Electrostatic chuck assembly

Abstract

Provided is an electrostatic chuck assembly in which space discharge does not readily occur in a gas passage plug. This electrostatic chuck assembly comprises: a ceramic plate having a top surface on which a wafer is to be placed and a bottom surface opposite the top surface, and incorporating an internal electrode that is an ESC electrode and / or an RF electrode; a cooling plate attached to the bottom surface of the ceramic plate; a plug placement hole penetrating the ceramic plate from the bottom surface to the top surface; a gas passage plug provided so as to close up the plug placement hole and configured to allow a gas to pass therethrough; and a gas introduction passageway provided in the cooling plate and communicating with the plug placement hole. At least a portion of a gas-contactable surface in the gas passage plug is formed from a low secondary electron emission coefficient (SEEC) material having a SEEC of 5.0 or less.

Description

Electrostatic chuck assembly

[0001] The present disclosure relates to an electrostatic chuck assembly.

[0002] Circuit formation in semiconductor device manufacturing is generally performed by plasma etching. Plasma etching is performed by introducing an inert gas into a vacuum chamber in a plasma etching apparatus to form a plasma. In the plasma etching apparatus, an electrostatic chuck assembly is provided that functions as a susceptor on which a wafer to be etched is placed. The electrostatic chuck assembly includes a ceramic plate with built-in electrodes that functions as an electrostatic chuck, and a cooling plate that supports the bottom surface of the ceramic plate with built-in electrodes. The wafer is electrostatically adsorbed to the ceramic plate with built-in electrodes, and plasma etching is performed while being fixed to the electrostatic chuck assembly. On the other hand, the cooling plate is provided on the bottom surface of the ceramic plate with built-in electrodes and is configured to remove the heat generated in the wafer by plasma etching.

[0003] In recent years, plasma etching equipment has been increasingly powered for deep etching. Within the plasma etching equipment, the wafer is placed on an electrode-embedded ceramic plate of an electrostatic chuck assembly to cool and maintain its shape. In such electrostatic chuck applications, gas is introduced between the wafer and the ceramic plate to improve the efficiency of heat conduction between the ceramic plate and the wafer and to suppress particle generation by reducing the contact area. Gas holes are provided in the ceramic plate to supply this gas. Figure 9 shows an example of such a conventional electrostatic chuck assembly. The conventional electrostatic chuck assembly 110 shown in Figure 9 comprises a ceramic plate 112, a cooling plate 114 attached to the ceramic plate 112 via a bonding layer 113, gas introduction holes 115 penetrating the ceramic plate 112 and the cooling plate 114, and insulating tubes 117 covering the bonding layer 113 and the surfaces of the cooling plate 114 facing the gas introduction holes 115. In this configuration, when high frequency (RF) is applied to the wafer W placed on the ceramic plate 112, plasma P is unintentionally generated in the gas introduction hole 115 due to abnormal discharge, even though the process gas above the wafer W should be plasmaized. This is due to the effects of recent high-frequency advancements.

[0004] To address these problems, a method has been proposed to prevent abnormal discharge by placing a plug in a through-hole corresponding to the gas introduction hole 115. For example, Patent Document 1 (Japanese Patent Application Publication No. 2024-88883) discloses a plug comprising a plug body made of dense ceramic and a spiral gas flow path provided inside the plug body, extending from the lower surface to the upper surface of the plug body. This plug body is made of dense ceramic and can therefore be called a dense plug. On the other hand, porous plugs are also known. Patent Document 2 (Japanese Patent No. 7514815) discloses a component for semiconductor manufacturing equipment comprising a ceramic plate, a conductive substrate provided on the lower surface of the ceramic plate, a first hole penetrating the ceramic plate in the vertical direction, a second hole penetrating the conductive substrate in the vertical direction and communicating with the first hole, and a porous plug whose upper surface is exposed to the upper opening of the first hole and whose lower surface is located below the upper surface of the conductive substrate.

[0005] Japanese Patent Publication No. 2024-88883, Japanese Patent Publication No. 7514815

[0006] Yoshikazu Araki, "Measurement of Secondary Electron Emission Coefficient Using AES Analyzer," Journal of Surface Analysis Vol.11 No.2 (2004) pp.71-76.

[0007] The dense material plugs are placed into the through-holes of the ceramic plate by press-fitting. Figure 10 shows an example of a structure in which dense material plugs are fixed by press-fitting. The electrostatic chuck assembly 110' shown in Figure 10 comprises a ceramic plate 112, a cooling plate 114 attached to the ceramic plate 112 via a bonding layer 113, a plug placement hole 116 that penetrates the ceramic plate 112 and the bonding layer 113, a gas passage plug 118 such as a dense material plug that is press-fitted into the plug placement hole 116, and a gas introduction passage 120 provided in the cooling plate 114 and communicating with the plug placement hole 116. With this configuration, plasma generation in the hole is suppressed compared to the configuration shown in Figure 9, which does not have a plug. However, since there is space through which gas can pass in the gas passage plug 118, and there is a large potential difference between the wafer W and the cooling plate 114, spatial discharge may occur.

