Wafer mounting stand

Abstract

A wafer mounting stand 10 comprises: a ceramic plate 20 which includes a wafer mounting surface 21 on the upper surface thereof; a gas passage 52 through which gas can pass in the vertical direction of the ceramic plate 20; a conductive base plate 30 which is joined to the lower surface of the ceramic plate 20 and is utilized as a plasma generation electrode; and a gas supply path 34 which is provided inside of the base plate 30 and communicates with the gas passage 52. The wafer mounting stand 10 also comprises an electric field adjusting conductor 60. The electric field adjusting conductor 60 is provided so as to extend, from the lower surface of the ceramic plate 20 or a position below the lower surface to an area in front of the wafer mounting surface 21 in the vertical direction in the vicinity of the gas passage 52, and is electrically connected to the base plate 30.

Description

Wafer mounting table

[0001] The present invention relates to a wafer stage.

[0002] Conventionally, wafer mounting tables are used in semiconductor manufacturing equipment. For example, the wafer mounting table disclosed in Patent Document 1 includes a ceramic plate having a wafer mounting surface on its upper surface, a gas passage through which gas can pass vertically through the ceramic plate, a conductive base plate bonded to the lower surface of the ceramic plate, and a gas supply passage provided within the base plate. The gas passage is configured with a porous plug disposed in a through-hole formed in the ceramic plate. In this wafer mounting table, a high-frequency voltage is applied between the base plate and an upper electrode provided above the wafer to generate plasma above the wafer, and the wafer is processed using the plasma. During this process, helium gas is introduced from the outside into the gas supply passage. The helium gas is then supplied from the gas supply passage through the gas passage to the underside of the wafer, improving thermal conduction between the wafer and the ceramic plate. Because the helium gas passes through the pores of the porous plug, arc discharge on the underside of the wafer can be suppressed compared to when the porous plug is not present. Without the porous plug, arcing would occur when electrons generated by ionization of helium accelerate and collide with other helium particles. However, with the porous plug, arcing is suppressed because the electrons strike the porous plug before colliding with other helium particles. Arcing on the underside of the wafer is undesirable because it alters the wafer and makes it unusable as a device.

[0003] Japanese Patent Application Laid-Open No. 2019-29384

[0004] However, there has been a demand for the development of a new structure for suppressing discharge in the gas passages of such wafer mounting tables.

[0005] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide a new structure for suppressing discharge in a gas passage.

[0006] [1] The wafer mounting table of the present invention comprises: a ceramic plate having a wafer mounting surface on its upper surface; a gas passage through which gas can pass in the vertical direction of the ceramic plate; a conductive base plate joined to the lower surface of the ceramic plate and used as a plasma generating electrode; a gas supply passage provided inside the base plate and communicating with the gas passage; and an electric field adjustment conductor electrically connected to the base plate, extending in the vertical direction near the gas passage from the lower surface of the ceramic plate or a position below it to just before the wafer mounting surface.

[0007] This wafer mounting table, equipped with an electric field adjustment conductor, can adjust the direction of the electric field (the direction perpendicular to the equipotential lines) during plasma generation to a horizontal direction or a direction close to it. As a result, the direction in which electrons generated by ionization of gas molecules accelerate is horizontal or a direction close to it. Therefore, if the length of the gas passage in the horizontal direction or a direction close to it is short, even if the vertical length inside the gas passage is increased, the distance over which the electrons accelerate does not increase, and even if the accelerated electrons collide with other gas molecules, discharge is less likely to occur. Therefore, compared to when the electric field adjustment conductor is not provided, discharge inside the gas passage can be suppressed even if the vertical length inside the gas passage is increased.

[0008] Although the present invention is sometimes described using terms such as up / down, left / right, front / back, etc., these terms merely refer to relative positional relationships. Therefore, when the orientation of the wafer table is changed, up / down may become left / right, or left / right may become up / down, and such cases are also within the technical scope of the present invention.

[0009] [2] In the wafer stage described in [1] above, the ceramic plate may have at least one electrode, the gas passage may be provided so as to pass through an electrode through-hole provided in each of the at least one electrode so that each of the at least one electrode is not exposed to the inner surface of the gas passage, and the electric field adjustment conductor may be provided so as to be electrically insulated from each of the at least one electrode. In this way, the direction of the electric field generated by the electrodes in the ceramic plate can be horizontal or nearly horizontal.

