Electrostatic chuck

Abstract

The invention provides an electrostatic chuck capable of making the Young's modulus value of a bonding layer proper and reducing thermal stress applied to a dielectric substrate. An electrostatic chuck (10) is provided with: a dielectric substrate (100) in which a through-hole (140) is formed; a base plate (200) formed of a metal material; and a bonding layer (300) that bonds between the dielectric substrate (100) and the base plate (200). When the Young's modulus of the bonding layer (300) is E (MPa) and the distance between the central axis (AX0) of the dielectric substrate (100) and the central axis (AX1) of the through-hole (140) is X (mm), the through-hole (140) located at the position farthest from the central axis (AX0) satisfies E < = 0.2063 * X2-59.3887 * X + 4278.8065, where E (MPa) is the Young's modulus of the bonding layer (300), and X (mm) is the distance between the central axis (AX0) of the dielectric substrate (100) and the central axis (AX1) of the through-hole (140).

Description

Technical Field

[0001] The invention relates to an electrostatic chuck. Background Art

[0002] For example, in a semiconductor manufacturing device such as an etching device, 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 supporting the dielectric substrate, and these have a structure in which they are joined to each other. When a voltage is applied to the adsorption electrode, an electrostatic force is generated to adsorb and hold the substrate placed on the dielectric substrate.

[0003] During the process, the temperature of the substrate rises due to exposure to plasma, and the temperature of the dielectric substrate also rises. On the other hand, since a low-temperature cooling medium is supplied to the base plate, the temperature of the base plate may drop to -60°C or below. The dielectric substrate is subjected to large thermal stress due to temperature changes of various parts accompanying the substrate processing or the temperature difference between the dielectric substrate and the base plate.

[0004] In order to prevent the dielectric substrate from being damaged due to thermal stress, it is necessary to select a material having appropriate physical properties as the material of the bonding layer connecting the dielectric substrate and the base plate. For example, the following patent document 1 proposes a technology for making the storage modulus of the bonding layer (adhesive member) at -60°C less than 100 MPa.

[0005] Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2020-23088 Summary of the invention

[0006] As the material of the bonding layer, if a material with a smaller Young's modulus is used as much as possible, the thermal stress applied to the dielectric substrate can be suppressed to a smaller value. However, in view of the heat transfer performance required for the bonding layer, it is not possible to reduce the Young's modulus of the bonding layer by any amount. On the basis of the condition that the Young's modulus is below the specified upper limit, it is necessary to appropriately select the material of the bonding layer in consideration of the required heat transfer performance, etc.

[0007] However, in the dielectric substrate, a through hole is formed for the purpose of supplying a cooling gas, etc. According to the experiments conducted by the inventors, the following knowledge is obtained, that is, the thermal stress applied to the dielectric substrate is particularly large at the through hole portion, and its size varies according to the position of the through hole. Specifically, when the distance between the central axis of the dielectric substrate and the central axis of the through hole is X, the larger the value of X, the larger the thermal stress applied to the through hole portion. In other words, the larger the value of X, the narrower the upper limit value of the allowable range of the Young's modulus of the bonding layer.

[0008] Therefore, in order to suppress the thermal stress applied to the dielectric substrate while satisfying the required specifications such as heat transfer performance, it is necessary to appropriately set the respective parameters while considering the correlation between "the distance between the central axis of the dielectric substrate and the central axis of the through hole" and "the upper limit of the Young's modulus of the bonding layer". However, no specific research has been conducted so far on how to consider these correlations.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrostatic chuck that can make the value of the Young's modulus of the bonding layer an appropriate value and reduce the thermal stress applied to the dielectric substrate.

[0010] In order to solve the above problems, the electrostatic chuck involved in the present invention comprises: a dielectric substrate having a through hole formed therein; a base plate formed of a metal material; and a bonding layer for bonding the dielectric substrate and the base plate. In the electrostatic chuck, when the Young's modulus of the bonding layer is E (MPa) and the distance between the central axis of the dielectric substrate and the central axis of the through hole is X (mm), E≤0.2063×X is established for the through hole located farthest from the central axis of the dielectric substrate. 2 -59.3887×X+4278.8065.

