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RTCVD
SiGe process
- The SiGe growth rate increases strongly with an
increasing GeH4 flow. This is attributed to an increased hydrogen
desorption caused by the presence of Ge atoms on the growing surface
that frees nucleation sites for the incoming Ge and Si atoms
- In high temp regime,H2 desorption rate is higher than
gas
adsorption rate. So gas adsorption rate is the key control for high
temp SiGe epi dep rate. In low temp regime, H2 desorption rate is the
key control for low temp SiGe dep rate.
Tthe growth rates rapidly increase when the
partial pressure of the hydrogen carrier is reduced during the growth
of silicon.
- The Ge concentration decreases significantly as the
growth temperature increases from lower Temp to Nominal Temp. The
associated parameter depends exponentially on the reverse
absolute
temperature, with an “activation energy” of the
order of -15/kcalmol-1. At the same time, the SiGe growth rate
increases strongly as the growth temperature increases, with an
activation energy dropping from 47 down to 12/kcalmol-1 as the Ge
content in the film goes up
- Adding HCl leads at
Nominal Temp to a significant increase in the Gex of SiGe layers
- The dopants react with HCl. The process development
of heavily boron doped selective SiGe-epitaxy is a much more
complicated task because boron doping makes the process window for
selective deposition narrow. Generally, when more boron
concentration is added to the flow, a higher HCl concentration
is necessary to achieve selectivity due to the increase growth rate of
deposited film(s) on any dielectric areas. This higher HCl flow rate
reduces boron incorporation into the epilayers presumably because the
B--Cl bond is stronger than Ge--Cl and Si--Cl bonds.
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