Electrostatic chuck

According to one embodiment, an electrostatic chuck includes a ceramic dielectric substrate, a base plate, and a first porous part. The ceramic dielectric substrate has a first major surface and a second major surface. The base plate supports the ceramic dielectric substrate and includes a gas feed channel. The first porous part is provided between the base plate and the first major surface. The ceramic dielectric substrate includes a first hole part. The first porous part includes a porous section, and a first compact section being more compact than the porous section. As projected on a plane perpendicular to a first direction from the base plate to the ceramic dielectric substrate, the first compact section is configured to overlap the first hole part, and the porous section is configured not to overlap the first hole part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-203749, filed on Oct. 30, 2018 and Japanese Patent Application No. 2019-166033, filed on Sep. 12, 2019; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electrostatic chuck.

BACKGROUND

A ceramic electrostatic chuck is fabricated by sandwiching an electrode between ceramic dielectric substrates made of e.g. alumina, followed by firing. Electric power for electrostatic suction is applied to the incorporated electrode. Thus, the electrostatic chuck sucks a substrate such as a silicon wafer by electrostatic force. In such an electrostatic chuck, an inert gas such as helium (He) is passed between the front surface of the ceramic dielectric substrate and the back surface of the suction target substrate to control the temperature of the suction target substrate.

For instance, the temperature increase of the substrate may be associated with processing in a device for processing a substrate such as a CVD (chemical vapor deposition) device, sputtering device, ion implantation device, and etching device. In the electrostatic chuck used in such devices, an inert gas such as He is passed between the ceramic dielectric substrate and the suction target substrate to bring the substrate into contact with the inert gas. Thus, the temperature increase of the substrate is suppressed.

In the electrostatic chuck for controlling the substrate temperature with an inert gas such as He, a hole (gas feed channel) for feeding an inert gas such as He is provided in the ceramic dielectric substrate and a base plate for supporting the ceramic dielectric substrate. The ceramic dielectric substrate is provided with a through hole communicating with the gas feed channel of the base plate. Thus, the inert gas fed from the gas feed channel of the base plate is guided through the through hole of the ceramic dielectric substrate to the back surface of the substrate.

Here, when the substrate is processed in the device, electric discharge (arc discharge) may occur from the plasma in the device toward the metallic base plate. The gas feed channel of the base plate and the through hole of the ceramic dielectric substrate may be likely to constitute a path of discharge. Thus, there is known a technique in which a porous part is provided in the gas feed channel of the base plate and the gas feed channel of the ceramic dielectric substrate to improve resistance (such as breakdown voltage) to arc discharge.

For instance, Japanese Unexamined Patent Publication No. 2010-123712 discloses an electrostatic chuck that suppresses the occurrence of arc discharge in the gas flow channel. In this electrostatic chuck, an insulative ceramic sintered porous body is provided inside the metallic base material. The ceramic sintered porous body is provided with a through hole for feeding an inert gas. However, in such a configuration, the through hole provided in the ceramic sintered porous body may constitute a path of discharge.

Japanese Unexamined Patent Publication No. 2005-347400 discloses that a gas dispersion layer composed of dielectric particles is provided inside the depression of the insulator. However, in such a configuration, the gap between the dielectric particles may constitute a path of discharge.

Thus, regarding an electrostatic chuck provided with a porous part, it has been desired to develop an electrostatic chuck capable of further suppressing the occurrence of arc discharge.

SUMMARY

An embodiment of the invention provides an electrostatic chuck comprising a ceramic dielectric substrate, a base plate, and a first porous part. The ceramic dielectric substrate has a first major surface for mounting a suction target and a second major surface on opposite side from the first major surface. The base plate supports the ceramic dielectric substrate and includes a gas feed channel. The first porous part is provided at a position between the base plate and the first major surface of the ceramic dielectric substrate. The position is opposed to the gas feed channel. The ceramic dielectric substrate includes a first hole part located between the first major surface and the first porous part. The first porous part includes a porous section including a plurality of pores, and a first compact section being more compact than the porous section. As projected on a plane perpendicular to a first direction from the base plate to the ceramic dielectric substrate, the first compact section is configured to overlap the first hole part, and the porous section is configured not to overlap the first hole part.

DETAILED DESCRIPTION

A first aspect of the invention is an electrostatic chuck comprising a ceramic dielectric substrate, a base plate, and a first porous part. The ceramic dielectric substrate has a first major surface for mounting a suction target and a second major surface on opposite side from the first major surface. The base plate supports the ceramic dielectric substrate and includes a gas feed channel. The first porous part is provided at a position between the base plate and the first major surface of the ceramic dielectric substrate. The position is opposed to the gas feed channel. The ceramic dielectric substrate includes a first hole part located between the first major surface and the first porous part. The first porous part includes a porous section including a plurality of pores, and a first compact section being more compact than the porous section. As projected on a plane perpendicular to a first direction from the base plate to the ceramic dielectric substrate, the first compact section is configured to overlap the first hole part, and the porous section is configured not to overlap the first hole part.

In this electrostatic chuck, the first compact section and the first hole part are configured to overlap each other. Thus, the generated current is caused to flow around the first compact section. Accordingly, the current can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge. In this electrostatic chuck, the occurrence of arc discharge can be effectively suppressed while ensuring the gas flow.

A second aspect of the invention is the electrostatic chuck according to the first aspect of the invention, wherein as projected on the plane perpendicular to the first direction from the base plate to the ceramic dielectric substrate, the porous section is provided around the first compact section.

In this electrostatic chuck, reduction of arc discharge can be made compatible with smoothing of the flow of gas.

A third aspect of the invention is the electrostatic chuck according to the first or second aspect of the invention, wherein length along the first direction of the first compact section is smaller than length along the first direction of the first porous part.

This electrostatic chuck can smooth the gas flow while suppressing the occurrence of arc discharge.

A fourth aspect of the invention is the electrostatic chuck according to one of the first to third aspects of the invention, wherein in the first direction, the porous section is provided between the first compact section and the base plate.

This electrostatic chuck can reduce arc discharge and smooth the flow of gas.

A fifth aspect of the invention is the electrostatic chuck according to one of the first to fourth aspects of the invention, wherein length along the first direction of the first compact section is generally equal to length along the first direction of the first porous part.

In this electrostatic chuck, the length along the first direction of the first compact section is made generally equal to the length along the first direction of the first porous part. This can suppress the occurrence of arc discharge more effectively.

A sixth aspect of the invention is the electrostatic chuck according to one of the first to seventh aspects of the invention, further comprising a second porous part provided between the first porous part and the gas feed channel and including a plurality of pores. Average value of diameter of the plurality of pores provided in the second porous part is larger than average value of diameter of the plurality of pores provided in the first porous part.

This electrostatic chuck is provided with a second porous part having a large pore diameter. This can smooth the flow of gas. The first porous part having a small pore diameter is provided on the suction target side. This can suppress the occurrence of arc discharge more effectively.

A seventh aspect of the invention is the electrostatic chuck according to one of the first to seventh aspects of the invention, further comprising a second porous part provided between the first porous part and the gas feed channel and including a plurality of pores. Average value of diameter of the plurality of pores provided in the second porous part is larger than average value of diameter of the plurality of pores provided in the porous section.

This electrostatic chuck is provided with a second porous part having a small pore diameter. This can suppress the occurrence of arc discharge more effectively.

An eighth aspect of the invention is the electrostatic chuck according to one of the first to eighth aspects of the invention, further comprising a second porous part provided between the first porous part and the gas feed channel and including a plurality of pores. Variation in diameter of the plurality of pores provided in the first porous part is smaller than variation in diameter of the plurality of pores provided in the second porous part.

In this electrostatic chuck, variation in the diameter of the plurality of pores provided in the first porous part is smaller than variation in the diameter of the plurality of pores provided in the second porous part. This can suppress the occurrence of arc discharge more effectively.

A ninth aspect of the invention is the electrostatic chuck according to one of the fifth to eighth aspects of the invention, wherein a plurality of pores provided in the second porous part are further dispersed in three dimensions than a plurality of pores provided in the first porous part. Proportion of pores penetrating in the first direction is higher in the first porous part than in the second porous part.

The example of three-dimensional dispersion of pores will be described later with reference toFIG. 10.

In this electrostatic chuck, a higher breakdown voltage can be obtained by providing a second porous part including a plurality of pores dispersed in three dimensions. This can suppress the occurrence of arc discharge more effectively. The flow of gas can be smoothed by providing a first porous part having a high proportion of pores penetrating in the first direction.

A tenth aspect of the invention is the electrostatic chuck according to one of the first to ninth aspects of the invention, wherein the first porous part and the ceramic dielectric substrate are composed primarily of aluminum oxide. Purity of the aluminum oxide of the ceramic dielectric substrate is higher than purity of the aluminum oxide of the first porous part.

This electrostatic chuck can ensure its performance such as plasma resistance, and ensure the mechanical strength of the first porous part. As an example, a trace amount of additive is contained in the first porous part. This facilitates sintering the first porous part, and can control the pores and ensure the mechanical strength.

An eleventh aspect of the invention is the electrostatic chuck according to one of the first to tenth aspects of the invention, wherein the porous section includes a plurality of sparse portions including a plurality of pores including the first pore and the second pore, and a dense portion having a higher density than the sparse portion. Each of the plurality of sparse portions extends in the first direction. The dense portion is located between the plurality of sparse portions. The sparse portion includes a wall part provided between the first pore and the second pore. In the second direction, minimum dimension of the wall part is smaller than minimum dimension of the dense portion.

In this electrostatic chuck, the first porous part is provided with the sparse portions and the dense portion extending in the first direction. This can improve the mechanical strength (rigidity) of the first porous part while ensuring arc discharge resistance and gas flow rate.

A twelfth aspect of the invention is the electrostatic chuck according to the eleventh aspect of the invention, wherein in the second direction, dimension of the plurality of pores provided in each of the plurality of sparse portions is smaller than dimension of the dense portion.

In this electrostatic chuck, the dimension of the plurality of pores can be made sufficiently small. This can further improve resistance to arc discharge.

A thirteenth aspect of the invention is the electrostatic chuck according to the eleventh or twelfth aspect of the invention, wherein aspect ratio of the plurality of pores provided in each of the plurality of sparse portions is 30 or more and 10000 or less.

This electrostatic chuck can further improve resistance to arc discharge.

A fourteenth aspect of the invention is the electrostatic chuck according to one of the eleventh to thirteenth aspects of the invention, wherein in the second direction, dimension of the plurality of pores provided in each of the plurality of sparse portions is 1 micrometer or more and 20 micrometers or less.

In this electrostatic chuck, pores having a pore dimension of 1-20 micrometers and extending in one direction can be arranged. This can achieve high resistance to arc discharge.

