D. Kruger et al., SECONDARY-ION MASS-SPECTROSCOPY ULTRASHALLOW DEPTH PROFILING FOR SI SI1-XGEX/SI HETEROJUNCTION BIPOLAR-TRANSISTORS/, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 14(1), 1996, pp. 287-293
Starting from a theoretical dopant and composition profile of a Si/Si1
-xGex/Si heterojunction bipolar transistor (HBT), the requirements for
high depth resolution secondary ion mass spectroscopy (SIMS) measurem
ents are discussed. To characterize the boron out-diffusion from the S
i1-xGex base, which can crucially degrade the transit frequency f(T),
a depth resolution of better than about 3 nm is necessary. SIMS measur
ements have been performed using low energy oxygen primary beams at no
rmal incidence to characterize sharp B profiles in Si and Si1-xGex lay
ers. Graded Ge concentrations have been measured quantitatively using
cesium primary beams and MCs(+) secondary ion detection. It is shown t
hat in the limit of low energy primary beams, the leading edges of the
SIMS profiles with upslopes of 1-2 nm/decade show sufficient resoluti
on for many of the HBT applications. For better characterization of ef
fects which are located on the trailing edge of the profile, deconvolu
tion procedures are necessary. (C) 1996 American Vacuum Society.