TWI565813B - Cu-Ga alloy sputtering target - Google Patents

Description

Cu-Ga alloy sputtering target

This invention relates to a Cu-Ga alloy sputtering target. In particular, the present invention relates to a Cu-Ga alloy sputtering target used in forming a Cu-In-Ga-Se (hereinafter referred to as CIGS) quaternary alloy thin film which is a light absorbing layer of a thin film solar cell layer.

In recent years, as a thin film solar cell, mass production of a CIGS-based solar cell having high photoelectric conversion efficiency has progressed. In general, a CIGS-based thin film solar cell has a structure in which a back surface electrode, a light absorbing layer, a buffer layer, a transparent electrode, and the like are sequentially laminated on a substrate. As a method of producing the light absorbing layer, a vapor deposition method and a selenization method are known. Although the solar cell manufactured by the vapor deposition method has the advantages of high conversion efficiency, it also has the disadvantages of low film formation speed, high cost, and low productivity, and the selenization method is more suitable for industrial mass production.

The general process of selenization is as follows. First, a molybdenum electrode layer is formed on a soda lime glass substrate, and a Cu-Ga layer and an In layer are sputter-deposited thereon, and then a CIGS layer is formed by high-temperature treatment in a hydrogenated selenium gas. A Cu-Ga alloy sputtering target is used in the sputtering deposition of the Cu-Ga layer in the CIGS layer formation process by the selenization method.

One of the characteristics required as a sputtering target is a characteristic that it is difficult to cause abnormal discharge at the time of film formation. As a cause of the abnormal discharge, particles entrapped in the ingot may be mentioned. It is known that the inclusions are exposed to the sputtering surface, and the projection shape (nodule) is partially charged, which causes abnormal discharge. In addition, the inclusions scattered from the sputtered surface are mixed into the sputtered film. It is the cause of lowering the conversion efficiency of solar cells.

The Cu-Ga alloy target can be produced by a melt casting method. For example, Japanese Laid-Open Patent Publication No. 2000-73163 (Patent Document 1) discloses a Cu-Ga alloy in which a composition of Ga is set to 15% by weight to 70% by weight and is cast by a melting method as the Cu. In the method for producing a -Ga alloy, it is described that a pure copper and pure Ga are melt-cast in a vacuum furnace to form a target having an oxygen value of 25 ppm and no segregation, and no abnormal discharge, particles, and spatter are generated during the film formation.

Japanese Laid-Open Patent Publication No. 2013-76129 (Patent Document 2) discloses a sputtering target in which a Cu-Ga alloy having a Ga concentration of 27% by weight or more and 30% by weight or less is formed by melt casting. It is described that the Cu-Ga alloy is a sputtering target in which pure Cu and pure Ga are melt-cast into a cylindrical sputtering target under Ar gas at atmospheric pressure. A description is given of a Cu-Ga alloy sputtering film which is excellent in quality and which is excellent in quality after sputtering using the sputtering target.

Japanese Laid-Open Patent Publication No. 2013-204081 (Patent Document 3) discloses a plate-shaped Cu in which Ga is 15 at% or more and 22 at% or less, and the remainder is composed of Cu and unavoidable impurities. -Ga alloy sputtering target. It is described that the Cu-Ga alloy is obtained by melting a purity of 4N Cu and a purity of 4N in a nitrogen atmosphere, and using a vertical continuous casting method. It is described that a Cu-Ga alloy film which is less likely to generate particles and which is homogeneous can be obtained by forming a target from the obtained Cu-Ga alloy and performing sputtering.

Prior art literature

Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-73163

Patent Document 2: Japanese Laid-Open Patent Publication No. 2013-76129

Patent Document 3: Japanese Laid-Open Patent Publication No. 2013-204081

As described above, when a sputtering target made of a Cu-Ga alloy is produced by a melt casting method, a usual method is to melt a high-purity Cu and Ga raw material under an inert gas such as Ar or N. By performing the melt casting under such conditions, the gas component which is an impurity contained in a trace amount in the raw material can be removed, and the inclusion obtained by the reaction with the molten metal can be prevented from remaining in the ingot.

