Nitridation of thin gate or tunnel oxides by nitric oxide

This work reports on the impact of nitric oxide (NO) nitridation on physica l and electrical properties of thin steam gate or tunnel oxides. The oxides (similar to 7 nm) have been annealed in NO ambient under different anneali ng times and NO fluxes, and for comparison in nitrous oxide (N2O). Nitridat ion causes nitrogen to pile up near the SiO2/Si interface, producing interf ace regions with quite different physical and chemical properties according to whether NO or N2O is used. Secondary ion mass spectroscopy, X-ray photo electron spectroscopy, and atomic force microscopy measurements, combined w ith etch-rate experiments, show that in the case of NO, nitrogen is built u p very close to the interface with a remarkably higher peak (at a lower the rmal budget than N2O) and a narrower distribution, whereas with N2O, nitrog en 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 inter face with a lower N content and fewer silicon nitride bonds. The two region s 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 ox ide robustness during gate injection. Furthermore, a correlation between po sitive 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 f ield effect transistor devices was investigated, showing that the higher ni trogen amount at the SiO2/Si interface the lower the B concentration reachi ng the silicon substrate. (C) 1999 The Electrochemical Society. S0013-3651( 98)08-003-3. All rights reserved.