High quality semicontinuous deep reactive ion etching of silicon for the creation of x-ray lenses

Abstract

In this work, the authors developed a deep reactive ion etching (DRIE) process to fabricate x-ray-nano-lenses and so-called adiabatic focusing lenses made of silicon. Based on the photolithographic fabrication of excellent etch masks, including a continued adjustment of the pattern layout and the application of a novel developed so-called semicontinuous DRIE process, the creation of several generations of silicon lenses was realized. This process enabled us to fulfill the extreme high demands on the pattern quality, which are an aspect ratio up to 10:1, a tilt angle of 90 ± 0.5°, a mask undercut ≤100 nm, parallelism of the sidewalls, and a surface roughness lower than 50 nm. Using this etching process, the authors successfully created patterns for x-ray-lenses in silicon with lateral dimensions from 20 μm down to 1 μm and etch depths of 19 μm for the 20-μm-lenses and 10 μm for the 1-μm-lenses.