JP5144766B2 - Cu-Ga sintered compact sputtering target and method for producing the same - Google Patents

Description

 The present invention relates to a Cu—Ga sintered body 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 the same. The present invention relates to a method for manufacturing a target.

 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.

 As a method for producing a Cu-Ga target, there are a dissolution method and a powder method. In general, the Cu-Ga target manufactured by the melting method has relatively little impurity contamination, but the compositional segregation is large and there is a problem such as a decrease in yield due to shrinkage. There were problems such as low density and easy cracking.

 Various factors affect the conversion efficiency of CIGS solar cells, but the CIGS film characteristics also have a significant effect, and the characteristics of the Cu-Ga film, which is the stage before forming the CIGS film, are also large in the conversion efficiency of the solar cell. Influence. The target obtained by sintering the powder is characterized by less component segregation compared to the melted product, easy production, and easy adjustment of the components as necessary, which is larger than the melted product. There are advantages.

 However, the target obtained by sintering has a problem that the Cu-Ga target is highly brittle and easily cracked. If the target is broken during the processing of the target, the target manufacturing yield is reduced, but if it is cracked during sputtering, there is a problem that the yield of CIGS solar cell manufacturing is reduced. In any case, the production cost of CIGS solar cells will eventually increase.

 The following patent document 1 can be given as one of the documents related to the Cu-Ga target so far. This patent document 1 is prepared by dissolving the Cu-Ga target. And the feature of this patent document 1 is inject | pouring In into a Cu-Ga target. In Patent Document 1, there is a description that there was no abnormal discharge or the like and a description that the relative density is 95% or more, but there is no special description about the cracking of the obtained target.

In general, the melted product naturally has a higher density than the sintered product, and it is rare that the density is usually less than 100%. However, paragraph [0010] of Patent Document 1 describes that “the relative density is a high density of 95% or more”, and there is a description that this level of density is realized.
Thus, a relative density of about 95% cannot be said to be a high density. In fact, in Patent Document 1, it is considered that nests for reducing the density and undesirable vacancies (voids) are generated in the melted product.
Moreover, although there is a description that compositional segregation was not observed, no analysis results or the like are shown. From the above description of the relative density of the level, only the segregation improvement of the recognized level is described.

In general, the melting method usually has a large compositional segregation, and since a special process for eliminating the segregation has not been performed, it is considered that a normal level of segregation remains.
Such segregation peculiar to a dissolved product has a problem that the film composition changes during sputtering. Also, the sputtering conditions are unknown.
Thus, the nest that lowers the density of the melted product, the undesirable voids (voids), or the target where segregation occurs is more likely to crack than the powder sintered body. .

In addition, another document (Patent Document 2) relating to a Cu-Ga target describes a sintered body target, which is an explanation of the prior art relating to brittleness that cracks and defects are likely to occur when the target is cut. In order to solve this problem, 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 involves manufacturing two types of powders in advance, the process is naturally complicated, and each powder has different physical properties such as hardness and structure, so simply mixing and sintering. It is difficult to make a uniform sintered body, and improvement in density cannot be expected. Naturally, a target with a low density causes cracking.

 In this patent document 2, although the evaluation of the crack at the time of cutting is good, the problem of the crack at the time of sputtering is unknown. Since the structure of the target is not a surface but an internal problem, the problem of cracking during sputtering of the two-phase coexisting structure is considered to be a problem different from the machinability of the surface. Even if the problem of cracking at the time of sputtering can be solved, the target structure is a two-phase coexisting structure, which may result in a non-uniform sputtered film. In any case, it can be said that the cost increase by producing two types of powders and the above problems are included.

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, in the Cu-Ga sintered body target, the present invention increases the bending strength, suppresses cracking of the target at the time of target production and sputtering film formation, improves yield, CIGS layer formation process, and It is an object of the present invention to provide a Cu—Ga sintered body target and a method for manufacturing the same, which can reduce the cost of manufacturing a CIGS solar cell.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, in order to prevent compositional segregation, there is a limit in the dissolution method, and it is necessary to use raw materials with a uniform composition in the powder method. In order to reduce this, it has been found that increasing the target density and setting the average particle diameter within a predetermined range are effective, and the present invention has been completed.

