Patent ID: 7015115

Claim:
A method for forming a deep trench isolation region in a substrate, said method comprising steps of: forming a layer of nitride over said substrate and over a first field oxide region in said substrate; forming a hard mask over said layer of nitride; forming a trench in said first field oxide region and said substrate, said trench defining first and second sidewall in said substrate, said forming said trench causing first and second field oxide portions to be formed adjacent to said first and second sidewalls of said trench, respectively; removing said hard mask after said forming said trench; thermally growing an oxide liner on said first and second sidewalls of said trench after said removing said hard mask; conformally depositing a layer of polysilicon on said layer of nitride and in said trench, said layer of polysilicon filling said trench; forming a continuous second field oxide region directly above said trench by growing oxide inside said trench to merge said first and second field oxide portions; wherein substantially no lateral etching occurs in said first and second field oxide portions prior to said thermally growing said oxide liner; and wherein a substantially flat topography is achieved over said deep trench isolation region.