Desorption and diffusion at pulsed-laser-melted surfaces: The case of chlorine on silicon

The kinetics of thermal desorption from an excimer-laser-melted surface, on which diffusion into the bulk competes with desorption, is numerically evaluated and compared with a variety of experimental data for the case of CI on Si: Auger electron spectroscopy, time-of-flight mass spectrometry, secondary-ion-mass spectrometry, and transient reflectivity. The model calculations involve nonequilibrium thermal diffusion, phase transition, segregation, and first- and second-order desorption kinetics. With the assumption that the preexponential factors of the desorption rates do not change on the liquid surface with respect to the solid one, activation desorption energies are found lower by approximate to 0.5 eV for the liquid surface than for the Si(100):Cl solid surface. This difference is of the order of magnitude of the latent heat of melting. The segregation coefficient of Cl at the liquid-solid interface is <0.02 at a recrystallization speed of approximate to 6 m/s. The calculations also bring information on the dynamics of desorption and melting. The desorption rate from the liquid reaches the large value of approximate to 1 ML/ns. However, the surface is depleted from Cl atoms by both desorption and diffusion in a fraction of nanosecond (allowing only approximate to 60% of the Cl to desorb). Multipulse experiments are also calculated. After only three laser pulses, only the level of CI contamination (not the shape of the CI depth profile) varies with laser count. The laser cleaning rate follows the laser-pulse count with a logarithmic law. It takes about five laser pulses to decrease the Cl contamination by one order of magnitude.