Chemical mechanical polishing process for forming shallow trench isolation structure

Abstract

A shallow trench isolation (STI) multistage chemical mechanical polishing (CMP) method for forming a shallow trench isolation structure is provided. The substrate comprising a dense region and an isolation region, a silicon nitride layer formed over the substrate, a plurality of trenches formed in the silicon nitride layer and the substrate, an oxide layer formed over the substrate, filling the trenches, wherein a width of the trenches in the dense region is smaller than that in the isolation region. A first polishing step is performed to remove a portion of the silicon oxide layer until a thickness of the remaining portion of the oxide layer reaches a predetermined thickness. A second polishing step is performed to remove a portion of the remaining portion of the silicon oxide layer until the silicon nitride layer is exposed.