The sputtering target in which the inclusions are suppressed as described above is not problematic as long as it conforms to the sputtering conditions for the conventional mainstream plate-shaped sputtering target. However, in recent years, plate-shaped sputtering targets have been gradually replaced by cylindrical sputtering targets that use high efficiency. In order to improve work efficiency, a cylindrical sputtering target needs to be increased in output to increase the film formation speed. According to the findings of the present inventors, it has been found that in the high-efficiency sputtering operation for increasing the deposition rate with such a high output, abnormal discharge occurs in the conventional sputtering target.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a Cu-Ga alloy sputtering target which does not cause abnormal discharge during high-output sputtering operation.

The present inventors conducted intensive studies to solve the above problems, and found that it is necessary to suppress minute inclusions which have hitherto been considered to cause no problem. So far, the minute inclusions formed by the impurity elements in the produced Cu-Ga alloy sputtering target have not been sufficiently studied, and in addition to the effective melting casting conditions for preventing such impurity elements from being mixed into the target, It has not been fully studied in an inactive environment or under vacuum. According to the study of the present inventors, it was found that even inactive The use of high-purity raw materials under the environment or under vacuum also produces inclusions mainly composed of carbon or oxide. Even if such inclusions are trace amounts, they cause abnormal discharge during sputtering in high-output sputtering operations.

Therefore, the inventors studied a method of suppressing minute inclusions. The additive or the electrolyte component during the electrowinning, the organic matter which is deposited by the device member such as a pipe, and the foreign matter mixed in from the environment around the device may be mixed as impurities and adhered to the electrolytic copper as a raw material. By mixing the electrolyte with an activated carbon filter or separating the cathode and the anode by partition walls during electrolytic refining, it is possible to reduce the incorporation of these impurities into the electrolytic copper. However, it is impossible to completely remove impurities such as copper compounds such as S and O or carbon-based suspensions which pass through the filter or the mesh of the partition walls. Also for the Ga raw material, it is impossible to make the impurity inevitably mixed into the raw material zero. Further, a Ga-based suspension derived from water vapor in the air contained in the graphite member used in the melting furnace or a carbon-based suspension derived from the material of the crucible is formed and remains as an inclusion.

In view of such circumstances, the inventors studied methods for improving the conditions at the time of melt casting. During the repetitive study, it was found that these oxide or carbon suspensions, in addition to leaving the furnace in an inactive environment, inject the inert gas into the molten metal, and at this time ensure flow and reduce the nozzle diameter to the off important. The present invention has been completed based on the above findings.

In one aspect of the present invention, a sputtering target is made of a Cu-Ga alloy containing 15 at% or more and less than 30 at% of Ga, and the balance being Cu and unavoidable impurities, and is an unavoidable impurity. The density of C is 30 ppm by mass or less, and the concentration of the unavoidable impurity O is 50 ppm by mass or less, and the number of inclusions having an equivalent circular diameter of 20 μm or more is exposed to the inclusions on the sputtering surface of the target. It is 0.5 / mm ² or less.

In one embodiment of the sputtering target according to the present invention, when the sputtering surface is observed The ratio of the total area of the inclusions to the observed area is 0.02% or less.

In another embodiment of the sputtering target according to the present invention, the number of inclusions having an equivalent circular diameter of less than 20 μm is 15/mm ² or less in the inclusions exposed to the sputtering surface of the target. .

In still another embodiment of the sputtering target according to the present invention, the number of inclusions having an equivalent circular diameter of 10 μm or more and less than 20 μm is 1 in an inclusion exposed to the sputtering surface of the target. / mm ² or less.

In still another embodiment of the sputtering target according to the present invention, the concentration of the unavoidable impurity S is 10 ppm by mass or less.

In still another embodiment of the sputtering target according to the present invention, it has a cylindrical shape.

According to the present invention, a Cu-Ga alloy sputtering target having very few inclusions can be obtained. Therefore, by performing sputtering using the sputtering target according to the present invention, it is extremely unlikely that inclusions are mixed into the sputtering film, in addition to remarkably suppressing the occurrence of abnormal discharge. In particular, the Cu-Ga alloy sputtering target according to the present invention can withstand a high-output sputtering operation not only in the form of a plate but also in the case of a cylindrical shape.

