The electromagnetic effects of complementary clear-opaque nano-imprint mold inspection and light scattering from small defects are analyzed through simulation. For a wavelength of 365 rim, 40 nm features, and 10 nm defects in an opaque layer with 10% transmission and with a 20 nm gap between complementary molds, leakage light from feature edges dominates the total transmitted light. However, a filter in the pupil can generally enhance defect intensity signals to about 10% of the defect-free intensity. The same polarization signals for defects on the edge are best enhanced by filters blocking signals perpendicular to that edge. The cross polarization signals are important for defects at corners and require no filter. Simulations of light scattering by small square-post defects show that scatter light scales with the square of defect volume at defect sizes up to 20 nm at a wavelength of 193 nm. The use of immersion at 193 nm increases the cross polarization by the refractive index of the liquid but there is little improvement for the same polarization. An opaque layer material with high refractive index contrast to silica and liquid is desirable. (C) 2004 American Vacuum Society.