Holding member and method for manufacturing the same

Abstract

A holding member that has α alumina as a main component and that holds an object, the holding member being characterized by the holding member comprising a holding surface which is the surface of the side that holds the object, projections and recesses being formed on the holding surface, and γ alumina being contained in the bottom surface that defines the bottom part of the recesses.

Description

[Technical Field]

[0001] The present invention relates to a holding member and a method for manufacturing the holding member. [Background technology]

[0002] Holding members that hold an object by electrostatic attraction are known. For example, Patent Document 1 discloses an electrostatic chuck in which recesses are formed by blasting on the holding surface of a ceramic member that holds the object. Blasting is a process in which a holding surface is polished by colliding with a medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-129632 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the electrostatic chuck described in Patent Document 1, recesses are formed in the holding member due to the collision of the media, which may cause microcracks to occur in the recesses or distortion to accumulate on the surface of the recesses. If microcracks occur in the recesses, particles may be generated from the microcracks due to thermal stress generated in the holding member during heating and cooling (thermal cycle) of the holding member when holding an object. Furthermore, if distortion accumulates in the recesses, cracks may be induced during use of the holding member, and particles may be generated from the cracks. For this reason, there is still room for improvement in suppressing particle generation.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to provide a technique capable of suppressing the generation of particles. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms. (1) According to one aspect of the present invention, there is provided a holding member, the holding member being composed primarily of alpha alumina and configured to hold an object, the holding member having a holding surface that holds the object, the holding surface having a protrusion and a recess, and a bottom surface that defines the bottom of the recess containing gamma alumina.

[0007] According to this configuration, the bottom surface of the recess formed on the holding surface (the surface that holds the object) contains gamma alumina, which has a lower Young's modulus than alpha alumina, the main component of the holding member. This allows the thermal stress generated in the holding member during thermal cycling to be alleviated at the bottom surface of the recess. This prevents microcracks from occurring at the bottom surface of the recess due to thermal stress, thereby reducing particle generation.

[0008] (2) In the holding member of the above embodiment, the bottom surface may further include an amorphous portion. According to this configuration, the bottom surface of the recess contains, in addition to gamma alumina, an amorphous portion with a lower Young's modulus than gamma alumina. This allows for further reduction of the thermal stress that occurs in the holding member during thermal cycling, particularly at the bottom surface of the recess. This further reduction in thermal stress further suppresses the generation of microcracks, which in turn further reduces the generation of particles.

[0009] (3) In the holding member of the above embodiment, the ratio of γ-alumina contained in the bottom surface may be 5% or more and 20% or less. Because gamma alumina has a lower Young's modulus than alpha alumina, including an appropriate amount on the bottom surface of the recess contributes to alleviating thermal stress generated in the holding member during thermal cycling. However, because gamma alumina has lower plasma resistance than alpha alumina, if excessive gamma alumina is included on the bottom surface of the recess, the gamma alumina itself can become a source of particle generation. This configuration prevents the gamma alumina included on the bottom surface of the recess from becoming a source of particle generation while contributing to the alleviation of thermal stress.

[0010] (4) According to another aspect of the present invention, there is provided a method for manufacturing a holding member, comprising a recess forming step of irradiating a processing surface of a member mainly composed of α-alumina with an ultrashort pulse laser to form recesses in the processing surface. According to this configuration, the recesses formed by irradiating the workpiece surface of a member primarily composed of α-alumina with an ultrashort pulse laser contain portions that are γ-alumina or amorphous. Therefore, of the thermal stresses that occur in the holding member during the thermal cycle, the thermal stresses that occur at the bottom surfaces of the recesses can be alleviated. Therefore, according to this configuration, the occurrence of microcracks at the bottom surfaces of the recesses due to thermal stress can be suppressed, and a holding member with suppressed particle generation can be manufactured.

[0011] (5) According to one aspect of the present invention, there is provided a holding member, the holding member being primarily composed of ceramic and configured to hold an object, the holding member having a holding surface that is a surface on the side that holds the object, at least a portion of the holding surface being composed of first ceramic crystal particles, and a portion inside the holding surface being composed of second ceramic crystal particles, the first particle diameter being smaller than the second particle diameter being the particle diameter of the second ceramic crystal particles.

