Semiconductor device and manufacturing method thereof

The present disclosure provides a semiconductor device and a manufacturing method thereof. The manufacturing method comprises: providing a substrate comprising a storage region, forming stacked gates of storage transistors on the substrate; forming side walls on two sides of each stacked gate wherein the top surfaces of side walls are arranged to be lower than the top surfaces of the stacked gates; performing ion implantation in the storage region defined by the side walls; and performing an ashing process and a wet cleaning process using the side walls as protective layers of the stacked gates to remove a photoresist remaining after the ion implantation. The present disclosure further provides a semiconductor device formed according to the manufacturing method. According to the semiconductor device and the manufacturing method thereof, the problem of stacked gate collapse from the ion implantation process can be solved, thereby improving the yield.