Thermal spray powder suitable for plasma etching apparatus member, etc., and spray coating film

Abstract

To provide: a thermal spray powder suitable for a plasma etching apparatus member, having plasma resistance comparable to Y2O3 without including a rare earth element and mainly using MgAl2O4 without forming factors causing contamination; a method for manufacturing the same; and a spray coating film.SOLUTION: A thermal spray powder mainly includes MgAl2O4 and includes Al2O3. The conversion molar quantity of Al2O3 to the total molar quantity of MgAl2O4 and Al2O3 is more than 50.0 mol% and 53.0 mol% or less, and MgO is not included as a crystal phase.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermal spray powder primarily composed of a novel magnesium-aluminum spinel, which is suitable for use as a component in an etching apparatus that uses plasma generated from a gas containing a halogen element, a method for producing the same, and a thermal spray coating formed using the thermal spray powder. [Background technology]

[0002] Plasma etching is used in the semiconductor manufacturing process to create circuits on wafers. Before plasma etching begins, the wafer is coated with a photoresist or hard mask (usually oxide or nitride), which is then exposed to the circuit pattern in a subsequent photolithography process. Plasma etching selectively removes material after tracing the pattern, and this patterning and etching sequence is repeated multiple times during the semiconductor chip manufacturing process. Plasma etching removes material not only through the physical sputtering effect, but also through the chemical sputtering effect by exposing the wafer to plasma using halogen-based gases such as fluorine and chlorine.

[0003] In plasma etching, the creation of highly integrated semiconductor circuits requires the creation of nearly vertical profiles, which releases high-energy, high-density ions and radicals from the plasma. This causes the plasma to erode not only the wafer being etched but also the material composing the interior surface of the etching chamber. The resulting products then adhere to the wafer's circuits, reducing the yield of semiconductor chip manufacturing.

[0004] The chambers used for plasma etching are typically made of metals such as aluminum alloys, which are not highly resistant to exposure to halogen-based gas plasma. In contrast, ceramic materials such as metal oxides have complex crystal structures and high chemical stability, making them expected to exhibit good durability against plasma exposure. For this reason, as etching conditions become more severe, sintered ceramics and ceramic-coated metal components have begun to be used as chamber construction materials.

[0005] Most ceramics used as the base material for plasma etching chamber components are aluminum oxide or yttrium oxide sintered bodies. In the case of the former, it is often necessary to coat them with ceramics with higher resistance to halogen-based plasmas in order to improve their resistance. On the other hand, yttrium oxide sintered bodies have sufficient plasma exposure resistance for practical use under most operating conditions, but they are expensive and there are concerns about supply stability. For this reason, Patent Document 1 proposes the use of magnesium aluminate (magnesium-aluminum spinel)-based sintered bodies as ceramic sintered bodies that can replace yttrium oxide sintered bodies. Furthermore, Non-Patent Document 1 reports that magnesium-aluminum spinel sintered bodies exhibit resistance to carbon tetrafluoride gas and oxygen gas plasmas equivalent to that of yttrium oxide sintered bodies.

[0006] Thus, when aluminum alloys or aluminum oxide are used as the substrate for plasma etching chamber components, ceramic coatings are often formed on the surfaces exposed to plasma. These coatings can also be formed by physical vapor deposition (PVD), chemical vapor deposition (CVD), or aerosol deposition (AD) methods, but these methods impose limitations on the shape and size of the substrate, and the thickness of the coating is limited to a few tens of micrometers or less. In contrast to these methods, thermal spraying is not limited by the shape and size of the substrate, and can be applied to a number of surfaces. It is widely used because it can form coatings with thicknesses of over 100 μm.

[0007] Yttrium oxide is a widely used ceramic spray material for coating plasma etching chamber components, but other yttrium compounds such as yttrium fluoride (YF), yttrium oxyfluoride (YOF, Y5O4F7, etc.), and yttrium-aluminum composite oxide (YAG, etc.) are also used. Various patent documents have also proposed ceramics in which some or all of the yttrium is replaced with rare earth elements such as lanthanum, neodymium, samarium, gadolinium, and erbium. However, these ceramics are primarily composed of rare earth elements, which makes them expensive and raises concerns about supply stability.

[0008] Aluminum oxide is an example of a ceramic spray coating material that does not contain rare earth elements and can be used for plasma resistance. However, when exposed to halogen-based plasma, the wear rate of an aluminum oxide coating is several times faster than that of an yttrium oxide coating, making it difficult to apply to etching processes under severe conditions due to concerns about the coating lifespan and contamination of semiconductors. Magnesium oxide (MgO) is another rare-earth element-free ceramic that has halogen plasma resistance comparable to that of rare-earth oxide, fluoride, or oxyfluoride ceramics, such as those containing yttrium. However, MgO is highly hygroscopic, and its powder tends to agglomerate, making it difficult to perform thermal spraying under stable conditions. Furthermore, MgO decomposes easily during thermal spraying, resulting in the inclusion of Mg in the coating. This raises concerns that the volatilized Mg may contaminate semiconductors when exposed to plasma. In order to suppress the hygroscopicity of MgO and make it more stable, it is effective to make it a composite oxide with Al2O3. Patent Document 2 proposes a spinel ceramic thermal spray coating consisting mainly of MgO and Al2O3 as a thermal spray coating to cover etching chamber components in semiconductor manufacturing processes, and also proposes a manufacturing method for this coating using raw materials prepared by adjusting a prescribed blend of MgO powder and Al2O3 powder, MgAl2O4 powder, or MgAl2O4 oxide powder containing MgO and Al2O3 with a Group 4A, 5A, or 6A element oxide powder.

