Electrostatic chuck

Abstract

To suppress breakage of a resin layer under low temperature.SOLUTION: An electrostatic chuck includes a base plate, a ceramic plate, and a resin layer. The ceramic plate is fixed to the base plate and attracts an object by electrostatic force generated by energization of a built-in electrode. The resin layer is a resin layer that bonds the base plate and the ceramic plate, and is formed from one or more laminated adhesives, and at least one of the one or more adhesives has a temperature corresponding to the extreme value of loss tangent is -70°C or less in a temperature range of -150°C to 250°C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] For example, when manufacturing semiconductor parts, electrostatic chucks (ESCs) are sometimes used to attract and hold wafers. An electrostatic chuck has a structure in which a ceramic plate with an electrode built in is bonded to a metal base plate with a resin layer. When a voltage is applied to the electrode built into the ceramic plate, the electrostatic chuck attracts the wafer to the ceramic plate using electrostatic force.

[0003] The adhesive for forming the resin layer is, for example, a flexible silicone resin adhesive, which maintains good thermal conductivity and absorbs the difference in thermal expansion between the base plate and the ceramic plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-23088 Summary of the Invention [Problem to be solved by the invention]

[0005] The manufacture of semiconductor components using an electrostatic chuck may be performed at low temperatures, such as temperatures below -60°C. When an electrostatic chuck is used at temperatures below -60°C, the flexibility of the resin layer between the base plate and the ceramic plate in the electrostatic chuck may decrease. This is because the storage modulus, a physical property that indicates the hardness of the adhesive forming the resin layer, increases rapidly around -60°C, causing the adhesive to harden. When the flexibility of the resin layer decreases at low temperatures, the resin layer may not adequately relieve stress caused by the difference in thermal expansion between the base plate and the ceramic plate, potentially resulting in damage to the resin layer. Damage to the resin layer locally reduces the heat transfer characteristics between the base plate and the ceramic plate via the resin layer, resulting in reduced thermal uniformity on the surface of the ceramic plate, which serves as the chucking surface.

[0006] The disclosed technology has been made in view of the above, and aims to provide an electrostatic chuck that can suppress damage to a resin layer at low temperatures. [Means for solving the problem]

[0007] In one embodiment, the electrostatic chuck disclosed herein includes a base plate, a ceramic plate, and a resin layer. The ceramic plate is fixed to the base plate and attracts an object by electrostatic force generated by energizing a built-in electrode. The resin layer bonds the base plate and the ceramic plate and is formed from one or more laminated adhesives, and at least one of the one or more adhesives has a temperature corresponding to an extreme value of loss tangent of −70°C or lower within a temperature range of −150°C to 250°C. [Effects of the Invention]

[0008] According to one aspect of the electrostatic chuck disclosed in the present application, it is possible to suppress damage to the resin layer at low temperatures. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a perspective view showing the configuration of an electrostatic chuck according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a cross section of the electrostatic chuck according to the embodiment. [Figure 3] FIG. 3 is a graph showing the measurement results of the loss tangent of the adhesive. [Figure 4] FIG. 4 is an explanatory diagram showing an example of the relationship between the thickness of the adhesive forming the resin layer and the delamination and thermal uniformity on the adsorption surface. [Figure 5] FIG. 5 is a schematic diagram showing a cross section of an electrostatic chuck according to a first modification of the embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a cross section of an electrostatic chuck according to a second modification of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the electrostatic chuck disclosed in the present application will be described in detail with reference to the drawings. However, the disclosed technology is not limited to these embodiments.

[0011] (Embodiment) 1 is a perspective view showing the configuration of an electrostatic chuck 100 according to an embodiment. The electrostatic chuck 100 shown in FIG.

[0012] The base plate 110 is a circular member made of metal such as aluminum. The base plate 110 serves as the base material of the electrostatic chuck 100. A coolant passage for passing a coolant such as cooling water is formed inside the base plate 110, and adjusts the temperature of the ceramic plate 120 and the wafer attracted to the ceramic plate 120.

[0013] The ceramic plate 120 is a circular member made of insulating ceramic. The diameter of the ceramic plate 120 is smaller than the diameter of the base plate 110, and the ceramic plate 120 is fixed to the center of the base plate 110. In other words, one surface of the ceramic plate 120 serves as an adhesive surface that is bonded to the base plate 110, and the ceramic plate 120 is fixed by being bonded to the base plate 110 by a resin layer. The surface of the ceramic plate 120 opposite the bonding surface serves as an adsorption surface that adsorbs an object to be adsorbed, such as a wafer.

