Disclosed is a method of fabricating an image sensor device, such as a BSI image sensor, and so-fabricated image sensor, in which undesired neutralization of charges in BARC layers caused by opposite charges in metal shield grounds is prevented to reduce dark current and enhance device performance. The image sensor comprises a substrate having a plurality of radiation sensors formed adjacent its front surface, a first insulation layer formed over the back surface of the substrate, a BARC layer formed over the first insulation layer, a metal grid disposed over the BARC layer, one or more metal grounds extending from the metal ground into the substrate for grounding purpose, and a sidewall insulating layer disposed between the sidewall of each metal ground and the surrounding BARC layer. The sidewall insulating layer electrically insulates the metal grounds from the surrounding BARC layer.