Al-Sc-Ga sputtering target and method for manufacturing the same

Abstract

This Al-Sc-Ga sputtering target comprises a body part that contains Al, Sc and Ga and does not contain a Ga phase. In the body part, the atomic number ratio (Sc / Ga) of Sc to Ga may be 0.5 or more. In the body part, the atomic number ratio (Sc / Ga) of Sc to Ga may be 20 or less. The Al-Sc-Ga sputtering target may further comprise a backing plate joined to the body part via a joining material.

Description

[Technical Field]

[0001] The present disclosure relates to an Al—Sc—Ga sputtering target and a method for manufacturing the same. [Background technology]

[0002] In recent years, there has been growing interest in non-volatile ferroelectric memories, and from the viewpoint of high ferroelectricity and reduced driving voltage, aluminum scandium gallium nitride (hereinafter also referred to as "AlScGaN") films are expected to be suitable films for ferroelectric memories (see Non-Patent Document 1).

[0003] Non-Patent Document 1 describes that the AlScGaN film is formed by a ternary simultaneous reactive sputtering method using an Al target, an Sc target, and a GaN target. However, as described in Non-Patent Document 1, when three types of targets are used, the power of each of the three types of targets must be controlled individually during sputtering, which makes the control process complicated. Therefore, it has been desired to use a single target, such as an Al-Sc-Ga sputtering target, for depositing an AlScGaN film. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ota, Reika, and six others, “Crystal Structure and Ferroelectricity of (Al1-x-yGaxScy)N Thin Films”, [online], September 20, 2022, Autumn Meeting of the Japan Society of Applied Physics, 20p-B103-10, [Retrieved February 10, 2023], Internet <URL:https: / / confit.atlas.jp / guide / event / jsap2022a / subject / 20p-B103-10 / tables?cryptoId=> Summary of the Invention [Problem to be solved by the invention]

[0005] However, when an actual sputtering target was produced by bonding an Al-Sc-Ga alloy body to a backing plate via a bonding material, a defect occurred in which the body peeled off from the backing plate during sputtering.

[0006] An object of the present disclosure is to provide at least one of an Al-Sc-Ga sputtering target capable of suppressing peeling of the main body portion and a method for manufacturing the same. [Means for solving the problem]

[0007] The inventors of the present disclosure investigated the cause of peeling of the main body. First, the inventors visually observed the surface of the main body and noticed that liquid metal was melting. Meanwhile, when powder X-ray diffraction measurements were performed on the cross section of the main body, it was found that an XRD peak of the (111) plane of metallic Ga appeared around a diffraction angle 2θ = 30.37°. Furthermore, the melting point of metallic Ga is 29.8°C. Based on this, the inventors of the present disclosure suspected that metallic Ga contained in the Al-Sc-Ga alloy melted and fused during sputtering, and that the molten metallic Ga came into contact with the bonding material to form a low-melting-point alloy, which melted a portion of the bonding material, causing peeling of the main body. This led the inventors to arrive at the present disclosure.

[0008] The contents of the present invention are as set forth in the claims, and the gist of the present disclosure is as follows. (1) An Al-Sc-Ga sputtering target having a main body containing Al, Sc, and Ga and not containing a Ga phase. (2) The Al-Sc-Ga sputtering target according to (1), wherein the atomic ratio of Sc to Al (Sc / Al) in the main body is 0.25 or more. (3) The Al—Sc—Ga sputtering target according to (1) or (2), wherein the atomic ratio of Sc to Ga (Sc / Ga) in the main body is 0.5 or more. (4) The Al—Sc—Ga sputtering target according to any one of (1) to (3), wherein the atomic ratio of Sc to Ga (Sc / Ga) in the main body is 20 or less. (5) The Al—Sc—Ga sputtering target according to any one of (1) to (4), further comprising a backing plate joined to the main body via a joining material. (6) A method for producing an Al-Sc-Ga sputtering target, comprising a first step of producing a main body portion containing Al, Sc, and Ga, but not containing a Ga phase. (7) The method for producing an Al-Sc-Ga sputtering target according to (6), wherein in the first step, the main body is produced so that the atomic ratio of Sc to Al (Sc / Al) is 0.25 or more. (8) The method for producing an Al-Sc-Ga sputtering target according to (6) or (7), wherein in the first step, the main body is produced so that the atomic ratio of Sc to Ga (Sc / Ga) is 0.5 or more. (9) The method for producing an Al-Sc-Ga sputtering target according to any one of (6) to (8), wherein in the first step, the main body is produced so that the atomic ratio of Sc to Ga (Sc / Ga) is 20 or less. (10) The method for producing an Al-Sc-Ga sputtering target according to any one of (6) to (9), further comprising a second step of bonding a backing plate to the main body portion via a bonding material. [Effects of the Invention]

