Experimental results on the effects of the As dopant concentration upon B out-diffusion in n-polycrystalline/p-monocrystalline structures were considered. It was found that the B diffusivity was only 30 times higher in polycrystalline material than in monocrystalline material if the degree of As doping was high enough to cause enhanced grain growth. The diffusivity increase was equal to about 130, if the polycrystalline material had a small grain size due to a low As dopant concentration. The B loss from the base region of an advanced bipolar transistor doping profile, by out-diffusion into the emitter polycrystalline Si, was of the order of 20% and had to be considered in order to ensure accurate device modelling.

J.N.Burghartz, C.L.Stanis, P.A.Ronsheim: Applied Physics Letters, 1995, 67[21], 3156-8