Method for producing delafossite-type oxide thin film, and oxide thin film

Abstract

The present invention provides: a method for producing a delafossite-type oxide thin film; and an oxide thin film having a delafossite-type crystal structure. The method for producing a delafossite-type oxide thin film comprises a film formation step for using a target which contains a first metal and a second metal to form a thin film via physical vapor deposition, wherein in the target, the first metal is palladium or platinum, and the second metal is cobalt, chromium, or rhodium.

Description

Method for producing delafossite-type oxide thin film and oxide thin film

[0001] The present disclosure relates to a method for producing a delafossite-type oxide thin film and an oxide thin film.

[0002] Patent Document 1 discloses a cobalt or cobalt-based alloy sputtering target and a method for manufacturing the same. This target has an average PTF (magnetic leakage flux) of 75% or more in the direction perpendicular to the sputtering surface when measured at a thickness of 3 mm, and a standard deviation of the PTF in the direction perpendicular to the sputtering surface of 5% or less. This target has a composition consisting of Co and unavoidable impurities, or contains one or more elements selected from the group consisting of Pt, Cr, Ni, Fe, Pd, Ir, Ru, B, Si, Ge, Mn, Ti, Zr, V, and Ta. Furthermore, this manufacturing method is also applicable to a semiconductor device having a composition consisting of Co and unavoidable impurities, or containing one or more elements selected from the group consisting of Pt, Cr, Ni, Fe, Pd, Ir, Ru, B, Si, Ge, Mn, Ti, Zr, V, and Ta, wherein the contents of each element are Pt: 5 mass% or less, Cr: 5 mass% or less, Ni: 25 mass% or less, Fe: 9 mass% or less, Pd: 25 mass% or less, Ir: 25 mass% or less, Ru: 25 mass% or less, B: 0.5 mass% or less, Si: 2 mass% or less, Ge: 18 mass% or less, Mn: 25 mass% or less, and Ti: 2 mass%. The method includes the steps of preparing a raw material powder having a composition of 1% by mass or less Zr, 1.5% by mass or less V, and 3% by mass or less Ta, with the remainder being Co and unavoidable impurities, and having a volumetric D10 of 10 μm or more and a D90 of 150 μm or less as measured by a laser diffraction method, and molding the raw material powder into a desired target shape by an additive manufacturing method under the conditions of a preheating temperature of 600 to 900°C, an electron beam acceleration voltage of 50 to 70 kV, a modeling layer thickness of 50 to 100 μm / layer, and a beam scan speed of 500 to 5,000 m / s. One example of the additive manufacturing method is powder bed fusion (PBF), which involves repeatedly heating the surface of a powder bed using electron beam melting (EBM) or laser melting (SLM) to selectively melt and solidify it, thereby forming the powder into a desired target shape.

[0003] Patent Document 2 describes a method for producing a sputtering target material. This production method is for a sputtering target material made of a magnetic alloy obtained by hot solidifying and molding powder, using a powder raw material composed of at least one element selected from the group of elements consisting of Fe, Co, and Ni, which are elements of Group 8A of the periodic table in period 4, or at least one element selected from the group of elements consisting of Fe, Co, and Ni, which are elements of Group 8A of the periodic table in period 4, in a total amount of 60 at. % or more as the main component, with the remainder being at least one element selected from the group consisting of Al, Ag, Au, B, C, Ce, Cr, Cu, Ga, Ge, Dy, Gd, Hf, In, La, Mn, Mo, Nb, Nd, P, Pd, Pt, Ru, Si, Sm, Sn, Ta, Ti, V, W, Y, Zn, and Zr, and unavoidable impurities, the sputtering target material is produced by solidifying and molding the powder and then cooling it to 300°C at a cooling rate of 144 to 36,000°C / hr. Patent Document 2 discloses a target containing Co as the main component and 1 at% Pd, and a target containing Co as the main component and 1 at% Pt.

[0004] For example, as disclosed in Patent Document 3, demand for power devices (also referred to as power semiconductors, power elements, or power semiconductor elements) used in power converters such as inverters and converters is increasing due to, for example, the spread of electric vehicles (EVs). Gallium oxide, for example, is known as an oxide for power devices.

[0005] Non-Patent Document 1 states that PdCoO ２ A case has been disclosed in which a large Schottky barrier of 1.8 eV was realized in a thin film. ２ The thin film was produced by pulsed laser deposition. ２ and β-Ga ２ O ３ Like the interface with PdCoO ２At the interface between the oxide and the thermally stable oxide, a polar layered structure electric dipole is naturally formed. Therefore, even in a high temperature environment such as 350°C, ８ It has been shown that current rectification can be achieved with a large on / off ratio approaching the order of 1000. Furthermore, Non-Patent Document 1 discloses that there is a great demand for semiconductor devices to operate at high temperatures for switching and sensing applications in the technical fields of automobiles, plants, and aerospace.

[0006] JP 2017-119904 A JP 2011-208265 A International Publication No. 2020 / 090491

[0007] Electric dipole effect in PdCoO2 / β-Ga2O3 Schottky diodes for high-temperature operation, Harada et al, Science Advances 5, eaax5733 (2019)

[0008] As disclosed in Patent Document 3, gallium oxide has a large band gap, a large breakdown field, and high thermal stability and excellent chemical resistance, making it an excellent semiconductor for power devices, and demand for it in power device applications is expected to increase. However, conventionally used Schottky electrodes using platinum, for example, have a small Schottky barrier and are insufficient in terms of heat resistance and reliability (voltage resistance) in applications where excellent power device semiconductors such as gallium oxide are used, such as applications requiring high output.

[0009] Here, palladium cobalt oxide (PdCoO ２ ), and palladium chromium oxide (PdCrO), which is a delafossite-type oxide similar to palladium cobalt oxide. ２ ), palladium rhodium oxide (PdRhO ２ ) or platinum cobalt oxide (PtCoO ２Despite being an oxide, gallium monoxide (GMO) exhibits high electrical conductivity comparable to that of elemental metals such as gold, silver, and copper. Therefore, it is expected to be used as a Schottky electrode for power devices, similar to that of gallium oxide.

[0010] In semiconductor devices, electrodes are formed by depositing a film of an electrode material by, for example, sputtering. Therefore, as disclosed in, for example, Patent Documents 1 and 2, sputtering targets suitable for producing desired thin films have been studied. However, Patent Documents 1 and 2 do not disclose the formation of a delafossite-type oxide thin film. Therefore, it is desirable to provide a new method for producing a delafossite-type oxide thin film. It is also desirable to provide a method for producing a delafossite-type oxide thin film having high electrical conductivity.

[0011] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a method for producing a delafossite-type oxide thin film and an oxide thin film that has a delafossite-type crystal structure and high electrical conductivity.

[0012] In order to achieve the above object, a method for producing a delafossite-type oxide thin film according to the present disclosure includes a film formation step of forming a thin film by physical vapor deposition using a target containing a first metal and a second metal, wherein the first metal in the target is palladium or platinum, and the second metal is cobalt, chromium, or rhodium.

[0013] To achieve the above object, the oxide thin film according to the present disclosure has a delafossite crystal structure, and has a residual resistivity ratio, which is a value obtained by dividing the electrical resistivity at 300 K by the electrical resistivity at 2 K, of 1.0 or more and 8.0 or less.

[0014] In order to achieve the above object, the oxide thin film according to the present disclosure has a delafossite crystal structure, and when the number of A site layers in the thickness direction is N, an area of ​​33% or more of the area of ​​the thin film has the same N.

[0015] To achieve the above object, the oxide thin film according to the present disclosure has a delafossite crystal structure, triangular or hexagonal crystal facets appear on the surface, and the root mean square of the irregularity height is 0.4 nm or less.

