Alloy thin film and sputtering target

Abstract

Provided are: an alloy thin film that exhibits excellent oxidation resistance at high temperatures even without containing Cr and even at a small film thickness; and a sputtering target for forming the same.　An alloy thin film according to the present invention comprises 20-60 atom% of Al and 4-30 atom% of Si, with the remainder being Ni and unavoidable impurities, and preferably comprises Al and Si in a total amount of 29-60 atom%. The alloy thin film according to the present invention contains 20-60 atom% of Al and 4-30 atom% of Si, with the remainder being Ni and unavoidable impurities, can be formed using a sputtering target having a Curie point that is not higher than room temperature, and preferably contains Al and Si in a total amount of 29-60 atom%.

Description

Alloy thin films and sputtering targets

[0001] The present invention relates to an alloy thin film suitable for preventing surface oxidation of components that require oxidation resistance at high temperatures, such as internal electrodes of electronic components and power devices, and components used in semiconductor manufacturing equipment and firing furnaces, and a sputtering target for forming the alloy thin film.

[0002] In recent years, Ni, Cu, and their alloys have been used for internal electrodes in electronic components that require miniaturization, and there is a demand for electrodes that are inhibited from oxidation even at higher manufacturing process temperatures. Furthermore, for power devices that operate at high temperatures, there is a demand for materials that are inhibited from oxidation even during long-term use. Furthermore, there is a demand for materials that are inhibited from oxidation in components used in electrodes, separators, semiconductor manufacturing equipment, and firing furnaces for battery components in fuel cells and other devices that exchange electrons at high temperatures. Known materials that are inhibited from oxidation, i.e., highly oxidation-resistant, include Cr, Ni, and Ni-Cr alloys, which are Ni plus Cr. These materials are formed as thin films by plating or PVD (Physical Vapor Deposition) methods such as vacuum deposition and sputtering.

[0003] In the manufacture of semiconductor devices, when insulating protective films such as oxide or nitride films are formed by chemical vapor deposition (CVD), corrosive gases may be used as raw material gases, and high-temperature oxidation resistance is required for the chambers and internal components that decompose and deposit the gases in plasma.Furthermore, high-temperature oxidation resistance is also required for components such as chambers, adhesion shields, and trays of firing furnaces used in an oxygen atmosphere to fire ionic active materials that affect the performance of large-capacity batteries essential for mobile products.

[0004] Currently, expensive Ni-based oxidation-resistant alloy members that have oxidation resistance at high temperatures and the necessary strength are used for components used in CVD equipment and firing furnaces. For example, Patent Document 1 proposes a Ni-based alloy that contains, by mass %, 3.6 to 4.4% Al, and optionally one or more of 0.1 to 2.5% Si, 0.8 to 4.0% Cr, and 0.1 to 1.5% Mn, with the balance being Ni and unavoidable impurities. Furthermore, Patent Document 2 proposes an intergranular corrosion resistant Ni-based alloy containing, by weight, 0.5 to 3% Cr, 0.3 to 2.5% Si, 0.5 to 1.8% Mn (but excluding 0.5% and 1.8%), and 0.05 to 2.5% Al (but excluding 0.05%), with a Si to Cr ratio (Si / Cr) of less than 1.1, and the balance being Ni and unavoidable impurities.

[0005] On the other hand, Patent Document 3 proposes a film forming treatment device member, in which a Ni-Al alloy layer is formed on the surface of a substrate made of pure Ni or a Ni-Cr-Fe alloy, as a CVD device member, a PVD device member, an LCD (Liquid Crystal Display) device member, and a semiconductor manufacturing device member.

