Reactively sputtered WOxNy films

A combined investigation of stress relaxation in WOxNy thin films sputter d eposited on silicon wafers in an Ar-N-2-O-2 gas mixture by in situ substrat e curvature measurements and of structural properties by ex situ x-ray diff raction, x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), electron energy loss spectroscopy, and transmission electron diffra ction is reported. It was found that the W2N films deposited under oxygen-f ree conditions had a high compressive stress of 1.45 GPa. As the oxygen con centration was increased, the stress became smaller and reached almost zero for films near 10-15 at.% oxygen. These results can be understood in terms of the decrease in the lattice parameter caused by substituting nitrogen a toms with oxygen in the lattice sites and the development of an amorphous n etwork in the WOxNy films as the incorporation of oxygen was increased. Pla n view and cross-sectional TEM analyses showed that 150-nm-thick oxygen-fre e crystalline W2N films had a columnar microstructure with an average colum n width of 15-20 nm near the Film surface, whereas oxygen imbedded in the f ilms provided a finer grain structure. The effect of oxygen in stabilizing the W2N structure was also elucidated and explained on the basis of structu ral and thermodynamic stability.