electrostatic chuck

Abstract

The present invention provides an electrostatic chuck capable of suppressing variations in the in-plane temperature distribution of a substrate. [Solution] The electrostatic chuck 10 comprises a dielectric substrate 100 having a plurality of gas holes 140 formed thereon, a base plate 200 supporting the dielectric substrate 100, and a bonding layer 300 that bonds the dielectric substrate 100 and the base plate 200. The bonding layer 300 includes a first bonding layer 310 and a second bonding layer 320 that surrounds the first bonding layer 310 in an annular shape from the outer circumference. The thermal conductivity of the first bonding layer 310 is higher than that of the first bonding layer 310. When the gas hole 140 formed at the outermost position among the plurality of gas holes 140 is called the outermost gas hole 140A, the inner end of the second bonding layer 320 is located on the inner side of the center of the outermost gas hole 140A.

Description

Technical Field

[0001] The present invention relates to an electrostatic chuck.

Background Art

[0002] For example, in semiconductor manufacturing equipment such as an etching apparatus, an electrostatic chuck is provided as a device for adsorbing and holding a substrate such as a silicon wafer to be processed. The electrostatic chuck includes a dielectric substrate provided with an adsorption electrode and a base plate for supporting the dielectric substrate, and these have a configuration in which they are joined to each other. When a voltage is applied to the adsorption electrode, an electrostatic force is generated, and the substrate placed on the dielectric substrate is adsorbed and held.

[0003] As described in Patent Document 1 below, the dielectric substrate and the base plate are joined via a joining layer such as a cured silicone adhesive.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] During processing, it is necessary to suppress the variation in the in-plane temperature distribution of the substrate as much as possible. As a countermeasure for suppressing the variation in the in-plane temperature distribution, the inventors have been studying to make the material of the joining layer different for each location. [[ID=四十]]

[0006] The present invention has been made in view of such problems, and an object thereof is to provide an electrostatic chuck capable of suppressing the variation in the in-plane temperature distribution of a substrate.

Means for Solving the Problems

[0007] To solve the above problems, the electrostatic chuck according to the present invention comprises a dielectric substrate having a mounting surface on which an object to be processed is placed and having a plurality of gas holes formed therein, a base plate supporting the dielectric substrate, and a bonding layer that bonds the dielectric substrate and the base plate. The bonding layer includes a first bonding layer and a second bonding layer that surrounds the first bonding layer in an annular shape from the outer circumference. The thermal conductivity of the second bonding layer is higher than that of the first bonding layer. When this electrostatic chuck is viewed from a direction perpendicular to the mounting surface, if the outermost gas hole is defined as the gas hole formed at the outermost position among the plurality of gas holes formed on the inner circumference side of the outer circumference end of the mounting surface, then the inner circumference end of the second bonding layer is located on the inner circumference side of the center of the outermost gas hole.

[0008] During the processing of the circuit board, the temperature of the outer circumference tends to rise more easily than that of the inner circumference. In particular, the area directly above the outermost gas holes may experience a localized temperature increase because heat is not easily drawn towards the base plate.

[0009] In the electrostatic chuck with the above configuration, the portion of the dielectric substrate near the outermost gas holes is bonded to the base plate via a second bonding layer with high thermal conductivity. Since this portion is efficiently cooled by the base plate, localized temperature rise directly above the outermost gas holes can be suppressed, and variations in the in-plane temperature distribution of the substrate can be reduced. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an electrostatic chuck that can suppress variations in the in-plane temperature distribution of a substrate. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing the configuration of the electrostatic chuck according to the first embodiment. [Figure 2] This figure shows the configuration of the dielectric substrate included in the electrostatic chuck. [Figure 3]This figure shows the configuration of the bonding layer provided by the electrostatic chuck. [Figure 4] This is a schematic cross-sectional view showing the configuration of an electrostatic chuck according to the second embodiment. [Modes for carrying out the invention]

[0012] This embodiment will be described below with reference to the attached drawings. To facilitate understanding of the explanation, the same reference numerals are used for identical components in each drawing whenever possible, and redundant explanations are omitted.

[0013] A first embodiment will be described. The electrostatic chuck 10 according to this embodiment is used to attract and hold a substrate W to be processed by electrostatic force inside a semiconductor manufacturing apparatus (not shown), such as an etching apparatus. The substrate W corresponds to the "work to be processed," and is, for example, a silicon wafer. The electrostatic chuck 10 may be used in apparatus other than semiconductor manufacturing apparatus.

