Correlation between interface nitrogen and the fixed charge in thermally nitrided silicon dioxide on silicon

Abstract

Silicon dioxide layers of 250 Å thick were grown on Si at 1000 °C in a dry O2/TCA ambient. Thermal nitridation of the samples was performed in a pure ammonia ambient at temperatures from 900 to 1100 °C with one hour time intervals up to a maximum of 4 h. The fixed charge state densities at the interface of the samples were determined from high frequency C-V measurements, and the breakdown fields from I-V curves. Secondary ion mass spectroscopy depth profiles show low levels of contaminants, and high levels of nitrogen at the interface for samples annealed at temperature greater than or equal to 1000 °C and for periods longer than 2 h. Post metal annealing of the nitrided samples appears to help in reducing the trapped charges. Better quality films with lower Qf and VFB shifts, and higher breakdown fields were achieved for samples annealed at 1100 °C. Metal-oxide-semiconductor device quality nitrided films with a Qf of 1010/cm2 were achieved by optimizing the process conditions at 1100 °C. The fixed charge build up for lower nitridation temperatures (<1000 °C) and times (<2 h)is due to the dissociation of Si—O bonds in the presence of hydrogen, and is in accordance with the earlier results in the literature. However, the reduction in the fixed charge buildup at 1100 °C, we believe, is due to the increased levels of nitrogen.