Electrostatic chuck

Abstract

An electrostatic chuck (1) comprises: a substrate (2) that is for attracting thereto an attraction object; a base that supports the substrate (2); and an adhesive layer (4) that bonds the substrate (2) to the base (3). The adhesive layer (4) has a first adhesive layer (4a) positioned at the center side of the substrate (2), and a second adhesive layer (4b) positioned at a side closer to the end of the substrate (2), as compared to the first adhesive layer (4a). A plasma protective layer (5) is provided at a side closer to the end of the substrate (2), as compared to the second adhesive layer (4b). The plasma protective layer (5) is bonded to the second adhesive layer (4b). The Young's modulus of the second adhesive layer (4b) at 100°C is 1 MPa or more, and the Young's modulus at 25°C is 1000 MPa or less.

Description

Electrostatic chuck

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

[0002] Conventionally, etching apparatuses that perform dry etching of wafers using plasma have been used as semiconductor manufacturing equipment. In such etching apparatuses, electrostatic chucks are used to fix planar workpieces using static electricity. In such electrostatic chucks, a substrate for attracting the planar workpiece and a base supporting the substrate are bonded to each other by an adhesive layer. To reduce damage to the adhesive layer caused by plasma, a plasma protection layer is bonded to the outer surface of the adhesive layer. International Patent Publication WO 2016 / 132909 discloses an electrostatic chuck in which the plasma protection layer is made of an organic material such as fluorine or acrylic resin.

[0003] If there is a large difference in the linear expansion coefficient between the substrate for adsorbing a flat-plate-shaped material and the base supporting the substrate, when the substrate and the base expand or contract due to a change in the temperature of the surrounding environment, the adhesive layer may be deformed, which may result in damage to the electrostatic chuck.

[0004] An object of the present invention is to provide an electrostatic chuck that can suppress such damage.

[0005] The electrostatic chuck of the present disclosure comprises: a substrate for attracting an object to be attracted; a base supporting the substrate; and an adhesive layer for adhering the substrate to the base, wherein the adhesive layer has a first adhesive layer located toward the center of the substrate and a second adhesive layer located closer to an edge of the substrate than the first adhesive layer; a plasma protective layer is provided closer to the edge of the substrate than the second adhesive layer, and the plasma protective layer is adhered to the second adhesive layer; and the second adhesive layer has a Young's modulus of 1 MPa or more at 100°C and a Young's modulus of 1000 MPa or less at 25°C.

[0006] In the electrostatic chuck of the present disclosure, the second adhesive layer may have a Young's modulus at 100°C of 10 MPa or more and a Young's modulus at 25°C of 500 MPa or less.

[0007] In the electrostatic chuck of the present disclosure, the first adhesive layer may have a Young's modulus at 25° C. in the range of 2000 to 5000 MPa.

[0008] In the electrostatic chuck of the present disclosure, the plasma protection layer may be disposed closer to the center of the substrate than to the edge of the substrate.

[0009] In the electrostatic chuck of the present disclosure, the plasma protection layer may be disposed at a distance in the range of 50 μm to 1000 μm from the edge of the substrate toward the center of the substrate.

[0010] In the electrostatic chuck of the present disclosure, the second adhesive layer may have a recessed shape toward the center of the substrate.

[0011] In the electrostatic chuck of the present disclosure, the first adhesive layer may include a thermally conductive filler.

[0012] In the electrostatic chuck of the present disclosure, the plasma protection layer may include an inorganic material.

[0013] In the electrostatic chuck of the present disclosure, the inorganic material may be made of at least one of yttrium, aluminum, zirconium, calcium, and magnesium.

[0014] 1A and 1B are cross-sectional views showing a schematic configuration of an electrostatic chuck according to an embodiment of the present disclosure, and FIG. 1C are cross-sectional views showing a schematic configuration of another electrostatic chuck according to an embodiment of the present disclosure.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will now be described with reference to the accompanying drawings, in which: Figures 1 and 2 are cross-sectional views showing a schematic configuration of an electrostatic chuck according to an embodiment of the present disclosure.

