REAL-TIME MONITORING AND CONTROL OF PLASMA-ETCHING

Real-time etch rate of thin transparent films is determined within sec onds by an in-situ two-color laser interferometer. The use of two colo rs improves the accuracy of the calculated rates, provides an absolute measure of film thickness for endpoint prediction, and differentiates between etching and deposition. The tool state parameters, rf power t o the antenna and the wafer stage, gas pressure and flow rates, are co mputer controlled and monitored. Real-time etch rate characterization is obtained by monitoring the etch dependence on varying tool state pa rameters. The density of the etch radicals, chlorine and fluorine. is obtained with xenon and argon actinometry using optical emission and m ass spectra. An etch rate model, based on the input power to the wafer stage and the relative density of the etch radicals, is used to devel op a model-based real-time control algorithm. This algorithm has been used to control the etch rate of unpatterned polysilicon and SiO2.