JP7458353B2 - holding device - Google Patents

Description

The present disclosure relates to a retention device.

2. Description of the Related Art Conventionally, as a holding device for holding an object, for example, an electrostatic chuck that holds an object such as a wafer when manufacturing a semiconductor is known. An electrostatic chuck generally includes a ceramic part on which an object is placed, a base part in which a coolant flow path is formed, and a joint part that joins the ceramic part and the base part. For example, Patent Document 1 describes an electrostatic chuck provided with a bonding layer (joint portion) containing a silicone adhesive and aluminum nitride particles on the surface of which a coating layer made of silicon oxide is formed. There is.

JP 2007-194320 A

According to the technology described in Patent Document 1, by using silicone resin as the material of the joint, stress generated at the joint due to the difference in thermal conductivity between the ceramic part and the base part can be alleviated. There is. Furthermore, by coating the surface of aluminum nitride particles, which have a relatively high thermal conductivity, with silicon oxide, the water resistance of the aluminum nitride particles is increased, and the durability of the joint and the electrostatic chuck is increased. However, when using an electrostatic chuck by exposing it to higher-power plasma, the heat input to the ceramic part increases, and the temperature of the base part must be lowered to sufficiently cool the object to be held. By setting the temperature difference between the ceramic part and the base part to be large, the stress generated at the joint may be larger as a result. Therefore, even in such a case, there has been a desire for a technology that can improve the cooling performance of the holding device and suppress problems caused by stress occurring at the joints.

The present disclosure can be realized as the following forms.
(1) According to one embodiment of the present disclosure, a holding device that holds an object is provided. This holding device includes a plate-shaped part formed in a plate shape, a cooling part formed in a plate shape to cool the plate-shaped part, and a cooling part disposed between the plate part and the cooling part, and a cooling part that cools the plate part. a joint portion that joins opposing surfaces of the shaped portion and the cooling portion, the joint portion including a silicone adhesive and surface-coated aluminum nitride particles, and wherein the surface-coated aluminum nitride particles The value of O/Al, which is the atomic ratio of oxygen atoms to aluminum atoms at the outermost surface, is 1.4 or more and 4.0 or less.
According to this type of holding device, the wettability between the surfaces of the surface-coated aluminum nitride particles and the silicone adhesive is enhanced, so that it is possible to suppress inconveniences caused by stress occurring in the joints. Even if the heat input to the plate-shaped portion increases, the cooling performance of the holding device can be improved by using the surface-coated aluminum nitride particles.
(2) In the holding device of the above embodiment, the joint portion may have a thermal resistance of 5.0×10 ⁻⁴ m ² K/W or less. With such a configuration, thermal resistance of the joint portion is suppressed, thereby improving heat transfer between the plate-like portion and the cooling portion, and further improving the cooling performance of the holding device.
(3) In the holding device of the above embodiment, the thickness of the joint portion may be 400 μm or less. With such a configuration, thermal resistance of the joint portion is suppressed, thereby improving heat transfer between the plate-like portion and the cooling portion, and further improving the cooling performance of the holding device.
(4) In the holding device of the above embodiment, the content ratio of the surface-coated aluminum nitride particles in the joint portion may be 70% by mass or more. With such a configuration, the thermal conductivity at the joint can be further increased.
(5) In the holding device of the above form, when the surface-coated aluminum nitride particles are viewed in cross section, and the radius of the inscribed circle is R1 and the radius of the circumscribed circle is R2, the average value of R2/R1 is 1. It may be .10 or more. With such a configuration, more contact points between the surface-coated aluminum nitride particles are formed in the joint, making it easier to form a heat conduction path within the joint, thereby suppressing the thermal resistance of the joint.
(6) In the holding device of the above embodiment, the maximum shear strain of the joint portion may be 0.5 mm or more. With such a configuration, it is possible to enhance the effect of suppressing inconveniences caused by stress occurring in the joint portion.
(7) According to another embodiment of the present disclosure, a holding device that holds an object is provided. This holding device includes a plate-shaped part formed in a plate shape, a cooling part formed in a plate shape to cool the plate-shaped part, and a cooling part disposed between the plate part and the cooling part, and a cooling part that cools the plate part. a joint portion that joins opposing surfaces of the shaped portion and the cooling portion, the joint portion includes a silicone adhesive and surface-coated aluminum nitride particles, and the thermal conductivity of the joint portion is is 0.8 W/(m·K) or more, and the maximum shear strain of the joint is 0.5 mm or more.
According to this form of the holding device, even when heat input to the plate-like portion increases, the cooling performance of the holding device can be improved and problems caused by stress occurring in the joint portion can be suppressed.
(8) In the holding device of the above embodiment, the plate-shaped portion is made of ceramic as a main component, includes an adsorption electrode for holding the object, and does not include a heater electrode for heating the object. Good too. With such a configuration, even if the object and the plate-shaped part are not heated by the heater electrode, the heat input to the plate-shaped part is large and the temperature difference between the plate-shaped part and the base tends to be large. In this case, it is possible to significantly improve the cooling performance of the holding device and to suppress inconveniences caused by stress occurring in the joints.
The present disclosure can be realized in various forms other than those described above, such as a semiconductor manufacturing apparatus including a holding device, a method for manufacturing a holding device, a method for forming a bonding part, and the like.

FIG. 1 is a perspective view schematically showing the appearance of an electrostatic chuck according to an embodiment. FIG. 2 is a cross-sectional view schematically showing the configuration of an electrostatic chuck. An explanatory diagram showing how to determine "R2/R1" of inorganic filler particles. FIG. 4 is an explanatory diagram showing how heat transfer paths are formed between particles of an inorganic filler. An explanatory diagram regarding stress generated at a joint. FIG. 3 is an explanatory diagram showing how a joint portion expands when shear stress is generated. FIG. 4 is an explanatory diagram showing the measurement results and evaluation results of each sample. FIG. 3 is an explanatory diagram showing an overview of the procedure for measuring the thermal conductivity of a joint. An explanatory diagram schematically showing how the amount of strain at maximum shear stress is determined.

