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

TRIM AU
0.04
0.03
0.02
0.01
TRIM simulation of B and F range in 1 & 3 keV BF 2 implants
0.22 keV B - R = 1.93 nm
p
0.39 keV F - R = 2.14 nm
p
0.67 keV B - R = 4.15 nm
p
1.16 keV F - R = 4.42 nm
p
0.00
0 5 10 15
Depth (nm)
SIMS analysis was used for detecting F and B since the sensitivity of MEIS for
low Z elements is relatively small and any scattering at the F and B concentrations
present would be contained within the noise level of the Si background. Figure 7.4a)
shows SIMS depth profiles for F, from pre-amorphised samples, as-implanted and after
various anneals. Figure 7.4b) shows F depth profiles from the non pre-amorphised
samples. The BF2 implant energy was 3 keV. Note that the use of SIMS for ultra
shallow junction profiling has some inherent difficulties in the first few nanometres,
caused by changing sputtering rates until an equilibrium erosion rate has been reached.
This can cause some inaccuracies to the depth scale and concentration calibration in the
first couple of nanometres (22). Disregarding a sharp spike within the first 2 nm that is
probably a SIMS surface artefact, the as-implanted samples shows profiles with maxima
that are in close agreement with the TRIM calculation.
The PAI samples are considered first. After annealing there has been F
migration to the surface, yielding a F surface peak within the first 3 – 4 nm. (The
concentration these may be partially influenced by SIMS artefacts). For the preamorphised
samples there is the additional migration of some of the F deeper in,
forming a second peak. An ~6 nm wide peak (FWHM) centred around 12 – 13 nm is
found. This depth recurs for all the anneal conditions, with a slightly wider distribution
for the 600 °C sample compared to the higher temperatures. Integration of the second
178
0.22 keV B
0.39 keV F
0.67 keV B
1.16 keV F
Figure 7.3 TRIM depth profiles for B and F from 1 and 3 keV BF2 implants.