JP2013194313A - Cu-Ga ALLOY SPUTTERING TARGET AND Cu-Ga ALLOY POWDER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cu-Ga alloy sputtering target, in which the density thereof is uniform at a center section and end sections, and which is excellent in the uniformity of the Ga concentration, and in which no cracking or chipping occurs during the target working and during sputtering, and generation of abnormal discharge is controlled.SOLUTION: A Cu-Ga alloy sputtering target is obtained by sintering after the heat treatment of Cu-Ga alloy powder, in which the Ga concentration is 15-45 mass%, the degree of compression is 0-25%, and the ratio of the tap density to the bulk density is 1.00-1.35.

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 Cu—Ga alloy powder used for this target. is there.

  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 to be a back electrode formed on a soda lime glass substrate and a CIGS film (Cu-In--) to be a light absorption layer formed on the Mo electrode layer. Ga-Se film or Cu-In-Ga-S-Se film), a buffer layer made of ZnS, CdS, etc. formed on the light absorption layer, and a transparent electrode formed on the buffer layer, Is provided.

  As a method for forming a CIGS light absorption layer made of a Cu—In—Ga—Se quaternary alloy film, a vapor deposition method is known, but a metal produced by sputtering to obtain a uniform film with a larger area. A method for selenizing a precursor film has been proposed (see, for example, Patent Document 1).

  The sputtering method is a method in which a metal precursor film is produced by sputtering using a Cu—Ga alloy sputtering target and an In target, and this is heat-treated in a Se or S atmosphere to form a CIGS film. Since the quality of the CIGS film formed by this sputtering method largely depends on the quality of the Cu—Ga alloy sputtering target, a high quality Cu—Ga alloy sputtering target is desired.

Japanese Patent No. 3249408 JP 2000-73163 A JP 2008-138232 A Japanese Patent No. 4649536 JP 2010-265544 A

  By the way, in recent years, optimization of CIGS layer composition by a solar cell manufacturer has progressed, and a Cu—Ga alloy sputtering target having a Ga concentration of 30% by mass or more has been demanded.

  As a method for producing a Cu—Ga alloy sputtering target, a production method by a melting method (for example, see Patent Document 2) or a powder metallurgy method (for example, see Patent Documents 3 to 5) is known.

  Patent Document 2 proposes a method for producing a Cu—Ga alloy sputtering target by a melting method, but the cast alloy having a Ga concentration of 30% by mass or more is brittle, and the target is cracked in subsequent processing. is there.

  Patent Document 3 proposes a method of manufacturing a Cu—Ga alloy sputtering target having a Ga concentration of 30% by mass or more and having no cracks or defects by a powder sintering method.

  In addition, when producing a Cu-Ga alloy sputtering target, if there is a difference in bulk density and tap density in the Cu-Ga alloy powder as a raw material, segregation occurs during filling of the powder with a hot press or the like, and further press application Sometimes powder leaks. As a result, the yield of the target is reduced, the molds, dirt or deformation of the members such as the press punch, etc., and the performance of the obtained sintered body is also deteriorated, for example, cracks, density unevenness, strength deterioration, Ga concentration There is a problem that non-uniformity in thickness, uneven thickness, and the like are caused.

  When the density of the Cu—Ga alloy sputtering target is not uniform or the strength is insufficient, abnormal discharge (arc discharge) occurs during sputtering, splash splashes and adheres to the metal precursor film. Then, a small piece comes off from the Cu—Ga alloy sputtering target and adheres to the metal precursor film, resulting in a problem that the solar cell characteristics are lowered and the yield is lowered. For this reason, a high-quality Cu—Ga alloy sputtering target is also required not to cause abnormal discharge or particle dropout.

  The present invention has been proposed in view of such circumstances, the density is uniform at the center and the end, the Ga concentration is uniform, and there are no cracks during target processing and sputtering. To provide a Cu-Ga alloy sputtering target in which the occurrence of abnormal discharge is suppressed, and to produce such a target, the difference between the bulk density and the tap density of the Cu-Ga alloy powder is small, and the particle size segregation. An object of the present invention is to provide a Cu-Ga alloy powder that is less likely to cause oxidization.

The Cu—Ga alloy sputtering target according to the present invention that achieves the above-described object is characterized in that the density difference between the central portion and the end portion is less than 0.10 g / cm ³ .

  This Cu—Ga alloy sputtering target is characterized in that the Ga concentration difference between the central portion and the end portion is within ± 2.0 wt%.

  This Cu—Ga alloy sputtering target has a porosity of 0.07% or less.

  This Cu-Ga alloy sputtering target has a Ga concentration of 15% by mass to 45% by mass, a compressibility of 0% to 25%, and a ratio of tap density to bulk density of 1.00 to 1.35. It is obtained by sintering a Cu-Ga alloy powder after heat treatment.

  The Cu—Ga alloy powder according to the present invention that achieves the above-mentioned object has a Ga concentration of 15% by mass to 45% by mass, a degree of compression of 0% to 25%, and a ratio of tap density to bulk density. It is 1.00-1.35.

In the present invention, since the density difference is less than 0.10 g / cm ³ between the central portion and the end portion of the Cu—Ga alloy sputtering target, it is possible to prevent abnormal discharge from occurring during sputtering.

