Crystallization of amorphous WNx films

The microstructural changes of WNx films during annealing were analyzed using transmission electron microscopy and x-ray diffraction. Amorphous WNx films eventually crystallized to a two-phase mixture of W and W2N through the primary crystallization and eutectic crystallization. The resulting microstructure after annealing at 800 °C consisted of large primary crystals with a eutectic mixture of W and W2N microcrystallites in the intergranular boundary region. In case of the amorphous film with near-eutectic composition of W0.79N0.21, it transformed directly into a two-phase mixture of W and W2N through the eutectic crystallization at 600 °C without the primary crystallization. On the other hand, polycrystalline W2N films had a columnar structure and did not undergo any microstructural change during annealing up to 800 °C. Barrier properties of WNx film versus Cu diffusion are discussed in relation with the microstructural changes of the films.