Cu—Ga alloy sputtering target and method for producing same

Abstract

According to the present invention, a CuGa alloy sputtering target which is a sintered body has a composition with 29.5 atom % to 43.0 atom % of Ga and a balance of Cu and inevitable impurities. A CuGa alloy crystal particle in the sintered body has a structure in which phase particles are dispersed in a .sub.1-phase crystal particle. A method for producing the sputtering target includes a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a pure Cu powder and a CuGa alloy powder in a reducing atmosphere, and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

Claims

1. A CuGa alloy sputtering target, wherein the CuGa alloy sputtering target is a sintered body which has a composition with 29.5 atom % to 43.0 atom % of Ga and a balance of Cu, and a CuGa alloy crystal particle in the sintered body has a structure in which phase particles are dispersed in .sub.1-phase crystal particle.

2. The CuGa alloy sputtering target according to claim 1, wherein an average number of the phase particles in one .sub.1 crystal particle is 6 to 36, and an average particle diameter of .sub.1 phase particles is 15.0 m to 75.0 m.

3. The CuGa alloy sputtering target according to claim 1, wherein an amount of oxygen in the sintered body is equal to or less than 200 mass ppm.

4. The CuGa alloy sputtering target according to claim 1, wherein the sintered body further contains 0.05 atom % to 10.0 atom % of Na, and a Na compound phase is dispersed in the sintered body.

5. The CuGa alloy sputtering target according to claim 4, wherein the Na compound phase is formed of at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6.

6. A method for producing the CuGa alloy sputtering target according to claim 1, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder and a CuGa alloy powder in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

7. A method for producing the CuGa alloy sputtering target according to claim 4, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder, a CuGa alloy powder, and a Na compound in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

8. The CuGa alloy sputtering target according to claim 2, wherein an amount of oxygen in the sintered body is equal to or less than 200 mass ppm.

9. The CuGa alloy sputtering target according to claim 2, wherein the sintered body further contains 0.05 atom % to 10.0 atom % of Na, and a Na compound phase is dispersed in the sintered body.

10. The CuGa alloy sputtering target according to claim 3, wherein the sintered body further contains 0.05 atom % to 10.0 atom % of Na, and a Na compound phase is dispersed in the sintered body.

11. The CuGa alloy sputtering target according to claim 8, wherein the sintered body further contains 0.05 atom % to 10.0 atom % of Na, and a Na compound phase is dispersed in the sintered body.

12. The CuGa alloy sputtering target according to claim 9, wherein the Na compound phase is formed of at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6.

13. The CuGa alloy sputtering target according to claim 10, wherein the Na compound phase is formed of at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6.

14. The CuGa alloy sputtering target according to claim 11, wherein the Na compound phase is formed of at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6.

15. A method for producing the CuGa alloy sputtering target according to claim 2, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder and a CuGa alloy powder in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

16. A method for producing the CuGa alloy sputtering target according to claim 3, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder and a CuGa alloy powder in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

17. A method for producing the CuGa alloy sputtering target according to claim 8, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder and a CuGa alloy powder in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

18. A method for producing the CuGa alloy sputtering target according to claim 5, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder, a CuGa alloy powder, and a Na compound in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

19. A method for producing the CuGa alloy sputtering target according to claim 9, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder, a CuGa alloy powder, and a Na compound in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

20. A method for producing the CuGa alloy sputtering target according to claim 10, the method comprising: a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a Cu powder, a CuGa alloy powder, and a Na compound in a reducing atmosphere; and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a state diagram of CuGa alloys.

(2) FIG. 2 is a graph showing a diffraction peak measured by X-ray diffraction, regarding a CuGa alloy sputtering target containing 35.0 atom % of Ga.

(3) FIG. 3 is an image obtained by electron backscatter diffraction (EBSD).

(4) FIG. 4 is a diagram showing a method of obtaining an average particle diameter of crystal particles by using an EBSD image shown in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

(5) Hereinafter, a CuGa alloy sputtering target according to an embodiment of the present invention, and an embodiment of a method of producing the CuGa alloy sputtering target will be specifically described.

(6) A phase in the present invention corresponds to a phase (Phase- in which Ga is provided so as to be in a range of 29.5 atom % to 34.7 atom %) which is stable at 490 C. or higher in the state diagram which is shown in FIG. 1 and relates to CuGa alloys. A .sub.1 phase in the present invention corresponds to a .sub.1 phase (Phase-.sub.1 in which Ga is provided so as to be in a range of 29.8 atom % to 37.6 atom %) which is stable at 645 C. or lower in the state diagram.

