Multiple-thickness gate oxide formed by oxygen implantation

摘要

A process for forming gate oxides of multiple thicknesses. Oxygen is implanted through a sacrificial oxide into selected regions of a silicon substrate according to a patterned photoresist mask. After stripping the sacrificial oxide, a thermal growth process produces a thicker oxide in the implanted regions than in the non-implanted regions. The oxygen-implanted oxide has excellent quality and thickness differentials of up to 20 Å may be obtained with relatively low oxygen implant doses. In an alternative process, a thin gate oxide may be grown prior to a polysilicon layer deposition, and oxygen is then implanted through the polysilicon according to a patterned photoresist mask. After stripping the photoresist, an anneal increases the thickness of the gate oxide in the implanted regions. In another embodiment, a high dielectric constant dielectric layer is deposited on the substrate prior to polysilicon deposition to limit subsequent silicon oxide growth.