[0016] According to the present disclosure, it is possible to provide a method for producing a delafossite-type oxide thin film and an oxide thin film having a delafossite-type crystal structure and high electrical conductivity.

[0017] 1 is a SEM-EDX mapping image of palladium of the target according to Example 1. FIG. 2 is a SEM-EDX mapping image of cobalt of the target according to Example 1. FIG. 3 is a SEM-EDX mapping image of palladium of the target according to Example 2. FIG. 4 is a SEM-EDX mapping image of cobalt of the target according to Example 2. FIG. 5 is an X-ray diffraction pattern of a thin film according to Condition 1. FIG. 6 is an X-ray diffraction pattern of a thin film according to Condition 2. FIG. 7 is an X-ray diffraction pattern of a thin film according to Condition 3. FIG. 8 is an X-ray diffraction pattern of a thin film according to Condition 5. FIG. 9 is an X-ray diffraction pattern of a thin film according to Condition 10. FIG. 11 is an X-ray diffraction pattern of a thin film according to Condition 12. FIG. 12 is an X-ray diffraction pattern of a thin film according to Condition 13. 10 is an X-ray diffraction pattern of a thin film according to condition 14. 11 is an X-ray diffraction pattern of a thin film according to condition 8 after heat treatment. 12 is an X-ray diffraction pattern of a thin film according to condition 15. 13 is an X-ray diffraction pattern of a thin film according to condition 16. 14 is an X-ray diffraction pattern of a thin film according to condition 17. 15 is an X-ray diffraction pattern of a thin film according to condition 18. 16 is an X-ray diffraction pattern of a thin film according to condition 19. 17 is an X-ray diffraction pattern of a thin film according to condition 20. 18 is an X-ray diffraction pattern of a thin film according to condition 21. 19 is an X-ray diffraction pattern of a thin film according to condition 22. 19 is an X-ray diffraction pattern of a thin film according to condition 23. 19 is an X-ray diffraction pattern of a thin film according to condition 24. 19 is an X-ray diffraction pattern of a thin film according to condition 25. 19 is an X-ray diffraction pattern of a thin film according to condition 26. 19 is an X-ray diffraction pattern of a thin film according to condition 27. 19 is an X-ray diffraction pattern of a thin film according to condition 28. 19 is an X-ray diffraction pattern of a thin film according to condition 31. 1 is an X-ray diffraction pattern of a thin film according to condition 32. 2 is an X-ray diffraction pattern of a thin film according to condition 33. 3 is an X-ray diffraction pattern of a thin film according to condition 34. 4 is an SEM image (500,000 magnification) of a thin film according to condition 23. 5 is an SEM image (2,000,000 magnification) of a thin film according to condition 23. 6 is an SEM image (500,000 magnification) of a thin film according to condition 24. 7 is an SEM image (2,000,000 magnification) of a thin film according to condition 24.10 is an SEM image (500,000 magnification) of a thin film according to condition 25. 11 is an SEM image (2,000,000 magnification) of a thin film according to condition 25. 12 is an SEM image (500,000 magnification) of a thin film according to condition 26. 13 is an SEM image (2,000,000 magnification) of a thin film according to condition 26. 14 is an SEM image (500,000 magnification) of a thin film according to condition 27. 15 is an SEM image (2,000,000 magnification) of a thin film according to condition 27. 16 is a graph obtained by investigating the relationship between the pressure during film formation and the peak intensity ratio. 17 is an SEM image (500,000 magnification) of a thin film according to condition 27. 18 is an SEM image (2,000,000 magnification) of a thin film according to condition 27. 19 is a graph obtained by investigating the relationship between the pressure during film formation and the peak intensity ratio. 19 is an SEM image (500,000 magnification) of a thin film according to condition 27. 20 is an SEM image (2,000,000 magnification) of a thin film according to condition 27. 21 is a graph obtained by investigating the relationship between the pressure during film formation and the peak intensity ratio. 19 is an SEM image (500,000 magnification) of a thin film according to condition 27. 22 is an SEM image (2,000,000 magnification) of a thin film according to condition 27. 23 is a graph obtained by investigating the relationship between the pressure during film formation and the peak intensity ratio. 19 is an SEM image (500,000 magnification) of a thin film according to condition 27. 24 is a SEM image (2,000,00 ２ O ３ PtCoO prepared on a substrate ２ / PdCoO ２ 1 is a schematic diagram of a laminated thin film. FIG. 1 is an X-ray diffraction pattern of a thin film according to condition 35. FIG. 2 is an X-ray diffraction pattern of a thin film according to condition 36. FIG. 3 is an X-ray diffraction pattern of a thin film according to condition 37. FIG. 4 is an enlarged view of the X-ray diffraction pattern of a thin film according to condition 37. FIG. 5 is an X-ray diffraction pattern of a thin film according to condition 38. FIG. 6 is X-ray diffraction patterns of thin films according to conditions 39 and 44. FIG. 7 is an enlarged view of the X-ray diffraction pattern of a thin film according to condition 39. FIG. 8 is X-ray diffraction patterns of thin films according to conditions 40 and 44. FIG. 9 is an enlarged view of the X-ray diffraction pattern of a thin film according to condition 40. FIG. 10 is an X-ray diffraction pattern of a thin film according to condition 41. FIG. 11 is an X-ray diffraction pattern of a thin film according to condition 42. FIG. 12 is an X-ray diffraction pattern of a thin film according to condition 43. FIG. 13 is a comparison of the X-ray diffraction pattern of a thin film according to condition 31 with a simulation result using a Laue function. FIG. 14 is an atomic force microscope image according to condition 31.

[0018] Hereinafter, a method for producing a delafossite-type oxide thin film and an oxide thin film according to an embodiment of the present disclosure will be described. First, an outline of a method for producing a delafossite-type oxide thin film according to this embodiment will be described.

[0019] The method for producing a delafossite-type oxide thin film according to this embodiment includes a film-forming step of forming a thin film by physical vapor deposition using a target containing a first metal and a second metal, wherein the first metal is palladium or platinum and the second metal is cobalt, chromium, or rhodium.

[0020] The oxide thin film according to this embodiment has a delafossite crystal structure, and has a residual resistivity ratio, which is the value obtained by dividing the electrical resistivity at 300K by the electrical resistivity at 2K, of 1.0 or more and 8.0 or less.

[0021] The oxide thin film according to this embodiment has a delafossite crystal structure, and when the number of A site layers in the thickness direction is N, an area of ​​33% or more of the area of ​​the thin film has the same N. The oxide thin film according to this embodiment can realize a delafossite oxide thin film having high electrical conductivity (high residual resistivity ratio).

[0022] The oxide thin film according to this embodiment has a delafossite-type crystal structure, with triangular or hexagonal crystal facets appearing on the surface, and the root mean square of the unevenness height in the thickness direction is 0.4 nm or less. The oxide thin film according to this embodiment has such good crystallinity that triangular or hexagonal crystal facets appear on the surface, making it possible to realize a delafossite-type oxide thin film with high electrical conductivity (high residual resistivity ratio).

[0023] The method for producing a delafossite-type oxide thin film according to this embodiment will be described in detail below.

[0024] The delafossite-type oxide has the general formula ABO ２ In the present embodiment, when simply referring to a delafossite-type oxide, it refers to a palladium cobalt oxide (PdCoO ２ ), palladium chromium oxide (PdCrO ２ ), platinum cobalt oxide (PtCoO ２ ) and palladium rhodium oxide (PdRhO ２ ) is included at least.

[0025] The target includes a first metal and a second metal. The first metal is element A (monovalent cation) in the above general formula. The second metal is element B (trivalent cation) in the above general formula. The target may include impurities.

[0026] The first metal is palladium (Pd) or platinum (Pt). The target contains the first metal in an amount of 45 at% to 90 at%. The target contains the first metal in an amount of preferably 45 at% to 60 at% and more preferably 50 at% to 55 at%. Here, "at%" refers to an element ratio expressed in %.

