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Characterization of dielectric layers for passivation of 4H-SiC devices
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicon carbide rectifiers and MESFET switches are commercially available since 2001 and 2005 respectively. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance, four inch wafers are available and the next step of technology is set to be the six inch substrate wafers. Despite this tremendous development in SiC technology the reliability issues, like bipolar device degradation, passivation, or low MOSFET channel mobility still remain to be solved.

This thesis focuses on SiC surface passivation and junction termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Five dielectrics with high dielectric constants, Al2O3, AlN, AlON, HfO2 and TiO2 have been investigated. The layers were deposited directly on SiC, or on the thermally oxidized SiC surfaces with several different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.7 kV, reaching 1.6 kV, compared to non passivated devices. Furthermore, AlON deposited on 4H SiC at room temperature provided interface quality comparable to that obtained with the thermally grown SiO2/SiC system.

As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury or deuterium lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments show also that the measured leakage currents of the order of pA are dominated by surface leakage.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , xi, 64 p.
Series
Trita-ICT/MAP, 2006:02
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4229ISBN: 978-91-7178-532-9 (print)OAI: oai:DiVA.org:kth-4229DiVA: diva2:11355
Public defence
2006-12-15, Aula N2, KTH-Electrum 3, Isafordsg. 28, Kista, 10:15
Opponent
Supervisors
Note
QC 20100928Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2010-09-28Bibliographically approved
List of papers
1. Influence of bulk and surface defects on electrical characteristics of SiC diodes with zone termination in the temperature range from 300K to 623 K
Open this publication in new window or tab >>Influence of bulk and surface defects on electrical characteristics of SiC diodes with zone termination in the temperature range from 300K to 623 K
(English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Article in journal (Other academic) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6593 (URN)
Note
QS 20120328Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2012-03-28Bibliographically approved
2. Analysis of bulk and surface components of leakage current in 4H-SiC PiN MESA diodes
Open this publication in new window or tab >>Analysis of bulk and surface components of leakage current in 4H-SiC PiN MESA diodes
2006 (English)In: Microelectronic Engineering, ISSN 0167-9317, Vol. 83, no 1, 75-78 p.Article in journal (Refereed) Published
Abstract [en]

The leakage current in circular- and ring-shaped epitaxial 4H-SiC PiN mesa diodes with different size and periphery to area ratios was evaluated under the influence of the U-V irradiation and temperature in the range from room temperature (RT) to 250 degrees C. The surface leakage current component was found to dominate the reverse current characteristics and was found to be dependent on time and temperature both after reactive ion etching (RIE) of the diodes in the SF6/Ar gas mixture and after the UV irradiation. Charging of the surface states is believed to be responsible for the observed behavior. The LTV irradiation is believed to charge the surface positively. The drift of the I(V) characteristics is due to the trapping of the electrons neutralizing the positive donor states.

Keyword
SiC PiN diodes, leakage current, UV irradiation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6594 (URN)10.1016/j.mee.2005.10.029 (DOI)000234950800022 ()2-s2.0-30344438824 (Scopus ID)
Conference
3rd International Conference on Materials for Advanced Technologies/9th International Conference on Advanced Materials Singapore, SINGAPORE, JUL 03-08, 2005
Note
QC 20100927 QC 20111003. Conference: 3rd International Conference on Materials for Advanced Technologies/9th International Conference on Advanced Materials. Singapore, SINGAPORE. JUL 03-08, 2005 Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2011-10-03Bibliographically approved
3. Reduction of leakage current of 4H-SiC PiN diodes after UV light exposition
Open this publication in new window or tab >>Reduction of leakage current of 4H-SiC PiN diodes after UV light exposition
2007 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 43, no 2, 130-131 p.Article in journal (Refereed) Published
Abstract [en]

A substantial reduction of the leakage current in 4H-SiC pin diodes is observed after <10 eV UV irradiation in air. The high energy UV is believed to remove carbon clusters from the SiC surface. Comparison of leakage current in 4H-SiC pin diodes after different surface treatments, including reactive ion etching, exposure to two different sources of UV light and different forms of chemical cleaning, is presented. Exposure to 4.9 eV UV light in nitrogen atmosphere enhances the leakage by one order of magnitude

Keyword
leakage currents, p-i-n diodes, silicon compounds, ultraviolet radiation effects
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6595 (URN)10.1049/el:20073494 (DOI)000248317300041 ()2-s2.0-33846564507 (Scopus ID)
Note
Uppdaterad från submitted till published QC 20100928Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2010-09-28Bibliographically approved
4. Electrical characterisation of gamma and UV irradiated epitaxial 1.2 kV 4H-SiC PiN diodes
Open this publication in new window or tab >>Electrical characterisation of gamma and UV irradiated epitaxial 1.2 kV 4H-SiC PiN diodes
2004 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2003, PTS 1 AND 2, 2004, Vol. 457-460, 1487-1490 p.Conference paper, Published paper (Refereed)
Abstract [en]

