A manufacturing method of a semiconductor device includes the steps of: (a) placing a semiconductor wafer over a stage provided in a chamber, the pressure in the inside of which is reduced by vacuum pumping; and (b) after the step (a), forming plasma in the chamber in a state where the semiconductor wafer is adsorbed and held by the stage, so that desired etching processing is performed on the semiconductor wafer. Herein, before the step (a), O2 gas, negative gas having an electronegativity higher than that of nitrogen gas, is introduced into the chamber to form O2 plasma in the chamber, thereby allowing the charges remaining over the stage to be eliminated.