TW201343941A - Cu-Ga alloy sputtering target and its manufacturing method - Google Patents

Abstract

This invention relates to a Cu-Ga alloy sputtering target containing 15 at% to 22 at% of Ga, the remainder being a melted and casted sheet of Cu and unavoidable impurities, characterized by comprising a tissue of an alpha phase of Ga dissolved in Cu or a mixed phase of alpha phase and zeta phase. In the tissue formed by the alpha phase or the mixed phase of alpha phase and zeta phase, dendrite-like crystalline tissues are distributed. The dendrite-like crystalline tissues are formed by primary arms and secondary arms grown from the primary arms laterally. The average length of the secondary arms is 30 to 60 micron, and the average width of the secondary arms is 10 to 30 micron. The average interval between the secondary arms is 20 to 80 micron. Compared with a sintered target, the casted tissue sputtering target has the advantage of reduced gas content such as the oxygen. By the continuous solidification at a solidification condition above the cooling speed of the sputtering target with the casted tissue, a high quality target with the casted tissue can be obtained with the reduced oxygen and a distributed segregation phase.

Description

Cu-Ga alloy sputtering target and manufacturing method thereof

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, and a method for producing the same.

In recent years, mass production of high-efficiency CIGS-based solar cells has progressed as a thin-film solar cell, and a vapor deposition method and a selenization method are known as a method for producing a light-absorbing layer. The solar cell manufactured by the vapor deposition method has the advantages of high conversion efficiency, but has the disadvantages of low film formation speed, high cost, and low productivity, and the selenization method is more suitable for mass production in the industry.

The outline process of the selenization method 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 target is used in the sputtering film formation of the Cu-Ga layer in the CIGS layer formation process using the selenization method.

Various manufacturing conditions or characteristics of constituent materials affect the conversion efficiency of CIGS-based solar cells, and the characteristics of CIGS films also have a large impact.

As a method for producing a Cu-Ga target, there are a melting method and a powder method. In general, the Cu-Ga target produced by the melting method has relatively less impurity contamination, but has many disadvantages. For example, since the cooling rate cannot be increased, the composition segregation is large, and the composition of the film produced by the sputtering method gradually changes.

Further, shrinkage tends to occur at the final stage of cooling of the melt, and the characteristics of the peripheral portion of the shrinkage are also inferior, and it cannot be used since it is processed into a specific shape, and thus the yield is inferior.

In the prior art (Patent Document 1) relating to the Cu-Ga target by the melting method, the content of the composition segregation is not observed, but the analysis results and the like are not disclosed at all.

Further, in the examples, only the Ga concentration was 30% by weight, and there was no description about the properties such as the structure or segregation of the Ga low concentration region below.

On the other hand, a target produced by a powder method generally has problems such as low sintered density and high impurity concentration. Patent Document 2 related to a Cu-Ga target describes a sintered body target, but there is a prior art description relating to brittleness which is liable to cause cracking or chipping when the target is cut, and to solve the problem, two powders are produced. , it is mixed and sintered. Further, one of the two powders is a powder which increases the Ga content, and the other is a powder which reduces the Ga content and becomes a two-phase coexisting structure surrounded by a grain boundary phase.

This step is one in which two kinds of powders are produced, so the steps are complicated, and the oxygen concentration of the metal powder becomes high, and the relative density of the sintered body cannot be expected to be improved.

The target with low density and high oxygen concentration naturally has abnormal discharge or particle generation. If there are particles and other irregularities on the surface of the sputter film, it will also adversely affect the characteristics of the subsequent CIGS film, which may eventually lead to CIGS solar cells. The conversion efficiency is greatly reduced.

A large problem of the Cu-Ga sputtering target produced by the powder method is that the steps are complicated, the quality of the sintered body produced is not necessarily good, and the production cost is increased. In this respect, the melting and casting methods are preferred, but there are problems in manufacturing as described above, and the quality of the target itself cannot be improved.

