Self-localization of degradation process in pre-breakdown stage of thin SiO/sub 2/ films: new model and experimental procedure

Abstract

We further consider the model for the degradation chain of thin SiO/sub 2/ films, which includes four stages: 1) generation of deep traps/negative space charge /spl rArr/; 2) self-localization of injection current /spl rArr/; 3) formation of local defect spot /spl rArr/; 4) appearance of leakage channel and its development into the breakdown region. A generation of space charge during stages 1 and 2 leads to the high local accumulation of energy in the polarized dielectric medium. The chaotic destabilization events between 2 and 3 stages (rapid detrapping/spl hArr/restoration of space charge) release this energy via strong mechanical relaxation and, as a consequence, form a leakage channel (area less than 10/sup -11/ cm/sup 2/). Thus, the second stage of degradation chain-SLDP (self-localization of degradation process)-plays a crucial role in oxide reliability. The main result of this work-SLDP Model, allowing to explain non-linear decrease of substrate hole current (DSHC effect), which was observed in small MOS structures, subjected to stresses caused by electron injection. It is also shown that the most popular degradation/breakdown models are inapplicable for interpretation of DSHC effect. The presence of local SiO/sub 2/ regions, resistant to the negative space charge formation (endurance up to 10/sup 4/ A/cm/sup 2/ and 10/sup 4/ Cl/cm/sup 2/), allows us to explain a positive feedback of SLDP. Temperature analysis strongly supports new degradation/breakdown model and models which involve hydrogen related effects in oxide films under the field/temperature stress.