Current gain increase of n-p-n transistors by electromigration of atomic hydrogen in emitter polysilicon

Abstract

The current gain ( beta ) increase of n-p-n transistors induced by forward current stress is investigated. The mechanism of beta increase is identified as electromigration of atomic hydrogen in polysilicon by high density current, and its subsequent passivation of silicon dangling bonds at the poly/monosilicon interface and poly grain boundaries. The hydrogen passivation results in a reduction of surface recombination velocity, thus decreasing base current and increasing beta . The effects of hydrogen in emitter poly must be taken into account if bipolar reliability is to be improved. >