Scaling of lateral device dimensions into the submicron range also requires the reduction of the vertical dimensions. Shallow ion implantation is necessary for channel formation of submicron MESFET's. Partial-ion-channeling tails were found for energies below 60 keV, and resulted in a significantly broader profile than predicted by LSS theory. Diffusion effects are investigated by comparing SIMS profiles from as-implanted, rapid thermal and furnace-annealed samples. Comparison of the CV and SIMS profiles gives information on the annealing behavior, and allows the definition of a differential activation efficiency. Our investigations showed that for vertical scaling, a simple reduction of implant energy is not enough. We found several procedures which yield shallower profiles. © 1987 Elsevier Science Publishers B.V.