Holding device

Abstract

To provide a holding device including a porous body that improves a gas flow rate while keeping necessary hardness.SOLUTION: A holding device includes a holding substrate including a plate-shaped member having a first surface that holds a wafer and mainly containing ceramics, and a gas flow channel formed in the plate-shaped member. A substrate side gas flow channel partially includes a porous region mainly containing ceramics, including a number of pores, and formed of a portion where a porous body 70 with gas permeability is disposed. The porous body 70 includes a columnar pore 71A extending in a columnar shape as a pore 71.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a retention device. [Background technology]

[0002] An electrostatic chuck described in Patent Document 1 is known as an example of a holding device for holding a wafer during semiconductor manufacturing. This type of electrostatic chuck has a chuck body made mainly of insulating ceramics such as alumina, and the wafer is held on the surface of the chuck body by electrostatic attraction. The electrostatic attraction is generated by applying a voltage to a chuck electrode provided inside a ceramic substrate.

[0003] In this type of electrostatic chuck, a thermally conductive gas such as helium gas is supplied between the ceramic substrate and the wafer during plasma processing such as plasma etching to remove heat from the wafer. For this reason, a conduit for flowing the thermally conductive gas supplied from the outside toward the wafer is formed inside the chuck body of the electrostatic chuck, extending from the back surface of the chuck body to the front surface on which the wafer is placed.

[0004] During plasma processing, high-frequency power is applied to the pedestal supporting the chuck body, generating a bias voltage on the wafer. In this case, the potential difference between the wafer and the pedestal increases, generating an arc discharge within the linear conduit, which can damage the wafer held by the chuck body. To suppress such arc discharge, a porous body is disposed within the conduit. In the electrostatic chuck described in Patent Document 1, the porous body is made of an insulating ceramic material such as alumina. A network of ventilation paths for passing a thermally conductive gas is formed within the porous body. These ventilation paths are formed by pores that remain after pore-forming materials, such as synthetic resin beads or carbon powder, are oxidized and lost during the sintering process. In other words, the ventilation paths are formed by multiple pores connected in a network within the porous body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4959905 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to increase the permeability of a porous body to a thermally conductive gas, it is necessary to increase the porosity of the porous body. However, in conventional methods, the higher the porosity of the porous body, the more likely the hardness of the porous body is to decrease. From the viewpoint of handling the porous body, it is preferable that the porous body has a certain hardness.

[0007] The present disclosure was completed based on the above circumstances, and aims to provide a holding device having a porous body that improves gas flow rate while maintaining the required hardness. [Means for solving the problem]

[0008] The holding device of the present disclosure is a holding device comprising a holding substrate including a first surface for holding an object, a plate-shaped member mainly composed of ceramic, and a gas flow path formed inside the plate-shaped member, wherein a portion of the gas flow path has a porous region consisting of a location where a gas-permeable porous body mainly composed of ceramic and containing a large number of pores is arranged, and the porous body includes columnar pores formed to extend in a columnar shape as the pores. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a holding device including a porous body that maintains the required hardness while improving the gas flow rate. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram that schematically shows the general configuration of a holding device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating the internal structure of the holding device according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the holding device, with a portion of the substrate-side gas flow path enlarged. [Figure 4] FIG. 4 is an explanatory diagram that schematically shows part of the internal structure of the porous body. [Figure 5] Figure 5 is an explanatory diagram summarizing the volume ratios of the first pore-forming material and the second pore-forming material in the unsintered porous body, and the volume ratio of columnar pores to the total volume of pores contained in the porous body. [Figure 6] FIG. 6 is an explanatory diagram illustrating the width, length and aspect ratio of the first pore-forming material. [Figure 7] FIG. 7 is an SEM image obtained by photographing a cut surface of the porous body according to the sample of the example. [Figure 8] FIG. 8 is a graph showing the He permeation rate vs. pressure for the examples and comparative examples. [Figure 9] FIG. 9 is a cross-sectional view of a holding device according to the second embodiment, showing an enlarged view of a part of a substrate-side gas flow path of the holding device. DETAILED DESCRIPTION OF THE INVENTION

[0011] First, embodiments of the present disclosure will be listed and described. (1) The holding device of the present disclosure is a holding device comprising a holding substrate including a first surface for holding an object, a plate-shaped member mainly composed of ceramic, and a gas flow path formed inside the plate-shaped member, wherein the gas flow path has a porous region in a portion thereof consisting of a gas-permeable porous body mainly composed of ceramic and containing a large number of pores, and the porous body includes columnar pores formed to extend in a columnar shape as the pores.

[0012] Each of the numerous columnar pores is formed in a columnar elongated shape. Therefore, the numerous columnar pores are interconnected, which facilitates the formation of a network-like ventilation path within the porous body with sufficient length. The ventilation path extends along the direction of the gas flow path, improving the gas permeability of the porous body. Furthermore, when ventilation paths are formed by numerous columnar pores, the porous body is less likely to become sparse than when ventilation paths are formed solely by pores of other shapes, such as spherical ones. Therefore, a holding device is provided that includes a porous body that maintains the required hardness while improving the gas flow rate.

[0013] (2) In the holding device described in (1), it is preferable that the porous body includes a large number of spherical pores formed as the pores.

[0014] By including a large number of spherical pores in addition to a large number of columnar pores as pores, each of the columnar pores and each of the spherical pores are connected to each other, making it easier to develop ventilation paths inside the porous body. This also reduces excessive linear connections between the columnar pores. Furthermore, this also reduces the possibility of the porous body becoming excessively sparse, which would be caused by multiple columnar pores overlapping in parallel. This maintains the hardness of the porous body, further improving the gas flow rate.

[0015] (3) In the holding device described in (1) or (2), it is preferable that the width of the columnar pores is 5 μm or more and 20 μm or less, and that the aspect ratio, which is expressed by the value obtained by dividing the length of the columnar pores by the width of the columnar pores, is 5 or more.

[0016] Since the columnar pores have a width within a predetermined range and a predetermined length, the porous body can ensure a desired gas flow rate. In addition, in such a case, the porous body is less likely to become sparse, and the hardness of the porous body is maintained at a predetermined level or higher.

[0017] (4) In the holding device described in (2), it is preferable that the diameter of the spherical pores is 25 μm or more and 55 μm or less.

