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

interface around the depth of the As peak and surface occurs. With regards to the As
profiles, for the sample annealed for 60 s, where there is more regrowth than in the case
of the 550 °C 600 s sample, there is a marginal change in the As peak relative to the asimplanted
spectra, consisting of a small but detectable reduction of the As peak at a
depth between 6 and 12 nm. Considering there is considerable recrystallisation of areas
of the Si within this depth region, the change in the Si shape at those depths is
remarkably small. A small amount of segregation has occurred, as seen by the slightly
increased As yield between 3 and 6 nm. Overall, integration of the peak shows a
reduction in the peak area of only 3.5 % compared to the area of the as-implanted
sample. For increasing anneal durations (≥70s) there is a greater amount of
substitutional As, as well as As segregation. During SPER on bulk Si, there is normally
very little or no As left visible in regrown layers, however this is not the case with these
samples. The sample annealed for 200s gives the clearest example of this, 58% of the
implanted As is still visible with the MEIS beam, 32% is within the segregated peak but
26% of the implanted As remains visible within the regrown layers at a depth between
4-12 nm. From this it must be concluded that the unusual regrowth behaviour also
appears to affect the perfection of the regrowth and the As moving into substitutional
positions. In view of the fact that for a 3 keV 2E15 As implant, ≥ 50% segregation is
found (4) only a small segregation effect would ever be expected for these conditions
for full regrowth, assuming that segregation is driven by solid solubility limitations.
The samples annealed at 650 °C go through the same stages of regrowth, albeit
achieved with shorter anneal durations, as seen in Figure 6.25c). The level of regrowth
of the sample annealed at 650 °C for 8s falls somewhere between those annealed at
550 °C for 200 s and 500 s. The sample annealed at 650 °C for 10 s is similar to the
sample annealed at 550 °C for 600 s. In both cases a wide a/c interface is present. With
longer anneal durations the level of the residual damage layers comes down with
increasing time and result in narrower surface peaks as the interface straightens around
the depth of the high As concentration. The redistributed As peak is related to the shape
of the regrown Si layer, however there is still As visible in regrown areas. For example
the 30s anneal causes a segregated As peak as well as visible As in the regrown layers
between 4 and 10 nm depth, similar to that observed after a 200s anneal at 600 °C. As
with the SPER studies discussed in section 6.3 the rate of regrowth slows down in the
As rich regions and may also be affected by the increasing proximity of the surface.
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