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. 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（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 N2 ions, 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.