Instability of post-Fowler-Nordheim stress measurements of MOS devices

MOS test device electrical measurements (C-VI charge pumping), performed after accelerated ageing stress based on Fowler-Nordheim injection, strongly modify the net oxide charge. This can lead to an incorrect evaluation of the oxide long-term stability. We ascribe the observed instabilities to partial annealing of unstable slow states and trapped holes which lie close to the Si/SiO2 interface. Finally we propose and compare different experimental approaches to get more ''stable'' measurements. (C) 1997 Elsevier Science Ltd.