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

The “zero” depth point in the MEIS depth profiles is always taken at the sample
surface, and the depth of the a/c interface is measured in relation to the surface. XRD
however takes the “zero” point of the depth scale at some depth in the region of the
amorphous to crystalline interface as it is only sensitive to the crystalline material and
hence does not “see” the amorphous Si. Obviously this point is at a different depth for
each sample. The other difference between the techniques that affects the
recrystallisation depth measured, results from differences in criteria for the end point.
The depths in MEIS are based upon the a/c interfaces and as such the regrown layer
thickness is determined by subtracting the depth of the a/c interface following annealing
from the depth of the original a/c interface. In XRD the end point is the strained region
around the EOR defects. This would be deeper than the a/c interface. The regrown layer
thickness is given from the distance between this point and the region of strain near to
the zero depth point below the a/c interface, i.e. the distance between region 1 and 3
shown in Figure 6.21a).
In Figure 6.23 the strain profiles obtained from XRD measurements (Figure
6.21a)) have been rescaled by a shift of each profile for direct comparison to the MEIS
spectra in the following way. The EOR damage region, which causes the strongest
contrast in XRD curves, has been arbitrarily located at the back edge of the asimplanted
Si amorphous layer and its position has been kept fixed during the annealing,
as would be expected for EOR defects in this temperature range. The peak is located at
a depth of 13.5 – 16.5 nm. As a result of this rescaling of the depth, Figure 6.23 shows
the disordered Si profile from MEIS superimposed by the lattice strain profile from the
fits of the XRD curves. The a/c interface from XRD always aligns with the back edge of
the Si peak in MEIS (i.e. area of strong lattice disorder).
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