[0014] Figure 1 shows a schematic cross-sectional view of the electrostatic chuck 10 in a state where the substrate W is adsorbed and held. The electrostatic chuck 10 comprises a dielectric substrate 100, a base plate 200, and a bonding layer 300.

[0015] The dielectric substrate 100 is a substantially disc-shaped component made of a ceramic sintered body. The dielectric substrate 100 contains, for example, high-purity aluminum oxide (Al2O3), but may also contain other materials. The purity and type of ceramics in the dielectric substrate 100, as well as the additives, can be appropriately set considering the plasma resistance and other properties required of the dielectric substrate 100 in semiconductor manufacturing equipment.

[0016] The upper surface 110 of the dielectric substrate 100 in Figure 1 is the "mounting surface" on which the substrate W is placed. The lower surface 120 of the dielectric substrate 100 in Figure 1 is the "bonded surface" that is bonded to the base plate 200 via the bonding layer 300 described later. The viewpoint from which the electrostatic chuck 10 is viewed from the surface 110 side, along a direction perpendicular to surface 110, will also be referred to as the "top view" below.

[0017] An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a thin, flat layer formed of a metallic material such as tungsten, and is arranged parallel to the surface 110. In addition to tungsten, molybdenum, platinum, palladium, etc. may be used as the material for the adsorption electrode 130. When a voltage is applied to the adsorption electrode 130 from the outside via a power supply path (not shown), an electrostatic force is generated between the surface 110 and the substrate W, thereby adsorbing and holding the substrate W. The adsorption electrode 130 may be provided as a single "monopolar" electrode as in this embodiment, or as two "bipolar" electrodes.

[0018] As shown in Figure 1, a space SP is formed between the dielectric substrate 100 and the substrate W. When etching or other processes are performed in the semiconductor manufacturing apparatus, an inert gas for temperature control is supplied to the space SP from the outside via a gas hole 140, etc., as described later. By interposing an inert gas between the dielectric substrate 100 and the substrate W, the thermal resistance between them is adjusted, thereby maintaining the temperature of the substrate W at an appropriate temperature. In this embodiment, helium gas is used as the inert gas for temperature control supplied to the space SP, but a different type of gas may be used.

[0019] Figure 2 is a top view of the dielectric substrate 100. As shown in the figure, a seal ring 111 and dots 112 are provided on the mounting surface 110, and the space SP described above is formed around them.

[0020] The seal ring 111 is an annular protrusion provided as a wall that partitions the space SP at the outermost peripheral position. The upper end of the seal ring 111 forms a part of the surface 110 and abuts against the substrate W. Incidentally, a plurality of seal rings 111 may be provided so as to divide the space SP. With such a configuration, it becomes possible to individually adjust the pressure of the helium gas in each space SP and to make the surface temperature distribution of the substrate W during processing closer to uniform.

[0021] In FIGS. 1 and 2, the portion marked with the reference numeral "116" is the bottom surface of the space SP. Hereinafter, this portion will also be referred to as the "bottom surface 116". The seal ring 111 is formed as a result of digging down a part of the surface 110 to the position of the bottom surface 116 together with the dots 112 described below.

[0022] The dot 112 is a circular protrusion protruding from the bottom surface 116. As shown in FIG. 2, a plurality of dots 112 are provided and are arranged substantially evenly dispersed on the mounting surface of the dielectric substrate 100. The upper end surface of each dot 112 forms a part of the surface 110 and abuts against the substrate W. By providing a plurality of such dots 112, the deflection of the substrate W is suppressed.

[0023] Gas holes 140 are formed in the dielectric substrate 100. The gas holes 140 are through holes formed so as to extend in a direction perpendicular to the surface 110 which is the mounting surface. The end portion on the surface 110 side of the gas holes 140 is connected to the space SP. The gas holes 140 are a part of the flow path for supplying helium gas toward the space SP.

[0024] A plurality of gas holes 140 are provided and are dispersed so as to supply helium gas to each part of the space SP. The arrangement of the gas holes 140 in the actual configuration is as shown in FIG. 2, but in FIG. 1, only four of these gas holes 140 are schematically drawn.

[0025] Of the multiple gas holes 140, the gas hole 140 formed at the outermost position in a top view will hereafter be referred to as the "outermost gas hole 140A". The outermost gas hole 140A can also be described as the gas hole 140 located closest to the outermost edge of the mounting surface 110 from the inner circumference side. As shown in Figure 2, in this embodiment, there are multiple outermost gas holes 140A arranged in a circular pattern along the seal ring 111.