It is a Cu-Ga type alloy phase diagram.

  The Cu—Ga alloy powder and the Cu—Ga alloy sputtering target to which the present invention is applied will be described in detail below. Note that the present invention is not limited to the following detailed description unless otherwise specified. First, the Cu-Ga alloy powder used as the raw material of a Cu-Ga alloy sputtering target is demonstrated.

<Cu-Ga alloy powder>
The Cu-Ga alloy powder has a tap density, a bulk density, and a particle size distribution that are controlled in an optimal range in order to obtain a uniform composition and density in a heat treatment process and a sintering process in producing a target. The Cu-Ga alloy powder has a Ga concentration of 15% by mass to 45% by mass, a compressibility of 0% to 25%, and a tap density to bulk density ratio (Hausner ratio) of 1.00 to 1.%. 35. The degree of compression and the Hausner ratio are well-known parameters representing the degree of fluidity.

  The degree of compression (%) can be determined by the degree of compression (%) = {(tap density−bulk density) / tap density} × 100. The Hausner ratio can be determined by the tap density / bulk density. The bulk density and the tap density can be measured based on JIS R1628 and JISZ2512.

  In general, the powder fluidity improves as the Hausner ratio decreases. That is, the bulk density approaches the tap density. That is, it becomes difficult for the space between the particles to be filled with finer particles. Accumulation of fine powder between particles of various dimensions increases the interparticle force and consequently impedes the overall fluidity of the powder. That is, the Hausner ratio means an arrangement state between particles.

  When the degree of compression is 26% or more and the Hausner ratio is greater than 1.35, the fluidity of the Cu—Ga alloy powder is poor, and cracks are likely to occur during the subsequent sintering. Further, if segregation occurs, powder leakage may occur when the powder is packed in a sintering mold, and the target density may become non-uniform. If a portion having a low target density occurs, that is, if the porosity increases, an arc or the like may be generated in the subsequent sputtering, which is not desirable.

  Therefore, in the Cu—Ga alloy powder, the degree of compression is 0% to 25%, and the ratio of the tap density to the bulk density is 1.00 to 1.35, so that the fluidity is good and segregation does not occur. The density of the target becomes uniform, the porosity can be reduced, and the generation of arc during sputtering can be suppressed.

  Moreover, the Cu-Ga alloy powder suppresses the variation in the Ga concentration in the Cu-Ga intermetallic compound layer, and the variation is within 3.0% by mass. Therefore, this Cu-Ga alloy powder has a uniform composition and high quality. Therefore, by using the Cu—Ga alloy powder, a Cu—Ga alloy sputtering target having a uniform composition can be manufactured.

<Cu-Ga alloy sputtering target>
The Cu—Ga alloy sputtering target can be manufactured by heat-treating and sintering the above-described Cu—Ga alloy powder as described later. The Cu—Ga alloy sputtering target uses a Cu—Ga alloy powder having a degree of compression of 0% to 25% and a ratio of tap density to bulk density (Hausner ratio) of 1.00 to 1.35. Thus, since Cu—Ga alloy powder does not leak from the mold of the hot press apparatus during sintering, the difference in density between the central portion and the end portion of the Cu—Ga alloy sputtering target is reduced. In the Cu—Ga alloy sputtering target, the density difference between the center and the end obtained by the Archimedes method is less than 0.10 g / cm ³ . In addition, it becomes dense with a porosity of 0.07% or less. Therefore, since there are few void | holes in a Cu-Ga alloy sputtering target, it can suppress that an arc generate | occur | produces at the time of sputtering.

  Further, this Cu—Ga alloy sputtering target is of high quality with a uniform composition because the difference in Ga concentration between the central portion and the end portion is within ± 2.0 wt% and the variation in Ga concentration is small. . Therefore, when sputtering is performed using a Cu—Ga alloy sputtering target, since the variation in Ga concentration is small, a sputtered film having a uniform composition can be formed.

  The above Cu-Ga alloy sputtering target has a uniform density at the center and at the end, excellent Ga concentration uniformity, no cracking during target processing and sputtering, and the occurrence of abnormal discharge is suppressed. In addition, it is possible to form a sputtered film with high quality and uniform Ga concentration without causing any trouble.

<Method for producing Cu-Ga alloy sputtering target>
First, the manufacturing method of Cu-Ga alloy powder is demonstrated, and the manufacturing method of a Cu-Ga alloy sputtering target is demonstrated next.

(material)
Cu powder and Ga are used as raw materials for the Cu—Ga alloy powder. 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.

  The purity of the Cu powder is appropriately selected so as not to affect the characteristics of the CIGS light absorption layer formed from the Cu—Ga alloy sputtering target. When the oxygen content in the Cu powder is more than 0.2% by mass, the stirring process described later takes a long time, so the oxygen content is preferably 0.2% by mass or less. . Further, when the content of Fe, Ni, and Cr in the Cu powder is more than 3 ppm, the quantum efficiency of the CIGS light absorption layer is lowered, so that Fe, Ni, and Cr are preferably 3 ppm or less. .