[0016] 1 and 2 , an electrostatic chuck 1 according to this embodiment includes a substrate 2 for attracting an object to be attracted, a base 3 for supporting the substrate 2, and an adhesive layer 4 for adhering the substrate 2 to the base 3. The adhesive layer 4 includes a first adhesive layer 4a located toward the center of the substrate 2 and a second adhesive layer 4b located closer to the edge of the substrate 2 than the first adhesive layer 4a. The electrostatic chuck 1 further includes a plasma protective layer 5 located closer to the edge of the substrate 2 than the second adhesive layer 4b, and the plasma protective layer 5 is adhered to the second adhesive layer 4b.

[0017] (Substrate 2) The substrate 2 is used to attract and hold an object to be attracted (not shown). The shape of the substrate 2 is not limited, and it can be disc-shaped or rectangular to match the shape of the object to be attracted. The dimensions of the substrate 2 can also be set appropriately to match the object to be attracted. The "object to be attracted" is also not limited, and can include various wafers for manufacturing semiconductor devices, flat panel display (FPD) panels and substrates, metal members, film members, glass members, etc.

[0018] Examples of materials for the substrate 2 include a ceramic substrate, a silicon carbide substrate, and a metal substrate made of aluminum, stainless steel, or the like.

[0019] The thickness of the substrate 2 is not particularly limited and can be in the range of 0.2 mm to 7 mm. Furthermore, when an internal electrode is provided on the substrate 2 as described below, the thickness of the substrate 2 may be in the range of 3 mm to 10 mm.

[0020] (Base 3) The base 3 supports the substrate 2 and also has a cooling function. The shape, material, thickness, etc. of the base 3 can be appropriately designed to suit the application. For example, the material of the base 3 can be ceramic, metal, or a combination thereof.

[0021] (Adhesive Layer 4) The adhesive layer 4 adheres the substrate 2 to the base 3. In the electrostatic chuck 1 according to this embodiment, the adhesive layer 4 has a first adhesive layer 4a located toward the center of the substrate 2 and a second adhesive layer 4b located closer to the edge of the substrate 2 than the first adhesive layer 4a (FIGS. 1 and 2).

[0022] The thickness of the adhesive layer 4 (first adhesive layer 4a and second adhesive layer 4b) is not particularly limited, but is preferably 50 μm to 500 μm, and more preferably 100 μm to 300 μm. If the thickness of the adhesive layer 4 is within this range, the adhesive layer 4 can suitably withstand stress caused by the difference in the linear expansion coefficient between the substrate and the base.

[0023] (First adhesive layer 4a) The Young's modulus of the first adhesive layer 4a at 25° C. is preferably 2000 to 5000 MPa, and more preferably 3000 to 4000 MPa. If the Young's modulus of the first adhesive layer 4a at 25° C. is within this range, the first adhesive layer 4a is moderately hard, thereby exhibiting sufficient adhesive strength, and furthermore, the flexibility of the second adhesive layer 4b (described later) is enhanced, which allows the second adhesive layer 4b to effectively absorb stress due to expansion and contraction of the substrate 2 and the base 3, thereby suppressing cracking and peeling of the electrostatic chuck.

[0024] The first adhesive layer 4 a may be made of a resin, such as a thermoplastic elastomer, a thermosetting elastomer, an epoxy resin, a urethane resin, a polyester resin, a polyimide resin, a polyamide resin, a fluororubber, an acrylic rubber, a silicone rubber, or a urethane rubber.

[0025] The first adhesive layer 4a preferably contains a thermally conductive filler. By including a thermally conductive filler, both adhesiveness and thermal conductivity can be achieved. Examples of the thermally conductive filler include, but are not limited to, alumina, aluminum nitride, silicon carbide, boron nitride, carbon black, and carbon nanotubes. The amount, shape, and other properties of the thermally conductive filler are also not particularly limited.

[0026] (Second adhesive layer 4b) The second adhesive layer 4b has a Young's modulus of 1 MPa or more at 100°C and a Young's modulus of 1000 MPa or less at 25°C. When the Young's modulus at 100°C is 1 MPa or more, the second adhesive layer 4b has appropriate fluidity, and deformation and cracking of the plasma protective layer 5 due to excessive fluidity can be suppressed. On the other hand, when a difference in the linear expansion coefficient occurs between the substrate 2 and the base 3, deformation and cracking of the electrostatic chuck can be suppressed by the Young's modulus at 25°C being 1000 MPa or less.