(composition)

The Cu-Ga alloy sputtering target according to the present invention, in one embodiment, has It has the following composition: Ga containing 15 at% or more and less than 30 at%, and the remainder consisting of Cu and unavoidable impurities. The lower limit of the Ga concentration is required to form a Cu-Ga alloy sputter film required for the production of a CIGS-based solar cell. However, if the Ga concentration is excessively increased, the soft ζ phase disappears and the brittle γ phase increases, so that it is difficult to obtain Practical strength. Therefore, the Ga concentration is set to be less than 30 at%. The Ga concentration is typically 20 at% or more and 29 at% or less, and more typically 25 at% or more and 28 at% or less.

In the Cu-Ga alloy sputtering target according to the present invention, the concentration of the unavoidable impurity C can be 30 ppm by mass or less, and the concentration of the unavoidable impurity S can be 10 ppm by mass or less. The concentration of the unavoidable impurity O can be 50 mass ppm or less. Among these impurities, impurities derived from Cu and Ga raw materials can be reduced by the conventional melt casting method, but it is difficult to prevent the incorporation of impurities from the melting furnace.

According to a preferred embodiment of the present invention, the concentration of C can be 20 ppm by mass or less, further 15 ppm by mass or less, and further 10 ppm by mass or less. The lower limit of the concentration of C is not particularly set, but even if it is an extremely low concentration, since the effect is saturated and the manufacturing cost is increased, it is typically 5 ppm by mass or more.

Further, according to a preferred embodiment of the present invention, the concentration of O can be 25 ppm by mass or less, further 15 ppm by mass or less, and further 10 ppm by mass or less, and further less than 5 ppm by mass.

Further, according to a preferred embodiment of the present invention, the concentration of S can be 8 ppm by mass or less, further 6 ppm by mass or less, and can be, for example, 4 to 8 ppm by mass.

(inclusions)

In one embodiment of the Cu-Ga alloy sputtering target according to the present invention, the number of inclusions having an equivalent circular diameter of 20 μm or more is 0.5 in the inclusions exposed to the sputtering surface of the target. Below mm ² . The number density is preferably 0.3/mm ² or less, more preferably 0.2 / mm ² or less, still more preferably 0.1 / mm ² or less, and most preferably 0 / mm ² . In the case of a Cu-Ga alloy sputtering target, although inclusions composed of gallium oxide are often present, the inclusions are not limited thereto. Carbon-based suspensions derived from bismuth materials or raw materials also remain as inclusions. Further, there is a case where a compound of S remains as an inclusion. In the present invention, a compound of Cu-Ga, C or S which is formed by reaction in a furnace, and further, a component which is caused by a foreign matter derived from a mixture outside the furnace and which forms a second phase different from the parent phase is carried out as an inclusion. deal with. In the present invention, coarse impurities such as oxides having an equivalent circular diameter of 20 μm or more can be eliminated by effectively removing impurities such as oxides from the furnace during the melt casting. When inclusions having an equivalent circle diameter of 20 μm or more are increased, abnormal discharge is often generated during sputtering, and thus it is particularly important to suppress such coarse inclusions. Here, the equivalent circle diameter means a diameter of a circle having the same area as that of the exposed portion of the amorphous inclusion.

In one embodiment of the Cu-Ga alloy sputtering target according to the present invention, the number of inclusions having an equivalent circular diameter of less than 20 μm is 15 in the inclusions exposed to the sputtering surface of the target. Below mm ² . Even the inclusion equivalent circular diameter of less than 20μm fine objects, is ² or less is also preferred to minimize, according to the present invention, enables a circle equivalent diameter less than the number density of inclusions of 20μm to 15 / mm It can be preferably 7 pieces/mm ² or less, more preferably 5 pieces/mm ² or less, still more preferably 3 pieces/mrm 2 or less, and more preferably 2 pieces/mm ² or less.

