Extreme Ultraviolet (EUV) lithography is under development to succeed 157nm lithography for commercial IC manufacturing for the 45nm technology node as defined by the ITRS 2001 Lithography Roadmap. EUV masks pose many manufacturing and technical challenges to meet the future commercial needs. Although some EUV mask manufacturing processes can be extended from current optical masks, many new issues arise due to transitioning to all reflective multi‐layer mirror system with patterned features versus conventional optical masks. EUV lithography operation at 13.4 – 13.5 nm wavelength requires optimal multi‐layer performance including peak reflectance, wavelength matching to the optical system, and very low defect levels. The Low Thermal Expansion Material (LTEM) that is used as a substrate for the multi‐layer reflector also requires demanding performance levels including Coefficient of Thermal Expansion (CTE), flatness, and roughness to support EUV mask needs. Performance improvements as large as several orders of magnitude are needed for some of these parameters. To aid these developments, specialized metrology tools are needed. These tools fall into two categories: Manufacturing process inspections tools include flatness interferometry, atomic force microscopy, EUV reflectometry, defect inspection, and others. Analytical tools include scanning electron microscopy, X‐Ray Diffraction, ion beam milling, and others used for problem solving. Both metrology types will play a major role in the successful development of EUV masks to meet the 45nm node requirements. This paper will review many applicable metrology techniques in addition to those listed, describe the application to EUV mask blank development or manufacturing, show problem solving examples of the techniques, and highlight particular problems or areas of need. © 2003 American Institute of Physics