[0008] The present inventors have now found that by constructing at least a portion of the gas-contacting surface within the gas passage plug with a low SEEC material having a secondary electron emission coefficient (SEEC) of 5.0 or less, it is possible to provide an electrostatic chuck assembly that is less prone to spatial discharge within the gas passage plug.

[0009] Therefore, an object of the present invention is to provide an electrostatic chuck assembly in which space discharge is less likely to occur within the gas passage plug.

[0010] The present disclosure provides the following embodiments: [Embodiment 1] An electrostatic chuck assembly comprising: a ceramic plate having an upper surface on which a wafer is placed and a lower surface opposite to the upper surface, and incorporating internal electrodes which are ESC electrodes and / or RF electrodes; a cooling plate attached to the lower surface of the ceramic plate; a plug placement hole penetrating the ceramic plate from the lower surface to the upper surface; a gas passage plug provided to close the plug placement hole and configured to allow gas to pass through its interior; and a gas introduction passage provided in the cooling plate and communicating with the plug placement hole, wherein at least a portion of the surface within the gas passage plug that can contact the gas is made of a low SEEC material having a secondary electron emission coefficient (SEEC) of 5.0 or less. [Embodiment 2] The electrostatic chuck assembly according to Embodiment 1, wherein the secondary electron emission coefficient (SEEC) is 2.0 or less. [Embodiment 3] The low SEEC material is TiN, Al, brass, SiO ２ and Cr ２ O ３[Aspect 4] An electrostatic chuck assembly according to aspect 1 or 2, comprising at least one selected from the group consisting of [Aspect 4] An electrostatic chuck assembly according to any one of aspects 1 to 3, wherein the gas passage plug is composed of a dense body having an internal gas flow path. [Aspect 5] An electrostatic chuck assembly according to aspect 4, wherein the entire dense body is composed of the low SEEC material. [Aspect 6] An electrostatic chuck assembly according to aspect 4, wherein at least a portion of the inner wall of the internal gas flow path is composed of the low SEEC material. [Aspect 7] An electrostatic chuck assembly according to aspect 6, wherein the surface of the inner wall of the internal gas flow path that extends in a direction crossing the electric field generated during use is composed of the low SEEC material. [Aspect 8] An electrostatic chuck assembly according to aspect 6 or 7, wherein at least a portion of the inner wall of the internal gas flow path located near the upper surface of the gas passage plug is composed of the low SEEC material. [Aspect 9] An electrostatic chuck assembly according to any one of aspects 6 to 8, wherein at least a portion of the inner wall of the internal gas flow path includes a coating film and / or a surface modification film of the low SEEC material. [Aspect 10] The electrostatic chuck assembly according to any one of aspects 1 to 3, wherein the gas passage plug is made of a porous body. [Aspect 11] The electrostatic chuck assembly according to aspect 10, wherein the entire porous body is made of the low SEEC material. [Aspect 12] The electrostatic chuck assembly according to aspect 10, wherein at least a portion of the inner surface of the porous body is made of the low SEEC material. [Aspect 13] The electrostatic chuck assembly according to aspect 12, wherein at least a portion of the inner surface of the porous body located near the upper surface of the gas passage plug is made of the low SEEC material. [Aspect 14] The electrostatic chuck assembly according to aspect 12 or 13, wherein at least a portion of the inner surface of the porous body includes a coating film and / or a surface modification film of the low SEEC material. [Aspect 15] The electrostatic chuck assembly according to any one of aspects 1 to 14, further comprising a conductive gas passage portion in the gas introduction passage that contacts the lower surface of the gas passage plug and is electrically conductive with the cooling plate, allowing gas to pass between the gas passage plug and the gas introduction passage.[Aspect 16] The electrostatic chuck assembly according to aspect 15, wherein the conductive gas passage portion includes a leaf spring that biases the gas passage plug upward.

[0011] This is a schematic top view showing an example of an electrostatic chuck assembly according to the present invention. This is a cross-sectional view taken along line A-A of the electrostatic chuck assembly shown in Figure 1. This is a schematic cross-sectional view showing an example of a gas passage plug to which a low SEEC material is applied. This is a schematic cross-sectional view showing another example of a gas passage plug to which a low SEEC material is applied. This is a schematic cross-sectional view showing another example of a gas passage plug to which a low SEEC material is applied. This is a schematic perspective view showing a measurement system for plasma generation voltage related to coatings of materials having various SEECs. This is a measurement result showing the relationship between plasma generation voltage and He pressure related to coatings of materials having various SEECs. This is a schematic cross-sectional view showing an example of a conventional electrostatic chuck assembly. This is a schematic cross-sectional view showing an example of an electrostatic chuck assembly not according to the present invention.

