uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Smith, Ulf
Publications (10 of 31) Show all publications
Mardani, S., Norström, H., Smith, U., Gustavsson, F., Olsson, J. & Zhan, S.-L. (2016). Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures. Journal of Vacuum Science & Technology B, 34(6), Article ID 060603.
Open this publication in new window or tab >>Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures
Show others...
2016 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 34, no 6, article id 060603Article in journal (Refereed) Published
Abstract [en]

High-temperature stability of Cu-based interconnects is of technological importance for electronic circuits based on wide band gap semiconductors. In this study, different metal stack combinations using Ta or TaN as capping- and/or barrier-layer, in the configuration cap/Cu/barrier, are evaluated electrically and morphologically prior to and after high-temperature treatments. The symmetric combinations Ta/Cu/Ta and TaN/Cu/TaN are characterized by a low and stable sheet resistance after annealing up to 700 °C. Asymmetric combinations of Ta/Cu/TaN and TaN/Cu/Ta, however, display an increase in sheet resistance values after annealing at 500 °C and above. This increase in sheet resistance is considered to result from Ta diffusion into the grain boundaries of the Cu film. The preliminary electromigration studies on the TaN/Cu/Ta and TaN/Cu/TaN structures show a twofold higher activation energy and a tenfold longer lifetime for the former, thus suggesting an important role of the interface between Cu and the cap and/or barrier.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-300795 (URN)10.1116/1.4967372 (DOI)000389530000054 ()
Funder
Swedish Foundation for Strategic Research , RE10-0011Swedish Foundation for Strategic Research , RIF-14-0053
Available from: 2016-08-13 Created: 2016-08-13 Last updated: 2017-11-28Bibliographically approved
Mardani, S., Norström, H., Smith, U. & Zhang, S.-L. (2016). High-temperature Ta diffusion in the grain boundary of thin Cu films. Journal of Vacuum Science & Technology B, 34, Article ID 040606.
Open this publication in new window or tab >>High-temperature Ta diffusion in the grain boundary of thin Cu films
2016 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 34, article id 040606Article in journal (Refereed) Published
Abstract [en]

In order to ascertain the applicability of the technologically well-established Cu metallization in high-temperature circuits, the authors have investigated layered metal stacks having one Ta/Cu interface at temperatures from 400 to 700 degrees C. The authors have found that Ta releases from the Ta layer and moves through the Cu film to the opposite interface via the grain boundaries. In the simplest bilayer stack with Cu on top of Ta, the up-diffused Ta on the surface spreads out over the Cu grains so as to cover the Cu grains completely at 650 degrees C. The activation energy for the grain boundary diffusion is found to be 1.060.3 eV. The Ta diffusion in the grain boundaries leads to stabilization of the Cu grain size at 360 nm and an increase in sheet resistance of the metal stack. The latter is in fact observed for all metal stacks having Cu in contact with Ta on one side and TaN or nothing at all on the other. The implication is that the Cu metallization with one Ta/Cu interface has to be stabilized by a preanneal at the highest anticipated operating temperature before use.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-294767 (URN)10.1116/1.4950744 (DOI)000382207700006 ()
Funder
Swedish Foundation for Strategic Research , RE10-0011
Available from: 2016-05-27 Created: 2016-05-27 Last updated: 2017-11-30Bibliographically approved
Mardani, S., Norström, H., Smith, U., Olsson, J. & Zhang, S.-L. (2015). Influence of tantalum/tantalum nitride barriers and caps on the high-temperature properties of copper metallization for wide-band gap applications. Microelectronic Engineering, 137, 37-42
Open this publication in new window or tab >>Influence of tantalum/tantalum nitride barriers and caps on the high-temperature properties of copper metallization for wide-band gap applications
Show others...
2015 (English)In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 137, p. 37-42Article in journal (Refereed) Published
Abstract [en]

