liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Chloride-based Silicon Carbide CVD
Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.ORCID iD: 0000-0002-7171-5383
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon carbide (SiC) is a promising material for high power and high frequency devices due to its wide bandgap, high break down field and high thermal conductivity. The most established technique for growth ofepitaxial layers of SiC is chemical vapor deposition (CVD) at around 1550 °C using silane, SiH4, and lighthydrocarbons e g propane, C3H8, or ethylene, C2H4, as precursors heavily diluted in hydrogen. For high-voltagedevices made of SiC thick (> 100 μm), low doped epilayers are needed. Normal growth rate in SiC epitaxy is~ 5 μm/h, rendering long growth times for such SiC device structures. The main problem when trying to achievehigher growth rate by increasing the precursor flows is the formation of aggregates in the gas phase; for SiCCVD these aggregates are mainly silicon droplets and their formation results in saturation of the growth ratesince if the gas flow does not manage to transport these droplets out of the growth zone, they will eventuallycome in contact with the crystal surface and thereby creating very large defects on the epilayer making theepilayer unusable. To overcome this problem, high temperature- as well as low pressure processes have beendeveloped where the droplets are either dissolved by the high temperature or transported out of the susceptor bythe higher gas flow. A different approach is to use chloride-based epitaxy that uses the idea that the silicondroplets can be dissolved by presence of species that bind stronger to silicon than silicon itself. An appropriatecandidate to use is chlorine since it forms strong bonds to silicon and chlorinated compounds of high purity canbe purchased. In this thesis the chloride-based CVD process is studied by using first a single molecule precursor,methyltrichlorosilane (MTS) that contributes with silicon, carbon and chlorine to the process. Growth of SiCepilayers from MTS is explored in Paper 1 where growth rates up to 104 μm/h are reported together withmorphology studies, doping dependence of growth rate and the influence of the C/Si- and Cl/Si-ratios on thegrowth rate and doping. In Paper 2 MTS is used for the growth of 200 μm thick epilayers at a growth rate of 100μm/h, the epilayers are shown to be of very high crystalline quality and the growth process stable. The growthcharacteristics of the chloride-based CVD process, is further studied in Paper 3, where the approach to add HClgas to the standard precursors silane and ethylene is used as well as the MTS approach. A comparison betweenliterature data of growth rates for different approaches is done and it is found that a precursor molecule withdirect Si-Cl bonds should be more efficient for the growth process. Also the process stability and growth ratedependence on C/Si- and Cl/Si are further studied. In Paper 4 the standard growth process for growth on 4° offaxis substrates is improved in order to get better morphology of the epilayers. It is also shown that the optimizedprocess conditions can be transferred to a chloride-based process and a high growth rate of 28 μm/h wasachieved, using the HCl-approach, while keeping the good morphology. In Paper 5 chloride-based CVD growthon on-axis substrates is explored using both the HCl- and MTS-approaches. The incorporation of dopants in SiCepilayers grown by the chloride-based CVD process is studied in Papers 6 and 7 using the HCl-approach. InPaper 6 the incorporation of the donor atoms nitrogen and phosphorus is studied and in Paper 7 theincorporation of the acceptor atoms boron and aluminum. The incorporation of dopants is found to follow thetrends seen in the standard growth process but it is also found that the Cl/Si-ratio can affect the amount ofincorporated dopants.

Abstract [en]

Kiselkarbid (SiC) är ett fascinerande material som samtidigt är mycket enkelt och mycketkomplicerat. Det är enkelt eftersom det byggs upp av bara två sorters atomer, kisel och kol.Atomerna bygger upp kristallens struktur genom att bilda Si-C bindningar och man kan beskrivakristallstrukturen som uppbyggd av tetraedrar med en kiselatom (eller kolatom) i mitten och enkolatom (eller kiselatom) i varje hörn på tetraedern. Samtidigt är SiC komplicerat eftersomberoende på hur man staplar dessa tetraedrar kan man få olika varianter på kristallstrukturen, såkallade polytyper. Det finns drygt 200 kända polytyper av kiselkarbid, men det är dock bara enhandfull av dessa polytyper som är tekniskt intressanta. Kiselkarbid är intressant eftersom det ärett hårt material som inte heller påverkas nämnvärt av kemiskt aggressiva miljöer ellertemperaturer upp till 2000 °C; dessutom är SiC en halvledare och tack vare dess tålighet är det ettmycket bra material för elektriska komponenter för högspänningselektronik eller för användningi aggressiva miljöer.