[0027] The second metal is cobalt (Co), chromium (Cr), or rhodium (Rh). The target contains the second metal in an amount of 10 at% to 55 at%. The target contains the second metal in an amount of preferably 40 at% to 55 at%, more preferably 45 at% to 50 at%.

[0028] When the target contains the first metal and the second metal in the above ratio, the target according to this embodiment becomes suitable for producing a delafossite-type oxide thin film (hereinafter, sometimes simply referred to as a thin film). Specifically, when this target is used to produce a thin film by physical vapor deposition (hereinafter, sometimes referred to as PVD), the proportion of the delafossite-type oxide in the thin film can be increased. In other words, the proportion of metals and metal oxides other than the delafossite-type oxide in the thin film can be reduced.

[0029] By reducing the proportion of metals and metal oxides other than the delafossite-type oxide, the electrical resistivity of the thin film when used as an electrode can be reduced, making the thin film more suitable for use as an electrode.

[0030] In this embodiment, impurities refer to elements that are not intentionally added. The impurity content of the target is suppressed to 500 ppm by mass or less (hereinafter simply referred to as ppm). The content of impurities contained in the target is preferably suppressed to 300 ppm or less, and even 200 ppm or less per element. That is, the total amount of impurities contained in the target is 500 ppm by mass or less, and the content of each individual impurity element is 300 ppm or less, preferably 200 ppm or less. Note that in this embodiment, the impurity concentration is a value measured using an ICP optical emission spectrometer.

[0031] The target may contain oxygen (O), nitrogen (N), carbon (C), sulfur (S), and other unavoidable impurities. Of these, the oxygen content is suppressed to 200 ppm or less. By reducing the oxygen content, it may be possible to reduce the content of metal oxides other than the delafossite-type oxide in the thin film.

[0032] The target may be a sintered body of a metal powder containing a first metal and a second metal. The metal powder may be a mixed powder of a powder of the first metal and a powder of the second metal, or may be a powder of an alloy of the first metal and the second metal (hereinafter referred to as alloy powder). The metal powder is preferably an alloy powder.

[0033] When the target is a sintered body, the thin film can be made homogeneous by using an alloy powder as the metal powder. A homogeneous thin film specifically refers to a state in which the distribution of delafossite-type oxide in the thin film is homogeneous, the distribution of constituent elements in the thin film is homogeneous, or the distribution of impurities in the thin film is homogeneous. In other words, a homogeneous thin film refers to a state in which, when the element distribution in the thin film is mapped using, for example, an SEM (scanning electron microscope) and an EDX (energy dispersive X-ray spectrometry), the variation in element distribution indicates that the elements are present in a solid solution state.

[0034] Here, the variation in element distribution is a variation in noise level, which means, for example, that when a cross section of a target is mapped by SEM-EDX, the size of the domain of the first metal is 5 μm or less in terms of circle-equivalent diameter. In this embodiment, the domain of the first metal is defined as a closed region on the side where the element ratio of the second metal is lower than a predetermined element ratio of the second metal (50 at % in this embodiment) when the image of the mapped second metal is binarized using the threshold value of the predetermined element ratio of the second metal. The size of this domain is preferably 5 μm or less in terms of circle-equivalent diameter converted from the area. The size of this domain is more preferably 3 μm or less, and even more preferably 1 μm or less.

[0035] The target preferably has a density of 90% or more and 99% or less. A low density of the target, i.e., a large number of voids present within the target, especially large voids, can cause abnormal discharge during PVD processes such as sputtering, leading to particle intrusion into the thin film during film formation (when forming a thin film). Increasing the density to this level suppresses particle intrusion into the thin film during PVD film formation. This makes the thin film more suitable as an electrode. The density is calculated based on the density of the alloy of the first metal and the second metal (hereinafter referred to as the alloy density), calculated based on the content ratio of the first metal to the second metal, and the apparent density of the target (hereinafter referred to as the target density). In other words, the density (%) is calculated by dividing the target density by the alloy density and multiplying the result by 100. The target density is calculated by dividing the mass of the target by the shape (volume) of the target.

[0036] When producing the target as a sintered body, it is sufficient to sinter metal powder containing 45 at% to 90 at% of the first metal and the remainder being the second metal and impurities.When producing the target according to this embodiment as a sintered body, it is sufficient to sinter metal powder containing preferably 45 at% to 60 at% of the first metal, more preferably 50 at% to 55 at% of the first metal.

[0037] During this sintering, if the metal powder is an alloy powder containing 45 at% to 90 at% of the first metal and the remainder being the second metal and impurities, the target can be produced as a sintered body of the alloy powder. This reduces the concentration unevenness (element ratio variation, distribution variation) of the first metal and the second metal in the target. By reducing the concentration unevenness of the first metal and the second metal in the target, the thin film can be made homogeneous.

[0038] If a mixed powder of a powder of the first metal and a powder of the second metal is used as the metal powder during sintering, the target can also be produced as a sintered body of the mixed powder.

[0039] The particle size of the metal powder used for sintering, in terms of volume average diameter, is preferably 20 μm or more and 120 μm or less, and more preferably 50 μm or more and 70 μm or less. Alternatively, it may be a product that passes through a sieve with a mesh size of 106 μm. If the particle size of the metal powder is within this range, it becomes easy to manufacture a target with high density. In this embodiment, the particle size and particle size distribution of the metal powder are measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model: SLDA-2300) while the metal powder is dispersed in water to which a surfactant has been added.

[0040] In particular, when the metal powder used for sintering is a mixed powder, the particle diameter of each of the first metal and second metal powders is preferably 20 μm or more and 120 μm or less in terms of volume average diameter. This may reduce the concentration unevenness (element ratio variation, distribution variation) of the first metal and the second metal in the target. By reducing the concentration unevenness of the first metal and the second metal in the target, the thin film can be made homogeneous.

[0041] The sintering step of sintering the metal powder may be carried out according to the procedure described below.

[0042] The sintering step may include a molding step of molding the metal powder into a predetermined shape, for example, a disk shape suitable for use as a target. In the sintering step, for example, the metal powder is pressurized while being heated, so that the metal powder can be sintered while being molded into the predetermined shape.

[0043] In the sintering step, the metal powder may be sintered at a temperature of 550° C. to 1300° C. In addition, in the sintering step, the metal powder may be sintered while applying a pressure of 30 MPa to 70 MPa. This makes it possible to obtain a target with a high density, specifically a density of 90% to 99%, as a sintered body.

[0044] The above target is suitable for producing a delafossite-type oxide thin film by a physical vapor deposition method (PVD method, hereinafter simply referred to as PVD) such as sputtering.

[0045] In this embodiment, the PVD method in the film formation step includes vapor deposition, ion plating, ion beam deposition, and sputtering, with sputtering being particularly preferred as the PVD method in the film formation step.

[0046] Among sputtering methods, RF sputtering, in which a high-frequency AC voltage is applied to a target and a chamber containing the target, and DC sputtering, in which a DC voltage is applied, are preferred. Furthermore, RF sputtering and DC sputtering are preferably reactive sputtering. The following description will be given taking as an example a case where reactive sputtering, in which a target reacts with oxygen, is employed as the sputtering method.

[0047] In the film formation step, when a thin film is formed (deposited) by RF sputtering, the sputtering conditions are as follows.

[0048] The pressure of the atmosphere during film formation is preferably 0.5 Pa or less, and more preferably 0.3 Pa or less. This makes it possible to further increase the proportion of delafossite-type oxide in the thin film.

