Composition, residual stress, and structural properties of thin tungsten nitride films deposited by reactive magnetron sputtering

Thin tungsten nitride (WNx) films were produced by reactive dc magnetron sp uttering of tungsten in an Ar-N-2 gas mixture. The effects of the variation of nitrogen partial pressure on the composition, residual stress, and stru ctural properties of these films as well as the influence of postdeposition annealing have been studied. The films were analyzed in situ by a cantilev er beam technique, and ex situ by x-ray photoelectron spectroscopy, electro n energy-loss spectroscopy, x-ray diffraction, and transmission electron mi croscopy (TEM). It was found that at N concentrations below 8 at. %, the fi lms (typical 150 nm in thickness) were essentially bcc alpha-W. An amorphou s phase was observed in the range of about 12-28 at. % N. When N concentrat ions reached similar to 32 at. % or above, a single-phase structure of W2N was formed. Annealing of the as-deposited films resulted in crystallization of the amorphous or an improved crystallinity of the W2N structure, which was related to the N concentration. Stresses of all W and WNx films were co mpressive. As the N concentration was increased, the stress decreased and r eached its lowest value for amorphous samples near 20 at. % N. Past this po int, the compression of films rose again. These results can be ascribed to structural changes induced by the pressure-dependent variation in the avera ge energy of particles bombarding the film during deposition. Cross-section al TEM studies showed that all crystalline WNx films had columnar microstru ctures. The average column width near stoichiometry of W2N was similar to 2 0 +/- 5 nm near the film surface. (C) 2000 American Institute of Physics. [ S0021-8979(00)02915-7].