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Investigation of electron beam nanolithography processes, mechanisms, and applications Open Access


Other title
Molecular Dynamics Simulations
Process Windows
Anchor Modeling
Polymer Physics
SML Resist
ZEP Resist
HSQ Resist
PMMA Resist
Dense Gratings
Nanomechanical Cantilevers
Resonant Nanostrings
Electron Beam Lithography
Sub-10 nm Nanofabrication
Silicon Carbon Nitride (SiCN)
Polymer Solutions
Flory-Huggins Theory
Type of item
Degree grantor
University of Alberta
Author or creator
Mohammad, Mohammad A.
Supervisor and department
Dew, Steven (Electrical and Computer Engineering)
Stepanova, Maria (Electrical and Computer Engineering)
Examining committee member and department
Choi, Phillip (Chemical and Materials Engineering)
Nojeh, Alireza (University of British Columbia, Electrical and Computer Engineering)
Evoy, Stephane (Electrical and Computer Engineering)
Department of Electrical and Computer Engineering
Microsystems and Nanodevices
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Electron beam lithography (EBL) is the leading technology for versatile two dimensional patterning at the deep (10-100 nm) nanoscale. In addition to its reputation as an enabling technology for next generation advances in industry, its ease of use, accuracy, and cost has made it the technology of choice for rapid sub-micron prototyping in academia and research institutes worldwide. Advances in EBL processing have enabled sub-10 nm fabrication using a variety of materials under limited conditions. Repeatable processing at the deep nanoscale, particularly for dense nanostructure fabrication, requires a systematic quantitative study of all processing steps and their intricate interdependencies. In addition, developing future nanofabrication strategies with features approaching molecular length scales, requires a thorough examination of the molecular interactions taking place in EBL processing. This research project investigates EBL processing using PMMA and ZEP resists through an in-depth quantitative study and analysis of process windows for dense grating fabrication. The effect of processing parameters from each EBL stage on process windows is thoroughly investigated. Through the study of process windows and contrast curves, EBL processing strategies are developed and high resolution processing limits in PMMA and ZEP resists are explored. Furthermore, the EBL development stage involving resist-solvent interactions is studied using molecular dynamics simulations in Accelrys Materials Studio software package, and analyzed using the Flory-Huggins polymer physics theory. Finally, optimized processing strategies for dense grating fabrication are demonstrated and techniques are employed for the fabrication of record ultra-narrow (8 nm) suspended SiCN cantilever structures and high aspect ratio polymer fabrication using novel SML resist.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
M. A. Mohammad, S. K. Dew, K. Westra, P. Li, M. Aktary, Y. Lauw, A. Kovalenko, and M. Stepanova, Nanoscale resist morphologies of dense gratings using electron-beam lithography, J. Vac. Sci. Technol. B 25, 745 (2007). DOI: 10.1116/1.2731330M. A. Mohammad, T. Fito, J. Chen, M. Aktary, M. Stepanova, and S. K. Dew, Interdependence of optimum exposure dose regimes and the kinetics of resist dissolution for electron beam nanolithography of polymethylmethacrylate, J. Vac. Sci. Technol. B 28, L1 (2010). DOI: 10.1116/1.3268131M. A. Mohammad, T. Fito, J. Chen, S. Buswell, M. Aktary, M. Stepanova, and S. K. Dew, Systematic study of the interdependence of exposure and development conditions and kinetic modelling for optimizing low-energy electron beam nanolithography, Microelectron. Eng. 87, 1104 (2010). DOI: 10.1016/j.mee.2009.11.047M. A. Mohammad, C. Guthy, S. Evoy, S. K. Dew, and M. Stepanova, Nanomachining and clamping point optimization of silicon carbon nitride resonators using low voltage electron beam lithography and cold development, J. Vac. Sci. Technol. B 28, C6P36 (2010). DOI: 10.1116/1.3517683M. A. Mohammad, S. K. Dew, S. Evoy, and M. Stepanova, Fabrication of sub-10 nm silicon carbon nitride resonators using a hydrogen silsesquioxane mask patterned by electron beam lithography, Microelectron. Eng. 88, 2338 (2011). DOI: 10.1016/j.mee.2010.11.045K. Koshelev, M. A. Mohammad, T. Fito, K. L. Westra, S. K. Dew, and M. Stepanova, Comparison between ZEP and PMMA resists for nanoscale electron beam lithography experimentally and by numerical modeling, J. Vac. Sci. Technol. B 29, 06F306 (2011). DOI: 10.1116/1.3640794M. A. Mohammad, M. Muhammad, S. K. Dew, and M. Stepanova, Fundamentals of electron beam exposure and development, In: Maria Stepanova and Steven Dew, Eds., Nanofabrication, Springer, Vienna, 2012, pp. 11-41, ISBN 9783709104248. DOI: 10.1007/978-3-7091-0424-8_2M. A. Mohammad, K. Koshelev, T. Fito, D. A. Z. Zheng, M. Stepanova, and S. Dew, Study of development processes for ZEP-520 as a high-resolution positive and negative tone electron beam lithography resist, Jpn. J. Appl. Phys. 51, 06FC05 (2012). DOI: 10.1143/JJAP.51.06FC05M. A. Mohammad, K. P. Santo, S. K. Dew, and M. Stepanova, Study of the interaction of polymethylmethacrylate fragments with methyl isobutyl ketone and isopropyl alcohol, J. Vac. Sci. Technol. B 30, 06FF11 (2012). DOI: 10.1116/1.4766318M. A. Mohammad, S. K. Dew, and M. Stepanova, SML resist processing for high-aspect-ratio and high-sensitivity electron beam lithography, Nanoscale Res. Lett. 8, 139 (2013). DOI: 10.1186/1556-276X-8-139M. A. Mohammad, T. Fito, J. Chen, S. Buswell, M. Aktary, S. K. Dew, and M. Stepanova, The interdependence of exposure and development conditions when optimizing low-energy EBL for nano-scale resolution, In: Michael Wang, Ed., Lithography, InTech, Rijeka, 2010, pp. 293-318, ISBN 9789533070643. DOI: 10.5772/8182

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