Impact of bilayered oxide stacks on the breakdown transients of metal-oxide-semiconductor devices: An experimental study

The role of the bilayered structure of the gate oxide on the dynamics of progressive breakdown is systematically studied on Au / Cr / HfO 2 / Al 2 O 3 / InGaAs metal-oxide-semiconductor stacks. Samples with bilayered oxides of 100 angstrom total thickness were fabricated using different Al 2 O 3 interfacial layer thicknesses to investigate the effects of combining insulator materials with largely different electrical and thermal properties. The breakdown current growth rate d I B D / d t was captured by means of low and high bandwidth measurement setups, and the results were compared in the framework of an electromigration-based progressive breakdown model, originally derived for single-layered oxides. Experimental results show that as the interfacial layer is thicker, a clear increase is observed on the applied voltage required to obtain d I B D / d t values in the same range. However, this effect is not observed for thicknesses above 10 angstrom for the Al 2 O 3 layer. This is linked to both the electrical stress distribution across the bilayered structure and to the thermal characteristics of Al 2 O 3 that contribute to reduce the temperature of the breakdown spot. The progressive breakdown model is modified to account for these features, showing good agreement with experimental results, behavior that cannot be explained by the model considering one of the layers as already broken during progressive breakdown.