[0049] The atmosphere during film formation preferably contains oxygen. The atmosphere during film formation is particularly favorable in terms of the ratio of oxygen to inert gas (hereinafter, O ２ It is preferable that the ratio of the inert gas (sometimes referred to as the / Ar ratio) is 2 or more and 7 or less. This makes it possible to further increase the proportion of the delafossite-type oxide in the thin film. Here, the inert gas may be any gas that does not easily react with other elements, such as rare gas elements and nitrogen gas, and argon is used below.

[0050] During film formation, the temperature of the substrate on which the thin film is formed is 500° C. or higher and 850° C. or lower, preferably 610° C. or higher and 800° C. or lower. This allows the proportion of delafossite-type oxide in the thin film to be increased. The substrate for forming the thin film is, for example, Al ２ O ３ A (0001) substrate can be used.

[0051] The thin film formed in the film formation step may then be heat-treated. This heat treatment makes the thin film highly crystalline. The atmosphere for this heat treatment is preferably the same as the atmosphere during film formation. This makes it possible to suppress decomposition of the delafossite-type oxide in the thin film.

[0052] (Production Example 1) A target according to Production Example 1 was produced as follows.

[0053] The alloy powder (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., volume average diameter: 60 μm) produced by gas atomization has a composition ratio (element ratio) of palladium and cobalt of 50:50 (the content of palladium and cobalt is approximately 50 at %), with the remainder being cobalt and impurities (the amount of impurities is 351 ppm or less, and oxygen is 25 ppm). 93 g of the alloy powder was weighed out and filled into a mold as the powder for sintering, followed by hot press sintering (the atmosphere during sintering was 5×10 －２ The alloy powder was prepared by weighing palladium and cobalt (both metals) so that the composition ratio (element ratio) of the alloy composition was 50:50, heating the molten alloy to 1500°C or higher, gas atomizing the molten alloy, and classifying the atomized powder using a sieve with 106 μm openings.

[0054] The sintered product was then shaped to obtain a disk-shaped target for this manufacturing example. The surface and sides of the disk were polished with emery paper to prepare the target for subsequent use. The shape of the target after shape adjustment was a disk-shaped target with a diameter of 48 mm and a thickness t of approximately 1.0 mm. The pressure during sintering using the hot press sintering method (pressure applied to the powder in the mold, hereinafter referred to as the sintering pressure) was 50 MPa, and the temperature inside the furnace during sintering (hereinafter referred to as the sintering temperature) was 700°C. The sintering time (the time during which the above sintering pressure and sintering temperature were maintained) was 60 minutes. The furnace was kept in a vacuum atmosphere during sintering.

[0055] The amounts of impurities in the target according to this production example were quantified using an ICP optical emission analyzer, and the results were 21 ppm for oxygen, 3 ppm for nitrogen, 17 ppm for carbon, and 6 ppm for sulfur. The palladium and cobalt had high purity, and a target in a metallic state (not oxidized) was obtained.

[0056] The elemental ratio of palladium to cobalt in the target according to this manufacturing example was maintained at the same level as that in the sintering powder (alloy powder). "Maintaining the elemental ratio in the sintering powder" means that the ratio of the elemental ratio of cobalt (element B) to the elemental ratio of palladium (element A) in the sintering powder was the same as the ratio of the elemental ratio of cobalt (element B) to the elemental ratio of palladium (element A) in the target, within an error of 1%.

[0057] The density of the target according to this manufacturing example was 95.9%.

[0058] 1 and 2 show a mapping image of palladium (L line) (see FIG. 1) and a mapping image of cobalt (K line) (see FIG. 2) in the target according to this manufacturing example, measured using an SEM-EDX (manufactured by JEOL Ltd., model: JCM-6000Plus, magnification: 400x). In FIGS. 1 and 2, the closer to white the image, the higher the element ratio (concentration) of the mapped element. The circle-equivalent diameter of the cobalt domain measured based on FIG. 2 was 5 μm or less. In these mapping images, almost no unevenness in the concentration of palladium or cobalt could be confirmed, confirming that the dispersion state was extremely good and that the target was in a solid solution state. From these results, it was determined that the target according to this manufacturing example was in a homogeneously alloyed state.

[0059] (Manufacturing Example 2) The target of Manufacturing Example 2 differs from Manufacturing Example 1 in that a mixed powder of palladium powder and cobalt powder was used as the sintering powder instead of the alloy powder, but the other aspects were the same as those of Manufacturing Example 1.

[0060] Palladium powder was prepared by chemical reduction with an impurity content of 245 ppm (Tanaka Kikinzoku Kogyo Co., Ltd., passed through a 106 μm sieve). Cobalt powder was prepared by gas atomization with an impurity content of 246 ppm. 59.85 g of palladium powder and 33.15 g of cobalt powder were weighed and mixed in a mortar for 10 minutes to obtain a mixed powder. 93 g of the mixed powder was then weighed and filled into a mold. A disk-shaped target was obtained in the same manner as in Production Example 1. Cobalt powder was obtained by heating cobalt to 1500°C or higher to obtain a molten metal, gas atomizing the molten metal, and then classifying the atomized powder through a 106 μm sieve.

[0061] The amounts of impurities in the target according to this manufacturing example were 171 ppm oxygen, 40 ppm nitrogen, 27 ppm carbon, and 9 ppm sulfur, and the purity of palladium and cobalt was high, resulting in a target in a metallic state (non-oxidized).

[0062] The element ratio between palladium and cobalt in the target according to this manufacturing example was maintained at the same element ratio as in the state of the powder (mixed powder) for sintering.

[0063] The density of the target according to this manufacturing example was 95.1%.

[0064] Figures 3 and 4 show mapping images of palladium (see Figure 3) and cobalt (see Figure 4) in the target of this manufacturing example, measured in the same manner as in Manufacturing Example 1. In Figures 3 and 4, the closer to white the color, the higher the element ratio (concentration) of the mapped element. In these mapping images, significant concentration variations in palladium and cobalt were observed. It was determined that the target of this manufacturing example was in a state where areas with high palladium element ratios (concentrations) and areas with high cobalt element ratios (concentrations) were mixed and dispersed. Observation of these images revealed that the domain sizes of the areas with high palladium element ratios (concentrations) and the areas with high cobalt concentration roughly corresponded to the particle diameter of the powder used for sintering. In other words, it is believed that in targets sintered using mixed powders, domains of each element corresponding to the particle diameter of the mixed powder used for sintering remain.

[0065] (Production Example 3) Furthermore, a thin film of palladium cobalt oxide was formed by reactive sputtering using RF sputtering using the targets of Production Examples 1 and 2. The thin film formation in Production Example 3 was carried out by changing the target and film formation conditions as follows.

[0066] The substrate for thin film formation is Al ２ O ３ A (0001) sapphire substrate was used, which had been annealed at 1100° C. for two hours.

[0067] The sputtering was carried out using a sputtering device (model: ESCS-232S) manufactured by Eiko Engineering Co., Ltd.

[0068] The RF output was set to 60 W or 100 W. The RF frequency was 13.56 MHz.

[0069] The pressure in the chamber where the film was formed was set to 0.10 Pa, 0.15 Pa, 0.20 Pa, 0.50 Pa, 3 Pa, or 20 Pa.

[0070] The TS distance (the distance from the target surface of the cathode of the sputtering device to the substrate) was set to 150 mm.

[0071] The reactive gases supplied to the chamber for reactive sputtering are argon (Ar) and oxygen (O ２ The flow rates of the reactive gases in the chamber were 3 to 5 sccm for argon and 10 to 14 sccm for oxygen. ２ The / Ar ratio was 2.0, 3.0, 3.5 or 4.0.

[0072] The substrate on which the thin film is formed is Al ２ O ３ A (0001) substrate was used. The substrate temperature during film formation was 470°C, 610°C, 700°C, 750°C, or 800°C. The substrate temperature was controlled by setting the temperature of the substrate heater in the sputtering apparatus to 500°C, 650°C, 750°C, 800°C, or 850°C, in that order.