[0012] Figures 1 and 2 show an example of an electrostatic chuck assembly. The electrostatic chuck assembly 10 shown in Figures 1 and 2 comprises a ceramic plate 12, a cooling plate 14, a plug placement hole 16, a gas passage plug 18, and a gas introduction passage 20. The ceramic plate 12 has an upper surface 12a on which the wafer W is placed, and a lower surface 12b facing the upper surface 12a. The ceramic plate 12 also incorporates internal electrodes 22, which are ESC electrodes and / or RF electrodes. The cooling plate 14 is attached to the lower surface 12b of the ceramic plate 12. The plug placement hole 16 is provided through the ceramic plate 12 from the lower surface 12b to the upper surface 12a. The gas passage plug 18 is configured to allow gas to pass through its interior and is provided to block the plug placement hole 16. The gas introduction passage 20 is provided inside the cooling plate 14 and communicates with the plug placement hole 16. Furthermore, at least a portion of the gas-contacting surface within the gas passage plug 18 is made of a low-SEEC material LS having a secondary electron emission coefficient (SEEC) of 5.0 or less. By making at least a portion of the gas-contacting surface within the gas passage plug 18 out of a low-SEEC material LS in this way, it is possible to provide an electrostatic chuck assembly 10 in which space discharge is less likely to occur within the gas passage plug 18.

[0013] As mentioned above, the dense material plugs are placed into the through-holes of the ceramic plate by press-fitting. With the electrostatic chuck assembly 110' shown in Figure 10, plasma generation in the hole is suppressed compared to the configuration shown in Figure 9 without plugs. However, there is still space within the gas passage plug 118 through which gas can pass, and because there is a large potential difference between the wafer W and the cooling plate 114, spatial discharge D can occur. To address this problem, the inventors focused on the secondary electron emission coefficient (SEEC). SEEC is an index defined as the ratio of the number of secondary electrons emitted from the sample to the number of electrons incident on the sample (primary electrons). Experimentally, it was found that the spatial discharge described above is influenced by SEEC, and that the discharge voltage decreases as the SEEC increases. Based on this finding, in the present invention, by composing at least a portion of the surface within the gas passage plug 18 that can come into contact with the gas with a low SEEC material LS having an SEEC of 5.0 or less, it is possible to suppress the generation of spatial discharge within the gas passage plug 18.

[0014] The electrostatic chuck assembly 10 is used as a platform on which a wafer W is placed for performing CVD, etching, or other processes using plasma, and is typically fixed to a vacuum chamber for semiconductor device manufacturing.

[0015] The ceramic plate 12 can have a configuration commonly used as an electrostatic chuck. Therefore, the ceramic plate 12 incorporates internal electrodes 22 which are ESC electrodes (electrostatic electrodes) and / or RF electrodes. A typical electrode-embedded ceramic plate 12 includes a disc-shaped ceramic substrate 12c and internal electrodes 22 embedded in the ceramic substrate 12c at a predetermined depth, parallel to the upper surface 12a or lower surface 12b. Examples of ceramic materials constituting the ceramic substrate 12c include aluminum nitride, silicon carbide, silicon nitride, and aluminum oxide. For example, the ceramic plate 12 may be a disc (e.g., 300 mm in diameter and 5 mm thick) made of a ceramic sintered body such as an aluminum oxide sintered body or an aluminum nitride sintered body.

[0016] An annular sealing band 12d may be formed on the upper surface 12a of the ceramic plate 12 along its outer edge. In addition, a plurality of circular protrusions 12e may be formed spaced apart from each other across the entire surface of the region inside the sealing band 12d. In this case, it is preferable that the sealing band 12d and the circular protrusions 12e are of the same height, which can be, for example, several micrometers to several tens of micrometers.

[0017] The internal electrode 22 can be a planar mesh electrode commonly used as an ESC electrode or RF electrode, and can be connected to an external DC power supply via a power supply member (not shown). A low-pass filter may be placed in the middle of the power supply member. It is desirable that the power supply member be electrically insulated from the cooling plate 14 and, if present, the conductive bonding layer 13. When a DC voltage is applied to the internal electrode 22, the wafer W is attracted and fixed to the upper surface 12a (specifically, the upper surface of the seal band 12d and the upper surface of the circular protrusion 12e) by electrostatic attraction force, and when the application of the DC voltage is removed, the attraction and fixation of the wafer W to 12a is released. The portion of the upper surface 12a that does not have the seal band 12d or the circular protrusion 12e is referred to as the reference surface 12f.

[0018] The ceramic plate 12 may further incorporate heater electrodes. In this case, the heater electrodes may be made of conductive coils or printed patterns and may be formed so as to connect from one end to the other in a single continuous line across the entire ceramic plate 12 when viewed from above. One end and the other end of the heater electrodes may be connected to a pair of power supply rods (not shown) that penetrate the cooling plate 14 and the bonding layer 13 and are inserted into the ceramic substrate 12c. The heater electrodes may be configured to have a voltage applied through these power supply rods.

