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Precursors and defect control for halogenated CVD of thick SiC epitaxial layers
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon carbide (SiC) is a very hard semiconductor material with wide band gap, high breakdown electric field strength, high thermal conductivity and high saturation electron drift velocity making it a promising material for high frequency and high power devices. The performance of electrical devices is strongly dependent on the quality, doping level and thickness of the grown epitaxial layers. The SiC epitaxial layers are usually grown by chemical vapor deposition (CVD), using silane (SiH4) and light hydrocarbons (C2H4 or C3H8) as precursors, diluted in a massive flow of hydrogen (H2), at growth temperatures and pressures of 1500-1600 °C and 100-300 mbar, respectively. A Silicon Carbide (SiC) device with a high breakdown voltage (> 10 kV) requires thick (> 100 μm) and low doped (1014cm-3) epitaxial layers. The typical growth rate is usually 5-10 μm/h, rendering very long growth times which result in a high cost for the final device. It is hard to increase the growth rate without running into problems with homogeneous gas phase nucleation, which badly affects the surface morphology and the usefulness of the epitaxial layers for devices. This problem can be avoided by lowering the growth pressure and/or increasing the carrier gas flow (H2) to minimize the homogeneous gas phase nucleation or by increasing the growth temperature to evaporate the silicon droplets. On the other hand introducing chlorine into the gas mixture, by adding HCl or using some chlorinated silicon precursor, such as trichlorosilane (SiHCl3) or tetrachlorosilane (SiCl4), or by methyltrichlorosilane (CH3SiCl3) as a single molecule will prevent nucleation in the gas phase. In this thesis a detailed study of the chloride-based processes and an investigation of a bromide-based CVD process is made using a horizontal hot wall reactor. Focus has been mainly on the study of various precursor molecules but also the effect of process parameters on the growth of thick epitaxial layers (100-200 μm). In paper 1 the growth of SiC epitaxial layers on 4° off-axis substrates manifesting very good morphology when using methane (CH4) as carbon precursor is demonstrated. A comparative study of SiCl4, SiHCl3, SiH4+HCl, C3H8, C2H4 and CH4 in an attempt to find the optimal precursor combination is presented in Paper 2 for growth of 4H-SiC epitaxial layers on 4° off-axis substrates with very good morphology. Paper 3 presents a direct comparison between chloride-based and bromide-based CVD chemistries for growth of SiC epitaxial layers using SiH4 and C2H4 as Si- respectively C-precursors with HCl or HBr as growth additives. The influence of temperature ramp up conditions on the carrot defect density on 8° off-axis 4H-SiC epitaxial layers using the single molecule precursor methyltrichlorosilane (MTS) as growth precursor is studied in Paper 4. In paper 5 growth of about 200 μm thick epitaxial layers with very good morphology at growth rates exceeding 100 μm/h using SiCl4+C2H4 and SiH4+HCl+C2H4 precursor approaches is reported. The effect of growth conditions on dislocation density by decorating the dislocations using KOH etching is reported in Paper 6. In Paper 7 the effect of varying parameters such as growth  temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio and in situ pre-growth surface etching time are studied in order to reduce the formation of step bunching and structural defects, mainly triangular defects for growth of about 100 μm thick epitaxial layers on 4° off-axis substrates with very good morphology at growth rates up to 115 μm/h.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 61 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1625
National Category
Physical Sciences Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-111076DOI: 10.3384/diss.diva-111076ISBN: 978-91-7519-213-0 (print)OAI: oai:DiVA.org:liu-111076DiVA: diva2:753060
Public defence
2014-10-31, Plank, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2015-03-11Bibliographically approved
List of papers
1. On the use of methane as a carbon precursor in Chemical Vapor Deposition of silicon carbide
Open this publication in new window or tab >>On the use of methane as a carbon precursor in Chemical Vapor Deposition of silicon carbide
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2014 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 390, 24-29 p.Article in journal (Refereed) Published
Abstract [en]

It is generally considered that methane is not a suitable carbon precursor for growth of silicon carbide (SiC) epitaxial layers by Chemical Vapor Deposition (CVD) since its use renders epitaxial layers with very high surface roughness. In this work we demonstrate that in fact SiC epitaxial layers with high-quality morphology can be grown using methane. It is shown that a key factor in obtaining high-quality material is tuning the C/Si ratio of the process gas mixture to a region where the growth is limited neither by carbon nor by silicon supplies. From the growth characteristics presented here, we argue that the reactivity of methane with the SiC surface is much higher than generally assumed in SiC CVD modeling today.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Chloride-based; Al CVD; BL Methane; Silicon carbide; SiC
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-107126 (URN)10.1016/j.jcrysgro.2013.12.033 (DOI)000335770000005 ()
Available from: 2014-06-05 Created: 2014-06-05 Last updated: 2017-12-05Bibliographically approved
2. Finding the Optimum Chloride-Based Chemistry for Chemical Vapor Deposition of SiC
Open this publication in new window or tab >>Finding the Optimum Chloride-Based Chemistry for Chemical Vapor Deposition of SiC
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2014 (English)In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 3, no 10, P320-P323 p.Article in journal (Refereed) Published
Abstract [en]

Chemical vapor deposition of silicon carbide with a chloride-based chemistry can be done using several different silicon and carbon precursors. Here, we present a comparative study of SiCl4, SiHCl3, SiH4+HCl, C3H8, C2H4 and CH4 in an attempt to find the optimal precursor combination. We find that while the chlorinated silanes SiCl4 and especially SiHCl3 give higher growth rate than natural silane and HCl, SiH4+HCl gives better morphology at C/Si around 1 and SiCl4 gives the best morphology at low C/Si. Our study shows no effect on doping incorporation with precursor chemistry. We suggest that these results can be explained by the number of reaction steps in the gas phase chemical reaction mechanisms for producing SiCl2, which is the most important Si species, and by formation of organosilicons in the gas phase. As carbon precursor, C3H8 or C2H4 are more or less equal in performance with a slight advantage for C3H8, CH4 is however not a carbon precursor that should be used unless extraordinary growth conditions are needed.