[0073] As described above, the targets and film formation conditions were changed to produce 14 types of thin films under conditions 1 to 14. Table 1 shows conditions 1 to 14 for producing these thin films.

[0074]

[0075] The thin films under conditions 1 to 14 were evaluated by X-ray diffraction (XRD). The results are shown in Table 1.

[0076] 5 to 18 show the X-ray diffraction patterns of the thin films according to conditions 1 to 14 in this order.

[0077] In these X-ray diffraction patterns, the peaks at diffraction angles 2θ of 15.0°, 30.2°, 46.0°, and 62.7° represent the peaks of the (0003), (0006), (0009), and (0012) planes of palladium cobalt oxide. The peak at a diffraction angle 2θ of 38.6° represents the peaks of tricobalt tetroxide (Co ３ O ４The peak at a diffraction angle 2θ of 33.8° represents the peak of the (101) plane of palladium oxide (PdO). The peak at a diffraction angle 2θ of 40.1° represents the peak of the (111) plane of metallic palladium (Pd). The peaks at diffraction angles 2θ of 20.5°, 41.7°, and 64.5° represent the peak of the (111) plane of Al. ２ O ３ This is the peak of the substrate.

[0078] From the results of observing the X-ray diffraction patterns of the thin films under conditions 1 to 14, palladium cobalt oxide (PdCoO) having a delafossite-type crystal structure was observed under conditions 2 to 13. ２ ) was detected. This result shows that it is possible to form a thin film containing palladium cobalt oxide if the atmospheric pressure during film formation is 0.50 Pa or less. A palladium oxide peak is observed in the thin film under condition 9 (see FIG. 13), but no palladium oxide peak is observed in the thin film under condition 8 (see FIG. 12). Therefore, it is preferable that the atmospheric pressure during film formation is 0.20 Pa or less, as this reduces the cobalt oxide in the thin film. A decrease in the atmospheric pressure during film formation increases the mean free path, suggesting the possibility that this may have reduced the cobalt oxide in the thin film.

[0079] The film thickness (nm) of the thin films under conditions 8 and 11 was determined to be 12.0 nm, respectively. The film thicknesses of these thin films were determined based on fringes observed in the X-ray diffraction patterns of these thin films.

[0080] Furthermore, the electrical resistivity (Ωcm) at a temperature of 300K and the electrical resistivity (Ωcm) at a temperature of 2K were measured for the thin films under Conditions 8 and 11. The electrical resistivity was determined based on the sheet resistance measured by a DC four-terminal method after wiring with Au (gold) wires by In (indium) pressure bonding to the thin film and the above-mentioned film thickness. The electrical resistivity (Ωcm) at 300K and the electrical resistivity (Ωcm) at 2K for Condition 8 were 7.74×10 －６ and 3.80 x 10 －６ The electrical resistivity (Ωcm) at 300 K and the electrical resistivity (Ωcm) at 2 K under condition 11 were 2.61 × 10－３ and 2.52 x 10 －２ It was.

[0081] Furthermore, the residual resistance ratio (RRR) of the thin films under conditions 8 and 11 was calculated by dividing the electrical resistivity at 300 K by the electrical resistivity at 2 K. The RRR under condition 8 was 2.04. The RRR under condition 11 was 0.10. Note that a larger RRR value indicates a greater effect of reducing electrical resistance in the low temperature region. The larger the RRR value, the lower the crystal defect density, making it preferable for electrodes such as Schottky electrodes for power devices.

[0082] O ２ Palladium oxide was observed in the thin film under condition 3 where the / Ar ratio was 4.0 (see FIG. 7). ２ In the thin films under conditions 2, 4 and 5 where the O / Ar ratio is 3.5 or less, no peak of cobalt oxide can be observed (see FIGS. 6, 8 and 9, respectively). ２ The thin film under condition 3, in which the O / Ar ratio is 4.0, has a weaker peak intensity of palladium cobalt oxide than the thin films under conditions 2, 4, and 5. ２ It can be seen that the / Ar ratio is preferably 4.0 or less, and more preferably 3.5 or less. ２ It can be judged that a palladium cobalt oxide film can be formed if the / Ar ratio is 2.0 or more.

[0083] The thin films according to conditions 2 to 5 have an RF output of 100 W, and the thin films according to conditions 6 to 9, 13, and 14 have an RF output of 60 W. However, if the substrate temperature is 500° C. or higher (conditions 6 to 9 and 13), it is possible to form a thin film containing palladium cobalt oxide with an atmospheric pressure of 0.50 Pa or less during film formation, just as in the case of an RF output of 100 W.

[0084] A comparison of conditions 6 to 9 shows that there is no significant difference in the thin film thickness when the substrate temperature is in the range of 700°C to 800°C. This result suggests that thin films can be formed at substrate temperatures of 500°C or higher and 850°C or lower. Under condition 8 (see FIG. 12), no palladium oxide peaks are observed, whereas slight palladium oxide peaks are observed under conditions 6 and 7 (see FIGS. 10 and 11), suggesting that a substrate temperature of less than 750°C is preferable. Furthermore, a comparison of conditions 6 and 8 shows that the metallic cobalt peak is weaker under the lower substrate temperature (condition 8) than under the higher substrate temperature (condition 6), suggesting that a substrate temperature of less than 750°C is preferable.

[0085] Furthermore, taking into consideration the results of conditions 13 and 14 (see FIGS. 17 and 18), it can be said that the substrate temperature is preferably 500° C. or higher.

[0086] Conditions 10 to 12 are cases where films were formed using the target of Production Example 2 (a target produced from a mixed powder of palladium powder and cobalt powder), while the other conditions used the target of Production Example 1 (a target produced from an alloy powder). The results for Conditions 10 to 12 (see FIGS. 14 to 16 ) show that it is possible to form a thin film containing palladium-cobalt oxide even when a target produced from a mixed powder is used instead of a target produced from an alloy powder.

[0087] In addition, even when a target manufactured from mixed powder is used as in conditions 10 to 12, O ２ It can be judged that a palladium cobalt oxide film can be formed if the / Ar ratio is 2.0 or more and 3.5 or less.

[0088] In addition, a comparison between Condition 10 (see FIG. 14 ) and Condition 8 (see FIG. 12 ) reveals that the use of a target manufactured from alloy powder (Condition 8) is preferable because the peak of palladium cobalt oxide is larger than the use of a target manufactured from mixed powder (Condition 10).

[0089] The elemental ratio of palladium to cobalt in the thin films under conditions 2 to 13 was measured using an ICP optical emission spectrometer, and the Pd:Co ratio was within the range of 48.8 to 49.0:51.2 to 51.0 in all thin films. The composition ratio (elemental ratio) of the alloy composition of palladium to cobalt in the targets used under conditions 1 to 14 was 50:50, and it is believed that the elemental ratio of the thin films was determined according to this ratio.

[0090] Tricobalt tetroxide tended to be detected in the thin films under all conditions from 1 to 13. Tricobalt tetroxide was not detected under condition 14.

[0091] The thin film under condition 8 was further subjected to a heat treatment. The heat treatment was carried out under the same atmosphere as the film formation conditions for the thin film under condition 8. That is, the pressure in the chamber where the heat treatment was carried out was set to 0.20 Pa, and the chamber was filled with argon (Ar) and oxygen (O ２ In the mixed gas supplied, the flow rate of oxygen was 14 SCCM and the flow rate of argon was 4 SCCM. ２ The / Ar ratio was set to 3.5.

[0092] The thin film was heated together with the substrate on which it was formed. The temperature of the substrate was set to 750°C, which was higher than the substrate temperature (700°C) during film formation under Condition 8. The heat treatment was carried out for 1 hour. Figure 19 shows the X-ray diffraction pattern of the thin film after this heat treatment.

