Atomic Layer Deposition of Tungsten-Rich Tungsten Carbide Films Using WCl6 and AlH2(tBuNCH2CH2NMe2) as Precursors

The thermal atomic layer deposition (ALD) of tungsten-rich tungsten carbide thin films is described using WCl6 and the aluminum dihydride co-reactant AlH2(tBuNCH(2)CH(2)NMe(2)). Smooth and stable films were grown at temperatures >200 degrees C. An ALD window was observed between 275-350 degrees C with a growth rate of 1.6 angstrom/cycle, according to SEM and XRR. Self-limiting growth was demonstrated at 300 degrees C for both precursors. XPS analysis showed that high purity tungsten-rich tungsten carbide (WxC, x = 2.8-3.7) films were deposited at 300 degrees C, with low levels of nitrogen (< 4 at.%), oxygen (< 4 at.%), chlorine (< 3 at.%), and aluminum (< 1 at.%). The as-deposited films were nanocrystalline and converted to the non-stoichiometric beta-WC1-x phase above 600 degrees C. Film densities of the as-deposited films according to XRR were 50-60% of bulk values, which may explain the relatively high film resistivities (1140 m Omega.cm at 300 degrees C) despite the high film purity.