As a prior art, for example, there is Patent Document 3. In this case, a technique of processing a target into a target by continuously casting a copper alloy containing high-purity copper and 0.04 to 0.15% by weight of a trace amount of titanium or 0.014 to 0.15 wt% of zinc is described.

In this alloy, the amount of added elements is a small amount, so it is not suitable for manufacturing Add an alloy with a larger amount of elements.

Patent Document 4 discloses a technique in which high-purity copper is continuously cast into a column shape in the absence of casting defects, and is rolled into a sputtering target. It is operated by pure metal and cannot be applied to the manufacture of alloys with a large amount of added elements.

Patent Document 5 describes a method in which a material selected from a single crystallized sputtering target is produced by continuously adding a material of 24 to 3.0% by weight of a material selected from Ag or Au to aluminum. Similarly, since the amount of the element added to the alloy is a small amount, it cannot be applied to the production of an alloy having a large amount of added elements.

In the above Patent Documents 3 to 5, there are disclosed examples in which the continuous casting method is used. However, any of them is a pure metal or a material added to a trace element-added alloy, and it can be said that the amount of the added element is not solved. The disclosure of problems in the manufacture of Cu-Ga alloy targets which are prone to segregation of intermetallic compounds.

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

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2008-138232

[Patent Document 3] Japanese Patent Laid-Open No. Hei 5-311424

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2005-330591

[Patent Document 5] Japanese Patent Laid-Open No. Hei 7-300667

Segregation of an intermetallic compound is likely to occur in a Cu-Ga alloy containing 15% or more of Ga, and segregation is less likely to be finely and uniformly dispersed in a usual melting method. On the other hand, the sputtering target of the cast structure has an advantage of reducing the gas component such as oxygen as compared with the sintered body target. An object of the present invention is to obtain a good-quality casting which reduces oxygen and disperses a segregation phase by continuously solidifying a sputtering target having the cast structure at a solidification temperature equal to or higher than a fixed cooling rate. The target of tissue formation.

In order to solve the above problems, the inventors of the present invention conducted intensive studies and found that by adjusting the composition of components and the continuous casting method, a CuGa alloy sputtering target which can reduce oxygen and disperse a large amount of dendritic crystals can be obtained. The present invention has been completed.

Based on the above findings, the present invention provides the following invention.

1) A Cu-Ga alloy sputtering target having a Ga content of 15 at% or more and 22 at% or less, and a remaining portion of a melted or cast plate composed of Cu and unavoidable impurities, characterized by having a Ga a structure in which a solid phase is dissolved in the α phase of Cu or a mixed phase of the α phase and the ζ phase, and a dendritic crystal structure (dendrite) is dispersed in a structure composed of the α phase or a mixed phase of the α phase and the ζ phase. It consists of a primary arm and a secondary arm that grows laterally from the primary arm. The average length of the secondary arm is 30-60 μm, and the average width of the secondary arm is 10-30 μm. The average interval between the secondary arms is 20~80μm.

2) The Cu-Ga alloy sputtering target according to the above 1), wherein the maximum diameter of the primary arm is 5 to 30 μm.

3) The Cu-Ga alloy sputtering target according to the above 1) or 2), wherein a phase having a Ga concentration richer than a dendritic structure (Ga-rich) is present between the secondary arms of the dendritic structure.

4) The Cu-Ga alloy sputtering target according to the above 3), wherein the phase in which the Ga concentration is richer than the dendritic structure is the α phase or the ζ phase.

5) The Cu-Ga alloy sputtering target according to any one of the above 1) to 4), which has an oxygen content of 20 wtppm or less.

6) A method for producing a Cu-Ga alloy sputtering target, which is characterized in that a target material is melted in a graphite crucible, and the molten metal is injected into a mold having a water-cooled probe to continuously manufacture a plate made of a Cu-Ga alloy. The cast body is further machined to produce a plate-shaped Cu-Ga alloy target, which is characterized in that the solidification rate from the melting point of the cast body to 300 ° C is controlled to 300 to 1000 ° C / min.

