Excimer laser annealing of ion-implanted silicon

Abstract

We have studied pulsed excimer laser (xenon chloride, wavelength 0.308 μm) annealing of boron, arsenic, and self-ion-implanted silicon specimens that contained dislocation loops and/or amorphous layers. Microstructural changes as a function of laser parameters were investigated by cross-section transmission electron microscopy and concomitant changes in dopant profiles were monitored by Rutherford backscattering spectroscopy. The depth of the annealed or melted regions was found to increase linearly with pulse energy density and inversely with pulse duration. While dopant redistribution can provide information on total melt-life time and depth of melting, a gross underestimate of depth of melting in amorphous layers may be obtained, particularly near the threshold, if the dopant redistribution is less than 100 Å. We found that transmission electron microscopy techniques were more reliable for accurate determination of melt depths. A minimum thickness of defect-free annealed or melted region of 400 Å was achieved in the case of boron-implanted specimens. A maximum depth of melting up to 1 μ in these specimens could be achieved by 2.5 J cm−2 (25 ns) pulses. The quality of excimer laser annealing in terms of residual point defects and spatial inhomogeneity was found to be better than that achieved by pulsed ruby laser annealing.