In one embodiment, a method is disclosed for manufacturing a semiconductor device. The method can include forming a resist on a subject layer containing silicon. The method can etch the subject layer using the resist as a mask and with a gas containing a halogen element, which is introduced into a processing chamber. After the etching of the subject layer, the method can slim a planner size of the resist with oxygen gas and a gas containing a halogen element, which are introduced into the same processing chamber.