[0012] According to this configuration, at least a portion of the holding surface is composed of first ceramic crystal particles, and a portion of the holding member that is inward from the holding surface is composed of second ceramic crystal particles. The first particle diameter of the first ceramic crystal particles is smaller than the second particle diameter of the second ceramic crystal particles. Therefore, since at least a portion of the holding surface is composed of first ceramic crystal particles having a first particle diameter smaller than the second particle diameter, the size of particles generated from the holding surface during use of the holding member can be reduced. Furthermore, since the first ceramic crystal particles correspond to ceramic crystal particles that are formed by partially scraping off the second ceramic crystal particles, the surface composed of the first ceramic crystal particles includes ceramic crystal particles that expose their inner grains (portions of the crystal particles that are inward from the grain boundaries) toward the surface. In other words, since fewer grain boundaries are exposed on such surfaces, the plasma resistance of the holding surface including such surfaces can be improved.

[0013] (6) In the holding member of the above aspect, the holding surface may have a convex portion and a concave portion formed thereon, and the front surface may be a bottom surface that defines the concave portion. According to this configuration, the bottom surface defining the recess is made of the first ceramic crystal grains, which reduces the size of particles generated from the holding surface when the holding member holds an object and an inert gas flows between the object and the recess.

[0014] (7) In the holding member of the above embodiment, the surface may be a laser-processed surface. According to this configuration, the laser-processed surface is a surface in which each crystal grain is finely removed from the grain boundary toward the grain interior, so the first particle diameter of the first ceramic crystal grains is smaller than the second particle diameter. Therefore, a holding member having a first particle diameter smaller than the second particle diameter can be accurately provided. Furthermore, compared to a blast-processed surface in which blasting is performed to remove crystal grains along the grain boundaries, the laser-processed surface can have a smaller surface roughness. In other words, the increase in surface area due to surface roughness can be reduced. As a result, the surface area eroded by plasma is reduced, thereby suppressing the generation of particles due to plasma erosion.

[0015] The present invention can be realized in various forms, for example, a holding member, an electrostatic chuck including an electrostatic electrode that generates electrostatic attraction between the holding member and the holding surface of the holding member, a vacuum chuck, a ceramic heater, a semiconductor manufacturing apparatus, a component including any of these, and a manufacturing method for these. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is an explanatory view schematically illustrating a cross-sectional configuration of an electrostatic chuck according to a first embodiment. [Figure 2] 10A to 10C are explanatory views showing a process of forming a recessed portion. [Figure 3] FIG. 2 is a schematic diagram showing the shape of ceramic crystal grains. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment FIG. 1 is an explanatory diagram schematically illustrating a cross-sectional configuration of an electrostatic chuck 1 according to a first embodiment. The electrostatic chuck 1 is a device that attracts and holds a semiconductor wafer W, which is an object, by electrostatic attraction. The arrows in FIG. 1 indicate the direction in which the semiconductor wafer W is attracted to the electrostatic chuck 1. The electrostatic chuck 1 is used, for example, to fix the semiconductor wafer W in a vacuum chamber of a semiconductor manufacturing device. The electrostatic chuck 1 includes a holding member 10 and an electrostatic electrode 30.

[0018] The holding member 10 is a disk-shaped member that holds the semiconductor wafer W as an object, and is composed primarily of alpha alumina. The "major component" refers to the component with the highest volumetric content. The holding member 10 has a holding surface 10f and a back surface 10b. The holding surface 10f is a circular surface on the side that holds the semiconductor wafer W. The back surface 10b is a circular surface located on the opposite side of the holding surface 10f.

[0019] The holding surface 10f is formed with an annular convex portion 12, a plurality of convex portions 14, and a plurality of concave portions 16. The annular convex portion 12 is formed along the outer edge of the holding surface 10f. Each of the convex portions 14 is formed inside the annular convex portion 12. Each of the concave portions 16 is formed between the convex portions 14. In other words, the concave portions 16 are formed at positions inside the annular convex portion 12 where no convex portion 14 is formed. In this embodiment, when the holding surface 10f is viewed from a direction facing the holding surface 10f (when viewed from above), the concave portions 16 are arranged in a scattered manner on the circular holding surface 10f, and the proportion of the concave portions 16 in the holding surface 10f is 90% or more.

[0020] A plurality of through-flow channels 22 are formed inside the holding member 10. Each of the through-flow channels 22 is a channel that penetrates between the holding surface 10f and the back surface 10b, and is a channel for supplying an inert gas such as helium gas supplied from the back surface 10b side to the holding surface 10f side. The through-flow channels 22 are connected to the recess 16 on the holding surface 10f side.

