Holding device and method for manufacturing the same

Abstract

To provide a holding device which can exhibit a high cooling performance without causing inconveniences due to the difference of thermal expansion between a metal base part and a ceramic part, and a method for manufacturing the holding device.SOLUTION: A holding device for holding a target object includes: a metal base part in which a coolant passage is formed; and a ceramic part formed in a surface of the metal base part, the target object being held in the ceramic part. The difference of thermal expansion between the metal base part and the ceramic part in a usage temperature range of the ceramic part is 2.0 ppm / °C at a maximum. The ceramic part is directly formed in the metal base part and the metal base part is an additive-manufactured material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a holding device for holding an object and a method for manufacturing the same.

Background Art

[0002] For example, in an apparatus for performing plasma processing such as etching, an electrostatic chuck has been conventionally known as a holding device for holding an object, and has a structure including a metal base portion in which a refrigerant flow path is formed, and a ceramic portion provided thereon on which the object is placed.

[0003] As such an electrostatic chuck, one using aluminum as the metal base portion and a sprayed film of alumina (Al2O3) as the ceramic portion is known (for example, Patent Document 1).

[0004] Further, as a technique for, for example, performing plasma processing on an object, Patent Document 2 proposes an electrostatic chuck having a metal base portion in which a refrigerant flow path is formed, a ceramic portion on which the object is placed, and a joint portion provided between the ceramic portion and the base portion and made of a composite including an adhesive and an inorganic filler for the purpose of thermal stress relaxation. Patent Document 2 also describes that by configuring the base portion using aluminum having a relatively high thermal conductivity and being easy to process, the cooling efficiency of the ceramic portion and the object thereon can be enhanced.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the technology described in Patent Document 1, the ceramic part on which the object is placed heats up due to heat input from the plasma, and peeling or deformation may occur due to the difference in thermal expansion between the surface ceramic and the metal base, which may reduce the processing accuracy of the object.

[0007] On the other hand, in the technology described in Patent Document 2, although the difference in thermal expansion is mitigated by the presence of the joint and cooling performance can be maintained, damage to the joint may not be sufficiently suppressed. Furthermore, it is necessary to control the thermal resistance of the joint and the amount of strain at maximum shear stress, making it difficult to reliably obtain the desired effect.

[0008] Therefore, the object of the present invention is to provide a holding device and a method for manufacturing the same that can exhibit high cooling performance without causing problems due to the difference in thermal expansion between the metal base and the ceramic part. [Means for solving the problem]

[0009] The present invention relates to the following (1)~( 4 ) provides means to do so.

[0011] ( 1 ) A holding device for holding an object, A metal base portion in which a refrigerant flow path is formed, and a surface formed on the metal base portion that holds the object. Made of alumina ceramics It has a ceramic part, The ceramic portion is formed directly on the metal base portion. The aforementioned metal base portion is The additive manufacturing material is an Fe-Ni alloy containing, by mass%, C: 0.1% or less, Si: 0.30% or less, Mn: 0.8% or less, and Ni: 41.0-43.0%, with the remainder being Fe and unavoidable impurities, and the difference in thermal expansion between the additive material and the ceramic portion is 1.0 ppm / °C or less within the operating temperature range of the ceramic portion, which is -100 to 50°C. A holding device characterized by the following features.

[0014] ( 2 The ceramic portion is characterized by being a plasma spray coating. (1) The holding device described above.

[0016] ( 3 A method for manufacturing a holding device for holding an object, A step of forming a metal base portion in which a refrigerant flow path is formed by additive manufacturing; On the surface of the metal base portion, an object is held Made of alumina ceramics A step of directly forming a ceramic portion; having The metal base portion The additive manufacturing material is an Fe-Ni alloy containing, by mass%, C: 0.1% or less, Si: 0.30% or less, Mn: 0.8% or less, and Ni: 41.0-43.0%, with the remainder being Fe and unavoidable impurities, and the difference in thermal expansion between the additive material and the ceramic portion is 1.0 ppm / °C or less within the operating temperature range of the ceramic portion, which is -100 to 50°C. A method for manufacturing a holding device, characterized in that.

[0019] ( 4 ) The ceramic portion is a sprayed coating formed by plasma spraying, characterized in that (3) The method for manufacturing a holding device according to the above.

Effect of the Invention

[0020] According to the present invention, there are provided a holding device and a method for manufacturing a holding device that can exhibit high cooling performance without causing inconvenience due to the difference in thermal expansion between the metal base portion and the ceramic portion.

