BSE Grey-Level-Based CD-SEM Metrology for Scumming Quantification of High-NA EUV Contact Holes

Abstract

High-NA EUV lithography has begun patterning hexagonal contact holes (CHs) with a center-to-center (C2C) pitch of 28 nm, which are expected to be first used in D0a DRAM technology generation. This extremely tight pitch challenges photoresist performance and process control, directly affecting pattern quality and yield. While CD-SEM can measure the CD and its uniformity, quantifying residual photoresist at the CH bottom—known as scumming— remains challenging. Scumming can transfer through subsequent etching steps and potentially cause contact failure. To address this, we developed a BSE grey-level-based metrology using 300 eV landing energy to detect and quantify scumming in CHs without requiring prior modeling. The scumming number dependence on the exposure dose and focus were evaluated for chemically-amplified resists (CAR). Cross-section TEM analysis was performed to directly observe the scumming status, which showed good consistency with the top-view CD-SEM measurement results. Enabling CD and scumming to be measured from SE and BSE images acquired simultaneously, CD-SEM provides a more comprehensive and efficient method for resist screening and lithography‑process monitoring in High‑NA EUV patterning.