BACKGROUND

In the formation of integrated circuits, devices such as transistors are formed on a semiconductor substrate. An interconnection structure is then formed over the integrated circuit devices. A redistribution layer (RDL) is formed over the interconnection structure. The RDL includes at least a conductive feature and a passivation layer, and the conductive feature is electrically connected to the interconnection structure. The passivation layer is formed over the conductive feature.

However, the different materials in the RDL may have different coefficients of thermal expansion. The coefficient of thermal expansion mismatch in the RDL leads to the formation of cracks extending from the RDL to the interconnection structure, which can cause device failure. Therefore, there is a need to solve the above problems.

