Electrostatic chuck

Abstract

To provide an electrostatic chuck capable of suppressing peeling of a ceramic dielectric substrate from a base plate and cracking of the ceramic dielectric substrate under an extremely low temperature environment.SOLUTION: An electrostatic chuck comprising: a ceramic dielectric substrate; a metal base plate supporting the ceramic dielectric substrate; and a bonding layer provided between the ceramic dielectric substrate and the base plate, the bonding layer including a resin material, wherein a ratio α 1 / α 2 of an elongation rate α 1 of the bonding layer at - 60 °C. to an elongation rate α 2 of the bonding layer at 25 °C. is 0.60 or more.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] Aspects of the present invention generally relate to electrostatic chucks. [Background technology]

[0002] Electrostatic chucks are used in substrate processing equipment that performs processes such as etching, CVD (Chemical Vapor Deposition), sputtering, ion implantation, ashing, exposure, and inspection, as a means for attracting and holding objects (targets) such as semiconductor wafers and glass substrates.

[0003] An electrostatic chuck is made by sandwiching an electrode between ceramic dielectric substrates such as alumina and then firing them. Electrostatic chucks apply electrostatic attraction power to the built-in electrodes, and use electrostatic force to attract a substrate such as a silicon wafer.

[0004] In recent years, in such substrate processing apparatuses, as processes become more miniaturized, it has been considered to perform processing in environments at lower temperatures than before in order to improve processing accuracy, and accordingly, electrostatic chucks are also required to have low-temperature resistance that allows them to be used in environments at lower temperatures than before. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-273202 Summary of the Invention [Problem to be solved by the invention]

[0006] It has been found that while conventional electrostatic chucks can be used in low-temperature environments, for example, at around -20°C, in extremely low-temperature environments of -60°C or below, the flexibility of the bonding layer bonding the ceramic dielectric substrate to the base plate decreases, and the ceramic dielectric substrate may peel off from the base plate, or the ceramic dielectric substrate may crack and break depending on, for example, the surface pattern, shape, thickness, etc.

[0007] The present invention has been made in recognition of the above-mentioned problems, and an object of the present invention is to provide an electrostatic chuck that can suppress peeling of a ceramic dielectric substrate from a base plate and cracking of the ceramic dielectric substrate in an extremely low temperature environment. [Means for solving the problem]

[0008] A first invention is an electrostatic chuck comprising: a ceramic dielectric substrate; a metal base plate supporting the ceramic dielectric substrate; and a bonding layer provided between the ceramic dielectric substrate and the base plate and containing a resin material, wherein the resin material contains silicone, and the silicone has a molecular structure in which at least one of a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, and a hexyl group is bonded to a siloxane skeleton; and wherein a ratio α1 / α2 of an elongation rate α1 of the bonding layer at -60°C to an elongation rate α2 of the bonding layer at 25°C is 0.80 or more, the elongation rate α1 is 120% or more, and the elongation rate α2 is 150% or more.

[0009] This electrostatic chuck can reduce the difference in thermal expansion coefficient between the ceramic dielectric substrate and the base plate when placed in an extremely low-temperature environment ranging from room temperature to -60° C. This can prevent the ceramic dielectric substrate from peeling off from the base plate and cracking.

[0010] The second invention is the first invention, wherein the silicone has a phenyl group in a siloxane skeleton. The electrostatic chuck is characterized by having a molecular structure in which

[0011] This electrostatic chuck can further reduce the difference in thermal expansion coefficient between the ceramic dielectric substrate and the base plate when placed in an extremely low-temperature environment ranging from room temperature to -60° C. This can further prevent the ceramic dielectric substrate from peeling off from the base plate and cracking.

[0012] A third invention is an electrostatic chuck according to the first or second invention, characterized in that the elastic modulus γ1 of the bonding layer at −60° C. is 0.1 MPa or more and 10 MPa or less.

[0013] According to this electrostatic chuck, the bonding layer has sufficient restorability in an extremely low-temperature environment of -60°C or less, making it easy to suppress warping of the ceramic dielectric substrate even when stress occurs between the ceramic dielectric substrate and the base plate. This makes it possible to suppress deterioration of the in-plane temperature uniformity of the object in an extremely low-temperature environment. Furthermore, according to this electrostatic chuck, it is possible to prevent the bonding layer from becoming too hard in an extremely low-temperature environment of -60°C or less. This makes it possible to suppress stress applied to the ceramic dielectric substrate in an extremely low-temperature environment, and to suppress peeling of the ceramic dielectric substrate from the base plate and cracking of the ceramic dielectric substrate.

[0014] The fourth invention is an electrostatic chuck characterized in that, in any one of the first to third inventions, the ratio γ1 / γ2 of the elastic modulus γ1 of the bonding layer at -60°C to the elastic modulus γ2 of the bonding layer at 25°C is 0.6 or more and 30 or less.

[0015] This electrostatic chuck allows the bonding layer to maintain sufficient resilience both at room temperature and in an extremely low-temperature environment of -60°C or below, making it easy to suppress warping of the ceramic dielectric substrate even when stress occurs between the ceramic dielectric substrate and the base plate. This makes it possible to suppress deterioration of the in-plane temperature uniformity of the object when placed in an environment ranging from room temperature to an extremely low temperature. Furthermore, this electrostatic chuck prevents the bonding layer from becoming too hard both at room temperature and in an extremely low-temperature environment of -60°C or below. This suppresses stress applied to the ceramic dielectric substrate when placed in an environment ranging from room temperature to an extremely low temperature, making it possible to suppress peeling of the ceramic dielectric substrate from the base plate and cracking of the ceramic dielectric substrate.