[0019] The cooling plate 14 is attached to the lower surface 12b of the ceramic plate 12. The cooling plate 14 may be a disc with good thermal conductivity (a disc with the same diameter as or larger than the ceramic plate 12). A refrigerant channel 24 through which the refrigerant circulates may be formed inside the cooling plate 14. The refrigerant flowing through the refrigerant channel 24 is preferably a liquid, and more preferably an electrically insulating liquid. An example of an electrically insulating liquid is a fluorinated inert liquid. In a plan view, the refrigerant channel 24 is formed in a single continuous line from one end (inlet) to the other end (outlet) across the entire cooling plate 14. A supply port and a recovery port of an external refrigerant device (not shown) are connected to one end and the other end of the refrigerant channel 24, respectively. The refrigerant supplied from the supply port of the external refrigerant device to one end of the refrigerant channel 24 passes through the refrigerant channel 24, returns to the recovery port of the external refrigerant device from the other end of the refrigerant channel 24, is temperature-adjusted, and then supplied again from the supply port to one end of the refrigerant channel 24.

[0020] The cooling plate 14 may be made of a metallic material or a composite material of a metal and a ceramic. Examples of metallic materials include Al, Ti, Mo, and alloys thereof. Examples of composite materials of a metal and a ceramic include metal matrix composites (MMCs) and ceramic matrix composites (CMCs). Preferred examples of such composite materials include materials containing Si, SiC, and Ti (also called SiSiCTi), materials in which Al and / or Si are impregnated into a porous SiC body, and Al ２ O ３ Examples include composite materials of TiC. It is preferable to select a material for the cooling plate 14 that has a similar coefficient of thermal expansion to the material for the ceramic plate 12 (particularly the ceramic substrate 12c). Such a cooling plate 14 can be a conductive plate. Therefore, the cooling plate 14 can also be used as an RF electrode. In this case, an upper electrode (not shown) is positioned above the ceramic plate 12 (particularly the upper surface 12a), and plasma can be generated by applying high-frequency power between the upper electrode, which is arranged parallel to the cooling plate 14, and the cooling plate 14.

[0021] The cooling plate 14 is preferably bonded to the lower surface 12b of the ceramic plate 12 via a bonding layer 13. The bonding layer 13 may be a conductive bonding layer. The bonding layer 13 may be a bonding sheet or a metal layer such as an aluminum alloy layer. In particular, when the cooling plate 14 is made of a metal matrix composite material (MMC) such as SiSiCTi, it is preferable to bond the cooling plate 14 to the lower surface 12b of the ceramic plate 12 by TCB (Thermal Compression Bonding). TCB is a known method in which a metal bonding material is sandwiched between two members to be bonded, and the two members are pressurized and bonded together while heated to a temperature below the solidus temperature of the metal bonding material. An example of a metal bonding material is an aluminum alloy.

[0022] The plug placement holes 16 are holes that penetrate the ceramic plate 12 from the lower surface 12b to the upper surface 12a. The plug placement holes 16 function as gas passages from the lower surface 12b to the upper surface 12a (particularly the reference surface 12f) of the ceramic plate 12. Only one plug placement hole 16 may be provided, but it is preferable to provide multiple plug placement holes 16 as shown in Figure 1. The number of plug placement holes 16 shown in Figure 1 is 36, but is not limited to this. A gas passage plug 18 is embedded in each of the plug placement holes 16.

[0023] The horizontal opening diameter of the plug placement hole 16 (meaning the equivalent diameter if the cross-section of the plug placement hole is not circular) is not particularly limited, but is typically in the range of 1 to 5 mm at any height position, and more typically in the range of 3 to 4 mm. The diameter of the plug placement hole 16 may be constant or vary from the lower surface 12b to the upper surface 12a (especially the reference surface 12f) of the ceramic plate 12. As shown in Figure 2, the plug placement hole 16 is tapered from top to bottom, and it is preferable that the area of ​​the upper opening is larger than the area of ​​the lower opening. Having such a tapered inner surface in the plug placement hole 16 makes it easier for the gas passage plug 18 to stop at a predetermined height position in the plug placement hole 16 when it is pressed into place. Therefore, the gas passage plug 18 can be embedded in the plug placement hole 16 with high positioning accuracy. Furthermore, since the gas passage plug 18 is difficult to remove downwards and relatively easy to remove upwards, there is the advantage that the gas passage plug 18 can be easily replaced. In addition, since the creepage distance is increased, an effect of suppressing discharge can also be expected. For this reason, it is preferable that the plug placement hole 16 has a frustoconical or truncated pyramidal space.

[0024] The gas passage plug 18 is provided to block the plug placement hole 16 and is configured to allow gas to pass through its interior. The gas passage plug 18 may be a dense plug made of a dense body having an internal gas passage 26, or a porous plug made of a porous body. In any case, it is preferable that the gas passage plug 18 has a shape that fits the plug placement hole 16 so that it can be embedded in the plug placement hole 16. It is preferable, but not limited to, that the gas passage plug 18 be fixed in the plug placement hole 16 by press-fitting. For example, the gas passage plug 18 may be fixed in the plug placement hole 16 by direct firing of the ceramic constituting the gas passage plug 18, or by applying adhesive to the side surface of the gas passage plug 18. It is preferable that the upper surface of the gas passage plug 18 is at the same height as the reference surface 12f of the ceramic plate 12. The lower surface of the gas passage plug 18 may be covered with a conductive coating layer 34 which may be part of the conductive gas passage section 30 described later. The coating layer 34 may be a conductive porous layer. The lower surface of the gas passage plug 18 may be located above the lower surface 12b of the ceramic plate 12, at the same height as the lower surface 12b, or below the lower surface 12b.

