PLANAR A1GAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS FABRICATED USING SELECTIVE W-CVD/

We describe a planar process for the AlGaAs/GaAs HBT's in which collec tor vias are buried selectively, even to the base layers, with CVD-W f ilms. By using WF6/SiH4 chemistry, W could be deposited on Pt films, w hich are overlapped 50 nm thick on the AuGe-based collector electrodes , without depositing W on the surrounding SiO2 layers. Current gains o f planar HBT's with 3.5 x 3.5-mu-m2 emitters were up to 150, for a col lector current density of about 2.5 x 10(4) A/cm2.