[0009] However, many of the thermal spray materials used to form the ceramic thermal spray coating proposed in Patent Document 2 contain MgO. Thermal spray materials containing MgO easily absorb moisture in the atmosphere, causing agglomeration and impairing the powder fluidity necessary for the thermal spraying process. Even if these raw materials are dried in advance and then used in the thermal spraying process, the fluidity of the raw powder decreases when coating an area larger than a certain size, often forcing the process to be interrupted. Furthermore, Non-Patent Document 2 reports that decomposition of MgO raw material occurs during the thermal spraying process, and that Mg metal is inevitably contained in the coating. Mg metal has an extremely high saturated vapor pressure, and when a coating containing this is used in the etching process of semiconductor manufacturing, the Mg volatilizes and diffuses into the semiconductor material or adheres to the surface as fine particles, significantly reducing the yield of the Si semiconductor manufacturing process. Patent Document 3 proposes an MgO-based ceramic film containing MgO and MgAl2O4 as crystalline phases as a protective film for semiconductor manufacturing equipment components. However, the thermal spray material used in Patent Document 3 is premised on containing MgO as a crystalline phase, and inevitably, it does not solve the problems of inadequacy due to the hygroscopicity of the thermal spray raw material and the volatilization of Mg from the coating surface exposed to plasma.

[0010] On the other hand, MgAl2O4-based spray coating materials, which contain Al2O3 in amounts far exceeding the stoichiometric ratio, are also unsuitable as halogen plasma-resistant coatings. A considerable amount of Al2O3 dissolves in MgAl2O4 at high temperatures, but at low temperatures it hardly dissolves, so the excess Al2O3 precipitates and disperses on its own in the spray coating material. The consumption of Al2O3 by halogen plasma is several times faster than that of MgAl2O4, and as a result, numerous depressions are formed on the surface of the material. The presence of these depressions accelerates the consumption by plasma and significantly reduces the process yield. This is the starting point for the generation of fine particles that cause Furthermore, in thermal spray coatings formed using a rapid solidification process, a small amount of Al2O3 can be kept within the spinel without precipitating. However, as the amount of Al2O3 precipitates increases, large strain is introduced into the thermal spray coating, making it more susceptible to microcracks. These microcracks can cause abnormal wear and the generation of fine particles when exposed to plasma. Low dust generation is the most important characteristic required for equipment materials in the dry etching process of semiconductors, which are becoming increasingly miniaturized and highly integrated. Therefore, such materials cannot be used. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-209248 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-18853 [Patent Document 3] International Publication No. 2016 / 002480 [Non-patent literature]

[0012] [Non-Patent Document 1] Nippon Tungsten Review Vol.40(2016) [Non-patent document 2] Surface and Coating Technology 169-170(2003), p579-582 Summary of the Invention [Problem to be solved by the invention]

[0013] In view of the above circumstances, an object of the present invention is to provide a novel thermal spray powder that can effectively suppress the generation of dust resulting from physical sputtering and fluorination reactions that occur when exposed to plasma using a halogen-based gas such as fluorine gas, has excellent plasma resistance, and does not contain rare earth elements that are expensive and have concerns about their stable supply, and to provide a thermal spray coating produced using such a thermal spray powder. [Means for solving the problem]

[0014] In order to achieve the above object, the present inventors have conducted extensive research as described below and have arrived at the present invention which can solve the above problem. Spinel (MgAlO) composed of MgO and AlO is prone to producing trace amounts of magnesia during synthesis or due to thermal history, which can lead to reduced fluidity and separation of Mg from thermal spray coatings due to its hygroscopicity when used as a thermal spray powder. The inventors believed that these problems could be solved by strictly controlling the composition ratio of MgO and AlO and, if necessary, performing heat treatment in advance to eliminate the MgO phase, and conducted four types of tests to confirm this.

[0015] (Preparation for Exams A-1, A-2, and B) Magnesia-alumina-spinel (MgAl2O4, manufactured by Tateho Chemical Co., Ltd., purity: 99.9%, median diameter: 0.8 μm), magnesia (MgO, manufactured by Tateho Chemical Co., Ltd., purity: 99.9%, median diameter: 0.6 μm), and alumina (hereinafter referred to as Al2O3, manufactured by Sumitomo Chemical Co., Ltd., purity: 99.99%, median diameter: 0.45 μm) powders were prepared. Using these powders, eight types of test samples were prepared: 100mol%MgAl2O4, MgAl2O4-2.5mol%MgO mixed powder, MgAl2O4-5mol%MgO mixed powder, MgAl2O4-0.2mol%Al2O3 mixed powder, MgAl2O4-0.5mol%Al2O3 mixed powder, MgAl2O4-1.0mol%Al2O3 mixed powder, MgAl2O4-2.5mol%Al2O3 mixed powder, and MgAl2O4-5mol%Al2O3 mixed powder. The mixed powders were prepared by weighing the raw material powders and then dry-mixing them in a planetary mill (PM-300, manufactured by Retsch) using a zirconia pot and balls. These sample powders were then heated in an electric furnace at 800, 1000, 1200, and 1400°C for 1 hour in the atmosphere. After being crushed, the material passed through a sieve #325 (opening size: 43 μm) was subjected to the tests A-1, A-2 and B described below.

