In one implementation, a method for manufacturing a chemical detection device is described. The method includes forming a chemical sensor having a sensing surface. A dielectric material is deposited on the sensing surface. A first etch process is performed to partially etch the dielectric material to define an opening over the sensing surface and leave remaining dielectric material on the sensing surface. An etch protect material is formed on a sidewall of the opening. A second etch process is then performed to selectively etch the remaining dielectric material using the etch protect material as an etch mask, thereby exposing the sensing surface.