A typical distribution of inclusions of a Cu-Ga alloy sputtering target according to the present invention, most of which has an equivalent circular diameter of less than 10 μm. Therefore, in one embodiment of the Cu-Ga alloy sputtering target according to the present invention, the inclusions exposed to the sputtering surface of the target according to the present invention have an equivalent circle diameter of 10 μm or more and less than 20 μm. The number density of the inclusions is 1 / mm ² or less, preferably 0.7 / mm ² or less, more preferably 0.4 / mm ² or less, still more preferably 0.2 / mm ² or less, for example, 0.1 to 1 /mm ² .

Thus, in the Cu-Ga alloy sputtering target according to the present invention, the generation of inclusions is stably suppressed. This matter can also be evaluated based on the index of the ratio of the total area of the inclusions in the observation of the sputtered surface to the observed area. The probability of occurrence of abnormal discharge is related to the ratio of the area occupied by the inclusions on the sputtering surface, and it is preferable that the ratio of the area occupied by the inclusions is as small as possible. In an embodiment of the Cu-Ga alloy sputtering target according to the present invention, the area ratio can be 0.02% or less, preferably 0.01% or less, more preferably 0.005% or less, and still more preferably 0.003% or less, for example, the area ratio can be made 0.001% to 0.1%.

The Cu-Ga alloy sputtering target according to the present invention can be provided, for example, in a plate shape or a cylindrical shape. In the sputtering target according to the present invention, for example, an indium-based alloy or the like can be bonded to a copper backing plate as a bonding metal.

(casting method)

An example of a suitable manufacturing method of the Cu-Ga alloy sputtering target according to the present invention will be described. In the manufacture of the Cu-Ga alloy sputtering target according to the present invention, the key is to use a high-purity Cu and Ga raw material of about 4 N, and in the case of melt casting, the inside of the furnace is a reduced pressure condition, or a rare gas (Ar, An inert gas such as He, Ne, or the like, or a nitrogen gas, is blown into the molten metal at a flow rate capable of repelling impurities derived from the melting furnace. The Cu-Ga alloy sputtering target according to the present invention can be produced in a continuous casting apparatus.

The Cu-Ga alloy sputtering target according to the present invention can be produced in a continuous casting apparatus.

As far as the flow rate of the inert gas is concerned, it is large depending on the amount of the raw material and the melting furnace. Since it is small, the shape, and the appropriate value also changes, it is difficult to normalize. For example, it can be used at a flow rate of 0.05 L/min or more per 1 kg of the raw material, preferably 0.1 L/min or more, and more preferably 0.2 L. A vertical continuous casting device in which a flow rate of /min or more is continuously flowed, and a horizontal continuous casting device or the like is cast. Further, by foaming the molten metal in these casting apparatuses, the inclusions can be moved to the surface of the molten metal, and the inclusions can be prevented from being caught and solidified. At the time of foaming, by reducing the inner diameter of the nozzle to increase the number and surface area of the bubbles, the amount of inclusions caught increases, and the convection of the molten metal is reduced, thereby suppressing the precipitation of inclusions, thereby improving Suspension separation effect of impurities such as carbon-based inclusions or oxygen-based inclusions. Further, by reducing the diameter of the nozzle, it is possible to obtain an advantage of preventing metal liquid scattering loss. Specifically, the inner diameter of the nozzle is preferably 10 mm or less, more preferably 7 mm or less, still more preferably 5 mm or less, and most preferably 3 mm or less. However, since the processing becomes difficult and the processing cost increases when the inner diameter of the nozzle is excessively reduced, it is usually 1 mm or more, and typically 2 mm or more.

[Examples]

The embodiments for better understanding of the invention and its advantages are shown below, but the invention is not limited to these embodiments.

(Example 1: Vertical continuous casting method)

A new Cu-Ga alloy (purity of 4N of Cu and purity of 4N of Ga) synthesized as the Ga concentration described in Table 1 was put into a graphite crucible in the amount described in Table 1, and heated to 1080 ° C, by The ingot is formed into a plate shape without being guided through a funnel (tundish) from the crucible downward into the mold to be cooled. The melt casting was carried out in a state in which the inside of the crucible and the inside of the mold were at a gas pressure, and Ar gas was blown into the molten metal (6 L/min) in the crucible to be foamed. The bubbling nozzle uses a nozzle having an inner diameter of 2 mm. Cutting the ingot to make a circle with a diameter of 6 inches and a thickness of 5 mm Disc-shaped sputtering target.

