Characterization and modeling of emitter-base leakage in high speed SiGe NPNs

Leakage through the base is a common yield detractor in SiGe NPNs. The defects are commonly referred to as dasiapipespsila and are manifested as a current path between emitter and collector independent of base bias. In this article we discuss pipes which have been observed due to retarded base growth. Advanced light/thermally induced voltage alterations (LIVA) and cross section transmission electron microscopy (XTEM) were used to identify these defects, which resulted in leakage paths through the base to the collector. The pipes were found to have resistances ranging 100-200 kOmega, and could be modeled as junction field-effect transistors (JFETs) in which the pipes serve as the channel and the base as the gate electrode. Technology computer-aided design (TCAD) was utilized to model the pipes and provide insight into their behavior. In particular, the higher CE leakage currents of NPNs containing a selective collector implant are explained by changes in the conduction band resulting from the SIC implant. This correlates with observed NPN yield trends.