  The average particle diameter of the Cu powder is preferably 5 μm to 300 μm. When the average particle size of the Cu powder is 5 μm or more, special handling for preventing the scattering of the Cu powder is not required, and the alloy powder production apparatus is increased in size due to the increase in the bulk capacity of the Cu powder. Can be prevented. In addition, when the average particle size of the Cu powder is 300 μm or less, the surface area (BET) of the Cu powder that must be coated with Ga is insufficient, and surplus unreacted liquid phase Ga tends to remain. Can be prevented. Thereby, when the average particle diameter of Cu powder is 300 micrometers or less, it can suppress that dispersion | variation arises in the composition of Cu-Ga alloy powder by presence of unreacted liquid phase Ga. Therefore, by setting the average particle size of the Cu powder to 5 μm to 300 μm, it is not necessary to take measures to prevent the Cu powder from scattering, the enlargement of the alloy powder manufacturing apparatus can be prevented, and the liquid phase of unreacted Ga can be reduced. The variation in the composition of the Cu—Ga alloy powder can be suppressed.

  The average particle size of the Cu powder is obtained by measuring the particle size distribution of the Cu powder by a laser diffraction method, integrating the abundance ratio (volume basis) from the small diameter side, and integrating the abundance ratio over the entire particle diameter. The particle size (D50) is half of the value. The value of the specific surface area (hereinafter referred to as BET value) can be determined by the BET method.

(Combination)
Cu powder and Ga are blended in the above-described mass ratio of 85:15 to 55:45. Since Ga is a metal having a low melting point (melting point: 29.78 ° C.), it is easily melted by heating, and the melted Ga covers the Cu powder. When the amount of Ga is 15% by mass or more, the surface of the Cu powder can be uniformly coated with Ga in a short time, and a uniform alloy structure can be obtained when the obtained powder is sintered. Become. Moreover, when the amount of Ga is 45% by mass or less, it is possible to prevent the powders from being combined with each other by a large amount of Ga present between the Cu powders, and to improve the yield of the alloy powder.

(Alloy powder production process)
Next, an alloy powder preparation process is performed in which a predetermined amount of Ga is added to the Cu powder to prepare a Cu—Ga alloy powder.

  Cu-Ga alloy powder is directly formed by stirring the mixed powder in which Cu powder and Ga are blended at the above-described mass ratio in a vacuum or an inert gas atmosphere at a temperature of 100 ° C to 300 ° C. Conventionally, Cu and Ga were once melted and alloyed at a high temperature, and the produced Cu—Ga alloy ingot was pulverized to obtain a Cu—Ga alloy powder. However, in this alloy powder production step, a Cu—Ga alloy ingot is produced and pulverized by stirring a mixed powder obtained by mixing Cu powder and Ga at a temperature of 100 ° C. to 300 ° C. under the above conditions. Even if it does not do, Cu-Ga alloy powder can be directly produced from the state of a raw material. Specifically, the Cu powder and Ga pieces weighed at the above-described ratio are controlled to a temperature higher than the melting point of Ga and lower than the melting point of Cu, that is, in the range of 30 ° C. to 300 ° C. A Cu—Ga binary alloy is formed.

  The Cu-Ga alloy 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 diffusion of Ga begins in the Cu powder, increasing the Ga concentration and forming an alloy while forming a Cu-Ga intermetallic compound. The reaction proceeds. At this time, the surface of the Cu—Ga alloyed material is a Cu—Ga intermetallic compound layer having a high Ga concentration, and the central portion is pure Cu.

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

  Similarly to Cu powder, 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 with the Cu powder, the purity of Ga is preferably 3 ppm or less because the quantum efficiency of the CIGS light-absorbing layer is lowered when Fe, Ni, and Cr are more than 3 ppm. When the oxygen content in Ga is more than 0.2% by mass, abnormal discharge is likely to occur during sputtering. Therefore, the oxygen content is preferably 0.2% by mass or less.

  Ga is a metal having a low melting point (melting point: 29.78 ° C.). Ga to be added to the Cu powder is preferably melted liquid Ga because stirring can be started immediately. 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.

  Cu powder and Ga are blended at a mass ratio of 85:15 to 55:45. In particular, in the alloy powder preparation process, Ga can be uniformly coated on the surface of the Cu powder in a short time because Ga is 15% by mass or more. The coated Ga can be alloyed. The Cu—Ga alloy powder formed in this alloy powder production step has a Cu—Ga alloy layer on the surface of the Cu powder.

  The alloy powder preparation step is performed in a vacuum or an inert gas atmosphere. In the alloy powder production step, it is possible to suppress the inclusion of oxygen in the Cu—Ga alloy powder by alloying in a vacuum or an inert gas atmosphere.

  The oxygen partial pressure in a vacuum or an inert gas atmosphere is preferably 20 Pa or less. When it is higher than 20 Pa, the oxygen content of the formed Cu—Ga alloy powder increases, the oxygen content of the produced sputtering target also increases, and abnormal sputtering occurs when sputtered with a large input power. The inert gas atmosphere is preferably nitrogen gas or argon gas.

