Pupil optimization for after etch defectivity: what imaging metrics matter?

Abstract

A series of experiments was conducted to study how defectivity depends on NILS, aerial image intensity and depth-offocus. Three sets of illuminations were designed to vary only one of these parameters while keeping the others constant for a 48 nm pitch orthogonal contact hole array. The focus was on the after etch defectivity, for which two different etch processes were studied. Both on-wafer LCDU and defectivity for the two etch processes were correlated to the different illumination settings. In summary, we found that defect levels correlate best with the maximum intensity for missing holes and minimum intensity for merging holes. Depth-of-focus appears to have little or no impact on defectivity for the nominal focus condition.