(7) A sintered body of the CuGa alloy sputtering target according to the embodiment has a composition of Ga and a balance. Ga is contained so as to be 29.5 atom % to 43.0 atom %, and as the balance, Cu and inevitable impurities are contained. The sintered body has a structure in which a CuGa alloy crystal particle is used as a parent phase (matrix phase), and the parent phase includes phase particles and .sub.1-phase crystal particles of CuGa alloy. Particularly, the parent phase has a structure in which phase particles of which the average particle number in a .sub.1-phase crystal particle having an average particle diameter of 15.0 m to 75.0 m is 6 to 36 are dispersed.

(8) In the manufacturing of a CuGa alloy sputtering target, which has been proposed in PTL 1, a powder mixture of a Cu powder and a Ga powder is subjected to hot pressing, and thus a CuGa alloy sintered body is obtained. Generally, the obtained sintered body is cooled from a hot pressing temperature, and thereby manufacturing a sputtering target. In this case, as known in the state diagram of the CuGa alloy (source of reference, Desk Handbook: Phase Diagrams for Binary Alloys (ASM International)) in FIG. 1, the structure of the sintered body is configured by only the CuGa alloy particle and the average particle diameter thereof is large. For example, in a case of CuGa alloys which contains 29.5 atom % to 34.7 atom % of Ga and a balance is Cu, a CuGa alloy particle in the sintered body is mainly configured by the phase. The phase originally has relatively fragile properties, and thus becomes a cause of the generation of particles and abnormal discharge during sputtering.

(9) In the present invention, the parent phase of the CuGa alloy particle is configured by two phases of the phase and the .sub.1 phase, and thus a structure in which the fine phase is dispersed in the .sub.1 phase which is softer than the phase is applied. The CuGa alloy particle in the CuGa alloy sputtering target has such a structure, and thus it is possible to improve fragility and to reduce the average particle diameter of a CuGa alloy phase. Accordingly, it is possible to suppress the generation of particles and abnormal discharge during sputtering.

(10) Here, in order to manufacture the CuGa alloy sputtering target according to the embodiment, a molded body formed from a powder mixture of a pure Cu powder and a CuGa alloy powder is heated in a reducing atmosphere. Therefore, normal pressure sintering is performed. Then, the obtained sintered body is cooled at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C. It has been found that a CuGa alloy particle which has an organizational structure configured by the two phases of the phase particle and the .sub.1-phase crystal particle can be formed in the sintered body if the above treatment is performed. As understood from the state diagram FIG. 1, which relates to the CuGa alloys, the above-described cooling condition (cooling rate) is adjusted in the process of cooling the sintered body, and thus it is possible to change the dispersion state of the phase in the .sub.1 crystal particle.

(11) The change of the dispersion state of the phase in the .sub.1 phase will be described. Firstly, because the phase is stable in the vicinity of a sintering temperature in the process of cooling after sintering of the molded body, if the molded body is rapidly cooled, a sintered body in which the main phase of the CuGa alloy particle is the phase is obtained. On the contrary, if the molded body is gradually cooled, for example, at a slow cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C. in the middle of the cooling, the fine .sub.1 phase in the phase appears. Since a percentage of the phase and the .sub.1 phase is gradually changed in the cooling process using the slow cooling rate, if the cooling rate becomes faster at a point of time when the fine phase is formed in the .sub.1 phase, a CuGa alloy particle having a structure in which fine phase particles are dispersed in a .sub.1-phase crystal particle can be obtained.

(12) In the CuGa alloy sputtering target according to the embodiment, the CuGa alloy particle has a structure in which the phase particles of which an average particle number in the .sub.1-phase crystal particle having an average particle diameter of 15.0 m to 75.0 m is 6 to 36 are dispersed. If the cooling rate is too slow, the CuGa alloy particle becomes larger, and the frequency abnormal discharge is increased even when fine phase particles are dispersed. Thus, the average particle diameter of the .sub.1-phase crystal particle is set to be equal to or less than 75.0 m. In a case where the average particle number of the phase particles is less than 6, an effect of prevention of abnormal discharge is not obtained. In a case where the average particle number of the phase particles is more than 36, the cooling rate is required to be set to be less than 0.1 C./min. Since the .sub.1 parent phase becomes coarse and the average particle diameter of the .sub.1 phase is more than 75 m under this condition, abnormal discharge is increased, sputtering is not performed well, and control of the cooling rate is difficult. The average particle diameter of the .sub.1-phase crystal particles is preferably 25 m to 50 m and the average particle number of the phase particles is preferably 10 to 30. However, it is not limited thereto.

