The present invention pertains to apparatus and methods for planarization of metal surfaces having both recessed and raised features, over a large range of feature sizes. The four-layer plating includes an underlayer plating, a palladium plating, a silver plating and a gold plating arranged in this order from bottom to top. The slip assemblies include a slip ring which has a plurality of slip segments. Since lattice vacancy is relatively large, the photoreactive group is capable of moving relatively freely in the main chain of the polymer, thus it is possible to improve a slow photoreaction rate, which is considered a disadvantage of a conventional polymer material.