A method and structure for good adhesion of Intermetallic Compounds (IMC) on Cu pillar bumps are provided. The method includes depositing Cu to form a Cu pillar layer, depositing a diffusion barrier layer on top of the Cu pillar layer, and depositing a Cu cap layer on top of the diffusion barrier layer, where an intermetallic compound (IMC) is formed among the diffusion barrier layer, the Cu cap layer, and a solder layer placed on top of the Cu cap layer. The IMC has good adhesion on the Cu pillar structure, the thickness of the IMC is controllable by the thickness of the Cu cap layer, and the diffusion barrier layer limits diffusion of Cu from the Cu pillar layer to the solder layer. The method can further include depositing a thin layer for wettability on top of the diffusion barrier layer prior to depositing the Cu cap layer.