Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, comprising:

• providing a substrate having an array area and a periphery area;
• forming an etch stop layer on a top surface of the substrate in the array area and the periphery area;
• forming a patterned mask layer on a top surface of the etch stop layer in the array area and the periphery area, wherein the patterned mask layer has a plurality of hollowed portions, and wherein the patterned mask layer includes oxide;
• forming a plurality of trenches on the top surface of the etch stop layer in the array area and the periphery area through the hollowed portions of the patterned mask layer, wherein the trenches run through the etch stop layer and are recessed from the top surface of the substrate;
• removing the patterned mask layer;
• overfilling the trenches by depositing an oxide layer;
• and
• removing a portion of the oxide layer by a planarization process, such that a top surface of the oxide layer and the top surface of the etch stop layer are coplanar.