A fifteenth aspect of the invention is the electrostatic chuck according to one of the eleventh to fourteenth aspects of the invention, wherein as viewed along the first direction, the first pore is located in a central part of the sparse portion. Among the plurality of pores, number of pores neighboring the first pore and surrounding the first pore is 6.

In this electrostatic chuck, in plan view, a plurality of pores can be arranged with high isotropy and high density. This can improve the rigidity of the first porous part while ensuring arc discharge resistance and gas flow rate.

An sixteenth aspect of the invention is the electrostatic chuck according to one of the first to fifteenth aspects of the invention, wherein the first compact section includes a plurality of pores. Diameter of the pore included in the first compact section is smaller than diameter of the pore included in the porous section.

In this electrostatic chuck, the diameter of the pore of the first compact section provided at the position opposed to the first hole part is relatively small. This can further enhance arc discharge resistance. The diameter of the pore of the porous section is relatively large. This can ensure sufficient gas flow.

A seventeenth aspect of the invention is the electrostatic chuck according to the sixteenth aspect of the invention, wherein when the first compact section includes the plurality of pores, porosity of the first compact section is 50% or less of porosity of the porous section, or diameter of the pore included in the first compact section is 80% or less of diameter of the pore included in the porous section.

This electrostatic chuck can ensure resistance to arc discharge and the flow rate of the flowing gas.

An eighteenth aspect of the invention is the electrostatic chuck according to one of the first to seventeenth aspects of the invention, wherein at least one of the ceramic dielectric substrate and the porous section includes a second hole part located between the first hole part and first porous part. In a second direction generally orthogonal to the first direction from the base plate to the ceramic dielectric substrate, dimension of the second hole part is smaller than dimension of the first porous part and larger than dimension of the first hole part.

This electrostatic chuck is provided with a second hole part smaller than the dimension of the first porous part and larger than the dimension of the first hole part. Thus, sufficient gas flow can be ensured even when the porous section is provided at a position not overlapping the first hole part as projected on the plane perpendicular to the first direction. This enables effective compatibility with resistance to arc discharge.

A nineteenth aspect of the invention is the electrostatic chuck comprising a ceramic dielectric substrate having a first major surface for mounting a suction target and a second major surface on opposite side from the first major surface, a base plate supporting the ceramic dielectric substrate and including a gas feed channel, a first porous part provided at a position between the base plate and the first major surface of the ceramic dielectric substrate, the position being opposed to the gas feed channel, and a second porous part provided between the first porous part and the gas feed channel. The ceramic dielectric substrate includes a first hole part located between the first major surface and the first porous part. The second porous part includes a second porous section including a plurality of pores, and a third compact section more compact than the porous section. As projected on a plane perpendicular to a first direction from the base plate to the ceramic dielectric substrate, the third compact section is configured to overlap the first hole part, and the second porous section is configured not to overlap the first hole part.

In this electrostatic chuck, the third compact section and the first hole part are configured to overlap each other. Thus, the generated current is caused to flow around the third compact section. Accordingly, the current can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge. In this electrostatic chuck, the occurrence of arc discharge can be effectively suppressed while ensuring the gas flow.

A twentieth aspect of the invention is the electrostatic chuck according to nineteenth aspects of the invention, wherein the first porous part includes a porous section including a plurality of pores, the porous section includes a plurality of first sparse portions including a first pore and a second pore and a dense portion having a density higher than a density of the first sparse portions, each of the plurality of first sparse portions extends in the first direction, the dense portion is located between the plurality of first sparse portions, the first sparse portion includes a wall part provided between the first pore and the second pore, and in the second direction, minimum dimension of the wall part is smaller than minimum dimension of the dense portion.

In this electrostatic chuck, the first porous section has the configuration described above. This can suppress the occurrence of arc discharge more effectively.

A twenty first aspect of the invention is the electrostatic chuck according to nineteenth or twenty first aspects of the invention, wherein the second porous section includes a plurality of second sparse portions including a plurality of pores including a third pore and a fourth pore, and a second dense portion having a density higher than a density of the second sparse portions, each of the plurality of second sparse portions extends in the first direction, the second dense portion is located between the plurality of second sparse portions, the second sparse portions includes a second wall part provided between the third pore and the fourth pore, and in the second direction, minimum dimension of the second wall part is smaller than minimum dimension of the second dense portion.

In this electrostatic chuck, the second porous section has the configuration described above. This can suppress the occurrence of arc discharge more effectively.

A twenty second aspect of the invention is the electrostatic chuck according to one of first to twenty first aspects of the invention, wherein when a direction generally orthogonal to the first direction is taken as a second direction, the first porous part includes a first region located on the ceramic dielectric substrate side in the second direction, the ceramic dielectric substrate includes a first substrate region located the first region side in the second direction, the first region is provided to be in contact with the first substrate region, and an average grain size in the first region is different from an average grain size in the first substrate region.

In this electrostatic chuck, an average grain size in the first region is different from an average grain size in the first substrate region. This can improve the coupling strength between the first porous part and the ceramic dielectric substrate at an interface between the first porous part and the ceramic dielectric substrate.

A twenty third aspect of the invention is the electrostatic chuck according to the twenty first or twenty second aspect of the invention, wherein the average grain size in the first substrate region is smaller than the average grain size in the first region.

In this electrostatic chuck, the coupling strength between the first porous part and the ceramic dielectric substrate can be improved at the interface between the first porous part and the ceramic dielectric substrate. The grain size in the first substrate region is small, and thus the strength of the ceramic dielectric substrate cab be increased and risk such as crack or the like due to a stress generated in manufacturing or processing can be suppressed.

A twenty fourth aspect of the invention is the electrostatic chuck according to one of the twenty first or twenty third aspects of the invention, wherein the ceramic dielectric substrate includes a second substrate region, the first substrate region is located between the second substrate region and the first porous part, and the average grain size in the first substrate region is smaller than the average grain size in the second substrate region.

In the first substrate region provided to be in contact with the first region, it is desirable to increase the interface strength between the first substrate region and the first region by interaction such as diffusion or the like between the first substrate region and the first region at sintering in the manufacturing process, for instance. On the other hand, in the second substrate region, it is desirable that intrinsic characteristics of the material of the ceramic dielectric substrate are expressed. In this electrostatic chuck, the average grain size in the first substrate region is made smaller than the average grain size in the second substrate region. The security of the interface strength in the first substrate region and the characteristics of the ceramic dielectric substrate in the second substrate region can be compatible.

A twenty fifth aspect of the invention is the electrostatic chuck of the twenty fourth aspect of the invention, wherein the average grain size in the first region is smaller than the average grain size in the second substrate region.

In this electrostatic chuck, the average grain size in the first region is smaller than the average grain size in the second substrate region. This can improve the mechanical strength in the first region.

A twenty sixth aspect of the invention is the electrostatic chuck according to one of the twenty first, twenty second, twenty fourth, twenty fifth aspects of the invention, wherein the average grain size in the first region is smaller than the average grain size in the first substrate region.

In this electrostatic chuck, the coupling strength between the first porous part and the ceramic dielectric substrate can be improved at the interface between the first porous part and the ceramic dielectric substrate. The average grain size in the first region is small, and the strength of the first porous part is increased. This can suppress detachment of the grains at processing and can reduce particles.

Embodiments of the invention will now be described with reference to the drawings. In the drawings, similar components are marked with the same reference numerals, and the detailed description thereof is omitted appropriately.

First Embodiment

FIG. 1is a schematic sectional view illustrating an electrostatic chuck according this embodiment.

As shown inFIG. 1, the electrostatic chuck110according to this embodiment includes a ceramic dielectric substrate11, a base plate50, and a first porous part90.

The ceramic dielectric substrate11is e.g. a flat plate-like base material made of sintered ceramic. For instance, the ceramic dielectric substrate11contains aluminum oxide (Al2O3). For instance, the ceramic dielectric substrate11is formed from high-purity aluminum oxide. The concentration of aluminum oxide in the ceramic dielectric substrate11is e.g. 99 atomic percent (atomic %) or more and 100 atomic % or less. Use of high-purity aluminum oxide can improve the plasma resistance of the ceramic dielectric substrate11. The ceramic dielectric substrate11has a first major surface11aon which a suction target W is mounted, and a second major surface11bon the opposite side from the first major surface11a. The suction target W is e.g. a semiconductor substrate such as a silicon wafer.

The ceramic dielectric substrate11is provided with an electrode12. The electrode12is provided between the first major surface11aand the second major surface11bof the ceramic dielectric substrate11. The electrode12is formed so as to be inserted in the ceramic dielectric substrate11. By application of a suction-holding voltage80to the electrode12, the electrostatic chuck110generates charge on the first major surface11aside of the electrode12and suction-holds the target W by electrostatic force.

Here, in the description of this embodiment, the direction from the base plate50to the ceramic dielectric substrate11is referred to as Z-direction (corresponding to an example of the first direction). One of the directions generally orthogonal to the Z-direction is referred to as Y-direction (corresponding to an example of the second direction). The direction generally orthogonal to the Z-direction and the Y-direction is referred to as X-direction (corresponding to an example of the second direction).

The electrode12is shaped like a thin film along the first major surface11aand the second major surface11bof the ceramic dielectric substrate11. The electrode12is a suction electrode for suction-holding the target W. The electrode12may be of the unipolar type or the bipolar type. The electrode12shown inFIG. 1is of the bipolar type, with electrodes12of two polarities provided on the same plane.

The electrode12is provided with a connection part20extending to the second major surface11bside of the ceramic dielectric substrate11. The connection part20is e.g. a via (solid type) or via hole (hollow type) in electrical continuity with the electrode12. The connection part20may be a metal terminal connected by a suitable method such as brazing.

The base plate50is a member for supporting the ceramic dielectric substrate11. The ceramic dielectric substrate11is fixed on the base plate50with a bonding part60shown inFIG. 2A. The bonding part60can be e.g. a cured silicone adhesive.

The base plate50is e.g. metallic. The base plate50is e.g. divided into an upper part50aand a lower part50bmade of aluminum. A communication channel55is provided between the upper part50aand the lower part50b. One end side of the communication channel55is connected to an input channel51. The other end side of the communication channel55is connected to an output channel52.

The base plate50also serves to adjust the temperature of the electrostatic chuck110. For instance, in the case of cooling the electrostatic chuck110, a cooling medium is caused to flow in from the input channel51, to pass through the communication channel55, and to flow out from the output channel52. This can absorb heat from the base plate50by the cooling medium to cool the ceramic dielectric substrate11attached onto the base plate50. On the other hand, in the case of keeping warm the electrostatic chuck110, a heat-retaining medium can be put into the communication channel55. Alternatively, a heating element can be incorporated in the ceramic dielectric substrate11or the base plate50. Thus, the temperature of the base plate50and the ceramic dielectric substrate11is adjusted. This can adjust the temperature of the target W suction-held by the electrostatic chuck110.

