Fabrication and Characterization of Three Dimensional Photonic Crystals Generated by Multibeam Interference Lithography
University of Illinois at Urbana-Champaign Urbana United States
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Multibeam interference lithography is investigated as a manufacturing technique for three-dimensional photonic crystal templates. In this research, optimization of the optical setup and the photoresist initiation system leads to a significant improvement of the optical quality ofthe crystal, as characterized by normal incidence optical spectroscopy. Theoretical spectra are calculated and demonstrate close agreement with experimental values, indicating that this fabrication process achieves excellent optical quality. X-ray microscopy provides nondestructive inspection of the fabricated crystals at nano-scale resolution. A reconstructed crystal model is generated by computed tomography which allows for comparison to a predicted structures geometry and optical spectra. Using the polymer crystal as a template, electrodeposition is performed to completely infiltrate the crystal with Cu2O. After polymer removal the inverted Cu2O crystal exhibits a high peak reflectance at the predicted wavelength, indicating the structure is an exact inverse of the template. A conformal growth algorithm is developed for the commonly used chemical vapor deposition infiltration technique to explaingrowth results and verified experimentally with atomic layer deposition of oxide materials. Finally, a customized chemically amplified positive photoresist system and its processing steps are developed as a route to zero-shrinkage template material for high fidelity patterning of the designed interference patterns.