[0014] A conductive electrode is disposed inside the ceramic plate 120 , and when a current is applied to the electrode, an electrostatic force is generated, and the target object is attracted to the attraction surface of the ceramic plate 120 by the electrostatic force.

[0015] A heater electrode is disposed inside the ceramic plate 120, and generates heat when energized to adjust the temperature of the ceramic plate 120 and the object such as a wafer attracted to the ceramic plate 120.

[0016] Fig. 2 is a schematic diagram showing a cross section of an electrostatic chuck 100 according to an embodiment. Fig. 2 shows a cross section taken along line II-II in Fig. 1. As shown in Fig. 2, the electrostatic chuck 100 is configured by bonding a ceramic plate 120 to a base plate 110 with a resin layer 130.

[0017] Base plate 110 is a metal member having a thickness of, for example, about 20 to 50 mm, and has coolant passages 111 therein for a coolant such as cooling water or cooling gas. As the coolant passes through coolant passages 111, ceramic plate 120 and a wafer adsorbed to ceramic plate 120 are cooled. As a result of cooling ceramic plate 120, an object such as a wafer adsorbed to ceramic plate 120 is cooled.

[0018] The ceramic plate 120 is a plate made of ceramic, having an electrode 121 and a heater electrode 122 inside, and having a thickness of, for example, about 4.5 mm. The ceramic is obtained by firing a green sheet made of, for example, aluminum oxide. The lower surface of the ceramic plate 120 is an adhesive surface that is bonded to the base plate 110, and is bonded to the upper surface of the base plate 110 by a resin layer 130.

[0019] When a voltage is applied to the electrode 121 of the ceramic plate 120, the ceramic plate 120 attracts an object such as a wafer by electrostatic force. That is, in Fig. 2, the upper surface of the ceramic plate 120 serves as the attracting surface, and when a voltage is applied to the electrode 121, the object is attracted to the attracting surface.

[0020] Furthermore, when a voltage is applied to the heater electrode 122 of the ceramic plate 120, the heater electrode 122 generates heat, which heats the ceramic plate 120 and the object attracted to the ceramic plate 120. The temperature of the ceramic plate 120 is then adjusted by the heating by the heater electrode 122 and the cooling by the base plate 110, and the temperature of the object attracted to the ceramic plate 120 is adjusted to a desired temperature.

[0021] The electrode 121 and the heater electrode 122 may be made of a conductor such as tungsten.

[0022] Resin layer 130 is a layer formed from a silicone resin-based adhesive, for example, with a thickness of approximately 0.05 mm to 3.0 mm, and bonds the lower surface of ceramic plate 120 to the upper surface of base plate 110. The adhesive that forms resin layer 130 has a temperature corresponding to the extreme value of the loss tangent of -70°C or lower. Fig. 3 is a graph showing the measurement results of the loss tangent of the adhesive that forms resin layer 130. Fig. 3 shows the measurement results obtained by dynamic viscoelasticity measurement (DMA) for test pieces of adhesive A and adhesive B used as adhesives to form resin layer 130.

[0023] The measurement conditions for the measurement results shown in FIG. 3 are as follows: Measurement equipment: DMA6100 (Hitachi High-Tech Science) Measurement temperature range: -150℃~250℃ Heating rate: 5℃ / min Measurement mode: Tensile Measurement frequency: 1Hz Test piece shape: Strip shape Test piece dimensions: length 15mm x width 15mm x thickness 0.1~1mm Strain amplitude: 10 μm

[0024] In DMA, the complex modulus (G * ), storage modulus (G') and loss modulus (G") were measured. G * =G'+G”i (1) Here, the storage modulus (G') is a value indicating the hardness of a viscoelastic body, and the loss modulus (G") is a value indicating the viscosity of the viscoelastic body.

[0025] In addition, in DMA, the loss tangent tanδ, expressed by the following formula (2), was calculated from the storage modulus (G') and loss modulus (G"): The loss tangent tanδ is a value that indicates the degree of contribution of viscosity to a viscoelastic body. The temperature corresponding to the extreme value of the loss tangent tanδ is also called the glass transition temperature (Tg). tanδ=G” / G' (2)

[0026] 3, the measurement data obtained from the test piece indicates that the temperature corresponding to the extreme value of the loss tangent tanδ for adhesive A is −102.5°C, and the temperature corresponding to the extreme value of the loss tangent tanδ for adhesive B is −118.5°C. In other words, it is found that the adhesive (adhesive A or adhesive B) forming the resin layer 130 has a temperature corresponding to the extreme value of the loss tangent, i.e., a glass transition temperature (Tg), of −70°C or lower.

