JP2012072468A - Cu-Ga ALLOY SPUTTERING TARGET AND METHOD FOR MANUFACTURING Cu-Ga ALLOY SPUTTERING TARGET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality Cu-Ga alloy sputtering target prepared by a powder sintering method, in which generation of particles in a sputtered film is suppressed even when high sputtering power is applied.SOLUTION: Mixed powder including Cu powder and Ga mixed at a mass ratio of 85:15 to 55:45 is alloyed by heating and stirring it in an inert atmosphere to obtain Cu-Ga alloy powder having an average particle size of ≤150 μm. The resulting Cu-Ga alloy powder is subjected to hot press sintering, whereby a Cu-Ga alloy sputtering target having a cross sectional structure containing particles each having an average crystal particle diameter of ≤40 μm is manufactured.

Description

  The present invention relates to a Cu—Ga alloy sputtering target used for forming a light absorption layer of a CIGS (Cu—In—Ga—Se quaternary alloy) solar cell and a method for producing the Cu—Ga alloy sputtering target. .

  In recent years, photovoltaic power generation has attracted attention as one of clean energy. Although crystalline Si solar cells are mainly used, CIGS (Cu—In—Ga—Se quaternary alloy) solar cells with high conversion efficiency are attracting attention because of supply and cost problems. Yes.

  The CIGS solar cell has, as a basic structure, a Mo electrode layer serving as a back electrode formed on a soda lime glass substrate and a Cu—In—Ga—Se serving as a light absorption layer formed on the Mo electrode layer. A quaternary alloy film, a buffer layer made of ZnS, CdS, etc. formed on the light absorption layer made of this Cu-In-Ga-Se quaternary alloy film, and formed on this buffer layer A transparent electrode.

  As a method for forming a light absorption layer made of a Cu—In—Ga—Se quaternary alloy film, a vapor deposition method is known, but in order to obtain a uniform film with a wider area, a method of forming by a sputtering method. Has been proposed.

  As a sputtering method, for example, first, an In film is formed by sputtering using an In target, and a Cu—Ga alloy film is formed on the In film by sputtering using a Cu—Ga alloy sputtering target. There is a method of forming a Cu—In—Ga—Se quaternary alloy film by forming a film and heat-treating the obtained laminated film composed of the In film and the Cu—Ga alloy film in a Se atmosphere.

  Since the quality of the Cu—In—Ga—Se quaternary alloy film formed by sputtering greatly depends on the quality of the Cu—Ga alloy sputtering target, it is desirable to use a high quality Cu—Ga alloy sputtering target. It is rare.

  As a method for producing a Cu—Ga alloy sputtering target, a melting method and a powder sintering method are known.

  For example, Patent Document 1 proposes a Cu—Ga alloy sputtering target produced by a melting method. The melting method has a problem that a Cu—Ga alloy having a composition for CIGS solar cells obtained by melting and casting is brittle and easily cracked.

  On the other hand, the powder sintering method is regarded as a promising method for producing a sputtering target because a uniform composition can be obtained. As a powder sintering method, for example, in Patent Document 2, a high Ga-containing Cu—Ga alloy powder and pure Cu or a low Ga-containing Cu—Ga alloy powder are blended to produce a sputtering target by hot pressing. It is described.

  Such a metal target may generate particles during sputtering film formation. Therefore, there is a proposal to improve the particle problem by limiting the particle size of the target structure and the specific metal phase.

  For example, Patent Document 3 proposes that the average particle size of the Mo-based sintered target is 10 μm or less and the maximum particle size is 40 μm or less. Patent Document 4 proposes that the maximum particle size of the In-containing alloy phase in the Cu—In—Ga ternary sintered alloy target is 10 μm or less. However, Patent Documents 3 and 4 do not show a method for improving the Cu—Ga binary alloy sintered target.

JP 2000-073163 A JP 2008-138232 A JP 2000-045066 A JP 2009-120862 A

  In the powder sintering method, since the melting point of Ga as a raw material is as extremely low as 29.78 ° C., a sintered body cannot be obtained directly from Cu powder and Ga. For this reason, in the powder sintering method, Cu—Ga alloy powder is used as a raw material.

