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Title:Photolithography and surface modification applications of a 172 nanometer xenon microplasma excilamp
Author(s):Sonoiki, Oluwayemisi
Director of Research:Eden, James G.
Doctoral Committee Chair(s):Eden, James G.
Doctoral Committee Member(s):Choquette, Kent; Gruev, Viktor; Lee, Minjoo L.
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:A high power 172 nm vacuum ultraviolet (VUV) excimer lamp has been utilized in defining patterns on a photoresist. The mechanism by which the lamp works is different from conventional methods as the photoresist is removed at a rate of 3.3 nm/s from the substrate and no development is required. This technique thus has the merit of reduced cost of fabrication and fewer processing steps, in addition to the lamp’s advantageous small size of 10 by 10 cm2. Besides, features as small as 500 nm have now been obtained. Furthermore, optical gratings were effectively manufactured from acrylic and appear to be promising as an alternative to e-beam lithography which has a low throughput. Experiments to better understand the photochemical mechanism by which the lamp acts on the photoresist were done by utilizing a residual gas analyzer (RGA) to investigate the product species from the photoresist upon exposure. The RGA results revealed that both crosslinking and main chain degradation contribute to resist removal from the semiconductor surface via ester elimination and Norrish type reactions. Observed fragments from these reactions included carbon monoxide, ethene and formaldehyde in large quantities; formaldehyde and methane in moderate quantities; 2-propenal and methyl formate in small quantities; and novel products at 39 and 69 amu, for which a mechanism of formation was presented. Importantly, this dissertation is the first to study not just the photochemical mechanism of action of this novel photolithographic mechanism with RGA, but also, to the best of the author’s knowledge, the photoresist photochemical behavior at 172 nm with an RGA. Furthermore, carbon nanotubes exposed to this lamp showed improved structural characteristics as observed from the G to D band intensity ratio via Raman spectroscopy, and exposure to the lamp in the presence of oxygen could serve as a way to functionalize these tubes as observed by x-ray photoelectron spectroscopy (XPS). In addition, the excilamp can be utilized for next generation semiconductor materials for the advancing of Moore’s law. In particular, when germanium, gallium nitride and graphene were exposed to the lamp under different conditions, the native oxide on germanium was removed, while gallium nitride had its binding energies modified. The lamp also has important implications for graphene transfer process utilizing PMMA. Numerous future applications are possible including etching, deposition, doping, PDMS-to-glass transitions, and the cleaning of optics for next-generation extreme ultraviolet lithography (EUVL). Above all, a novel lamp in which microplasma is generated in the depletion region of a reverse-biased silicon carbide diode was demonstrated as a robust technique to obtain future xenon excilamps with high electron densities.
Issue Date:2019-11-25
Rights Information:Copyright 2019 Oluwayemisi Sonoiki
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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