[0021] The electrostatic electrode 30 is a disk-shaped member provided inside the holding member 10 and is made of a conductive material such as tungsten or molybdenum. When power is supplied from an external power source (not shown), the electrostatic electrode 30 generates an electrostatic attractive force on the holding surface 10f. The semiconductor wafer W is attracted toward the holding surface 10f by this electrostatic attractive force and is thereby held on the holding surface 10f.

[0022] When electrostatic attraction is generated on the holding surface 10f, the semiconductor wafer W comes into contact with the annular protrusion 12 and the protrusion 14, thereby being held on the holding surface 10f. With the semiconductor wafer W held on the holding surface 10f in this manner, an inert gas is supplied between the semiconductor wafer W and the holding surface 10f to increase thermal conductivity between the semiconductor wafer W and the holding surface 10f. More specifically, the inert gas is supplied from the rear surface 10b side through the through-flow passage 22 and from the recess 16 to the holding surface 10f side. The inert gas supplied to the holding surface 10f side flows through the space between the semiconductor wafer W and the recess 16 and diffuses throughout the space.

[0023] 2(A) and 2(B) are explanatory diagrams showing the process of forming the recesses 16. FIG. 2(A) shows a portion of a workpiece 10p that serves as the base of the holding member 10. The workpiece 10p has a workpiece surface 10fp. The workpiece surface 10fp is the surface that becomes the holding surface 10f in the holding member 10 shown in FIG. 1, and corresponds to the holding surface 10f before the annular protrusion 12, the multiple protrusions 14, and the multiple recesses 16 are formed. Laser processing is performed on each of the recess formation regions (not shown) of the workpiece surface 10fp where the recesses 16 are to be formed, thereby forming each of the recesses 16 in the recess formation regions. Laser processing is a process in which a laser is irradiated toward the workpiece. The arrows in FIG. 2(A) indicate the laser that is irradiated during laser processing. As a result of the formation of the multiple recesses 16, as shown in FIG. 2(B) described below, the recesses 16 are formed in the recess formation regions, and the portions adjacent to each recess 16 become the annular protrusion 12 and the multiple protrusions 14.

[0024] In this embodiment, the laser used for laser processing is an ultrashort pulse laser. The ultrashort pulse laser has a pulse width in the femtosecond range (10 ―15 ) to picosecond range (10 ―10 ) and has a high energy density. When this ultrashort pulse laser is used to form the recess 16, the pulse width is shorter than the time it takes for heat to diffuse from the laser-irradiated processing target area, and the material that makes up the processing target area is instantly vaporized before the heat is transmitted to the surrounding area, making it possible to perform precise processing with little thermal impact.

[0025] 2(B) shows a portion of the holding member 10. The recess 16 has a side surface 16S and a bottom surface 16B. The side surface 16S is a surface that defines the side of the recess 16. The bottom surface 16B is a surface that defines the bottom of the recess 16. In other words, the side surface 16S and the bottom surface 16B define the recess 16.

[0026] As described above, the holding member 10 is primarily composed of α-alumina, and the workpiece 10p (FIG. 2(A)), which is the target of laser processing, is also primarily composed of α-alumina. Of the side surface 16S and bottom surface 16B formed by laser processing on the workpiece surface 10fp of the workpiece 10p, at least the bottom surface 16B contains γ-alumina, which is formed when the α-alumina melted by the laser processing is cooled and transformed. The bottom surface 16B also contains an amorphous portion. The amorphous portion has a more disrupted crystal structure than α-alumina or γ-alumina. It is believed that this amorphous portion is formed by the α-alumina cooling more rapidly than the cooling that occurs when molten α-alumina transforms to γ-alumina. When the workpiece surface 10fp is subjected to blasting to form recesses 16, α-alumina does not transform to γ-alumina, and therefore the bottom surface 16B defining the bottom of the recesses 16 does not contain γ-alumina.

