The electrical activation of B in Si following excimer laser annealing has been investigated with transmission electron microscopy (TEM) and spreading resistance profiling. Ultrashallow profiles, extending to a depth of 35 rim. have formed in Si following laser annealing. The lateral distribution of the implanted B following laser annealing has been studied with two-dimensional measurement.,, using selective etching and cross-sectional TEM on samples where the implanted dopant was confined within an oxide mask. The results show that there is substantial lateral diffusion of B under the oxide mask when melting occurs in this region. However it is shown in this article that the melting of the Si under the masked region can be controlled by the oxide thickness. Dopant diffusion into the bulk was observed after a combination of laser and rapid thermal annealing (RTA). The TEM results suggest that there is considerable lattice strain at the liquid-crystal interface after regrowth of the layer, which,vas subsequently removed following a RTA process step,