In other words, the present invention
1) It consists of a sintered body of Cu-Ga alloy powder with Ga concentration of 20-60at%, the balance being Cu and inevitable impurities, the relative density of the sintered body is 97% or more, and the average crystal grain size is 5 ~ Cu-Ga alloy sintered sputtering target characterized by 30 μm and a bending strength of 150 Mpa or more 2) Folding force of the target is F (MPa) and Ga concentration is N (at%) 1) The Cu—Ga alloy sintered body sputtering target according to 1) above, wherein the relationship of F> −10 × N + 600 is satisfied. 3) The Cu—Ga alloy has a single composition. The Cu-Ga alloy sintered body sputtering target described in 1) or 2) above, wherein 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. The Cu—Ga alloy sintered body sputtering target according to any one of the above 1) to 3), characterized in that the Cu—Ga alloy composition is Qualitatively or main phase is γ phase to provide a Cu-Ga alloy sintered sputtering target, according to any one of the above 1) to 4), which is a γ phase.

The present invention also provides:
6) A method for producing a Cu-Ga alloy sintered compact sputtering target according to any one of claims 1 to 5, wherein the mixed raw material powder obtained by melting and cooling Cu and Ga raw materials is hot-pressed. 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 pressurizing pressure to the mixed raw material powder is 30 to 30 Manufacturing method of Cu-Ga alloy sintered compact sputtering target characterized by hot pressing as 40 MPa 7) Melting of Cu and Ga raw materials, and pulverization after cooling by mechanical pulverization method, gas atomization method or water atomization method The manufacturing method of the Cu-Ga alloy sintered compact sputtering target of said 6) characterized by performing.

  According to the present invention, in the Cu-Ga sintered body target, the yield strength can be improved by increasing the bending strength and suppressing the cracking of the target during the production of the target and during the sputtering film formation. It has the excellent effect of being able to reduce the cost of the process and CIGS solar cell manufacturing.

It is a graph which shows the relationship between Ga density | concentration and the bending strength of a Cu-Ga type target in an Example and a comparative example.

Next, modes for carrying out the invention, that is, the definition of the constituent 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 sputtering target of the present invention is 20 to 60 at%, and the balance is Cu and inevitable impurities. This is because the Ga concentration range is appropriate and suitable for manufacturing an actual CIGS solar cell. However, the technical idea of the present invention can be applied to compositions outside this range.

In the Cu—Ga alloy sintered body sputtering target of the present invention, the relative density of the sintered body is 97% or more, preferably 98% or more, more preferably 99% or more. The relative density is a ratio of values obtained by dividing the actual absolute density of the sintered compact target by the theoretical density of the target having the composition.
The low relative density of the target means that there are many internal vacancies in the target, which causes embrittlement of the Cu—Ga alloy sintered compact target. As shown in Examples and Comparative Examples described later, the Cu—Ga alloy sintered compact target rapidly becomes brittle as the Ga content increases. Therefore, increasing the density of the target has a function of suppressing the embrittlement of the Cu—Ga alloy sintered compact target and increasing the bending strength.

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.
When the average particle size is small, it is easy to increase the density, and the occurrence of cracks can be suppressed through the above-described high-density features. Conversely, if the average grain size is large, each crystal grain has a random orientation, so that the progress of cracking is likely to proceed.

From the above mechanism, cracking can be suppressed by reducing the average particle size. As the average particle size increases, the bending strength decreases. However, since the average particle size exceeds 30 μm, cracks and cracks are likely to occur in relation to the force applied during processing and sputtering applied to the target. In addition, although it is preferable that the average particle size is small, it is practically inferior to make the average particle size less than 5 μm because an additional step is required for production.
The average particle diameter can be adjusted by the holding temperature at the time of hot pressing, and the higher the temperature, the larger the particle diameter.

