A new method for making shallow p-type junctions

We present a new method for making shallow p-type junctions in silicon by molecular ion implantation. Unlike current molecular ion implantation methods which use BF/sub 2/ molecules, this new method uses BSi/sub x/, where the silicon is completely miscible in silicon. Note that fluorine is an element that saturates at a very low concentration in silicon. The compounds used in this new method are boron silicides and boron germanium molecules. These compounds have several distinct advantages including the fact that the co-element silicon (or germanium) has a very high saturation value in the silicon matrix, the co-element is massive and therefore creates more damage during implantation, and the co-element has a larger projected range than the boron. Note that the R/sub p/ for fluorine is shallower than that of boron for a BF/sub 2/ implant. Recent experiments indicate that BSi/sub x/ ion beams can be generated in a sputter ion source with efficiencies of 0.5% with respect to the generated Si beam. A plan to develop a new ion source that is compatible with current ion implantation systems is presented.