  The temperature at the time of alloying is 100 ° C to 300 ° C. When the temperature is lower than 100 ° C., the reactivity between the Cu powder and Ga becomes insufficient, unreacted Ga remains, and the Ga concentration of the Cu—Ga alloy powder varies. When the temperature is higher than 300 ° C., the surface of the Cu powder is alloyed, but when the temperature is increased, the Cu—Ga alloy powder begins to aggregate. Since this agglomeration can be solved by a shearing motion by stirring, a Cu-Ga alloy powder can be formed at a temperature higher than 300 ° C., but the thermal deterioration of the stirring device is severe and the frequency of replacement of device parts is increased. It becomes expensive. Therefore, by setting the temperature to 100 ° C. to 300 ° C., Cu powder and Ga can be sufficiently reacted without aggregation.

  The temperature holding time is preferably 30 minutes to 4 hours. When the holding time is shorter than 30 minutes, the reactivity between the Cu powder and Ga becomes insufficient, unreacted Ga remains, and the Ga concentration of the Cu—Ga alloy powder varies. When the holding time is longer than 4 hours, the oxygen content of the Cu—Ga alloy powder increases even in a vacuum or an inert gas atmosphere. Therefore, by setting the temperature holding time to 30 minutes to 4 hours, the Cu powder and Ga can be sufficiently reacted to suppress an increase in the oxygen content of the Cu-Ga alloy powder.

  The agitation is effective for directly forming the Cu—Ga alloy powder while suppressing aggregation and increasing the contact frequency between the Cu powder and Ga.

  As the stirring device, a rotating vessel type stirring device such as a cylinder, a double cone, or a twin shell similar to the stirring step, or a stirring device in which a stirring bar such as a stirring blade or a stirring blade moves in a fixed vessel can be used. . When the Cu powder subjected to the stirring step described above is exposed to the air, the surface is immediately oxidized and the reactivity with Ga is lowered. For this reason, the alloy powder production process is preferable because it can be performed while being isolated from the atmosphere by performing alloying after the stirring process in the same stirring apparatus that performs the stirring process.

  The material of the stirrer vessel and stirrer used in the stirring step and the alloy powder preparation step is titanium nitride (TiN) from the viewpoint of heat resistance, wear resistance, suppression of metal impurities such as Fe, Ni, Cr, etc. ), Chromium nitride (CrN), and diamond-like carbon (DLC) (Diamond like Carbon) coated stainless steel material is preferable.

(Mixing and grinding)
By pulverizing and mixing the obtained Cu—Ga alloy powder, it is possible to make the particle sizes uniform and to suppress variations in particle sizes. The atmosphere for pulverization / mixing is preferably air or an inert gas atmosphere. Examples of the pulverizing / mixing device include a ball mill capable of simultaneously pulverizing and mixing. The ball can also be ZrO ₂ or Teflon-coated SUS balls. In addition, a jet mill / hammer mill can be used for pulverization. It is also possible to put a ball in a beaker used for agitation and rotate the blade to pulverize. For mixing, a V-type mixer or a rocking mixer can be used.

  As mentioned above, in the manufacturing method of Cu-Ga alloy powder, Ga density | concentration is 15 mass%-45 mass%, a compressibility is 0%-25%, and the ratio of tap density and bulk density is 1. Cu-Ga alloy powders that are 00 to 1.35 can be produced. Therefore, according to the method for producing Cu—Ga alloy powder, it is possible to produce a Cu—Ga alloy powder in which the difference between the bulk density and the tap density is small and particle size segregation hardly occurs.

  Next, the manufacturing method which manufactures a Cu-Ga alloy sputtering target using the Cu-Ga alloy powder obtained by the stirring process and alloy powder preparation process mentioned above is demonstrated. The manufacturing method of the Cu-Ga alloy sputtering target includes a heat treatment step of heat-treating the Cu-Ga alloy powder, a sintering step of producing a sintered body with the heat-treated Cu-Ga alloy powder, and surface-treating the sintered body. And a finishing step for forming a Cu-Ga alloy sputtering target.

(Heat treatment process)
In the heat treatment step, the Cu—Ga alloy powder obtained by the above-described alloy powder production step is heat-treated at a temperature of 250 ° C. to 830 ° C. in a vacuum or an inert gas atmosphere.

  The Cu—Ga alloy powder produced in the previous alloy powder production step has a Cu—Ga alloy layer on the surface of the Cu particles. The Ga concentration of the Cu—Ga alloy layer is higher than the proportion of Ga blended in the alloy powder production process. That is, in the state before the heat treatment, interdiffusion between the inside of the Cu particles and Ga does not occur sufficiently, so that a large amount of Ga exists on the surface of the Cu powder. Since the temperature at which the liquid phase appears decreases as the Ga concentration increases, the Cu-Ga alloy powder is sintered when heated in a state in which the Cu-Ga alloy powder is pressed with a hot press device to produce a sputtering target. A liquid phase will appear from the high Ga alloy layer at a temperature lower than that at which it is initiated. Thereby, Cu-Ga alloy powder will flow and will be pushed out from the crevice of a press type.

  Therefore, in the heat treatment step, the Cu—Ga alloy powder is heat treated before sintering by hot pressing. With this heat treatment, the low melting point Ga contained in the Cu-Ga alloy layer on the surface of the Cu particles begins to melt, and at the same time, the Cu-Ga alloy powder in the Cu-Ga alloy layer on the Cu particle surface and the Cu inside the particles. Interdiffusion, the Ga concentration on the surface of the Cu particles is lowered, and the appearance temperature of the liquid phase can be increased. Thereby, in the sintering process performed later, sintering progresses without producing a Ga liquid phase during sintering by hot pressing, and a sputtering target can be produced.

