Degradation of metal/oxide/semiconductor structures by Fowler-Nordheim tunnelling injection

Abstract

The behaviour of thin metal/oxide/semiconductor (MOS) structures with polycrystalline silicon (poly-Si) or silicon aluminium gates subjected to stresses caused by Fowler-Nordheim tunnelling injection was analysed. Native electron capture centres in the bulk SiO 2 were characterized by their capture cross-section, their density and their centroid localization in the oxide layer by means of capacitance and conductance measurements. The trapping was independent of the gate bias polarity during injection. The other aging mechanism is interface (SiO 2-Si and gate-SiO 2) degradation owing to the generation of new centres in the oxide. The new electrically active sites acting as stable electron traps were analysed in correlation with the technological process parameters such as oxidation ambient environment (dry or wet, with or without HCl) and gate type (aluminium or poly-Si). Our results seem to be consistent with the hypothesis that aging of MOS structures under electrical injection is essentially controlled by interfacial phenomena involving the formation of intrinsic defects at the Si-SiO 2 interface. It appears that poly-Si gate structures are the least sensitive to intense Fowler-Nordheim injection stresses.