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

to the accumulation of small pockets of damage at the buried oxide interface, due to
interstitial trapping and this resulted in the local absence of a seed for the damaged Si to
rearrange upon. For the cases where the range of the implantation was not sufficient to
reach the buried oxide, this effect was attributed to the accumulation of mobile
interstitials that were trapped at the buried oxide interface. TEM micrographs showed
that the amorphous / crystalline interface was wavy over the same depth range as
observed with MEIS. It is proposed that locally, where there is no seed, regrowth is
initially delayed. The initial delay is responsible for producing the wavy interface. The
regrowth of SOI samples was observed to either proceed with a slower rate, or be
initially delayed compared to bulk Si samples. This observation fits in with the
proposed explanation.
MEIS studies also demonstrated an interaction between Xe, used to pre –
amorphise the samples, and F and B, from a subsequent BF2 implantation following
annealing. It was observed that approximately half of the Xe became trapped at a depth
that was dependent on the energy of the BF2 implant, which corresponded to ~ 3 × Rp of
the F and B atoms. SIMS analysis showed that following annealing most of the
implanted F had segregated to the surface, but a small fraction had moved in deeper and
was trapped at the same depth as the Xe in an ~ 1:1 ratio. B similarly was observed to
be trapped at the same depth albeit with a concentration of around a quarter or lower of
the other species. EFTEM studies showed that the Xe was present in spherical
agglomerates or bubbles. It was proposed that this interaction is caused by some defect
structure (e.g. a density variation or volume defect) at the EOR of the F and B implant
within amorphous Si, and some chemical interaction between F and Xe. The possibility
of the formation of a Xe F compound cannot be excluded either.
Further studies may be carried out in several areas. In terms of improvement of
the techniques, there is scope for further experiments to compare the results between
MEIS, SIMS and the X-ray methods with the aim of a better understanding of the
effects studied and a further optimisation of the techniques.
There is also scope for further studies regarding the regrowth behaviour in SOI.
It would of interest to carry out more experiments directly comparing bulk Si with SOI
samples and to vary systematically the depths of implantation damage. This area of
study would also benefit from more TEM experiments.
In order to understand the Xe F and B interaction better, experiments should be
carried out with individual B and F implantations rather than BF2 to try to understand
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