JP2013091822A - Alloy slab and sputtering target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Cu-Ga alloy slab in which cracks are prevented from generating upon cutting etc., and a sputtering target made by using such Cu-Ga alloy slab.SOLUTION: The Cu-Ga alloy slab contains a high-melting point metal, whose melting point is higher than that of the Cu-Ga alloy, in an amount of 1 atom% or lower by atomic percent. The sputtering target is made by using the Cu-Ga alloy slab.

Description

  The present invention relates to an alloy slab mainly composed of a Cu-Ga alloy and a sputtering target produced using the alloy slab.

  A Cu—Ga alloy having a relatively large composition ratio of Ga (gallium) is mainly used as a sputtering target for forming a thin film of a light absorption layer constituting a thin film solar cell.

  The sputtering target is cut by cutting an ingot (slab) of a rectangular parallelepiped shape (for example, a size of 300 mm × 400 mm × 1000 mm) manufactured by a melt casting method into several pieces using a lathe or a circular saw. It is manufactured by rolling and cutting an alloy piece (slab).

  For example, Patent Document 1 discloses a method of manufacturing a Cu—Ga alloy slab for a sputtering target made of a Cu—Ga alloy by melt casting. However, with the technique disclosed in Patent Document 1, only a relatively small size Cu—Ga alloy slab can be manufactured, and a mold that matches the desired size of the Cu—Ga alloy slab is prepared each time. Productivity is extremely low.

  As another method of manufacturing a Cu—Ga alloy slab for a sputtering target, there is a method of forming (manufacturing) a desired shape by sintering a Cu—Ga alloy powder as in the case of forming ceramics or the like. A Cu—Ga alloy slab produced by sintering Cu—Ga alloy powder has a low relative density of 95% or less and a high oxygen content of several thousand ppm when processed into a sputtering target. In addition, abnormal discharge during sputtering film formation and contamination with oxides are involved.

  Therefore, when using a Cu-Ga alloy slab at the time of sputtering target preparation, it is desirable that the Cu-Ga alloy slab is generally manufactured by melt casting.

  A Cu—Ga alloy having a relatively large Ga composition ratio used as a sputtering target has poor ductility and malleability, has high hardness, and is easily cracked (brittle). Therefore, the Cu-Ga alloy slab made of Cu-Ga alloy manufactured by melt casting may have cracks. In order to commercialize such a cracked Cu-Ga alloy slab, for example, the cracked portion must be cut and removed. In addition, since impurities are mixed into the generated cutting scraps by cutting, for example, when using a Cu-Ga alloy slab when producing a sputtering target, the cutting scraps are melt cast into the Cu-Ga alloy slab. It cannot be reused when manufacturing. Therefore, a large amount of cutting waste that cannot be reused is generated, and the yield of Cu-Ga alloy slab products deteriorates.

  For example, in Non-Patent Document 1, as a method for suppressing the occurrence of cracks when a copper alloy casting is produced by melt casting, a method of eliminating a stress generation source due to a change in mold shape, each part of the casting is uniformly cooled. A method of reducing the stress by reducing the temperature gradient, a method of providing a heat generating material, a heat insulating material, or the like in a hot metal part such as the upper part of the mold are disclosed.

JP 2000-73163 A

“Copper alloy casting production technology”, Foundation Materials Center, p. 391-392

  However, since a Cu-Ga alloy having a relatively large Ga composition ratio is a hard and brittle material having high hardness, it is disclosed in Non-Patent Document 1 as a countermeasure against cracking when a Cu-Ga alloy slab is manufactured by melt casting. Even if the disclosed technology is applied, a large-sized Cu—Ga alloy slab cannot be manufactured with sufficiently suppressed generation of cracks.

  Moreover, even if there is no crack at the time of manufacture, the Cu—Ga alloy slab made of a Cu—Ga alloy, which is a hard and brittle material, may be cracked at the time of cutting.

  Accordingly, an object of the present invention is to provide a Cu—Ga alloy slab capable of suppressing the occurrence of cracks during cutting and the like, and a sputtering target produced using such a Cu—Ga alloy slab. is there.

The present invention is an alloy slab mainly composed of a Cu-Ga alloy,
The alloy slab is characterized in that a high melting point metal having a melting point higher than that of the Cu—Ga alloy is contained in an atomic percentage of 1 at% or less.
In the present invention, the refractory metal is Mo.