[0016] A fifth invention is an electrostatic chuck according to any one of the first to fourth inventions, characterized in that the ceramic dielectric substrate contains at least one of aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, and yttrium oxide.

[0017] In the electrostatic chuck according to the embodiment, for example, by using a ceramic dielectric substrate containing these ceramics, it is possible to provide an electrostatic chuck that is excellent in various properties such as plasma resistance, stability of mechanical properties, thermal conductivity, and electrical insulation.

[0018] A sixth invention is the electrostatic chuck according to the fifth invention, characterized in that the ceramic dielectric substrate contains aluminum oxide.

[0019] According to this electrostatic chuck, since the ceramic dielectric substrate contains aluminum oxide, it is possible to achieve both plasma resistance and mechanical strength. [Effects of the Invention]

[0020] According to an aspect of the present invention, there is provided an electrostatic chuck that can suppress peeling of a ceramic dielectric substrate from a base plate and cracking of the ceramic dielectric substrate in an extremely low temperature environment of −60° C. or below. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view schematically illustrating an electrostatic chuck according to an embodiment. [Figure 2] 2(a) to 2(c) are explanatory diagrams showing a method for measuring the elongation rate and bonding strength of the bonding layer. [Figure 3] FIG. 10 is an explanatory diagram showing a method for calculating the elastic modulus of a bonding layer. [Figure 4] 10A and 10B are explanatory diagrams illustrating measurement points for the elongation rate and bonding strength of a bonding layer. [Figure 5] 1 is a graph showing physical properties of an example of a bonding layer of an electrostatic chuck according to an embodiment. [Figure 6] 1 is a graph showing physical properties of an example of a bonding layer of an electrostatic chuck according to an embodiment. [Figure 7] 1 is a table showing physical properties of an example of a bonding layer of an electrostatic chuck according to an embodiment. [Figure 8] 1 is a table showing physical properties of an example of a bonding layer of an electrostatic chuck according to an embodiment. [Figure 9] 1 is a cross-sectional view schematically illustrating a wafer processing apparatus including an electrostatic chuck according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, like components are designated by like reference numerals and detailed descriptions thereof will be omitted where appropriate.

[0023] FIG. 1 is a schematic cross-sectional view illustrating an electrostatic chuck according to an embodiment. As shown in FIG. 1, the electrostatic chuck 110 includes a ceramic dielectric substrate 11, a base plate 50, and a bonding layer 60.

[0024] The ceramic dielectric substrate 11 is a flat base material made of, for example, sintered ceramic. The ceramic dielectric substrate 11 contains, for example, at least one of aluminum oxide (alumina: Al2O3), aluminum nitride, silicon carbide, silicon nitride, and yttrium oxide (yttria: Y2O3). In the electrostatic chuck 110 according to the embodiment, by using the ceramic dielectric substrate 11 containing, for example, these ceramics, it is possible to provide an electrostatic chuck that is excellent in various properties, such as plasma resistance, stability of mechanical properties (e.g., mechanical strength), thermal conductivity, and electrical insulation.

[0025] The ceramic dielectric substrate 11 preferably contains aluminum oxide. When the ceramic dielectric substrate 11 contains aluminum oxide, it can achieve both plasma resistance and mechanical strength. Furthermore, when the ceramic dielectric substrate 11 contains aluminum oxide, it is possible to increase the transparency of the ceramic dielectric substrate 11, improve infrared transmittance, and promote heat transfer. Furthermore, because it has high sinterability, it is possible to form a dense sintered body without using a sintering aid, for example, and to minimize in-plane heat distribution.

[0026] The ceramic dielectric substrate 11 is preferably formed of high-purity aluminum oxide. The concentration of aluminum oxide in the ceramic dielectric substrate 11 is, for example, 90 mass percent (mass%) or more and 100 mass percent or less, preferably 95 mass percent (mass%) or more and 100 mass percent or less, and more preferably 99 mass percent (mass%) or more and 100 mass percent or less. By using high-purity aluminum oxide, the plasma resistance of the ceramic dielectric substrate 11 can be improved. The concentration of aluminum oxide can be measured by fluorescent X-ray analysis or the like.

[0027] The ceramic dielectric substrate 11 has a first main surface 11a and a second main surface 11b. The first main surface 11a is the surface on which an object W to be attracted is placed. The second main surface 11b is the surface opposite to the first main surface 11a. The object W to be attracted is, for example, a semiconductor substrate such as a silicon wafer.

[0028] In this specification, the direction from the base plate 50 toward the ceramic dielectric substrate 11 is referred to as the Z-axis direction. The Z-axis direction is, for example, the direction connecting the first main surface 11a and the second main surface 11b, as illustrated in each drawing. The Z-axis direction is, for example, a direction approximately perpendicular to the first main surface 11a and the second main surface 11b. One of the directions perpendicular to the Z-axis direction is referred to as the X-axis direction, and the direction perpendicular to the Z-axis direction and the X-axis direction is referred to as the Y-axis direction. In this specification, "in-plane" refers to, for example, the XY plane.

[0029] An electrode layer 12 is provided inside the ceramic dielectric substrate 11. The electrode layer 12 is provided between the first main surface 11a and the second main surface 11b. That is, the electrode layer 12 is provided so as to be inserted into the ceramic dielectric substrate 11. The electrode layer 12 may be embedded in the ceramic dielectric substrate 11 by, for example, being integrally sintered therewith.

[0030] The electrode layer 12 is provided as a thin film along the first main surface 11a and the second main surface 11b of the ceramic dielectric substrate 11. The electrode layer 12 is an attraction electrode for attracting and holding the object W. The electrode layer 12 may be of either a monopolar or bipolar type. The electrode layer 12 shown in FIG. 1 is of a bipolar type, and two electrode layers 12 are provided on the same surface.

