New insights into the oxygen content of copper-gallium thin films
The residual gases in the vacuum equipment during the sputtering process determines the oxygen content of copper-gallium (CuGa) precursor layers much more than the target material itself. This result of a research project undertaken by our coating experts is important for the manufacture of CIGS thin-film solar cells. The detailed results were presented as a poster contribution at this year's EU-PVSEC in Paris and are now available in the EU-PVSEC proceedings.
Impurities in the CIGS layer lower the efficiency of the solar cell. Although a small proportion of oxygen is present in all sputtering targets, the actual quantity varies depending on the manufacturing process. The oxygen content is lower in cast targets than in targets manufactured using powder metallurgical techniques which, however, possess a significantly improved microstructure.
"Our investigations were driven by the question whether the higher oxygen content in powder metallurgical targets also has an impact on the sputtered layers, or not." explains Christian Linke, R&D project manager at Plansee. A sputtering test using a cast target showed that the oxygen content of the film was 200 times greater than that of the target. In the case of powder metallurgical targets, the level of impurities increased by a factor of 2, with the result that the oxygen content in the sputtered films was practically identical for the two manufacturing methods (approximately 0.4 atomic percent).
The oxygen content is therefore determined mainly by the residual gas in the sputtering chamber. The higher oxygen content of powder-metallurgical CuGa targets is therefore not critical for the production of CuGa precursor films.
As a result, customers can take full advantage of powder metallurgical targets compared to cast targets: An extremely fine-grained microstructure which leads to a more homogeneous gallium distribution in the film. This significantly improves process stability – which has been confirmed by a comparative study in a pilot production system.
Would you like all the details? The detailed research results can be found in the Proceedings of the 28th EU-PVSEC 2013 published under the title “Chemical purity of copper-gallium thin films deposited from different sputtering targets”: https://www.eupvsec-proceedings.com/proceedings?fulltext=chemical+purity&paper=23907
Press contact:
Nadine Kerber
Marketing Communications
Plansee High Performance Materials
nadine.kerber@plansee.com
+43 5672 600 2422
Plansee High Performance Materials:
The Plansee Group is a leading enterprise in the field of powder metallurgy and covers the entire production process from the ore right through to the customer-specific component.
The Plansee High Performance Materials division is an expert in the field of molybdenum, tungsten, tantalum, niobium and chromium components. Alloys and composite materials from Plansee come into their own in electronics, coating technology or high-temperature furnaces - wherever traditional materials are stretched beyond their limits. Discover more about Plansee and find your local contact person: www.plansee.com
