Atomic-Scale Analysis of the SiC/Oxide Interface to Improve High-Power MOSFET Devices

Dutta, Dipanwita. Atomic-Scale Analysis of the SiC/Oxide Interface to Improve High-Power MOSFET Devices. 2021, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: https://edoc.unibas.ch/83443/

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“The history of solid-state physics in general and of semiconductors in particular,
is not so much about great men and women and their glorious deeds,
as about the unsung heroes of thousands of clever ideas and skillful experiments
—reflection of an age of organization rather than of individuality.”
— Ernest Braun
This thesis entitled “Atomic-Scale Analysis of the SiC/Oxide Interface to Improve High-Power MOSFET Devices” aims at a technology innovation critical for stepping up the energy efficiency in advanced silicon carbide (SiC) based metal oxide semiconductor field effect transistors (MOSFET) for high power semiconductor technology. While the wide band gap, high thermal conductivity, and high saturation velocity are very desirable, SiC has a major is advantage in comparison with Si or gallium arsenide (GaAs). Compared to state-of-the-art silicon technology, the channel mobility in SiC MOSFETs is very low compared to the bulk mobility and is strongly dependent on its crystallographic orientation and the interface.
In contrast to Si where the passivation of surface states due to the SiO2 layer was a breakthrough, the more complex nature of the oxidation process is still hampering such developments in SiC. It remains a pestering question, even after decades of intensive R&D, which kind of defects degrade the near interface mobility of SiC-MOS devices and whether and how the proposed carbon clusters could be involved.
This thesis comprises a new approach in that multiple experimental techniques are combined with minima-hopping density functional theory for atomistic simulations and property prediction. It is by the iterative multi-technique investigation of structures, properties and processes down to the atomic level that in-depth understanding of complex phenomena and mechanisms occurring at the interface during oxidation can be inferred.
In the present thesis spectro-microscopy and theory investigations have been used to investigate defects in
particular C-defect formation during the fabrication of thermal oxides on SiC. The presence of carbon defects at this interface affecting the near interface channel mobility are consistently evidenced i) by a wide range of starting conditions in Density Function Theory and Monte Carlo simulations, and most importantly ii) by in-depth high resolution secondary transmission electron microscopy, EELS and Raman spectra iii) by few of the first Local Electrode Atom Probe (LEAP) experiments performed on SiC/SiO2 interface samples and iv) by the most recent high resolution STEM data obtained by us allowing for in-depth analysis of the defect structure in addition to modelling, defect spectroscopy and transport
The thesis has been allocated into six chapters. Chapter I introduces SiC as a semiconducting material and its usefulness in power devices. It also briefly establishes the origin and role of various defects at the interface towards reducing the channel mobility. In Chapter II we get an overview of how C as a defect has been a controversial topic for decades and unveils the various methods and techniques we have been using in order to detect this C-nucleates. Chapter III explains how the sample preparation plays a very important role in order to achieve high-resolution data. Also here, we describe how different samples are prepared for different experiments: AFM measurements required removal of oxide using an etching solution in order to gain morphological information of the interface. FIB has been used to mill thin lamellae and pillars for HRTEM and LEAP experiments respectively. Chapter IV pertains to the atomistic analysis in order to find the C-defects at the interface. Using AFM we perceived the architecture of SiC interfaces and consolidated the speculations of C-nucleates being present at the interface. In order to gain knowledge about the various chemical bonds present at the interface we used Raman spectroscopy. HRTEM and LEAP proved that there are also dangling bonds along with stoichiometric
dislocations at the interface leading to a broadening of the interface via the imperfect layer by layer oxidation and the penetration of defects into the SiC resulting in deterioration of the channel mobility.
EELS and STEM analysis revealed the exact positions at which the C-defects are present and where they are attached to the interface. After reporting the concerting evidence of C-nucleates as defects in chapter IV, the following Chapter V deals with passivation and interface treatment methods; and on their potentially beneficial influence on near interface defect densities and electronic properties. Finally, in Chapter VI we conclude our thesis with the final results we obtained and provide an outlook towards future investigations and what is to be done next.
Advisors:Jung, Thomas A.
Committee Members:Meyer, Ernst
Faculties and Departments:05 Faculty of Science
UniBasel Contributors:Jung, Thomas A. and Meyer, Ernst
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:14246
Thesis status:Complete
Number of Pages:105
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss142464
edoc DOI:
Last Modified:10 Sep 2021 04:30
Deposited On:09 Sep 2021 07:32

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