Sputtering target

Abstract

Providing sputtering targets capable of producing high-quality thin films. [Solution] The material of the sputtering target is an alloy mainly composed of Co or Fe. This alloy contains 2 at% to 10 at% amorphous elements. The remainder of this alloy is unavoidable impurities. The oxygen content in this alloy is 200 wt ppm or less. This alloy has a polycrystalline metallic structure with a grain size of 20 μm or less. Preferred amorphous elements are Y, Hf, and Zr. The grain size difference in the in-plane direction of this target is 2 μm or less, and the grain size difference in the perpendicular direction is 2 μm or less.

Description

Technical Field

[0001] This specification discloses a sputtering target. Specifically, this specification discloses a sputtering target for thin films suitable for magnetic devices.

Background Art

[0002] Magnetic devices such as magnetic heads and magnetic random access memories (MRAMs) have a tunneling magnetoresistance film. A typical tunneling magnetoresistance film has two magnetic thin films and a shielding layer sandwiched between these thin films. A typical material for the shielding layer is MgO. On the other hand, a typical material for the thin films is an alloy containing a large amount of B. This alloy further contains Fe or Co. An alloy suitable for the magnetic thin film is disclosed in International Publication WO2011 / 070860.

[0003] Soft magnetism is also required for the underlayer film of a perpendicular magnetic recording medium. Japanese Unexamined Patent Application Publication No. 2008-127588 discloses a Co-Fe-based alloy for this underlayer film. This alloy contains Zr, Hf, Nb, and Ta.

[0004] Japanese Unexamined Patent Application Publication No. 2010-159491 discloses a Co-Fe-Ni-based alloy suitable for the underlayer film. This alloy contains Zr, Hf, Ta, Nb, Y, and B.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Magnetic thin films can be obtained by sputtering. This sputtering process can generate particles, which impair the quality of the thin film. Therefore, targets that minimize particle generation are desired. Furthermore, the thin film must be amorphous, have a high saturation magnetic flux density, and have a uniform thickness.

[0007] The applicant's intention is to provide a sputtering target capable of producing high-quality thin films. [Means for solving the problem]

[0008] The material of the sputtering target disclosed herein is an alloy mainly composed of Co or Fe. This alloy contains 2 at% to 10 at% amorphous elements. The remainder of this alloy is unavoidable impurities. The oxygen content in this alloy is 200 wt ppm or less. This alloy has a polycrystalline metallic structure with a grain size of 20 μm or less. The grain size difference in the in-plane direction of this sputtering target is 2 μm or less, and the grain size difference in the perpendicular direction is 2 μm or less.

[0009] Preferably, this alloy contains one or more elements selected from the group consisting of Y, Hf, and Zr as amorphous elements.

[0010] The method for manufacturing a magnetic thin film disclosed herein is: (1) A step of preparing a target, wherein the material is an alloy mainly composed of Co or Fe, the alloy contains 2 at% to 10 at% amorphous elements, the remainder of the alloy is unavoidable impurities, the oxygen content of the alloy is 200 wt ppm or less, the alloy has a polycrystalline metal structure with a grain size of 20 μm or less, the grain size difference in the in-plane direction is 2 μm or less, and the grain size difference in the perpendicular direction is 2 μm or less. and (2) The process of subjecting the target to sputtering. Includes. [Effects of the Invention]

[0011] Because this sputtering target has a low oxygen content, particle generation can be suppressed during sputtering with this target. Since this target contains an appropriate amount of amorphous elements, the thin film obtained from it is amorphous and has a high saturation magnetic flux density. Because the metallic structure of this target is fine, thin films with minimal thickness variation can be obtained. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a micrograph showing the metallic structure of a sputtering target according to one embodiment. [Modes for carrying out the invention]

[0013] Preferred embodiments are described in detail below.

[0014] [Target material] The material of the sputtering target according to this embodiment is an alloy mainly composed of Co or Fe. This alloy contains 2 at% to 10 at% amorphous elements. Preferably, the remainder is unavoidable impurities.

