand, if the volume resistivity of the ceramic part 20 is made relatively high with the above main component being alumina, a Coulomb force type electrostatic chuck can be achieved. In this case, the yield of the wafer W is improved, and since de-chucking is fast, the production efficiency can be enhanced.

[0011] As shown in FIG. 2, an adsorption electrode 22 is disposed inside the ceramic part 20. The adsorption electrode 22 is formed of a conductive material such as tungsten or molybdenum, for example. When a voltage is applied from a power source (not shown) to the adsorption electrode 22, an electrostatic attraction force is generated, and the wafer W is adsorbed and fixed to the mounting surface 24 of the ceramic part 2 by this electrostatic attraction force. The adsorption electrode 22 may be bipolar or unipolar. Further, inside the ceramic part 20, a heater electrode (not shown) for heating the wafer W adsorbed and fixed to the mounting surface 24 may be provided, which is constituted by a resistance heating element formed of a conductive material (for example, tungsten, molybdenum, etc.).

[0012] The base part 30 is a plate-shaped member made of cemented carbide and formed in a substantially circular shape. Inside the base part 30, a plurality of refrigerant flow paths 32 are formed along the XY plane. By flowing a refrigerant such as a fluorine-based inert liquid, water, or liquid nitrogen through the refrigerant flow paths 32, the base part 30 is cooled. Then, the ceramic part 20 is cooled by heat transfer between the base part 30 and the ceramic part 20 via the connecting part 40, and the wafer W held on the mounting surface 24 of the ceramic part 20 is cooled. Thereby, temperature control of the wafer W is realized. However, in addition to the form having the refrigerant flow paths 32 inside the base part 30, a configuration in which the base part 30 is cooled from the outside of the base part 30 to give the base part 30 a cooling function is also possible. The constituent material and the like of the base part 30 will be described in detail later.

[0013] The connecting part 40 is disposed between the ceramic part 20 and the base part 30 and joins the ceramic part 20 and the base part 30. It is desirable that the connecting part 40 be made of a metal material. As the metal material constituting the connecting part 40, for example, a metal brazing material or solder can be used. As the metal brazing material, for example, silver brazing material or aluminum brazing material can also be used. However, since ceramics have relatively poor wettability with respect to general molten brazing materials, in this case, it is necessary to perform brazing after metallizing the surface of the ceramic part 20. By using an active metal brazing material added with an active metal as the metal material constituting the connecting part 40, it becomes easy to directly perform brazing on the ceramic part 20. As the active metal brazing material, for example, those obtained by adding an active metal such as titanium (Ti) or zirconium (Zr) to a metal brazing material such as a Cu-Ag system, a Cu-Au system, a Cu-Ni system, or an Au-Ni system can be used. For example, when the ceramic part 20 is made of aluminum oxide, by using an AgCuTi-based active metal brazing material and joining the ceramic part 20 and the base part 30 at 850 °C for 30 minutes in a vacuum (1.0×10 -4 Torr), a connecting part 40 showing good joining properties can be formed.

[0014] By constructing the connecting portion 40 from a metal material as described above, the connecting portion 40 can be made to have superior thermal conductivity compared to when the connecting portion 40 is constructed from an adhesive made of, for example, a resin material, thereby improving the heat dissipation from the ceramic portion 20 in the electrostatic chuck 10. Furthermore, the heat resistance of the connecting portion 40 can be increased compared to when the connecting portion 40 is constructed from a resin material, making it possible to use the electrostatic chuck 10 under higher temperature conditions. However, if the heat dissipation from the ceramic portion 20 is reduced due to the connecting portion 40, or if the heat resistance of the connecting portion 40 is within an acceptable range, the connecting portion 40 can be made from a resin material such as a silicone adhesive. It may be further composed of the following. If the connecting part 40 is made of a resin material, the connecting part 40 may further contain an inorganic filler such as ceramic powder.

[0015] The electrostatic chuck 10 is further provided with a plurality of gas supply passages 50. The gas supply passages 50 are provided penetrating the ceramic part 20, the connecting part 40, and the base part 30 in the Z direction, and open at gas outlets 52 formed on the mounting surface 24. The gas supply passages 50 are supplied with an inert gas, such as helium gas, from a gas supply device (not shown), and the inert gas is supplied from the gas outlets 52 to the space between the mounting surface 24 and the wafer W. This enhances the heat transfer between the ceramic part 20 and the wafer W, further improving the controllability of the temperature distribution of the wafer W. Note that the gas supply passages 50 are not essential, and the electrostatic chuck 10 may be provided without them.

