In-situ monitoring of etch uniformity using plasma emission interferometry

A method for in-situ real-time monitoring of the etch uniformity of a dielectric film during plasma etching in a restricted geometry is reported. The method is based on interferometry using the natural plasma emission as the light source. Interference patterns are created by light reflections at the Brewster angle between the electrodes of parallel-plate capacitively coupled plasma reactors with small interelectrode gap. The method can be useful as a monitor for statistical process control.