Electrostatic chuck

Abstract

To provide an electrostatic chuck which can make the thickness and the Young modulus of a joining layer appropriate and can reduce the thermal stress applied to a dielectric substrate.SOLUTION: An electrostatic chuck 10 includes: a dielectric substrate 100; a base plate 200 formed of a metal material; and a joining layer 300 provided between the dielectric substrate 100 and the base plate 200. If T (μm) refers to the thickness of the joining layer 300 and E (MPa) refers to the Young modulus of the joining layer 300 at -100°C, then the condition, E≤0.04×T-0.04, is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, semiconductor manufacturing equipment such as CVD equipment is equipped with an electrostatic chuck as a device for attracting and holding a substrate, such as a silicon wafer, to be processed. An electrostatic chuck includes a dielectric substrate on which an attracting electrode is provided and a base plate that supports the dielectric substrate, which are joined together. The attracting electrode is generally built into the dielectric substrate, but the metal base plate may also be used as the attracting electrode. When a voltage is applied to the attracting electrode, an electrostatic force is generated, attracting and holding a substrate placed on the dielectric substrate.

[0003] During processing, the temperature of the substrate rises due to exposure to plasma, and the temperature of the dielectric substrate also rises. Meanwhile, because a low-temperature coolant is supplied to the base plate, the temperature of the base plate may drop to -60°C or even lower. Due to temperature changes in various parts during substrate processing and the temperature difference between the dielectric substrate and the base plate, a large thermal stress is applied to the dielectric substrate.

[0004] To prevent damage to the dielectric substrate due to thermal stress, it is necessary to select a material with appropriate physical properties for the bonding layer connecting the dielectric substrate and the base plate. For example, Patent Document 1 below proposes that the storage modulus of the bonding layer (adhesive member) at -60°C be 100 MPa or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-23088 Summary of the Invention [Problem to be solved by the invention]

[0006] If a material with as small a Young's modulus as possible is used as the material for the bonding layer, the thermal stress applied to the dielectric substrate can be reduced. However, in consideration of the heat transfer performance required of the bonding layer, the Young's modulus of the bonding layer cannot be reduced as much as desired. The material for the bonding layer must be appropriately selected taking into account the required heat transfer performance, etc., under the condition that the Young's modulus is below a predetermined upper limit.

[0007] The thicker the bonding layer, the smaller the thermal stress applied to the dielectric substrate. Therefore, the thicker the bonding layer, the larger the upper limit of the Young's modulus of the bonding layer. In this way, the "thickness of the bonding layer" and the "upper limit of the Young's modulus of the bonding layer" are parameters that are correlated with each other.

[0008] However, considering the heat transfer performance required for the bonding layer, the bonding layer cannot be made as thick as desired. 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 each parameter while considering the correlation between the "thickness of the bonding layer" and the "upper limit value of the Young's modulus of the bonding layer." However, no specific study has been conducted so far on how to consider these correlations.

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

[0010] In order to solve the above problems, the present invention provides an electrostatic chuck including a dielectric substrate, a base plate made of a metal material, and a bonding layer provided between the dielectric substrate and the base plate, where the thickness of the bonding layer is T (μm) and the Young's modulus of the bonding layer at −100° C. is E (MPa), satisfying the condition E≦0.04×T−0.04.

[0011] According to experiments conducted by the present inventors, it has been found that if the thickness and Young's modulus of the bonding layer are set so as to satisfy the condition E≦0.04×T−0.04, it is possible to sufficiently reduce the thermal stress on the dielectric substrate during processing, etc. Therefore, by configuring the electrostatic chuck as described above, it is possible to reduce the thermal stress applied to the dielectric substrate while maintaining the appropriate thickness and Young's modulus of the bonding layer.

[0012] In the electrostatic chuck according to the present invention, it is also preferable that a through hole is formed in the dielectric substrate.

[0013] The dielectric substrate of an electrostatic chuck often has a through-hole formed therein for the purpose of supplying an inert gas between the substrate and the through-hole. In such cases, thermal stress tends to be large, particularly in the portion of the through-hole near the end on the substrate side. By setting the thickness and Young's modulus of the bonding layer so as to satisfy the condition E≦0.04×T−0.04, thermal stress can be suppressed to a level that does not cause damage to the dielectric substrate, even when a through-hole is formed in the dielectric substrate.

[0014] In the electrostatic chuck according to the present invention, it is also preferable that the through hole has a diameter of 0.2 mm or less at the end opposite to the bonding layer.