A. Structure of electrostatic chuck:
FIG. 1 is a perspective view schematically showing the appearance of an electrostatic chuck 10 in an embodiment. FIG. 2 is a cross-sectional view schematically showing the configuration of the electrostatic chuck 10. As shown in FIG. In FIG. 1, a part of the electrostatic chuck 10 is shown broken away. 1, FIG. 2, and FIGS. 5 and 8, which will be described later, show XYZ axes that are orthogonal to each other in order to specify directions. The X-axis, Y-axis, and Z-axis shown in each figure represent the same direction. In this specification, the Z axis indicates the vertical direction, and the X axis and Y axis indicate the horizontal direction. Note that each of the above figures schematically represents the arrangement of each part, and does not accurately represent the ratio of the dimensions of each part.

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

The ceramic portion 20 is a substantially circular plate-like member, and is formed mainly of ceramic (for example, aluminum oxide, aluminum nitride, etc.). In the present specification, when a specific component "is the main component" or "is the main forming material", it means that the content of the specific component is 50% by volume or more. The diameter of the ceramic portion 20 may be, for example, about 50 mm to 500 mm, and usually about 200 mm to 350 mm. The thickness of the ceramic portion 20 may be, for example, approximately 1 mm to 10 mm. The ceramic part 20 is also called a "plate-shaped part".

As shown in FIG. 2, an adsorption electrode 22 is arranged inside the ceramic part 20. The adsorption electrode 22 is made of, for example, a conductive material such as tungsten or molybdenum. When a voltage is applied to the attraction electrode 22 from a power supply (not shown), electrostatic attraction is generated, and the wafer W is attracted and fixed to the mounting surface 24 of the ceramic section 20 by this electrostatic attraction. The adsorption electrode 22 may be of a bipolar type or a unipolar type. Further, inside the ceramic part 20, a resistance heating element made of a conductive material (for example, tungsten, molybdenum, etc.) is used to heat the wafer W that is suctioned and fixed to the mounting surface 24. A heater electrode (not shown) may be provided.

The base portion 30 is a substantially circular plate-like member that includes metal. The base portion 30 may include, for example, at least one metal selected from aluminum, magnesium, molybdenum, titanium, tungsten, and nickel. Molybdenum, titanium, and tungsten have relatively small coefficients of thermal expansion among the above-mentioned metals, so when the base portion 30 is constructed using at least one of these metals, the base portion 30 and the ceramic portion 20 are This is desirable because it can suppress the difference in thermal expansion coefficient between the two. In addition, in this specification, "coefficient of thermal expansion" refers to "coefficient of linear expansion." Further, since magnesium has a relatively small Young's modulus, it is desirable to configure the base portion 30 using magnesium because thermal stress generated in the base portion 30 can be reduced. Additionally, aluminum has relatively high thermal conductivity, is easy to process, and is low cost. Therefore, when the base portion 30 is formed using aluminum, it is desirable because the cooling efficiency of the ceramic portion 20 and the wafer W by the base portion 30 can be increased, and the manufacturing cost of the electrostatic chuck 10 can be suppressed. From the viewpoint of suppressing manufacturing costs while increasing the cooling efficiency of the base part 30, it is desirable that the content ratio of metal in the base part 30 is high, and it is desirable that the base part 30 has metal as a main component. For example, it is desirable to contain 90% by mass or more of aluminum, which has high versatility (for example, to be composed of an aluminum alloy such as A6061 or A5052). However, the base portion 30 may contain components other than metal, such as ceramic. The diameter of the base portion 30 may be, for example, approximately 220 mm to 550 mm, and is usually 220 mm to 350 mm. The thickness of the base portion 30 may be, for example, approximately 20 mm to 40 mm. The base portion 30 is also referred to as a “cooling portion”.

A plurality of coolant channels 32 are formed inside the base portion 30 along the XY plane. The base portion 30 is cooled by flowing a refrigerant such as a fluorine-based inert liquid, water, or liquid nitrogen through the refrigerant channel 32 . Then, the ceramic part 20 is cooled by heat transfer between the base part 30 and the ceramic part 20 via the joint 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. In addition to the configuration in which the coolant flow path 32 is provided inside the base portion 30, the base portion 30 may be provided with a cooling function by cooling the base portion 30 from the outside of the base portion 30.

The joining part 40 is arranged between the ceramic part 20 and the base part 30 and joins the facing surfaces of the ceramic part 20 and the base part 30. Joint portion 40 includes a silicone adhesive and further includes surface-coated aluminum nitride particles. The thickness of the joint portion 40 can be, for example, about 0.1 mm to 1.0 mm. The configuration of the joint portion 40 including surface-coated aluminum nitride particles will be described in detail later.

The electrostatic chuck 10 further has a plurality of gas supply paths 50 formed therein. The gas supply path 50 is provided to penetrate the ceramic part 20, the joint part 40, and the base part 30 in the Z direction, and opens at a gas discharge port 52 formed on the mounting surface 24 (see FIG. reference). The gas supply path 50 is 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 discharge port 52 to the space between the mounting surface 24 and the wafer W. supply. Thereby, the heat transfer between the ceramic part 20 and the wafer W is improved, and the controllability of the temperature distribution of the wafer W is further improved. Note that the gas supply path 50 is not essential, and the electrostatic chuck 10 may not be provided with the gas supply path 50.

B. Joint configuration:
Below, the configuration of the joint portion 40 will be explained. As described above, the joint portion 40 contains a silicone adhesive and further contains surface-coated aluminum nitride particles. Silicone adhesive has a relatively low modulus of elasticity, so it has a high ability to relieve thermal stress generated at the joint 40, and has a relatively high heat resistance, so it is excellent as a resin for forming the joint 40. . Surface-coated aluminum nitride particles are particles that have a coating layer containing a compound containing aluminum and oxygen (hereinafter also referred to as "oxygen-containing aluminum compound") on the surface of aluminum nitride particles. Particles can have a diameter of 0.1 to 50 μm. The surface-coated aluminum nitride particles of this embodiment are provided with a coating layer containing an oxygen-containing aluminum compound on the surface, so that the atomic ratio of oxygen atoms to aluminum atoms at the outermost surface of the surface-coated aluminum nitride particles (hereinafter, (also referred to as "O/Al value") is 1.4 or more and 4.0 or less. By having such a configuration, the joint portion 40 of this embodiment ensures low thermal resistance and high flexibility and durability.

