Effect of deposition conditions on internal stresses and microstructure ofreactively sputtered tungsten nitride films

A combined investigation of internal stress generation by in situ substrate curvature measurements during the growth of tungsten nitride (WNx) thin fi lms and of structural properties by ex situ X-ray diffraction (XRD), transm ission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), a nd electron energy-loss spectroscopy (EELS) is reported. It was found that the properties of the deposited films not only depended on the nitrogen par tial pressure in Ar-N-2 gas mixtures but also on the total sputtering-gas p ressure. The stress of the films was strongly related to their microstructu re, which depended mainly on the incorporation of nitrogen in the films. An nealing of as-deposited films at 600 degrees C or above resulted in crystal lization of the amorphous phases, forming either a two-phase structure cons isting of W2N and b.c.c. W or a single-phase structure of W2N, which was re lated to the initial nitrogen concentration (C-N,) in the films. Cross-sect ional TEM studies showed that an average column width for 150-nm-thick film s near stoichiometry of W2N was similar to 15 nm, whereas the column grains were larger with decreasing C-N,. XPS results revealed that W2N had an ion ic bonding character, Wdelta+-Ndelta-. It was also found that once the W2N phase was formed, the density, microstructure and bonding feature were simi lar and insensitive to the total sputtering-gas pressure used in this study . (C) 2000 Elsevier Science S.A. All rights reserved.