[0015] The smaller the diameter of the through-hole at the end opposite the bonding layer (i.e., the end facing the substrate), the greater the thermal stress generated in the dielectric substrate. Through-holes intended for supplying inert gas are often small holes with a diameter of 0.2 mm or less to prevent dielectric breakdown. By selecting a bonding layer material that satisfies the condition E≦0.04×T-0.04, thermal stress can be suppressed to a level that does not damage the dielectric substrate, even when the diameter of the through-hole is 0.2 mm or less, as mentioned above.

[0016] In the electrostatic chuck according to the present invention, it is also preferable that the thickness of the bonding layer is 100 μm or less.

[0017] The thinner the bonding layer, the greater the thermal stress on the dielectric substrate. However, even if the bonding layer is thinned to 100 μm or less, if the bonding layer material is selected to satisfy the condition E≦0.04×T-0.04, the thermal stress can be suppressed to a level that does not damage the dielectric substrate.

[0018] In the electrostatic chuck according to the present invention, the bonding layer is preferably made of a cured silicone adhesive.

[0019] By selecting from various types of silicone adhesives one that satisfies the condition E≦0.04×T−0.04 and forming a bonding layer using this adhesive, it is possible to prevent damage to the dielectric substrate due to thermal stress. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an electrostatic chuck in which the thickness and Young's modulus of the bonding layer are appropriate and the thermal stress applied to the dielectric substrate can be reduced. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of an electrostatic chuck according to an embodiment of the present invention. [Figure 2] 2 is a diagram showing the configuration of a dielectric substrate provided in the electrostatic chuck of FIG. 1. [Figure 3] FIG. 10 is a diagram showing the relationship between the Young's modulus of the bonding layer and the maximum stress generated in the dielectric substrate. [Figure 4] FIG. 10 is a diagram showing the relationship between the thickness of the bonding layer and the allowable Young's modulus. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0023] The electrostatic chuck 10 according to this embodiment is configured to electrostatically attract and hold a substrate W to be processed inside a semiconductor manufacturing apparatus (not shown), such as a CVD film forming apparatus. The substrate W is, for example, a silicon wafer. The electrostatic chuck 10 may also be used in apparatuses other than semiconductor manufacturing apparatuses.

[0024] 1 is a schematic cross-sectional view showing the configuration of an electrostatic chuck 10 in a state where the electrostatic chuck 10 attracts and holds a substrate W. The electrostatic chuck 10 includes a dielectric substrate 100, a base plate 200, and a bonding layer 300.

[0025] The dielectric substrate 100 is a substantially disk-shaped member made of a sintered ceramic body. The dielectric substrate 100 contains, for example, high-purity aluminum oxide (Al2O3), but may also contain other materials. The purity, type, and additives of the ceramics in the dielectric substrate 100 can be appropriately set in consideration of the plasma resistance and other properties required of the dielectric substrate 100 in semiconductor manufacturing equipment.

[0026] 1 of the dielectric substrate 100 is a "mounting surface" on which the substrate W is placed. Also, a lower surface 120 of the dielectric substrate 100 in FIG. 1 is a "bonded surface" that is bonded to the base plate 200 via a bonding layer 300 described later. The viewpoint when the electrostatic chuck 10 is viewed from the side of the surface 110 along a direction perpendicular to the surface 110 will hereinafter also be referred to as a "top view."

[0027] An attraction electrode 130 is embedded inside the dielectric substrate 100. The attraction electrode 130 is a thin, flat layer made of a metal material such as tungsten, and is disposed parallel to the surface 110. In addition to tungsten, the attraction electrode 130 may be made of molybdenum, platinum, palladium, or the like. When a voltage is applied to the attraction electrode 130 from the outside via the power supply line 13, an electrostatic force is generated between the surface 110 and the substrate W, thereby attracting and holding the substrate W. Two attraction electrodes 130 may be provided as so-called "bipolar" electrodes as in this embodiment, or only one may be provided as so-called "monopolar" electrode.

[0028] 1, the entire power feed line 13 is depicted in a simplified manner. The portion of the power feed line 13 inside the dielectric substrate 100 is configured, for example, as a long, narrow via (hole) filled with a conductor, and an electrode terminal (not shown) is provided at the bottom end of the via. The portion of the power feed line 13 that penetrates the base plate 200 described below is a conductive metal member (e.g., a bus bar) with one end connected to the electrode terminal. A through hole (not shown) is formed in the base plate 200 for inserting the power feed line 13. A cylindrical insulating member, for example, may be provided between the inner surface of the through hole and the power feed line 13.