 In general, cracks and cracks during processing and sputtering tend to occur more easily when the target has a smaller bending force, but it does not correspond one-on-one with the value of the bending force. Even if the width is within a certain range and the bending strength is the same, if the density and the particle size are different, there is a slight difference in the ease of cracking. In the present invention, the bending strength to the extent that cracks and cracks do not occur during processing or sputtering is defined as 150 MPa or more.

Cu-Ga alloys have a tendency that the bending strength decreases as the Ga concentration increases. In the present invention, when the target bending strength is F (MPa) and the Ga concentration is N (at%), a target having a high bending strength is specified to satisfy the relationship of F> −10 × N + 600. To do.
There is no previous document that describes the bending strength of Cu-Ga based targets, and the bending strength according to the present invention is high at each concentration, so it is effective in suppressing cracking of Cu-Ga based targets. There is something. The bending strength can be obtained by a three-point bending method.

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 characteristics, 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 peak intensity of the other composition is 5% or less as compared with the peak of the main composition, substantially the same effect as that of the single composition 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.

 A Cu—Ga alloy has a gamma (γ) phase when the Ga composition is about 30 to 43 at%. This phase is brittle and has a feature of being easily broken. The Cu—Ga composition used for CIGS solar cells is often in this Ga concentration range. In order to avoid such brittleness of the Cu—Ga alloy, it is particularly effective to improve the density and the bending strength.

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

 Cu and Ga raw materials are weighed so as to have a predetermined composition ratio, and then put into 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 a mechanical pulverization method, a gas atomization method, a water atomization method, and the like. Any method can be used, but the water atomization method is capable of mass processing at a relatively low cost.

 In the case of water atomization, the primary synthetic raw material is again dissolved in a crucible, and a raw material liquid that has become liquid is dropped, and high pressure water of about 10 MPa is injected into the dropped liquid to obtain fine powder. The obtained fine powder is then used as a mixed fine powder raw material through a filter press, drying and the like.

 The mixed fine powder raw material 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.

 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. By appropriately selecting the conditions for this hot pressing, it is possible to improve the density of the Cu—Ga alloy target and further improve the bending strength.

 With regard to the relationship between the temperature profile such as the rate of temperature rise and holding time and the pressure application profile, the pre-pressure method in which pressure is applied first is sintered rather than the post-pressure method in which pressure is applied after the temperature has been set to the maximum temperature. Since the raw material powder is crushed more finely before, it is effective for increasing the sintered density.

 Further, if the cooling rate of the hot press is slow, a heterogeneous phase is generated between them, so that it is effective to set the cooling rate to a high temperature of 5 ° C./min or more.

 The density of the Cu—Ga sintered body produced by the above method can be obtained by the Archimedes method, the average particle diameter can be obtained by the planimetric method after the surface etching, and the composition can be obtained by the X-ray diffraction method.

 The Cu-Ga sintered body is processed into, for example, a diameter of 6 inches and a thickness of 6 mm, and indium is pasted on a backing plate as a brazing material to form a sputtering target to form a film. The situation of abnormal discharge etc. can be investigated.

Next, examples and comparative examples of the present invention will be described. Note that the following embodiments are merely representative examples, and the present invention is not limited to these embodiments, and is interpreted within the scope of the technical idea described in the specification. It should be.

Example 1
Cu raw material and Ga raw material are weighed so that the composition is Ga concentration 30at%, put in a carbon crucible, dissolved at 1000 ° C in a heating furnace to which 0.5 Mpa of argon is applied, and then a cooling rate of 5 to 10 The synthetic raw material was taken out after cooling at ° 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, and the X-ray diffraction peak intensity ratio between the main phase and the different phase was 0.2%. This sintered body was processed into a disk shape having a diameter of 6 inches and a thickness of 6 mm, and was used as a sputtering target for sputtering.
As sputtering conditions, the atmosphere gas was argon, the gas flow rate was 50 sccm, and the sputtering pressure was 0.5 Pa. In particular, the sputtering power, which is an important condition for target cracking, was increased to a direct current (DC) 1000 W. After 20 hours of sputtering time and 20 kWhr of total sputtering amount, the target surface was observed, but no cracks were confirmed.
The results are shown in Table 1.