The oxygen-containing aluminum compound contained in the coating layer of the surface-coated aluminum nitride particles can be, for example, aluminum oxide (α-alumina: α-Al ₂ O ₃ ), aluminum phosphate (AlPO ₄ ), β-alumina, γ-alumina, YAG (Y ₃ Al ₅ O ₁₂ ), or lanthanum aluminate (LaAlO ₃ ), or a mixture thereof. These oxygen-containing aluminum compounds have relatively high thermal conductivity. Specifically, such oxygen-containing aluminum compounds exhibit a thermal conductivity higher than that (1.38 W/(m·K)) of silicon dioxide (silica: SiO ₂ ), which is conventionally known as a compound constituting a coating layer provided on aluminum nitride particles to enhance the water resistance of the aluminum nitride particles. For example, the thermal conductivity of α-Al ₂ O ₃ is 30 W/(m·K), the thermal conductivity of YAG is 10 W/(m·K), and the thermal conductivity of lanthanum aluminate is 11 W/(m·K). Here, if the thermal conductivity of the material constituting the coating layer is lower than that of aluminum nitride (150 to 200 W/(m·K)), the thermal conductivity of the surface-coated aluminum nitride particles may be lower than that of aluminum nitride. However, by forming the coating layer of the surface-coated aluminum nitride particles using the oxygen-containing aluminum compound as described above, it is possible to suppress the decrease in thermal conductivity caused by providing the coating layer on the aluminum nitride particles.

Moreover, when the above-described oxygen-containing aluminum compound is included in the coating layer, hydroxyl groups are present on the surface of the surface-coated aluminum nitride particles. As a result, the polarity between the surface of the surface-coated aluminum nitride particles and the silicone adhesive becomes close to each other, resulting in improved compatibility. Therefore, by providing a coating layer containing an oxygen-containing aluminum compound as described above on the surface of aluminum nitride particles and setting the O/Al value to 1.4 or more and 4.0 or less, silicone can be added to the aluminum nitride particles. A similar effect of increasing wettability with the adhesive can be obtained. In addition, when using a silane coupling agent together with a silicone adhesive, the silane coupling agent easily bonds with the hydroxyl group on the surface of the surface-coated aluminum nitride particles, so the bond between the silicone adhesive and the surface-coated aluminum nitride particles increases. Familiarity becomes even better.

Surface-coated aluminum nitride particles having a coating layer composed of alpha-alumina can be produced by subjecting aluminum nitride particles to an oxidation treatment. The oxidation treatment can be a treatment in which the aluminum nitride particles are heated in an oxygen-containing atmosphere (e.g., in air or water vapor) at temperatures of 600 to 1000°C. When the surfaces of the aluminum nitride particles are completely coated with alpha-alumina by the oxidation treatment, the theoretical value of the O/Al value in the surface-coated aluminum nitride particles is 1.5.

Surface-coated aluminum nitride particles having a coating layer made of aluminum phosphate can be produced by subjecting aluminum nitride particles to phosphoric acid treatment. The above-mentioned phosphoric acid treatment is, for example, a treatment in which an inorganic phosphoric acid compound is dropped into a dispersion of aluminum nitride particles in a solvent, the reaction is caused to occur at a temperature of about room temperature to 80°C, and then the solvent is evaporated. can do. The inorganic phosphoric acid compound used can be, for example, phosphoric acid (orthophosphoric acid: H ₃ PO ₄ ), pyrophosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, metaphosphoric acid and mixtures thereof. Further, the above-mentioned phosphoric acid treatment can be a treatment in which an organic phosphoric acid compound is dropped into a dispersion of aluminum nitride particles dispersed in a solvent, and then heated under a temperature condition of 150 to 800°C.

When aluminum nitride particles are treated with phosphoric acid as described above to form a coating layer made of aluminum phosphate, the O/Al value exceeds 4.0. This is because the phosphoric acid compound used in the phosphoric acid treatment remains on the surface of the surface-coated aluminum nitride particles after the phosphoric acid treatment. When the surface-coated aluminum nitride particles subjected to such phosphoric acid treatment are further heat-treated at a temperature of 100°C or higher (for example, about 300°C), the phosphoric acid compounds remaining on the surface-coated aluminum nitride particles are removed. As the aluminum phosphate is removed, a reaction proceeds in which a portion of the aluminum phosphate constituting the coating layer becomes aluminum oxide (mainly alpha alumina). The amount of phosphoric acid compound removed and the amount of aluminum oxide generated depend on the degree of heat treatment after phosphoric acid treatment (at least one of increasing the heating time and increasing the heating temperature). ) can be increased. As a result, the value of O/Al gradually decreases from a value exceeding 4.0 and approaches 1.5. At this time, by performing the heat treatment so that the O/Al value becomes 4.0 or less, the phosphoric acid compound remaining on the surface of the surface-coated aluminum nitride particles can be sufficiently removed.

In the electrostatic chuck 10 of this embodiment, the thermal resistance of the bonding portion 40 is desirably 5.0×10 ⁻⁴ (m ² K/W) or less. The thermal resistance of the joint 40 is more preferably 3.5×10 ⁻⁴ (m ² K/W) or less, and even more preferably 2.5×10 ⁻⁴ (m ² K/W) or less. desirable. Note that the thermal conductivity λ and the thermal resistance R refer to values at room temperature (22° C.) here. If the thermal resistance of the joint 40 is R (m ² K/W), the thickness of the joint 40 is t (m), and the thermal conductivity of the joint 40 is λ (W/(m・K)), then the joint The thermal resistance R of 40 is determined by the following equation (1).

R (m ² K/W) = t (m) ÷ λ (W/(m・K)) …(1)

By setting the thermal resistance of the joint part 40 to the above value, heat transfer between the base part 30 and the ceramic part 20 via the joint part 40, that is, heat drawing from the ceramic part 20 to the base part 30, is carried out. The cooling efficiency of the electrostatic chuck 10 can be improved.

According to equation (1), the thermal resistance of the joint 40 can be reduced by reducing the thickness of the joint 40. For example, it is desirable that the thickness of the joint 40 be 500 μm or less, and by setting the thickness to 400 μm or less, the thermal resistance of the joint 40 can be made 5.0×10 ⁻⁴ (m ² K/W) or less. , becomes easier. However, the thickness of the joint 40 may exceed the above value. For example, if the thermal conductivity of the joint 40 is to be increased, even if the thickness of the joint 40 is 400 μm or more, the thermal resistance of the joint 40 may be It becomes relatively easy to reduce the amount of energy to 5.0×10 ⁻⁴ (m ² K/W) or less. Note that the thickness of the joint portion 40 may be, for example, 50 μm or more from the viewpoint of ensuring flexibility and strength of the joint portion 40.

