Low temperature growth of oxynitride thin films using plasma techniques

Full Text:The letter insulation and reliability properties of Oxynitride (SiON) thin films, with respect to SiO2 thin films, both which were grown by conventional (thermal) growth systems, makes the SiON films an attractive potential alternative as gate insulators in a variety of MOS devices. The growth temperature of Oxynitride films in these systems is around 900 degrees C - 1000 degrees C. This temperature result a severe limitation on the fabrication of future scaled down ULSI devices, featuring precise doping profile control and System On Glass (SOG) devices. This imposes an uncompromising demand for a drastic reduction in their growth temperature. However, lowering the growth temperature in the conventional systems is prohibitive since it results a severe unacceptable degradation of the insulating films electrical properties. Members of this group has previously reported the growth of thin insulating films grown by using microwave-excited high-density inert gas plasma mixed with other gas elements. SiO2 and SiON films were grown at 400 degrees C by this technique using Kr/O2 and Kr/O2/N2 gas mixtures respectively, introduced into the plasma system. In this work we report the growth of oxynitride films at 400 degrees C substrate temperature, by Kr/O2/NH3 mixture. The electrical properties of these SiON films were measured by fabricating MOS capacitors in which they have been used as insulators. The results were compared to those of identical MOS capacitors fabricated with SiO2 insulators made either by the conventional thermal method at 1000 degrees C or to those grown at 400 degrees C using the above Kr/O2 plasma. The experimental results, show that the electrical properties of the oxynitride films grown by this mixture, which contained only a small amount of NH3 (0.5 %) in 96.5 %, Kr and 3% O2 (pressure ratios), are superior to those of both above SiO2 films. They exhibited lower leakage currents and higher breakdown fields. This was found to be the case for both thick (7 nm) SiON films, which operate in the Fowler-Nordheim (F-N) tunneling regime and for thin (3 nm) films which operate in the direct tunneling regime, demonstrating the potential of this approach