Semiconductor device having insulating layer higher than a top surface of the substrate, and method for reducing the difficulty of filling an insulating layer in a recess

A method for forming a semiconductor device, comprising at least the following steps:

• providing a substrate, defining a memory cell region and a periphery region;
• forming a gate oxide layer on the substrate and within the memory cell region and the periphery region;
• after the gate oxide layer is formed, forming a periphery gate stacking structure in the periphery region, wherein the periphery gate stacking structure includes at least a first gate layer, and a second gate layer disposed on the first gate layer;
• and
• after the gate oxide layer is formed, forming a cell stacking structure in the memory cell region, the cell stacking structure comprising at least a first insulating layer, partially disposed in the substrate, a top surface of the first insulating layer being higher than a top surface of the substrate, and the top surface of the first insulating layer and a top surface of the first gate layer of the periphery gate stacking structure being on a same level.