[0018] By making the spherical pores have a predetermined size, the numerous columnar pores and the numerous spherical pores are easily dispersed and arranged in the porous body, thereby providing a holding device including a porous body that maintains the required hardness while improving the gas flow rate.

[0019] (5) In the holding device described in (2), it is preferable that the volume ratio of the columnar pores to the total volume of the pores contained in the porous body is 40% or more and 60% or less.

[0020] By ensuring that the volume ratio of columnar pores to the total volume of pores contained in the porous body is within a specified range, it is possible to provide a holding device equipped with a porous body that maintains the required hardness while improving the gas flow rate.

[0021] <Details of the first embodiment of the present disclosure> The schematic configuration of a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 4. The present disclosure is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included. In the following description, for multiple identical components, only some components may be designated by reference numerals, and the reference numerals for other components may be omitted. In this specification, the configuration of the holding device 100 will be described with the positive Z-axis direction as the upward direction, the negative Z-axis direction as the downward direction, and the XY plane direction as the horizontal direction. However, in actual use of the holding device 100, different arrangements may be used. Furthermore, in this specification, "orthogonal" also includes arrangements that are recognized as substantially orthogonal.

[0022] The holding device 100 of the first embodiment is an electrostatic chuck that can attract and hold an object (hereinafter referred to as a "wafer W") to be processed, such as by film formation or etching, by electrostatic attraction. The object to be processed is a semiconductor wafer, a glass substrate, or the like. The electrostatic chuck is attached, for example, inside a processing chamber of a semiconductor manufacturing device (not shown), and is used to perform processes, such as film formation or etching, on the wafer W using plasma.

[0023] 1, the holding device 100 of the first embodiment includes a disk-shaped holding substrate 10 and a disk-shaped base member 20 that is larger than the holding substrate 10. For example, if the holding substrate 10 is disk-shaped with a diameter of 300 mm and a thickness of 3 mm, the base member 20 is set to be disk-shaped with a diameter of 340 mm and a thickness of 20 mm. Note that the holding substrate 10 and the base member 20 may each be provided with an uneven surface or the like for mutual alignment.

[0024] The holding substrate 10 and the base member 20 are stacked one on top of the other in the vertical direction, with the holding substrate 10 disposed on the upper side and the base member 20 disposed on the lower side. The holding substrate 10 and the base member 20 are bonded to each other by a bonding material 30 interposed therebetween.

[0025] The holding substrate 10 has a substantially circular first surface S1 disposed on the upper side, and a substantially circular second surface S2 disposed on the lower side opposite the first surface S1 and facing the base member 20. The base member 20 has a substantially circular third surface S3 disposed on the upper side and facing the second surface S2 of the holding substrate 10, and a substantially circular fourth surface S4 disposed on the lower side opposite the third surface S3. The above-mentioned bonding material 30 is sandwiched between the second surface S2 of the holding substrate 10 and the third surface S3 of the base member 20 and spreads out in a planar shape.

[0026] The holding substrate 10 includes a disk-shaped plate-like member 11 and a substrate-side gas flow path 12 formed inside the plate-like member 11. The upper surface of the plate-like member 11 is a first surface S1 of the holding substrate 10. The lower surface of the plate-like member 11 is a second surface S2 of the holding substrate 10.

[0027] The plate-shaped member 11 is a disc-shaped insulating member whose main component is ceramic. In this specification, the term "main component" refers to the component with the highest content. In this embodiment, the plate-shaped member 11 is made of alumina (Al2O3). In other embodiments, the plate-shaped member 11 may be made of other ceramics such as aluminum nitride (AlN).

[0028] The substrate-side gas flow path 12 constitutes a part of the flow path 60 for flowing an inert gas provided in the holding device 100. The inert gas is, for example, helium gas, which is a heat transfer fluid. The substrate-side gas flow path 12 is an example of a gas flow path formed inside the plate-shaped member 11 of the holding substrate 10. The substrate-side gas flow path 12 includes an inlet 12a opening on the second surface S2 of the holding substrate 10 and an outlet 12b opening on the first surface S1. The substrate-side gas flow path 12 is generally provided to penetrate the inside of the plate-shaped member 11 from the inlet 12a to the outlet 12b. Therefore, when the inert gas is supplied from the inlet 12a, the inert gas passes through the substrate-side gas flow path 12 and is finally discharged to the outside from the outlet 12b. The substrate-side gas flow path 12 includes a horizontal flow path 121, a first vertical flow path 122, and a second vertical flow path 123.

[0029] The lateral flow passage 121 is a flow passage that extends inside the plate-shaped member 11 in a direction perpendicular to the thickness direction of the plate-shaped member 11. That is, the lateral flow passage 121 extends inside the plate-shaped member 11 in the left-right direction in FIG. 2, which is a direction along the first surface S1, etc.

[0030] The first vertical flow path 122 is a flow path that extends inside the plate-like member 11 in the thickness direction of the plate-like member 11 and connects the inlet 12a and the horizontal flow path 121.

[0031] The second vertical flow path 123 is a flow path that extends inside the plate-like member 11 in the thickness direction of the plate-like member 11 and connects the outlet 12b and the horizontal flow path 121. In the present embodiment, a plurality of second vertical flow paths 123 are connected to one horizontal flow path 121. As will be described later, the second vertical flow path 123 includes a storage chamber 123a that stores a porous body, and a discharge path 123b that is connected to the storage chamber 123a and includes the outlet 12b.

[0032] The holding substrate 10 further includes a chuck electrode 40 and a heater electrode 50 inside the plate-like member 11 .

[0033] The chuck electrode 40 is formed into a planar shape and is made of a conductive material. Examples of the conductive material include tungsten, molybdenum, and platinum. As shown in FIG. 2, the chuck electrode 40 is disposed inside the plate-shaped member 11 on the first surface S1 side. When viewed from above and below, the chuck electrode 40 has a generally circular shape. When a high DC voltage is applied to the chuck electrode 40 from an external power supply (not shown), an electrostatic attraction force is generated, and the wafer W is attracted and fixed to the first surface S1 of the holding substrate 10 by this electrostatic attraction force. A well-known power supply terminal (not shown) is electrically connected to the chuck electrode 40.

