ABSTRACT
A way of improving the performance of SiGe HBTs is to increase the base doping in order to reduce the base resistance. This has to be accompanied by a higher Ge content which in addition will result in a smaller turn-on voltage giving lower power consumption. For more than 50% Ge the collector saturation current of the HBT will be larger than that of a PtSi n-Schottky diode. This opens new fabrication possibilities with self-aligned PtSi base contacts without ion implantation and high-temperature anneal. This paper investigates SiGe HBTs with very high base Ge contents up to 57% with excellent high frequency performance and with collector currents two orders of magnitude higher than PtSi-diodes. Fabrication of devices with a self-aligned PtSi base, however, is hindered by the formation of PtSiGe alloys which have a smaller barrier height than PtSi.
