One of the key
processes in the fabrication of state-of-the-art CMOS devices is ion
implantation. Ion implantation is the primary technology to introduce
doping atoms into semiconductors to form devices and integrated
circuits. Strained silicon/relaxed SiGe CMOS devices show significant
performance improvements compared to pure silicon devices. The
silicon-germanium (SiGe) material technology offers the possibility of
bandgap engineering, enhanced carrier mobility, and a higher dopant
solubility. The capability of accurately predicting doping profiles by
Monte Carlo simulation tools can significantly reduce integrated
process development and implementation time.
The Monte Carlo ion implantation simulator MCIMPL-II
is an object-oriented, multi- dimensional simulator, embedded in a
process simulation environment. The simulator is based on the binary
collision approximation (BCA), and cells arranged on an ortho-grid are
used to count the number of implanted ions and of generated
point-defects. We have extended the simulator from silicon to SiGe
targets in order to analyze the applicability for advanced CMOS
devices.
The penetration depth of ion implanted dopants in relaxed SiGe is
significantly reduced compared to pure silicon due to the larger
nuclear and electronic stopping power. The heavier germanium atom leads
to a higher backscattering probability, which can be derived from the
scattering integral. This integral is evaluated by the simulator to
determine the scattering angle of a nuclear collision event. The larger
electronic stopping power of SiGe compared to silicon is caused by the
higher electron density due to the electron-rich germanium atom. It
turned out that the Lindhard correction parameter of the electronic
stopping model can be adjusted by a linear function of the germanium
content to adopt the strength of electronic stopping in SiGe alloys.
The successful calibration for the simulation of arsenic and boron
implantations was demonstrated by comparing the predicted doping
profiles with SIMS measurements. Thereby, the shift toward shallower
profiles with increasing germanium content was found in a non-linear
manner. Relaxed SiGe considerably facilitates the forming of shallow
junctions which are a prerequisite to further scale the MOSFET
structure into the sub-100nm regime.
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