[0031] The electrode layer 12 is provided with a connection portion 20 extending toward the second main surface 11b of the ceramic dielectric substrate 11. The connection portion 20 is a via (solid type) or a via hole (hollow type) that is electrically connected to the electrode layer 12, or a metal terminal that is connected by an appropriate method such as brazing.

[0032] The electrostatic chuck 110 generates an electric charge on the first main surface 11a side of the electrode layer 12 by applying a voltage (adsorption voltage) from an adsorption power source 505 (see FIG. 9) to the electrode layer 12, and adsorbs and holds the object W by electrostatic force.

[0033] The thickness T1 of the ceramic dielectric substrate 11 is, for example, 5 mm or less. The thickness T1 of the ceramic dielectric substrate 11 is the length of the ceramic dielectric substrate 11 in the Z-axis direction. In other words, the thickness T1 of the ceramic dielectric substrate 11 is the distance between the first main surface 11a and the second main surface 11b in the Z-axis direction. By thinning the ceramic dielectric substrate 11 in this way, the distance between the base plate 50 connected to the high-frequency power supply 504 (see FIG. 9) and the upper electrode 510 (see FIG. 9) can be shortened.

[0034] The base plate 50 is a member that supports the ceramic dielectric substrate 11. The ceramic dielectric substrate 11 is fixed onto the base plate 50 via a bonding layer 60. In other words, the bonding layer 60 is provided between the ceramic dielectric substrate 11 and the base plate 50.

[0035] The bonding layer 60 includes a resin material. In this embodiment, the bonding layer 60 is configured to be able to maintain flexibility at cryogenic temperatures. For example, the bonding layer 60 includes a silicone-based, acrylic-based, modified silicone-based, or epoxy-based polymer material containing at least one of carbon (C), hydrogen (H), nitrogen (N), silicon (Si), and oxygen (O) as a main component. In this specification, the term "extremely low temperature" refers to a low temperature environment of -60°C or lower, specifically, -60°C to -120°C.

[0036] The bonding layer 60 preferably contains silicone. When the bonding layer 60 contains silicone, which has excellent flexibility, the flexibility of the bonding layer 60 is likely to be maintained in an extremely low temperature environment. This more reliably prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking in the ceramic dielectric substrate 11 in an extremely low temperature environment.

[0037] The silicone used in the bonding layer 60 may have a molecular structure in which various functional groups are bonded to a siloxane skeleton. More specifically, the functional group bonded to the siloxane skeleton preferably includes at least one of a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, and a hexyl group. By using silicone containing such functional groups in the bonding layer 60, the cold resistance, strength, elongation, and the like of the bonding layer 60 can be improved in an extremely low temperature environment.

[0038] Preferably, the bonding layer 60 further contains an inorganic filler. When the bonding layer 60 further contains an inorganic filler, the in-plane temperature uniformity of the object W can be improved in an extremely low temperature environment.

[0039] The inorganic filler preferably contains at least one compound having at least one element selected from silicon (Si) and aluminum (Al) and at least one element selected from carbon (C), nitrogen (N), and oxygen (O). More specifically, the inorganic filler preferably contains at least one of Al2O3, SiC, AlN, Si3N4, AlON, SIALON, and SiO2. When the bonding layer 60 contains such an inorganic filler, the thermal conductivity and mechanical stability of the bonding layer 60 can be improved in an extremely low temperature environment.

[0040] The base plate 50 is made of a metal such as aluminum. The base plate 50 is divided into an upper portion 50a and a lower portion 50b, for example, and a communication passage 55 is provided between the upper portion 50a and the lower portion 50b. One end of the communication passage 55 is connected to an input path 51, and the other end is connected to an output path 52.

[0041] The base plate 50 also serves to adjust the temperature of the electrostatic chuck 110. For example, to cool the electrostatic chuck 110, a cooling medium such as helium gas flows in through the input path 51, passes through the connecting path 55, and flows out through the output path 52. This allows the cooling medium to absorb heat from the base plate 50 and cool the ceramic dielectric substrate 11 attached thereto. On the other hand, to keep the electrostatic chuck 110 warm, a heat-retaining medium can be placed in the connecting path 55. A heating element can also be built into the ceramic dielectric substrate 11 or the base plate 50. By adjusting the temperatures of the base plate 50 and the ceramic dielectric substrate 11, the temperature of the object W attracted and held by the electrostatic chuck 110 can be adjusted.

[0042] In this example, grooves 14 are provided on the first main surface 11a of the ceramic dielectric substrate 11. The grooves 14 are recessed in the direction from the first main surface 11a toward the second main surface 11b (the Z-axis direction) and extend continuously within the XY plane. A plurality of protrusions 13 (dots) are provided in at least a portion of the first main surface 11a where the grooves 14 are not provided. The object W is placed on the plurality of protrusions 13 and is supported by the plurality of protrusions 13. The protrusions 13 are surfaces that contact the back surface of the object W. If a plurality of protrusions 13 are provided, a space is formed between the back surface of the object W placed on the electrostatic chuck 110 and the first main surface 11a. By appropriately selecting the height, number, area ratio, shape, etc. of the protrusions 13, it is possible to, for example, make particles adhere to the object W in a desirable state. For example, the height (dimension in the Z-axis direction) of the plurality of protrusions 13 can be set to 1 μm or more and 100 μm or less, preferably 1 μm or more and 30 μm or less, and more preferably 5 μm or more and 15 μm or less.

