Thesis

A flexible single-step 3D nanolithography approach via local anodic oxidation : theoretical and experimental studies

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Awarding institution
  • University of Strathclyde
Date of award
  • 2023
Thesis identifier
  • T16659
Person Identifier (Local)
  • 201984205
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Qualification Name
Department, School or Faculty
Abstract
  • The field of nanotechnology has experienced rapid growth in recent years, fuelled by the increasing need for high-performance next-generation nano/quantum devices/products possessing 3D nanostructures with sub-10 nm feature sizes. As a result, there is a high demand for a new flexible nanofabrication technique capable of generating various 3D nanostructures with high precision and efficiency. Local anodic oxidation (LAO) nanolithography is a promising nanofabrication technique for the in-lab prototyping of nanoproducts due to its high precision, low environmental requirement, and ease of use. However, challenges remain with current LAO nanofabrication techniques to meet the processing demands of next-generation nanoproducts. These challenges include limited throughput, high defect rates, and inflexibility in generating various nanostructures. Consequently, the existing 3D LAO nanofabrication methods suffer from high costs and inefficiencies. Addressing these challenges is crucial for advancing the capabilities of LAO nanolithography and unlocking its full potential in nanofabrication. In this thesis, a novel flexible single-step nanofabrication approach was developed to generate diverse 3D nanostructures with sub-10 nm feature sizes through pulse-modulated LAO nanolithography. Compared with other tool and condition control methods, pulse modulation is easier to achieve with precise tunability, enabling flexible, high-precision, and cost-effective 3D nanofabrication. A clear and in-depth understanding of the manufacturing mechanisms at the atomic and molecular scales is crucial in determining the influencing factors during the manufacturing process. This thesis thus first used the reactive force field (ReaxFF) molecular dynamics simulation method to investigate the reaction mechanisms of the LAO process. A comprehensive analysis of bonding, molecular, and charge indicates that the bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film and the consumption of H2O. In contrast, the oxidised surface’s chemical composition remained unchanged during the bias-induced oxidation process. In addition, parametric studies further revealed the dependence of electric field strength and humidity on the bias-induced oxidation process and their respective influencing mechanisms. A good agreement was achieved through qualitative comparison between simulation and experimental results. Secondly, this thesis proposed a new pulse-modulated LAO nanolithography approach to realise flexible and efficient fabrication of various 3D nanostructures. The process was designed on the principle that the amplitude or width of the pulse can control the lateral and vertical growth of each nanodot while the tuning of pulse periods can determine the position of each nanodot based on certain tip scan speeds and trajectories. Feasibility tests were conducted on an atomic force microscope (AFM) to demonstrate the capability of this approach in fabricating various nanostructures with the minimum linewidth at sub-10 nm and height variations at sub-nm. Finally, nanofabrication experiments were conducted to investigate the capabilities of pulse-modulated LAO nanolithography in achieving flexible, accurate, and efficient fabrication of 3D nanostructures. Based on the systematic parametric study on the effects of pulse period, amplitude, and width through the LAO experiment, a process model was developed to provide a clear and detailed interpretation of the nanofabrication process. This model links the geometry of 3D nanostructures with arrays of pulse periods, amplitudes, and widths, allowing for active control of the LAO process. The fabrication of several 3D nanostructures was experimentally validated by comparing the fabricated and predicted results, demonstrating good agreement. The fabricated three-dimensional curved surface could achieve the average form accuracy and precision at sub-nm levels. Higher efficiency was achieved by using a high scan rate, enabling the creation of a nanoscale lens structure consisting of four thousand nanodots within 50 seconds. The efficiency and accuracy of the proposed flexible single-step nanofabrication approach were, therefore, fully demonstrated.
Advisor / supervisor
  • Luo, Xichun
Resource Type
DOI

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