[0034] When a voltage is applied to the heater electrode 50 and a current flows through the heater electrode 50, the heater electrode 50 generates heat and heats the wafer W held on the first surface S1 of the holding substrate 10. As shown in FIG. 2, the heater electrode 50 is disposed inside the plate-shaped member 11 below the chuck electrode 40 (i.e., on the second surface S2 side). The heater electrodes 50 are composed of multiple electrodes, and when viewed from above and below, they form a concentric or spiral pattern as a whole. The heater electrodes 50 are formed in a planar shape using a conductive material such as aluminum, nickel, copper, or stainless steel. Each heater electrode 50 is electrically connected to a known power supply terminal (not shown). The temperature of the wafer W held on the first surface S1 can be controlled by appropriately adjusting the current supplied to each heater electrode 50. The holding substrate 10 may further include a temperature measuring element such as a thermistor.

[0035] 1 and 2, a plurality of outlets 12b are provided on the first surface S1 of the holding substrate 10. The outer peripheral edge of the first surface S1 is formed in an annular shape and protrudes slightly upward compared to the inner portion thereof. Therefore, when the wafer W is held by suction on the first surface S1, a gap G is formed between the wafer W and the inner portion of the first surface S1, as shown in FIG.

[0036] The base member 20 is mainly made of, for example, a metal (aluminum, aluminum alloy, etc.), a composite of metal and ceramics (Al-SiC), or ceramics (SiC).

[0037] A coolant flow path 21 is provided inside the base member 20. A coolant such as a fluorine-based inert liquid or water is flowed through the coolant flow path 21 to cool the plasma heat. When the coolant flows through the coolant flow path 21, the base member 20 is cooled, and the holding substrate 10 is cooled by heat transfer (heat dissipation) between the base member 20 and the holding substrate 10 via the bonding material 30. As a result, the wafer W held on the first surface S1 of the holding substrate 10 is cooled. By appropriately adjusting the flow rate of the coolant in the coolant flow path 21, the temperature of the wafer W held on the first surface S1 can be controlled.

[0038] A base-side gas flow path 22 that constitutes a part of the flow path 60 is provided inside the base member 20. The base-side gas flow path 22 is generally in the form of a through hole extending in the thickness direction of the base member 20, and includes an inlet 22a that opens to the fourth surface S4 of the base member 20 and an outlet 22b that opens to the third surface S3 of the base member 20. The inlet 22a serves as the inlet of the base-side gas flow path 22, and also serves as the inlet of the entire flow path 60 provided in the holding device 100.

[0039] The bonding material 30 is made of, for example, a bonding sheet containing a silicone-based organic bonding agent, an inorganic bonding agent, or an Al-based metal adhesive. The bonding material 30 preferably has high adhesive strength to both the holding substrate 10 and the base member 20, as well as high heat resistance and thermal conductivity.

[0040] The bonding material 30 also has a bonding-side gas flow passage 31 that constitutes a part of the flow passage 60. The bonding-side gas flow passage 31 is made of a hole that penetrates the planar bonding material 30 in the thickness direction.

[0041] The flow path 60 supplies the inert gas to the first surface S1 side of the holding device 100. A large number of outlets 12b of the flow path 60 are provided on the first surface S1, and the inert gas is supplied to the first surface S1 side by being discharged from each of the outlets 12b. As described above, the flow path 60 includes the base-side gas flow path 22, the bonding-side gas flow path 31, and the substrate-side gas flow path 12.

[0042] A plurality of inlets 22a of the flow path 60 are provided on the fourth surface S4 of the base member 20. As shown by arrows H in Fig. 2, an inert gas is supplied from each inlet 22a. The inert gas supplied from each inlet 22a passes sequentially through the base-side gas flow path 22, the bonding-side gas flow path 31, and the substrate-side gas flow path 12 connected to each inlet 22a, and is finally discharged from a plurality of outlets 12b provided on the first surface S1.

[0043] The outlet 22b of the base-side gas flow passage 22 is connected to an opening on the lower side (base member 20 side) of the bonding-side gas flow passage 31. In addition, the opening on the upper side (holding substrate 10 side) of the bonding-side gas flow passage 31 is connected to an inlet 12a of the substrate-side gas flow passage 12. A plurality of inlets 12a of the substrate-side gas flow passage 12 are provided on the second surface S2 of the holding substrate 10.

[0044] The first vertical flow path 122, which has the inlet 12a of the substrate-side gas flow path 12 on its upstream side, is connected to a horizontal flow path 121 on its downstream side. A plurality of second vertical flow paths 123 are connected to the horizontal flow path 121. In other words, the substrate-side gas flow path 12 is branched into a plurality of paths from the upstream side to the downstream side inside the plate-like member 11.

[0045] 3 is a cross-sectional view of the holding device 100, enlarging a portion of the substrate-side gas flow path 12. As shown in FIG. 3, the second vertical flow path 123 of the substrate-side gas flow path 12 includes an accommodating chamber 123a and an exhaust path 123b.

[0046] The accommodation chamber 123a is a part of the second vertical flow path 123, and has a larger inner diameter than the second vertical flow path 123 located further upstream. The accommodation chamber 123a is formed inside the plate-shaped member 11 of the holding substrate 10. That is, the accommodation chamber 123a is formed from alumina, which is a ceramic that constitutes the plate-shaped member 11. The accommodation chamber 123a has a substantially cylindrical space therein. The porous body 70 is arranged without gaps in the space inside the accommodation chamber 123a. In this way, the portion of the substrate-side gas flow path 12 where the porous body 70 is arranged in the accommodation chamber 123a of the second vertical flow path 123 is referred to as the "porous region R."

[0047] The discharge channels 123b are flow channels connected to the downstream side of the storage chambers 123a and have the shape of through-holes extending in the thickness direction of the plate-like member 11. A plurality of discharge channels 123b are connected to one storage chamber 123a. The diameter of each discharge channel 123b is smaller than the diameter of the storage chamber 123a and the diameter of the second vertical flow channel 123 located upstream of the storage chamber 123a. The downstream open end of each of these discharge channels 123b serves as an outlet 12b of the flow channel 60. Because the porous region R is formed on the first surface S1 side, when the first surface S1 is viewed from above, the porous body 70 is exposed from each outlet 12b.

