Analysis of reactive sputtering mechanisms for NbN film deposition

Abstract

A model for the reactive sputtering mechanism is discussed to assist in the selection of the optimum sputtering parameters for the deposition of NbN films with a high critical temperature Tc and low resistivity (at 20 K). The model is based on the assumption that the reaction between the target material and the reactive gas molecules takes place at the surface of the target. Optical emission spectroscopic studies of the plasma were conducted during the deposition of NbN films by reactive dc and rf magnetron sputtering in an Ar–N2 mixture. The substrates were not heated and the substrate temperatures were kept ≲100 °C during deposition. The intensity of a Nb emission line, which gives a measure of the sputtering rate, was monitored as a function of N2 pressure. The data were fitted to the model to select the optimum nitrogen pressure at different power densities and Ar pressures. The Tc of NbN films deposited at a high rate (>25 Å/s) by dc magnetron sputtering was ∼16 K. The highest Tc of films deposited by rf magnetron sputtering reached only ∼14 K due to higher levels of positive ion bombardment.