Comparison of dry etch damage in GaAs/AlGaAs heterojunction bipolar transistors exposed to ECR and ICP Ar plasmas

A detailed study has been performed of the damage introduced into GaAs/AlGaAs heterojunction bipolar transistors (HBT) during exposure to two different types of high ion density plasma used for mesa formation during device fabrication, namely electron cyclotron resonance (ECR) and inductively coupled plasma (ICP). Base and emitter sheet resistance increase with plasma source power in both systems until well-defined values where the ion energy falls below threshold values for defect creation. Under these conditions there is no measurable effect on device layer sheet resistance, de current gain or base-collector reverse breakdown voltage. The basic reason for this window of damage-free processing conditions is identified as the suppression of cathode self-bias as the high-density plasma source power is increased. Ion energy, ion flux and plasma exposure time may all have an effect on HBT device parameters. (C) 1998 Elsevier Science Ltd. All rights reserved.