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  Welzel, T.; Ellmer, K.: Negative oxygen ion formation in reactive magnetron sputtering processes for transparent conductive oxides. Journal of Vacuum Science & Technology A 30 (2012), p. 061306/1-12

10.1116/1.4762815

Abstract:
Reactive d.c. magnetron sputtering in Ar/O₂ gas mixtures has been investigated with energy-resolved mass spectrometry. Different metal targets (Mg, Ti, Zn, In, InSn, and Sn), which are of importance for transparent conductive oxide thin film deposition, have been used to study the formation of negative ions, mainly high-energetic O^-, which are supposed to induce radiation damage in thin films. Besides their energy distribution, the ions have been particularly investigated with respect to their intensity in comparison of the different target materials. To realize the comparability, various calibration factors had to be introduced. After their application, major differences in the negative ion production have been observed for the target materials. The intensity, especially of O^-, differs by about two orders of magnitude. It is shown that this difference results almost exclusively from ions that gain their energy in the target sheath. Those may gain additional energy from the sputtering process or reflection at the target. Low-energetic negative ions are, however, less affected by changes of the target material. The results concerning O^. formation are discussed in term of the sputtering rate from the target and are compared to models for negative ion formation.