Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device, comprising:

• providing a substrate having a memory region and a high voltage region;
• sequentially forming a floating gate layer and a hard mask layer on the substrate, wherein the floating gate layer and the hard mask layer span in the ranges of the memory region and the high voltage region;
• patterning the hard mask layer to form a first opening exposing a portion of the floating gate layer located in the range of the memory region;
• patterning the hard mask layer and the floating gate layer to form a second opening overlapped with the high voltage region;
• performing a first thermal growth process to simultaneously form a first oxide structure on the portion of the floating gate layer exposed by the first opening, and to form a second oxide structure on a portion of the substrate overlapped with the second opening;
• removing the hard mask layer;
• and
• patterning the floating gate layer by using the first oxide structure as a mask, to form a floating gate structure in the range of the memory region.