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

Figure 6.7 and 6.8b) show that the 1 keV implant produces a 5.5 – 6 nm wide
amorphous layer (FWHM). The as-implanted As profiles (Figure 6.7 and 6.8a)) have a
peak at a depth of around 3.5 nm which corresponds well with TRIM simulation value
of Rp = 3.75 nm.
The NoPAI and PAI samples show the same general behaviour after
implantation and annealing with only minor differences between the two. Following
annealing the samples have largely recrystallised. The extra width of the Si peaks
compared to the virgin Si peak with a thickness of 2.5 nm, is mainly a result of the
increased oxide layer thickness. It also has a contribution from Si atoms in the distortion
around the segregated As (discussed later) and an accumulation of interstitials trapped at
the surface sink during annealing.
The 600 °C 20 min annealed samples have a Si surface peak with a thickness of
~ 4.8 nm, including the increased oxide thickness of ~ 2.4 nm. This anneal has the
poorest regrowth. The RTA samples of 1000 °C 5 s and 1025 °C 10 s also have a Si
peak with a width of 4.8 nm but the higher temperature RTAs produce more oxide
growth, to a thickness of ~ 3.4 nm. The spike annealed sample has a Si peak width of
4.4 nm and an oxide layer thickness of just over 2.8 nm. The dechannelling background
level (between the Si and O peaks) is consequently lowest for the spike annealed
samples, albeit only by a small amount.
In the samples annealed to 600 °C a shoulder, located at 0–2 nm, to the Si peak
around 3-4 nm represents the transition point from pure SiO2 (with concentration
2.3E15 cm -2 (30)), to region of suboxides and damaged Si. The damage level in this
region in the other samples is lower as a consequence of less distortion around the
segregated As.
As seen before, during SPER some of the As takes substitutional positions
invisible to the MEIS beam in the regrown layers and the remainder, that exceeds the
solubility segregates underneath the oxide layer. In the 600 °C sample only a small
amount of As takes up substitutional positions, 94% remains visible to the MEIS beam
as indicated in Table 6.2. This amount is significantly higher than for the equivalent 3
keV implant and anneal where 40% of the implanted As became substitutional, (Table
6.1). The reason is as follows, for the 3 keV implant with the deeper implant more
amorphous Si layer can regrow, as indicated in Figure 6.4 b). The 1 keV samples with
shallower implant depths have a narrower damage region that regrows and hence less
As is incorporated within the regrown region. In the 1keV 600 °C annealed sample,
only a small amount of As is ‘snowploughed’ in front of the crystalline/amorphous
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