[0010] [3] In the wafer mounting table described above (the wafer mounting table described in [1] or [2] above), the ceramic plate may have a ceramic plate through-hole that passes through the ceramic plate in the vertical direction, the gas passage may be provided inside or around a plug placed in the ceramic plate through-hole, and the electric field adjustment conductor may be provided inside the plug. This may make it easier to form the gas passage or the electric field adjustment conductor compared to providing the gas passage or the electric field adjustment conductor directly in the ceramic plate itself.

[0011] [4] In the wafer stage described above (the wafer stage described in [1] or [2] above), the gas passage and the electric field adjustment conductor may be provided in the ceramic plate. In this way, the gas passage and the electric field adjustment conductor can be formed when the ceramic plate is manufactured.

[0012] [5] In the wafer stage described above (the wafer stage described in any one of [1] to [4] above), the gas passage may be provided linearly in the vertical or oblique direction. This allows the gas to flow more easily than when a spiral passage is used as the gas passage or when micropores inside a porous body are used, thereby increasing the gas flow rate.

[0013] [6] In the wafer stage described above (the wafer stage described in any one of [1] to [5] above), the electric field adjustment conductor may be a flexible conductive wire. The electric field adjustment conductor may be a needle-shaped member with high rigidity, but is preferably a flexible conductive wire in consideration of misalignment during manufacturing and deformation during use.

[0014] [7] In the above-mentioned wafer mounting table (the wafer mounting table described in any one of [1] to [6]), the lower part of the electric field adjustment conductor may be arranged so as to be in direct contact with the base plate, or may be electrically connected to the base plate by a conductive elastic body arranged between the base plate and the lower end of the electric field adjustment conductor, which maintains communication between the gas supply path and the gas passage, or may be electrically connected to the base plate via a conductive film arranged on the underside of the ceramic plate, which maintains communication between the gas supply path and the gas passage.

[0015] A plan view of the wafer mounting table 10. A cross-sectional view taken along line A-A in FIG. 1. A partially enlarged view of FIG. 2. A partially enlarged cross-sectional view of a comparative embodiment. A manufacturing process diagram of the wafer mounting table 10. A partially enlarged cross-sectional view of another embodiment. A partially enlarged cross-sectional view of another embodiment. A partially enlarged cross-sectional view of another embodiment. A partially enlarged cross-sectional view of another embodiment. A partially enlarged cross-sectional view of another embodiment. A partially enlarged cross-sectional view of another embodiment.

[0016] A preferred embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a plan view of a wafer mounting table 10, Fig. 2 is a cross-sectional view taken along the line A-A in Fig. 1, and Fig. 3 is an enlarged view of a portion of Fig. 2. For convenience, the seal band 21a, small circular protrusions 21b, and reference surface 21c of the wafer mounting surface 21 are omitted in Figs. 2 and 3.

[0017] The wafer stage 10 includes a ceramic plate 20 , a gas passage 52 , a base plate 30 , a metal bonding layer 40 , and an electric field adjusting conductor 60 .

[0018] The ceramic plate 20 is a circular ceramic plate (e.g., 300 mm in diameter and 5 mm in thickness) made of alumina sintered body, aluminum nitride sintered body, or the like. The upper surface of the ceramic plate 20 serves as a wafer mounting surface 21. The ceramic plate 20 incorporates an electrostatic electrode 22 and a bias electrode 23. The electrostatic electrode 22 is located close to the wafer mounting surface 21 (e.g., 0.05 to 0.2 mm from the wafer mounting surface 21), while the bias electrode 23 is located far from the wafer mounting surface 21. As shown in FIG. 1 , the wafer mounting surface 21 of the ceramic plate 20 is formed with a seal band 21a along its outer edge and with a plurality of small circular protrusions 21b formed all over its surface. The seal band 21a and the small circular protrusions 21b have the same height, e.g., several μm to several tens of μm. The electrostatic electrode 22 is, for example, a planar mesh electrode to which a DC voltage can be applied. When a DC voltage is applied to the electrostatic electrode 22, the wafer W is attracted and fixed to the wafer mounting surface 21 (specifically, the upper surfaces of the seal bands 21a and the small circular protrusions 21b) by electrostatic attraction, and when the application of the DC voltage is stopped, the wafer W is released from the attraction and fixation to the wafer mounting surface 21. Note that the portion of the wafer mounting surface 21 on which the seal bands 21a and the small circular protrusions 21b are not provided is referred to as the reference surface 21c. The bias electrode 23 is, for example, a planar mesh electrode, and a high frequency bias voltage is applied to attract ions to the wafer W. The bias electrode 23 is a type of plasma generating electrode (RF electrode).

