An attempt to explain thermally induced soft failures during low level ESDstresses: study of the differences between soft and hard NMOS failures

This work focuses on the thermal soft failure mechanism occurring in NMOS t ransistors during low level ESD stresses. Soft and hard failure modes are b oth precisely characterized using atomic-force microscope (AFM) technique. Thermally induced soft failures are shown to be the first step of the hard failure mechanism. Furthermore, a strong relationship between both soft and hard failures is revealed. Contrary to what was reported until now, our in vestigation underlines the presence of two different hot spots during the f ormation of the large molten silicon filament leading to the disastrous sho rt circuit called hard failure. (C) 1998 Elsevier Science Ltd. All rights r eserved.