Reliability evaluation of GaAs HBT technologies

This work describes the implementation of an experimental procedure to evaluate the reliability of Heterojunction Bipolar Transistors (HBT) on a GaAs substrate. It is based on the separation of ageing test accelerating factors applied to HBTs and TLM (“Transmission Line Model”) structures associated with emitter base and collector layers. Three different technological manufacturing processes are investigated : AlGaAs/GaAs double-mesa HBT, GaInP/GaAs self-aligned HBT and GaInP/GaAs fully planar HBT. HBTs submitted to combined bias and temperature stresses exhibit either a degradation of the SiN/GaAs interface correlated with the increase of the emitter-base leakage current and/or a detachment of Ge/Mo/W emitter ohmic contact related to the base and collector current decrease for high level injection in the forward regime. These investigations have assessed that GaInP over the extrinsic base acts as a better passivation layer than the conventional SiN does