The application of a helicon plasma source in reactive sputter deposition of tungsten nitride thin films

A reactive helicon wave plasma(HWP) sputtering method is used for the deposition of tungsten nitride(WNx) thin films. N2is introduced downstream in the diffusion chamber. The impacts of N2on the Ar-HWP parameters, such as ion energy distribution functions(IEDFs), electron energy probability functions(EEPFs), electron temperature(Te) and density(ne), are investigated. With the addition of N2, a decrease in electron density is observed due to the dissociative recombination of electrons with N2~+.The similar IEDF curves of Ar+and N2~+indicate that the majority ofN2~+stems from the charge transfer in the collision between Ar+and N2. Moreover, due to the collisions between electrons and N2ions, EEPFs show a relatively lower Tewith a depletion in the high-energy tail. With increasing negative bias from 50 to 200 V,a phase transition from hexagonal WN to fcc-WN0.5is observed, together with an increase in the deposition rate and roughness.