[0027] The upper limit of the Young's modulus of the second adhesive layer 4b at 100° C. is, for example, 100 MPa or less, and the lower limit of the Young's modulus at 25° C. is 10 MPa or more. Preferably, the Young's modulus of the second adhesive layer 4b at 100° C. is 10 MPa or more, and the Young's modulus at 25° C. is 500 MPa or less. Such a second adhesive layer 4b is expected to more reliably suppress cracking of the electrostatic chuck due to differences in the linear expansion coefficient between the second adhesive layer 4b and the substrate 2 or the base 3.

[0028] Suitable materials for the second adhesive layer 4b include thermoplastic elastomers, thermosetting elastomers, epoxy resins, urethane resins, polyester resins, polyimide resins, polyamide resins, fluororubber, acrylic rubber, silicone rubber, and urethane rubber. The second adhesive layer 4b may also contain a thermally conductive filler, such as alumina, aluminum nitride, silicon carbide, boron nitride, carbon black, and carbon nanotubes.

[0029] The method for measuring Young's modulus is not particularly limited, but a dynamic viscoelasticity measurement method can be used. Young's modulus can be measured at 25°C and 100°C using a Rheovibron DDV-II (manufactured by Orientec Co., Ltd.) as a measuring device under set conditions of a vibration frequency of 11 Hz and a temperature rise rate of 5°C / min.

[0030] The volume ratio of the first adhesive layer 4a to the second adhesive layer 4b in the horizontal direction is not limited to that shown in Figures 1 and 2 and can be appropriately designed so that the first adhesive layer 4a bonds the substrate 2 and the base 3 while the second adhesive layer 4b absorbs stress due to expansion and contraction of the substrate 2 and the base 3. As an example, the ratio of the volume of the second adhesive layer 4b to the volume of the first adhesive layer 4a is 0.01 volume % or more and 20 volume % or less, and preferably 1 volume % or more and 10 volume % or less. Note that the first adhesive layer 4a and the second adhesive layer 4b do not necessarily have to be formed concentrically. Furthermore, the length of the adhesive layer 4 in the horizontal direction (the total length of the first adhesive layer 4a and the second adhesive layer 4b) can also be appropriately designed.

[0031] The second adhesive layer 4b can be formed to have a recessed shape toward the center of the substrate 2. In Figures 1 and 2, the second adhesive layer 4b (and the plasma protective layer 5 described later) are recessed in an angular shape, but they may also be formed in an arc shape.

[0032] (Plasma protective layer 5) The plasma protective layer 5 is adhered to the second adhesive layer 4b to protect the adhesive layer 4 from plasma. The material of the plasma protective layer 5 may contain an inorganic material. Examples of inorganic materials include those containing at least one of yttrium, aluminum, zirconium, calcium, and magnesium, and may be oxides, hydroxides, or mixtures of these elements, and the mixture may contain hydroxyapatite.

[0033] In the electrostatic chuck 1, the plasma protective layer 5 may be disposed closer to the center of the substrate 2 than the edge of the substrate 2 ( FIG. 2 ). Specifically, the plasma protective layer 5 may be disposed at a distance ranging from 50 μm to 1000 μm from the edge of the substrate 2 toward the center of the substrate 2. For example, if the plasma protective layer 5 is disposed 1000 μm away from the edge of the substrate 2 (start point: 0 μm) shown in FIG. 2 , deterioration of the plasma protective layer 5 due to plasma or the like can be suppressed, and the adhesive layer 4 is also disposed farther away from the plasma source, thereby providing more reliable protection. In this case, the horizontal length of the substrate 2 can be within a range of 30 mm to 600 mm.

[0034] The thickness of the plasma protective layer 5 is not particularly limited, but may be in the range of 1 μm to 300 μm, and preferably 20 μm to 150 μm. Such a plasma protective layer 5 can protect the adhesive layer 4 from plasma, while also suppressing cracking and peeling of the plasma protective layer 5 itself.

[0035] (Others) In the electrostatic chuck 1 according to the present embodiment, an internal electrode (not shown) can be provided on the substrate 2 in order to apply a voltage to generate an electrostatic force (Coulomb force) to attract an object to be attracted. Alternatively, such an internal electrode may be provided on the base 3.

