Abstract: A metal etching system has an etching chamber defined by quartz walls. Coils provided around the quartz walls of the etching chamber are used to apply a high frequency electrical field to at least a portion of the etching chamber. Containment walls are provided around the coils. An endpoint detection system is provided for the etching system which includes an optical fiber which extends through the containment wall and the coils, with an end of the optical fiber disposed in fixed relationship to the quartz walls of the etching chamber. A fixture mounts the optical fiber in the containment wall. An air-tight seal, such as an O-ring compressed around the optical fiber and compressed against the containment wall, is provided to limit air flow along the optical fiber to the surface of the etching chamber walls.