Dots13are provided as necessary on the first major surface11aside of the ceramic dielectric substrate11. A groove14is provided between the dots13. That is, the first major surface11ais a protrusion-depression surface and includes a depression and a protrusion. The protrusion of the first major surface11acorresponds to the dot13. The depression of the first major surface11acorresponds to the groove14. The groove14extends continuously in the X-Y plane. A space is formed between the back surface of the target W mounted on the electrostatic chuck110and the first major surface11aincluding the groove14.

The ceramic dielectric substrate11includes a through hole15connected to the groove14. The through hole15is provided from the second major surface11bto the first major surface11a. That is, the through hole15extends in the Z-direction from the second major surface11bto the first major surface11aand penetrates through the ceramic dielectric substrate11.

The height of the dot13(the depth of the groove14), the area ratio between the dots13and the grooves14, the shapes thereof and the like can be appropriately selected to control the temperature of the target W and particles attached to the target W in a desirable state.

The base plate50is provided with a gas feed channel53. For instance, the gas feed channel53is provided so as to penetrate through the base plate50. The gas feed channel53may not penetrate through the base plate50, but may branch halfway from another gas feed channel53and extend to the ceramic dielectric substrate11side. The gas feed channel53may be provided at a plurality of locations in the base plate50.

The gas feed channel53communicates with the through hole15. That is, the gas (such as helium (He)) flowing into the gas feed channel53passes through the gas feed channel53, and then flows into the through hole15.

The gas flowing into the through hole15passes through the through hole15, and then flows into the space provided between the target W and the first major surface11aincluding the groove14. This can directly cool the target W with the gas.

The first porous part90can be provided at a position e.g. between the base plate50and the first major surface11aof the ceramic dielectric substrate11in the Z-direction. The position is opposed to the gas feed channel53. For instance, the first porous part90is provided in the through hole15of the ceramic dielectric substrate11. For instance, the first porous part90is inserted into the through hole15.

FIGS. 2A and 2Bare schematic views illustrating the electrostatic chuck according the embodiment.FIG. 2Aillustrates the neighborhood of the first porous part90.FIG. 2Acorresponds to an enlarged view of region A shown inFIG. 1.FIG. 2Bis a plan view illustrating the first porous part90.

FIG. 2Cis a schematic sectional view for illustrating a first compact section92according to an alternative embodiment.

In order to avoid complexity, the dots13(see e.g.FIG. 1) are omitted inFIGS. 2A and 2C.

In this example, the through hole15includes a hole part15aand a hole part15b(corresponding to an example of the first hole part). One end of the hole part15ais located on the second major surface11bof the ceramic dielectric substrate11.

The ceramic dielectric substrate11can include a hole part15blocated between the first major surface11aand the first porous part90in the Z-direction. The hole part15bcommunicates with the hole part15aand extends to the first major surface11aof the ceramic dielectric substrate11. That is, one end of the hole part15bis located on the first major surface11a(groove14). The hole part15bis a link hole for linking the first porous part90and the groove14. The diameter (length along the X-direction) of the hole part15bis smaller than the diameter (length along the X-direction) of the hole part15a. Providing a hole part15bhaving a small diameter can improve the design flexibility of the space formed between the ceramic dielectric substrate11and the target W (e.g. the first major surface11aincluding the groove14). For instance, as shown inFIG. 2A, the width (length along the X-direction) of the groove14can be made shorter than the width (length along the X-direction) of the first porous part90. This can suppress discharge in e.g. the space formed between the ceramic dielectric substrate11and the target W.

The diameter of the hole part15bis e.g. 0.05 millimeters (mm) or more and 0.5 mm or less. The diameter of the hole part15ais e.g. 1 mm or more and 5 mm or less. The hole part15bmay communicate indirectly with the hole part15a. That is, a hole part15c(corresponding to an example of the second hole part) may be provided to connect the hole part15aand the hole part15b. As shown inFIG. 2A, the hole part15ccan be provided in the ceramic dielectric substrate11. Alternatively, the hole part15ccan be provided in the first porous part90. Alternatively, the hole part15ccan be provided in the ceramic dielectric substrate11and the first porous part90. That is, at least one of the ceramic dielectric substrate11and the first porous part90can include a hole part15clocated between the hole part15band the first porous part90. In this case, when the hole part15cis provided in the ceramic dielectric substrate11, the strength around the hole part15ccan be increased, and the occurrence of e.g. chipping can be suppressed around the hole part15c. This can suppress the occurrence of arc discharge more effectively. When the hole part15cis provided in the first porous part90, the hole part15cis easily aligned with the first porous part90. This further facilitates the compatibility between reduction of arc discharge and smoothing of the flow of gas. Each of the hole part15a, the hole part15b, and the hole part15cis shaped like e.g. a circular cylinder extending in the Z-direction.

In this case, in the X-direction or the Y-direction, the dimension of the hole part15ccan be made smaller than the dimension of the first porous part90and larger than the dimension of the hole part15b. In the electrostatic chuck110according to this embodiment, the first porous part90is provided at a position opposed to the gas feed channel53. This can improve resistance to arc discharge while ensuring the flow rate of the gas flowing in the hole part15b. The dimension in the X-direction or the Y-direction of the hole part15cis made larger than the dimension of the hole part15b. Thus, most of the gas fed into the first porous part90having a large dimension can be fed through the hole part15cinto the hole part15bhaving a small dimension. That is, reduction of arc discharge can be made compatible with smoothing of the flow of gas.

As described above, the ceramic dielectric substrate11includes at least one groove14opened to the first major surface11aand communicating with the first hole part15. In the Z-direction, the dimension of the hole part15ccan be made smaller than the dimension of the groove14. Thus, gas can be supplied to the first major surface11aside through the groove14. This facilitates supplying gas in a broader range of the first major surface11a. The dimension in the X-direction or the Y-direction of the hole part15cis made smaller than the dimension of the groove14. This can reduce the time taken by the gas to pass through the hole part15c. That is, the occurrence of arc discharge can be suppressed more effectively while smoothing the flow of gas.

As described above, a bonding part60can be provided between the ceramic dielectric substrate11and the base plate50. In the Z-direction, the dimension of the hole part15ccan be made smaller than the dimension of the bonding part60. This can improve the bonding strength between the ceramic dielectric substrate11and the base plate50. The dimension of the hole part15cin the Z-direction is made smaller than the dimension of the bonding part60. Thus, the occurrence of arc discharge can be suppressed more effectively while smoothing the flow of gas.

In this example, the first porous part90is provided in the hole part15a. Thus, the upper surface90U of the first porous part90is not exposed to the first major surface11a. That is, the upper surface90U of the first porous part90is located between the first major surface11aand the second major surface11b. On the other hand, the lower surface90L of the first porous part90is exposed to the second major surface11b.

The first porous part90can include a porous section91, a first compact section92, and a second compact section93.

The porous section91includes a plurality of pores. The first compact section92is more compact than the porous section91. As projected on a plane (X-Y plane) perpendicular to a first direction (Z-direction) from the base plate50to the ceramic dielectric substrate11, the first compact section92is configured to overlap the first hole part15b, and the porous section91is configured not to overlap the first hole part15b. In such a configuration, the generated current is caused to flow around the first compact section. Accordingly, the current can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge. In this electrostatic chuck, the occurrence of arc discharge can be effectively suppressed while ensuring the gas flow.

In this example, as projected on the plane perpendicular to the Z-direction, the porous section91is provided around the first compact section92. At a position opposed to the first hole part15b, the first compact section92is placed to improve resistance to arc discharge. On the other hand, the porous section91is provided therearound. This can ensure sufficient gas flow. That is, reduction of arc discharge can be made compatible with smoothing of the flow of gas.

The length along the Z-direction of the first compact section92may be made smaller than the length along the Z-direction of the first porous part90. In the Z-direction, the porous section91may be provided between the first compact section92and the base plate50. These configurations can smooth the gas flow while suppressing the occurrence of arc discharge.

The length along the Z-direction of the first compact section92may be generally equal to the length along the Z-direction of the first porous part90. The occurrence of arc discharge can be suppressed more effectively by sufficiently increasing the length of the first compact section92.

The first compact section92may be configured as a compact body including substantially no pores. Alternatively, the first compact section92may be configured to include a plurality of pores as long as it is more compact than the porous section91. When the first compact section92includes a plurality of pores, preferably, the diameter of the pore is made smaller than the diameter of the pore included in the porous section91.

The porosity (percent, %) of the first compact section92can be made lower than the porosity (%) of the porous section91. Thus, the density (gram/cubic centimeter, g/cm3) of the first compact section92can be made higher than the density (g/cm3) of the porous section91.

Here, arc discharge often occurs when the current flows inside the hole part15bfrom the ceramic dielectric substrate11side to the base plate50side. Thus, when the first compact section92having a low porosity is provided near the hole part15b, the current200is caused to flow around the first compact section92as shown inFIG. 2A. Accordingly, the current200can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge.

The porosity of the first compact section92is e.g. the proportion that the volume of the space (pores) included in the first compact section92occupies in the total volume of the first compact section92. The porosity of the porous section91is e.g. the proportion that the volume of the space (pores) included in the porous section91occupies in the total volume of the porous section91. For instance, the porosity of the porous section91is 5% or more and 40% or less, and preferably 10% or more and 30% or less. The porosity of the first compact section92is 0% or more and 5% or less. In this case, preferably, the porosity of the first compact section92is made 50% or less of the porosity of the porous section91. That is, the first compact section92is provided in the porous section91. The first compact section92is opposed to the hole part15b. The porosity of the first compact section92is 50% or less of the porosity of the porous section91.

The diameter of the pore included in the first compact section92may be made 80% or less of the diameter of the pore included in the porous section91.

Alternatively, the first compact section92may be configured to include no pores.

The diameter of the pore included in the first compact section92is 80% or less of the diameter of the pore included in the porous section91, or the first compact section92includes no pores. These configurations can also achieve an effect similar to the case of having the aforementioned porosity. That is, even in these cases, the current200can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge.

In the Z-direction, the surface of the first compact section92on the gas feed channel53side may be provided inside the porous section91, or exposed from the surface of the porous section91on the gas feed channel53side. The surface of the first compact section92on the hole part15bside may be provided inside the porous section91, or exposed from the surface of the porous section91on the hole part15bside. When the surface of the first compact section92on the hole part15bside is exposed from the surface of the porous section91on the hole part15bside, the insulation distance can be made longer. This can suppress that the hole part15bconstitutes a path of discharge. When the surface of the first compact section92on the gas feed channel53side is exposed from the surface of the porous section91on the gas feed channel53side, the insulation distance can be made longer. This can suppress that the hole part15bconstitutes a path of discharge. For instance, as shown inFIG. 2C, preferably, the first compact section92extends in the Z-direction from the surface of the porous section91on the gas feed channel53side to the surface of the porous section91on the hole part15bside. This can further suppress the occurrence of arc discharge.

