The in situ, at-temperature, real-time monitoring of
open-volume defect formation, migration, coalescence and
annealing has long been possible in bulk solids by measuring
the Doppler broadening of annihilation radiation arising from
the implantation of energetic positrons from a radioactive
source. However, equivalent measurements on vacancy-type
defects in thin films or within ~102 nm of a solid
surface have not been made, principally because of the
distorting influence on the data of surface annihilations. This
paper describes the first measurements known to the authors of
in situ, at-temperature annealing studies of
near-surface open-volume defects, using as an example a silicon
sample implanted with 50 keV Si+ ions. The technique
involves the measurement of the fraction of controllable-energy
positrons which diffuse back to the surface and there form
positronium. The applicability and limitations of this method
are discussed.
Positron annihilation spectroscopy has been used to profile the distribution of defects following implantation of 120keV Ge÷ into (100) Si in the dose range lxlO1 0 -lxl10 4 cm 2 . The openvolume defect profiles can be adequately fitted assuming a simple rectangular block distribution extending to 350nm. Using anodic oxidation and etching, a procedure is described which allows details of the defect tails beyond the range of the implanted ion, usually inaccessible to positron -2 annihilation measurements, to be determined. For a time averaged dose-rate (Jr) of 0.02gtA cm and incident angle of 70, open-volume defects are found to exist at concentrations exceeding 101 6 cm-3 at depths upto 600nm whereas the peak of the depth distribution of the implanted ions (Rp) is 76nm, measured using SIMS. When the time-average dose-rate is increased by a factor of 10, defects persist at concentrations in excess of 101 7 cm-3 beyond l4tm and the Rp increases to 101rnm. The open-volume defect profiles are compared to those deduced from Rutherford backscattering-channeling using the fitting routine DICADA.
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