Nanometer-scale analysis of current limited stresses impact on SiO2 gate oxide reliability using C-AFM

The effect of current limited stresses (CLS) on the breakdown (BD) of thin (<6nm) SiO2 gate oxides ha's been analyzed at a nanometric scale with a Conductive Atomic Force Microscope (C-AFM). Bare oxide regions have been stressed and broken down using the tip of the C-AFM as the metal electrode of a metal-oxide-semiconductor (MOS) structure. Afterwards, post-BD IN characteristics and topographical and current images of the affected areas have been obtained to analyze the post-BD conduction, the structural damage induced in the oxide and the BD propagation. The results show that BD phenomenon, although triggered at one point, is electrically propagated to neighbor regions. Moreover, the area affected by BD, the structural damage and the post-BD conduction depend on the breakdown hardness. In particular, it is shown that these magnitudes are smaller when the current through the structure is limited during BD transient.