[0029] 1, a space SP is formed between the dielectric substrate 100 and the substrate W. When a process such as film formation is performed in the semiconductor manufacturing apparatus, helium gas for temperature adjustment is supplied to the space SP from the outside via gas holes 140 (described later). By providing helium 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. Note that the temperature adjustment gas supplied to the space SP may be a type of gas other than helium.

[0030] 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 a surface 110, which is a mounting surface, and the space SP is formed around these.

[0031] The seal rings 111 are walls that divide the space SP, and multiple seal rings 111 are provided so as to be arranged concentrically in a top view. The upper end of each seal ring 111 forms part of the surface 110 and abuts against the substrate W. In this embodiment, a total of four seal rings 111 are provided, thereby dividing the space SP into four parts. With this configuration, it is possible to individually adjust the pressure of the helium gas in each space SP and make the surface temperature distribution of the substrate W during processing more uniform.

[0032] 1 and 2, the portion designated by 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, together with the dots 112 described below, is formed by digging down a portion of the surface 110 to the position of the bottom surface 116.

[0033] The dots 112 are circular protrusions that protrude from the bottom surface 116. As shown in FIG. 2, a plurality of dots 112 are provided and are distributed approximately evenly on the mounting surface of the dielectric substrate 100. The upper end of each dot 112 forms part of the surface 110 and comes into contact with the substrate W. By providing a plurality of such dots 112, bending of the substrate W is suppressed.

[0034] Groove 113 is formed in bottom surface 116 of space SP. Groove 113 is formed so as to recede further from bottom surface 116 toward surface 120. Groove 113 is formed for the purpose of quickly diffusing helium gas supplied from gas holes 140 into space SP and making the pressure distribution in space SP approximately uniform within a short period of time.

[0035] Dielectric substrate 100 has gas holes 140 formed therein, extending perpendicularly from surface 120 toward surface 110. As shown in Fig. 2, the ends of gas holes 140 on the surface 110 side open at the bottom of groove 113. A plurality of gas holes 140 are formed in dielectric substrate 100, and these are lined up along groove 113. In this embodiment, a plurality of gas holes 140 are connected to each of four divided spaces SP.

[0036] 2, for convenience of illustration, the diameter of the gas hole 140 is depicted as being larger than the width of the groove 113, but as shown in FIG. 1, the diameter of the gas hole 140 is actually smaller than the width of the groove 113. The width of the groove 113 may be locally larger at the position of the gas hole 140 so that the gas hole 140 fits inside the groove 113.

[0037] 1, the portion of gas hole 140 on the side of surface 120 has a larger diameter than the portion on the side of surface 110, and a vent plug 145 is disposed inside the portion. Vent plug 145 is a porous body made of alumina, for example, and is entirely breathable. By disposing such a vent plug 145 inside gas hole 140, it is possible to ensure the flow of gas through gas hole 140 while suppressing the occurrence of dielectric breakdown in the path through gas hole 140.

[0038] In FIG. 2, the reference numeral "115" denotes holes through which lift pins (not shown) provided in the semiconductor manufacturing equipment are inserted. These holes are also referred to as "lift pin holes 115" below. A total of three lift pin holes 115 are formed, and these are arranged at equal intervals of 120 degrees. The lift pins that move up and down through the lift pin holes 115 are used to attach and detach the substrate W to and from the surface 110 of the dielectric substrate 100.

[0039] 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. An upper surface 210 of the base plate 200 in FIG. 1 is a "bonded surface" that is bonded to the dielectric substrate 100 via a bonding layer 300.

[0040] 1, gas holes 240 are formed in the base plate 200, extending vertically from the surface 210 toward the opposite surface 220. The gas holes 240 are formed at positions that overlap with the gas holes 140 in the dielectric substrate 100 in a top view, and are connected to the gas holes 140 via through holes 310 provided in the bonding layer 300. The gas holes 240, together with the gas holes 140 in the dielectric substrate 100, form part of a path for supplying helium gas toward the space SP.

