Method of making insulator for electrical structures

摘要

Structures and methods are disclosed for insulating a polysilicon gate adjacent to an electrically active region with a silicon base layer. A layer of silicon nitride having a thickness in a range from about 100 Å to about 150 Å is conformally deposited over the polysilicon gate. A layer of silicon dioxide is formed over the layer of silicon nitride on the polysilicon gate. The layer of silicon dioxide is subjected to a spacer etch to form spacers upon the layer of silicon nitride and on lateral sidewalls of the polysilicon gate. A portion of the layer of silicon nitride situated between the polysilicon gate and the spacer is removed by an etching process that is selective to silicon dioxide and to polysilicon. The etch forms a recess defined between the polysilicon gate and each respective spacer. A cover layer is formed to close an opening to the recess so as to enclose a void therein. Alternatively, the etch can be a series of selective etches that extends the recess into the silicon base layer, after which the silicon base layer is implanted so that the recess isolates electrically active areas in the silicon base layer. A void is then enclosed below the opening to the recess within the silicon base layer by a cover layer deposited non-conformally thereover.