Semiconductor gate conductor with a substantially uniform doping profile having minimal susceptibility to dopant penetration into the underlying gate dielectric

摘要

A semiconductor fabrication process is presented which optimizes the position of impurities within a gate conductor a the source/drain straddling the gate conductor. Optimal positioned is achieved by using separate implants of different energies depending upon whether the gate conductor connotes a PMOS or NMOS transistor. A layer of polysilicon used to form the gate conductor is doped before patterning so that the source and drain regions are protected. A low energy implant is performed when implanting a fast diffuser such as boron, and a high energy implant is performed when implanting a slow diffuser like arsenic. This enables optimum positioning of the impurities throughout the gate conductor cross-section after heat cycles are applied. Fast diffusers are initially placed far from the bottom surface of the polysilicon, and diffuse near the bottom surface of the polysilicon when heat is applied. Slow diffusers are initially placed closer to the bottom surface of the polysilicon, since they do not diffuse as readily. The source and drain regions are implanted using a very low energy implant, separately from the polysilicon implants, to produce a desirable shallow source and drain region within the semiconductor substrate.