JP5591370B2 - Cu-Ga target and manufacturing method thereof - Google Patents

Description

The present invention relates to a Cu—Ga alloy sputtering target used when forming a Cu—In—Ga—Se (hereinafter referred to as CIGS) quaternary alloy thin film which is a light absorption layer of a thin film solar cell layer, and a method for producing the same. The present invention also relates to a light absorption layer made of a Cu-Ga alloy film and a CIGS solar cell using the light absorption layer.

In recent years, mass production of high-efficiency CIGS-based solar cells as thin-film solar cells has progressed, and vapor deposition and selenization methods are known as methods for producing the light absorption layer. Solar cells manufactured by vapor deposition have advantages of high conversion efficiency, but have disadvantages of low film formation speed, high cost, and low productivity, and selenization is more suitable for industrial mass production.

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

Various production conditions and characteristics of constituent materials affect the conversion efficiency of CIGS solar cells, but the CIGS film characteristics also have a significant effect. If the Cu-Ga film contains metal impurities, a deep level is formed in the energy level of the CIGS film produced by selenizing the film, and electron-hole pairs generated by sunlight irradiation are formed. The trapping action reduces the conversion efficiency of CIGS solar cells. Therefore, it is necessary to reduce such metal impurity concentration as much as possible.

As a method for producing a Cu-Ga target, there are a dissolution method and a powder method. In general, a Cu-Ga target manufactured by a melting method is said to have relatively little impurity contamination, but has many drawbacks. For example, since the cooling rate cannot be increased, the compositional segregation is large, and the composition of the film produced by the sputtering method gradually changes.
In addition, shrinkage cavities are likely to occur at the final stage when the molten metal is cooled, the properties around the shrinkage cavities are poor, and the yield is poor because it cannot be used for processing into a predetermined shape.
Furthermore, as the Ga concentration increases, the brittleness increases and cracks easily occur, and cracks and chips are likely to occur during processing of the target and during sputtering, which also causes an increase in cost due to a decrease in yield. Therefore, the production of Cu-Ga target by dissolution method is not appropriate in terms of cost and characteristics.

Although there is a description that compositional segregation was not observed in the prior document (Patent Document 1) relating to the Cu-Ga target by the dissolution method, no analysis results or the like are shown. Further, although there is a description that there was no brittleness and no cracks, there is no description of processing conditions and sputtering conditions, and the contents are unclear.
Furthermore, in the examples, the upper limit of the Ga concentration range is only up to 30% by weight, and there is no description about the characteristics including brittleness and cracks in the Ga high concentration region beyond this. The impurity concentration is only described for oxygen and there is no description for metal impurities.

On the other hand, targets prepared by the powder method generally have problems such as low sintering density and high impurity concentration. Patent Document 2 relating to a Cu-Ga target describes a sintered body target, but there is an explanation of the prior art relating to brittleness in which cracking and chipping are likely to occur when the target is cut. As mentioned above, two types of powders are manufactured, mixed and sintered.
One of the two types of powders is a powder with a high Ga content, and the other is a powder with a low Ga content, which is a two-phase coexisting structure surrounded by a grain boundary phase.

Since this process produces two types of powders, the process is complicated, and each powder has different physical properties such as hardness and structure. It is difficult to form a body, and an improvement in relative density cannot be expected.
Naturally, the target with low density has abnormal discharge and particle generation, and if there are irregular shapes such as particles on the surface of the sputtered film, it will adversely affect the characteristics of the subsequent CIGS film, and eventually the conversion of CIGS solar cells. There is often a risk of a significant reduction in efficiency. Moreover, there is no description about a sintered compact density and a metal impurity density | concentration.

Patent Document 3 describes that CuGa ₂ is exemplified as one of the recording layer materials of the optical recording medium, and an AuZn recording layer is laminated by sputtering. However, rather than the fact of sputtered CuGa _2, merely suggesting the sputtering of CuGa _2.
Patent Document 4 describes that CuGa ₂ is exemplified as one of the recording layer materials of an optical recording medium, and an AuSn recording layer is laminated by sputtering. There is no description that CuGa ₂ has been sputtered, and it merely suggests sputtering of CuGa ₂ .

Patent Document 5 discloses a copper alloy target that contains Ga in an amount of 100 ppm or more and less than 10% by weight, has an average grain size of 1 to 20 μm, and has a standard deviation of grain size uniformity of the whole target of less than 15%. It is written in. The object is to make the Ga concentration low and the target made by forging and rolling have a predetermined texture.
Patent Document 6 claims a copper alloy to which an additive element containing Ga is added in a solid solubility limit of 0.1 to 20.0 at%. However, only the Cu-Mn alloy is shown in the examples, and the manufacturing method of the target is not specifically described, but is considered to have been made by the melting method. The use is for display devices.

