Incorporation of an Alloy-Though Passivating-Ledge Process into a Fully Self-Aligned InGaP/GaAs HBT Process

M.L. Hattendorf, Q.J. Hartmann*, and M. Feng
Department of Electrical and Computer Engineering,
University of Illinois Microelectronics Laboratory
*Epiworks, Inc.

Alloying base contacts directly through an InGaP emitter layer provides excellent passivation of the GaAs base in HBTs. Processes which utilize this ledge formation scheme and a self-aligned, wet-chemical base-collector etch can suffer degradation in DC performance. Layouts with a hexagonal emitter can circumvent any DC performance degradation because the base electrode can be used as the etch mask on all sides of the device.