[0009] According to the present disclosure, there is provided at least one of an Al-Sc-Ga sputtering target capable of suppressing peeling of the main body portion and a method for manufacturing the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing one embodiment of an Al—Sc—Ga sputtering target according to the present disclosure. [Figure 2]1A and 1B are diagrams showing an SEM image and an element mapping image of the sputtering target according to Example 1. [Figure 3] 1A and 1B are diagrams showing an SEM image and an element mapping image of the sputtering target according to Comparative Example 1. [Figure 4] FIG. 1 is a diagram showing the results of powder X-ray diffraction measurement according to Example 1. [Figure 5] FIG. 1 is a diagram showing the results of powder X-ray diffraction measurement according to Example 2. [Figure 6] FIG. 1 is a diagram showing the results of powder X-ray diffraction measurement according to Example 3. [Figure 7] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Example 4. [Figure 8] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Example 5. [Figure 9] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Example 6. [Figure 10] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Example 7. [Figure 11] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Example 8. [Figure 12] FIG. 1 is a diagram showing the results of powder X-ray diffraction measurement according to Comparative Example 1. [Figure 13] FIG. 10 is a diagram showing the results of powder X-ray diffraction measurement according to Comparative Example 2. [Figure 14] FIG. 10 is a diagram showing the results of measuring the peak pattern of X-ray diffraction of an Al—Sc—Ga—N film obtained using the sputtering target according to Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present disclosure will be described in detail using an example. However, the present disclosure is not limited to the following embodiment. In addition, the present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of the upper and lower limits of the values ​​disclosed herein.

[0012] <Al-Sc-Gaスパッタリングターゲット> First, one embodiment of an Al—Sc—Ga sputtering target of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing one embodiment of an Al—Sc—Ga sputtering target of the present disclosure.

[0013] As shown in FIG. 1, an Al—Sc—Ga sputtering target (hereinafter also simply referred to as “target”) 100 includes a main body 10 containing Al, Sc, and Ga but not containing a Ga phase. The target 100 may further include a backing plate 20 bonded to the main body 10 via a bonding material 30 .

[0014] According to the target 100, when the backing plate 20 is joined to the main body 10 via the joining material 30, even if the main body 10 is sputtered in that state and the temperature of the main body 10 rises, the melting of metallic Ga on the surface is suppressed, the formation of a low-melting point alloy between the joining material 30 and Ga is suppressed, and peeling of the main body 10 from the backing plate 20 due to melting of the low-melting point metal is suppressed. Furthermore, even when the target 100 is placed in the sputtering device with the main body 10 facing downward relative to the backing plate 20, the liquid metal Ga is prevented from falling, thereby suppressing the adverse effects on the sputtering device caused by the falling metal Ga. Furthermore, since the main body 10 does not contain a Ga phase, which has a melting point of 29.8°C, even if the main body 10 is heated, the Ga phase is prevented from melting and melting out of the main body 10 as liquid metallic Ga. This prevents metallic Ga melted on the surface of the main body 10 from making the plasma unstable during sputtering while the main body 10 of the target 100 is being sputtered. This prevents the uniformity of the characteristics from decreasing when an AlScGaN film is formed by reactive sputtering while supplying nitrogen into the sputtering apparatus.

[0015] The main body 10, the backing plate 20, and the bonding material 30 will be described in detail below.