[0027] If the glass transition temperature (Tg) of the resin layer 130 is higher than −70°C, the flexibility of the resin layer 130 may decrease at low temperatures, for example, at −60°C or below. This is because the storage modulus (G′) of the adhesive forming the resin layer 130 increases rapidly at temperatures around −60°C, causing the adhesive to harden. If the flexibility of the resin layer 130 decreases at low temperatures, the stress caused by the difference in thermal expansion between the base plate 110 and the ceramic plate 120 may not be fully alleviated by the resin layer 130, resulting in the risk of the resin layer 130 being destroyed. The destruction of the resin layer 130 locally reduces the heat transfer characteristics between the base plate 110 and the ceramic plate 120 via the resin layer 130, which ultimately reduces the thermal uniformity on the surface of the ceramic plate 120, which serves as the adsorption surface.

[0028] In contrast, by forming the resin layer 130 from an adhesive having a glass transition temperature (Tg) of −70°C or lower in the temperature range of −150°C to 250°C, the resin layer 130 maintains good flexibility even when the electrostatic chuck 100 is used at low temperatures, such as −60°C or lower. Since the resin layer 130 has a glass transition temperature (Tg) of −70°C or lower, the storage modulus (G′) of the resin layer 130 at low temperatures, such as −60°C or lower, is maintained at approximately the same value as that at room temperature, thereby suppressing hardening of the resin layer 130. Therefore, even when the electrostatic chuck 100 is used at low temperatures, the resin layer 130 deforms to sufficiently relieve stress caused by the difference in thermal expansion between the base plate 110 and the ceramic plate 120. This suppresses damage to the resin layer 130 at low temperatures, thereby reducing the temperature difference on the attracting surface of the ceramic plate 120 and enabling the electrostatic chuck 100 to achieve sufficiently high thermal uniformity. The glass transition temperature (Tg) of the adhesive forming the resin layer 130 is more preferably −100° C. or lower.

[0029] The adhesive forming the resin layer 130 has a thermal conductivity of 0.5 W / mK or more at -60°C. For example, adhesive A shown in FIG. 3 has a thermal conductivity of 2.16 W / mK at -60°C, and adhesive B has a thermal conductivity of 1.12 W / mK at -60°C. The thermal conductivity is calculated based on the thermal diffusivity, specific heat capacity, and density. The thermal diffusivity can be measured by, for example, the laser flash method, the specific heat capacity can be measured by, for example, the adiabatic continuous method, and the density can be measured by, for example, the liquid weighing method.

[0030] If the thermal conductivity of the adhesive forming the resin layer 130 is less than 0.5 W / mK at -60°C, the thermal conductivity of the resin layer 130 will decrease at low temperatures, for example, at or below -60°C. In contrast, by forming the resin layer 130 from an adhesive having a thermal conductivity of 0.5 W / mK or more at -60°C, it is possible to prevent the thermal conductivity of the resin layer 130 from decreasing at low temperatures. The thermal conductivity of the adhesive forming the resin layer 130 at -60°C is preferably 1 W / mK or more.

[0031] However, if the resin layer 130 is thin, the resin layer 130 cannot adequately relieve the stress caused by the adhesion of dissimilar materials, which can lead to the destruction of the resin layer 130. Therefore, the inventors of the present application conducted an experiment to investigate the relationship between the thickness of the adhesive forming the resin layer 130 and delamination and thermal uniformity on the adsorption surface. The results of this experiment are shown in FIG. 4. FIG. 4 is an explanatory diagram showing an example of the relationship between the thickness of the adhesive forming the resin layer 130 and delamination and thermal uniformity on the adsorption surface. Note that delamination refers to, for example, delamination between the resin layer 130 and the ceramic plate 120.

[0032] 4, the thickness of the adhesive forming the resin layer 130 was set to four different values, and a thermal cycle test was performed 1,000 cycles within a predetermined temperature range. After the thermal cycle test, the electrostatic chuck 100 was evaluated for the presence or absence of delamination and the temperature difference on the chucking surface. In this experiment, the thickness of the adhesive forming the resin layer 130 was set to four different values: 0.3 mm, 0.25 mm, 0.2 mm, and 0.15 mm. In addition, in this experiment, the temperature range in the thermal cycle test was set to -40°C to 60°C.