As viewed along the Z-direction, preferably, the hole part15boverlaps the first compact section92. Then, the current flowing inside the hole part15bfrom the ceramic dielectric substrate11side to the base plate50side can be reliably caused to flow around the first compact section92. Thus, the insulation distance can be made longer. This can suppress that the hole part15bconstitutes a path of discharge.

The second compact section93can be a region including fewer pores than the porous section91, or a region including substantially no pores. Alternatively, the second compact section93may be a porous structure having a smaller pore diameter than the porous section91. The porosity (percent, %) of the second compact section93can be made lower than the porosity (%) of the porous section91. Thus, the density (gram/cubic centimeter, g/cm3) of the second compact section93can be made higher than the density (g/cm3) of the porous section91. The second compact section93is more compact than the porous section91. Thus, the rigidity (mechanical strength) of the second compact section93is higher than the rigidity of the porous section91.

The porosity of the second compact section93is e.g. the proportion that the volume of the space (pores) included in the second compact section93occupies in the total volume of the second compact section93. For instance, the porosity of the second compact section93is 0% or more and 5% or less.

The first porous part90is shaped like a column (e.g. circular column).

The porous section91is shaped like a column (e.g. circular column).

The first compact section92is shaped like a plate (e.g. disk) or a column (e.g. circular column).

The second compact section93is in contact with the porous section91, or is continuous (formed integrally) with the porous section91. As shown inFIG. 2B, as viewed along the Z-direction, the second compact section93surrounds the outer periphery of the porous section91. The second compact section93is shaped like a cylinder (e.g. circular cylinder) surrounding the side surface91sof the porous section91. In other words, the porous section91is provided so as to penetrate through the second compact section93in the Z-direction. The gas flowing from the gas feed channel53into the through hole15passes through a plurality of pores provided in the porous section91and is supplied to the groove14.

Thus, the first porous part90includes the porous section91as described above. This can improve resistance to arc discharge while ensuring the flow rate of the gas flowing in the through hole15. The first porous part90includes the second compact section93. This can improve the rigidity (mechanical strength) of the first porous part90. The first porous part90includes the first compact section92. This can further suppress the occurrence of arc discharge.

For instance, the first porous part90is integrated with the ceramic dielectric substrate11. The state in which two members are integrated refers to the state in which the two members are chemically coupled by e.g. sintering. No material (e.g. adhesive) for fixing one member to the other is provided between the two members. That is, no other member such as adhesive is provided between the first porous part90and the ceramic dielectric substrate11. Thus, the first porous part90and the ceramic dielectric substrate11are integrated with each other.

More specifically, in the state in which the first porous part90and the ceramic dielectric substrate11are integrated with each other, the side surface of the first porous part90(the side surface93sof the second compact section93) is in contact with the inner wall15wof the through hole15. The first porous part90is supported by the inner wall15wbeing in contact with the first porous part90. Thus, the first porous part90is fixed to the ceramic dielectric substrate11.

For instance, a through hole is provided in a base material constituting the ceramic dielectric substrate11before sintering. The first porous part90is fitted into the through hole. In this state, by sintering the ceramic dielectric substrate11(and the fitted first porous part90), the first porous part90and the ceramic dielectric substrate11can be integrated with each other.

Thus, the first porous part90is fixed to the ceramic dielectric substrate11by integration with the ceramic dielectric substrate11. This can improve the strength of the electrostatic chuck110compared with the case of fixing the first porous part90to the ceramic dielectric substrate11with e.g. adhesive. For instance, there is no degradation of the electrostatic chuck due to e.g. corrosion or erosion of adhesive.

When the first porous part90and the ceramic dielectric substrate11are integrated with each other, the side surface of the outer periphery of the first porous part90is subjected to a force from the ceramic dielectric substrate11. On the other hand, when the first porous part90is provided with a plurality of pores to ensure the flow rate of gas, the mechanical strength of the first porous part90decreases. Thus, when the first porous part is integrated with the ceramic dielectric substrate11, the first porous part90may be broken by the force applied from the ceramic dielectric substrate to the first porous part90.

In this regard, the first porous part90includes the second compact section93. This can improve the rigidity (mechanical strength) of the first porous part90. Thus, the first porous part90can be integrated with the ceramic dielectric substrate11.

In the embodiment, the first porous part90does not necessarily need to be integrated with the ceramic dielectric substrate11. For instance, as shown inFIG. 12, the first porous part90may be attached to the ceramic dielectric substrate with adhesive.

The second compact section93is located between the inner wall15wof the ceramic dielectric substrate11forming the through hole15, and the porous section91. That is, the porous section91and the first compact section92are provided inside the first porous part90. The second compact section93is provided outside the first porous part90. In the X-direction or the Y-direction, the first compact section92is provided in a central region of the porous section91. The second compact section93is provided outside the first porous part90. This can improve the rigidity against the force applied from the ceramic dielectric substrate11to the first porous part90. Thus, the first porous part90and the ceramic dielectric substrate11can be easily integrated with each other. For instance, a bonding member61(seeFIG. 12) may be provided between the first porous part90and the ceramic dielectric substrate11. In this case, the second compact section93can suppress that the bonding member61is exposed to the gas passing in the first porous part90. This can suppress degradation of the bonding member61. The porous section91is provided inside the first porous part90. This can suppress that the through hole15of the ceramic dielectric substrate11is occluded with the second compact section93. Thus, the flow rate of gas can be ensured.

The thickness of the second compact section93(length L0between the side surface91sof the porous section91and the side surface93sof the second compact section93) is e.g. 100 μm or more and 1000 μm or less.

The material of the first porous part90is an insulative ceramic. The first porous part90(each of the porous section91, the first compact section92, and the second compact section93) contains at least one of aluminum oxide (Al2O3), titanium oxide (TiO2), and yttrium oxide (Y2O3). This can achieve high breakdown voltage and high rigidity of the first porous part90.

For instance, the first porous part90is composed primarily of one of aluminum oxide, titanium oxide, and yttrium oxide.

In this case, the purity of aluminum oxide of the ceramic dielectric substrate11can be made higher than the purity of aluminum oxide of the first porous part90. This can ensure the performance of the electrostatic chuck110such as plasma resistance, and ensure the mechanical strength of the first porous part90. As an example, a trace amount of additive is contained in the first porous part90. This facilitates sintering the first porous part90, and can control the pores and ensure the mechanical strength.

In this specification, the ceramic purity of e.g. aluminum oxide of the ceramic dielectric substrate11can be measured by e.g. fluorescent X-ray analysis or ICP-AES method (inductively coupled plasma-atomic emission spectrometry).

For instance, the material of the porous section91, the material of the first compact section92, and the material of the second compact section93are the same. However, the material of the porous section91, the material of the first compact section92, and the material of the second compact section93may be different. The composition of the material of the porous section91, the composition of the material of the first compact section92, and the composition of the material of the second compact section93may be different.

As shown inFIG. 2A, the distance D1in the X-direction or the Y-direction between the porous section91(a plurality of sparse portions94described later) and the electrode12is longer than the distance D2in the Z-direction between the first major surface11aand the electrode12. Thus, the distance D1in the X-direction or the Y-direction between the porous section91provided in the first porous part90and the electrode12is made longer. This can suppress discharge in the first porous part90. The distance D2in the Z-direction between the first major surface11aand the electrode12is made shorter. This can increase the force for sucking the target W mounted on the first major surface11a.

FIGS. 3A and 3Bare schematic views illustrating the first porous part of the electrostatic chuck according the embodiment.

FIG. 3Ais a plan view of the first porous part90as viewed along the Z-direction.FIG. 3Bis a sectional view taken along Z-Y plane of the first porous part90.

As shown inFIGS. 3A and 3B, in this example, the porous section91includes a plurality of sparse portions94and a dense portion95. Each of the plurality of sparse portions94includes a plurality of pores. The dense portion95is more compact than the sparse portion94. That is, the dense portion95is a portion including fewer pores than the sparse portion94, or a portion including substantially no pores. The porosity of the dense portion95is lower than the porosity of the sparse portion94. Thus, the density of the dense portion95is higher than the density of the sparse portion94. The porosity of the dense portion95may be equal to the porosity of the first compact section92or the porosity of the second compact section93. The dense portion95is more compact than the sparse portion94. Thus, the rigidity of the dense portion95is higher than the rigidity of the sparse portion94.

The porosity of one sparse portion94is e.g. the proportion that the volume of the space (pores) included in that sparse portion94occupies in the total volume of that sparse portion94. The porosity of the dense portion95is e.g. the proportion that the volume of the space (pores) included in the dense portion95occupies in the total volume of the dense portion95. For instance, the porosity of the sparse portion94is 20% or more and 60% or less, and preferably 30% or more and 50% or less. The porosity of the dense portion95is 0% or more and 5% or less.

Each of the plurality of sparse portions94extends in the Z-direction. For instance, each of the plurality of sparse portions94is shaped like a column (e.g. circular column or polygonal column) and provided so as to penetrate through the porous section91in the Z-direction. The dense portion95is located between the plurality of sparse portions94. The dense portion95is shaped like a wall partitioning between the sparse portions94neighboring each other. As shown inFIG. 3A, as viewed along the Z-direction, the dense portion95is provided so as to surround the outer periphery of each of the plurality of sparse portions94. The dense portion95is continuous with the second compact section93at the outer periphery of the porous section91.

The number of sparse portions94provided in the porous section91is e.g. 50 or more and 1000 or less. As shown inFIG. 3A, as viewed along the Z-direction, the plurality of sparse portions94have a size generally equal to each other. For instance, as viewed along the Z-direction, the plurality of sparse portions94are dispersed isotropically and uniformly in the porous section91. For instance, the distance between the neighboring sparse portions94(i.e. the thickness of the dense portion95) is generally constant.

For instance, as viewed along the Z-direction, the distance L11between the side surface93sof the second compact section93and the sparse portion94of the plurality of sparse portions94nearest to the side surface93sis 100 μm or more and 1000 μm or less.

The porous section91may be dispersed with a plurality of pores randomly in three dimensions.

However, the porous section91can be provided with a plurality of sparse portions94, and a dense portion95more compact than the sparse portion94. This can improve the rigidity of the first porous part90while ensuring resistance to arc discharge and the flow rate of the gas flowing in the through hole15compared with the case where a plurality of pores are dispersed randomly in three dimensions in the porous region.

For instance, the increase of the porosity of the porous region results in increasing the flow rate of gas, but decreasing arc discharge resistance and rigidity. In contrast, by providing the dense portion95, the decrease of arc discharge resistance and rigidity can be suppressed even when the porosity is increased.

For instance, as viewed along the Z-direction, suppose a minimum circle, ellipse, or polygon containing all the plurality of sparse portions94. The inside of the circle, ellipse, or polygon can be regarded as the porous section91. The outside of the circle, ellipse, or polygon can be regarded as the second compact section93.