[0048] The porous body 70 is a gas-permeable member containing a large number of pores 71 and composed primarily of insulating ceramics. FIG. 4 is a schematic diagram illustrating a portion of the internal structure of the porous body 70. The porous body 70 is generally cylindrical. A network of ventilation paths for passing an inert gas is formed inside the porous body 70. These ventilation paths are composed of a large number of interconnected pores 71 inside the porous body 70. The pores 71 are formed as traces of oxidized and lost pore-forming material when the porous body 70 is produced by firing. Examples of pore-forming materials that can be oxidized and lost when the porous body 70 is produced by firing include synthetic resin beads, carbon powder, and carbon fiber. In this specification, the skeletal portion of the porous body 70 other than the pores 71 is referred to as aggregate 72.

[0049] In this embodiment, the porous body 70 is mainly composed of alumina, similar to the plate-like member 11 of the holding substrate 10. In other embodiments, the porous body 70 may be mainly composed of other ceramics such as aluminum nitride.

[0050] The porous body 70 includes columnar pores 71A as pores 71. The columnar pores 71A have a certain width and a columnar shape that extends substantially straight over a predetermined length in a direction substantially perpendicular to the width. The columnar pores 71A have a shape that has a width and a length, and include various pores that extend in a columnar shape, such as a cylindrical shape, a rectangular shape, a rod shape, or a needle shape. The width of the columnar pores 71A is preferably 5 μm or more and 20 μm or less.

[0051] The width of the columnar pores 71A is preferably shorter than the length of the columnar pores 71A. Specifically, the aspect ratio, which is the value obtained by dividing the length of the columnar pores 71A by the width of the columnar pores 71A, is preferably 5 or more.

[0052] The porous body 70 also includes spherical pores 71B as pores 71. The spherical pores 71B are pores having a spherical shape. The spherical shape of the spherical pores 71B includes not only a true spherical shape, but also shapes that approximate a true spherical shape, such as an approximately spherical shape, an ellipsoidal shape, or a polyhedral shape. The spherical shape of the spherical pores 71B also includes shapes that are partially or entirely distorted, such as a true spherical shape, an approximately spherical shape, an ellipsoidal shape, or a polyhedral shape. In other words, the spherical pores 71B may have a shape that is recognized as substantially spherical. The pore diameter of the spherical pores 71B is preferably 25 μm or more and 55 μm or less.

[0053] By ensuring that the spherical pores 71B have a predetermined size, the numerous columnar pores 71A and the numerous spherical pores 71B are easily dispersed and arranged in the porous body 70. Furthermore, the columnar pores 71A arranged between adjacent spherical pores 71B are easily arranged so as to face in various directions along the spherical pores 71B. Furthermore, by entering between adjacent spherical pores 71B and connecting the columnar pores 71A facing in various directions, the ventilation paths are easily formed in various directions, forming a network-like structure. This reduces the likelihood of the ventilation paths being formed in a linearly excessive manner in only one specific direction, or of the columnar pores 71A piling up in one specific location, resulting in a ventilation path having an ineffective length. This makes it easier for the porous body 70 to ensure a desired gas flow rate. The "specific direction" refers to, for example, a direction substantially perpendicular to the first surface S1 of the holding device 100, that is, the thickness direction of the holding device 100. Furthermore, a ventilation path is also formed inside the porous body 70 by the columnar pores 71A and the spherical pores 71B adjacent to the columnar pores 71A being connected to each other.

[0054] In order to prevent the ventilation paths from being formed so as to extend excessively linearly in only one specific direction, the aspect ratio of the columnar pores 71A is preferably 40 or less, and more preferably 20 or less.

[0055] In this specification, the width and length of the columnar pores 71A are calculated by dividing the width and length of the pore-forming material used to form the columnar pores 71A by the calculative rate. The pore diameter of the spherical pores 71B is calculated by dividing the particle size of the pore-forming material used to form the spherical pores 71B by the calculative rate. The calculative rate here refers to the degree to which a ceramic molded body (an unsintered molded body, as described below) used to manufacture the porous body 70 shrinks during firing, and is the reciprocal of the rate of firing shrinkage. The calculative rate for the porous body 70 of this embodiment is 119.5% to 126.5% in the direction perpendicular to the thickness direction (in-plane direction) and 115.4% to 127.7% in the thickness direction (axial direction). Because the porous body 70 contains columnar pores 71A, anisotropy may occur, in which the calculative rate in the axial direction is smaller than the calculative rate in the in-plane direction.

[0056] The width and length of the pore-forming material for forming the columnar pores 71A are width and length such that the cumulative frequency of the width and length distribution of the pore-forming material for forming the columnar pores 71A measured by light scattering is 50% by volume. The particle size of the pore-forming material for forming the spherical pores 71B is particle size such that the cumulative frequency of the particle size distribution of the pore-forming material for forming the spherical pores 71B measured by light scattering is 50% by volume.

[0057] The pore-forming material for forming the columnar pores 71A may be, for example, a synthetic resin fiber or a carbon fiber. The shape of the pore-forming material for forming the columnar pores 71A may be cylindrical, prismatic, rod-like, needle-like, or the like. The width and length of the pore-forming material for forming the columnar pores 71A are determined as the median minor axis length and the median major axis length of the fibrous particles that are the pore-forming material for forming the columnar pores 71A. In this embodiment, the pore-forming material used to form the columnar pores 71A is also referred to as a first pore-forming material.

[0058] The pore-forming material used to form the spherical pores 71B is a particulate material such as synthetic resin beads or carbon powder. The particulate pore-forming material used to form the spherical pores 71B may have a shape such as a perfect sphere, a nearly spherical sphere, an ellipsoid, or a polyhedron. The particle size of the pore-forming material used to form the spherical pores 71B is determined as the median particle size assuming that the pore-forming material used to form the spherical pores 71B has a perfect spherical shape. In this specification, the pore size of the spherical pores 71B is determined by dividing the particle size of the pore-forming material used to form the spherical pores 71B by a scaling factor. In this embodiment, the pore-forming material used to form the spherical pores 71B is also referred to as a second pore-forming material.

