Thermal conductivity and softening of gate oxide breakdown

The TDDB under accumulation and inversion mode was investigated. It is shown that the generation probability of soft breakdown dramatically increases with the stress mode changing from accumulation to inversion. In the accumulation stress mode, there exists a depletion region serving as a thermal barrier; however, in the inversion mode, better thermal conduction induces larger temperature gradient, which causes higher channel current due to the Seebeck effect. Based on the above concept, we develop a modified ramp voltage test which can detect soft defects which can´t be detected by the conventional ramp voltage test.