[0016] B. Base section configuration: The base portion 30 is made of a non-magnetic material, a cemented carbide alloy. Specifically, the saturation magnetization value of the base portion 30 at room temperature is 5 × 10⁻⁶. -7 Tm 3 The value is less than / kg. By constructing the base portion 30 from a non-magnetic material as described above, even when the electrostatic chuck 10 is used in a high-power plasma environment, heat generation due to high-frequency induction associated with plasma irradiation can be suppressed. The value of saturation magnetization generally increases as the temperature decreases, but the value of saturation magnetization at room temperature is 5 × 10⁻⁶.-7 Tm 3 For cemented carbides with a saturation magnetization of less than / kg, they are typically non-magnetic materials with a sufficiently small saturation magnetization value, for example, in a temperature range of -70°C or higher.

[0017] Furthermore, in this embodiment, the difference in the average linear thermal expansion coefficient between the base portion 30 and the ceramic portion 20 from -70°C to 200°C is 1 ppm / K or less. Such a difference in the average linear thermal expansion coefficient cannot be achieved when using metal materials such as aluminum, which have been widely used in the past, as the constituent material of the base portion 30. By reducing the difference in the average linear thermal expansion coefficient between the base portion 30 and the ceramic portion 20 in this way, when using the electrostatic chuck 10 in a wide temperature range of -70°C to 200°C, it is possible to suppress the generation of undesirable stress between the base portion 30 and the ceramic portion 20 due to the difference in the degree of thermal expansion between the base portion 30 and the ceramic portion 20. For example, when the ceramic portion 20 is made of aluminum oxide (Al2O3), the average linear thermal expansion coefficient of aluminum oxide from -70°C to 200°C is 5.61, so the average linear thermal expansion coefficient of the base portion 30 from -70°C to 200°C should be 4.61 to 6.61.

[0018] Furthermore, it is desirable that the average thermal conductivity of the base portion 30 between 50°C and 200°C be 50 W / mK or higher. By providing such a base portion 30, it becomes easier to ensure heat dissipation from the ceramic portion 20 even when the electrostatic chuck 10 is used in a relatively high and wide temperature range of 50°C to 200°C. Note that when the operating temperature of the electrostatic chuck 10 is below 50°C, the difference between the operating temperature (ambient temperature of the electrostatic chuck 10) and the temperature of the electrostatic chuck 10 becomes larger, which increases the heat dissipation from the ceramic portion 20. Therefore, by setting the average thermal conductivity of the base portion 30 between 50°C and 200°C to 50 W / mK or higher, it becomes easier to ensure heat dissipation in the electrostatic chuck 10 when using the electrostatic chuck 10 in a wide temperature range, for example, from -70°C to 200°C.

[0019] Examples of the cemented carbide constituting such a base portion 30 include a WC-Ni based cemented carbide including a hard phase mainly composed of tungsten carbide (WC) and a bonding layer mainly composed of nickel (Ni). By reducing the amount of alloy carbon in the cemented carbide including a hard phase mainly composed of tungsten carbide, the value of saturation magnetization can be reduced. Here, the amount of alloy carbon refers to the content rate (mass%) of carbon in the hard phase mainly composed of WC. By reducing the amount of alloy carbon, the amount of tungsten (W) dissolved in the bonding phase increases, and the saturation magnetization of the cemented carbide decreases. Without adjusting the amount of alloy carbon, When producing a cemented carbide including a hard phase composed of tungsten carbide and a bonding layer composed of nickel, the amount of alloy carbon becomes about 6.13%, and usually, by setting the amount of alloy carbon to 5.90 to 5.95 mass% or less, the WC-Ni based cemented carbide can be demagnetized. Therefore, by configuring the base portion 30 using a WC-Ni based cemented carbide with the amount of alloy carbon adjusted, the value of saturation magnetization of the base portion 30 at room temperature can be easily made 5×10 -7 Tm 3 / kg or less.

[0020] Note that the WC-Ni based cemented carbide constituting the base portion 30 may further contain elements such as molybdenum (Mo), tantalum (Ta), titanium (Ti), etc. These elements can be dissolved, for example, in the bonding layer mainly composed of nickel. Also, tungsten carbide may be dissolved in these elements.