För att kunna tillverka dessa komponenter måste man kunna odla kristaller av kiselkarbid. Detfinns i princip två typer av kristallodling; i) odling av bulkkristaller, där stora kristaller odlas föratt sedan kan skivas och poleras till kristallskivor (dessa skivor benämns oftast substrat), och ii)odling av epitaxiella skikt, där man odlar ett tunt lager kristall med mycket hög renhet ovanpå ettsubstrat (ordet epitaxi kommer från grekiskans epi = ovanpå och taxis = i ordning, epitaxiellaskikt odlas alltså ovanpå ett substrat och kopierar den kristallina ordningen hos substratet). I detepitaxiella skiktet, eller epilagret som det även kallas, kan man styra den elektriskaledningsförmågan med mycket hög precision genom att blanda in små mängder orenheter iepilagret, man pratar här om att dopa halvledarkristallen. För att odla epilager av SiC använderman CVD, CVD betyder Chemical Vapor Deposition, någon riktigt bra svensk översättningfinns inte men det är en teknik för att framställa ett tunt lager av ett material genom kemiskareaktioner med gaser som startmaterial.

I standard CVD-processen för odling av SiC epilager använder man silan (SiH4) som kiselkälla och lätta kolväten som eten (C2H4) eller propan (C3H8) som kolkälla. Dessa gaser späds kraftigtut i vätgas och man odlar epilagret vid ungefär 1500-1600 °C. Med denna process kan man odlaca 5 mikrometer (mikrometer = miljondelsmeter) epilager på en timme. Men för vissakomponenter behöver man ett epilager som är över 100 mikrometer tjockt, vilket görtillverkningen av sådana komponenter både tidsödande och kostsam. Ett problem som manmåste lösa för att få högre tillväxthastighet i processen är att när man ökar mängden silan,kommer kiseldroppar att bildas i gasfasen och om de kommer i kontakt med substratet blirepilagret förstört. I denna avhandling undersöks ett sätt att lösa problemet med kiseldropparnaoch därmed kunna tillåta höga tillväxthastigheter för SiC epilager. Idén är att man kan lösa uppkiseldropparna genom att tillsätta något i gasblandningen som binder starkare till kisel än kisel.En mycket bra atom att använda för detta ändamål är klor eftersom klor binder mycket starkt tillkisel. Man kallar denna process för klorid-baserad CVD.

Till att börja med använde vi molekylen metyltriklorsilan (MTS), som innehåller både kol, kiseloch klor, för klorid-baserad tillväxt av SiC epilager. Genom att använda MTS lyckades vi fåtillväxthastigheter mellan 2 och 104 mikrometer i timmen. Vi har även visat att det är möjligtanvända MTS för att odla 200 mikrometer tjocka epilager med en tillväxthastighet på 100mikrometer i timmen utan att den kristallina kvalitén på epilagren försämras. Ett alternativ till attanvända MTS är att addera saltsyra (HCl) i gasform till standard processen. För att förstå denklorid-baserade processen bättre, jämfördes de olika alternativen med litteraturdata från enprocess där man istället för vanlig silan hade använt triklorsilan (TCS) för att få en klorid-baserad process. Det visade sig att MTS- och TCS-processerna krävde mindre kiselhalt i gasfasen för attfå en hög tillväxthastighet, med andra ord var de mer effektiva. Vi förklarade detta med atteftersom dessa startmolekyler har tre kisel-kol bindningar är det enkelt att bilda SiCl2 molekylen,som har visat sig vara ett viktigt mellansteg i den klorid-baserade processen, eftersom man dåbara behöver bryta kemiska bindningar. Om man istället börjar från silan och saltsyra måstekemiska reaktioner ske för att skapa kisel-kol bindningar och därmed SiCl2.

När man odlar kristaller underlättar man tillväxten genom att preparera ytan på substratet medatomära steg. Om man tittar på ytan med atomär förstoring kan säga att ytan liknar en trappa,detta är bra eftersom atomerna som bygger upp epilagret gärna fastnar vid atomära steg eftersomde kan binda in till kristallen både neråt och åt sidan. Vi har optimerat standard processen för attfå bättre morfologi, alltså en finare yta, när man odlar på substrat som har mindre andel atomärasteg på ytan och visat att denna optimering går att överföra till en klorid-baserad process medhög tillväxthastighet . Vi har även visat att man kan använda den klorid-baserade processen föratt odla epilager med hög tillväxthastighet på substrat helt utan atomära steg.

