Forming different depth trenches simultaneously by microloading effect

Abstract

A new method of forming simultaneously both shallow and deep trenches is described. A pad oxide layer is provided over a semiconductor substrate. A silicon nitride layer is deposited overlying the pad oxide layer. A silicon dioxide layer is deposited overlying the silicon nitride layer. A photoresist mask is formed over the silicon dioxide layer wherein the photoresist mask has a first opening having a first width and a second opening having a second width and wherein the second width is larger than the first width. Trench openings are etched through the silicon dioxide, silicon nitride, and pad oxide layers to the underlying semiconductor substrate within the first and second openings. The photoresist mask is removed. The substrate is etched into through the trench openings to form first and second trenches wherein the first trench within the first opening having the first width is a shallow trench having a first depth and wherein the second trench within the second opening having the second width is a deep trench having a second depth greater than the first depth completing the formation of shallow and deep trenches simultaneously in the fabrication of an integrated circuit.