Nanofabrication of a CMOS Compatible Device For Macro-to-Atom Interfacing

  • Author / Creator
    Yong, Stephanie
  • Advancements in scanning tunneling microscopy (STM) have enabled atomic-scale lithographic patterning of logic gates, memory, and wires, by selectively passivating hydrogen (H) atoms on a H-terminated silicon (Si) surface. However, atomically fabricated systems encounter challenges of developing from research labs into commercial applications. This thesis focuses on developing a complementary metal-oxide semiconductor (CMOS) compatible process flow to nanofabricate a device capable of injecting and making signal measurements between CMOS and atomic circuitry; a macro-to-atom device.

    The design of the macro-to-atom device is capable of withstanding the high-temperature flashing required to prepare an area of H-terminated Si. By isolating the high-temperature flashing to a small area at the center of the device, damage to any prefabricated CMOS circuitry can be prevented. An initial design utilized tungsten-silicide (W-Si) conduction lines on a heavily-doped Si substrate to connect between the atomic and CMOS circuitry. However, the high-temperature surface preparation caused metal particulates to contaminate the center region where atomic circuitry would be fabricated, which could impede atomic circuit functionality. The high-temperature surface preparation also caused thin conduction lines to coagulate causing discontinuities. Another disadvantage to the initial device was that deposited W-Si on the Si surface increases the risk of STM tip crashing, as the surface is no longer flat. This would also make patterning continuous DB wires closely connecting to the W-Si conduction wires difficult.

    To circumvent these issues, a device using heavily-doped arsenic (As) conduction lines on a lightly-doped silicon substrate is to be utilized instead. Fabrication and testing of the device has been separated into three individual components to isolate and address development issues. The first component focuses on the main design and nanofabrication process flow of the bulk of the macro-to-atom device, and ensuring the process flow remains contaminant free. The second component focuses on the contact junctions that would directly interface with the atomic circuitry. By patterning atomic circuitry between the junctions, transport measurements are enabled that help further understand how the conductive contacts interact with the atomic circuitry and perturb the transmission spectra. The third component focuses on implanting a heavily-doped antimony (Sb) reservoir under the surface where atomic-scale lithography would occur, to provide the STM with the required carriers for low temperature operation and surface dangling bonds (DBs) with the required charge state. Once all components of the device are further realized, the three components can then be implemented together as a single macro-to-atom device.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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