Electrostatic chuck assembly

Abstract

Provided is an electrostatic chuck assembly in which creepage discharge is unlikely to occur at the interface between a gas passage plug and a ceramic plate while being provided with the gas passage plug. This electrostatic chuck assembly comprises: a ceramic plate having an upper surface on which a wafer is to be placed and a lower surface facing the upper surface, the ceramic plate also having built therein an internal electrode that is an electrostatic chuck (ESC) electrode and / or a radio frequency (RF) electrode; a cooling plate attached to the lower surface of the ceramic plate; a plug arrangement hole penetrating the ceramic plate from the lower surface to the upper surface; a gas passage plug configured to be press-fitted into the plug arrangement hole and allow gas to pass therethrough; and a gas introduction pathway provided in the cooling plate and communicating with the plug arrangement hole. At least one of a side surface of the gas passage plug and the plug arrangement hole is composed of 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. An electrostatic chuck assembly that functions as a susceptor for placing a wafer to be etched is provided in the plasma etching apparatus. The electrostatic chuck assembly includes a ceramic plate with a built-in electrode that functions as an electrostatic chuck, and a cooling plate that supports the bottom surface of the ceramic plate with the built-in electrode. The wafer is electrostatically adsorbed to the ceramic plate with the built-in electrode, 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 the built-in electrode and is configured to take away 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 5 shows an example of such a conventional electrostatic chuck assembly. The conventional electrostatic chuck assembly 110 shown in Figure 5 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 6 shows an example of a structure in which dense material plugs are fixed by press-fitting. The electrostatic chuck assembly 110' shown in Figure 6 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, although the generation of plasma in the hole is suppressed compared to the configuration shown in Figure 5 which does not have a plug, there is a large potential difference between the wafer W and the cooling plate 114, so creepage discharge D may occur along the interface between the gas passage plug 118 and the ceramic plate 112.

[0008] The present inventors have now found that by structuring at least one side surface of the gas passage plug and the plug placement hole 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 in which surface discharge is less likely to occur at the interface between the gas passage plug and the ceramic plate.

[0009] Therefore, an object of the present invention is to provide an electrostatic chuck assembly that includes a gas passage plug, while minimizing surface discharge at the interface between the gas passage plug and the ceramic plate.

[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 press-fitted into 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 one side surface of the gas passage plug and the plug placement hole 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 embodiment 1 or 2, comprising at least one selected from the group consisting of [the above]. [Aspect 5] An electrostatic chuck assembly according to any one of embodiments 1 to 3, wherein at least one side surface of the gas passage plug and the plug placement hole comprises a coating film and / or surface modification film of the low SEEC material. [Aspect 6] An electrostatic chuck assembly according to embodiment 5, wherein at least one of the upper and lower surfaces of the gas passage plug is made of the low SEEC material. [Aspect 7] An electrostatic chuck assembly according to any one of embodiments 1 to 6, wherein there is no adhesive between the plug placement hole and the gas passage plug. [Aspect 8] An electrostatic chuck assembly according to any one of embodiments 1 to 6, wherein there is a partial adhesive between the plug placement hole and the gas passage plug, and the portion of at least one side surface of the gas passage plug and the plug placement hole where the adhesive is absent is made of the low SEEC material. [Aspect 9] The electrostatic chuck assembly according to any one of aspects 1 to 8, wherein the gas passage plug is made of a dense body having an internal gas flow path. [Aspect 10] The electrostatic chuck assembly according to any one of aspects 1 to 8, wherein the gas passage plug is made of a porous body. [Aspect 11] The electrostatic chuck assembly according to any one of aspects 1 to 10, 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 12] The electrostatic chuck assembly according to aspect 11, wherein the conductive gas passage portion comprises 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 and ceramic plate (particularly the plug placement hole) to which low SEEC material is applied. This is a schematic cross-sectional view showing an example of a gas passage plug to which low SEEC material is applied. 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 a 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 press-fitted into the plug placement hole 16. The gas introduction passage 20 is provided within the cooling plate 14 and communicates with the plug placement hole 16. Furthermore, at least one side surface of the gas passage plug 18 and the plug placement hole 16 is made of a low SEEC material LS having a secondary electron emission coefficient (SEEC) of 5.0 or less. By making at least one side surface of the gas passage plug 18 and the plug placement hole 16 out of the low SEEC material LS in this way, it is possible to provide an electrostatic chuck assembly 10 in which surface discharge is less likely to occur at the interface between the gas passage plug 18 and the ceramic plate 12.

[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 6, which has such a configuration, plasma generation in the hole is suppressed compared to the configuration shown in Figure 5, which does not have a plug. However, because there is a large potential difference between the wafer W and the cooling plate 114, surface discharge D can occur at the interface between the gas passage plug 118 and the cooling plate 114. In this regard, since the gas passage plug 118, such as a dense material plug, is typically fixed in the plug placement hole 116 by press-fitting, there is a small gap at the interface between the gas passage plug 118 and the cooling plate 114, and it is thought that this small gap allows the generation of surface discharge D. In other words, in the case of fixation by press-fitting, unlike fixation by direct firing of the ceramic constituting the plug or fixation by applying adhesive over the entire side surface of the plug, it is not possible to completely seal the gap at the interface between the gas passage plug 118 and the cooling plate 114. Therefore, the formation of a small gap at the interface between the gas passage plug 118 and the cooling plate 114 and the resulting surface discharge 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 a sample to the number of electrons incident on the sample (primary electrons). The inventors found that the surface discharge described above is influenced by SEEC, and that the larger the SEEC, the longer the electron avalanche continues, causing the discharge voltage to decrease and resulting in surface discharge D occurring as an abnormal discharge in the gas supply section (i.e., the plug placement hole 116 to which the gas passage plug 118 is fixed). Based on this finding, in the present invention, by composing at least one side surface of the gas passage plug 18 and the plug placement hole 16 with a low SEEC material LS having an SEEC of 5.0 or less, it is possible to suppress the occurrence of surface discharge at the interface between the gas passage plug 18 and the ceramic plate 12. For example, in the case of a ceramic plate with a thickness of 2.5 mm, it is possible to realize a configuration in which the withstand voltage under vacuum in the part of the gas supply section that is not filled with adhesive is 3 kV or more.