[0036] The internal electrode is not particularly limited as long as it is made of a conductive material that can exert an electrostatic adsorption force when a voltage is applied. Suitable internal electrodes include, for example, thin films made of metals such as copper, aluminum, gold, silver, platinum, chromium, nickel, and tungsten, and thin films made of at least two metals selected from the above metals. Examples of such metal thin films include those formed by vapor deposition, plating, sputtering, etc., and those formed by applying and drying a conductive paste, specifically, metal foils such as copper foil.

[0037] (Method and Use of Electrostatic Chuck 1) The electrostatic chuck 1 can be manufactured, for example, as follows. First, a substrate 2 and a base 3 are prepared. As described above, a metal such as copper is patterned on either the substrate 2 or the base 3 to form an internal electrode. Next, the substrate 2 and the base 3 are bonded together via an adhesive layer 4 (first adhesive layer 4a in this state). The area where the first adhesive layer 4a is formed is determined so that a gap is formed at a predetermined distance from each end of the substrate 2 and the base 3. The second adhesive layer 4b and the plasma protective layer 5 are formed in this gap. Next, the plasma protective layer 5 is formed to fill this gap. Next, a coating liquid that will become the second adhesive layer 4b is injected between the substrate 2, the base 3, the first adhesive layer 4a, and the plasma protective layer 5 using surface tension. The second adhesive layer 4b and the plasma protective layer 5 that protrude from the end of the substrate 2 are then scraped off to obtain the electrostatic chuck 1 shown in FIG. 1 or FIG. 2 . The electrostatic chuck 1 can also be manufactured using a manufacturing method described in the following examples.

[0038] The electrostatic chuck 1 according to the present embodiment attracts an object to be attracted by generating a Coulomb force by applying a voltage to an internal electrode embedded in the substrate 2 or the base 3. For example, the electrostatic chuck 1 can be used to attract a wafer (object to be attracted) in a dry etching or CVD process in a semiconductor manufacturing process. In particular, in an apparatus or method using plasma, the electrostatic chuck 1 according to the present embodiment can protect the adhesive layer 4 from the plasma by the plasma protective layer 5. At the same time, even if the substrate 2 or the base 3 becomes hot and expands due to plasma irradiation, the second adhesive layer 4 b can accommodate the thermal expansion, thereby suppressing cracking of the electrostatic chuck due to differences in the linear expansion coefficient between the substrate 2 and the base 3. As a result, the life and productivity of the electrostatic chuck 1 itself are improved compared to conventional electrostatic chucks.

[0039] The electrostatic chuck 1 of the present embodiment, configured as described above, includes a substrate 2 for attracting an object to be attracted, a base supporting the substrate 2, and an adhesive layer 4 for adhering the substrate 2 to the base 3. The adhesive layer 4 includes a first adhesive layer 4a located toward the center of the substrate 2 and a second adhesive layer 4b located closer to the edge of the substrate 2 than the first adhesive layer 4a. A plasma protective layer 5 is provided closer to the edge of the substrate 2 than the second adhesive layer 4b, and the plasma protective layer 5 is adhered to the second adhesive layer 4b. The second adhesive layer 4b has a Young's modulus of 1 MPa or more at 100°C and a Young's modulus of 1000 MPa or less at 25°C. Since the second adhesive layer 4b has an appropriate fluidity, deformation and cracking of the electrostatic chuck due to excessive fluidity can be suppressed. Furthermore, even if the substrate 2 or the base 3 expands or contracts due to a temperature change in the surrounding environment caused by plasma etching or the like, the second adhesive layer 4b absorbs the stress caused by the expansion and contraction, thereby suppressing deformation or cracking of the electrostatic chuck due to the difference in linear expansion coefficient between the substrate 2 and the base 3.

[0040] Furthermore, in the electrostatic chuck 1 of the present embodiment, the Young's modulus of the second adhesive layer 4 b may be 10 MPa or more at 100° C. and 500 MPa or less at 25° C. Such a second adhesive layer 4 b is expected to more reliably suppress cracking of the electrostatic chuck due to differences in the linear expansion coefficient between the second adhesive layer 4 b and the substrate 2 or the base 3.