(Example 2: Vertical continuous casting method)

The ingot was melt-cast and sputtered under the same conditions as in Example 1 except that the Ga concentration was changed to the value of Table 1 and the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material. Plating target. When the chips are used, the effect of foaming can be confirmed by mixing the amount of carbon derived from the cutting oil.

(Example 3: Vertical continuous casting method)

The ingot was melt-cast and sputtered under the same conditions as in Example 1 except that the Ga concentration was changed to the value of Table 1 and the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material. Plating target.

(Example 4: Vertical continuous casting method)

The same as in Example 1, except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the inner diameter of the foaming nozzle was set to 5 mm. Conditions The ingot is melt-cast and cast to form a sputtering target.

(Example 5: Vertical continuous casting method)

The same as in Example 1, except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the inner diameter of the foaming nozzle was set to 5 mm. Conditions The ingot is melt-cast and cast to form a sputtering target.

(Example 6: Vertical continuous casting method)

The ingot was melt-casted under the same conditions as in Example 1 except that the Ga concentration was changed to the value of Table 1 and the inner diameter of the foaming nozzle was set to 5 mm to prepare a sputtering target.

(Example 7: Vertical continuous casting method)

The same as in Example 1, except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the inner diameter of the foaming nozzle was set to 7 mm. Conditions The ingot is melt-cast and cast to form a sputtering target.

(Example 8: Vertical continuous casting method)

The ingot was melt-casted under the same conditions as in Example 1 except that a part of the Cu-Ga alloy scrap (cutting powder) was used as a raw material, and the inner diameter of the foaming nozzle was set to 7 mm. Sputter target.

(Example 9: Vertical continuous casting method)

The same as in Example 1, except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the inner diameter of the foaming nozzle was set to 7 mm. Conditions The ingot is melt-cast and cast to form a sputtering target.

(Comparative Example 1: Vertical Continuous Casting Method)

The same conditions as in Example 1 were carried out except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the diameter of the foaming nozzle was set to 10 mm. The ingot was subjected to melt casting to prepare a sputtering target.

(Comparative Example 2: Vertical continuous casting method)

The same conditions as in Example 1 were carried out except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the diameter of the foaming nozzle was set to 15 mm. The ingot was subjected to melt casting to prepare a sputtering target.

(Comparative Example 3: Vertical continuous casting method)

The ingot was subjected to the same conditions as in Example 1 except that a part of the Cu-Ga alloy scrap (cutting powder) was used as a raw material, and the diameter of the foaming nozzle was set to 12 mm. Melt casting, making a sputtering target.

(Comparative Example 4: Vertical continuous casting method)

The same conditions as in Example 1 were carried out except that the Ga concentration was changed to the value of Table 1, the crumb (cutting powder) of the Cu-Ga alloy was used as a raw material, and the diameter of the foaming nozzle was set to 20 mm. The ingot was subjected to melt casting to prepare a sputtering target.

(Comparative Example 5: Vertical continuous casting method)

In addition to changing the Ga concentration to the value of Table 1, using a part of the Cu-Ga alloy crumb (cutting powder) as a raw material, and placing the furnace in an Ar gas atmosphere without foaming, 1 The same conditions were used to melt-cast the ingot to form a sputtering target.

(Comparative Example 6: Vertical continuous casting method)

The ingot was melt-casted under the same conditions as in Example 1 except that the Ga concentration was changed to the value shown in Table 1 and the furnace was placed in an Ar gas atmosphere without foaming, thereby forming a sputtering target.

<Equivalent circle diameter and area of inclusions>

The sputtered surface of the sputter target obtained was ground, and the area of each inclusion present in the area of 3 mm × 3 mm under the microscope was measured by EPMA element mapping. The measurement conditions of EPMA were acceleration voltage: 15.0 kV; irradiation current: 20 nA; detection time: 20 μsec/point; and measurement was performed at intervals of 3 μm and in the range of 1000 dots × 1000 dots (ie, 3 mm × 3 mm). Next, the range of the detection sensitivity of the background is 5 or more in the binarization processing, and the exposed area of the inclusion element exceeding the strength of the lower limit is measured. From the area of each inclusion, the equivalent circle diameter is assumed to be assumed to be a perfect circle, and the inclusions having an equivalent circle diameter of 20 μm or more, inclusions having an equivalent circle diameter of less than 20 μm, and equivalent are derived. The number of inclusions having a diameter of 10 μm or more and less than 20 μm was calculated for each 1 mm ² . Further, the ratio of the total area of the inclusions to the observation area was determined. The results are shown in Table 1.