(13) The other method of producing a CuGa alloy sputtering target according to the embodiment includes a step of performing normal pressure sintering by heating a molded body formed of a powder mixture of a pure Cu powder, a CuGa alloy powder, and a Na compound in a reducing atmosphere, and a step of cooling the obtained sintered body at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C. The above-described method of producing a CuGa alloy sputtering target according to the present invention corresponds to a case of a powder mixture of the pure Cu powder and the CuGa alloy powder. However, the other method of producing a CuGa alloy sputtering target according to the present invention corresponds to a case of a powder mixture obtained by the Na compound being contained in the powder mixture. The cooling process is similar to the case of the above-described producing method according to the present invention. The added Na compound is confirmed to be present as a form of a Na compound phase at an interface between the CuGa alloy particles in the sintered body. The preferable temperature range in the cooling process is 490 C. to 645 C., and the cooling rate is preferably 0.2 C./min to 0.9 C./min. However, it is not limited thereto.

(14) In the producing method of a sputtering target, which is disclosed in PTL 2, Na is added to a CIG alloy. On the contrary, in the producing method according to the present invention, Na in a state of a compound is added instead of Na singleton, coarsening of the Na compound phase is suppressed, and the oxygen content of a sputtering target is restricted. In the producing method according to the present invention, the average particle diameter of the parent phase (matrix phase) of the CuGa alloy in a sputtering target is optimized, and the parent phase contains the phase particle and the .sub.1-phase crystal particle. Thus, a CuGa alloy sputtering target which contains Na and suppresses abnormal discharge is realized.

(15) The reason that the content of Na contained as a state of a Na compound is set to have the above range is because if the Na content exceeds 10 atom %, ensuring of sufficient sintered density is impossible and abnormal discharge in sputtering is increased. If the Na content is smaller than 0.05 atom %, the Na content of a sputter film is insufficient and obtaining a desired Na-added CuGa alloy film is impossible. The Na content is preferably 1.0 atom % to 6.0 atom %, but it is not limited thereto.

(16) The CuGa alloy sputtering target according to the embodiment preferably has an oxygen content of 200 mass ppm or less. If oxygen is present in the CuGa alloy sputtering target into which the Na compound is added, oxygen and the Na compound may react with each other and NaO having a high hygroscopic property is likely to be generated. Particularly, if the oxygen content exceeds 200 mass ppm, the probability of abnormal discharge in the sputtering target is high. Thus, the oxygen content is set to be equal to or less than 200 mass ppm. The lower limit value of the oxygen content may be 10 mass ppm. The oxygen content is preferably 50 mass ppm to 100 mass ppm, but is not limited thereto.

(17) In the CuGa alloy sputtering target according to the present invention, since the average particle diameter of the .sub.1-phase crystal particles in the metal matrix is 15.0 m to 75.0 m, the coarse Na compound phase is not generated even though the Na compound is contained. If the average particle diameter of the .sub.1-phase crystal particles is greater than 75.0 m, the Na compound phase is easily coarsened. Thus, it is not preferable. If the average particle diameter of the .sub.1-phase crystal particles is less than 15.0 m, a fine dispersion structure for phase particles does not appear, and the oxygen content easily exceeds 200 mass ppm. Thus, it is not preferable.

(18) As described above, in the CuGa alloy sputtering target according to the present invention, the fine phase particles are dispersed in the .sub.1-phase crystal particle, in the metal matrix. The average particle diameter of the .sub.1-phase crystal particles is 15.0 m to 75.0 m. The Na compound phase having an average particle diameter which is equal to or less than 8.5 m is finely dispersed. Since the oxygen content is equal to or less than 200 mass ppm, the oxygen content is low, and the particle diameter is small. Thus, abnormal discharge is significantly reduced.

(19) The reason that the Ga content is equal to or greater than 29.5 atom % is because the average particle diameter of the .sub.1-phase crystal particles is reduced and the oxygen content is easily increased if the Ga content is less than 29.5 atom %. The reason that the Ga content is equal to or less than 43.0 atom % is because if the Ga content is greater than 43.0 atom %, the percentage of the phase is reduced, the average particle diameter of the .sub.1-phase crystal particles is increased, and the coarse Na compound phase is easily generated. As the Na compound, at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6 may be used. Here, F, S, Se, and Al which are elements other than Na in the Na compound serve as impurities in the composition of a target and are included in inevitable impurities. The Ga content is preferably 30.0 atom % to 34.7 atom %, but it is not limited thereto.

