Alloy thin film and sputtering target

Abstract

Provided are: an alloy thin film having a high resistivity and excellent environmental resistance; and a sputtering target capable of easily forming the alloy thin film.　This alloy thin film contains Ti and one or more elements selected from Cr, Mo, and W, with the balance being Ni and inevitable impurities. The alloy thin film has an electric resistivity of 150 μΩ·cm or more. The sputtering target is used to form the alloy thin film. The content of Ti is preferably 15 atom% or more. The total content of Ti and said one or more elements selected from Cr, Mo, and W is preferably 35 atom% or more.

Description

Alloy thin films and sputtering targets

[0001] The present invention relates to an alloy thin film that can be used for, for example, thin film resistors, thin film sensors, heating elements of thin film heaters, etc., and to a sputtering target for forming this alloy thin film.

[0002] In recent years, the demand for smaller, lighter, and more highly integrated electronic components has led to a demand for thin films with high electrical resistivity (hereinafter also referred to as "specific resistance") and excellent environmental resistance. A known thin film with high electrical resistivity (hereinafter also referred to as "high resistance") is a thin film made of a Ni-Cr alloy (nichrome) with a resistivity of about 110 μΩ cm, which is used in heating wires. Furthermore, in order to obtain a higher electrical resistivity, a transparent conductive oxide film made of indium tin oxide (hereinafter referred to as "ITO") has been proposed (see Patent Document 1).

[0003] Furthermore, in order to further increase the resistance of Ni, alloy thin films have been proposed in which 20 to 80 wt % of the light element B (boron) has been added to a transition metal such as Cr or Mo, and thin films containing 0 to 50 atomic % of gas components such as nitrogen and carbon, and further containing 5 to 60 mass % of B. To form such B-containing thin films, a multi-source evaporation method has been proposed in which metal and B are simultaneously evaporated from independent evaporation sources, and a sputtering method using a sputtering target containing B has been proposed.

[0004] Furthermore, in order to incorporate gas components, it has been proposed to use reactive vapor deposition or reactive sputtering, in which gas components are introduced into a vacuum chamber when forming a thin film by vacuum vapor deposition or sputtering. This is an effective technique that can produce a thin film with a resistance five times higher than that of a Ni-Cr alloy (see Patent Document 2).

[0005] JP-A No. 01-038990 JP-A No. 06-112009

[0006] According to the inventors' investigations, the resistivity of the ITO thin film, which is an oxide as described in Patent Document 1, is 150 to 300 μΩ cm, which is higher than that of Ni-Cr alloys. However, it has been confirmed that when this thin film is heated to 250°C or higher, it crystallizes, reducing the resistivity and increasing the roughness of the thin film surface. This temperature change in resistivity poses a problem, making it difficult to apply to thin film sensors and thin film heaters.

[0007] Furthermore, Patent Document 2 discloses that thin films containing 20 to 80 mass % of transition metals such as Cr and Mo and the light element B in Ni, and thin films containing 0 to 50 atomic % of gas components such as nitrogen and carbon exhibit high resistivity. However, when forming such thin films, depending on the deposition apparatus, the amount of gas components incorporated into the thin film may vary depending on the position of the gas supply port and gas flow in the chamber, resulting in increased variation in resistivity within the thin film. Furthermore, sputtering methods have the problem of reactive products called nodules, which are formed by reaction between the sputtering target and the gas components, accumulating on the sputtering target and forming protrusions, which can easily induce abnormal discharges and particles. Furthermore, thin films containing 30 atomic % or more of gas components may exhibit reduced environmental resistance, such as high-temperature and high-humidity resistance.

[0008] An object of the present invention is to provide an alloy thin film that has high resistance and excellent environmental resistance, and a sputtering target that can easily form this alloy thin film.

[0009] The present invention relates to an alloy thin film containing one or more elements selected from Cr, Mo and W, and Ti, with the balance being Ni and unavoidable impurities, and having an electrical resistivity of 150 μΩ·cm or more.

