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

The effect of the amorphous layer on the dechannelling level is clearly visible
for the implanted and annealed samples. An increase in amorphous layer thickness
causes a substantial increase in the dechannelling yield. The energy spread of the low
energy edges becomes wider for increasing amorphous thickness as can be seen. The
energy straggling increases as a function of the square root of the amorphous layer
width, as described in equation 4.10.
Yield (counts per 5 uC)
450
400
350
300
250
200
150
100
50
Epi Si 3keV As 2E15 ion/cm 2 [111] Blocking direction
O depth (nm)
6 4 2 0
0
66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96
4.2.3 Improvements to methodology
Si depth (nm)
16 14 12 10 8 6 4 2 0
Energy (keV)
Throughout the project improvements to the MEIS methodology were carried
out and its validity checked. The main aim was to be able to produce depth scales as
accurate as possible. The work has followed three main strands: 1) finding stopping
powers that produce reliable depth scales, 2) determining the beam energy / accounting
for beam energy differences from day to day of operation, 3) improving the method of
depth scale conversion. The improvements in the accuracy that this section is concerned
87
virgin
Random
3keV Epi as-impl
3keV Epi 550C 200s
As depth (nm)
14 12 10 8 6 4 2 0
Figure 4.16 Typical MEIS spectra for different samples with a 100 keV He beam and using
the [īīı] channelling and [ııı] blocking directions. The effect of energy straggling and system
resolution on the gradient of the low energy edge of the peaks and differences in
dechannelling level for different amorphous layer widths are highlighted.