NITROGEN IMPLANTATION USING A SHADOW EFFECT TO CONTROL GATE OXIDE THICKNESS IN STI DRAM SEMICONDUCTORS

摘要

Process for forming dual gate oxides for DRAM systems by using a "shadow effect" to control gate oxide thickness at active area corners adjacent a STI region, comprising: - forming the active area by depositing over a semiconductor substrate a patterned nitride layer exposing portions of the substrate to define an isolation region and a capacitor region within the isolation region - etching exposed regions of substrate using patterned nitride layer to form isolation and capacitor trenches -depositing an oxide layer over a thermal oxide layer to fill unfilled portions of isolation trench and capacitor trench - affecting masking so that nitrogen ions N2+ to be implanted do not penetrate masked region and - causing nitrogen ion implantation by a "shadow effect" inducing means to provide lesser amounts of nitrogen ion dosage in inner part of active area adjacent the STI oxide than in remaining non-shadowed active area, to provide increased thickness gate oxide at the active area corners.