[0027] The presence of γ-alumina in the bottom surface 16B can be confirmed by the presence of a high relative intensity near the γ-alumina peak in the XRD pattern obtained by measuring the support surface 10f using thin-film XRD. Thin-film XRD is an XRD method in which X-rays are incident on the surface of the object to be measured at a low angle of incidence (e.g., 1° or less). In this embodiment, if a high relative intensity near the γ-alumina peak is confirmed in the measurement results obtained by irradiating X-rays on the bottom surface 16B at an incidence angle of 2°, the bottom surface 16B is deemed to contain γ-alumina. The presence of an amorphous portion in the bottom surface 16B can be confirmed by the presence of a halo pattern in the XRD pattern obtained by measuring the support surface 10f using thin-film XRD. The absence of γ-alumina in the bottom surface 16B of the recess 16 formed by blasting the processing target surface 10fp can be confirmed by the absence of a high relative intensity near the γ-alumina peak in the XRD pattern obtained by measuring the bottom surface 16B using thin-film XRD.

[0028] Furthermore, the ratio of gamma alumina contained in the bottom surface 16B of the holding member 10 is 5% or more and 20% or less. The ratio here refers to the intensity ratio of gamma alumina to alpha alumina. This intensity ratio is calculated by dividing the peak intensity of the (400) plane of gamma alumina among the peaks representing gamma alumina measured by thin-film XRD by the peak intensity of the (113) plane of alpha alumina among the peaks representing alpha alumina.

[0029] 3(A) to 3(C) are schematic diagrams showing the shape of ceramic crystal particles. The ceramic crystal particles referred to here refer to alumina crystal particles. FIG. 3(A) shows the shape of ceramic crystal particles constituting the vicinity of the processing target surface 10fp. The lines defining the crystal particles P1 to P4 represent grain boundaries. FIG. 3(B) shows the shape of ceramic crystal particles when blasting is performed on the processing target surface 10fp shown in FIG. 3(A). Blasting is a process in which an abrasive is projected toward the processing target. The processed surface 10fb in FIG. 3(B) is the surface exposed when the processing target surface 10fp is removed by blasting. FIG. 3(C) shows the shape of ceramic crystal particles when laser processing is performed on the processing target surface 10fp shown in FIG. 3(A). The processed surface 10fc in FIG. 3(C) is the surface exposed when the processing target surface 10fp is removed by laser processing. In FIGS. 3(A) to 3(C), the processing target surface 10fp, the processed surface 10fb, and the processed surface 10fc are indicated by thick lines.

[0030] Using Figures 3(A) to 3(C), we will explain how the particle size of the ceramic crystal grains that make up the processed surface 10fp varies depending on the type of processing performed on the processed surface 10fp. In Figure 3(B), the exposed portion Eb of the processed surface 10fb is a portion where the grain boundaries are exposed due to the detachment of crystal particles P1 and P2 during blasting of the processed surface 10fp. Blasting involves projecting an abrasive to detach crystal particles along the grain boundaries, which tends to increase the surface roughness of the processed surface 10fb and increase the area of ​​the grain boundaries exposed on the processed surface 10fb, as shown in Figure 3(B). On the other hand, in Figure 3(C), the exposed portion Ec of the processed surface 10fc is a portion where the grain interior (the portion inside the grain boundaries) is exposed due to the removal of some of the crystal particles P1 and P2 during laser processing of the processed surface 10fp. Crystal grains p1 and p2 shown in Figure 3(C) correspond to partially removed crystal grains P1 and P2. Because laser processing finely removes each crystal grain from the grain boundary toward the interior of the grain, the surface roughness of the processed surface 10fc is unlikely to increase, and the area of ​​the grain boundary exposed on the processed surface 10fc is unlikely to increase, as shown in Figure 3(C). Furthermore, because the interior of the grains is likely to be exposed on the processed surface 10fc, the grain diameter of the ceramic crystal grains that make up the surface of the processed surface 10fc is likely to be smaller than that of the processed surface 10fp and the processed surface 10fb.

