It is an object of the present invention to a method for manufacturing a semiconductor device, by which a reaction product formed when a conductive layer is etched can be removed. A method for manufacturing a semiconductor device according to the present invention includes a step of felling a reaction product adhering to a conductive layer so as to extend in a perpendicular direction so that the thickness of the reaction product with respect to a direction in which an active species excited by plasma discharge is accelerated. It is to be noted that the reaction product is produced when the conductive layer is etched.