Growth mechanism of Co thin films formed by plasma-enhanced atomic layer deposition using NH3 as plasma reactant

We investigated reaction mechanisms for the formation of Co thin films by plasma-enhanced atomic layer deposition (PE-ALD) using NH3 plasma as a counter-reactant. To investigate surface reactions during the PE-ALD Co, the process was divided into two half-reactions and these reactions were monitored using ex situ X-ray photoelectron spectroscopy (XPS) and an in situ residual gas analyzer (RGA). The cobaltocene (bis(cyclopentadienyl)-cobalt(II), CoCp2) precursor reacts with the N-terminated surface formed by NH3 plasma exposure, resulting in the formation of Co-Co bonds and the release of the Cp ligand and an N-containing byproduct. The NH3 plasma species adsorb to Co-Cp sites and promote dissociation of Cp. Therefore, N atoms on the surface are a key medium for the deposition of Co thin films during sequential adsorption and desorption reactions between CoCp2 and the surface. This result provides an insight into complicated chemical reactions involving PE-ALD and can be extended to other PE-ALD processes.