Dopant redistribution by pulsed-laser annealing of ion-implanted silicon

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Abstract
The redistribution of impurity atoms implanted in Si(100) caused by Q-switched ruby-laser annealing has been studied using 2 MeV He+-backscattering plus channeling. The elements implanted were Ga, In, Ge, Sn, As, Sb, Bi, Se, Te and Kr, the projected range and the implanted dose being the same in all cases but Kr. It is found that as a result of the laser-pulse the depth profile of the impurity has broadened, while in the case of Ga, Sn, Bi and Kr we also observe a more or less pronounced surface accumulation. Channeling experiments indicate that, except for In, a considerable fraction of the impurity atoms is on or close to substitutional positions, which corresponds to concentrations which in some cases exceed the solid solubility by orders of magnitude. A computer model of solute diffusion and segregation at a moving phase boundary is described. Fitting the measured impurity redistribution with this model results in interfacial distribution coefficients exceeding values for equilibrium freezing, in some cases by orders of magnitude. The extent to which these findings provide evidence for a strictly thermal melting model based on transient melting and freezing of a surface layer is discussed.