High Current Density Implantation and Ion Beam Annealing in Si
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HIGH CURRENT DENSITY IMPLANTATION AND ION BEAM ANNEALING IN Si*
0. W. HOLLAND AND J. NARAYAN Solid State Division, Oak Ridge National Laboratory,
Oak Ridge,
TN 37831
ABSTRACT Annealing of amorphous layers in Si by high flux, selfion irradiation will be discussed. The mechanism for the lattice recovery is presented and related to the structure of the residual damage. It will be shown that highly supersaturated, alloyed regions, free from extended defects, result from the annealing process.
The characteristics of high flux implantation in Si will be presented including a study of 'dynamic annealing'; a process whereby a high dose rate beam self-anneals its own displacement damage; and annealing of preexisting amorphous layers on crystal substrates by high flux irradiation. The mechanism for lattice recovery during ion bombardment and its relation to the morphology of the residual damage will be discussed. Various aspects of ion beam annealing (IBA) of Si were investigated including metastable phase formation and solid solubility under irradiation. One motivation for this study was to determine if new metastable materials or more highly supersaturated alloys could be produced by IBA; materials which cannot be formed by more conventional techniques such as furnace processing [1,2] or various transient thermal techniques including RTA [3] (rapid thermal annealing) and cw laser annealing [4,5]. The crystals were analyzed after implantation by ion channeling techniques using a 2.5 MV Van de Graaff accelerator. The channeling technique not only gives the depth distribution of the damage in the crystal but also the lattice location and distribution of the implanted dopant. Selected samples were also viewed in cross-section by transmission electron microscopy to determine the detail structure of the residual damage. Shown in Fig. 1 are channeling spectra from single crystal Si(100) 2 28 samples which were irradiated with a 100 pamp/cm , Si (self-ion) beam at two different fluences. By comparison with the random spectrum in the 16 2 figure, it can clearly be seen that at a fluence of 0.375 x 10 Si/cm , a buried amorphous layer has formed as a result of the displacement damage produced by the incident ions. The rapid change in the scattered yield at the location of the crystal-amorphous interface on both sides of this buried layer indicates that the transition between the phases is sharp and 2 the interface is planar. At an increased fluence of 0.75 x 1016 Si/cm , there is no evidence of an amorphous layer at any depth as seen in the aligned spectrum from this sample. It is clear that at this fluence a significant amount of the lattice damage has been dynamically annealed. The minimum yield (which is the ratio of the aligned to random yield) is 2.8% just behind the surface peak which is comparable to that of a virgin (nonimplanted) crystal. There are however, two distinct damage regions in this sample which can be identified in the aligned spectrum by an increase in the scattered ion yield. The damage peak centered at 290
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