Empirical correlator for stochastic local CD uniformity in extreme ultraviolet lithography

Abstract

We present experimental evidence for an empirical correlator (or model) for stochastic local CD uniformity (LCDU) of contact holes printed in resist with 0.33-NA EUV lithography. The key component of this correlator is a term that has the “traditional” inverse proportionality to the image log-slope (ILS). We also show that, when the contact CD is close to (one of) the stochastic pattern-failure cliffs (i.e., missing contacts or merging contacts), additional terms need to be added. These terms represent the steep rise in LCDU that is typically observed in the vicinity of these cliffs. We also demonstrate an approach for generating the image-intensity function from which ILS is calculated to obtain the best LCDU correlation result (a procedure which we call “image calibration”). Several experimental LCDU data sets that support the validity of the proposed correlator are presented.