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

The slower, or initially delayed, regrowth on SOI is also apparent with these
samples. It is most noticeable with the samples annealed for 50s. For the SOI sample,
regrowth to a depth around 20 nm has occurred but the bulk sample has regrown to a
depth of approximately 6 nm. The samples annealed for 200s also show a large
difference in the amount of damage regrowth between SOI and bulk Si. The samples
annealed for 70s appear to show a similar level of regrowth between bulk Si and SOI.
However for both samples the a/c interface is at a depth where there is a high As
concentration and hence the regrowth rate is very slow. The bulk sample has regrown
by an extra 2nm compared to the SOI sample. With the regrowth rate so low in this area
this is a significant difference in depth. Indeed the depth of the a/c interface of the bulk
Si sample annealed for 70s is close to the depth of the SOI sample annealed for 200s.
6.4.4 Discussion
Before the regrowth mechanisms can be considered it is important to discuss the
detail of the a/c interfaces. In Figure 6.28a) and b) are 2D schematic illustrations
showing entirely different possible damage scenarios. In these illustrations black
represents fully amorphous Si and white represents fully crystalline Si. Different levels
of shading of grey represent different levels of damage between amorphous and
crystalline. The right hand side of each illustration represents the surface. The
approximate shape of the idealised MEIS profile (ignoring energy straggling and system
resolution convolution) is given underneath each image. Figure 6.28a) illustrates a
situation where there is a gradual transition from the crystalline region with increasing
damage until an amorphous layer is reached. In Figure 6.28b) a sharp wavy interface
between fully crystalline and fully amorphous Si is presented. Both scenarios would
produce a similar shape in a MEIS profile, hence MEIS alone cannot distinguish
between them.
To determine the profile XTEM was carried out on the 60 nm SOI sample, preamorphised,
implanted with 3keV As to 1E15 cm -2 , and annealed at 550 °C for 600s
(MEIS result Figure 6.25a)). The result is shown in Figure 6.29. It shows that the a/c
interface is indeed wavy in an irregular fashion, over a depth range of ~ 14 nm. This in
excellent agreement with the depth range of the a/c interface from MEIS results.
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