The present invention provides an electrode stack structure capable of preventing moisture from entering a photodiode, comprising: a semiconductor layer; an inner electrode layer provided on the semiconductor layer; a dielectric layer coating a sidewall of the semiconductor layer; an intermediate metal layer provided on, bonded to, and in electrical conduction with the inner electrode layer, wherein the intermediate metal layer has a bottom side extending over and covering a portion of the dielectric layer to provide airtightness; and an anti-reflection layer coating on an outer side of the semiconductor layer, an outer side of the intermediate metal layer, and an outer side of the dielectric layer, with a groove formed in the anti-reflection layer by leaving a predetermined area of a top side of the intermediate metal layer uncoated or by removing a portion of the anti-reflection layer that coats the predetermined area of the top side of the intermediate metal layer, and an outer electrode layer plated on the predetermined area of the top side of the intermediate metal layer.