WNx film is one of the most promising materials for self-aligned GaAs NASFET because of its low electrical resistivity and high Schottky Barrier Height at the WNx /GaAs contact.
In this paper, the effect of the sputtering conditions and the annealing environment on the chemical composition and structure of the WNx films deposited on Si and GaAs by RF reactive sputtering are studied.
The results show that with the increase of the partial pressure ratio of nitrogen gas or decrease of the working pressure, deposition rate of WNx film decreases, whereas the atomic percentage of N in the deposited film increases before approaching saturation. The WNx films formed at high working pressure (≈5 × 10−2 torr) consist of W, WN or W2N phases depending on the nitrogen partial pressure ratio. Whereas the films formed at low working pressure (≈ 3 × 10−3 torr) are usually amorphous. Annealing in a flowing N2 gas causes the crystallization of the amorphous films, which mainly consist of W+W2N. There is no change for the crystalline films. However, annealing in H2 gas causes severe loss of nitrogen of the film, the film becoming single W phase eventually.