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

The energy spectra have been converted into depth profiles. The profiles for both
the NoPAI and PAI samples are shown in Figure 6.4a) and 6.4b) for As and Si,
respectively. Figure 6.4 b) shows that the 3 keV As implant produces a ∼11 nm deep
amorphous layer, as evidenced by the extra Si scattering yield behind the surface peak
that reaches the random level and extends to a depth of ∼11 nm (half height). Arsenic
implant profiles for the PAI and NoPAI implants are in close agreement. This is
expected since Si is amorphised after a As dose of 10 14 cm -2 (14, chapter 5). MEIS
shows that the peak of the As distribution is at 6.3 nm depth, in close agreement with
TRIM calculations that yield an Rp = 6.4 nm (profiles not shown). Following a 600 °C
20 min anneal the amorphous layer has recrystallised by SPER. The regrowth is not
perfect, leaving a surface damage peak of greater width (5 nm) than the surface peak
width of the virgin sample (2.5 nm) and greater height. The As profile too has
undergone considerable change with the disappearance from “ beam view” of most of
the As in the implanted profile and the appearance of a narrow, segregated As peak with
a maximum at a depth of 3 nm. The former is due to As taking up substitutional
positions within the regrown Si, where it is no longer visible to the beam. The latter is
due to the As concentration that exceeds the solid solubility and cannot be
accommodated in the regrown layer due to solid solubility restrictions, although the
operation of a simple activated segregation process cannot be excluded. In either case it
is “snowploughed” ahead of the advancing amorphous/ crystalline interface and forms
the segregated surface peak (7).
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