[0093] From a comparison of the X-ray diffraction pattern of the thin film after the heat treatment shown in FIG. 19 with the X-ray diffraction pattern of the thin film under condition 8 (thin film before the heat treatment) shown in FIG. 12, no change in the peak intensity of palladium cobalt oxide before and after the heat treatment was confirmed.

[0094] (Production Example 4) Now, from the results of conditions 1 to 14, O ２ It was found that a / Ar ratio of about 3.5 is often favorable. It was also suggested that the substrate temperature should be less than 750°C. It was also found that a pressure of 0.20 Pa or less in the atmosphere during film formation is preferable because it reduces the amount of cobalt oxide in the thin film.

[0095] Therefore, using the target of Production Example 1, thin films according to conditions 15 to 28 (see Table 2) and conditions 29 to 34 (see Table 3) were produced and evaluated under the film formation conditions shown in Table 2 or Table 3. The other conditions were the same as those of Production Example 3. Tables 2 and 3 also show the evaluation results of these thin films. Note that the substrate heater temperature in the sputtering apparatus when the substrate temperature was 730°C was 775°C. The thin film according to condition 27 was obtained by subjecting the thin film according to condition 26 to heat treatment (post-annealing) at 800°C for 12 hours. Similarly, the thin film according to condition 31 was obtained by subjecting the thin film according to condition 30 to heat treatment at 800°C for 12 hours.

[0096]

[0097]

[0098] 20 to 33 show the X-ray diffraction patterns of the thin films under conditions 15 to 28, in that order. Also, FIGS. 34 to 38 show the X-ray diffraction patterns of the thin films under conditions 29 and conditions 31 to 34, in that order. Also, FIGS. 39 to 48 show SEM images of the thin films under conditions 23 to 27. The SEM images were taken using the SEM-EDX method described above. Furthermore, the elemental ratio of palladium to cobalt in the thin films under conditions 15 to 28 was measured using an ICP optical emission spectrometer. As with conditions 1 to 14, the Pd:Co ratio in all of the thin films was within the range of 48.8 to 49.0:51.2 to 51.0.

[0099] For the thin films under conditions 18 to 29 and conditions 31 to 33, the film thickness (nm) was determined in the same manner as in Production Example 3. The film thicknesses of these thin films are also shown in Tables 2 and 3. The thin films under conditions 18 to 28, 29, and 31 to 33 were produced with a film thickness of approximately 7.0 nm or more and 165.0 nm or less.

[0100] The electrical resistivity (Ωcm) at a temperature of 300 K and the electrical resistivity (Ωcm) at 2 K of the thin films formed under conditions 18 to 28 and 31 were measured in the same manner as in Production Example 3. The RRR was also determined in the same manner as in Production Example 3. The electrical resistivities and RRR of these thin films are shown in Tables 2 and 3.

[0101] As shown in Tables 2 and 3, in this production example, palladium cobalt oxide (PdCoO ２ ) was detected, and it was confirmed that a thin film containing palladium cobalt oxide could be formed under these conditions. Also, Fig. 49 shows a graph obtained by investigating the relationship between the pressure during film formation and the peak intensity ratio in X-ray diffraction under conditions 24, 29, and 32 to 34. The peak intensity ratio in X-ray diffraction is ２ (006) peak intensity I PdCoO2 As shown in FIG. 49, when the pressure during film formation is 0.5 Pa or less, the sum of the X-ray diffraction peak intensities of the impurities, ΣIimp, is ２ (006) peak intensity I PdCoO2 The content is kept to less than 1% of the original value, resulting in high-quality PdCoO ２ A thin film is obtained.

[0102] As described above, the larger the RRR value, the lower the crystal defect density, which is preferable for an electrode. In this production example, the thin films under the conditions for which RRR was evaluated (conditions 18 to 28 and condition 31) all had an RRR of 1 or more, which was favorable.

[0103] Furthermore, in the thin films obtained under the conditions under which the RRR was evaluated in this production example (conditions 18 to 28 and 31), the RRR was 1 or greater even when the film thickness was 20 nm or greater, 30 nm or greater, or even 100 nm or greater, and therefore it can be determined that the thin films are suitable for use in various devices. For example, the thin films are considered to be extremely suitable for use in Schottky electrodes in combination with gallium oxide or the like.

[0104] It can be seen that a higher (larger) RRR can be achieved by post-annealing the thin film (see condition 27). In the thin film under condition 27, which is obtained by post-annealing the thin film under condition 26, the RRR reaches 7.63, which is close to 8. Furthermore, under condition 31, the RRR is even higher, reaching 7.9, even though the film thickness is less than 30 nm. When the thin film used in this embodiment is used as a Schottky electrode or wiring, it is particularly preferable that the film has a film thickness of less than 30 nm and a high RRR. The thin film under condition 31 satisfies this requirement, and can be said to have extremely good properties as a Schottky electrode or wiring.

[0105] Here, the RRR of the metallic conductive delafossite oxide thin film produced using the target of the prior art is 1 or more and less than 3.

[0106] In contrast, an RRR of 3.0 or more and 8.0 or less was achieved under conditions 26, 27, and 31. From the above results, it became clear that this embodiment can form a delafossite-type oxide thin film with extremely low resistance, which has not been possible with the prior art.

[0107] Information on the RRR of metallic conductive delafossite-type oxide thin films prepared using targets according to the prior art is disclosed in, for example, the following Papers 1 to 5.

[0108] Paper 1: T. Harada et al., APL Materials 6, 046107 (2018)

[0109] Paper 2: P. Yordanov et al., Physical Review Materials 3, 085403 (2019)

[0110] Paper 3: JM Ok et al., APL Materials 8, 051104 (2020)

[0111] Paper 4: T. Miyakawa et al., Journal of Applied Physics 128, 025302 (2020)

[0112] Paper 5: T. Harada et al., Journal of Applied Physics 133, 085302 (2023)

[0113] In addition, as shown in FIGS. 39 to 48, a beautiful triangular crystal structure, which is characteristic of delafossite-type oxides, was observed in each thin film.

[0114] (Production Example 5) A target according to Production Example 5 was produced as follows.

[0115] An alloy powder (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) produced by gas atomization, in which the composition ratio (element ratio) of the platinum and cobalt alloy composition was 50:50 (the contents of platinum and cobalt were each approximately 50 at%), with the remainder being impurities, was filled into a mold as the powder to be sintered and sintered at 1250°C by a hot press sintering method in which pressure was applied in the thickness direction. The alloy powder was prepared by weighing both elements (both metals) so that the composition ratio (element ratio) of the alloy composition between platinum and cobalt was 50:50, heating the mixture to form a molten alloy, and then gas atomizing the molten alloy to obtain atomized powder.

[0116] The platinum to cobalt composition ratio in the obtained sintered product was 50.02:49.98 (the platinum and cobalt contents were 50.02 at% and 49.98 at%, respectively). 20 impurities were detected in the sintered product, resulting in an impurity concentration of 211 ppm. The purity of the platinum and cobalt alloy was 99.97 wt%. The sintered product was then processed to obtain a disk-shaped target for this manufacturing example. The disk surface and side surfaces of the target were ground to prepare it for subsequent use. After shape adjustment, the target was disk-shaped with a diameter of 50.8 mm and a thickness t of approximately 1.0 mm.

[0117] (Production Example 6) A thin film of platinum cobalt oxide (PtCoO2) was formed by reactive sputtering using the target of Production Example 5. The thin film formation in Production Example 6 was carried out by changing the target and film formation conditions as follows.

[0118] The substrate for thin film formation is Al ２ O ３A (sapphire) substrate (0001) was used. The substrate had been annealed at 1100°C for 2 hours. Fig. 50 shows a schematic cross-sectional view of the substrate on which a thin film of platinum cobalt oxide was formed. In Production Example 6, as shown in Fig. 50, a palladium cobalt oxide (PdCoO ２ A thin film of platinum-cobalt oxide was formed on the palladium-cobalt oxide film to a thickness of 13.8 nm.