[0031] As described above, the recesses 16 are formed by laser processing the processing surface 10fp, and at least the bottom surface 16B of the side surface 16S and the bottom surface 16B corresponds to the laser-processed surface. Therefore, as described with reference to FIG. 3(C), the particle diameter of the ceramic crystal grains constituting the bottom surface 16B is smaller than the particle diameter of the ceramic crystal grains constituting the portion inside the holding surface 10f (e.g., crystal grains p1 and p2 in FIG. 3(C)) because at least a portion of the grains has been removed by laser processing. In the following description, the ceramic crystal grains constituting the bottom surface 16B are referred to as first ceramic crystal grains, and the particle diameter of the first ceramic crystal grains is referred to as the first particle diameter. Furthermore, the ceramic crystal grains constituting the portion of the holding member 10 inside the holding surface 10f are referred to as second ceramic crystal grains, and the particle diameter of the second ceramic crystal grains is referred to as the second particle diameter. That is, in the holding member 10, the bottom surface 16B is a surface composed of first ceramic crystal particles, and the first particle diameter is smaller than the second particle diameter. The first ceramic crystal particles and the second ceramic crystal particles are both particles that make up the holding member 10. That is, even if a coating is applied to the holding surface 10f, the crystal particles that make up the layer formed by the coating are not considered first ceramic crystal particles. Furthermore, the first ceramic crystal particles and the second ceramic crystal particles are composed of the same ceramic material. That is, the comparison of the first particle diameter and the second particle diameter is made between crystal particles of the same material.

[0032] The fact that the first particle diameter is smaller than the second particle diameter can be confirmed by comparing the results (XRD pattern) of measuring the holding surface 10f by thin-film XRD with the results (XRD pattern) of measuring the interior of the holding member 10 by conventional XRD. Conventional XRD is XRD in which X-rays are incident toward the interior of the object being measured. For the comparison, the values ​​of the half width measured by thin-film XRD and XRD are used. Specifically, the fact that the first particle diameter is smaller than the second particle diameter can be confirmed by the value of the half width measured by thin-film XRD being larger than the value of the half width measured by XRD. Furthermore, the values ​​of the first particle diameter and the second particle diameter can be calculated from the values ​​of the half width using Scherrer's formula, represented by the following formula (1). r=(K·λ) / βcosθ …(1) r: particle diameter, K: Scherrer constant, λ: wavelength of X-ray used for measurement, β: half-width, θ: Bragg angle

[0033] In this embodiment, the ceramic member 10p (FIG. 2(A)), which is the target of laser processing, is made of α-alumina, and therefore the portion of the holding member 10 that is inside the holding surface 10f is also made of α-alumina. On the other hand, of the side surface 16S and the bottom surface 16B, at least the vicinity of the bottom surface 16B is made of γ-alumina, which is formed when the α-alumina is cooled and transformed by the laser processing. The presence of γ-alumina is confirmed by the fact that the relative intensity is high near the peak position of γ-alumina in the XRD pattern obtained when the holding surface 10f is measured by thin-film XRD.

[0034] Furthermore, since the first ceramic crystal grains correspond to ceramic crystal grains in which portions of the second ceramic crystal grains have been removed by laser processing, among the ceramic crystal grains constituting at least the bottom surface 16B of the side surface 16S and bottom surface 16B that define the recess 16, there are ceramic crystal grains whose interiors are exposed toward the surface of the bottom surface 16B (for example, crystal grains p1 and p2 in Figure 3(C)).

[0035] Furthermore, when the cross section of the holding member 10 was observed using an SEM, multiple tiny pores (cavities) were confirmed near the bottom surface 16B. Furthermore, the shape of the ceramic crystal grains constituting the bottom surface 16B tended to be rounded compared to the bottom surface of the recess formed by blasting. Furthermore, the length of the cracks extending from the interior of the holding member 10 to the bottom surface 16B tended to be shorter compared to the bottom surface of the recess formed by blasting. Furthermore, the number of cracks extending from the interior of the holding member 10 to the bottom surface 16B tended to be fewer compared to the bottom surface of the recess formed by blasting. Furthermore, as explained in Figures 3(B) and (C), the surface roughness of the bottom surface 16B tended to be smaller compared to the bottom surface of the recess formed by blasting.

[0036] As described above, according to the holding member 10 included in the electrostatic chuck 1 of this embodiment, of the side surface 16S and the bottom surface 16B formed on the holding surface 10f, at least the bottom surface 16B contains γ-alumina, which has a lower Young's modulus than α-alumina, which is the main component of the holding member 10. This makes it possible to alleviate the thermal stress that occurs in at least the bottom surface 16B among the thermal stresses that occur in the holding member 10 during thermal cycling. This makes it possible to suppress the generation of microcracks on the bottom surface 16B due to thermal stress, thereby suppressing the generation of particles.