[0016] Test A-1 (pH measurement of suspension) In this study, we investigated the hygroscopicity of MgAl2O4 powder and powders mixed with MgO or Al2O3, as well as the effect of heat treatment. For the powders with the mixing ratios shown in Table 1, the unheat-treated mixed powder and the powders heat-treated in air at temperatures of 800°C, 1000°C, 1200°C, and 1400°C, then crushed and passed through a #325 (43 μm opening) sieve were suspended in ion-exchanged water, stirred, and allowed to stand. The pH of the supernatant water was measured, and the results in Table 1 were obtained. The pH of the ion-exchanged water was 7.2. Table 1 also shows the molar amount of Al2O3 calculated using the following formula: Equivalent molar amount of Al2O3 = (equivalent molar amount of Al2O3 in MgAl2O4 + molar amount of simple Al2O3) / (molar amount of MgAl2O4 + molar amount of simple MgO + molar amount of simple Al2O3) × 100

[0017] [Table 1] It is already known that when hygroscopic MgO powder comes into contact with water, basic Mg(OH)2 is produced on the surface, and the increase in pH here occurs as the Mg(OH)2 dissolves in water.

[0018] Test A-2 (humid atmosphere exposure test) Next, we investigated the effect of the amount of MgO and Al2O3 added on the water absorption of MgAl2O4 powder. In this test, powders with the mixture ratios shown in Table 2 were heat-treated in air at 1200°C, crushed, and passed through a #325 (43 μm opening) sieve. A fixed amount (10 g) of these powders was placed in an aluminum moisture meter sample dish and exposed to a humid atmosphere (40°C, 80% relative humidity) for 48 hours, followed by air drying at 105°C for 3 hours and then air drying in a room simulating a typical room environment (25°C, 60% relative humidity) for 24 hours each. The constant temperature and humidity exposure test was performed using an Espec Corporation "LUH-113," and the air drying test was performed using a Masuda Rika Kogyo Co., Ltd. "SA312." The weight gain / loss ratio at each stage compared to the initial weight is shown in Table 2.

[0019] [Table 2]

[0020] From Table 2 above, we can see that when MgAl2O4-based materials contain more than the stoichiometric ratio of MgO to MgAl2O4, they readily absorb moisture in high-temperature, high-humidity atmospheres, and that drying treatment cannot easily remove all of the moisture, causing them to reabsorb moisture when stored in air. It can also be assumed that commercially available MgAl2O4 powders are hygroscopic. On the other hand, it is clear that moisture absorption can be suppressed by adding 0.2 mol% or more of Al2O3 (50.1 mol% or more in terms of Al2O3 molar amount) to MgAl2O4 powder and heating it to 1200°C or higher.

[0021] Test B (high temperature exposure test) In this test, we evaluated the volatilization tendency of MgAl2O4 powder and powders containing added MgO or Al2O3 when they were heat treated in a non-oxidizing and reduced pressure atmosphere. Using the same method as in Test A, 100 mol% MgAl2O4 powder, MgAl2O4-5 mol% MgO powder, and MgAl2O4-2.5 mol% Al2O3 powder were heat-treated at 1000°C and used in the experiment. 25 g of each of these three powders was placed on a 99.9% alumina crucible lid to prepare a sample, which was then dried in a thermostatic chamber at 105°C for 3 hours. The initial weight was measured using an electronic balance (Shimadzu Corporation, UW420HV). These samples were heat-treated by holding them at 1400°C in argon gas at 1 atmosphere (101 kPa) or at 700°C in air at 6 kPa for one hour. The heating in argon gas was performed using the Marusho Electric Co., Ltd. "SPX2025-17V," while the heating in air was performed using the Hi-Dental Japan "KDF-75plus." After cooling, each sample was weighed and the weight loss from the initial weight was calculated. This value, divided by the initial weight, was used as the weight loss rate, which is shown in Table 3.

[0022] [Table 3]

[0023] As can be seen from Table 3 above, the weight loss rate of the powder samples after heat treatment in either argon gas or air was greatest for the MgAl2O4-5mol%MgO mixed powder, about half that of the MgAl2O4 powder, and about one-sixth that of the MgAl2O4-2.5mol%Al2O3 mixed powder. The results of Tests A and B above show that the rate of weight loss due to heat treatment tends to increase as the amount of MgO contained in the powder increases relative to the stoichiometric ratio, and therefore it is believed that the weight loss occurred because the MgO in the powder decomposed into Mg during heat treatment, and then the Mg volatilized away. In other words, the more MgO a thermal spray powder contains relative to the stoichiometric ratio of MgAl2O4, the more likely it is that Mg will be included in the thermal spray coating due to the decomposition of MgO. Conversely, it is clear that a thermal spray coating with a lower MgO content relative to the stoichiometric ratio of MgAl2O4 is less likely to include Mg.

