Evolution from soft to hard breakdown in thin gate oxides: effect of oxidethickness, capacitor area and stress current

The breakdown of oxide films with thickness ranging from 7 to 4 nm is studi ed as a function of the stress current and of the capacitor area. The tests were carried out using Hg- and poly-Si-gated capacitors. It is found that the probability of soft breakdown (SBD) decreases if the capacitor area is decreased or if the stress current is increased. It is shown that these exp erimental observations can be explained if (a) SBD is considered as an inco mplete hard breakdown, i.e. a breakdown mode in which the energy dissipated into the percolative path is not enough to trigger its thermal expansion; (b) the SBD probability depends not only on the energy stored in the capaci tor and measurement system at the moment of breakdown, but also on the disc harge current flowing in the conductive spot. (C) 2001 Elsevier Science Ltd . All rights reserved.