As described above, the first porous part90can include a plurality of sparse portions94and a dense portion95. The plurality of sparse portions94include a plurality of pores96including a first pore and a second pore. The dense portion95has a higher density than the sparse portion94. Each of the plurality of sparse portions94extends in the Z-direction. The dense portion95is located between the plurality of sparse portions94. The sparse portion94includes a wall part97provided between the pore96(first pore) and the pore96(second pore). In the X-direction or the Y-direction, the minimum dimension of the wall part97can be made smaller than the minimum dimension of the dense portion95. Thus, the first porous part90is provided with the sparse portions94and the dense portion95extending in the Z-direction. This can improve the mechanical strength (rigidity) of the first porous part90while ensuring arc discharge resistance and gas flow rate. The details of the pore96and the wall part97will be described later (seeFIG. 5).

In the X-direction or the Y-direction, the dimension of the plurality of pores96provided in each of the plurality of sparse portions94can be made smaller than the dimension of the dense portion95. Thus, the dimension of the plurality of pores96can be made sufficiently small. This can further improve resistance to arc discharge.

The aspect ratio of the plurality of pores96provided in each of the plurality of sparse portions94can be set to 30 or more and 10000 or less. This can further improve resistance to arc discharge. More preferably, the lower limit of the aspect ratio of the plurality of pores96is 100 or more, and the upper limit is 1600 or less.

In the X-direction or the Y-direction, the dimension of the plurality of pores96provided in each of the plurality of sparse portions94can be set to 1 micrometer or more and 20 micrometers or less. Thus, the pores96having a pore dimension of 1-20 micrometers and extending in one direction can be arranged. This can achieve high resistance to arc discharge.

As shown inFIGS. 6A and 6Bdescribed later, as viewed along the Z-direction, the first pore96ais located in a central part of the sparse portion94. Among the plurality of pores96, the number of pores96b-96gneighboring the first pore96aand surrounding the first pore96acan be set to 6. Thus, in plan view (as viewed along the Z-direction), a plurality of pores96can be arranged with high isotropy and high density. This can improve the rigidity of the first porous part90while ensuring arc discharge resistance and gas flow rate.

FIG. 4is a schematic plan view illustrating the first porous part of the electrostatic chuck according the embodiment.

FIG. 4shows part of the first porous part90as viewed along the Z-direction, and corresponds to an enlarged view ofFIG. 3A.

As viewed along the Z-direction, each of the plurality of sparse portions94is generally shaped like a hexagon (shaped like a generally regular hexagon). As viewed along the Z-direction, the plurality of sparse portions94include a first sparse portion94aand six sparse portions94(second to seventh sparse portions94b-94g) surrounding the first sparse portion94a.

The second to seventh sparse portions94b-94gneighbor the first sparse portion94a. The second to seventh sparse portions94b-94gare sparse portions94of the plurality of sparse portions94nearest to the first sparse portion94a.

The second sparse portion94band the third sparse portion94care juxtaposed with the first sparse portion94ain the X-direction. That is, the first sparse portion94ais located between the second sparse portion94band the third sparse portion94c.

The length L1along the X-direction of the first sparse portion94a(the diameter of the first sparse portion94a) is longer than the length L2along the X-direction between the first sparse portion94aand the second sparse portion94b, and longer than the length L3along the X-direction between the first sparse portion94aand the third sparse portion94c.

Each of the length L2and the length L3corresponds to the thickness of the dense portion95. That is, the length L2is the length along the X-direction of the dense portion95between the first sparse portion94aand the second sparse portion94b. The length L3is the length along the X-direction of the dense portion95between the first sparse portion94aand the third sparse portion94c. The length L2and the length L3are generally equal. For instance, the length L2is 0.5 times or more and 2.0 times or less of the length L3.

The length L1is generally equal to the length L4along the X-direction of the second sparse portion94b(the diameter of the second sparse portion94b), and generally equal to the length L5along the X-direction of the third sparse portion94c(the diameter of the third sparse portion94c). For instance, each of the length L4and the length L5is 0.5 times or more and 2.0 times or less of the length L1.

Thus, the first sparse portion94aneighbors and is surrounded with six sparse portions94of the plurality of sparse portions94. That is, as viewed along the Z-direction, in the central part of the porous section91, the number of sparse portions94neighboring one sparse portion94is 6. Thus, in plan view (as viewed along the Z-direction), a plurality of sparse portions94can be arranged with high isotropy and high density. This can improve the rigidity of the first porous part90while ensuring arc discharge resistance and the flow rate of the gas flowing in the through hole15. This can also suppress variation in arc discharge resistance, variation in the flow rate of the gas flowing in the through hole15, and variation in the rigidity of the first porous part90.

The diameter of the sparse portion94(e.g. length L1, L4, or L5) is e.g. 50 μm or more and 500 μm or less. The thickness of the dense portion95(e.g. length L2or L3) is e.g. 10 μm or more and 100 μm or less. The diameter of the sparse portion94is larger than the thickness of the dense portion95. The thickness of the dense portion95is thinner than the thickness of the second compact section93.

FIG. 5is a schematic plan view illustrating the first porous part of the electrostatic chuck according the embodiment.

FIG. 5shows part of the first porous part90as viewed along the Z-direction.FIG. 5is an enlarged view of the neighborhood of one sparse portion94.

As shown inFIG. 5, in this example, the sparse portion94includes a plurality of pores96and a wall part97provided between the plurality of pores96.

Each of the plurality of pores96extends in the Z-direction. Each of the plurality of pores96is shaped like a capillary extending in one direction (one-dimensional capillary structure), and penetrates through the sparse portion94in the Z-direction. The wall part97is shaped like a wall partitioning the pores96neighboring each other. As shown inFIG. 5, as viewed along the Z-direction, the wall part97is provided so as to surround the outer periphery of each of the plurality of pores96. The wall part97is continuous with the dense portion95at the outer periphery of the sparse portion94.

The number of pores96provided in one sparse portion94is e.g. 50 or more and 1000 or less. As shown inFIG. 5, as viewed along the Z-direction, the plurality of pores96have a size generally equal to each other. For instance, as viewed along the Z-direction, the plurality of pores96are dispersed isotropically and uniformly in the sparse portion94. For instance, the distance between the neighboring pores96(i.e. the thickness of the wall part97) is generally constant.

Thus, the pores96extending in one direction are arranged in the sparse portion94. This can achieve high resistance to arc discharge with small variation compared with the case where a plurality of pores are dispersed randomly in three dimensions in the sparse portion.

Here, the “capillary structure” of the plurality of pores96is further described.

In recent years, for the purpose of high integration of semiconductor devices, the circuit line width is growing narrower, and the circuit pitch is growing finer. The electrostatic chuck is subjected to higher power. The temperature control of the suction target is desired at higher level. Against this background, it is desired to ensure sufficient gas flow rate and to control the flow rate with high accuracy while reliably suppressing arc discharge in high-power environment. The electrostatic chuck110according to this embodiment includes a ceramic plug (first porous part90). The ceramic plug is conventionally provided to prevent arc discharge in the helium supply port (gas feed channel53). In this embodiment, the pore diameter (the diameter of the pore96) of the ceramic plug is decreased to the level of e.g. several to several ten μm (the details of the diameter of the pore96will be described later). The diameter decreased to this level may make it difficult to control the flow rate of gas. Thus, in the invention, for instance, the shape of the pore96is further devised so as to lie along the Z-direction. Specifically, in the conventional art, the flow rate is ensured using a relatively large pore, and its shape is made three-dimensionally complex to achieve prevention of arc discharge. In contrast, in the invention, the dimension of the pore96is made finer to the level of e.g. several to several ten μm to achieve prevention of arc discharge. Conversely, its shape is simplified to ensure flow rate. That is, the invention has been conceived based on the idea totally different from the conventional art.

The shape of the sparse portion94is not limited to the hexagon, but may be a circle (or ellipse) or other polygons. For instance, as viewed along the Z-direction, suppose a minimum circle, ellipse, or polygon containing all the plurality of pores96arranged with a pitch of 10 μm or less. The inside of the circle, ellipse, or polygon can be regarded as the sparse portion94. The outside of the circle, ellipse, or polygon can be regarded as the dense portion95.

FIGS. 6A and 6Bare schematic plan views illustrating the first porous part of the electrostatic chuck according the embodiment.

FIGS. 6A and 6Bshow part of the first porous part90as viewed along the Z-direction, and are enlarged views showing the pores96in one sparse portion94.

As shown inFIG. 6A, as viewed along the Z-direction, the plurality of pores96include a first pore96alocated in the central part of the sparse portion94, and six pores96(second to seventh pores96b-96g) surrounding the first pore96a. The second to seventh pores96b-96gneighbor the first pore96a. The second to seventh pores96b-96gare pores96of the plurality of pores96nearest to the first pore96a.

The second pore96band the third pore96care juxtaposed with the first pore96ain the X-direction. That is, the first pore96ais located between the second pore96band the third pore96c.

For instance, the length L6along the X-direction of the first pore96a(the diameter of the first pore96a) is longer than the length L7along the X-direction between the first pore96aand the second pore96b, and longer than the length L8along the X-direction between the first pore96aand the third pore96c.

Each of the length L7and the length L8corresponds to the thickness of the wall part97. That is, the length L7is the length along the X-direction of the wall part97between the first pore96aand the second pore96b. The length L8is the length along the X-direction of the wall part97between the first pore96aand the third pore96c. The length L7and the length L8are generally equal. For instance, the length L7is 0.5 times or more and 2.0 times or less of the length L8.

The length L6is generally equal to the length L9along the X-direction of the second pore96b(the diameter of the second pore96b), and generally equal to the length L10along the X-direction of the third pore96c(the diameter of the third pore96c). For instance, each of the length L9and the length L10is 0.5 times or more and 2.0 times or less of the length L6.

For instance, when the diameter of the pore is small, arc discharge resistance and rigidity are improved. On the other hand, when the diameter of the pore is large, the flow rate of gas can be increased. The diameter of the pore96(e.g. length L6, L9, or L10) is e.g. 1 micrometer (μm) or more and 20 μm or less. Thus, pores having a diameter of 1-20 micrometers and extending in one direction are arranged. This can achieve high resistance to arc discharge with small variation. More preferably, the diameter of the pore96is 3 μm or more and 10 μm or less.

Here, a method for measuring the diameter of the pore96is described. A scanning electron microscope (e.g. Hitachi High-Technologies, S-3000) is used to capture an image with a magnification of 1000 times or more. Commercially available image analysis software is used to calculate100circle-equivalent diameters for pores96. Their average value is used as the diameter of the pore96.

