RESOLVING THE MECHANISMS OF CURRENT GAIN INCREASE UNDER FORWARD CURRENT STRESS IN POLYEMITTER N-P-N TRANSISTORS

The mechanisms behind moderate bias current gain (beta) increase of n- p-n transistors under forward current stress are investigated in polys ilicon emitter transistors processed with different dopant impurities and concentrations, and with different amounts of hydrogen plasma trea tment. The results suggest that transport of atomic hydrogen toward po ly/monosilicon interface region and its subsequent passivation of dang ling bonds at both poly grain boundaries and poly/monosilicon interfac e are responsible for the moderate bias beta increase. To alleviate th e beta instability, elimination of hydrogen involvement and/or a highe r doping concentration inside poly emitter in back-end-of-line (BEOL) processes are/is recommended.