Lithographic aerial-image contrast measurement in the extreme ultraviolet engineering test stand

TLDR: In this paper, the authors describe aerial-image contrast characterization for the extreme ultraviolet (EUV) Engineering Test Stand prototype EUV stepper using the resist-clearing (Kirk) method and compared to simulations based on the known system parameters.

Abstract: An important metric in determining both system and optic performance is aerial-image contrast. Here, we describe aerial-image contrast characterization for the extreme ultraviolet (EUV) Engineering Test Stand prototype EUV stepper. The system has been characterized operating with a developmental projection optic (the set-1 optic). Characterization was performed using the resist-clearing (Kirk) method and the results were compared to simulations based on the known system parameters. In this method, the image contrast is determined from the dose required to clear the bright features and the dose required to clear the dark features in a pattern of dense lines and spaces. Comparisons to simulations have shown discrepancies that increase as the contrast dose is reduced. Although various potential sources exist for these discrepancies (as described herein), analysis points to finite resist resolution as being the primary cause. An empirical model that accounts for finite resist resolution in aerial-image contrast measurements is presented.