[0016] (Main body) The main body 10 is made of Al, Sc, and Ga, and does not contain a Ga phase. The Ga phase is a phase made of metallic Ga. "Does not contain a Ga phase" means that when powder X-ray diffraction (hereinafter also referred to as "XRD") measurement is performed on a cross section of the main body 10 in the thickness direction under the following conditions, an XRD peak of the (111) plane of metallic Ga does not appear near 2θ=30.37°. Here, "no XRD peak appears" means that "the XRD peak intensity is 10% or less of the maximum peak intensity at 2θ=20 to 40°." The XRD measurement can be performed using, for example, a crystallography X-ray diffractometer (device name: Ultima IV, manufactured by RIGAKU Corporation). <Condition> Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation Measurement mode: Continuous scan Scan condition: 2° / min Measurement range: 2θ=20° to 80° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1 / 2° Receiving slit: 0.3 mm

[0017] The main body 10 may include an alloy phase. An example of the alloy phase is a phase composed of an alloy containing two or more metal elements. Examples of such alloys include an alloy of Sc and Al, and an alloy of Sc and Ga. Two or more of these alloys may be included. The main body 10 may also include at least one of an Al phase and an Sc phase.

[0018] In the main body 10, the Al content is not particularly limited, but is preferably 80% or less, and more preferably 70% or less, based on the total number of Al, Sc, and Ga atoms (100%). When the Al content is 80% or less, based on the total number of Al, Sc, and Ga atoms (100%), the thin film formed by sputtering using the Al-Sc-Ga sputtering target of the present disclosure can exhibit high dielectric properties. The Al content is preferably 20% or more, and more preferably 30% or more, based on the total number of Al, Sc, and Ga atoms (100%). The upper and lower limits may be any combination of the above.

[0019] In the main body 10, the Sc content is not particularly limited, but is preferably 30% or more, and more preferably 40% or more, based on the total number of Al, Sc, and Ga atoms (100%). When the Sc atom content is 30% or more, based on the total number of Al, Sc, and Ga atoms (100%), the target does not contain a metallic Ga phase, making it easy to process the target. The Sc content is preferably 90% or less, and more preferably 80% or less, based on the total number of Al, Sc, and Ga atoms (100%). The upper and lower limits may be any combination of the above.

[0020] In the main body 10, the Ga content is not particularly limited, but is preferably 30% or less, and more preferably 20% or less, based on the total number of Al, Sc, and Ga atoms (100%). When the Ga content is 30% or less, based on the total number of Al, Sc, and Ga atoms (100%), the target does not contain a metallic Ga phase, making it easy to process the target. The content of Ga is preferably 5% or more, and more preferably 10% or more, based on the total number of Al, Sc, and Ga atoms (100%). The upper and lower limits may be any combination of the above. The total of the Al content, the Sc content, and the Ga content is 100%.

[0021] In the main body 10, the atomic ratio of Sc to Ga (Sc / Ga) is not particularly limited as long as it is greater than 0, but may be greater than 0.25, preferably greater than 0.5, more preferably greater than 2, and particularly preferably greater than 4. When Sc / Ga is 0.5 or greater, melting of metallic Ga in the target 100 is effectively suppressed. Sc / Ga is preferably equal to or less than 20, more preferably equal to or less than 10, and particularly preferably equal to or less than 8. When Sc / Ga is equal to or less than 20, the main body 10 can be manufactured inexpensively. The upper and lower limits may be any combination of the above.

[0022] The atomic ratio of Sc to Al (Sc / Al) is not particularly limited as long as it is greater than 0, but is preferably 0.25 or greater, and more preferably 0.5 or greater. When the Sc / Al ratio is 0.25 or greater, when a sputtering thin film is formed using the Al-Sc-Ga sputtering target of the present disclosure, the thin film can exhibit high dielectric properties. The Sc / Al ratio is preferably 2 or less, and more preferably 1.5 or less. The upper and lower limits may be any combination of the above.

[0023] The thickness of the main body 10 is not particularly limited, but may be 30 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, or 8 mm or less. The thickness of the main body 10 may be 1 mm or more, 2 mm or more, 3 mm or more, or 5 mm or more. The upper and lower limits may be any combination of the above.

