- Benk, Markus;
- Zaytsev, Dmytro;
- Orman, Chris;
- Vollmer, Brandon;
- Santos, Daniel;
- Gamsby, Jeffrey;
- Mentz, Jeremy;
- Salmassi, Farhad;
- Allezy, Arnaud;
- Rekawa, Senajith;
- Miyakawa, Ryan;
- Chao, Weilun;
- Gullikson, Eric;
- Chegwidden, Scott;
- Zhang, Guojing;
- Naulleau, Patrick;
- La Fontaine, Bruno
Mirror-based and zone plate-based imaging systems are being used in actinic extreme ultraviolet (EUV) reticle review tools. With regard to zone plates, a short working distance is advantageous in terms of the required spectral bandwidth, manufacturability, and potential throughput and imaging performance. Zone plates therefore typically have a short working distance. The industry has adopted the use of an EUV pellicle to protect the photomask. Imaging photomask through-pellicle requires a working distance larger than 2.5 mm. A zone-plate-based EUV mask microscope with a 3-mm working distance has been commissioned at beamline 11.3.2 of the Advanced Light Source. Through-pellicle imaging at an exposure time of 2 s is demonstrated. The instrument achieves an image contrast of 95% on large features on a photomask with a tantalum-based absorber. Imaging down to 45-nm half pitch (mask scale) is demonstrated. A NILS of 2.55 is achieved on 60-nm half-pitch (mask scale) lines and spaces. These results demonstrate that zone-plate-based imaging systems can meet the requirements of an actinic EUV mask review tool in terms of imaging performance and throughput in an instrument compatible with EUV pellicles.