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 first portion 101 including a surface 110 which is a mounting surface, and a second portion 102 which protrudes further outward from the outer peripheral end of the first portion 101 and is thinner than the first portion 101; a base plate 200 bonded to 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 which surrounds the first bonding layer 310 in an annular shape from the outer peripheral side. The thermal conductivity of the second bonding layer 320 is higher than that of the first bonding layer 310. In this electrostatic chuck 10, in a top view, the inner peripheral end of the second bonding layer 320 is in a position that overlaps with the first portion 101.

Description

Technical Field

[0006] ,

[0007] , ,

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

Background Art

[0002] For example, in a semiconductor manufacturing apparatus 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 has a configuration in which these 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.

[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 the 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 first portion including a mounting surface on which an object to be processed is placed, and a second portion that protrudes further outward from the outer peripheral end of the first portion and is thinner than the first portion; a base plate bonded to 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 peripheral side. 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, the inner peripheral end of the second bonding layer is in a position that overlaps with the first portion.

[0008] During the processing of the substrate, the temperature of the outer circumference of the substrate tends to rise more easily than that of the inner circumference. In addition, an annular component, such as a "focus ring," is placed directly above the second component, and the temperature of this annular component also tends to rise during processing.

[0009] In the electrostatic chuck with the above configuration, the portion of the dielectric substrate that supports each of the above parts, that is, the portion that supports from below the part that is prone to temperature rise during processing, is bonded to the base plate via a second bonding layer with high thermal conductivity. This configuration suppresses the temperature rise of the annular member and also suppresses variations in the in-plane temperature distribution of the substrate. [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 this embodiment. [Figure 2] This figure shows the configuration of the bonding layer provided by the electrostatic chuck. [Modes for carrying out the invention]

[0012] This embodiment will now be described 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] 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 also 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, additives, etc., 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] The dielectric substrate 100 has a first portion 101 and a second portion 102. The first portion 101 is a substantially cylindrical portion that extends from surface 110 toward the lower side of Figure 1 to surface 120. Such a first portion 101 can be said to be the portion of the dielectric substrate 100 that includes surface 110, which is the mounting surface. In a top view, the outer shape of the mounting surface and the outer shape of the first portion 101 may or may not coincide with each other.

[0018] The second part 102 is an annular portion that protrudes further outward from the outer edge of the first part 101, and is also referred to as the "flange" of the dielectric substrate 100. In Figure 1, the boundary between the first part 101 and the second part 102 is shown by the dotted line DL. The second part 102 is thinner than the first part 101. The surface 120 mentioned earlier is the lowest surface of the first part 101 in Figure 1, and is also the lowest surface of the second part 102. The highest surface 160 of the second part 102 is located lower than surface 110 in Figure 1.

[0019] When a substrate W is processed in a semiconductor manufacturing apparatus, an annular member RE, sometimes called a "focus ring," is placed around the substrate W. The surface 160 of the second part 102 is the part that supports this annular member RE from below. Surface 160 is parallel to surface 110.

[0020] An adsorption electrode 130 is embedded inside the first portion 101 of 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 so-called "monopolar" electrode, as in this embodiment, or as a so-called "bipolar" electrode, with two electrodes provided.

[0021] Inside the second part 102, an internal electrode different from the adsorption electrode 130 may be provided. Examples of such an internal electrode include an adsorption electrode for generating an electrostatic force between the annular member RE, an RF electrode, and the like.

[0022] As shown in FIG. 1, a space SP is formed between the dielectric substrate 100 and the substrate W. When a process such as etching is performed in the semiconductor manufacturing apparatus, an inert gas for temperature adjustment is supplied from the outside to the space SP through a gas hole 140 and the like described later. By interposing an inert gas between the dielectric substrate 100 and the substrate W, the thermal resistance between the two is adjusted, and thereby the temperature of the substrate W is maintained at an appropriate temperature. In the present embodiment, helium gas is used as the inert gas for temperature adjustment supplied to the space SP, but a gas of a type different from helium gas may be used.

[0023] A seal ring 111 and dots 112 are provided on the surface 110 which is the placement surface, and the above-mentioned space SP is formed around them.

[0024] 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 is a part of the surface 110 and abuts on the substrate W. Note that a plurality of seal rings 111 may be provided so as to divide the space SP. With such a configuration, the pressure of the helium gas in each space SP can be individually adjusted, and the surface temperature distribution of the substrate W during processing can be made closer to uniform. In the present embodiment, the outer peripheral side end of the seal ring 111 in a top view coincides with the outer peripheral side end of the first part 101.

[0025] The portion marked with reference numeral "116" in FIG. 1 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, together with the dots 112 described below, is formed as a result of digging down a part of the surface 110 to the position of the bottom surface 116.

[0026] The dots 112 are circular protrusions that extend from the bottom surface 116. Multiple dots 112 are provided and are distributed approximately evenly on the mounting surface of the dielectric substrate 100. The upper end surface of each dot 112 is part of the surface 110 and contacts the substrate W. By providing multiple such dots 112, the bending of the substrate W is suppressed.

