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

greater than MEIS. SIMS is not sensitive to the lattice position of the dopant and so sees
all of the As present. In combination with MEIS depth profiles SIMS allows the
substitutional As fraction to be implied.
For the as-implanted samples there is virtually no difference between the PAI
and NoPAI samples. The only difference is that there is a small amount of As
channelled to greater depths that accounts for the slightly higher level in the depth range
20 – 40 nm in the NoPAI sample. MEIS does not have the sensitivity or depth range to
observe this.
The changes in the depth profile following annealing at 600 °C for 20 minutes in
the SIMS profile are far less dramatic than in the MEIS profile. The pile up of
segregated As at the surface is visible, with a small reduction in concentration in the
depth range 5-10 nm to account for this, otherwise the profile is largely the same. In
combination with MEIS this suggests that As has become substitutional. As has not
diffused deeper into the sample for the 600 °C anneals.
Spike annealing causes a dramatic change in the SIMS profile and shows the
diffusion of As deeper into the bulk. Taking the junction depth to occur at a
concentration of nominally 1E18 cm -3 this would result in a junction depth of 43.6 nm
for the PAI sample and 45.9 nm for the NoPAI sample. SIMS suffers from inaccuracies
in the depth scale in the first few nm and although the segregated As peak can be
observed, the accuracy of the concentration and depth scale in this region is limited.
MEIS results are considered much more quantitative. The combined results suggests
that all the As has been retained, based on the integration of the SIMS profile at depths
beyond the segregated peak, and using the MEIS results to determine the dose contained
within the segregated peak.
128