Copper-gallium sputtering target

Abstract

A Ga-containing and Cu-containing sputtering target has a Ga content of from 30 to 68 at %. The sputtering target contains only CuGa.sub.2 as Ga-containing and Cu-containing intermetallic phase or the proportion by volume of CuGa.sub.2 is greater than the proportion by volume of Cu.sub.9Ga.sub.4. The sputtering target is advantageously produced by spark plasma sintering or cold gas spraying. Compared to Cu.sub.9Ga.sub.4, CuGa.sub.2 is very soft, which aids the production of defect-free sputtering targets having homogeneous sputtering behavior.

Claims

1. A sputtering target, comprising: a target body consisting of Ga and Cu and, optionally, an amount of an alkali metal; said Ga being present at a Ga content of from 30 to 68 at %; and at least one Ga-containing and Cu-containing intermetallic phase selected from the group of intermetallic phases consisting of: only CuGa.sub.2, CuGa.sub.2 plus pure Cu, CuGa.sub.2 plus Ga-containing Cu mixed crystal, CuGa.sub.2 plus pure Cu plus Ga-containing Cu mixed crystal, CuGa.sub.2 plus other intermetallic CuGa phases, CuGa.sub.2 plus pure Cu plus other intermetallic CuGa phases, CuGa.sub.2 plus Ga-containing Cu mixed crystal plus other intermetallic CuGa phases, and CuGa.sub.2 plus pure Cu plus Ga-containing Cu mixed crystal plus other intermetallic CuGa phases.

2. The sputtering target according to claim 1, which comprises regions having said at least one Ga-containing and Cu-containing intermetallic phase with an average microhardness of <500 HV0.01.

3. The sputtering target according to claim 1, wherein at least 90% of said Ga is present as CuGa.sub.2.

4. The sputtering target according to claim 1, wherein said Ga content is from 40 to 68 at %.

5. The sputtering target according to claim 1, which further comprises a Cu-rich phase having a Cu content of >80 at % and being selected from the group consisting of pure Cu and Ga-containing Cu mixed crystal.

6. The sputtering target according to claim 5, wherein said Cu-rich phase is pure Cu.

7. The sputtering target according to claim 1, which further comprises >30% by volume of said CuGa.sub.2.

8. The sputtering target according to claim 1, which further comprises a volume ratio of CuGa.sub.2/Cu.sub.9Ga.sub.4 being >2.

9. The sputtering target according to claim 1, which further comprises a total of from 0.01 to 5 at % of at least one element selected from the group of alkali metals.

10. The sputtering target according to claim 1, wherein said at least one Ga-containing and Cu-containing intermetallic phase consists of only CuGa.sub.2 or a proportion by volume of CuGa.sub.2 is greater than a proportion by volume of Cu.sub.9Ga.sub.4.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows the CuGa phase diagram (source: Subramanian P. R., Laughlin D. E.: ASM Alloy Phase Diagrams Center, P. Villars, editor-in-chief; H. Okamoto and K. Cenzual, section editors).

(2) FIG. 2 shows a scanning electron micrograph of CuGa powder according to the invention having a Ga content of 66 at %, balance Cu.

(3) FIG. 3 shows the result of an XRD measurement on CuGa powder according to the invention having a Ga content of 66 at %, balance Cu (concentration indicated in the figure in % by mass).

(4) FIG. 4 shows an optical micrograph of a CuGa sputtering target according to the invention having a Ga content of 58 at %, balance Cu.

DESCRIPTION OF THE INVENTION

(5) The specimens were produced from the following powders: CuGa powder comprising 60% by mass of Cu and 40% by mass of Ga (60% by mass of Cu correspond to 62.20 at %, 40% by mass of Ga correspond to 37.80 at %; the powder will be referred to as Cu62Ga38 in the further text): for production of the comparative specimens CuGa powder comprising 48% by mass of Cu and 52% by mass of Ga (48% by mass of Cu correspond to 50.32 at %, 52% by mass of Ga correspond to 49.68 at %; the powder will be referred to as Cu50Ga50 in the further text): for production of the specimens according to the invention CuGa powder comprising 32% by mass of Cu and 68% by mass of Ga (32% by mass of Cu correspond to 34.05 at %, 68% by mass of Ga correspond to 65.95 at %; the powder will be referred to as Cu34Ga66 in the further text): for production of the specimens according to the invention.