[0027] Gas holes 140 are formed in the dielectric substrate 100. The gas holes 140 are through holes formed to extend perpendicular to the mounting surface 110. The end of the gas hole 140 on the surface 110 side is connected to the space SP. The gas holes 140 are part of a flow path for supplying helium gas to the space SP. Multiple gas holes 140 are formed in the dielectric substrate 100, but only two of them are shown in Figure 1.

[0028] As shown in Figure 1, the portion of the gas hole 140 facing the surface 120 is larger in diameter than the portion facing the surface 110. 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 material formed, for example, from alumina, and is permeable throughout. By placing such a vent plug 150 inside the gas hole 140, it is possible to ensure gas flow 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] As shown in Figure 1, 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 through 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Figure 2 schematically shows the structure of the bonding layer 300 in a top view. Through holes are formed in the bonding layer 300 in areas overlapping with the gas holes 140 and in areas overlapping with lift pin holes (not shown), but these through holes are not shown in Figure 2.

[0037] 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.

[0038] 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.

[0039] Incidentally, when a substrate W is being processed 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. In addition, the temperature of the annular member RE, which is arranged to surround the substrate W from the outer peripheral side, also often rises, and this can cause the temperature of the outer peripheral portion of the substrate W to rise even further. Therefore, in the electrostatic chuck according to this embodiment, the arrangement of the first bonding layer 310 and the second bonding layer 320 is designed to suppress the localized temperature rise described above.

[0040] In Figure 1, the dashed line DL1 represents the position of the outer edge of the first bonding layer 310. The dashed line DL2 represents the position of the inner edge of the second bonding layer 320. The dashed line DL3 represents the position of the outer edge of the first part 101. "The position of the outer edge of the first part 101" may be read as "the position of the inner edge of the second part 102".

[0041] In this embodiment, the shape of the second bonding layer 320 is set such that the inner end of the second bonding layer 320 (dash-dotted line DL2) is located on the inner side of the first part 101 when viewed from above, compared to the outer end of the first part 101 (dash-dotted line DL3). As a result, the inner end of the second bonding layer 320 is located in a position that overlaps with the first part 101 when viewed from above.

[0042] The reason is as follows: As mentioned earlier, during the 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, and the temperature of the annular member RE surrounding the substrate W from the outer circumference also tends to rise more easily.

[0043] Therefore, in the electrostatic chuck 10 according to this embodiment, as described above, the inner circumferential end (dotted line DL2) of the second bonding layer 320 is positioned to overlap with the first portion 101 when viewed from above. Note that "position overlapping with the first portion 101" refers to a position that is on the inner circumferential side than the outer circumferential end of the first portion 101.

[0044] In this configuration, the portion of the dielectric substrate 100 that overlaps with the second bonding layer 320 in a top view is the portion that supports the outer peripheral portion of the substrate W and the annular member RE from below. In other words, the portion of the dielectric substrate 100 that supports the part that is prone to temperature rise as described above is bonded to the base plate 200 via the second bonding layer 320, which has high thermal conductivity. This configuration suppresses the temperature rise of the annular member RE, as well as the temperature rise of the outer peripheral portion of the substrate W, thereby making the in-plane temperature distribution of the substrate W uniform.

[0045] Furthermore, the positional relationship between the second bonding layer 320 and the first portion 101 as described above may be established in all arbitrary cross-sections including the central axis of the dielectric substrate 100 (i.e., cross-sections as shown in Figure 1), or it may be established in only any cross-section including the central axis of the dielectric substrate 100. In other words, the inner circumference end of the second bonding layer 320 may be in a position where it overlaps with the first portion 101 in a top view, or a part of that end may be in a position where it does not overlap with the first portion 101 in a top view.

[0046] In a top view, the distance from the inner edge of the second bonding layer 320 (dash-dotted line DL2) to the outer edge of the first portion 101 (dash-dotted line DL3) will hereafter be referred to as "distance D2". If distance D2 is too small, the outer edge of the substrate W cannot be cooled efficiently. On the other hand, if distance D2 is too large, not only the outer edge of the substrate W but also the inner part will be cooled excessively. 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.

[0047] 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.

[0048] 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.

[0049] 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]

[0050] 10: Electrostatic Chuck 100: Dielectric substrate 101: Part 1 102:Second part 110: Face 200: Base plate 300: Bonding layer 310: 1st bonding layer 320:Second bonding layer W: Circuit board

Claims

1. A dielectric substrate having a first portion including a mounting surface on which the object to be processed is placed, and a second portion that protrudes further outward from the outer peripheral end of the first portion and is thinner than the first portion, A base plate bonded to 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, An electrostatic chuck characterized in that the inner circumferential end of the second bonding layer is located in a position that overlaps with the first portion.

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 inner circumferential end of the second bonding layer to the outer circumferential end of the first portion 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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