Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

A WF6–H2–N2 precursor system was used for plasma-enhanced chemical vapor deposition (PECVD) of WNx films. We examined the microstructural changes of the WNx films depending on N2/H2 flow-rate ratio and post-annealing (600–800 °C for 1 h). As the N2/H2 flow rate was increased from 0 to 1.5, as-deposited WNx films exhibited various different crystalline states, such as nanocrystalline and/or amorphous structure comprising W, WN, and W2N phases, a fine W2N granular structure embedded in an amorphous matrix, and a crystalline structure of β-W2N phase. After post-annealing above 600 °C, crystalline recovery with phase separation to β-W2N and α-W was observed from the WNx films deposited at an optimized deposition condition (flow-rate ratio = 0.25). From this PECVD method, an excellent step coverage of ∼90% was obtained from the WNx films at a contact diameter of 0.4 μm and an aspect ratio of 3.5.