Influence of process parameters on properties of reactively sputtered tungsten nitride thin films

Abstract

Tungsten nitride (WNx) thin films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The influence of the deposition power on the properties of tungsten nitride has been analyzed and compared with that induced by nitrogen content variation in the sputtering gas. A combined analysis of structural, electrical and optical properties on thin WNx films obtained at different deposition conditions has been performed. It was found that at an N2 content of 14% a single phase structure of W2N films was formed with the highest crystalline content. This sputtering gas composition was subsequently used for fabricating films at different deposition powers. Optical analysis showed that increasing the deposition power created tungsten nitride films with a more metallic character, which is confirmed with resistivity measurements. At low sputtering powers the resulting films were crystalline whereas, with an increase of power, an amorphous phase was also present. The incorporation of an excess of nitrogen atoms resulted in an expansion of the W2N lattice and this effect was more pronounced at low deposition powers. Infrared analysis revealed that in WNx films deposited at low power, chemisorbed N2 molecules did not behave as ligands whereas at high deposition power they clearly appeared as ligands around metallic tungsten. In this study, the influence of the most meaningful deposition parameters on the phase transformation reaction path was established and deposition conditions suitable for producing thermally stable and highly crystalline W2N films were found.