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

damage evolution behaviour observed is strongly influenced by, on the one hand, the
proximity of the surface, that acts as a nucleation centre for a fraction of the interstitials
produced along the collision cascade and on the other by the operation of dynamic
annealing effects even at room temperature. These cause a substantial reduction in the
disorder at depths where the interstitial and vacancy distributions, which for low
energies are closely overlapping, have their maxima.
The work reported here consists of a detailed MEIS study of the mode of
damage evolution as a function of implant dose and its correlation with dopant
movement for 2.5 keV As and 2 keV Sb ions implanted into Si at room temperature to
doses from a few times 10 13 cm -2 upwards.
It will be seen that for both As and Sb ion implantation, the energy deposition
rate is sufficiently high for the Si matrix to become amorphised at room temperature for
doses above 10 14 cm -2 . This study exploits the ability of MEIS to provide quantitative
information on either the As or Sb implants and the Si damage depth distributions.
MEIS shows the operation at room temperature of a damage accumulation process for
low doses that is explained in terms of interstitial trapping at pre-existing nucleation
sites formed by the oxide / Si crystal interface and the planar growth of the amorphous
layer from the surface inwards into the bulk through the accumulation of point defects
produced in the collision cascade. In particular, this work shows a novel dopant
movement correlated to the growth of the amorphous layer that is driven by differences
in the energetics of accommodation of these heavy ions in damaged crystalline and
amorphous Si.
5.2 Experimental
Implants of 2.5 keV As ions into Cz, p-type Si (100) samples of resistivity 10 –
20 Ω cm were performed under UHV conditions using the ultra-low energy ion
implanter at Salford (21). Sb implants at 2 keV, were carried out in p-type (100) Si
wafers of resistivity of 2– 10 Ω.cm at Applied Materials. In all cases the targets were
held at room temperature and all implants were performed through the native oxide.
The MEIS studies reported were carried out using a nominally 200 keV He ion
beam and the double alignment configuration, in which the [ 1 1 1]
channelling direction
was combined with the [332] and [111] blocking directions. Using a 200 keV He beam,
sufficient separation of the dopant and Si peaks could be obtained for the [332] blocking
direction. Results from the [332] direction only are presented here. The overall depth
resolution obtained for these conditions was better than 0.7 nm (20). Energy spectra
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