Antireflection microstructures fabricated upon fluorine-doped SiO_2 films

Two-dimensional periodic structures were fabricated upon a fluorine-doped SiO(2) film in which the fluorine content changed gradually in the direction of film thickness. The films were deposited by plasma-enhanced chemical-vapor deposition. The film was periodically patterned into a 1-mum period and an ~1-mum -groove depth by inductive coupled plasma reactive-ion etching followed by chemical etching in a diluted HF solution. A surface reflectance of 0.7% was attained at 1.85-mum wavelength, a value that is one fifth as large as the 3.5% Fresnel reflection of a SiO(2) substrate with a flat surface.