[0015] [Cobalt (Co) and Iron (Fe)] As described above, the alloy of the sputtering target contains Co or Fe. The alloy may have a composition containing Co and not containing Fe, may have a composition not containing Co and containing Fe, or may have a composition containing Co and Fe. A thin film containing Co or Fe can be formed from a target containing Co or Fe. Co and Fe can contribute to the magnetism of this thin film. From this perspective, the total content ratio of Co and Fe in the alloy is preferably 85 at% or more, more preferably 90 at% or more, and particularly preferably 95 at% or more. From the perspective that the alloy can contain sufficient elements for amorphization, the total content ratio of Co and Fe is preferably 99 at% or less, more preferably 97 at% or less, and particularly preferably 96 at% or less.

[0016] [Elements for amorphization] As described above, the alloy of the sputtering target contains elements for amorphization. A thin film having an amorphous structure can be obtained from a target containing elements for amorphization. Since this thin film does not have a crystal structure, it has excellent soft magnetic properties and smoothness.

[0017] Preferred elements for amorphization include yttrium (Y), hafnium (Hf), and zirconium (Zr). In other words, this alloy contains one or more elements selected from the group consisting of Y, Hf, and Zr.

[0018] The difference between the atomic radius of each element for amorphization and the atomic radius of Co is large. The difference between the atomic radius of this element for amorphization and the atomic radius of Fe is also large. The ratio of the atomic radius of each element for amorphization to the atomic radius of Co is preferably 110% or more, more preferably 120% or more, and particularly preferably 125% or more. The ratio of the atomic radius of each element for amorphization to the atomic radius of Fe is preferably 110% or more, more preferably 120% or more, and particularly preferably 125% or more. These ratios are calculated based on the metallic bonding radius of each element.

[0019] The diffusion coefficient of each amorphization element is smaller than that of B. This amorphization element is less likely to diffuse from the thin film to other layers in the magnetic device. This magnetic device has a long lifespan.

[0020] The content of the amorphization element in the alloy of the sputtering target is preferably 2 at% or more. From a target with this content of 2 at% or more, a thin film containing sufficient amorphous in its structure can be obtained. From this perspective, this content is more preferably 3 at% or more, and particularly preferably 4 at% or more. Excessive amorphization elements inhibit the saturation magnetic flux density of the thin film. From the perspective of obtaining a thin film with a high saturation magnetic flux density, this content is preferably 10 at% or less, more preferably 8 at% or less, and particularly preferably 6 at% or less.

[0021] [Oxygen (O)] The alloy of the sputtering target may contain O as an unavoidable impurity. As described above, this alloy contains an amorphization element. O can combine with the amorphization element to form an oxide. This oxide is a factor of particles during sputtering. In sputtering using a target with a low O content, particles can be suppressed. High-quality thin films can be obtained from a target containing an appropriate amount of amorphization element and having a low oxygen content. From this perspective, the O content (by mass) is preferably 200 wtppm or less, more preferably 150 wtppm or less, and particularly preferably 100 wtppm or less.

[0022] The O content is measured by gas analysis using the melting non-dispersive infrared absorption method in an inert gas. The size of the test piece subjected to this analysis is 3 mm × 3 mm × 30 mm. This size is cut out from the target by the wire cutting method.

[0023] [Metallographic structure] Figure 1 is a micrograph showing the microstructure of a sputtering target. The microstructure of this sputtering target is polycrystalline. In other words, this microstructure has many crystal grains. In Figure 1, the white areas are solid solution phases of Co or Fe, where the dendrite structure is the primary crystal, and the gray areas are intermetallic compound phases of amorphous elements and Co or Fe. Only small amounts of amorphous elements are solid-dissolved in the matrix Co phase, Fe phase, or Co-Fe phase. The remaining amorphous elements exist in the intermetallic compound structure without being solid-dissolved in the matrix.

[0024] [Crystal grain size] The grain size in this metal structure is preferably 20 μm or less. In other words, this metal structure is fine. A thin film with uniform thickness can be obtained from this target. From this viewpoint, the grain size is more preferably 10 μm or less, and particularly preferably 5 μm or less.