[0033] As shown in FIG. 4, when the adhesive thickness was 0.25 mm or more, delamination between the resin layer 130 and the ceramic plate 120 did not occur. Furthermore, when the adhesive thickness was 0.25 mm or more, the temperature difference on the adsorption surface of the ceramic plate 120 was smaller than when the adhesive thickness was less than 0.25 mm. That is, the results in FIG. 4 show that when the adhesive forming the resin layer 130 is 0.25 mm or more thick, delamination can be suppressed and high thermal uniformity can be maintained on the adsorption surface. Therefore, it is preferable that the thickness of the adhesive forming the resin layer 130 be 0.25 mm or more.

[0034] (Variation) In the above embodiment, the resin layer 130 that bonds the base plate 110 and the ceramic plate 120 is formed from a single layer of adhesive. However, the bonding layer may be formed by stacking multiple adhesives. In other words, the bonding layer may be formed from one or more laminated adhesives. Specifically, for example, as shown in FIG. 5 , in an electrostatic chuck 100A according to Modification 1, the resin layer 130A may be formed by stacking a first adhesive 131 and a second adhesive 132. FIG. 5 is a schematic diagram showing a cross section of the electrostatic chuck 100A according to Modification 1 of the embodiment. The first adhesive 131 is applied to the base plate 110. The second adhesive 132 is applied between the first adhesive 131 and the ceramic plate 120. The first adhesive 131 and the second adhesive 132 have a glass transition temperature (Tg) of −70°C or lower, which corresponds to the extreme value of the loss tangent, in a temperature range of −150°C to 250°C. The glass transition temperature (Tg) of the first adhesive 131 and the glass transition temperature (Tg) of the second adhesive 132 may be the same or different. By forming the resin layer 130A by applying the first adhesive 131 and the second adhesive 132 in this way, deformation of the resin layer 130A at low temperatures is promoted and horizontal displacement is absorbed, thereby making it possible to further suppress damage to the resin layer 130 at low temperatures. The resin layer 130 may also be formed by laminating a sheet-like first adhesive 131 and a sheet-like second adhesive 132.

[0035] Furthermore, when the bonding layer is formed from one or more laminated adhesives, it is sufficient that the temperature corresponding to the extreme value of the loss tangent of at least one of the one or more adhesives is −70°C or less in the temperature range of −150°C to 250°C. For example, the temperature corresponding to the extreme value of the loss tangent of only one of the one or more adhesives forming the bonding layer may be −70°C or less in the temperature range of −150°C to 250°C. A modification in this case is shown in FIG. 6. FIG. 6 is a schematic diagram showing a cross section of an electrostatic chuck 100B according to a second modification of the embodiment. As shown in FIG. 6, in the electrostatic chuck 100B according to the second modification, the resin layer 130B is formed by laminating a sheet-shaped first adhesive 133 and a sheet-shaped second adhesive 132. The first adhesive 133 is laminated on the base plate 110. The second adhesive 132 is laminated between the first adhesive 133 and the ceramic plate 120. Of the first adhesive 133 and the second adhesive 132, the second adhesive 132 has a temperature corresponding to the extreme value of its loss tangent that is −70°C or lower in a temperature range of −150°C to 250°C. On the other hand, the temperature corresponding to the extreme value of the loss tangent of the first adhesive 133 is higher than 70°C. In this case, the first adhesive 133 may have a higher viscosity before thermal curing and a higher storage modulus after thermal curing than the second adhesive 132. This allows the hardness of the first adhesive 133 to be appropriately maintained, and the thickness of the resin layer 130B can be appropriately adjusted by adjusting the thickness of the first adhesive 133. In the example of FIG. 6, the thickness of the first adhesive 133 is greater than the thickness of the second adhesive 132. For example, the thickness of the first adhesive 133 is approximately 0 to 1 mm, and the thickness of the second adhesive 132 is approximately 0.05 to 0.5 mm.

[0036] In the examples of FIGS. 5 and 6, the resin layers 130A and 130B are formed by laminating two layers of adhesive, but the resin layers may be formed by laminating three or more layers of adhesive.

[0037] (Other variations) In the electrostatic chuck 100 described above, the resin layer 130 may contain a filler such as aluminum oxide, silicon carbide, or zinc oxide to improve the thermal conductivity of the resin layer 130. In addition, from the viewpoint of improving the adhesiveness between the base plate 110 and the ceramic plate 120 by the resin layer 130, a silane coupling agent layer may be provided on the upper and lower surfaces of the resin layer 130, as necessary.

