Image sensor with pad structure

The present disclosure describes the formation of a pad structure in an image sensor device using a sacrificial isolation region and a silicon oxide based stack with no intervening nitride etch-stop layers. The image sensor device includes a semiconductor layer comprising a first horizontal surface opposite to a second horizontal surface; a metallization layer formed on the second horizontal surface of the semiconductor layer, where the metallization layer includes a dielectric layer. The image sensor device also includes a pad region traversing through the semiconductor layer from the first horizontal surface to the second horizontal surface. The pad region includes an oxide layer with no intervening nitride layers formed on the dielectric layer of the metallization layer and a pad structure in physical contact with a conductive structure of the metallization layer.