  In the Cu-Ga alloy, the present invention is characterized in that the Ga composition ratio is 10 at% or more and 50 at% or less in atomic percentage.

  Moreover, this invention is produced using the said alloy slab, It is a sputtering target characterized by the above-mentioned.

  According to the present invention, an alloy slab mainly composed of a Cu—Ga alloy contains a high melting point metal having a melting point higher than that of the Cu—Ga alloy in an atomic percentage of 1 at% or less. This alloy slab mainly composed of a Cu-Ga alloy has a refractory metal as a crystal nucleus, a crystal of the Cu-Ga alloy is refined and grown, and a slab having a large amount of deformation until fracture occurs. It has become. Therefore, the alloy slab of the present invention can suppress the occurrence of cracks during cutting.

  Further, according to the present invention, since the refractory metal is Mo, the refractory metal can function as a crystal nucleus, resulting in an alloy slab with increased strength. Therefore, an alloy slab in which the occurrence of cracks during cutting or the like is reliably suppressed is obtained.

  According to the present invention, in the Cu—Ga alloy, the Ga composition ratio is 10 at% or more and 50 at% or less in atomic percentage. When the Ga concentration is low, Ga solid solution occurs in Cu, so that the occurrence of cracks is small. When the Ga concentration is too high, the solid solution limit is exceeded, so that an intermetallic compound is formed, cracking is increased, and segregation is likely to occur during casting. When the composition ratio of Ga is 10 at% or more and 50 at% or less in terms of atomic percentage, a high-strength alloy slab without cracking is obtained.

  Moreover, according to this invention, a sputtering target is produced using the alloy slab of this invention. Since the alloy slab of the present invention is a slab that can suppress the occurrence of cracks during cutting or the like, the sputtering target produced using the alloy slab has the occurrence of cracks suppressed. Therefore, the sputtering target of this invention can be used suitably as a sputtering target for thin film formation of the light absorption layer which comprises a thin film type solar cell, for example.

It is a perspective view which shows the structure of the casting apparatus 100 used in order to produce the alloy slab which is one Embodiment of this invention. FIG. 3 is a perspective view showing configurations of a mold 2 and a storage tank 3. It is a figure which shows the arrangement position of the storage tank 3 with respect to the casting_mold | template 2. FIG. It is a figure which shows a mode that a 3 point | piece bending test is performed.

  The alloy slab which is one embodiment of the present invention contains a Cu—Ga alloy composed of Cu (copper) and Ga (gallium) as a main component. The alloy slab mainly composed of the Cu—Ga alloy of the present embodiment (hereinafter simply referred to as “Cu—Ga alloy slab”) has a high melting point metal having a melting point higher than that of the Cu—Ga alloy. Contains below.

  The Cu—Ga alloy slab of the present embodiment is manufactured by melt casting, which will be described later, and is made of Cu, Ga, and a refractory metal having a melting point higher than that of the Cu—Ga alloy (hereinafter simply referred to as “refractory metal”). As described above, the high melting point metal is contained by being manufactured by melt casting.

  At the time of manufacturing a Cu—Ga alloy slab by melt casting, the refractory metal functions as a crystal nucleus, whereby the crystal of the Cu—Ga alloy is refined and crystal grows. Therefore, the Cu—Ga alloy slab of the present embodiment containing a refractory metal in an atomic percentage of 1 at% or less is a slab that has a large amount of deformation until breakage, which causes cracks during cutting and the like. Can be suppressed.

  If the content of the refractory metal is too small, the effect of crystal growth of the Cu—Ga alloy is refined and crystal growth cannot be achieved. If the content is too large, the crystal structure of the Cu—Ga alloy changes. Therefore, the refractory metal is preferably contained in an atomic percentage of 0.1 at% or more and 1 at% or less. The melting point of the refractory metal is preferably higher than the melting point of the Cu—Ga alloy by 500 ° C. or more.

  The refractory metal contained in the Cu—Ga alloy slab is not particularly limited as long as it has a higher melting point than the Cu—Ga alloy and does not become a metal contamination source as a sputtering target described later. Examples include Mo (molybdenum), Ti (titanium), and Si (silicon).

  The composition ratio of Ga in the Cu—Ga alloy is not particularly limited, but is preferably 10 at% or more and 50 at% or less, more preferably 20 at% or more and 40 at% or less. In the present invention, “at%” is treated as a term similar to “mol%”. When the Ga concentration is low, Ga solid solution occurs in Cu, so that the occurrence of cracks is small. When the Ga concentration is too high, the solid solution limit is exceeded, so that an intermetallic compound is formed, cracking is increased, and segregation is likely to occur during casting.