[0021] When using a WC-Ni cemented carbide as the cemented carbide constituting the base portion 30, it is desirable that the WC-Ni cemented carbide further contains chromium carbide (Cr3C2). By adding chromium carbide to the WC-Ni cemented carbide, a portion of the chromium carbide dissolves into the nickel-based bonding layer, thereby suppressing the emergence of magnetism in the WC-Ni cemented carbide. Furthermore, adding chromium carbide to the WC-Ni cemented carbide facilitates sintering of the WC-Ni cemented carbide, making it possible to lower the firing temperature, for example. Since cemented carbide deteriorates more easily at higher firing temperatures, the addition of chromium carbide can suppress the deterioration of the WC-Ni cemented carbide.

[0022] Furthermore, in the base portion 30, which is made of a WC-Ni cemented carbide having a binder phase mainly composed of nickel, it is desirable that the nickel content in the WC-Ni cemented carbide be 18 to 27 mass%. This is because the hardness of the base portion 30 tends to increase as the nickel content decreases, so if the nickel content is less than 18 mass%, the machinability of the base portion 30 tends to decrease. Also, if the nickel content exceeds 27 mass%, the thermal conductivity of the base portion 30 tends to decrease.

[0023] The base portion 30 may be made of a cemented carbide other than a WC-Ni cemented carbide. From the viewpoint of ensuring the thermal conductivity of the base portion 30, it is desirable that the cemented carbide constituting the base portion 30 is a cemented carbide having a hard phase mainly composed of tungsten carbide (WC), which has excellent thermal conductivity. Furthermore, in order to make the cemented carbide non-magnetic, the cemented carbide may have a bonding phase (metallic phase) containing a metal selected from silicon (Si), aluminum (Al), copper (Cu), iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), and molybdenum (Mo) instead of nickel (Ni). Alternatively, the bonding phase (metallic phase) may contain an alloy of two or more metals selected from nickel (Ni), silicon (Si), aluminum (Al), copper (Cu), iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), and molybdenum (Mo). In other words, the cemented carbide that constitutes the base portion 30 can be a cemented carbide having, for example, a hard phase mainly composed of tungsten carbide (WC) and a binder phase consisting of a metal selected from nickel (Ni), silicon (Si), aluminum (Al), copper (Cu), iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), and molybdenum (Mo), or an alloy of two or more metals.

[0024] As described above, the electrostatic chuck 10 of this embodiment has the effect of suppressing heat generation in the base portion 30 even under relatively high-power plasma irradiation, suppressing the difference in thermal expansion coefficient between the base portion 30 and the ceramic portion 20, and ensuring machinability of the base portion 30, thereby improving the performance of the electrostatic chuck 10. Specifically, the base portion 30 has a saturation magnetization value of 5 × 10 at room temperature. -7 Tm 3 Since it is made of materials with a magnetic charge of less than / kg, that is, non-magnetic materials, it is possible to suppress heat generation in response to high-frequency induction from semiconductor manufacturing equipment. In addition, in the base portion 30, from -70°C to 20°C Since the difference in average linear thermal expansion coefficients between the base portion 30 and the ceramic portion 20 at 0°C is 1 ppm / K or less, when using the electrostatic chuck 10 in a temperature range of -70°C to 200°C, the stress generated between the base portion 30 and the ceramic portion 20 due to the difference in the degree of thermal expansion between them can be suppressed. Furthermore, since the base portion 30 is made of a cemented carbide alloy comprising a hard phase mainly composed of tungsten carbide, which is a ceramic, and a bonding layer mainly composed of nickel, which is a metal, the machinability of the base portion 30 can be improved compared to when, for example, a ceramic material is used as the constituent material of the base portion 30.

[0025] Since cemented carbide is generally an electrically conductive material, electrical discharge machining can be applied, for example, to further improve the machinability of the base portion 30. By improving the machinability of the base portion 30 as described above, the degree of freedom in forming the refrigerant flow path 32 (see Figures 1 and 2) in the base portion 30 is increased, and the shape of the refrigerant flow path 32 makes it possible to further improve the heat dissipation performance of the electrostatic chuck 10.

[0026] In addition to cemented carbide, other materials known to minimize the difference in average linear thermal expansion coefficients with respect to the ceramic portion 20 while ensuring machinability include, for example, cermet, a composite material of metal and ceramic. However, cermet generally has insufficient thermal conductivity. By constructing the base portion 30 from cemented carbide as in this embodiment, the thermal conductivity of the base portion 30 can be increased, and the heat dissipation performance of the electrostatic chuck 10 can be further improved.

