Method of manufacturing semiconductor device

1. A method of manufacturing a semiconductor device, comprising:

forming an isolation region defining an active region in a semiconductor substrate;

forming a silicon oxide film in the isolation region and polishing an upper portion of the silicon oxide film formed in the isolation region;

forming a sacrifice oxide film over the active region;

forming wells in the active region:

removing the sacrifice oxide film, a recess being formed in the isolation region adjacent to the boundary between the active region and the isolation region as a result of the removal of the sacrifice oxide film;

after removing the sacrifice oxide film, forming a first insulating film over the semiconductor substrate;

forming a second insulating film having etching properties different from those of the first insulating film over the first insulating film;

selectively removing the second insulating film from a first region over the active region and the isolation region by dry etching using a fluorocarbon-based etching gas to form a fluorocarbon film over the first insulating film;

removing the fluorocarbon film using a mixed gas including an oxygen gas, a CF 4 gas, and a forming gas in a downflow etching apparatus; and

selectively removing the first insulating film from the first region by wet etching.

2. The method according to claim 1 , wherein

the removing the fluorocarbon film is performed by using the mixed gas having the flow rate of the CF 4 gas being 0.05% to 10% of the total flow rate.

3. The method according to claim 1 , wherein

the forming gas includes 3% of hydrogen and 97% of nitrogen.