Sputtering target

Abstract

Provided is a sputtering target which is not susceptible to breakage during sputtering and enables the achievement of a high-quality thin film by being used for sputtering. This sputtering target is composed of a Cr-based alloy. The Cr-based alloy contains 5 at% to 30 at% of B, and 5 at% to 30 at% in total of at least one element that is selected from the group consisting of Mo and W. In the Cr-based alloy, the B content is the same as or higher than the total content of Mo and W, and the total content of B, Mo, and W is 40 at% or less. The ratio of the intensity of an X-ray diffraction peak P2 with respect to the (110) plane of the Mo phase to the intensity of an X-ray diffraction peak P1 with respect to the (110) plane of the Cr phase is 10% or less. The ratio of the intensity of an X-ray diffraction peak P3 with respect to the (110) plane of the W phase to the intensity of the peak P1 is 50% or less.

Description

Sputtering Target

[0001] The present disclosure relates to a sputtering target used in sputtering for forming a metal thin film.

[0002] Sputtering is a well-known method for forming thin films. In sputtering, a target is used. In sputtering, positive ions in the plasma collide with the target. These collisions cause atoms to fly out of the target. These atoms then adhere to the substrate, forming a thin film.

[0003] An example of a sputtering target is disclosed in Patent Document 1 (JP 2014-164780 A). The target disclosed in this document is obtained by sintering powder. This powder is made of a Cr-based alloy. From this target, a thin film (adhesion layer) that is homogeneous and has fine crystal grains can be obtained. This thin film is suitable for perpendicular magnetic recording media.

[0004] JP 2014-164780 A

[0005] Thin films are required to have a fine crystalline structure and good adhesion to the glass substrate. The target disclosed in Patent Document 1 (JP 2014-164780 A) does not provide a thin film with a sufficiently fine crystalline structure and good adhesion. From the viewpoint of fine crystalline structure and good adhesion to the glass substrate, it is effective to add B, W, and Mo to the Cr alloy. However, the addition of these elements can cause problems such as particles and cracking of the target during sputtering.

[0006] An object of the present invention is to provide a target that is less likely to crack during sputtering and that can provide a high-quality thin film when subjected to sputtering.

[0007] The present disclosure provides the following aspects: [Aspect 1] A sputtering target made of a Cr-based alloy, the Cr-based alloy comprising: B: 5 at% to 30 at% inclusive, and at least one element selected from the group consisting of Mo and W: a total content of 5 at% to 30 at% inclusive, wherein in the Cr-based alloy, the B content is equal to or greater than the total content of Mo and W, and the total content of B, Mo, and W is 40 at% or less, a ratio of an X-ray diffraction peak intensity corresponding to the (110) plane of the Mo phase to an X-ray diffraction peak intensity corresponding to the (110) plane of the Cr phase is 10% or less, and a ratio of an X-ray diffraction peak intensity corresponding to the (110) plane of the W phase to an X-ray diffraction peak intensity corresponding to the (110) plane of the Cr phase is 50% or less. [Aspect 2] The sputtering target according to Aspect 1, wherein the Cr-based alloy consists of: B: 5 at% to 30 at%; at least one selected from the group consisting of Mo and W: 5 at% to 30 at% in total; and the balance being Cr and inevitable impurities. [Aspect 3] The sputtering target according to Aspect 1 or 2, wherein the sputtering target has a flexural strength of 300 MPa or more as measured by a three-point bending test in accordance with JIS Z 2511:2006. [Aspect 4] The sputtering target according to any one of Aspects 1 to 3, wherein the Cr-based alloy has an oxygen content of 3000 ppm or less. [Aspect 5] A method for manufacturing a sputtering target, comprising: (1) preparing a first powder consisting of CrB, (2) preparing a second powder consisting of MoB or WB, (3) preparing a third powder consisting of Cr, (4) mixing the first powder, second powder, and third powder to obtain a mixed powder, and (5) pressurizing and heating the mixed powder. [Aspect 6] A method for manufacturing a sputtering target according to Aspect 5, wherein in step (1) a first powder having an average particle diameter D50 of 1 μm or more and 10 μm or less is prepared, in step (2) a second powder having an average particle diameter D50 of 1 μm or more and 10 μm or less is prepared, and in step (3) a third powder having an average particle diameter D50 of 20 μm or more is prepared.

