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

cross section has an E -2 dependence, the scattering yield is higher for lower beam
energies. The sin -4 (θ/2) dependence shows that for smaller scattering angles there is a
sharp increase in yield. The sensitivity of MEIS to detect B and F is such that it has not
been possible to profile B or F.
Using a lower beam energy improves the depth resolution because of a smaller
absolute energy error of the energy detector / analyser but as the stopping power is
higher with higher beam energy over the range used, then peak overlap may be reduced
using a higher beam energy. Figure 4.13 shows that higher masses have a higher
kinematic factor. This determines the order that any peaks will appear in the energy
spectrum, but is not significant in terms of the choice of conditions.
The conditions considered best for these studies was the use of a He + beam of
either 100 keV or 200 keV. The ions were incident along the [ 1 1 1 ] channelling
direction and the analyser positioned to include the [111] and [332] blocking directions.
These directions resulted in scattering angles of 70.5° and 60.5°, respectively, and are
illustrated in Figure 4.14. These conditions are an optimum compromise between good
energy and hence mass separation between the As and the Si peaks and depth resolution.
They all result in sub-nm depth resolution and the detection of clear experimental
blocking dips (17, 31). The [332] direction gives a better depth resolution but a
decreased mass separation can cause a slight overlap of the silicon and arsenic peaks.
With the [111] blocking direction, this peak overlap is often avoided. Values of the
kinematic factor for the elements and scattering angles used in this study are given in
Table 4.1 along with the depth resolution obtained.
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