[0006] Patent No. 3814822 Publication JP 2-163336 Publication JP 2012-219369 Publication

[0007] In recent years, as electronic components become smaller, lighter, and more highly integrated, thinner electrodes are being required, and high-temperature oxidation resistance is required to prevent electrode oxidation even at high process temperatures, for example, 700°C. In response to this, materials with excellent oxidation resistance include the Cr-containing Ni-based alloys disclosed in the aforementioned Patent Documents 1 and 2. While Cr-containing Ni—Cr alloy thin films have excellent moisture resistance and other properties, they have the drawback of forming an oxide layer on the surface when heated to 400°C, which discolors the alloy thin film and diffuses into the functional films of electronic devices, thereby degrading their electrical characteristics.

[0008] In recent years, fuel cell technology using hydrogen has been attracting attention as part of efforts to build a carbon-neutral hydrogen society. For example, in highly efficient solid oxide fuel cells (SOFCs) operating at temperatures above 700°C, there is a need for oxidation-resistant Cr-free materials due to concerns about the deterioration of performance in electrodes and separators that exchange electrons at high temperatures due to Cr evaporation from the components. Furthermore, in large-capacity batteries, there is a need for improved performance of ionic active materials, and there is concern that Cr contained in the internal components of the CVD equipment and firing furnaces used in their manufacture may be included as an impurity in the active species, resulting in performance degradation. Patent Document 3 also describes how corrosion resistance and plasma reactivity can be improved by forming a Ni-Al layer on the surface of a substrate made of pure Ni or a Ni-Cr-Fe alloy by a calorizing process. However, the calorizing process requires heating at around 1000°C in a sealed container, and the Ni-Al layer must be at least 10 μm thick, which requires many processing steps. Furthermore, to make a Ni-Al layer of 10 μm or more into a highly accurate component, the surface must be polished, which poses the problem of requiring even more processing steps.

[0009] An object of the present invention is to provide an alloy thin film that does not contain Cr and that can exhibit excellent oxidation resistance at high temperatures even when the film thickness is thinner than the conventional Ni-Al layer described above, and a sputtering target for forming the same.

[0010] In view of the above problems, the present inventors have conducted extensive research into new alloys that can provide high oxidation resistance even at high temperatures, and as a result have discovered that by newly alloying Ni, Al, and Si within specific ranges, it is possible to achieve excellent oxidation resistance at high temperatures without containing Cr, even with a film thickness thinner than the conventional Ni-Al layer described above, and have arrived at the present invention.

[0011] That is, the present invention is an alloy thin film containing 20 to 60 atomic % of Al, 4 to 30 atomic % of Si, and the balance being Ni and unavoidable impurities.

[0012] The alloy thin film of the present invention preferably contains 29 to 60 atomic % of Al and Si in total.

[0013] The present invention also provides a sputtering target containing 20 to 60 atomic % of Al, 4 to 30 atomic % of Si, and the balance being Ni and unavoidable impurities, and having a Curie point below room temperature.

[0014] The sputtering target of the present invention preferably contains the Al and Si in a total amount of 29 to 60 atomic %.

[0015] The present invention can exhibit excellent oxidation resistance at high temperatures without containing Cr, even at a thickness thinner than the conventional Ni-Al layer described above. Therefore, the present invention can contribute to the miniaturization, weight reduction, and high integration of various power devices and electronic components, as well as to reducing the environmental impact at the time of disposal. Furthermore, because the alloy thin film of the present invention can be formed as a dense insulating film or protective film using a CVD apparatus or the like, it is a useful technology that can contribute to the stable production of highly integrated semiconductor elements and the increase in the capacity of batteries using ionic active materials manufactured using a sintering furnace or the like.

[0016] 1 is a schematic cross-sectional view of an example in which the alloy thin film of the present invention is applied.

[0017] Figure 1 shows a schematic cross-sectional view of an example of an application of the alloy thin film of the present invention. The alloy thin film 1 of the present invention is formed, for example, on the surface of a substrate 2, and is characterized by exhibiting excellent oxidation resistance at high temperatures even though it does not contain Cr, which is an essential element in existing oxidation-resistant alloys, and has a thickness thinner than the conventional Ni-Al layer described above. Note that "oxidation resistance" can be confirmed by the discoloration that occurs due to surface oxidation when heated in an oxygen-containing atmosphere, and can be quantitatively evaluated, for example, by reflectance.

