Leakage Current Control in Recessed SiGe Source/Drain Junctions

The impact of different process parameters, namely, the trench etch depth, the total epitaxial SiGe thickness, and the epi elevation, on the leakage current of recessed Si 0.8 Ge 0.2 source/drain junctions has been systematically investigated. Besides the behavior of the forward and the reverse currents, attention is also given to the temperature dependence of the leakage current. It is found that both the bulk and the peripheral leakage current density increase strongly with increasing etch depth. Empirically, an exponential dependence has been observed between the area leakage current density at - 1 V and the distance d j between the Si 0.8 Ge 0.2 -Si interface and the electrical p-n junction, whereby an increase by 1 dec for every 43 nm of reduction in d j occurs. This can be understood by the fact that the responsible defects originate mainly at the SiGe-Si interface. The perimeter current density shows for certain process splits an exponential dependence on the total thickness of the epitaxial layer t SiGe , with an increase by a decade for every 50 nm increase in thickness. Also, the generation and recombination lifetimes have been studied in order to determine an effective energy level of the electrically active defects.