Reactive ion etching (CF4/Ar) and ion beam etching of various glasses for diffractive optical element fabrication

The paper reports on the reactive ion etching (RIE) and ion beam etching (IBE) of commercially available glasses and their usability for the fabrication of diffractive optical elements as an alternative for expensive quartz glass. Fused quartz, borosilicate glasses BF33, BF40, D263, alkaline‐free aluminoborosilicate glasses AF45 and AF37, and alkaline‐alkaline‐earth silicate B270 were processed with RIE using CF4/Ar gas mixtures. EDX investigations displayed the dependence of the measured etch rates on nonvolatile reaction products. CF4/Ar flow rates influence the etch rates which show maximum values in the range 10‐20 sccm Ar flow. Etch rates as a function of etch depth were investigated as well. Variations in surface roughness are determined by AFM and SEM investigations. Etch rate, surface roughness, and structure shape depend on the alkaline and alkaline‐earth content of the various glass materials is displayed. The usability of the different glass types regarding optical performance was evaluated by comparison of simulated and measured diffraction efficiencies of IBE line gratings, since IBE provides comparable surface qualities. It offers a process alternative for the patterning of micro‐optical elements with high surface quality. Therefore, IBE etch rates were measured as well.