CHEMICAL-INSTABILITY OF THE TARGET SURFACE DURING DC-MAGNETRON SPUTTERING OF ITO-COATINGS

Indium-tin oxide (ITO) coatings on polymer film substrates should have the required properties already in their as-deposited state and shoul d be chemically and thermally stable. The coatings can be produced eit her by reactive DC-magnetron sputtering of In/Sn (e.g., 80/20, wt.%) m etallic alloy targets or by pseudo-reactive sputtering of ITO (In2O3Sn O2 90/10, wt%) targets. In the former process (and to a lesser extent in the latter process), a surface instability of the target arises: bl ack crystals of a dark phase grow on the target surface, changing the target voltage and causing pronounced arcing in the plasma. This harmf ul phenomenon grows worse during a sputter run and finally necessitate s abortion of the run and mechanical cleaning of the target. This phen omenon has never been explained in literature. In this paper, it will be shown that the black crystals are In2O and that they originate from an equilibrium reaction at the target surface in which In2O3 is decom posed into In2O and O-2. This reaction is especially annoying with rea ctive processes in which optical plasma emission monitoring (PEM) is u sed as a control means to obtain the correct stoichiometry of the coat ings at relatively high sputter deposition rates. (C) 1998 Elsevier Sc ience S.A.