Investigation of the Growth Behaviour of Cobalt Thin Films from Chemical Vapour Deposition, Using Directly Coupled X-ray Photoelectron Spectroscopy

Abstract

Abstract Thin films and coatings are a basis for many technological processes, including microelectronics, electrochemistry and catalysis. The successful deposition of metal films and nanoparticles by chemical vapour deposition (CVD) needs control over a number of physico-chemical processes such as precursor and substrate selection, delivery, temperature, pressure and flow conditions. Here, cobalt thin films were deposited by means of pulsed-spray evaporation chemical vapour deposition (PSE-CVD) from ethanol solutions of Co(acac)2 and Co(acac)3 on bare glass and silicon substrates. The physico-chemical properties of the grown films were characterised by XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and HIM (helium ion microscopy). Co(acac)2 enabled the growth of cobalt metal at lower temperatures than Co(acac)3. The difference in deposition temperature was attributed to the ability of ethanol to reduce Co(acac)2 better than Co(acac)3. In addition, the film deposited from Co(acac)2 exhibited a higher metal content and a less porous structure than that deposited from Co(acac)3. Increasing the substrate temperature enhanced the carbon content because of the thermal decomposition of both precursors. Using a nickel seed layer improved the growth rate until a critical temperature of 360 ℃, at which the thermal decomposition of the precursor becomes predominant. A decrease in the deposition temperature when using the nickel seed layer was only observed with Co(acac)2 precursor; the growth behaviour under these conditions was monitored with a unique UHV-compatible PSE-CVD reactor directly attached to an XPS system and ascribed to an enhancement of its catalytic reduction by ethanol.