A semiconductor structure includes a semiconductor substrate, a metal layer, an interlayer dielectric (ILD) layer. The metal layer is disposed over the semiconductor substrate. The ILD layer is over the semiconductor substrate and laterally surrounding the metal layer, in which the ILD layer has a first portion in contact with a first sidewall of the metal layer and a second portion in contact with a second sidewall of the metal layer opposite to the first sidewall of the metal layer, and a width of the first portion of the ILD layer decreases as a distance from the semiconductor substrate increases.