Dynamics of reactive sputtering affecting phase formation of Co–N thin films

Abstract

Target poisoning is one of the major drawbacks of reactive sputtering (RS) affecting the stoichiometry of a compound film depositing onto a substrate. The dynamics of RS has been understood in terms of the well-known ‘Berg’s Model’ (Berg et al. in Thin Solid Films 565:186, 2014; Berg and Nyberg in Thin Solid Films 476(2):215, 2005) which demonstrates that by reducing the size of a sputter target, the drawbacks of RS can be minimized. In the present work, we compare the evolution of cobalt–nitride (Co–N) phases in an RS process from two different sized magnetron sources having diameter of 1 and 3 in. Samples were studied for their long-range ordering and local structure using X-ray diffraction and X-ray absorption spectroscopy. Quantification of N at.% was carried out using secondary ion mass spectroscopy. Polarized neutron reflectivity and bulk magnetization measurements were carried out to study the magnetic properties of Co–N thin film samples. We found that the N incorporation in Co–N films can be accelerated utilizing the smaller source. In addition, by reducing the target size from 3 to 1 in., the range of metallic state can be extended. The $${\mathrm {Co}}_{4}{\mathrm {N}}$$ phase emerging from the metallic state of the smaller target has a lattice parameter more closer to its theoretical value. An insight has been presented on the RS process and it can be readily seen from this work that the poisoning of the target can be minimized for the growth of the $${\mathrm {Co}}_{4}{\mathrm {N}}$$ film from the smaller target and can be understood in accordance with the available theoretical models.