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Optical Waveguide Devices And Improvement Of Their Sidewall Surface Roughness In Silicon-on-Insulator

Posted on:2006-10-17Degree:MasterType:Thesis
Country:ChinaCandidate:F GaoFull Text:PDF
GTID:2178360182960241Subject:Microelectronics and Solid State Electronics
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Different from conventional materials, SOI (Silicon-on-insulator) consists of a thin silicon layer on top of an oxide cladding layer carried on a bare silicon wafer, with a high vertical refractive index contrast. Due to its special structure, SOI material system, which has very good optical and electronic properties, provides a common platform for VLSI (Very Large Scale Integration) and PLC (PlanarLightwave Circuit). Fabrication process of SOI optical waveguide is very compatible with standard CMOS fabrication processes. Passive and active optoelectronic devices can be fabricated on the SOI wafer, and MEMS devices also can be integrated on the SOI wafer. Monolithic integration of optoelectronic devices on the SOI wafer is the main trend for future optoelectronic industry. Our work in this dissertation is focused on the optical waveguide devices and the improvement of rib waveguide sidewall surface roughness in SOI materials.The SOI single-mode waveguides with large cross-section can be realized by rib structure. Using the effective index method (EIM), three-dimensional rib waveguide is equivalent to two-dimensional planar waveguide. In order to minimize the modes mismatch losses between SOI rib waveguides and single-mode fibers, the effects of waveguide rib etch depth and width on the coupling losses have been analyzed by the finite difference beam propagation method (FD-BPM). The optical rib waveguides are designed and fabricated with SIMOX SOI wafers, using inductive coupled plasma reactive ion etching (ICPRIE) process. In order to reduce the Fresnel reflection loss, SiNxOy:H films are deposited on the waveguide interfaces by Ion Beam Enhanced Deposition( IBED) method.The paper introduces MMI coupler based on multimode interference theory. Using EIM and FD-BPM, the optical field is simulated, and the fabrication errors of multimode waveguide width and etch depth are analyzed. Using EIM and FD-BPM, the optical propagation field of two novel 1x3 equal-power dividers are simulated. Restricted to experimental equipments, only the output optical field is measured.Endface roughness, surface roughness and sidewall roughness result in increasing scattering losses for waveguides. According to Payne and Lacey's theory, scattering loss induced by the rms (root-mean-square) roughness was studied systematically. And the scattering loss is proportional to the square of the sidewall nns roughness. A series of atomic force microscope (AFM) measurements were carried out to demonstrate the rms roughness of SOI rib waveguide etched by ICPRIE method. To smooth the sidewall surface, various methods have been explored. In order not to change the waveguide configuration, low-temperature thermal oxidation, hydrogen annealing and mixed ICPRIE were used to reduce the rms roughness of the rough surfaces. After such treatments, the ripples of the sidewall surfaces disappeared, and the rms roughness could be reduced to below 0.3 nm.
Keywords/Search Tags:integrated photics, SOI rib waveguide, inductively coupled plasma reactive ion etching, sidewall surface roughness, scattering loss
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