Nitrogen liner beneath transistor source/drain regions to retard dopant diffusion

Abstract

A nitrogen implanted region formed substantially below and substantially adjacent to a source/drain region of an IGFET forms a liner to retard the diffusion of the source/drain dopant atoms during a subsequent heat treatment operation such as an annealing step. The nitrogen liner may be formed by implantation of nitrogen to a given depth before the implantation of source/drain dopant to a lesser depth. Nitrogen may also be introduced into regions of the IGFET channel region beneath the gate electrode for retarding subsequent lateral diffusion of the source/drain dopant. Such nitrogen introduction may be accomplished using one or more angled implantation steps, or may be accomplished by annealing an implanted nitrogen layer formed using a perpendicular implant aligned to the gate electrode. The liner may be formed on the drain side of the IGFET or on both source and drain side, and may be formed under a lightly-doped region or under a heavily-doped region of the drain and/or source. Such a liner is particularly advantageous for boron-doped source/drain regions, and may be combined with N-channel IGFETs formed without such liners.