JP7747847B1 - Wafer mounting table - Google Patents

Abstract

Discharge is suppressed around the end of an insulating gas passing plug on the conductive plate side.
[Solution] A wafer mounting table (10) has a wafer mounting surface (21) on its upper surface and includes a ceramic plate (20) incorporating an electrode (22), a conductive plate (30) bonded to the underside of the ceramic plate (20), a ceramic plate penetration (50) penetrating the ceramic plate (20), a dense plug (55) provided in the ceramic plate penetration (50) and allowing gas to pass therethrough, a gas introduction passage (60) provided at least inside the conductive plate (30) and communicating with the ceramic plate penetration (50), and a conductive gas passage (70) provided within the gas introduction passage (60), in contact with the underside of the dense plug (55), electrically connected to the conductive plate (30), and allowing gas to pass between the dense plug (55) and the gas introduction passage (60). The conductive gas passage (70) has a leaf spring (72) that elastically presses the dense plug (55) upward.
[Selected Figure] Figure 2

Description

The present invention relates to a wafer mounting table.

Conventionally, wafer mounting tables have been known that include a ceramic plate having a wafer mounting surface on its upper surface and a base plate bonded to the underside of the ceramic plate and having a gas introduction passage. Patent Document 1 discloses such a wafer mounting table, which includes an insulating first porous portion disposed within a through-hole in the ceramic plate and an insulating second porous portion fitted in a recess on the ceramic plate side of the base plate so as to face the first porous portion. Gas supplied to the gas introduction passage passes through the second and first porous portions and flows into the space between the wafer mounting surface and the wafer, where it is used to cool the object. The publication states that the presence of the first and second porous portions ensures the flow rate of gas from the gas introduction passage to the wafer mounting surface while suppressing the occurrence of plasma-induced discharge (arc discharge) during wafer processing.

Japanese Patent Application Laid-Open No. 2020-72262

However, even when an insulating second porous portion is present as in Patent Document 1, discharges can still occur around the end of the first porous portion facing the base plate.

The present invention was made to solve these problems, and its main purpose is to suppress discharge around the end of the insulating gas-passing plug on the conductive plate side.

The present invention employs the following means to achieve the above-mentioned primary objective.

[1] The wafer mounting table of the present invention comprises:
a ceramic plate having a wafer mounting surface on its upper surface and incorporating an electrode;
a conductive plate bonded to the lower surface of the ceramic plate;
a ceramic plate penetration portion that penetrates the ceramic plate;
an insulating gas-passing plug that is provided in the ceramic plate penetration part and allows gas to pass therethrough;
a gas introduction passage provided at least inside the conductive plate and communicating with the ceramic plate penetration portion;
a conductive gas passage provided in the gas introduction passage, in contact with a lower surface of the insulating gas passage plug, electrically connected to the conductive plate, and allowing gas to pass between the insulating gas passage plug and the gas introduction passage;
Equipped with
the conductive gas passage portion has a leaf spring that presses the insulating gas passage plug upward with an elastic force;
It is something.

In this wafer mounting table, the conductive gas passage is located within the gas introduction passage, contacts the underside of the insulating gas passage plug, and is electrically connected to the conductive plate. This makes it less likely that a potential difference will occur around the end of the insulating gas passage plug facing the conductive plate, compared to when an insulating porous member is present on the underside of the insulating gas passage plug. Therefore, discharge around the end of the insulating gas passage plug facing the conductive plate can be suppressed. Furthermore, because the leaf spring presses the insulating gas passage plug upward with its elastic force, electrical continuity is easily maintained from the contact point of the conductive gas passage with the insulating gas passage plug to the conductive plate.

[2] In the wafer mounting table described above (the wafer mounting table described in [1] above), the leaf spring may be arranged in a state in which it is stretched in a horizontal direction perpendicular to the up-down direction by being pressed from above by the insulating gas passing plug. In this way, the leaf spring stretches and spreads in the horizontal direction, which makes it easier to reduce the area directly below the insulating gas passing plug where no leaf spring is present. This makes it possible to further suppress discharge around the end of the insulating gas passing plug on the conductive plate side.

[3] In the wafer mounting table described above (the wafer mounting table described in [2] above), the leaf spring may have multiple folded portions folded along the vertical direction.

[4] In the wafer mounting table described above (the wafer mounting table described in [3] above), the multiple folded portions may include a first folded portion folded from top to bottom and a second folded portion folded from bottom to top, the first folded portion having a first plate-shaped portion extending horizontally and an upper surface that forms the upper surface of the leaf spring, and the second folded portion having a second plate-shaped portion extending horizontally and an under surface that forms the lower surface of the leaf spring. In this way, the leaf spring has a first plate-shaped portion that increases the contact area with the member above it, and the leaf spring has a second plate-shaped portion that increases the contact area with the member below it. This allows for more reliable contact between the leaf spring and the members above and below it, and ultimately more reliable continuity from the portion of the conductive gas passage that contacts the insulating gas passage plug to the conductive plate.

[5] In the above-described wafer mounting table (the wafer mounting table described in any one of [1] to [4] above), the conductive gas passage portion may have a coating layer that covers the lower surface of the insulating gas passage plug. In this case, the coating layer may be a dense layer having pores that allow gas to pass through. Alternatively, the coating layer may be a porous layer that allows gas to pass through. Alternatively, the coating layer may cover a portion of the lower surface of the insulating gas passage plug and allow gas to pass through the uncovered portion of the lower surface.

[6] In the wafer stage described above (the wafer stage described in any one of [1] to [5] above), the insulating gas-permeable plug may be a dense body having an internal gas flow path, or may be a porous body.

[7] In the above-described wafer mounting table (the wafer mounting table described in any one of [1] to [6] above), the insulating gas-passing plug may be a dense body having an internal gas flow path, and the opening at the lower end of the internal gas flow path may be located, in a plan view, outside the range of movement caused by misalignment of the upper surface of the leaf spring within the gas introduction path. In this way, even if the leaf spring is misaligned within the gas introduction path, the upper surface of the leaf spring does not overlap with the opening at the lower end of the internal gas flow path in a plan view, making it less likely that the leaf spring will obstruct the flow of gas between the gas introduction path and the internal gas flow path.

[8] In the wafer stage described above (the wafer stage described in any one of [1] to [7] above), the leaf spring may have holes that allow gas to pass through. This makes it easier for gas to pass through the conductive gas passage portion.

[9] The wafer mounting table described above (the wafer mounting table described in [5] above) may include a conductive layer covering a portion of the underside of the ceramic plate that is exposed to the gas introduction passage, and the leaf spring may be in contact with the conductive layer. In this way, the portion of the underside of the ceramic plate that is exposed to the gas introduction passage is covered with a conductive layer, and the conductive layer comes into contact with the leaf spring, thereby establishing electrical conduction with the conductive plate via the leaf spring. This makes it difficult for a potential difference to occur around the portion of the underside of the ceramic plate that faces the inside of the gas introduction passage. Therefore, discharge around the portion of the underside of the ceramic plate that faces the inside of the gas introduction passage can be suppressed.

[10] The wafer mounting table described above (the wafer mounting table described in [5] above) may include a conductive layer covering the portion of the underside of the ceramic plate that is exposed inside the gas introduction passage, and a conductive conducting member in contact with the conductive plate and the conductive layer. In this way, the underside of the ceramic plate is covered with a conductive layer, and the conductive layer is electrically connected to the conductive plate via the conductive member, making it difficult for a potential difference to occur around the portion of the underside of the ceramic plate that faces the inside of the gas introduction passage. Therefore, discharge around the portion of the underside of the ceramic plate that faces the inside of the gas introduction passage can be suppressed.

[11] In the wafer mounting table described above (the wafer mounting table described in [10] above), the conductive member may be an elastic body that presses the conductive layer upward with an elastic force. In this way, the conductive member presses the conductive layer upward with an elastic force, making it easier to maintain conductivity from the conductive layer to the conductive plate.

[12] In the wafer stage described above (the wafer stage described in any one of [1] to [11] above), the conductive gas passage may include a gas passage member that electrically connects the conductive plate and the leaf spring.

[13] In the wafer stage described above (the wafer stage described in [12] above), the gas passage member may be an elastic body.

FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1; FIG. 4 is a partially enlarged cross-sectional view showing the periphery of the second gas passage 62 and the conductive gas passage 70. FIG. 4 is a perspective view of a leaf spring 72 of the conductive gas passage portion 70. 10 is a cross-sectional view of the wafer stage 10 cut along a horizontal plane passing through the second gas passage 62, as viewed from above. FIG. 10 is a cross-sectional view of the wafer stage 10 cut by a horizontal plane passing through the coolant flow path 32, as viewed from above. FIG. FIG. 2 is an explanatory diagram in which a coolant flow path 32 and the like are drawn on a plan view of the wafer mounting table 10. 5A to 5C are diagrams showing the manufacturing process of the wafer mounting table 10. 10 is an explanatory diagram showing a state in which a leaf spring 72 is pressed against a dense plug 55 during manufacturing of the wafer mounting table 10. FIG. FIG. 10 is a partially enlarged cross-sectional view showing the porous plug 155 and the covering layer 171. FIG. 4 is a partially enlarged cross-sectional view showing a conductive gas passage 270. FIG. 10 is a partially enlarged cross-sectional view showing a leaf spring 372. FIG. 10 is a partially enlarged cross-sectional view showing a leaf spring 472. FIG. 10 is a partially enlarged cross-sectional view showing another example of the leaf spring 472. FIG. 10 is a partially enlarged cross-sectional view showing a leaf spring 572. FIG. 10 is an explanatory diagram showing the positions of an upper surface 572a of a leaf spring 572 and an internal gas flow path 55a in a plan view. FIG. 10 is an explanatory diagram showing the horizontal movement range of a leaf spring 572. FIG. 10 is a partially enlarged cross-sectional view showing an example of a leaf spring 472 having a hole 672c. FIG. 19 is a perspective view of the leaf spring 472 of FIG. 18 . FIG. 10 is a partially enlarged cross-sectional view showing the conductive layer 25 and the leaf spring 772. FIG. 10 is a partially enlarged cross-sectional view showing a conductive member 875. FIG. 10 is a partially enlarged cross-sectional view showing a gas passage member 975. 9 is an explanatory diagram showing how the ceramic plate 20 and the conductive plate 30 are joined by an insulating joining layer 940. FIG.

Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of the wafer mounting table 10, FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1, FIG. 3 is a partially enlarged cross-sectional view showing the second gas passage 62 and the conductive gas passage 70, and its surroundings, FIG. 5 is a cross-sectional view of the wafer mounting table 10 cut along a horizontal plane passing through the second gas passage 62, as viewed from above, FIG. 6 is a cross-sectional view of the wafer mounting table 10 cut along a horizontal plane passing through the refrigerant passage 32, as viewed from above, and FIG. 7 is an explanatory diagram with the refrigerant passage 32 and other components written into the plan view of the wafer mounting table 10. FIG. 3 is a partially enlarged cross-sectional view of the wafer mounting table 10 cut along a vertical plane passing through the second gas passage 62 and the conductive gas passage 70. In this specification, "upper" and "lower" do not represent absolute positional relationships, but rather represent relative positional relationships. Therefore, depending on the orientation of the wafer mounting table 10, "upper" and "lower" may be "lower" and "upper," "left" and "right," or "front" and "rear."

As shown in Figure 2, the wafer mounting table 10 includes a ceramic plate 20, a conductive plate 30, a conductive bonding layer 40, a ceramic plate penetration 50, a gas introduction passage 60, and a conductive gas passage 70.

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 support surface 21 on which a wafer W is placed. The ceramic plate 20 incorporates an electrode 22. As shown in FIG. 1, an annular seal band 21a is formed along the outer edge of the wafer support surface 21 of the ceramic plate 20, and multiple circular small protrusions 21b are formed on the entire inner surface of the seal band 21a. The seal band 21a and the circular small protrusions 21b have the same height, e.g., several micrometers to several tens of micrometers. The electrode 22 is a planar mesh electrode used as an electrostatic electrode and is connected to an external DC power source via a power supply member (not shown). A low-pass filter may be disposed along the power supply member. The power supply member is electrically insulated from the conductive bonding layer 40 and the conductive plate 30. When a DC voltage is applied to this electrode 22, the wafer W is attracted and fixed to the wafer mounting surface 21 (specifically, the upper surfaces of the seal band and small circular protrusions) 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. The portion of the wafer mounting surface 21 that is not provided with the seal band 21a or small circular protrusions 21b is referred to as the reference surface 21c.

The conductive plate 30 is a circular plate with good thermal conductivity (a circular plate with the same or larger diameter as the ceramic plate 20). A refrigerant flow path 32 is formed within the conductive plate 30, through which a refrigerant circulates. The refrigerant flowing through the refrigerant flow path 32 is preferably a liquid, preferably electrically insulating. Examples of electrically insulating liquids include fluorine-based inert liquids. The refrigerant flow path 32 is formed in a single stroke from one end (inlet) to the other end (outlet) across the entire conductive plate 30 in a planar view. As shown in Figure 6, the refrigerant flow path 32 is arranged in a single stroke from one end to the other end based on a multiple circle consisting of multiple imaginary circles (dotted and dashed circles C1 to C4, here circles C1 to C4 are concentric circles) of different diameters arranged so that they do not overlap each other in a planar view. Specifically, the refrigerant flow path 32 is routed from one end to the other in a single stroke, tracing the imaginary circles while connecting two imaginary circles that are the inner and outermost of the multiple circles. One end and the other end of the refrigerant flow path 32 are connected to a supply port and a recovery port, respectively, of an external refrigerant device (not shown). The refrigerant supplied to one end of the refrigerant flow path 32 from the supply port of the external refrigerant device passes through the refrigerant flow path 32, returns from the other end of the refrigerant flow path 32 to the recovery port of the external refrigerant device, and is temperature-adjusted before being supplied again from the supply port to one end of the refrigerant flow path 32. The conductive plate 30 is connected to a radio frequency (RF) power source and also serves as an RF electrode.

Examples of materials for the conductive plate 30 include metal materials and composite materials of metal and ceramic. Metal materials include Al, Ti, Mo, and alloys thereof. Metal-ceramic composite materials include metal matrix composites (MMCs) and ceramic matrix composites (CMCs). Specific examples of such composite materials include materials containing Si, SiC, and Ti (also known as SiSiCTi), materials in which porous SiC is impregnated with Al and/or Si, and composite materials _{of Al2O3} and TiC. It is preferable to select a material for the conductive plate 30 that has a thermal expansion coefficient close to that of the material for the ceramic plate 20.

The conductive bonding layer 40 is, for example, a metal bonding layer, and bonds the lower surface of the ceramic plate 20 to the upper surface of the conductive plate 30. The conductive bonding layer 40 is formed, for example, by TCB (thermal compression bonding). TCB is a well-known method in which a metal bonding material is sandwiched between two components to be joined, and the two components are pressure-bonded while heated to a temperature below the solidus temperature of the metal bonding material.

As shown in FIG. 2, the ceramic plate through-holes 50 are holes that penetrate the ceramic plate 20 in the vertical direction. The ceramic plate through-holes 50 are gas passages that lead from the underside of the ceramic plate 20 to the reference surface 21c (FIG. 1) of the wafer mounting surface 21. As shown in FIG. 1, multiple ceramic plate through-holes 50 (36 in this example) are provided. As shown in FIG. 2, the ceramic plate through-holes 50 are spaces whose cross-sectional area decreases from the upper opening to the lower opening (e.g., an inverted truncated cone shape). The ceramic plate through-holes 50 have an electrically insulating dense plug 55 (an example of an insulating gas-passing plug) that allows gas to flow in the vertical direction.

The dense plug 55 is a component with a shape (e.g., a truncated cone shape) whose cross-sectional area decreases from the top to the bottom, similar to the shape of the ceramic plate penetration 50. The dense plug 55 has an internal gas flow path 55a. The internal gas flow path 55a allows gas to flow between the top and bottom sides of the dense plug 55. The internal gas flow path 55a is a passage that bends and penetrates the top and bottom sides of the dense plug 55, and is more specifically configured as a zigzag passage. Another example of a passage that bends and penetrates the dense plug 55 is a spiral passage. The internal gas flow path 55a may also be a linear through-hole extending vertically. The cross-sectional diameter of the internal gas flow path 55a is preferably 0.1 mm or more and 1 mm or less. One dense plug 55 may have multiple internal gas flow paths 55a. The porosity of the dense portion of the dense plug 55 is preferably less than 0.1%. The dense plug 55 is fixed by being press-fitted into the ceramic plate penetration portion 50. The dense plug 55 can be made of ceramics such as alumina or aluminum nitride. The dense plug 55 may be manufactured by firing a compact formed using a 3D printer, or by firing a mold-cast compact. Details of the dense plug having a curved internal gas flow path and mold-cast molding are disclosed, for example, in Japanese Patent No. 7149914.

The upper surface of the dense plug 55 is flush with the reference surface 21c of the wafer mounting surface 21. The lower surface of the dense plug 55 is covered with a coating layer 71, which is part of the conductive gas passage 70. As shown in Figures 2 and 3, the lower surface of the dense plug 55 is located above the lower opening of the ceramic plate through-hole 50 (which is flush with the lower surface of the ceramic plate 20). The lower surface of the dense plug 55 may be flush with the lower opening of the ceramic plate through-hole 50. The lower surface of the dense plug 55 may also be located below the lower opening of the ceramic plate through-hole 50. In other words, the lower end of the dense plug 55 may protrude below the lower surface of the ceramic plate 20.

The gas introduction passage 60 is a gas passage provided at least inside the conductive plate 30 and communicates with the ceramic plate penetration 50. The gas introduction passage 60 includes a first gas passage 61, a second gas passage 62, a gas auxiliary passage 63 (Figure 5), and a bonding layer penetration 64. The gas introduction passage 60 includes gas passages (first gas passage 61, second gas passage 62, and gas auxiliary passage 63) provided inside the conductive plate 30, and a gas passage (bonding layer penetration 64) provided inside the conductive bonding layer 40.

The first gas passages 61 penetrate the conductive plate 30 in the vertical direction. The first gas passages 61 penetrate between the refrigerant flow paths 32 of the conductive plate 30 in the vertical direction. Multiple first gas passages 61 (three in this example) are provided.