From formula (1), the thermal resistance of the joint 40 can also be reduced by increasing the thermal conductivity of the joint 40. As already mentioned, one method of increasing the thermal conductivity of the joint 40 is to form the coating layer of the surface-coated aluminum nitride particles from an oxygen-containing aluminum compound with a higher thermal conductivity. Another method of increasing the thermal conductivity of the joint 40 is, for example, to increase the content of surface-coated aluminum nitride particles in the joint 40. The content of surface-coated aluminum nitride particles in the joint 40 is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. For example, by making the content of surface-coated aluminum nitride particles in the joint 40 70% by mass or more, it becomes easy to make the thermal conductivity of the joint 40 0.8 W/(m·K) or more.

Note that the larger the content of the inorganic filler in the joint 40, the smaller the amount of strain at the maximum shear stress in the joint 40 tends to be. The amount of strain at maximum shear stress is a numerical value that is an index of the flexibility and stress relaxation performance of the joint 40, and the larger the amount of strain at maximum shear stress, the better the flexibility and stress relaxation performance of the joint 40. Show that there is. The amount of strain at maximum shear stress will be explained in detail later. In this way, the higher the content ratio of the inorganic filler in the joint 40, the smaller the amount of strain at the maximum shear stress in the joint 40. This is thought to be because the extent to which the composition (composition) is restrained increases, the flexibility of the bonded portion 40 decreases, and the bonded portion 40 becomes less likely to be distorted. Therefore, from the viewpoint of suppressing the amount of strain at maximum shear stress in the joint 40 and ensuring flexibility, it is desirable that the content of surface-coated aluminum nitride particles in the joint 40 is 90% by mass or less.

The lower limit value of the thermal resistance of the joint portion 40 can be, for example, 0.6×10 ⁻⁴ (m ² K/W). In order to suppress the thermal resistance of the joint portion 40, it is possible to appropriately select the material constituting the inorganic filler and increase the content ratio of the inorganic filler, as described above. However, if the content of the inorganic filler is increased excessively, the flexibility of the joint portion 40 may be impaired. Further, in order to suppress the thermal resistance of the joint portion 40, a method of making the joint portion 40 thinner can be considered. However, if the joint part 40 is made excessively thin, the strength of the joint part 40 will decrease, and it may become difficult to ensure the flexibility of the joint part 40. Therefore, it is desirable that the thermal resistance of the bonding portion 40 be equal to or greater than the above-mentioned 0.6×10 ⁻⁴ (m ² K/W).

Further, the thermal resistance of the joint 40 can be changed depending on the shape of the inorganic filler particles included in the joint 40. In order to reduce the thermal resistance of the joint 40, when the inorganic filler is viewed in cross section, the radius of the inscribed circle is R1, and the radius of the circumscribed circle is R2, and the average value of "R2/R1" is It is desirable that the value is 1.05 or more, and more preferably 1.10 or more. The closer "R2/R1" is to 1.0, the closer the particle shape is to a perfect sphere (hereinafter also referred to as high sphericity).

The specific method for determining the inscribed circle and circumscribed circle and the method for determining "R2/R1" are as follows. That is, in an image obtained by observing a cross section of the joint portion 40 using a scanning electron microscope (SEM), attention is paid to one particle observed. Then, a circle is drawn so as to enclose the particle of interest and touch three vertices of the particle, and this is defined as a circumcircle. Further, a circle is drawn so as to be included in the particle and touch the outer periphery of the particle at three points, and this is defined as an inscribed circle. If multiple circles can be drawn, the circle with the smallest radius is used as the inscribed circle and circumscribed circle. The inscribed circle and circumscribed circle are similarly specified for 20 particles, the radius R1 of the inscribed circle and the radius R2 of the circumscribed circle are measured, and "R2/R1" is calculated from the average value.

FIG. 3 is an explanatory diagram showing how to determine "R2/R1" when particles of inorganic filler 42 are viewed in cross section, and FIG. 4 is an explanatory diagram showing how heat transfer paths are formed between inorganic fillers 42. It is a diagram. In FIG. 3, when the inorganic filler 42 is viewed in cross section, the inscribed circle is shown by a dashed-dot line, and the circumscribed circle is shown by a dashed-two dotted line. Further, the center of the inscribed circle is shown as O ₁ , and the center of the circumscribed circle is shown as O ₂ . In FIG. 4, double-headed arrows represent the formation of heat conduction paths where the inorganic fillers 42 come into contact with each other. The value of "R2/R1" when the inorganic filler 42 is viewed in cross section is equal to or higher than the above-mentioned lower limit value, and the shape of the inorganic filler 42 is different from a perfect sphere and has irregularities on the surface, as shown in FIG. The number of points of contact between the inorganic fillers 42 increases, making it easier to form a heat conduction path within the joint 40, thereby reducing the thermal resistance of the joint 40. Note that the value of "R2/R1" can be changed in various ways by adjusting the manufacturing method of the aluminum nitride particles, or by subjecting the aluminum nitride particles to a treatment to increase the sphericity.

Furthermore, in this embodiment, it is desirable that the strain amount of the joint portion 40 at the time of maximum shear stress is 0.5 mm or more. The amount of strain at maximum shear stress of the joint portion 40 is more preferably 1.0 mm or more, and even more preferably 1.3 mm or more. Note that the amount of strain at the maximum shear stress of the joint portion 40 is usually 5.0 mm or less. As mentioned above, the "amount of strain at maximum shear stress" is a value that is an index representing the flexibility and stress relaxation performance of the joint 40, and when a shear force is applied to the joint 40, the strain at the joint 40 is It refers to the magnitude of strain (displacement in the shear force direction) that occurs in the joint 40 when the shear stress generated at the joint 40 reaches its maximum, that is, when the maximum shear stress occurs at the joint 40. The larger the amount of strain at maximum shear stress, the higher the flexibility of the joint 40. A specific measuring method using a tensile testing machine for measuring the amount of strain at maximum shear stress will be described in detail later. By setting the amount of strain at maximum shear stress of the bonded portion 40 to the above value, it becomes possible to ensure sufficient flexibility and stress relaxation performance of the bonded portion 40.

