CMOS integrated method for the release of thermopile pixel on a substrate by using anisotropic and isotropic etching

A method for manufacturing an imaging device is presented. The method starts with providing a wafer having a membrane with an opening bonded to a substrate (block 210). A photoresist layer is deposited over the membrane and wafer surface (block 220). A portion of the substrate back surface under a central part of the membrane is etched anisotropicly (block 240). A first region of the photoresist layer is removed, exposing an opening in the membrane (block 250), so that a first isotropic etching of the substrate is performed through the membrane opening (block 260). A second region of the photoresist layer is stripped (block 270), exposing a second membrane opening, providing access for a second isotropic etching of the substrate through the first and/or second membrane opening (block 280).