[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 press-fitted into the plug placement hole 16 and 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 flow path 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 by press-fitting. 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 and 4. 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. A single 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 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, 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] 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).

[0029] At least one side surface of the gas passage plug 18 and the plug placement hole 16 is made of a low SEEC material LS having a secondary electron emission coefficient (SEEC) of 5.0 or less. As shown in Figure 3, both sides of the gas passage plug 18 and the plug placement hole 16 may be made of the low SEEC material LS. 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 side surface of the gas supply section where creepage discharge can occur, electron avalanches caused by high SEEC are less likely to occur, the discharge voltage will be higher, and as a result, the occurrence of creepage discharge in the gas supply section (i.e., the plug placement hole 16 to which the gas passage plug 18 is fixed) 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.

[0030] 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.

[0031] The method for constructing the sides of the gas passage plug 18 and / or the sides of the plug placement hole 16 with a low-SEEC material LS is not particularly limited. For example, the sides of the gas passage plug 18 and / or the sides of the plug placement hole 16 may be coated with a low-SEEC material, or the sides of the gas passage plug 18 and / or the sides 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 a low-SEEC material. Examples of surface modification methods to lower SEEC include sputtering and plasma CVD.

[0032] As shown in Figure 4, at least one of the upper and lower surfaces of the gas passage plug 18 may be made of a low SEEC material LS. This makes it possible to more effectively suppress abnormal discharges, including creepage discharges. In this case, the upper and / or lower surfaces of the gas passage plug 18 may be coated with the low SEEC material, or the upper and / or lower surfaces of the gas passage plug 18 may be surface modified to produce the low SEEC material. That is, it is preferable that at least one of the upper and lower surfaces of the gas passage plug 18 includes a coating film and / or a surface modification film of the low SEEC material.

[0033] Typically, there is no adhesive between the plug placement hole 16 and the gas passage plug 18. That is, since the gas passage plug 18 is fixed into the plug placement hole 16 by press-fitting, there is no need to interpose adhesive between the plug placement hole 16 and the gas passage plug 18. However, adhesive may be partially present between the plug placement hole 16 and the gas passage plug 18 to assist in the fixation of the gas passage plug 18 into the plug placement hole 16 by press-fitting. In this case, it is preferable that the portion without adhesive on at least one side of the gas passage plug 18 and the plug placement hole 16 is made of a low SEEC material. This is because surface discharge is less likely to occur where adhesive is present between the plug placement hole 16 and the gas passage plug 18, so it is sufficient to make the other portions out of a low SEEC material.

[0034] 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.

[0035] 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.

[0036] The coating layer 34 covers the lower surface of the gas passage plug 18 and is in contact with the lower surface of the gas passage plug 18. If 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 is preferable that it has through-holes 34a in the coating layer that allow gas to pass through in the vertical direction. The through-holes 34a in the coating layer connect the opening of the internal gas flow path 26 on the lower surface of the gas passage plug 18 to the gas introduction passage 20. The coating layer 34 can be manufactured, for example, by forming the coating layer 34 in advance on the lower surface of the gas passage plug 18 by sputtering or electroless plating before press-fitting the gas passage plug 18 into the ceramic plate 12, and then creating holes 32a. The coating layer 34 is preferably made of a metallic material, and examples of metallic materials include metals with excellent corrosion resistance such as Au, Ag, Al, Ti, stainless steel (e.g., SUS316L), and Hastelloy (Ni-Fe-Mo alloy, Hastelloy is a registered trademark). If the gas passage plug 18 is a porous plug, the coating layer 34 may be a conductive porous layer. In this case, by using porous plating, the coating layer 34 as a metallic porous layer can be formed on the lower surface of the gas passage plug 18.

[0037] 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: Coolant flow path, 26: Internal gas flow path, 30: Conductive gas passage section, 32: Leaf spring, 34: Coating layer, 34a: Through-hole in coating layer, 115: Gas introduction hole, 117: Insulating tube, W: Wafer, P: Plasma, D: Surface 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 press-fitted into 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 one side surface of the gas passage plug and the plug placement hole 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 at least one side surface of the gas passage plug and the plug placement hole includes a coating film and / or a surface modification film of the low SEEC material.

5. The electrostatic chuck assembly according to claim 1 or 2, wherein at least one of the upper and lower surfaces of the gas passage plug is made of the low SEEC material.

6. The electrostatic chuck assembly according to claim 5, wherein at least one of the upper and lower surfaces of the gas passage plug includes a coating film and / or a surface modification film of the low SEEC material.

7. The electrostatic chuck assembly according to claim 1 or 2, wherein no adhesive is present between the plug placement hole and the gas passage plug.

8. The electrostatic chuck assembly according to claim 1 or 2, wherein adhesive is partially present between the plug placement hole and the gas passage plug, and the portion of at least one side of the gas passage plug and the plug placement hole where the adhesive is absent is made of the low SEEC material.

9. 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.

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 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.

12. The electrostatic chuck assembly according to claim 11, wherein the conductive gas passage portion comprises a leaf spring that biases the gas passage plug upward.

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