[0038] As described above, an electrostatic chuck according to an embodiment (e.g., electrostatic chuck 100) includes a base plate (e.g., base plate 110), a ceramic plate (e.g., ceramic plate 120), and a resin layer (e.g., resin layers 130, 130A, 130B). The ceramic plate is fixed to the base plate and attracts an object by electrostatic force generated by energizing a built-in electrode. The resin layer bonds the base plate and the ceramic plate and is formed from one or more laminated adhesives, at least one of which has a temperature corresponding to an extreme value of the loss tangent of −70°C or lower in a temperature range of −150°C to 250°C. This makes it possible for the electrostatic chuck according to the embodiment to suppress breakdown of the resin layer at low temperatures, thereby achieving sufficiently high thermal uniformity.

[0039] At least one of the one or more adhesives may have a thermal conductivity of 0.5 W / mK or more at −60° C. Thus, according to the electrostatic chuck according to the embodiment, it is possible to prevent a decrease in the thermal conductivity of the resin layer at low temperatures.

[0040] At least one of the one or more adhesives may contain a filler, which allows the electrostatic chuck according to the embodiment to improve the thermal conductivity of the resin layer.

[0041] The resin layer may also include a first adhesive (e.g., first adhesives 131 and 133) applied to the base plate and a second adhesive (e.g., second adhesive 132) applied between the first adhesive and the ceramic plate. At least one of the first adhesive and the second adhesive may have a temperature corresponding to an extreme value of the loss tangent of −70° C. or less in a temperature range of −150° C. to 250° C. As a result, according to the electrostatic chuck of the embodiment, deformation of the resin layer at low temperatures is promoted and horizontal displacement is absorbed, thereby further suppressing damage to the resin layer at low temperatures.

[0042] Furthermore, one of the first adhesive and the second adhesive may have a temperature corresponding to an extreme value of the loss tangent of -70°C or less in a temperature range of -150°C to 250°C. The other of the first adhesive and the second adhesive may have a viscosity before thermal curing and a storage modulus after thermal curing greater than those of one of the first adhesive and the second adhesive. This allows the electrostatic chuck according to the embodiment to appropriately adjust the thickness of the resin layer.

[0043] The thickness of the other of the first adhesive and the second adhesive may be greater than the thickness of one of the first adhesive and the second adhesive, thereby allowing the electrostatic chuck according to the embodiment to appropriately adjust the thickness of the resin layer. [Explanation of symbols]

[0044] 100, 100A, 100B electrostatic chuck 110 base plate 111 Refrigerant passage 120 Ceramic Plate 121 Electrode 122 heater electrode 130, 130A, 130B resin layer 131, 133 First adhesive 132 Second Adhesive

Claims

1. A base plate and a ceramic plate fixed to the base plate, which attracts an object by electrostatic force generated by energizing a built-in electrode; a resin layer that bonds the base plate and the ceramic plate, the resin layer being formed from one or more laminated adhesives, at least one of which has a temperature corresponding to an extreme value of loss tangent of −70° C. or less in a temperature range of −150° C. to 250° C.; and At least one of the one or more adhesives has a thermal conductivity at −60° C. of 0.5 W / mK or more and 2.16 W / mK or less.

2. 2. The electrostatic chuck of claim 1, wherein at least one of the one or more adhesives contains a filler.

3. The resin layer a first adhesive applied to the base plate; a second adhesive applied between the first adhesive and the ceramic plate; and 2. The electrostatic chuck according to claim 1, wherein at least one of the first adhesive and the second adhesive has a temperature corresponding to an extreme value of a loss tangent of −70° C. or less in a temperature range of −150° C. to 250° C.

4. One of the first adhesive and the second adhesive has a temperature corresponding to an extreme value of a loss tangent of −70° C. or less in a temperature range of −150° C. to 250° C.; 4. The electrostatic chuck according to claim 3, wherein the other of the first adhesive and the second adhesive has a viscosity before thermal curing and a storage modulus after thermal curing greater than those of one of the first adhesive and the second adhesive.

5. 5. The electrostatic chuck according to claim 4, wherein the thickness of the other of the first adhesive and the second adhesive is greater than the thickness of one of the first adhesive and the second adhesive.

6. 2. The electrostatic chuck according to claim 1, further comprising a silane coupling agent layer provided on an upper surface or a lower surface of the resin layer.

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