[0043] The ceramic dielectric substrate 11 has through holes 15 connected to the grooves 14. The through holes 15 are provided from the second main surface 11b to the first main surface 11a. That is, the through holes 15 extend in the Z-axis direction from the second main surface 11b to the first main surface 11a and penetrate the ceramic dielectric substrate 11.

[0044] A gas introduction path 53 is provided in the base plate 50. The gas introduction path 53 is provided, for example, so as to penetrate the base plate 50. The gas introduction path 53 may not penetrate the base plate 50, but may branch off from another gas introduction path 53 and extend to the ceramic dielectric substrate 11 side. Furthermore, the gas introduction path 53 may be provided in multiple locations on the base plate 50.

[0045] The gas introduction path 53 communicates with the through-hole 15. That is, the carrier gas (helium (He) or the like) that has flowed into the gas introduction path 53 passes through the gas introduction path 53 and then flows into the through-hole 15.

[0046] The transmission gas that has flowed into the through-holes 15 passes through the through-holes 15 and then flows into the space provided between the object W and the grooves 14. This allows the object W to be directly cooled by the transmission gas.

[0047] Conventional electrostatic chucks can be used in low-temperature environments, for example, at around -20°C. However, in extremely low-temperature environments at around -60°C, the flexibility of the bonding layer 60 that bonds the ceramic dielectric substrate 11 to the base plate 50 decreases, and there is a risk that the ceramic dielectric substrate 11 may peel off from the base plate 50 or, in some cases, the ceramic dielectric substrate 11 may crack and break.

[0048] Therefore, in the embodiment, attention is focused on, for example, the elongation rate α as a physical property related to the flexibility of the bonding layer 60. In the following description, the elongation rate of the bonding layer 60 at −60° C. is defined as α1, and the elongation rate of the bonding layer 60 at 25° C. is defined as α2.

[0049] In the embodiment, the elongation percentage α1 of the bonding layer 60 at −60° C. is, for example, 120% or more, preferably 175% or more, more preferably 200% or more, even more preferably 220% or more, and still more preferably 240% or more.

[0050] If the elongation percentage α1 is 120% or more, the bonding layer 60 has a sufficient elongation percentage α in an extremely low temperature environment, and therefore sufficient flexibility can be ensured for the bonding layer 60. This reduces the stress applied to the ceramic dielectric substrate 11 in an extremely low temperature environment, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking. The upper limit of the elongation percentage α1 is not particularly limited, but is, for example, 1000% or less.

[0051] The elongation percentage α2 of the bonding layer 60 at 25° C. is, for example, 150% or more, preferably 200% or more, and more preferably 250% or more.

[0052] If the elongation percentage α2 is 150% or more, the bonding layer 60 has a sufficient elongation percentage α in a room temperature environment, and therefore sufficient flexibility can be ensured for the bonding layer 60. This reduces the stress applied to the ceramic dielectric substrate 11 in a room temperature environment, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking. The upper limit of the elongation percentage α2 is not particularly limited, but is, for example, 1650% or less.

[0053] The ratio α1 / α2 of the elongation percentage α1 to the elongation percentage α2 is, for example, 0.60 or more, preferably 0.80 or more, and more preferably 0.90 or more.

[0054] If the ratio α1 / α2 of the elongation percentage α is 0.60 or more, the difference in the thermal expansion coefficient between the ceramic dielectric substrate 11 and the base plate 50 can be reduced when the ceramic dielectric substrate 11 is placed in an environment ranging from room temperature to an extremely low temperature. This can prevent the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking of the ceramic dielectric substrate 11. The upper limit of the ratio α1 / α2 of the elongation percentage α is not particularly limited, but is, for example, 1.5 or less.

[0055] In the embodiment, attention is focused on, for example, bonding strength β as a physical property related to the flexibility of the bonding layer 60. In the following description, the bonding strength of the bonding layer 60 at −60° C. is designated as β1, and the bonding strength of the bonding layer 60 at 25° C. is designated as β2.

[0056] In the embodiment, the bonding strength β1 of the bonding layer 60 at −60° C. is, for example, 0.4 MPa or more and 10 MPa or less, preferably 0.4 MPa or more and 2.0 MPa or less, more preferably 0.4 MPa or more and 1.9 MPa or less, and even more preferably 0.4 MPa or more and 1.4 MPa or less. In addition, the bonding strength β1 is preferably 0.7 MPa or more.

[0057] If the bonding strength β1 is 0.4 MPa or more, the anchor effect of the bonding layer 60 located between the ceramic dielectric substrate 11 and the base plate 50 does not become too weak in an extremely low temperature environment. This allows the ceramic dielectric substrate 11 and the base plate 50 to be more reliably bonded together in an extremely low temperature environment.

[0058] If the bonding strength β1 is 10 MPa or less, the anchor effect of the bonding layer 60 located between the ceramic dielectric substrate 11 and the base plate 50 does not become too strong in an extremely low temperature environment. This reduces the stress applied to the ceramic dielectric substrate 11 in an extremely low temperature environment, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking.

[0059] The bonding strength β2 of the bonding layer 60 at 25° C. is, for example, 0.5 MPa or more and 1.5 MPa or less, and preferably 0.5 MPa or more and 0.8 MPa or less.

[0060] If the bonding strength β2 is 0.5 MPa or more, the anchor effect of the bonding layer 60 that penetrates into the surface of the ceramic dielectric substrate 11 and the surface of the base plate 50 is not too weak in a room temperature environment. This allows the ceramic dielectric substrate 11 and the base plate 50 to be more reliably bonded together in a room temperature environment.

