Multiple high-period-accuracy gratings fabricated by holographic exposure and ion-beam etching with nanometer depth accuracy in silicon

摘要

Diffraction gratings can be manufactured in a large variety of ways depending on the required grating characteristics. In this work we have concentrated on surface relief gratings etched into large blocks of silicon with a polished surface. The applications for this kind of gratings are for mirrors and monochromators in the beam-line of a synchrotron. This application requires gratings with sub 100 nm etching depths-in some cases even sub 10 nm-with a very high control of the grating period and etching depth over the entire gratings ranging from 90 mm * 30 mm to 200 mm * 30 mm with useful areas from 80 mm * 10 mm to 190 mm * 10 mm. In some cases there are two grating tracks with different structure design on the same Si substrate. In this work we have shown that a combination of holographic exposure in a standard photo-resist and ion beam etching with a dwell time mode using a sub-aperture gaussian shaped removal function is an excellent fabrication procedure to meet the tight tolerances for this special type of gratings. We fabricate gratings for spectral ranges from 10-20 eV to 1000-2000 eV with etching depths ranging from 100 nm to a few nm and characterize them thoroughly by Atomic Force Microscopy.