The second gas passage 62 is disposed at the interface between the conductive bonding layer 40 and the conductive plate 30, parallel to the wafer mounting surface 21. Note that "parallel" refers not only to perfect parallelism, but also to imperfect parallelism within an allowable error range (e.g., tolerance). The second gas passage 62 has a groove 31 (first recess) disposed on the upper surface of the conductive plate 30, and the upper surface of the groove 31 is covered by the conductive bonding layer 40. As shown in FIG. 7, the second gas passage 62 is disposed in an annular shape so as to overlap one of multiple imaginary circles C1 to C4 in a plan view. Specifically, of the three second gas passages 62, the first gas passage 62 from the outer periphery of the wafer mounting table 10 overlaps with the imaginary circle C1 with the largest diameter, the second gas passage 62 overlaps with the imaginary circle C2 with the second largest diameter, and the third gas passage 62 overlaps with the imaginary circle C3 with the third largest diameter. Each second gas passage 62 has an overlapping portion 62p (shaded portion in Figure 7) that overlaps with the refrigerant flow path 32 along the refrigerant flow path 32 in a plan view.

The gas auxiliary passage 63 is a passage connecting the first gas passage 61 and the second gas passage 62, and is provided at the interface between the conductive bonding layer 40 and the conductive plate 30, parallel to the wafer mounting surface 21. Multiple (12 in this case) ceramic plate penetrations 50 are provided for each second gas passage 62, but the number of first gas passages 61 and gas auxiliary passages 63 provided is fewer than the number of ceramic plate penetrations 50 (one for each second gas passage 62 in this case).

As shown in FIG. 2, the bonding layer penetrations 64 are holes that penetrate the conductive bonding layer 40 in the vertical direction. The bonding layer penetrations 64 are gas passages that extend from the upper surface of the conductive plate 30 to the lower surface of the ceramic plate 20. Multiple bonding layer penetrations 64 (36 in this example) are provided, and are arranged in one-to-one correspondence with the ceramic plate penetrations 50. In this embodiment, the diameter of the bonding layer penetrations 64 is the same as or larger than the diameter of the lower opening of the ceramic plate penetration 50.

The conductive gas passage 70 is disposed within the gas introduction passage 60, contacts the lower surface of the dense plug 55, is electrically connected to the conductive plate 30, and allows gas to pass between the dense plug 55 and the gas introduction passage 60. The conductive gas passage 70 includes a coating layer 71 and a leaf spring 72. The coating layer 71 covers the lower surface of the dense plug 55, thereby contacting the lower surface of the dense plug 55. The coating layer 71 is formed as a dense layer and has holes 71a that allow gas to pass in the vertical direction. The holes 71a connect the openings of the internal gas flow paths 55a on the lower surface of the dense plug 55 to the gas introduction passage 60. The coating layer 71 can be manufactured, for example, by forming a coating layer on the lower surface of the dense plug 55 by sputtering or electroless plating, and then drilling the holes 71a before press-fitting the dense plug 55 into the ceramic plate 20. The material for the coating layer 71 can be, for example, a metal material, preferably a highly corrosion-resistant metal such as Au, Ag, Al, Ti, SUS316L, or Hastelloy (a Ni-Fe-Mo alloy; Hastelloy is a registered trademark).

The leaf spring 72 is a conductive elastic body that presses the dense plug 55 upward with its elastic force. Examples of materials that can be used for the leaf spring 72 include metal materials such as Al, Ti, Mo, or alloys thereof, steel, SUS316L, and Hastelloy (registered trademark). The leaf spring 72 is manufactured by bending a metal plate, and in this embodiment, the metal plate has a zigzag shape. The zigzag folds of the leaf spring 72 are aligned in the vertical direction. That is, the leaf spring 72 has multiple folds 73 that are folded in the vertical direction. The folds 73 of the leaf spring 72 are formed in a V-shape. The leaf spring 72 has multiple folded portions 73, including one or more (here, multiple, specifically, four) first folded portions 73a folded from top to bottom and one or more (here, multiple, specifically, three) second folded portions 73b folded from bottom to top. Therefore, in this embodiment, the leaf spring 72 is folded seven times. The upper surface 72a of the leaf spring 72 (the upper surface of the first folded portion 73a of the leaf spring 72; also see FIG. 4 ) is in contact with the lower surface of the coating layer 71. The leaf spring 72 is provided across the interior of the ceramic plate penetration portion 50, the interior of the bonding layer penetration portion 64 of the gas introduction passage 60, and the interior of the second gas passage 62. The lower surface 72b of the leaf spring 72 (the lower surface of the second folded portion 73b of the leaf spring 72; see also FIG. 4 ) contacts the conductive plate 30 at a portion of the lower surface (bottom surface) of the second gas passage 62 (groove 31) located directly below the bonding layer penetration portion 64. By contacting the conductive plate 30, the leaf spring 72 is electrically connected to the conductive plate 30. In this embodiment, the zigzag folding direction of the leaf spring 72 is along the vertical direction, so the main direction of expansion and contraction of the leaf spring 72 is the horizontal direction in FIG. 2 , rather than the vertical direction in FIG. 2 , i.e., the direction in which it presses against the dense plug 55. In other words, the leaf spring 72 is arranged horizontally. However, because the leaf spring 72 is zigzag-shaped and is pressed from above by the dense plug 55, it stretches laterally, perpendicular to the vertical direction (the plates of the leaf spring 72 become more tilted from the vertical direction), and as a result, the leaf spring 72 exerts an elastic force in the vertical direction as well, tending to return to its original stretched state (the plates of the leaf spring 72 return to the vertical direction from their tilted state). This elastic force causes the leaf spring 72 to press the dense plug 55 upward. Similarly, the leaf spring 72 also presses the conductive plate 30 downward with its elastic force.

At least one of the shape and placement position of the leaf spring 72 is adjusted so that it does not completely block the holes 71a in the coating layer 71 (and the opening at the lower end of the internal gas flow path 55a) and prevent gas from flowing through them. In this embodiment, as shown in FIG. 2 , the width of each of the four upper surfaces 72a of the leaf spring 72, which come into contact with the coating layer 71, is smaller than the diameter of the holes 71a. This prevents the leaf spring 72 from completely blocking the holes 71a (and the opening at the lower end of the internal gas flow path 55a) regardless of its placement position. Because the coating layer 71 has the holes 71a and the leaf spring 72 does not prevent gas from flowing through the holes 71a, gas in the gas introduction path 60 can flow through and/or around the conductive gas passage 70 and into the ceramic plate penetration 50. In other words, the conductive gas passage 70 allows gas to pass between the dense plug 55 and the gas introduction path 60.

The leaf spring 72 is arranged so that the surface direction of the leaf is aligned with the gas flow direction in the second gas passage 62 in which the leaf spring 72 is arranged (the tangent direction of the arc of the second gas passage 62 shown in FIG. 5) (FIGS. 2 and 3). This makes it less likely that the leaf spring 72 will obstruct the flow of gas in the second gas passage 62. However, the leaf spring 72 may also be arranged so that the surface direction of the leaf is perpendicular to the gas flow direction in the second gas passage 62 in which the leaf spring 72 is arranged.

In this embodiment, multiple conductive gas passages 70 (36 in this example) are provided, and are arranged in one-to-one correspondence with the dense plugs 55. That is, the coating layers 71 and leaf springs 72 are each arranged in one-to-one correspondence with the dense plugs 55.

Next, we will explain an example of how to use the wafer mounting table 10 configured as described above. First, with the wafer mounting table 10 installed in a chamber (not shown), a wafer W is placed on the wafer mounting surface 21. The chamber is then depressurized using a vacuum pump to adjust the pressure to a predetermined level, and a DC voltage is applied to the electrode 22 of the ceramic plate 20 to generate an electrostatic attraction force, thereby adsorbing 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, a reactive gas atmosphere at a predetermined pressure (e.g., several tens to several hundreds of Pa) is created inside the chamber. In this state, an RF voltage is applied between an upper electrode (not shown) installed on the ceiling of the chamber and the conductive plate 30 of the wafer mounting table 10 to generate plasma. The surface of the wafer W is then processed by the generated plasma. A coolant circulates through the coolant flow path 32 of the conductive plate 30. Backside gas is introduced from a gas cylinder into the first gas passage 61 of the gas introduction passage 60. A thermally conductive gas (e.g., He gas) is used as the backside gas. The backside gas introduced into the first gas passage 61 passes through the gas auxiliary passage 63, the second gas passage 62, and the conductive gas passage 70, in this order, and is distributed to the multiple ceramic plate penetrations 50. The gas is then supplied to and sealed in the space between the backside of the wafer W and the reference surface 21c of the wafer mounting surface 21. The presence of this backside gas ensures efficient thermal conduction between the wafer W and the ceramic plate 20. Furthermore, the provision of a dense plug 55 in the ceramic plate penetrations 50 suppresses electrical discharge within the ceramic plate penetrations 50. Furthermore, the curved internal gas flow path 55a suppresses electrical discharge in the internal gas flow path 55a compared to a straight flow path.

Next, a manufacturing example of the wafer mounting table 10 will be described with reference to Figures 8 and 9. Figure 8 is a manufacturing process diagram for the wafer mounting table 10. Figure 9 is an explanatory diagram showing the state of the leaf spring 72 being pressed against the dense plug 55 during the manufacturing of the wafer mounting table 10. Here, an example is shown in which the conductive plate 30 is manufactured using MMC. First, a ceramic plate 20 incorporating an electrode 22 is prepared (Figure 8A). For example, a ceramic powder compact incorporating the electrode 22 is produced, and the compact is hot-press fired to obtain the ceramic plate 20. A ceramic plate penetration 50 is formed in the ceramic plate 20 (Figure 8B). The ceramic plate penetration 50 is formed to penetrate the ceramic plate 20 in the vertical direction, avoiding the electrode 22.