[0010] The alloy thin film of the present invention preferably contains 15 atomic % or more of Ti, and preferably contains 35 atomic % or more of Ti and one or more elements selected from Cr, Mo, and W in total.

[0011] The present invention relates to a sputtering target for forming an alloy thin film having an electrical resistivity of 150 μΩ cm or more, which contains one or more elements selected from Cr, Mo, and W, and Ti, with the balance consisting of Ni and unavoidable impurities, and has a Curie point of room temperature or lower.

[0012] The sputtering target of the present invention preferably contains 15 atomic % or more of Ti. Also, the sputtering target of the present invention preferably contains 35 atomic % or more in total of Ti and one or more elements selected from Cr, Mo, and W.

[0013] The present invention can stably provide alloy thin films with high resistance and excellent environmental resistance. This will be an extremely useful technology for thin film resistors, thin film sensors, heating elements for thin film heaters, and other devices for which miniaturization is becoming increasingly demanded, and will greatly contribute to the stable production and improved reliability of electronic components.

[0014] 1 is a schematic cross-sectional view of an example of an alloy thin film according to the present invention.

[0015] An example of a cross-sectional schematic diagram of the alloy thin film of the present invention is shown in Figure 1. The alloy thin film 1 of the present invention is formed directly on a substrate 2 such as glass. The alloy thin film of the present invention may also be formed on a ceramic substrate or a metal plate on which an insulating film is formed, and the substrate can be appropriately selected depending on the required electrical resistivity and the heating temperature and atmosphere in the manufacturing process.

[0016] The alloy thin film of the present invention contains one or more elements selected from Cr, Mo, and W, and Ti, with the balance being Ni and unavoidable impurities, and has an electrical resistivity of 150 μΩ cm or more. In the following description, the term "environmental resistance" refers to surface deterioration caused by heating in the atmosphere and in a high-temperature, high-humidity environment, which can be confirmed by discoloration of the thin film and can be quantitatively evaluated, for example, by reflectance.

[0017] Generally, when adding an additive element to pure metal, resistivity increases, and reaches a maximum value when the additive amount is around 50 atomic %.In addition, when adding elements with different crystal structures, resistivity tends to further increase.The crystal structures of the elements that constitute the present invention are as follows: Ni has a face-centered cubic lattice (fcc), Ti has a hexagonal close-packed lattice (hcp), and Cr, Mo, W all have a body-centered cubic lattice (bcc), and all three kinds have different crystal structures, so the alloy thin film of the present invention achieves high resistance.

[0018] Furthermore, Ni, an element constituting the present invention, is an element with high moisture resistance and relatively low resistivity among transition metals. Ti has high moisture resistance but is prone to discoloration due to surface oxidation, a resistivity several times higher than Ni, and a larger atomic radius than Ni. Therefore, it is believed that dissolving Ti in Ni significantly distorts the crystal lattice, increasing electron scattering and thereby increasing resistivity. Cr has excellent oxidation resistance and moisture resistance and is an element with a common resistivity among transition metals. When added to Ni, it is an element that can significantly improve environmental resistance, such as oxidation resistance and moisture resistance. Furthermore, Mo and W are elements of the same group as Cr, and although their resistivity is lower than Cr, their large atomic radius means that when dissolved in Ni, they distort the crystal lattice, increasing electron scattering and thus increasing resistivity. The present invention achieves high resistivity and environmental resistance of 150 μΩ·cm or more by incorporating one or more elements selected from Cr, Mo, and W, and Ti into Ni.

[0019] The alloy thin film according to the embodiment of the present invention preferably contains 15 atomic % or more of Ti. As described above, Ti is an element with high resistivity, and therefore a stable high resistivity can be obtained by including 15 atomic % or more of Ti. To obtain even higher resistivity, it is more preferable to include 20 atomic % or more of Ti. On the other hand, since a high Ti content can decrease oxidation resistance, the Ti content is more preferably 60 atomic % or less.

