Nitridation of thin gate or tunnel oxides by nitric oxide

This work reports on the impact of nitric oxide (NO) nitridation on physical and electrical properties of thin steam gate or tunnel oxides. The oxides (similar to 7 nm) have been annealed in NO ambient under different annealing times and NO fluxes, and for comparison in nitrous oxide (N2O). Nitridation causes nitrogen to pile up near the SiO2/Si interface, producing interface regions with quite different physical and chemical properties according to whether NO or N2O is used. Secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy measurements, combined with etch-rate experiments, show that in the case of NO, nitrogen is built up very close to the interface with a remarkably higher peak (at a lower thermal budget than N2O) and a narrower distribution, whereas with N2O, nitrogen distribution is broadened with a lower peak slightly displaced from the interface. The different behavior under reoxidation of NO- and N2O-annealed samples confirms the results mentioned previously. Physical analysis shows that the nitrided region is divided into an N-rich region at the interface with predominant Si-N bonds and a transition region further from the interface with a lower N content and fewer silicon nitride bonds. The two regions depend on the annealing conditions: the higher exposure produces a bigger N-rich and a smaller transition region. Electrical characterization shows that NO nitridation improves the oxide resistance to electrical stress for substrate carrier injection. However, a strong NO treatment degrades the oxide robustness during gate injection. Furthermore, a correlation between positive and negative trapping with transition and N-rich regions is observed under substrate injection conditions. Finally, the role of NO nitridation as boron diffusion barrier in surface p-channel metal-oxide semiconductor field effect transistor devices was investigated, showing that the higher nitrogen amount at the SiO2/Si interface the lower the B concentration reaching the silicon substrate. (C) 1999 The Electrochemical Society. S0013-3651(98)08-003-3. All rights reserved.