Controlling the profile of high aspect ratio gratings in diamond

Diamond is an excellent material for infrared optics and for applications in harsh environments. Some of those desirable properties, i.e. hardness and chemical inertness, also make it a challenging material to machine and etch. In this study we have tested a wide range of etch parameters in an inductively coupled plasma etcher, in order to produce highly controlled, high aspect ratio gratings in diamond. We discuss the effects of pressure, bias power, and some gas mixture variation (pure oxygen and argon-oxygen) on the etch results and how it impacts the etch mask sputtering and redeposition. We also present a method for applying a fresh aluminum mask, in order to etch even deeper optical grating. Gratings with aspect ratios as high as 1:13.5 have been achieved with a 1.42 μm grating period.