[0019] The gas passage 52 is a passage through which gas can pass in the vertical direction of the ceramic plate 20. Here, the gas passage 52 is provided inside the plug 50 fixed in the plug arrangement hole 24. The plug arrangement hole 24 is provided to vertically penetrate the ceramic plate 20 and communicate with the gas supply path 34 of the base plate 30. The plug arrangement hole 24 vertically penetrates the electrostatic electrode 22 and the bias electrode 23, but the electrostatic electrode 22 and the bias electrode 23 are not exposed on the inner circumferential surface of the plug arrangement hole 24. The plug arrangement hole 24 is a tapered hole having an inverted truncated cone space in which the area of ​​the upper opening is larger than the area of ​​the lower opening. The plug arrangement hole 24 is provided at multiple locations on the ceramic plate 20 (e.g., multiple locations equally spaced around the circumference) in a plan view. The plug 50 is a dense ceramic inverted truncated cone (e.g., made of the same material as the ceramic plate 20) and is provided in the plug arrangement hole 24. The plug 50 is provided with a gas passage 52 that extends linearly from the bottom surface to the top surface of the plug 50 in the vertical direction. The vertical length L of the gas passage 52 is the same as the thickness of the ceramic plate 20. A plurality of (e.g., six) gas passages 52 are provided on the top surface of the plug 50 along the circumferential direction in a plan view. The diameter (horizontal length) of each gas passage 52 is preferably set to 0.5 mm or less, more preferably 0.2 mm or less, to suppress arc discharge. In this embodiment, the equipotential lines EL are oriented not horizontally but vertically or obliquely, as shown in FIG. 3 . Arc discharge occurs when electrons generated by ionization of a gas (e.g., helium gas) in the gas passage 52 accelerate in the direction of the electric field lines (a direction perpendicular to the equipotential lines EL, which is approximately horizontal in this embodiment) and collide with other helium gas. However, if the horizontal length, i.e., diameter, of the gas passage 52 is 0.5 mm or less (preferably 0.2 mm or less), such arc discharge can be suppressed.

[0020] The base plate 30 is a conductive circular plate (having the same diameter as or larger than the ceramic plate 20) with good thermal conductivity. A coolant flow path 32 through which a coolant (e.g., an electrically insulating liquid such as a fluorine-based inert liquid) circulates and a gas supply path 34 through which gas is supplied to the gas passage 52 are formed within the base plate 30. The coolant flow path 32 is formed in a single line from the inlet to the outlet across the entire surface of the base plate 30 in a plan view. Examples of materials for the base plate 30 include metals and composite materials. Examples of metals include Mo. Examples of composite materials include composite materials of metals and ceramics. Examples of composite materials of metals and ceramics include metal matrix composites (MMCs) and ceramic matrix composites (CMCs). Specific examples of such composite materials include materials containing Si, SiC, and Ti, and materials in which porous SiC is impregnated with Al and / or Si. A material containing Si, SiC, and Ti is called SiSiCTi, a material in which a porous SiC body is impregnated with Al is called AlSiC, and a material in which a porous SiC body is impregnated with Si is called SiSiC. It is preferable to select a material for the base plate 30 that has a thermal expansion coefficient close to that of the material for the ceramic plate 20. The base plate 30 is used as a source electrode (a type of plasma generating electrode (RF electrode)) to which a source high frequency is applied to generate plasma. For example, the bias high frequency is several hundred kHz, and the source high frequency is several tens to several hundred MHz.

[0021] The gas supply path 34 includes a ring portion 34b that is concentric with the base plate 30 in a plan view, and an inlet portion 34a that introduces gas into the ring portion 34b from the underside of the base plate 30. The ring portion 34b communicates with the gas passages 52 via through holes 42 in the metal bonding layer 40. The number of inlet portions 34a may be, for example, one. The gas introduced into the inlet portion 34a passes through the ring portion 34b and is distributed to each gas passage 52.

