Bird's beak profile of field oxide region

A method, comprising:

• forming an oxide layer on a semiconductor substrate;
• forming a patterned mask layer on the oxide layer, wherein part of the oxide layer is removed as a result of forming the patterned mask layer, a ratio of a thickness of the patterned mask layer to a thickness of a remaining portion of the oxide layer being greater than 5 and less than 25;
• forming a field oxide region based on a thermal oxidation process performed through the remaining portion of the oxide layer, wherein the field oxide region is formed through an opening in the patterned mask layer that exposes the remaining portion of the oxide layer;
• removing the oxide layer and the patterned mask layer after forming the field oxide region;
• and
• forming a dielectric oxide layer over the semiconductor substrate, the field oxide region being connected to the dielectric oxide layer through a bird's beak region.

A method, comprising:

• forming a silicon oxide layer on a silicon substrate;
• forming a patterned silicon nitride layer on the silicon oxide layer, wherein part of the silicon oxide layer is removed as a result of forming the patterned silicon nitride layer, a ratio of a thickness of the patterned silicon nitride layer to a thickness of a remaining portion of the silicon oxide layer being greater than 5 and less than 25;
• forming a field oxide region based on a thermal oxidation process performed through the remaining portion of the silicon oxide layer, wherein the field oxide region is formed through an opening in the patterned silicon nitride layer that exposes the remaining portion of the silicon oxide layer;
• removing the silicon oxide layer and the patterned silicon nitride layer after forming the field oxide region;
• and
• forming a dielectric oxide layer over the silicon substrate, the field oxide region being connected to the dielectric oxide layer through a bird's beak region.