REDUCTION OF BORON PENETRATION FOR A P(-DIFFUSION SOURCE() POLYCIDE GATE BY USING COBALT SILICIDES AS A BORON)

A scheme for forming a p(+) polycide gate is described, by using BF2 i mplantation into CoSi/poly-Si bilayer films and subsequent annealing. Instead of the conventional BF2 implantation into thin poly-Si films, this scheme employs the CoSi layer as an implant barrier as well as a boron diffusion source to retard the boron diffusion. The improved gat e oxide integrity and the reduced flat-band voltage shift can be obtai ned without causing other side effects. In addition, it is found that the stack layer of CoSi/a-Si can serve as an excellent implant barrier for suppressing the boron penetration through a gate oxide. (C) 1998 Elsevier Science Ltd. All rights reserved.