7) A method for producing a Cu-Ga alloy sputtering target, which comprises melting a target material in a graphite crucible, injecting the melt into a mold having a water-cooled probe, and continuously manufacturing a plate made of a Cu-Ga alloy The cast body is further machined to produce a plate-shaped Cu-Ga alloy target, which is characterized in that the solidification speed from the melting point of the cast body to 300 ° C is controlled to 300 to 1000 ° C / min, The target of any of the above 1) to 6) is produced.

8) The method for producing a Cu-Ga alloy sputtering target according to the above 6), wherein the drawing is performed at a drawing speed of 50 mm/min to 150 mm/min.

9) A method for producing a Cu-Ga alloy sputtering target according to the above 6) or 7), which is produced by a horizontal continuous casting method.

(10) The method for producing a Cu-Ga alloy sputtering target according to any one of the above 6), wherein the solidification rate from the melting point of the casting body to 300 ° C is controlled to 300 to 1000 ° C / Min, and adjust the amount and concentration of the α phase or the mixed phase of the α phase and the ζ phase formed during casting.

According to the present invention, compared with the sintered body target, it has a large advantage of reducing a gas component such as oxygen, and has an effect of continuously causing the sputtering target having the cast structure to be continuous under a solidification condition above a fixed cooling rate. Curing to obtain a target of a good cast structure that reduces oxygen and disperses dendrites.

As described above, by sputtering using a Cu-Ga alloy target having a cast structure having less oxygen and segregation and dispersion, there is an effect that a small amount of particles are generated, and a homogeneous Cu-Ga-based alloy film can be obtained, and Cu can be greatly reduced. The manufacturing cost of the -Ga alloy target. Since the light absorbing layer and the CIGS-based solar cell can be produced from such a sputtering film, there is an excellent effect of suppressing a decrease in conversion efficiency of the CIGS solar cell and producing a low-cost CIGS-based solar cell.

Figure 1 is a conceptual illustration of a dendritic structure.

2 is a view showing a micrograph of the surface of the target polished surfaces of Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2 which were etched with a hydrochloric acid-containing hydrochloric acid solution.

Fig. 3 is a view showing the result of surface analysis of FE-EPMA of the target polishing surface of Example 2 (top) and Example 4 (bottom).

The Cu-Ga alloy sputtering target system Ga of the present invention has a Ca-Ga alloy sputtering target of 15 at% or more and 22 at% or less, and the remainder is composed of Cu and unavoidable impurities, which are melted and cast.

Generally, the target of the sintered product is to have a relative density of 95% or more. The reason for this is that if the relative density is low, the progress of the generation or surface irregularity of the particles on the film due to the splash or abnormal discharge starting from the periphery of the hole during the exposure of the internal pores during sputtering will occur early. It is easy to cause abnormal discharge such as surface protrusion (tuberculosis) as a starting point. The cast product can achieve a relative density of almost 100%, and as a result, it has an effect of suppressing the difference in sputtering. It can be said that it is one of the great advantages of casting.

The content of Ga is required according to the requirements for formation of a Cu-Ga alloy sputtering film necessary for producing a CIGS-based solar cell, and the Ga-Ga alloy sputtering target system Ga of the present invention is 15 at% or more and 22 at% or less. The remaining portion is a melted, cast plate-shaped Cu-Ga alloy sputtering target composed of Cu and unavoidable impurities.

Further, the melted and cast plate-shaped Cu-Ga alloy sputtering target has a structure in which Ga is dissolved in the α phase of Cu or a mixed phase of the α phase and the ζ phase. Further, a dendritic structure is dispersed in the structure, and the dendritic crystal structure is composed of a primary arm and a secondary arm that grows laterally from the primary arm. The average length of the secondary arm is 30~60 μm, two The average width of the secondary arms is 10 to 30 μm, and the average interval between the secondary arms is 20 to 80 μm.

