The demand for ever-smaller electronic and photonic devices shows no sign of stopping, and in fact it is accelerating. Fabricating patterns with sizes less than 10 nanometers (10 billionths of a meter, or about 10,000 times smaller than a human hair) is essential for the manufacturing of future integrated circuits with speeds and functionality far exceeding current capabilities, that could revolutionize computers, information storage, and clean energy devices. Biological applications such as rapid DNA sequencing also require such small dimensions. Although techniques have demonstrated this resolution, their integration into manufacturing is hampered by serious technical and/or economic issues. Previously, the researchers demonstrated a nanopantography method that could address these issues. In this process, patterns are formed on a substrate such as a silicon wafer by directing a beam of positive ions at the substrate. Ions are focused to write patterns at sizes as small as 3 nanometers simultaneously at billions of locations. The past research was limited by the fact that the focusing structure (an array of lenses that focus ions much as glass lenses focus light) had to be incorporated on the substrate, which resulted in low throughput. The new studies will solve this problem by allowing the lens array to be separate, so that it can be used on multiple substrates. This will enable many applications for advanced electronic devices that benefit all aspects of modern life, especially the energy and health industries, with clear societal benefits. This challenging project will lead to new knowledge and will advance education in this important area of science and technology.
The electrostatic microlenses were built on the substrate, using standard microelectronic manufacturing methods. Voltages applied to the lens array cause ion beamlets entering each of billions of microlenses to be focused on the substrate. Using nanopantography, arrays of 300 nm diameter electrostatic lenses create nano-patterns in Si with sizes as small as 3 nm. While nanopantography can form complex patterns with very high resolution, the technique relies on the fabrication of a microlens array on each substrate, adding complexity to the process. To address this issue, the PIs plan on separating the microlens array from the substrate, so that it can be reused for patterning of subsequent substrates. This involves the fabrication of a stencil mask, containing the microlens array, which will be placed on sequential substrates to demonstrate a print-and-repeat process. Following this approach will greatly improve throughput, making nanopantography a manufacturing-worthy process. Experimental work will be complemented by ion trajectory simulations to achieve best focus, as a function of gap between the stencil mask and the substrate, and plasma beam conditions. Molecular Dynamics simulations will be used to study nanofeature etching in graphene on SiO2 by O+ and O2+, with an emphasis on the effect of ion energy and mass on feature size. Quality control measures will be demonstrated for potential pilot line manufacturing. The work will demonstrate a massively parallel method to repeatedly write nanopatterns in 2-D materials (graphene and WS2) on a substrate with a better than the state-of-the-art resolution of 3 nm, using a reusable stencil mask lens array. Nano holes, dots, and ribbons formed in the 2D layers will be characterized for plasmonic and other optoelectronic properties. Nanodisks will be carved out of large area WS2 films. Micro-photoluminescence will be used to characterize their light emitting properties.
