A method for manufacturing an imaging device in a semiconductor substrate is disclosed. The substrate includes a first surface, a second surface substantially opposite the first surface, and a thickness defined by a distance between the first surface and the second surface. A trench is fabricated in the semiconductor substrate first surface. A passivation layer is applied over the substrate first surface and the trench, optionally filling the trench by depositing a conformal layer over the substrate first surface. The conformal layer and the passivation layer are planarized from the substrate first surface, and a membrane is fabricated on the substrate first surface. From the substrate second surface, a cavity is formed in the substrate abutting the membrane and at least a portion of the trench via the unmasked region.