CO2 laser annealing of silicon

Publisher Website
Google Scholar
Abstract
Boron doped silicon crystals, amorphized by 15N or 121Sb‐ion implantation, were annealed with 100‐ns CO2 laser pulses. 4He‐ion backscattering and channeling spectra, and sychrotron x‐ray topographs of heavily doped (1019...1020 atoms/cm3) samples show an almost complete recrystallization at peak intensities of about 40 MW/cm2, caused at 10.6 μm mainly by free carrier absorption. At intensities of about 20–35 MW/cm2, a rapid increase of the reflectivity to almost 100% at 10.6 μm, and a corresponding decrease in the transmitted intensity was observed. Time resolved transmission and reflection measurements at 10.6 μm and reflection measurements at 0.6.3 μm revealed that a liquid layer was formed at the surface of the crystal. Samples doped with 5×1015 and 3×1016 atoms/cm3 were not fully recrystallized. To estimate the annealing threshold at different doping levels, the maximum surface temperature of the sample was calculated as a function of the laser intensity. The calculations are in agreement with the observations. According to ( p,γ) measurements, some nitrogen segregates to the surface or moves out of the sample. Damage produced on the doped bulk silicon by a CO2 laser pulse at intensities of 20...100 MW/cm2 is also shown.