Process for forming field isolation structure with minimized encroachment effect

A process for forming isolation regions on a semiconductor substrate, the process comprising:

• forming a polysilicon layer on a laminate comprising a substrate having thereon a pad oxide;
• forming a first silicon oxide layer on the polysilicon layer;
• defining isolation regions by forming a photo-resist mask over the first silicon oxide layer;
• removing unmasked portions of the first silicon oxide layer and the polysilicon layer;
• forming a second silicon oxide layer over the first silicon oxide layer;
• etching anisotropically the second silicon oxide layer to form spacers on the side walls of the polysilicon layer and the first silicon oxide layer;
• forming a silicon nitride layer above the spacers and the first silicon oxide layer;
• chemical-mechanical polishing (CMP) until the polysilicon layer is exposed, thereby planarizing the polysilicon layer, the spacer and the silicon nitride layer;
• removing the polysilicon layer;
• implanting ions of a first type into the substrate, wherein the planarized spacer and the silicon nitride layer serving as an implant mask;
• removing the spacers;
• and
• oxidation so as to form the isolation regions.

A process for forming isolation regions on a semiconductor substrate, the process comprising:

• forming a second polysilicon layer on a laminate comprising a substrate having thereon a pad oxide, a first polysilicon layer on the pad oxide and a first silicon nitride layer on the first polysilicon layer;
• forming a first silicon oxide layer on the second polysilicon layer;
• defining isolation regions by forming a photo-resist mask over the first silicon oxide layer;
• removing unmasked portions of the first silicon oxide layer and the second polysilicon layer;
• forming a second silicon oxide layer over the first silicon oxide layer;
• etching anisotropically the second silicon oxide layer to form spacers on the side walls of the second polysilicon layer and the first silicon oxide layer;
• forming a second silicon nitride layer above the spacers, the first silicon oxide layer and the first silicon nitride layer;
• chemical-mechanical polishing (CMP) until the second polysilicon layer is exposed thereby planarizing the spacers, the second polysilicon layer and the second silicon nitride layer;
• etching anisotropically the second polysilicon layer, the first silicon nitride layer and the first polysilicon layer;
• implanting ions of a first type into the substrate, wherein the spacers and the second silicon nitride serving as an implant mask;
• removing the spacers;
• etching anisotropically portions of the first silicon nitride layer and the polysilicon layer, wherein the second silicon nitride layer serving as a mask;
• removing the second silicon nitride layer;
• and
• oxidation so as to form the isolation regions.