[0024] (backing plate) The backing plate 20 is used to cool the main body 10 during sputtering of the main body 10, and is made of, for example, oxygen-free copper, titanium, stainless steel, or the like.

[0025] (Bonding material) The bonding material 30 is not particularly limited as long as it is composed of a material capable of bonding the main body 10 and the backing plate 20. However, at least one of indium and tin (indium, tin, or an alloy of indium and tin) is preferably used in terms of suppressing heat diffusion and thermal expansion during sputtering.

[0026] (Manufacturing method of Al-Sc-Ga sputtering target) Next, the manufacturing method of the Al-Sc-Ga sputtering target of the present disclosure will be described. The manufacturing method of the Al-Sc-Ga sputtering target of the present disclosure includes a step of manufacturing the main body 10 so as to contain Al, Sc, and Ga and not contain a Ga phase (hereinafter, also referred to as "the first step"). The manufacturing method of the Al-Sc-Ga sputtering target of the present disclosure may further include a second step of bonding the backing plate 20 to the main body 10 via the bonding material 30 after the first step to obtain the Al-Sc-Ga sputtering target 100. That is, the main body 10 obtained in the first step may be used as the Al-Sc-Ga sputtering target as it is, or the one obtained by bonding the backing plate 20 to the main body 10 via the bonding material 30 in the second step may be used as the Al-Sc-Ga sputtering target 100.

[0027] According to the manufacturing method of the Al-Sc-Ga sputtering target, the Al-Sc-Ga sputtering target 100 capable of suppressing the peeling of the main body 10 can be manufactured.

[0028] Hereinafter, the first step will be described in detail. Specifically, the main body 10 is obtained by melting a mixture of Al, Sc, and Ga raw materials to form a fused mass, and then performing post-processing on the fused mass as needed. In this case, the Ga raw material does not easily form an alloy with the Al raw material, but readily forms an alloy with the Sc raw material. Therefore, by adjusting the atomic ratio of Al, Sc, and Ga in the Al, Sc, and Ga raw materials in a well-balanced manner, the formation of a Ga phase can be easily prevented. The method for melting the mixture of Al, Sc, and Ga raw materials is not particularly limited, and examples include a melting method and an arc melting method. These methods allow for easy production of a fused mass. Post-processing of the fused mass includes, for example, gas atomizing the fused mass into fine powder particles, and then sintering the powder particles using any sintering method, such as hot pressing. This post-processing method allows for the production of a main body 10 having fine crystal grains.

[0029] The mixture of the raw materials is prepared so that Sc / Ga is, for example, greater than 0.25, preferably 0.5 or more, more preferably 2 or more, and particularly preferably 4 or more. When Sc / Ga is 0.5 or more, it becomes easier to prevent the formation of a Ga phase. The mixture of the above raw materials is prepared so that Sc / Ga is preferably 20 or less, more preferably 10 or less, and particularly preferably 8 or less. When Sc / Ga is 20 or less, the main body 10 can be manufactured inexpensively. The upper and lower limits may be any combination of the above.

[0030] The mixture of raw materials is prepared so that the atomic ratio of Sc to Al (Sc / Al) is preferably 0.25 or more, more preferably 0.5. When Sc / Al is 0.25 or more, the Sc raw material is likely to form an alloy with the Ga raw material, making it easier to prevent the formation of a Ga phase. The mixture of the above raw materials is prepared so that Sc / Al is preferably 2 or less, more preferably 1.5 or less. The upper and lower limits may be any combination of the above.

[0031] The form of each raw material is not particularly limited, and may be in the form of powder, flakes, or ingots.

[0032] The mixture of Al, Sc, and Ga raw materials can be heated in a container such as a crucible or a mold. The crucible and mold may be made of a material that does not melt at the melting point of the Sc raw material, which has the highest melting point among the Al, Sc, and Ga raw materials, and may be made of, for example, alumina, zirconia, or water-cooled copper.

[0033] The heating temperature of the raw materials may be any temperature equal to or higher than the melting point of the Al raw material, the Sc raw material, and the Ga raw material. Of the Al raw material, the Sc raw material, and the Ga raw material, the Sc raw material has the highest melting point, which is 1541°C, so the heating temperature may be any temperature equal to or higher than 1541°C. However, the heating temperature of the raw material is preferably 1800°C or lower, and more preferably 1700°C or lower. The upper and lower limits may be any combination of the above.

[0034] The heating time for the raw materials is not particularly limited, and may be 0.25 hours or more, 0.5 hours or more, 1 hour or more, or 3 hours or more. However, in consideration of production efficiency, the heating time of the raw material may be 10 hours or less, 8 hours or less, 6 hours or less, or 5 hours or less. The upper and lower limits may be any combination of the above.

[0035] Post-processing may involve processing the fused material into a plate shape by, for example, grinding or cutting. Specific processing means include machining machines such as a surface grinder, a cylindrical grinder, a lathe, a cutting machine, or a machining center. [Example]

[0036] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0037] Example 1 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were placed in an alumina crucible with an inner diameter of 25 mm, an outer diameter of 35 mm, and a height of 60 mm so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga=30:50:20. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the crucible in order of increasing melting point (i.e., Sc, Al, Ga). The crucible was then placed in a heating furnace. The mixture was heated to 1600°C in an Ar atmosphere for 0.5 hours to melt, and then cooled to room temperature. Thus, an Al-Sc-Ga sputtering target having an ingot as the main body, with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=30:50:20, was obtained by the melting method.

[0038] Example 2 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were charged into an alumina crucible so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga=30:60:10. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the crucible in order of increasing melting point (i.e., Sc, Al, Ga). The crucible was then placed in a heating furnace. The mixture was heated to 1600°C in an Ar atmosphere for 0.5 hours to melt, and then cooled to room temperature. Thus, an Al-Sc-Ga sputtering target having an ingot as the main body, with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=30:60:10, was obtained by the melting method.

[0039] Example 3 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were charged into an alumina crucible so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga=50:30:20. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the crucible in descending order of melting point (i.e., Sc, Al, Ga). The crucible was then placed in a heating furnace. The mixture was heated to 1600°C in an Ar atmosphere for 0.5 hours to melt, and then cooled to room temperature. Thus, an Al-Sc-Ga sputtering target having an ingot main body with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga = 50:30:20 was obtained by the melting method.

[0040] Example 4 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were placed in an alumina crucible with an inner diameter of 25 mm, an outer diameter of 35 mm, and a height of 60 mm so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 30:30:40. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the crucible in order of increasing melting point (i.e., Sc, Al, Ga). The crucible was then placed in a heating furnace. The mixture was heated to 1600°C in an Ar atmosphere for 0.5 hours to melt, and then cooled to room temperature. Thus, an Al-Sc-Ga sputtering target having an ingot as the main body, with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=30:30:40, was obtained by the melting method.

[0041] Example 5 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were charged into a water-cooled copper mold with a diameter of 35 mm and a height of 10 mm so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 30:30:40. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the mold in descending order of melting point (i.e., Sc, Al, Ga). The raw materials in the mold were then melted in an arc melting furnace under an Ar atmosphere at 100 A for 5 minutes, and then cooled to room temperature. In this way, an Al-Sc-Ga sputtering target having an ingot as the main body with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=30:30:40 was obtained by the arc melting method.

[0042] Example 6 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were charged into a water-cooled copper mold with a diameter of 65 mm and a height of 12 mm so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 40:50:10. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the mold in descending order of melting point (i.e., Sc, Al, Ga). The raw materials in the mold were then melted in an arc melting furnace under an Ar atmosphere at 100 A for 5 minutes, and then cooled to room temperature. In this way, an Al-Sc-Ga sputtering target having an ingot main body with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=40:50:10 was obtained by the arc melting method.

[0043] Example 7 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were charged into a water-cooled copper mold with a diameter of 35 mm and a height of 10 mm so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 20:75:5. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the mold in descending order of melting point (i.e., Sc, Al, Ga). The raw materials in the mold were then melted in an arc melting furnace under an Ar atmosphere at 100 A for 5 minutes, and then cooled to room temperature. In this way, an Al-Sc-Ga sputtering target having a main body with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga=20:75:5 was obtained by the arc melting method.