  The temperature of heat processing is 250 to 830 degreeC. When the temperature is lower than 250 ° C., interdiffusion between Ga in the alloy layer on the Cu particle surface and Cu inside the particle does not proceed sufficiently, and a high Ga concentration alloy layer remains, and during sintering by hot pressing. The Ga liquid phase appears and the Cu—Ga alloy powder leaks. When the temperature is higher than 830 ° C., a large amount of liquid phase is generated and separated from the Cu—Ga alloy powder.

  It is preferable to adjust the temperature of heat processing with the mixing | blending ratio of Ga in an alloy powder preparation process. When a small amount of liquid phase is generated during the heat treatment and aggregates are formed, the aggregation is weak and does not affect the sintering in the subsequent sintering process. When a phase appears, the liquid phase collects and separates from the Cu—Ga alloy powder, resulting in a large variation in composition. Such separation of the liquid phase can be effectively suppressed by controlling the heat treatment temperature in accordance with the Ga mixing ratio in the alloy powder production process.

  Specifically, the relationship between the blending ratio of Ga and the heat treatment temperature in the alloy powder production process is represented by the state diagram shown in FIG. In the phase diagram, the region above the temperature indicated by the liquidus is the liquid phase region where only the liquid phase exists, and the region below the temperature indicated by the solidus is the solid phase region where only the solid phase exists. The temperature region between the lines is the coexistence region of the liquid phase and the solid phase. Therefore, the temperature of the heat treatment is preferably 250 ° C. or more and not more than the solidus. In the heat treatment step, by setting the heat treatment temperature to 250 ° C. or higher and below the solidus line, mutual diffusion of Ga in the alloy layer on the surface of the Cu particles and Cu inside the particles is achieved without generating a liquid phase. Can do.

  The holding time of the heat treatment temperature is preferably from 30 minutes to 4 hours. When the holding time is shorter than 30 minutes, interdiffusion between Cu and Ga becomes insufficient, and a liquid phase appears in a hot press in the next sintering step, and Cu—Ga alloy powder is pushed out from the press die. . If the holding time is longer than 4 hours, the oxygen content of the Cu-Ga alloy powder increases even in a vacuum or inert gas atmosphere with an oxygen partial pressure of 20 Pa or less, and the oxygen content of the produced sputtering target When the amount is increased and sputtering is performed with a large input power, abnormal discharge occurs.

  The heat treatment is performed in a vacuum or an inert gas atmosphere. The oxygen partial pressure in a vacuum or inert atmosphere is preferably 20 Pa or less. When the pressure is higher than 20 Pa, the oxygen content of the heat-treated Cu—Ga alloy powder increases, the oxygen content of the produced sputtering target also increases, and abnormal sputtering occurs when sputtering is performed with a large input power. The inert atmosphere is preferably nitrogen gas or argon gas.

  This heat treatment step is preferably performed in the same hot press apparatus as the sintering step described later. When heat treatment is performed in the same hot press apparatus as the sintering process, it is not necessary to provide a separate heat treatment apparatus, and the cooling time after the heat treatment and the step of taking out the Cu—Ga alloy powder can be eliminated. As a result, when the heat treatment step and the sintering step are performed with the same hot press apparatus, the cooling time is not required as compared with the case where the heat treatment is performed with another heat treatment apparatus. Since the time can be shortened and there is no need to take out the Cu—Ga alloy powder, it is possible to prevent the yield from being lowered.

  When the heat treatment step is performed in the same hot press apparatus as the sintering step, it is preferable that the press pressure is no load on the Cu—Ga alloy powder or a pressure of 0.1 MPa or less. The pressure of 0.1 MPa or less corresponds to the pressure due to the weight of the upper punch of the hot press apparatus, and the pressure of no load or 0.1 MPa or less substantially does not apply pressure to the Cu-Ga alloy powder. State. By setting it as such a state, even if a liquid phase appears, it can prevent that Cu-Ga alloy powder leaks out from the press die of a hot press apparatus.

(Sintering process)
Next, the Cu—Ga alloy powder heat-treated in the heat treatment step is sintered by a hot press method at a temperature of 250 ° C. to 830 ° C. and a press pressure of 5 MPa to 30 MPa in a vacuum or an inert gas atmosphere.

  By setting the atmosphere of hot pressing in a vacuum or an inert gas atmosphere, an increase in the oxygen content of the sintered body can be suppressed. The oxygen partial pressure in a vacuum or an inert gas atmosphere is preferably 20 Pa or less. When the pressure is higher than 20 Pa, the oxygen content of the formed Cu—Ga alloy sintered body increases, the oxygen content of the produced sputtering target also increases, and abnormal sputtering occurs when sputtering is performed with a large input power. The inert gas atmosphere is preferably nitrogen gas or argon gas.