Patent Document 7 discloses a copper alloy target produced by cold isostatic pressing of powder raw material components. Example 3 describes a target production method using a mixture of indium powder and Cu-Ga alloy powder as a raw material. It is written. Compared with the present invention, sintering is not performed, the composition is different, and there are no related elements.
In Patent Document 8, there is a description of a sputtering target for a Cu alloy recording layer containing 1 to 20 at% of Ga. However, in the examples, a material obtained by adding Zn or Mn to Cu is used in an arc melting furnace. There is no specific description about the copper alloy target to which Ga is added, and is obtained as an ingot.

Patent Document 9 describes examples of the use of 10, 20, and 30 wt% Ga CuGa alloy targets for use in CIGS type thin film solar cell production. There is no description. Similarly, there are no descriptions of various characteristics of the target.
Patent Document 10 describes a method of manufacturing a CuGa alloy target containing 25 to 67 at% Ga by a forging and quenching method. Although it is the same thin-film solar cell use as that of the present invention, it has disadvantages peculiar to forging, and the problems solved by the present invention still remain.

In Patent Document 11, a CuGa alloy target containing 20 to 96% by weight of Ga is defined, and Ga25 and Cu75% by weight are described as particularly effective in Examples. However, there is no description about the manufacturing method of the CuGa alloy target itself, and there is no description about various characteristics of the target as well. In any of the above-mentioned patent documents, it has not been possible to find a disclosure of a technology that serves as a reference for the problem of the present invention and the means for solving it.

JP 2000-73163 A JP 2008-138232 A JP-A-63-37834 JP-A-62-379533 JP 2005-533187 A International Publication No. WO2006-025347 International Publication WO2007-137824 International Publication WO2007-004344 JP-A-10-135498 Japanese Unexamined Patent Publication No. 1719626 Japanese Patent Laid-Open No. 11-260724

  In view of the above situation, an object of the present invention is to provide a Cu-Ga target having a high density and a low metal impurity concentration, and a manufacturing method capable of producing the Cu-Ga target with a high yield and a low cost.

  In order to solve the above problems, the present inventors have conducted intensive studies and found that the mixing process of the metal impurities mixed in the Cu—Ga target differs depending on the type. By reducing the metal impurity concentration in the raw material, clarifying the metal impurity contamination source and the contamination mechanism during the Cu-Ga target manufacturing process, and taking measures to prevent impurity contamination for each cause, various metal impurity concentrations The present invention has been completed.

From the above findings, the present invention is 1) Cu-Ga alloy sintered body having a Ga concentration of 20 to 60 at%, a relative density of 97% or more, an average particle size of 5 to 30 μm, and a content of metal impurities. Cu-Ga alloy sintered sputtering target characterized in that is less than 10 ppm 2) Cu-Ga alloy sintered sputtering target according to 1) above, wherein the metal impurity is a transition metal 3) Metal The Cu-Ga alloy sintered sputtering target 4 according to any one of 1) to 2) above, wherein the impurity is one or more elements selected from Fe, Cr, Ni, Co, and Mn. 1) The Cu-Ga alloy sintered sputtering target according to 1) above, wherein the metal impurity is a heavy metal. 5) The metal impurity is one or more elements selected from Pb, Bi and Cd. The Cu-Ga alloy bonded body according to any one of 1), 2) and 4) above The sputtering target 6) The Cu-Ga alloy sintered body sputtering target according to 1) above, wherein the metal impurity is a light metal. 7) The metal impurity is one or more elements selected from Si and Al. The Cu—Ga alloy sintered body sputtering target according to claim 1, wherein the Cu—Ga alloy has a single composition. 8. The Cu-Ga alloy sintered sputtering target according to any one of 9), wherein the peak intensity of the Cu-Ga alloy other than the main peak by X-ray diffraction is 5% or less with respect to the main peak intensity. The Cu-Ga alloy sintered compact sputtering target as described in any one of 1) -8) is provided.

