A 42-GHz (fmax) SiGe-base HBT using reduced pressure CVD

A SiGe HBT having a f(max) higher than f(T) has been fabricated using a production CVD reactor which allows SiH2Cl2-based Si collector epi-growth at high rate as well as SiH4-based SiGe base epi-growth at low rate. Transistor design together with process integration was focused on lowering the extrinsic base resistance and the collector-base capacitance. To this purpose, a TiSi2 layer with a sheet resistance of 1.3 Omega/sq was used as a base electrode and a selectively implanted collector was utilized. For the base layer, an undoped-Si (300 Angstrom)/p-SiGe (200 Angstrom, N-A = 4.4 x 10(18) cm(-3), linearly-graded Ge composition from 0 to 0.19)/undoped-Si0.81Ge0.19 (110 Angstrom)/undoped-Si (500 Angstrom) multilayer was deposited on a LOCOS-patterned wafer. In order to form the emitter-base junction and to activate the arsenic dopants in the polysilicon-emitter, rapid thermal annealing (RTA) at 900 degrees C for 20 s was performed only one time so that outdiffusion of the boron in the base could be suppressed. The collector and base currents are shown nearly ideal. We obtained a f(T) of 37 GHz which is near the theoretical limit imposed by BVCEO and a f(max) of 42 GHz. The base resistance and the collector-base capacitance extracted from measured S-parameters have a value of 37 Omega and 27.2 fF, respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.