Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

Abstract

Abstract. The authors are expanding the capabilities of the SHARP microscope by implementing complementary imaging modes. SHARP (the SEMATECH High-NA Actinic Reticle Review Project) is an actinic, synchrotron-based microscope dedicated to extreme ultraviolet photomask research. SHARP's programmable Fourier synthesis illuminator and its use of Fresnel zoneplate lenses as imaging optics provide a versatile framework, facilitating the implementation of diverse modes beyond conventional imaging. In addition to SHARP's set of standard zoneplates, we have created more than 100 zoneplates for complementary imaging modes, all designed to extract additional information from photomasks, to improve navigation, and to enhance defect detection. More than 50 new zoneplates are installed in the tool; the remaining lenses are currently in production. We discuss the design and fabrication of zoneplates for complementary imaging modes and present image data, obtained using Zernike phase contrast and different implementations of differential interference contrast (DIC). First results show that Zernike phase contrast can significantly increase the signal from phase defects in SHARP image data, thus improving the sensitivity of the microscope. DIC is effective on a variety of features, including phase defects and intensity speckle from substrate and multilayer roughness. The additional imaging modes are now available to users of the SHARP microscope.

Zernike phase-contrast full-field transmission X-ray nanotomography for 400 micrometre-sized samples

“…It is true that using OAI imaging helps to increase the resolution in 1D but introduces aberration and sideband artifacts, which effectively lower the resolution in the 2D image. This aspect has also been reported in OAI lithography (Benk et al, 2015). As a result, in the middle of the FOV (within a diameter of $200 mm = half the diameter of zone plate), the resolution of the system is reasonable (in the range 200-300 nm) and determined by the effective pixel size (because Áp > Ár), but gradually decreases in the outer part.…”

Nanometer resolution optical coherence tomography using broad bandwidth XUV and soft x-ray radiation

“…The ability of XCT to nondestructively produce tomographic images of silicon-based samples with nanometer axial resolution holds promise for applications in the growing sector of semiconductor metrology. Especially, the investigation of lithographic masks could be a promising application 25 . We expect that XCT can become a widely applied microscopy technique, in particular when more prevalent XUV sources like high harmonic generation in gases 9 10 or radiation from laser plasmas 26 27 are used.…”

Phase singularities and optical vortices in photonics

“…In addition, it has been found that the quality of the OV beams formed by an SFZP decreases as the focal length modulus increases at a fixed waist radius of the illuminating beam [149]. Nevertheless, the unique properties of SFZPs allow them to be used in various applications, such as detection of wavefront helicity [150,151], optical profilometry [152], the formation of vortex beams in the extreme ultraviolet range [153], optical microscopy [154], and the formation of the inverse energy flux [155]. Such elements can be used, among other things, to create stable `rainbow' OV beams in white light that persist at sufficiently large distances (up to 80 m for a beam diameter of several millimeters), which is important for solving various fundamental and applied scientific problems [146].…”

“…To fabricate SFZPs, approaches similar to those used to fabricate fork-shaped holograms and gratings can be used: lithography and liquid etching methods [160,170], LCSLMs [149], projection lithography [171], direct laser recording methods [162,163,172,173] (Fig. 5b, c), laser printing [174], electron beam lithography [152,154,158], and element template transfer using an electronic exposure device [165]. An interesting option for fabricating SFZPs on the surface of a zinc oxide crystal by etching was shown in [175]: such a diffractive element allows not only forming an optical beam but also performing a nonlinear frequency conversion of the initial radiation to higher-order harmonics.…”