Reactive magnetron sputtering of highly (001)-textured WS2−xfilms: Influence of Ne+, Ar+and Xe+ion bombardment on the film growth

Layer-type van der Waals semiconductor WS2−x films were grown by radio frequency reactive magnetron sputtering from a metallic tungsten target onto oxidized silicon substrates. The sputtering atmosphere consisted of 75% hydrogen sulfide and 25% neon, argon or xenon. The substrate voltage and hence the energy of the ions bombarding the growing film, was varied from about 20 V (floating potential) to −80 V. By in situ energy-dispersive X-ray diffraction the growth of the films was monitored and by elastic recoil detection analysis the film composition was measured. It was found that with xenon in the sputtering atmosphere a substrate voltage of −20 V is sufficient to suppress the crystalline film growth, while for argon as the sputtering rare gas this occurs only at −80 V. The disturbed film growth is accompanied by a sulfur loss of the growing WS2−x films down to x  = 1.1 for sputtering in Ar + H2S at a substrate potential of −60 V. The results are tentatively explained by the different momentum transfers to sulfur atoms, which is highest for argon ions. It has also to be taken into account that the low-energy xenon bombardment is a many-body cascade process with a much higher local energy density compared to argon and neon bombardment and leading to a higher defect density and a supression of the crystalline growth. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)