It was noted that B out-diffusion from epitaxially grown n-Si/p+-SiGe/n-Si heterojunction bipolar transistors was significantly enhanced during rapid thermal annealing (850C, 10s), following As emitter contact implantation. Here, 3 techniques were introduced which markedly reduced B out-diffusion during implantation activation. The limitation of post-implantation processing to 600C for 120s led to minimal diffusion and to acceptable device performance. Another technique involved pulsed laser annealing of the As implant. This removed residual defects and eliminated enhanced diffusion during subsequent thermal processing. It was shown that high bulk O concentrations (of the order of 1020/cm3) in the SiGe sharply reduced implantation damage-enhanced B diffusion. In addition to the depth profiles, electrical measurements of heterojunction bipolar transistors which had been subjected to these fabrication techniques revealed ideal collector current characteristics and confirmed the absence of deleterious B out-diffusion effects.

T.Ghani, J.L.Hoyt, A.M.McCarthy, J.F.Gibbons: Journal of Electronic Materials, 1995, 24[8], 999-1002