Process control for the low temperature deposition of niobium-nitride thin films

The authors investigated the process of DC and RF magnetron reactive sputtering of NbN with the purpose of clarifying the issues which are important for process control. Based on a simple physical model of the deposition process, parameters (plasma impedance and plasma concentration of reactive species) have been selected for study and their effects on the properties of the films (transition temperature, room temperature resistance, and RF surface impedance) have been evaluated experimentally. Based on these experiments, a simple feedback scheme using the plasma impedance as a control parameter was implemented, allowing for the consistent deposition of high-quality films. The same scheme can be used for the control of the stoichiometry of any reactive sputtering process, including the deposition of the high-transition-temperature oxide films