[0011] The through hole located farthest from the central axis of the dielectric substrate is usually the part of the dielectric substrate that receives the greatest thermal stress. 2 By setting the position of the through hole (X) and the Young's modulus (E) of the bonding layer in the manner of -59.3887×X+4278.8065, respectively, the thermal stress in the through hole portion of the dielectric substrate can be sufficiently reduced. By making the electrostatic chuck into the above structure, the value of the Young's modulus of the bonding layer can be made appropriate, and the thermal stress applied to the dielectric substrate can be reduced.

[0012] The above-mentioned formula related to the Young's modulus of the bonding layer may be established for all through-holes formed in the dielectric substrate, not just for the through-hole located farthest from the central axis of the dielectric substrate.

[0013] According to the present invention, it is possible to provide an electrostatic chuck that can make the value of the Young's modulus of the bonding layer an appropriate value and reduce the thermal stress applied to the dielectric substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a cross-sectional view schematically showing the structure of the electrostatic chuck according to the present embodiment. Figure 2 It means by Figure 1 A diagram showing the structure of a dielectric substrate included in an electrostatic chuck. Figure 3 It is a diagram showing the actual shape of the electrostatic chuck according to the present embodiment. Figure 4 This is a graph showing the relationship between the Young's modulus of the bonding layer and the maximum stress generated in the dielectric substrate. Figure 5 This is a diagram showing the relationship between the position of the through hole and the allowable Young's modulus. Explanation of symbols 10-electrostatic suction cup; 100-dielectric substrate; 140-through hole; 200-base plate; 300-bonding layer; AX0, AX1-center axis. DETAILED DESCRIPTION

[0015] Hereinafter, the present embodiment will be described with reference to the drawings. In order to facilitate the description, the same components are denoted by the same reference numerals as much as possible in each of the drawings, and repeated descriptions are omitted.

[0016] The electrostatic chuck 10 according to the present embodiment absorbs and holds a substrate W to be processed by electrostatic force in a semiconductor manufacturing device (not shown), such as an etching device. The substrate W is, for example, a silicon wafer. The electrostatic chuck 10 can also be used in devices other than semiconductor manufacturing devices.

[0017] Figure 1 , the structure of the electrostatic chuck 10 in a state of sucking and holding the substrate W is shown as a schematic cross-sectional view. The electrostatic chuck 10 includes a dielectric substrate 100 , a base plate 200 , and a bonding layer 300 .

[0018] The dielectric substrate 100 is a roughly disk-shaped member composed 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. may be appropriately set in consideration of the plasma resistance required of the dielectric substrate 100 in the semiconductor manufacturing device.

[0019] In the dielectric substrate 100, Figure 1 The upper surface 110 in the dielectric substrate 100 is a "placing surface" on which the substrate W is placed. Figure 1The lower surface 120 in the figure becomes the "joined surface" joined to the base plate 200 by the joining layer 300 described later. Hereinafter, the viewpoint when observing the electrostatic chuck 10 from the surface 110 side in a direction perpendicular to the surface 110 is also expressed as "top view". The thickness of the dielectric substrate 100, that is, the distance between the surface 110 and the surface 120, is 0.9 mm in the present embodiment, but may be a different thickness.

[0020] An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a relatively thin flat plate-shaped layer formed of a metal material such as tungsten, and is arranged parallel to the surface 110. As a material of the adsorption electrode 130, molybdenum, platinum, palladium, etc. can be used in addition to tungsten. If a voltage is applied to the adsorption electrode 130 from the outside through the power supply circuit 13, an electrostatic force is generated between the surface 110 and the substrate W, thereby the substrate W is adsorbed and held. The adsorption electrode 130 can be provided as two so-called "bipolar" electrodes as in the present embodiment, or only one so-called "monopolar" electrode can be provided.

[0021] Figure 1 , the entire power supply circuit 13 is simplified. In the power supply circuit 13, the portion inside the dielectric substrate 100 is constituted as, for example, an elongated via (hole) filled with a conductor, and an electrode terminal (not shown) is provided at its lower end. In the power supply circuit 13, the portion that passes through the base plate 200 described later is a conductive metal member (such as a busbar) whose one end is connected to the above-mentioned electrode terminal. In the base plate 200, a through hole (not shown) for passing the power supply circuit 13 is formed. Between the inner surface of the through hole and the power supply circuit 13, for example, a cylindrical insulating member may also be provided.

