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.