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Total quality on EUV mask blanks have to be improved toward future volume production. In this paper, progress in EUV blank development and improvement in flatness, bow and ML blank defects as critical issues on EUV blanks were reported. Steadily progress in flatness improvement was made in the past five years by improving polishing processes. A LTE substrate with a high flatness of 78 nm PV in 142 mm square area was achieved in average. Annealing process was developed to make small bow of less than 600 nm after ML coating. It was confirmed that annealed ML blank has stable performance in bow and centroid wavelength values through mask making process. Small bow of less than 300 nm was successfully demonstrated using annealing process and a CrN back side film with high compressive stress. Low defects of 0.05 defects/cm 2 at 70 nm SiO 2 sensitivity inspected by a Lasertec M1350 was demonstrated on a multilayer (ML) blank with a LTE substrate as best. Small defects over 50 nm in a M7360 were effectively reduced by improvement of polishing process consisting of local polish, touch polish and cleaning.

An aerial image mask inspection system for extreme ultraviolet lithography (EUVL) is developed. This system consists of microscopes using the same wavelength of light as is used for the exposure and produces a magnified image of defects on a mask. Using this microscope, amplitude defects on finished masks and phase defects on glass substrates are observed. A phase defect was formed by a multilayer coated on a line pattern with 5 nm high and 90 nm wide on a glass substrate. Although the defect detected is made beforehand, it is detected by reflection of the light which penetrated the multilayer. These results show that it is possible to detect the internal reflectivity distribution without depending on surface perturbations. We tried to observe “pit defects”, but it was not possible to observe these at this time. The pit defects, such as scratches on glass substrates may not become defects depending on the process of formation of the multilayer.

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This paper presents a touch probe system with improved sensitivity and repeatability. In this probe, a tip ball is attached to the probe stylus through elastic bodies that enable the ball to be displaced in three directions. When the tip ball touches the workpiece, three fibre optic lever displacement sensors measure directly the ball's displacement and direction. Because the ball is located in sensitive directions of all of the sensors, this probe complies with Abbe's principle, which is a basis of precision measurement. Various performance tests have been performed using one-dimensional stages. The measurement resolution of the tip ball displacement was less than 12 nm in these experiments. Thus, the probe triggering level was set safely to 50 nm, taking into account the associated noise levels. The variation of the pretravel was less than 25 nm in all directions. The measurement force was approximately 0.6 mN in the horizontal direction and 4.5 mN in the vertical direction.