[0044] Example 8 An Al raw material, an Sc raw material, and a Ga raw material were prepared. Next, these raw materials were weighed so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 40:50:10, and then poured into a water-cooled copper mold with a diameter of 35 mm and a height of 10 mm. At this time, the Al raw material, the Sc raw material, and the Ga raw material were placed from the bottom of the mold in descending order of melting point (i.e., Sc, Al, Ga). The raw materials in the mold were then melted by arc melting. Specifically, the raw materials in the mold were heated in an arc melting furnace under an Ar atmosphere at 100 A for 5 minutes to melt them. In this way, an ingot was produced with an atomic ratio of Al, Sc, and Ga of Al:Sc:Ga = 40:50:10. The ingot was placed in an alumina crucible for gas atomization, and powder was produced under the gas atomization conditions described below. In this way, a powder with an Al:Sc:Ga = 40:50:10 was obtained by the gas atomization method. <Gas atomization conditions> Temperature: 1400℃ Gas: Ar Gas pressure: 3MPa Thereafter, the powder was sintered by hot pressing under the following conditions to obtain an Al-Sc-Ga sputtering target having a main body made of a sintered body with Al:Sc:Ga=40:50:10. <Condition> Temperature: 1050℃ Holding time: 3h Atmosphere: Vacuum Pressure: 20 MPa

[0045] (Comparative Example 1) An Al raw material and a Ga raw material were prepared. Next, these raw materials were charged into an alumina crucible so that the atomic ratio of Al to Ga was Al:Ga = 80:20. At this time, the Al raw material and the Ga raw material were placed from the bottom of the crucible in descending order of melting point (i.e., Al, Ga). The crucible was then placed in a heating furnace. The mixture was then heated to 1200°C for 0.5 hours in an Ar atmosphere to melt it. Thus, an Al-Ga-based sputtering target having an ingot as the main body, with an Al:Ga atomic ratio of Al:Ga = 80:20, was obtained by the melting method.

[0046] (Comparative Example 2) Al raw materials, Sc raw materials, and Ga raw materials were prepared. Next, these raw materials were put into a crucible made of alumina so that the atomic ratio of Al, Sc, and Ga was Al:Sc:Ga = 25:15:60. At this time, the Al raw materials, Sc raw materials, and Ga raw materials were placed in order of decreasing melting point (i.e., in the order of Sc, Al, Ga) from the bottom of the crucible. After that, the crucible was placed in a heating furnace. Then, the mixture was heated and melted at 1600 °C for 0.5 hours in an Ar atmosphere. Thus, an Al - Sc - Ga sputtering target having an ingot with an atomic ratio of Al:Sc:Ga = 25:15:60 as the main body was obtained by the melting method.

[0047] <Confirmation of the presence or absence of the Ga phase> Regarding the cross-section in the thickness direction of the main body of the sputtering targets of Examples 1 to 8 obtained as described above, powder X-ray diffraction (XRD) measurement was performed at room temperature (25 °C or lower) under the following conditions. The XRD measurement was performed using a crystalline analysis X-ray diffractometer (device name: UltimaIV, manufactured by Rigaku Corporation). <Conditions> Accelerating current · voltage: 40 mA · 40 kV X-ray source: CuKα ray Measurement mode: Continuous scan Scan condition: 2° / min Measurement range: 2θ = 20° to 80° Divergence vertical limiting slit: 10 mm Divergence / incidence slit: 1 / 2° Receiving slit: 0.3 mm On the other hand, regarding the sputtering targets of Comparative Examples 1 to 2 obtained as described above, since the main body would break into pieces and turn into powder when cut, XRD measurement was performed in the same manner as in Example 1 in the form of powder. In the above measurement, the presence or absence of an XRD peak of the (111) plane of metallic Ga appearing near 2θ=30.37° was determined to confirm whether the main body of the sputtering target contained a Ga phase. The results are shown in Table 1. Note that for Examples 1 to 8 and Comparative Examples 1 and 2, the results of the XRD measurements are shown in Figures 4 to 13. In Figures 4 to 11, an XRD peak of the (111) plane of metallic Ga was not observed near 2θ=30.37°. In contrast, in Figures 12 and 13, an XRD peak of the (111) plane of metallic Ga was observed near 2θ=30.37°. The sputtering targets of Examples 1 to 8 and Comparative Examples 1 and 2 obtained as described above were cut in the thickness direction, and then the cross sections were mirror-polished. The cross sections were observed using an EDS-equipped SEM (manufactured by JEOL Ltd., product name "JSM-IT800") to obtain a mapping image of Ga elements. For Example 1 and Comparative Example 1, SEM images and element mapping images are shown in Figures 2 and 3. In Figure 2, (a) shows an SEM image, (b) shows a mapping image of Al element, (c) shows a mapping image of Sc element, and (d) shows a mapping image of Ga element. In Figure 3, (a) shows an SEM image, (b) shows a mapping image of Al element, and (c) shows a mapping image of Ga element. In Figure 2(d), no color shading is visible, and the image is entirely dark. This indicates that Ga elements are not segregated, i.e., Ga phase (single phase of Ga elements) is not present. On the other hand, in Figure 3(c), there is a difference in color. Here, the dark areas indicate that Ga elements are not segregated, i.e., Ga phase is not present. In contrast, the light areas indicate that Ga elements are segregated, i.e., Ga phase is present. Therefore, it is clear that in Example 1, the main body does not contain a Ga phase, whereas in Comparative Example 1, the main body contains a Ga phase.