[0119] Sputtering was performed using a sputtering device (model: ESCS-232S) manufactured by Eiko Engineering Co., Ltd. RF or DC power was applied between the target and substrate. The RF output was 60 W, 100 W, or 140 W, and its frequency was 13.56 MHz. The DC output was 60 W.

[0120] The pressure in the chamber where the film was formed was set to 0.15 Pa, 0.30 Pa, 1 Pa, or 5 Pa. The TS distance was set to 150 mm.

[0121] The reactive gas supplied to the chamber for reactive sputtering was a mixed gas of argon (Ar) and oxygen (O2). The flow rates of the reactive gases in the chamber were 4 sccm for argon and 14 sccm or 28 sccm for oxygen. ２ The / Ar ratio was set to 3.5 or 7.0.

[0122] The temperature of the substrate during film formation was 700° C. or 750° C. The temperature of the substrate was controlled by setting the temperature of the heater for the substrate in the sputtering apparatus to 750° C. or 800° C. in that order.

[0123] The film formation conditions were changed as described above to produce nine types of platinum-cobalt oxide thin films under conditions 35 to 42. Table 4 shows the film formation conditions under conditions 35 to 42. Table 5 also shows the evaluation results (described below) under conditions 35 to 42.

[0124]

[0125]

[0126] In Production Example 6, films were formed under Conditions 43 and 44, which will be described later, to compare with the platinum-cobalt oxide thin films under Conditions 35 to 42. Table 4 also shows the film formation conditions under Condition 43. Table 5 also shows the evaluation results under Conditions 43 and 44.

[0127] Under condition 43, a thin film of palladium cobalt oxide was not formed, and Al ２ O ３ A thin film of platinum cobalt oxide was formed directly on the substrate.

[0128] In addition, under condition 44, a thin film of platinum-cobalt oxide was not formed, and Al ２ O ３ Only a thin film of palladium cobalt oxide was formed on the substrate. Platinum cobalt oxide was deposited on this thin film of palladium cobalt oxide (a thin film of platinum cobalt oxide was formed) under conditions 37 to 42. The column for condition 44 in Table 5 shows the electrical resistivity and RRR values ​​for only the thin film of palladium cobalt oxide.

[0129] For the thin films under conditions 35 to 42, the film thickness (nm) was determined in the same manner as in Production Example 3. The film thicknesses of these thin films are also shown in Table 5. The platinum-cobalt oxide thin films under conditions 35 to 42 were produced with a film thickness of approximately 2.6 nm or more and 9.6 nm or less.

[0130] The electrical resistivity (Ωcm) at a temperature of 300 K and the electrical resistivity (Ωcm) at 2 K of the entire laminated film of palladium cobalt oxide and platinum cobalt oxide under conditions 37, 39, and 41 were measured in the same manner as in Production Example 3. Then, the RRR of the entire laminated film was determined in the same manner as in Production Example 3.

[0131] The electrical resistivity (Ωcm) at a temperature of 300 K and the electrical resistivity (Ωcm) at 2 K of the palladium cobalt oxide alone under conditions 37, 39 and 41 are the values ​​shown under condition 44 in Table 5.

[0132] Sheet resistance R of the entire laminated film total (Ω / sq) is the sheet resistance R of palladium cobalt oxide ＰｄＣｏＯ２ , and the sheet resistance R of platinum cobalt oxideＰｔＣｏＯ２ Using this, 1 / R total = 1 / R ＰｄＣｏＯ２ +1 / R ＰｔＣｏＯ２ The thin film under each condition was measured and R total Calculate the value of R ＰｄＣｏＯ２ By substituting this into the above equation, R ＰｔＣｏＯ２ asked for.

[0133] Electrical resistivity ρ of platinum cobalt oxide ＰｔＣｏＯ２ (Ωcm) is the thickness of the platinum-cobalt oxide film d ＰｔＣｏＯ２ (cm), ρ ＰｔＣｏＯ２ =R ＰｔＣｏＯ２ ×d ＰｔＣｏＯ２ The thickness of the entire delafossite phase is calculated from the period of the fringes near the delafossite phase (0006) peak in the X-ray diffraction, and the thickness of the palladium cobalt oxide is subtracted from this to obtain d ＰｔＣｏＯ２ By this procedure, ρ at 300K and 2K was calculated. ＰｔＣｏＯ２ and the ratio was calculated to calculate the RRR of the palladium cobalt oxide alone under conditions 37, 39, and 41. The electrical resistivity and RRR of these thin films are also shown in Table 5.

[0134] As shown in Table 5, under conditions 37, 39, and 41, the RRR was 2.1 to 5.0, which is 1 or more. In particular, under conditions 37 and 39, very high RRR values ​​of 3.0 to 5.0 were obtained. Since the RRR was 1 or more, it can be determined that the material can be suitably used in a variety of devices. For example, it is believed to be extremely suitable for use in Schottky electrodes in combination with gallium oxide or the like.

[0135] It can be seen that a good RRR can be achieved by post-annealing the thin film (see condition 41). The thin film according to condition 41, which is obtained by post-annealing the thin film according to condition 40, has a good RRR of 2.1.

[0136] Figures 51 to 53 show X-ray diffraction patterns of thin films according to conditions 35 to 37, in this order. Figure 54 shows an enlarged view of the X-ray diffraction pattern of the thin film according to condition 37. Figure 55 shows the X-ray diffraction pattern of the thin film according to condition 38. Figure 56 shows X-ray diffraction patterns of thin films according to conditions 39 and 44. Figure 57 shows an enlarged view of the X-ray diffraction pattern of the thin film according to condition 39. Figure 58 shows X-ray diffraction patterns of thin films according to conditions 40 and 44. Figure 59 shows an enlarged view of the X-ray diffraction pattern of the thin film according to condition 40. Figures 60 to 62 show X-ray diffraction patterns of thin films according to conditions 41 to 43.

[0137] 51 to 61, it was found that by using a thin film of palladium cobalt oxide (a first layer having a delafossite-type crystal structure) as a base, a platinum cobalt oxide having a delafossite-type crystal structure with good RRR can be deposited, that is, a thin film of platinum cobalt oxide (a second layer having a delafossite-type crystal structure, separate from the first layer) can be formed (an example of a multi-layer process). Furthermore, as shown in Fig. 62 (condition 43), it was also found that a platinum cobalt oxide layer having a delafossite-type crystal structure can be deposited under similar conditions on a sapphire substrate without a base of palladium cobalt oxide.

[0138] Now, a large RRR (residual resistance ratio) means that there is less scattering due to defects in the thin film or surface irregularities.

[0139] In the X-ray diffraction pattern under condition 31 shown in Figure 35, a clear oscillation of the diffraction intensity can be seen in the intermediate region between the 006 diffraction point (30.2°) and the 009 diffraction point (46.1°). The oscillation period is determined by the thickness of the thin film and is called the Laue oscillation, Laue flange, or film thickness flange.

[0140] This intensity oscillation is expressed by the Laue function shown in the following equation 1.

[0141]

[0142] Here, A is a coefficient, N is the number of planes, d is the plane spacing, θ is the diffraction angle, and λ is the wavelength of the X-rays. In a thin film with unevenness, functions with different vibration periods are added together and canceled out, causing the vibrations to disappear. Furthermore, when the crystallinity is low, the diffraction intensity is weak and vibrations are not observed. For this reason, Laue oscillations are observed only when both the crystallinity and flatness are extremely high.

[0143] The delafossite-type oxide has the general formula ABO ２ (A is Pd or Pt, and B is Co, Cr or Rh).

