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.
Highlights
SHARP is designed to emulate image formation in printing tools such as the ASML ADT, 3100 and 3300 scanners[1,2] in terms of mask-side numerical aperture (NA), illumination and variation of the plane of incidence across the ring field
An overview of the SHARP microscope and detailed descriptions of its components can be found in Refs. 4 and 5
Zoneplates for the SHARP microscope are structured in silicon-nitride membrane windows on silicon chips
Summary
SHARP is designed to emulate image formation in printing tools such as the ASML ADT, 3100 and 3300 scanners[1,2] in terms of mask-side numerical aperture (NA), illumination and variation of the plane of incidence across the ring field. SHARP’s zoneplate imaging optics match the mask-side NA values of current and future lithography generations from (wafer side) 0.25 NA at a 6 deg central ray angle (CRA) up to 0.625 NA at a 10 deg CRA. These NAs are available at different azimuthal angles covering Æ25 deg to emulate the rotation of the plane of incidence. The unique design of the SHARP microscope, using off-axis zoneplate lenses as imaging optics, facilitates the implementation of additional imaging modes and allows, to our knowledge, the first demonstration of DIC and Zernike phase contrast in an EUV optical system. An overview of the SHARP microscope and detailed descriptions of its components can be found in Refs. 4 and 5
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