Order-sorting filters for a grating spectrometer and multichannel detection system:  application to real-time...

A multichannel detection system with a grating spectrometer was employed for rapid spectroscopic ellipsometry measurements. Although a grating spectrometer is convenient for dispersing light, it suffers from overlapping orders. Here, we developed novel techniques to eliminate overlapping orders of spectra from a reflection grating. First, an optical filter is properly positioned in the measurement system. Second, a numerical filter is developed. A monochromatic source was used to deduce the exact amount of the overlapping orders, which were determined as the irradiance ratio of the second- to the first-order diffraction. The ratios were found to be increased from 5 to 11% in the 1.5-2.5 eV region. We used the values to correct for overlapping irradiance using the numerical filter. Finally, second-order reflection in real-time rotating element spectroellipsograms were corrected using the filters developed in this work.