[0025] The method for measuring grain size is as follows: A specimen for measuring grain size is cut from a target. The surface of this specimen is mirror-polished. Furthermore, this surface is etched with a nitric acid alcohol-based etchant. This surface is observed with an optical microscope, and an image with a vertical dimension of 170 μm and a horizontal dimension of 220 μm is taken. Three straight lines with a length L of 220 μm are drawn on this image, and the number of intersections N between these lines and grain boundaries is counted. The average grain size Dg is calculated based on the following formula. Dg = (3 · L) / N

[0026] [In-plane grain size difference] The in-plane grain size difference of this sputtering target is preferably 2 μm or less. A homogeneous thin film can be obtained from a sputtering target with this grain size difference of 2 μm or less. From this viewpoint, a grain size difference of 1 μm or less is particularly preferred.

[0027] In measuring the grain size difference in the in-plane direction, three test specimens are taken from the target within the same plane, and the average grain size is measured for each specimen. The grain size difference is calculated by subtracting the minimum value from the maximum value of these average grain sizes.

[0028] [Grain size difference in the vertical direction] The grain size difference in the vertical direction of this sputtering target is preferably 2 μm or less. A homogeneous thin film can be obtained from a sputtering target with a grain size difference of 2 μm or less. From this viewpoint, a grain size difference of 1 μm or less is particularly preferred.

[0029] To measure the grain size difference in the vertical direction, a test specimen is taken from the target. The average grain size is measured at the surface, center, and bottom of this specimen in the thickness direction. The grain size difference is calculated by subtracting the minimum value from the maximum value of these average grain sizes.

[0030] [Target manufacturing method] In the manufacturing of the target, powder is first prepared. This powder can be produced by atomization, grinding, etc. Examples of atomization methods include gas atomization, water atomization, and disc atomization. From the viewpoint of minimizing the inclusion of oxygen in the powder, gas atomization and disc atomization are preferred. From the viewpoint of minimizing the inclusion of oxygen in the powder, atomization in an inert gas atmosphere is preferred. From the viewpoint of mass production, gas atomization is preferred.

[0031] This powder is subjected to pressure and heating. A preferred method of pressure and heating is hot isostatic pressing (HIP). This pressure and heating process yields a sputtering target, which is a sintered body. This target is then processed to a predetermined size and subjected to sputtering. The target may also be obtained by methods such as hot pressing, discharge plasma sintering, or hot extrusion.

[0032] A target having a metallic structure with a crystal grain size of 20 μm or less can be obtained by preparing a powder with a crystal grain size of 20 μm or less and forming a molded body under conditions that minimize crystal grain coarsening. Crystal grain growth can be suppressed by lowering the heating temperature and shortening the heating time during molding, as long as excessive pores do not form in the molded body.

[0033] Generally, the grain size of atomized powder is influenced by the particle size of the individual particles. Specifically, coarse particles tend to have coarse grain sizes, while fine particles tend to have fine grain sizes. By suppressing the particle size distribution of the powder (for example, by removing coarse particles from the powder through classification after atomization), it is possible to obtain a sputtering target with a grain size difference of 2 μm or less in the in-plane direction and a grain size difference of 2 μm or less in the perpendicular direction.

[0034] [Sputtering] This specification also applies to methods for manufacturing thin films. This manufacturing method is (1) A step of preparing a target, wherein the material is an alloy mainly composed of Co or Fe, the alloy contains 2 at% to 10 at% amorphous elements, the remainder of the alloy is unavoidable impurities, the oxygen content of the alloy is 200 wt ppm or less, the alloy has a polycrystalline metal structure with a grain size of 20 μm or less, the grain size difference in the in-plane direction is 2 μm or less, and the grain size difference in the vertical direction is 2 μm or less. and (2) The process of subjecting the target to sputtering. This method includes [specific components]. This manufacturing method can yield a thin film with an amorphous structure and magnetic properties. This thin film is of high quality. This sputtering method can yield a thin film suitable for tunnel magnetoresistance films in magnetic devices. [Examples]

[0035] The effects of the sputtering target according to the examples will be revealed below, but the scope disclosed herein should not be interpreted as limiting based on the description of these examples.

