Patent ID: 6054368
Filing Date: 2000-04-25
Classification: H01L

Abstract:
A method of forming modified field oxide isolation regions on the surface of a silicon substrate with increased threshold voltages and reduced leakage currents, comprising the steps of:forming a silicon oxide layer on said surface of said silicon substrate thereby forming a pad oxide layer;depositing a silicon nitride layer on said pad oxide layer thereby providing an oxidation barrier layer;patterning said silicon nitride layer and said pad oxide layer and leaving portions over device areas while providing openings in said silicon nitride layer that surround said device areas where said field oxide isolation regions are required;thermally oxidizing said silicon substrate in said openings while said silicon nitride layer prevents oxidation of said device areas thereby forming field oxides having thinner portions on the perimeter of said field oxides extending under said silicon nitride layer;removing said silicon nitride layer and said pad oxide layer by wet etching;forming a sacrificial oxide layer by thermal oxidation in said openings on said silicon substrate and removing said sacrificial oxide layer by wet etching;depositing a conformal insulating layer on said substrate having said field oxides;anisotropically plasma etching back said insulating layer to said substrate leaving sidewall portions of said insulating layer on said thinner portions of said field oxides thereby modifying the shape of said field oxides;forming a thermal oxide implant layer on said device areas;forming a well photoresist implant mask and forming in said device areas doped wells by ion implantation;implanting channel-stop implant regions through said field oxides and through said sidewall portions of said insulating layer, said sidewall portions of said insulating layer changing the profile of said channel-stop implant regions in said substrate;forming deep implant regions in said substrate by ion implantation;removing said well photoresist implant mask, and thereby completing said field oxide isolation regions having said increased threshold voltages and said reduced leakage currents.