Concurrently, two MMC disk members 81, 82 are prepared (Figure 8C). Then, grooves and holes are formed in these MMC disk members 81, 82 by machining (Figure 8D). Specifically, a groove 32a, which will ultimately become the refrigerant flow path 32, is formed in the underside of the upper MMC disk member 81, and a groove 31, which will ultimately become the second gas passage 62, is formed in the upper surface of the MMC disk member 81. A through-hole 61a, which will ultimately become part of the first gas passage 61, is formed from the groove 31 to the underside of the MMC disk member 81. Furthermore, a through-hole 61b, which will ultimately become part of the first gas passage 61, is formed in the lower MMC disk member 82. If the ceramic plate 20 is made of alumina, the MMC disk members 81, 82 are preferably made of SiSiCTi or AlSiC. This is because the thermal expansion coefficient of alumina can be made roughly the same as that of SiSiCTi or AlSiC.

A SiSiCTi disk member can be produced, for example, as follows: First, silicon carbide, metallic Si, and metallic Ti are mixed to produce a powder mixture. Next, the resulting powder mixture is uniaxially pressed to produce a disk-shaped compact, which is then hot-press sintered in an inert atmosphere to obtain the SiSiCTi disk member.

Next, the ceramic plate 20, MMC disc members 81, and MMC disc members 82 are TCB-bonded together, the overall shape is adjusted, and a dense plug 55 is attached to obtain the wafer mounting table 10 (Figures 8E and 8F). Specifically, a metal bonding material 83 is sandwiched between the upper surface of the lower MMC disc member 82 and the lower surface of the upper MMC disc member 81, and a metal bonding material 90 is sandwiched between the upper surface of the upper MMC disc member 81 and the lower surface of the ceramic plate 20 to obtain a laminate. A through-hole that will eventually become part of the first gas passage 61 is pre-formed in the metal bonding material 83, and a through-hole that will eventually become the bonding layer penetration 64 is pre-formed in the metal bonding material 90. After the metal bonding material 90 is placed on the upper surface of the MMC disc member 81, the leaf spring 72 is pre-inserted into the through-hole that will eventually become the bonding layer penetration 64 and into the recessed groove 31 directly below it. Next, the laminate is pressed and bonded at a temperature below the solidus temperature of the metal bonding materials 83, 90 (for example, a temperature between the solidus temperature minus 20°C and the solidus temperature), and then returned to room temperature. This bonds the two MMC disk members 81, 82 together with the metal bonding material 83 to form the conductive plate 30. The ceramic plate 20 and the conductive plate 30 are also bonded together with the metal bonding material 90. The metal bonding material 90 forms the conductive bonding layer 40. Al-Mg-based bonding materials or Al-Si-Mg-based bonding materials can be used as the metal bonding materials 83, 90. For example, when performing TCB using an Al-Si-Mg-based bonding material, the laminate is pressed while heated in a vacuum atmosphere. It is preferable to use metal bonding materials 83, 90 with a thickness of approximately 100 μm.

The dense plug 55 is attached, for example, as follows. First, a dense plug 55 is prepared by firing, and a coating layer 71 is formed on the underside of the dense plug 55. The dense plug 55 is then inserted from above the ceramic plate penetration 50, bringing the coating layer 71 on the underside of the dense plug 55 into contact with the leaf spring 72 ( Figures 9A and 9B ). The dense plug 55 is then pressed downward. This presses the dense plug 55 into the ceramic plate penetration 50, and the dense plug 55 presses the leaf spring 72 (the dense plug 55 presses the leaf spring 72 via the coating layer 71), causing the leaf spring 72 to elastically deform ( Figure 9C ). As a result, in the manufactured wafer mounting table 10, the leaf spring 72 is arranged stretched in the horizontal direction, perpendicular to the vertical direction. That is, the leaf spring 72 stretches from a horizontal width W1 ( FIG. 9A ), which is the natural length before being pressed against the dense plug 55, to a width W2 ( FIG. 9C ), which is larger than width W1. In addition, as the leaf spring 72 stretches horizontally, it also changes from a vertical height T1 ( FIG. 9A ), which was the height before being pressed against the dense plug 55, to a height T2 ( FIG. 9C ), which is smaller than height T1. As a result, the leaf spring 72 generates elastic force not only in the lateral direction but also in the vertical direction, as described above, and the upper surface 72 a of the leaf spring 72 presses the dense plug 55 upward. In this way, not only does the dense plug 55 contact the leaf spring 72 via the coating layer 71, but by press-fitting the dense plug 55 into the ceramic plate penetration portion 50 so that the dense plug 55 presses downward against the leaf spring 72, the dense plug 55 more reliably contacts the leaf spring 72 via the coating layer 71, thereby ensuring more reliable electrical conduction between the coating layer 71, leaf spring 72, and conductive plate 30.

In the wafer mounting table 10 described above, the conductive gas passage 70 is provided in the gas introduction passage 60 (here, in the second gas passage 62 and the bonding layer penetration portion 64), contacts the underside of the dense plug 55, and is electrically connected to the conductive plate 30. Therefore, the conductive gas passage 70, which has the same potential as the conductive plate 30, contacts the dense plug 55, thereby suppressing discharge around the end of the dense plug 55 facing the conductive plate 30, i.e., around the lower end of the dense plug 55. Note that, for example, discharge around the lower end of the dense plug 55 can be suppressed even if an insulating porous member is present on the underside of the dense plug 55 instead of the conductive gas passage 70. However, the presence of the conductive gas passage 70 makes it less likely for a potential difference to occur around the end of the dense plug 55 facing the conductive plate 30, thereby further suppressing discharge. As a result, in the wafer mounting table 10 of this embodiment, a radio frequency (RF) power supply connected to the conductive plate 30 can be made more powerful than when an insulating porous member is used instead of the conductive gas passage 70. There is a demand for increasing the gas pressure of the backside gas to further improve the efficiency of thermal conduction between the wafer W and the ceramic plate 20. However, increasing the gas pressure generally makes discharge more likely. In the wafer mounting table 10 of this embodiment, the conductive gas passage 70 can further suppress discharge, allowing for a higher gas pressure than when an insulating porous member is used instead of the conductive gas passage 70. Furthermore, the conductive gas passage 70 includes a leaf spring 72 that elastically presses the dense plug 55 upward. This ensures more reliable contact between the dense plug 55 and the leaf spring 72 via the coating layer 71, making it easier to maintain electrical continuity from the contact portion of the conductive gas passage 70 with the dense plug 55 (here, the upper surface of the coating layer 71) to the conductive plate 30. Furthermore, because discharge can be suppressed by the conductive gas passage 70 equipped with the leaf spring 72, it is easy to reduce the height of the space around the lower end of the dense plug 55 (here, the height from the lower surface of the coating layer 71 to the bottom surface of the groove 31) and suppress discharge at the same time. For example, the height of the space around the lower end of the dense plug 55 may be 0.5 mm or less, 0.3 mm or less, or 0.17 mm or less.

Furthermore, the leaf spring 72 is arranged in a state of being stretched laterally, perpendicular to the vertical direction, by being pressed from above by the dense plug 55. This allows the leaf spring 72 to stretch laterally, thereby reducing the area directly below the dense plug 55 where the leaf spring 72 is not present. This further suppresses discharges around the end of the dense plug 55 on the conductive plate 30 side. For example, if the leaf spring 72 is not stretched laterally, as shown in FIG. 9B, there is a concern that the discharge suppression effect will be reduced in the space directly below the dense plug 55 to the left and right of the leaf spring 72. In contrast, by spreading the leaf spring 72 laterally, as shown in FIG. 9C, the discharge suppression effect is enhanced. Furthermore, there are cases in which the leaf spring 72 in the wafer mounting table 10 needs to be replaced, for example, when the elastic force of the leaf spring 72 decreases due to long-term use of the wafer mounting table 10. In this case, in the embodiment described above, removing the dense plug 55 from the ceramic plate 20 of the wafer mounting table 10 returns the leaf spring 72 to its state before it was laterally stretched, as shown in FIG. 9A (the lateral width becomes W1, which is smaller than W2), making it easier to remove and replace the leaf spring 72.

It goes without saying that the present invention is in no way limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

For example, in the above-described embodiment, the ceramic plate penetration portion 50 is provided with a dense plug 55 having an internal gas flow path 55a. However, the ceramic plate penetration portion 50 may be provided with any insulating gas-permeable plug, not limited to the dense plug 55, as long as the insulating gas-permeable plug allows gas to pass through. For example, a porous plug may be used as the insulating gas-permeable plug. Similarly, the coating layer 71 may be any material that allows gas to pass through. For example, the coating layer 71 may be a conductive porous layer without pores 71a. For example, the porous plug 155 and coating layer 171 shown in FIG. 10 are configured as porous bodies. The porous plug 155 may be a porous bulk body obtained by sintering ceramic powder, for example. Examples of ceramics that can be used include alumina and aluminum nitride. The porosity of the porous plug 155 is preferably 30% or more, and the average pore diameter is preferably 20 μm or more. The porosity of the porous plug 155 may be 70% or less. Furthermore, porous plating can be used to form the coating layer 171 as a metal porous layer on the underside of the porous plug 155. The dense plug 55 may be combined with the coating layer 171, or the porous plug 155 may be combined with the coating layer 71. Furthermore, in the above-described embodiment, the coating layer 71 has holes 71a to allow gas to pass through, but the coating layer 71 may cover a portion of the lower surface of the dense plug 55, and the uncovered portion of the lower surface may allow gas to pass through.