[0036] [Example 1] The raw metal was placed in an alumina crucible. This raw metal was induction heated in an argon gas atmosphere and melted. The molten metal was removed from a nozzle with an inner diameter of 8 mm in the crucible, and high-pressure argon was sprayed onto it to obtain a powder. This powder was subjected to classification to adjust the particle size to 300 μm or less. This powder was filled into a capsule with an outer diameter of 230 mm, an inner diameter of 220 mm, a length of 100 mm, and made of SC material. This capsule was degassed and sealed. This powder was subjected to hot isostatic pressing (HIP) at a temperature of 1200°C, a pressure of 140 MPa, and a time of 3 hours to obtain a sintered body. This sintered body was subjected to wire cutting and turning, and then surface polishing to obtain a sputtering target. This target had a disc shape. This target had a diameter of 100 mm and a thickness of 2 mm. The composition of this target is shown in Table 1 below.

[0037] [Examples 2-13 and Comparative Examples 2 and 4] Sputtering targets for Examples 2-13 and Comparative Examples 2 and 4 were obtained in the same manner as in Example 1, except that raw material metals with different compositions were used.

[0038] [Comparative Example 1] A sputtering target for Comparative Example 1 was obtained in the same manner as in Example 1, except that a powder obtained by mixing 65 at% Co powder, 30 at% Fe powder, and 5 at% Y powder was used.

[0039] [Comparative Example 3] An ingot was obtained by melting. This ingot was subjected to wire cutting and turning, and then surface grinding to obtain a sputtering target.

[0040] [Tissue observation] When the microstructure of the sputtering target of Example 1 was observed using EDX, the amount of Y in the matrix was 0.5 at% or less. This indicates that a large amount of Y was not dissolved in the matrix. When the microstructure of the sputtering target of Example 2 was observed using EDX, the amount of Hf in the matrix was 0.5 at% or less. This indicates that a large amount of Hf was not dissolved in the matrix.

[0041] [Crystal grain size] The grain size and grain size difference of each target were measured using the method described above. The results are shown in Table 1 below.

[0042] [Intrinsic resistance] Each target was sputtered to form a sputtered film measuring 60 mm x 30 mm with a thickness of 100 nm on a glass substrate. Test pieces measuring 20 mm x 10 mm were taken from these sputtered films. The intrinsic resistance and sheet resistance were measured using a four-probe method with a resistance meter (Mitsubishi Chemical's "Loresta GP"). The mean value Rave and standard deviation σ were calculated for the three sheet resistances. The resistance distribution DR was calculated based on the following formula. DR = (σ / Rave) × 100 If the resistivity was 100 μΩcm or higher, the sputtered film was determined to have an amorphous structure.

[0043] [Table 1]

[0044] As is clear from Table 1, thin films with an amorphous structure can be obtained from the sputtering targets of each example. Furthermore, homogeneous thin films can be obtained from these targets. The superiority of this target is evident from these evaluation results. [Industrial applicability]

[0045] The sputtering targets described above are suitable for manufacturing various magnetic thin films.

Claims

1. The material is an alloy whose main component is Co or Fe. The above alloy contains 2 at% to 10 at% amorphous elements. The remainder of the above alloy consists of unavoidable impurities. The oxygen content in the above alloy is 200 wt ppm or less. The above alloy has a polycrystalline metal structure with a crystal grain size of 20 μm or less. A sputtering target having a grain size difference of 2 μm or less in the in-plane direction and a grain size difference of 2 μm or less in the perpendicular direction.

2. The sputtering target according to claim 1, wherein the alloy contains one or more elements selected from the group consisting of Y, Hf, and Zr as the amorphous element.

3. (1) A step of preparing a target, wherein the material is an alloy mainly composed of Co or Fe, the alloy contains 2 at% to 10 at% amorphous elements, the remainder of the alloy is unavoidable impurities, the oxygen content of the alloy is 200 wt ppm or less, the alloy has a polycrystalline metal structure with a grain size of 20 μm or less, the grain size difference in the in-plane direction is 2 μm or less, and the grain size difference in the perpendicular direction is 2 μm or less. and (2) The process of subjecting the target to sputtering. A method for manufacturing a magnetic thin film, including

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