The present invention also provides:
10) After the Cu and Ga raw materials are dissolved and cooled, the mixed raw material powder obtained by pulverization is manufactured by hot pressing to produce the Cu—Ga based alloy sintered sputtering target according to any one of 1) to 9) above. The holding temperature during hot pressing is 50 to 200 ° C. lower than the melting point of the mixed raw material powder, the holding time is 1 to 3 hours, the cooling rate is 5 ° C./min or more, and the mixed raw material powder A method for producing a Cu-Ga based alloy sintered sputtering target characterized by a pressure of 30 to 40 MPa. 11) Dissolution of Cu and Ga raw material and pulverization after cooling by a water atomizing method. A method for producing a Cu—Ga based alloy sintered sputtering target according to 10) above, characterized in that:

Furthermore, the present invention provides
12) Light absorption layer 13 comprising the Cu—Ga based alloy film formed on the substrate using the Cu—Ga alloy sintered body sputtering target according to any one of 1) to 9) above. The CIGS solar cell using the light absorption layer described in 1).

  According to the present invention, a high-quality Cu-Ga alloy sintered compact target with a low metal impurity concentration can be produced at low cost, and a Cu-Ga alloy can be produced using this Cu-Ga alloy sintered compact sputtering target. Since it is possible to manufacture a light absorption layer made of a film and a CIGS solar cell, it is possible to produce a low-cost CIGS solar cell while suppressing a decrease in conversion efficiency of the CIGS solar cell. Have

  Next, the definition of the structural requirements of the present invention, the reason and significance of the range definition, the adjustment method, the measurement method, etc. will be described.

The Ga concentration range of the Cu—Ga alloy sintered body of the present invention is 20 to 60 at%. This is because the Ga concentration range is appropriate and suitable for manufacturing actually manufactured CIGS solar cells. However, the technical idea of the present invention can be applied to compositions outside this range.

  The relative density of the Cu—Ga alloy sintered compact sputtering target of the present invention is 97% or more. The relative density is the ratio of the actual absolute density of the target divided by the theoretical density of the target of the composition. If the relative density is low, the splash that starts from the periphery of the vacancy when the internal vacancies appear during sputtering. In addition, the generation of particles on the film due to abnormal discharge and the progress of surface unevenness progress at an early stage, and abnormal discharge or the like starting from surface protrusions (nodules) is likely to occur. Accordingly, at least the relative density needs to be 97% or more, preferably 98% or more, more preferably 99% or more.

Furthermore, the Cu—Ga alloy sintered compact sputtering target of the present invention has an average crystal grain size of 5 to 30 μm. The average particle diameter can be obtained by a planimetric method after lightly etching the target surface as necessary to clarify the grain boundary.
If the average particle size is small, it is easy to increase the density, and abnormal discharge and particle generation can be suppressed through the above-described high-density characteristics. Conversely, if the average grain size is large, each crystal grain is randomly oriented, so the surface is likely to have large irregularities due to the difference in sputtering speed depending on the crystal plane orientation. Will increase. Therefore, by reducing the average particle size, the density of the target can be improved and the number of generated particles can be further reduced.

From the mechanism as described above, there is a great advantage in reducing the average crystal grain size of the target to about 5 to 30 μm. However, setting the average particle size to less than 5 μm is practically inferior because an additional process is required for production. Further, if the average particle diameter exceeds 30 μm, the effect of improving the density decreases and the number of particles generated increases.
The average particle diameter can be adjusted by the holding temperature during hot pressing, and the particle diameter increases as the temperature increases. Further, it is possible to further exceed 30 μm and to be larger than 50 μm, but it can be said that it is not preferable because the density is lowered overall.
In general, when a target is produced by a dissolution method, it is difficult to increase the cooling rate, so that the particle size tends to be large, and the particle size cannot be 30 μm or less.

As one of the preferable conditions of the Cu-Ga alloy sintered compact sputtering target of this invention, the Cu-Ga alloy sintered compact sputtering target in which a Cu-Ga alloy consists of a single composition is provided.
In the present invention, the term “single composition” is used to mean a composition composed of only a composition that cannot be detected by other physical means. Also, microscopically, even if a small amount of other composition is contained, if no adverse effects are observed in various properties, the effect is substantially the same as that of a single composition.

As one of the preferable conditions for the Cu-Ga alloy sintered body sputtering target of the present invention, the peak intensity other than the main peak by X-ray diffraction of the Cu-Ga alloy is 5% or less with respect to the main peak intensity. -Ga alloy sintered compact sputtering target is provided.
The standard of unity can be defined by the X-ray peak intensity ratio. If the other peak intensities are 5% or less as compared with the main peak , substantially the same effect as the single phase is exhibited.

