TRAPPED CHARGE-DISTRIBUTIONS IN THIN (10 NM) SIO2-FILMS SUBJECTED TO STATIC AND DYNAMIC STRESSES

Thin (10 nm) gate oxide MOS capacitors have been subjected to static a nd dynamic stress conditions, The evolution of the trapped charge dist ributions (characterized by average density and centroid) has been mea sured as a function of the stress time, The evolution of the average c harge density for DC stresses shows that both polarities have identica l trap generation rates and a constant average density of traps at bre akdown, However, the final density of traps is much smaller for inject ion from the gate, so that the time-to-breakdown is also much shorter for this stress polarity, The evolution of the centroid shows that tra ps are always mainly generated near the cathodic interface. Unipolar d ynamic stresses give results which are qualitatively very similar to t hose obtained under DC conditions and without a relevant frequency dep endence, In contrast, bipolar stress experiments show significant qual itative differences, the frequency dependence being very important, In general, the trap generation and trapping rates are reduced in compar ison to the DC and unipolar cases, being this reduction more important at high frequencies, In addition, the average density of trapped elec trons at the breakdown is larger than that obtained in DC experiments, Both observations explain the tremendous increase in the mean-time-to -breakdown obtained under high-frequency stress conditions, The presen ted results are qualitatively explained in terms of microscopic degrad ation models.