[0061] If the bonding strength β2 is 1.5 MPa or less, the anchor effect of the bonding layer 60 adhered to the surface of the ceramic dielectric substrate 11 is not too strong in a room temperature environment. This reduces the stress applied to the ceramic dielectric substrate 11 in a room temperature environment, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking.

[0062] The ratio β1 / β2 of the bonding strength β1 to the bonding strength β2 is, for example, 0.6 or more and 10 or less, preferably 0.6 or more and 5 or less, and more preferably 0.6 or more and 3 or less. The ratio β1 / β2 is preferably 0.8 or more, more preferably 1.1 or more. The ratio β1 / β2 is preferably 1.9 or less.

[0063] If the ratio β1 / β2 of the bonding strength β is 0.6 or more, sufficient bonding strength of the bonding layer 60 located between the ceramic dielectric substrate 11 and the base plate 50 can be maintained both at room temperature and in an extremely low temperature environment, and a strong bond between the ceramic dielectric substrate 11 and the base plate 50 can be maintained.

[0064] If the ratio β1 / β2 of the bonding strength β is 10 or less, the effect of the bonding layer 60 located between the ceramic dielectric substrate 11 and the base plate 50 can be sufficiently suppressed both at room temperature and in an extremely low temperature environment. This suppresses the stress applied to the ceramic dielectric substrate 11 when placed in an environment ranging from room temperature to an extremely low temperature, and suppresses peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11.

[0065] In the embodiment, attention is focused on, for example, the elastic modulus γ as a physical property related to the flexibility of the bonding layer 60. In the following description, the elastic modulus of the bonding layer 60 at −60° C. is defined as γ1, and the elastic modulus of the bonding layer 60 at 25° C. is defined as γ2.

[0066] In the embodiment, the elastic modulus γ1 of the bonding layer 60 at −60° C. is, for example, 0.1 MPa or more and 10 MPa or less, preferably 0.1 MPa or more and 3 MPa or less, and more preferably 0.1 MPa or more and 1 MPa or less. The elastic modulus γ1 is preferably 0.3 MPa or more, and more preferably 0.4 MPa or more.

[0067] If the elastic modulus γ1 is 0.1 MPa or more, the bonding layer 60 has sufficient restorability in an extremely low temperature environment, and therefore warping of the ceramic dielectric substrate 11 can be easily suppressed even when stress occurs between the ceramic dielectric substrate 11 and the base plate 50. This makes it possible to suppress deterioration of the in-plane temperature uniformity of the object W in an extremely low temperature environment.

[0068] If the elastic modulus γ1 is 10 MPa or less, the bonding layer 60 can be prevented from becoming too hard in an extremely low temperature environment, thereby suppressing the stress applied to the ceramic dielectric substrate 11 in an extremely low temperature environment, and preventing the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking.

[0069] The elastic modulus γ2 of the bonding layer 60 at 25° C. is, for example, 0.2 MPa or more and 1.0 MPa or less, and preferably 0.2 MPa or more and 0.4 MPa or less.

[0070] If the elastic modulus γ2 is 0.2 MPa or more, the bonding layer 60 has sufficient restorability in a room temperature environment, and therefore warping of the ceramic dielectric substrate 11 is easily suppressed even when stress occurs between the ceramic dielectric substrate 11 and the base plate 50. This makes it possible to suppress deterioration of the in-plane temperature uniformity of the object W in a room temperature environment.

[0071] If the elastic modulus γ2 is 1.0 MPa or less, the bonding layer 60 can be prevented from becoming too hard in a room temperature environment. This reduces the stress applied to the ceramic dielectric substrate 11 in a room temperature environment, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking.

[0072] The ratio γ1 / γ2 of the elastic modulus γ1 to the elastic modulus γ2 is, for example, 0.6 to 30, preferably 0.6 to 10, and more preferably 0.6 to 3. The ratio γ1 / γ2 is preferably 0.8 or more, more preferably 0.9 or more. The ratio γ1 / γ2 is preferably 2.1 or less.

[0073] If the ratio γ1 / γ2 of the elastic moduli γ is 0.6 or more, the bonding layer 60 maintains sufficient restorability both at room temperature and in an extremely low temperature environment, and therefore warping of the ceramic dielectric substrate 11 is easily suppressed even when stress occurs between the ceramic dielectric substrate 11 and the base plate 50. This makes it possible to suppress deterioration of the in-plane temperature uniformity of the object W when placed in an environment ranging from room temperature to an extremely low temperature.

[0074] If the ratio γ1 / γ2 of the elastic moduli γ is 30 or less, the bonding layer 60 can be prevented from becoming too hard both at room temperature and in an extremely low temperature environment. This reduces the stress applied to the ceramic dielectric substrate 11 when placed in an environment ranging from room temperature to an extremely low temperature, and prevents the ceramic dielectric substrate 11 from peeling off from the base plate 50 and cracking.

[0075] As described above, it is preferable to make the ceramic dielectric substrate 11 thin in order to shorten the distance between the base plate 50 connected to the high-frequency power supply 504 and the upper electrode 510, or from the viewpoint of heat uniformity. On the other hand, if the ceramic dielectric substrate 11 is thin, there is a risk that the ceramic dielectric substrate 11 may crack and break if the bonding layer 60 loses flexibility in an extremely low-temperature environment. In contrast, according to the embodiment, the bonding layer 60 has sufficient flexibility in an extremely low-temperature environment, so that defects such as breakage can be effectively suppressed even when the ceramic dielectric substrate 11 is as thin as 5 mm or less.

[0076] 2(a) to 2(c) are explanatory diagrams showing a method for measuring the elongation rate and bonding strength of the bonding layer. FIG. 3 is an explanatory diagram showing a method for calculating the elastic modulus of the bonding layer. FIG. 4 is an explanatory diagram illustrating measurement points for the elongation rate and bonding strength of the bonding layer. In the embodiment, the elongation percentage α and bonding strength β of the bonding layer 60 can be measured by the method shown in FIGS. 2(a) to 2(c).

