High-efficiency focusing and imaging by dielectric kinoform zone plate lenses with soft X-rays

Abstract

With fast advances in enhancing the focusing/imaging resolution of Fresnel zone plate lenses toward sub-10 nm, low diffraction efficiency in connection with their rectangular zone shape still remains a big issue in both soft and hard X-ray microscopy. In hard X-ray optics, encouraging progress has recently been reported in our earlier attempts of high focusing efficiency by 3D kinoform shaped metallic zone plates, formed by greyscale electron beam lithography. This paper addresses our efforts towards high focusing/imaging efficiency by developing a novel dielectric kinoform zone plate lens for soft X-rays. The effects of the zone materials and zone shapes on the focusing/imaging quality were first theoretically investigated by a modified thin-grating-approximation method, revealing superior efficiencies of dielectric kinoform zone plates over rectangular ones in metals. Optical characterizations of replicated dielectric kinoform zone plates by greyscale electron beam lithography demonstrate a focusing efficiency of 15.5% with a resolution of 110 nm in the water window of X-rays. Apart from high efficiency, the novel kinoform zone plate lenses developed in this work exhibit significant advantages over conventional zone plates, i.e. simplified process, low cost and no need for a beamstop.

Refractive X-ray optics: towards wavelengths of 13.5 nm and beyond

“… photons). At the same time, for the tasks of X-ray nanolithography, a number of research groups propose concepts of optical elements that are alternative to multilayer Bragg mirrors in modern EUV scanners [17]: diffraction optics (Fresnel zone plates [18]), refractive optics (biconcave parabolic lenses [19]), as well as composite (refractive-diffraction) kinoform lenses [20]. The use of the above types of mirrors can help increase the spectral range to the level of ~10% dE E , which, together with the use of the effect of total external reflection instead of diffraction from periodical multilayers, will make it possible to collect the radiation dose required for exposure of X-ray resists several times faster.…”

“…Using the frequency response ( , ) z H u v from (20), obtained in the Fresnel approximation, we can find the connection between the spectra at the input and output of the filters 1 L and 2 L :…”

Refractive X-ray optics: towards wavelengths of 13.5 nm and beyond

“… photons). At the same time, for the tasks of X-ray nanolithography, a number of research groups propose concepts of optical elements that are alternative to multilayer Bragg mirrors in modern EUV scanners [17]: diffraction optics (Fresnel zone plates [18]), refractive optics (biconcave parabolic lenses [19]), as well as composite (refractive-diffraction) kinoform lenses [20]. The use of the above types of mirrors can help increase the spectral range to the level of ~10% dE E , which, together with the use of the effect of total external reflection instead of diffraction from periodical multilayers, will make it possible to collect the radiation dose required for exposure of X-ray resists several times faster.…”

“…Using the frequency response ( , ) z H u v from (20), obtained in the Fresnel approximation, we can find the connection between the spectra at the input and output of the filters 1 L and 2 L :…”