Soft breakdown and hard breakdown in ultra-thin oxides

Abstract

Soft breakdown (SBD) and hard breakdown (HBD) events are characterised separate of each other for a 3.4 nm gate oxide. It is shown that both breakdown events can have significantly different voltage and temperature acceleration behaviour. Further it is demonstrated by photoemission microscopy (PEM) for a 2.2 nm oxide that different types of breakdown paths exist. HBD-like and SBD-like breakdowns are found on the same gate area during constant voltage stress. PEM also points out that a structural change of a breakdown path can occur, usually referred to as thermal breakdown of SiO 2. It is concluded that a separate characterisation of SBD and HBD events is correct, if the stress conditions do not cause this structural change for the first SBD event.