[0059] When the width and aspect ratio of the columnar pores 71A are within the above-described ranges, adjacent columnar pores 71A inside the porous body 70 are connected to each other, which facilitates the formation of ventilation paths with effective lengths inside the porous body 70. This makes it easier for the porous body 70 to maintain a desired gas flow rate. Furthermore, since the width of the columnar pores 71A is 5 μm or more and 20 μm or less, the width of the ventilation paths formed inside the porous body 70 by the connection of the columnar pores 71A is also 5 μm or more and 20 μm or less. If a ventilation path having a length similar to that formed by the connection of adjacent columnar pores 71A is formed by the connection of spherical pores 71B, the ventilation path will have a width of 25 μm or more and 55 μm or less, based on the pore diameter of the spherical pores 71B. That is, when a ventilation path having a predetermined length is formed by connecting columnar pores 71A, the width of the formed ventilation path is likely to be smaller than when a ventilation path of a similar length is formed by connecting spherical pores 71B. Therefore, when a ventilation path having a predetermined length is formed by connecting columnar pores 71A, the porous body 70 is less likely to become sparse than when a ventilation path of a similar length is formed by connecting spherical pores 71B. Therefore, when the porous body 70 includes columnar pores 71A as pores 71, the hardness of the porous body 70 is more likely to be maintained at a predetermined level or higher.

[0060] In this embodiment, the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 is set to be 40% or more and 60% or less. The unit of volume ratio is vol%. With this setting, the columnar pores 71A and the spherical pores 71B are balanced inside the porous body 70, making it easier for the columnar pores 71A to enter between adjacent spherical pores 71B. Furthermore, when the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 is in the above-mentioned range, the porous body 70 can ensure the required hardness.

[0061] When the columnar pores 71A and the spherical pores 71B are arranged adjacently in a balanced manner, sufficient ventilation paths are easily formed inside the porous body 70. When sufficient ventilation paths are formed inside the porous body 70, the porous body 70 can easily ensure a desired gas flow rate. In order to arrange the columnar pores 71A and the spherical pores 71B adjacently in a balanced manner, it is preferable that the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 be approximately ±10% of the volume ratio of the spherical pores 71B to the total volume of the pores 71. Therefore, it is more preferable that the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 be 45% or more and 55% or less.

[0062] The volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 can be set to a desired value by appropriately adjusting the amount of the first pore-forming material used during the production of the porous body 70. The volume ratio of the spherical pores 71B to the total volume of the pores 71 contained in the porous body 70 can be set to a desired value by appropriately adjusting the amount of the second pore-forming material used during the production of the porous body 70.

[0063] The "volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70" refers to the ratio, in vol%, of the volume of all the columnar pores 71A to the volume of all the pores (100 vol%) of the porous body 70. The volume of all the pores in the porous body 70 is calculated as the sum of the volume of all the columnar pores 71A in the porous body 70 and the volume of all the spherical pores 71B in the same porous body 70.

[0064] In this embodiment, the volume of all columnar pores 71A in the porous body 70 is considered to be the volume of the first pore-forming material mixed with the alumina powder to form the aggregate 72 when producing an unsintered molded product for the porous body 70. The volume of all spherical pores 71B in the porous body 70 is considered to be the volume of the second pore-forming material mixed with the alumina powder when producing an unsintered molded product for the same porous body 70. The total volume of the first pore-forming material and the second pore-forming material mixed with the alumina powder is considered to be the total volume of the pores 71 contained in the porous body 70. The ratio of the volume value of the first pore-forming material to the total volume of the first pore-forming material and the second pore-forming material is calculated as the "volume ratio of columnar pores 71A to the total volume of the pores 71 contained in the porous body 70."

[0065] The volume of the pores 71 contained in the porous body 70 may be calculated from the porosity of the porous body 70. The porosity of the porous body 70 can be determined using the Archimedes method. The porosity of the porous body 70 can also be measured based on an SEM image obtained by photographing with a scanning electron microscope (SEM). Specifically, the porous body 70 is cut along an arbitrary direction, and the resulting cross section is photographed with the scanning electron microscope. The photographed SEM image is binarized, and the resulting binarized image is analyzed using predetermined material development simulation software to determine the porosity of the porous body 70. When using simulation software, rectangular black areas scattered within the binarized image can be extracted as columnar pores 71A, thereby measuring the "volume ratio of columnar pores 71A to the total volume of pores 71 contained in the porous body 70." In addition, by extracting the circular black areas scattered within the binary image as spherical pores 71B, it is possible to measure the "volume ratio of spherical pores 71B to the total volume of pores 71 contained in porous body 70."

[0066] <Method of manufacturing the holding device 100> An example of a method for manufacturing the holding device 100 of this embodiment will be described below. First, the holding substrate 10 and the base member 20 are fabricated.

[0067] The method for producing the holding substrate 10 is, for example, as follows. First, a mixture of alumina powder, an acrylic binder, an appropriate amount of dispersant, and a plasticizer is mixed with an organic solvent in a ball mill to produce a green sheet slurry. This green sheet slurry is formed into a sheet using a casting device, and the resulting formed product is then dried to produce multiple green sheets.

[0068] Alternatively, a metallization paste is prepared by adding conductive powder such as tungsten or molybdenum to a mixture of alumina powder, an acrylic binder, and an organic solvent, and kneading the mixture. This metallization paste is printed, for example, using a screen printing device, to form an unsintered conductor layer on each specific green sheet, which will later become a heater electrode, a chuck electrode, or the like.

[0069] Furthermore, holes and grooves are formed in each specific green sheet to become the substrate-side gas flow passages 12, etc. At this time, holes for forming the accommodation chambers 123a are formed in the specific green sheet.

[0070] Furthermore, a mixture of alumina powder, a pore-forming material, and a binder is molded to obtain a green molded product of a predetermined size for the porous body 70. Examples of the pore-forming material include synthetic resin beads, carbon powder, and carbon fiber. The particle size of the alumina powder (ceramic powder) is adjusted as appropriate. The green molded product is then filled into holes in a specific green sheet to form the receiving chambers 123a. The green molded product for the porous body 70 may be attached to the holes in the green sheet using an adhesive or the like.

[0071] Next, multiple green sheets are stacked and thermocompressed together, and the outer peripheries are cut as needed to produce a green sheet laminate. This green sheet laminate is machined to produce a disk-shaped compact, which is then degreased and fired to produce a fired body. During firing of this compact, the unsintered molded product for the porous body 70 described above is also fired to produce the porous body 70. The pore-forming material in the unsintered molded product is oxidized and lost during firing, forming a three-dimensional network of ventilation paths within the porous body 70.

