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

Inelastic energy loss (eV/Ang)
32
28
24
20
16
12
60 80 100 120 140 160 180 200 220
He + energy (keV)
4.2.3.2 Determination of beam energy
He + in Si stopping powers.
SRIM 2000
SRIM 2003
Fit to SRIM 2003
Fit parameters
Y =4.41388+0.22226 X-6.88878E-4 X 2 +8.73673E-7 X 3
Figure 4.18 He inelastic energy loss rates in Si as a function of energy, taken from
SRIM 2000 and SRIM 2003. The function, of a best fit to the values from SRIM 2003
is given.
With the MEIS system it is not possible to set the beam energy to a reproducible
energy with sufficient accuracy so that any minor energy differences occurring from one
day to another would not be noticeable on the energy and hence depth scales. A
difference of approximately a few hundred volts would cause a difference around 0.5
nm on a depth scale, depending on scattering conditions and element. With the original
power supply used earlier in the project this level of variation was common and despite
an improvement later on in the project with a new power supply, beam energy
variations still needed to be accounted for.
The original approach for this was to align the Si peaks of all data sets, to the Si
peak on the spectra from a reference virgin Si sample, using a multiplication factor of
the energy scales. All the samples could be compared with the “same” beam energy.
This alignment approach is in theory reasonable in view of the fact that the energy for
scattering at the surface is dependant on the kinematic factor and the beam energy only.
Complications with this alignment method arose however. The most significant problem
was the lack of a perfectly definable position on each spectrum to align to the virgin. A
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