Metal-Assisted Chemical Etching Of High Throughput, High Aspect Ratio Critical-Angle Transmission Gratings With Vertical And Smooth Sidewalls

This paper reports the development of a critical-angle transmission (CAT) grating fabrication process based on metal-assisted chemical etching (MACE), from which grating prototypes with a period of 1 mu m were fabricated. The prototype was composed of four 5 mm x 5 mm membrane cells, each of which comprising freestanding grating lines and a large-period cross-support structure. The support structure had a 60 mu m period and a 4.5 mu m line width. The grating line width was about 200 nm, the duty cycle was about 0.2, and the aspect ratio was up to 50. The effective open grating area reached 92.5%, and the grating sidewall had a roughness less than 0.8 nm and a perpendicularity reaching 89.2 degrees. For the MACE process, the influence of etching solution ratio on the grating sidewall roughness and perpendicularity was explored on a 100 silicon wafer.