(20) The method for producing a CuGa alloy sputtering target according to the embodiment is the above-described method for producing a CuGa alloy sputtering target according to the present invention. The method for producing a CuGa alloy sputtering target according to the present invention includes a step of performing normal pressure sintering by heating a molded body formed from a powder mixture of a pure Cu powder, a CuGa alloy powder, and a Na compound, in a reducing atmosphere. That is, in the method for producing a CuGa alloy sputtering target, normal pressure sintering is performed by heating a molded body formed from a powder mixture of a pure Cu powder, a CuGa alloy powder, and a Na compound, in a reducing atmosphere. Thus, mutual diffusion occurs from a raw material powder thereof during sintering in a sintered body, and the phase of the CuGa alloy is set to a first phase. However, the sintered body is gradually cooled at a slow cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C. in the middle of the cooling. Therefore, the .sub.1 phase appears in the phase. Then, the phase becomes finer, and the .sub.1 phase grows on the other side. Accordingly, a crystal structure of a state where the fine phase particles are dispersed in the .sub.1-phase crystal particle is obtained in the CuGa alloy particle of the sintered body which has been cooled.

(21) Here, regarding a CuGa alloy sputtering target which contains Ga so as to be 35.0 atom % as a representative example according to the present invention, FIG. 2 shows results obtained by measuring a diffraction peak through X-ray diffraction (XRD). As known from the results, both of a diffraction peak belonging to the phase of the CuGa alloy and a diffraction peak belonging to the .sub.1 phase thereof are observed.

(22) Equipment and a measurement condition used in the X-ray diffraction (XRD) are as follows. Equipment: RINT-Ultima/PC manufactured by Rigaku Denki Co., Ltd. Bulb: Cu Bulb voltage: 40 kV Bulb current: 40 mA Scanning range (2):40 to 70 Slit size: diffusion (DS) degrees, scattering (SS) degrees, and light receiving (RS) 0.8 mm Measurement step width: 0.02 degrees at 2 Scanning speed: 1 degree per minute Number of revolutions of sample stand: 30 rpm

(23) In a case of FIG. 2, it is understood that a ratio of intensity of the diffraction peak belonging to the phase, and intensity of the diffraction peak belonging to the .sub.1 phase is about 1:2 and two phases of the phase and the .sub.1 phase are clearly formed in a structure.

(24) FIG. 3 shows an image obtained by electron backscatter diffraction (EBSD), regarding the CuGa alloy sputtering target of the representative example. An actual EBSD image is a color image in which a difference between crystal orientations relating to crystal particles is separated by color. However, in the image shown in FIG. 3, the difference is displayed by using densities of white and black in accordance with the color. Thus, an area shown by shading indicates crystal particles of the .sub.1 phase. The main phase in a sintered body of the sputtering target may be determined to be the .sub.1 phase which is more stable at a low temperature, based on the state diagram in FIG. 1, which relates to the CuGa alloy. When observing each area shown by shading, that is, each of the CuGa alloy particles of the .sub.1 phase, it is possible to observe a form in which spot-like regions which are different from the crystal orientation of the .sub.1-phase crystal particle are dispersed in each area. That is, the spot-like regions dispersed in the .sub.1-phase crystal particle indicate crystal particles of the phase, which are more stable at a high temperature.

(25) It is confirmed that the CuGa alloy sputtering target according to the present invention is formed from a sintered body which has a composition of Ga (29.5 atom % to 43.0 atom %) and the balance (Cu and inevitable impurities), and has a structure in which the fine phase particles are dispersed in the .sub.1-phase crystal particle, based on the above results.

(26) A shape is easily held by using a pure Cu powder which is easily plastically-deformed as a raw material, when a molded body is formed. Since the pure Cu powder is oxidized in a room-temperature air, but is easily reduced by heating in the reducing atmosphere, the pure Cu powder is not the cause of an increase of the oxygen content. A liquid phase is generated in sintering and a high-density sintered body is obtained by using the CuGa alloy powder of 50 atom % of Ga.

(27) The CuGa alloy sputtering target according to the embodiment includes two cases: a case of being a sintered body which has a composition with 29.5 atom % to 43.0 atom % of Ga and a balance of Cu and inevitable impurities; and a case of being a sintered body which has a composition with 29.5 atom % to 43.0 atom % of Ga, 0.05 atom % to 10.0 atom % of Na, and a balance of Cu and inevitable impurities (including elements other than Na in the Na compound). The phase and the .sub.1 phase of the CuGa alloy are present together in each of metal matrixes of the fired bodies, and the sintered body has a structure in which fine phase particles are dispersed in a .sub.1-phase crystal particle. In a case where Na is contained, the sintered body has a structure in which a Na compound phase formed from at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6 is dispersed at a particle boundary of CuGa alloy particles. In the sintered body of the CuGa alloy sputtering target according to the embodiment, the main phase (parent phase) has a crystal structure of the .sub.1 phase.

