Effects of film reoxidation on the growth and material properties of ultrathin dielectrics grown by rapid thermal nitridation in ammonia

Abstract

Ultrathin silicon oxynitrides have been used successfully as gate dielectrics for advanced complementary metal-oxide semiconductor technologies. Here, the authors compare the growth and material properties of oxynitrides grown by rapid thermal nitridation of silicon in ammonia (RT-NH3) followed by reoxidation in NO, O2, or N2O. While the nitrogen concentration of the film is primarily determined by the RT-NH3 condition, reoxidation causes a slight change in nitrogen content and increase in film thickness which varies depending on the initial nitrogen concentration in the film and the oxidizing conditions used. The nitrogen/oxygen concentration ratio was determined to be sensitive to the reoxidizing species, process pressure, and exposure time. Compositional analysis by medium energy ion scattering indicates similarities in microstructure but differences in nitrogen and oxygen profiles among the different films. Results indicate that reoxidation in NO, O2, or N2O can result in different nitrogen concentrations at the bottom interface under the same process conditions. Thus, the choice of reoxidizing species may be an important decision for a gate dielectric process since the amount and placement of nitrogen needs to be optimized to reduce the impact on device peak mobility and threshold voltage, while still be sufficient to improve hot carrier reliability, reduce defect generation rates and gate leakage current, and suppress boron penetration from the gate electrode [D. A. Buchanan, IBM J. Res. Dev. 43, 245 (1999); M. L. Green et al., J. Appl. Phys. 90, 205 (2001); E. Gusev et al., IBM J. Res. Dev. 43, 265 (1999)].