In the above-described embodiment, the conductive gas passage 70 does not have to have the coating layer 71. For example, the conductive gas passage 270 shown in FIG. 11 does not have the coating layer 71 but has a leaf spring 72. In FIG. 11, the upper surface 72a of the leaf spring 72 is in direct contact with the dense plug 55, pressing the dense plug 55 upward with its elastic force. Even in this case, as in the above-described embodiment, discharge can be suppressed around the end of the dense plug 55 on the conductive plate 30 side, i.e., around the lower end of the dense plug 55.

In the above-described embodiment, the leaf spring 72 is arranged in a state of extending horizontally, perpendicular to the up-down direction, by being pressed from above by the dense plug 55. However, this is not limited to this; the leaf spring 72 does not have to extend horizontally. For example, the leaf spring 372 shown in FIG. 12 has a zigzag fold that runs horizontally and has multiple (here, two) folded portions 373 that are folded horizontally. The multiple folded portions 373 of the leaf spring 372 include one or more (here, one) first folded portions 373a that are folded from left to right and one or more (here, one) second folded portions 373b that are folded from right to left. Therefore, the extension direction of the leaf spring 372 is the up-down direction, i.e., the direction in which it presses against the dense plug 55. In other words, the leaf spring 372 is arranged vertically. This leaf spring 372 can also press the dense plug 55 upward with its elastic force, making it easier to maintain conductivity from the contact portion of the conductive gas passage 70 with the dense plug 55 (here, the upper surface of the coating layer 71) to the conductive plate 30.

In the above-described embodiment, the folded portion 73 of the leaf spring 72 is formed in a V-shape, but this is not limited thereto. For example, the wafer mounting table 10 may be equipped with a leaf spring 472 shown in FIG. 13 instead of the leaf spring 72. The leaf spring 472 has multiple folded portions 473 folded in the vertical direction. The multiple folded portions 473 of the leaf spring 472 include one or more (here, multiple, specifically, four) first folded portions 473a folded from top to bottom and one or more (here, multiple, specifically, three) second folded portions 473b folded from bottom to top. Therefore, the leaf spring 472 is folded seven times. The first folded portion 473a extends horizontally and has a first plate-shaped portion 475 whose upper surface forms the upper surface 472a of the leaf spring 472. The second folded portion 473b has a second plate-shaped portion 476 extending horizontally and whose lower surface constitutes the lower surface 472b of the leaf spring 472. Therefore, each of the folded portions 473 of the leaf spring 472 is trapezoidal, not V-shaped, but has an upper base and adjacent hypotenuses. The leaf spring 472 shown in FIG. 13 , like the leaf spring 72, is pressed from above by the dense plug 55 and arranged in a state stretched in a lateral direction perpendicular to the up-down direction. The leaf spring 472 has the first plate-shaped portion 475, which makes it easier to widen the horizontal width of the upper surface 472a compared to, for example, the upper surface 72a of the leaf spring 72 shown in FIG. 2 . This increases the contact area between the upper surface 472a and the member above the leaf spring 472 (here, the coating layer 71). Similarly, the leaf spring 472 has a second plate-shaped portion 476, which makes it easier to increase the horizontal width of the lower surface 472b compared to the lower surface 72b of the leaf spring 72 in FIG. 2 . This increases the contact area between the lower surface 472b and the component below the leaf spring 472 (here, the conductive plate 30). This allows for more reliable contact between the leaf spring 472 and the components above and below it, thereby more reliably maintaining electrical continuity from the contact portion of the conductive gas passage 70 with the dense plug 55 to the conductive plate 30. Furthermore, the large contact area between the leaf spring 472 and the components above and below it reduces contact resistance, enhancing the effectiveness of suppressing discharge around the lower end of the dense plug 55. The leaf spring 72 of the above-described embodiment can be considered a leaf spring 472 without the first plate-shaped portion 475 and second plate-shaped portion 476.

In the leaf spring 472 shown in FIG. 13, the corners of the leaf spring 472 may be curved as shown in FIG. 14. This prevents electric field concentration at the corners of the leaf spring 472, thereby further suppressing discharge around the lower end of the dense plug 55. The corners of the leaf spring 72 and leaf spring 372 may also be curved in a similar manner.

While the leaf spring 72 shown in FIG. 2 and the leaf spring 472 shown in FIG. 13 have seven folds, the number of folds of the leaf spring is not limited to seven, and may be any number of folds, as long as it is one or more, and may be multiple folds. For example, the leaf spring 572 shown in FIG. 15 is a leaf spring 472 with three folds. The leaf spring 572 has multiple folds 573 folded in the vertical direction. The multiple folds 573 of the leaf spring 572 include two first folds 573a folded from top to bottom and one second fold 573b folded from bottom to top. The first fold 573a has a first plate-shaped portion 575 extending horizontally and whose upper surface forms the upper surface 572a of the leaf spring 572. The second folded portion 573b has a second plate-shaped portion 576 that extends horizontally and whose lower surface forms the lower surface 572b of the leaf spring 572. Similar to the leaf spring 72, the leaf spring 572 shown in FIG. 15 is arranged in a state where it is stretched in the horizontal direction perpendicular to the up-down direction by being pressed from above by the dense plug 55. Reducing the number of folds, as in the case of the leaf spring 572, makes it easier to reduce the volume of the leaf spring, and reducing the volume makes it less likely that the leaf spring 572 will obstruct the flow of gas within the gas introduction passage 60.

In the above-described embodiment, the shape and/or placement of the leaf spring 72 was adjusted so as not to completely block the hole 71a in the coating layer 71 (and the opening at the lower end of the internal gas flow path 55a) and prevent gas flow. In this case, the leaf spring 72 may block a portion of the hole 71a in the coating layer 71, i.e., the upper surface 72a of the leaf spring 72 may overlap a portion of the hole 71a in a planar view. However, it is preferable that the upper surface 72a of the leaf spring 72 not overlap any portion of the hole 71a in a planar view. Furthermore, horizontal positional displacement of the leaf spring 72 may occur within the gas introduction path 60. Therefore, it is more preferable that the opening at the lower end of the internal gas flow path 55a be located outside the range of movement of the upper surface 72a of the leaf spring 72 within the gas introduction path 60 in a planar view. The same applies to leaf springs 372, 472, and 572. This will be described in detail using leaf spring 572 as an example. FIG. 16 is an explanatory diagram showing the positions of the upper surface 572a of the leaf spring 572 and the internal gas flow passage 55a in a plan view. FIG. 17 is an explanatory diagram showing the horizontal movement range of the leaf spring 572. In FIG. 16, the outline of the upper surface 572a of the leaf spring 572 (i.e., the outline of the first plate-shaped portion 575) is shown by a dashed line, the outline of the lower end surface of the dense plug 55 and the outline of the opening at the lower end of the internal gas flow passage 55a are shown by a dashed line, and the outline of the gas introduction passage 60 (more specifically, the groove 31 of the second gas passage 62) is shown by a two-dot chain line. The outline of the opening at the lower end of the internal gas flow passage 55a and the outline of the opening of the hole 71a in the coating layer 71 are located at the same position in a plan view. In FIG. 17, the leaf spring 572 is shown in the leftmost position within the groove 31 by a solid line, and in the rightmost position within the groove 31 by a dashed line. 16, the upper surface 572a of the leaf spring 572 does not overlap with the opening at the lower end of the internal gas flow path 55a, but if the leaf spring 572 is misaligned within the groove 31 of the gas introduction path 60, the position of the upper surface 572a also changes. However, as shown in FIG. 17, the opening at the lower end of the internal gas flow path 55a (and the hole 71a) does not overlap with the ranges M1 and M2 of movement caused by the misalignment of the upper surface 572a within the groove 31, and is located outside the ranges M1 and M2. Therefore, no matter how much the leaf spring 572 is misaligned left and right, the upper surface 572a will not overlap with the opening at the lower end of the internal gas flow path 55a (and the hole 71a) in a plan view. 17 only shows the ranges M1 and M2 of movement of the upper surface 572a due to lateral misalignment of the leaf spring 572, but it is preferable that the opening at the lower end of the internal gas flow path 55a (and the hole 71a) be positioned outside the range of movement of the upper surface 572a due to misalignment, regardless of any horizontal misalignment (including rotation along the horizontal direction). For example, the opening at the lower end of the internal gas flow path 55a (and the hole 71a) can be positioned outside the range of movement of the upper surface 572a due to misalignment by reducing the difference between the left and right widths of the leaf spring 572 and the left and right widths of the recessed groove 31, or by reducing the diameter of the opening at the lower end of the ceramic plate penetration portion 50 so that the range of movement of the upper end of the leaf spring 572 is restricted by this opening diameter. As a result, even if the leaf spring 572 becomes misaligned within the gas introduction passage 60, the upper surface 572a of the leaf spring 572 does not overlap the opening at the lower end of the internal gas flow passage 55a in a plan view, and the leaf spring 572 is therefore less likely to obstruct the flow of gas between the gas introduction passage 60 and the internal gas flow passage 55a.