FIG. 5 is an explanatory diagram regarding the stress generated at the joint 40. When the electrostatic chuck 10 is used, the ceramic part 20 is heated and expanded due to heat input to the ceramic part 20 due to exposure to plasma or the like. Further, the base portion 30 is cooled and contracts by being provided with the coolant flow path 32. In FIG. 5, outline arrows indicate how the ceramic part 20 is heated and expands, and how the base part 30 is cooled and contracts. At this time, a force that pulls the ceramic part 20 and the base part 30 acts on the joint part 40 . In FIG. 5, the force by which the joint part 40 pulls the ceramic part 20 and the force by which the base part 30 is pulled are shown by arrows, respectively. Furthermore, in FIG. 5, the amount of displacement in the X-axis direction that occurs in the joint portion 40 is shown as the amount of strain δ.

Further, in the electrostatic chuck 10, the base portion 30 generally has a higher coefficient of thermal expansion than the ceramic portion 20, and expands and contracts significantly due to temperature changes. Therefore, depending on the temperature conditions, the extent to which the base portion 30 thermally expands may be greater than the extent to which the ceramic portion 20 thermally expands. As described above, since the degree of expansion and contraction differs between the ceramic part 20 and the base part 30, shear force in the X-axis direction is applied to the joint part 40, and shear stress is generated. Therefore, by increasing the amount of strain at maximum shear stress of the joint 40 as described above, even when a large shear force is applied to the joint 40, the shear stress generated at the joint 40 can be reduced. damage to the joint portion 40 can be suppressed.

Figure 6 is an explanatory diagram showing how the joint 40 expands when shear stress occurs in the joint 40. The greater the strain at maximum shear stress of the joint 40 containing an inorganic filler such as surface-coated aluminum nitride particles, the greater the flexibility of the adhesive (resin) constituting the joint 40 and the better the compatibility (wettability) between the adhesive constituting the joint 40 and the inorganic filler (the better the wettability). In this embodiment, a silicone-based adhesive with excellent flexibility is used as the adhesive constituting the joint 40. And, surface-coated aluminum nitride particles with a coating layer containing an oxygen-containing aluminum compound are used as the inorganic filler. Such surface-coated aluminum nitride particles have good wettability with the silicone-based adhesive, which is an oxide, and have good compatibility with the silicone-based adhesive. Therefore, the strain at maximum shear stress of the entire joint 40 becomes large. In Figure 6, (a) shows how shear stress is applied to the joint 40 containing an inorganic filler with good wettability, and (b) shows how shear stress is applied to the joint 40 containing an inorganic filler with insufficient wettability. As shown in Figure 6 (b), if the wettability of the inorganic filler is insufficient, even if the adhesive has flexibility, when the adhesive stretches due to shear stress, breakage is likely to occur at the interface between the adhesive and the inorganic filler, resulting in a small amount of strain at maximum shear stress.

Note that the amount of strain at the maximum shear stress of the bonded portion 40 can also be increased by increasing the thickness of the bonded portion 40. Furthermore, as described above, the larger the content of the inorganic filler in the joint 40, the smaller the amount of strain at the maximum shear stress of the joint 40 tends to be.

The joint 40 further contains a filler other than the surface-coated aluminum nitride particles as a filler (inorganic filler) for adjusting the properties of the joint 40 and the properties of the paste for forming the joint 40. You can stay there. Examples of the other fillers mentioned above include aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ), yttrium oxide (yttria: Y ₂ O ₃ ), yttrium fluoride (YF ₃ ), Aluminum nitride (AlN), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), silicon dioxide (silica: SiO ₂ ), iron oxide, barium sulfate, calcium carbonate, etc. can be used. The content of the other filler in the joint portion 40 may be such that the effect of the joint portion 40 containing the surface-coated aluminum nitride particles is within a permissible range.

Note that the joint portion 40 further includes a catalyst that promotes the curing reaction of the adhesive, a silane coupling agent that promotes curing and adhesion to provide adhesive properties, a crosslinking agent, and a material for adjusting the curing speed of the adhesive. It may also contain a reaction inhibitor, a viscosity modifier, etc.

According to the electrostatic chuck 10 of the present embodiment configured as described above, the joint portion 40 included in the electrostatic chuck 10 includes a silicone adhesive and surface-coated aluminum nitride particles, and includes a silicone-based adhesive and surface-coated aluminum nitride particles. The value of O/Al, which is the atomic ratio of oxygen atoms to aluminum atoms at the outermost surface, is 1.4 or more and 4.0 or less. In this way, by setting the O/Al value to 1.4 or more, it is possible to improve the wettability with the silicone adhesive, which is an oxide, on the surface of the surface-coated aluminum nitride particles. As a result, it is possible to achieve sufficient flexibility in the joint 40 to stretch when shear stress occurs, and it is possible to suppress inconveniences caused by stress occurring in the joint 40, such as damage to the joint 40. Further, by including the surface-coated aluminum nitride particles, high thermal conductivity can be achieved in the joint portion 40, and the cooling performance in the electrostatic chuck 10 can be improved. Specifically, it becomes easy to make the amount of strain at maximum shear stress of the joint part 40 0.5 mm or more, and to make the thermal conductivity of the joint part 40 0.8 W/(m·K) or more.

Such an effect is particularly noticeable when the electrostatic chuck 10 is exposed to high-power plasma, where the heat input to the ceramic portion is large. For example, even if a heater electrode for heating the ceramic part 20 is not provided, if the electrostatic chuck 10 is used with high plasma power, there is a gap between the mounting surface of the ceramic part 20 and the base part 30. Since the temperature difference between the two temperatures tends to become large, the effects of this embodiment can be significantly obtained.

In addition, according to this embodiment, since the O/Al value is 4.0 or less as described above, it is possible to prevent substances contained in the coating layer from volatilizing into the plasma atmosphere during use of the electrostatic chuck 10 and becoming a source of contamination for objects such as the wafer W. This is because if the O/Al value is 4.0 or less, it is believed that substances contained in the material used to form the coating layer that could be a source of contamination (for example, phosphate compounds such as phosphoric acid used in the phosphate treatment when aluminum phosphate is used as the oxygen-containing aluminum compound) have been removed.