  By the way, in manufacture of a CIGS solar cell, when forming a light absorption layer using a Cu-Ga alloy sputtering target, it is desired to raise the speed of sputtering film formation from a viewpoint of productivity improvement.

  However, when a large electric power is applied to the Cu—Ga alloy sputtering target in order to increase the deposition rate, the generation of particles in the sputtering film becomes obvious. When the particles are generated, the yield of the solar cell is lowered.

  Therefore, the present invention has been proposed in view of the above circumstances, and in a Cu—Ga alloy sputtering target produced by a powder sintering method, particles are generated in the sputtered film even when a large sputtering power is applied. The present invention provides a high-quality Cu—Ga alloy target capable of suppressing this.

  The Cu—Ga alloy sputtering target according to the present invention that achieves the above-described object is characterized in that the cross-sectional structure is composed of particles having an average crystal grain size of 40 μm or less.

  The manufacturing method of the Cu-Ga alloy sputtering target which concerns on this invention which achieves the objective mentioned above is a mixed powder in which Cu powder and Ga were mix | blended in the ratio of 85: 15-55: 45 by mass ratio in inert atmosphere. A Cu-Ga alloy powder having an average particle size of 150 μm or less obtained by stirring and alloying while heating at a hot-press sintering, Cu having a cross-sectional structure containing particles having an average crystal particle size of 40 μm or less -Ga alloy sputtering target is manufactured.

  In the present invention, particles having an average crystal grain size of 40 μm or less are contained in the cross-sectional structure of the Cu—Ga alloy sputtering target, that is, the size of the particles is small. For this reason, in this invention, when a sputtered film is formed using this Cu—Ga alloy sputtering target, generation of particles can be suppressed.

2 is a photograph showing a cross-sectional structure of the Cu—Ga alloy sputtering target of Example 1. FIG. 4 is a photograph showing a cross-sectional structure of a Cu—Ga alloy sputtering target of Comparative Example 1;

  Below, the Cu-Ga alloy sputtering target to which this invention is applied and the manufacturing method of this Cu-Ga alloy sputtering target are demonstrated in detail. Note that the present invention is not limited to the following detailed description unless otherwise specified.

<Cu-Ga alloy sputtering target>
First, a Cu—Ga alloy sputtering target will be described. The Cu—Ga alloy sputtering target can be produced by a powder sintering method using Cu—Ga alloy powder as a raw material, and is composed of particles having an average crystal grain size of 40 μm or less. Since the cross-sectional structure of the Cu-Ga alloy sputtering target is composed of particles having an average crystal grain size of 40 μm or less, the generation of particles in the sputtered film can be suppressed, and the generation of particles in the sputtered film even when the sputter input power is increased. Can be suppressed, and a sputtered film having a smooth surface can be formed. It is expected that the release of particles in the target structure during film formation is effectively suppressed even when a large amount of power is applied to form a sputtered film due to the fine structure with a small average crystal grain size. The Moreover, the intensity | strength of a Cu-Ga alloy sputtering target can be raised rather than a thing with a large average crystal grain diameter because the average crystal grain diameter of the particle | grains in the cross-sectional structure | tissue of a Cu-Ga alloy sputtering target is 40 micrometers or less.

  On the other hand, when the average crystal grain size of the particles in the cross-sectional structure of the Cu—Ga alloy sputtering target is larger than 40 μm, the particles in the target structure are likely to be liberated and particles are likely to be generated when a large sputtering power is applied. Become.

  Here, the average crystal grain size of the particles is a particle cut by a line drawn on a photograph of the target cross-sectional structure based on the cutting method described in JIS H 0501 “Copper grain size test method” Obtained from the number and the cutting length.

<Method for producing Cu-Ga alloy sputtering target>
Next, the manufacturing method of a Cu-Ga alloy sputtering target is demonstrated. The manufacturing method of a Cu-Ga alloy sputtering target manufactures Cu-Ga alloy powder from Cu powder and Ga, sinters the obtained Cu-Ga alloy powder, and manufactures a Cu-Ga alloy sputtering target.

<1. Method for producing Cu-Ga alloy powder>
First, the manufacturing method of Cu-Ga alloy powder is demonstrated.

