Control of locos structure thickness without a mask

A method of fabricating an integrated circuit (IC), comprising:

• determining a deposition thickness of a sacrificial layer to be formed over a semiconductor substrate having an oxygen diffusion barrier (ODB) layer located thereover, the ODB layer having first and second openings respectively having a first width and a greater second width that expose the semiconductor substrate, the determining being based on one or both of the first width and the second width;
• forming a first LOCOS structure under the first opening and a second LOCOS structure under the second opening;
• forming the sacrificial layer having the deposition thickness over the semiconductor substrate, the ODB layer and the first and second openings;
• and
• blanket etching the sacrificial layer, the deposition thickness being such that the first LOCOS structure is completely covered by a first remaining portion of the sacrificial layer after the blanket etching, and the second LOCOS structure is exposed between sidewall spacers located over the second LOCOS structure.

A method of forming an integrated circuit, the method comprising:

• selecting a polysilicon thickness of a polysilicon layer predetermined to result in a continuous first remaining portion of the polysilicon layer remaining in a first opening having a first width in a first oxygen diffusion barrier (ODB) layer over a silicon substrate after removing the polysilicon layer over the first ODB layer;
• selecting a second width based on the polysilicon thickness, the second width predetermined to result in a space between second remaining portions of the polysilicon layer in a second opening having the second width in the first ODB layer after removing the polysilicon layer over the first ODB layer;
• forming the first ODB layer over the silicon substrate;
• forming in the first ODB layer the first opening having the first width and the second opening having the second width;
• forming a first LOCOS structure in the first opening and a second LOCOS structure in the second opening;
• and
• forming the polysilicon layer over the silicon substrate, filling the first and second openings.