Aerial Image Mask Inspection System for Extreme Ultraviolet Lithography

Abstract

We constructed an extreme ultraviolet microscopy (EUVM) system for actinic mask inspection that consists of Schwarzschild optics and an X-ray zooming tube. Using this system, a finished extreme ultraviolet lithography (EUVL) mask and Mo/Si glass substrates were inspected. An EUVM image of a 100-nm-width pattern on a 6025 glass mask was clealy observed. The resolution was estimated to be 50 nm or less from this pattern. The programmed phase defect on the glass substrate was also used for inspection. By using the EUV microscope, a programmed phase defect with widths of 90, 100, and 110 nm, a bump of 5 nm and a length of 400 mm was observed finely. The programmed phase defect of a 100-nm-wide and 2-nm-deep pit was also observed. Thus, in this research, the observation of a programmed phase defect was advanced using the EUV microscope, which succeeded in observing a topological defect structure image of a multilayer film. These results show that it is possible to detect the internal reflectance distribution of a multilayer film under the EUV microscope, without depending on surface pertubation.

Wavelength-specific reflections: A decade of extreme ultraviolet actinic mask inspection research

“…A number of published studies show that the EUVM clearly detects defects buried below the multilayer coating. 8,44,[46][47][48] Line defects as small as 90 nm wide and 4 nm tall, or 100 nm wide and 2 nm tall ͑at the substrate͒ have been observed.…”

“…Readers may also wish to consult Ref. 8, an earlier review paper that described several of the most significant actinic mask inspection projects in Japan and the United States in more detail. The public record may be incomplete, and we offer our apologies to projects and research not known to us at the time of writing.…”

EUV microscopy for defect inspection by dark-field mapping and zone plate zooming

“…The achieved spatial resolutions with photon energies of approximately 100 eV amounted to < 100 nm. With the availability of wavelength-adapted EUV multilayer coatings and compact, efficient sources (gas discharge based or laser produced) for this spectral region the EUV technology is used for setting up EUV laboratory microscopes with reflecting optics [6] - [8]. For the demonstration of the application potential of laboratory scale devices a first synchrotronindependent EUV transmission microscope was developed at the Fraunhofer Institute for Laser Technology (ILT) together with the Fraunhofer IOF and IWS in Jena and Dresden, Germany.…”

13.5 nm Schwarzschild microscope with high magnification and high resolution

“…Different from a grazing incidence system [1] and zone plate [2] , a normal incidence multilayer Schwarzschild objective, which operates at a wavelength from 5 to 40 nm, has been widely used for diagnosing laser-produced plasma [3,4] , inspecting extreme ultraviolet lithography (EUVL) masks [5][6][7] , manufacturing electronic devices with smaller structure sizes [8][9][10] , and contributing to biology and medicine [11] . The Schwarzschild objective utilizes two spherical mirrors with concentric radii of curvature that are chosen so that the third-order spherical aberration and coma are eliminated.…”