A technique for the formation of gate quality ultrathin oxynitride films at a low temperature (150 degreesC) by a three-step (NO/O-2/NO) process in a microwave plasma is reported. Oxynitride films have been grown on strained-Si0.74Ge0.26 films. The mechanism of nitrogen incorporation has been studied in detail. The electrical properties of the oxynitride films have been characterized using a metal-insulator-semiconductor (MIS) structure. Capacitance-voltage (C V), conductance voltage (G-V), constant current and voltage stressing characteristics have been measured. It is shown that a NO/O-2/NO three-step process, in general, gives rise to better electrical properties and reliability compared to a single-step O-2- and NO-plasma grown oxide films. (C) 2003 Elsevier Ltd. All rights reserved.