Fabrication of a low-noise beam-leaded microwave bipolar transistor by electron- and photolithography

A low-noise beam-leaded microwave bipolar transistor was fabricated with a combination of electron- and photolithography. Four of the eleven levels which were related to the patterning of the active region were patterned directly on the silicon wafers by the Bell Laboratories Electron Beam Exposure System (EBES). The registration tolerance of the 1-µm emitter stripes to the thin-gold metallization fingers was ± ¼-µm. This was routinely achieved on the 2-in wafers for all the levels written on EBES. The device processing employed a modified self-aligned emitter process which allows very highly doped inactive base and emitters without the problem of soft emitter-base junction. RF measurements of typical transistors show a minimum noise figure of 1.8 dB and an available gain of 12 dB at 1.7 GHz.