[0022] The metal bonding layer 40 bonds the lower surface of the ceramic plate 20 to the upper surface of the base plate 30. The metal bonding layer 40 is formed, for example, by TCB (thermal compression bonding). TCB is a known method in which a metal bonding material is sandwiched between two components to be bonded and the two components are pressure-bonded while heated to a temperature below the solidus temperature of the metal bonding material. The metal bonding layer 40 may be a layer formed of solder or a metal brazing material. The metal bonding layer 40 has a through hole 42. The through hole 42 is provided at a position that connects the gas passage 52 and the gas supply path 34.

[0023] The electric field adjustment conductor 60 is a needle-shaped metal member provided inside the plug 50 and extending vertically near the gas passage 52. The electrostatic electrode 22 has an electrostatic electrode through-hole 22a facing the plug 50, and the bias electrode 23 has a bias electrode through-hole 23a facing the plug 50. The electric field adjustment conductor 60 is embedded in the ceramic plate 20 inside the electrostatic electrode through-hole 22a and inside the bias electrode through-hole 23a while being electrically insulated from the electrostatic electrode 22 and the bias electrode 23. The upper part of the electric field adjustment conductor 60 is inserted into a blind hole provided on the underside of the plug 50, and the lower part of the electric field adjustment conductor 60 is in direct contact with the base plate 30. The lower part of the electric field adjustment conductor 60 may be joined to the base plate 30 by solder or brazing material while inserted into a hole provided in the base plate 30, or may be screwed into a hole provided in the base plate 30. The upper end of the electric field adjustment conductor 60 reaches just before the wafer mounting surface 21. The upper end of the electric field adjustment conductor 60 is positioned so as to maintain a withstand voltage between the electric field adjustment conductor 60 and the wafer W. As described above, the electric field adjustment conductor 60 is provided so as to extend in the vertical direction near the gas passage 52 from below the lower surface of the ceramic plate 20 to just before the wafer mounting surface 21, and is electrically connected to the base plate 30. Therefore, the electric field adjustment conductor 60 has the same potential as the base plate 30. For example, the electric field adjustment conductor 60 is provided at a position spaced 0.3 to 2.0 mm from the gas passage 52.

[0024] Next, an example of how the wafer mounting table 10 configured as described above is described. First, the wafer mounting table 10 is installed in a chamber (not shown), and a wafer W is placed on the wafer mounting surface 21. The chamber is then depressurized using a vacuum pump to a predetermined vacuum level, and a DC voltage is applied to the electrostatic electrode 22 of the ceramic plate 20 to generate an electrostatic attraction force, thereby attracting and fixing the wafer W to the wafer mounting surface 21 (specifically, the upper surface of the seal band 21a or the upper surface of the small circular protrusions 21b). Next, the chamber is filled with a reactive gas atmosphere at a predetermined pressure (e.g., several tens to several hundreds of Pa). In this state, a source high-frequency voltage is applied between an upper electrode (not shown) installed on the ceiling of the chamber and the base plate 30, and a bias high-frequency voltage is applied between the upper electrode and the bias electrode 23, thereby generating plasma. The surface of the wafer W is processed by the generated plasma. A coolant is circulated through the coolant flow path 32 of the base plate 30. A backside gas is introduced into the gas supply path 34 from a gas cylinder (not shown). A thermally conductive gas (e.g., helium) is used as the backside gas. The backside gas is supplied and sealed in the space between the back surface of the wafer W and the reference surface 21c of the wafer mounting surface 21 through the gas supply path 34, the through-hole 42, and the gas passage 52. The presence of this backside gas ensures efficient thermal conduction between the wafer W and the ceramic plate 20.

[0025] The wafer mounting table 10 includes an electric field adjusting conductor 60, which allows the direction of the electric field (the direction perpendicular to the equipotential lines EL) during plasma generation to be adjusted to a horizontal direction or a direction close to the horizontal direction. An example of the equipotential lines EL in this embodiment is shown in FIG. 3 . As a result, the direction of acceleration of electrons generated by ionization of gas molecules is horizontal or a direction close to the horizontal direction. Therefore, if the length of the gas passage 52 in the horizontal direction or a direction close to the horizontal direction is short, even if the vertical length L within the gas passage 52 is increased, the distance over which the electrons are accelerated does not increase, and even if the accelerated electrons collide with other gas molecules, discharge is unlikely to occur. In contrast, without the electric field adjusting conductor 60, horizontal equipotential lines EL exist throughout the entire vertical direction of the gas passage 52, as shown in the comparative example in FIG. 4 . In this case, the direction of the electric field is vertical. Therefore, if the vertical length L within the gas passage 52 is increased, the distance over which the electrons are accelerated also increases. Since the accelerated electrons have high energy, they are more likely to collide with other gas molecules and cause discharge. Therefore, when the electric field adjusting conductor 60 is not provided, discharge within the gas passage 52 is suppressed by employing, for example, a spiral passage (with a short internal vertical length (e.g., 0.5 mm or less)) instead of the gas passage 52 that extends linearly in the vertical direction. According to this embodiment, discharge within the gas passage 52 can be suppressed even if the internal vertical length L of the gas passage 52 is made longer than when the electric field adjusting conductor 60 is not provided.