[0008] The sputtering target of the present disclosure can produce high-quality thin films, and the target is less likely to crack during sputtering.

[0009] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0010] [Cr-based alloy] The sputtering target according to this embodiment is made of a Cr-based alloy. This Cr-based alloy contains B. This Cr-based alloy further contains Mo and / or W. The Cr-based alloy may contain Mo and substantially no W, or may be substantially free of Mo and contain W. The Cr-based alloy may contain Mo and also contain W. Preferably, in this Cr-based alloy, the balance of Cr, B, Mo, and W is unavoidable impurities. In other words, a preferred Cr-based alloy contains B and at least one selected from the group consisting of Mo and W, with the balance being Cr and unavoidable impurities.

[0011] [Metal Structure] The preferred metal structure of this target has a matrix of Cr phase. Chromium boride phases are dispersed in this matrix. Examples of chromium boride phases include CrB phase and Cr ２ The matrix further contains a molybdenum boride phase or a tungsten boride phase dispersed therein. Examples of the molybdenum boride phase include the MoB phase and the Mo ２ Examples of tungsten boride phases include WB phase and W ２ Examples of the molybdenum boride phase include a molybdenum boride phase and a tungsten boride phase. The target may have a metal structure in which a molybdenum boride phase is dispersed in a matrix, and a tungsten boride phase is not dispersed in the matrix. The target may have a metal structure in which a molybdenum boride phase is not dispersed in the matrix, and a tungsten boride phase is dispersed in the matrix. The target may have a metal structure in which a molybdenum boride phase is dispersed in the matrix, and a tungsten boride phase is dispersed in the matrix. A Mo phase or a W phase may be dispersed in the matrix.

[0012] [Applications] A thin film can be formed by sputtering using this target. Since the Cr-based alloy contains B and Mo and / or W, the crystal grains of the thin film are fine. This thin film is suitable for various applications. A typical application of the thin film is as an adhesion layer for perpendicular magnetic recording media. This adhesion layer can suppress orientation in perpendicular magnetic recording media.

[0013] [Chromium (Cr)] Cr can contribute to the non-magnetic properties, adhesion, and corrosion resistance of the adhesive layer. Cr has a BCC structure and has a lattice constant with a small mismatch with the (001) layer (such as an MgO layer) on which the adhesive layer is laminated. Cr can suppress the orientation of the layer on which the adhesive layer is laminated. From these viewpoints, the Cr content in the Cr-based alloy is preferably 60 at% or more. From the viewpoint that the Cr-based alloy can contain sufficient Cr, the total content of B, Mo, and W is preferably 40 at% or less.

[0014] As described above, a Cr-based alloy may contain a Cr phase and a CrB phase. The Cr phase has extremely excellent toughness. The toughness of the CrB phase is inferior to that of the Cr phase. However, the CrB phase has superior toughness to other chromium borides. A metal structure containing the Cr phase and the CrB phase can suppress cracking of the target during sputtering.

[0015] [Boron (B)] B combines with Cr, Mo, or W. In the target, B exists as a boride. This boride is thought to pin the growth of crystal grains. From this target, a thin film with a small crystal grain size can be formed. Furthermore, B can realize a structure without crystal grain boundaries (amorphous). This structure is homogeneous and isotropic. This structure can contribute to the smoothness of the thin film. From these viewpoints, the B content in the Cr-based alloy is preferably 5 at% or more, more preferably 10 at% or more, and particularly preferably 15 at% or more. From the viewpoint of suppressing cracking of the target during sputtering, this content is preferably 30 at% or less. Furthermore, B improves the hardness of the thin film. The adhesion layer has a problem of reduced adhesion due to small scratches and defects that occur during film formation. Therefore, a hard material that is resistant to scratches is required for the adhesion layer. From the viewpoint of hardness to ensure adhesion, the B content in the Cr-based alloy is preferably 5 at% or more, more preferably 10 at% or more, and particularly preferably 15 at% or more. From the viewpoint of suppressing cracking of the target during sputtering, this content is preferably 30 at% or less.