[0024] Test C (Plasma exposure test of sintered body) To understand the effect of the mixing ratio of MgAl2O4 powder and Al2O3 powder on the rate of wear caused by plasma, several sintered bodies with different mixing ratios were produced using a spark plasma sintering device ("LABOX-325R" manufactured by Sinterland), and then plasma exposure tests were conducted. The following raw material powders were prepared to produce the sintered bodies. MgAl2O4 manufactured by Tateho Chemical Co., Ltd., purity 99.9%, median diameter 0.45 μm Al2O3···Manufactured by Sumitomo Chemical Co., Ltd., purity 99.99%, median diameter 0.58μm These powders were weighed out to obtain the compounding ratios shown in Table 4 and mixed using a V-type mixer (Tsutsui Rikagaku Co., Ltd., VM-2). Each mixed powder was filled into an alumina crucible and then heat-treated in air at 1200°C for 3 hours using an electric furnace (Koyo Thermo Systems Co., Ltd., KBF624-N1). The heat-treated powder was crushed and used to prepare a sintered body. Each powder was filled into a carbon mold, and the sintering conditions were a heating temperature of 1250°C and a pressure of 80 MPa. The sintered body was removed from the carbon mold and polished. As a comparative material, a sintered body was produced by sintering Y2O3 coarse powder (manufactured by Shin-Etsu Chemical Co., Ltd., purity: 99.9%, median diameter: 0.96 μm) using the same equipment under the conditions of a heating temperature of 1350°C and a pressure of 80 MPa.

[0025] One surface of each sintered body was polished to a mirror finish using wet emery paper and a buff with diamond paste, and then ultrasonically cleaned in pure water and ethyl alcohol. A plasma exposure test was then conducted with the mirror-polished surface facing the surface. For the plasma exposure test, a parallel-plate dry etching apparatus, the schematic of which is shown in Figure 1, was used, and the sintered body 5 was placed on a 4-inch Si wafer 4 placed on the cathode 2 side and exposed to plasma 7. Plasma generation was performed under the following conditions: Plasma gas species and flow rate: CF4...50sccm, O2...10sccm, Ar···50sccm RF output: 800W, Bias: 600W The rate of plasma wear of each sintered body was calculated based on the measured difference in height between the exposed area and the masked, unexposed area, and expressed as a relative value when the wear rate of the simultaneously exposed Si wafer was set at 100. The results are shown in Table 4.

[0026] [Table 4]

[0027] The results shown in Table 4 above reveal that the consumption rate of sintered bodies with an Al2O3 equivalent molar amount of 50.1 mol% or more and 52.0 mol% or less in fluorine-based plasma is comparable to that of Y2O3, but that the consumption rate increases sharply for sintered bodies with an Al2O3 equivalent molar amount of over 53.0%. Note that the relatively high consumption rate of the sintered body with 100% MgAl2O4 in this test is thought to be due to grain growth that occurred as a result of using the same sintering conditions as the sintered body with Al2O3 added, resulting in an increase in pores at the grain boundary triple junctions.

[0028] From the results of the above-mentioned tests A to C, the present inventors discovered the following. MgAl2O4-based powders containing more MgO than the stoichiometric ratio of MgAl2O4 are highly hygroscopic and prone to agglomeration and reduced fluidity in air, making them unsuitable as thermal spray feedstocks. Furthermore, even when thermal spray coatings are formed using this powder, metallic Mg is present in the coating due to the decomposition of MgO. When such thermal spray coatings are exposed to plasma during the etching process in semiconductor manufacturing, metallic Mg volatilizes, contaminating the Si wafer. For this reason, it is extremely difficult to produce thermal spray coatings using MgAl2O4-based powders containing more MgO than the stoichiometric ratio of MgAl2O4. Even if such coatings are successfully produced, they are unsuitable for use as protective coatings for etching chambers. Furthermore, even when the MgO to Al2O3 ratio of the powder is exactly the stoichiometric ratio of MgAl2O4, problems can arise due to the presence of MgO and / or metallic Mg, resulting from unreacted components remaining during powder synthesis, decomposition during the thermal spraying process, or increased temperatures on the coating surface exposed to plasma.

[0029] However, by setting the Al2O3 component ratio in the MgAl2O4-based powder to a range exceeding the stoichiometric ratio of MgAl2O4, it is possible to suppress aggregation due to moisture absorption of the powder and also to suppress the generation of metallic Mg due to decomposition during heating, making it possible to use it as a raw material for creating plasma spray-resistant coatings for the etching process of semiconductor manufacturing.However, if the Al2O3 content becomes too high, the resistance of MgAl2O4 to halogen-based plasma decreases, so the Al2O3 content is limited. Therefore, the molar amount of Al2O3 relative to the total molar amount of MgAl2O4 and Al2O3 must be more than 50.0 mol% and not more than 53.0 mol%, and preferably is 50.1 mol% or more and 52.0 mol% or less. If the molar amount of Al2O3 is 50.0 mol% or less, MgO may remain due to weighing accuracy or non-uniform mixing during the powder manufacturing process, resulting in residual moisture absorption, etc. Also, if the molar amount of Al2O3 exceeds 53.0 mol%, the presence of a large amount of simple Al2O3 significantly reduces halogen plasma resistance, and the coating sprayed using this will not have sufficient plasma resistance.

[0030] To prevent the thermal spray powder containing MgAlO4 containing more AlO than the stoichiometric ratio from containing MgO, it is preferable to subject it to high-temperature heat treatment, with the heat treatment temperature preferably being 1000° C. to 1400° C., more preferably 1100° C. to 1300° C. If excess AlO3 is present, this heat treatment will cause any unreacted MgO to react with AlO3 to form MgAlO4 with a spinel structure. As is evident from the Al2O3-MgO phase diagram shown in Figure 2, MgAl2O4 exhibits a single spinel structure over a wide range of MgO / Al2O3 ratios at temperatures above 1000°C. However, this range narrows as the temperature decreases, and at room temperature, it exhibits a mixed phase of MgAl2O4 and MgO or Al2O3. Therefore, when high-temperature heat treatment is performed on powder containing Al2O3 in excess of the stoichiometric ratio of MgAl2O4, the excess Al2O3 dissolves in MgAl2O4 and then precipitates again as the temperature decreases, resulting in a homogenized material structure. Heat treatment temperatures below 1100°C not only leave unreacted MgO, but also result in insufficient dissolution and precipitation of Al2O3 into MgAl2O4, leading to a non-uniform structure. On the other hand, heat treatment temperatures above 1400°C result in sintering of the powder particles, and a milling process is required to achieve the desired particle size distribution, which can easily lead to contamination from the milling equipment.