(6) The powders were produced by atomizing a melt by means of Ar. The bulk density, tapped density, flowability, particle size determined by the Fisher method (FSSS) and the particle size (d.sub.0.10, d.sub.0.50, d.sub.0.90) measured by laser light scattering were determined on the powders. The measured values are shown in Table 1. All powders have a spherical shape due to the production process (for Cu.sub.34Ga.sub.66 powder, see FIG. 2). GDMS analyses were carried out to determine the trace elements. The gas contents and C contents were determined by means of hot extraction and combustion analysis, respectively. Impurities warranting mention are oxygen (Cu.sub.62Ga.sub.38: 1186 g/g, Cu.sub.50Ga.sub.50 1064 g/g and Cu.sub.34Ga.sub.66 1266 g/g). The C content of the samples was in the range from 8 to 18 g/g, and the H content was in the range from 41 to 59 g/g. All other impurities had values below 50 g/g. The indentation hardness H.sub.IT was determined on powder polished sections. The measurement was carried out in accordance with ISO 14577 (2002 version) using a Berkovich indentation body, the evaluation method according to Oliver and Pharr and the procedure as described in detail in the description.

(7) Cu.sub.62Ga.sub.38 has only one maximum of the indentation hardness at 7.7 GPa. Cu.sub.50Ga.sub.50 has two maxima at 3 GPa and 7.5 GPa. Cu.sub.34Ga.sub.66 displays a maximum at 2.8 GPa.

(8) In the case of large particles in the upper region of the particle size distribution, it is also possible to measure the microhardness HV.sub.0.01. A value of 719 HV.sub.0.01 was measured in the case of Cu.sub.62Ga.sub.38, 469 HV.sub.0.01 was determined in the case of Cu.sub.50Ga.sub.50 and 142 HV.sub.0.01 was determined in the case of Cu.sub.34Ga.sub.66.

(9) TABLE-US-00001 TABLE 1 Bulk density Tapped density FSSS Flowability Powder [g/cm.sup.3] [%] [g/cm.sup.3] [%] [m] [sec/50 g] Cu62Ga38 5.21 63.2 5.50 66.7 22.9 21.1 Cu50Ga50 4.69 59.6 5.17 65.7 20.8 24.6 Cu34Ga66 4.14 57.4 4.58 63.5 18.7 32.5 Particle size (laser light scattering) Powder d0.10 [m] d0.50 [m] d0.90 [m] Cu62Ga38 6.5 20.2 41.0 Cu50Ga50 8.6 24.0 46.3 Cu34Ga66 4.4 12.9 29.1

(10) The phases were determined by means of XRD as described in detail in the description. In the case of the Cu62Ga38 powder, only Cu.sub.9Ga.sub.4 phase could be detected. The Cu50Ga50 powder comprises 48% by volume of Cu.sub.9Ga.sub.4 phase and 52% by volume of CuGa.sub.2 phase. In the case of the Cu34Ga66 powder, only the CuGa.sub.2 phase could be determined. The measurement result for Cu34Ga66 is shown in FIG. 3.

(11) To study any phase transformations, DSC measurements were carried out. The Cu34Ga66 displayed an endothermic peak at about 260 C., which indicates the decomposition of CuGa.sub.2 into Cu.sub.9Ga.sub.4 and melt. In addition, a pure Cu powder produced by atomization and having a particle size d.sub.50 of 28 m was also used for the experiments.