  The melting point of the Cu—Ga alloy varies depending on the Ga composition ratio in the Cu—Ga alloy. For example, when the Ga composition ratio is 30 at%, the melting point of the Cu—Ga alloy is 850 ° C.

  Next, the manufacturing method which manufactures a Cu-Ga alloy slab is demonstrated. FIG. 1 is a perspective view showing a configuration of a casting apparatus 100 used for producing the alloy slab of the present embodiment. FIG. 2 is a perspective view showing configurations of the mold 2 and the storage tank 3. FIG. 3 is a diagram illustrating an arrangement position of the storage tank 3 with respect to the mold 2.

  The Cu—Ga alloy slab of the present embodiment can be manufactured using the casting apparatus 100. The casting apparatus 100 is an apparatus for producing a Cu—Ga alloy slab by melt casting.

  The casting apparatus 100 is disposed in the chamber so that melt casting can be performed under reduced pressure. The casting apparatus 100 includes a crucible 1, a mold 2, and a storage tank 3.

  The crucible 1 accommodates a molten metal of Cu—Ga alloy (hereinafter simply referred to as “molten metal”) 5 containing a refractory metal, and is provided with a tapping opening 12 for tapping the accommodated molten metal 5. It has been.

  The material constituting the crucible 1 is not particularly limited as long as it can be dissolved and stirred, but ceramics, graphite and the like are preferable in view of not being a metal contamination source in the Cu-Ga alloy.

  The crucible 1 has a crucible main body 11 formed in a bottomed cylindrical shape, and a hot water outlet 12 that penetrates the side wall in the thickness direction is provided in the vicinity of the upper end of the side wall of the crucible main body 11. In addition, a funnel-shaped tapping guide 13 that protrudes outward from the side wall is formed on the side wall of the crucible body 11 so as to surround the tapping opening 12. The hot water guide part 13 guides the molten metal 5 discharged from the hot water opening 12 in one direction so that the molten metal 5 accommodated in the crucible body 11 is not discharged from the hot water opening 12 while being scattered in multiple directions.

  The size of the crucible 1 is not particularly limited, but the height H1 of the crucible body 11 is 300 mm or more and 1000 mm or less, and the opening diameter D1 of the opening is 150 mm or more and 500 mm or less. Moreover, in this embodiment, the hot water opening 12 is formed in the circular shape whose opening diameter is 10 mm or more and 20 mm or less.

  The casting mold 2 is formed in a bottomed cylindrical shape, and is provided with a pouring opening 22 into which the molten metal 5 discharged from a discharge opening 33 of the storage tank 3 to be described later flows, and flows into the pouring opening 22 to be poured. The molten metal 5 is formed into a slab shape.

  Examples of the material constituting the mold 2 include sand, metal, ceramics, graphite (carbon) and the like, but considering that they do not become a source of metal contamination into the Cu—Ga alloy, sand, ceramics, graphite, etc. Graphite is particularly preferable in that it has a high heat capacity and thermal conductivity and high cooling efficiency.

  The mold 2 has a mold body 21 formed in a bottomed cylindrical shape. The mold body 21 is a hollow rectangular parallelepiped that opens upward in the vertical direction Z, and has a rectangular flat plate-shaped bottom portion and a plurality of (four in the present embodiment) side walls that stand vertically from the sides of the bottom portion. (Rectangular flat plate shape). In the mold 2, the pouring opening 22 is formed in a rectangular shape with the upper end portions of the plurality of side walls connected to each other, and is opened facing the upper side in the vertical direction Z. Moreover, in the casting_mold | template 2, in the upper end part of the some side wall, ie, the upper end part of the opening part which forms the pouring opening 22, as shown in FIG. A chamfered portion 23 that is chamfered at an angle is formed.

  The mold 2 has a length in the vertical direction Z inside the mold body 21, that is, the height Z1 inside the mold body 21 is 20 mm or more and 1000 mm or less, preferably 50 mm or more and 900 mm or less. The length X of the direction parallel to the short side (hereinafter referred to as “short side direction”), that is, the length X1 of the short side of the pouring opening 22 is 20 mm or more and 1000 mm or less, preferably 30 mm or more and 150 mm or less, The length Y in the direction parallel to the long side of the pouring opening 22 (hereinafter referred to as “long side direction”), that is, the length Y1 of the long side of the pouring opening 22 is 100 mm or more and 1000 mm or less, preferably 150 mm or more and 800 mm. It is as follows. Further, in the mold body 21, the relationship between the length X1 of the short side of the pouring opening 22, the length Y1 of the long side of the pouring opening 22 and the height Z1 inside the mold body 21 is Z1> Y1. It is preferable that> X1.

  If the size of the mold main body 21 is too small, the productivity of the Cu—Ga alloy slab decreases, and further, the Cu—Ga alloy melt 5 is rapidly cooled, which may cause brittle cracks. Further, if the size of the mold body 21 becomes too large, not only will stress build up inside the Cu—Ga alloy slab after casting and cause brittle cracks, but also the final solidification position of the molten metal 5 of the Cu—Ga alloy. Becomes the central part, which causes internal defects.

  In the mold body 21, the length ratio between the length X1 of the short side of the pouring opening 22 and the length Y1 of the long side of the pouring opening 22 is X1: Y1 when X1 is “1”. Is preferably 1: 2 to 1:15. More preferably, X1: Y1 is 1: 3 to 1:10. When the value of Y1 in this “X1: Y1” is too small, the solidification form in the mold main body 21 of the molten metal 5 of the Cu—Ga alloy changes, and stress accumulates in the central portion in the vertical direction Z, causing brittle cracking. In order to reduce the generation of stress, segregation may occur even when slow cooling is performed. In addition, when the value of Y1 is too large in “X1: Y1”, when a Cu—Ga alloy slab obtained after casting is lifted and processed, a large amount of force is applied to the central portion in the long side direction Y. There is a high possibility that cracks will occur in the part.

  Further, the internal volume of the mold body 21 is appropriately determined based on conditions such as specific heat, density, and thermal conductivity of the material constituting the mold 2 and conditions such as a casting temperature at the time of casting and an adjustment temperature of the mold body 21. It only has to be selected.

  The storage tank 3 is a bottomed cylindrical member that is disposed below the crucible 1 in the vertical direction Z between the crucible 1 and the mold 2 and stores the molten metal 5 discharged from the outlet 12 of the crucible 1.

  Examples of the material constituting the storage tank 3 include sand, metal, ceramics, and graphite (carbon). However, considering that they do not become a metal contamination source in the Cu—Ga alloy, sand, ceramics, graphite, and the like. Is preferred.

  The storage tank 3 is provided below the inflow opening 32 into which the molten metal 5 discharged from the outflow opening 12 of the crucible 1 flows, and below the inflow opening 32 in the vertical direction Z. 5 is provided with a discharge opening 33 that can overflow and discharge.

  Specifically, the storage tank 3 has a storage tank body 31 formed in a bottomed cylindrical shape. The storage tank main body 31 is a hollow rectangular parallelepiped opened upward in the vertical direction Z, and has a rectangular flat plate-shaped bottom portion 311 and a plurality of (in this embodiment) vertically rising from each side of the bottom portion 311 with respect to the bottom portion 311. 4) side walls 312 (rectangular flat plate shape). In the storage tank 3, the inflow opening 32 is formed in a rectangular shape by connecting the upper ends of the plurality of side walls 312, and opens upward in the vertical direction Z. The discharge opening 33 is formed so as to penetrate one side wall 312 of the plurality of side walls 312, specifically, one side wall 312 rising vertically from the long side of the bottom 311 in the thickness direction. The discharge opening 33 is formed in a slit shape (rectangular shape) extending in parallel with the long side of the bottom 311.

  The size of the storage tank 3 is the length of the storage tank body 31 in the vertical direction Z, that is, the height Z2 of the storage tank body 31 is 65 mm or more and 1130 mm or less, preferably 80 mm or more and 200 mm or less. The length in the direction X parallel to the side, that is, the length X2 of the short side of the inflow opening 32 is 50 mm or more and 1000 mm or less, preferably 100 mm or more and 200 mm or less, and the length in the direction Y parallel to the long side of the inflow opening 32 That is, the length Y2 of the long side of the inflow opening 32 is not less than 100 mm and not more than 1000 mm, preferably not less than 150 mm and not more than 800 mm. Furthermore, in the storage tank main body 31, the discharge opening 33 has a height Z4 from the bottom 311 to the lower end in the vertical direction Z of the opening forming the discharge opening 33 of 30 mm to 100 mm, preferably 40 mm to 60 mm. Formed in position. Further, the length in the direction Y parallel to the long side of the discharge opening 33, that is, the length Y3 of the long side of the discharge opening 33 is 10 mm or more and 1000 mm or less, preferably 15 mm or more and 800 mm or less. The length of Z, that is, the length Z3 of the short side of the discharge opening 33 exceeds 0 mm and is 100 mm or less, preferably 5 mm or more and 50 mm or less.

