Thermal Cleaning of Silicon Nitride with Fluorine and Additive Mixture

Abstract

We describe improved gas mixtures for the thermal cleaning of low pressure CVD reactors used for silicon nitride deposition. F2 and HF mixture are widely used for thermal chamber cleaning today, however the F utilization rate is low, and the required cleaning temperature is higher than desired for productivity and equipment maintenance considerations. We identified NO as a promising low concentration additive that could be used to enhance the performance of fluorine. While F2 - N2 mixtures were unable to thermally clean CVD chambers with an acceptable rate, small additions of NO dramatically improved the cleaning rate. We performed numerous experiments to optimize the thermal cleaning condition. A thermal cleaning temperature of 300C, and a cleaning gas composition of 10% F2, 2% NO with a balance of N2 at 10Torr was the best recipe identified. Experiments were also performed to clarify the gas phase chemistry and to indicate the role of the NO for improving the thermal cleaning process.