[0016] [Molybdenum (Mo) and / or Tungsten (W)] Mo and W have high hardness. Mo and W have high melting points. A thin film with high hardness and excellent thermal stability can be obtained from a sputtering target containing Mo and / or W. This characteristic improves the adhesion of the film, similar to that of B. From this viewpoint, the total content of Mo and W in the Cr-based alloy is preferably 5 at% or more, more preferably 10 at% or more, and particularly preferably 15 at% or more. From the viewpoint of suppressing cracking of the target during sputtering, this content is preferably 30 at% or less.

[0017] In a target, most of the Mo can exist as the MoB phase. The amount of Mo present as a single phase is small or zero. The MoB phase can contribute to the toughness of the target. The MoB phase is less likely to become a starting point for cracks during sputtering than the Mo phase. A target that contains sufficient Mo and in which most of this Mo exists as the MoB phase can achieve both suppression of cracks during sputtering and high quality of the thin film.

[0018] Among the multiple peaks of the Cr phase obtained by X-ray diffraction, the peak P1 relating to the (110) plane has the greatest intensity. Among the multiple peaks of the Mo phase obtained by X-ray diffraction, the peak P2 relating to the (110) plane has the greatest intensity. The Mo phase is brittle and is likely to become the starting point of cracks, so it should be as fine and zero as possible. If Mo exists in the form of a MoB compound, it contributes to hardness and toughness. The brittle structure disappears and cracks are eliminated. When Mo50B is used as the Mo source, the MoB compound is mainly composed of Mo. ２ Exists in B. MoB ４ is brittle, so it's better not to have it. ２ It has the same level of toughness as B, so it doesn't matter whether it's present or not. CrB compounds have the most stable CrB phase, ２ and Cr ５ B ３ When Cr50B is used as the starting material, all CrB compounds are in the CrB phase, and CrB ２ and Cr ５ B ３ does not exist. The parent phase is pure Cr, which has higher toughness than pure Mo or pure W, and Mo and W exist as borides, making the target less likely to crack. Therefore, the target is less likely to crack during sputtering. From this perspective, the ratio (P2 / P1) of the intensity of the X-ray diffraction peak P2 relating to the (110) plane of the Mo phase to the intensity of the X-ray diffraction peak P1 relating to the (110) plane of the Cr phase is preferably 10% or less, more preferably 7% or less, and particularly preferably 5% or less. Ideally, this ratio is 0%.

[0019] W is easily precipitated, and pure W is scattered even when W50B is used as the W source and pure W is not used as the starting material. However, since this W is present in trace amounts and is scattered small, it is unlikely to cause cracking. Therefore, a peak of pure W may be observed as long as the ratio (P3 / P1) of the intensity of the X-ray diffraction peak P3 relating to the (110) plane of the W phase to the intensity of the X-ray diffraction peak P1 relating to the (110) plane of the Cr phase is 50% or less. Much of the W in the target can exist as the WB phase. W can also exist as a single phase, albeit in small amounts. The WB phase can contribute to the toughness of the target. Compared to the W phase, the WB phase is less likely to be the starting point of cracks during sputtering. A target containing sufficient W and in which much of this W exists as the WB phase can achieve both suppression of cracks during sputtering and high quality of the thin film. The WB compound is mainly composed of W. ２ When W50B is used as the W source, the WB compound is mainly W ２ Exists in B. WB ２ is fragile, so it is better not to have it. ２ It has the same level of toughness as B, so it doesn't matter whether it's there or not.

