Method of reducing silicon oxynitride gate insulator thickness in some transistors of a hybrid integrated circuit to obtain increased differential in gate insulator thickness with other transistors of the hybrid circuit

Abstract

A relatively thin gate insulator of a digital switching transistor is formed from a layer of silicon oxynitride which was initially formed by implanting nitrogen atoms in a silicon substrate and oxidizing the nitrogen and silicon. It has been discovered that an outer layer of silicon dioxide is formed as a part of the silicon oxynitride layer. Removing this outer layer of silicon dioxide from the silicon oxynitride layer leaves a thin remaining layer of substantially-only silicon oxynitride as the gate insulator. Thinner gate insulators of approximately 15-21 angstroms, for example, can be formed from a grown thickness of 60 angstroms, for example. Gate insulators for digital and analog transistors may be formed simultaneously with a greater differential in thickness been possible by using conventional nitrogen implantation techniques.