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

duration, is observed. MEIS results have shown that the segregated As is located
underneath the oxide layer. Figure 6.8 c) shows the O depth profiles for the NoPAI
samples. The 0.6 nm increase in the oxide layer width is exactly replicated in the shift in
depths of the As peaks of Figure 6.8a). It is likely from a simple consideration of the
shape of the O peaks that the oxide layer contains some suboxides (15). The back edge
of the peak is substantially less steep than the front edge and also less steep than the
back edge of the corresponding Si peak plotted on the same depth scale in Figure 6.8d).
This result again shows that the segregated As clearly sits underneath the SiO2 layer,
although probably in a region of some suboxides. The Si is probably distorted around
the segregated As and this is reflected in increased backscattering.
6.2.5 BF2 implanted samples
Similar sets of experiments have been carried out using BF2 implanted samples.
The regrowth is seen to proceed in the same way. Neither B nor F is visible in MEIS at
the concentrations used; therefore the results are not presented here. However a novel
effect involving the interaction between Xe, F and the defect structure was identified.
This is the subject of chapter 7 of this thesis.
6.3 SPER studies
6.3.1 Introduction
There is interest in studies of low temperature SPER, i.e. ~ 550 °C – 800 °C as
this temperature range has been suggested as a possible solution for the formation of
USJs in the 65 nm and 45 nm nodes (1-3). These temperatures are currently not used
due to problems of lower electrical activation / solubility and a high level of defects left
after annealing. However the real strength of this type of annealing is less diffusion, as
the results in this section will corroborate.
The first part of this section shows results of annealing a 3 keV As implanted
wafer. An isothermal annealing series at 600 °C and an isochronal series for 10 s were
carried out. MEIS results show the same effects as discussed before, i.e. segregation of
As, with a fraction of As taking up substitutional positions and the movement of the a/c
crystalline interface towards the surface in a layer by layer fashion. The As
substitutionality is observed to follow the depth of the a/c interface. SIMS
measurements show the same movement of As, seen in MEIS, and also show that the
As invisible to MEIS is retained and importantly does not diffuse deeper into the bulk.
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