[0020] The alloy thin film according to the embodiment of the present invention preferably contains one or more elements selected from Cr, Mo, and W and Ti in a total content of 35 atomic % or more. This makes it possible to stably obtain high resistivity and improve environmental resistance. Among environmental resistance properties, oxidation resistance is significantly improved by adding Cr, Mo, and W, and this effect becomes clear at 10 atomic % or more. To obtain a resistivity of 170 μΩ cm or more, it is more preferable to select Cr or W and set its content to 20 atomic % or more. In addition, from the viewpoint of maintaining high-temperature oxidation resistance among environmental resistance properties, the alloy thin film according to the embodiment of the present invention more preferably contains one or more elements selected from Cr, Mo, and W and Ti in a total content of 75 atomic % or less.

[0021] The alloy thin film according to the embodiment of the present invention preferably has a thickness of 100 nm or more to ensure the continuity of the thin film, and preferably has a thickness of 1000 nm or less in consideration of the productivity of film formation.

[0022] To form the alloy thin film of the present invention, a sputtering method using a sputtering target can be applied. To form the alloy thin film of the present invention having an electrical resistivity of 150 μΩ cm or more, it is optimal to use a sputtering target having the same composition as the alloy thin film, from the viewpoints of ease of setting sputtering conditions and ease of obtaining an alloy thin film of the desired composition. Alternatively, a method of forming the film by co-sputtering using sputtering targets of each element can be applied. Furthermore, a method of forming the film by co-sputtering using a sputtering target of a Ni—Ti alloy, a Ni—Cr alloy, a Ni—Mo alloy, a Ni—W alloy, or the like can also be applied.

[0023] Furthermore, in order to perform efficient and stable sputtering in a sputtering method, the sputtering target must be nonmagnetic, i.e., have a Curie point below room temperature at the room temperature where it is used. Note that "a Curie point below room temperature" refers to the sputtering target being nonmagnetic when its magnetic properties are measured at room temperature (25°C). Since Ni, one of the constituent elements of the alloy thin film of the present invention, is magnetic, to perform efficient and stable sputtering, it is necessary to adjust the type and amount of additive elements so that the Curie point is below room temperature. In the present invention, Ti and Cr, which are constituent elements other than Ni, are nonmagnetic elements that have the effect of lowering the Curie point of Ni, which is magnetic. For example, by containing 15 atomic % or more of Ti and 9 atomic % or more of Cr, the Curie point can be set below room temperature. Furthermore, it is preferable that the sputtering target according to an embodiment of the present invention contains at least one element selected from Cr, Mo, and W, and Ti in a total amount of 35 atomic % or more. In the sputtering target according to the embodiment of the present invention, from the viewpoint of maintaining high temperature oxidation resistance, which is one of the environmental resistance properties, in the above-mentioned alloy thin film, it is more preferable that the total content of one or more elements selected from Cr, Mo, and W and Ti is 75 atomic % or less.

[0024] The sputtering target of the present invention can be manufactured by, for example, a method of manufacturing a sputtering target by melting raw materials adjusted to a predetermined composition to produce an ingot and then machining the resulting ingot, or by a powder sintering method. In the powder sintering method, for example, the raw material powder can be produced by producing an alloy powder by a gas atomizing method, or the raw material powder can be a mixed powder obtained by mixing multiple alloy powders or pure metal powders to achieve the final composition of the present invention. As a method for sintering the raw material powder, pressure sintering such as hot isostatic pressing, hot pressing, spark plasma sintering, and extrusion press sintering can be used.

