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Fabrication and Characterization of Si-on-SiC Hybrid Substrates
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Device Group)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we are making a new approach to fabricate silicon on insulator (SOI). By replacing the buried silicon dioxide and the silicon handling wafer with silicon carbide through hydrophilic wafer bonding, we have achieved silicon on crystalline silicon carbide for the first time and silicon on polycrystalline silicon carbide substrates at 150 mm wafer size. The conditions for the wafer bonding are studied and the surface and bond interface are characterized. Stress free and interfacial defect free hybrid wafer bonding has been achieved.

The thermally unfavourable interfacial oxide that originates from the hydrophilic treatment has been removed through high temperature annealing, denoted as Ox-away. Based on the experimental observations, a model to explain the dynamics of this process has been proposed. Ox-away together with spheroidization are found to be the responsible theories for the behaviour. The activation energy for this process is estimated as 6.4 eV.

Wafer bonding of Si and polycrystalline SiC has been realised by an intermediate layer of amorphous Si. This layer recrystallizes to some extent during heat treatment.

Electronic and thermal testing structures have been fabricated on the 150 mm silicon on polycrystalline silicon carbide hybrid substrate and on the SOI reference substrate. It is shown that our hybrid substrates have similar or improved electrical performance and 2.5 times better thermal conductivity than their SOI counterpart. 2D simulations together with the experimental measurements have been carried out to extract the thermal conductivity of polycrystalline silicon carbide as κpSiC = 2.7 WK-1cm-1.

The realised Si-on-SiC hybrid wafer has been shown to be thermally and electrically superior to conventional SOI and opens up for hybrid integration of silicon and wide band gap material as SiC and GaN.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1093
Keyword [en]
hydrophilic wafer bonding, silicon on silicon carbide, hybrid substrate, oxygen out-diffusion
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-221664ISBN: 978-91-554-8794-2 (print)OAI: oai:DiVA.org:uu-221664DiVA: diva2:709753
Public defence
2014-05-16, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2014-04-11 Created: 2014-04-03 Last updated: 2014-07-25
List of papers
1. Oxide-Free Silicon to Silicon Carbide Heterobond
Open this publication in new window or tab >>Oxide-Free Silicon to Silicon Carbide Heterobond
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2008 (English)In: ESC Transactions, ISSN 1938-6737, Vol. 16, no 8, 377-383 p.Article in journal (Refereed) Published
Abstract [en]

Thin crystalline device layersof Si were bonded to Si-faced SiC wafers, with eithera chemical or a thermal oxide interface layer. The interfacethermal oxide was successfully removed by oxygen out-diffusion for 2.5h in an Ar atmosphere at 1250 oC. XTEM micrographsshowed that an abrupt transition between Si and SiC withcomplete removal of the interlayer oxide had been obtained. Stressgenerated during the cool-down process after oxygen out-diffusion was shownto be compressive. IR imaging and an optical microscopy verifiedthat no cracks occurred during cool-down.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-110868 (URN)10.1149/1.2982890 (DOI)
Note

T. Suga J. Bagdahn H. Baumgart C. Colinge K. Hobart H. Moriceau

Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2016-05-06
2. Oxygen out-diffusion from buried layers in SOI and SiC-SOI substrates
Open this publication in new window or tab >>Oxygen out-diffusion from buried layers in SOI and SiC-SOI substrates
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2010 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 54, no 2, 153-157 p.Article in journal (Refereed) Published
Abstract [en]

We have made a comparative study of the oxygen out-diffusion process during heat treatment of SOI wafers and SiC-SOI hybrid substrates. SOI materials with three different thicknesses (2, 20 and 410 nm) of buried oxide (BOX) were used in the investigation High-resolution cross-sectional transmission electron microscopy (HRXTEM) together with laser interferometry was used to determine the remaining thickness of the BOX-layer after heat treatment. After complete removal of the BOX-layer of SOI wafers, the St/Si interface appears to be sharp and defect-free. Similar results were obtained for SiC-SOI hybrid substrates after removal of the entire buried oxide layer. For all combinations investigated oxide removal was accompanied by a thickness reduction and roughening of the silicon surface layer as verified by atomic force microscopy (AFM).