A conceptual illustration of the dendritic structure is shown in Figure 1. As shown in Fig. 1, there is a primary arm at the center, and the secondary arm grows on the side. The length of the secondary arm refers to the length of the side wall of the primary arm to the front end, and the width of the secondary arm refers to the width of the wall as shown in FIG. The interval between the secondary arms refers to the spacing between the central axes of the secondary arms.

Thus, a uniformly dispersed dendrite is extremely effective for film formation. The dendritic structure is affected by the cooling rate, and if the cooling rate is fast, the fine dendrites rapidly grow. Since Ga is an element which lowers the melting point, the Ga content is small in the dendritic structure which can be formed initially. That is, a dendritic structure having a small Ga content is formed. Thereafter, a (Ga-rich) phase having a Ga concentration richer than the dendritic structure is formed between the secondary arms of the dendritic structure.

The rich (Ga-rich) phase of Ga can be referred to as a segregation phase, and the dendrites are finely dispersed, resulting in a rich concentration of Ga between the dendritic structures (rich in Ga). The phases are also finely dispersed. It is one of the larger features of the invention of the present invention. When the overall structure of the sputtering target is observed, it is understood that there is no large segregation and it is a uniform structure.

Further, as one of the characteristics of the dendritic structure of the present invention, the maximum diameter of the primary arm is 5 to 30 μm. It also means the characteristic of the form in which the dendrites are finely dispersed.

The Cu-Ga alloy sputtering target is characterized in that the Ga concentration is richer than the phase of the dendritic structure as the α phase or the ζ phase of the solid solution. The Cu-Ga alloy sputtering target of the present invention can provide a Cu-Ga alloy sputtering target with a comprehensive oxygen content of less than 20 wtppm.

A method for producing a Cu-Ga alloy sputtering target is to melt a target material in a graphite crucible, and to inject the melt into a mold having a water-cooled probe to continuously produce a plate-shaped cast body composed of a Cu-Ga alloy, and further Machining it to produce a plate-shaped Cu-Ga alloy target, Preferably, the solidification rate from the melting point of the cast body to 300 ° C is controlled to 300 to 1000 ° C / min. Thereby, the above target can be manufactured.

Further, in the method of efficiently and effectively manufacturing the Cu-Ga alloy sputtering target, it is preferable to set the drawing speed to 50 mm/min to 150 mm/min. Moreover, such a continuous casting method is more effective in manufacturing using a horizontal continuous casting method.

Thus, by controlling the solidification rate from the melting point of the cast body to 300 ° C to 300 to 1000 ° C / min, the amount and concentration of the α phase or the mixed phase of the α phase and the ζ phase formed during casting can be easily adjusted.

As described above, the Cu-Ga alloy sputtering target of the present invention can have an oxygen content of 20 wtppm or less, which can be prevented by the degassing of the Cu-Ga alloy melt and the prevention of atmospheric mixing in the casting stage (for example, with a mold) The choice of the sealing material of the refractory material and the introduction of argon or nitrogen in the sealing portion are achieved.

In the same manner as described above, it is a preferred component for improving the characteristics of the CIGS-based solar cell. Further, this has the effect of suppressing the generation of particles during sputtering, reducing the oxygen in the sputtering film, and suppressing the formation of oxides or secondary oxides due to internal oxidation.

When manufacturing a Cu-Ga alloy sputtering target, a cast body having a section width of 50 mm to 320 mm and a thickness of 5 mm to 30 mm can be produced from the mold, and machined and surface-ground, thereby Although the processing conditions are arbitrary, it can be said that it is a preferable condition.

In the production of the light absorbing layer composed of the Cu-Ga-based alloy film and the CIGS-based solar cell, the variation in composition greatly changes the characteristics of the light absorbing layer and the CIGS-based solar cell, but the Cu-Ga alloy is splashed using the present invention. When the target was formed into a film, such compositional deviation was not observed at all. Compared with sintered products, it is one of the great advantages of castings.