[0077] When measuring the elongation percentage α and bonding strength β of the bonding layer 60, first, a test piece TP is taken from the electrostatic chuck 110 as shown in FIG. 2(a). The test piece TP is taken so as to penetrate the electrostatic chuck 110 in the Z-axis direction. In other words, the test piece TP is taken so as to include the base plate 50, the bonding layer 60, and the ceramic dielectric substrate 11, which are stacked in the Z-axis direction. The test piece TP is taken in the shape of a cylinder with a diameter of 30 mm. The taking method can be, for example, helical cutting or water jet cutting.

[0078] Next, as shown in FIG. 2(b), pressure is applied to the ceramic dielectric substrate 11 and the base plate 50 of the test piece TP in opposite directions along the XY plane. In this example, pressure is applied to the ceramic dielectric substrate 11 in the negative direction of the X-axis, and pressure is applied to the base plate 50 in the positive direction of the X-axis. The pressure is applied, for example, using an autograph. While measuring the elongation rate α and shear stress of the bonding layer 60, the pressure applied to the test piece TP is gradually increased until the bonding layer 60 breaks, as shown in FIG. 2(c).

[0079] The relationship between the elongation rate α measured by the above method and the shear stress is represented, for example, by the curve shown in Fig. 3. As shown in Fig. 3, the shear stress increases until the bonding layer 60 breaks, and then decreases when the bonding layer 60 breaks. In other words, the point at which the shear stress reaches its maximum can be considered to be the point at which the bonding layer 60 breaks.

[0080] The elongation rate α is expressed as 100 × (elongation L1 of the bonding layer 60 at the time of fracture) / (thickness T2 of the bonding layer 60). The elongation L1 of the bonding layer 60 at the time of fracture is the change in length of the bonding layer 60 in the pressure direction (in this example, the X-axis direction) at the time of fracture. The thickness T2 of the bonding layer 60 is the length of the bonding layer 60 in the Z-axis direction. The bonding strength β is the magnitude of the shear stress when the bonding layer 60 fractures. In other words, the bonding strength β can be calculated from the magnitude of the shear stress when the bonding layer 60 fractures.

[0081] The elongation percentage α and the bonding strength β can be measured using, for example, an autograph (AGS-X (5 kN) manufactured by Shimadzu Corporation). The measurement conditions are, for example, a compression speed of 0.1 to 10 mm / min, a load cell used of 5 kN, and measurement temperatures of 25°C and -60°C.

[0082] 3, the elastic modulus γ of the bonding layer 60 is represented by the slope of the curve until the bonding layer 60 breaks. In other words, the elastic modulus γ is calculated from the elongation percentage α and the bonding strength β. Specifically, the elastic modulus γ is represented by (bonding strength β of the bonding layer 60 at break) / (strain of the bonding layer 60 at break ((elongation L1 of the bonding layer 60 at break) / (thickness T2 of the bonding layer 60))).

[0083] In an embodiment, it is sufficient that the bonding layer 60 of the test piece TP collected from at least one location on the electrostatic chuck 110 has the above-described elongation rate α (elongation rate ratio), bonding strength β (bonding strength ratio), or elastic modulus γ (elastic modulus ratio). It is preferable that the bonding layer 60 of each of the test pieces TP collected from multiple locations on the electrostatic chuck 110 has the above-described elongation rate α (elongation rate ratio), bonding strength β (bonding strength ratio), or elastic modulus γ (elastic modulus ratio). It is also preferable that the average value of the elongation rate α (elongation rate ratio), bonding strength β (bonding strength ratio), or elastic modulus γ (elastic modulus ratio) of the test pieces TP collected from multiple locations on the electrostatic chuck 110 satisfies the above-described elongation rate α (elongation rate ratio), bonding strength β (bonding strength ratio), or elastic modulus γ (elastic modulus ratio).

[0084] 4, test pieces TP are collected from multiple locations on the electrostatic chuck 110, and the elongation α and bonding strength β of the bonding layer 60 are measured for each test piece TP by the methods shown in FIGS. 2(b) and 2(c). This example shows a case where test pieces TP are collected from a total of nine locations: four locations at the central portion 110a and outer peripheral portion 110b on the XY plane of the electrostatic chuck 110, and four locations at an intermediate portion 110c between the central portion 110a and outer peripheral portion 110b.

[0085] For example, in at least one of the test pieces TP taken from the above nine locations, the bonding layer 60 may have the above-mentioned elongation rate α (elongation rate ratio), bonding strength β (bonding strength ratio), or elastic modulus γ (elastic modulus ratio).

[0086] 5 and 6 are graphs showing the physical properties of an example of the bonding layer of the electrostatic chuck according to the embodiment. FIG. 6 is an enlarged graph of part A in FIG. FIG. 7 is a table showing physical properties of an example of the bonding layer of the electrostatic chuck according to the embodiment. Example 1 is an example of the electrostatic chuck 110 according to the embodiment. Reference example 1 is an example of an electrostatic chuck having a bonding layer 60 with different physical properties from those of Example 1.

[0087] The elongation percentage α, bonding strength β, and elastic modulus γ of the bonding layer 60 of Example 1 and Reference Example 1 measured and calculated using the measurement and calculation methods shown in Figures 2(a) to 2(c) and Figure 3 are shown in Figures 5 to 7.

