Silicon nitride and silicon dioxide gate insulator transistors and method of forming same in a hybrid integrated circuit

Abstract

Silicon nitride gate insulators for digital transistors and silicon dioxide gate insulators for analog transistors of a hybrid integrated circuit (IC) are formed in a single integrated fabrication process. A first area of a silicon substrate of the IC is exposed while a second area is initially covered by a silicon dioxide layer. A layer of silicon nitride is formed on the exposed first area while the initial silicon dioxide layer inhibits the formation of silicon nitride on the second area. Thereafter the initial silicon dioxide layer is removed from the second area to allow a new silicon dioxide layer to be formed there from the exposed silicon substrate. The silicon dioxide layer shields against the adverse influences from silicon nitride formation and permits the initial silicon dioxide layer to be removed by etching. The silicon nitride layer shields against the adverse influences of oxidizing new silicon dioxide layer. A slight, beneficial silicon dioxide interface is created between the silicon nitride and the silicon substrate as a result of oxidizing the new layer of silicon dioxide.