[0027] Furthermore, in this embodiment, as described above, the difference in average linear thermal expansion coefficient between the base portion 30 and the ceramic portion 20 is kept to 1 ppm / K or less, thus reducing the need for the connecting portion 40 to absorb the difference in thermal expansion between the base portion 30 and the ceramic portion 20. As a result, the connecting portion 40 can be constructed from a metal material that is less flexible than a resin adhesive. Consequently, the electrostatic chuck 10 can be used under higher temperature conditions, and the heat dissipation performance of the electrostatic chuck 10 can be further improved.

[0028] C. Other embodiments: This disclosure may also be applied to holding devices other than electrostatic chucks that hold a wafer W using electrostatic attraction. That is, it is similarly applicable to other holding devices that hold an object on the surface of a plate-shaped member, comprising a plate-shaped member, a base portion, and a connecting portion that joins the plate-shaped member and the base portion, such as heater devices for vacuum equipment such as CVD, PVD, and PLD, and vacuum chucks.

[0029] Furthermore, in the above-described embodiment, the plate-like portion having a mounting surface is a ceramic portion 20 mainly composed of ceramic, but the plate-like portion may be mainly composed of a material other than ceramic. Even with such a configuration, by applying the configuration of the present disclosure exemplified in the embodiment, the same effect can be obtained in which problems such as overheating in the holding device and problems caused by the difference in thermal expansion coefficients between the plate-like member and the base portion are suppressed while ensuring the processability of the base portion. [Examples]

[0030] Figure 3 is an explanatory diagram summarizing the composition, manufacturing conditions, and evaluation results of 16 types of WC-Ni cemented carbides, from Sample S1 to Sample S16. Each sample differs in composition (mixing ratio of materials used) and manufacturing conditions. In Figure 3, "4πσ" represents the saturation magnetization at room temperature, and "TC" represents the average thermal conductivity from -70°C to 200°C.

[0031] <Preparation of each sample> [Sample S1] The raw material powders include tungsten carbide (WC) powder with an average particle size of 0.5 μm, nickel (Ni) powder with an average particle size of 2.5 μm, and chromium carbide (Cr3C2) powder with an average particle size of 1.0 μm. In addition, tungsten (W) powder with an average particle size of 1.0 μm was used. These raw material powders were blended to achieve the composition shown as sample S1 in Figure 3. The raw material powders blended as described above were ground and mixed using a ball mill under the following conditions. Specifically, a resin pot and balls made of WC-Ni cemented carbide were used, and the mixture was ground and mixed wet with ethanol as a solvent for a grinding time of 40 hours. The resulting mixed slurry was dried in a vibrating dryer to obtain a dried mixed powder.

[0032] Using the obtained dried mixed powder, a non-pressurized firing (atmospheric pressure firing) was performed under the following conditions to obtain the cemented carbide of sample S1. Specifically, using a carbon mold and an alumina (Al2O3) base plate, non-pressurized firing was performed in nitrogen gas (N2) at 1 atmosphere at the firing temperature shown in Figure 3. In addition to nitrogen gas, argon gas (Ar) may also be used as the firing atmosphere, or a vacuum atmosphere may be used.

[0033] Figure 4 is an explanatory diagram showing the temperature progression based on the firing program set during the firing of sample S1. The highest temperature of the firing process based on the firing program is shown in Figure 3 as the firing temperature. Generally, WC-Ni cemented carbide is thought to be able to be fired at around 1500°C, so each sample was pre-fired at various temperatures below 1500°C, and the density was measured after firing using the Archimedes method. The minimum temperature at which no decrease in density was observed was set as the firing temperature. As shown in Figures 3 and 4, the firing temperature of sample S1 was set to 1380°C.

[0034] In Figure 3, the composition of each sample is shown as a value based on the mixing ratio of the raw material powders. The content of each component constituting the obtained cemented carbide can be determined by wavelength-dispersive X-ray fluorescence analysis (WDX). Specifically, the obtained cemented carbide is processed into a cylindrical shape with a diameter of 45 mm and a height of 20 mm, and a region with a diameter of 30 mm and a depth of 0.1 mm can be measured by WDX. In the samples shown in Figure 3, the raw material powders contain virtually no volatile components, so the composition shown in Figure 3 represents the composition of the obtained cemented carbide.