[0037] Furthermore, according to the holding member 10 included in the electrostatic chuck 1 of this embodiment, an ultrashort pulse laser is irradiated onto the workpiece surface 10fp of the workpiece member 10p, which is primarily composed of α-alumina, to form recesses 16 in the workpiece surface 10fp. Therefore, compared to forming the recesses 16 by media collision (blasting), the possibility of microcracks occurring in the recesses 16 can be reduced. Thus, in this embodiment, by forming the recesses 16 by laser processing, the bottom surface 16B contains γ-alumina, which suppresses the generation of microcracks due to thermal stress. Furthermore, the generation of microcracks and accumulation of strain due to media collision in blasting is also avoided, thereby suppressing the generation of particles.

[0038] Furthermore, in the holding member 10 included in the electrostatic chuck 1 of this embodiment, the bottom surface 16B further contains, in addition to gamma alumina, an amorphous portion having a lower Young's modulus than gamma alumina. This allows for further reduction in thermal stress occurring on the bottom surface 16B among the thermal stresses occurring on the holding member 10 during thermal cycling. Further reduction in thermal stress further suppresses the occurrence of microcracks, which in turn leads to further reduction in the generation of particles.

[0039] Because γ-alumina has a lower Young's modulus than α-alumina, an appropriate amount of γ-alumina contained in the bottom surface 16B contributes to alleviating thermal stress generated in the holding member 10 during thermal cycling. On the other hand, because γ-alumina has lower plasma resistance than α-alumina, if γ-alumina is contained in excess in the bottom surface 16B, the γ-alumina itself can become a source of particle generation. In the holding member 10 provided in the electrostatic chuck 1 of this embodiment, the ratio of γ-alumina contained in the bottom surface 16B is 5% or more and 20% or less, so that the γ-alumina contained in the bottom surface 16B can contribute to alleviating thermal stress while preventing it from becoming a source of particle generation.

[0040] Furthermore, in the holding member 10, at least the bottom surface 16B of the holding surface 10f is composed of first ceramic crystal grains, and the portion inside the holding surface 10f is composed of second ceramic crystal grains. The first particle diameter, which is the particle diameter of the first ceramic crystal grains, is smaller than the second particle diameter, which is the particle diameter of the second ceramic crystal grains. Therefore, at least the bottom surface 16B of the holding surface 10f is composed of first ceramic crystal grains having a first particle diameter smaller than the second particle diameter, thereby reducing the size of particles generated from the holding surface 10f during use of the holding member 10. Furthermore, since the first ceramic crystal grains correspond to ceramic crystal grains formed by partially scraping off the second ceramic crystal grains, the bottom surface 16B composed of the first ceramic crystal grains contains ceramic crystal grains whose grain interiors (portions of the crystal grains inside the grain boundaries) are exposed toward the bottom surface 16B. In other words, since fewer grain boundaries are exposed at the bottom surface 16B, the plasma resistance of the holding surface 10f including such bottom surfaces 16B can be improved.

[0041] Furthermore, in the holding member 10, the particle diameter (second particle diameter) of the ceramic crystal grains constituting the portion inside the holding surface 10f is larger than the particle diameter (first particle diameter) of the ceramic crystal grains constituting the bottom surface 16B. When the particle diameter of the crystal grains is small, there tends to be more contact between the particles, resulting in increased heat loss. In the holding member 10, the particle diameter of the ceramic crystal grains constituting the portion inside the holding surface 10f is the second particle diameter, which is larger than the first particle diameter. This reduces contact between the particles in this portion, thereby reducing heat loss in this portion.

[0042] Furthermore, in the holding member 10, the bottom surface 16B defining the recess 16 is made of the first ceramic crystal particles. Therefore, when the holding member 10 holds the semiconductor wafer W as an object, the size of particles generated from the holding surface 10f due to an inert gas flowing between the semiconductor wafer W and the recess 16 can be reduced.

[0043] Furthermore, in the holding member 10, at least the bottom surface 16B of the side surface 16S and the bottom surface 16B corresponds to a laser-processed surface. Therefore, the bottom surface 16B, which is the laser-processed surface, is a surface obtained by finely grinding each ceramic crystal grain from the grain boundary toward the grain interior, so that the first particle diameter of the first ceramic crystal grain is smaller than the second particle diameter. This makes it possible to accurately provide a holding member 10 in which the first particle diameter is smaller than the second particle diameter. Furthermore, compared to a blast-processed surface that has been subjected to a blasting process that removes crystal grains along the grain boundaries, the laser-processed surface can have a smaller surface roughness. In other words, the increase in surface area due to surface roughness can be minimized. As a result, the surface area eroded by plasma is reduced, thereby suppressing the generation of particles due to plasma erosion.