[Examples]

Next, an embodiment of the present invention will be described. Furthermore, this embodiment is only one For example, it is not limited to this example. That is, all the aspects or modifications other than the invention and the embodiments that can be understood from the specification are included in the scope of the technical idea of the present invention.

(Example 1)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the dummy bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 15 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 50 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 350 ° C / min.

The obtained cast piece had a structure in which Ga was dissolved in Cu (α phase), and the oxygen concentration was less than 10 wtppm, forming a fine dendritic structure. The secondary dendritic arm spacing is 37 μm, the secondary dendritic crystal is 38 μm long and the width is 24 μm.

Furthermore, the interval and size of the secondary arms of the dendrites were measured from the average of 5 points from the five dendrites randomly selected. Therefore, the number of secondary arms selected in the number of dendrites 5× is 25 = the average of 25. The same is true below.

A phase with a high concentration of Ga (segregation phase, heterophase) was observed between the secondary dendrite arms. It becomes a structure sandwiched between the secondary dendritic arms, so the dendritic microstructure is micro Finely formed, so the segregation phase (heterogeneous phase) is also uniformly dispersed.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . As a result, a cast structure in which the Ga phase (segregation phase) is uniformly dispersed can be obtained. Thus, by performing sputtering using a Cu-Ga alloy target having a small amount of oxygen and having a Ga phase (segregation phase) uniformly dispersed cast structure, a Cu-Ga alloy film which is less and homogeneous in particle generation can be obtained. .

(Example 2)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the spindle bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 15 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 90 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 650 ° C / min.

The obtained cast sheet had a structure in which Ga was dissolved in Cu (α phase), and the oxygen concentration was less than 10 wtppm. A fine dendritic crystal structure composed of a primary dendrite arm and a secondary dendrite arm is formed in the cast structure. The secondary dendritic arm spacing is 28 μm, the secondary dendritic crystal is 33 μm long and the width is 19 μm.

A phase with a high concentration of Ga (segregation phase, heterophase) was observed between the secondary dendrite arms. Since it is sandwiched between the secondary dendrite arms, the dendritic crystal structure is finely formed, and thus the segregation phase (heterogeneous phase) is uniformly dispersed.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . Further, the results of the surface analysis of FE-EPMA are shown in the upper view of Fig. 3. If As shown in the figure, a cast structure in which a Ga phase (segregation phase) is uniformly dispersed can be obtained.

As described above, by sputtering using a Cu-Ga alloy target having a small amount of oxygen and a cast structure in which the Ga phase (segregation phase) is uniformly dispersed, a Cu-Ga-based alloy film having less generation and uniformity of particles can be obtained.

(Example 3)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the spindle bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 20 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 50 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 350 ° C / min.

The obtained cast piece had a structure in which Ga was dissolved in Cu (α phase), and the oxygen concentration was less than 10 wtppm, forming a fine dendritic structure. The secondary dendritic arm spacing is 48 μm, the secondary dendritic crystal is 45 μm long and the width is 25 μm.

A phase with a high concentration of Ga (segregation phase, heterophase) was observed between the secondary dendrite arms. Since it is sandwiched between the secondary dendrite arms, the dendritic crystal structure is finely formed, and thus the segregation phase (heterogeneous phase) is uniformly dispersed.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . As a result, a cast structure in which the Ga phase (segregation phase) is uniformly dispersed can be obtained. As described above, by sputtering using a Cu-Ga alloy target having a small amount of oxygen and a cast structure in which the Ga phase (segregation phase) is uniformly dispersed, a Cu-Ga-based alloy film having less generation and uniformity of particles can be obtained.

(Example 4)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the spindle bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 20 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 90 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 650 ° C / min.

