Planar AlGaAs/GaAs heterojunction bipolar transistors fabricated using selective W-CVD

The authors describe a planar process for the AlGaAs/GaAs HBTs in which collector vias are buried selectively, even to the base layers, with chemical vapor deposited tungsten (CVD-W) films. By using WF/sub 6//SiH/sub 4/ chemistry, W could be deposited on Pt films, which were overlapped 50 nm thick on the AuGe-based collector electrodes, without depositing W on the surrounding SiO/sub 2/ layers. Current gains of planar HBTs with 3.5- mu m*3.5- mu m emitters were up to 150, for a collector current density of about 2.5*10/sup 4/ A/cm/sup 2/.<
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