Epitaxial 4H-SiC 1.2 kV PiN diodes have been evaluated using IN measurement techniques after exposure to 1, 2, 3.8 and 10 Mrad irradiation from the Co-60 gamma source. After accumulated gamma dose of 10 Mrad the diodes were exposed to UV irradiation. The forward and reverse diode characteristics were measured successively in the temperature range from RT to 350 degrees C. The leakage current increases with gamma irradiation dose up to about 4 Mrads by a factor of 20 compared to the pre-irradiation values. After an accumulated dose of 10 Mrads the leakage current decreases by about one order of magnitude but is still about 2-3 times larger than before irradiation. The decrease in reverse current is accompanied by the appearance of the high noise. The apparent thermal activation energies increase with the gamma irradiation dose and show a relatively large spread in values especially at lower temperatures (150 degrees C to 250 degrees C).

The UV irradiation has a positive effect on the IN characteristics. The reverse current is lowered by one order of magnitude compared to the pre-irradiation level. The large noise in the leakage current is absent after UV exposure. The low energy level of 0.2 eV appears clearly in the temperature range between 150 degrees C and 250 degrees C after the UV irradiation. The thermal activation energy of 0.91 eV has been determined for the deep energy level in the temperature range from 250 degrees C to 350 degrees C. The values of the thermal activation energies are very consistent between diodes and show less spread as a function of the applied voltage. The Poole-Frenkel dependence with local field enhancement can be fitted to the 0.91 eV level.

Series
MATERIALS SCIENCE FORUM, ISSN 0255-5476
Keyword
4H-SiC, Gamma irradiation, UV irradiation, thermal activation energy, PiN diodes
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6596 (URN)10.4028/www.scientific.net/MSF.457-460.1487 (DOI)000222802200354 ()2-s2.0-8744310135 (Scopus ID)
Conference
10th International Conferece on Silicon Carbide and Related Materials 2003 (ICSCRM 2003) Lyon, FRANCE, OCT 05-10, 2003
Note

QC 20100928

Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2015-06-17Bibliographically approved
5. Characterization of aluminum and titanium oxides deposited on 4H SiC by atomic later deposition technique
Open this publication in new window or tab >>Characterization of aluminum and titanium oxides deposited on 4H SiC by atomic later deposition technique
Show others...
2005 (English)In: Silicon Carbide and Related Materials 2004, Trans Tech Publications Inc., 2005, Vol. 483-485, 701-704 p.Conference paper, Published paper (Refereed)
Abstract [en]

Aluminium oxide and titanium oxide films were deposited using the Atomic Layer Deposition method on n-type 4H Sic and p-type Si {001} substrates, with doping 6.10(15) cm(-3) and 2.10(16) cm(-3), respectively, and on 1.2 kV PiN 4H Sic diodes for passivation studies. The Al2O3 and Sic interface was characterised for the existence of an effective negative charge with a density of 1.10(12) -2.10(12) cm(-2). The dielectric constant of Al2O3 as determined from capacitance-voltage data was about 8.3. The maximum electric field supported by the Al2O3 film was up to 7.5 MV/cm and 8.4 MV/cm on Sic and Si, respectively.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2005
Series
Materials Science Forum, ISSN 0255-5476 ; 483
Keyword
4h-sic, ald, aluminum oxide, atomic layer deposition, passivation, titanium oxide
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6597 (URN)10.4028/www.scientific.net/MSF.483-485.701 (DOI)000228549600165 ()2-s2.0-33144488398 (Scopus ID)978-087849963-2 (ISBN)
Conference
5th European Conference on Silicon Carbide and Related Materials, ECRSCRM2004; Bologna; Italy; 31 August 2004 through 4 September 2004
Note

QC 20100928.

Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2014-12-01Bibliographically approved
6. Characterisation of the Al2O3 films deposited by ultrasonic spray pyrolysis and atomic layer deposition methods for passivation of 4H–SiC devices
Open this publication in new window or tab >>Characterisation of the Al2O3 films deposited by ultrasonic spray pyrolysis and atomic layer deposition methods for passivation of 4H–SiC devices
Show others...
2006 (English)In: Microelectronics and reliability, ISSN 0026-2714, E-ISSN 1872-941X, Vol. 46, 743-755 p.Article in journal (Refereed) Published
Abstract [en]

Al2O3 films were deposited using atomic layer deposition (ALD) and ultrasonic spray pyrolysis (USP) methods on p- and n-type Si substrates, n-type 4H–SiC substrates and 4H–SiC diodes for passivation studies. UV exposure in N2 atmosphere and 5% HF treatment were used as two separate surface preparation procedures prior to Al2O3 deposition. The films deposited with USP technique contain a large amount of fixed negative charge and are vulnerable to water incorporation into the material. The Al2O3 film prepared by ALD method shows much better uniformity and less negative charge. Decrease of the leakage current in the 4H–SiC diodes is observed after Al2O3 passivation using both methods.