[0018] The alloy thin film of the present invention is composed primarily of Ni, Al, and Si, with 20 to 60 atomic % Al, 4 to 30 atomic % Si, and the remainder consisting of Ni and unavoidable impurities. Both Al and Si are elements that are more easily oxidized than Ni and are more easily diffused in Ni. When a Ni-Al alloy film containing only Al in a few atomic % of Ni is heated in air, Al diffuses to the surface layer, forming an oxide layer. Similarly, when a Ni-Si alloy film containing only Si in a few atomic % of Ni is heated in air, Si diffuses to the surface layer, forming an oxide layer. Because none of these Ni alloys contain Cr, at temperatures as high as 700°C, the oxide layer in the surface layer increases and oxidation also invades the Ni matrix, resulting in insufficient oxidation resistance at high temperatures.

[0019] The alloy thin film of the present invention exhibits high oxidation resistance even at temperatures as high as 700°C despite not containing Cr by alloying Ni, Al, and Si within specific ranges. Specifically, the Al content is 20 atomic % or more and the Si content is 4 atomic % or more. Furthermore, by keeping the Al content at 60 atomic % or less, a decrease in melting point can be suppressed, contributing to maintaining oxidation resistance at high temperatures. On the other hand, when Si is added to Ni, the reflectivity decreases from about 300°C. Therefore, Si is an element whose oxidation resistance may decrease with increasing addition amount, and keeping the content of Si at 30 atomic % or less contributes to ensuring stable oxidation resistance. For the same reasons as above, the alloy thin film according to the present invention preferably contains 29 to 60 atomic % of Al and Si in total. For the same reasons as above, the alloy thin film according to the present invention more preferably contains 20 to 30 atomic % of Al and 20 to 30 atomic % of Si. The preferred lower limit of the total content of Al and Si is 35 atomic %, and even more preferably 40%. The upper limit of the total content of Al and Si is preferably 55 atomic %, more preferably 52 atomic %.

[0020] A sputtering method using a sputtering target (hereinafter also simply referred to as "target") is suitable for forming the alloy thin film of the present invention. In this case, for example, a method of forming the film using a target having the same composition as the alloy thin film, or a method of forming the film by co-sputtering using a Ni-Al alloy target and a Ni-Si alloy target can be applied. From the viewpoints of ease of setting sputtering conditions and ease of obtaining an alloy thin film of the desired composition, it is optimal to form the film by sputtering using a target having the same composition as the alloy thin film.

[0021] The target of the present invention has a Curie point below room temperature. The phrase "a Curie point below room temperature" refers to a target that is nonmagnetic when its magnetic properties are measured at room temperature (25°C). Ni, one of the elements constituting the target of the present invention, is magnetic. To achieve a Curie point below room temperature, it is important to alloy Ni with nonmagnetic elements Al and Si, with 20 to 60 atomic % Al and 4 to 30 atomic % Si. For the same reasons as above, the target according to the present invention preferably contains a total of 29 to 60 atomic % Al and Si. The target of the present invention can be obtained by machining a component obtained by a melt casting method or a sintered compact obtained by a powder sintering method into the target shape. The preferred lower limit of the total Al and Si content is 35 atomic %, more preferably 40 atomic %. The preferred upper limit of the total Al and Si content is 55 atomic %, more preferably 52 atomic %.

[0022] The alloy thin film and target of the present invention preferably contain small amounts of unavoidable impurities, which are the remainder other than the main constituent elements Ni, Al, and Si for ensuring the above-mentioned properties, and may contain impurities such as gas components oxygen, nitrogen, and carbon, and transition metals Cr, Mn, Fe, and Cu, as long as the effects of the present invention are not impaired. For example, the gas components oxygen and nitrogen are each 1000 ppm by mass or less, carbon is 200 ppm by mass or less, and Cr, Mn, Fe, and Cu are each 200 ppm by mass or less, and the purity excluding the gas components is preferably 99.9% by mass or more.

