FABRICATION OF HETEROJUNCTION BIPOLAR-TRANSISTORS WITH BURIED SUBCOLLECTOR LAYERS FOR REDUCTION OF BASE-COLLECTOR CAPACITANCE BY MOLECULAR-BEAM EPITAXY REGROWTH

A process for fabrication of heterojunction bipolar transistors (HBTs) with selectively buried subcollectors by molecular beam epitaxy (MBE) regrowth is described. This process can be used to reduce parasitic b ase-collector capacitance of HBTs and improve the speed of these devic es. In situ etching by iodine prior to the regrowth was used for the f irst time to improve the quality of the substrate epilayer interface i n a semiconductor device grown by MBE. The secondary ion mass spectros copy depth profiles of regrown HBT structures suggest that the in situ surface cleaning by molecular iodine was not sufficient to remove all contamination from the substrate epilayer interface and that the micr owave performance of HBTs fabricated by this process may have been aff ected by that contamination. The de performance of devices which were fabricated by our process was not affected, however, by the contaminat ion and was comparable to the de performance of conventional HBTs. Our results suggest that the described process for fabrication of HBTs wi th selectively buried subcollectors by MBE regrowth would be feasible in conjunction with a more effective surface treatment. (C) 1998 Ameri can Vacuum Society.