Atomic Layer Deposition of Cobalt Carbide Thin Films from Cobalt Amidinate and Hydrogen Plasma

Atomic layer deposition (ALD) of cobalt carbide thin films is reported by using bis(N,N′-diisopropylacetamidinato)cobalt(II) (Co(amd)2) and H2 plasma. The process shows a good self-limiting ALD film growth behavior for a fairly wide temperature range from 70 to 160 °C, and the growth rate is 0.066 nm/cycle for the deposition within the temperature range. The deposited cobalt carbide thin films are generally smooth and pure, and the film composition is approximately Co3C0.7 for the deposition at 80–200 °C. Notably, all the carbon in the as-deposited films forms cobalt carbide, and no carbon–carbon bonds are detected by X-ray photoelectron spectroscopy. Raman spectroscopy also confirms the absence of graphite or amorphous carbon in the as-deposited films. The films are nano-polycrystalline as deposited, and the crystal structure is the hexagonal Co3C structure. The films can decompose into hcp-Co metal and amorphous carbon upon the thermal annealing in N2 at 400 °C. The resistivity and magnetization of the as-deposited films are also characterized. It is further shown that by use of this plasma-assisted ALD process highly conformal cobalt carbide films can be deposited into the trench structures with a high aspect ratio of 20:1. In the last, the ALD growth chemistry is studied by using the in situ quartz crystal microbalance (QCM) technique, and the QCM results suggest that the structure of the amidinate ligand in the Co(amd)2 precursor largely falls apart upon its reaction with the surface during the ALD.