[0022] like Figure 1 As shown in FIG. 1 , a space SP is formed between the dielectric substrate 100 and the substrate W. When etching or other processing is performed in the semiconductor manufacturing apparatus, helium gas for temperature adjustment is supplied from the outside to the space SP through the through hole 140 described later. By making the helium gas exist between the dielectric substrate 100 and the substrate W, the thermal resistance between the two is adjusted, so that the temperature of the substrate W is maintained at an appropriate temperature. In addition, the gas for temperature adjustment supplied to the space SP may be a gas of a different type from helium.

[0023] Figure 2 1 is a diagram showing a dielectric substrate 100 in a plan view. As shown in the figure, a sealing ring 111 and dots 112 are provided on a surface 110 which is a placement surface, and the above-mentioned space SP is formed around these surfaces.

[0024] The sealing ring 111 is a wall that divides the space SP, and a plurality of sealing rings 111 are arranged in a concentric circle when viewed from above. The upper end of each sealing ring 111 becomes a part of the surface 110 and contacts the substrate W. In the present embodiment, a total of four sealing rings 111 are provided, and the space SP is divided into four parts by these. With such a structure, the pressure of the helium gas in each space SP can be adjusted individually, and the surface temperature distribution of the substrate W can be made uniform during processing.

[0025] Figure 1 and Figure 2 In FIG. 1 , the portion marked with the symbol “116” is the bottom surface of the space SP. Hereinafter, this portion is also referred to as “bottom surface 116”. The sealing ring 111 is formed as a result of digging out a portion of the surface 110 to the position of the bottom surface 116 together with the point 112 described below.

[0026] Point 112 is a circular protrusion protruding from bottom surface 116. Figure 2 As shown, a plurality of points 112 are provided and are dispersed approximately evenly on the placement surface of the dielectric substrate 100. The upper end of each point 112 forms a part of the surface 110 and contacts the substrate W. By providing a plurality of such points 112, the substrate W is prevented from being bent.

[0027] A groove 113 is formed on the bottom surface 116 of the space SP. The groove 113 is formed in a manner that it is further retreated from the bottom surface 116 toward the surface 120. The groove 113 is formed for the purpose of rapidly diffusing the helium gas supplied from the through hole 140 in the space SP and making the pressure distribution in the space SP roughly uniform in a short time. In addition, depending on the number or arrangement of the through holes 140, the groove 113 may not be required.

[0028] The dielectric substrate 100 is formed with a through hole 140, which vertically extends from the surface 120 toward the surface 110. Figure 2 As shown, the end of the through hole 140 on the side of the surface 110 opens on the bottom surface of the groove 113. A plurality of through holes 140 are formed in the dielectric substrate 100, and are arranged along the groove 113. In this embodiment, a plurality of through holes 140 are connected to each of the four divided spaces SP.

[0029] and, Figure 2 In the figure, for the convenience of illustration, although the diameter of the through hole 140 is depicted as being larger than the width of the groove 113, Figure 1As shown, in fact, the diameter of the through hole 140 is smaller than the width of the groove 113. At the position of the through hole 140, the width of the groove 113 can also be partially enlarged so that the through hole 140 completely enters the inner side of the groove 113. In the through hole 140, the diameter at the end on the opposite side of the bonding layer 300 (that is, the end on the side of the surface 110) is less than 0.2 mm in this embodiment.

[0030] like Figure 1 As shown, the portion on the side of the surface 120 in the through hole 140 is further enlarged in diameter than the portion on the side of the surface 110, and a vent plug 145 is arranged inside the through hole 140. The vent plug 145 is a porous body formed of, for example, alumina, and has air permeability as a whole. By arranging such a vent plug 145 inside the through hole 140, the flow of gas in the through hole 140 is ensured, and at the same time, the occurrence of insulation breakdown on the path through the through hole 140 can be suppressed. In addition, in the case where insulation breakdown can be sufficiently prevented, it is also possible to configure the through hole 140 without vent plug 145. In this case, the inner diameter of the through hole 140 can also be uniform in the entire vertical direction.