  The composition of the mixed raw material powder produced by the gas atomization method or the water atomization method is almost uniform, and the target composition obtained by hot pressing the mixed raw material can be nearly uniform. If the cooling rate is low during hot press cooling, a heterogeneous phase may precipitate during cooling. Such a heterogeneous phase can be detected by an X-ray diffraction peak when the amount is large.

  The target manufacturing method of the present invention, the reason and significance of the range definition, and the influence on the target characteristics will be described below.

Cu and Ga raw materials are weighed so as to have a predetermined composition ratio. In order to make the metal impurity concentration of the finally obtained Cu-Ga target less than 10 ppm, it is necessary to use a high-purity product having a raw material purity of 5N or more.

The weighed raw materials are put in a carbon crucible, and the mixed raw materials are dissolved at a temperature higher by about 50 to 200 ° C. than the melting point in a heating furnace pressurized to about 0.5 MPa atmospheric pressure. Hold for about 1 hour or more, and after the melted raw materials are sufficiently mixed, after stopping heating and cooling, the primary synthetic raw material is taken out.

This primary synthetic raw material is pulverized to obtain a fine powder raw material. As the pulverization method, there are mechanical pulverization, gas atomization, water atomization, and the like. In the case of mechanical pulverization, mixing of elements constituting the material of the pulverization media and the mortar is likely to occur. In particular, silicon and aluminum are easily mixed as impurities. Further, the gas atomization method is said to contain relatively little impurities, but has disadvantages in terms of productivity and cost. The water atomization method is superior in productivity because it can be processed at a relatively low cost and in large quantities.

In the case of the water atomization method, the primary synthetic raw material is again dissolved in the crucible, and the raw material liquid made liquid is dropped, and high pressure water of about 10 Mpa is injected into the dropped liquid to obtain fine powder. . When the material of the inner wall of the furnace that receives fine powder generated after high-pressure water injection is stainless steel, impurities such as Fe, Cr, Ni, which are constituent elements, are likely to be mixed. In the case of the same material, it is possible to adopt a method of reducing the collision with the inner wall material by changing the traveling direction and speed of the generated raw material to make the material less brittle. In the present invention, the last method is adopted.

The resulting fine powder is then subjected to a process such as filter pressing and drying. At that time, if the drying method is a rotating drum drying method that dries while rotating the raw material powder, there is contamination of the inner wall material of the drying device. Therefore, as a countermeasure, it is possible to adopt a method such as stationary drying or changing the material. In the present invention, the former method is adopted.

The Cu—Ga mixed fine powder raw material thus obtained is passed through a sieve having a predetermined opening to adjust the particle size distribution, and then hot pressing is performed. For example, when the Ga concentration is 30 at%, the hot press conditions are a temperature of 600 to 700 ° C. and a pressure of about 30 to 40 MPa.
If the cooling rate of the hot press is low, heterogeneous phases are likely to occur between them, and it is effective to increase the cooling rate to 5 ° C./min or more.
That is, as suitable conditions for this hot press, the holding temperature at the time of hot pressing is 50 to 200 ° C. lower than the melting point of the mixed raw material powder, the holding time is 1 to 3 hours, and the cooling rate is 5 ° C. / It is effective to set it to min or more and to set the pressure applied to the mixed raw material powder to 30 to 40 MPa. It is possible to improve the density of the Cu—Ga alloy target by appropriately selecting the conditions of this hot press.

The density of the Cu-Ga sintered body produced by the above method is the Archimedes method, the average particle size is the planimetric method after surface etching, the impurity concentration is the GDMS analysis method, and the presence or absence or degree of composition or different composition is X-ray Each can be obtained by a diffraction method.

Example 1
5N purity Cu raw material and Ga raw material were weighed so that the composition had a Ga concentration of 30at%, put in a carbon crucible, dissolved at 1000 ° C in a heating furnace to which 0.5Mpa of argon was applied, and then the cooling rate The synthetic raw material was taken out after cooling at 5 to 10 ° C / min.

Next, this synthetic raw material is put into a carbon crucible of a water atomizer and melted at 1000 ° C., and then 10 Mpa of high-pressure water is injected into the dropping liquid while dropping the melting liquid to obtain a Cu—Ga mixed fine powder. It was. The mixed fine powder was filtered and dried at 120 ° C. to obtain a mixed fine powder raw material. The mixed fine powder was heated from room temperature to 650 ° C. at a temperature rising rate of 5 ° C./min, then held at 650 ° C. for 2 hours, and a pressure of 35 MPa was applied. Thereafter, the sintered body was taken out after cooling at a temperature lowering rate of 5 ° C./min.