  Here, the Cu—Ga alloy powder to be produced preferably has an average particle size of 150 μm or less so that the cross-sectional structure contains particles having an average crystal particle size of 40 μm or less. When the average particle size of the Cu—Ga alloy powder exceeds 150 μm, the average crystal particle size of the particles in the cross-sectional structure of the Cu—Ga alloy sputtering target exceeds 40 μm. When the average particle size is 150 μm or less, the average crystal particle size of the cross-sectional structure of the Cu—Ga alloy sputtering target is 40 μm or less, and particles of the sputtered film are suppressed. The average particle diameter of the Cu—Ga alloy powder is adjusted by the particle diameter or pulverization of the Cu powder described later.

  The average particle size of the Cu-Ga alloy powder is determined by measuring the particle size distribution of the alloy powder by a laser diffraction method, integrating the abundance ratio (volume basis) from the small diameter side, and the value of the abundance ratio over the entire particle diameter. The particle size (D50) is half of the integrated value. Note that the numerical value of the average particle diameter of the alloy powder does not match the numerical value of the average crystal particle diameter of the particles in the target cross-sectional structure. This is considered to be caused by the difference in particle shape and measurement method.

(material)
Cu powder and Ga are used as raw materials for the Cu—Ga alloy powder. The purity of the Cu powder and Ga is appropriately selected so as not to affect the characteristics of the CIGS light absorption layer formed from the Cu—Ga alloy sputtering target.

  As the Cu powder, for example, electrolytic Cu powder or atomized Cu powder produced by an electrolytic method or an atomizing method can be used. The electrolytic Cu powder is produced by depositing spongy or dendritic Cu on the cathode by electrolysis in an electrolytic solution such as a copper sulfate solution. As for the atomized Cu powder, spherical or irregular shaped Cu powder is produced by a gas atomization method, a water atomization method, a centrifugal atomization method, a melt extraction method, or the like. In addition, you may use what was manufactured by Cu methods other than these methods.

  It is preferable that the average particle diameter of Cu powder is 1-150 micrometers. When the average particle size of the Cu powder is less than 1 μm, special handling for preventing the scattering of the Cu powder is required, the bulk capacity of the Cu powder is increased, the size of the alloy powder manufacturing apparatus is increased, and the cost is increased. A device is required. When the average particle size of the Cu powder exceeds 150 μm, the average particle size of the Cu—Ga alloy powder exceeds 150 μm, and the average crystal particle size of the particles in the cross-sectional structure of the Cu—Ga alloy sputtering target is more than 40 μm. It gets bigger. In addition, when the average particle diameter of the Cu powder exceeds 150 μm, the surface area (BET) of the Cu powder that must be coated with Ga decreases, and the amount of Ga required for coating also decreases, resulting in surplus Since the unreacted Ga liquid phase remains, Ga cannot be used effectively. Therefore, by setting the average particle size of the Cu powder to 1 to 150 μm, the average crystal particle size of the particles in the cross-sectional structure of the Cu—Ga alloy sputtering target can be made 40 μm or less, and it is necessary to take measures to prevent the Cu powder from scattering. Therefore, it is possible to prevent the alloy powder manufacturing apparatus from becoming large, reduce the liquid phase of unreacted Ga, and use Ga effectively.

  The average particle size of the Cu powder is determined by measuring the particle size distribution of the Cu powder by the laser diffraction method, integrating the abundance ratio (volume basis) from the small diameter side, and the value is the integrated value of the abundance ratio over the entire particle diameter. The particle size (D50) is halved.

  Ga is a metal having a low melting point (melting point: 29.78 ° C.) and is easily melted by heating. The molten Ga is coated with Cu powder to form a binary alloy. Although there is no restriction | limiting in the shape of Ga, when it is a small piece, weighing is easy. The small piece can be obtained by melting and casting Ga in the vicinity of room temperature and crushing the casting.

  Since Ga becomes a liquid at a low temperature, the average particle size (size) of Ga to be blended is not limited from the viewpoint of the average crystal particle size of particles in the cross-sectional structure of the target. Therefore, Ga should just select the ease of weighing for mixing | blending, and the shape easy to handle.

(Combination)
Cu powder and Ga are mix | blended in the ratio of 85: 15-55: 45 by mass ratio. When the amount of Ga is 15% by mass or more, uniform coating with Ga becomes possible, and a uniform alloy structure can be obtained when the obtained powder is sintered. Moreover, when the amount of Ga is 45% by mass or less, Cu powders can be prevented from being combined and formed into a lump by a large amount of Ga existing between Cu powders, and the yield of the alloy powder is improved. be able to.

