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 (WN_x) thin films. N₂ is introduced downstream in the diffusion chamber. The impacts of N₂ on the Ar-HWP parameters, such as ion energy distribution functions (IEDFs), electron energy probability functions (EEPFs), electron temperature (T_e) and density (n_e), 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 of N₂⁺ stems from the charge transfer in the collision between Ar⁺ and N₂. Moreover, due to the collisions between electrons and N₂ ions, EEPFs show a relatively lower T_e with a depletion in the high-energy tail. With increasing negative bias from 50 to 200 V, a phase transition from hexagonal WN to fcc-WN_0.5 is observed, together with an increase in the deposition rate and roughness.