Printing 28nm Pitch Hexagonal Contact Arrays with Metal Oxide Resist and High NA EUV lithography

Abstract

As semiconductor scaling advances toward sub‑30nm pitch contact layers, High Numerical Aperture Extreme Ultraviolet (High-NA EUV) lithography becomes a critical enabler for next‑generation device integration. In this work, we demonstrate the patterning of 28nm pitch hexagonal contact holes (CHs) using a metal‑oxide resist (MOR) on a High-NA EUV exposure platform. We introduce a metrology methodology based on Critical Dimension Scanning Electron Microscopy (CD‑SEM) to characterize CH shape, Local Pattern Placement Error (LPPE), and Local Critical Dimension Uniformity (LCDU). By performing this metrology after pattern transfer, we capture not only surface-level variations but also in‑feature deviations such as scumming and profile changes. In a second phase, we employ massive e‑beam metrology to inspect approximately one million CHs, enabling statistical extraction of the Failure‑Free Latitude (FFL) and Failure‑Free Depth of Focus (FFDOF). Using this methodology, we evaluate how scanner settings, reticle characteristics, and etch conditions affect the defect-free process window. We first optimized exposure and etch conditions using 32nm‑pitch hexagonal CHs printed with a Low-NA EUV (0.33NA) system and subsequently transferred this learning to 28nm‑pitch hexagonal CHs printed on a High‑NA tool. With these optimized conditions, we achieved an FFL of 2nm and an FFDOF of 25nm, despite limitations associated with the Bright Field (BF) reticle used.