Imaging Performance Improvement of an Extreme Ultraviolet Microscope

Abstract

The extreme ultraviolet microscope (EUVM) has been developed for an actinic mask inspection of a EUV finished mask and a EUV blank mask. Using this microscope, amplitude defects on a finished mask and phase defects on a glass substrate are observed. However, it has a problem of low contrast, which originates from 1) thermal noise of a charge coupled device (CCD) camera, 2) wave aberrations of an optical component, and 3) a nonuniform illumination intensity. To resolve these issues, EUVM was improved. 1) To reduce a thermal noise, a cooled CCD camera is installed. 2) To remove wave aberrations of a back-end turning mirror, a Mo/Si multiplayer-coated thick glass substrate with a high surface accuracy is employed instead of a Si wafer substrate. Furthermore, in situ alignment was carried out to remove wavefront aberrations for a Schwarzschild imaging optics. In addition, 3) by installing a scanning system on the front-end turning mirror, a highly uniform illumination intensity was achieved. As a result, images of less than 100 nm without astigmatism were obtained.

Non-contact XUV metrology of Ru/B4C multilayer optics by means of Hartmann wavefront analysis

“…Applications benefiting from the extreme ultraviolet (XUV) spectral range, such as imaging at nano-scale [1,2,3], next generation lithography [4,5], or spectroscopy [6,7,8], all need normal incidence optics based on multilayer coatings [9] which demand highquality finishing tolerances.…”

Actinic critical dimension measurement of contaminated extreme ultraviolet mask using coherent scattering microscopy

“…However, it is difficult to measure the actual CDs of extreme ultraviolet (EUV) lithography masks, given that the optical properties of the mask materials are wavelength specific and the angle of incidence of the EUV light is oblique. [1][2][3] Several actinic mask inspection and metrology techniques have been developed for use with EUV masks, [4][5][6][7][8][9] and mask contamination is mostly investigated through topography analysis. 10 However, there is no appropriate tool to investigate the effects of mask contamination on the imaging properties.…”

Imaging of extreme-ultraviolet mask patterns using coherent extreme-ultraviolet scatterometry microscope based on coherent diffraction imaging

“…The repair of the defect feature is also important. As a bright-field microscope, we have developed an EUV microscope using Schwarzschild optics and an x-ray zooming tube 8,9 that is installed at the NewSUBARU synchrotron facility. An EUV mask consists of a glass substrate (150 Â 150) mm 2 in size, a Mo/Si multilayer, and absorber patterns.…”