[0025] The sputtering target of the present invention contains one or more elements selected from Cr, Mo, and W, and Ti, with the remainder consisting of Ni and unavoidable impurities. This composition may result in the formation of intermetallic compounds, resulting in reduced ductility and difficulty in plastic processing. Therefore, in order to reliably produce sputtering targets, it is preferable to pressure-sinter an alloy powder of the final composition. Furthermore, since the sputtering target of the present invention contains Ni, which is a magnetic material, it is preferable to select elements to be added to Ni and pressure-sinter an alloy powder having a Curie point below room temperature. For example, in the case of a Ni-Ti-Cr alloy, it is preferable to produce a Ni-Ti-Cr alloy powder adjusted to the final composition and having a Curie point below room temperature by atomization. Alternatively, a non-magnetic Ni-Cr alloy powder can be produced by atomization, mixed with Ti powder or Cr powder to obtain the final composition, and then pressure-sintered. Alternatively, alloy powder can be produced by pulverizing a melted ingot.

[0026] By setting the average particle size of the alloy powder to 5 μm or more, it is possible to suppress impurities in the resulting sputtering target. On the other hand, by setting the average particle size of the alloy powder to 300 μm or less, it is possible to obtain a high-density sintered body. The average particle size referred to in the present invention is represented by the spherical equivalent diameter determined by the light scattering method using laser light, as specified in JIS Z 8901.

[0027] The sputtering target of the present invention preferably has a low content of inevitable impurities other than the main constituent elements Ni, Ti, Cr, Mo, and W, and may contain inevitable impurities such as oxygen, nitrogen, carbon, Fe, Al, and Si within a range that does not impair the effects of the present invention. For example, the oxygen and nitrogen contents are each 1000 ppm by mass or less, the carbon content is 200 ppm by mass or less, and the Al and Si content is 100 ppm by mass or less, and the purity excluding gas components is preferably 99.9% by mass or more.

[0028] Sputtering targets were prepared to form alloy thin films. Predetermined amounts of 3N-purity electrolytic Ni and massive Cr, Mo, W, and Ti blocks were weighed to yield Ni-50 atomic % Cr, Ni-20 atomic % Mo, Ni-20 atomic % W, and Ni-50 atomic % Ti alloys. Ni alloy ingots were then fabricated by melting and casting using a vacuum melting furnace. Each Ni alloy ingot obtained above was machined to produce sputtering targets with a diameter of 100 mm and a thickness of 5 mm. Pure Mo and pure W sputtering targets were also prepared. Each of the sputtering targets obtained above was brazed to a copper backing plate, and then attached to a sputtering apparatus (model number: SME-200E) manufactured by ULVAC, Inc. A 25 mm × 50 mm glass substrate (product number: EagleXG) manufactured by Corning Incorporated was attached to the substrate holder, and an alloy thin film having the composition shown in Table 1 was formed to a thickness of 200 nm by co-sputtering using simultaneous discharge.

[0029] The electrical resistivity of each alloy thin film was measured using a four-terminal thin film resistivity meter (model number: MCP-T400) manufactured by Dia Instruments Co., Ltd. The reflectance was measured using a spectrophotometer (model number: CM2500d) manufactured by Konica Minolta, Inc. The oxidation resistance, which is one type of environmental resistance, was measured by heating an alloy thin film formed on a glass substrate on a hot plate and measuring the electrical resistivity and reflectance of the alloy thin film. The results are shown in Table 1.

[0030]

[0031] As shown in Table 1, comparative sample No. 4, which is Ni-50 atomic % Ti, has the highest electrical resistivity, but when heated to 300°C or higher, its reflectivity drops significantly, indicating poor oxidation resistance. Furthermore, the electrical resistivities of comparative samples Nos. 1, 2, and 3 and samples Nos. 12 and 13, which are alloy thin films containing no Ti, were less than 140 μΩ·cm, failing to achieve high electrical resistivities. In contrast, inventive samples Nos. 5 to 11 all had electrical resistivities of 150 μΩ·cm or higher as deposited, demonstrating high resistance and maintaining high reflectivity even after heating to 300°C, demonstrating excellent oxidation resistance. Furthermore, as shown in samples No. 5 and 10, it was confirmed that a high resistivity of 170 μΩ·cm or higher could be achieved by incorporating 20 atomic % or more of Cr or W.