[0041] 1, the portion of gas hole 240 on the side of surface 210 has a larger diameter than the portion on the side of surface 220, and a vent plug 245 is disposed inside the portion. Ventilation plug 245 is a porous body made of alumina, for example, and is entirely breathable. By disposing such a vent plug 245 inside gas hole 240, it is possible to ensure the flow of gas through gas hole 240 while suppressing the occurrence of dielectric breakdown in the path through gas hole 240.

[0042] The gas holes 240 may be formed so as to extend linearly as in the present embodiment, or may be formed so as to bend on the way to the surface 220. Alternatively, the gas holes 240 on the surface 210 side may be aggregated into a small number of flow paths inside the base plate 200, and the flow paths may be extended to the surface 220 side.

[0043] A coolant flow path 250 for flowing a coolant is formed inside the base plate 200. When a process such as film formation is performed in the semiconductor manufacturing equipment, a coolant is supplied to the coolant flow path 250 from the outside, thereby cooling the base plate 200. Heat generated in the substrate W during the process is transferred to the coolant 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 coolant.

[0044] In the base plate 200, through holes (not shown) for passing lift pins are formed at positions that overlap with the lift pin holes 115 in a top view.

[0045] 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 over an area that includes at least the entire face 210. The insulating film may be, for example, an alumina film formed by thermal spraying. By covering the surface of the base plate 200 with an insulating film, the dielectric strength of the base plate 200 can be increased.

[0046] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and bonds them together. The bonding layer 300 is formed 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 formed by curing another type of adhesive. In either case, it is preferable to use a material with as high a thermal conductivity as possible as the material for the bonding layer 300 so as to reduce the thermal resistance between the dielectric substrate 100 and the base plate 200.

[0047] The dielectric substrate 100 is bonded to the base plate 200 with the surface 120 parallel to the surface 210 of the base plate 200. Therefore, the thickness of the bonding layer 300 is uniform throughout. The numerical value representing the thickness of the bonding layer 300 in units of μm will be referred to as "T" below. For example, if the thickness of the bonding layer 300 is 0.1 mm, T=100.

[0048] Note that there may be cases where the thickness of bonding layer 300 is not uniform overall, such as when an electrode terminal is embedded on surface 120 of dielectric substrate 100 or when a groove is formed in part of surface 210 of base plate 200. In such cases, the thickness of the bonding layer 300 excluding the portions of bonding layer 300 that have a locally different thickness as described above is defined as the "thickness of bonding layer 300" and may be represented by T.

[0049] The bonding layer 300 has a smaller Young's modulus (modulus of longitudinal elasticity) than the dielectric substrate 100 and the base plate 200. Even if a difference in thermal expansion occurs between the dielectric substrate 100 and the base plate 200, the bonding layer 300 deforms and absorbs the difference in thermal expansion, thereby making it possible to keep the thermal stress in the dielectric substrate 100 etc. small.

[0050] The Young's modulus of the bonding layer 300 changes depending on the temperature of the bonding layer 300. The Young's modulus of the bonding layer 300 when the temperature of the bonding layer 300 is −100° C., expressed in units of “MPa,” will be referred to as “E” hereinafter. For example, when the Young's modulus of the bonding layer 300 at −100° C. is 0.01 GPa, E=10. Note that the temperature “−100° C.” above is merely a convenient standard for identifying the physical property (Young's modulus) of the bonding layer 300, and does not limit the temperature of the coolant actually supplied to the coolant flow path 250.

[0051] In recent years, with an increase in the amount of energy incident on the substrate W during processing, there is a tendency for the base plate 200 to be required to have higher cooling performance than before. For example, a coolant at a temperature of -60°C or lower may be supplied to the coolant flow path 250 of the base plate 200. As the plasma power becomes higher, the coolant temperature will become even lower, and it is possible that a coolant at about -100°C will be supplied in the future.

[0052] Large thermal stress is applied to the dielectric substrate 100 due to temperature changes in various parts when processing of the substrate W begins, temperature differences between the dielectric substrate 100 and the base plate 200, etc. In particular, thermal stress tends to concentrate at the outlet portions of the gas holes 140 in the dielectric substrate 100, and damage to the dielectric substrate 100 may occur starting from these portions.

[0053] If a material with as small a Young's modulus as possible is used as the material for the bonding layer 300, it is possible to reduce the thermal stress applied to the dielectric substrate 100. However, in consideration of the heat transfer performance, etc. required for the bonding layer 300, the Young's modulus of the bonding layer 300 cannot be made as small as desired. The material for the bonding layer 300 needs to be appropriately selected in consideration of the required heat transfer performance, etc., under the condition that the Young's modulus is equal to or less than a predetermined upper limit.

