A combination of X-ray photoelectron spectroscopy (XPS), parallel electron
energy-loss spectroscopy (PEELS), X-ray diffraction (XRD), transmission ele
ctron microscopy (TEM) and transmission electron diffraction (TED) were use
d to investigate structural properties and nitrogen-loss characteristics of
thin WNx films prepared by reactive magnetron sputtering of tungsten in an
Ar-N-2 gas mixture. XRD theta-2 theta scans combined with plan-view and cr
oss-sectional TEM showed that the as-deposited WNx films were amorphous in
structure. Annealing of the as-deposited films at 600 degrees C or above re
sulted in crystallization of the amorphous phases, forming either a two-pha
se structure consisting of W2N and b.c.c. W or a single-phase structure of
W2N, which was related to the initial nitrogen concentration in the films.
The 150-nm thick crystalline films near a stoichiometry of W2N had a column
ar microstructure with an average column width of 15-20 nn near the film su
rface, whereas the column grains were larger for substoichiometric films. T
hermal stability and nitrogen-loss characteristics of nitride films were al
so studied by in situ annealing in the TEM and PEELS system. The results in
dicate that between 600 and 800 degrees C the W2N phase was stable. Nitroge
n in the film started to evaporate to vacuum at approximately 820 degrees C
and was fully released after 900 degrees C annealing. (C) 2000 Elsevier Sc
ience S.A. All rights reserved.