Optimized fabrication of silicon nanofocusing x-ray lenses using deep reactive ion etching
Nanofocusing refractive x-ray lenses made of silicon. (a) Several blocks of NFLs can be accommodated on a silicon wafer. (b) Scanning electron micrograph of a block of NFLs. (c) Magnified view on single lenses.
Comparison of the sidewalls of silicon lenses fabricated on a small wafer piece (a) and using wafer technology (b). The sidewalls in (a) are tilted and concavely bulged, while they are nearly vertical and flat in (b). Note the different length scales in (a) and (b), whereas the etch time and parameters were equal. Narrow structures, such as the trenches next to the lenses, are not etched as deeply as larger structures are, such as the lenses themselves. This loading effect is, however, not of x-ray optical relevance.
(a) Fit of a parabola to the lens shape recorded by scanning electron microscopy. (b) Difference between the position of the edge of the lens and the parabolic fit.
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