Improvement of device characteristics by multiple step implants or introducing a C gettering layer

Ion implantation is used for realization of the collector in vertical bipolar transistors in a BiCMOS process. Secondary defects, remaining after annealing the implant damage, can give rise to an increased leakage current and to collector-emitter shorts. Two methods are proposed to avoid dislocation formation. First, by using multiple step implants, and second, by application of a carbon gettering layer. Experimental results show that these schemes can lower leakage currents, and moreover dramatically increase device yield. However, the carbon profile needs a further optimization with respect to the quality of the collector-substrate junction.