[0025] The gas passage plug 18 shown in Figures 1 and 2 is a dense plug composed of a dense body having an internal gas passage 26. In this specification, "dense body" refers to the portion of the gas passage plug 18 that has a porosity of 5% or less as measured in accordance with JIS R 1634:1998.

[0026] The internal gas passage 26 is a passage that allows gas to flow between the upper and lower surfaces of the gas passage plug 18, which is a dense plug. The internal gas passage 26 is preferably a passage that penetrates the inside of the dense plug, bending from the lower surface to the upper surface, and can be, for example, a zigzag passage as shown in Figure 2 or a spiral passage as shown in Figures 3 to 5. The internal gas passage 26 may also be a straight through-hole along the vertical direction. The diameter of the cross-section of the internal gas passage 26 is preferably 0.1 to 1 mm. One dense plug may have multiple internal gas passages 26. The porosity of the dense portion of the dense plug, as measured in accordance with JIS R 1634:1998, is preferably less than 1%, and more preferably less than 0.1%. The gas passage plug 18, as a dense plug, is preferably fixed by press-fitting into the plug placement hole 16. As the dense plug, ceramics such as alumina or aluminum nitride can be used. The dense plug may be manufactured, for example, by firing a molded body formed using a 3D printer, or by firing a molded body formed using mold casting.

[0027] Alternatively, the gas passage plug 18 may be a porous plug made of a porous material. In this case, as shown in Figure 6, if it is a porous plug, it is not necessary to form the gas internal passage 26 as described above, and the open pore structure of the porous material itself allows gas to flow between the upper and lower surfaces of the gas passage plug 18. A typical example of a porous plug is a porous bulk body obtained by sintering ceramic powder. Examples of ceramics that make up the porous plug include alumina and aluminum nitride. The porosity of the porous plug, as measured in accordance with the mercury intrusion method of JIS R 1655:2003, is preferably 30% or more, and the average pore diameter is preferably 20 μm or more. The porosity of the porous plug may be 70% or less. In addition, a coating layer 34 as a metal porous layer may be formed on the lower surface of the porous plug by using porous plating.

[0028] At least a portion of the gas-contacting surfaces within the gas passage plug 18 is made of a low SEEC material LS having a secondary electron emission coefficient (SEEC) of 5.0 or less. Typically, the gas-contacting surfaces within the gas passage plug 18 are the surfaces of the internal gas flow channels 26 in the case of a dense plug, and the surfaces of the open pore structure in the case of a porous plug. The SEEC of the low SEEC material LS is 5.0 or less, preferably 2.0 or less, and more preferably 1.0 or less. In particular, if the SEEC is less than 1.0, the ceramic plate 12 and the gas passage plug 18 will be in a direction that absorbs secondary electrons, so theoretically, no discharge will occur. Even if this is not the case, by applying a low SEEC material with an SEEC of 5.0 or less, preferably 2.0 or less, to the gas-contacting surfaces within the gas passage plug 18 where space discharge can occur, electron avalanches caused by high SEEC are less likely to occur, the discharge voltage increases, and as a result, the occurrence of space discharge within the gas passage plug 18 can be suppressed. Examples of low SEEC materials include TiN (SEEC: 1.3), aluminum (SEEC: 1.0), brass (SEEC: 1.5), and SiO ２ (SEEC; 2.0), and Cr ２ O ３ Examples include (SEC: 1.2), which may be used individually or in combination.

[0029] As mentioned above, the secondary electron emission coefficient (SEEC) is defined as the ratio of the number of secondary electrons emitted from the sample to the number of electrons incident on the sample (primary electrons). SEEC can be measured according to a known procedure, for example, Non-Patent Document 1 (Yoshikazu Araki, "Measurement of Secondary Electron Emission Coefficient Using an AES Analyzer," Journal of Surface Analysis Vol.11 No.2 (2004) pp.71-76). In this case, it is preferable to set the primary electron energy to 3000 eV and perform the measurement within the range of 120 V or less for the bias voltage.