[0035] [Samples S2-S16] The cemented carbide alloys were prepared in the same manner as sample S1, except that the raw material powders were prepared to have the composition shown in Figure 3 for each sample, and that the firing was performed at the firing temperature shown in Figure 3. However, samples S10, S15, and S16 did not use chromium carbide (Cr3C2) powder as a raw material powder. Also, for samples S11 and S12, tungsten carbide (WC) powder with an average particle size of 2.0 μm was used as the raw material powder.

[0036] <Measurement of saturation magnetization> For saturation magnetization measurements at room temperature, a magnetic saturation induction measuring device (model: MSM-1025S, manufactured by Denshi Jiki Kogyo Co., Ltd.) was used. Each sample was processed into a rectangular parallelepiped shape with dimensions of 10 mm in length and width and 5 mm in height for measurement. The measured values ​​were corrected using 99.9% pure aluminum oxide (Al2O3) as a reference.

[0037] <Measurement of linear thermal expansion coefficient> Each sample was processed into a cylindrical shape with a diameter of 5 mm and a height of 20 mm. Thermomechanical analysis (TMA) was performed to determine the average linear thermal expansion coefficient by compression in a nitrogen atmosphere over a temperature range of -70 to 200°C. Figure 3 shows the average linear thermal expansion coefficients measured similarly for samples S1 to S16, as well as for aluminum oxide (alumina). Furthermore, Figure 3 also shows the difference in the average linear thermal expansion coefficient between each sample and aluminum oxide over a temperature range of -70°C to 200°C (labeled "Difference in Linear Thermal Expansion Coefficient (-70°C~200°C)" in Figure 3).

[0038] <Measurement of average thermal conductivity> Each sample was processed into a disc shape with a diameter of 10 mm and a thickness of 2 mm, and the average thermal conductivity was measured using the laser flash method in a temperature range of 50°C to 200°C.

[0039] <Alloy carbon content> The alloy carbon content refers to the carbon content (mol%) in the hard phase, which is mainly composed of tungsten carbide (WC). The alloy carbon content can be calculated using the following equation (1). Specifically, the "amount of substance (mol) of carbon contained" in equation (1) can be said to be "the total amount of carbon (mol) contained in the raw material powder used to manufacture each sample." Also, "the amount of substance (mol) of carbides contained" This can be described as "the sum of the amount of tungsten carbide (WC) (mol), chromium carbide (Cr3C2) (mol), and tungsten (W) (mol) used in the production of each sample." Note that when the raw material powder contains chromium carbide powder, some of the chromium carbide is dissolved in the nickel-based binder layer, but this amount is said to be a maximum of 15 atm%. Therefore, assuming that the total amount of chromium carbide added as raw material powder is 100%, the remaining 85 atm% of the maximum dissolved amount is present in the hard phase mainly composed of WC, and the alloy carbon content was calculated accordingly. Alloy carbon content (mol%) = [Amount of carbon contained (mol) / Amount of carbides contained (mol)] × 100 … (1)

[0040] <Hardness> The hardness of each sample was measured using the Rockwell hardness scale (HRA). The Rockwell hardness was measured in accordance with JIS Z 2245 (2021).

[0041] <Evaluation Results> As shown in Figure 3, in all samples with an alloy carbon content of 5.85%, the saturation magnetization value at room temperature was 5 × 10⁻⁶. -7 Tm 3 The result was less than / kg. In contrast, sample S14, which has an alloy carbon content of 6.05%, had a saturation magnetization of 19.02 × 10⁻⁶. -7 Tm 3 The value was / kg, which was a larger value. In this way, by demagnetizing the base part, the saturation magnetization value was 5 × 10 -7 Tm 3 It was confirmed that reducing the amount of carbon in the alloy is important in order to keep the amount below / kg.

[0042] As shown in Figure 3, the average linear thermal expansion coefficient for all samples was in the range of 4.61 to 6.61 ppm / K from -70°C to 200°C. That is, when the base portion was constructed using each sample and combined with a plate-shaped member made of aluminum oxide to form a holding device, the difference in the average linear thermal expansion coefficient between the base portion and the plate-shaped member from -70°C to 200°C was less than 1 ppm / K. At this time, as shown in Figure 3, a tendency was observed for the average linear thermal expansion coefficient to increase as the nickel (Ni) content increased (for example, a comparison of samples S1 to S7). Thus, it was confirmed that by adjusting the nickel content in the WC-Ni cemented carbide that constitutes the base portion, the average linear thermal expansion coefficient of the base portion can be brought closer to that of the plate-shaped member.