  The temperature of hot press shall be 250 to 830 degreeC. When the temperature is lower than 250 ° C., the Cu—Ga alloy powder is not sufficiently sintered, resulting in a sintered body with many voids. When sputtering is performed using a sintered body having a large number of pores as a sputtering target, abnormal discharge or splash occurs. When temperature is higher than 830 degreeC, a liquid phase will appear and it will become impossible to produce a sintered compact. Therefore, by setting the temperature of the hot press to 250 ° C. to 830 ° C., liquid leakage does not occur and a sintered body with few voids can be produced.

  The press pressure of the hot press is 5 MPa to 30 MPa. When the pressing pressure is lower than 5 MPa, the sintering of the Cu—Ga alloy powder is insufficient and a sintered body with many voids is obtained. When the pressing pressure is increased, the sintered body is increased in density by decreasing the number of pores, but the density hardly increases even if the pressure is higher than 30 MPa. When trying to press at a press pressure higher than 30 MPa, the press die needs to be changed to a special material or large electric power is required.

  In the sintering process, the Cu-Ga alloy powder is not taken out from the hot press apparatus used in the heat treatment process, and pressure sintering is performed in the same hot press apparatus following the heat treatment process, and the temperature of the hot press is set as the heat treatment in the heat treatment process. The temperature is preferably the same. When heat treatment and sintering are performed with the same hot press apparatus, it is not necessary to prepare a separate heat treatment apparatus for the heat treatment step, and cooling time after the heat treatment is unnecessary. In the sintering step, by setting the hot press temperature to the same temperature as the heat treatment, a press pressure is applied subsequent to the heat treatment, so that the sintering can be easily performed. In the sintering process, the heat treatment and the sintering are performed in the same hot press apparatus, whereby the composition of the Cu—Ga alloy sputtering target can be prevented from changing and the yield can be prevented from being lowered.

  In the method for producing a Cu—Ga alloy sputtering target, it is desirable that the difference between the weight of the alloy powder charged in the heat treatment / sintering step and the weight of the finished sintered body is small. When the weight difference is large, it can be said that powder leakage occurred from the mold of the hot press apparatus during heat treatment and sintering. When powder leakage occurs, a difference in density occurs between the central portion and the end portion of the Cu—Ga alloy sputtering target. If the density is low, an arc is generated during sputtering, which is not desirable.

(Finishing process)
In the finishing step, the surface of the sintered body of the Cu—Ga alloy obtained in the sintering step is finished to a flat surface by grinding and bonded to a Cu backing plate to obtain a Cu—Ga alloy sputtering target.

In the method for producing a Cu—Ga alloy sputtering target as described above, it is possible to produce a Cu—Ga alloy sputtering target having a uniform density at the center and end portions and excellent Ga concentration uniformity. In this method for producing a Cu—Ga alloy sputtering target, a Cu—Ga alloy sputtering target having a density difference between the central portion and the end portion of less than 0.10 g / cm ³ can be produced. Furthermore, in the obtained Cu—Ga alloy sputtering target, the Ga concentration difference between the central portion and the end portion is within ± 2.0 wt%, and the porosity is 0.07% or less. Therefore, in this method for producing a Cu—Ga alloy sputtering target, it is possible to produce a Cu—Ga alloy sputtering target that is free from cracks during target processing and sputtering and in which the occurrence of abnormal discharge is suppressed.

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

<Example 1>
[Alloy powder production process]
First, 4250 g of electrolytic Cu powder (average particle size 156 μm) was charged into a biaxial planetary type 5 L mixing and stirring device (5XDmv-rr type manufactured by Kodaira Seisakusho) equipped with a TiN coating container and a stirrer. After evacuating the inside of the container to a degree of vacuum of 100 Pa or less (oxygen partial pressure of 20 Pa or less), 750 g (Ga content ratio: 15 mass%) of liquid Ga heated to 50 ° C. was put into the container containing Cu powder. . It was kept at 150 ° C. for 1 hour with stirring. When the Cu—Ga alloy powder taken out after being cooled to room temperature was observed with a microscope, a part of the surface of the Cu powder was alloyed and turned grayish white. A sample of 1 g of the alloy powder was taken and the Ga concentration was examined by ICP analysis. As a result, it was 15.0% by mass.

[Mixing and grinding process]
Next, 7000 g of the obtained Cu—Ga alloy powder was transferred to a 10 L plastic container, and 7000 g of a 10 mmφ zirconia ball having the same weight as the alloy powder was charged, and dry ball milling was performed at 60 rpm for 3 hours. This powder was recovered and the average particle diameter (D50) was determined by the laser diffraction method described above, and it was 119 μm. The bulk density was 2.80 g / cm ³ and the tap density was 3.48 g / cm ³ . As a result, the degree of compression was 20% and the Hausner ratio was 1.24, and it can be said that powder with good fluidity was obtained.

[Heat treatment process]
Next, in the heat treatment step, 7000 g of Cu—Ga alloy powder was set in a graphite mold having an inner diameter of 500 × 130 mm for hot pressing, and attached to a hot pressing apparatus (manufactured by IHI Corporation). While the inside of the apparatus was evacuated to 50 Pa or less (oxygen partial pressure of 10 Pa or less), the press pressure was heated in an unloaded state, and heat treatment was performed at a temperature of 820 ° C. for 1 hour.