  In the storage tank 3, the distance Z4 from the bottom 311 to the lower end in the vertical direction Z of the opening that forms the discharge opening 33 is too large, and the short side length X2 and the long side length Y2 of the inflow opening 32 are set. If it becomes too large, the amount of the molten metal 5 that overflows from the discharge opening 33 and is not discharged and is stored in the storage tank 3 becomes too large, which may reduce the production efficiency of the Cu—Ga alloy slab.

  Further, in the storage tank 3, the distance Z4 from the bottom 311 to the lower end in the vertical direction Z of the opening that forms the discharge opening 33 becomes too small, and the short side length X2 and the long side length of the inflow opening 32 If the length Y2 becomes too small, there is a possibility that the effect of reducing the kinetic energy of the molten metal 5 when pouring the molten metal 5 discharged from the outlet 12 of the crucible 1 into the mold 2 through the storage tank 3 may be reduced. is there.

  Further, the storage tank 3 may be heated before pouring. The heating temperature is preferably 50 ° C. or higher and 900 ° C. or lower, and more preferably 100 ° C. or higher and 500 ° C. or lower. When the heating temperature is too high, the use of energy required for heating leads to an increase in manufacturing cost. In addition, when the heating temperature is too low, the viscosity of the molten metal 5 increases with a decrease in the temperature of the molten metal 5, which may cause a shortage of the molten metal 5 in the mold 2. Furthermore, the molten metal 5 may be solidified in the storage tank 3, and the molten metal 5 may not be poured into the mold 2.

  The method for heating the storage tank 3 is not particularly limited as long as the temperature of the storage tank 3 can be increased, but a method of heating the storage tank 3 with electromagnetic induction, a heater, infrared rays, or the like can be given. Among them, a heater that is simple to use and capable of fine temperature adjustment is preferable.

  When a Cu-Ga alloy slab is produced by melt casting using the casting apparatus 100 configured as described above, the molten metal 5 accommodated in the crucible 1 is discharged from the hot water opening 12 and the inflow opening 32 is formed. And temporarily stored in the storage tank 3. Thus, the molten metal 5 stored in the storage tank 3 overflows from the discharge opening 33 and is discharged from the storage tank 3 when the molten metal surface 51 exceeds the lower surface 33a of the opening forming the discharge opening 33. Will be. Then, the molten metal 5 overflowed and discharged from the discharge opening 33 of the storage tank 3 is poured into the mold 2 through the pouring opening 22.

  When the Cu—Ga alloy slab is produced by melt casting using the casting apparatus 100, the molten metal 5 is not directly poured into the mold 2 from the crucible 1 as described above, but is stored in the storage tank. Since the molten metal 5 is poured into the mold 2 through 3, the kinetic energy of the molten metal 5 when poured into the mold 2 can be reduced, and at the inner surface (particularly the bottom surface) of the mold 2 at the time of pouring. Scattering of the molten metal 5 due to the collision can be prevented. Accordingly, the convection of the molten metal 5 when poured into the mold 2 can be suppressed, and the molten metal 5 can be prevented from being scattered, so that the molten metal 5 can be uniformly solidified in the mold 2. Therefore, a large-sized Cu—Ga alloy slab can be manufactured with sufficiently suppressed generation of cracks and internal defects.

  As shown in FIG. 3, the storage tank 3 is disposed at a position where the outer surface of the side wall 312 where the discharge opening 33 is formed is continuous above the inner surface of the mold 2 (the inner surface of the mold body 21).

  In the casting apparatus 100 including such a storage tank 3, the molten metal 5 stored in the storage tank 3 has a discharge opening 33 when the molten metal surface 51 exceeds the lower surface 33 a of the opening that forms the discharge opening 33. And then flows along the outer surface of the side wall 312 where the discharge opening 33 is formed, and further flows through the chamfered portion 23 along the inner surface of the mold 2 connected to the outer surface of the side wall 312. 2 is poured. As a result, the convection of the molten metal 5 when poured into the mold 2 can be suppressed, so that the molten metal 5 can be uniformly solidified in the mold 2, so that a large-sized Cu—Ga alloy slab can be obtained. Can be produced while sufficiently suppressing the occurrence of cracks.

