Effects of H-2 plasma exposure on GaAs/AlGaAs heterojunction bipolar transistors

GaAs/AlGaAs heterojunction bipolar transistors with highly C-doped base layers (p = 7 x 10(19) cm(-3)) were exposed to Inductively Coupled Plasma (ICP) or Electron Cyclotron Resonance (ECR) H-2 plasmas at different source powers and rf chuck powers to simulate the effects of ion damage and hydrogen passivation during CH4/H-2 dry etch fabrication of the devices. The HBT d.c. current gain decreases with increasing rf chuck powers in both types of reactor because of increased ion damage. This gain is less affected at high ICP source power because of the suppression of cathode de self-bias and hence ion energy, but is more degraded at high ECR source power since cathode d.c. self-bias increases under these conditions. The ICP tool is preferred for CH4/H-2 dry etching of HBTs because there is less disruption of the electrical properties of these devices. (C) 1997 Elsevier Science Ltd.