[0023] First, raw materials were weighed to produce a nonmagnetic binary composition of Ni-13 atomic % Al and Ni-10 atomic % Si, and a ternary composition of Ni-30 atomic % Al-10 atomic % Si. Ingots were then produced by melting and casting in a vacuum melting furnace. These ingots were then machined to produce disk-shaped targets with a diameter of 100 mm and a thickness of 5 mm. For the Ni-50 atomic % Al target, a disk-shaped target with a diameter of 100 mm and a thickness of 5 mm was machined from an ingot sintered from alloy powder of the same composition. When a SmCo magnet was brought close to the Ni-30 atomic % Al-10 atomic % Si target obtained above, the magnet was not attracted to the target, confirming that the target was nonmagnetic at room temperature. Furthermore, as a result of component analysis of the Ni-30 atomic % Al-10 atomic % Si target, it was confirmed that the carbon content was 200 mass ppm or less, the Cr, Mn, Fe, and Cu contents were each 200 mass ppm or less, and the purity excluding gas components was 99.9 mass % or more.

[0024] Each target was brazed to a copper backing plate with In, and then attached to a sputtering device (CS-200) manufactured by ULVAC, Inc., and a sputtering test was conducted under conditions of an Ar atmosphere, a pressure of 0.5 Pa, and a power of 500 W. All targets were able to be sputtered normally without any abnormal discharge or the like. These targets were combined and co-sputtered to form a 100 nm alloy thin film having the composition shown in Table 1 on the surface of a Corning glass substrate (Eagle-XG).

[0025] Each alloy thin film sample obtained above was subjected to heat treatment in the atmosphere at 200°C, 250°C, 300°C, 350°C, and 400°C, and the reflectance of the alloy thin film surface before and after heating was measured. The reflectance was measured using a spectrophotometric colorimeter (CM-2500d) manufactured by Konica Minolta, Inc. The measurement results are shown in Table 1.

[0026]

[0027] The results in Table 1 show that the pure Ni film of sample No. 1, a comparative example, showed a significant decrease in reflectance after heating at 350°C. Furthermore, the thin films made of binary alloys, Ni-Al alloys of samples Nos. 2 and 3, and Ni-Si alloy of sample No. 4, also comparative examples, showed a significant decrease in reflectance after heating at 300°C or higher, confirming that their oxidation resistance deteriorates when exposed to high temperatures. In contrast, the alloy thin film of sample No. 5, an example of the present invention, was a thin film with a thickness of 100 nm, less than 1 μm, and even after heating at 400°C, its reflectance exceeded 45%, demonstrating properties equal to or greater than those at the time of film formation, confirming that it had excellent oxidation resistance even at high temperatures.

[0028] The various targets prepared in Example 1 were combined and simultaneously deposited by co-sputtering to form 500 nm alloy thin films having the component compositions shown in Table 2 on the surface of a Corning glass substrate (Eagle-XG). Each alloy thin film sample obtained above was subjected to a heat treatment in the atmosphere at 300°C, 400°C, 500°C, 600°C, and 700°C, and the reflectance of the alloy thin film surface before and after heating was measured. The reflectance was measured using a spectrophotometric colorimeter (CM-2500d) manufactured by Konica Minolta, Inc. The measurement results are shown in Table 2.

[0029]

[0030] The results in Table 2 show that the reflectivity of sample No. 10, a comparative example, decreased by more than 30% compared to the time of deposition after heating at 400°C. In particular, the reflectivity decreased by nearly 20% compared to the time of deposition after heating at 700°C, confirming that exposure to high temperatures reduces oxidation resistance. In contrast, the alloy thin films of samples 6 to 9, which are examples of the present invention, all showed a decrease in reflectivity of 17.0% or less compared to the time of deposition after heating at 700°C, confirming that they have excellent oxidation resistance even at high temperatures. In particular, the decrease in reflectivity of sample No. 6 was 11.0% or less, and the decrease in reflectivity of sample No. 8 was 5.0% or less, demonstrating excellent oxidation resistance even at high temperatures.