Brief Description of the Drawings

[0021] [Figure 1] It is a cross-sectional view showing a holding device according to an embodiment of the present invention. [Figure 2] It is a diagram showing the thermal expansion coefficients of an Fe-Ni-based additive manufacturing alloy (the material of the present invention) and alumina from 20°C to each temperature. [Figure 3] It is a diagram for explaining the cooling performance test in the examples.

Mode for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a holding device according to an embodiment of the present invention. The holding device 10 is configured as an electrostatic chuck and holds an object S in a plasma processing device such as a plasma etching device. The object S may be a substrate such as a semiconductor wafer.

[0023] The holding device 10 has a metal base portion 1 in which a refrigerant flow path is formed, and a ceramic portion 2 formed on the surface of the metal base portion 1, which holds the object. When the holding device is an electrostatic chuck, when plasma processing is performed in the plasma processing apparatus, a DC voltage is applied to an electrode provided in the ceramic portion 2, and the object is held by electrostatic attraction due to Coulomb force or the like.

[0024] The metal base portion 1 has a refrigerant flow path 3 formed within it, through which a refrigerant at a predetermined temperature flows. The metal base portion 1 may have a structure as shown in the figure, comprising a flow path forming portion 1a in which the refrigerant flow path 3 is formed, and a heat transfer adjustment portion 1b below it, for example, having a hollow structure. The ceramic portion 2 is formed directly on the metal base portion 1, for example, as a thermal spray coating. The thermal spray coating may be a plasma thermal spray coating.

[0025] When the holding device 10 is used in a device that performs plasma processing, such as plasma etching, in order to suppress the temperature rise of the object S due to heat input from the plasma and maintain processing accuracy, a refrigerant with a temperature of -100°C or lower, for example, around -110°C, is passed through the refrigerant flow path 3, and the operating temperature range of the ceramic part heated by the plasma is set to -100 to 50°C. For example, a fluorine-based refrigerant can be used.

[0026] The metal base part 1 and the ceramic part 2 are, Use of ceramic parts The materials are designed so that the difference in thermal expansion between the two materials over a given temperature range is 2.0 ppm / °C or less. This reduces the difference in thermal expansion between the two materials compared to the conventional case where aluminum is used as the metal base member 1, and thus reduces thermal stress even when the ceramic part 2 is directly formed on the metal base part 1. The method of directly forming the ceramic part 2 on the metal base part 1 is not limited, but it is preferable to form the ceramic part 2 as a thermal spray coating, such as a plasma spray coating. By directly forming the ceramic part 2 on the metal base part 1 in this way, a joint is not required, and the joint is not damaged by the plasma.

[0027] The material constituting the metal base 1 is not particularly limited as long as it is a material that, within the operating temperature range of the ceramic part, has a thermal expansion difference of 2.0 ppm / °C or less compared to the ceramic part 2. For example, an Fe-Ni alloy can be suitably used. Fe-Ni alloys exhibit low expansion close to zero at a Ni content of 36%Ni, and thermal expansion increases as the Ni content increases or decreases. Therefore, by adjusting the Ni content, the thermal expansion difference between the metal base 1 and the ceramic part 2 within the operating temperature range of the ceramic part can be adjusted to 2.0 ppm / °C or less.

[0028] Furthermore, the metal base part 1 is an additively manufactured material. Additive manufacturing is a technology that melts alloy powder using a laser beam, electron beam, or plasma as a heat source while supplying alloy powder, and builds up the material in three dimensions. By appropriately selecting the parameters of the laser beam, electron beam, or plasma, the cooling rate during solidification can be made extremely fast, exceeding 5000°C / sec, which is not achievable with conventional casting. Fe-Ni additively manufactured alloys to which this additive manufacturing technology is applied have a refined microstructure, and the microsegregation of Ni seen in conventional castings and forgings is reduced. As a result, they tend to have a lower coefficient of thermal expansion than conventional castings and forgings, and possess higher properties such as toughness and strength.

[0029] The ceramic part 2 is not particularly limited as long as it has the required resistance for the usage conditions, such as heat resistance and plasma resistance, but typical examples include alumina (Al2O3) and aluminum nitride (AlN).

[0030] When the holding device 10 is used in a device that performs plasma processing such as plasma etching, as described above, a refrigerant is passed through the refrigerant flow path 3, and the operating temperature range of the ceramic part is -100 to 50°C. In this case, the average thermal expansion coefficient of alumina is 4.1 ppm / °C at -100 to 20°C and 5.4 ppm / °C at 20 to 50°C.

