The mechanism of forming a metal bump structure described above resolves the delamination issues between a conductive layer on a substrate and a metal bump connected to the conductive layer. The conductive layer can be a metal pad, a post passivation interconnect (PPI) layer, or a top metal layer. By performing an in-situ deposition of a protective conductive layer over the conductive layer (or base conductive layer), the under bump metallurgy (UBM) layer of the metal bump adheres better to the conductive layer and reduces the occurrence of interfacial delamination. In some embodiments, a copper diffusion barrier sub-layer in the UBM layer can be removed. In some other embodiments, the UBM layer is not needed if the metal bump is deposited by a non-plating process and the metal bump is not made of copper.