OCD Measurement with the Illuminated Light Spot Size Being Larger than the Grating Region

Abstract

This work studied the case that the illumination light spot size is larger than the grating region during optical critical dimension (OCD) measurement. The analysis is based on Mueller matrix formulism. The total Mueller matrix output is the combination of both the grating Mueller matrix contribution and the surrounding film Mueller matrix contribution. The spectroscopic reflectometry (SR) and spectroscopic ellipsometry (SE) outputs are calculated from total Mueller matrix elements. The measurements with different ratios of illuminated grating area to illuminated film area are carried out. The measured spectra coincide well with the simulated ones. The work will be useful for IC industry, as the measurement pad size becomes even smaller.