[0072] Next, a mask is placed on the surface of the obtained sintered body to shield the portion corresponding to the convex outer periphery, and the surface is subjected to shot blasting, for example, by projecting ceramic particles, etc., to form the convex outer periphery on the surface of the sintered body. Thereafter, the surface of this sintered body is polished to obtain the holding substrate 10.

[0073] The method for manufacturing the base member 20 is basically the same as the manufacturing method for the conventional product, and therefore a detailed description thereof will be omitted.

[0074] After the holding substrate 10 and the base member 20 are fabricated, they are bonded together using a bonding material 30. The bonding of the holding substrate 10 and the base member 20 using the bonding material 30 is basically the same as that used in conventional products. Therefore, a detailed description thereof will be omitted. In this manner, the holding device 100 is manufactured. [Example]

[0075] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0076] <Examples 1, 2, and 3> A sample was prepared for evaluation of the porous body.

[0077] A mixture of alumina powder, an acrylic binder, an appropriate amount of dispersant, and a plasticizer was mixed with an organic solvent in a ball mill to prepare a green sheet slurry. This green sheet slurry was formed into a sheet using a casting device, and the resulting formed product was then dried to prepare 10 green sheets. Each green sheet had a thickness of 0.45 mm. A hole with a diameter of 4.32 mm was drilled in each of the 10 prepared green sheets. Ten of these green sheets were stacked together to form a hole corresponding to the accommodation chamber 123a. The 10 stacked green sheets were thermocompression bonded to prepare a green sheet laminate.

[0078] Next, unsintered molded porous bodies were produced. Specifically, carbon fibers having a width of 5 μm or more and 20 μm or less and an aspect ratio of 5 or more were prepared as the first pore-forming material. The prepared first pore-forming material was weighed for each of Examples 1, 2, and 3 so that the volume ratio of the first pore-forming material in the unsintered molded porous body was the volume ratio shown in FIG. 5. The volume ratio of the first pore-forming material in the unsintered molded porous body corresponds to the volume ratio of the columnar pores 71A in the total volume of the porous body. Synthetic resin beads and carbon powder having a diameter of 25 μm or more and 55 μm or less were prepared as the second pore-forming material. The prepared second pore-forming material was weighed for each of Examples 1, 2, and 3 so that the volume ratio of the first pore-forming material in the unsintered molded porous body was the volume ratio shown in FIG. 5. The volume ratio of the second pore-forming material in the unsintered porous body corresponds to the volume ratio of the spherical pores 71B to the total volume of the porous body. A mixture of the weighed first and second pore-forming materials, alumina powder, and a binder was molded to obtain an unsintered porous body of a predetermined size.

[0079] Next, the hole corresponding to the accommodation chamber 123a was filled with an unsintered porous body. The periphery of the hole corresponding to the accommodation chamber 123a of the green sheet laminate was machined to produce a cylindrical compact. The cylindrical compact was obtained by filling the inside of a cylinder formed from the green sheet material with the unsintered porous body. The obtained cylindrical compact was degreased, and then fired to produce a fired body. In this way, samples according to Examples 1, 2, and 3, which simulated the accommodation chamber 123a and its vicinity of the holding substrate 10, were produced. The outer diameter of the fired body was 5.20 mm. That is, the calculative rate was 121.5%.

[0080] In preparing the sample of Example 1, four types of carbon fibers with different widths and lengths were prepared as the first pore-forming material. The widths, lengths, and aspect ratios of the four types of carbon fibers are shown in FIG. 6. As shown in FIG. 6, the sample using carbon fibers with a width of 18 μm, a length of 150 μm, and an aspect ratio of 8.3 as the first pore-forming material corresponds to the sample of Example 1A. The sample using carbon fibers with a width of 14.5 μm, a length of 90 μm, and an aspect ratio of 6.2 as the first pore-forming material corresponds to the sample of Example 1B. The sample using carbon fibers with a width of 13 μm, a length of 120 μm, and an aspect ratio of 9.2 as the first pore-forming material corresponds to the sample of Example 1C. The sample using carbon fibers with a width of 7.2 μm, a length of 100 μm, and an aspect ratio of 13.9 as the first pore-forming material corresponds to the sample of Example 1D. Examples 1A, 1B, 1C, and 1D are included in Example 1.

[0081] <Comparative Example 1> A sample according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the first pore-forming material was not used and only the second pore-forming material was used when preparing an unsintered molded article of the porous body. The amount of the second pore-forming material used was adjusted so that the porosity of the porous body of Comparative Example 1 was equivalent to that of the porous body of Example 1.

[0082] <Evaluation> The samples according to Examples 1 to 3 and Comparative Example 1 were evaluated as follows.

[0083] (Volume ratio of columnar pores to the total volume of pores contained in a porous body) The volume ratio of the columnar pores 71A to the total volume of the pores contained in the porous body was calculated based on the respective volumes of the first pore-forming material and the second pore-forming material used when producing the green molded product for the porous body. The calculation results are shown in FIG. 5, and were 45.68% for Example 1, 8.43% for Example 2, and 26.83% for Example 3. Note that for the sample of Comparative Example 1, the first pore-forming material was not used when producing the green molded product of the porous body, so the pores did not include columnar pores 71A. Therefore, for Comparative Example 1, the volume ratio of the columnar pores 71A to the total volume of the pores contained in the porous body was not calculated.

[0084] (Observation of ventilation paths inside the porous body 70) The porous body 70 of the sample of Example 1 was cut in an arbitrary direction, and the resulting cross section was photographed using a scanning electron microscope. FIG. 7 is an SEM image obtained by photographing the cross section of the sample of Example 1D. As shown in FIG. 7, columnar pores 71A extending in an elongated rectangular shape and approximately circular spherical pores 71B were observed in the SEM image. It was also observed that the columnar pores 71A and the spherical pores 71B were connected to each other, forming a network of ventilation paths inside the porous body 70.

