Antireflection structures for visible and infrared wavelengths fabricated on silicon substrates by fast atom beam etching

Subwavelength structured (SWS) surface directly patterned on a substrate performs as antireflection surface. We fabricated the two-dimensional SWS surfaces on crystal silicon substrates and tested the reflection properties for visible and infrared wavelengths. The SWS surfaces were patterned by electron beam lithography and etched by SF₆ fast atom beam (FAB). In this work, the FAB process was first applied to fabricate the SWS surface. We fabricated the hole type SWS surface and the column type SWS surface. In both types, the grating period was 200 nm and the grooves were approximately 275 nm deep. The dependence of the reflectivity on the free-space wavelength between 200 nm and 2500 nm was examined. In addition, dependence of the reflectivity on the incident angle was examined with He-Ne laser light. From those experimental results, it was shown that the fabricated SWS surfaces, especially column type SWS surface, prevented the reflection in the wide ranges of wavelength (200 nm<λ₀<2500 nm) and incident angle (5°<θ<60°).