[0020] Among the multiple peaks of the W phase obtained by X-ray diffraction, the intensity of peak P3 corresponding to the (110) plane is the greatest. From the viewpoint of preventing cracking of the target during sputtering, the ratio (P3 / P1) of the intensity of X-ray diffraction peak P3 corresponding to the (110) plane of the W phase to the intensity of X-ray diffraction peak P1 corresponding to the (110) plane of the Cr phase is preferably 50% or less, more preferably 30% or less, and particularly preferably 10% or less. Ideally, this ratio is 0%.

[0021] From the viewpoint of achieving small ratios (P2 / P1) and (P3 / P1), it is preferable that the B content (at %) is equal to or greater than the total content (at %) of Mo and W. The ratio (Pa / Pb) of the B content Pa (at %) to the total content Pb (at %) of Mo and W is preferably 1 / 1 or more and 6 / 1 or less. This ratio (Pa / Pb) is more preferably 4 / 1 or less, and particularly preferably 3 / 1 or less.

[0022] Peaks P1, P2, and P3 are measured using an X-ray diffraction device. A test piece for X-ray diffraction is cut out from the target by wire cutting. The surface of this test piece is smoothed by polishing. The measurement conditions are as follows: - Test piece size: 10 mm x 20 mm x 5 mm - X-ray source: CuKα ray - Scan speed: 4° / min - 2θ: 20 to 80°. The peaks (peak intensity) are read from the chart obtained by this X-ray diffraction.

[0023] [Impurities] The Cr-based alloy may contain oxygen as an inevitable impurity. The oxygen content (by mass) in the Cr-based alloy is preferably 3000 ppm or less. A target made of this Cr-based alloy is less likely to crack during sputtering. Furthermore, a thin film with fewer particles can be obtained from this target. From these viewpoints, the oxygen content of the Cr-based alloy is more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. Ideally, the oxygen content is less than the detection limit.

[0024] [Flexural Strength] The flexural strength of the target is preferably 300 MPa or more. This target is less likely to crack during sputtering. From this viewpoint, the flexural strength is more preferably 400 MPa or more, and particularly preferably 500 MPa or more.

[0025] The flexural strength is measured by a three-point bending test in accordance with the provisions of "JIS Z 2511:2006". Test pieces for the three-point bending test are cut out from the target by the wire cutting method. The measurement conditions are as follows: - Test piece size: 2 mm x 2 mm x 20 mm - Distance between supports: 10 mm. The flexural strength BS (MPa) is calculated using the following formula: BS = 3 / 2 x P x L / (t ２ × W) - P: Load at break (kN) - L: Distance between supports (mm) - t: Thickness of test piece (mm) - W: Width of sample (mm)

[0026] [Manufacturing Method] This sputtering target can be obtained by powder metallurgy. A preferred manufacturing method for a sputtering target includes the steps of: (1) preparing a first powder composed of CrB; (2) preparing a second powder composed of MoB or WB; (3) preparing a third powder composed of Cr; (4) mixing the first powder, the second powder, and the third powder to obtain a mixed powder; and (5) pressurizing and heating the mixed powder. By pressing and heating, a sputtering target that is a sintered body is obtained. This target is processed to a predetermined size and used for sputtering.

[0027] Since the first powder is composed of CrB, this first powder contains 50 at% Cr and 50 at% B. Since the second powder is composed of MoB or WB, this second powder contains 50 at% Mo or W and 50 at% B. The B contained in the Cr-based alloy of the target comes from the first powder and the second powder. This Cr-based alloy does not contain any component derived from a powder composed of only B. In this target, B can be uniformly dispersed. A homogeneous thin film can be formed from this target. A thin film with few particles can be obtained from this target.

[0028] The Mo contained in the Cr-based alloy of the target originates from the second powder. This Cr-based alloy does not contain any components derived from the powder composed of Mo alone. A small ratio (P2 / P1) can be achieved in this target. This target is less likely to crack during sputtering. Mo can be uniformly dispersed in this target. A homogeneous thin film can be formed from this target. Because the Cr-based alloy does not contain any components derived from the powder composed of Mo alone, the intensity of peak P2 is almost zero.

