Development of an Implant Isolation Process for Heterojunction Bipolar Transistors.

Abstract : There is great interest in heterojunction bipolar transistors (HBT) for high speed, high power electronic devices. The major problem in the fabrication of HBT circuits is the electrical isolation of individual devices in power device design, where it is desirable to have collector and sub-collector layers 1 micrometers thick or more. The objective of Phase I research was to develop device isolation schedules based on MeV energy O(+) and B(+) implantations. A number of ion implantation schedules based on O(+), O(+) + Ga(+), and B(+) implantations have been developed by using computer simulations. These schedules have been tested for the isolation of AlGaAs/GaAs and InGaP/GaAs HBTs. Low leakage currents and high breakdown voltages necessary for the optimum device performance have resulted from selected implantation schedules. Hall measurements were performed after various implantations using single layer n and p-type GaAs of known thickness and carrier concentrations. These data will be useful in optimizing dose levels for the above mentioned ion species for the desired isolation of devices.