[0044] Furthermore, in the electrostatic chuck 1 including the holding member 10, an electrostatic attraction force (adsorption force) is generated by supplying power to the electrostatic electrode 30, and the semiconductor wafer W can be held on the holding surface 10f side by this electrostatic attraction force. Furthermore, since the first particle diameter is smaller than the second particle diameter, it is possible to provide an electrostatic chuck 1 having improved plasma resistance while reducing the particle size generated from the holding surface 10f when the holding member 10 is used.

[0045] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0046] In the above embodiment, the holding surface 10f is formed with the annular protrusion 12, the plurality of protrusions 14, and the plurality of recesses 16, but is not limited to this. For example, the holding surface 10f may not be formed with the annular protrusion 12, but may instead have the plurality of protrusions 14 and the plurality of recesses 16.

[0047] In the above embodiment, a plurality of through-flow passages 22 are formed inside the holding member 10, but this is not limiting. For example, in addition to the plurality of through-flow passages 22, a passage connecting the through-flow passages 22 inside the holding member 10, and a passage branching from the passage and connecting to the recess 16 may be formed inside the holding member 10.

[0048] In the above embodiment, the recesses 16 are formed by irradiating an ultrashort laser, but this is not limiting. For example, as long as the recesses 16 contain gamma alumina, the recesses 16 may be formed by laser processing using a laser other than an ultrashort pulse laser or by any other processing other than laser processing.

[0049] In the above embodiment, the proportion of γ-alumina contained in the bottom surface 16B is 5% or more and 20% or less, but this is not limited thereto. For example, the proportion of γ-alumina contained in the bottom surface 16B may be less than 5% or more than 20%. Of course, in order to simultaneously suppress the γ-alumina contained in the bottom surface 16B from becoming a particle generation source and contribute to the reduction of thermal stress, the proportion of γ-alumina contained in the bottom surface 16B is preferably 5% or more and 20% or less.

[0050] In the above embodiment, a plurality of heater electrodes formed of a conductive material such as tungsten or molybdenum may be further provided inside the holding member 10. In such a configuration, when an object is held by the holding member 10, the heater electrodes generate heat due to power supplied from an external power source, thereby warming the object.

[0051] In the above embodiment, a plate-shaped base member may be further joined to the back surface of the holding member 10. If a refrigerant flow path is formed inside this base member, when an object is held by the holding member 10, the refrigerant flows through the refrigerant flow path, and the object can be cooled from the base member through the holding member.

[0052] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0053] The present invention can also be realized in the following forms. [Application example 1] A holding member containing alpha alumina as a main component and holding an object, the holding member has a holding surface that is a surface on which the object is held, The holding surface has a protrusion and a recess, A holding member, wherein a bottom surface defining the bottom of the recess contains gamma alumina. [Application example 2] The holding member according to Application Example 1, The holding member, wherein the bottom surface further includes an amorphous portion. [Application example 3] The holding member according to Application Example 1 or Application Example 2, A holding member, characterized in that the ratio of gamma alumina contained in the bottom surface is 5% or more and 20% or less. [Application example 4] A method for manufacturing a holding member, A method for manufacturing a holding member, comprising a recess forming step of forming a recess in a surface to be processed of a member whose main component is alpha alumina by irradiating the surface with an ultrashort pulse laser. [Explanation of symbols]

[0054] 1...Electrostatic chuck 10...Holding member 10b…Back side 10f…Holding surface 12...Ring-shaped protrusion 14...Convex part 16...Recess 16B…Bottom surface 16S…Side 22...Through-flow passage 30...Electrostatic electrode

Claims

1. A holding member containing alpha alumina as a main component and holding an object, the holding member has a holding surface that is a surface on which the object is held, The holding surface has a protrusion and a recess, a bottom surface defining a bottom of the recess includes gamma alumina; The holding member, wherein the bottom surface further includes an amorphous portion.

2. A holding member for holding an object, the holding member comprising alpha alumina as a main component, the holding member has a holding surface that is a surface on which the object is held, The holding surface has a protrusion and a recess, a bottom surface defining a bottom of the recess includes gamma alumina; A holding member, characterized in that the ratio of gamma alumina contained in the bottom surface is 5% or more and 20% or less.

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