We compare several parameter identification methods for data-driven identification and validation of an empirical linear dynamic model for a helicon plasma reactor. The model relates easily measurable process variables to ellipsometry measurements from which the etch depth can be determined in real time. The potential use of such a model for process control is obvious. The model developed shows improvement over a neural network model developed in a previous study based upon the same data.
The optical constants of Zircaloy 2 and 4, which are alloys of zirconium and their thermal oxides, are determined by ellipsometry over a 0.3131-3.39-microm wavelength range. Both the refractive index and extinction coefficient of both types of Zircaloy are similar to those of zirconium. Both components of the complex index increase with wavelength from nominal values of 1.135-il.523 at 0.3131 microm to 4.846-i7.345 at 3.39 microm. The refractive indices of the oxide of Zircaloy 2 and 4 heated in air are similar to that of zirconium oxide and decrease in value as a function of wavelength from ~2.3 at 0.3131 microm to ~2.0 at 3.39 microm. The extinction coefficient is both thickness and temperature dependent and varies between ~0.1 and 0.3.
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