[0041] Furthermore, in the electrostatic chuck 1 of the present embodiment, the Young's modulus of the first adhesive layer 4a at 25° C. may be within a range of 2000 to 5000 MPa. In this manner, the moderately hard first adhesive layer 4a exerts sufficient adhesive strength, and further, the second adhesive layer 4b, which is softer than the first adhesive layer 4a, more effectively absorbs stress due to expansion and contraction of the substrate 2 and the base 3, thereby more reliably suppressing cracking and peeling of the electrostatic chuck.

[0042] In the electrostatic chuck 1 of the present embodiment, the plasma protective layer 5 may be disposed closer to the center of the substrate 2 than the edge of the substrate 2, and further, the plasma protective layer 5 may be disposed at a distance in the range of 50 μm to 1000 μm from the edge of the substrate 2 toward the center of the substrate 2 ( FIG. 2 ). In this way, the plasma protective layer 5 does not protrude beyond the edge of the substrate 2, so that deterioration of the plasma protective layer 5 due to plasma or the like can be suppressed, and the adhesive layer 4 is less likely to be exposed to plasma and is more reliably protected.

[0043] In the electrostatic chuck 1 of the present embodiment, the second adhesive layer 4 b may have a recessed shape toward the center of the substrate 2. In this manner, the second adhesive layer 4 b can be protected from plasma heat.

[0044] In the electrostatic chuck 1 of the present embodiment, the first adhesive layer 4 a may contain a thermally conductive filler, which can suppress variations in thickness and temperature distribution within the first adhesive layer 4 a and allow heat from the surrounding environment to escape.

[0045] In the electrostatic chuck 1 of the present embodiment, the plasma protective layer 5 may contain an inorganic material. Furthermore, this inorganic material may be made of at least one of yttrium, aluminum, zirconium, calcium, and magnesium. Such a material can preferably exhibit plasma resistance.

[0046] The electrostatic chuck 1 according to this embodiment is not limited to the above-described aspects and combinations.

[0047] For example, the number of internal electrodes provided on the substrate 2 or the base 3 may be two, instead of one.

[0048] Furthermore, the plasma protective layer 5 is provided on the edge side of the substrate 2, but the plasma protective layer 5 may be provided not only on a part of the edge of the substrate 2 but also along the entire periphery of the substrate 2. Furthermore, the plasma protective layer 5 (second adhesive layer 4b) may be provided symmetrically (for example, in four locations) on the periphery of the substrate 2.

[0049] The present disclosure will be described in more detail below using examples and comparative examples.

[0050] Example 1 An evaluation sample was manufactured using the materials listed in Table 1. Specifically, an alumina substrate (300 mm diameter, disc-shaped, 3.0 mm thick) and an aluminum base (295 mm diameter, disc-shaped, 15 mm thick) were prepared. A silicone adhesive was concentrically applied to the substrate from the edge of the substrate toward the center, extending 4.0 mm from the edge, leaving an uncoated area along the entire periphery. The substrate was then bonded to the base. The silicone adhesive had a thickness of 150 μm. Next, a polyimide adhesive was applied to the entire periphery of the silicone adhesive, and the polyimide adhesive was allowed to dry in a thermostatic chamber set at 120°C for 10 minutes. The polyimide adhesive had a thickness of 150 μm after drying. Subsequently, a plasma spraying device was used to spray alumina particles onto the entire periphery of the polyimide adhesive, forming a 75 μm-thick plasma protective layer at the position shown in Table 1 (substrate edge: 0 μm). The polyimide adhesive and plasma protective layer protruding from the outer periphery of the substrate and base were polished using an electric router to obtain a sample for evaluation.

