Fabrication of Long Range Surface Plasmon Polariton Bragg Waveguide Biosensors on Cytop and Multilayer Substrates

Abstract

This thesis documents the micro-fabrication of a Long Range Surface Plasmon Polariton (LRSPP) biosensor device design that incorporates Bragg grating waveguides. The majority of the work involved the fine tuning of the bi-layer lithography, ultraviolet (UV) exposure and metal deposition micro-fabrication procedures. The goal was to resolve very fine features, accurately produce thin metallization and achieve a high quality metal surface. Repeatable resolution of Bragg gratings having a step-in-width from 8μm to 2μm, a 50% duty cycle and a period of 1690nm to 1800nm, was achieved with bi-layer lithography and UV exposure. A gold thickness of 35nm±5% and surface roughness of better than 2nm rms and average was achieved using thermal vacuum chamber deposition. The fabrication was performed on two different substrates; Cytop and a prefabricated Ta 2 O 5 /SiO 2 multilayer stack. iii Acknowledgments I would like to thank my thesis supervisors Dr. Niall Tait and Dr. Pierre Berini for the opportunity to contribute to the optical biosensor project, a fascinating introduction to the field of micro-fabrication, and for their consultation and direction. Very much appreciation extended to my project colleagues, Sa'ad Hassan who acted as a close mentor for much of the project, and Norm Fong and Wei Ru Wong for much consultation. I would like to particularly thank the staff of the Carleton micro-fabrication facilities, Angela McCormick, Rob Vandusen, and Rick Adams for their training, assistance and consultation on the fabrication techniques, and with equipment operation. Appreciation also to personnel at the University of Ottawa opto-electronic facilities, Ewa Lisicka and Anthony Olivieri, for time spent assisting with equipment usage and a special note of thanks to my wife Angela for copy editing.

Fabrication of Long Range Surface Plasmon Polariton Biosensors Incorporating a Channel Etch Stop Layer and Wafer Bonded Cover

“…The S-grade was used as an optical cladding material in the previous work [40] [41] [42] [43]. Since the S-grade was not designed for adhesion to metal, an additional diluted M-grade was applied on the top of the cladding to improve adhesion with Au waveguides [44]. However, severe cracking issues were found when spinning the first thinner layer of CYTOP S-grade on top of the lower cladding CYTOP stack, leading to a zero yield of the whole wafer.…”

“…An additional issue is that M type CYTOP does not exhibit sufficient mechanical stability during wafer dicing [45]. Successful fabrication trials with CYTOP A-grade led to selection of this material for this research as it demonstrated good adhesion to Au waveguides and thickness could be increased through multiple coats without severe cracking issues observed in [44].…”

“…The other is that Al mask was patterned to replace the photoresist SPR-220 in order to eliminate the photoresist cracking which is believed to result from the soft bake step in patterning SPR-220. Some process modifications based on the previous research [40] [41] [42] [43] [44] are discussed in this chapter as well.…”

“…The wafer preparation in this process was significantly modified from the previous work in [40] [41] [42] [43] [44] due to the use of CYTOP A-grade, which offered the best adhesion when used in conjunction with the APTES. Previous processes applied a diluted M-grade on the substrate as an adhesion layer, with subsequent S-grade layers used as a cladding dielectric material.…”

“…The lower CYTOP cladding preparation was adapted with moderate modifications from the previous work [40] [41] [42] [43] [44]. Specifically, there were two modifications involving baking temperature and time.…”