D. Caffin et al., BASE METALLIZATION STABILITY IN INP INGAAS HETEROJUNCTION BIPOLAR-TRANSISTORS AND ITS INFLUENCE ON LEAKAGE CURRENTS/, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 15(4), 1997, pp. 854-861
For InP/InGaAs heterojunction bipolar transistors (HBTs), base-collect
or leakage current can be quite impairing by restricting their operati
onal conditions to a very narrow emitter-collector voltage range. Resu
lts of a study on morphological degradations of various p-type metalli
zations to InGaAs and their effect on base-collector leakage current o
f InP/InGaAs double HBTs are reported here. Two kinds of base contacts
were investigated. Mn/Au/Ti/Au induces high leakage current after con
tact annealing at temperatures as low as 300 degrees C. This is due to
important interdiffusion of the species, and precipitation inside the
base layer. Ti/Pt/Au is a good alternative, provided that the platinu
m layer is not too thick, and the contact annealing temperature not to
o high. Leakage current was found to be related to the strain induced
by metal deposition, or to the morphological degradation taking place
during annealings at high temperatures (metal precipitates formation i
nside the base layer inducing strain, and III-V elements exodiffusion)
. However, HBTs with Ti/Pt/Au base contacts annealed at 300 degrees C
showed no excess leakage current and almost no morphological alteratio
n, and contact resistances below 10(-5) Omega cm(2) were obtained for
base doping levels above 10(19) cm(-3). (C) 1997 American Vacuum Socie
ty.