[Sintering process]
Subsequently, in the sintering process, a hot press is performed under the condition of pressurizing 30 MPa while maintaining the temperature at 820 ° C. and maintaining for 1 hour, and a Cu—Ga alloy sintered body (target material) having a length of 500 mm × 140 mm and a thickness of 13 mm. Was taken out. The weight of the Cu—Ga alloy sintered body at this time is 6972 g, and the amount of powder leaking from the graphite-type gap is as very small as 28 g. Also, no cracks were found.

[Evaluation]
A plurality of Cu—Ga alloy sintered bodies were produced in the same manner, and these sintered bodies were used for optical microscope observation, electron beam microanalyzer analysis (EPMA analysis, Electron Probe MicroAnalyser), and Archimedes density measurement. In addition, a Cu-Ga alloy sintered body is processed into a 6-inch diameter, bonded to a backing plate to produce a target, attached to a sputtering apparatus, and sputtered to obtain sputtered film uniformity, particles, abnormal discharge, and target. The presence or absence of cracks was examined.

(Porosity / Archimedes density)
One portion randomly selected from the central portion and the four corners of the 500 × 130 × 13 mm Cu—Ga alloy sintered body was cut into a 1 cm square, and the cross section was polished. When this polished surface was observed with an optical microscope, both the center and end portions were dense. As for the porosity, the area ratio was obtained by extracting the void portion from the images of five different fields of view obtained by photographing the polished surface at 200 times using image analysis software ImageJ. As a result, the porosity was very small with 0.03% at the center and 0.05% at the end. Was measured Archimedes density, central portion 8.33 g / cm ^3, an end portion 8.29 g / cm ^3, the density difference is 0.04 g / cm ^3, was observed little difference in both. When the Ga concentration was investigated by ICP, it was 15.1 wt% at the center and 15.0 wt% at the end, the concentration difference was 0.1 wt%, and there was almost no difference in the Ga concentration. Therefore, it can be seen that the Cu—Ga alloy sintered body of Example 1 has a small density difference between the central portion and the end portion, and both the central portion and the end portion have few holes. It can also be seen that the Ga concentration is uniform.

(Average crystal grain size)
In observing the average crystal grain size, switching to polarization observation so that crystal grains could be observed revealed a small crystal grain structure. A reflection electron image was taken with an electron microscope, and the crystal grain size was determined by the quadrature method described in JISH0501, and found to be 18.9 μm.

(Abnormal discharge)
A Cu—Ga alloy sintered body prepared in a sputtering apparatus (SH-450 manufactured by ULVAC, Inc.) is attached and evacuated to a vacuum degree of 5 × 10 ⁻⁴ Pa, and then sputtered for 30 minutes under conditions of Ar gas 1 Pa and DC input power 500 W. did. As a result of measuring the abnormal discharge at this time with an arc monitor (manufactured by Advanced Energy), no arc was observed.

(Target cracks)
When the sputtered Cu—Ga alloy sintered body was observed, no cracks were found.

<Example 2>
In Example 2, the Cu—Ga alloy powder was processed in the same manner as in Example 1 except that 3500 g of electrolytic Cu powder (average particle size 108 μm) treated with a rust preventive agent, 1500 g of Ga, and the heat treatment step and the sintering step were set to 800 ° C. Cu-Ga alloy sintered compact (target material) was produced.

For Cu-Ga alloy powder with a D50 of 47 [mu] m, a bulk density of 3.46 g / cm ^3, was tapped density 4.02 g / cm ^3. A powder with very good fluidity was obtained with a degree of compression of 14% and a Hausner ratio of 1.16.

About the Cu-Ga alloy sintered compact, when the powder leakage weight was confirmed similarly to Example 1, it was as small as 76g and the crack was not seen. Similarly light microscopy as in Example 1, EPMA analysis, porosity central portion, 0.05% to end both Archimedes density center portion 8.48 g / cm ^3, there at the end 8.43 g / cm ³ The difference in density was 0.05 g / cm ³ , and almost no difference was observed between the two. When the Ga concentration was investigated, it was 30.1 wt% at the center and 30.0 wt% at the end, the concentration difference was 0.1 wt%, and there was almost no difference in the Ga concentration. Therefore, it can be seen that the Cu—Ga alloy sintered body of Example 2 has a small difference in density between the central portion and the end portion, and both the central portion and the end portion have few holes. It can also be seen that the Ga concentration is uniform.

  The average crystal grain size was 8.8 μm. The abnormal discharge at the time of sputtering for DC500W for 30 minutes was very small as one time. The target was not cracked or chipped.

<Example 3>
In Example 3, Cu-Ga alloy powder and Cu-Ga alloy were obtained in the same manner as in Example 1 except that 1800 g of electrolytic Cu powder, 1200 g of Ga, the temperature of the heat treatment step was 400 ° C., and the temperature of the sintering step was 780 ° C. A sintered body was produced.

Regarding the Cu—Ga alloy powder, D50 was 68 μm, bulk density was 4.30 g / cm ³ , and tap density was 5.09 g / cm ³ . The degree of compression was 25% and the Hausner ratio was 1.33.

