Additional spiked area for back deep trench isolation

CMOS image sensor (100) with: a pixel region (103a, 103b, 103c) disposed in a semiconductor substrate (102) and having an image sensing element (104) configured to convert radiation (120) into an electrical signal; a plurality of BDTI structures (204a-204b; backside deep trench isolation) extending from a back side of the semiconductor substrate (102) to locations in the semiconductor substrate (102) located on opposite sides of the pixel region (103a, 103b, 103c); and a doped region (110) disposed laterally between the plurality of BDTI structures (204a-204b) and separating the image sensing element (104) from the plurality of BDTI structures (204a-204b), wherein the plurality of BDTI structures (204a-204b) comprises: a passivation layer (316) covering a trench in the back side of the semiconductor substrate (102); and an oxide layer (114) disposed in the trench and separated vertically and sideways from the passivation layer (316) by a high-k dielectric layer (318).