Investigation and process control of the grating fill-factor and sidewall angle impacts on 2-D metamaterial infrared mirrors

We report the first study of the effects of grating fill-factor variation and sidewall angle on 2-D subwavelength grating shortwave infrared mirrors, and the first development of a geometry compensation approach to correct for the grating fill-factor patterning error caused by EBL proximity effect and a plasma etching process based on CHF₃ passivation to control grating sidewall angle. Mirrors with a large grating air-hole diameter-to-pitch ratio of 0.954 and vertical sidewall angle of 89.8° are demonstrated with an average reflectivity of 99% over an ultrabroad wavelength range of 560 nm (1.92-2.48 µm), which represents an unprecedented fractional bandwidth of 26%.