IN-SITU ARSENIC-DOPED POLYCRYSTALLINE SILICON AS A LOW THERMAL BUDGETEMITTER CONTACT FOR SI SI1-XGEX HETEROJUNCTION BIPOLAR-TRANSISTORS/

A low thermal budget emitter contact with low specific contact resisti vity (rho(c)) with the absence of transient enhanced diffusion (TED) e ffects is essential to fabricate integratable high performance Si/SiGe heterojunction bipolar transistors (HBTs). We report the use of in si tu As-doped polycrystalline silicon (polysilicon) from a low base pres sure rapid thermal episystem for this purpose and find that it meets a ll the requirements. We used secondary ion mass spectrometry to find t hat 18 nm, heavily B-doped layers remain intact after implantation int o the surface polysilicon and annealing at 800 degrees C for 40 s. Sim ilar samples without the surface polylayer displayed extreme broadenin g of B profile. Kelvin crossbridge resistors together with 2D device s imulations revealed that rho(c) is an extremely low value of 1.2x10(-8 ) Ohm cm(2) in as-deposited material. Fabrication of simple 30X30 mu m (2) mesa isolated HBT devices showed le to be more than two decades hi gher in devices with only an in situ as-doped polyemitter compared wit h devices that incorporated a surface implant into the single crystal portion of the emitter before polysilicon deposition. These results de monstrate that this doped polycrystalline silicon material is an excel lent choice for emitter contacts to HBT devices. (C) 1996 American Ins titute of Physics.