[0032] As one of the environmental resistance evaluations, moisture resistance was evaluated using the alloy thin film obtained in Example 1. To evaluate moisture resistance, the alloy thin film obtained above was left in an atmosphere at a temperature of 85°C and a relative humidity of 85% for 300 hours, and the electrical resistivity and reflectance were measured in the same manner as in Example 1. The results are shown in Table 2.

[0033]

[0034] As shown in Table 2, all of the alloy thin films according to the present invention showed little change in electrical resistivity and reflectance even after 300 hours had passed, confirming that they had high moisture resistance.

[0035] Predetermined amounts of 3N pure electrolytic Ni, massive Cr, and Ti blocks were weighed to produce high-electrical resistance alloy thin films with a ternary composition of Ni-25 atomic % Ti-25 atomic % Cr and a binary composition of Ni-10 atomic % Cr. Ingots were then produced by melting and casting using a vacuum melting furnace. When a SmCo magnet was brought close to each of the resulting ingots, it was confirmed that they did not adhere to the magnet. Ti ingots were also produced by a powder sintering method using Ti raw material with a purity of 3N or higher. Each of the ingots obtained above was machined to produce a sputtering target with a diameter of 100 mm and a thickness of 5 mm. These targets were then brazed to a copper backing plate and mounted in a sputtering apparatus (model number: SME-200E) manufactured by ULVAC, Inc., as in Example 1. A sputtering test was conducted under conditions of an Ar atmosphere, a pressure of 0.6 Pa, and a power of 500 W. As a result, all sputtering targets were successfully sputtered. Using these sputtering targets and the Ni-50 atomic % Cr sputtering target prepared in Example 1, a 25 mm × 50 mm glass substrate (product number: Eagle XG) manufactured by Corning Incorporated was attached to the substrate holder of the above-mentioned sputtering apparatus, and an alloy thin film having the composition shown in Table 3 was formed to a thickness of 200 nm by a co-sputtering method using simultaneous discharge.

[0036] The electrical resistivity of each alloy thin film was measured using a four-terminal thin film resistivity meter (model number: MCP-T400) manufactured by Dia Instruments Co., Ltd., as in Example 1. The reflectance was measured using a spectrophotometer (model number: CM2500d) manufactured by Konica Minolta, Inc. The oxidation resistance, which is one type of environmental resistance, was measured by heating an alloy thin film formed on a glass substrate on a hot plate and measuring the electrical resistivity and reflectance of the alloy thin film. The results are shown in Table 3. The electrical resistivity values ​​marked with * in Table 3 are outside the conditions of the present invention.

[0037]

[0038] As shown in Table 3, it was confirmed that all of the alloy thin films according to the present invention had an electrical resistivity of 150 μΩ cm or more. Here, the electrical resistivity tends to increase as the Ti content increases, with Samples Nos. 17 to 19, which had a Ti content of more than 20 atomic %, having an electrical resistivity of 170 μΩ cm or more, and Samples Nos. 20 and 21, which had a Ti content of 60 atomic % or more, having an electrical resistivity of 210 μΩ cm or more.

[0039] 1. Alloy thin film 2. Substrate

Claims

1. An alloy thin film containing one or more elements selected from Cr, Mo, and W, Ti, with the balance being Ni and unavoidable impurities, and having an electrical resistivity of 150 μΩ·cm or more.

2. The alloy thin film according to claim 1, containing at least 15 atomic % of Ti.

3. The alloy thin film according to claim 1 or 2, containing at least one element selected from the group consisting of Cr, Mo and W, and Ti in a total amount of at least 35 atomic %.

4. A sputtering target for forming an alloy thin film having an electrical resistivity of 150 μΩ cm or more, the sputtering target containing one or more elements selected from Cr, Mo, and W, and Ti, with the remainder consisting of Ni and unavoidable impurities, and having a Curie point at or below room temperature.

5. The sputtering target according to claim 4, containing 15 atomic % or more of Ti.

6. A sputtering target according to claim 4 or 5, containing at least one element selected from the group consisting of Cr, Mo and W, and Ti in a total amount of 35 atomic % or more.

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