Grinding and chemical mechanical polishing process for micropore x-ray optics fabricated with deep reactive ion etching.

Silicon micropore optics using deep reactive ion etching of silicon wafers has been being developed for future x-ray astronomy missions. Sidewalls of the micropores through a thin wafer with a typical thickness of hundreds of micrometers and a pore width of ∼20 µm are used for x-ray mirrors. However, burr structures observed after etching with a typical height of a few micrometers at the micropore edges are known to significantly reduce x-ray reflectivity. A new grinding and chemical mechanical polishing process is introduced to remove the burr structures. Both sides of the silicon wafer were ground and precisely polished after etching. X-ray reflectivity measurements confirmed an increase of reflectivity by 2-15 times at incident angles of 0.8-0.2 deg. The surface microroughness worsened from 2.0±0.2 nm rms to 7.8-0.8+0.6 nm rms; however, an additional annealing recovered the smooth surface and the estimated surface microroughness was <1.4 nm rms. This new process enables not only removing the burr structures but also choosing a flat part of the sidewalls for better angular resolution.