  Moreover, it is preferable that content of Ga is 25-41 mass%. When Ga is 25% by mass or more, Cu powder can be uniformly coated in a short time, and when Ga is 41% by mass or less, Ga coated in a short time can be alloyed. it can. Therefore, a uniform alloy powder can be produced in a short time by setting the Ga content to 25 mass% or more and 41 mass% or less.

(Alloying)
The mixed powder in which Cu powder and Ga are blended in the mass ratio described above is stirred and alloyed at a temperature of 30 ° C. to 400 ° C. in an inert atmosphere. Specifically, Cu powder and Ga pieces weighed at the above-described mass ratio are put into a mixing apparatus, the temperature is controlled in the range of 30 ° C. or more and 400 ° C. or less with a heating means, and stirring is performed with a stirrer. The powder and Ga are mixed to produce a Cu—Ga binary alloy powder in which Ga is dispersed on the surface or inside of the Cu powder.

  The Cu—Ga alloy powder is considered to be formed through the following process. Ga, which has become liquid beyond the melting point, is uniformly dispersed between Cu powders while becoming small droplets by the shearing motion of mixing. The dispersed Ga droplets adhere to the periphery of the Cu powder, and when the Cu powder and Ga droplets come into contact with each other, the Ga powder begins to diffuse into the Cu powder, and the Ga concentration increases while alloying while forming a Cu-Ga intermetallic compound. The reaction proceeds. At this time, the surface of the Cu—Ga alloy powder is a Cu—Ga intermetallic compound layer having a high Ga concentration, and the central portion is a Cu phase in which pure Cu or Ga is dissolved.

  This mixing of Cu powder and Ga is effective for the progress of a uniform alloying reaction. Moreover, it is considered that the shearing motion of mixing also suppresses the formation of a lump due to the adhesion between the powders. If a lump is generated, voids are generated in the sintered body in a sintering process such as hot pressing, and the density becomes non-uniform.

  For heating for mixing and alloying of the Cu powder and Ga, a mixing device in which a stirrer such as a stirring blade or a stirring blade moves in the container can be used. Moreover, you may use rotating container type mixing apparatuses, such as a cylinder, a double cone, and a twin shell. Also, mixing may be strengthened by throwing balls into the container.

  The container material is selected from the viewpoints of heat resistance against heating and suppression of adhesion of Ga and Cu—Ga alloys. Examples of the container include glass containers such as borosilicate glass and quartz glass, ceramic containers such as alumina and zirconia, Teflon resin containers, Teflon-coated containers, and enamel containers.

  The Cu—Ga alloy powder produced in this way is not only excellent in strength and formability, but also because the production temperature is low, the equipment used for production becomes simple, so the alloy powder can be produced at low cost. It has the advantage of being able to.

  In the manufacturing method of the above Cu-Ga alloy powder, Cu powder and Ga are mix | blended in the ratio of mass ratio 85: 15-55: 45, and it heats in the range of 30 to 400 degreeC, and is alloyed. As a result, Cu—Ga alloy powder having excellent formability can be obtained. Moreover, in this manufacturing method of Cu-Ga alloy powder, the process of grind | pulverizing a Cu-Ga alloy ingot is not required unlike the past, and Cu-Ga alloy powder can be manufactured easily.

<2. Manufacturing method of Cu-Ga alloy sputtering target>
Next, the manufacturing method of the Cu-Ga alloy sputtering target using the Cu-Ga alloy powder mentioned above is demonstrated.

(Sintering)
First, the Cu—Ga alloy powder is pressed and sintered. Sintering uses a hot press method in which a Cu—Ga alloy powder is pressed and heated by a hot press apparatus in a vacuum or in an inert gas atmosphere. According to the hot press method, a high-density sintered body can be obtained at low cost. Sintering is performed by applying a hot press pressure of, for example, about 5 MPa to 30 MPa to the Cu—Ga alloy powder with an upper punch and a lower punch of a hot press apparatus, and pressurizing and sintering at a heating temperature of 400 ° C. to 900 ° C. .