C. Other embodiments:
The present disclosure may be applied to holding devices other than electrostatic chucks that hold wafers W using electrostatic attraction. That is, other holding devices that include a plate-like part, a cooling part (base part), and a joint part that joins the plate-like part and the cooling part and hold an object on the surface of the plate-like part, for example, , CVD, PVD, PLD, etc., and vacuum chucks.

Further, in each of the above-described embodiments, the plate-like part having the mounting surface is the ceramic part 20 mainly made of ceramic, but the plate-like part may be made mainly of a material other than ceramic. . Even with such a configuration, by applying the configuration of the present disclosure exemplified in the embodiment, the cooling performance of the holding device can be improved to suppress the stress generated at the joint, and the problems caused by the stress generated at the joint can be solved. A similar effect can be obtained.

The holding device of the present disclosure will be described below based on examples. Here, sheet-like samples S1 to S9 were prepared as various samples having different O/Al values, thermal resistance of the joint, amount of strain at maximum shear stress, etc. Further, a sample in the form of an electrostatic chuck was produced, which had a bonded portion having the same composition as each of the sheet-like samples S1 to S9 and had the same configuration as the electrostatic chuck 10 of the embodiment shown in FIG. In the following, a sample in the form of an electrostatic chuck will be referred to by the same sample number as a sheet-like sample having the same composition as the joint.

Figure 7 shows the O/Al value and "R2/R1" value of the surface-coated aluminum nitride particles included in each sample, as well as the joint thickness, thermal resistance, content ratio of surface-coated aluminum nitride particles, and maximum shear stress. Explanation that summarizes the results of evaluating the heat-resistance response, which indicates the cooling performance of the ceramic part through the joint, and the ease of damage (peeling) of the joint, along with the values of strain and thermal conductivity. It is a diagram.

<Preparation of each sample>
Below, first, a method for producing a sheet-like sample and an electrostatic chuck-type sample common to each sample will be explained, and then the materials and production conditions of each sample will be explained. Samples S1 to S9 all have joints made of a silicone adhesive mixed with an inorganic filler.

[Preparation of inorganic filler]
Samples S1 to S5 used aluminum nitride particles (surface-coated aluminum nitride particles) provided with a coating layer made of an oxygen-containing aluminum compound as an inorganic filler. Samples S6 to S8 used aluminum nitride particles without a coating layer as the inorganic filler. Sample S9 used aluminum nitride particles provided with a coating layer made of silicon dioxide as an inorganic filler.

As the aluminum nitride particles, powder with an average particle diameter of 15.0 μm manufactured by Toyo Aluminum was used. The aluminum nitride particles used in Samples S1 to S3 and Samples S6 and S7 were subjected to nylon ball milling in a solvent for 72 hours in order to make the particle shape closer to a true sphere.

In samples S1 to S3 and sample S5, aluminum nitride particles and phosphoric acid were mixed using a mixer, and the surface of the aluminum nitride was coated with phosphoric acid (phosphoric acid treatment). Thereafter, heat treatment was performed at a temperature of 100° C. or higher to form aluminum phosphate on the surface of the aluminum nitride particles to provide a coating layer. The obtained powder was washed with pure water to obtain surface-coated aluminum nitride particles having a coating layer of aluminum phosphate. Note that the coating layer provided on the surface-coated aluminum nitride particles of Samples S1 to S3 and Sample S5 obtained as described above is considered to contain α-alumina in addition to aluminum phosphate.

In sample S4, aluminum nitride particles were heat-treated (oxidized) at 800° C. in an air atmosphere to form an α-alumina coating layer on the particle surface. In sample S9, aluminum nitride particles were mixed with tetraethoxysilane in a solvent, and after removing the solvent, heat treatment was performed at a temperature of 150° C. or higher. Thereafter, sufficient washing was performed to obtain aluminum nitride particles having a coating layer of silicon dioxide.

[Preparation of sheet sample]
The method for producing the sheet-like sample is as follows. In addition to the silicone adhesive before curing and the inorganic filler for each sample, a silane coupling agent, a crosslinking agent, and a catalyst were added and mixed to obtain a varnish-like silicone adhesive composition (adhesive paste). Note that the same type of silicone adhesive was commonly used in samples S1 to S9. The obtained adhesive paste was formed into a sheet shape by a doctor blade method. At this time, the thickness of the sheet sample was varied depending on the sample by changing the conditions of the molding machine that applied the adhesive paste using a doctor blade. The sheet-shaped adhesive paste was heat-treated at a temperature of 100° C. or lower to semi-cure.

[Preparation of sample in electrostatic chuck form]
A sample in the form of an electrostatic chuck was produced by bonding a ceramic part (plate-like part) and a base part (cooling part) using the semi-cured adhesive paste described above. The ceramic part was produced as follows. First, a plurality of ceramic green sheets containing alumina as a main component were produced by a conventionally known method. Then, heaters, adsorption electrodes, vias, and ventilation holes are formed on the ceramic green sheets, and these ceramic green sheets are laminated, thermocompressed, and fired at 1400 to 1600°C in a reducing atmosphere to form a 50 mm thick ceramic. I got the department. Next, the semi-cured adhesive paste described above was placed between the ceramic part and the base part, and then the adhesive paste was thermally cured to obtain a sample in the form of an electrostatic chuck.

[Samples S1 to S5]
Samples S1 to S5 were produced using surface-coated aluminum nitride particles as an inorganic filler, as described above. When producing the adhesive paste described above, the mixing ratio of the silicone adhesive before curing and the surface-coated aluminum nitride particles was changed depending on the sample. Therefore, as shown in FIG. 7, the content ratio (particle content ratio) of surface-coated aluminum nitride particles in the joint portion differs depending on the sample. Specifically, the particle content of sample S1 was 60% by mass, the particle content of sample S2 was 70% by mass, and the particle content of samples S3 to S5 was 80% by mass. Moreover, by making the thickness of the sheet-like samples different, the thickness of the joint part of each sample was 500 μm for sample S1, 300 μm for samples S2 and S4, and 200 μm for samples S3 and S5.

