Silicon Metalens Fabrication from Electron Beam to UV-Nanoimprint Lithography

Abstract

This study presents the design and manufacture of metasurface lenses optimized for focusing light with 1.55 µm wavelength. The lenses are fabricated on silicon substrates using electron beam lithography, ultraviolet-nanoimprint lithography and cryogenic deep reactive-ion etching techniques. The designed metasurface makes use of the geometrical phase principle and consists of rectangular pillars with target dimensions of height h = 1200 nm, width w = 230 nm, length l = 354 nm and periodicity p = 835 nm. The simulated efficiency of the lens is 60%, while the master lenses obtained by using electron beam lithography are found to have an efficiency of 45%. The lenses subsequently fabricated via nanoimprint are characterized by an efficiency of 6%; the low efficiency is mainly attributed to the rounding of the rectangular nanostructures during the pattern transfer processes from the resist to silicon due to the presence of a thicker residual layer.

Pulsed Laser Deposition of Transparent Conductive Oxides on UV-NIL Patterned Substrates for Optoelectronic Applications

“…From this master, in the case of UV-NIL, rigid or soft stamps (negative copies of the master pattern designs) based on elastomeric materials can be manufactured. Thus, common materials based on silicone polymers (usually modified formulas of polydimethylsiloxane), polyimides, or polyurethanes are applied as free-standing membranes or attached to a flexible or rigid backplane [33,37,38,70]. Actually, these cheaper manufactured stamps are used in the lithography process reducing the production costs and thus prolonging the lifetime of the master, this being fabricated by more time-consuming and expensive methods.…”

“…The advantages of using NIL in comparison to other photolithography techniques are arising from the fact that using a direct contact between the stamp and the coated substrate, the resolution is given by the resolution of the patterns existing on the surface of stamp, which can be beyond the diffraction limits or beam scattering. However, exactly this advantage can easily become the disadvantage of the technique due to the resist filling rheology behavior and demolding capabilities [32,33]. Therefore, one of the common defect mechanisms that appear in the NIL processes is connected with the detachment of the stamp after resist curing, when the polymer may stick on the stamp surface due to the interfacial forces (adhesion and friction forces) that appear between the resist and the stamp material.…”

“…Patterning techniques such as X-ray lithography, electron projection lithography, ion beam projection lithography, multiple e-beam lithography, extreme ultraviolet lithography, or nanoimprint lithography (NIL) are essential in the niche technology that manufactures high-volume and low-cost nanoscale devices [31][32][33][34]. The development and improvement of NIL technique have extended the nanoscale fabrication from standard semiconductor devices for electronics and optoelectronics to complex ones for optics, plasmonics, microfluidics, or biomimetic area [35][36][37][38][39].…”

Robustness Analysis of Metasurfaces: Perfect Structures Are Not Always the Best

“…Significant efforts have been devoted to the development of precise nanofabrication techniques for metasurfaces. − In most cases, the meta-atoms are defined using electron-beam (E-beam) lithography; − sometimes ultraviolet photolithography is used, − or they are directly carved using focused ion beams. − Meta-atoms are fabricated in either dielectrics ,, or plasmonic metals. , The latter has an especially important interaction with light, due to the excitation of free electron resonances . After the exposure step, the meta-atoms are created either by lift-off or by etching .…”

High-Efficiency, 80 mm Aperture Metalens Telescope

“…Currently, electron-beam (e-beam) lithography and focused ion beam (FIB) are commonly used to define the subwavelength-scale meta-atoms, thanks to their power to resolve nanometer-scale features with high precision. However, being scanning-based techniques, e-beam lithography and FIB come with slow speed, high expense, and limited scalability, making it challenging to fabricate large-aperture meta-optical devices even for mere prototyping, let alone mass production. , To date, most of the metalenses reported have only (sub-) millimeter scale apertures. In contrast, conventional lenses with at least centimeter-scale apertures are commonly seen in our daily life, even considered entry-level for applications like telescopic imaging.…”