(Finishing)
A finishing process is performed after sintering. For finishing, the surface of the sintered body of the Cu—Ga alloy is flattened by grinding and bonded to a Cu backing plate. Thereby, a Cu—Ga alloy sputtering target in which particles having an average crystal grain size of 40 μm or less are contained in the cross-sectional structure can be obtained.

  In addition, you may make it heat-process to Cu-Ga alloy powder before sintering. The heat treatment is unloaded with respect to the Cu-Ga alloy powder in a vacuum or an inert atmosphere, or 0.1 MPa or less (when the upper punch is installed in a hot press apparatus, it is applied by the weight of the upper punch. By heating to 400 ° C. to 900 ° C. under a pressure corresponding to the pressure. The heat treatment time is preferably 1 hour or more and 8 hours or less. By performing heat treatment on the Cu-Ga alloy powder before sintering, the homogenization reaction between the Cu powder and Ga progressed, Ga diffused in the center of Cu, and the appearance of the Ga liquid phase was suppressed. A high-quality sintered body can be manufactured.

  As mentioned above, in the manufacturing method of a Cu-Ga alloy sputtering target, it stirs, heating the mixed powder in which Cu powder and Ga were mix | blended by the ratio of 85: 15-55: 45 by mass ratio in inert atmosphere. By subjecting the Cu—Ga alloy powder thus alloyed to hot press sintering, a Cu—Ga alloy sputtering target having a cross-sectional structure containing particles having an average crystal grain size of 40 μm or less can be produced.

  The obtained Cu-Ga alloy sputtering target has an average crystal grain size of 40 μm or less of particles having a cross-sectional structure, so that a sputtered film is formed by applying a large amount of power to the fine structure having a small average crystal grain size. Even so, the release of particles in the target tissue during film formation can be effectively suppressed. Thereby, the surface of a Cu-Ga alloy sputtering target becomes smooth. Therefore, for example, when a light absorption layer of a solar cell is formed using this Cu—Ga alloy sputtering target, a light absorption layer with few particles can be formed, and the yield of the solar cell can be increased.

  Hereinafter, specific examples to which the present invention is applied will be described, but the present invention is not limited to these examples.

Example 1
In Example 1, first, 68 g of electrolytic copper powder (average particle size 140 μm) and 32 g of Ga were charged into a glass beaker. This beaker, a mantle heater and a stirrer were set in a glove box, and after evacuating, Ar gas was introduced. The copper powder and Ga were stirred while heating the inside of the beaker at 300 ° C. to prepare a Cu—Ga alloy powder. The average particle diameter of the obtained Cu—Ga alloy powder by a laser diffraction method was 150 μm.

Next, this Cu—Ga alloy powder was put into a hot press and evacuated to 5 × 10 ⁻³ Pa, and then Ar gas was introduced, hot pressed under conditions of 700 ° C. and 25 MPa, φ60 mm, thickness 3 mm Cu-Ga alloy sputtering target was prepared.

  A Cu backing plate was joined to this target and attached to a sputtering apparatus (manufactured by ULVAC). A 3-inch Si wafer was attached to the substrate. Sputter deposition was carried out by applying a DC current of 100 W at an Ar gas pressure of 0.7 Pa for 1 hour. The Si wafer was taken out and the sputtered film particles were observed with an optical microscope. Subsequently, a new 3-inch Si wafer substrate was attached to the sputtering apparatus, and the sputter film formation was carried out for 1 hour by increasing the input power to 200 W DC. Furthermore, DC 300 W and sputtering film formation for 1 hour were also performed. The sputtered film formed on the Si wafer with each input power was observed with an optical microscope. The results are shown in Table 1.

  The Cu—Ga alloy sputtering target after sputtering was removed and polished, and a plurality of fields of view of the target cross-sectional structure were photographed with a polarizing microscope. The photograph taken is shown in FIG. Based on the cutting method described in JIS H 0501 “Copper Product Grain Size Test Method”, a line segment is drawn on this photograph, and the average grain size is calculated from the number of particles cut by this line segment and the cut length. The diameter was determined. As a result, the average crystal grain size was 17 μm.