(12) Production of Compacted Specimens:

(13) 1. Production of comparative specimens by hot isostatic pressing (HIP): A specimen which was not according to the invention was produced by HIP using Cu62Ga38 powder. The powder was for this purpose introduced into a steel can and hot isostatically compacted at 500 C. The heating rate was 5 K/min, the hold time at 500 C. was 2 h and the pressure was 100 MPa. The compacted specimen was cooled at about 2 K/min. An attempt to part the compacted material by means of wire cutting led to cracks and chipping of the material. Only Cu.sub.9Ga.sub.4 phase was detected by means of the phase determination method presented in the description. The compacted body had a density of 8.2 g/cm.sup.3 (>99% of the theoretical density). The microhardness was, as presented in detail in the description, determined and was 628 HV0.01. 2. Production of comparative specimens by spark plasma sintering (SPS): A specimen which was not according to the invention was produced by SPS using Cu62Ga38 powder. The powder was for this purpose introduced into a graphite tool. The sintering operation was carried out under temperature control, with the temperature measurement being carried out by means of a thermocouple. The specimen was sintered by application of a DC voltage which led to heat evolution due to the Joule effect in the specimen. The following conditions were set: Heating rate: 10 K/min Sintering temperature: 300 and 450 C. Hold time: 10 min Pressure: 30 MPa The specimen sintered at 300 C. had a relative density of 81%, and the specimen sintered at 450 C. had a relative density of 99.3%. Neither specimen could be worked mechanically. Only Cu.sub.9Ga.sub.4 phase was detected by means of the phase determination method presented in the description. The microhardness was determined as indicated in the description and was 611 HV0.01. 3. Production of specimens according to the invention by spark plasma sintering (SPS): The powder batches listed in Table 2 were densified by SPS. The process parameters are shown in Table 3. The determinations of the relative density, of the CuGa.sub.2 to Cu.sub.9Ga.sub.4 ratio, of the Ga present as CuGa.sub.2 and of the microhardness were carried out using the methods indicated in the description. The results are shown in Table 4. All specimens could be worked mechanically, with the workability being best in the case of the specimens in which the total Ga was present as CuGa.sub.2. An optical micrograph is shown by way of example for specimen B in FIG. 4.

(14) TABLE-US-00002 TABLE 2 Specimen Composition Components of the powder No. (at %/at %) mixture A Cu34Ga66 Only Cu34Ga66 powder (CuGa.sub.2 phase) B Cu42Ga58 Cu34Ga66 powder (CuGa.sub.2 phase) + Cu powder C Cu42Ga58 Cu34Ga66 powder (CuGa.sub.2 phase) + Cu powder D Cu62Ga38 Cu50Ga50 powder (CuGa.sub.2 phase + Cu.sub.9Ga.sub.4 phase) + Cu powder E Cu70Ga30 Cu50Ga50 powder (CuGa.sub.2 phase + Cu.sub.9Ga.sub.4 phase) + Cu powder F Cu50Ga50 Cu34Ga66 powder (CuGa.sub.2 phase) + Cu powder G Cu42Ga58 Cu34Ga66 powder (CuGa.sub.2 phase) + Cu powder H Cu42Ga58 Cu34Ga66 powder (CuGa.sub.2 phase) + CuGa mixed crystal powder (comprising 10% of the Ga of the sputtering target)

(15) TABLE-US-00003 TABLE 3 Heating Hold time at Specimen rate Sintering sintering Pressure No. [K/min] temperature temperature [min] [MPa] A 10 230 10 30 B 10 230 20 40 C 10 230 30 22 D 10 230 30 22 E 20 230 1 40 F 20 230 1 40 G 30 230 1 40 H 10 230 20 40

