High aspect-ratio two-dimensional silicon subwavelength gratings fabricated by fast atom beam etching

We fabricated the two-dimensional subwavelength structured (SWS) surface on crystal silicon and SiO₂ substrates. The SWS surface patterns were generated by electron beam lithography and etched by SF₆ fast atom beam. In the case of the silicon SWS surface with the period of 150nm, the grating had conical profile and the groove was approximately 350nm deep. The reflectivity was examined at the wavelengths between 200nm and 2500nm. At 400nm, the reflectivity decreased to 0.5% from 54.7% of the silicon substrate. The reflectivity was also examined for the incident angle with He-Ne laser light. Thus, it was shown that the silicon SWS surface prevented the reflection in the wide ranges of wavelength (200nm<λ₀<2500nm) and incident angle (5° < θ <60°). We also fabricated the hole type SWS surface and the column type SWS surface on silicon substrates. In both types, the grating period was 200nm and the grooves were approximately 275nm deep. Moreover, the SiO₂ SWS surface with the period of 150nm was fabricated and the reflectivity was examined at the wavelengths between 200nm and 2500nm.