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

nearest neighbour distance (52). By doing this, the five and seven membered ring
structure can be restored to the crystalline state. This model was extended to Si (100)
and the activation energy for SPER was identified with the sum of the energy to break a
bond at the interface and the increase in distortion energy accompanying bond
rearrangement (51). It was suggested that SPER proceeds through the propagation of
[110] ledges on {111} planes and ledges (53). The energy to break every bond was not
required for recrystallisation to occur. It was found to be possible to make major
readjustments with the breaking of just one bond and propagating the loose ends
through the structure. The shortcomings of this type of model are that they do not
account for the differences observed in the SPER rate with implanted group III and V
dopant and other impurities.
Electric field models based on electronic processes make a much better attempt
to explain the SPER rate dependence on dopant concentration. Several different models
exist and the crux of these arguments is to identify specific defects that give rise to the
bond breaking process. An important model of this type extended the models using
crystallisation along kink sites, to incorporate doping effects (14). It was proposed that
SPER is mediated by the generation and motion of kink like steps along [110] ledges.
Here SPER is viewed as a cooperative process in which the motion of a kink is
accompanied by crystallisation of many atoms before the kink is annihilated. Addition
of a doping impurity can either increase the concentration of charged kinks or reduce
the kink migration energy and enhance the SPER rate. Kinks can be pinned by the
formation of a strong bond between a Si atom and an impurity atom. This model is
illustrated in Figure 3.7. This model describes intrinsic as well as doping enhancement.
The growth site of this model can be visualised as some bond breaking defect.
Figure 3.7 Schematic representation of SPER of Si(100) in terms of
kink (BB’) generation and motion along [110] ledges (AA’). From (14).
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