The obtained cast piece had a structure in which Ga was dissolved in Cu (α phase), and the oxygen concentration was less than 10 wtppm, forming a fine dendritic structure. The interval between the secondary dendritic arms was 32 μm, the length of the secondary dendrites was 35 μm, and the width was 21 μm.

A phase with a higher concentration of Ga was observed between the secondary dendritic arms (segregation phase, Out of phase). Since it is sandwiched between the secondary dendrite arms, the dendritic crystal structure is finely formed, and thus the segregation phase (heterogeneous phase) is uniformly dispersed.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . Further, the results of the surface analysis of FE-EPMA are shown in the upper view of Fig. 3. As shown in the figure, a cast structure in which the Ga phase (segregation phase) is uniformly dispersed can be obtained.

As described above, by sputtering using a Cu-Ga alloy target having a small amount of oxygen and a cast structure in which the Ga phase (segregation phase) is uniformly dispersed, a Cu-Ga-based alloy film having less generation and uniformity of particles can be obtained.

(Comparative Example 1)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the spindle bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 15 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 30 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 200 ° C / min.

The obtained cast piece has a structure in which Ga is dissolved in Cu (α phase), oxygen The concentration is less than 10 wtppm, and the dendritic crystal structure is formed. The secondary dendritic arm spacing was 94 μm, the secondary dendritic crystal was 64 μm long and the width was 61 μm. A phase with a high concentration of Ga (segregation phase, heterogeneous phase) was observed between the secondary dendrite arms, but the dendritic crystals were large, and the segregation phase (heterogeneous phase) also became large.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . In this way, a Cu-Ga alloy target having a cast structure having a small amount of oxygen but having a Ga phase (segregation phase) is obtained. By sputtering using this target, the generation of particles is increased, and a homogeneous Cu-Ga-based alloy film cannot be obtained.

(Comparative Example 2)

First, 20 kg of copper (Cu: purity 4 N) raw material was placed in a graphite crucible, and the crucible was placed in a nitrogen atmosphere and heated to 1,250 °C. This high temperature heating is to weld the spindle bar to the Cu-Ga alloy melt.

Next, Ga (purity: 4 N) as an additive element was adjusted so that the Ga concentration became a composition ratio of 20 at%, and it was introduced into a heated crucible. For the heating of the crucible, a resistance heating device (graphite element) is used. The shape of the melting crucible is 140 mm ×400 mm The material of the mold was made of graphite, and the shape of the cast block was set to 65 mmw × 12 mmt for continuous casting.

After the raw material is melted, the temperature of the melt is lowered to 1080 ° C, and the drawing is started at the time when the temperature of the melt and the temperature of the mold are stabilized. A spindle rod is inserted at the front end of the mold, so that the solidified cast piece is extracted by withdrawing the spindle rod.

The pull mode is repeated for 0.5 second drive, 2.5 seconds stop, the frequency is changed, and the pull speed is set to 30 mm/min. The drawing speed (mm/min) has a proportional relationship with the cooling rate (°C/min), and if the drawing speed (mm/min) is increased, the cooling rate also increases. As a result, it became a cooling rate of 200 ° C / min.

The obtained cast piece has a structure in which Ga is dissolved in Cu (α phase), oxygen The concentration is less than 10 wtppm, forming a coarse dendritic structure. The secondary dendrite arm spacing was 98 μm, the secondary dendritic crystal was 62 μm long and the width was 65 μm.

A phase with a high concentration of Ga (segregation phase, heterogeneous phase) was observed between the secondary dendrite arms, but the dendritic crystals were large, and the segregation phase (heterogeneous phase) also became large.

The results are shown in Table 1. Next, the cast piece was machined into a target shape and further polished, and a micrograph of the surface of the polished surface etched with a hydrochloric acid solution containing ferric chloride was shown in Fig. 2 . In this way, a Cu-Ga alloy target having a cast structure having a small amount of oxygen but having a Ga phase (segregation phase) is obtained. By sputtering using this target, the generation of particles is increased, and a homogeneous Cu-Ga-based alloy film cannot be obtained.

