Fundamental characterization of stochastic variation for improved single-expose EUV patterning at aggressive pitch
With aggressive scaling of single-expose EUV lithography to the sub-7 nm node, stochastic variations play a prominent role in defining the lithographic process window. Fluctuations in photon shot noise, absorption and subsequent chemical reactions can lead to stochastic failure, directly impacting electrical yield. Fundamental characterization of the mode and magnitude of these variations is required to define the threshold for failure. In this work, a complementary series of techniques is enlisted to probe the nature and modulation of stochastic variation in single exposure EUV patterning. Unbiased line edge roughness (LER), local critical dimension uniformity (LCDU) and defect inspection techniques are employed to monitor the frequency of stochastic variations leading to failures in line/space and via patterning. Using this methodology, we explore the modulation of stochastic variations by different photoresists and illuminations, with emphasis on material and process down-selection for improved yield at the sub-7 nm node.