New demonstration technique of 20 nm spatial resolution soft X-ray microscopy

This study deals with a new demonstration technique of full-field transmission soft X-ray imaging microscopy. The microscope´s resolution is measured by utilizing a new type of test patterns, by the use of multilayer coatings. Processed with conventional TEM sample preparation technique, the cross sections of the coatings can be thinned to be sufficiently transparent for imaging in the microscope. Resolution measurements are done by using test patterns which consist of forty chromium/silicon bilayer pairs, with measured periods of 39.0 nm and 48.6 nm. At the half-periods of 19.5 nm and 24.3 nm, the modulations measured from the lineouts are 20% and 75%, respectively. A straight-line approximation between the measured points indicate that the microscope achieves the 26.5% modulation at a half-period of 20 nm. The calculated resolution, based on evaluation of the Hopkins theory of partially coherent imaging, is 19 nm. The microscope is thus 1.1× diffraction limited at λ = 2.07 nm.