[Industrial availability]

According to the present invention, compared with a sintered body target, there is a great advantage of reducing a gas component such as oxygen, and the sputtering target having the cast structure is continuously solidified under solidification conditions above a fixed cooling rate. The effect is that a target of a cast structure which is reduced in oxygen and formed with a large amount of fine dendrites can be obtained.

Thus, by sputtering using a Cu-Ga alloy target having less oxygen and having a cast structure in which a large amount of fine dendrites are dispersed, there is an effect that a Cu-Ga alloy film which is less and uniform in particle generation can be obtained. And the manufacturing cost of the Cu-Ga alloy target can be greatly reduced.

Since the light absorbing layer and the CIGS-based solar cell can be produced from such a sputtering film, there is an excellent effect of suppressing a decrease in conversion efficiency of the CIGS solar cell and producing a low-cost CIGS-based solar cell. Since a light absorbing layer and a CIGS-based solar cell can be produced from such a sputtering film, it is useful for a solar cell for suppressing a decrease in conversion efficiency of a CIGS solar cell.

Claims (10)

A Cu-Ga alloy sputtering target having a Ga content of 15 at% or more and 22 at% or less, and a remaining portion of a melted or cast plate composed of Cu and unavoidable impurities, characterized in that it has a solid solution by Ga a structure composed of a phase of Cu or a mixed phase of an α phase and a ζ phase, wherein a dendritic structure is dispersed in a structure composed of the α phase or a mixed phase of the α phase and the ζ phase, and the dendrite is composed of a dendrite The primary arm is formed by a secondary arm that grows laterally from the primary arm. The average length of the secondary arm is 30 to 60 μm, the average width of the secondary arm is 10 to 30 μm, and the average interval between the secondary arms is 20~. 80μm. For example, in the Cu-Ga alloy sputtering target of claim 1, wherein the maximum diameter of the primary arm is 5 to 30 μm. A Cu-Ga alloy sputtering target according to claim 1 or 2, wherein a phase having a Ga concentration richer than a dendritic structure (Ga-rich) is present between the secondary arms of the dendritic structure. The Cu-Ga alloy sputtering target according to claim 3, wherein the phase in which the Ga concentration is richer than the dendritic structure is an α phase or a ζ phase. The Cu-Ga alloy sputtering target according to any one of claims 1 to 4, which has an oxygen content of 20 wtppm or less. A method for producing a Cu-Ga alloy sputtering target, which is characterized in that a target material is melted in a graphite crucible, and the molten metal is injected into a mold having a water-cooled probe to continuously produce a plate-shaped casting composed of a Cu-Ga alloy. The body is further machined to produce a plate-shaped Cu-Ga alloy target, which is characterized in that the solidification rate from the melting point of the cast body to 300 ° C is controlled to 300 to 1000 ° C / min. A method for producing a Cu-Ga alloy sputtering target, which is characterized in that a target material is melted in a graphite crucible, and the molten metal is injected into a mold having a water-cooled probe to continuously produce a plate-shaped casting composed of a Cu-Ga alloy. The body is further machined to produce a plate-shaped Cu-Ga alloy target, characterized by: a solidification rate from a melting point of the cast body to 300 ° C The control is 300 to 1000 ° C / min, and the target of any one of claims 1 to 6 is manufactured. The method for producing a Cu-Ga alloy sputtering target according to claim 6, wherein the drawing is performed at a drawing speed of 50 mm/min to 150 mm/min. A method of producing a Cu-Ga alloy sputtering target according to claim 6 or 7, wherein the method is produced by a horizontal continuous casting method. The method for producing a Cu-Ga alloy sputtering target according to any one of claims 6 to 9, wherein the solidification rate from the melting point of the casting body to 300 ° C is controlled to 300 to 1000 ° C / Min, and adjust the amount and concentration of the α phase or the mixed phase of the α phase and the ζ phase formed during casting.