Optical emission end point detector

摘要

A method for determining the optimum time at which a plasma etching operation should be terminated. The optical emission intensity (S1) of the plasma in a narrow band centered about a predetermined spectral line, indicative of the gas phase concentration of a plasma etch product or reactant species. The optical emission intensity (S2) of the plasma in a wide band centered about the predetermined spectral line, indicative of a background emission signal is also monitored. The intensity (S1L) of the spectral line is then determined in accordance with the equation S1L=S1-k ( alpha S2-S1). The etching process is terminated when the monitored signal intensity (S1L) or its time derivative reaches a predetermined value.