Investigation of Low-n Mask in 0.33NA EUV Single Patterning at Pitch 28nm Metal Design

Abstract

Extending 0.33NA EUV single patterning to 28nm pitch becomes very challenging in terms of stochastic defectivity, which demands high contrast lithographic images. The low-n attenuated phase-shift mask (attPSM) can provide superior solutions for individual pitches by mitigating mask three-dimensional effects. The simulation and experiment results have shown substantial imaging improvements: higher depth of focus at similar normalized image log slope and smaller telecentricity error values than the best binary mask configuration. In this paper, the exploration of low-n attPSM patterning opportunity for pitch 28nm metal design is investigated. The lithographic performance of the low-n attPSM is compared to the standard binary Ta-based absorber mask. As well, the impact of mask tonality (bright-field vs. dark-field) on the pattern fidelity and process window is evaluated both by simulations and experiments.