Hot-Carrier-Damage-Induced Current Gain Enhancement (CGE) Effects in SiGe HBTs

We investigate high current stress mechanisms and demonstrate how Auger hot carriers can damage both oxide interfaces and polysilicon regions of the emitter and base. A new current gain enhancement (CGE) effect is proposed, which involves hot-carrier damage to the polysilicon emitter and extrinsic base leading to the degradation of the associated minority carrier mobilities. We demonstrate the different CGE mechanisms in SiGe HBTs under forward and inverse modes of operation. The hot-carrier damage responsible for CGE at high injection is explored in depth with the help of TCAD simulations. Evidence for this effect has been gathered with good statistical significance from various stress conditions, various technologies, complimentary (NPN + PNP) devices, and from dc and ac measurements. The new polysilicon degradation mechanism proposed in this paper has been generalized and is important for accurately modeling the changes in base resistance and current gain (β ) at high injection, where circuits are typically biased to extract maximum device performance.