Abstract: An apparatus for semiconductor processing reduces etch endpoint interference by analyzing the plasma while excluding reflections from the semiconductor wafer. The apparatus includes a chamber having a semiconductor substrate holder, a plasma generator, and a window. An optical fiber is connected to the window so as to be optically connected to the plasma from outside the chamber. A processor is connected to a second end of the optical fiber for analyzing the plasma. The window has a substantially planar portion and a substantially tubular portion extending outwardly therefrom. The tubular window portion has a closed end opposite the planar window portion, and the optical fiber is connected to the closed end of the tubular window portion. The tubular window portion is positioned at a predetermined angle relative to the planar window portion so as to be optically coupled to view the plasma, while avoiding reflections from the semiconductor substrate to thereby reduce the interference.