[0029] The W contained in the Cr-based alloy target originates from the second powder. This Cr-based alloy does not contain any components derived from the powder consisting of W alone. A small ratio (P3 / P1) can be achieved in this target. This target is less likely to crack during sputtering. W can be uniformly dispersed in this target. A homogeneous thin film can be formed from this target. Although the Cr-based alloy does not contain any components derived from the powder consisting of W alone, a small amount of W can be generated from WB during heating. Therefore, a small peak P3 can be observed in this target.

[0030] In this manufacturing method, MoB is prepared as the Mo source, and WB is prepared as the W source. MoB and WB are also B sources. However, MoB and WB alone are insufficient as B sources. In this manufacturing method, CrB is also prepared as the B source. With a sufficient B source, a target in which the B content is equal to or greater than the total content of Mo and W can be obtained. In this target, small ratios (P2 / P1) and (P3 / P1) can be achieved.

[0031] [Average particle diameter D50] The average particle diameter D50 of the first powder is preferably 10 μm or less. This first powder can contribute to the uniform dispersion of B. From this viewpoint, the average particle diameter D50 is more preferably 8 μm or less, and particularly preferably 7 μm or less. From the viewpoint of handleability, the average particle diameter D50 is preferably 1 μm or more.

[0032] The second powder preferably has an average particle diameter D50 of 10 μm or less. This second powder can contribute to uniform dispersion of Mo and W. From this viewpoint, the average particle diameter D50 is more preferably 8 μm or less, and particularly preferably 7 μm or less. From the viewpoint of handleability, the average particle diameter D50 is preferably 1 μm or more.

[0033] The average particle diameter D50 of the third powder is preferably 20 μm or more. The particles of this third powder are generally larger than the particles of the first and second powders. Because this third powder is mixed with the first and second powders, a target with a low oxygen content can be obtained despite the small average particle diameter D50 of the first and second powders. Specifically, a target with an oxygen content of 3000 ppm or less can be obtained by this manufacturing method. This target is less likely to crack during sputtering. Since B, Mo, and W are not derived from the third powder, uniform dispersion of B, Mo, and W can be achieved even if the average particle diameter D50 of the third powder is large. From the perspective of target crack resistance, the average particle diameter D50 of the third powder is more preferably 40 μm or more, and particularly preferably 50 μm or more. This average particle diameter D50 is preferably 250 μm or less.

[0034] The average particle diameter D50 of each powder is measured using a laser diffraction / scattering particle size distribution analyzer, and is determined by finding the particle diameter at which the cumulative volume is 50% on the cumulative volume curve of the powder.

[0035] From this target, an adhesion layer for a perpendicular magnetic recording medium can be obtained by sputtering, and from this target, other thin films can be obtained by sputtering.

[0036] This specification is also directed to a method for producing a thin film. This method includes the steps of: (1) preparing a sputtering target made of the Cr-based alloy of the present disclosure; and (2) subjecting the target to sputtering. This method can produce a high-quality thin film. An example of such a thin film is an adhesion layer of a perpendicular magnetic recording medium.

[0037] The effects of the sputtering targets according to the examples will be explained below, but the scope of the present disclosure should not be construed as being limited based on the descriptions of these examples.

[0038] Example 1: A Cr powder having an average particle diameter D50 of 60 μm was prepared as the third powder. Furthermore, a MoB powder containing 50 at% Mo and 50 at% B and having an average particle diameter D50 of 5 μm was prepared as the second powder. The third powder and the second powder were charged into a V-type mixer to obtain a mixed powder. The mixed powder was filled into a carbon steel can having a diameter of 200 mm and a length of 10 mm. After vacuum degassing, the powder was subjected to HIP to produce a billet. The HIP conditions were as follows: sintering temperature: 1000°C, pressure: 120 MPa, and holding time: 5 hours. The billet was sliced ​​to obtain the sputtering target of Example 1.

[0039] [Examples 2 to 21 and Comparative Examples 1 to 18] Sputtering targets of Examples 2 to 21 and Comparative Examples 1 to 18 were obtained in the same manner as in Example 1, except that the starting materials and sintering temperatures were as shown in Tables 1 and 2 below.

