Inductively coupled oxygen plasma in H mode for removal of carbon from mixed a-C:H, W films

Abstract

A method for selective removal of carbon from mixed deposits of tungsten and hydrogenated amorphous carbon films likely to be deposited in fusion reactors with divertors containing carbon and tungsten tiles has been elaborated. Mixed deposits were prepared on highly polished stainless steel substrates by sputtering of a tungsten target in acetylene-rich atmosphere. Samples were exposed to fully dissociated non-equilibrium oxygen plasma created by inductively coupled electrodeless radio frequency discharge created in pure H-mode. Auger electron depth profiling was applied for determination of the compositional changes upon plasma treatment. Carbon from about 200nm thick mixed deposit has been removed effectively in about 45s of plasma treatment. Further treatment caused inter-diffusion of sample elements until a rather uniform W, Fe, O film was formed on substrates. The same samples treated by plasma created with the discharge in E-mode did not affect the composition of coatings even after treatment for 15min indicating important advantages of H-mode discharges.