[0048] <Evaluation of sputtering targets> A metallic Ga melting test was conducted on the sputtering targets of Examples 1 to 8 and Comparative Examples 1 and 2. Specifically, the sputtering targets were held in an incubator at 60°C for 3 hours, and the presence or absence of metallic Ga melting was visually confirmed. After holding, the targets were removed from the incubator, and if no liquid metal had melted in the area where the target had been placed in the incubator, the presence or absence of metallic Ga melting was judged to be "absent." If liquid metal had melted, the targets were cooled and the presence or absence of metallic Ga melting was judged to be "present." The results are shown in Table 1. When the melted liquid metal in Comparative Examples 1 and 2 was subjected to XRD measurement under the above conditions, an XRD peak of the (111) plane of metallic Ga was confirmed near 2θ = 30.37°.

[0049] [Table 1]

[0050] From the results shown in Table 1, no dissolution of metallic Ga was observed in the sputtering targets of Examples 1 to 8. In contrast, in Comparative Examples 1 and 2, a Ga phase was "present." From this, it was confirmed that, according to the Al—Sc—Ga sputtering target of the present disclosure, the main body does not contain a Ga phase, and therefore, the melting of metallic Ga can be suppressed. Therefore, according to the Al-Sc-Ga sputtering target of the present disclosure, even when it is bonded to a backing plate via a bonding material, the molten metallic Ga does not come into contact with the bonding material to form a low-melting point alloy, and it is therefore believed that peeling of the main body due to melting of the low-melting point alloy can be suppressed.

[0051] (Sputtering deposition) The main body obtained in each example was bonded to a copper backing plate via an indium bonding material to obtain a sputtering target. A film formation test was then performed using this target under the following conditions. An 800 nm thick Al-Sc-Ga-N film was obtained without any peeling between the main body and the backing plate. The ratio of Al, Sc, and Ga in the thin film (Al:Sc:Ga) can be considered to be the same as the ratio of Al, Sc, and Ga in the main body (Al:Sc:Ga). The ratio of nitrogen contained in the Al-Sc-Ga-N film is not particularly limited, but may be, for example, 20% or more, 30% or more, or 40% or more, or 70% or less, 60% or less, or 50% or less, as the ratio of the number of nitrogen atoms to the total number of Al, Sc, Ga, and N atoms. Further examples include 20% or more and 70% or less, 30% or more and 60% or less, or 40% or more and 50% or less. <Condition> Equipment used: CMS-6400 combi sputtering equipment Film formation method: Magnetron sputtering Ultimate pressure: 1.0×10 -5 Pa Sputtering gas: Ar + 25% N2 Sputtering pressure: 0.3 Pa Substrate: Silicon Lower electrode layer: Molybdenum (thickness: 200 nm) Upper electrode layer: Molybdenum (thickness: 100 nm) Film forming temperature: 500℃ Power: RF200W

