CMOS-compatible Si metasurface at visible wavelengths prepared by low-temperature green laser annealing

Abstract

A low-temperature laser crystallization is newly devised for producing polycrystalline silicon (poly-Si) thin films of low-loss, low surface roughness enough for nanoscale patterning, applicable to practical Si metasurface elements on complementary metal-oxide semiconductor (CMOS) electronic architectures in visible lights. The method is based on dielectric encapsulation of an amorphous Si film and subsequent laser-induced local crystallization. Such poly-Si thin film yields order-of-magnitude smaller surface roughness and grain size than those obtained with the conventional laser annealing processes. The mechanism of the formation of small and uniform crystalline grains during solidification is studied to ensure the smooth surfaces enough for nanoscale patterning. By obtaining root mean square of surface roughness <2.49 nm and extinction coefficient <4.8×10 -2 at 550 nm, visible metasurface color-filter elements are experimentally demonstrated with the resonant transmission-peak efficiency approaching ∼85%. This low-loss poly-Si metasurface is favorably compatible with embedded CMOS electronic architectures in contrast to the conventional thermal annealing processes that often cause failure of electrical device functionalities due to delamination and material-property degradation problems. The proposed fabrication in this study provides a practical method for further development of various Si metasurfaces in the visible domain and their integration with CMOS electronic devices as well.

Review of Metasurfaces and Metadevices: Advantages of Different Materials and Fabrications

“…The primary materials used for dielectric metasurfaces include Si, GaN, TiO 2 , and SiN x . Si is an abundant element and can be easily processed using standard CMOS-compatible manufacturing techniques [117][118][119][120][121]. Therefore, Si-based metasurfaces are regarded as low-cost metasurface platforms.…”

Polarization-enabled tunable focusing by visible-light metalenses with geometric and propagation phase

“…In contrast, it is found that an arbitrary phase delay can also be provided by subwavelength structures based on various mechanisms, such as electromagnetic resonance and geometric phase [1,2]. The related area, termed as a metasurface with planar features, has attracted increasing attention due to its flexible design scheme and great reduction in fabrication burden [3,4]. In particular, by elaborately manipulation the phase delay distribution, metasurfaces can act as a metalens with a single focus or multifocal function [5][6][7][8][9][10][11].…”