[0031] The present invention is based on new findings from the above four types of tests and has the following aspects. (1) A thermal spray powder mainly composed of MgAl2O4 and containing Al2O3, wherein the molar amount of Al2O3 converted to the total molar amount of MgAl2O4 and Al2O3 is more than 50.0 mol% and not more than 53.0 mol%, and the thermal spray powder does not contain MgO as a crystalline phase. (2) The thermal spray powder according to (1) above, wherein the molar amount of Al2O3 converted into Al2O3 is 50.1 mol % or more and 52.0 mol % or less. (3) A thermal spraying method using the thermal spray powder according to (1) or (2) above. (4) A method for manufacturing a member for a plasma etching apparatus, in which a thermal spray coating is formed on a substrate by the thermal spraying method described in (3) above. (5) A method for producing a thermal spray powder according to claim 1 or 2, comprising heat treating (a) a mixed powder of MgO and Al2O3, or (b) a mixed powder of MgAl2O4 and Al2O3, wherein the equivalent molar amount of Al2O3 relative to the total molar amount of MgO and Al2O3 in (a) or the equivalent molar amount of Al2O3 relative to the total molar amount of MgAl2O4 and Al2O3 in (b) is both more than 50.0 mol% and 53.0 mol% or less, at 1000°C or more and 1400°C or less. (6) A thermal spray coating mainly composed of MgAl2O4 and containing Al2O3, wherein the molar amount of Al2O3 converted to the total molar amount of MgAl2O4 and Al2O3 is more than 50.0 mol% and 53.0 mol% or less, and wherein metallic Mg is not contained. (7) The thermal spray coating according to (6) above, wherein the molar amount of Al2O3 converted to Al2O3 is 50.1 mol % or more and 52.0 mol % or less. (8) A member for a plasma etching apparatus having the thermal spray coating according to (6) or (7) on its surface. [Effects of the Invention]

[0032] The present invention provides a novel thermal spray coating suitable for formation on the surface of a chamber subjected to dry etching with plasma generated from a fluorine-containing gas, which protects the inner surface of the chamber from the plasma and suppresses dust generation during the process, and a method for producing the same. The present invention also provides a novel thermal spray powder for obtaining the thermal spray coating, particularly by atmospheric plasma spraying. [Brief explanation of the drawings]

[0033] [Figure 1] The schematic diagram of the parallel plate type dry etching apparatus used in the plasma exposure tests of the sintered body and the thermal spray coating is shown. [Figure 2] This is a binary phase diagram of Al2O3 and MgO. [Figure 3] FIG. 1 is an XRD diagram of the thermal spray powder of Example 2. [Figure 4] FIG. 1 is an XRD diagram of the thermal spray powder of Example 3. [Figure 5] FIG. 1 is an XRD diagram of the thermal spray coating of Example 2. [Figure 6] FIG. 1 is an XRD diagram of the thermal spray coating of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] (thermal spray powder) The thermal spray powder of the present invention is a thermal spray powder mainly composed of MgAl2O4, contains Al2O3, and does not contain MgO as a crystalline phase. In the present invention, a thermal spray powder mainly composed of MgAl2O4 refers to a thermal spray powder in which the content of MgAl2O4 of all components in the thermal spray powder is 90 mol % or more, and preferably 95 mol % or more. Furthermore, the absence of MgO as a crystalline phase refers to the fact that no peak of an MgO crystalline phase is detected when the thermal spray powder is subjected to X-ray diffraction (XRD). MgAl2O4, the main component of the thermal spray coating of the present invention, is known as one of the materials with high resistance to fluorine-containing plasma. However, if MgO is contained in the thermal spray raw material, there is a concern that the fluidity is easily reduced due to the hygroscopicity of MgO, and that Mg generated in the thermal spray coating by decomposition during thermal spraying may become a source of contamination. Therefore, by adding Al2O3 in an amount greater than the stoichiometric ratio of MgAl2O4 and performing sufficient heat treatment, excess MgO is removed, and by strictly controlling the amount of Al2O3 added, a thermal spray powder with high plasma resistance can be produced.

[0035] MgAl2O4 is a stable double oxide with a spinel-type cubic crystal structure and excellent mechanical properties. It can be obtained by reacting equimolar amounts of MgO and Al2O3 at high temperatures. To use MgAl2O4 as a thermal spray powder, the thermal spray powder must contain Al2O3 in a proportion greater than the stoichiometric ratio of MgAl2O4 to MgAl2O4, ensuring complete reaction without leaving any MgO behind. However, increasing the amount of unreacted Al2O3 in the thermal spray powder can result in the formation of a single Al2O3 phase in the thermal spray coating. As this phase expands, cracks develop in the thermal spray coating due to the difference in solidification rate between the Al2O3 phase and the MgAl2O4 phase. The presence of these cracks, along with the poor resistance of Al2O3 to fluorine-based plasmas, significantly reduces the plasma resistance of the coating.

