With the complexity of recent semiconductor device structures, in-situ monitoring and control for semiconductor processing have become prerequisite to do research and develop the semiconductor devices. Spectroscopic ellipsometry(SE) is an inherently sensitive technique due to the measurement of complex reflection ratios as a function of wavelength. Recent development of high-performance SE setups has enabled the non-contact measurement of thicknesses and compositions for multilayer structures, real-time data acquisition and analysis of the processing and the understanding of monolayer-level surface processes.