About the Cu-Ga alloy sintered compact, when the powder leakage weight was confirmed similarly to Example 1, it was as small as 67g and the crack was not seen. As a result of optical microscope observation, EPMA analysis, and Archimedes density measurement in the same manner as in Example 1, the porosity was 0.05% at the center and 0.07% at the end, and the Archimedes density was at the center. Part was 8.17 g / cm ³ , end part was 8.13 g / cm ³ , and the density difference was 0.04 g / cm ³ , and there was almost no difference between the two. When the Ga concentration was investigated, it was 40.2 wt% at the center and 40.1 wt% at the end, the concentration difference was 0.1 wt%, and there was almost no difference in the Ga concentration. Therefore, it can be seen that the Cu—Ga alloy sintered body of Example 3 has a small density difference between the central portion and the end portion, and both the central portion and the end portion have few holes. It can also be seen that the Ga concentration is uniform.

  The average crystal grain size was 9.9 μm. Abnormal discharge during DC500W for 30 minutes sputtering was as few as 5 times. The target was not cracked or chipped.

<Comparative Example 1>
In Comparative Example 1, a Cu—Ga alloy powder and a Cu—Ga alloy sintered body were produced in the same manner as in Example 2 except that the ball mill was not performed.

Regarding the Cu—Ga alloy powder, D50 was 105 μm, the bulk density was 2.46 g / cm ³ , and the tap density was 3.34 g / cm ³ . The degree of compression was 26%, the Hausner ratio was as high as 1.36, and the fluidity was poor.

About the Cu-Ga alloy sintered compact, when the powder leakage weight was confirmed similarly to Example 1, it was as many as 263g and the whole had a crack. As a result of optical microscope observation, EPMA analysis, and Archimedes density measurement in the same manner as in Example 1, the porosity was 0.04% at the center and 0.93% at the end. Archimedes density center portion 8.48 g / cm ^3, an end portion 8.35 g / cm ^3, the density difference is 0.13 g / cm ^3, the difference was seen. The Ga concentration was 30.1 wt% at the center and 27.9 wt% at the end, and the difference in concentration was 2.2 wt%, indicating a difference in Ga concentration. Since the entire Cu—Ga alloy sintered body cracked and the target area could not be secured, a sputtering test could not be performed. Therefore, it can be seen that the Cu—Ga alloy sintered body of Comparative Example 1 has a density difference between the central portion and the end portion, and there are many holes in the end portion. It can also be seen that there is a variation in Ga concentration between the center and the edge.

<Comparative example 2>
In Comparative Example 2, a Cu—Ga alloy powder and a Cu—Ga alloy sintered body were produced in the same manner as in Comparative Example 1 except that 2250 g of electrolytic Cu powder treated with a rust inhibitor and 750 g of Ga were used.

Regarding the Cu—Ga alloy powder, D50 was 121 μm, the bulk density was 2.27 g / cm ³ , and the tap density was 3.19 g / cm ³ . The compressibility was 29% and the Hausner ratio was as high as 1.41, and it was confirmed that powder having a large particle size was accumulated on the upper part of the glass tube after the tap density measurement.

About the Cu-Ga alloy sintered compact, when the powder leakage weight was confirmed similarly to Example 1, it was as many as 318g and the crack had entered in part. As a result of performing optical microscope observation, EPMA analysis, and Archimedes density measurement in the same manner as in Example 1, the porosity was 0.05% at the center and 4.56% at the end. Archimedes density is a central portion 8.52 g / cm ^3, an end portion 7.15 g / cm ^3, the density difference is 1.37 g / cm ^3, was observed significant difference. The Ga concentration was 25.1 wt% at the center and 21.8 wt% at the end, and the concentration difference was 3.3 wt%, showing a considerable difference. Moreover, in Comparative Example 2, although a part of the Cu—Ga alloy sintered body was cracked, an area used as a target could be secured, and thus a sputtering test could be performed. As a result of the sputter test, there were as many as 19 abnormal discharges during DC 500 W 30 minute sputtering. The target after the sputter test was not cracked or chipped. Therefore, it can be seen that the Cu—Ga alloy sintered body of Comparative Example 2 has a density difference between the central portion and the end portion, and there are many holes in the end portion. It can also be seen that there is a variation in Ga concentration between the center and the edge.

  The Cu—Ga alloy powders of Examples and Comparative Examples are summarized in Table 1, and the Cu—Ga alloy targets are summarized in Tables 2 and 3.

Claims (5)

A Cu—Ga alloy sputtering target, wherein the density difference between the central portion and the end portion is less than 0.10 g / cm ³ .   The Cu-Ga alloy sputtering target according to claim 1, wherein a Ga concentration difference between the central portion and the end portion is within ± 2.0 wt%.   The Cu-Ga alloy sputtering target according to claim 1 or 2, wherein the porosity is 0.07% or less.   After heat-treating a Cu—Ga alloy powder having a Ga concentration of 15 mass% to 45 mass%, a compressibility of 0% to 25%, and a ratio of tap density to bulk density of 1.00 to 1.35 The Cu—Ga alloy sputtering target according to claim 3, obtained by sintering. Ga concentration is 15% by mass to 45% by mass,
Cu-Ga alloy powder characterized by having a compressibility of 0% to 25% and a ratio of tap density to bulk density of 1.00 to 1.35.