(16) TABLE-US-00004 TABLE 4 Relative Proportion Specimen density Microhardness by volume of Ga present No. [%] [HV0.01] CuGa.sub.2/Cu.sub.9Ga.sub.4 as CuGa.sub.2 A 90.3 151 No Cu.sub.9Ga.sub.4 100% detectable B 95.1 146 No Cu.sub.9Ga.sub.4 100% detectable C 87.9 139 No Cu.sub.9Ga.sub.4 100% detectable D 82.3 390 1.1 about 75% E 88.1 410 1.1 about 75% F 85.9 132 No Cu.sub.9Ga.sub.4 100% detectable G 89.0 158 No Cu.sub.9Ga.sub.4 100% detectable H 94.7 161 No Cu.sub.9Ga.sub.4 100% detectable

(17) All specimens according to the invention displayed very uniform sputtering behaviour; the sputtering test is explained in detail below for specimen C. A sputtering target having a diameter of 105 mm was used for the experiments. The coating rate was comparable to specimens having a lower or higher Ga content. The coating rate at a power of 200 W was about 100 nm/min, that at 400 W was about 260 nm/min and that at 600 W was about 325 nm/min. Layers sputtered at 200 W and 400 W (Ar pressure of 2.510.sup.3 mbar, 510.sup.3 mbar and 7.510.sup.3 mbar) had low compressive stresses of <25 MPa. Layers sputtered at 600 W (Ar pressure of 2.510.sup.3 mbar, 510.sup.3 mbar and 7.510.sup.3 mbar) had low tensile stresses of <25 MPa. The phases in a layer deposited at 400 W were detected by means of an XRD measurement. 200 nm thick layers deposited on soda-lime glass were examined by scanning electron microscopy. The layers have a fine-grain microstructure, with the grain size increasing with decreasing power. 4. Production of comparative specimens by cold gas spraying (CGS): A mixture of Cu62Ga38 (only Cu.sub.9Ga.sub.4 phase) and pure Cu powder was used to produce comparative specimens. The GA content of the mixture was 27 at %. The CGS parameters are summarized in Table 5.

(18) TABLE-US-00005 TABLE 5 Austenitic steel Substrate tube Activation of the surface Blasting with Al.sub.2O.sub.3 Process gas temperature 450 C./800 C. Process gas pressure 29 bar/45 bar Amount of process gas 70-100 m.sup.3/h

(19) At a process gas temperature of 450 C., the Cu62Ga38 particles broke on impingement on the substrate. This resulted in crack formation and detachments between the individual layers of the coating and also in pore formation. In addition, chemical analysis showed that only a small proportion of the Cu62Ga38 particles had been incorporated into the layer (Ga content of the layer only 9 at %). It can be assumed that the remainder has bounced off the substrate or layer surface. Although increasing the process gas temperature to 800 C. had a favourable effect on incorporation of the Cu62Ga38 particles, it lead to blocking of the Laval nozzle after a short time. 5. Production of specimens according to the invention by cold gas spraying (CGS): Specimens according to the invention were produced using a mixture of Cu50Ga50 powder (proportion by volume of CuGa.sub.2>proportion by volume of Cu.sub.9Ga.sub.4) and pure Cu powder and also a mixture of Cu34Ga66 powder (only CuGa.sub.2-phase) and pure Cu powder. The Ga content of the mixture was 38 at % (in the case of the Cu50Ga50-containing mixture) or 58 at % (in the case of the Cu34Ga66-containing mixture). The CGS parameters are summarized in Table 6. Dense tube sections having a wall thickness of about 10 mm could be sprayed by means of both powder mixtures. After an annealing treatment at 200 C., the tube sections were worked mechanically. The sputtering target sections produced in this way had good bonding to the steel tube, which in use can assume the function of a support tube. The surface of the sputtering target was free of defects. The Ga content of the sputtering targets produced in this way corresponded to the Ga content of the powders used. The proportions of the phases in the sputtering target corresponded to the proportions of the phases in the powder. Initial exploratory sputtering tests displayed very homogeneous sputtering behaviour.

(20) TABLE-US-00006 TABLE 6 Austenitic steel Substrate tube Activation of the surface Blasting with Al.sub.2O.sub.3 Process gas temperature 250 C. Process gas pressure 45 bar Amount of process gas 100 m.sup.3/h