[0144] FIG. 63 shows a comparison between an enlarged view of the X-ray diffraction pattern of the thin film according to condition 31 (shown as "Experimental Results" in FIG. 63) and a simulation result showing how the Laue oscillation changes depending on the number N of Pd atomic layers, which is an example of atoms at the A site of the delafossite-type oxide.

[0145] 63 shows the simulation results for N=47, where N=46, 47, and 48 exist with equal probability (when N=47 is about 33%), and N=45, 46, 47, 48, and 49 exist with equal probability (when N=47 is 20%). Here, as with the X-ray diffraction pattern of the thin film under condition 31, the value of coefficient A was set so that the peak intensity of the 006 diffraction point and the 009 diffraction point would be approximately 2000 times the noise level described below. The interplanar spacing d was set to PdCoO ２ 63, the simulation result when N=47 is shown as "Simulation (N=47)," the simulation result when N=46, 47, and 48 exist with equal probability is shown as "Simulation (N=46, 47, 48)," and the simulation result when N=45, 46, 47, 48, and 49 exist with equal probability is shown as "Simulation (N=45, 46, 47, 48, 49)."

[0146] As mentioned above, the interplanar spacing d is PdCoO ２When the Pd interlayer distance is substituted, it can be seen that the diffraction pattern of the experimental data can be well reproduced by adding a noise level equivalent to that of the X-ray diffraction pattern of the thin film according to condition 31 to the function when N=47. Therefore, the number N of A site layers in the thickness direction of the thin film according to condition 31 is considered to be 47.

[0147] In a simulation in which N=46, 47, and 48 exist with equal probability (N=47 is approximately 33%), it can be seen that the vibration in the region between the 006 diffraction point and the 009 diffraction point is partially suppressed and disappears.

[0148] Furthermore, in a simulation in which N=45, 46, 47, 48, and 49 exist with equal probability (N=47 is 20%), the oscillation in the region between the 006 diffraction point and the 009 diffraction point is further suppressed.

[0149] In the X-ray diffraction pattern of the thin film under condition 31, a tendency for the Laue oscillations in the region between the 006 diffraction point and the 009 diffraction point to continue uninterrupted can be seen. Comparing this tendency with the simulation results, it is found that this tendency applies to both the case of N = 47 (when N = 47 is 100%) and the cases of N = 46, 47, and 48 (when N = 47 is approximately 33%). Therefore, the thin film under condition 31 is considered to have high homogeneity, with the proportion of N = 47 being 33% or more, which is considered to contribute to the realization of a high RRR. Note that the thin film under condition 31 having high homogeneity, with the proportion of N = 47 being 33% or more, means that 33% or more of the area of ​​the thin film is composed of 47 A-site layers, the same number as the number of A-site layers in the thickness direction of the thin film under condition 31. Thus, from the results of the thin film under condition 31, when the number of A site layers in the thickness direction is N, a high RRR is achieved when 33% or more of the area of ​​the thin film has the same N.

[0150] Figure 64 shows a topography image (atomic force microscope image) of the thin film according to condition 31 measured with an atomic force microscope. In this topography image, triangular or hexagonal crystal facets derived from the trigonal crystal structure of delafossite are observed. Such crystal facets are generally observed when the sample has high crystallinity.

[0151] 64, it can be seen that the surface of the thin film according to condition 31 is flat, with the root mean square (RMS) of the unevenness height in the thickness direction being 0.35 nm (0.4 nm or less). It is believed that the flatness of the surface of the thin film according to condition 31 contributes to the high RRR.

[0152] As described above, the thin film according to condition 31 has a structural feature of high crystallinity, with 33% or more of the area of ​​the thin film being homogeneous with the same N, an RMS of 0.4 nm or less, minimal surface irregularities, and clear triangular or hexagonal crystal facets observed in the thin film. These features are the reason why the thin film according to condition 31 achieves a high RRR. This is thought to be true for other delafossite-type oxide thin films (oxide thin films having a delafossite-type crystal structure) according to this embodiment.

[0153] In this manner, a method for producing a delafossite-type oxide thin film can be provided.

[0154] It should be noted that the embodiments disclosed in this specification are merely examples, and the embodiments of the present disclosure are not limited to these, and can be modified as appropriate within the scope of the purpose of the present disclosure.

[0155] The present disclosure can be applied to a method for producing a delafossite-type oxide thin film and to an oxide thin film.

Claims

1. The process includes a film deposition step in which a thin film is formed by physical vapor deposition using a target containing a primary metal and a secondary metal, The aforementioned target is The first metal is palladium or platinum, A method for producing a delafossite-type oxide thin film, wherein the secondary metal is cobalt, chromium, or rhodium.

2. The aforementioned target is The above first metal contains 45 at% or more and 90 at% or less, The remainder consists of the second metal and impurities. The content of the aforementioned impurities is 500 ppm by mass or less. The method for producing a delafossite-type oxide thin film according to claim 1, wherein the amount of oxygen as an impurity is 200 ppm by mass or less.

3. A method for producing a delafossite-type oxide thin film according to claim 1 or 2, further comprising a sintering step of producing the target by sintering a metal powder containing 45 at% or more and 90 at% or less of the first metal, with the remainder being the second metal and impurities.

4. The method for producing a delafossite-type oxide thin film according to claim 3, wherein the metal powder is an alloy powder of the first metal and the second metal.

5. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the pressure of the atmosphere when forming the thin film is 0.5 Pa or less in the film formation step.

6. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein in the film formation step, the ratio of oxygen to argon in the atmosphere when forming the thin film is 2 or more and 4 or less.

7. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the temperature of the substrate on which the thin film is formed during the thin film formation step is 500°C or higher and 850°C or lower.

8. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the temperature of the substrate on which the thin film is formed is 610°C or higher and 800°C or lower when the thin film is formed in the thin film formation step.

9. In the aforementioned film formation process, The atmospheric pressure when forming the thin film is 0.5 Pa or less. The ratio of oxygen to argon in the atmosphere when forming the thin film is 2 or more and 7 or less. A method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the temperature of the substrate on which the thin film is formed is 500°C or higher and 850°C or lower when the thin film is formed.

10. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the target comprises 45 at% or more and 60 at% or less of the first metal.

11. The method for producing a delafossite-type oxide thin film according to claim 1 or 2, wherein the film formation step includes a multilayering step of laminating a second layer having a delafossite-type crystal structure, which is different from the first layer, on a first layer having a delafossite-type crystal structure as a substrate.

12. An oxide thin film having a delafossite-type crystal structure, and a residual resistivity ratio, which is the value obtained by dividing the electrical resistivity at 300 K by the electrical resistivity at 2 K, is between 1.0 and 8.

0.

13. The oxide thin film according to claim 12, wherein the residual resistance ratio is 3.0 or more and 8.0 or less.

14. The oxide thin film according to claim 12 or 13, wherein the film thickness is 7.0 nm or more and 165.0 nm or less.

15. The oxide thin film according to claim 12 or 13, wherein the film thickness is 30 nm or more.

16. A first layer having a delafossite-type crystalline structure, The oxide thin film according to claim 12 or 13, comprising a second layer having a delafossite-type crystalline structure, which is laminated on the first layer and is different from the first layer.

17. The oxide thin film according to claim 12 or 13, where N is the number of A-site layers in the thickness direction, and 33% or more of the area of ​​the thin film has the same N.

18. The oxide thin film according to claim 12 or 13, wherein triangular or hexagonal crystalline facets appear on the surface, and the root mean square of the surface irregularity height is 0.4 nm or less.

19. An oxide thin film having a delafossite-type crystal structure, in which, when N is the number of A-site layers in the thickness direction, 33% or more of the area of ​​the thin film has the same N.

20. An oxide thin film having a delafossite-type crystal structure, with triangular or hexagonal crystal facets appearing on the surface, and the root mean square of the surface irregularity height in the thickness direction being 0.4 nm or less.