Deposition of metals at low temperatures by chemical vapor deposition (CVD) is challenging when precursor reduction is thermodynamically unfavorable. We recently demonstrated electron CVD (e-CVD) of Fe, Co, and Ni from their respective metallocenes, where free electrons from a plasma drive reduction instead of using a molecular co-reactant. Prior work on Fe e-CVD reported substantial C and O incorporation, although a pulsed approach appeared to improve film density. Here, we quantify how pulsed e-CVD lowers C in Fe-containing films. Using ferrocene, bis(cyclopentadienyl)iron(II), the C content decreases from ∼32 at. % in continuous e-CVD to ∼10 at. % in a pulsed e-CVD process, with the Fe fraction increasing from ∼27 to ∼38 at. %. We attribute these changes to a more favorable surface chemistry in a pulsed process where there are less plasma volume reactions. We also evaluate an Fe amidinate precursor, bis(N,N'-di-tert-butylacetamidinato)iron(II). Based on quartz crystal microbalance measurements, we speculate that this ligand system enables a more controllable surface chemistry, albeit it yields the same level of impurities. These results establish pulsed e-CVD as a viable route to low-temperature Fe films with reduced C content.
Niiranen et al. (Mon,) studied this question.