[0040] [Oxygen Content] A test piece was cut out from the target by a wire cutting method. The mass of this test piece was approximately 1 g. The surface of this test piece was polished, and the oxygen content was measured using an oxygen / nitrogen analyzer (manufactured by Horiba, Ltd., trade name "EMGA-920"). The results are shown in Tables 1 and 2 below.

[0041] [X-ray Diffraction] X-ray diffraction was performed on the target using the method described above. The ratio (P2 / P1) of the intensity of X-ray diffraction peak P2 associated with the (110) plane of the Mo phase to the intensity of X-ray diffraction peak P1 associated with the (110) plane of the Cr phase was calculated. Furthermore, the ratio (P3 / P1) of the intensity of X-ray diffraction peak P3 associated with the (110) plane of the W phase to the intensity of peak P1 was calculated. The results are shown in Tables 3 and 4 below. When peak P2 was indistinguishable from noise and the ratio (P2 / P1) was 5% or less, it was indicated as "<5%." When peak P3 was indistinguishable from noise and the ratio (P3 / P1) was 5% or less, it was indicated as "<5%."

[0042] [Transverse Strength Test] The transverse strength of the target was measured by the method described above, and the results are shown in Tables 3 and 4 below.

[0043] [Number of particles in thin film] A thin film was formed by sputtering a target (diameter: 95 mm, thickness: 2 mm). The sputtering conditions were as follows: Substrate: cleaned glass substrate Chamber atmosphere: atmospheric pressure of 1×10 －４ The chamber was evacuated to a pressure of 0.6 Pa or less, and 99.99% pure Ar gas was introduced to 0.6 Pa - film thickness: 20 nm. The film was observed with an optical surface analyzer, and the number of particles with a size of 0.1 μm or more was counted. The results are shown in Tables 3 and 4 below.

[0044] [Grain size] The thin film was observed by TEM to measure the average grain size. The ratio of this average grain size to the grain size of Cr in Comparative Example 1 was calculated. The results are shown in Tables 3 and 4 below.

[0045] [Hardness of sputtered film] Test pieces were taken from the single layer film obtained by the above-mentioned sputtering, and the hardness of the thin film was measured by nanoindentation. The ratio of this hardness to the hardness of Cr in Comparative Example 1 was calculated. The results are shown in Tables 3 and 4 below.

[0046]

[0047]

[0048]

[0049]

[0050] As is clear from Tables 3 and 4, the sputtering targets of each example have excellent bending strength. Furthermore, the thin films obtained from these targets have few particles, small crystal grain sizes, and excellent hardness. These evaluation results clearly demonstrate the superiority of these sputtering targets.

[0051] Thin films for a variety of applications can be produced from the sputtering targets described above.

Claims

1. A sputtering target composed of a Cr-based alloy, the Cr-based alloy comprising: B: 5 at% or more and 30 at% or less; and at least one selected from the group consisting of Mo and W: a total of 5 at% or more and 30 at% or less; in the Cr-based alloy, the B content is the same as or greater than the total content of Mo and W, and the total content of B, Mo and W is 40 at% or less; a ratio of an X-ray diffraction peak intensity for a (110) plane of the Mo phase to an X-ray diffraction peak intensity for a (110) plane of the Cr phase is 10% or less; and a ratio of an X-ray diffraction peak intensity for a (110) plane of the W phase to an X-ray diffraction peak intensity for a (110) plane of the Cr phase is 50% or less.

2. The sputtering target according to claim 1, wherein the Cr-based alloy consists of B: 5 at% or more and 30 at% or less, at least one selected from the group consisting of Mo and W: 5 at% or more and 30 at% or less in total, and the remainder being Cr and unavoidable impurities.

3. The sputtering target according to claim 1 or 2, wherein the sputtering target has a flexural strength of 300 MPa or more as measured by a three-point bending test in accordance with the provisions of JIS Z 2511:2006.

4. The sputtering target according to claim 1 or 2, wherein the oxygen content of the Cr-based alloy is 3000 ppm or less.

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