(Example 2 to Example 6)
Table 1 summarizes the results of producing targets with different Ga compositions and average particle diameters by the same method as in Example 1 and performing sputtering evaluation. From these results, the target having a Ga composition, average particle size, and bending strength within predetermined ranges was a good result that there was no cracking during processing or sputtering.

(Comparative Examples 1 to 2)
A target was produced under substantially the same conditions as in Example 1, but a low-density target was produced by reducing the temperature during hot pressing to 600 ° C. and 550 ° C., respectively.
Table 1 summarizes the results of the target characteristics and the presence or absence of cracks. “Slightly” described in the column of cracking at the time of processing did not go until the target was broken and separated, but it showed a slight crack. From this result, when the density of the target was lower than a predetermined value, cracks were observed during processing. However, no cracks on the target surface after sputtering were confirmed.

(Comparative Example 3 to Comparative Example 5)
The target was fabricated under substantially the same conditions as in Example 1, but the average particle size was increased by reducing the cooling rates to 1 ° C / min, 2 ° C / min, and 0.5 ° C / min, respectively. A target having a large intensity ratio and a different phase was produced.
Table 1 summarizes the results of the target characteristics and the presence or absence of cracks. From these results, no cracks were observed during sputtering, but slight cracks were observed during processing.

(Comparative Example 6 to Comparative Example 8)
A Cu-Ga target was prepared by a dissolution method. Cu and Ga raw materials were weighed so that the Ga composition had a predetermined concentration, placed in a carbon crucible, and heated in a heating furnace to which 0.5 Mpa of argon was applied. Table 1 summarizes the characteristics of the target taken out after melting at about 200 ° C higher than the melting point of each material and cooled at a cooling rate of about 5 ° C / min. .
From these results, it was confirmed that the target produced by the melting method had a very large average particle diameter and a very small bending force, and cracks during processing and sputtering.

 FIG. 1 is a graph showing the relationship between the Ga concentration and the bending strength of a Cu—Ga based target in Examples and Comparative Examples of the present invention. From this figure, since the bending strength of the target in the embodiment of the present invention is large, there is no crack at the time of processing or sputtering, and a Cu—Ga based target or film can be manufactured with high yield.

  According to the present invention, it is possible to provide a high Ga concentration Cu-Ga target having a compositional segregation and less brittleness with a Ga concentration of 25 to 45 at% and a method for manufacturing the target, and CIGS solar cell manufacturing. Since the yield is improved and the manufacturing cost can be reduced, it is useful as a material for manufacturing CIGS solar cells by the selenization method.

Claims (7)

It consists of a sintered body of Cu-Ga alloy powder with Ga concentration of 20-60at%, the balance being Cu and unavoidable impurities, the sintered body has a relative density of 97% or more and an average crystal grain size of 5-30μm Further, a Cu-Ga alloy sintered compact sputtering target characterized by having a bending strength of 150 Mpa or more. 2. The Cu—Ga alloy according to claim 1, wherein the relationship of F> −10 × N + 600 is satisfied when the target bending strength is F (MPa) and the Ga concentration is N (at%). Sintered sputtering target. The Cu-Ga alloy sintered compact sputtering target according to claim 1 or 2, wherein the Cu-Ga alloy has a single composition. The Cu-Ga alloy according to any one of claims 1 to 3, 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 Cu-Ga alloy sintered sputtering target according to any one of claims 1 to 4, wherein the Cu-Ga alloy composition is substantially a γ phase or the main phase is a γ phase. Dissolved Cu and Ga raw material, after cooling, crushed mixed raw material powder was hot pressed by a hot press method, for producing a Cu-Ga alloy sintered sputtering target according to any one of claims 1 to 5 A 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, the cooling rate is 5 ° C./min or more, and the pressure applied to the mixed raw material powder A method for producing a Cu-Ga alloy sintered compact sputtering target, wherein hot pressing is performed at 30 to 40 MPa. The method for producing a Cu-Ga alloy sintered sputtering target according to claim 6, wherein the Cu and Ga raw materials are melted and pulverized after cooling by a mechanical pulverization method, a gas atomization method or a water atomization method.

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