An image sensor is described in which the imaging pixels have reduced noise by blocking nitridation in selected areas. In one example, a method includes forming a first and second gate oxide layer over a substrate, forming a layer of photoresist over the first gate oxide layer, applying nitridation to the photoresist and the second gate oxide layer such that the first gate oxide layer is protected from the nitridation by the photoresist, and forming a polysilicon gate over the first and second gate oxide layers.