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 CoCp 2 as a cobalt precursor and with remote O 2 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/cm 3 ), stoichiometric Co 3 O 4 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). CO 2 and H 2 O are detected by mass spectrometry measurements as reaction by-products during the remote O 2 plasma step, revealing a combustion-like reaction process.