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Highly conductive ultrathin Co films by high-power impulse magnetron sputtering
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.ORCID iD: 0000-0003-4317-9701
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
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2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 4, article id 043103Article in journal (Refereed) Published
Abstract [en]

Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018. Vol. 112, no 4, article id 043103
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-340315DOI: 10.1063/1.5011109ISI: 000423724300039OAI: oai:DiVA.org:uu-340315DiVA, id: diva2:1178358
Funder
Swedish Foundation for Strategic Research , SE13-0033Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, C0514401Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2019-06-13Bibliographically approved
In thesis
1. Contacts and Interconnects for Germanium-based Monolithic 3D Integrated Circuits
Open this publication in new window or tab >>Contacts and Interconnects for Germanium-based Monolithic 3D Integrated Circuits
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Three-dimensional integrated circuits have great potential for further increasing the number of transistors per area by stacking several device tiers on top of each other and without the need to continue the evermore complicated and expensive down-scaling of transistor dimensions. Among the different approaches towards the realization of such circuits, the monolithic approach, i.e. the tier-by-tier fabrication on a single substrate, is the most promising one in terms of integration density. Germanium is chosen as a substrate material instead of silicon in order to take advantage of its low fabrication temperatures as well as its high carrier mobilities. In this thesis, the work on two key components for the realization of such germanium-based three-dimensional integrated circuits is presented:the source/drain contacts to germanium the interconnects.

As a potential source/drain contact material, nickel germanide is investigated.In particular, the process temperature windows for the fabrication of morphologically stable nickel germanide layers formed from initial nickel layers below 10 nm are identified and the reaction between nickel and germanium is further studied by means of in-situ x-ray diffraction. The agglomeration temperature of nickel germanide is increased by 100 °C by the addition of tantalum and tungsten interlayers and capping layers. In an effort to more thoroughly characterize the contacts, a method to reliably extract the specific contact resistivity is implemented on germanium.

As a potential interconnect material cobalt is investigated. In a first step, highly conductive cobalt thin films are demonstrated by means of high-power impulse magnetron sputtering. The high conductivity of the cobalt films is owing to big grains, high density, high purity, and smooth interfaces. In a second step, the potential of high-power impulse magnetron sputtering for the metallization of nanostructures is further explored.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 85
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1824
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-380573 (URN)978-91-513-0687-2 (ISBN)
Public defence
2019-09-20, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , SE13-0033
Available from: 2019-07-15 Created: 2019-06-13 Last updated: 2019-08-23

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