Slutligen har vi studerat doping av kiselkarbid vid höga tillväxthastigheter med den kloridbaseradeprocessen, både n-typ doping (där man dopar med ämnen som har fler valenselektronerän kol och kisel så att man får ett överskott av elektroner i materialet) med kväve och fosfor, ochp-typ doping (där man dopar med ämnen som har färre valenselektroner än kol och kisel så attman får ett underskott av elektroner i materialet) med bor och aluminium.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 47 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1225
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-15428ISBN: 978-91-7393-752-8 (print)OAI: oai:DiVA.org:liu-15428DiVA: diva2:114173
Public defence
2008-12-10, Plank, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2015-03-11Bibliographically approved
List of papers
1. Very high growth rate of 4H-SiC epilayers using the chlorinated precursor methyltrichlorosilane (MTS)
Open this publication in new window or tab >>Very high growth rate of 4H-SiC epilayers using the chlorinated precursor methyltrichlorosilane (MTS)
Show others...
2007 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 307, no 2, 334-340 p.Article in journal (Refereed) Published
Abstract [en]

The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall chemical vapour deposition (CVD) reactor with growth rates higher than 100 μm/h. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard silicon carbide (SiC) epitaxial growth using only silane, SiH4, and hydrocarbons as precursors. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate, morphology, and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor. The growth rate dropped for C/Si<1 but was constant for C/Si>1. Further, the growth rate decreased with lower Cl/Si ratio. This study shows that MTS is a promising precursor for homoepitaxial growth of SiC within the concept of chloride-based SiC growth.

Keyword
A3. Chemical vapour deposition processes; B. Methyltrichlorosilane; B. Silicon carbide
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15246 (URN)10.1016/j.jcrysgro.2007.07.002 (DOI)
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2017-12-14Bibliographically approved
2. Very high crystalline quality of thick 4H-SiC epilayers grown from methyltrichlorosilane (MTS)
Open this publication in new window or tab >>Very high crystalline quality of thick 4H-SiC epilayers grown from methyltrichlorosilane (MTS)
Show others...
2008 (English)In: Physica status solidi (RRL) - Rapid Research Letters, ISSN 1862-6254, Vol. 2, no 4, 188-190 p.Article in journal (Refereed) Published
Abstract [en]

200 µm thick 4H-SiC epilayers have been grown by chloride-based chemical-vapor deposition using methyltrichlorosilane (MTS) as single precursor. The very high crystalline quality of the grown epilayer is demonstrated by high resolution X-Ray Diffraction rocking curve with a full-width-half-maximum value of only 9 arcsec. The high quality of the epilayer is further shown by low temperature photoluminescence showing strong free exciton and nitrogen bound exciton lines. The very high crystalline quality achieved for the thick epilayer grown in just two hours at 1600 °C suggests that MTS is a suitable precursor molecule for SiC bulk growth.

Place, publisher, year, edition, pages
Wiley InterScience, 2008
Keyword
61.05.cp, 68.55.ag, 78.55.Hx, 81.05 Hd, 81.10.Bk, 81.15.Gh
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15248 (URN)10.1002/pssr.200802081 (DOI)
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2015-03-11Bibliographically approved
3. Growth characteristics of chloride-based SiC epitaxial growth
Open this publication in new window or tab >>Growth characteristics of chloride-based SiC epitaxial growth
Show others...
2008 (English)In: Physica status solidi (RRL) - Rapid Research Letters, ISSN 1862-6270, Vol. 2, no 6, 278-280 p.Article in journal (Refereed) Published
Abstract [en]

In this study some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the C/Si and Cl/Si ratios have on the growth are studied. It is found that MTS is the most efficient precursor and that the growth becomes carbon limited at C/Si < 1.

Place, publisher, year, edition, pages
Wiley InterScience, 2008
Keyword
68.55.ag, 81.05 Hd, 81.15.Gh
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15249 (URN)10.1002/pssr.200802183 (DOI)
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2015-03-11Bibliographically approved
4. Improved morphology for epitaxial growth on 4° off-axis 4H-SiC substrates
Open this publication in new window or tab >>Improved morphology for epitaxial growth on 4° off-axis 4H-SiC substrates
Show others...
2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 12, 3265-3272 p.Article in journal (Refereed) Published
Abstract [en]