When manufacturing a Cu-Ga alloy slab using the casting apparatus 100 as described above, first, necessary amounts of Cu, Ga and a refractory metal are charged into the crucible 1. At this time, as the refractory metal, a particulate solid powder is used. In such a particulate refractory metal, the volume average particle diameter is, for example, 1 μm or more and 100 μm or less. Thereafter, the pressure in the chamber in which the crucible 1 is charged is reduced to 10 ⁻¹ Torr or less.

After confirming that the pressure in the chamber has been reduced to 10 ⁻¹ Torr or less, the temperature is raised from 800 ° C. to 1100 ° C. at a temperature rising rate of 5 to 20 ° C./min, preferably 7 to 18 ° C./min. If the rate of temperature increase is too fast, bumping may occur, and if the rate of temperature increase is too slow, productivity will decrease. The holding temperature (casting temperature) after the temperature rise varies depending on the melting point of the alloy composition, the material of the mold 2, the volume, the specific heat, the density, etc., but is higher than the melting point of Cu and Ga and lower than the melting point of the refractory metal. Thereby, Cu and Ga melt, but the refractory metal does not melt, so that the refractory metal can function as a crystal nucleus. For example, when Mo (molybdenum) having a melting point of 2622 ° C. is used as the refractory metal and the melting point of the alloy composition is 850 ° C., the holding temperature (casting temperature) after the temperature rise is 900 ° C. or more and 1000 ° C. or less. Preferably, 920 degreeC or more and 980 degrees C or less are more preferable. If the holding temperature after the temperature rise is too high, power consumption and the like increase, leading to an increase in product cost. If the holding temperature after the temperature rise is too low, the molten metal 5 may harden at the outlet 12 and the outlet 12 may be clogged. Note that when the temperature is raised in the atmosphere, problems such as oxidation of the raw material occur, leading to a decrease in yield.

  Thereafter, the temperature is raised for 30 minutes to 12 hours, preferably 1 hour to 5 hours, after the temperature is raised (casting temperature) to obtain a molten Cu-Ga alloy 5 (alloy liquid) containing a refractory metal. If the holding time is too short, the alloy does not mix completely, or the gas remaining in the molten metal 5 cannot be completely removed, which can cause bumping in the subsequent higher vacuuming process. This is not preferable because it causes a decrease in properties.

Thereafter, the pressure is reduced to 8 × 10 ⁻⁴ Torr or less, preferably 5 × 10 ⁻⁴ Torr, and maintained for 30 minutes to 12 hours, preferably 1 hour to 5 hours. When the pressure in the chamber at the time of casting is high, entrainment of gas occurs in the Cu-Ga alloy slab after casting, causing internal defects. On the other hand, if it is too low, there is a need to increase the pump performance, leading to an increase in the cost of manufacturing equipment. Furthermore, if the pressure is reduced too much before raising the temperature, it may cause bumping and should be avoided. If the holding time is short, the gas present in the molten metal 5 cannot be removed, causing internal defects. On the other hand, if the length is too long, productivity is lowered, which is not preferable.

  Through the steps as described above, a molten Cu-Ga alloy 5 containing a refractory metal is obtained in the crucible 1. Next, the molten metal 5 in the crucible 1 is discharged from the hot water opening 12. The molten metal 5 discharged from the hot water opening 12 is temporarily stored in the storage tank 3 through the inflow opening 32. The molten metal 5 stored in the storage tank 3 overflows from the discharge opening 33 and is discharged from the storage tank 3 when the molten metal surface 51 exceeds the lower surface of the opening that forms the discharge opening 33. The Then, the molten metal 5 overflowed and discharged from the discharge opening 33 of the storage tank 3 is poured into the mold 2 through the pouring opening 22.

  It is also possible to cast a plurality of molds 2 and storage tanks 3 side by side and cast them at once. Next, after the Cu—Ga alloy containing the refractory metal cast in the mold 2 is naturally cooled to room temperature, the Cu—Ga alloy is taken out from the mold 2.