(28) The average particle diameter of the .sub.1-phase crystal particles is obtained in the following manner. A surface of a sample cut out from the sputtering target is polished so as to become a mirror surface, and is etched by using an etchant which is formed from nitric acid and pure water. Then, a microphotograph is captured by an optical microscope which can distinguish a crystal particle boundary at a magnification of a range from 50 times to 1000 times. As shown in FIG. 4, 10 straight lines (displayed by using white lines) for dividing one side of the obtained photograph into 11 equal parts are drawn. The number of crystal particles through which the 10 straight lines pass is calculated, and the average particle diameter of the .sub.1-phase crystal particles is obtained by the following calculation formula.
Average particle diameter=(value obtained by correcting lengths of the 10 straight lines on the photograph to be actual lengths)/(the number of .sub.1-phase crystal particles through which the 10 straight lines pass)

(29) The average particle number of the phase particles is also obtained by using 10 straight lines of the photograph shown in FIG. 4. That is, the number of phase crystal particles through which the 10 straight lines pass is calculated. A value obtained by the calculating is divided by the number of .sub.1-phase crystal particles through which the 10 straight lines pass, and the average particle number thereof is obtained.

(30) The average particle diameter of the Na compound phase may be measured based on an element distribution mapping image of Na obtained by the EPMA. In the image, a white area indicates the presence of Na and represents the size of the Na compound phase. An occupied area S (m.sup.2) is measured and obtained by setting this white area as one Na compound particle. The particle diameter D of the Na compound phase is obtained from an expression of particle diameter D=(S/).sup.1/2. The average particle diameter (average value of D) and the maximum particle diameter (maximum value of D) are calculated from the number of Na compound particles which are observed in 10 square areas having one side of 100 m, and particle diameters D.

(31) The oxygen content is measured by an infrared absorbing method which is described in General rules for determination of oxygen in metallic materials of JIS Z 2613.

(32) The method for producing a sputtering target in this embodiment has a step of performing normal pressure sintering by heating a molded body in a reducing atmosphere. The molded body is formed from a powder mixture of a pure Cu powder, a CuGa alloy powder, and a Na compound.

(33) An example of the producing method will be described in detail. First, a pure Cu powder in which D50 measured by Microtrac is 2 m to 3 m and a CuGa alloy atomized powder in which D50 is 20 m to 30 m are weighed so as to be a target composition. Then, the powders are mixed with each other in an Ar atmosphere by using a Henschel mixer at a number of revolutions of 2800 rpm for 1 minute, thereby a powder mixture of the pure Cu powder and the CuGa alloy atomized powder is obtained. The CuGa alloy atomized powder is produced in such a manner that a CuGa alloy is dissolved in a gas atomizing device so as to cause the concentration of Ga to be 50 atom %, and is atomized by using an Ar gas.

(34) Then, a pressure powder (molded body) is obtained at a molding pressure of 500 kgf/cm.sup.2 to 2000 kgf/cm.sup.2 by using the obtained powder mixture. The pressure powder is arranged in a furnace. A reducing gas flows at 10 L/min to 100 L/min, and the pressure powder is heated up to a sintering temperature of 700 C. to 1000 C. at 10 C./min and is held for 5 hours. Then, cooling is performed to a temperature of 450 C. in a temperature range of 450 C. to 650 C. at a cooling rate of 0.1 C./min to 1.0 C./min, and thereby natural cooling is performed. In a cooling process from a sintering temperature to 450 C., a fine structure of the phase is generated by adjusting a cooling rate to the above cooling rate. Turning processing is performed on a surface portion and an outer circumference portion of the obtained sintered body. Thereby, a sputtering target having a diameter of 50 mm and a thickness of 6 mm is manufactured.

(35) Then, the processed sputtering target is bonded to a Cu backing plate. The CuGa alloy sputtering target manufactured in this manner is provided for a direct-current (DC) magnetron sputtering device by using an Ar gas as a sputtering gas.

(36) A CuGa alloy sputtering target in a case where Na is added is produced through procedures similar to a case where Na is not added, except that a Na compound of which the weight is measured so as to obtain a desired composition is added to the powder mixture.

(37) The CuGa alloy sputtering target according to the embodiment is a sintered body which has a composition with 29.5 atom % to 43.0 atom % of Ga and a balance of Cu and inevitable impurities. The CuGa alloy crystal particle in the sintered body has a structure in which phase particles are dispersed in a .sub.1-phase crystal particle. Particularly, the average particle number of the phase particles is 6 to 36, and the average particle diameter of .sub.1 phase particles is 15.0 m to 75.0 m. Accordingly, a structure in which fine phase particles are uniformly dispersed in a .sub.1 phase is formed, and thus it is possible to reduce the generation of particles and to significantly reduce abnormal discharge.

