Extreme ultraviolet mask substrate surface roughness effects on lithographic patterning

Abstract

In extreme ultraviolet lithography exposure systems, mask substrate roughness-induced scatter contributes to line edge roughness (LER) at the image plane. In this article, the impact of mask substrate roughness on image plane speckle is explicitly evaluated. A programed roughness mask was used to study the correlation between mask roughness metrics and wafer plane aerial image inspection. The authors find that the roughness measurements by the top surface topography profile do not provide complete information on the scatter related speckle that leads to LER at the image plane. They suggest at-wavelength characterization by imaging and/or scatter measurements into different frequencies as an alternative for a more comprehensive metrology of the mask substrate/multilayer roughness effects.