Soft breakdown and hard breakdown in ultra-thin oxides

Soft breakdown (SBD) and hard breakdown (HBD) events are characterised sepa rate: of each other for a 3.4 nm gate oxide. It is shown that both breakdow n events can have significantly different voltage and temperature accelerat ion 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 vo ltage stress. PEM also points out that a structural change of a breakdown p ath can occur, usually referred to as thermal breakdown of SiO2. It is conc luded that a separate characterisation of SBD and HBD events is correct, if the stress conditions do not cause this structural change for the first SB D event. (C) 2001 Elsevier Science Ltd. All rights reserved.