Backside illuminated image sensor device having an oxide film and method of forming an oxide film of a backside illuminated image sensor device

Disclosed is a method of fabricating an image sensor device, such as a BSI image sensor, and more particularly, a method of forming a dielectric film in a radiation-absorption region without using a conventional plasma etching causing roughness on the surface and non-uniformity within a die and a wafer. The method includes providing layers comprising a substrate having radiation sensors adjacent its front surface, an anti-reflective layer formed over the back surface of the substrate, a sacrificial dielectric layer formed over the anti-reflective layer, and a conductive layer formed over the sacrificial dielectric layer in a radiation-blocking region. The method further includes removing the sacrificial dielectric layer in the radiation-absorption region completely by a highly selective etching process and forming a dielectric film on the anti-reflective layer by deposition such as CVD or PVD while precisely controlling the thickness.