It is more preferable to suppress variation in the diameter of the plurality of pores96. By decreasing variation in the diameter, the flow rate of the flowing gas and the breakdown voltage can be controlled more precisely. The variation in the diameter of the plurality of pores96can be based on the cumulative distribution of the100circle-equivalent diameters obtained in the above calculation of the diameter of the pore96. Specifically, the concept of particle diameter D50(median diameter) for the cumulative distribution 50 vol % and particle diameter D90for the cumulative distribution 90 vol % are applied. These are generally used in granularity distribution measurement. The cumulative distribution graph for the pores96is produced in which the horizontal axis represents pore diameter (μm) and the vertical axis represents relative pore amount (%). This graph is used to determine the pore diameter for the cumulative distribution 50 vol % (corresponding to D50diameter) and the pore diameter for the cumulative distribution 90 vol % (corresponding to D90diameter). Preferably, the variation in the diameter of the plurality of pores96is suppressed so as to satisfy the relation D50:D90≤1:2.

The thickness of the wall part97(e.g. length L7or L8) is e.g. 1 μm or more and 10 μm or less. The thickness of the wall part97is thinner than the thickness of the dense portion95.

Thus, the first pore96aneighbors and is surrounded with six pores96of the plurality of pores96. That is, as viewed along the Z-direction, in the central part of the sparse portion94, the number of pores96neighboring one pore96is 6. Thus, in plan view, a plurality of pores96can be arranged with high isotropy and high density. This can improve the rigidity of the first porous part90while ensuring arc discharge resistance and the flow rate of the gas flowing in the through hole15. This can also suppress variation in arc discharge resistance, variation in the flow rate of the gas flowing in the through hole15, and variation in the rigidity of the first porous part90.

FIG. 6Bshows an alternative example of the arrangement of the plurality of pores96in the sparse portion94. As shown inFIG. 6B, in this example, the plurality of pores96are arranged concentrically about the first pore96a. Thus, in plan view, a plurality of pores can be arranged with high isotropy and high density.

The first porous part90having the structure as described above can be manufactured using e.g. extrusion molding. Each of the lengths L0-L10can be measured by observation using a microscope such as a scanning electron microscope.

The evaluation of porosity in this specification is described. In this description, the evaluation of porosity in the first porous part90is taken as an example.

An image like the plan view ofFIG. 3Ais captured. Image analysis is used to calculate the proportion R1of the plurality of sparse portions94occupied in the porous section91. The image is captured using a scanning electron microscope (e.g. Hitachi High-Technologies, S-3000). A BSE image is captured at an acceleration voltage of 15 kV and a magnification of 30 times. For instance, the image size is 1280×960 pixels, and the image gray scale assumes 256 levels.

The proportion R1of the plurality of sparse portions94occupied in the porous section91is calculated using image analysis software (e.g. Win-ROOF Ver. 6.5 (Mitani Corporation)).

Calculation of the proportion R1using Win-ROOF Ver. 6.5 can be performed as follows.

The evaluation range ROI1(seeFIG. 3A) is set to the minimum circle (or ellipse) including all the sparse portions94.

Binarization by a single threshold (e.g. 0) is performed to calculate the area S1of the evaluation range ROI1.

Binarization by two thresholds (e.g. 0 and 136) is performed to calculate the total area S2of the plurality of sparse portions94in the evaluation range ROI1. At this time, filling in the sparse portions94and deletion of regions having a small area regarded as noise (threshold being 0.002 or less) are performed. The two thresholds are appropriately adjusted by the brightness and contrast of the image.

The proportion R1is calculated as the proportion of the area S2to the area S1. That is, the proportion R1is given by proportion R1(%)=(area S2)/(area S1)×100.

In the embodiment, the proportion R1of the plurality of sparse portions94occupied in the porous section91is e.g. 40% or more and 70% or less, and preferably 50% or more and 70% or less. The proportion R1is e.g. approximately 60%.

An image like the plan view ofFIG. 5is captured. Image analysis is used to calculate the proportion R2of the plurality of pores96occupied in the sparse portion94. The proportion R2corresponds to e.g. the porosity of the sparse portion94. The image is captured using a scanning electron microscope (e.g. Hitachi High-Technologies, S-3000). A BSE image is captured at an acceleration voltage of 15 kV and a magnification of 600 times. For instance, the image size is 1280×960 pixels, and the image gray scale assumes 256 levels.

The proportion R2of the plurality of pores96occupied in the sparse portion94is calculated using image analysis software (e.g. Win-ROOF Ver. 6.5 (Mitani Corporation)).

Calculation of the proportion R2using Win-ROOF Ver. 6.5 can be performed as follows.

The evaluation range ROI2(seeFIG. 5) is set to a hexagon approximating the shape of the sparse portion94. The evaluation range ROI2includes all the pores96provided in one sparse portion94.

Binarization by a single threshold (e.g. 0) is performed to calculate the area S3of the evaluation range ROI2.

Binarization by two thresholds (e.g. 0 and 96) is performed to calculate the total area S4of the plurality of pores96in the evaluation range ROI2. At this time, filling in the pores96and deletion of regions having a small area regarded as noise (threshold being 1 or less) are performed. The two thresholds are appropriately adjusted by the brightness and contrast of the image.

The proportion R2is calculated as the proportion of the area S4to the area S3. That is, the proportion R2is given by proportion R2(%)=(area S4)/(area S3)×100.

In the embodiment, the proportion R2of the plurality of pores96occupied in the sparse portion94(the porosity of the sparse portion94) is e.g. 20% or more and 60% or less, and preferably 30% or more and 50% or less. The proportion R2is e.g. approximately 40%.

The porosity of the porous section91corresponds to e.g. the product of the proportion R1of the plurality of sparse portions94occupied in the porous section91and the proportion R2of the plurality of pores96occupied in the sparse portion94. For instance, when the proportion R1is 60% and the proportion R2is 40%, the porosity of the porous section91can be calculated as approximately 24%.

Thus, the first porous part90includes a porous section91having the porosity as described above. This can improve breakdown voltage while ensuring the flow rate of the gas flowing in the through hole15.

Likewise, the porosity of the ceramic dielectric substrate and the second porous part70can be calculated. Preferably, the magnification of the scanning electron microscope is appropriately selected within the range of several ten times to several thousand times depending on the observation target.

FIGS. 7A and 7Bare schematic views illustrating an alternative first porous part according the embodiment.

FIG. 7Ais a plan view of the first porous part90as viewed along the Z-direction.FIG. 7Bcorresponds to an enlarged view of part ofFIG. 7A.

As shown inFIGS. 7A and 7B, in this example, the planar shape of the sparse portion94is circular. Thus, the planar shape of the sparse portion94does not need to be hexagonal.

FIG. 8is a schematic sectional view illustrating the electrostatic chuck according the embodiment.

FIG. 8corresponds to an enlarged view of region B shown inFIG. 2. That is,FIG. 8shows the neighborhood of the interface F1between the first porous part90(second compact section93) and the ceramic dielectric substrate11. In this example, the material of the first porous part90and the ceramic dielectric substrate11is aluminum oxide.

As shown inFIG. 8, the first porous part90includes a first region90plocated on the ceramic dielectric substrate11side in the X-direction or the Y-direction, and a second region90qcontinuous with the first region90pin the X-direction or the Y-direction. The first region90pand the second region90qare part of the second compact section93of the first porous part90.

The first region90pis located between the second region90qand the ceramic dielectric substrate11in the X-direction or the Y-direction. The first region90pis a region of approximately 40-60 μm in the X-direction or the Y-direction from the interface F1. That is, the width W1along the X-direction or the Y-direction of the first region90p(the length of the first region90pin the direction perpendicular to the interface F1) is e.g. 40 μm or more and 60 μm or less.

The ceramic dielectric substrate11includes a first substrate region11plocated on the first porous part90(first region90p) side in the X-direction or the Y-direction, and a second substrate region11qcontinuous with the first substrate region11pin the X-direction or the Y-direction. The first region90pand the first substrate region11pare provided in contact with each other. The first substrate region11pis located between the second substrate region11qand the first porous part90in the X-direction or the Y-direction. The first substrate region11pis a region of approximately 40-60 μm in the X-direction or the Y-direction from the interface F1. That is, the width W2along the X-direction or the Y-direction of the first substrate region11p(the length of the first substrate region11pin the direction perpendicular to the interface F1) is e.g. 40 μm or more and 60 μm or less.

FIGS. 9A and 9Bare schematic sectional views illustrating the electrostatic chuck according the embodiment.

FIG. 9Ais an enlarged view of part of the first region90pshown inFIG. 8.FIG. 9Bis an enlarged view of part of the first substrate region11pshown inFIG. 8.

As shown inFIG. 9A, the first region90pincludes a plurality of grains g1(crystal grains). As shown inFIG. 9B, the first substrate region11pincludes a plurality of grains g2(crystal grains).

The average grain size in the first region90p(the average value of the diameter of the plurality of grains g1) is different from the average grain size in the first substrate region11p(the average value of the diameter of the plurality of grains g2).

Thus, the average grain size in the first region90pis different from the average grain size in the first substrate region11p. This can improve the coupling strength (interfacial strength) between the crystal grain of the first porous part90and the crystal grain of the ceramic dielectric substrate11at the interface F1. For instance, this can suppress peeling of the first porous part90from the ceramic dielectric substrate11and removal of crystal grains.

The average grain size can be the average value of the circle-equivalent diameter of the crystal grain in the cross-sectional image as shown inFIGS. 9A and 9B. The circle-equivalent diameter is the diameter of a circle having an area equal to the area of the target planar shape.

Preferably, the ceramic dielectric substrate11and the first porous part90are integrated with each other. The first porous part90is fixed to the ceramic dielectric substrate11by integration with the ceramic dielectric substrate11. This can improve the strength of the electrostatic chuck compared with the case of fixing the first porous part90to the ceramic dielectric substrate11with e.g. adhesive. For instance, this can suppress the degradation of the electrostatic chuck due to e.g. corrosion or erosion of adhesive.

In this example, the average grain size in the first substrate region11pis smaller than the average grain size in the first region90p. The small grain size in the first substrate region11pcan improve the coupling strength between the first porous part and the ceramic dielectric substrate at the interface between the first porous part and the ceramic dielectric substrate. The small grain size in the first substrate region can increase the strength of the ceramic dielectric substrate11and suppress the risk of e.g. cracks due to stress produced during manufacturing or processing. For instance, the average grain size in the first region90pis 3 μm or more and 5 μm or less. For instance, the average grain size in the first substrate region11pis 0.5 μm or more and 2 μm or less. The average grain size in the first substrate region11pis 1.1 times or more and 5 times or less of the average grain size in the first region90p.

For instance, the average grain size in the first substrate region11pis smaller than the average grain size in the second substrate region11q. In the first substrate region11pprovided in contact with the first region90p, preferably, the interfacial strength with the first region90pis increased by interaction such as diffusion with the first region90pduring e.g. sintering in the manufacturing process. On the other hand, in the second substrate region11q, preferably, the material of the ceramic dielectric substrate11develops its intrinsic characteristics. Thus, the average grain size in the first substrate region11pis made smaller than the average grain size in the second substrate region11q. Accordingly, ensuring the interfacial strength in the first substrate region11pcan be made compatible with the characteristics of the ceramic dielectric substrate11in the second substrate region11q.