[0051] The silicone adhesive and polyimide adhesive used in each example were prepared as follows: A commercially available silicone adhesive ("One-component additive RTV silicone rubber KE-8101" manufactured by Shin-Etsu Chemical Co., Ltd.) was mixed and stirred with aluminum nitride filler ("AlN filler FAN-f05" manufactured by Furukawa Denshi Co., Ltd., average particle size 3 to 10 μm) in the blending ratios (amount blended per 100 parts by weight of silicone adhesive) shown in Tables 1 to 4, to obtain silicone adhesives exhibiting Young's moduli as shown in Tables 1 to 4. A commercially available polyimide adhesive ("Solvent-soluble thermoplastic polyimide PI-1" manufactured by T&K TOKA Corporation) was dissolved in tetrahydrofuran to prepare a 25% solution. Thereafter, alumina filler ("Taimicron TM-UF" manufactured by Taimei Chemical Industry Co., Ltd., average particle size 0.09 μm) was mixed and stirred in the compounding ratios shown in Tables 1 to 4 (amount compounded relative to 100 parts by weight of polyimide adhesive), to obtain polyimide adhesives exhibiting Young's moduli as shown in Tables 1 to 4.

[0052] Examples 2 to 5, 8, 9, 11 to 23 As shown in Tables 1 to 4, evaluation samples were obtained in the same manner as in Example 1.

[0053] Example 6 An evaluation sample was obtained in the same manner as in Example 1, except that the silicone adhesive was applied concentrically to the substrate so that an uncoated area was left over the entire periphery extending 2.0 mm from the edge of the substrate toward the center.

[0054] Example 7 An evaluation sample was obtained in the same manner as in Example 1, except that the silicone adhesive was applied concentrically to the substrate so that an uncoated area was left over the entire periphery extending 7.5 mm from the edge of the substrate toward the center.

[0055] Example 10 An evaluation sample was obtained in the same manner as in Example 1, except for the formation of the plasma protective layer. That is, a 20% by mass solution of aluminum nitrate nonahydrate in 1,3-butanediol was prepared and applied to the entire outer periphery of the polyimide adhesive by spraying. The resultant was then placed in a thermostatic chamber set at 200°C and dried for two hours to form a plasma protective layer. The polyimide adhesive and plasma protective layer protruding from the periphery of the substrate and base were polished using an electric mill to obtain an evaluation sample.

[0056] Comparative Examples 1 and 2 As shown in Table 4, evaluation samples were obtained in the same manner as in Example 1. In Comparative Examples 1 and 2, a thermoplastic polyethylene (TPE) adhesive was used instead of a polyimide adhesive. That is, a styrene-based thermoplastic elastomer (TPE) (Kraton G1651, manufactured by Kraton Corporation) was dissolved in toluene to prepare a 25% solution, and then alumina filler (Taimicron TM-UF, manufactured by Taimei Chemical Industry Co., Ltd., average particle size 0.09 μm) was mixed and stirred at the blending ratio (amount blended relative to 100 parts by weight of the solution) shown in Table 4, and each TPE-based adhesive exhibiting a Young's modulus as shown in Table 4 was obtained.

[0057] <Evaluation> (Evaluation of Plasma Resistance) The plasma resistance of Examples 1 to 23 and Comparative Examples 1 and 2 was evaluated. That is, each evaluation sample was placed in a parallel plate RIE apparatus, and then oxygen gas (10 sccm) and carbon tetrafluoride gas (40 sccm) were introduced under vacuum (20 Pa or less) using a high-frequency power source (output 250 W). After 24 hours of exposure, the change in the surface condition of the outer periphery of each evaluation sample was visually observed. Samples in which the plasma layer remained intact over the entire periphery were marked with "◎", samples in which the plasma protective layer was partially cracked but the plasma protective layer remained over the entire periphery were marked with "◯", and samples in which the plasma protective layer was cracked, peeled off, and partially missing were marked with "×".

[0058] (Evaluation of cracking and peeling: heat cycle resistance) Each evaluation sample of Examples 1 to 23 and Comparative Examples 1 and 2 was evaluated for cracking and peeling after a thermal cycle. That is, each evaluation sample was placed in a thermostatic chamber (TCC-151W manufactured by Espec Corporation) set to 0°C. Thereafter, the temperature was increased to 120°C at a temperature increase rate of 50°C / hour, and then immediately decreased to 0°C at a temperature decrease rate of 50°C / hour, and this process was repeated for 200 cycles. After 200 cycles, each evaluation sample was removed from the thermostatic chamber, and the appearance of each evaluation sample (plasma protective layer, substrate, base) was observed. Those in which no cracking or peeling occurred were evaluated as "◎", those in which cracking only occurred in the plasma protective layer were evaluated as "◯", those in which peeling occurred in part of the plasma protective layer were evaluated as "△", and those in which cracking or peeling occurred in the substrate or base were evaluated as "X".

