Abstract: A method and apparatus can produce a sound metal deposit inside fine cavities fabricated on a substrate such as a semiconductor wafer through pre-plating treatment process for smoothly filling the fine cavities with plating solution. The method comprises disposing the substrate in a hermetic chamber, filling the chamber with a treatment medium which is liquid at normal temperature and pressure, maintaining the treatment medium within the chamber at a subcritical or supercritical state. The treatment medium within the chamber is finally converted into liquid phase without passing through a vapor phase by controlling pressure and temperature within the chamber so as to infiltrate the treatment medium into the fine cavities.