High-energy ion implantation is used for forming the collector in vertical bipolar transistors in a BiCMOS process. Secondary defects, remaining after annealing the implant damage, give rise to an increased leakage current and to collector-emitter shorts. These shorts reduce the transistor yield. The use of multiple step implants or the introduction of a C gettering layer are demonstrated to avoid dislocation formation. Experimental results show that these schemes subsequently lower the leakage current and dramatically increase device yield. The presence of C can cause increased collector/substrate leakage, indicating that the C profile needs to be optimized with respect to the doping profiles.

IEEE Trans. Electron Devices

Liefting, R. J, Wijburg, R. C. M, Custer, J. S, Wallinga, H, & Saris, F.W. (1994). Improved device performance by multistep or carbon co-implants. IEEE Trans. Electron Devices, 41, 50–55.