The above-mentioned leaf springs 72, 372, 472, and 572 may be configured to have holes that allow gas to pass through. For example, in the example shown in Figures 18 and 19, a hole 672c that allows gas to pass through is provided in the plate-shaped portion of leaf spring 472 that is inclined from the vertical direction. This makes it less likely that leaf spring 472 will obstruct the flow of gas, allowing gas to pass through the conductive gas passage 70 more easily.

The above-described leaf springs 72, 372, 472, and 572 may be provided with an insertion hole for inserting a tool for holding the leaf spring, such as tweezers, when replacing the leaf spring. There may be two or more such holes. A hole that allows gas to pass through, such as hole 672c shown in Figures 18 and 19, may also serve as this insertion hole.

In the above-described embodiment, the leaf spring 72 has a shape formed by bending a metal plate into a zigzag shape, but this is not limited to this. For example, the leaf spring 72 may be a U-shaped leaf spring.

In the above-described embodiment, the second gas passage 62 is formed by having a groove 31 (first recess) on the upper surface of the conductive plate 30 and placing the lower surface (flat surface) of the conductive bonding layer 40 on the groove 31. However, this is not particularly limited. For example, the second gas passage 62 may be formed by having a groove (second recess) on the lower surface of the conductive bonding layer 40 and placing the upper surface (flat surface) of the conductive plate 30 below the groove. Alternatively, the conductive bonding layer 40 may have a two-layer structure, with a groove (groove penetrating in the vertical direction) that will ultimately become the second gas passage 62 in the lower layer and the above-described bonding layer penetration 64 in the upper layer. In this case, too, a conductive gas passage 70 is provided inside the gas introduction passage 60 (bonding layer penetration 64). The conductive gas passage 70 is provided so as to contact the lower surface of the dense plug 55 and be electrically connected to the conductive plate 30, thereby suppressing discharge around the end of the dense plug 55 facing the conductive plate 30.

In the above-described embodiment, the second gas passage 62 and the auxiliary gas passage 63 may be omitted, and multiple first gas passages 61 may be connected one-to-one to multiple ceramic plate penetrations 50.

In the above-described embodiment, the upper surface of the dense plug 55 is at the same height as the reference surface 21c of the wafer mounting surface 21, but this is not particularly limited. For example, the difference between the height of the reference surface 21c of the wafer mounting surface 21 and the height of the upper surface of the dense plug 55 may be 0.5 mm or less (preferably 0.2 mm or less, more preferably 0.1 mm or less). In other words, the upper surface of the dense plug 55 may be positioned 0.5 mm or less (preferably 0.2 mm or less, more preferably 0.1 mm or less) lower than the reference surface 21c of the wafer mounting surface 21. Even in this case, the height of the space between the lower surface of the wafer W and the upper surface of the dense plug 55 can be kept relatively low. This prevents glow discharge and, ultimately, arc discharge from occurring in this space.

In the above-described embodiment, the ceramic plate 20 and the conductive plate 30 are joined by the conductive bonding layer 40. However, a non-conductive bonding layer, such as a resin bonding layer, may be used instead of the conductive bonding layer 40. In this case, metals such as Al and Ti can be used for the conductive plate. If the conductive bonding layer 40 is a resin bonding layer, the ceramic plate 20 and the conductive plate 30 may be joined via the resin bonding layer while being pressurized in an autoclave.

In the above-described embodiment, the ceramic plate 20 incorporates an electrostatic electrode as the electrode 22. However, instead of or in addition to this, a heater electrode (resistance heating element) may be incorporated. In this case, a heater power supply is connected to the heater electrode. The ceramic plate 20 may incorporate a single layer of electrodes, or two or more layers spaced apart.

In the above-described embodiment, lift pin holes may be provided that penetrate the wafer mounting table 10. The lift pin holes are holes for inserting lift pins that move the wafer W up and down relative to the wafer mounting surface 21. When the wafer W is supported by, for example, three lift pins, lift pin holes are provided in three locations.

In the above-described embodiment, the ceramic plate 20 was produced by hot-pressing and firing a ceramic powder compact. However, the compact may also be produced by stacking multiple tape compacts, by mold casting, or by compressing ceramic powder.

In the above-described embodiment, the dense plug 55 is fixed by being press-fitted into the ceramic plate penetration portion 50, but this is not limited to this. For example, the outer peripheral surface of the dense plug 55 and the inner peripheral surface of the ceramic plate penetration portion 50 may be bonded together, or a male threaded portion on the outer peripheral surface of the dense plug 55 may be threaded into a female threaded portion on the inner peripheral surface of the ceramic plate penetration portion 50.

In the enlarged cross-sectional view of Figure 2, the diameter of the bonding layer penetration 64 is shown as being the same as the diameter of the lower opening of the ceramic plate penetration 50. However, as described above, the diameter of the bonding layer penetration 64 may be larger than the diameter of the lower opening of the ceramic plate penetration 50. In this case, the configuration shown in Figure 20 may be adopted. In Figure 20, the wafer mounting table 10 has a non-conductive (insulating) insulating bonding layer 740 such as a resin bonding layer instead of the conductive bonding layer 40. Resins used for the insulating bonding layer 740 include silicone resin, acrylic resin, polyimide resin, and epoxy resin. Furthermore, a leaf spring 772 is provided instead of the leaf spring 72. This insulating bonding layer 740 has a bonding layer penetration 764, which is a hole that vertically penetrates the insulating bonding layer 740. The bonding layer penetration 764 is part of the gas introduction passage 60 and is a gas passage from the second gas passage 62 to the hole 71a in the coating layer 71. As shown in FIG. 20 , the diameter of the bonding layer through-hole 764 is larger than the diameter of the lower opening of the ceramic plate through-hole 50. Therefore, a portion of the lower surface of the ceramic plate 20 (around the opening of the ceramic plate through-hole 50) is located directly above the bonding layer through-hole 764 and is exposed to the bonding layer through-hole 764 of the gas introduction passage 60. However, in FIG. 20 , the conductive layer 25 is disposed so as to cover the portion of the lower surface of the ceramic plate 20 exposed to the bonding layer through-hole 764. Therefore, the presence of the bonding layer through-hole 764 prevents the lower surface of the ceramic plate 20 from being exposed to the bonding layer through-hole 764. The conductive layer 25 has a larger diameter than the bonding layer through-hole 764 in a top view, and as shown in FIG. 20 , a portion of the conductive layer 25 is sandwiched between the lower surface of the ceramic plate 20 and the upper surface of the insulating bonding layer 740. The conductive layer 25 may be any conductive material, and may be made of the same material (e.g., a metal material) as the material of the coating layer 71 described above. Like the coating layer 71, the conductive layer 25 may be a layer formed in advance on the underside of the ceramic plate 20 by sputtering, electroless plating, or the like. The leaf spring 772 has multiple folded portions 773, including two first folded portions 773a folded from top to bottom and three second folded portions 773b folded from bottom to top. Like the leaf spring 72, the leaf spring 772 is pressed from above by the dense plug 55, thereby extending in a lateral direction perpendicular to the up-down direction. Similarly to the leaf spring 72, the upper surface 772a of the first folded portions 773a contacts the lower surface of the coating layer 71, and the lower surface 772b of the second folded portions 773b contacts the conductive plate 30, thereby electrically connecting the coating layer 71 and the conductive plate 30. Furthermore, the leaf spring 772 also contacts the conductive layer 25. Specifically, the upper surface 774a of each of the two plate-shaped members located at both ends of the leaf spring 772 contacts the lower surface of the conductive layer 25. Thus, in FIG. 20 , the portion of the underside of the ceramic plate 20 exposed to the bonding layer penetration 764 of the gas introduction passage 60 is covered with the conductive layer 25, and the conductive layer 25 contacts the leaf spring 772, thereby establishing electrical conduction with the conductive plate 30 via the leaf spring 772. Therefore, a potential difference is unlikely to occur around the portion of the underside of the ceramic plate 20 facing the gas introduction passage 60 (the portion of the underside of the ceramic plate 20 located directly above the bonding layer penetration 764 in FIG. 20 ). This suppresses discharge around the portion of the underside of the ceramic plate 20 facing the gas introduction passage 60.

20, unlike FIG. 2, the lower end of the dense plug 55 protrudes below the underside of the ceramic plate 20. In the leaf spring 772 of FIG. 20, the length of the two plate-shaped members located at the left and right ends is longer than the four plate-shaped members located at other positions so that they can reliably contact the conductive layer 25 even in such cases. However, even if the multiple (here, six) plate-shaped members are all the same length, the height of only the plate-shaped members in the portion of the leaf spring 772 that is pressed against the dense plug 55 becomes smaller (the angle of inclination of the plate-shaped members relative to the vertical direction becomes larger), so that the upper surfaces 774a of the plate-shaped members that are not pressed against the dense plug 55 (here, the two plate-shaped members located at the left and right ends) can be brought into contact with the conductive layer 25.

