Negative bias temperature stress on low voltage p-channel DMOS transistors and the role of nitrogen

The instability of MOS devices under negative-bias temperature stress (NBTS) conditions is known to cause the buildup of fixed positive oxide charge Q(f) and interface traps Q(it). The power-law time dependence of this build up has been described theoretically by a diffusion-reaction model introduced by Jeppson and Svensson [1]. In this work we show that the model can be used to explain the degradation of the transfer characteristics of a new, low voltage, vertical power DMOS technology. Various process steps were analyzed in view of their impact on the NBTS behavior. The results indicate that nitrogen, introduced into the MOS system during a long-time, high-temperature diffusion step, plays the key role in the NBTS characteristics. Finally ways of improving NBTS hardness are proposed. (C) 2002 Elsevier Science Ltd. All rights reserved.