Fabrication of structures with high aspect ratios (HAR) enables creation of metasurface optics with ever-increasing functionality. Dielectric meta-atoms consist of transverse (x,y) shapes extruded in the z-dimension. The phase discontinuity imparted by the meta-atom is a function of the dielectric constant of the material and the z-height of the meta-atom. The performance of the meta-optic improves with larger phase swings. Here we demonstrate HAR etched structures in silicon and gallium arsenide. Initial etch development employs interferometric lithography while final patterns are realized using e-beam patterning. The paper will discuss this etch development process for both material sets.
KEYWORDS: Silicon, Polymers, Metamaterials, Scanning electron microscopy, Projection lithography, Chemical mechanical planarization, Lithography, Electron beam lithography, Etching, Microelectromechanical systems
Membrane projection lithography (MPL) is a fabrication approach in which a novel process flow and mature silicon processing equipment combine to create three-dimensional metamaterials with size scales operational at optical frequencies. In its most common realization, MPL leverages microelectromechanical (MEMS) processing techniques to create cubic unit cells with silicon walls, planarized by chemical mechanical polishing (CMP), a technique that is not omnipresent in fabrication facilities. Here we show several variants of MPL, two of which do not require CMP to make the MPL process compatible with low-tech fabrication environments and open the MPL process to a wider audience.
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