Morphological, compositional and phase evolutions in sulfur-rich W-S targets during magnetron sputtering

Abstract

A sulfur-rich WS2.7 target was manufactured via ball milling of sulfur and tungsten-disulfide powders, followed by sintering. The target morphology, composition, and phase changes induced by sputtering processes were investigated by a number of analytical methods and compared to a stoichiometric WS2 target used as a control. Radio frequency magnetron sputtering of the WS2.7 target was conducted with progressively increasing time intervals, from a few minutes to several hours, where the target was intermittently removed for characterization. Selective sputtering of sulfur within both the control WS2 and the sulfur-rich WS2.7 targets yielded sulfur depletion over the extended sputtering time. Depressions on the target surface formed from the selective sputtering of sulfur, where at the base of these regions developed growth of metallic tungsten dendrites and additional unbonded sulfur segregation over sputtering time. A catalytically enhanced WS2 phase decomposition mechanism was proposed based on detailed analysis of phases and oxidation states from site specific spectroscopic and x-ray diffraction analysis. The observed phenomenological process exemplifies the need for monitoring and maintenance of sulfur-rich sputtered targets in their use for thin film growth.