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Title:Deciphering the role of surface composition and topography in self-organized ion-induced nanopatterning of multicomponent semiconductors with in-situ and in-operando metrology
Author(s):Holybee, Brandon Jay
Director of Research:Allain, Jean Paul
Doctoral Committee Chair(s):Allain, Jean Paul
Doctoral Committee Member(s):Ruzic, David; Lyding, Joseph; Zhang, Yang
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Semiconductors, nanopatterning, ion, XPS, LEISS
Abstract:This dissertation has investigated the early stages of both topographical and compositional evolution of ion-induced nanopatterning on GaSb utilizing in-operando Grazing-Incidence Small-Angle X-ray Scattering (GISAXS), X-ray Photoelectron Spectroscopy (XPS), and Low Energy Ion Scattering Spectroscopy (LEISS) techniques, the effects of both cryogenic and high temperatures on ion-induced nanopatterning of GaSb, and utilized the developed in-operando XPS and LEISS techniques to investigate the previously reported ion-induced nanopatterning of the Au-Si system. The development of the in-operando compositional techniques has given new abilities to investigate the compositional evolution of material surface with high temporal resolution and has the ability to be used as a process control in a wide variety of material systems. To study the topographical evolution of ion-induced nanopatterning of GaSb, in-operando GISAXS experiments were performed on GaSb during 500eV Ne+, Ar+, and Kr+ ion irradiation before and during the early stages of nanopattern formation. Results show that for all ion conditions, an ion threshold fluence must be reached before ion-induced nanopatterning begins, with the topographical response of the surface before nanopattern formation shown to be minimal. The lack of overall coarsening on the GaSb surface before ion-induced nanopatterning suggests that a topographical instability is not the primary mechanism driving nanopattern formation. The work shows that likely compositional-driven instabilities are the primary driving mechanisms leading to the initial development of ion-induced nanopatterning and motivated the in-operando XPS and LEISS compositional studies. The in-operando XPS and LEISS experiments of GaSb under ion irradiation are the first experiments to investigate the compositional evolution with high temporal resolution before and during the early stages of ion-induced nanopatterning. The rigorous development of these techniques, specifically with the empirical calibration of the 500eV Ne+ LEISS quantification and the use of the Sb4d and Ga3d XPS regions, show the importance of understanding the information depth of the techniques used with surfaces that have a non-uniform depth profile. The combined in-operando XPS and LEISS studies done in this dissertation show that just before ion-induced nanopatterning formation, the very surface is highly enriched with Sb (>70%) and that the sub-surface region is Ga enriched. This non-uniform depth profile is very consistent with the expected profile caused by ion-induced Gibbsian segregation as being the primary compositional driving mechanism at the surface of GaSb before ion-induced nanopatterning begins. In addition to the in-operando XPS and LEISS experiments, a massive-scale MD simulation – led by Mike Lively – of the GaSb surface under 500eV Kr+ ion irradiation was performed, with a pre-constructed compositional depth profile based on the previous experimental works. These MD results, combined with the known topographical and compositional surface evolution measured with the in-operando techniques, suggest that ion-induced segregation of Sb to the surface creates the compositional gradient necessary for Ga and Sb phase separation to occur. Additionally, this phase separation is predicted based on the phase diagram of GaSb; GaSb only exists as a 1:1 stoichiometric compound and any deviation would result in phase separation. This phase separation leads to the formation of Ga and Sb cluster formation in the sub-surface of GaSb and ultimately leads to a sputter shield type mechanism resulting in the cone-like nanofeatures observed. In addition to the in-operando characterization studies, a survey experiment was performed on ion-induced nanopatterning of GaSb at cryogenic and high sample temperatures. The results for this study were a bit unexpected, especially for the room temperature irradiations of GaSb. Specifically, no ion-induced nanopatterning was observed for 500eV Ar+ irradiations under 100C and for 500eV Kr+ irradiations under 300C, despite going up to an ion fluence of 2E18cm-2 – well past the ion fluence threshold for nanopatterning. However, for the high temperature patterns that did form, the diameter and height of the nanofeatures, as measured with AFM, are shown to increase drastically with increasing sample temperature. In addition, the overall order of the nanopatterns is also shown to decrease with sample temperature. The last experimental investigation for this dissertation was the investigation and process control experiments looking at ion-induced nanopatterning of the Au-Si system. The purpose of this chapter was to look at the compositional evolution of the Au-Si system up to the expected formation of ion-induced nanofeatures and to utilize the developed in-operando XPS and LEISS techniques as a process control for stopping ion irradiation at specific Au surface compositions. The partial removal results showed that the in-operando XPS and LEISS techniques were both successful in controlling the amount of Au removed from the Au-Si system, generally being within 15% of the target compositions. As for the ion-induced nanopatterning results from the Au-Si system, no nanofeatures were observed for the primary experiments looking at 1keV Kr+ and 500eV Ar+ irradiations. In quantifying the Si2p and Au4f XPS peaks versus ion fluence, it was also found that the peak shifts correspond to changes in the surface charge state and not to the formation of a metastable gold silicide. Additionally, broad beam irradiations were performed with a source known to produce Mo contamination. These results show that nanofeatures form when Mo contamination is present on the surface. These results suggest that the lack of gold silicide formation results in no ion-induced nanofeature formation and that likely previous results were due to Mo contamination.
Issue Date:2018-11-20
Rights Information:Copyright 2018 Brandon Holybee
Date Available in IDEALS:2019-02-07
Date Deposited:2018-12

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