20, the leaf spring 772 contacts both the coating layer 71 and the conductive layer 25, electrically connecting them to the conductive plate 30. Alternatively, a conductive member separate from the leaf spring 772 may be provided on the wafer mounting table 10 to electrically connect the conductive layer 25 and the conductive plate 30. For example, in the example shown in FIG. 21, the wafer mounting table 10 includes a leaf spring 872 instead of the leaf spring 772 shown in FIG. 20, and also includes a conductive member 875. The leaf spring 872 has multiple folded portions 873, including one first folded portion 873a folded from top to bottom and two second folded portions 873b folded from bottom to top. Like the leaf spring 772, the leaf spring 872 is pressed from above by the dense plug 55, stretching it in a horizontal direction perpendicular to the vertical direction. Similar to the leaf spring 772, the leaf spring 872 has an upper surface 872a of the first folded portion 873a in contact with the lower surface of the coating layer 71, and a lower surface 872b of the second folded portion 873b in contact with the conductive plate 30. Unlike the leaf spring 772, the leaf spring 872 also has upper surfaces 874a of the two plate-shaped members located at both ends in contact with the lower surface of the coating layer 71. This provides electrical continuity between the coating layer 71 and the conductive plate 30. Meanwhile, the leaf spring 872 does not contact the conductive layer 25. The conductive member 875 is a conductive elastic body and is configured as a coil spring in FIG. 21 . The conductive member 875 can be made of the same material (e.g., a metal material) as the leaf spring 72 described above. The conductive member 875 is disposed in the gas introduction passage 60 so that the axial direction of the coil is in the vertical direction, with its upper end in contact with the lower surface of the conductive layer 25 and its lower end in contact with the conductive plate 30. This allows the conductive member 875 to electrically connect the conductive layer 25 and the conductive plate 30. The leaf spring 872 is disposed inside the coil of the conductive member 875. That is, the leaf spring 872 is surrounded by the conductive member 875 in a top view. The conductive member 875 expands and contracts in the vertical direction, and is disposed in the gas introduction passage 60 in a state contracted from its natural length. Therefore, the conductive member 875 presses the conductive layer 25 upward with its elastic force. Similarly, the conductive member 875 presses the conductive plate 30 downward with its elastic force. In this way, even when a conductive member 875 provided separately from the leaf spring 872 electrically connects the conductive layer 25 and the conductive plate 30, discharge can be suppressed around the portion of the underside of the ceramic plate 20 that faces the inside of the gas introduction passage 60, as in the embodiment shown in Figure 20. Furthermore, because the conductive member 875 presses the conductive layer 25 upward with its elastic force, conductivity from the conductive layer 25 to the conductive plate 30 is easily maintained.

The conductive member 875 is not limited to a coil spring as long as it is an elastic member. For example, the conductive member 875 may be a leaf spring separate from the leaf spring 872. However, gas passes more easily through a coil spring in the axial direction of the coil or between the wires than through a leaf spring. Furthermore, by placing the leaf spring 872 inside the coil of the conductive member 875, the leaf spring 872 and the conductive member 875 can be arranged compactly in the gas introduction passage 60. Therefore, when the conductive member 875 is used as a separate member from the leaf spring 872, it is preferable that the conductive member 875 be a coil spring. Note that the conductive member 875 does not have to be an elastic member as long as it is conductive. However, as described above, it is preferable that the conductive member 875 be an elastic member because this makes it easier to maintain conductivity between the conductor layer 25 and the conductive plate 30.

20 and 21, if the lower end surface of the dense plug 55 is positioned at the same height as or close to the lower surface of the ceramic plate 20, the conductive layer 25 and the coating layer 71 will come into contact and become conductive. In this case, even if the leaf spring 772 or conductive member 875 is not in contact with the conductive layer 25, electrical continuity can be achieved between the conductive layer 25 and the conductive plate 30. Furthermore, during the manufacture of the wafer mounting table 10, before bonding the ceramic plate 20 and the conductive plate 30, the dense plug 55 can be inserted into the ceramic plate 20 so that the lower end surface of the dense plug 55 is positioned at the same height as or close to the lower surface of the ceramic plate 20, thereby integrally forming the coating layer 71 and the conductive layer 25. However, because misalignment of the dense plug 55 may prevent the coating layer 71 and the conductive layer 25 from coming into contact, it is preferable for the leaf spring 772 to come into contact with the conductive layer 25, as shown in FIG. 20.

In Figures 20 and 21, the conductive layer 25 covers the entire portion of the underside of the ceramic plate 20 that is exposed at the bonding layer penetration portion 764, but this is not limited to this and it may cover only a portion. However, it is preferable to cover the entire portion as shown in Figures 20 and 21.

In the above-described embodiment, the conductive gas passage 70 includes a coating layer 71 and a leaf spring 72, and the leaf spring 72 is in direct contact with the conductive plate 30 for electrical conduction. However, this is not limited to this. For example, the conductive gas passage 70 may include a gas passage member that electrically connects the conductive plate 30 and the leaf spring 72. FIG. 22 is a partially enlarged cross-sectional view showing a gas passage member 975. The conductive gas passage 70 in FIG. 22 includes a coating layer 71, a leaf spring 972, and a gas passage member 975. Also, in FIG. 22, an insulating bonding layer 940 made of the same material as the insulating bonding layer 740 in FIG. 20 bonds the ceramic plate 20 and the conductive plate 30. The insulating bonding layer 940 includes a bonding layer penetration 964, which is a hole that vertically penetrates the insulating bonding layer 940. The bonding layer penetration 964 constitutes part of the gas introduction passage 60. The leaf spring 972 has multiple folded portions 973, including two first folded portions 973a folded from top to bottom and one second folded portion 973b folded from bottom to top. Like the leaf spring 72, the leaf spring 972 is pressed from above by the dense plug 55, thereby extending in a horizontal direction perpendicular to the up-down direction. The upper surface 972a of the leaf spring 972 contacts the lower surface of the coating layer 71, and the lower surface 972b contacts the upper surface of the gas passage member 975. The gas passage member 975 is a conductive member that allows gas to pass between the dense plug 55 and the second gas passage 62. The gas passage member 975 is, for example, a generally cylindrical member that is circular in top view. The upper surface of the gas passage member 975 contacts the lower surface 972b of the leaf spring 972, and the lower surface contacts the upper surface of the conductive plate 30. As a result, the gas passage member 975 electrically connects the leaf spring 972 and the conductive plate 30. The gas passage member 975 has a hole 975a penetrating the gas passage member 975 in the vertical direction. Gas from the second gas passage 62 can reach the hole 71a in the coating layer 71 through the hole 975a and the bonding layer penetration portion 964. Examples of materials for the gas passage member 975 include metal. The material for the gas passage member 975 is preferably low-resistance and non-magnetic. The material for the gas passage member 975 is preferably selected to have a thermal expansion coefficient close to that of the ceramic plate 20 and the conductive plate 30. Specific examples of materials for the gas passage member 975 include Ti. The gas passage member 975 may be a component independent of the conductive plate 30, or may be a film formed on the upper surface of the conductive plate 30. Even when the conductive gas passage 70 has the gas passage member 975 in this way, similar to the above-described embodiment, discharge can be suppressed around the end of the dense plug 55 on the conductive plate 30 side, i.e., around the lower end of the dense plug 55.

Furthermore, as shown in FIG. 22 , the presence of the gas passage member 975 occupies a portion of the bonding layer penetration portion 964, allowing the height T3 of the space within the bonding layer penetration portion 964 to be smaller than the thickness T4 of the insulating bonding layer 940 (i.e., the overall height of the bonding layer penetration portion 964). This allows for suppression of discharge within the bonding layer penetration portion 964. The thickness T3 is preferably 0.2 mm or less, and more preferably 0.1 mm or less. Because the presence of the gas passage member 975 reduces the height T3 and suppresses discharge, unlike FIG. 20 , in FIG. 22 , a conductive layer 25 is not provided on the exposed portion of the underside of the ceramic plate 20. Therefore, discharge within the bonding layer penetration portion 964 can be suppressed without the conductive layer 25. Of course, a conductive layer 25 may also be provided on the underside of the ceramic plate 20, as in FIG. 22 . Furthermore, the presence of the gas passage member 975 allows the height T3 to be reduced and discharge to be suppressed, making it easier to both suppress discharge and increase the thickness T4 of the insulating bonding layer 940 to increase the thermal resistance of the insulating bonding layer 940. Increasing the thermal resistance of the insulating bonding layer 940 suppresses heat conduction from the ceramic plate 20 to the conductive plate 30, thereby suppressing cooling of the wafer W. Suppressing cooling of the wafer W also allows the wafer W to be heated to a higher temperature, for example. Note that, because conductors generally have lower thermal resistance than insulators, from the perspective of increasing thermal resistance, it is preferable to bond the ceramic plate 20 and the conductive plate 30 with the insulating bonding layer 940 rather than the conductive bonding layer 40.

When suppressing discharge within the bonding layer penetration portion 964 by having the gas passage member 975 occupy a portion of the bonding layer penetration portion 964, it is preferable to minimize the gap (space) between the side of the gas passage member 975 (the left and right sides in FIG. 22 ) and the insulating bonding layer 940. It is more preferable that the side of the gas passage member 975 be in contact with the insulating bonding layer 940, and even more preferable that the entire side of the gas passage member 975 be in contact with the insulating bonding layer 940, with no gap, as shown in FIG. 22 . Furthermore, in FIG. 22 , a portion of the insulating bonding layer 940 forms a protruding portion 940a that covers part of the upper surface of the gas passage member 975. Therefore, the diameter of the space portion of the bonding layer penetration portion 964 above the gas passage member 975 is smaller than the diameter of the gas passage member 975. The protruding portion 940a separates a gap from the space above the gas passage member 975 in the bonding layer penetration portion 964, even if a gap exists in a portion of the side surface of the gas passage member 975. This also suppresses discharge. For example, by utilizing the fact that the insulating bonding layer 940 collapses when the ceramic plate 20 and the conductive plate 30 are bonded, it is possible to eliminate a gap between the side surface of the gas passage member 975 and the insulating bonding layer 940 or to form the protruding portion 940a. FIG. 23 is an explanatory diagram showing how the ceramic plate 20 and the conductive plate 30 are bonded by the insulating bonding layer 940. When manufacturing the wafer mounting table 10, as shown in FIG. 23A , a sheet-like insulating bonding material 990 is placed on the upper surface of the conductive plate 30 (or the MMC disc member 81), and the gas passage member 975 and the leaf spring 972 are placed in a through-hole pre-formed in the insulating bonding material 990. The through-hole of the insulating bonding material 990 is formed to have a diameter larger than the final diameter of the bonding layer penetration portion 964 of the insulating bonding layer 940. In this state, as shown in FIG. 23A , a gap may exist between the side surface of the gas passage member 975 and the insulating bonding material 990. After the gas passage member 975 and the leaf spring 972 are arranged in this manner, the insulating bonding material 990 is sandwiched between the ceramic plate 20 and the conductive plate 30, and the insulating bonding material 990 is heated and pressurized to bond the ceramic plate 20 and the conductive plate 30 together. As a result, the insulating bonding material 990 becomes the insulating bonding layer 940 ( FIG. 23B ). Then, a dense plug 55 is installed, resulting in the state shown in FIG. 22 . When the ceramic plate 20 and the conductive plate 30 are joined, the insulating bonding material 990 is compressed by pressure from above and below, narrowing the through hole of the insulating bonding material 990 in which the gas passage member 975 is disposed, forming a bonding layer through-hole 964. This allows the side of the gas passage member 975 to be in contact with the insulating bonding layer 940, eliminating a gap between the side of the gas passage member 975 and the insulating bonding layer 940. Furthermore, when the through hole of the insulating bonding material 990 narrows, a portion of the insulating bonding material 990 protrudes onto the gas passage member 975, forming a protruding portion 940a. By adjusting the diameter of the through hole of the insulating bonding material 990 and the diameter of the gas passage member 975, it is possible to adjust the degree of contact between the side of the gas passage member 975 and the insulating bonding layer 940, the protruding amount of the protruding portion 940a, and whether or not the protruding portion 940a is present. From the standpoint of ensuring gas flow within the bonding layer penetrating portion 964, it is preferable that the protruding portion 940a not be located directly below the hole 71a (i.e., not block a portion of the hole 71a). As shown in FIG. 22, it is even more preferable that the protruding portion 940a not be located directly below the lower surface of the dense plug 55 (and the coating layer 71).

As shown in FIG. 22 , the diameter of the gas passage member 975 is preferably larger than the lower surface (and coating layer 71) of the dense plug 55. More specifically, the gas passage member 975 and the dense plug 55 are preferably positioned such that the lower surface (and coating layer 71) of the dense plug 55 is included inside the contour of the upper surface of the gas passage member 975 when viewed from above. In this way, the gas passage member 975 extends outside the lower surface (and coating layer 71) of the dense plug 55 when viewed from above, making it easier to ensure that the side of the gas passage member 975 and the insulating bonding layer 940 are in contact and that the protruding portion 940a is not directly below the lower surface (and coating layer 71) of the dense plug 55.

In Figure 22, gas passes through the holes 975a of the gas passage member 975, but it is sufficient that the gas can pass through the gas passage member 975; for example, the gas passage member 975 may be porous. In this case, the porosity of the gas passage member 975 may be 50% or more and 80% or less. The gas passage member 975 may also be elastic. For example, by making the gas passage member 975 a porous metal (porous metal), the gas passage member 975 can be made to be an elastic member that allows gas to pass through.

In Figure 22, it has been explained that the conductive gas passage section 70 may have a gas passage member 975 that provides electrical continuity between the leaf spring 972 and the conductive plate 30. Similarly, the conductive gas passage section 70 may have a gas passage member that provides electrical continuity between the leaf spring 972 and the coating layer 71. For example, the positional relationship between the leaf spring 972 and the gas passage member 975 in Figure 22 may be reversed upside down. Alternatively, gas passage members similar to the gas passage member 975 may be arranged above and below the leaf spring 72.

The present invention can be used, for example, in wafer processing devices.

10 wafer mounting table, 20 ceramic plate, 21 wafer mounting surface, 21a seal band, 21b small circular protrusion, 21c reference surface, 22 electrode, 25 conductive layer, 30 conductive plate, 31 groove, 32 coolant flow path, 32a groove, 40 conductive bonding layer, 50 ceramic plate penetration, 55 dense plug, 55a internal gas flow path, 60 gas introduction passage, 61 first gas passage, 61a through hole, 61b through hole, 62 second gas passage, 62p overlapping portion, 63 auxiliary gas passage, 64, 764, 964 bonding layer penetration, 65 third gas passage, 66 fourth gas passage, 70, 270 conductive gas passage, 71, 171 coating layer, 71a Hole, 72, 372, 472, 572, 772, 872, 972 Leaf spring, 72a, 472a, 572a, 772a, 872a, 972a Upper surface, 72b, 472b, 572b, 772b, 872b, 972b Lower surface, 73, 373, 473, 573, 773, 873, 973 Folded portion, 73a, 373a, 473a, 573a, 773a, 873a, 973a First folded portion, 73b, 373b, 473b, 573b, 773b, 873b, 973b Second folded portion, 81, 82 MMC disc member, 83, 90 Metal joining material, 155 Porous plug, 475, 575 First plate-shaped portion, 476, 576; second plate-shaped portion, 672c; hole, 740, 940; insulating bonding layer, 774a, 874a; upper surface, 875; conductive member, 940a; protruding portion, 975; gas passage member, 975a; hole, 990; insulating bonding material.

Claims (13)

a ceramic plate having a wafer mounting surface on its upper surface and incorporating an electrode;
a conductive plate bonded to the lower surface of the ceramic plate;
a ceramic plate penetration portion that penetrates the ceramic plate;
an insulating gas-passing plug that is provided in the ceramic plate penetration part and allows gas to pass therethrough;
a gas introduction passage provided at least inside the conductive plate and communicating with the ceramic plate penetration portion;
a conductive gas passage provided in the gas introduction passage, in contact with a lower surface of the insulating gas passage plug, electrically connected to the conductive plate, and allowing gas to pass between the insulating gas passage plug and the gas introduction passage;
Equipped with
the conductive gas passage portion has a leaf spring that presses the insulating gas passage plug upward with an elastic force;
Wafer stage. 2. The wafer mounting table according to claim 1,
the leaf spring is arranged in a state of being stretched in a horizontal direction perpendicular to the up-down direction by being pressed from above by the insulating gas passing plug;
Wafer stage. 3. The wafer mounting table according to claim 2,
The leaf spring has a plurality of folded portions folded along the up-down direction.
Wafer stage. 4. The wafer mounting table according to claim 3,
the plurality of folded portions include a first folded portion folded from top to bottom and a second folded portion folded from bottom to top,
the first folded portion has a first plate-shaped portion extending along a horizontal direction and having an upper surface that constitutes an upper surface of the leaf spring;
The second folded portion has a second plate-shaped portion extending along the horizontal direction and having a lower surface that constitutes the lower surface of the leaf spring.
Wafer stage. The wafer mounting table according to any one of claims 1 to 4,
the conductive gas passage portion has a coating layer that covers the lower surface of the insulating gas passage plug.
Wafer stage. The wafer mounting table according to any one of claims 1 to 4,
the insulating gas-permeable plug is a dense body having an internal gas flow path, or a porous body;
Wafer stage. The wafer mounting table according to any one of claims 1 to 4,
the insulating gas-permeable plug is a dense body having an internal gas flow path,
an opening at a lower end of the internal gas flow path is located outside a range of movement of the upper surface of the leaf spring within the gas introduction passage due to positional displacement in a plan view;
Wafer stage. The wafer mounting table according to any one of claims 1 to 4,
The leaf spring has a hole that allows gas to pass through.
Wafer stage. 6. The wafer mounting table according to claim 5,
a conductive layer covering a portion of the lower surface of the ceramic plate that is exposed to the gas introduction passage;
Equipped with
the leaf spring is in contact with the conductive layer;
Wafer stage. 6. The wafer mounting table according to claim 5,
a conductive layer covering a portion of the lower surface of the ceramic plate that is exposed in the gas introduction passage;
a conductive member in contact with the conductive plate and the conductive layer, respectively;
A wafer mounting table comprising: The wafer mounting table according to claim 10,
the conductive member is an elastic body that presses the conductive layer upward with an elastic force;
Wafer stage. The wafer mounting table according to any one of claims 1 to 4,
the conductive gas passage portion has a gas passage member that electrically connects the conductive plate and the leaf spring.
Wafer stage. The wafer stage according to claim 12,
The gas passage member is an elastic body.
Wafer stage.