(38) The sintered body further contains 0.05 atom % to 10.0 atom % of Na, and a Na compound phase is dispersed in the sintered body. The Na compound phase formed of at least one of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6 is dispersed in the sintered body. The oxygen content is suppressed so as to be equal to or less than 200 mass ppm. Thus, it is possible to contribute to the improvement of photoelectric conversion efficiency in the light-absorbing layer of a CIGS thin-film solar cell by suppressing an increase of an amount of oxygen in a precursor film obtained through sputtering.

(39) In the method of producing a sputtering target according to the embodiment, a molded body is formed from a powder mixture of the pure Cu powder and the CuGa alloy powder, or a powder mixture of the pure Cu powder, the CuGa alloy powder, and the Na compound. The normal pressure sintering is performed by heating the molded body in the reducing atmosphere, and thereby a sintered body is obtained. Then, the sintered body is cooled at a cooling rate of 0.1 C./min to 1.0 C./min, at a temperature having a range of 450 C. to 650 C. in the cooling process of the sintered body. Since the cooling rate is slower than a general cooling rate in this temperature range, as known from the state diagram of CuGa series, which is shown in FIG. 1, the main phase of the CuGa alloy at first is the phase. However, the .sub.1 phase appears in the phase while the temperature becomes lower. If the temperature becomes further lowered, the .sub.1 phase grows largely in the phase. Here, the cooling rate is adjusted to a general rate, and thus the structure in which fine phase particles are dispersed in a .sub.1-phase crystal particle is maintained and cooled. In this manner, a sintered body formed from CuGa alloy crystal particles which have a structure in which phase particles are dispersed in a .sub.1-phase crystal particle, in the sintered body is obtained.

EXAMPLE

(40) Next, a result which is obtained by evaluating the sputtering target and the method for producing the same according to the present invention using examples manufactured based on the embodiment will be described.

(41) Firstly, a CuGa alloy atomized powder (CuGa powder in the table) having a Ga concentration of 50 atom %, a pure Cu powder, and a Na compound (NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6) were mixed so as to have a weight ratio as shown in Table 1, thereby powder mixtures of Examples 1 to 13 were obtained. Then, a pressure powder (molded body) was formed at a molding pressure of 1500 kgf/cm.sup.2 by using each of the obtained powder mixtures. As shown in Table 2, among the powder mixtures, Examples 1 to 9 were subjected to normal pressure sintering in a hydrogen atmosphere. Examples 10 and 11 were subjected to normal pressure sintering in a carbon monoxide atmosphere. Examples 12 and 13 were subjected to normal pressure sintering in an atmosphere of an ammonia decomposition gas. The normal pressure sintering was performed by holding the powder mixture for 5 hours at a sintering temperature of 840 C. with a reducing gas flowing at 50 L/min. In the cooling process of the sintered body which was obtained after sintering, cooling was performed at a cooling rate shown in Table 2 at a temperature having a range of 450 C. to 650 C. After the temperature became lower than the temperature range, natural cooling was performed.

(42) For comparative examples, CuGa alloy atomized powder (CuGa powder in the table) being 50 atom % in concentration of Ga, a Cu powder, and a Na compound were mixed so as to have a weight ratio shown in Table 1, thereby powder mixtures of Comparative Examples 1 to 5 were obtained. In Comparative Examples 3 and 4, the CuGa alloy powder was mixed so as to cause the content of Ga to be out of the range in the present invention. In Comparative Example 5, the Na compound was mixed excessively. Then, a pressure powder (molded body) was formed by using each of the obtained powder mixtures, similarly to the above examples.

(43) As presented in Table 2, Comparative Examples 1 to 5 were subjected to normal pressure sintering in a hydrogen atmosphere, and were cooled at the cooling rate presented by Table 2 at a temperature having a range of 450 C. to 650 C. After the temperature became lower than the temperature range, natural cooling was performed. Among the comparative examples, Comparative Examples 1 and 2 had a cooling rate having a value departing from the scope of the present invention.

(44) Table 2 shows results of composition analysis relating to Ga, Na, and Cu in sputtering targets of Examples 1 to 13 and Comparative Examples 1 to 5 in a target composition (atom %) field. This composition of each of the targets was measured by using an ICP method (high frequency inductively coupled plasma method).