[0026] Next, a manufacturing example of the wafer mounting table 10 will be described with reference to FIG. 5. FIG. 5 is a manufacturing process diagram of the wafer mounting table 10. First, a ceramic plate 20, a base plate 30, and a metal bonding material 90 are prepared (FIG. 5A). The ceramic plate 20 incorporates an electrostatic electrode 22 and a bias electrode 23 and is provided with a plug placement hole 24. The base plate 30 is provided with a coolant flow path 32 and a gas supply path 34. However, at this stage, the top of the ring portion 34b is open. In addition, a hole is provided at a predetermined position of the ring portion 34b into which the lower portion of the electric field adjustment conductor 60 is inserted. The metal bonding material 90 is provided with a through-hole 92 at a position opposite the plug placement hole 24.

[0027] Next, a metal bonding material 90 is sandwiched between the underside of the ceramic plate 20 and the upper side of the base plate 30 to form a laminate. The laminate is then pressed and bonded at a temperature below the solidus temperature of the metal bonding material 90 (e.g., a temperature 20°C below the solidus temperature but below the solidus temperature), and then returned to room temperature (TCB). As a result, the metal bonding material 90 and the through-hole 92 become the metal bonding layer 40 and the through-hole 42, respectively. The upper portion of the ring portion 34b is covered with the metal bonding layer 40 except for the portion facing the through-hole 42. As a result, a bonded body 94 is obtained in which the ceramic plate 20 and the base plate 30 are bonded with the metal bonding layer 40 ( FIG. 5B ). The metal bonding material 90 can be an Al-Mg-based bonding material or an Al-Si-Mg-based bonding material. It is preferable to use a metal bonding material 90 with a thickness of approximately 100 μm.

[0028] Next, an electric field adjustment conductor 60 and a truncated conical plug 50 are prepared ( FIG. 5B ). The plug 50 has multiple gas passages 52 and a blind hole 54 on its underside. This blind hole 54 is a hole for inserting the upper part of the electric field adjustment conductor 60 and is located at the center of the circle in which the multiple gas passages 52 are arranged in a plan view. First, the electric field adjustment conductor 60 is inserted into the hole in the ring portion 34b and fixed therein by brazing or the like. Next, the plug 50 is inserted into the plug placement hole 24 and fixed therein with an adhesive. At this time, the electric field adjustment conductor 60 is positioned so that it is inserted into the blind hole 54 of the plug 50. The upper surface of the ceramic plate 20 is then processed (forming the seal band 21a and the small circular protrusions 21b) to obtain the wafer mounting table 10 ( FIG. 5C ).

[0029] The wafer mounting table 10 described above includes the electric field adjusting conductor 60, which allows the direction of the electric field (the direction perpendicular to the equipotential lines EL) during plasma generation to be adjusted to the horizontal direction or a direction close to it. As a result, the direction in which electrons generated by ionization of gas molecules accelerate is horizontal or a direction close to it. Therefore, if the length of the gas passage 52 in the horizontal direction or a direction close to it is short, even if the vertical length L within the gas passage 52 is increased, the distance over which the electrons accelerate does not increase, and discharge is less likely to occur even if the accelerated electrons collide with other gas molecules. Therefore, discharge within the gas passage 52 can be suppressed even if the vertical length L within the gas passage 52 is increased, compared to when the electric field adjusting conductor 60 is not provided.

[0030] The ceramic plate 20 also has an electrostatic electrode 22 and a bias electrode 23. The gas passage 52 passes through an electrostatic electrode through-hole 22a so that the electrostatic electrode 22 is not exposed to the inner surface of the gas passage 52, and the bias electrode 23 passes through a bias electrode through-hole 23a so that the bias electrode 23 is not exposed to the inner surface of the gas passage 52. The electric field adjustment conductor 60 is provided in a state where it is electrically insulated from each of the electrostatic electrode 22 and the bias electrode 23. Therefore, the direction of the electric field generated by the electrostatic electrode 22 and the bias electrode 23 in the ceramic plate 20 can also be horizontal or nearly horizontal.