  Next, the Cu—Ga alloy taken out from the mold 2 is subjected to a heat treatment under atmospheric pressure or vacuum (preferably under atmospheric pressure). As temperature at the time of heat processing, it is 450 degreeC or more and less than 700 degreeC, More preferably, it is 500 degreeC or more and 600 degrees C or less. In the Cu—Ga alloy obtained by solidifying the molten metal 5 in the mold 2 by performing heat treatment on the Cu—Ga alloy, the Cu— The stress generated in the Ga alloy can be released. If the temperature during the heat treatment is too low, the stress generated during solidification cannot be released, and if it is too high, segregation occurs. The time for the heat treatment is preferably 1 hour or more and 12 hours or less, more preferably 2 hours or more and 8 hours or less. When the heat treatment time is too short, the internal stress of the Cu—Ga alloy cannot be released, and when it is too long, productivity is lowered.

  As described above, a Cu—Ga alloy slab containing a Cu—Ga alloy as a main component and containing a refractory metal can be obtained.

  In this embodiment, the refractory metal is charged at the stage of charging into the crucible 1, but only Cu and Ga are first melted to obtain a molten Cu—Ga alloy, and then the molten Cu—Ga alloy is used. A refractory metal may be added.

  The obtained Cu—Ga alloy slab can be suitably used as a slab for producing a sputtering target.

  As a method of processing a Cu-Ga alloy slab into a sputtering target, wire electric discharge machining, electric discharge machining, laser machining, diamond cutting with a grinding machine, cutting using a diamond band saw, cutting, water jet machining, wire saw A general method such as a blade saw can be employed. Among these processing methods, considering that the Cu-Ga alloy is a hard and brittle material, wire electric discharge machining, diamond band saw, electric discharge machining, laser machining, wire saw, water jet machining, etc. are preferable, wire electric discharge machining, diamond A band saw and a wire saw are more preferable.

  When processing a Cu-Ga alloy slab into a sputtering target by wire electric discharge machining, it is preferable to use a wire wire of 0.1 mm or more and 0.4 mm or less, more preferably a wire of 0.2 mm or more and 0.4 mm or less. Use lines. Moreover, the cutting speed (working speed) in wire electric discharge machining is preferably 0.1 mm / min or more and 8 mm / min or less, more preferably 0.1 mm / min or more and 3 mm / min or less. If the thickness of the wire is too thin, it will cause the wire to break during processing, and if the processing speed is too slow, it will lead to a decrease in productivity, and if it is too fast, it will cause cracking.

  Since the Cu—Ga alloy slab of the present embodiment is a slab that can suppress the occurrence of cracks during cutting, etc., the sputtering target produced using the alloy slab has suppressed the occurrence of cracks. It becomes a thing. Therefore, the sputtering target of this embodiment can be suitably used as, for example, a sputtering target for forming a thin film of a light absorption layer constituting a thin film solar cell.

(Example)
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, an Example is one embodiment of this invention and does not limit this invention.

Example 1
<Casting device>
As the casting apparatus, the casting apparatus including a storage tank shown in FIG. 1 was used.

[crucible]
・ Material: High purity graphite (carbon)
・ Opening opening diameter: 12mm

[template]
・ Material: High purity graphite (carbon)
-Height Z1: 650mm inside the mold body
・ Length of short side of pouring opening X1: 70mm
・ Long side length Y1: 350mm of the pouring opening

[Reservoir]
・ Material: High purity graphite (carbon)
・ Temperature of the storage tank just before the molten metal is poured: 200 ° C
-Height of storage tank body Z2: 120 mm
・ Short side length X2 of the inflow opening: 128mm
・ Long side length Y2 of the inflow opening: 251 mm
・ Distance Z4 from the bottom to the lower end of the opening forming the discharge opening: 45 mm
-Long side length Y3 of discharge opening: 200 mm
・ Short side length Z3 of the discharge opening: 30 mm

First, 67,660 g of copper (Cu), 31840 g of gallium (Ga), and 500 g of molybdenum (Mo) were charged in a crucible, and after the pressure in the chamber into which the crucible was charged was reduced to 1 × 10 ⁻¹ Torr level, 940 ° C. (casting temperature ) For 1 hour, and after that, the pressure was reduced to 2 × 10 ⁻⁴ Torr level and held for 2 hours to obtain a molten Cu—Ga alloy containing Mo. In addition, as Mo which is a refractory metal, the particulate fine powder whose volume average particle diameter is 3 micrometers was used.

