Method for poly-buffered locos without pitting formation

A method for forming isolation regions on a semiconductor substrate, said method comprising the steps of:

• forming a first pad oxide layer on said semiconductor substrate;
• forming a silicon layer on said first pad oxide layer;
• performing a first oxidation to convert said silicon layer into polysilicon layer and grow a second pad oxide layer on the surface of said polysilicon layer;
• forming a silicon nitride layer on said second pad oxide layer;
• patterning said silicon nitride layer to define active regions on said semiconductor substrate, thereby exposing portions of said second oxide layer which defines said isolation region;
• and
• performing a second oxidation to form isolation oxide regions on said semiconductor substrate by using said patterned silicon nitride layer as an oxidation mask, wherein portions of said silicon layer and said semiconductor substrate exposed by said patterned silicon nitride layer are oxidized with oxygen passing through portions of said second pad oxide layer and said first pad oxide layer exposed by said patterned silicon nitride layer.

A method for forming isolation regions on a semiconductor substrate, said method comprising the steps of:

• forming a first pad oxide layer on said semiconductor substrate;
• forming a silicon layer on said first pad oxide layer;
• forming a second pad oxide layer on the surface of said silicon layer;
• forming a silicon nitride layer on said second pad oxide layer;
• patterning said silicon nitride layer, said second pad oxide layer, said silicon layer and said first pad oxide layer to define active regions on said semiconductor substrate by exposing said isolation regions;
• and
• performing an oxidation to form isolation oxide regions on said isolation regions of said semiconductor substrate.