[0031] In the temperature range of -100 to 50°C, the difference in thermal expansion between Fe-Ni alloys and alumina can be reduced to 1.0 ppm / °C or less by adjusting the composition of the Fe-Ni alloy. Such Fe-Ni alloys can be those with a Ni content in the range of 41.0 to 43.0 mass%. Specifically, alloys containing C: 0.1% or less, Si: 0.3% or less, Mn: 0.8% or less, and Ni: 41.0 to 43.0% by mass, with the remainder being Fe and unavoidable impurities, can be used. Since C is an element that increases thermal expansion, its content is preferably 0.1% or less. While Si and Mn are effective elements for deoxidation, too much of them increases thermal expansion, so it is preferable to have Si: 0.3% or less and Mn: 0.8% or less. Fe-Ni additive manufacturing alloys of this composition have a thermal expansion coefficient in the range of 4.5 to 4.9 ppm / °C in the range of -100 to 50°C, and the difference in thermal expansion between them and alumina (4.2 to 5.4 ppm / °C) is well below 1.0 ppm / °C.

[0032] As an example, Figure 2 shows the thermal expansion coefficients of an Fe-Ni additive manufacturing alloy with the composition C:0.001%, Si:0.01%, Mn:0.03%, Ni:41.88%, and the remainder being Fe + unavoidable impurities, and alumina, from 20°C to various temperatures. For comparison, Figure 2 also shows the thermal expansion coefficient of 42Ni alloy (forged alloy), which has been conventionally known as an alloy whose thermal expansion coefficient approximates that of alumina ceramics. As shown in Figure 2, the thermal expansion coefficient of the Fe-Ni additive manufacturing alloy with the above composition is very close to that of alumina in the range of -100 to 50°C, and the difference in thermal expansion with alumina is 1.0 ppm / °C or less in this temperature range. However, the difference in thermal expansion with alumina of the 42Ni alloy (forged alloy) is larger than that of the Fe-Ni additive manufacturing alloy with the above composition below 10°C, and it can be seen that the difference exceeds 1.0 ppm / °C below -50°C.

[0033] Another major advantage of the metal base 1 being made from an additively manufactured material is that, compared to machining, the design flexibility of the refrigerant flow path 3 is dramatically increased, allowing for adjustment of the cooling performance.

[0034] Conventional aluminum metal base materials are machineable, and therefore, refrigerant channels are formed by machining. While machining can only create relatively simple refrigerant channels, aluminum has high thermal conductivity, so even relatively simple channels can provide good cooling performance. On the other hand, if a material with lower thermal conductivity than aluminum is used, even if refrigerant channels can be formed by machining, it is difficult to ensure cooling performance equivalent to that of aluminum. In particular, Fe-Ni alloys have lower thermal conductivity than aluminum and are difficult to machine, making it difficult to form refrigerant channels by machining. In contrast, when the metal base part 1 is made from an additively manufactured material, the structure can be manufactured as designed, giving greater design freedom to the refrigerant channels 3. Therefore, it is possible to form refrigerant channels 3 with higher cooling performance, and even if the metal base part is made from a material with low thermal conductivity, cooling performance close to that of conventional aluminum metal base parts can be obtained. In particular, when an Fe-Ni additively manufactured alloy is used as the metal base material 1, the difference in thermal expansion coefficients between it and the ceramic part can be set to a desired small value, and the refrigerant channels can be optimized by additive manufacturing to achieve the desired cooling performance.

[0035] Although embodiments of the present invention have been described above, these should be considered merely illustrative and not restrictive. The above embodiments may be omitted, substituted, or modified in various ways without departing from the spirit of the present invention.

[0036] For example, in the above embodiment, an Fe-Ni additive manufacturing alloy was exemplified as the metal base portion, but it is not limited to this as long as the difference in thermal expansion between the metal base portion and the ceramic portion within the operating temperature range of the ceramic portion is 2.0 ppm / °C or less. Also, although alumina was exemplified as the ceramic portion, the ceramic portion is not limited to alumina. Furthermore, although -100 to 50°C was exemplified as the operating temperature range of the ceramic portion, it is not limited to this, and these materials should be selected so that the difference in thermal expansion between the metal base portion and the ceramic portion is 2.0 ppm / °C or less within the selected operating temperature range. [Examples]

[0037] The following describes embodiments of the present invention. First, aluminum, a comparative material, and the material of the present invention (an Fe-Ni additive manufacturing alloy consisting of C:0.001%, Si:0.01%, Mn:0.03%, Ni:41.88%, the remainder being Fe + unavoidable impurities) were used as base materials (φ40mm × 10mm). A 300 μm thick alumina spray coating was formed on these materials by plasma spraying to produce Sample A (base material is aluminum) and Sample B (base material is the material of the present invention). The average thermal expansion coefficients at -100 to 20°C were approximately 4.5 ppm / °C for the material of the present invention, approximately 21 ppm / °C for aluminum, and approximately 4.1 ppm for the alumina spray coating.

