Fabrication of Si-based two-dimensional photonic quasicrystals by using multiple-exposure holographic lithography

摘要

Two-dimensional (2D) photonic quasicrystal (PQC) template patterns have been fabricated by using multiple-exposure holographic lithography (MHL). The MHL technique is based on Lloyd's mirror setup using interference of two equivalent beams, which is an excellent method for fabricating periodic structures of a large area. The 2D PQC array shows various sizes and shapes with a change in the incident angle (θ) and rotation angle (γ) of the multiple-exposure beams. In addition, the filling factor (η), which is a very important factor for optical characteristic of 2D PQCs, was controlled by the exposure time (τ). The fabricated PQCs showed eight-, ten-, and 12-fold patterns with high-order rotational symmetries. Diffraction patterns using 632.8 nm HeNe laser were also observed with n-rotation symmetry for the corresponding n-fold PQCs. After fabricating the PQCs, reactive-ion etching of the silicon wafer was performed with 50-nm-thick chromium (Cr) as a mask in CF_4/O_2 plasma to a 1.3 μm depth. The authors confirmed that fabrication of n-fold 2D PQCs in a large area with suitable optical characteristics could be controlled by some parameters of MHL.