Characterization of the Origin of Mobility Loss at the SiC/SiO2 Interface

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Title: Characterization of the Origin of Mobility Loss at the SiC/SiO2 Interface
Author: Biggerstaff, Trinity Leigh
Advisors: Dr. Nadia El Masry, Committee Member
Dr. Salah Bedair, Committee Member
Dr. Lewis Reynolds, Committee Member
Dr. Gerd Duscher, Committee Chair
Abstract: Silicon carbide (SiC) is a wide band gap semiconductor with material properties which make it ideally suited for high temperature, high frequency, and high power metal oxide semiconductor field effect transistor (MOSFET) applications. The wide scale commercial development of these devices has been hindered due to disappointing electron mobility when compared to properties of the bulk material. This mobility loss has been associated with the interface between SiC and the native oxide formed (SiO2). Many improvements in mobility have been realized, but it is currently still significantly less than that of the bulk material. The work in this dissertation is aimed at understanding the origin of this mobility loss from an atomic perspective. Analytical electron microscopy techniques including scanning transmission electron microscopy (STEM), Z-contrast imaging, electron energy loss spectroscopy (EELS), convergent beam electron diffraction (CBED) are used in this study to characterize the 4H-SiC/SiO2 interface. The effect of aluminum implantation, nitric oxide annealing, oxidation rate, and activation annealing temperature on the interface was examined. We found a carbon rich transition layer present on the SiC side of the interface which varies in thickness depending on processing conditions. The thickness of this transition region is linearly related to the electron mobility. We were also able to determine that this transition region occurs as a result of the oxidation process. During oxidation, carbon interstitials are emitted on both sides of the interface, causing a carbon pileup on the SiC side of the interface, which we detect as a transition region. The rate of oxidation is also very important as oxidizing at a fast rate leads greater carbon pileup. The extra carbon in this transition region acts as electron scattering centers, which ultimately lead to a reduced electron mobility. This study is able to directly correlate the microstructure on an atomic scale with macro-scale properties. Using analytical electron microscopy, we are able to detect a carbon rich transition region in the SiC at the interface, determine that it is linearly related to mobility, and fundamentally establish how this transition region is detrimental to the electron mobility.
Date: 2008-11-17
Degree: PhD
Discipline: Materials Science and Engineering

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