A method for manufacturing a back-side illuminated image sensor, including the steps of: forming, inside and on top of an SOI-type silicon layer, components for trapping and transferring photogenerated carriers and isolation regions; forming a stack of interconnection levels on the silicon layer and attaching, on the interconnect stack, a semiconductor handle; removing the semiconductor support; forming, in the insulating layer and the silicon layer, trenches reaching the isolation regions; depositing a doped amorphous silicon layer, more heavily doped than the silicon layer, at least on the walls and the bottom of the trenches and having the amorphous silicon layer crystallize; and filling the trenches with a reflective material.