[0054] The thicker the thickness (T) of the bonding layer 300, the smaller the thermal stress applied to the dielectric substrate 100, and therefore the larger the upper limit of the allowable Young's modulus (E). In this way, the thickness (T) of the bonding layer 300 and the upper limit of the Young's modulus (E) of the bonding layer 300 at -100°C are parameters that are correlated with each other. The present inventors have conducted various experiments and analyses, and have obtained the following new findings regarding the above correlation.

[0055] 3 show the relationship between the Young's modulus (horizontal axis) of the bonding layer 300 at -100°C and the maximum stress (vertical axis) generated in the dielectric substrate 100 for each thickness (T1 to T5) of the bonding layer 300. The Young's modulus on the horizontal axis is the individual value of "E" mentioned above, and "T1", "T5", etc. are the individual values ​​of "T" mentioned above.

[0056] 3 were obtained by performing an analysis each time while changing the Young's modulus of the bonding layer 300 (specifically, the Young's modulus at −100° C.) and plotting the maximum value of stress generated in the dielectric substrate 100 at low temperatures. Specifically, the above-mentioned “low temperature” refers to the time when the bonding layer 300 is cured when the temperature of the entire electrostatic chuck 10 is 40° C., and then the temperature of the entire electrostatic chuck 10 is lowered to −100° C. In each analysis, the portion of the dielectric substrate 100 that was calculated to have the highest thermal stress was a portion near the end of the gas holes 140 arranged on the outermost periphery, on the surface 110 side.

[0057] The character strings such as "T1" and "T2" added to the right of each graph indicate the thickness of the bonding layer 300. Of these, T1 is the thinnest and T5 is the thickest.

[0058] 3, it can be seen that the maximum stress generated in the dielectric substrate 100 at low temperatures increases as the Young's modulus of the bonding layer 300 increases. Furthermore, when compared under conditions where the Young's modulus of the bonding layer 300 is the same, it can be seen that the thinner the thickness of the bonding layer 300, the greater the maximum stress generated in the dielectric substrate 100 at low temperatures.

[0059] The "threshold" shown on the vertical axis of FIG. 3 is the upper limit of the range of maximum stress that will not cause damage to the dielectric substrate 100.

[0060] In the figure, "E1" is the Young's modulus (E) value at which the maximum stress value reaches the threshold value when the electrostatic chuck 10 has a bonding layer 300 with a thickness of "T1." "E2" is the Young's modulus (E) value at which the maximum stress value reaches the threshold value when the electrostatic chuck 10 has a bonding layer 300 with a thickness of "T2." The same applies to "E3," "E4," and "E5." Each of E1 to E5 can be considered an upper limit value of the allowable range for the "Young's modulus at -100°C" to prevent damage to the dielectric substrate 100. Such an upper limit value of the Young's modulus is hereinafter also referred to as the "allowable Young's modulus." As is clear from FIG. 3, the allowable Young's modulus (E1 to E5) varies depending on the thickness (T1 to T5) of the bonding layer 300.

[0061] 4 shows the relationship between the thicknesses T1 to T5 (horizontal axis) of the bonding layer 300 and the allowable Young's moduli E1 to E5 (vertical axis). As shown in the figure, there is a roughly linear correlation between the two. The linear correlation shown in FIG. 4 can be expressed by the following equation (1): (allowable Young's modulus)=0.04×(thickness of bonding layer 300)−0.04 (1)

[0062] Therefore, if the Young's modulus E of the bonding layer 300 at -100°C and the thickness T of the bonding layer 300 satisfy the condition shown in the following formula (2), the value of the maximum stress generated in the dielectric substrate 100 will be below the "threshold" in Figure 3, and damage to the dielectric substrate 100 will be reliably prevented. E≦0.04×T-0.04 (2)

[0063] As described above, the present inventors have obtained the above formula (2) as the conditions for optimizing the thickness and Young's modulus of the bonding layer 300 through the analysis and the like recently performed. If the thickness and Young's modulus of the bonding layer 300 are selected so as to satisfy the condition of the above formula (2), the thermal stress of the dielectric substrate 100 during processing of the substrate W can be reduced to a level that does not cause damage. The specific values ​​of E and T may be appropriately set within a range that satisfies the required specifications, such as the heat transfer performance, required of the bonding layer 300 and also satisfies the condition of the above formula (2).