[0031] Figure 2 In the figure, the structure marked with the symbol "115" is a through hole penetrated by a lifting pin (not shown) provided in the semiconductor manufacturing device. Hereinafter, the through hole is also referred to as "through hole 115". Like the through hole 140 described above, the through hole 115 is formed to extend vertically from the surface 120 toward the surface 110 side. A total of three through holes 115 are provided, and these are arranged at equal intervals of 120 degrees. The substrate W is detachably mounted on the surface 110 of the dielectric substrate 100 by the lifting pin that moves up and down through the through hole 115.

[0032] The base plate 200 is a substantially disk-shaped member that supports the dielectric substrate 100. The base plate 200 is formed of a metal material such as aluminum. Figure 1 The upper surface 210 in FIG. 1 becomes a “joined surface” to be joined to the dielectric substrate 100 via the joining layer 300 .

[0033] like Figure 1 As shown, a through hole 240 is formed in the base plate 200, which extends vertically from the surface 210 toward the surface 220 on the opposite side thereof. When viewed from above, the through holes 240 are respectively formed at positions overlapping with the through holes 140 of the dielectric substrate 100, and are connected to the through holes 140 via the through holes 310 provided in the bonding layer 300. The through holes 240, together with the through holes 140 of the dielectric substrate 100, form a part of the path for supplying helium gas to the space SP.

[0034] like Figure 1As shown, the portion on the side of the surface 210 in the through hole 240 is further enlarged in diameter than the portion on the side of the surface 220, and a vent plug 245 is arranged inside the through hole 240. The vent plug 245 is a porous body formed of, for example, alumina, and has air permeability as a whole. By arranging such a vent plug 245 inside the through hole 240, the flow of gas in the through hole 240 is ensured, and at the same time, the occurrence of insulation breakdown on the path through the through hole 240 can be suppressed. In addition, in the case where insulation breakdown can be sufficiently prevented, it is also possible to configure that the vent plug 245 is not arranged in the through hole 240. In this case, the inner diameter of the through hole 240 can also be uniform in the entire vertical direction.

[0035] Although the through hole 240 can be formed to extend in a straight line as a whole as in the present embodiment, it can also be formed to bend on the way to the surface 220. In addition, the plurality of through holes 240 on the surface 210 side can also be configured so that a small number of flow paths are concentrated inside the base plate 200, and the flow paths are extended to the surface 220 side.

[0036] A cooling medium flow path 250 for flowing a cooling medium is formed inside the susceptor plate 200. When a process such as film formation is performed in the semiconductor manufacturing apparatus, a cooling medium is supplied from the outside to the cooling medium flow path 250, thereby cooling the susceptor plate 200. During the process, the heat generated on the substrate W is transferred to the cooling medium via the helium gas in the space SP, the dielectric substrate 100, and the susceptor plate 200, and is discharged to the outside together with the cooling medium.

[0037] Through holes (not shown) for passing lift pins are formed in the base plate 200 at positions overlapping with the through holes 115 in a plan view.

[0038] An insulating film may be formed on the surface of the base plate 200. The insulating film is preferably formed on the surface of the base plate 200 at least in the range including the entire surface 210. As the insulating film, for example, an aluminum oxide film formed by spraying can be used. By covering the surface of the base plate 200 with the insulating film, the insulation withstand voltage of the base plate 200 can be improved.

[0039] and, Figure 1 In FIG. 1 , although the diameter of the surface 120 of the dielectric substrate 100 and the diameter of the surface 210 of the base plate 200 are schematically drawn as being the same, they are usually different from each other. Figure 3, the actual structure of the electrostatic chuck 10 is shown in FIG. As shown in the figure, in the electrostatic chuck 10 of the present embodiment, the diameter of the surface 120 of the dielectric substrate 100 is slightly larger than the diameter of the surface 210 of the base plate 200. Therefore, the outer peripheral side portion of the dielectric substrate 100 protrudes further outward than the base plate 200 and is not supported from the lower side. However, such a structure is only an example, and the above-mentioned diameters of each may be made to coincide with each other.

