The capabilities and limitations of angular scatterometry for a structure pitch much less than the optical wavelength
are experimentally investigated using a 100-nm pitch Al-wire grid polarizer on a SiO2 substrate. Three CW laser sources
of wavelengths (244 nm, 405 nm and 633 nm) are used to measure the 0-order diffraction (reflection) across an incident
angle range of 8° to 80°. The grating profile is defined by seven parameters (pitch, bottom linewidth, top linewidth, fused
silica undercut, Al thickness, horizontal and vertical extent of top rounding). Rigorous coupled wave analysis (RCWA)
simulations show that the reflectivity versus angle results are sensitive to changes in all of these parameters. The
simulations act as a baseline library for the scatterometry measurements. Fitting the experimental curves with the
corresponding simulation parameters results in a determination of the grating profile. As expected the shorter wavelength
measurements provide the most sensitivity, but good precision is obtained at all three wavelengths. The measurements
are in good agreement with destructive cross section scanning electron microscopy measurements.
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