Fabrication of three-dimensional near-IR photonic crystals using deep- UV contact photolithography and silicon micromachining

摘要

We report our progress on the fabrication of three-dimensional (3D) photonic crystals to operate at near-infrared (IR) wavelengths using conventional planar silicon micromachining. The method involves patterning a single layer of planar etch mask and a custom etch process to create a 3D array of spherical voids. The etch mask is patterned in polymethyl methacrylate (PMMA) using conventional deep-UV contact photolithography and then transferred to a silicon dioxide (SiO_2) hard mask. The 3D spherical voids are fabricated using a sequence of etching and passivation steps. In the etch step performed in a fluorine-based inductively coupled plasma-etching system, first a layer of spherical voids is created. Then, the spherical voids are passivated by dry silicon oxidation. A subsequent anisotropic removal of oxide at the bottom of the sphere is achieved by high-energy ion bombardment thus enabling the creation of etch mask for the successive layers. Plasma chemistry with high selectivity to oxide is utilized for opening the subsequent layer of spherical voids. By repeating these steps, buried 3D array of spherical voids is obtained. This way, a 3D structure with simple cubic symmetry can be obtained from an etch mask initially patterned with a square lattice of circular holes. Our fabrication method has numerous advantages over alternative approaches as it is based on the well-established CMOS mass fabrication technology, which is compatible with the next generation optoelectronic circuits.