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3D Photonic Crystal Fabrication through Holographic Lithography

Ying-Chieh (Christy) ChenYing-Chieh (Christy) Chen
Former Graduate Student in Materials Science and Engineering

B.S. Materials Science and Engineering Department, National Tsing Hua University, Taiwan

Multi-beam interference lithography is a method of the 3D photonic crystal fabrication methods that is attracting great interest. The 3D periodic interference patterns are generated with coherent laser beams and recorded in photoresists (Fig.1). The method is versatile for constructing crystals with different symmetry and basis by tuning the parameters of each beam including angles, polarizations and intensities. The resulting crystals are large-area, defect free, and the size of the crystals can be easily scaled up by increasing laser beam size without increasing processing time (Fig.2). We have fabricated high quality crystals with optical properties comparable to theoretical values calculated by finite difference time domain and transfer matrix methods (Fig3). The created crystals can then serve as templates for photonic crystals with other functional materials.

 

Figure 1

Fig. 1 Multibeam interference lithography for 3D photonic crystal fabrication.

 

Figure 2

Fig. 2 Scanning electron micrographs of SU-8 photonic crystal.

 

Figure 3

Fig. 3 (a) Reflection and transmission spectra of the fabricated photonic crystal in the 111 direction. (b) Simulation result from the transfer matrix method (dotted) and FDTD (solid). (APL, 91, 241103)

 

X-ray transmission microscopy is used to image our fabricated 3D photonic crystals. Transmission images are taken at a range of angles and the 3D images are reconstructed with computed tomography (Fig.4). The microscope (Xradia nanoXCT) has a resolution around 50nm when using a Cu anode source (8keV) and Fresnel zone plate as the objective. This technique allows us to study the internal structure of the fabricated crystal in real space non-destructively and can provide insight to control and refine the fabrication process and structural design route.

Figure 4

Fig. 4 (a) X-ray transmission microscope configuration (b) 3D reconstructed photonic crystal with X-ray CT. (Courtesy of Xradia)            

 

Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign