Remote plasma atomic layer deposition of Co3O4 thin films

Cobalt oxide thin films have been deposited with remote plasma atomic layer deposition (ALD) within a wide temperature window (100–400°C), using CoCp2 as a cobalt precursor and with remote O2 plasma as the oxidant source. The growth rate was 0.05 nm/cycle and both the precursor dosing and plasma exposure exhibit saturation after 2 s, all independent of the substrate temperature. This novel combination resulted in the deposition of high density (~5.8 g/cm3), stoichiometric Co3O4 showing a preferential (111) orientation for all temperatures. X-ray diffraction, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy independently indicate an increasing crystallinity with increasing substrate temperature, whereas the surface roughness remains low (1 nm). CO2 and H2O are detected by mass spectrometry measurements as reaction by-products during the remote O2 plasma step, revealing a combustion-like reaction process