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

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 200 nm thick mixed deposit has been removed effectively in about 45 s 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 15 min indicating important advantages of H-mode discharges.

► First report on removal of C from a:H-C/W layers by O2 discharge in different modes. ► Clear differences in removal of the deposits in different discharge modes. ► H-mode allows for quick removal of carbon from mixed deposit. ► E-mode is not capable of removal carbon deposits even after long treatment times.