Sims Depth Profiling of AlGaAs/GaAs Self-Aligned Thin Emitter Heterojunction Bipolar Transistor (SATE HBT)

Secondary ion mass spectrometry (SIMS) has been used to study the development of a new processing technology for the fabrication of AlGaAs/GaAs heterojunction bipolar transistor. An epitaxial layer structure is grown on a two inch diameter (100) semi-insulating GaAs water by an electron beam source molecular beam epitaxy (MBE). After device isolation, the emitter metal is depositied and the emitter area is defined. Selective rapid ion etch (RIE) is used to etch the n sup + emitter contact layer stopping at the ultra-thin AlGaAs emitter with the metallization serving as an etch mask. A similar procedure is used to fabricate the collector region. SIMS depth profiles will be used to study the undercut obtained by the RIE process that yields a self-aligned Be doped base at 2 x 10 sup (20) cm sup (-3) with a base width of (600-150)angstroms. An important process that is crucial to the overall performance of this device is the off-set region that is established between the AlGaAs - emitter layer and Be-dope base. SIMS depth profiles have been utilized to monitor this offset region and have successfully helped to achieve optimum device operation: i.e. 0. 5 to 26.5 Ghz; f sub t - 38Ghz and f sub (max) = 36 Ghz (Be base of 2 x 10 sup (20) cm sup 3, width=600angstroms) for a collector current density of J sub c = 50KA/cm sup 2.