[Samples S6 to S8]
As described above, samples S6 to S8 were produced using aluminum nitride particles without a coating layer as an inorganic filler. In samples S6 to S8, the mixing ratio of the silicone adhesive before curing and the aluminum nitride particles was changed depending on the sample when preparing the adhesive paste, and as a result, as shown in FIG. The content ratio of aluminum nitride particles (particle content ratio) differs depending on the sample. Specifically, the particle content ratio of sample S6 was 30% by mass, and the particle content ratio of samples S7 and S8 was 46% by mass. Further, by making the thickness of the sheet-like samples different, the thickness of the joint portion of each sample was 300 μm for sample S6, 400 μm for sample S7, and 600 μm for sample S8.

[Sample S9]
As described above, sample S9 was produced using aluminum nitride particles provided with a coating layer made of silicon dioxide (silica: SiO ₂ ) as an inorganic filler. The particle content of sample S9 was 46% by mass, and the thickness of the joint was 500 μm.

<Measurement of O/Al value>
The value of O/Al is based on the inorganic filler that is the material used to make each sample (surface-coated aluminum nitride particles with a coating layer made of an oxygen-containing aluminum compound, aluminum nitride particles without a coating layer, or made of silica). The surface of aluminum nitride particles (with a coating layer) was analyzed by X-ray photoelectron spectroscopy (XPS) to identify the elements that constitute the outermost surface of the inorganic filler. . Specifically, for all compounds containing aluminum, the composition ratio was calculated from the peak area, and the value of O/Al was calculated.

<Measurement of thermal conductivity>
FIG. 8 is an explanatory diagram showing an overview of the procedure for measuring the thermal conductivity of a joint. When measuring the thermal conductivity of a joint, first, for each sample in the form of the electrostatic chuck 10, an arbitrary part is measured in the thickness direction (Z direction) with a size of 50 mm x 50 mm in the XY direction. (from (A) in FIG. 8 to (B) in FIG. 8), and the joint portion 40 was removed from the obtained test piece with a cutter ((B) in FIG. 8 to (B) in FIG. 8). C)). In FIGS. 8A and 8B, the cut out portion is shown surrounded by a dashed line. The joint portion cut out as shown in FIG. 8C was punched out to a size of 10 mm in diameter, and the thermal diffusivity was measured by a laser flash method. Further, the density of the bonded portion was measured by the Archimedes method using the bonded portion cut out as shown in FIG. 8(C). Then, the thermal conductivity was calculated from the measured thermal diffusivity and density value.

<Calculation of thermal resistance>
In order to calculate the thermal resistance of the joint, an arbitrary part of each sample in the form of the electrostatic chuck 10 is cut out in the XY direction to a size of 50 mm x 50 mm (from (A) in FIG. 8 to (B)) The thickness of the joint was measured by observing the cross section of the obtained test piece with an optical microscope. Then, the thermal resistance value of the joint was calculated from the thickness of the joint thus measured and the thermal conductivity of the joint calculated as described above. The thermal resistance value was calculated using the above-mentioned equation (1).

<Particle content ratio>
Inclusion of an inorganic filler in the joint (surface-coated aluminum nitride particles with a coating layer made of an oxygen-containing aluminum compound, aluminum nitride particles without a coating layer, or aluminum nitride particles with a coating layer made of silica) The ratio (particle content ratio) was measured as follows. First, for each sample in the form of the electrostatic chuck 10, an arbitrary part was cut out in a size of 50 mm x 50 mm in the XY direction ((A) in FIG. 8 to (B) in FIG. 8), and the obtained test The joint portion 40 was removed from the piece using a cutter (FIG. 8(B) to FIG. 8(C)). After measuring the mass of the cut joint, the silicone resin was dissolved with a silicone dissolving agent, and the inorganic filler contained therein was collected. The mass of the obtained inorganic filler was measured and the ratio to the mass before dissolving the silicone adhesive was calculated to calculate the particle content ratio of the joint portion.

<Calculation of R2/R1>
In order to calculate the value of "R2/R1", an arbitrary portion of each sample in the form of the electrostatic chuck 10 was cut out in the XY direction to a size of 50 mm x 50 mm (FIG. 8A to FIG. 8B), and the joint 40 was removed from the obtained test piece with a cutter (FIG. 8B to FIG. 8C). The cross section of the cut joint was mirror-polished and then observed using a scanning electron microscope (SEM), and the shapes of 10 particles of the inorganic filler observed in a field of view of 200 μm x 200 μm were observed. The image analysis software WinROOF was used to measure the radius R1 of the inscribed circle and the radius R2 of the circumscribed circle to determine the value of "R2/R1" (see FIG. 3), and the value of "R2/R1" of each sample was calculated as the average value of the 10 particles.

<Measurement of strain amount at maximum shear stress>
FIG. 9 is an explanatory diagram schematically showing how the amount of strain at maximum shear stress is determined. The amount of strain at maximum shear stress is obtained by determining the maximum shear stress as the maximum value of shear stress by a tensile test, and measuring the amount of strain when the shear stress reaches the maximum shear stress. FIG. 9(A) shows the tensile test as seen from the front, and FIG. 9(B) shows the state as seen from the side. The test pieces 70 of samples S1 to S9 were obtained by pasting the semi-cured adhesive sheet of each sample on a 25 mm x 12 mm area from the edge of two aluminum plates 72 of 25 mm width x 150 mm length to a position 12 mm from the edge. After attaching the two aluminum plates 72 to each other in a direction that allows them to be pulled in opposite directions, the semi-cured adhesive sheet described above was cured. The thickness t of the test piece 70 at the start of the test is the thickness of the joint shown in FIG. Next, the two aluminum plates 72 were moved relative to each other so that shear force was applied to the test piece. In FIG. 9(B), the direction of relative movement (shearing direction) between the two aluminum plates is shown by a white arrow. The shear stress was calculated by dividing the load by the adhesive area (25 mm x 12 mm) of the test piece before movement. Such relative movement of the two aluminum plates was continued until the test piece 70 broke, and the shear stress when the shear stress reached the maximum was defined as the maximum shear stress (unit: MPa). The amount of strain at maximum shear stress (unit: mm) was defined as the amount of displacement in the shear direction of the test piece 70 when the shear stress reached the maximum in the tensile test shown in FIG.

