Effect of nitridation on Fowler-Nordheim tunneling coefficients in SiO2 MOS capacitors with WSi2-polysilicon gate

In this work we have studied the influence of N2O nitridation of thin EEPRO M SiO2 tunnel oxides on Fowler-Nordheim tunnel injection potential barrier heights in WSi2-polysilicon gate MOS structures. In particular we have paid attention to the effect of the nitridation temperature by means of a compa rison with standard (dry-wet-dry) oxides annealed in N-2 at the same temper ature. The temperatures considered were 900 degreesC, 950 degreesC and 1000 degreesC. It has been shown that the Si/SiO2 barrier is systematically sma ller than the poly-Si/SiO2 one (similar to0.05 eV) in the whole set of samp les and that the nitridation in N2O systematically decreases both the Si/Si O2 and the poly-Si/SiO2 barrier heights all the more as the nitridation tem perature increases. The effects of neglecting the contribution of Si/SiO2 i nterface states and of the gate depletion phenomenon in the evaluation of t he oxide electric field and, as a consequence, in the evaluation of the tun nel injection potential barrier heights have also been considered. It has b een shown that neglecting the polysilicon gate depletion phenomenon leads t o a strongly over-evaluated value of the Si/SiO2 barrier height while negle cting the interface states gives an error of approximately 1%. Moreover, we have shown that N2O nitridation increases the oxide dielectric constant al l the more as the nitridation temperature increases while fluorine incorpor ation into the oxide induced by the WSi2 polycide deposition process decrea ses the same constant. (C) Kluwer Academic Publishers.