Impact of Electrical Stress on $\gamma$ Ray Irradiated Double Polysilicon Self-Aligned (DPSA) PNP Bipolar Transistors

Abstract

Anomalous irradiation response to total ionizing dose effects of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co γ ray in double polysilicon selfaligned (DPSA) bipolar PNP transistors at a low dose rate was observed. It is experimentally revealed that the anomalous current gain (β) enhancement in Emitter-Base (E-B) forward-biased transistors during irradiation originates from a base current decrease. Based on the comparative forward high-current stress and forward-biased irradiation experimental results, the anomalous phenomenon can be ascribed to the atomic hydrogen electromigration and subsequent passivation of electronic interface traps located at the polysilicon grain boundaries and poly/monosilicon interfaces of DPSA's poly emitter contact layers. Although current gain enhancement occurs both in high-current stress and forward-biased irradiation stress PNP transistors, the physical mechanisms responsible for the variations are quite different. In the case of forward high-current stress, the damage mainly affects excessive base current of non-ideal components and decreases the emitter resistance. For forward-biased ionizing radiation stress, the damage not only induces both ideal and non-ideal components of the base current increase in the low bias region but also increases emitter resistance.