[0040] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and the two are bonded. The bonding layer 300 is a layer formed by curing an adhesive material composed of an insulating material. In the present embodiment, a silicone adhesive is used as the above-mentioned adhesive. However, the bonding layer 300 can also be a layer formed by curing other types of adhesives. In either case, it is preferred to use a material with a higher thermal conductivity as much as possible as the material of the bonding layer 300 so that the thermal resistance between the dielectric substrate 100 and the base plate 200 is small. It can also be configured that a plurality of granular fillers (fillers) for improving thermal conductivity are arranged inside the bonding layer 300. As a filler, for example, particles with aluminum oxide as the main component can be used.

[0041] The thickness of the bonding layer 300 can be appropriately set according to the heat transfer performance required of the bonding layer 300. In the present embodiment, although the thickness of the bonding layer 300 is 250 μm, it can also be a thickness different from this. In addition, the thickness of the bonding layer 300 may not be uniform as a whole, such as when an electrode terminal is embedded in the surface 120 side of the dielectric substrate 100 or a groove is formed in a part of the surface 210 of the base plate 200. In this case, the "thickness of the bonding layer 300" is the thickness of the range excluding the portion whose local thickness is different from other portions as described above.

[0042] The bonding layer 300 has a smaller Young's modulus (longitudinal elastic coefficient) than the dielectric substrate 100 or the base plate 200. Even if a thermal expansion difference occurs between the dielectric substrate 100 and the base plate 200, the bonding layer 300 deforms and absorbs the thermal expansion difference, so that the thermal stress in the dielectric substrate 100 and the like can be suppressed to a small value.

[0043] The Young's modulus of the bonding layer 300 changes in accordance with the temperature of the bonding layer 300. Hereinafter, "E" is used to express the numerical value of the Young's modulus of the bonding layer 300 at a temperature of -60°C of the bonding layer 300 expressed in the unit of "MPa". For example, when the Young's modulus of the bonding layer 300 at -60°C is 0.01GPa, E=10. In addition, the above-mentioned temperature of "-60°C" is merely a convenient reference for determining the physical properties (Young's modulus) of the bonding layer 300, and does not impose any limitation on the temperature of the cooling medium actually supplied to the cooling medium flow path 250, etc.

[0044] In recent years, with the increase in the energy incident on the substrate W during processing, there is a tendency to require higher cooling performance than before for the susceptor plate 200. For example, a cooling medium with a temperature of -60°C or lower is sometimes supplied to the cooling medium flow path 250 of the susceptor plate 200. As the temperature of the cooling medium further decreases with the increase in the output of plasma, it is possible that a cooling medium of about -100°C will be supplied in the future.

[0045] The dielectric substrate 100 is subjected to large thermal stress due to temperature changes of various parts accompanying the start of processing of the substrate W or the temperature difference between the dielectric substrate 100 and the base plate 200. According to experiments conducted by the present inventors, it has been found that the thermal stress applied to the dielectric substrate 100 is particularly large at the through-hole portion (for example, the exit portion of the through-hole 140), and the magnitude thereof varies depending on the position of the through-hole.

[0046] Hereinafter, for convenience of explanation, the central axis of the dielectric substrate 100 is also referred to as “central axis AX0” (refer to Figure 1 ). The central axis AX0 is an axis that passes through the center of the dielectric substrate 100 that is circular when viewed from above and is perpendicular to the surface 110. In addition, for example, a positioning edge is formed in a portion of the outer peripheral side of the dielectric substrate 100, and the shape of the dielectric substrate 100 may not be strictly circular when viewed from above. In this case, assuming that the above-mentioned positioning edge is not formed, the overall shape of the dielectric substrate 100 is regarded as a circle, and on this basis, the central axis AX0 is defined as an axis passing through the center of the circle.

[0047] In addition, the central axis of the through hole 140 is also referred to as the "central axis AX1" (refer to Figure 1 As described above, the through hole 140 is a hole formed in a manner extending vertically from the surface 120 toward the surface 110. Therefore, like the central axis AX0, the central axis AX1 is an axis perpendicular to the surface 110. For each of the plurality of through holes 140, the central axis AX1 is defined separately.