(45) TABLE-US-00001 TABLE 1 Raw material mixing ratio (weight %) Cu CuGa NaF Na.sub.2S Na.sub.2Se Na.sub.3AlF.sub.6 powder powder powder powder powder powder Example 1 36.5 63.5 Example 2 27.2 72.8 Example 3 34.0 62.8 3.2 Example 4 32.0 65.1 2.9 Example 5 20.0 77.4 1.4 1.2 Example 6 13.3 86.1 0.6 Example 7 26.9 70.3 1.0 1.8 Example 8 16.6 78.8 1.5 3.1 Example 9 18.0 75.6 6.4 Example 10 20.6 78.9 0.5 Example 11 26.2 70.0 0.7 3.1 Example 12 32.7 62.9 4.4 Example 13 24.7 72.8 0.9 1.6 Comparative 25.9 71.7 2.4 Example 1 Comparative 46.2 52.5 1.3 Example 2 Comparative 42.9 54.2 2.9 Example 3 Comparative 11.5 85.4 3.1 Example 4 Comparative 30.7 61.6 4.5 3.2 Example 5

(46) TABLE-US-00002 TABLE 2 Target composition (atom %) Cu and Sintering Cooling rate inevitable atmosphere ( C./min) Ga Na impurities Example 1 Hydrogen 0.21 31.2 Remaining Example 2 Hydrogen 0.96 35.9 Remaining Example 3 Hydrogen 0.17 30.3 5.0 Remaining Example 4 Hydrogen 0.13 32.7 2.6 Remaining Example 5 Hydrogen 0.21 38.1 4.2 Remaining Example 6 Hydrogen 0.76 42.6 1.0 Remaining Example 7 Hydrogen 0.42 34.8 3.4 Remaining Example 8 Hydrogen 0.83 40.0 5.6 Remaining Example 9 Hydrogen 0.95 36.1 9.8 Remaining Example 10 Carbon 0.76 39.2 0.4 Remaining monoxide Example 11 Carbon 0.84 35.2 4.0 Remaining monoxide Example 12 Ammonia 0.52 30.2 6.7 Remaining decomposed gas Example 13 Ammonia 0.76 36.5 2.5 Remaining decomposed gas Comparative Hydrogen 1.04 34.9 3.7 Remaining Example 1 Comparative Hydrogen 0.08 25.9 1.3 Remaining Example 2 Comparative Hydrogen 0.52 26.1 4.5 Remaining Example 3 Comparative Hydrogen 0.21 43.4 3.0 Remaining Example 4 Comparative Hydrogen 0.73 30.2 10.5 Remaining Example 5

(47) In the above descriptions, regarding CuGa alloy sputtering targets of Examples 1 to 13 and Comparative Examples 1 to 5, the average particle diameter of the parent phase (matrix phase), the average number of dispersed phase particles, and the oxygen content were measured, and the number of abnormal discharge occurring during sputtering was measured.

(48) <Average Particle Diameter of Matrix Phase>

(49) The average particle diameter of .sub.1-phase crystal particles which correspond to the parent phase (matrix phase) was obtained in the following manner. A surface of a sample cut out from the sputtering target was polished so as to become a mirror surface, and was etched by using an etchant which is formed from nitric acid and pure water. Then, a microphotograph was captured by an optical microscope which could distinguish a crystal particle boundary at a magnification of a range from 50 times to 1000 times. As shown in FIG. 4, 10 straight lines (displayed by using white lines) for dividing one side of the obtained photograph into 11 equal parts were drawn. The number of crystal particles through which the 10 straight lines pass was calculated, and the average particle diameter of .sub.1-phase crystal particles was obtained by the following calculation expression.
(Average particle diameter)=(value obtained by correcting lengths of the 10 straight lines on the photograph to be actual lengths)/(the number of .sub.1-phase crystal particles through which the 10 straight lines pass)

(50) The average particle number of dispersed phase particles was also obtained by using 10 straight lines of the photograph shown in FIG. 4. That is, the number of phase crystal particles through which the 10 straight lines pass was calculated. A value obtained by the calculating was divided by the number of .sub.1-phase crystal particles through which the 10 straight lines pass, and the average particle number thereof was obtained.

(51) Results of measurement as described above were shown in an average particle diameter (m) of a matrix phase field, and an average number (piece) of dispersed particles field of Table 3. In a case where the phase was not present, a mark of none was indicated. In a case where measurement was not possible because the particle diameter of phase crystal particles is small, a mark of unobservability was indicated.

(52) <Oxygen Content>

(53) The oxygen content was measured by an infrared absorbing method which was described in General rules for determination of oxygen amount in metallic materials of JIS Z 2613. Results of the measurement were shown in an oxygen amount (mass ppm) field of Table 3.

