Browsing by Author "Wang, Zijian"
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Item Mechanistic studies of magnetic and electronic materials atomic layer etching using in situ X-ray photoelecton spectroscopy(University of Delaware, 2022) Wang, ZijianSurface chemistry and analysis plays an important role in many science and engineering disciplines. This dissertation is focused on a mechanistic understanding of Atomic Layer Etching (ALE) process in terms of understanding the chemical changes during the etching of materials one atomic layer at a time. Shrinking dimensions and pattern fidelities at the atomic scale demand high processing precision in the semiconductor and electronic device industry. ALE is an atomic scale technique, which consists of sequential, self-limiting reactions of the targeted material surface. A molecular-scale, mechanistic understanding facilitates a better design of reactive precursors for ALE wherein the top monolayer of the material is activated chemically, then subsequently removed by exposure to physical or chemical species. More specifically, my thesis is centered on a mechanistic understanding of the ALE of Co and Co alloys and silicon compounds with potential applications in MRAM and electronic devices. Successful etching of Co and CoFeB thin films was performed via forming volatile metal complexes at low temperature with cyclic sequential reactions of Cl2 and acetylacetone (acac) or hexafluoroacetylacetone (Hfac). Moreover, the extent of Cl2 reaction determines the etching rate of the metal, whereas the substrate temperature of the second organic precursor determines the reactivity of the ALE process. Cl2/acac etching of FeCoB alloys was performed. B reacts upon dosing of Cl2, and a surface enrichment in Co was observed after 5 cycles of Cl2/acac dosing. ☐ To elucidate the mechanism of the ALE process of Co metal, I carried out an in situ study using our homemade in operando X-ray Photoelectron Spectrometer (XPS). Our in operando XPS spectrometer features a temperature-monitored reaction chamber connected to the XPS spectra-characterization main chamber which enables the monitoring and probing of the surface chemistry and chemical bonding types in films without interference from surface contamination during the ALE process. Reaction intermediates of Co ALE process are captured and thoroughly studied via in operando XPS. Furthermore, surface chemistry and morphology dictate the reactivity of material surfaces. Dramatic surface smoothing and morphological changes accompany the Co ALE processes indicating that surface defects play an important role in the etching process. ☐ Finally, as a part of on-going collaboration with Lam research on investigation of ALE process of silicon materials with, we have successfully utilized homemade unique in situ XPS spectrometer to investigate the first chlorination step of the etching process of Si compound. The trend of chlorination of Si>SiN>SiOx offers a partial explanation of high etching material selectivity of Si over SiN and SiOx.