[0048] Hereinafter, "X" or "distance X" is used to represent the numerical value of the distance from the central axis AX0 of the dielectric substrate 100 to the central axis AX1 of the through hole 140 in the unit of "mm". The distance X is defined separately for each of the plurality of through holes 140. According to experiments conducted by the present inventors, the larger the distance X from the central axis AX0 to the central axis AX1 of the through hole 140, the larger the magnitude of the thermal stress applied to the portion of the through hole 140. In other words, the portion of the dielectric substrate 100 that is subjected to the greatest thermal stress is generally the portion of the through hole 140 formed at the outermost periphery.

[0049] If a material with a small Young's modulus is used as the material of the bonding layer 300, the thermal stress applied to the dielectric substrate 100 can be suppressed to a small value. However, in view of the heat transfer performance required for the bonding layer 300, it is not possible to reduce the Young's modulus of the bonding layer 300 by any amount. On the basis of the condition that the Young's modulus is below a predetermined upper limit, the material of the bonding layer 300 needs to be appropriately selected in consideration of the required heat transfer performance.

[0050] The smaller the distance X from the central axis AX0 of the dielectric substrate 100 to the central axis AX1 of the through hole 140, the smaller the thermal stress applied to the through hole 140 portion, and thus the upper limit of the allowable Young's modulus (E) becomes larger. In this way, the position (X) of the through hole 140 and the upper limit of the Young's modulus (E) of the bonding layer 300 become parameters that are correlated with each other. The inventors have conducted various experiments and analyses, and thus have been able to obtain new knowledge as shown below regarding the above-mentioned correlation.

[0051] Figure 4 The four graphs shown show the relationship between the Young's modulus (horizontal axis) of the bonding layer 300 at -60°C and the maximum stress (vertical axis) generated in the dielectric substrate 100 .

[0052] For example, with respect to the dielectric substrate 100 in which the through hole 140 located at the position farthest from the central axis AX0 (that is, the outermost periphery) becomes X=X1, the analysis is performed while changing the value of the Young's modulus of the bonding layer 300 (specifically, the Young's modulus at -60°C), and the maximum value of the thermal stress generated in the dielectric substrate 100 at low temperature (hereinafter also referred to as the "maximum stress") is plotted, thereby obtaining a curve graph marked with "X1" on the right.

[0053] Specifically, the above-mentioned "low temperature" means that the bonding layer 300 is cured when the temperature of the electrostatic chuck 10 as a whole is 40° C., and then the temperature of the electrostatic chuck 10 as a whole is lowered to -60° C. In any analysis, "the maximum value of the stress generated in the dielectric substrate 100" refers to the value of the stress generated in the portion near the end of the through hole 140 (that is, the through hole 140 with X=X1) arranged on the outermost periphery on the side of the surface 110.

[0054] The graphs labeled "X2" to "X4" on the right are also graphs obtained based on the same analysis as above. X2 is a distance greater than X1, X3 is a distance greater than X2, and X4 is a distance greater than X3.

[0055] observe Figure 4 As can be seen from the various graphs, the maximum stress generated in the dielectric substrate 100 at low temperatures increases as the Young's modulus of the bonding layer 300 increases. In addition, it is known that there is a tendency that, if the Young's modulus of the bonding layer 300 is the same, the greater the distance X of the through hole 140 arranged at the outermost periphery, the greater the maximum stress generated in the dielectric substrate 100 at low temperatures.

[0056] However, the maximum stress when X=X4 is slightly smaller than the maximum stress when X=X3, which is opposite to the above tendency. This is because the position of the through hole 140 corresponding to X4 is located closer to the outer peripheral side than the surface 210 of the base plate 200, that is, it is located at the lower side of the dielectric substrate 100 and is not supported by the base plate 200. In fact, it is considered that the possibility of the through hole 140 being formed at such a position is low.

[0057] exist Figure 4 The “threshold value” indicated on the vertical axis of refers to the upper limit value of the range of the maximum stress within which the dielectric substrate 100 will not be damaged.