Keyword
Oxygen out-diffusion, SOI, silicon carbide, SiC-SOI
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-117563 (URN)10.1016/j.sse.2009.12.011 (DOI)000275691400012 ()
Available from: 2012-08-23 Created: 2010-02-19 Last updated: 2017-12-12Bibliographically approved
3. Fabrication and Characterization of 150 mm Silicon-on-polycrystalline-Silicon Carbide Substrates
Open this publication in new window or tab >>Fabrication and Characterization of 150 mm Silicon-on-polycrystalline-Silicon Carbide Substrates
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2012 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 41, no 3, 480-487 p.Article in journal (Refereed) Published
Abstract [en]

Silicon-on-insulator (SOI) substrates can reduce RF-substrate losses due to their buried oxide (BOX). On the other hand, the BOX causes problems since it acts as a thermal barrier. Oxide has low thermal conductivity and traps the heat that is generated in devices on the SOI. This paper presents a hybrid substrate which uses a thin layer of poly-crystalline silicon and poly-crystalline silicon carbide (Si-on-poly-SiC) to replace the thermally unfavorable buried oxide and the silicon substrate. 150 mm substrates were fabricated by wafer bonding and shown to be stress and strain free. Various electronic devices and test structures were processed on the hybrid substrate as well as on a low resistivity SOI reference wafer. The substrates were characterized electrically and thermally and compared to each other. Results showed that the Si-on-poly-SiC wafer had a 2.5 times lower thermal resistance and was equally or better in electrical performance compared to the SOI reference wafer.

National Category
Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-162180 (URN)10.1007/s11664-011-1827-2 (DOI)000299930100009 ()
Available from: 2011-12-12 Created: 2011-11-25 Last updated: 2017-12-08Bibliographically approved
4. Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar
Open this publication in new window or tab >>Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar
2014 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 43, no 2, 541-547 p.Article in journal (Refereed) Published
Abstract [en]

Silicon-on-silicon-carbide substrates could be ideal for high-power and radiofrequency silicon devices. Such hybrid wafers, when made by wafer bonding, contain an intermediate silicon dioxide layer with poor thermal characteristics, which can be removed by high-temperature annealing in an inert atmosphere. To understand the dynamics of this process, removal of 2.4-nm-thick SiO2 layers from Si-SiO2-Si and Si-SiO2-SiC substrates has been studied at temperatures ranging from 1100A degrees C to 1200A degrees C. The substrates were analyzed by transmission electron microscopy, electron energy-loss spectroscopy, secondary-ion mass spectroscopy, and ellipsometry, before and after annealing. For oxide thickness less than 2.4 nm, the activation energy for oxide removal was estimated to be 6.4 eV, being larger than the activation energy reported for removal of thicker oxides (4.1 eV). Under the same conditions, the SiO2 layer became discontinuous. In the time domain, three steps could be distinguished: bulk diffusion, bulk diffusion with void formation, and bulk diffusion with disintegration. The void formation, predominant here, has an energetic cost that could explain the larger activation energy. The oxide remaining after prolonged annealing corresponds to one layer of oxygen atoms.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2014
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-209754 (URN)10.1007/s11664-013-2861-z (DOI)000329656700034 ()
Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06Bibliographically approved
5. Thermal characterization of polycrystalline SiC
Open this publication in new window or tab >>Thermal characterization of polycrystalline SiC
2014 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 43, no 4, 1150-1153 p.Article in journal (Refereed) Published
Abstract [en]

A study is made using fabricated thermal resistors in combination with two-dimensional (2D) electrothermal simulations to determine the thermal conductivity of polycrystalline SiC, single-crystalline SiC, and Si. The results show that the poly-SiC substrate has thermal conductivity of κ poly-SiC = 2.7 W K−1 cm−1, which is significantly lower than that of single-crystalline SiC.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-209759 (URN)10.1007/s11664-014-3032-6 (DOI)000334182700046 ()
Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06Bibliographically approved

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