Manufacturing method of semiconductor device and etching gas

A method for manufacturing a semiconductor device, the method comprising:

• etching a film using etching gas that has a first molecule or second molecule, the etching gas having a C3F4 group, the etching gas having a number of carbon atoms of four or five,
• wherein the first molecule has an R1 group that bonds to a carbon atom in the C3F4 group through a double bond, and wherein the R1 group contains carbon and at least one of chlorine, bromine, iodine, or oxygen, and
• wherein the second molecule has an R2 group that bonds to a carbon atom in the C3F4 group through a single bond and an R3 group that bonds to the carbon atom in the C3F4 group through a single bond;
• the R2 group or the R3 group or both the R2 and R3 groups containing carbon;
• and both the R2 group and the R3 group containing at least one of hydrogen, fluorine, chlorine, bromine, iodine, or oxygen.