[0058] Figure 4 "E1" is a value of Young's modulus (E) at which the value of maximum stress becomes the above-mentioned threshold value in the dielectric substrate 100 where the distance X of the through hole 140 located at the outermost periphery becomes X1. "E2" is a value of Young's modulus (E) at which the value of maximum stress becomes the above-mentioned threshold value in the dielectric substrate 100 where the distance X of the through hole 140 located at the outermost periphery becomes X2. The same is true for "E3" and "E4". It can be said that E1 to E4 are respectively the upper limits of the permissible range of the value of Young's modulus (E) of the bonding layer 300 for preventing damage to the dielectric substrate 100. Hereinafter, such an upper limit value of Young's modulus is also referred to as "allowable Young's modulus". As shown from Figure 4As is clear, the allowable Young's modulus (E1 to E4) takes different values ​​depending on the distance X (X1 to X4) of the through hole 140 located at the outermost periphery.

[0059] The corresponding relationship between the distance X (horizontal axis) of the through hole 140 located at the outermost periphery and the allowable Young's modulus (vertical axis) is as follows: Figure 5 As shown in the graph, there is a roughly two-dimensional curve-shaped correlation between the two. The allowable Young's modulus gradually decreases with the increase of the distance X. However, if the distance X increases to a certain extent, the allowable Young's modulus increases with the increase of the distance X. The reason for this increase trend is that the outermost portion of the dielectric substrate 100 is not supported by the base plate 200 from below. It can be expressed by the following formula (1): Figure 5 Shown is the relationship between the two. Allowable Young's modulus = 0.2063 × X 2 -59.3887×X+4278.8065···(1)

[0060] Therefore, if the Young's modulus E of the bonding layer 300 and the distance X of the through hole 140 located at the outermost periphery satisfy the condition expressed by the following formula (2), the value of the maximum stress generated in the dielectric substrate 100 is within Figure 4 The dielectric substrate 100 is surely prevented from being damaged by keeping the dielectric substrate 100 below the “threshold value”. E≤0.2063×X 2 -59.3887×X+4278.8065···(2)

[0061] Furthermore, for example, when the outer diameter of the dielectric substrate 100 is different from that of the present embodiment, the coefficients of the equations (1) and (2) calculated by the above method accordingly also become values ​​different from those described above in strict terms. Figure 4 Since the “threshold value” shown in FIG. 1 is a threshold value, even when the structure of electrostatic chuck 10 is slightly different from that of the present embodiment, it is possible to make a determination using equation (2) as it is.

[0062] As described above, the inventors, through the analysis conducted this time, were able to obtain the above formula (2) as a condition for making the distance X of the through hole 140 located at the outermost periphery and the Young's modulus E of the bonding layer 300 have appropriate values. If the position of the through hole 140 and the Young's modulus E of the bonding layer 300 are selected in a manner that satisfies the condition of the above formula (2), the thermal stress of the dielectric substrate 100 during the processing of the substrate W can be reduced to a level that does not cause damage. As values ​​within the range of satisfying the condition (2) while satisfying the required specifications such as the heat transfer performance required for the bonding layer 300, the specific values ​​of E and X can be appropriately set.

[0063] Furthermore, although a group of through holes 140 satisfying the condition of the above formula (2) only needs to include at least the through hole 140 located at the position farthest from the central axis AX0 of the dielectric substrate 100, it may also include other through holes 140. It is preferred that all through holes 140 formed in the dielectric substrate 100 satisfy the condition of formula (2). By making such a structure, it is possible to more reliably prevent the dielectric substrate 100 from being damaged by thermal stress.

[0064] Furthermore, it is found that the smaller the diameter of the through hole 140, etc. at the end on the opposite side of the bonding layer 300 (that is, the end on the side of the surface 110), the greater the thermal stress generated in the dielectric substrate 100. As in the through hole 140, in order to prevent insulation breakdown, the through hole for the purpose of supplying an inert gas is usually a smaller hole with a diameter of less than 0.2 mm. Through analysis, etc., it is confirmed that if the thickness and Young's modulus of the bonding layer 300 are set in a manner that satisfies the conditions of the above formula (2), even when the diameter of the through hole is less than 0.2 mm, the thermal stress can be suppressed to a degree that the dielectric substrate 100 will not be damaged. Furthermore, the above description does not negate the situation where the diameter of the through hole is made greater than 0.2 mm.

