The present disclosure provides a method for forming a semiconductor device. The method includes providing a substrate having a metal pattern, and forming an etch stop layer over the substrate. The etch stop layer includes a first material. The method also includes forming a diffused area in the etch stop layer by diffusing a second material from the metal pattern to the etch stop layer, and forming an insulative layer over the etch stop layer. The diffused area includes a lower etch rate to a first etchant than the insulative layer. A semiconductor device is also provided.