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Ohmic Contacts for High Temperature Integrated Circuits in Silicon Carbide
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In electrical devices and integrated circuits, ohmic contacts are necessary and a prerequisite for the current transport over the metal-semiconductor junctions. At the same time, a desired property of the ohmic contacts is to not add resistance or in other way disturb the performance. For high temperature electronics, the material demands are high regarding functionality and stability at elevated working temperatures, during and after temperature cycling and during long time of use. 

Silicon carbide, SiC, is a suitable substrate material for fabrication of high temperature electronics with a large band gap, good thermal conductivity and chemical inertness. The large bandgap causes however difficulties in finding a common material for ohmic contacts to both n- and p-type SiC. The goal of this project is to find a suitable metallization for n- as well as p-type contacts to epitaxially doped SiC for use in integrated circuits. The circuit technology developed and used in KTH for SiC is built on bipolar junction transistors. The p-doped base layer in the transistors is relatively low doped; 5 x 1017 – 1 x 1018 cm-3. P-type SiC is more difficult to form ohmic contacts to than n-type SiC, with such a low doping concentration it is even more complicated. 

Today, the metallizations used in the contacts consists of Ni for n-type contacts and Ni/Ti/Al to p-type SiC. Experiments of the specific contact resistivity ρc and the sheet resistance Rsh of these contacts, characterized to two types of samples, are presented for the extreme temperature range of -40 °C – 500 °C. Ohmic contact test chips with transfer length method structures have been compared to similar test structures on samples from the KTH SiC integrated circuits. The metals were also tested on the opposite doping polarity. 

Sputter deposition of Co and Si in layers to form CoSi2 contacts was made to chips from the same contact test wafer for comparison with the behavior of the presently used contacts. Since this was a new metallization, the process development of the high temperature anneal and contact formation made an important part of the work. 

Out of the tested contacts, Ni has been the best for n-SiC and Ni/Ti/Al for p-SiC. None of the three metallizations formed ohmic contacts to both n- and p-SiC. However, the CoSi2 contacts showed specific contact resistivity ρc <4 x 10-6 Ωcm2 at 25 °C and non-linear I-V characteristics but without barriers to p-SiC after voltage sweeps of ± 75V.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , viii, 39 p.
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:19
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
URN: urn:nbn:se:kth:diva-156239ISBN: 978-91-7595-352-6OAI: diva2:765965
2014-12-17, Sal C, Kistagången 16, KTH- Electrum, Kista, 13:15 (English)

QC 20141203

Available from: 2014-12-03 Created: 2014-11-25 Last updated: 2014-12-03Bibliographically approved
List of papers
1. Characterization of Ohmic Ni/Ti/Al and Ni Contacts to 4H-SiC from-40 degrees C to 500 degrees C
Open this publication in new window or tab >>Characterization of Ohmic Ni/Ti/Al and Ni Contacts to 4H-SiC from-40 degrees C to 500 degrees C
2014 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 778-780, 681-684 p.Article in journal (Refereed) Published
Abstract [en]

Extreme temperature measurements of Ni/Ti/Al contacts to p-type SiC (N-a = 1.10(18)cm(-3)), with a specific contact resistivity rho(c) = 6.75.10(-4) Omega cm(2) at 25 degrees C, showed a five time increase of the specific contact resistivity at -40 degrees C (rho(c) = 3.16.10(-3) Omega cm(2)), and a reduction by almost a factor 10 at 500 degrees C (rho(c) = 7.49.10(-5) Omega cm(2)). The same response of rho(c) to temperature was seen for contacts on lower doped epitaxial layer. Also N-type nickel contacts improved with higher operational temperature but with a considerably smaller variation over the same temperature interval. No degradation of the performance was seen to either the Ni/Ti/Al or the Ni contacts due to the high temperature measurements.

Contacts, TLM
National Category
Materials Engineering
urn:nbn:se:kth:diva-147445 (URN)10.4028/ (DOI)000336634100161 ()2-s2.0-84896092522 (ScopusID)978-303835010-1 (ISBN)
15th International Conference on Silicon Carbide and Related Materials (ICSCRM 2013), SEP 29-OCT 04, 2013, Miyazaki, JAPAN

QC 20140627. QC 20160304

Available from: 2014-06-27 Created: 2014-06-27 Last updated: 2016-03-04Bibliographically approved
2. Sputtered Ohmic Cobalt Silicide Contacts to 4H-Sic
Open this publication in new window or tab >>Sputtered Ohmic Cobalt Silicide Contacts to 4H-Sic
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-156845 (URN)

QS 2014

Accepted with minor revision in Materials Science Forum.

Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2014-12-03Bibliographically approved

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