[0026] The base plate 200 is a roughly disc-shaped member that supports the dielectric substrate 100. The base plate 200 is made of a metallic material such as aluminum. Of the base plate 200, the upper surface 210 in Figure 1 is the "bonded surface" which is bonded to the dielectric substrate 100 via the bonding layer 300.

[0027] A refrigerant channel 260 for circulating refrigerant is formed inside the base plate 200. When etching or other processes are performed in the semiconductor manufacturing equipment, refrigerant is supplied from the outside to the refrigerant channel 260, thereby cooling the base plate 200. During processing, the heat generated in the substrate W is transferred to the refrigerant via the helium gas in the space SP, the dielectric substrate 100, and the base plate 200, and is discharged to the outside together with the refrigerant. The supply and discharge of refrigerant to and from the refrigerant channel 260 is performed through an opening (not shown) formed on the surface 220 of the base plate 200 opposite to the surface 210.

[0028] Gas holes 240 are formed in the base plate 200. The gas holes 240 are through holes formed to extend perpendicularly from surface 210 toward the opposite surface 220. The gas holes 240 are formed at positions that overlap with the gas holes 140 of the dielectric substrate 100 when viewed from above, and are in communication with the gas holes 140 via through holes provided in the bonding layer 300. Together with the gas holes 140 of the dielectric substrate 100, the gas holes 240 form part of a flow path for supplying helium gas toward the space SP.

[0029] Furthermore, the gas holes 240 may be formed to extend in a straight line as in this embodiment, but they may also be formed to bend midway from surface 210 to surface 220. Alternatively, the multiple gas holes 240 on surface 210 may be consolidated into a few flow paths inside the base plate 200, and these flow paths may be extended to surface 220.

[0030] An insulating film may be formed on the surface of the base plate 200. The insulating film may be formed to cover only a portion of the surface of the base plate 200, rather than the entire surface. For example, the insulating film may be formed to cover only the side portions excluding surfaces 210 and 220, i.e., the exposed portions that are exposed to plasma or the like inside the semiconductor manufacturing equipment. Alternatively, the insulating film may be formed to cover an area that includes at least the entire surface 210. As the insulating film, for example, an alumina film formed by thermal spraying can be used. By covering the surface of the base plate 200 with an insulating film, the dielectric strength of the base plate 200 can be increased.

[0031] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and it bonds the two together. The bonding layer 300 is made by curing an adhesive made of an insulating material. In this embodiment, a silicone adhesive is used as the adhesive. However, the bonding layer 300 may be made by curing another type of adhesive. In any case, it is preferable to use a material with the highest possible thermal conductivity for the bonding layer 300 so that the thermal resistance between the dielectric substrate 100 and the base plate 200 is reduced.

[0032] Figure 3 schematically shows the structure of the bonding layer 300 in a top view. Although through holes are formed in the bonding layer 300 in areas overlapping with the gas holes 140 and lift pin holes (not shown), these through holes are not shown in Figure 3.

[0033] The bonding layer 300 of this embodiment includes a first bonding layer 310 and a second bonding layer 320. The shape of the first bonding layer 310 in a top view is circular. The center of the first bonding layer 310 in a top view coincides with the center of the dielectric substrate 100. The second bonding layer 320 surrounds the first bonding layer 310 in an annular shape from the outer periphery. The outer periphery end of the first bonding layer 310, the inner periphery end of the second bonding layer 320, and the outer periphery end of the second bonding layer 320 are all circular in a top view, and these are arranged concentrically.

[0034] The materials of the first bonding layer 310 and the second bonding layer 320 are different from each other. Specifically, the materials are selected such that the thermal conductivity of the second bonding layer 320 is higher than that of the first bonding layer 310. This difference in thermal conductivity is achieved, for example, by varying the amount of filler added to the silicone adhesive that forms the bonding layer 300 before it hardens.

[0035] Incidentally, when processing the substrate W in a semiconductor manufacturing apparatus, it is preferable to minimize the variation in the in-plane temperature distribution of the substrate W as much as possible. However, the temperature of the substrate W during processing tends to rise locally in the outer peripheral portion. Therefore, in this embodiment, as described above, the thermal conductivity of the second bonding layer 320 located on the outer peripheral side is made higher than that of the first bonding layer 310 located on the inner peripheral side. Since the outer peripheral portion of the dielectric substrate 100 (i.e., the portion supporting the outer peripheral side of the substrate W) is more easily cooled by the base plate 200, the localized temperature rise in the outer peripheral side of the substrate W can be suppressed.

[0036] In this embodiment, in order to further suppress variations in the in-plane temperature distribution of the substrate W, the relative positional relationship between the second bonding layer 320 and the outermost gas hole 140A is also devised.

[0037] In Figure 1, the dashed line DL1 represents the position of the outermost end of the first bonding layer 310. The dashed line DL2 represents the position of the innermost end of the second bonding layer 320. The dashed line DL3 represents the position of the center of the outermost gas hole 140A. Note that "the position of the center of the outermost gas hole 140A" refers to the position of the central axis of the outermost gas hole 140A in a top view.

[0038] In this embodiment, the shape of the second bonding layer 320 is set such that the inner circumferential end of the second bonding layer 320 (dash-dotted line DL2) is located on the inner circumferential side when viewed from above, compared to the center of the outermost gas hole 140A (dash-dotted line DL3).

[0039] The reason is as follows: As mentioned earlier, during processing of the substrate W, the temperature of the outer circumference of the substrate W tends to rise more easily than that of the inner circumference. In particular, in the area directly above the outermost gas hole 140A, heat is not easily drawn towards the base plate 200 because there is no low-temperature solid area directly below it. For this reason, depending on the overall configuration of the electrostatic chuck 10, the temperature of the substrate W may rise locally in that area.

[0040] Therefore, in the electrostatic chuck 10 according to this embodiment, as described above, the inner circumference end (dotted-dotted line DL2) of the second bonding layer 320 is positioned on the inner circumference side of the center (dotted-dotted line DL3) of the outermost gas hole 140A. In this configuration, the portion of the dielectric substrate 100 near the outermost gas hole 140A is bonded to the base plate 200 via the second bonding layer 320, which has high thermal conductivity. Since this portion is efficiently cooled by the base plate 200, a localized temperature rise directly above the outermost gas hole 140A can be suppressed, and variations in the in-plane temperature distribution of the substrate W can be suppressed.

[0041] Furthermore, the positional relationship between the second bonding layer 320 and the outermost gas hole 140A as described above only needs to be established in a cross-section that includes at least both the central axis of the dielectric substrate 100 and the central axis of the outermost gas hole 140A (i.e., a cross-section like that shown in Figure 1).

[0042] In a top view, the distance from the center of the outermost gas hole 140A (dash-dotted line DL3) to the inner edge of the second bonding layer 320 (dash-dotted line DL2) will hereafter be referred to as "distance D2". If distance D2 is too small, the portion directly above the outermost gas hole 140A cannot be cooled efficiently. On the other hand, if distance D2 is too large, not only the portion directly above the outermost gas hole 140A but also other nearby portions will be overcooled. Experiments conducted by the inventors have confirmed that if distance D2 is kept within the range of 1 mm or more and 30 mm or less, variations in the in-plane temperature distribution of the substrate W can be sufficiently suppressed.

[0043] In this embodiment, the outer peripheral end of the first bonding layer 310 (dash-dotted line DL1) and the inner peripheral end of the second bonding layer 320 (dash-dotted line DL2) are separated, and a space is formed between them. This configuration prevents the first bonding layer 310 and the second bonding layer 320, which are dissimilar adhesives, from mixing when bonding the dielectric substrate 100 and the base plate 200, thereby preventing changes in their respective physical properties.

[0044] The distance from the outer edge of the first bonding layer 310 (dotted-dotted line DL1) to the inner edge of the second bonding layer 320 (dotted-dotted line DL2) will hereafter be referred to as "distance D1". It is preferable to keep distance D1 to 2 mm or less so that the thermal resistance between the dielectric substrate 100 and the base plate 200 does not become too large. If mixing of the first bonding layer 310 and the second bonding layer 320 during bonding is not a problem, distance D1 may be set to 0 mm. In addition, a bonding layer 300 made of another material may be placed between the first bonding layer 310 and the second bonding layer 320.

[0045] The second embodiment will be described with reference to Figure 4. Below, we will mainly describe the differences from the first embodiment, and will omit explanations of points common to both embodiments as appropriate.

[0046] The dielectric substrate 100 of this embodiment is provided with a flange portion 101. The flange portion 101 is a part that protrudes further outward than the mounting surface 110. In a top view, the flange portion 101 surrounds the entire surface 110 from the outside. The surface of the flange portion 101 on the substrate W side (the upper surface in Figure 4) is located on the base plate 200 side (the lower side in Figure 4) of the surface 110. When processing the substrate W, an annular member, not shown, referred to as a "focus ring," is placed on the flange portion 101.

[0047] Gas holes may be formed in the flange portion 101 so that helium gas can be supplied directly beneath the annular member. Such gas holes would be located further outward than the outermost gas hole 140A in the first embodiment. However, the term "outermost gas hole" is defined as the gas hole 140 formed at the outermost position among a plurality of gas holes 140 formed on the inner side of the outer edge of the mounting surface (surface 110) on which the workpiece (substrate W) is placed. Therefore, even if gas holes are formed in the flange portion 101, these gas holes do not qualify as "outermost gas holes".

[0048] As shown in Figure 4, the portion of the gas hole 140 on the surface 120 side of this embodiment is enlarged in diameter compared to the portion on the surface 110 side. This enlarged portion will also be referred to as the "enlarged diameter portion 141" below. A vent plug 150 is placed inside the enlarged diameter portion 141. The vent plug 150 is a porous body made of, for example, alumina, and is permeable throughout. By placing such a vent plug 150 inside the gas hole 140, it is possible to ensure the flow of gas in the gas hole 140 while suppressing the occurrence of dielectric breakdown along the path through the gas hole 140. Note that the permeable portion of the vent plug 150 may be only a part of it, not the entire vent plug 150. For example, only the central portion of the vent plug 150 may be permeable, while the outer peripheral portion may not be permeable.

[0049] As shown in Figure 4, the portion of the gas hole 240 on the surface 210 side of this embodiment is enlarged in diameter compared to the portion on the surface 220 side. This enlarged portion will also be referred to as the "enlarged diameter portion 241" below. A vent plug 250 is placed inside the enlarged diameter portion 241. The vent plug 250 is a porous body made of, for example, alumina, and is permeable throughout. By placing such a vent plug 250 inside the gas hole 240, it is possible to ensure the flow of gas in the gas hole 240 while suppressing the occurrence of dielectric breakdown along the path through the gas hole 240. Note that the permeable portion of the vent plug 250 may be only a part of it, not the entire vent plug 250. For example, only the central portion of the vent plug 250 may be permeable, while the outer peripheral portion may not be permeable.

[0050] Even with the above configuration, the same effects as those described in the first embodiment can be achieved.

[0051] The embodiments have been described above with reference to specific examples. However, this disclosure is not limited to these specific examples. Modifications made to these specific examples by those skilled in the art are also included within the scope of this disclosure, as long as they retain the features of this disclosure. The elements, their arrangement, conditions, shapes, etc., of each of the aforementioned specific examples are not limited to those illustrated and can be modified as appropriate. The elements of each of the aforementioned specific examples can be combined in different ways as appropriate, as long as no technical inconsistencies arise. [Explanation of symbols]

[0052] 10: Electrostatic Chuck 100: Dielectric substrate 110: Face 140: Gas hole 140A: Outermost gas hole 200: Base plate 300: Bonding layer 310: 1st bonding layer 320:Second bonding layer W: Circuit board

Claims

1. A dielectric substrate having a mounting surface on which an object to be processed is placed, and having a plurality of gas holes formed therein, A base plate supporting the dielectric substrate, The dielectric substrate and the base plate are joined together by a bonding layer, The bonding layer includes a first bonding layer and a second bonding layer that surrounds the first bonding layer in an annular shape from the outer periphery. The thermal conductivity of the second bonding layer is higher than that of the first bonding layer. When viewed from a direction perpendicular to the mounting surface, Of the multiple gas holes formed on the inner circumference side of the outer circumference end of the mounting surface, when the gas hole formed at the outermost position is defined as the outermost gas hole, An electrostatic chuck characterized in that the inner circumferential end of the second bonding layer is located on the inner circumferential side of the center of the outermost gas hole.

2. The electrostatic chuck according to claim 1, characterized in that there is a gap between the first bonding layer and the second bonding layer.

3. When viewed from a direction perpendicular to the mounting surface, The electrostatic chuck according to claim 1, characterized in that the distance from the center of the outermost gas hole to the inner end of the second bonding layer is 1 mm or more and 30 mm or less.

4. When viewed from a direction perpendicular to the mounting surface, The electrostatic chuck according to claim 1, characterized in that the distance from the outer peripheral end of the first bonding layer to the inner peripheral end of the second bonding layer is 2 mm or less.

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