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A Quantum Chemical Exploration of SiC Chemical Vapor Deposition
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-6175-1815
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

SiC is a wide bandgap semiconductor with many attractive properties. It hasattracted particular attentions in the areas of power and sensor devices as wellas biomedical and biosensor applications. This is owing to its properties suchas large bandgap, high breakdown electric field, high thermal conductivitiesand chemically robustness. Typically, SiC homoepitaxial layers are grownusing the chemical vapor deposition (CVD) technique. Experimental studiesof SiC CVD have been limited to post-process measuring of the layer ratherthan in situ measurements. In most cases, the observations are presented interms of input conditions rather than in terms of the unknown growth conditionnear the surface. This makes it difficult to really understand the underlyingmechanism of what causes the features observed experimentally. Withhelp of computational methods such as computational fluid dynamic (CFD)we can now explore various variables that are usually not possible to measure.CFD modeling of SiC CVD, however, requires inputs such as thermochemicalproperties and chemical reactions, which in many cases are not known. In thisthesis, we use quantum chemical calculations to provide the missing detailscomplementary to CFD modeling.

We first determine the thermochemical properties of the halides and halohydridesof Si and C species, SiHnXm and CHnXm, for X being F, Cl and Brwhich were shown to be reliable compared to the available experimentaland/or theoretical data. In the study of gas-phase kinetics, we combine ab initiomethods and DFTs with conventional transition state theory to derive kineticparameters for gas phase reactions related to Si-H-X species. Lastly, westudy surface adsorptions related to SiC-CVD such as adsorptions of small CHand Si-H-X species, and in the case of C-H adsorption, the study was extendedto include subsequent surface reactions where stable surface productsmay be formed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , p. 52
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1828
National Category
Inorganic Chemistry Condensed Matter Physics Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-133941DOI: 10.3384/diss.diva-133941ISBN: 9789176855898 (print)OAI: oai:DiVA.org:liu-133941DiVA, id: diva2:1065694
Public defence
2017-02-16, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-01-16 Created: 2017-01-16 Last updated: 2017-02-10Bibliographically approved
List of papers
1. Shortcomings of CVD modeling of SiC today
Open this publication in new window or tab >>Shortcomings of CVD modeling of SiC today
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2013 (English)In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 132, no 11, p. 1398-Article in journal (Refereed) Published
Abstract [en]

The active, epitaxial layers of silicon carbide (SiC) devices are grown by chemical vapor deposition (CVD), at temperatures above 1,600 °C, using silane and light hydrocarbons as precursors, diluted in hydrogen. A better understanding of the epitaxial growth process of SiC by CVD is crucial to improve CVD tools and optimize growth conditions. Through computational fluid dynamic (CFD) simulations, the process may be studied in great detail, giving insight to both flow characteristics, temperature gradients and distributions, and gas mixture composition and species concentrations throughout the whole CVD reactor. In this paper, some of the important parts where improvements are very much needed for accurate CFD simulations of the SiC CVD process to be accomplished are pointed out. First, the thermochemical properties of 30 species that are thought to be part of the gas-phase chemistry in the SiC CVD process are calculated by means of quantum-chemical computations based on ab initio theory and density functional theory. It is shown that completely different results are obtained in the CFD simulations, depending on which data are used for some molecules, and that this may lead to erroneous conclusions of the importance of certain species. Second, three different models for the gas-phase chemistry are compared, using three different hydrocarbon precursors. It is shown that the predicted gas-phase composition varies largely, depending on which model is used. Third, the surface reactions leading to the actual deposition are discussed. We suggest that hydrocarbon molecules in fact have a much higher surface reactivity with the SiC surface than previously accepted values.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2013
Keywords
Silicon carbide, Chemical vapor deposition, Computational fluid dynamics, Thermochemical data, Gas-phase reactions, Surface reactions
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-103136 (URN)10.1007/s00214-013-1398-9 (DOI)000325107800001 ()
Funder
Swedish Foundation for Strategic Research , SM11-0051Swedish Foundation for Strategic Research , EM11-0034
Available from: 2014-01-13 Created: 2014-01-13 Last updated: 2017-12-06
2. Thermochemical Properties of Halides and Halohydrides of Silicon and Carbon
Open this publication in new window or tab >>Thermochemical Properties of Halides and Halohydrides of Silicon and Carbon
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2016 (English)In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 5, no 2, p. P27-P35Article in journal (Refereed) Published
Abstract [en]

Atomization energies, enthalpies of formation, entropies as well as heat capacities of the SiHnXm and CHnXm systems, with X being F, Cl and Br, have been studied using quantum chemical calculations. The Gaussian-4 theory (G4) and Weizman-1 theory as modified by Barnes et al. 2009 (W1RO) have been applied in the calculations of the electronic, zero point and thermal energies. The effects of low-lying electronically excited states due to spin orbit coupling were included for all atoms and diatomic species by mean of the electronic partition functions derived from the experimental or computational energy splittings. The atomization energies, enthalpies of formation, entropies and heat capacities derived from both methods were observed to be reliable. The thermochemical properties in the temperature range of 298-2500 K are provided in the form of 7-coefficient NASA polynomials. (C) The Author(s) 2015. Published by ECS. All rights reserved.

Place, publisher, year, edition, pages
ELECTROCHEMICAL SOC INC, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-124117 (URN)10.1149/2.0081602jss (DOI)000365748800023 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research

Available from: 2016-01-22 Created: 2016-01-19 Last updated: 2017-11-30

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