[0064] The above findings are particularly useful when through holes such as the gas holes 140 are formed in the dielectric substrate 100, as in this embodiment. In such a configuration, thermal stress tends to be large in the through holes, particularly in the portion near the end on the substrate W side. However, it has been confirmed by analysis and the like that, if the thickness and Young's modulus of the bonding layer 300 are set to satisfy the condition of the above formula (2), thermal stress can be suppressed to a level that does not cause damage to the dielectric substrate 100, even when through holes are formed in the dielectric substrate 100.

[0065] It has been found that the smaller the diameter of a through-hole, such as the gas hole 140, at the end opposite the bonding layer 300 (i.e., the end on the surface 110 side), the greater the thermal stress generated in the dielectric substrate 100. Through-holes for supplying inert gas, such as the gas hole 140, are often small holes with a diameter of 0.2 mm or less to prevent dielectric breakdown. It has been confirmed through analysis and other means that if the thickness and Young's modulus of the bonding layer 300 are set to satisfy the condition of the above formula (2), thermal stress can be suppressed to a level that does not cause damage to the dielectric substrate 100, even if the diameter of the through-hole is 0.2 mm or less. The above description does not in any way negate the possibility of setting the diameter of the through-hole to 0.2 mm or more.

[0066] The thinner the bonding layer 300, the greater the thermal stress applied to the dielectric substrate 100. However, even when the thickness of the bonding layer 300 is reduced to 100 μm or less, by selecting a material for the bonding layer 300 that satisfies the condition of the above formula (2), the thermal stress can be suppressed to a level that does not cause damage to the dielectric substrate 100. In other words, according to the above findings obtained by the inventors, it is possible to reduce the thickness of the bonding layer 300 to 100 μm or less, which is thinner than conventional, thereby sufficiently improving the heat transfer performance of the bonding layer 300 while preventing damage to the dielectric substrate 100 due to thermal stress. Note that the above description does not in any way negate the possibility of the bonding layer 300 having a thickness of 100 μm or more.

[0067] Various types of adhesives can be used for the bonding layer 300 as long as they satisfy the condition of the above formula (2). For example, in addition to the silicone adhesive used in this embodiment, various adhesives such as epoxy, polyimide, acrylic, and modified silicone resin can be used to form the bonding layer 300. However, since the Young's modulus of a silicone adhesive after curing is relatively small, it is easy to select one that satisfies the condition of the above formula (2) from various types of silicone adhesives. For this reason, it is preferable that the bonding layer 300 be made by curing a silicone adhesive, as in this embodiment.

[0068] The adhesive for forming the bonding layer 300 may be a commercially available adhesive as is, or an existing adhesive whose Young's modulus has been adjusted to satisfy the condition of formula (2). Various known methods can be used to adjust the Young's modulus of the adhesive. For example, by adding functional groups or fillers to the adhesive and adjusting the type and amount of each, the Young's modulus at low temperatures such as -100°C can be changed to a desired value. For example, when the adhesive is a silicone resin, the Young's modulus can be adjusted, particularly at low temperatures, by adjusting the amount of phenyl groups added. The Young's modulus can also be lowered by reducing the amount of inorganic filler added.

[0069] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-described specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-described specific examples can be combined in various ways as appropriate, as long as no technical contradictions arise. [Explanation of symbols]

[0070] 10: Electrostatic chuck 100: Dielectric substrate 140: Gas hole 200: Base plate 300: Bonding layer

Claims

1. Dielectric substrate and A base plate formed from a metal material, A bonding layer is provided between the dielectric substrate and the base plate, The surface of the bonding layer on the base plate side is in direct contact with the surface of the base plate on the bonding layer side, or through an insulating layer. Let T be the thickness of the bonding layer (μm). When the Young's modulus of the bonding layer at -100°C is E (MPa), E ≤ 0.04 × T - 0.04 An electrostatic chuck characterized by satisfying the following conditions.

2. The electrostatic chuck according to claim 1, characterized in that a through hole is formed in the dielectric substrate.

3. The electrostatic chuck according to claim 2, characterized in that the diameter of the through hole at the end opposite to the bonding layer is 0.2 mm or less.

4. The electrostatic chuck according to claim 1, characterized in that the thickness of the bonding layer is 100 μm or less.

5. The electrostatic chuck according to claim 1, characterized in that the bonding layer is made of a cured silicone adhesive.

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