Silicided mos transistor

Abstract

A process for forming N-channel MOS sources and drains, by implanting both phosphorus and arsenic. The high diffusivity of phosphorus causes it to diffuse in advance of the bulk of the arsenic, so that, after annealing, the source/drain regions have graded regions of gradually decreasing conductivity adjacent to the end of the channels. Thus the electric potential gradient at the ends of the channels is reduced, and impact ionization and hot carrier effects are avoided. The effective radius of the source (or drain) junction is increased, providing increased breakdown voltage. The implantation of both phosphorus and arsenic with the resultant phosphorus peripheral band after annealing is used with self-aligned silicided source/drain regions to prevent silicide spiking through shallow arsenic regions to the P substrate and to prevent source/drain junction consumption during silicidation.