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

the bulk Si becomes wavy in the early stages. This wavy-ness is retained for the full
regrowth and this may explain the XTEM and MEIS results. This initial formation of
the wavy layer is the probable reason for the SOI samples lagging behind the bulk Si in
terms of the amount of regrowth that occurs for the same anneal duration. The proposed
mechanism is illustrated schematically in Figure 6.32 for one such region.
Figure 6.32 Illustration of proposed regrowth
mechanism on SOI wafers.
Once the leading edge of the interface reaches a depth where there is a high As
concentration, regrowth slows down effectively allowing the back edge to catch up.
This causes the straightening up of the interface as is observed by MEIS. Arsenic atoms
that cannot be accommodated as areas of the a/c interface pass by are pushed into
neighbouring amorphous areas, explaining why there is less modification of the As peak
at depths where there has been some recrystallisation.
A previous RBS study of samples where an amorphous Si was deposited on a
layer containing at least one atomic layer of native oxide showed that upon annealing
the height of the RBS peak from the amorphous Si was reduced but not the width (27).
Columnar regrowth of the Si above regions where at isolated points crystal growth
centres occur, most likely at gaps of the oxide layer, was suggested (27). This is
consistent with the proposed mechanism in the sense that regrowth could occur
selectively above small areas of seed and not above other areas without seed. If an
implant produced an amorphous layer to the BOX, then random nucleation and growth
would be expected (28, 29).
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