[0085] (Instrumented indentation test) The hardness of the porous body 70 of the sample of Example 1 was evaluated. Specifically, an instrumented indentation test conforming to the international standard ISO14577 was performed on the porous body 70 of the sample according to Example 1, and the Martens hardness HM of the porous body 70 was measured. As a result, the Martens hardness HM of the porous body 70 of each sample according to Examples 1A, 1B, and 1D was 6.235 N / mm 2 ,4.300N / mm 2 ,2.712N / mm 2 These Martens hardnesses HM are the average values ​​obtained by measuring four or five samples. From the viewpoint of handling the porous body 70 when manufacturing the holding device 100, it is preferable that the Martens hardness HM of the porous body 70 is 2 N / mm 2The instrumented indentation test on the porous body 70 sample according to Example 1 confirmed that the porous body 70 sample according to Example 1 has the hardness required for the fabrication of the holding device 100, etc.

[0086] (Gas permeability of porous body 70) The gas permeability was evaluated for the porous body 70 of the sample according to Example 1 and the porous body of the sample according to Comparative Example 1. To evaluate the gas permeability, a differential pressure method was used, in which one side separated by the porous body was kept in vacuum (low-pressure side), a test gas was introduced into the other side (high-pressure side), and the amount of test gas permeated from the high-pressure side to the low-pressure side was measured. He (helium) was used as the test gas. Specifically, the He permeation amount through the porous body 70 of each sample according to Examples 1A, 1B, 1C, and 1H at a constant temperature was measured by varying the He introduction pressure. The He permeation amount was also measured for the porous body of the sample according to Comparative Example 1 in the same manner. As a result of the test, the He permeation amount vs. pressure diagram shown in FIG. 8 was obtained.

[0087] As shown in FIG. 8 , the He permeation rates of the porous bodies 70 of the samples according to Examples 1A, 1B, 1C, and 1H exceeded 1 sccm when the He introduction pressure was approximately 1000 Pa. In particular, a relatively high He permeation rate of approximately 2 sccm was obtained in Examples 1C and 1H. On the other hand, the He permeation rate of the porous body of the sample according to Comparative Example 1, which does not include columnar pores 71A, when the He introduction pressure was approximately 1000 Pa was lower than that of Example 1, falling below 1 sccm. That is, it was confirmed that the porous body 70 of the sample according to Example 1, which includes columnar pores 71A, has higher gas permeability than the porous body of the sample according to Comparative Example 1, which does not include columnar pores 71A. This is presumably because, since the columnar pores 71A have a shape having a length, when the pores 71 include the columnar pores 71A, the gas passage paths of the porous body 70 are more likely to be formed with a length than when the pores 71 do not include the columnar pores 71A.

[0088] Furthermore, as shown in FIG. 8, in both Example 1 and Comparative Example 1, the higher the He introduction pressure, the higher the He permeation amount of the porous body. It was confirmed that the porous body 70 of the sample according to Example 1 had higher gas permeability than the porous body of the sample according to Comparative Example 1, even when the He introduction pressure was higher than 1000 Pa. It was also confirmed that the rate of increase in He permeation amount with increasing introduction pressure was higher in Example 1 than in Comparative Example 1. Specifically, as shown in FIG. 8, the rate of increase in He permeation amount with increasing introduction pressure was higher in Example 1C than in Example 1B, higher in Example 1I than in Example 1C, and higher in Example 1A than in Example 1I.

[0089] Although not shown in Fig. 8, in Examples 2 and 3, the He permeation amount was not as good as that of Example 1. From this, it was confirmed that in order to ensure good gas permeability, the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 is preferably at least 40% or more, and more preferably 45% or more.

[0090] It is conceivable that gas permeability could be improved by further increasing the number of spherical pores 71B contained in the pores 71 of Comparative Example 1. However, if the porosity of the porous body exceeds a certain level, the porous body will no longer maintain the required hardness. The results of the instrumented indentation test and the gas permeability evaluation confirmed that when the pores 71 of the porous body 70 include columnar pores 71A, it is easier to improve the gas permeability of the porous body 70 while maintaining the required hardness, compared to when the pores 71 do not include columnar pores 71A.

[0091] As described above, the holding device 100 includes a first surface S1 for holding a wafer W, and is equipped with a holding substrate 10 having a plate-like member 11 made mainly of ceramic and a substrate-side gas flow path 12 formed inside the plate-like member 11. The substrate-side gas flow path 12 has a porous region R in part, where a gas-permeable porous body 70 is arranged, the gas-permeable porous body 70 being made mainly of ceramic and containing a large number of pores 71. The porous body 70 includes, as the pores 71, columnar pores 71A formed to extend in a columnar shape.

[0092] Each of the numerous columnar pores 71A is formed in a columnar elongated shape. Therefore, the numerous columnar pores 71A communicate with one another, which facilitates the formation of long, mesh-like ventilation paths within the porous body 70. The ventilation paths extend along the extension direction of the substrate-side gas flow path 12, thereby improving the gas permeability of the porous body 70. Furthermore, when ventilation paths are formed by numerous columnar pores 71A, the porous body 70 is less likely to become sparse than when ventilation paths are formed solely by pores of other shapes, such as spherical ones. Therefore, a holding device 100 is provided that includes a porous body 70 that maintains the required hardness while improving the gas flow rate.

[0093] The porous body 70 includes, as pores 71, a large number of spherical pores 71B formed in a spherical shape.

[0094] The pores 71 include a large number of columnar pores 71A and a large number of spherical pores 71B, which makes it easier for the columnar pores 71A to be arranged so as to fit between adjacent spherical pores 71B. This makes it easier for each of the columnar pores 71A to be connected to each of the spherical pores 71B, thereby developing air passages inside the porous body. This also reduces excessive linear connections between the columnar pores 71A. This also reduces the possibility of the porous body 70 becoming excessively sparse in parts, which would be caused by multiple columnar pores 71A overlapping in parallel. This maintains the hardness of the porous body 70 and further improves the gas flow rate of the porous body 70.

[0095] The width of the columnar pores 71A is 5 μm or more and 20 μm or less, and the aspect ratio, which is expressed by the value obtained by dividing the length of the columnar pores 71A by the width of the columnar pores 71A, is 5 or more.

[0096] When the width of the columnar pores 71A is in the range of 5 μm to 20 μm and the aspect ratio is 5 or more, the columnar pores 71A have a predetermined length, so that the desired gas flow rate can be ensured in the porous body 70. In such a case, the porous body 70 is less likely to become sparse, and the hardness of the porous body 70 is maintained at a level that makes it easy to handle when fabricating the holding device 100, for example.

