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

theory predictions and X-ray fluorescence (XRF) studies (8, 9). Broadening of the
MEIS peak may also occur since MEIS samples a large area of the samples over which
there may be a distribution of depths of the SiO2 layer. The small shift of the As peak to
increased depth is consistent with a small growth in the thickness of the oxide layer
during annealing at higher temperatures which pushes the segregated As layer in. Spike
annealing at 1050 °C finally, results in the highest level of damage annealing as
indicated by the lowest dechannelling level. The increase in the width of the damage
peak compared to the 700 °C anneal is entirely accounted for by the growth of the oxide
layer to 2.4 nm. Spike annealing also leads to the highest fraction of substitutional As
atoms being accommodated in the regrown layer, leaving only 40 % of the implanted
As, the amount that can be contained in one monolayer (ML) i.e. 7E14 cm -2 , visible in
the segregated layer. Observations of such high levels of segregated As dopant in a very
shallow layer have been reported previously (10).
Returning briefly to the movement of As atoms into substitutional sites upon
SPER regrowth, this observation is consistent with activation and/or the formation of an
inactive As-vacancy cluster, AsnV (n ≤ 4) (11). For n = 4 the cluster consists of four
substitutional As atoms tetragonaly clustered around a vacancy that accommodates the
larger dopant size. The formation of AsnV clusters is accompanied by the ejection of Si
interstitials (10) that migrate and are trapped at the oxide/Si interface sink (12), and
their accumulation contributes to the growth in depth of an amorphous layer and thus,
the width of the surface peak. This is the second effect, referred to above that may
explain the increase in width of this peak upon RTA.
The annealing and segregation behaviour described above in Figure 6.1 is
confirmed by SIMS depth profiling measurements. The results are given in Figure 6.2
which shows the profiles using both logarithmic and linear concentration scales. The
Si 30 signal (3.09% abundance, multiplied by 32 to give ~ 100 % Si) is shown in Figure
6.2 for the as-implanted profile only. It was monitored in all cases and found to coincide
to within 1 %, confirming the current stability of the measurements. The excellent
quality of SIMS profile of the as implanted sample may be judged in comparison with
the MEIS result also shown in the bottom part of the figure. Only the marginally
increased FWHM (∼ 10 %) in the SIMS profile and minor shift (< 0.5 nm) towards the
surface reflect collisional mixing effects and sputter rate changes in the transient region,
respectively. The development of the SIMS profiles following annealing wholly
confirms the MEIS observations. Integration of the profiles shows no As dose loss and
hence the As invisible in MEIS can only represent dopant atoms that have moved into
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