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

Figure 3.4 Structure of crystalline Si (left) showing the 6 ring structure and amorphous
Si (right) where the 5 and 7 ring structure is visible. From (4)
3.2.2.2 Ion implantation amorphisation
Ion implantation of Si can produce amorphous Si layers or a damaged but
essentially still crystalline structure depending on implantation conditions (4). For
transistor device production there are distinct advantages for using implants that
amorphise the Si therefore the focus of this thesis is on amorphising implants. The
reasons for amorphising the Si will be discussed in some detail throughout this thesis
but as a brief summary the main reasons are the production of higher quality defect free
regrown layers compared to the regrowth of highly damaged layers. The junction depth
can be spatially separated from the end of range, and channelling of the ions can be
suppressed. The experiments carried out in this thesis on the whole use amorphised Si
or are concerned with the formation of a continuous amorphous layer.
Amorphous Si layers can also be produced by deposition, e.g. chemical vapour
deposition (CVD) or using low energy ion beams. However deposited amorphous Si
layers are less well characterised and with less reproducible characteristics than ion
implanted amorphous Si (17).
3.2.2.3 Collision Cascades, produced by single heavy and light ions
When an ion is implanted into Si it will probably undergo a hard collision with
an atom near the surface. Energy will be transferred in the collision as described in
chapter 2 (18). It is likely that the energy transferred will exceed the displacement
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