Mask Blank Development Center Research Articles

Applications of advanced metrology techniques for the characterization of extreme ultraviolet mask blank defects

Characterization of defects and their sources is essential for developing mitigation solutions to support the production of defect-free extreme ultraviolet (EUV) mask blanks. The characterization of sub-100-nm defects pose challenges to the conventional metrology techniques, such as atomic force microscopy and scanning electron microscopy, limiting mitigation of nanoscale defects. SEMATECH’s Mask Blank Development Center houses advanced metrology capabilities that include transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) to address these shortcomings. Scanning TEM was used to study the disruption of the Mo/Si multilayer of phase defects and to perform elemental analysis with energy dispersive x-ray spectroscopy that has supported projects including substrate smoothing activities, deposition simulation development, and defect printability studies. The Auger instrument was used to create elemental maps for defect identification and to characterize the ion beam deposition tool. Using advanced metrology, mitigation of small defects is being realized, yielding mask blanks with defect counts as low as eight defects at 50-nm sensitivity (Lasertec M7360 SiO 2 sphere equivalent) measured over the quality area of 132×132 mm 2 . The issues with the metrology of increasingly small EUV mask blank defects will be outlined, and comprehensive defect characterization results using TEM and AES will be presented.

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 ~0.5 defects/cm2 to ~0.055 defects/cm2 for particles 80 nm in size (polystyrene latex equivalent). We also obtain a "champion" mask blank with an added defect density of only ~0.005 defects/cm2. 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/cm2.