Progress in the fabrication of low-defect density mask blanks for extreme ultraviolet lithography

Extreme ultraviolet lithography (EUVL) is the leading next-generation lithography (NGL) technology to succeed optical lithography at the 32-nm node and beyond. The technology uses a multilayer-based reflective optical system, and the development of suitable, defect-free mask blanks is the greatest challenge facing the commercialization of EUVL. We describe recent progress toward the development of a commercial tool and process for the production of EUVL mask blanks. Using the resources at Mask Blank Development Center at SEMATECH-North in Albany, New York, we are able to decrease the mean multilayer-coating-added defect density on 6-in. square quartz substrates by almost an order of magnitude, from similar to 0.5 defects/cm(2) to similar to 0.055 defects/cm(2) for particles >= 80 nm in size (polystyrene latex equivalent). We also obtain a champion mask blank with an added defect density of only similar to 0.005 defects/cm(2). This advance is due primarily to a compositional analysis of the particles using focused ion beam and energy dispersive analysis of x-rays (EDX) followed by tool and procedural upgrades based on best engineering practices and judgment. Another important specification for masks blanks is the coating uniformity, and we have simultaneously achieved a centroid wavelength uniformity of 0.4% and a coating-added defect density of 0.06 def/cm(2). (C) 2006 Society of Photo-Optical Instrumentation Engineers.