Novel materials and methods for nanolithography: extending Moore's law
Creators: name: Li, Mengjun
Publisher: name: No Publisher Supplied
Year: 2019

description: We are standing at the stage that a technical and material renovation must be introduced into the semiconductor industry for continuous advancing computational power. With further scaling of the physical dimensions of electrical devices, the lithography technique stands out to be a key enabler for a reliable processing and higher yield. For high volume manufacturing, the printed feature size with single exposure is limited by incident photon wavelength. To achieve sub-10 nm features, the high cost and chances of failure from multiple patterning using 193 nm photon drive the industry to switch to extreme ultraviolet (EUV) photon with 13.5 nm (92eV).EUV lithography requires the development of photoresists accordingly. Conventional organic resists may start to fall behind inorganic resists due to the ultimate resolution limited by the molecule size. Metal-containing resists became popular with high resolution and sensitivity in EUV lithography. In this thesis, we first discussed three tin-based EUV resist candidates. By exploring the film uniformity and compositions, we chose a model resist that can provide a good thin film with little contaminants. The irradiation chemistry was then investigated through various in situ characterization methods. High energy x-ray exposure was used to estimate the chemical composition changes while low energy ultraviolet exposure was used to mimic the reaction with EUV photons and give comparable evidences. Ambient pressure synchrotron x-ray exposure helped further understand the chemically active species that could exist under the irradiation. Eventually two possible reaction pathways were proposed to first explain the chemical behavior of this type of novel resists under photon exposure.Instead of using hundreds of millions commercial EUV scanner, we took advantage of the focused helium ion beam with less than 0.5 nm spot size to investigate the patterning property of our model resist. The ion exposure shares similar irradiation mechanism with photon exposure which mainly produces secondary electron to trigger the chemical reaction inside photoresist films. The three main patterning performances, Sensitivity, Resolution and LER (RLS), as well as the etching selectivity were determined which proved our model resist to be a good candidate for EUVL. We further manipulated the interface bondings and substrates to understand the effects from thin film stacking structures. Uniform weak interface bonding showed to improve the development step and substrates with higher secondary electron yield can provide extra back exposure to improve the sensitivity.The physical scaling of the device will eventually reach its limit. Novel device materials will replace current MOSFET model and new computing paradigms like neuromorphic or quantum computing will be required to move beyond ultimately scaled CMOS. Device technology breakthroughs using charges or in the longer term alternative state/hybrid state variables like superconducting qubits become the popular topics that need massive research and development efforts. For some specific applications like voltage standards and SQUID devices, Josephson junction tunneling devices have already been employed. We have known that the focused helium ion beam can directly write nanometer scale structures without chemically react with the targets. Instead of applying a conventional three-layer structure, we fabricated planar Josephson Junctions with focused helium ion beam successfully on high critical temperature superconducting materials. Ion damage events were simulated to understand the relation between the junction creation and helium ion doses. Large array junctions with good uniformity were also fabricated for the first time and showed good consistency between the normal resistance of the array scaled and the number of junctions in the array. The results were significantly better than other nanofabrication techniques.In summary, we proposed a systematic workflow to prescreen the EUV resist candidates with good understanding of the irradiation chemistry and patterning performance. We proved the focused helium ion beam direct writing to be an alternative method for research level study for resist materials as well as a novel nanofabrication technique for Josephson Junction devices.