[0031] Furthermore, the ceramic plate 20 has a plug placement hole 24 (ceramic plate through-hole) that passes through the ceramic plate 20 in the vertical direction. The gas passage 52 and the electric field adjustment conductor 60 are provided inside the plug 50 that is placed in the plug placement hole 24. Therefore, it may be easier to form the gas passage 52 and the electric field adjustment conductor 60 compared to when the gas passage 52 and the electric field adjustment conductor 60 are provided directly in the ceramic plate 20 itself.

[0032] Furthermore, the gas passages 52 are provided linearly in the vertical direction. This allows the gas to flow more easily than when spiral passages are used as gas passages or when micropores inside a porous body are used, thereby increasing the gas flow rate. As a result, the number of gas passages 52 can be reduced, thereby reducing manufacturing costs. Furthermore, the gas passages 52 become temperature singularities of the wafer W, but reducing the number of gas passages 52 reduces the temperature singularities and improves thermal uniformity.

[0033] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0034] In the above-described embodiment, the gas passage 52 extending linearly in the vertical direction is provided inside the plug 50. However, a gas passage 152 shown in FIG. 6 may be used instead of the gas passage 52. In FIG. 6, the same components as those in the above-described embodiment are denoted by the same reference numerals. The gas passage 152 extends linearly in a diagonal direction around the periphery of the plug 50. Specifically, the gas passage 152 is formed by a groove provided on the outer circumferential surface of the plug 50 and the inner circumferential surface of the plug placement hole 24. As shown in FIG. 7, a plurality of gas passages 152 are provided at approximately equal intervals along the outer periphery of the plug 50 (a circle centered on the field adjustment conductor 60) in a plan view. The vertical length L (FIG. 3) of the gas passage 52 is the same as the thickness of the ceramic plate 20, but the vertical length L (FIG. 6) of the gas passage 152 is shorter than the thickness of the ceramic plate 20. This configuration also achieves the same effects as the above-described embodiment. The gas passage 152 may be provided inside the plug 50 rather than around the periphery. Alternatively, the gas passage 152 may be formed by a longitudinal groove provided on the outer peripheral surface of the plug 50 and the inner peripheral surface of the plug placement hole 24 .

[0035] In the above-described embodiment, the plug 50 disposed in the plug placement hole 24 of the ceramic plate 20 is provided with a gas passage 52 and an electric field adjustment conductor 60. However, instead of these, a gas passage 252 and an electric field adjustment conductor 260 shown in FIG. 8 may be employed. In FIG. 8, the same components as those in the above-described embodiment are denoted by the same reference numerals. The gas passage 252 is provided in the ceramic plate 20 and extends linearly in the vertical direction. The gas passage 252 communicates with the gas supply path 34 and the through-hole 42. As shown in FIG. 9, a plurality of gas passages 252 are provided at approximately equal intervals along a circle centered on the electric field adjustment conductor 260 in a plan view. The upper portion of the electric field adjustment conductor 260 is inserted into a blind hole provided on the underside of the ceramic plate 20, and the lower portion of the electric field adjustment conductor 260 is in direct contact with the base plate 30. This configuration also achieves the same effects as the above-described embodiment. Furthermore, the gas passage 252 and the electric field adjustment conductor 260 (or a hole for inserting the electric field adjustment conductor 260) can be fabricated during the manufacturing of the ceramic plate 20. The gas passages 252 may be provided linearly in an oblique direction within the ceramic plate 20 .

[0036] In the above-described embodiment, the electric field adjustment conductor 60 erected on the base plate 30 is inserted into the blind hole 54 of the plug 50. However, the structure shown in FIG. 10 may be employed instead. In FIG. 10, the same components as those in the above-described embodiment are denoted by the same reference numerals. The electric field adjustment conductor 360 is a via provided in the plug 50. For example, a conductive paste, which is a precursor of the electric field adjustment conductor 360, may be embedded in a ceramic compact, which is a precursor of the plug 50, so that the electric field adjustment conductor 360 is formed simultaneously when the ceramic compact is fired to obtain the plug 50. A metal spring 370 is disposed in a compressed state between the lower end of the electric field adjustment conductor 360 and the bottom surface of the gas supply path 34 (ring portion 34b) of the base plate 30. The electric field adjustment conductor 360 is electrically connected to the base plate 30 via the metal spring 370. The metal spring 370 maintains communication between the gas supply path 34 and the gas passage 52. This configuration also achieves the same effects as the above-described embodiment. While a metal spring 370 is illustrated in FIG. 10 , any conductive elastic member that allows gas to pass through in the vertical direction is not limited to the metal spring 370. For example, a metal mesh or a mass of metal fibers that can expand and contract in the vertical direction may be used. This structure is particularly useful when a resin adhesive layer is used instead of the metal bonding layer 40. Note that the electric field adjustment conductor 360 and metal spring 370 in FIG. 10 may be used instead of the electric field adjustment conductors 60 and 260 in FIG. 6 and FIG. 8 .

[0037] Furthermore, instead of the metal spring 370 shown in FIG. 10 , a conductive film 372 may be provided, covering the underside of the plug 50 and a portion of the underside of the ceramic plate 20 (around the plug placement hole 24), as shown in FIG. 11 . In FIG. 11 , the same components as those in the above-described embodiment are denoted by the same reference numerals. The conductive film 372 is formed, for example, by sputtering. A through-hole 372a is provided in the conductive film 372 at a position facing the gas passage 52. Therefore, the conductive film 372 maintains communication between the gas supply path 34 and the gas passage 52. The electric field adjustment conductor 360 is electrically connected to the base plate 30 via the conductive film 372 and the metal bonding layer 40. This configuration also achieves the same effects as the above-described embodiment. The electric field adjustment conductor 360 and conductive film 372 shown in FIG. 11 may be used instead of the electric field adjustment conductors 60 and 260 shown in FIGS. 6 and 8 .

[0038] In the above-described embodiment, the electrostatic electrode 22 and the bias electrode 23 are embedded in the ceramic plate 20. However, at least one of the electrostatic electrode 22, the bias electrode 23, and the heater electrode capable of heating the wafer W may be embedded in the ceramic plate 20. Alternatively, these electrodes may not be embedded in the ceramic plate 20. FIG. 12 shows an example of a structure in which electrodes are not embedded in the ceramic plate 20. In FIG. 12, the same components as in the above-described embodiment are denoted by the same reference numerals. FIG. 12 also shows equipotential lines EL. In FIG. 12, the electric field adjustment conductor 60 is provided, so that the direction of the electric field (the direction perpendicular to the equipotential lines EL) during plasma generation can be adjusted to a direction close to horizontal. As a result, the direction of acceleration of electrons generated by ionization of gas molecules is close to horizontal. Therefore, compared to a case in which the electric field adjustment conductor 60 is not provided, discharge within the gas passage 52 can be suppressed even if the vertical length of the gas passage 52 is increased.

[0039] In the above-described embodiment, a flexible conductive wire may be used as the electric field adjusting conductor 60. This makes it possible to absorb misalignment during manufacturing and deformation during use, compared to when a highly rigid needle-shaped member is used as the electric field adjusting conductor 60. This also applies to the electric field adjusting conductor 260 in FIG. 8 and the electric field adjusting conductor 360 in FIGS. 10 and 11.

[0040] In the above-described embodiment, the plug 50 is provided with a plurality of gas passages 52 that extend linearly in the vertical direction, but instead of the plurality of gas passages 52, a single spiral passage may be employed, or a porous body may be employed as the plug 50 and the micropores inside the porous body may be used as the gas passages. In these cases, discharge in the gas passages may be more easily suppressed, but the gas may flow more slowly than in the above-described embodiment.

[0041] In the above-described embodiment, the ceramic plate 20 and the base plate 30 are joined together by the metal joining layer 40, but a resin adhesive layer may be used instead of the metal joining layer 40.

[0042] In the above-described embodiment, the gas supply path 34 includes the inlet portion 34 a and the ring portion 34 b, but is not limited to this. For example, the gas supply path may be a base plate through-hole that vertically penetrates the base plate 30 and communicates with the gas passage 52.

[0043] In the above-described embodiment, the internal space of the plug placement hole 24 is an inverted truncated cone space, but it may be a cylindrical space. In this case, the plug 50 is also cylindrical.