[0036] One method for obtaining a thermal spray powder containing MgAlO as the main component and free of MgO, which allows for the production of thermal spray coatings with sufficient resistance to fluorine-based plasma, is to pulverize and mix powders of MgO and AlO, or powders of MgAlO and AlO, using a rotary ball mill or other device, followed by high-temperature heat treatment at 1000°C or higher in air or an inert atmosphere using an electric furnace or other device. However, the mixing ratio of the two oxides must be strictly controlled; if the ratio is too low, unreacted MgO remains, and if the ratio is too high, an excess of the AlO phase remains. That is, to obtain a thermal spray powder that achieves the effects of the present invention, the equivalent molar amount of AlO relative to the total molar amount of MgO and AlO, or MgAlO and AlO, must be greater than 50.0 mol% and less than 53.0 mol%. Preferably, the equivalent molar amount of AlO is greater than 50.1 mol% and less than 52.0 mol%.

[0037] The purity of the powder used when grinding and mixing the mixed powder of MgO and Al2O3 or the mixed powder of MgAl2O4 and Al2O3 is preferably 99.5% by weight or more. Furthermore, the average particle size of these oxides subjected to the mixing and grinding process is preferably 3 μm or less, and the average particle size of the mixed powder after grinding and mixing is preferably 1 μm or less. Unless otherwise specified, the average particle size is the median size, and refers to the particle size at 50% cumulative volume (D50) in the particle size distribution determined by a laser diffraction / scattering method.

[0038] By subjecting the mixed and pulverized mixed powder to high-temperature heat treatment, MgO and Al2O3 react to produce MgAl2O4, resulting in the removal of MgO as a single oxide. This also removes moisture from the mixed powder, which was absorbed by the coarse MgO powder. This heat treatment can be performed in an air or inert atmosphere using an electric furnace or similar. The heat treatment temperature is preferably between 1000°C and 1400°C. A temperature below 1000°C may leave unreacted MgO, while a temperature above 1400°C may cause the particles to solidify, making the powder unsuitable for use as a thermal spray raw material. The appropriate holding time for each temperature varies depending on the particle size of the mixed particles, but is generally between 3 hours and 12 hours.

[0039] The synthesized powder, which has been subjected to high-temperature heat treatment and consolidated, is preferably loosened and made into a slurry by adding a solvent such as water, a dispersant, and an organic binder, and then granulated into spherical particles by a method such as spray drying. These granulated particles are then heated to 1100 to 1300°C in an oxidizing atmosphere using an electric furnace or the like to remove the organic binder and improve the fracture strength of the spherical particles, and then used as thermal spray powder. The presence or absence of MgO crystalline phase in the thermal spray powder can be determined by suspending and stirring the powder in ion-exchanged water, allowing it to stand, and then subjecting the supernatant water to inductively coupled plasma mass spectrometry (ICP-MS) analysis. This is because when MgO comes into contact with water, it generates Mg(OH)2, which dissolves.

[0040] The preparation of thermal spray powders according to the present invention is not limited to the above-mentioned methods. Usable powders include magnesium compounds such as magnesium hydroxide and magnesium nitrate as Mg sources, and aluminum compounds such as aluminum hydroxide, aluminum oxide hydroxide, and aluminum nitrate as Al sources. Alternatively, if the Mg or Al compound is water-soluble, grinding and mixing using a ball mill or the like can be omitted. After preparing an aqueous solution, other powders can be suspended and stirred, and the resulting solution can be subjected to the granulation process using a spray dryer. Alternatively, an Al2O3 sol can be used in place of the aqueous solution in the granulation process using a spray dryer.

[0041] (thermal spray coating) The thermal spray coating of the present invention is a thermal spray coating mainly composed of MgAl2O4, which contains Al2O3 but does not contain metallic Mg. Here, in the present invention, a thermal spray coating mainly composed of MgAl2O4 refers to one in which the content of MgAl2O4 of all components in the thermal spray coating is 90 mol % or more, preferably 95 mol % or more, and "not containing metallic Mg" means that no peak of metallic Mg is detected when X-ray diffraction (XRD) measurement is performed. Because the thermal spray coating of the present invention does not contain metallic Mg, it is possible to suppress the generation of particles due to the volatilization of metallic Mg. Furthermore, the thermal spray coating of the present invention has high plasma resistance by strictly controlling the Al2O3 content. To achieve the effects of the present invention, the equivalent molar amount of Al2O3 relative to the total molar amount of MgAl2O4 and Al2O3 in the thermal spray coating must be more than 50.0 mol% and not more than 53.0 mol%. The equivalent molar amount of Al2O3 is preferably not less than 50.1 mol% and not more than 52.0 mol%. The thermal spray coating of the present invention can be suitably produced by using a thermal spray powder prepared by any of the methods described above. The average particle size of the thermal spray powder is preferably 10 to 60 μm, more preferably 15 to 45 μm.

[0042] The thermal spraying method used in the present invention is preferably a thermal spraying method using plasma, such as atmospheric plasma spraying or low-pressure plasma spraying, and particularly preferably atmospheric plasma spraying. As the atmospheric plasma spraying method, a known method can be used. In the thermal spraying method of the present invention, for example, the following conditions are used. Thermal spraying equipment: Oerlikon Metco, F4 Operating voltage: 65V Operating current: 700A Primary gas (Ar) flow rate: 60 NL / min Secondary gas (H2) flow rate: 5NL / min Spray distance: 140mm Whether metallic Mg is present in the thermal spray coating can be determined by subjecting a coating sample to heat treatment to remove distortion, and then subjecting it to X-ray diffraction measurement to confirm the presence or absence of an Mg peak. [Example]

[0043] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples.

