Threshold Energy Density for Pulsed Laser Annealing of Silicon
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THRESHOLD ENERGY DENSITY FOR PULSED LASER ANNEALING OF SILICON
DICK HOONHOUT AND FRANS SARIS FOM-Institute for Atomic and Molecular Physics, 1098 SJ Amsterdam, The Netherlands
Kruislaan 407,
ABSTRACT We have made a systematic investigation of the threshold energy density for recrystallization of ion-implanted silicon by Q-switched laser irradiation as function of thickness of the disordered layer, temperature during implantation, type and dose of implanted impurity, laser wavelength, and substrate orientation. Most results have been obtained with a Q-switched ruby laser. A linear dependence of the threshold on layer thickness (in the region of 60-300 nm) was found for arsneic-implanted silicon, but not for silicon-implanted silicon. For an amorphous layer thickness of 200 nm we found very little dependence of the threshold on type of dopant. In the case of the Nd:YAG laser, however, the lowest threshold was observed for column VI elements, the highest for column IV elements and intermediate and equal thresholds for the elements from column III and B. The influence of temperature during implantation was found to be small, but the threshold appeared to be different for (100)- and (111)oriented substrates.
INTRODUCTION With the intention to gain more insight in the physical processes involved in pulsed laser annealing, we have made a systematic investigation of the influence of various parameters on the effects of pulsed-laser irradiation of ion-implanted silicon. The parameters varied were laser energy density, thickness of the disordered layer, type and dose of the implanted dopant, wavelength of the laser-light and surface orientation of the substrate. The type and dose of the implanted impurity and the wavelength of the laser were varied in order to get information on the absorption of the laserlight. Different substrate orientation and thicknesses of the amorphous layer were compared to test the simple thermal melting model, starting from the notion that the energy needed to melt a specific layer should be proportional to the amorphous layer thickness and independent of substrate orientation. Here we can only give a brief A full description account of this work drawing attention to some anomalies. 1 and discussion is presented elsewhere .
EXPERIMENTAL Silicon wafers of 2 inch diameter with a resistivity of 1-10 0 cm were used. In all cases, except in one series of experiments (section- Influence of Substrate Orientation), the surface normal was along of (100) direction. All crystals were implanted, elements used were: Ga, In, Si, Ge, Sn, As, Sb, Bi, Se and Te. Implantation energies varied from 35 keV to 340 keV leading to amorphous-layer thicknesses of 60-300 nm, whereas implanted doses were between 16 2 1.1015 and 2.3x10 ions/cm .
32 The implanted samples were cut into smaller pieces. Every piece was annealed with a single shot from a Q-switched ruby laser, having a maximum output of 10 J over a 16 mm diameter spot with a pulse width at half maximum of 20-25 ns. The laser output was monitored by a pho
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