Silicon-on-Silicon Oxide Metalens: Design and Fabrication Aspects

A metalens operating at 4 µm is numerically designed. By adjusting the diameters of the pillar array from 500 to 1000 nm, the metalens achieves 2π-phase modulation with over 75% transmission efficiency. Further analysis indicates that the designed metalens achieves expected axial dispersion, but the transmission efficiency shows strong dependency on the incident angle. Then fabrication aspects are shown. Firstly, conditions of silicon-on-silicon oxide structure fabrication are studied in terms of plasma deposition and annealing temperature and their effect on the physical and mechanical (roughness, grain size, stress) and optical properties (refractive index) of the layers. Both should be adjusted to provide enhanced features of metalens. In particular, refractive index could be tuned in range from 1.45 to 1.9 and from 3.71 to 5.15 for silicon oxide and silicon layer, respectively. Finally, experimental dependences of microstructure formation on the silicon surface by plasma chemical etching technique in a combined discharge of fluoride plasma are presented. Thus, structures with a height of 246 nm and a relatively low roughness of 0.63 nm were obtained.