[0044] (Examples 1 to 5 and Comparative Examples 1 to 5) The following raw material powders were prepared: MgAl2O4...Tateho Chemical Co., Ltd., purity 99.9%, median diameter 0.8μm Al2O3···Manufactured by Sumitomo Chemical Co., Ltd., purity 99.99%, median diameter 0.58μm MgO (Tateho Chemical Co., Ltd., purity 99.9%, median diameter: 0.6 μm) These powders were weighed out to give combinations of MgAl2O4 and Al2O3, or combinations of MgAl2O4 and MgO, such as MgAl2O4-0.2 mol% Al2O3 (Example 1), MgAl2O4-1.0 mol% Al2O3 (Example 2), MgAl2O4-2.5 mol% Al2O3 (Example 3), MgAl2O4-5.0 mol% Al2O3 (Examples 4 and 5), MgAl2O4-7.5 mol% Al2O3 (Comparative Example 1), and MgAl2O4-2.5 mol% MgO (Comparative Example 3), and mixed using a V-type mixer (Tsutsui Rikagaku Co., Ltd., "VM-2").

[0045] Each mixed powder and only MgAl2O4 powder (Comparative Example 2) were dispersed in pure water, and a carboxymethyl cellulose binder (Kimica Corporation's "PL-4") and a carboxylic acid deflocculating agent (Kao Chemicals Corporation's "Caocera 2020") were added and stirred to prepare slurries. These slurries were then granulated using a spray dryer (Okawahara Chemical Engineering Co., Ltd.'s "L-8").

[0046] The granulated powder was then calcined in an electric furnace at 1200°C for 3 hours in air to remove organic components and induce a solid-state reaction between the two components. This increased particle strength was achieved by crushing the powder after calcination and sieving it to a size range of 25 to 53 μm using a sieve shaker (Retsch AS200). Only the powder obtained was subjected to testing. For MgAl2O4-5.0 mol%Al2O3, powder heat-treated at 900°C for 3 hours was also tested. The resulting powder was porous and spherical, with a median diameter of 29 to 32 μm.

[0047] For comparison with the MgAl2O4-Al2O3-based spray samples, a commercially available Al2O3 powder (manufactured by Fujimi Incorporated, purity: 99.9%, particle size: 10 μm to 45 μm) was prepared as Comparative Example 4, and a commercially available Y2O3 powder (manufactured by Fujimi Incorporated, purity: 99.9%, particle size: 10 μm to 45 μm) was prepared as Comparative Example 5.

[0048] Table 5 shows the compounding ratio of the thermal spray powder prepared as described above, the converted molar amount of Al2O3 obtained using the following calculation formula, and the heat treatment temperature. Equivalent molar amount of Al2O3 = (Al2O3 equivalent molar amount in MgAl2O4 + Al2O3 molar amount) / (MgAl2 O4 moles + MgO moles + Al2O3 moles × 100

[0049] [Table 5]

[0050] (XRD measurement of thermal spray powder) Of the prepared thermal spray powders, the MgAl2O4-1.0 mol%Al2O3 powder (Example 2) and the MgAl2O4-2.5 mol%Al2O3 powder (Example 3) were subjected to X-ray diffraction (XRD) measurement to identify the crystalline phase. Figure 3 is an XRD diagram of the thermal spray powder of Example 2, and Figure 4 is an XRD diagram of the thermal spray powder of Example 3. As shown in Figures 3 and 4, peaks corresponding to the MgAl2O4 crystalline phase were detected in the thermal spray powders of Examples 2 and 3, but no peaks corresponding to the MgO crystalline phase were detected.

[0051] (Fluidity measurement) Of the prepared thermal spray powders, MgAl2O4-2.5 mol% Al2O3 powder heat-treated at 1200°C (Example 3), MgAl2O4-5 mol% Al2O3 powder heat-treated at 900°C (Example 5), MgAl2O4 powder (Comparative Example 2), and MgAl2O4-2.5 mol% MgO powder (Comparative Example 3) were used and held in environments with different temperatures and humidities, after which their fluidity was measured.

[0052] The fluidity measurement was carried out as follows. The sample powder was measured using a thermo-hygrostat (LHU-113) manufactured by Espec Corporation at a temperature and humidity of 6°C / 44% (volume absolute humidity: 3.2 g / m) in Chiba Prefecture in January 2022. 3 ), or Chiba Prefecture in July 2022, average daytime temperature / relative humidity = 27°C / 74% (volume absolute humidity: 19.1g / m 3 The measurements were carried out using a vibrating capillary flow tester (IMP's "DPF-01"), and the evaluation was based on the time it took for 15 ml and 30 ml of powder to fall from a glass tube with a specified inner diameter at the tip. The measurement conditions were as follows, and the measurement results are shown in Table 6. Measurement mode: Constant vibration ·Vibration waveform: sine wave ·Powder amount: 15ml, 30ml Flow tube material: Glass ·Maximum amplitude: 100μm Frequency: 290Hz Flow tube tip diameter: Φ2.0mm

[0053] [Table 6]

[0054] The suitability for thermal spraying tests was determined based on the results shown in Table 6 above. It was found that the MgAl2O4 powder (Comparative Example 2) and the MgAl2O4-5 mol% Al2O3 powder heat-treated at 900°C (Example 5) exhibit sufficient fluidity when stored in a low-humidity atmosphere, but that poor powder supply may occur when stored in a high-humidity atmosphere. It was also found that the MgAl2O4-2.5 mol% MgO powder (Comparative Example 3) is not suitable for continuous thermal spraying, regardless of the storage atmosphere. On the other hand, the MgAl2O4-2.5 mol% Al2O3 powder heat-treated at 1200°C (Example 3) exhibited no poor powder supply regardless of the atmosphere in which it was stored, demonstrating that it had fluidity suitable for thermal spraying.

