Real-Time Monitoring of Epitaxial Processes by Parallel-Polarized Reflectance Spectroscopy

Abstract

The engineering of advanced micro-electronic circuits, optoelectronic devices, and integrated optical circuits requires precise control of the lateral dimensions and thicknesses of device features and of the stoichiometry and doping of epitaxial semiconductor regions. This is preferably achieved by real-time monitoring and control of the individual deposition and etching processes that constitute the processing sequence. The use of optical probe techniques for the real-time monitoring of etching and/or growth processes is favored because of their nondestructive character and their potential use in real-time feedback control. Some of these methods are ideal in monitoring the overall growth process and/or substrate temperature in industrial applications, requiring low cost and maintenance. For example, in situ reflectance-spectroscopy methods, such as dynamic optical reflectivity (DOS), spectral-resolved normal incidence reflectance spectroscopy (MRS), or pyrometric interferometry (PI), are successfully applied to various deposition processes and provide information on both the growth rate and the composition of the deposits. However, small changes in the reflectance (because of chemical interactions at the surface of the films with the reactants supplied from the vapor phase) are of the order of 10−3 to 10−4 and are hardly observable with normal-incidence reflectance techniques because of the high reflectivity of substrate/film interface, which is typically of the order of 40%–60% for many semiconductors.In order to increase the sensitivity to surface- and interface-related growth properties, alternative optical-observation methods such as reflectance difference spectroscopy (RDS), surface photoabsorption (SPA), and spectral ellipsometry (SE) have been developed.