[0088] The results of a peeling / crack test for Example 1 and Reference Example 1 are shown in FIG. 7 . In the peeling / crack test, a sample was prepared by bonding a ceramic dielectric substrate 11 and a base plate 50 with a bonding layer 60. The sample was then left at −60°C for at least 3,000 hours and then returned to room temperature. The presence or absence of peeling of the ceramic dielectric substrate 11 from the base plate 50 and the presence or absence of cracks in the ceramic dielectric substrate 11 were evaluated. The presence or absence of peeling of the bonding layer 60 was determined by direct observation, in which a cross section of the bonding layer 60 was observed under a microscope to evaluate the presence or absence of cracks, and ultrasonic flaw detection, in which ultrasonic waves were applied to evaluate the presence or absence of cracks inside the bonding layer 60. A sample in which cracks were observed by at least either direct observation or ultrasonic flaw detection was evaluated as having peeling “present,” and a sample in which no cracks were observed by both direct observation and ultrasonic flaw detection was evaluated as having peeling “not present.” The presence or absence of cracks in the ceramic dielectric substrate 11 was evaluated by visually observing the ceramic dielectric substrate 11. A sample in which cracks were observed was evaluated as having cracks “present,” and a sample in which no cracks were observed was evaluated as having cracks “not present.”

[0089] 5 to 7, in Reference Example 1, the elongation rate α1 is 107%, the elongation rate α2 is 195%, and the ratio of the elongation rates α, α1 / α2, is 0.5. In Reference Example 1, since the bonding layer 60 has such an elongation rate α (elongation rate ratio), the ceramic dielectric substrate 11 does not peel off from the base plate 50 or crack in the ceramic dielectric substrate 11 in a room temperature (25°C) environment, but the ceramic dielectric substrate 11 peels off from the base plate 50 or cracks in the ceramic dielectric substrate 11 in an extremely low temperature (-60°C) environment.

[0090] In contrast, in Example 1, the elongation rate α1 is 225%, the elongation rate α2 is 190%, and the ratio of the elongation rates α, α1 / α2, is 1.2. In Example 1, since the bonding layer 60 has such an elongation rate α (elongation rate ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 and the ceramic dielectric substrate 11 does not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0091] In this way, by setting the elongation rate α1 of the bonding layer 60 to 120% or more, or by setting the ratio of the elongation rates α, α1 / α2, to 0.60 or more, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0092] 5 to 7, in Reference Example 1, the bonding strength β1 is 29.8 MPa, the bonding strength β2 is 0.56 MPa, and the bonding strength β ratio β1 / β2 is 53.2. In Reference Example 1, because the bonding layer 60 has such a bonding strength β (bonding strength ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 or crack in the ceramic dielectric substrate 11 in a room temperature (25°C) environment, but the ceramic dielectric substrate 11 peels from the base plate 50 or cracks in the ceramic dielectric substrate 11 in an extremely low temperature (-60°C) environment.

[0093] In contrast, in Example 1, the bonding strength β1 is 1.42 MPa, the bonding strength β2 is 0.83 MPa, and the bonding strength β ratio β1 / β2 is 1.7. In Example 1, since the bonding layer 60 has such a bonding strength β (bonding strength ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 and the ceramic dielectric substrate 11 does not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0094] In this way, by setting the bonding strength β1 of the bonding layer 60 to be 0.4 MPa or more and 10 MPa or less, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0095] 5 to 7, in Reference Example 1, the elastic modulus γ1 is 28 MPa, the elastic modulus γ2 is 0.29 MPa, and the ratio of the elastic moduli γ, γ1 / γ2, is 96.6. In Reference Example 1, since the bonding layer 60 has such an elastic modulus γ (elastic modulus ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 or crack in the ceramic dielectric substrate 11 in an environment at room temperature (25°C), but the ceramic dielectric substrate 11 peels from the base plate 50 or cracks in the ceramic dielectric substrate 11 in an environment at an extremely low temperature (-60°C).

[0096] In contrast, in Example 1, the elastic modulus γ1 is 0.63 MPa, the elastic modulus γ2 is 0.44 MPa, and the ratio of the elastic moduli γ, γ1 / γ2, is 1.4. In Example 1, since the bonding layer 60 has such an elastic modulus γ (elastic modulus ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 and the ceramic dielectric substrate 11 does not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0097] In this way, by setting the elastic modulus γ1 of the bonding layer 60 to be 0.1 MPa or more and 10 MPa or less, or by setting the elastic modulus γ ratio γ1 / γ2 to be 0.6 or more and 30 or less, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0098] FIG. 8 is a table showing physical properties of an example of the bonding layer of the electrostatic chuck according to the embodiment. Examples 2 to 14 are examples of the electrostatic chuck 110 according to the embodiment. The elongation percentage α, bonding strength β, and elastic modulus γ of the bonding layer 60 of Examples 2 to 14, which were measured and calculated in the same manner as in Example 1 and Reference Example 1, are shown in Fig. 8. The results of a peel / crack test conducted in the same manner as in Example 1 and Reference Example 1 are also shown in Fig. 8.