[0030] When the gas passage plug 18 is a dense plug composed of a dense body having an internal gas flow path 26, the entire dense body may be composed of a low-SEEC material LS, as shown in Figures 2 and 3, or at least a portion of the inner wall of the internal gas flow path 26 may be composed of a low-SEEC material LS, as shown in Figures 4 and 5. In the latter case, as shown in Figures 4 and 5, it is preferable to make the surface of the inner wall of the internal gas flow path 26 that extends in a direction that crosses the electric field generated during use (for example, a substantially horizontal direction) out of a low-SEEC material, as this has a high effect in suppressing spatial discharge. In this case, it can be said that the surface of the inner wall that extends in a direction along the electric field generated during use (for example, a substantially vertical direction) does not need to be composed of a low-SEEC material. That is, when the internal gas flow path 26 is viewed in a cross section perpendicular to the flow direction, it is not necessary to make the entire inner wall surface out of a low-SEEC material LS. However, the entire inner wall surface of the internal gas flow path 26 may be composed of a low-SEEC material LS. Furthermore, in the embodiment shown in Figure 4, the low-SEEC material LS is applied to the inner wall of the gas internal passage 26 over the entire thickness from the lower surface to the upper surface of the gas passage plug 18, but the embodiment is not limited to this. In particular, as shown in Figure 5, it is preferable that at least the inner wall portion of the gas internal passage 26 located near the upper surface of the gas passage plug 18 is made of the low-SEEC material. By applying the low-SEEC material near the upper surface of the gas passage plug 18 in this way, spatial discharge can be suppressed particularly effectively. In this case, as shown in Figure 5, it is more preferable that not only the inner wall portion of the gas internal passage 26 located near the upper surface of the gas passage plug 18 but also the inner wall portion of the gas internal passage 26 located near the lower surface of the gas passage plug 18 is made of the low-SEEC material. Note that the vicinity of the upper surface of the gas passage plug 18 means the range within 1.0 mm from the upper surface of the gas passage plug 18. Similarly, the vicinity of the lower surface of the gas passage plug 18 means the range within 1.0 mm from the lower surface of the gas passage plug 18.

[0031] The method for constructing the inner wall of the internal gas channel 26 with a low-SEEC material LS is not particularly limited. For example, the inner wall of the internal gas channel 26 may be coated with a low-SEEC material, or the inner wall of the internal gas channel 26 may be surface modified to generate a low-SEEC material. Therefore, it is preferable that at least a portion of the inner wall of the internal gas channel 26 includes a coating film and / or a surface-modified film of a low-SEEC material. Examples of surface modification methods to lower SEEC include sputtering and plasma CVD.

[0032] If the gas passage plug 18 is a porous plug composed of a porous body, the entire porous body may be composed of a low-SEEC material LS, as shown in Figure 6, or at least a part of the inner surface of the porous body (i.e., the surface of the open pore structure) may be composed of a low-SEEC material. In the latter case, at least the inner surface portion of the porous body located near the upper surface of the gas passage plug 18 is composed of a low-SEEC material. By applying a low-SEEC material near the upper surface of the gas passage plug 18 in this way, spatial discharge can be suppressed particularly effectively. In this case, it is more preferable that not only the inner surface portion of the porous body located near the upper surface of the gas passage plug 18 but also the inner surface portion of the porous body located near the lower surface of the gas passage plug 18 is composed of a low-SEEC material. Note that "near the upper surface of the gas passage plug 18" means the area within 1.0 mm from the upper surface of the gas passage plug 18. Similarly, "near the lower surface of the gas passage plug 18" means the area within 1.0 mm from the lower surface of the gas passage plug 18.

[0033] The method for constructing the inner surface of a porous body (i.e., the surface of the open pore structure) with a low SEEC material LS is not particularly limited. For example, the inner surface of the porous body may be coated with a low SEEC material, or the inner surface of the porous body may be modified to produce a low SEEC material. Therefore, it is preferable that at least a portion of the inner surface of the porous body includes a coating film and / or a surface modification film of a low SEEC material. Examples of surface modification methods to lower SEEC include sputtering and plasma CVD.

[0034] The gas introduction passage 20 is a passage for introducing gas, provided within the cooling plate 14 and communicating with the plug placement hole 16. The gas introduction passage 20 is not particularly limited in its configuration as long as it is a passage that can introduce gas into the plug placement hole 16 by passing through the inside of the cooling plate 14. For example, as shown in Figure 2, it may include a vertical hole extending vertically within the cooling plate 14 and a horizontal hole communicating with this vertical hole and extending horizontally within the cooling plate 14. In a configuration that includes a bonding layer 13, the gas introduction passage 20 may include a bonding layer through hole 13a provided in the bonding layer 13 as part of the gas passage, in addition to the gas passage provided inside the cooling plate 14. Similarly, in a configuration that includes a coating layer 34, a coating layer through hole 34a provided in the coating layer 34 may also form part of the gas passage. In this way, the gas introduction passage 20 is configured to introduce gas into the plug placement hole 16 by passing through the cooling plate 14, the coating layer 34 (if present), and the bonding layer 13 (if present).