Keyword
mesa diodes, silicon, oxides
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6598 (URN)10.1016/j.microrel.2005.08.002 (DOI)000236838500009 ()2-s2.0-33645217987 (Scopus ID)
Note
QC 20100928 QC 20111004. Conference: 26th Annual EOS/ESD Symposium. Dallas, TX. SEP 19-23, 2004.Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2011-10-04Bibliographically approved
7. Aluminium nitride deposition on 4H-SiC by means of physical vapour deposition
Open this publication in new window or tab >>Aluminium nitride deposition on 4H-SiC by means of physical vapour deposition
2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, 456-459 p.Article in journal (Refereed) Published
Abstract [en]

190 nm thick aluminium nitride (AlN) with a dielectric constant of 8.8 was deposited by physical vapour deposition (PVD) on n- and p-type Si and n-type 4H-SiC samples. The Metal-Insulator-Semiconductor, MIS, structures were analysed by IV and CV techniques and 1.2 kV SiC diodes were used to evaluate leakage current before and after AlN deposition. The samples were prepared both with and without 5% HF dip after UV exposure, prior to the AlN deposition. Structural AlN analysis showed polycrystalline composition with a dominant [002] phase, a density of 3.27 g/cm(3) and stochiometry of Al0.4N0.6. Surface pre-treatment did not have much influence on the IV characteristics of Si samples (breakdown field similar to 3 MV/cm). However, the non-HF-etched sample is characterised by 2.5 times smaller CV hysteresis for the p-type sample at 100 kHz. The SiC MIS structures have a high leakage current, nevertheless a beneficial influence of UV irradiation is observed in the case of the non-HF-etched sample (soft breakdown field similar to 3 MV/cm compared to similar to 2 MV/cm for HF-etched sample). The diode reverse current was about 2 pA before UV irradiation and 4 and 600 pA after AlN deposition at room temperature and at 150 degrees C, respectively.

Keyword
silicon carbide, SiQ AlN, passivation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6599 (URN)10.1016/j.tsf.2005.12.261 (DOI)000241220600017 ()2-s2.0-33748762749 (Scopus ID)
Note
QC 20100928. Conference: 12th International Conference on Thin Films. BRATISLAVA, SLOVAKIA. SEP 15-20, 2002Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2011-09-29Bibliographically approved
8. Improved properties of AION/4H-SiC interface for passivation studies
Open this publication in new window or tab >>Improved properties of AION/4H-SiC interface for passivation studies
Show others...
2009 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 600-603, 763-766 p.Article in journal (Refereed) Published
Abstract [en]

Aluminium oxynitride (AlON) films of variable composition were grown by reactive sputter deposition in a N2/O2 ambient at room temperature and studied for device passivation. The films were deposited on Si and 4H-SiC substrates as well as on SiC PiN diodes. The AlON/SiO2/SiC stack provided superior interface properties compared to the AlON/SiC structure. Samples with 8% oxygen content, in the AlON film, and subjected to a UV exposure prior to deposition, exhibited the smallest net positive interface charge. A large net negative interface charge was observed for samples with 10% oxygen content and for the samples with 8% oxygen content and subjected to a RCA1 surface clean, prior to deposition. Diodes passivated with AlON films demonstrated reduced leakage current compared to as-processed diodes

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2009
Keyword
SiC, passivation, leakage currents
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6600 (URN)10.4028/www.scientific.net/MSF.600-603.763 (DOI)000263555300183 ()2-s2.0-84955443699 (Scopus ID)
Note

QC 20100928

Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2016-06-14Bibliographically approved
9. Characterization of HfO films deposited on 4H-SiC by atomic layer deposition
Open this publication in new window or tab >>Characterization of HfO films deposited on 4H-SiC by atomic layer deposition
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12, 124105- p.Article in journal (Refereed) Published
Abstract [en]

Hafnium oxide films with a measured relative dielectric constant of 15.4 were deposited at room temperature on Si and 4H-SiC substrates, as well as on 4H-SiC p-i-n diodes. An 8 nm thick SiO2 interfacial layer on SiC increased the breakdown field of the HfO2/SiO2 stack by 6%, while a 13 nm thick SiO2 layer reduced it by 35%. The evidence of different current conduction mechanisms in SiO2 is shown to be related to the oxide thickness. For the diodes, the breakdown voltage was extended by at least 20%, compared to nonpassivated devices. Annealing at 400 °C in a forming gas changed the crystallinity and increased the relative dielectric constant of the HfO2 layers. There is an indication of reaction between HfO2 and SiO2 in the stacked films after annealing.

Keyword
kappa gate dielectrics, interfacial layer, hafnium oxide, thin-films, decomposition, reliability, precursor, stability, silicon, devices
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6601 (URN)10.1063/1.2734956 (DOI)000247625700109 ()2-s2.0-34547425844 (Scopus ID)
Note
QC 20100928Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2010-09-28Bibliographically approved

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