Breakdown Transients in Ultrathin Gate Oxides: Transition in the Degradation Rate

We report a sharp threshold at 4 V in the growth rate of breakdown spots in thin films of ${\mathrm{S}\mathrm{i}\mathrm{O}}_2$ on silicon. This provides some of the first information concerning the electronic structure of the breakdown spot.

Figure 1

Examples of BD transients on FETs with 1.55 nm oxides and channel lengths of $0.4\mu \mathrm{m}$, during stresses at 4.0 V (a), 4.2 V (b), and 4.4 V (c). Five transients, measured by using a current preamplifier, are reported in each figure. Note the change of the time scale among the various figures.

Figure 2

Rate for the BD current increase, $d{I}_{\mathrm{B}\mathrm{D}}/dt$, as a function of the stress voltage measured in 1.55 nm oxides by using a current preamplifier.

Figure 3

Transient durations measured with high time resolution under stress voltages of $\approx 4.5\mathrm{V}$. Through the larger bandwidth, the $d{I}_{\mathrm{B}\mathrm{D}}/dt$ values are much larger than those reported in Fig. 2, and, in particular, equal to or larger than ${10}^5\mathrm{A}/\mathrm{s}$.

Figure 4

Top figures: BD transients measured on FETs with 2.25 nm oxides during stresses at 4.1 V (a), 4.3 V (b), and 4.5 V (c). Five transients are reported in each figure. Bottom figures: same as top but in FETs with 1.50 nm oxides during stresses at 4.1 V (d), 4.3 V (e), and 4.5 V (f). By comparing top and bottom figures, though the oxide thicknesses are different, note that the transition to the mode with a fast BD transient takes place at about the same voltage.