Method for producing recessed field oxide with improved sidewall characteristics

A method for producing field isolation regions for a silicon-based semicondutor substrate comprising:

• forming four-layer blocking structures over field regions of said substrate by:
• forming a first insulation layer of a silicon oxide over a surface of said substrate;
• forming a first inhibiting layer of a silicon nitride over said first insulation layer;
• forming a second insulation layer of a silicon oxide over said first inhibiting layer, said second insulation layer being thicker than said first insulation layer;
• forming a second inhibiting layer of a silicon nitride over said second insulation layer, said second inhibiting layer being thicker than said first inhibiting layer;
• patterning said first insulation layer, said first inhibiting layer, said second insulation layer, and said second inhibiting layer such that portions of said substrate surface where said isolation regions are to be formed become uncovered, and such that remaining portions of said substrate surface are covered by four layer insulation/inhibiting/insulation/inhibiting blocking structures;
• and
• forming field isolation regions at portions of said surface of said substrate which are not covered by said blocking structures.