Deep Diffusion of Phosphorus in Silicon using Microsecond-pulsed Laser Doping

Deep diffusion of phosphorus atoms in monocrystalline silicon using laser doping process has been studied in this work. A pulse modulated CW fiber laser of wavelength 1070 nm with microsecond pulses has been used to diffuse phosphorus from pre-deposited spin-on-dopant film. The surface and cross-sectional morphology has been studied using SEM and AFM. The concentration-depth profiling was done using PP-TOFMS. Deep junctions of more than 10 µm have been obtained under various laser doping conditions while a maximum junction depth of 51.3 µm has been obtained through optimization. Diffusion depth enhancement is made possible by increasing the pulse length and reducing laser scan speed. Laser doping led to formation of n+ region with surface concentration varying in the range of 3×1020-5×1020 cm−3 for varying scan speed. Cross-sectional TEM and diffraction studies on laser irradiated samples show presence of only monocrystalline silicon phase after laser induced melting and solidification.