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

Kinematic factor (K)
1.0
0.8
0.6
0.4
B/He
O/He
Si/He
As/He
Sb/He
0.2
Au/He
0 20 40 60 80 100 120 140 160
B/H
O/H
Si/H
As/H
Sb/H
0.4
Au/H
0.2
0 20 40 60 80 100 120 140 160 180
Scattering angle (deg)
Figure 4.13 Variation in the kinematic factor K with scattering angle, for different atom /
He or H combinations.
The depth resolution can be varied with scattering angle. Increasing the path
lengths of an ion in a sample produces an improvement in depth resolution; therefore
using small scattering angles produces an enhancement of the depth resolution. This is
evident in Table 4.1, shown later, where the depth resolutions obtained for different
scattering angles is given. Once an appropriate scattering angle is chosen, to satisfy the
requirements of peak overlap and depth resolution, the specific crystallographic
directions need to be chosen for the channelling and blocking. More open channels
produce better blocking dips which makes the set up of the double alignment up more
sensitive to the surface and also makes sample alignment easier. He ions have a wider
shadow cone compared to H and this means the shadowing and blocking will be more
effective and hence He should give deeper channels. The choice of ion has an effect on
the depth resolution, He with its higher stopping power produces better depth resolution
than H + .
A high scattering yield is advantageous to improve the sensitivity for detecting
particles. As given in equations 4.5 and 4.6 the Z1 2 dependence of the scattering cross
section shows that the scattering yield would be four times higher for He + ions than for
H + ions. Likewise the Z2 2 dependence shows there is a much higher scattering yield for
scattering off heavy elements such as As than light ones such as B. Since the scattering
82
1.0
0.8
0.6