An optical image sensor is fabricated by forming a pixel array and a peripheral region surrounding the pixel array on a semiconductor substrate, the peripheral region containing peripheral circuitry. An inter-level-dielectric layer is formed over the substrate and a plurality of interconnect wiring layers are formed over the inter-level-dielectric layer. Each interconnect wiring layer includes interconnecting metal features and a layer of inter-level-dielectric material covering the interconnecting metal features. The plurality of interconnect wiring layers are provided in a manner that there are N levels of wiring layers in the peripheral region and 1 to (N−1) levels of wiring layers over the pixel array. An etch-stop layer is formed over the top-most level interconnecting metal features in the peripheral region.