Base contact resistance limits to lateral scaling of fully self-aligned double mesa SiGe-HBTs

A significant reduction of parasitic resistances and capacitances of the double mesa SiGe Heterojunction Bipolar Transistors (SiGe-HBT) was achieved by using self-aligned processing steps, such as planarization of transistor contacts, outside-spacer-technology for micromasking, contact implantation and low ohmic silicidation. This article presents and analyses the lateral optimization of the double mesa SiGe-HBT by on-wafer measurements and demonstrates lateral scaling limitation resulting from the increasing base metal-semiconductor contact resistance. The increase of the more important base contact resistance is proven by two-dimensional contact simulation. This is shown experimentally by using a fully self-aligned double mesa SiGe-HBT transistor which combines the advantages of superior high frequency characteristics with a simple and low cost fabrication procedure being used mainly in compound semiconductor technology.