The present invention provides an image sensor and a fabricating method thereof capable of approaching higher quantum efficiency and reducing cost. The method comprises: providing a substrate; forming a pixel region on a top surface of the substrate; forming an interlayer insulating layer and at least a metal line on the pixel region; forming an isolation carrier layer having a hole array therein on the interlayer insulating layer; grinding a lower surface of the substrate to reduce the thickness of the substrate; placing a plurality of conductors into the hole array to form a plurality of bumps on the isolation carrier layer.