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0934-I09-14

Oxidation of Structured Silicon Thin Films for Inverse Silicon Square Spiral Photonic Crystal Fabrication Mark A Summers, and Michael J Brett Department of Electrical and Computer Engineering, University of Alberta, 9107 116 St. NW, Edmonton, AB, T6G 2V4, Canada ABSTRACT Square spiral nanostructured silicon thin films are fabricated using glancing angle deposition with a thickness of 3.6 µm on a tetragonal array of relief structures with a periodicity of 800 nm. Thin film samples are oxidized at temperatures ranging from 600°C to 1000°C and analyzed with scanning electron microscopy to examine the increase in fill factor. Samples oxidized at 700°C are further analyzed using x-ray photoelectron spectroscopy and spectroscopic ellipsometry. Fully oxidized samples are inverted with photoresist, demonstrating their utility as an inversion template. This study provides a foundation for experimental realization of the inverse silicon square spiral photonic crystal. INTRODUCTION Fabrication of photonic crystals exhibiting a full three-dimensional photonic band gap (PBG) has been demonstrated with a number of techniques, achieving varying degrees of success. Some techniques offer the direct-write advantages of easy parameter modification and defect inclusion [1], while others offer large scale manufacturability [2]. In nearly all cases, a property desirable in photonic crystal manufacturing is a large PBG width, which primarily depends on two factors: refractive index contrast and geometry. A limited number of materials are available that provide the necessary refractive index contrast for a complete PBG. Silicon is used widely because of its large refractive index and optical properties in the near infrared. Exploring the fabrication of new geometries has been a major research effort over the past few years. The optimized direct [001]-diamond:1 silicon square spiral structure proposed by O. Toader et al. was predicted to exhibit a PBG of 14.8% [3], and the corresponding optimized inverse[001]-diamond was predicted to exhibit a PBG of 22.3%, an increase of greater than 50%. The glancing angle deposition (GLAD) technique has previously demonstrated the ability to fabricate the direct [001]-diamond:1 silicon square spiral structure exhibiting a full PBG over large substrate areas [4]. Development of a simple, scalable process for fabrication of the inverse structure has hitherto been elusive. Template inversion with a non-silicon square spiral should be able to achieve this goal, however materials used in developing this process typically yield structurally inferior geometries compared to those created with silicon. Furthermore, the optimized inverse-[001]-diamond structure has a filling fraction of approximately 0.2, demanding a template with a filling fraction of 0.8. This provides a significant challenge for the GLAD process, which typically produces thin films with a filling fraction on the order of 0.3-0.5 [5]. In this paper, we present a method for creating a non-silicon square spiral while utilizing the str