Progress in EUV lithography towards manufacturing from an exposure tool perspective

Abstract

EUV lithography is a candidate for device manufacturing for the 16nm node and beyond. To prepare for insertion into manufacturing, the challenges of this new technology need to be addressed. Therefore, the ASML NXE:3100 preproduction tool was installed at imec replacing the ASML EUV Alpha Demo Tool (ADT). Since the technology has moved to a pre-production phase, EUV technology has to mature and it needs to meet the strong requirements of sub 16nm devices. We discuss the CD uniformity and overlay performance of the NXE:3100. We focus on EUV specific contributions to CD and overlay control, that were identified in earlier work on the ADT. The contributions to overlay originate from the use of vacuum technology and reflective optics inside the scanner, which are needed for EUV light transmission and throughput. Because the optical column is in vacuum, both wafer and reticle are held by electrostatic chucks instead of vacuum chucks and this can affect overlay. Because the reticle is reflective, any reticle (clamp) unflatness directly translates into a distortion error on wafer (non-telecentricity). For overlay, the wafer clamping performance is not only determined by the exposure chuck, but also by the wafer type that is used. We will show wafer clamping repeatability with different wafer types and discuss the thermal stability of the wafer during exposure.