The present disclosure provides a method of forming an integrated circuit structure. The method includes depositing a first metal layer on a semiconductor substrate; forming a hard mask on the first metal layer; patterning the first metal layer to form first metal features using the hard mask as an etch mask; depositing a dielectric layer of a first dielectric material on the first metal features and in gaps among the first metal features; performing a chemical mechanical polishing (CMP) process to both the dielectric layer and the hard mask; removing the hard mask, thereby having portions of the dielectric layer extruded above the metal features; forming an inter-layer dielectric (ILD) layer of the second dielectric material different from the first dielectric material; and patterning the ILD layer to form openings that expose the first metal features and are constrained to be self-aligned with the first metal features by the extruded portions of the first dielectric layer.