A controlled growth of WNx and WCx thin films prepared by atomic layer deposition

Abstract

This work reports a capability for a controlled preparation of tungsten nitride and carbide thin films via an atomic layer deposition (ALD) approach. Those films were deposited by ALD using a fluorine- and nitrogen-free W metallorganic precursor of tungsten tris(3-hexyne) carbonyl [W(CO)(CH3CH2C≡CCH2CH3)] and a N2+H2 mixture plasma as a reactant at a deposition temperature of 250°C. It was found that a phase, microstructure and composition of the films could be controlled in precision by varying a gas flow rate ratio of N2/H2 in the plasma reactant. With the N2/H2 gas ratio of 1:3 and 1:5, W-rich polycrystalline WNx thin films (W/N ratio:~1.39) were deposited with a resistivity of 700–900µΩcm, while nano-crystalline (close to an amorphous) W-rich WCx films (W/C ratio:~1.26) with a much lower resistivity of ~510µΩcm, without any nitrogen incorporation, were formed when H2 gas became extremely rich (N2/H2 gas ratio of 1:10). Both X-ray diffraction and electron diffraction analyses revealed that the ALD-WCx films were composed of hexagonal W2C, WC, and non-stoichiometric cubic β-WCx. while the ALD-WNx films of cubic W2N.