Normal-incidence spectroscopic ellipsometry for critical dimension monitoring

In this letter, we show that normal-incidence spectroscopic ellipsometry ca n be used for high-accuracy topography measurements on surface relief grati ngs. We present both experimental and theoretical results which show that s pectroscopic ellipsometry or reflectance-difference spectroscopy at near-no rmal incidence coupled with vector diffraction theory for data analysis is capable of high-accuracy critical dimension (CD), feature height, and sidew all angle measurements in the extreme submicron regime. Quantitative compar isons of optical and cross-sectional scanning electron microscopy (SEM) top ography measurements from a number of 350 nm line/space reactive-ion-etched Si gratings demonstrate the strong potential for in situ etching monitorin g. This technique can be used for both ex situ and in situ applications and has the potential to replace the use of CD-SEM measurements in some applic ations. (C) 2001 American Institute of Physics.