Development of an Implant Isolation Process for Heterojunction Bipolar Transistors

Heterojunction bipolar transistors (HBT) are attracting much interest in high speed device applications, especially where high efficiency and high power density operation are of interest. A key issue for the manufacturability of HBTs is electrical isolation of individual devices from each other. The major problem with HBT isolation is the thickness of the power device structure where it is desirable to have collector and sub-collector layers 1 um thick or more. Such thick structures create problems for conventional mesa and keV implant isolation schemes. UES proposes to develop implant isolation schemes involving multiple does MeV B+ and O+ implants. The formation of high resistivity regions in GaAs-AlGaAs HBT structures will be investigated for different implant schemes formulated on the basis of computer simulations. The leakage current, breakdown voltage and sheet resistance measurements will be performed to optimize the implant parameters such as energy and dose.