Chemical mechanical polishing for forming a shallow trench isolation structure

A method of chemical-mechanical polishing for forming a shallow trench isolation, wherein a substrate having a plurality of active regions, including a plurality of relatively large active regions and a plurality of relatively small active regions, is provided, the method comprising the steps of:

• forming a plurality of shallow trenches between the active regions;
• forming an oxide layer over the substrate, so that the shallow trenches are filled therewith;
• forming a partial reverse active mask on the oxide layer, wherein the partial reverse active mask has an opening at a central part of each relatively large active region when the reverse active mask completely covers each relatively small active region and trenches, wherein the opening exposes a portion of the oxide layer, and wherein the opening has at least a dummy pattern and wherein the dummy pattern comprises at least one protrusion portion in the opening;
• removing the oxide layer on the central part of each large active region;
• removing the partial reverse active mask;
• and
• planarizing the oxide layer.