Electronic devices and circuits based on wide-band gap (WBG) semiconductors and intended for operation at temperatures significantly exceeding 300 degrees C are currently being developed. It is important that the adjunct metallization matches the high-temperature properties of the devices. In the case of the technologically important Cu metallization, the most frequently used cap and barrier layer materials are Ta, TaN and combinations of these. They stabilize the interconnects and prevent Cu from diffusing into the surrounding material. In this study, different combinations of Ta and TaN layers are evaluated electrically and morphologically after high-temperature treatments. The cap/Cu/barrier stack shows an appreciable increase in sheet resistance above 600 degrees C for the asymmetric combinations Ta/Cu/TaN and TaN/Cu/Ta. This degradation is shown to be closely related to a substantial diffusion of Ta across the Cu film and on to the TaN layer, where Ta1+xN forms. The symmetrical combinations Ta/Cu/Ta and TaN/Cu/TaN show only small changes in sheet resistance on even after anneals at 800 degrees C. A less pronounced Ta diffusion into the Cu film is found for the Ta/Cu/Ta combination. The experimental observations are interpreted in terms of Cu grain growth, Ta segregation in the Cu grain boundaries and morphological degradation of the Cu film.

Keywords
Wide band gap application, Copper metallization, High-temperature, Tantalum, Tantalum nitride
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-256858 (URN)10.1016/j.mee.2015.01.023 (DOI)000355047500008 ()
Funder
Swedish Research Council, 2010-4460
Available from: 2015-06-26 Created: 2015-06-26 Last updated: 2017-12-04Bibliographically approved
Chen, S., Nyholm, L., Jokilaakso, N., Karlström, A. E., Linnros, J., Smith, U. & Zhang, S.-L. (2011). Current Instability for Silicon Nanowire Field-Effect Sensors Operating in Electrolyte with Platinum Gate Electrodes. Electrochemical and solid-state letters, 14(7), J34-J37
Open this publication in new window or tab >>Current Instability for Silicon Nanowire Field-Effect Sensors Operating in Electrolyte with Platinum Gate Electrodes
Show others...
2011 (English)In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 7, p. J34-J37Article in journal (Refereed) Published
Abstract [en]

Current instability is observed for silicon nanowire field-effect transistors operating in electrolytes with Pt gate electrodes. A comparative study involving an Ag/AgCl-reference gate electrode reveals that the effect results from a drift in the potential at the Pt-electrode/electrolyte interface. In a phosphate buffer saline of pH 7.4, the stabilization of the potential of the Pt electrode was found to require approximately 1000 s. A concurrent potential drift, with a comparable time constant, occurring at the electrolyte/oxidized-nanowire interface rendered a complex device current response which complicated the interpretation of the results.

National Category
Engineering and Technology Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-154111 (URN)10.1149/1.3584082 (DOI)000290276400027 ()
Available from: 2011-05-26 Created: 2011-05-26 Last updated: 2017-12-11Bibliographically approved
Gao, X., Andersson, J., Kubart, T., Nyberg, T., Smith, U., Lu, J., . . . Zhang, S.-L. (2011). Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness [Letter to the editor]. Electrochemical and solid-state letters, 12, H268-H270
Open this publication in new window or tab >>Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness
Show others...
2011 (English)In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 12, p. H268-H270Article in journal, Letter (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-222463 (URN)
Available from: 2014-04-10 Created: 2014-04-10 Last updated: 2017-12-05
Gao, X., Andersson, J., Kubart, T., Nyberg, T., Smith, U., Lu, J., . . . Zhang, S.-L. (2011). Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness. Electrochemical and solid-state letters, 14(7), H268-H270
Open this publication in new window or tab >>Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness
Show others...
2011 (English)In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 7, p. H268-H270Article in journal (Refereed) Published
Abstract [en]

This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-154110 (URN)10.1149/1.3580618 (DOI)000290276400013 ()
Available from: 2011-05-26 Created: 2011-05-26 Last updated: 2017-12-11Bibliographically approved
Vallin, Ö., Li, L., Norström, H., Smith, U. & Olsson, J. (2010). 150 mm Silicon-on-polycrystalline-Silicon Carbide. In: Sorin Cristoloveanu, Olivier Faynot (Ed.), Proceedings of EUROSOI: Sixth Workshop of the Thematic Network on Silicon-On-Insulator. Paper presented at EUROSOI 2010 (pp. 101-102).
Open this publication in new window or tab >>150 mm Silicon-on-polycrystalline-Silicon Carbide
Show others...
2010 (English)In: Proceedings of EUROSOI: Sixth Workshop of the Thematic Network on Silicon-On-Insulator / [ed] Sorin Cristoloveanu, Olivier Faynot, 2010, p. 101-102Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