[0035] At least one side of the gas passage plug 18 and the plug placement hole 16 may also be made of a low-SEEC material LS having an SEEC of 5.0 or less, preferably 2.0 or less, and more preferably 1.0 or less, as described above. This can also suppress creepage discharge at the interface between the gas passage plug 18 and the ceramic plate 12. The method of making the side of the gas passage plug 18 and / or the side of the plug placement hole 16 out of low-SEEC material LS is not particularly limited. For example, the side of the gas passage plug 18 and / or the side of the plug placement hole 16 may be coated with a low-SEEC material, or the side of the gas passage plug 18 and / or the side of the plug placement hole 16 may be surface modified to produce a low-SEEC material. Therefore, it is preferable that at least one side of the gas passage plug 18 and the plug placement hole 16 includes a coating film and / or a surface modification film of low-SEEC material, as described above.

[0036] The electrostatic chuck assembly 10 may further include a conductive gas passage section 30. The conductive gas passage section 30 is provided within the gas introduction passage 20, in contact with the lower surface of the gas passage plug 18 and electrically connected to the cooling plate 14, and is configured to allow the passage of gas between the gas passage plug 18 and the gas introduction passage 20. This makes it less likely for a potential difference to occur around the end of the gas passage plug 18 on the cooling plate 14 side compared to when an insulating porous member is present on the lower surface side of the gas passage plug 18. In other words, current can be discharged to the conductive cooling plate 14 via the conductive gas passage section 30, thereby suppressing discharge around the end of the gas passage plug 18 on the cooling plate 14 side. The conductive gas passage section 30 preferably includes a leaf spring 32 that biases the gas passage plug 18 upward, and more preferably includes a conductive coating layer 34 that covers the lower surface of the gas passage plug 18 as described above. The leaf spring 32 elastically biases the gas passage plug 18 upward, making it easier to ensure electrical conductivity from the contact point between the conductive gas passage section 30 and the gas passage plug 18 to the cooling plate 14.

[0037] The leaf spring 32 is a conductive elastic member that biases the gas passage plug 18 upward with elastic force and presses it upward. The leaf spring 32 is preferably made of a metal material, and examples of metal materials include Al, Ti, Mo or their alloys, iron and steel, stainless steel (e.g., SUS316L), Hastelloy®, etc. The leaf spring 32 may be manufactured, for example, by bending a metal plate. The leaf spring 32 in the illustrated example has a shape in which a metal plate is bent in a zigzag shape, but it is not limited to this, and can have various shapes as long as the desired function is ensured.

[0038] The coating layer 34 covers the lower surface of the gas passage plug 18 and thus is in contact with the lower surface of the gas passage plug 18. When the gas passage plug 18 is a dense plug, the coating layer 34 is preferably formed as a dense layer, and in that case, it preferably has a coating layer through-hole 34a that allows gas to pass through in the vertical direction. The coating layer through-hole 34a connects the opening of the gas internal flow path 26 on the lower surface of the gas passage plug 18 and the gas introduction passage 20. The coating layer 34 can be manufactured, for example, by previously forming the coating layer 34 on the lower surface of the gas passage plug 18 by sputtering, electroless plating, or the like before press-fitting the gas passage plug 18 into the ceramic plate 12 and then opening the hole 32a. The coating layer 34 is preferably made of a metal material. Examples of the metal material include metals with excellent corrosion resistance such as Au, Ag, Al, Ti, stainless steel (e.g., SUS316L), Hastelloy (registered trademark) (Ni-Fe-Mo-based alloy), etc. When the gas passage plug 18 is a porous plug, the coating layer 34 may be a conductive porous layer. In this case, the coating layer 34 as a metal porous layer can be formed on the lower surface of the gas passage plug 18 by using porous plating.

[0039] The present invention will be described more specifically by the following examples. However, the present invention is not limited to the following examples.

[0040] Example 1 For a coating of alumina, which is a low-SEEC material with SEEC = 1.0 (literature value), the relationship between the plasma generation voltage and the He pressure was investigated as follows.

[0041] (1) Construction of the measurement system A measurement system 40 as shown in Fig. 7 was prepared as follows. This measurement system 40 includes an upper electrode 42, a lower electrode 44, and an insulating member 46 interposed between the upper electrode 42 and the lower electrode 44. The upper electrode 92 and the lower electrode 94 were fabricated by bonding an alumina plate with a thickness of 4 mm to the surface of a brass electrode. The insulating member 46 is a transparent acrylic resin disc-shaped member with a diameter of 4 mm and a thickness of 5 mm, and a through-hole 46a with a diameter of 2 mm is formed at the center. In this way, a cylindrical closed space for evaluating the space discharge was formed by sandwiching and closing the cylindrical space formed at the center of the insulating member 46 with the upper electrode 42 and the lower electrode 44 from above and below. At this time, the upper electrode 42 and the lower electrode 44 were arranged such that the alumina coating faced the cylindrical space.

[0042] (2) Measurement procedure The measurement system was placed in a vacuum chamber, a predetermined He pressure was introduced, and various voltages were applied to the upper electrode 42. The voltage at which light emission could be confirmed in the through-hole 46a was recorded as the plasma generation voltage. Then, the He pressure was increased and the same test was performed to obtain a plasma generation voltage curve.

