Damage formation and annealing studies of low energy ion implants ...

Pulsed lasers can produce rapid heating of the surface layers, with times of 10 -11
to 10 -6 s. This is known as the adiabatic regime, and affects only the near surface. It is
possible with pulsed lasers to either regrow the surface region through liquid phase
epitaxy or through solid phase epitaxy in the sub melt region (36).
In device production it is currently most common to use RTA or SA but as the
need for shallower junctions becomes greater, different types of annealing methods,
including laser annealing, are being increasingly considered (37).
The annealing of ion implanted amorphous Si produces a variety of effects,
depending strongly on the initial state of the implanted region. Effects include epitaxial
crystallisation, random nucleation and growth, dopant segregation and defect enhanced
diffusion, which are described in this chapter. Regrown layers contain fewer defects
when the starting point is amorphous Si compared to initially highly damaged layers.
3.3.2 Solid phase epitaxial regrowth (SPER)
Solid phase epitaxial regrowth (SPER) is a process whereby amorphised Si is
recrystallised upon thermal annealing from temperatures above half that of the melting
temperature of the crystal, i.e. for Si from approximately 500 °C, to approximately
1350 °C. The underlying Si crystal acts as a template for the amorphised Si to be
arranged upon (epitaxy). This occurs while the Si is still a solid, hence the term solid
phase epitaxial regrowth (14, 38, 39).
During SPER the amorphous Si rearranges itself on the underlying crystalline
substrate starting from the amorphous / crystalline (a/c) interface and proceeds to the
surface in a layer-by-layer fashion. Since crystalline Si has lower free energy there is
always a driving force towards rearrangement to the crystal structure. During SPER, the
implanted dopants take up substitutional lattice sites as the crystal-amorphous interface
passes through their location. Time resolved reflectivity (TRR) (38) is the main
technique that has been used for measuring SPER rates. It has been observed that
impurities (dopants) affect the regrowth behaviour and the rate of SPER. Intrinsic
(undoped) Si will be described first and then the addition of impurities is considered.
3.3.2.1 Intrinsic Si
It has been shown for intrinsic amorphous layers, produced by self ion
implantation, that the regrowth velocity is temperature and orientation dependant. The
orientation dependence is related to the density of atomic packing on the different
planes. The regrowth rate on (100) Si is approximately 2.5 times greater than (110) Si
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