Optimized fabrication of silicon nanofocusing x-ray lenses using deep reactive ion etching

Abstract

The authors describe an improved production route for silicon nanofocusing lenses for hard x rays using e-beam lithography and deep reactive ion etching. As compared to previous prototypes, these optics have a significantly improved from fidelity, reducing spherical aberrations. Close to an ideal performance for the focusing of hard x rays is achieved with these optics, reaching a lateral beam size of about 50nm. The lens profile is checked by scanning electron microscopy.

Sacrificial structures for deep reactive ion etching of high-aspect ratio kinoform silicon x-ray lenses

“…[34][35][36] Although the spot size does not reach $50 nm, as was previously demonstrated with a 60 lm deep etched silicon lens with $11 mm focal length, 34 the lens depth achieved here is three times higher and the focal length of 215 mm provides ample space for sample surroundings. The over-depth uniformity of our lens was accomplished by the use of sacrificial structures.…”

“…Line-focusing lenses were successfully manufactured by lithography and DRIE of silicon. 20,31,[34][35][36][37] While planar technology offers great design freedom and precision, silicon lenses are subject to relatively high x-ray absorption, which ultimately limits their effective optical apertures and thus their optical performance. 38 To overcome this constraint, passive parts of lens material that merely cause absorption and a 2p wave front phase shift were removed from the light path to obtain a so-called kinoform lens [cf.…”

Diamond nanofocusing refractive X-ray lenses made by planar etching technology

“…With the aim of expanding the applicability of a lens chip for a wide range of energies, we structured four different blocks of lenses in a row, each with different radii of curvature of the lenses. Each block holds N = 100 lenses with a given curvature and each lens row has corrections in five steps of 200 nm for shape displacement of the fabrication process [for details of corrections see, for instance, Kurapova et al (2007)]. The radius of curvature R lies between 5 mm and 8 mm with 1 mm steps.…”

Nanofocusing refractive X-ray lenses: Fabrication and modeling

“…In the final step, the lens structure is transferred into the silicon bulk material (see Figure 2) by deep reactive ion etching (Bosch process) at a multiplex ICP standard rate etch tool. Process parameters and further details are described in [2].…”

“…The great demand for smaller spot sizes to obtain higher spatial resolution led to the development of nanofocusing refractive x-ray lenses (NFLs). With these lenses made out of silicon spot sizes down to 50 nm are accomplished [1,2]. Further improvement of the fabrication process and the combination with coherent diffraction techniques allows to achieve resolutions of a few nanometers [3].…”