An extrusion-free wet cleaning process for post-etch Cu-dual damascene structures is developed. The process includes the following steps: (1). providing a wafer having a silicon substrate and at least one post-etch Cu-dual damascene structure, the post-etch Cu-dual damascene structure having a via structure exposing a portion of a Cu wiring line electrically connected with an N.sup.+ diffusion region of the silicon substrate, and a trench structure formed on the via structure; (2). applying a diluted H.sub.2O.sub.2 solution on the wafer to slightly oxidize the surface of the exposed Cu wiring line; (3). washing away cupric oxide generated in the oxidation step by means of an acidic cupric oxide cleaning solution containing diluted HF, NH.sub.4F or NH.sub.2OH; and (4). providing means for preventing Cu reduction reactions on the Cu wiring line.