150 mm Silicon-on-polycrystallin-Silicon Carbie (poly-SiC) bybrid substrate, without intermediate oxide layers have been realised by hydrophilic wafer bonding of SOI- and poly-SiC wafers. A novel rapid thermal treatment step was introduced before furnace annealing to avoid bubble formation, cracks and breakage. After removal of the Si handle and the buried oxide, the reamining Si device layer was shown to be stress free by Raman spectroscopy and X-ray diffraction (XRD) measurements.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-120565 (URN)
Conference
EUROSOI 2010
Available from: 2010-03-15 Created: 2010-03-15 Last updated: 2016-04-19
Li, L.-G., Vallin, Ö., Lu, J., Smith, U., Norström, H. & Olsson, J. (2010). Oxygen out-diffusion from buried layers in SOI and SiC-SOI substrates. Solid-State Electronics, 54(2), 153-157
Open this publication in new window or tab >>Oxygen out-diffusion from buried layers in SOI and SiC-SOI substrates
Show others...
2010 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 54, no 2, p. 153-157Article 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).

Keywords
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
Vallin, Ö., Li, L.-G., Norström, H., Smith, U. & Olsson, J. (2009). LDMOS transistors on Si-on-SiC hybrid substrates having crystalline or poly-crystalline SiC - Electrical and thermal characterization. In: Proceedings of IEEE SOI conference: . Paper presented at IEEE SOI conference, June (2009).
Open this publication in new window or tab >>LDMOS transistors on Si-on-SiC hybrid substrates having crystalline or poly-crystalline SiC - Electrical and thermal characterization
Show others...
2009 (English)In: Proceedings of IEEE SOI conference, 2009Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-121242 (URN)
Conference
IEEE SOI conference, June (2009)
Available from: 2010-03-19 Created: 2010-03-19 Last updated: 2016-04-14
Li, L., Vallin, Ö., Lu, J., Smith, U., Norström, H. & Olsson, J. (2009). Study of Oxygen Out-diffusion from buried oxide layers in Si/SiC hybrid- and SOI-substrates. In: Olof Engström (Ed.), EUROSOI 2009 CONFERENCE PROCEEDINGS: Fifth Workshop of the Thematic Network on Silicon-on-Insulator, Technology, Devices and Circuits. Paper presented at EuroSOI 2009 (pp. 85-86).
Open this publication in new window or tab >>Study of Oxygen Out-diffusion from buried oxide layers in Si/SiC hybrid- and SOI-substrates
Show others...
2009 (English)In: EUROSOI 2009 CONFERENCE PROCEEDINGS: Fifth Workshop of the Thematic Network on Silicon-on-Insulator, Technology, Devices and Circuits / [ed] Olof Engström, 2009, p. 85-86Conference paper, Published paper (Refereed)
Abstract [en]

We have studied the SiO2 out-diffusion (Ox-away) process from Si/SiC hybrid substrates (Si-SiO2-SiC), thin BOX SOI and commercial SOI. For the former two kinds of substrates, HRXTEM micrographs show that after complete oxygen out-diffusion, the Si/SiC or Si/Si interfaces are sharp, and apparently defect-free. The BOX of commercial SOI has partially been diffused away. For all three substrate types, the thickness of top thin Si layers has become thinner and the Si was discovered under HRXTEM above the top Si. XPS results indicate that it only contains Si.

National Category
Condensed Matter Physics Engineering and Technology
Research subject
Electronics
Identifiers
urn:nbn:se:uu:diva-120532 (URN)
Conference
EuroSOI 2009
Available from: 2010-03-12 Created: 2010-03-12 Last updated: 2016-04-14
Organisations

Search in DiVA

Show all publications