(54) <Number of Abnormal Discharge Occurring>

(55) Regarding abnormal discharge during sputtering, sputtering was performed under the following film formation conditions for 12 hours and the number of abnormal discharge occurring was measured. Power: Pulse DC500 W Full pressure: 0.4 Pa Sputtering gas: Ar=47.5 sccm, O.sub.2=2.5 sccm Target substrate (TS) distance: 70 mm

(56) The number of abnormal discharge occurring was measured by an accounting function of a DC power source (type number: RPDG-50A) manufactured by MKS Instruments Inc.

(57) Results of the measurement were shown in an abnormal discharge (times) field of Table 3.

(58) TABLE-US-00003 TABLE 3 Matrix phase Average number Oxygen average par- of dispersed amount Abnormal ticle diameter particles (mass discharge (m) (piece) ppm) (times) Example 1 74.2 34.3 110 0 Example 2 29.9 11.5 120 0 Example 3 56.6 33.2 170 0 Example 4 47.7 35.1 120 0 Example 5 39.1 30.8 100 0 Example 6 33.5 13.2 70 0 Example 7 40.8 24.2 80 0 Example 8 30.6 14.4 60 0 Example 9 20.4 6.9 180 0 Example 10 31.1 9.5 110 0 Example 11 28.9 8.1 90 0 Example 12 31.5 8.6 170 0 Example 13 29.4 11.7 110 0 Comparative 11.3 None 90 2 Example 1 Comparative 81.4 40.1 210 3 Example 2 Comparative 25.7 Unobserv- 120 3 Example 3 ability Comparative 43.2 Unobserv- 60 5 Example 4 ability Comparative 8.3 Unobserv- 330 8 Example 5 ability

(59) According to the results shown in Table 3, the following were confirmed. That is, in any of the CuGa alloy sputtering targets of Examples 1 to 13, the average particle diameter relating to the .sub.1 phase of the CuGa alloy was in a range of 15.0 m to 75.0 m, the average number of dispersed particles relating to the phase particle of the CuGa alloy was in a range of 6 to 36. The parent phase in the CuGa alloy sputtering target was configured by .sub.1 phase particles, and a structure in which fine phase particles are dispersed in the parent phase was provided. In addition, there was no abnormal discharge during sputtering. Further, it was also confirmed that there were cases where Na is added, but the oxygen content of the target was reduced so as to be equal to or less than 200 ppm in any of the CuGa alloy sputtering targets of Examples 3 to 13.

(60) In a case of Comparative Example 1, since the cooling rate is high, it was not confirmed that a phase particle was generated in the .sub.1 phase particles, and abnormal discharge occurred. In a case of Comparative Example 2, since the cooling rate is excessively low, the average particle diameter of the .sub.1 phase becomes greater. Even when fine phase particles were dispersed, abnormal discharge occurred. Since Ga was insufficient in a case of Comparative Example 3, and since Ga was excessive in a case of Comparative Example 4, a phase particle was small enough such that observation of the presence of phase particles in the .sub.1 phase particle was not possible, and abnormal discharge occurred. In a case of Comparative Example 5, since Na was excessively added, dispersion of Na oxide phase caused the average particle diameter of .sub.1 phase particles to be small. In addition, in the case of Comparative Example 5, the phase particle was small enough such that observation of the presence of phase particles in the .sub.1 phase particle was not possible, it was not confirmed that a phase particle was generated in the .sub.1 phase particles, and abnormal discharge occurred.

(61) As described above, it was confirmed that the CuGa alloy crystal particle in the CuGa alloy sintered body of a Ga component having a high concentration according to the present invention has a structure in which fine phase particles were dispersed in the .sub.1-phase crystal particle. It was understood that the parent phase in the CuGa alloy sputtering target was configured by the .sub.1 phase, and it was possible to improve fragility of the target and to reduce the generation of particles during sputtering by dispersing fine phase particles in the parent phase. Regarding the CuGa alloy sputtering target in which the Na compound (one or more of NaF, Na.sub.2S, Na.sub.2Se, and Na.sub.3AlF.sub.6) phase was dispersed in the sintered body, it was also understood that the parent phase was configured by the .sub.1 phase, and it was possible to improve fragility, to reduce the generation of particles during sputtering, to further reduce the oxygen content of the target, and to further suppress abnormal discharge even when Na having a high concentration is contained.

INDUSTRIAL APPLICABILITY

(62) According to the CuGa alloy sputtering target of the present invention, it is possible to reduce generation of particles, to enable further reduction of the oxygen content, and to further suppress abnormal discharge even when Na having a high concentration is contained. According to the CuGa alloy sputtering target of the present invention, it is possible to contribute to the improvement of photoelectric conversion efficiency in the light-absorbing layer of a CIGS thin-film solar cell.