A method for forming a semiconductor device, includes: forming a metal layer on a semiconductor substrate; forming a dielectric layer over the metal layer; etching a top portion of the dielectric layer; after etching the top portion of the dielectric layer, removing first mist from a bottom portion of the dielectric layer; removing the bottom portion of the dielectric layer to expose the metal layer; performing a pre-clean operation, using an alcohol base vapor or an aldehyde base vapor, on the dielectric layer and the metal layer; and forming a conductor extending through the dielectric layer and in contact with the metal layer.