Place, publisher, year, edition, pages
ECS, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111074 (URN)10.1149/2.0111410jss (DOI)000341962100011 ()
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
3. Brominated chemistry for chemical vapor deposition of electronic grade SiC
Open this publication in new window or tab >>Brominated chemistry for chemical vapor deposition of electronic grade SiC
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2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 3, 793-801 p.Article in journal (Refereed) Published
Abstract [en]

Chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has paved the way for very thick epitaxial layers in short deposition time as well as novel crystal growth processes for SiC. Here, we explore the possibility to also use a brominated chemistry for SiC CVD by using HBr as additive to the standard SiC CVD precursors. We find that brominated chemistry leads to the same high material quality and control of material properties during deposition as chlorinated chemistry and that the growth rate is on average 10 % higher for a brominated chemistry compared to chlorinated chemistry. Brominated and chlorinated SiC CVD also show very similar gas phase chemistries in thermochemical modelling. This study thus argues that brominated chemistry is a strong alternative for SiC CVD since the deposition rate can be increased with preserved material quality. The thermochemical modelling also suggest that the currently used chemical mechanism for halogenated SiC CVD might need to be revised.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-111075 (URN)10.1021/acs.chemmater.5b00074 (DOI)000349934500016 ()
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
4. Carrot defect control in chloride-based CVD through optimized ramp up conditions
Open this publication in new window or tab >>Carrot defect control in chloride-based CVD through optimized ramp up conditions
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, 109-112 p.Conference paper, Published paper (Refereed)
Abstract [en]

Epitaxial growth of 4H-SiC on 8 degrees off-axis substrates has been performed under different condition during the temperature ramp up in order to study the effect on the carrot defect. The study was done in a hot wall chemical vapor deposition reactor using the single molecule precursor methyltrichlorosilane (MTS). During the temperature ramp up, a small flow of HCl or C2H4 was added to the H-2 ambient to study different surface etching conditions. The best result was obtained when HCl was added from 1175 to 1520 degrees C during the ramp up to growth temperature (1575 degrees C).

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keyword
Carrot defects; Chloride-based CVD; Ramp up condition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87565 (URN)10.4028/www.scientific.net/MSF.717-720.109 (DOI)000309431000025 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2015-03-11
5. Process stability and morphology optimization of very thick 4H-SiC epitaxial layers grown by chloride-based CVD
Open this publication in new window or tab >>Process stability and morphology optimization of very thick 4H-SiC epitaxial layers grown by chloride-based CVD
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2013 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 380, 55-60 p.Article in journal (Refereed) Published
Abstract [en]

The development of a chemical vapor deposition (CVD) process for very thick silicon carbide (SiC) epitaxial layers suitable for high power devices is demonstrated by epitaxial growth of 200 nm thick, low doped 4H-SiC layers with excellent morphology at growth rates exceeding 100 nm/h. The process development was done in a hot wall CVD reactor without rotation using both SiCl4 and SiH4+HCl precursor approaches to chloride based growth chemistry. A C/Si ratio andlt;1 and an optimized in-situ etch are shown to be the key parameters to achieve 200 nm thick, low doped epitaxial layers with excellent morphology.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Crystal morphology, CVD, Chloride-based, SiC
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-98217 (URN)10.1016/j.jcrysgro.2013.05.037 (DOI)000324042000011 ()
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||

Available from: 2013-10-03 Created: 2013-10-03 Last updated: 2017-12-06
6. Effect of process parameters on dislocation density in thick 4H-SiC epitaxial layers grown by chloride-based CVD on 4 degrees off-axis substrates
Open this publication in new window or tab >>Effect of process parameters on dislocation density in thick 4H-SiC epitaxial layers grown by chloride-based CVD on 4 degrees off-axis substrates
2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, 159-162 p.Conference paper, Published paper (Refereed)
Abstract [en]

The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H2 ratio on dislocation density was investigated by performing KOH etching on 100 mu m thick epitaxial layers grown on 4 degrees off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 mu m/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keyword
Silicon Carbide; SiC; CVD; Dislocation; 4 degrees off-axis substrates; Epitaxial layers
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108191 (URN)10.4028/www.scientific.net/MSF.778-780.159 (DOI)000336634100037 ()
Conference
The International Conference on Silicon Carbide and Related Materials, September 29-October 4, 2013, Phoenix Seagaia Resort, Miyazaki, Japan
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2015-03-11
7. Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates
Open this publication in new window or tab >>Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 22Article in journal (Refereed) Published
Abstract [en]

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96469 (URN)10.1063/1.4809928 (DOI)000320675300004 ()
Available from: 2013-08-23 Created: 2013-08-20 Last updated: 2017-12-06Bibliographically approved

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