A VIRTUAL INTERFACE METHOD FOR EXTRACTING GROWTH-RATES AND HIGH-TEMPERATURE OPTICAL-CONSTANTS FROM THIN SEMICONDUCTOR-FILMS USING IN-SITU NORMAL INCIDENCE REFLECTANCE

A method is presented in which both optical constants and growth rates may be simultaneously extracted from the in situ normal incidence reflectance of a growing thin film. The method employs a virtual interface model, thus avoiding cumulative errors that are encountered if a standard multiple-layer model is used. No a priori knowledge of underlying film materials, structures, or locations of interfaces is required. A method to accurately estimate all parameters for starting values in the least-squares fitting of the data is also presented. This allows one to use a fully automated procedure for extracting information that requires no prior knowledge other than the starting reflectance of the substrate. Monte Carlo simulations are presented to study the ultimate accuracy of the method under ideal conditions for a film structure typical of compound semiconductor growth. Optical constants of GaAs and AlAs at 634 C have been obtained over a wavelength range of 400-990 nm with this method and agree with values obtained by others using ellipsometry. The method provides a pre-growth calibration tool analogous to the use of reflection high energy electron diffraction in molecular beam epitaxy (MBE) that can be used in chemical vapor deposition applications as well as in MBE. Multiple calibrations can be performed for different materials within a single growth run.