The average grain size in the first region90pmay be smaller than the average grain size in the first substrate region11p. This can improve the coupling strength between the first porous part and the ceramic dielectric substrate at the interface between the first porous part and the ceramic dielectric substrate. The small grain size in the first region90pincreases the strength of the first porous part90. This can suppress removal of grains during processing and reduce particles.

For instance, in each of the first porous part90and the ceramic dielectric substrate11, the average grain size can be adjusted by adjusting the composition of materials and the sintering condition such as temperature. For instance, the amount or concentration of the sintering aid added in sintering the ceramic material is adjusted. For instance, magnesium oxide (MgO) used as a sintering aid suppresses abnormal growth of crystal grains.

Similarly to the foregoing, the average grain size in the first region90pcan be made smaller than the average grain size in the second substrate region11q. This can improve mechanical strength in the first region90p.

Referring again toFIG. 2A, the structure of the electrostatic chuck110is further described. The electrostatic chuck110may further include a second porous part70. The second porous part70can be provided between the first porous part90and the gas feed channel53in the Z-direction. For instance, the second porous part70is fitted into the ceramic dielectric substrate11side of the base plate50. As shown inFIG. 2A, for instance, a countersink part53ais provided on the ceramic dielectric substrate11side of the base plate50. The countersink part53ais provided like a cylinder. The second porous part70is fitted into the countersink part53aby appropriately designing the inner diameter of the countersink part53a.

The upper surface70U of the second porous part70is exposed to the upper surface50U of the base plate50. The upper surface70U of the second porous part70is opposed to the lower surface90L of the first porous part90. In this example, a space SP is formed between the upper surface70U of the second porous part70and the lower surface90L of the first porous part90. The space SP may be filled with at least one of the second porous part70and the first porous part90. That is, the second porous part70and the first porous part90may be in contact with each other.

The second porous part70includes a ceramic porous body71including a plurality of pores, and a ceramic insulating film72. The ceramic porous body71is provided like a cylinder (e.g. circular cylinder) and fitted into the countersink part53a. The shape of the second porous part70is preferably a circular cylinder, but is not limited to a circular cylinder. The ceramic porous body71is made of an insulative material. The material of the ceramic porous body71is e.g. Al2O3, Y2O3, ZrO2, MgO, SiC, AlN, or Si3N4. The material of the ceramic porous body71may be glass such as SiO2. The material of the ceramic porous body71may be e.g. Al2O3—TiO2, Al2O3—MgO, Al2O3—SiO2, Al6O13Si2, YAG, or ZrSiO4.

The porosity of the ceramic porous body71is e.g. 20% or more and 60% or less. The density of the ceramic porous body71is e.g. 1.5 g/cm3or more and 3.0 g/cm3or less. The gas such as He flowing from the gas feed channel53passes through a plurality of pores of the ceramic porous body71and is fed from the through hole15provided in the ceramic dielectric substrate11to the groove14.

The ceramic insulating film72is provided between the ceramic porous body71and the gas feed channel53. The ceramic insulating film72is more compact than the ceramic porous body71. The porosity of the ceramic insulating film72is e.g. 10% or less. The density of the ceramic insulating film72is e.g. 3.0 g/cm3or more and 4.0 g/cm3or less. The ceramic insulating film72is provided on the side surface of the ceramic porous body71.

The material of the ceramic insulating film72is e.g. Al2O3, Y2O3, ZrO2, or MgO. The material of the ceramic insulating film72may be e.g. Al2O3—TiO2, Al2O3—MgO, Al2O3—SiO2, Al6O13Si2, YAG, or ZrSiO4.

The ceramic insulating film72is formed on the side surface of the ceramic porous body71by thermal spraying. In thermal spraying, a coating material is melted or softened by heating and turned to fine particles. The fine particles are accelerated and caused to impinge on the side surface of the ceramic porous body71. Thus, the flattened particles are solidified or deposited to form a coating. This method is referred to as thermal spraying. Alternatively, the ceramic insulating film72may be fabricated by e.g. PVD (physical vapor deposition), CVD, sol-gel method, or aerosol deposition method. When the ceramic insulating film72is formed from a ceramic by thermal spraying, the film thickness is e.g. 0.05 mm or more and 0.5 mm or less.

The porosity of the ceramic dielectric substrate11is e.g. 1% or less. The density of the ceramic dielectric substrate11is e.g. 4.2 g/cm3.

The porosity in the ceramic dielectric substrate11and the second porous part70is measured by a scanning electron microscope as described above. The density is measured based on JIS C 2141 5.4.3.

The second porous part70is fitted in the countersink part53aof the gas feed channel53. Then, the ceramic insulating film72is in contact with the base plate50. That is, the ceramic porous body71and the ceramic insulating film72having high insulation performance are interposed between the through hole15for guiding the gas such as He to the groove14and the metallic base plate50. Use of such a second porous part70can achieve higher insulation performance than in the case where only the ceramic porous body71is provided in the gas feed channel53.

In the X-direction or the Y-direction, the dimension of the second porous part70can be made larger than the dimension of the first porous part90. A higher breakdown voltage can be obtained by providing such a second porous part70. This can suppress the occurrence of arc discharge more effectively.

The plurality of pores provided in the second porous part70are further dispersed in three dimensions than the plurality of pores provided in the first porous part90. The proportion of pores penetrating in the Z-direction can be made higher in the first porous part90than in the second porous part70. A higher breakdown voltage can be obtained by providing the second porous part70including a plurality of pores dispersed in three dimensions. This can suppress the occurrence of arc discharge more effectively. The flow of gas can be smoothed by providing the first porous part90having a high proportion of pores penetrating in the Z-direction.

In the Z-direction, the dimension of the second porous part70can be made larger than the dimension of the first porous part90. Thus, a higher breakdown voltage can be obtained. This can suppress the occurrence of arc discharge more effectively.

The average value of the diameter of the plurality of pores provided in the second porous part70can be made larger than the average value of the diameter of the plurality of pores provided in the first porous part90. Thus, the second porous part70having a large pore diameter is provided. This can smooth the flow of gas. The first porous part90having a small pore diameter is provided on the suction target side. This can suppress the occurrence of arc discharge more effectively.

Variation in the diameter of the plurality of pores can be decreased. This can suppress arc discharge more effectively.

FIG. 10is a schematic sectional view illustrating the second porous part70of the electrostatic chuck according the embodiment.

FIG. 10is an enlarged view of part of the cross section of the ceramic porous body71.

A plurality of pores71pprovided in the ceramic porous body71are dispersed in three dimensions in the X-direction, the Y-direction, and the Z-direction inside the ceramic porous body71. In other words, the ceramic porous body71has a three-dimensional network structure spread in the X-direction, the Y-direction, and the Z-direction. The plurality of pores71pare dispersed in the ceramic porous body71e.g. randomly or uniformly.

The plurality of pores71pare dispersed in three dimensions. Thus, part of the plurality of pores71pare exposed to the surface of the ceramic porous body71. Accordingly, fine irregularities are formed at the surface of the ceramic porous body71. That is, the ceramic porous body71has a rough surface. The surface roughness of the ceramic porous body71can facilitate forming the ceramic insulating film72as a thermal spray film. For instance, this improves contact between the thermal spray film and the ceramic porous body71. Peeling of the ceramic insulating film72can be suppressed.

The average value of the diameter of the plurality of pores71pprovided in the ceramic porous body71is larger than the average value of the diameter of the plurality of pores96provided in the porous section91. The diameter of the pore71pis e.g. 10 μm or more and 50 μm or less. The porous section91having a small pore diameter can control (limit) the flow rate of the gas flowing in the through hole15. This can suppress variation in the gas flow rate caused by the ceramic porous body71. The diameter of the pore71pand the diameter of the pore96can be measured by a scanning electron microscope as described above.

The average value of the diameter of the plurality of pores71pprovided in the ceramic porous body71can be smaller than the average value of the diameter of the plurality of pores96provided in the porous section91. This causes a current to flow hardly. This can suppress the occurrence of arc discharge more effectively.

The average value of the diameter of the plurality of pores71pmay be appropriately determined under consideration of the flow rate of gas to ne necessary and suppression of arc discharge.

FIG. 11is a schematic sectional view illustrating an alternative electrostatic chuck according the first embodiment.

FIG. 11illustrates the neighborhood of the first porous part90as inFIG. 2A.

In this example, the through hole15provided in the ceramic dielectric substrate11is not provided with the hole part15b(the link hole for linking the first porous part90and the groove14). For instance, the diameter (length along the X-direction) of the through hole15is generally constant without changing in the Z-direction.

As shown inFIG. 11, at least part of the upper surface90U of the first porous part90is exposed to the first major surface11aside of the ceramic dielectric substrate11. For instance, the position in the Z-direction of the upper surface90U of the first porous part90is the same as the position in the Z-direction of the bottom of the groove14.

Thus, the first porous part90may be provided generally entirely in the through hole15. The through hole15is not provided with a link hole having a small diameter. This can increase the flow rate of the gas flowing in the through hole15. The first porous part90having high insulation performance can be placed in most of the through hole15. This can achieve high resistance to arc discharge.

FIG. 12is a schematic sectional view illustrating an alternative electrostatic chuck according the first embodiment.

FIG. 12illustrates the neighborhood of the first porous part90as inFIG. 2A.

In this example, the first porous part90is not integrated with the ceramic dielectric substrate11.

A bonding member61(adhesive) is provided between the first porous part90and the ceramic dielectric substrate11. The first porous part90is bonded to the ceramic dielectric substrate11with the bonding member61. For instance, the bonding member61is provided between the side surface of the first porous part90(the side surface93sof the second compact section93) and the inner wall15wof the through hole15. The first porous part90and the ceramic dielectric substrate11do not need to be in contact with each other.

The bonding member61is e.g. a silicone adhesive. The bonding member61is e.g. an elastic member having elasticity. The elastic modulus of the bonding member61is e.g. lower than the elastic modulus of the second compact section93of the first porous part90, and lower than the elastic modulus of the ceramic dielectric substrate11.

In the structure in which the first porous part90and the ceramic dielectric substrate11are bonded by the bonding member61, the bonding member61can be used as a cushioning material against the difference between the thermal contraction of the first porous part90and the thermal contraction of the ceramic dielectric substrate11.

Second Embodiment

FIG. 13Ais a schematic cross sectional view illustrating an electrostatic chuck according to the second embodiment.

FIG. 13Bis a plan view illustrating a second porous part70a.

FIG. 13Cis a schematic cross sectional view illustrating a modification of the electrostatic chuck according to the second embodiment.

