Co-diffusion of As and B in and from polysilicon during rapid thermal annealing

Abstract

This work provides an experimental and theoretical insight into the physical mechanisms involved in the co-diffusion of As and B in polysilicon/monocrystalline Si bilayers, during the formation of shallow N+ emitters for bipolar-CMOS technology. The RTA-induced redistribution of As and B successively implanted in a 380 nm LPCVD polysilicon layer has been studied by SIMS measurements. A strong retardation in the diffusion was observed for B, which was attributed essentially to grain growth in the polysilicon layer, detected by X-ray diffraction. A weak retardation effect was also noticed for As in the presence of B, but with no significant consequence in the doping profile of the monocrystalline emitter region. The electrical activation of As in the co-implanted structures is satisfactory from a RTA temperature of 1100 degrees C, although slightly lower than in wafers without B. First results of the authors process modelling have permitted the authors to fit diffusivities of the dopants.