Multiple thin film interference effect on 0.25 mu m line width variation in optical lithography

Abstract

The line width variations with illumination type and with sublayer are studied for deep UV light source and developed 0.25 mu m isolated line pattern. The line width variation is the result of the reflectivity variation caused by multiple thin film interference effect. Off-axis illumination makes larger variation due to the larger reflectance and worse aerial image at best focus. The line width varies a lot with the total reflectance and depends on the optical properties and the thicknesses of sublayers. Antireflection coating should be used in order to control the line width variation. The desired variation of less than 0.05 mu m can be obtained with 0.19 mu m thick ARC whose refractive index is 1.663+0.2i.