[0099] 8, in Examples 2 to 14, the elongation percentage α1 was 175% or more and 247% or less, the elongation percentage α2 was 150% or more and 280% or less, and the ratio of the elongation percentages α, α1 / α2, was 0.80 or more and 1.17 or less. In Examples 2 to 14, since the bonding layer 60 had such elongation percentages α (elongation percentage ratios), the ceramic dielectric substrate 11 did not peel off from the base plate 50 and the ceramic dielectric substrate 11 did not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0100] In this way, by setting the elongation rate α1 of the bonding layer 60 to 120% or more, or by setting the ratio of the elongation rates α, α1 / α2, to 0.60 or more, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0101] 8, in Examples 2 to 14, the bonding strength β1 was 0.70 MPa or more and 1.90 MPa or less, the bonding strength β2 was 0.51 MPa or more and 1.60 MPa or less, and the bonding strength β ratio β1 / β2 was 0.8 or more and 1.9 or less. In Examples 2 to 14, since the bonding layer 60 had such a bonding strength β (bonding strength ratio), the ceramic dielectric substrate 11 did not peel from the base plate 50 and the ceramic dielectric substrate 11 did not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0102] In this way, by setting the bonding strength β1 of the bonding layer 60 to be 0.4 MPa or more and 10 MPa or less, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0103] 8, in Examples 2 to 14, the elastic modulus γ1 is 0.34 MPa or more and 1.02 MPa or less, the elastic modulus γ2 is 0.19 MPa or more and 0.81 MPa or less, and the ratio of the elastic moduli γ, γ1 / γ2, is 0.9 or more and 2.1 or less. In Examples 2 to 14, since the bonding layer 60 has such elastic moduli γ (elastic modulus ratio), the ceramic dielectric substrate 11 does not peel from the base plate 50 and the ceramic dielectric substrate 11 does not crack under either a room temperature (25°C) environment or an extremely low temperature (-60°C) environment.

[0104] In this way, by setting the elastic modulus γ1 of the bonding layer 60 to be 0.1 MPa or more and 10 MPa or less, or by setting the elastic modulus γ ratio γ1 / γ2 to be 0.6 or more and 30 or less, peeling of the ceramic dielectric substrate 11 from the base plate 50 and cracking of the ceramic dielectric substrate 11 can be suppressed in an extremely low temperature environment.

[0105] FIG. 9 is a cross-sectional view schematically illustrating a wafer processing apparatus including an electrostatic chuck according to the embodiment. 9, the wafer processing apparatus 500 includes a processing vessel 501, a radio-frequency power supply 504, a chucking power supply 505, an upper electrode 510, and an electrostatic chuck 110. A processing gas inlet 502 for introducing a processing gas into the processing vessel 501 and the upper electrode 510 are provided in the ceiling of the processing vessel 501. An exhaust port 503 for evacuating the interior of the processing vessel 501 is provided in the bottom plate of the processing vessel 501. The electrostatic chuck 110 is disposed below the upper electrode 510 inside the processing vessel 501. The base plate 50 and the upper electrode 510 of the electrostatic chuck 110 are connected to the radio-frequency power supply 504. The electrode layer 12 of the electrostatic chuck 110 is connected to the chucking power supply 505.

[0106] The base plate 50 and the upper electrode 510 are disposed substantially parallel to each other with a predetermined distance therebetween. The object W is placed on the first main surface 11a located between the base plate 50 and the upper electrode 510.

[0107] When a voltage (high frequency voltage) is applied from the high frequency power supply 504 to the base plate 50 and the upper electrode 510, a high frequency discharge occurs, the processing gas introduced into the processing vessel 501 is excited and activated by plasma, and the target object W is processed.

[0108] When a voltage (adsorption voltage) is applied to the electrode layer 12 from the adsorption power supply 505, an electric charge is generated on the first main surface 11a side of the electrode layer 12, and the object W is adsorbed and held by the electrostatic chuck 110 by electrostatic force.

[0109] The above describes the embodiments of the present invention. However, the present invention is not limited to these descriptions. Design modifications made by a person skilled in the art to the above-described embodiments are also included within the scope of the present invention as long as they incorporate the features of the present invention. For example, the shape, dimensions, materials, arrangement, installation form, etc. of each element of the electrostatic chuck are not limited to those exemplified and can be modified as appropriate. Furthermore, the elements of the above-described embodiments can be combined to the extent technically possible, and such combinations are also included within the scope of the present invention as long as they incorporate the features of the present invention. [Explanation of symbols]

[0110] 11 ceramic dielectric substrate, 11a first main surface, 11b second main surface, 12 electrode layer, 13 convex portion, 14 groove, 15 through hole, 20 connection portion, 50 base plate, 50a upper portion, 50b lower portion, 51 input path, 52 output path, 53 gas introduction path, 55 communication path, 60 bonding layer, 110 electrostatic chuck, 110a central portion, 110b outer peripheral portion, 110c intermediate portion, 500 wafer processing apparatus, 501 processing vessel, 502 processing gas introduction port, 503 exhaust port, 504 high frequency power supply, 505 chucking power supply, 510 upper electrode, TP test piece, W target object

Claims

1. a ceramic dielectric substrate; a metal base plate that supports the ceramic dielectric substrate; a bonding layer including a resin material provided between the ceramic dielectric substrate and the base plate; Equipped with An electrostatic chuck, characterized in that a ratio α1 / α2 of an elongation rate α1 of the bonding layer at −60° C. to an elongation rate α2 of the bonding layer at 25° C. is 0.60 or more.

2. 2. The electrostatic chuck according to claim 1, wherein the ratio α1 / α2 is 0.80 or more.

3. 3. The electrostatic chuck according to claim 1, wherein the elastic modulus γ1 of the bonding layer at −60° C. is 0.1 MPa or more and 10 MPa or less.

4. 4. The electrostatic chuck according to claim 1, wherein a ratio γ1 / γ2 of the elastic modulus γ1 of the bonding layer at −60° C. to the elastic modulus γ2 of the bonding layer at 25° C. is 0.6 or more and 30 or less.

5. 5. The electrostatic chuck according to claim 1, wherein the ceramic dielectric substrate contains at least one of aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, and yttrium oxide.

6. 6. The electrostatic chuck of claim 5, wherein the ceramic dielectric substrate comprises aluminum oxide.

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