<Measurement of impurity concentration>

From the target sample (2 mm × 2 mm × 18 mm), the concentration of S was measured using GD-MS (manufactured by Nu-Instruments, device name: AstruM), and the infrared absorption method (manufactured by LECO, device name: CS844) was measured. The concentration of C was measured, and the concentration of O was measured by an infrared absorption method (manufactured by LECO, device name: CS6000). The results are shown in Table 1.

<sputtering characteristics>

The resulting sputtering target was brazed to a high-purity copper backing plate, and the SPL-500 sputtering apparatus manufactured by Canon Anelva, and the ultimate vacuum pressure in the gas chamber before the start of sputtering was 5 × 10 ^-4 Pa, splashed. The frequency of abnormal discharge after sputtering for 10 hours under the conditions of a plating pressure of 0.5 Pa, an argon sputtering gas flow rate of 50 SCCM, and a sputtering power of 1500 W is shown in Table 1. The evaluation criteria for the abnormal discharge frequency are as follows.

None: 0 times

There are: 1~10 times

More: more than 10 times

*Evaluation only allows "None".

<inspection>

As is apparent from the results of Table 1, in Examples 1 to 9, by using a foaming nozzle having a small inner diameter to flow through Ar to perform melt casting, the suspension separation of impurities such as carbon-based inclusions and oxygen-based inclusions is efficiently performed. By reducing the amount of C, S, and O as impurities and reducing inclusions, no abnormal discharge occurs when sputtering is performed using the obtained sputtering target. Further, even in the case where the crumb to which the oil component is attached is used as the raw material, inclusions can be effectively suppressed by foaming. In this test case, As a result, the conditions of the sputtering power of 1500 W are quite strict, and as a result, it can be said that the sputtering target according to the present invention clearly achieves an excellent abnormal discharge suppressing effect.

On the other hand, in Comparative Examples 1 to 6, the inclusions were increased by the insufficient suspension separation of the carbon-based inclusions, and abnormal discharge occurred during sputtering.

(Example 10: Production of a cylindrical shape target based on a vertical continuous casting method)

A cylindrical Cu-Ga alloy billet was produced by vertical continuous casting under the same conditions as in Example 1 except that the mold shape was a cylindrical shape. With respect to this Cu-Ga alloy steel slab, the equivalent circle diameter and area of the inclusions were determined in the same manner as the above method, and the impurity concentration was measured. The results are shown in Table 1.

Claims (6)

A sputtering target made of a Cu-Ga alloy containing 15 at% or more and less than 30 at% of Ga, and the balance being Cu and unavoidable impurities, and the concentration of C as an unavoidable impurity is 30 The mass ppm or less is an unavoidable impurity O. The concentration of O is 20 ppm by mass or less, and the number of inclusions having an equivalent circular diameter of 20 μm or more is 0.5/mm in the inclusions exposed to the sputtering surface of the target. ² or less. The sputtering target according to the first aspect of the invention, wherein the ratio of the total area of the inclusions to the observation area when the sputtering surface is observed is 0.02% or less. The sputtering target according to claim 1 or 2, wherein the number of inclusions having an equivalent circular diameter of less than 20 μm is 15/mm ² or less in the inclusions exposed to the sputtering surface of the target. . The sputtering target according to claim 1 or 2, wherein the number of inclusions having an equivalent circular diameter of 10 μm or more and less than 20 μm is 1 in an inclusion exposed to the sputtering surface of the target. /mm ² or less. As a sputtering target of the first or second aspect of the patent application, the concentration of the unavoidable impurity S is 10 ppm by mass or less. A sputtering target according to claim 1 or 2, which has a cylindrical shape.