The relative density of the obtained Cu-Ga sintered body was 99.9%, the average particle size was 11 μm, the X-ray diffraction peak intensity ratio between the main phase and the different phase was 0.2, and the metal impurities were all less than 10 ppm. It was.
The results are shown in Table 1.

(Example 2 to Example 4)
In the same manner as in Example 1, targets with different Ga compositions and average particle sizes were produced. The results of target characteristics and metal impurity concentrations are summarized in Table 1. From these results, all metal impurities were less than 10 ppm, which was a good result.

(Comparative Example 1)
A target was produced under the same conditions as in Example 1 except that the hot pressing temperature was 550 ° C. and a low temperature. The results of target characteristics and metal impurity concentrations are summarized in Table 1. The metal impurity concentration was less than 10 ppm, but the relative density was as low as 95%.

(Comparative Example 2 to Comparative Example 3)
In the target production conditions of Example 1, mixed raw material powder was produced by mechanical pulverization in an air atmosphere instead of powder production by water atomization. At that time, mechanical grinding of Comparative Example 2 was performed for 1 hour, and Comparative Example 3 was performed for 30 minutes. Table 1 summarizes the results of target characteristics and metal impurity concentrations. From these results, the average particle size was large, and the concentrations of silicon and aluminum as metal impurities were high concentrations of 10 ppm or more.

(Comparative Example 4 to Comparative Example 5)
Each target was prepared in the same manner as in Example 1, but in Comparative Example 4, the water flow direction was such that it collided with the stainless steel inner wall material that received fine powder generated after high-pressure water injection in the water atomization method at a high incident angle. At the same time, drying was performed using a rotary drum type dryer with a stainless steel inner wall material. In addition, water used for water atomization was used especially during normal experiments. Comparative Example 5 is almost the same as the conditions of Comparative Example 4, except that the water of Comparative Example 4 is changed to a new one. Table 1 summarizes the results of target characteristics and metal impurity concentrations. From these results, the transition metals of Fe, Cr and Ni and the heavy metals of Pb, Bi and Cd were at a high concentration of 10 ppm or more.

  According to the present invention, a Cu-Ga target having a high density and a low metal impurity concentration and a method for producing the same can be provided. Therefore, as a material for producing a solar cell for suppressing a reduction in conversion efficiency of a CIGS solar cell. Useful.

Claims (11)

A Cu-Ga alloy sintered body having a Ga concentration of 20 to 60 at%, having a relative density of 97% or more, an average crystal grain size of 5 to 30 μm, and a content of each metal impurity of less than 10 ppm Cu-Ga alloy sintered body sputtering target. The Cu—Ga alloy sintered compact sputtering target according to claim 1, wherein the metal impurity is a transition metal. The Cu-Ga alloy sintered compact sputtering target according to any one of claims 1 to 2, wherein the metal impurity is at least one element selected from Fe, Cr, Ni, Co, and Mn. The Cu-Ga alloy sintered compact sputtering target according to claim 1, wherein the metal impurity is a heavy metal. The Cu—Ga alloy combined sputtering target according to claim 1, wherein the metal impurity is one or more elements selected from Pb, Bi, and Cd. The Cu-Ga alloy sintered compact sputtering target according to claim 1, wherein the metal impurity is a light metal. The Cu-Ga alloy sintered compact sputtering target according to any one of claims 1 and 6, wherein the metal impurity is one or more elements selected from Si and Al. The Cu-Ga alloy sintered compact sputtering target according to any one of claims 1 to 7, wherein the Cu-Ga alloy comprises a single phase . The Cu-Ga alloy according to any one of claims 1 to 8, wherein a peak intensity other than the main peak by X-ray diffraction of the Cu-Ga alloy is 5% or less with respect to the main peak intensity. Sintered sputtering target. The component-adjusted (including impurity reduction) Cu and Ga raw materials are dissolved, cooled, and then pulverized mixed raw material powder is hot-pressed by a hot press method to make Cu according to any one of claims 1 to 9 -Ga-based alloy sintered body sputtering target manufacturing method, in which the holding temperature during hot pressing is 50 to 200 ° C lower than the melting point of the mixed raw material powder, the holding time is 1 to 3 hours, and the cooling rate Is 5 ° C./min or more, and the pressure applied to the mixed raw material powder is 30 to 40 MPa. The method for producing a Cu-Ga based alloy sintered sputtering target according to claim 10, wherein the Cu and Ga raw materials are melted and pulverized after cooling by a water atomizing method.