  Next, the molten metal in the crucible is discharged from the outlet. The molten metal discharged from the hot water opening is temporarily stored in the storage tank through the inflow opening. When the molten metal stored in the storage tank in this way exceeds the lower surface of the opening that forms the discharge opening, it overflows from the discharge opening and is poured into the mold. At this time, the amount of molten metal per unit time of the molten metal flowing from the molten metal opening and poured into the mold was 22.4 kg / min.

  Next, after the Cu—Ga alloy cast in the mold is naturally cooled to room temperature, the Cu—Ga alloy is taken out from the mold and subjected to heat treatment at 570 ° C. for 2 hours using a hot air circulating furnace, and the length of 340 mm × A rectangular parallelepiped Cu-Ga alloy slab having a width of 450 mm and a thickness of 50 mm was obtained.

(Comparative Example 1)
A rectangular parallelepiped Cu-Ga alloy slab having a length of 340 mm, a width of 450 mm, and a thickness of 50 mm was obtained in the same manner as in Example 1 except that Mo, which is a refractory metal, was not added.

  The Cu-Ga alloy slab obtained in Example 1 and Comparative Example 1 was evaluated as follows.

<Evaluation of maximum strain>
The Cu—Ga alloy slab obtained in Example 1 and Comparative Example 1 was processed using a wire electric discharge machine (0.3 mm wire wire) at a processing speed of 0.7 mm / min, length 340 mm × width 450 mm × thickness. This was processed into a slice plate having a thickness of 10 mm. Thereafter, under the same conditions, the slice plate was processed into a test piece for bending test having a length of 40 mm, a width of 140 mm, and a thickness of 10 mm.

  Using the obtained test piece, a three-point bending test was performed by the method as described below, and the maximum strain was measured. The maximum strain shown here is measured by adhering a strain gauge to the center of the back surface of the test piece, and is the strain at the time of breaking the test piece.

The strain is calculated using the length of the test piece and the amount of change in the length of the test piece when a load is applied to the test piece. Using the amount of change in resistance of the strain gauge when a load is applied to the piece, it is calculated as in the following formula (1).
Strain ε (%) = ΔL / L = (ΔR / R) / K (1)
(In the formula, L represents the length of the test piece, ΔL represents the amount of change in the length of the test piece when a load is applied to the test piece, K represents the gauge factor of the strain gauge, and R represents the strain gauge. And ΔR indicates the amount of change in resistance of the strain gauge when a load is applied to the test piece.) The larger the maximum strain value, the greater the deformation of the test piece until it breaks. It can be said that the test piece is a material that is easy to be subjected to plastic working.

  FIG. 4 is a diagram illustrating a state in which a three-point bending test is performed. In the three-point bending test, first, as shown in FIG. 4, a strain gauge (not shown) (KFG-made by Kyowa Denki Co., Ltd.) is placed on two fulcrum rods 202 spaced apart by a fixed distance (100 mm). The test piece 200 was placed so that the back surface 200b of the test piece 200 to which 5-120-C1-11-L1M3R) was adhered was in contact with the two fulcrum bars 202. The support bar 201 is placed on the surface 200a of the test piece 200 corresponding to the center between the two fulcrum bars 202, and a load is applied at a crosshead speed of 1 mm / min from the direction of the arrow 203 until the test piece 200 breaks. The stress and strain were measured. As the two fulcrum rods 202 and the support rods 201, Φ12.7 mm × 50 mm rods were used, respectively. The evaluation results are shown in Table 1.

  From the results in Table 1, it can be seen that the test piece using the Cu—Ga alloy slab obtained in Example 1 is a material that has a large maximum strain value and is easily subjected to plastic working.

DESCRIPTION OF SYMBOLS 1 Crucible 2 Mold 3 Storage tank 11 Crucible body 12 Outlet opening 13 Outlet guide part 21 Mold body 22 Pouring opening 31 Reservoir body 32 Inflow opening 33 Outlet opening 100 Casting apparatus

Claims (4)

An alloy slab mainly composed of a Cu-Ga alloy,
An alloy slab comprising a high melting point metal having a melting point higher than that of the Cu-Ga alloy in an atomic percentage of 1 at% or less.   The alloy slab according to claim 1, wherein the refractory metal is Mo.   3. The alloy slab according to claim 1, wherein the Cu—Ga alloy has a Ga composition ratio of 10 at% or more and 50 at% or less in atomic percentage.   It is produced using the alloy slab as described in any one of Claims 1-3, The sputtering target characterized by the above-mentioned.