[0044] The present invention can be used for wafer mounting tables used in semiconductor manufacturing equipment, such as ceramic heaters, electrostatic chuck heaters, and electrostatic chucks.

[0045] 10 wafer mounting table, 20 ceramic plate, 21 wafer mounting surface, 21a seal band, 21b small circular protrusion, 21c reference surface, 22 electrostatic electrode, 22a electrostatic electrode through hole, 23 bias electrode, 23a bias electrode through hole, 24 plug placement hole, 30 base plate, 32 coolant flow path, 34 gas supply path, 34a introduction portion, 34b ring portion, 40 metal bonding layer, 42 through hole, 50 plug, 52 gas passage, 54 blind hole, 60 electric field adjustment conductor, 90 metal bonding material, 92 through hole, 94 bonded body, 152 gas passage, 252 gas passage, 260 electric field adjustment conductor, 360 electric field adjustment conductor, 370 metal spring, 372 conductive film, 372a through hole.

Claims

1. A ceramic plate having a wafer mounting surface on its upper surface, A gas passage through which gas can pass in the vertical direction of the ceramic plate, A conductive base plate is bonded to the lower surface of the ceramic plate and used as a plasma generating electrode, A gas supply passage is provided inside the base plate and communicates with the gas passage, An electric field adjusting conductor is provided, extending vertically in the vicinity of the gas passage from the lower surface of the ceramic plate or a position below it to the front of the wafer mounting surface, and electrically connected to the base plate, Equipped with, The ceramic plate has a through-hole that penetrates the ceramic plate vertically, the gas passage is provided inside or around the plug positioned in the through-hole, and the electric field adjusting conductor is provided inside the plug. Wafer mounting stand.

2. A ceramic plate having a wafer mounting surface on its upper surface, A gas passage through which gas can pass in the vertical direction of the ceramic plate, A conductive base plate is bonded to the lower surface of the ceramic plate and used as a plasma generating electrode, A gas supply passage is provided inside the base plate and communicates with the gas passage, An electric field adjusting conductor is provided, extending vertically in the vicinity of the gas passage from the lower surface of the ceramic plate or a position below it to the front of the wafer mounting surface, and electrically connected to the base plate, Equipped with, The electric field adjusting conductor is a flexible conductive wire. Wafer mounting stand.

3. A ceramic plate having a wafer mounting surface on its upper surface, A gas passage through which gas can pass in the vertical direction of the ceramic plate, A conductive base plate is bonded to the lower surface of the ceramic plate and used as a plasma generating electrode, A gas supply passage is provided inside the base plate and communicates with the gas passage, An electric field adjusting conductor is provided, extending vertically in the vicinity of the gas passage from the lower surface of the ceramic plate or a position below it to the front of the wafer mounting surface, and electrically connected to the base plate, Equipped with, The lower part of the electric field adjusting conductor is provided so as to be in direct contact with the base plate, or is electrically connected to the base plate by a conductive elastic body disposed between the base plate and the lower end of the electric field adjusting conductor, which maintains communication between the gas supply path and the gas passage, or is electrically connected to the base plate via a conductive film provided on the lower surface of the ceramic plate, which maintains communication between the gas supply path and the gas passage. Wafer mounting stand.

4. The gas passage and the electric field adjusting conductor are embedded in the ceramic plate. The wafer mounting platform according to claim 2 or 3.

5. The gas passage is provided linearly in the vertical or diagonal direction of the ceramic plate. A wafer mounting platform according to any one of claims 1 to 3.

6. The electric field adjusting conductor is a flexible conductive wire. A wafer mounting platform according to claim 1 or 3.

7. The lower part of the electric field adjusting conductor is provided so as to be in direct contact with the base plate, or is electrically connected to the base plate by a conductive elastic body disposed between the base plate and the lower end of the electric field adjusting conductor, which maintains communication between the gas supply path and the gas passage, or is electrically connected to the base plate via a conductive film provided on the lower surface of the ceramic plate, which maintains communication between the gas supply path and the gas passage. The wafer mounting platform according to claim 1.

8. The ceramic plate has at least one electrode, The gas passage is provided so as to pass through an electrode through-hole provided in each of the at least one electrode, such that each of the at least one electrode is not exposed to the inner surface of the gas passage. The electric field adjusting conductor is provided in a state where it is electrically insulated from each of the at least one electrode. A wafer mounting platform according to any one of claims 1 to 3.