[0065] As the bonding layer 300, various types of adhesives can be used as long as they can satisfy the conditions of the above formula (2). For example, in addition to the silicone adhesive as in the present embodiment, various adhesives such as epoxy, polyimide, acrylic acid, and modified silicone resin can also be used to form the bonding layer 300. However, since the Young's modulus of the silicone adhesive after curing is relatively small, it is easy to select an adhesive that satisfies the conditions of the above formula (2) from among the various types of silicone adhesives. Therefore, as in the present embodiment, it is preferred that the bonding layer 300 is a layer in which the silicone adhesive is cured.

[0066] As an adhesive for forming the bonding layer 300, although an existing adhesive sold on the market can be directly used, an adhesive in which the Young's modulus of the existing adhesive is adjusted in a manner that satisfies the conditions of formula (2) can also be used. As a method for adjusting the Young's modulus of the adhesive, various known methods can be used. For example, a functional group or filler is added to the adhesive, and the type and amount of each added are adjusted, thereby changing the Young's modulus in a low temperature domain such as -60 degrees to a desired value. As an example, when the adhesive is a silicone resin, the amount of phenyl added is adjusted, thereby adjusting the Young's modulus particularly in the low temperature domain. In addition, the Young's modulus can also be reduced by reducing the amount of inorganic filler added.

[0067] As described above, the greater the distance X of the through hole 140, the greater the thermal stress applied to the through hole 140 portion. In the dielectric substrate 100 in which at least one through hole 140 is formed in the outer peripheral side portion where X ≥ 75 mm, the thermal stress applied to the through hole 140 portion is often so large that it cannot be ignored. However, if the material of the bonding layer 300 is selected so as to satisfy the condition of the above formula (2), the thermal stress can be suppressed to a degree that the dielectric substrate 100 is not damaged.

[0068] In this embodiment, the through hole (not the through hole 115) formed on the outermost side among the plurality of through holes formed in the dielectric substrate 100 is the through hole 140. When other through holes are formed at positions closer to the outside than the through hole 140, the Young's modulus (E) of the bonding layer 300 may be set so that the position (X) of the through hole satisfies the condition of formula (2).

[0069] Above, the present embodiment has been described with reference to specific examples. However, the present invention is not limited to these specific examples. With regard to these specific examples, as long as they have the characteristics of the present invention, the technology that is appropriately designed and changed by those skilled in the art is also included in the scope of the present invention. The various elements and their configurations, conditions, shapes, etc. possessed by the aforementioned specific examples are not limited to the illustrated contents, but can be appropriately changed. As long as there is no technical contradiction, the various elements possessed by the aforementioned specific examples can be appropriately changed and combined.

Claims

1. An electrostatic chuck, characterized in that: The invention comprises: a dielectric substrate having a through hole formed therein; a base plate formed of a metal material; and a bonding layer for bonding the dielectric substrate and the base plate, When the Young's modulus of the bonding layer is taken as E (MPa), When the distance between the central axis of the dielectric substrate and the central axis of the through hole is X (mm), With respect to the through hole located at a position farthest from the central axis of the dielectric substrate, Establish E≤0.2063×X 2 -59.3887×X+4278.8065.

2. The electrostatic chuck according to claim 1, characterized in that: The through hole has a diameter of 0.2 mm or less at an end portion on the opposite side to the bonding layer.

3. The electrostatic chuck according to claim 1, wherein: The bonding layer is formed by curing the silicone adhesive.

4. The electrostatic chuck according to claim 1, wherein: At least one of the through holes is formed at a position where X≥75 mm.

5. An electrostatic chuck, characterized in that: The invention comprises: a dielectric substrate having a through hole formed therein; a base plate formed of a metal material; and a bonding layer for bonding the dielectric substrate and the base plate, When the Young's modulus of the bonding layer is taken as E (MPa), When the distance between the central axis of the dielectric substrate and the central axis of the through hole is X (mm), With respect to all of the through holes, Establish E≤0.2063×X 2 -59.3887×X+4278.8065.

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