Two-dimensional delineation of ultrashallow junctions obtained by ion implantation and excimer laser annealing

Junctions shallower than 100 nm, obtained by ion implantation and excimer l aser annealing, have been characterized in two dimensions by transmission e lectron microscopy (TEM) on chemically treated samples. The chemical treatm ent selectively removes silicon as a function of the B concentration, makin g thinner the regions where B is present in the cross section of the sample , with respect to the n-type substrate. Both secondary ion mass spectrometr y and spreading resistance profiling measurements have been performed, in o rder to quantify the contour line obtained by TEM in terms of B concentrati on. The results achieved by the two-dimensional technique show interesting features, related to the particular redistribution of B occurring when sili con is melted by excimer laser annealing irradiation. In particular, a rect angular shape of the doped region obtained by laser annealing could be evid enced, caused by the fast diffusion in the melted material, completely diff erent from the typical half-moon-shaped, thermally annealed, two-dimensiona l B profile. The feasibility of ultrashallow junctions by laser annealing, with depths below 100 nm and high electrical activation, is demonstrated. H owever, a huge lateral diffusion in the melted silicon is also to be taken into account when considering excimer laser treatments as an alternative to standard rapid thermal annealing. (C) 2000 American Institute of Physics. [S0003-6951(00)02230-0].