Locos technology with narrow silicon trench

Abstract

A new method of local oxidation by means of stress-releasing narrow trenches is described. Pad silicon oxide, silicon nitride, and silicon dioxide layers are formed on a silicon substrate. Portions of these layers not covered by a mask are etched away to provide an opening to the silicon substrate where the field oxidation region is to be formed. The silicon substrate is etched into where it is exposed to form a shallow trench within the opening. Silicon dioxide spacers and silicon nitride spacers are formed on the sidewalls of the opening. The silicon substrate is coated with a spin-on-glass layer. The spin-on-glass layer is cured, then etched back so that the spin-on-glass layer remains only within the shallow trench not covered by the spacers. The silicon nitride spacers are stripped away. Narrow trenches are etched into the silicon substrate under the silicon nitride spacers. The silicon dioxide spacers and spin-on-glass layer are removed leaving the opening entirely exposed. Channel-stops are selectively ion implanted through the opening into the substrate underneath the trenches. The silicon substrate is oxidized within the opening wherein the silicon substrate is transformed to silicon dioxide and wherein the silicon dioxide expands to fill the narrow trenches. The narrow trenches act to relieve stress within the silicon substrate. The silicon dioxide expands vertically to provide a fully recessed surface of the field oxidation region.