[0031] Similar to Example 1, targets with a binary composition of Ni-20 atomic % Si were prepared by melting and Ni-50 atomic % Si by powder sintering. A 500 nm alloy thin film with the composition shown in Table 3 was formed on the surface of a Corning glass substrate (Eagle-XG) by co-sputtering, simultaneously depositing the Ni-30 atomic % Al-10 atomic % Si ternary composition prepared in Example 1 and the Ni-50 atomic % Al target prepared by sintering. Each alloy thin film sample obtained above was subjected to heat treatment in air at 300°C, 400°C, 500°C, 600°C, and 700°C, and the reflectance of the alloy thin film surface before and after heating was measured. Reflectance measurements were performed using a spectrophotometer (CM-2500d) manufactured by Konica Minolta, Inc. The measurement results are shown in Table 3.

[0032]

[0033] The results in Table 3 show that the comparative Ni-Al and Ni-Si binary alloys (Samples 11-13), the alloy with less than 20 atomic % Al and less than 29 atomic % combined Al and Si (Sample 19), and the alloy with less than 20 atomic % Al (Sample 24) all showed a decrease in reflectance of 23.0% or more after heating at 700°C compared to the as-deposited state, confirming their poor oxidation resistance. In contrast, the inventive samples (Samples 14, 15, 17, 18, 20, 21, 22, and 23) all showed a decrease in reflectance of 22.6% or less after heating at 700°C compared to the as-deposited state, demonstrating excellent oxidation resistance even at high temperatures. Of these, Samples 14, 17, 18, and 20-24 showed a decrease in reflectance of 16.0% or less after heating at 700°C compared to the as-deposited state. The rate of decrease was 15.0% or less in Nos. 14, 18, and 20 to 22. From these results, it is clear that the alloy thin film of the present invention has excellent oxidation resistance even when heated at 700°C.

[0034] Because glass substrates tend to warp, melt, and deform at temperatures above 800°C, in order to evaluate oxidation resistance at higher temperatures, a 50 μm-thick SUS foil and a 1.5 mm-thick Ni plate were used as the substrates. Using the Ni-30 atomic % Al-10 atomic % Si ternary composition prepared in Example 1, a 500 nm-thick alloy thin film was formed on the substrate in the same manner as in Examples 2 and 3 to obtain samples for evaluating oxidation resistance, as shown in Table 4. Each sample obtained above was subjected to heat treatment in air at 300°C, 500°C, 700°C, 800°C, and 900°C, and the reflectance of the substrate and the alloy thin film surface was measured before and after heating. Reflectance measurements were performed using a spectrophotometer (CM-2500d) manufactured by Konica Minolta, Inc. The measurement results are shown in Table 4.

[0035]

[0036] The results in Table 4 confirm that with only SUS foil without an alloy thin film, the surface oxidizes and turns brown from 500° C., and with only Ni plate, the reflectance drops significantly above 700° C. In contrast, the sample of the present invention with an alloy thin film of Ni-30 atomic % Al-10 atomic % Si maintained a high reflectance even when exposed to high temperatures of 800° C. or higher, confirming that surface oxidation can be suppressed.

[0037] 1. Alloy thin film 2. Substrate

Claims

1. An alloy thin film containing 20 to 60 atomic % of Al, 4 to 30 atomic % of Si, and the remainder consisting of Ni and unavoidable impurities.

2. The alloy thin film according to claim 1, containing 29 to 60 atomic % of said Al and said Si in total.

3. A sputtering target containing 20 to 60 atomic % of Al, 4 to 30 atomic % of Si, the remainder being Ni and unavoidable impurities, and having a Curie point below room temperature.

4. The sputtering target according to claim 3, wherein the total content of said Al and said Si is 29 to 60 atomic %.

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