A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item LOW TEMPERATURE PLASMA-METAL INTERACTIONS: PLASMA-CATALYSIS AND ELECTRON BEAM-INDUCED METAL ETCHING(2024) Li, Yudong; Oehrlein, Gottlieb G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Low-temperature plasma can generate different types of chemically reactive species at gas temperatures far below what is required to form such species from thermal excitation. Interactions between these reactive plasma-generated species and material surfaces have great potential for various applications, such as semiconductor etching or gas conversion. Synergistic effects, where the production rate with two inputs is greater than the sum of the consequences of each individually, have been demonstrated by combining the plasma with other energy inputs such as heat or kinetic energy from ions or electrons. Understanding the mechanisms by which these species interact with relevant surfaces is vital for the future development of plasma processing, chemistry and physics. In this work, we focus on the interaction of long-lived plasma species, particularly neutrals, with metal. A remote plasma-surface configuration was applied, where the plasma itself does not directly contact the surface. Two examples of plasma-metal interactions will be discussed, one taking place at atmospheric and the other at low pressure. The first case is plasma-assisted catalytic oxidation of methane (CH4) using a nickel (Ni) catalyst at atmospheric pressure, implemented by combining a remote plasma jet. The interrelation of real-time measurements of reaction products and surface adsorbates and plasma diagnostics allowed the identification of atomic oxygen as the key plasma-generated species that drives the synergistic plasma-catalytic reaction. The in-situ characterizations of the surface and gas phase reactions reveal the possible key reaction pathways for the plasma-catalysis reactions. We also observed the activation of the catalyst resulting from long-lasting catalyst surface modification induced by plasma species interaction. The second case is the damage-free etching of refractory metals, ruthenium (Ru) and tantalum (Ta), at low pressure. This was implemented by combining a remote plasma source (RPS) with an electron beam (EB) source. We investigated the effects of CF4 and Cl2 additions to Ar/O2 RPS effluents and we find that Ar/O2 with Cl2 addition induces the highest Ru etch rate (ER) and best removal selectivity over Ta. The surface chemistry characterization by spatially-resolved XPS reveals the possible mechanism of the electrons and neutrals induced materials etching. We also proposed a model that considers the fundamental aspects of the etching reaction and successfully predicts the major features of the electron and neutral induced etching reactions.Item PLASMA-BASED ATOMIC SCALE ETCHING APPROACHES USING EITHER ION OR ELECTRON BEAM ACTIVATION(2022) Lin, Kang-Yi; Oehrlein, Gottlieb; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma dry etching has been extensively employed in semiconductor manufacturing processes for anisotropic pattern transfer. With device miniaturization, the conventional approach utilizing continuous wave plasma etching does not meet the requirement for sub-nanometer processing nodes, including profile control and atomic-scale etching selectivity. Additionally, the direct plasma exposure of a substrate raises the concern of plasma damage and undesired material removal. We describe improvements of plasma-based etching techniques and identified novel ways for enabling material removal. We have systematically studied different precursor chemistries for atomic layer etching on etching selectivity of SiO2 to Si3N4 and SiO2 to Si and obtained an understanding of the surface chemistry evolution. Compared to the conventional approach that mixes fluorocarbon and hydrogen precursors, selected hydrofluorocarbon can deliver optimal plasma chemistry that produces a reduced F/C film in the deposition step and realizes atomic-scale etching selectivity. We also report a new approach for establishing etching selectivity of HfO2 over Si by integrating substrate-selective deposition into an atomic layer etching sequence. The optimal precursor chemistry can selectively deposit on the Si surface as a passivation layer and convert HfO2 to metal-organic compounds for desorption. Finally, we designed and built a system that consists of an electron flood gun and a remote plasma source to demonstrate the concept of a new etching approach by exploiting electron-neutral synergistic effects. This configuration achieves precisely controlled SiO2 or Si3N4 etching by co-introducing an electron beam and Ar/CF4/O2 remote plasma. This approach also addresses the issue of limited precursor chemistries in electron beam-induced etching.