In the case of the electrostatic chuck according to the first embodiment, the first compact section92is provided in the first porous part90. On the other hand, in the case of the electrostatic chuck according to the second embodiment, a third compact section74is provided in the second porous part70a. Components other than this can be the same as the case of the electrostatic chuck according to the first embodiment.

As shown inFIGS. 13A to 13C, the first porous part90ais provided with the porous section91and the second compact section93. The first porous part90ais not provided with the first compact section92.

The second porous part70acan include a ceramic porous body73(second porous section), a third compact section74, and a fourth compact section75.

The ceramic porous body73can be, for instance, the same as the ceramic porous body71described above.

As described above, arc discharge often occurs when the current flows inside the hole part15bfrom the ceramic dielectric substrate11side to the base plate50side. Thus, when the first compact section92having a low porosity is provided near the hole part15b, the current200is caused to flow around the third compact section74as shown inFIG. 13A. Accordingly, the current200can be caused to flow a longer distance (conduction path). This can suppress acceleration of electrons, and can suppress the occurrence of arc discharge.

The fourth compact section75can be, for instance, the same as the second compact section93described above.

The fourth compact section75is in contact with the ceramic porous body73or continuous with the ceramic porous body73(formed integrally). As shown inFIG. 13B, as viewed along the Z-direction, the fourth compact section75surrounds the outer periphery of the ceramic porous body73. The fourth compact section75is shaped like a cylinder (e.g. circular cylinder) surrounding the side surface73sof the ceramic porous body73. In other words, the ceramic porous body73is provided so as to penetrate through the fourth compact section75in the Z-direction. The gas flowing from the gas feed channel53into the second porous part70apasses through a plurality of pores provided in the ceramic porous body73and is supplied to the first porous part90a.

Thus, the second porous part70aincludes the ceramic porous body73as described above. This can improve resistance to arc discharge while ensuring the flow rate of the gas flowing in the through hole15. The second porous part70aincludes the fourth compact section75. This can improve the rigidity (mechanical strength) of the second porous part70a. The second porous part70aincludes the third compact section74. This can further suppress the occurrence of arc discharge.

For instance, the first porous part90ais integrated with the ceramic dielectric substrate11. The state in which two members are integrated refers to the state in which the two members are chemically coupled by e.g. sintering. No material (e.g. adhesive) for fixing one member to the other is provided between the two members. That is, no other member such as adhesive is provided between the first porous part90aand the ceramic dielectric substrate11. Thus, the first porous part90aand the ceramic dielectric substrate11are integrated with each other.

More specifically, in the state in which the first porous part90aand the ceramic dielectric substrate11are integrated with each other, the side surface of the first porous part90a(the side surface93sof the second compact section93) is in contact with the inner wall15wof the through hole15. The first porous part90ais supported by the inner wall15wbeing in contact with the first porous part90a. Thus, the first porous part90ais fixed to the ceramic dielectric substrate11.

For instance, a through hole is provided in a base material constituting the ceramic dielectric substrate11before sintering. The first porous part90ais fitted into the through hole. In this state, by sintering the ceramic dielectric substrate11(and the fitted first porous part90a), the first porous part90aand the ceramic dielectric substrate11can be integrated with each other.

Thus, the first porous part90ais fixed to the ceramic dielectric substrate11by integration with the ceramic dielectric substrate11. This can improve the strength of the electrostatic chuck110compared with the case of fixing the first porous part90ato the ceramic dielectric substrate11with e.g. adhesive. For instance, there is no degradation of the electrostatic chuck due to e.g. corrosion or erosion of adhesive.

When the first porous part90aand the ceramic dielectric substrate11are integrated with each other, the side surface of the outer periphery of the first porous part90is subjected to a force from the ceramic dielectric substrate11. On the other hand, when the first porous part90ais provided with a plurality of pores to ensure the flow rate of gas, the mechanical strength of the first porous part90adecreases. Thus, when the first porous part90ais integrated with the ceramic dielectric substrate11, the first porous part90amay be broken by the force applied from the ceramic dielectric substrate11to the first porous part90a.

In this regard, the first porous part90aincludes the second compact section93. This can improve the rigidity (mechanical strength) of the first porous part90a. Thus, the first porous part90acan be integrated with the ceramic dielectric substrate11.

In the embodiment, the first porous part90adoes not necessarily need to be integrated with the ceramic dielectric substrate11. For instance, as shown inFIG. 19, the first porous part90amay be attached to the ceramic dielectric substrate11with adhesive.

FIG. 14is a schematic view illustrating the second porous part70a.FIG. 14is a plan view of the second porous part70awhen viewed along the Z-direction.

As shown inFIG. 14, the ceramic porous body73includes a plurality of sparse portions76and a dense portion77. Each of the plurality of sparse portions76includes a plurality of pores. The dense portion77is more compact than the sparse portion76. That is, the dense portion77is a portion including fewer pores than the sparse portion76, or a portion including substantially no pores. The configuration of the second porous part70acan be the same as the configuration of the first porous part90described above. In this case, the ceramic porous body73can correspond to the porous section91, the fourth compact section75can correspond to the second compact section93, the sparse portions76can correspond to the sparse portions94, and the dense portion77can correspond to the dense portion95. Therefore, the detailed description is omitted.

In this example, in the case where the first porous part90ais integrated with the ceramic dielectric substrate11and the configuration of the second porous part70ais the same as the configuration of the first porous part90described above, when the average value of the plurality of pores of the first porous part90ais larger than the average value of the plurality of pores of the second porous part70a, the mechanical strength of the first porous part90acan be increased more, and the high arc resistance and the strength can be compatible.

As viewed along the Z-direction, a distance L21between the side surface75sof the fourth compact section75and the sparse portion76nearest to the side surface75sof the plurality of sparse portions76can be not less than 100 μm and not more than 1000 μm.

FIG. 15shows a part of the second porous part70aviewed along the Z-direction, and corresponds to an enlarged view ofFIG. 14.

As viewed along the Z-direction, each of the plurality of sparse portions76is generally shaped like a hexagon (shaped like a generally regular hexagon). As viewed along the Z-direction, the plurality of sparse portions76include a first sparse portion76aand six sparse portions76(second to seventh sparse portions76b-76g) surrounding the first sparse portion76a. As described above, other than the first compact section92and the third compact section74, the configuration of the second porous part70acan be the same as the configuration of the first porous part90. In this case, the sparse portions76ato76gcan correspond to the sparse portions94ato94g. The lengths L21to L25can correspond to the lengths L1to L5. Therefore, the detailed description of these is omitted.

FIG. 16shows a part of the second porous pet70aviewed along the Z-direction.FIG. 16is an enlarged view of the neighborhood of one sparse portion76.

As shown inFIG. 16, in this example, the sparse portions76include a plurality of pores78and a wall part79provided between the plurality of pores78. As described above, other than the first compact section92and the third compact section74, the configuration of the second porous part70acan be the same as the configuration of the first porous part90. In this case, the sparse portions76can correspond to the sparse portions94, the dense portion77can corresponds to the dense portion95, the pores78can correspond to the pores96, and the wall part79can corresponds to the wall part97. Therefore, the detailed description is omitted.

FIG. 17shows a part of the second porous part70aviewed along the Z-direction, and is an enlarged view showing the pore78in the one sparse portion76.

As shown inFIG. 17, the plurality of pores78include a first pore78alocated at the center portion of the sparse portion76and six pores78(second to seventh pores78bto78g) surrounding the first pore78a. The second to seventh pores78bto78gare adjacent to the first pore78a. The second to seventh pores78bto78gare pores78nearest to the first pore78aof the plurality of pores78. As described above, other than the first compact section92and the third compact section74, the configuration of the second porous part70acan be the same as the configuration of the first porous part90. In this case, the first pore78acan correspond to the first pore96a, the second pore78bcan correspond to the second pore96b, the third pore78ccan correspond to the third pore96c, the fourth pore78dcan correspond to the fourth pore96d, the fifth pore78ecan correspond to the fifth pore96e, the sixth pore78fcan correspond to the sixth pore96f, and the seventh pore78gcan correspond to the seventh pore96g. Therefore, the detailed description is omitted.

FIG. 18is a schematic cross sectional view illustrating another electrostatic chuck according to the second embodiment.

FIG. 18illustrates the neighborhood of the second porous part70aas well asFIG. 13A.

In this example, the hole part15b(a link hole for linking the first porous part90aand the groove14) is not provided in the through hole15provided in the ceramic dielectric substrate11. For instance, a diameter of the through hole15(a length along the X-direction) does not change in the Z-direction and is generally constant.

As shown inFIG. 18, at least a part of an upper surface90aU of the first porous part90ais exposed to the first major surface11aside of the ceramic dielectric substrate11. For instance, the position in the Z-direction of the upper surface90aU of the first porous part90ais the same as the position in the Z-direction of the bottom of the groove14.

In this way, the first porous portion90amay be disposed generally over the through hole15. A link hole having a small diameter cannot be provided in the through hole15. This can make the flow rate of the gas flowing in the through hole15large. The first porous part90ahaving high insulating property can be disposed in the most part of the through hole15. The high resistance to arc discharge can be obtained.

FIG. 19is a schematic cross sectional view illustrating another electrostatic chuck according to the second embodiment.

FIG. 19illustrates the neighborhood of the first porous part90aas well asFIG. 13A.

In this example, the first porous part90ais not integrated with the ceramic dielectric substrate11.

A bonding member61(adhesive) is provided between the first porous part90aand the ceramic dielectric substrate11. The first porous part90ais bonded to the ceramic dielectric substrate11with the bonding member61. For instance, the bonding member61is provided between the side surface of the first porous part90a(the side surface93sof the second compact section93) and the inner wall15wof the through hole15. The first porous part90aand the ceramic dielectric substrate11do not need to be in contact with each other.

The bonding member61is e.g. a silicone adhesive. The bonding member61is e.g. an elastic member having elasticity. The elastic modulus of the bonding member61is e.g. lower than the elastic modulus of the second compact section93of the first porous part90a, and lower than the elastic modulus of the ceramic dielectric substrate11.

In the structure in which the first porous part90aand the ceramic dielectric substrate11are bonded by the bonding member61, the bonding member61can be used as a cushioning material against the difference between the thermal contraction of the first porous part90aand the thermal contraction of the ceramic dielectric substrate11.

The embodiments of the invention have been described above. However, the invention is not limited to the above description. For instance, the electrostatic chuck110has been illustrated with reference to the configuration based on the Coulomb force. However, the electrostatic chuck110is also applicable to the configuration based on the Johnsen-Rahbek force. Those skilled in the art can appropriately modify the above embodiments, and such modifications are also encompassed within the scope of the invention as long as they include the features of the invention. Furthermore, various components in the above embodiments can be combined with each other as long as technically feasible. Such combinations are also encompassed within the scope of the invention as long as they include the features of the invention.