[0097] The diameter of the spherical pores 71B is 25 μm or more and 55 μm or less.

[0098] When the diameter of the spherical pores 71B is in the range of 25 μm or more and 55 μm or less, the numerous columnar pores 71A and the numerous spherical pores 71B are easily dispersed and arranged in the porous body 70. Therefore, it is possible to provide a holding device 100 including a porous body 70 that has an improved gas flow rate while maintaining the required hardness.

[0099] The volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 is 40% or more and 60% or less.

[0100] By setting the volume ratio of columnar pores 71A to the total volume of pores 71 contained in porous body 70 to be in the range of 40% or more and 60% or less, a holding device 100 is provided that includes porous body 70 that maintains the required hardness while improving the gas flow rate.

[0101] Second Embodiment Next, a holding device 100B according to a second embodiment will be described with reference to Fig. 9. Fig. 9 is an enlarged cross-sectional view of a portion of the substrate-side gas flow path 12B of the holding device 100B according to the second embodiment. The basic configuration of the holding device 100B of this embodiment is the same as that of the first embodiment. Therefore, in Fig. 9, parts corresponding to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment with the addition of the letter "B," and detailed description thereof will be omitted.

[0102] The holding device 100B of this embodiment includes a disk-shaped holding substrate 10B, a disk-shaped base member 20B, and a planar bonding material 30B interposed therebetween, as in the first embodiment. The holding substrate 10B includes a plate-shaped member 11B, a substrate-side gas flow path 12B formed therein, a chuck electrode 40B, and a heater electrode 50B.

[0103] The substrate-side gas flow path 12B constitutes a part of the flow path 60B through which the inert gas passes, and FIG. 9 shows a horizontal flow path 121B, a first vertical flow path 122B, and a second vertical flow path 123B.

[0104] The second vertical flow path 123AB is provided with a storage chamber 123Ba that stores the porous body 70B, and a discharge path 123Bb that is connected to the storage chamber 123Ba and includes an outlet 12Bb. The outlet 12Bb is located on the first surface SB1 of the holding substrate 10B. The portion of the storage chamber 123Ba where the porous body 70B is located forms a porous region RB.

[0105] In the second embodiment, a porous region RB is also provided in the first vertical flow path 122B. This porous region RB is provided near the inlet 12Ba that opens to the second surface SB2. A storage chamber 122Ba that stores a porous body 70B is provided in the first vertical flow path 122B, and the location where the porous body 70B is arranged in the storage chamber 122Ba forms the porous region RB in the first vertical flow path 122B.

[0106] The porous body 70B of the second embodiment is the same as the porous body 70 of the first embodiment. Therefore, the porous body 70B includes a large number of columnar pores 71A as the pores 71. The porous body 70B also includes a large number of spherical pores 71B as the pores 71.

[0107] In the second embodiment, the width of the columnar pores 71A is 5 μm or more and 20 μm or less, similar to the first embodiment, and the aspect ratio, which is expressed by the value obtained by dividing the length of the columnar pores 71A by the width of the columnar pores 71A, is 5 or more.

[0108] In the second embodiment, the diameter of the spherical pores 71B is 25 μm or more and 55 μm or less, similar to the first embodiment.

[0109] In the second embodiment, the volume ratio of the columnar pores 71A to the total volume of the pores 71 contained in the porous body 70 is set to 40% or more and 60% or less, similarly to the first embodiment.

[0110] As described above, in the holding device 100B of the second embodiment, the porous region RB may be provided in a part of the substrate-side gas flow path 12B disposed near the second surface SB2 side.

[0111] <Other embodiments> The present disclosure is not limited to the embodiments described above and in the drawings, and for example, the following embodiments are also included within the technical scope of the present disclosure. Furthermore, various modifications other than those described below can be made without departing from the spirit of the present disclosure.

[0112] (1) In the above embodiment, the ceramics of the porous bodies 70, 70B and the ceramics of the plate-shaped members of the holding substrates 10, 10B are made of the same type of ceramic. For example, the ceramics of the porous bodies 70, 70B and the ceramics of the plate-shaped members 11, 11B may be made of different types of ceramics, as long as the object of the present disclosure is not impaired. For example, the porous bodies 70, 70B may be made of alumina and the plate-shaped members 11, 11B may be made of aluminum nitride, or the porous bodies 70, 70B may be made of aluminum nitride and the plate-shaped members 11, 11B may be made of alumina.

[0113] (2) In the above embodiment, the flow path for passing the inert gas was also formed in the base member 20, but in other embodiments, it may not be formed in the base member 20, and may be formed only in the holding substrates 10, 10B.

[0114] (3) The manufacturing method of the holding devices 100, 100B shown in the above embodiment is merely an example, and other manufacturing methods may be used as long as they do not impair the purpose of the present disclosure. [Explanation of symbols]

[0115] 10, 10B: holding substrate 11, 11B: plate-shaped member 12, 12B: substrate side gas flow path 12a: inlet, 12b: outlet 121: Horizontal flow path 122: First vertical flow path 123: Second vertical flow path 20, 20B: base member 60: flow path 70, 70B: porous body 71: Pore 71A: Columnar pore 71B: Spherical pore 72: Aggregate 100,100B: Holding device R, RB: porous region S1, SB1: first surface W: wafer

Claims

1. A holding device including a holding substrate having a first surface for holding an object, the holding substrate having a plate-shaped member mainly made of ceramic, and a gas flow path formed inside the plate-shaped member, the gas flow path has a porous region in a part thereof, the porous region being made of a location where a gas-permeable porous body containing a ceramic as a main component and containing a large number of pores is disposed; The porous body includes columnar pores formed to extend in a columnar shape as the pores.

2. The holding device according to claim 1 , wherein the porous body includes a large number of spherical pores formed as the pores.

3. The width of the columnar pores is 5 μm or more and 20 μm or less, 3. The holding device according to claim 1, wherein an aspect ratio, which is expressed by a value obtained by dividing the length of the columnar pore by the width of the columnar pore, is 5 or more.

4. The holding device according to claim 2 , wherein the diameter of the spherical pores is 25 μm or more and 55 μm or less.

5. The holding device according to claim 2 , wherein the volume ratio of the columnar pores to the total volume of the pores contained in the porous body is 40% or more and 60% or less.

Images