[0038] Samples A and B underwent a five-cycle heat treatment test between -196°C and 500°C. Sample A, which used aluminum as a comparison material, showed delamination of the alumina spray coating after the fourth cycle, while sample B, which used the material of the present invention, showed no delamination of the alumina spray coating even after five cycles.

[0039] Next, a cooling performance test was conducted. Three cooling performance test samples (Samples C, D, and E) were prepared, as shown in Figures 3(a) to 3(c). Each sample had a structure in which a 3 mm thick alumina plate was placed on a φ400 mm base material with a refrigerant channel. Sample C, as shown in Figure 3(a), was made of aluminum, the comparative material, as the base material, and the refrigerant channel was formed 10 mm from the surface. Sample D, as shown in Figure 3(b), was made of the material of the present invention (C: 0.001%, Si: 0.01%, Mn: 0.03%, Ni: 41.88%, remainder: Fe + unavoidable impurities, Fe-Ni additive manufacturing alloy) as the base material, and the refrigerant channel was formed 10 mm from the surface, similar to Sample C. Sample E, as shown in Figure 3(c), was made of the same material of the present invention as Sample D as the base material, and the cooling channel was formed 1 mm from the surface.

[0040] A silicon wafer (φ300 mm) was placed on the surface of the ceramic portion of these samples, and the cooling performance test was performed by passing a -110°C refrigerant through the refrigerant channel at a flow rate of 0.5 L / s and measuring the wafer temperature. The heat transfer to the wafer was 5 kW.

[0041] As a result, the wafer temperature of sample C was -94.8°C, while the wafer temperature of sample D was -74.0°C. This is thought to be because, despite using an Fe-Ni alloy as the base material, which has a lower thermal conductivity than aluminum, sample D had the same refrigerant flow path as sample C, resulting in insufficient cooling (heat dissipation). On the other hand, the wafer temperature of sample E was -94.1°C, close to that of sample C. This is thought to be because the cooling flow path was positioned closer to the wafer, improving the wafer's cooling performance (heat dissipation).

[0042] Next, for samples C, D, and E, the same refrigerant was used, but the refrigerant flow rate was increased to 0.8 L / s, and the wafer temperature was measured in the same manner. As a result, the wafer temperatures were -97.1°C for sample C, -76.3°C for sample D, and -96.4°C for sample E. In other words, it was confirmed that when an Fe-Ni alloy is used as the base material, increasing the flow rate (e.g., increasing the cross-sectional area of ​​the refrigerant flow path) also improves the cooling performance (heat dissipation) of the wafer.

[0043] These results confirm that by forming the base material using a material with a low coefficient of thermal expansion similar to that of the ceramic part, such as an Fe-Ni alloy, through additive manufacturing, and by adjusting the position and cross-sectional area of ​​the refrigerant flow path, wafer cooling performance (heat dissipation) similar to that obtained when aluminum is used as the base material can be achieved. [Explanation of symbols]

[0044] 1; Metal base 1a; Flow channel forming section 1b; Heat transfer adjustment unit 2; Ceramics section 3; Refrigerant flow path 10; Holding device

Claims

1. A holding device for holding an object, It has a metal base portion in which a refrigerant flow path is formed, and a ceramic portion made of alumina ceramics formed on the surface of the metal base portion, which holds the object. The ceramic portion is formed directly on the metal base portion. The metal base portion is a layered Fe-Ni alloy material containing, by mass%, C: 0.1% or less, Si: 0.30% or less, Mn: 0.8% or less, Ni: 41.0 to 43.0%, with the remainder being Fe and unavoidable impurities, and the holding device is characterized in that, in the operating temperature range of the ceramic portion, -100 to 50°C, the difference in thermal expansion between the metal base portion and the ceramic portion is 1.0 ppm / °C or less.

2. The holding device according to claim 1, characterized in that the ceramic part is a plasma spray coating.

3. A method for manufacturing a holding device for holding an object, The process involves forming a metal base part with a refrigerant flow path using additive manufacturing, A step of directly forming a ceramic part made of alumina ceramics on the surface of the metal base part, in which the object to be held, It has, The present invention relates to a method for manufacturing a holding device, characterized in that the metal base portion is a layered material of an Fe-Ni alloy containing, by mass%, C: 0.1% or less, Si: 0.30% or less, Mn: 0.8% or less, Ni: 41.0 to 43.0%, with the remainder being Fe and unavoidable impurities, and the difference in thermal expansion between the metal base portion and the ceramic portion is 1.0 ppm / °C or less in the operating temperature range of the ceramic portion, which is -100 to 50°C.

4. The method for manufacturing a holding device according to claim 3, characterized in that the ceramic part is a thermal spray coating formed by plasma spraying.

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