[0055] Based on the results of the fluidity measurements, seven types of granulated and sintered powders (Examples 1 to 5, Comparative Examples 1 and 2), excluding the MgAlO-2.5 mol% MgO powder of Comparative Example 3, as well as commercially available AlO powder (Comparative Example 4) and commercially available YO powder (Comparative Example 5), were used to produce thermal spray coatings under the following conditions. Thermal spraying equipment: Plasma spray gun (Oerlikon Metco, F4) Operating voltage: 65V Operating current: 700A Primary gas: Ar Secondary gas: H2 Spray distance: 140mm Base material: Aluminum alloy (plate-shaped body, 20 mm long, 20 mm wide, 3 mm thick) Sprayed coating thickness: approx. 200 μm

[0056] (XRD measurement of thermal spray coating) Of the thermal sprayed coatings produced, the thermal sprayed coating produced using MgAl2O4-1.0 mol%Al2O3 powder (Example 2) and the thermal sprayed coating produced using MgAl2O4-2.5 mol%Al2O3 powder (Example 3) were subjected to XRD measurement to identify the crystalline phase. Figure 5 is an XRD diagram of the thermal sprayed coating of Example 2, and Figure 6 is an XRD diagram of the thermal sprayed coating of Example 3. As shown in Figures 5 and 6, in the thermal sprayed coatings of Examples 2 and 3, peaks corresponding to the MgAl2O4 crystalline phase were detected, but no peaks corresponding to the metallic Mg crystalline phase were detected.

[0057] (Plasma resistance measurement) The surfaces of the various thermal spray coatings prepared above were polished with #1000 wet emery paper, ultrasonically cleaned in pure water, and then dried in a thermostatic chamber at 85°C before being subjected to a plasma exposure test. In the test, a parallel plate dry etching device, the outline of which is shown in Figure 1, was used, and the thermal sprayed surface was placed on a silicon wafer placed on the cathode side so that it faced the anode, and exposed to plasma. The conditions for plasma generation are as follows:

[0058] Plasma gas species and flow rate: CF4...50sccm, O2...10sccm, Ar···50sccm RF output: 800W, Bias: 600W

[0059] The results of the plasma exposure test are shown in Table 7. The wear rates in the table were calculated based on the measured step difference between the exposed area and the masked, unexposed area, and are expressed as relative values when the wear rate of the exposed Si wafer is set at 100.

[0060] [Table 7]

[0061] The results in Table 7 above make it clear that thermal spray coatings with an Al2O3-equivalent molar amount of more than 50.0 mol % and 53.0 mol % or less have excellent plasma resistance. [Industrial Applicability]

[0062] The thermal spray coating of the present invention is effective in a wide range of applications, including components for chamber devices used in plasma dry etching, which uses halogen-based gases such as fluorine gas in semiconductor manufacturing processes. [Explanation of symbols]

[0063] 1: Thermal spray sample 2: Wafer 3: Anode 4: Cathode 5: Plasma 6: Plasma gas 7: Exhaust 8: Power supply

Claims

1. MgAl ２ O ４ Mainly composed of Al ２ O ３ A thermal spray powder containing MgAl ２ O ４ and Al ２ O ３ Al relative to the total molar amount ２ O ３ and wherein the converted molar amount of is more than 50.0 mol % and 53.0 mol % or less, and wherein MgO is not contained as a crystalline phase.

2. The Al ２ O ３ 2. The thermal spray powder according to claim 1, wherein the molar amount of

3. A thermal spraying method using the thermal spray powder according to claim 1 or 2.

4. A method for manufacturing a member for a plasma etching apparatus, comprising forming a thermal sprayed coating on a substrate by the thermal spraying method according to claim 3.

5. 3. The method for producing a thermal spray powder according to claim 1 or 2, comprising: (a) mixing MgO and Al ２ O ３ or (b) a mixed powder of MgAl ２ O ４ and Al ２ O ３ It is a mixed powder of MgO and Al in (a) ２ O ３ Al relative to the total molar amount ２ O ３ or the molar amount of MgAl in (b) ２ O ４ and Al ２ O ３ Al relative to the total molar amount ２ O ３ and heat treating a mixed powder having a molar amount of each of the above in terms of the total amount of the elements greater than 50.0 mol % and not more than 53.0 mol % at a temperature of 1000°C or higher and 1400°C or lower.

6. MgAl ２ O ４ Mainly composed of Al ２ O ３ A thermal spray coating containing MgAl ２ O ４ and Al ２ O ３ Al relative to the total molar amount ２ O ３ and wherein the molar amount of Mg in terms of SiO2 is more than 50.0 mol % and 53.0 mol % or less, and wherein metallic Mg is not contained as a crystalline phase.

7. The Al ２ O ３ The thermal spray coating according to claim 6, wherein the molar amount of the converted Cr is 50.1 mol % or more and 52.0 mol % or less.

8. A member for a plasma etching apparatus having the thermal spray coating according to claim 6 or 7 on its surface.

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