A method and apparatus for use in a wafer processing are disclosed. In an embodiment a includes providing the wafer on a receptacle, wherein the receptacle comprises a light port, and wherein the light port includes a source of light, shining a light from the source of light at an edge of the wafer thereby passing light by the edge of the wafer and processing the wafer on the receptacle based on the light passing by the edge of the wafer and received by a light sensitive element.