[0043] Furthermore, as shown in Figure 3, a tendency was observed for hardness to increase as the nickel (Ni) content decreased (the WC) content increased). For example, sample S16, which had a nickel content of 15.6 mass%, had a hardness (HRA) of 90 or higher. Generally, higher hardness tends to lead to problems such as increased wear on the diamond grinding wheel used in processing. As a result, it becomes necessary to reduce processing efficiency to suppress grinding wheel wear, leading to decreased productivity. The results shown in Figure 3 confirm that the decrease in productivity can be suppressed by adjusting the nickel content to reduce hardness.

[0044] As shown in Figure 3, the average thermal conductivity from 50°C to 200°C was 50 W / mK or higher for all samples. At this time, the above average thermal conductivity changed according to the amount of chromium carbide added, regardless of the Ni / WC content ratio, and a tendency was observed for the average thermal conductivity to decrease as the chromium content increased. In addition, a tendency was observed for the firing temperature to decrease as the chromium content increased (comparison of samples S1 to S10). Furthermore, a tendency was observed for the average thermal conductivity from 50°C to 200°C to increase as the particle size of the raw material powder, tungsten carbide (WC), increased (comparison of sample S7 and sample S11, and comparison of sample S4 and sample S12).

[0045] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0046] This disclosure can also be implemented in the following forms: [Application Example 1] A holding device for holding an object, A plate-shaped member, The plate-shaped member is joined to the aforementioned plate-shaped member, and is made of cemented carbide, with a saturation magnetization value of 5 × 10 at room temperature. -7 Tm 3 The base portion has a coefficient of thermal expansion of 1 ppm / K or less, and the difference in average linear thermal expansion coefficient between it and the plate-like member from -70°C to 200°C is 1 ppm / K or less. Features that holding device. [Application Example 2] The holding device described in Application Example 1, The main component of the plate-like member is alumina. holding device. [Application Example 3] A holding device as described in Application Example 1 or 2, The aforementioned cemented carbide is A hard phase mainly composed of tungsten carbide (WC), A bonding phase containing nickel (Ni) as the main component, wherein the nickel content in the cemented carbide is 18 to 27% by mass, Features that holding device. [Application Example 4] A holding device according to any one of the application examples 1 to 3, The base portion is characterized by having an average linear thermal expansion coefficient of 4.61 to 6.61 ppm / K between -70°C and 200°C. holding device. [Application Example 5] A holding device according to any one of the application examples 1 to 4, The base portion is characterized by having an average thermal conductivity of 50 W / mK or more between 50°C and 200°C. holding device. [Application Example 6] A holding device according to any one of the application examples 1 to 5, further, It is made of a metal material and includes a connecting portion that connects the plate-shaped member and the base portion. Characterized by holding device. [Explanation of Symbols]

[0047] 10…Electrostatic chuck 20…Ceramic part 22...Adsorption electrode 24… Mounting surface 30...Base section 32… Refrigerant flow path 40…Connection part 50…Gas supply lines 52...Gas outlet

Claims

1. A holding device for holding an object, A plate-shaped member, The plate-shaped member is joined to the aforementioned plate-shaped member, and is made of cemented carbide, with a saturation magnetization value of 5 × 10 at room temperature. －７ Tm ３ The base portion has a coefficient of thermal expansion of 1 ppm / K or less, and the difference in average linear thermal expansion coefficient between it and the plate-like member from -70°C to 200°C is 1 ppm / K or less. Features that holding device.

2. A holding device according to claim 1, The main component of the plate-like member is alumina. holding device.

3. A holding device according to claim 1, The aforementioned cemented carbide is A hard phase mainly composed of tungsten carbide (WC), A bonding phase containing nickel (Ni) as the main component, wherein the nickel content in the cemented carbide is 18 to 27% by mass, Features that holding device.

4. A holding device according to claim 2, The base portion is characterized by having an average linear thermal expansion coefficient of 4.61 to 6.61 ppm / K between -70°C and 200°C. holding device.

5. A holding device according to claim 1, The base portion is characterized by having an average thermal conductivity of 50 W / mK or more between 50°C and 200°C. holding device.

6. A holding device according to any one of claims 1 to 5, further, It is characterized by being made of a metal material and having a connecting portion that connects the plate-shaped member and the base portion. holding device.

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