[0059] (Overall evaluation) If two of the evaluations of plasma resistance and cracking and peeling were "◎", the evaluation was marked "◎◎". If one was "○" or "△" and the other was "◎", the evaluation was marked "◎". Also, if two evaluations were "○", or one was "○" and the other was "△", the evaluation was marked "○". If two evaluations were "△", the evaluation was marked "△". If even one was evaluated as "×", the evaluation was marked "×".

[0060]

[0061]

[0062]

[0063]

[0064] As shown in Tables 1 to 4, in the evaluation samples (Comparative Examples 1 and 2) having a second adhesive layer with a Young's modulus at 100°C of less than 1 MPa or a Young's modulus at 25°C of more than 1000 MPa, cracks or peeling occurred in the plasma protective layer, substrate, and base (heat cycle test). In contrast, the evaluation samples (Examples) according to the present disclosure having a second adhesive layer with a Young's modulus at 100°C of 1 MPa or more and a Young's modulus at 25°C of 1000 MPa or less not only had plasma resistance but also had higher heat cycle resistance, and were able to suppress peeling of the plasma protective layer, substrate, and base. In other words, compared to the comparative examples, the electrostatic chuck of the present disclosure was able to suppress damage to the electrostatic chuck due to differences in the thermal expansion coefficient between the electrostatic chuck and the substrate or base.

[0065] Furthermore, a comparison of Examples 13 to 16 with Examples 17 and 18 showed that when the Young's modulus (25°C) of the first adhesive layer was within the range of 2000 to 5000 MPa, the plasma resistance and heat cycle resistance were even better. When the Young's modulus (25°C) of the first adhesive layer was within the range of 3000 to 4000 MPa, the plasma resistance and heat cycle resistance were particularly good.

[0066] Furthermore, a comparison of Examples 1 to 8 with Examples 9 and 12 shows that both the plasma resistance and heat cycle resistance were good even when the plasma protective layer was disposed at a distance of 50 μm to 1000 μm from the edge of the substrate toward the center of the substrate.

[0067] Furthermore, for example, a comparison between Example 1 and Examples 10 and 11 reveals that when the thickness of the plasma protective layer 5 is in the range of 1 μm to 300 μm, plasma resistance and heat cycle resistance can be exhibited in a well-balanced manner.

Claims

1. An electrostatic chuck comprising: a substrate for adsorbing an object to be adsorbed; a base supporting the substrate; and an adhesive layer for adhering the substrate to the base, the adhesive layer having a first adhesive layer located toward the center of the substrate and a second adhesive layer located closer to an edge of the substrate than the first adhesive layer, a plasma protective layer being provided closer to the edge of the substrate than the second adhesive layer, the plasma protective layer being adhered to the second adhesive layer, and the second adhesive layer having a Young's modulus at 100°C of 1 MPa or more and a Young's modulus at 25°C of 1000 MPa or less.

2. An electrostatic chuck as recited in claim 1, wherein the second adhesive layer has a Young's modulus of 10 MPa or more at 100°C and a Young's modulus of 500 MPa or less at 25°C.

3. An electrostatic chuck as recited in claim 1, wherein the Young's modulus at 25° C. of said first adhesive layer is within the range of 2000 to 5000 MPa.

4. The electrostatic chuck of claim 1, wherein said plasma protective layer is disposed closer to a center of said substrate than to an edge of said substrate.

5. An electrostatic chuck according to claim 4, wherein said plasma protective layer is disposed at a distance within a range of 50 μm to 1000 μm from the edge of said substrate toward the side closer to the center of said substrate.

6. The electrostatic chuck according to claim 1, wherein said second adhesive layer is recessed toward the center of said substrate.

7. The electrostatic chuck of claim 1, wherein said first adhesive layer comprises a thermally conductive filler.

8. The electrostatic chuck of any one of claims 1 to 7, wherein the plasma protective layer comprises an inorganic material.

9. The electrostatic chuck of claim 8, wherein said inorganic material is comprised of at least one of yttrium, aluminum, zirconium, calcium, and magnesium.

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