[0043] (3) Measurement results The measurement results were as shown in Fig. 8.

[0044] Example 2 The measurement of the plasma generation voltage was performed in the same manner as in Example 1, except that brass, a low-SEEC material with a SEEC of 1.5 (literature value), was used instead of aluminum. The results were as shown in Fig. 8.

[0045] Example 3 (comparison) The measurement of the plasma generation voltage was performed in the same manner as in Example 1, except that alumina, a high-SEEC material with a SEEC of 10 (literature value), was used instead of aluminum. The results were as shown in Fig. 8.

[0046] The results from Examples 1-3 shown in Figure 8 indicate that the lower the SEEC of a material, the higher the plasma generation voltage in the low He pressure range (especially below 2 Torr). Specifically, aluminum with an SEEC of 1.0 had the highest plasma generation voltage, followed by brass with an SEEC of 1.5, and alumina with an SEEC of 10 had the lowest. This suggests that using low-SEEC materials such as aluminum and brass can significantly suppress the occurrence of spatial discharges compared to high-SEEC materials such as alumina.

[0047] 10, 110: Electrostatic chuck assembly, 12, 112: Ceramic plate, 12a: Top surface, 12b: Bottom surface, 12c: Ceramic substrate, 12d: Seal band, 12e: Small circular protrusion, 12f: Reference surface, 13, 113: Bonding layer, 13a: Through hole in bonding layer, 14, 114: Cooling plate, 16, 116: Plug placement hole, 18, 118: Gas passage plug, 20, 120: Gas introduction passage, 22: Internal electrode, 24: Refrigerant flow path, 26: Internal gas flow path, 30: Conductive gas passage section, 32: Leaf spring, 34: Coating layer, 34a: Through hole in coating layer, 40: Measurement system, 42: Upper electrode, 44: Lower electrode, 46: Insulating member, 46a: Through hole, 115: Gas introduction hole, 117: Insulating tube, W: Wafer, P: Plasma, D: Spatial discharge, LS: Low SEEC material

Claims

1. An electrostatic chuck assembly comprising: a ceramic plate having an upper surface on which a wafer is placed and a lower surface opposite to the upper surface, and incorporating internal electrodes which are ESC electrodes and / or RF electrodes; a cooling plate attached to the lower surface of the ceramic plate; a plug placement hole penetrating the ceramic plate from the lower surface to the upper surface; a gas passage plug provided to close the plug placement hole and configured to allow gas to pass through its interior; and a gas introduction passage provided in the cooling plate and communicating with the plug placement hole, wherein at least a portion of the surface within the gas passage plug that is in contact with the gas is made of a low SEEC material having a secondary electron emission coefficient (SEEC) of 5.0 or less.

2. The electrostatic chuck assembly according to claim 1, wherein the secondary electron emission coefficient (SEEC) is 2.0 or less.

3. The low SEEC material is TiN, Al, brass, SiO ２ and Cr ２ O ３ The electrostatic chuck assembly according to claim 1 or 2, comprising at least one selected from the group consisting of the following.

4. The electrostatic chuck assembly according to claim 1 or 2, wherein the gas passage plug is made of a dense body having an internal gas flow path.

5. The electrostatic chuck assembly according to claim 4, wherein the entire dense body is made of the low SEEC material.

6. The electrostatic chuck assembly according to claim 4, wherein at least a portion of the inner wall of the gas internal flow path is made of the low SEEC material.

7. The electrostatic chuck assembly according to claim 6, wherein the surface of the inner wall of the gas internal flow path that extends in a direction crossing the electric field generated during use is made of the low SEEC material.

8. The electrostatic chuck assembly according to claim 6, wherein at least the inner wall portion of the gas internal passage located near the upper surface of the gas passage plug is made of the low SEEC material.

9. The electrostatic chuck assembly according to claim 6, wherein at least a portion of the inner wall of the gas internal flow path includes a coating film and / or a surface modification film of the low SEEC material.

10. The electrostatic chuck assembly according to claim 1 or 2, wherein the gas passage plug is made of a porous material.

11. The electrostatic chuck assembly according to claim 10, wherein the entire porous body is made of the low SEEC material.

12. The electrostatic chuck assembly according to claim 10, wherein at least a portion of the inner surface of the porous body is made of the low SEEC material.

13. The electrostatic chuck assembly according to claim 12, wherein at least the inner surface portion of the porous body located near the upper surface of the gas passage plug is made of the low SEEC material.

14. The electrostatic chuck assembly according to claim 12, wherein at least a portion of the inner surface of the porous body includes a coating film and / or a surface modification film of the low SEEC material.

15. The electrostatic chuck assembly according to claim 1 or 2, further comprising a conductive gas passage portion within the gas introduction passage that contacts the lower surface of the gas passage plug and is electrically conductive with the cooling plate, allowing gas to pass between the gas passage plug and the gas introduction passage.

16. The electrostatic chuck assembly according to claim 15, wherein the conductive gas passage portion comprises a leaf spring that biases the gas passage plug upward.

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