The influence of furnace and rapid thermal annealing (RTA) on X-ray-amorphous, chemically vapor deposited (CVD) W-Si-N barrier layers on SiO2/Si structures have been investigated. Enhanced amount of nitrogen loss from the barrier films with increased annealing temperatures has been observed. Spectral emissometry has been employed as a novel tool to study the changes in the optical properties of the W-Si-N films in the infrared region. Annealing the structures at 800 degrees C has resulted in a significant increase in surface reflectance along with a decrease in transmittance, while that at 450 degrees C has resulted in a relatively small decrease in both reflectance and transmittance. All of the annealing conditions have led to reduced film resistivity. It is postulated that nitrogen occupies two different interstitial sites in the micro/nanocrystallites of as-deposited W-Si-N structure and leaves these sites upon annealing at high temperatures. Majority of the N atoms or molecules in the annealed W-Si-N films are assigned to the grain boundaries.