<Evaluation of heat removal response>
For each sample S1 to S9 in the form of an electrostatic chuck, the heat removal response (cooling performance of the ceramic part via the joint) was evaluated. Specifically, the initial temperature of the ceramic part of each sample was set to 150°C, and the ceramic part was heated until the temperature reached 150°C. In addition, a 30° C. refrigerant was supplied to the refrigerant channel of the base to cool the base. After the temperature of the ceramic part reaches 150°C, heating of the ceramic part is stopped and the temperature of the surface of the ceramic part is measured with a thermo camera, and the time until the temperature of the surface of the ceramic part cools to 40°C is measured. did. If it takes longer than 500 seconds for the ceramic part to cool down to 40°C, the heat removal response is evaluated as low (×), and if it takes 300 seconds or less, the heat removal response is very good. It was evaluated as (◎). If the time it takes for the ceramic part to cool to 40°C is longer than 300 seconds and less than 400 seconds, the heat removal response is evaluated as excellent (○); In the following cases, the heat response was evaluated as good (△).

<Evaluation of peeling of joints>
A peel test was conducted on each of the samples S1 to S9 in the form of an electrostatic chuck, and peeling of the bonded portion was evaluated. Specifically, each sample was placed in a commercially available heat cycle tester and subjected to 100 cycles of a heat cycle test with a maximum temperature of 150°C and a minimum temperature of 0°C, and then returned to room temperature to test the bond between the ceramic part and the base part. The presence or absence of peeling was evaluated. The presence or absence of peeling at the joint was determined using a known ultrasonic flaw detector. Ultrasonic waves are irradiated from the ceramic part side, and if a reflected echo (flaw echo) is detected from the depth corresponding to the bonding interface between the ceramic part and the joint, it is determined that there is peeling at the bonding interface between the ceramic part and the joint. did. Ultrasonic waves were irradiated from the base side, and if a reflected echo (flaw echo) was detected from a depth corresponding to the joint interface between the base and the joint, it was determined that there was peeling at the joint interface between the base and the joint. A test piece in which peeling was observed on at least one of the two interfaces described above was evaluated as "presence of peeling", and a sample in which no peeling was observed by ultrasonic flaw detection was evaluated as "no peeling".

As shown in FIG. 7, when the value of O/Al, which is the atomic ratio of oxygen atoms to aluminum atoms at the outermost surface of the surface-coated aluminum nitride particles, is 1.4 or more (samples S1 to S5), It was confirmed that the responsiveness was evaluated as good (△) or higher.

On the other hand, when the O/Al value was less than 1.4, sufficient performance in terms of heat resistance was not obtained. As shown in samples S6 to S8, when the aluminum nitride particles did not have a coating layer, peeling occurred at the joint, and sufficient heat resistance was not achieved at the joint. This is thought to be because the wettability of the aluminum nitride particles was inferior to that of the surface-coated aluminum nitride particles, and the aluminum nitride particles did not become intimately attached to the silicone adhesive. Also, as shown in sample S9, when aluminum nitride particles with a coating layer made of silicon dioxide were used, peeling did not occur at the joint, but the heat resistance was poor. This is thought to be because the thermal conductivity of the coating layer made of silicon dioxide was lower than the thermal conductivity of the coating layer made of an oxygen-containing aluminum compound.

In addition, as shown in Figure 7, in addition to the O/Al value being 1.4 or more (sample S1), the thickness of the joint was made thinner (400 μm or less), and the thermal resistance of the joint was It was confirmed that the heat removal response was further improved by setting the temperature to 5.0×10 ⁻⁴ m ² K/W or less (sample S2). Here, in the heat removal response evaluation results shown in FIG. 7, both sample S2 and sample S3 have excellent heat removal response (○), but the heat removal response is The time required for cooling after stopping the heating used in the evaluation was shorter for sample S3 than for sample S2. In other words, it was confirmed that increasing the particle content (for example, 70% by mass or more) improves the heat removal response. Further, as can be seen by comparing Sample S3 and Sample S5, it was confirmed that the heat removal response was further improved by setting the average value of "R2/R1" to 1.10 or more. Furthermore, as can be seen by comparing samples S4 and S5, it was confirmed that similar effects can be obtained even if the content ratios of aluminum oxide and aluminum phosphate are different in the coating layer of surface-coated aluminum nitride particles. It was done.

The present disclosure is not limited to the above-described embodiments, etc., and can be implemented in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary column of the invention may be used to solve some or all of the above-mentioned problems, or to achieve one of the above-mentioned effects. In order to achieve some or all of the above, it is possible to replace or combine them as appropriate. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

10... Electrostatic chuck 20... Ceramic part 22... Adsorption electrode 24... Placement surface 30... Base part 32... Refrigerant channel 40... Joint part 42... Inorganic filler 50... Gas supply path 52... Gas discharge port 70... Test piece 72 ...Aluminum plate

Claims (7)

A holding device for holding an object,
a plate-shaped part formed in a plate-shape;
a cooling part formed in a plate shape and cooling the plate part;
a joint part that is disposed between the plate-like part and the cooling part and connects opposing surfaces of the plate-like part and the cooling part;
Equipped with
The joint portion includes a silicone adhesive and surface-coated aluminum nitride particles,
A holding device characterized in that the value of O/Al, which is the atomic ratio of oxygen atoms to aluminum atoms at the outermost surface of the surface-coated aluminum nitride particles, is 1.4 or more and 4.0 or less. 2. The holding device according to claim 1,
A holding device, characterized in that the thermal resistance of the joint is 5.0×10 ⁻⁴ m ² K/W or less. 3. A holding device according to claim 1 or 2,
A holding device, characterized in that the thickness of the joint is 400 μm or less. A holding device according to any one of claims 1 to 3,
A holding device characterized in that a content ratio of the surface-coated aluminum nitride particles in the joint portion is 70% by mass or more. A holding device according to any one of claims 1 to 4,
When the surface-coated aluminum nitride particles are viewed in cross section, the radius of the inscribed circle is R1, and the radius of the circumscribed circle is R2, and the average value of R2/R1 is 1.10 or more. holding device. A holding device according to any one of claims 1 to 5, comprising:
A holding device, characterized in that the joint portion has a maximum shear strain of 0.5 mm or more. A holding device according to any one of claims 1 to 6 ,
The holding device, wherein the plate-shaped portion is mainly made of ceramic, includes an attraction electrode for holding the object, and does not include a heater electrode for heating the object.

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