[0052] (Thin film structure analysis) The Al-Sc-Ga-N film obtained in Example 6 was subjected to structural evaluation by measuring the X-ray diffraction peak pattern under the following conditions using an X-ray diffractometer (D8 DISCOVER, manufactured by Bruker AXS). The measured X-ray diffraction peak pattern is shown in Figure 14. The results shown in Figure 14 indicate that the obtained Al-Sc-Ga-N film is a single layer with a hexagonal wurtzite structure. <Condition> Radiation source: CuKα radiation Monochromator: Ge(220) Pathfinder: Crystal3B Measurement mode: 2θ-θ scan Measurement interval: 0.02 degrees Measurement speed: 4 degrees / min Measurement range: 20 degrees to 80 degrees

[0053] (Piezoelectric property evaluation) The obtained Al-Sc-Ga-N film was analyzed using a piezoelectric wafer evaluation system. 33 The piezoelectric properties were evaluated using a meter (manufactured by Lead Techno Co., Ltd.) under the following conditions: Piezoelectric coefficient d 33 was 53 pC / N. <Condition> Measurement temperature: room temperature Upper electrode diameter: φ1mm Probe diameter: 60 μm Number of measurements: 50

[0054] This application is based on a Japanese patent application (Patent Application No. 2023-039496) filed on March 14, 2023, the entire contents of which are incorporated by reference. In addition, all references cited herein are incorporated in their entirety. [Industrial Applicability]

[0055] The Al-Sc-Ga sputtering target of the present disclosure can be used as a sputtering target for forming AlScGaN films used in, for example, memory elements such as ferroelectric memories, piezoelectric elements such as pressure sensors and vibration sensors, and the like. [Explanation of symbols]

[0056] 10...Main body, 20...Backing plate, 30...Joint material, 100...Al-Sc-Ga sputtering target.

Claims

1. An Al-Sc-Ga sputtering target having a main body containing Al, Sc, and Ga but not containing a Ga phase, wherein the Ga content is 30% or less, based on the total number of atoms of Al, Sc, and Ga (100%), the atomic ratio of Sc to Al (Sc / Al) is 0.25 or more, and the atomic ratio of Sc to Ga (Sc / Ga) is 0.5 or more.

2. 2. The Al--Sc--Ga sputtering target according to claim 1, wherein the atomic ratio of Sc to Al (Sc / Al) in the main body is 0.5 or more.

3. 3. The Al--Sc--Ga sputtering target according to claim 1, wherein the atomic ratio of Sc to Ga (Sc / Ga) in the main body is 2 or more.

4. 3. The Al--Sc--Ga sputtering target according to claim 1, wherein the atomic ratio of Sc to Ga (Sc / Ga) in the main body is 20 or less.

5. 3. The Al--Sc--Ga sputtering target according to claim 1, further comprising a backing plate joined to the main body portion via a joining material.

6. A method for producing an Al-Sc-Ga sputtering target includes a first step of producing a main body portion that contains Al, Sc, and Ga, is free of Ga phase, has a Ga content of 30% or less relative to the total atomic number of Al, Sc, and Ga (100%), has an atomic ratio of Sc to Al (Sc / Al) of 0.25 or more, and has an atomic ratio of Sc to Ga (Sc / Ga) of 0.5 or more.

7. 7. The method for producing an Al--Sc--Ga sputtering target according to claim 6, wherein in the first step, the main body is produced so that an atomic ratio of Sc to Al (Sc / Al) is 0.5 or more.

8. 8. The method for manufacturing an Al—Sc—Ga sputtering target according to claim 6, wherein in the first step, the main body is manufactured so that an atomic ratio of Sc to Ga (Sc / Ga) is 2 or more.

9. 8. The method for manufacturing an Al—Sc—Ga sputtering target according to claim 6, wherein in the first step, the main body is manufactured so that an atomic ratio of Sc to Ga (Sc / Ga) is 20 or less.

10. 8. The method for manufacturing an Al--Sc--Ga sputtering target according to claim 6, further comprising a second step of joining a backing plate to the main body portion via a joining material.

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