(Example 2)
In Example 2, Cu—Ga alloy powder was produced in the same manner as in Example 1 except that 55 g of electrolytic copper powder (average particle size 100 μm) and 45 g of Ga were used. The average particle size of this alloy powder by laser diffraction was 80 μm. A Cu—Ga alloy sputtering target was produced in the same manner as in Example 1 except that the hot press temperature was 400 ° C. And it attached to the sputter apparatus (made by ULVAC) and observed the particle | grains of the sputter | spatter film | membrane formed by input power DC100W, DC200W, and DC300W like Example 1. FIG. The results are shown in Table 1.

  The sputtered Cu—Ga alloy sputtering target was removed and polished, and a cross-sectional structure photograph of the target was taken with a polarizing microscope. From this photograph, the average crystal grain size determined by the same method as in Example 1 was 40 μm.

(Example 3)
In Example 3, Cu—Ga alloy powder was prepared in the same manner as in Example 1 except that 85 g of atomized copper powder (average particle size 90 μm) and Ga 15 g were used. The average particle diameter of this alloy powder as determined by laser diffraction was 90 μm. A Cu—Ga alloy sputtering target was produced in the same manner as in Example 1 except that the hot press temperature was 400 ° C. And it attached to the sputter apparatus (made by ULVAC) and observed the particle | grains of the sputter | spatter film | membrane formed by input power DC100W, DC200W, and DC300W like Example 1. FIG. The results are shown in Table 1.

  The target after sputtering was removed and polished, and a cross-sectional structure photograph of the target was taken with a polarizing microscope. From this photograph, the average crystal grain size determined in the same manner as in Example 1 was 20 μm.

(Comparative Example 1)
In Comparative Example 1, a Cu—Ga alloy powder was produced in the same manner as in Example 1 except that atomized copper powder (average particle size 400 μm) was used. The average particle diameter of this alloy powder as measured by the laser diffraction method was 190 μm. Then, this Cu—Ga alloy powder was hot pressed in the same manner as in Example 1 to prepare a Cu—Ga alloy target having a diameter of 60 mm and a thickness of 3 mm. A Cu backing plate was bonded to this target and attached to a sputtering apparatus (manufactured by ULVAC), and the particles of the sputtered film formed with input power of DC100W, DC200W and DC300W were observed in the same manner as in Example 1. The results are shown in Table 1.

  The target after sputtering was removed and polished, and a cross-sectional structure photograph of the target was taken with a polarizing microscope. The photograph taken is shown in FIG. From this photograph, the average crystal grain size determined by the same method as in Example 1 was 50 μm.

  It shows in Table 1 about the manufacturing conditions of the Cu-Ga alloy sputtering target about the above Examples 1-3, and the comparative example 1, and the presence or absence of a particle.

  From the results shown in Table 1, in Examples 1 to 3 in which the average crystal grain size of the particles in the cross-sectional structure of the Cu—Ga alloy sputtering target is 40 μm or less, no particles are generated in the sputtered film even when the input power is DC 200 W. In addition, the number of particles is extremely small even in DC300W in which the input power is further increased, and the generation of particles is effectively suppressed. Therefore, as in Examples 1 to 3, the Cu—Ga alloy sputtering target having an average crystal grain size of 40 μm or less in the cross-sectional structure can form a film without particles even when the film formation rate is increased. Productivity can be improved.

  On the other hand, in Comparative Example 1, particles were generated when the input power was set to DC 200 W, and a large number of particles were generated in DC 300 W where the input power was further increased. A film cannot be formed.

  Therefore, even if the film formation rate is increased, a film without particles can be formed, and the productivity can be improved because the average crystal of particles in the cross-sectional structure as in Examples 1 to 3. A Cu—Ga alloy sputtering target having a particle size of 40 μm or less.

Claims (2)

  A Cu—Ga alloy sputtering target, wherein the cross-sectional structure is composed of particles having an average crystal grain size of 40 μm or less.   Cu— with an average particle size of 150 μm or less obtained by stirring and alloying a mixed powder containing Cu powder and Ga in a mass ratio of 85:15 to 55:45 while heating in an inert atmosphere. A method for producing a Cu-Ga alloy target comprising producing a Cu-Ga alloy sputtering target having a cross-sectional structure composed of particles having an average crystal grain size of 40 µm or less by hot-press sintering Ga alloy powder. .

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