A process optimization of the growth of SiC epilayers on 4° off-axis 4H-SiC substrates is reported. Process parameters such as growth temperature, C/Si-ratio and temperature ramp up conditions are optimized for the standard non-chlorinated growth in order to grow smooth epilayers without step-bunching and triangular defects. The growth of 6 μm thick n-type doped epitaxial layers on 75 mm diameter wafers is demonstrated as well as that of 20 μm thick layer. The optimized process was then transferred to a chloride-based process and a growth rate 28 μm/h was achieved without morphology degradation. A low growth temperature and a low C/Si ratio are the key parameters to reduce both the step-bunching and the formation of triangular defects.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15251 (URN)10.1016/j.jcrysgro.2009.03.037 (DOI)
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2017-12-14Bibliographically approved
5. Homoepitaxial growth of 4H-SiC on on-axis Si-face substrates using chloride-based CVD
Open this publication in new window or tab >>Homoepitaxial growth of 4H-SiC on on-axis Si-face substrates using chloride-based CVD
Show others...
2009 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The homoepitaxial chloride-based CVD growth is demonstrated on Si-face on-axis 4HSiC substrates. The use of chloride-based CVD has allowed growth of 100% 4H-SiC epitaxial layers with a growth rate of 20μm/h, thus about seven times higher than with standard precursors. It was also found that chlorine etches preferentially the 3C-SiC inclusions that tends to nucleate on Siface on-axis substrates. Therefore the Cl/Si ratio is a fundamental process parameter to optimize.

Keyword
chloride-based CVD growth, epilayers, on-axis, Si-face, high growth rate
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15250 (URN)10.4028/www.scientific.net/MSF.600-603.107 (DOI)000263555300025 ()
Conference
International Conference on Silicon Carbide and Related Materials(ICSCRM-2007), 14-19 October 2007, Lake Biwa Resort, Otsu, Japan
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2015-03-11Bibliographically approved
6. Donor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD
Open this publication in new window or tab >>Donor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD
Show others...
2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 5, 1321-1327 p.Article in journal (Refereed) Published
Abstract [en]

A systematic n-type doping study has been performed on 4H- and 6H-SiC epilayers grown at high growth rate using chloride-based CVD. The effect of temperature, pressure, growth rate, C/Si-, Cl/Si ratio and dopant flow on the incorporation of the nitrogen and phosphorus donor atoms have been investigated. It is found that the effect of the C/Si-ratio on the incorporation of nitrogen or phosphorus atoms is similar to what has been reported for the standard low growth rate process without addition of chlorine. The Cl/Si-ratio seems to affect the nitrogen incorporation at growth rates higher than 65 μm/h. The doping concentration is stable against variations in growth rate, growth pressure and growth temperature for the nitrogen doped layers.

Keyword
Doping, Chemical vapor deposition processes, Hot wall epitaxy, Silicon carbide
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15252 (URN)10.1016/j.jcrysgro.2008.12.029 (DOI)
Available from: 2008-10-29 Created: 2008-10-27 Last updated: 2017-12-14Bibliographically approved
7. Acceptor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD
Open this publication in new window or tab >>Acceptor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD
2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 13, 3364-3370 p.Article in journal (Refereed) Published
Abstract [en]

A systematic p-type doping study has been performed on 4H- and 6H-SiC epilayers grown at high growth rate using chloride-based chemical vapor deposition. The effect of temperature, pressure, growth rate, C/Si-, Cl/Si ratio and dopant flow on the incorporation of the acceptor atoms aluminum and boron has been studied. The C/Si-ratio on the aluminum incorporation has similar behavior to what has been reported for the standard non-chlorinated low-growth rate process, while no clear effect of C/Si-ratio was observed for the boron incorporation. A higher Cl/Si-ratio seems to lead to lower aluminum and boron incorporation either due to more effective silicon supply at high Cl/Si ratio or due to removal of dopant atoms from the surface by chlorine. The doping concentration is stable to the variations in silicon molar fraction, growth pressure and growth temperature for the aluminum doped layers. Also p-type doping with gallium was tested.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-15291 (URN)10.1016/j.jcrysgro.2009.03.049 (DOI)
Available from: 2008-10-29 Created: 2008-10-29 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(491 kB)3829 downloads
File information
File name FULLTEXT01.pdfFile size 491 kBChecksum SHA-512
3bbf21373c8dbea7b302d4279c7b0c1f855bf8124887ee8be9c1b8d6d78f42ee34c4bb0136b866f450be8445aafe71829998632ab0188891a7da2a0c362e4082
Type fulltextMimetype application/pdf
cover(561 kB)45 downloads
File information
File name COVER01.pdfFile size 561 kBChecksum SHA-512
7c1f595d4b2ed409825622e798fde47a69758c4eee7c93cf68308bca442d0b0c42bd42e5c3fb573b1491ff845e4c4a3199655110c57d8e0ef5d95c6999e1825b
Type coverMimetype application/pdf

Authority records BETA

Pedersen, Henrik

Search in DiVA

By author/editor
Pedersen, Henrik
By organisation
Materials Science The Institute of Technology
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 3829 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 3230 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf