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Stress evolution in TiN and TaN layers and multilayers prepared by reactive magnetron sputtering and studied with in-situ laser reflection curvature technique
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Time-resolved in-situ curvature measurements have been used to measure the stress evolution during UHV-based reactive magnetron sputter deposition of TiN and TaN layers and multilayers at 750° C onto Si wafers. It was fmmd that the stress in the initial TiN layers is compressive and reaches a maximum value of -1.2 GPa at 10 nm, there after the stress evolves to tensile during steady state columnar growth. It is suggested that the initial compressive stress is caused by the affinity of reducing any SiO2 to TixSiyOz and the heat transfer from the discharge to the substrate, corresponding to a temperature raise of ~35 °C on the substrate. The stress evolution in TaN layers gwwn on TiN template layers depends strongly on the nitrogen partial pressure in the discharge, from 1 to 3.5 mTorr. This can be correlated with the condition that TaN undergoes phase transformations as the nitrogen partial pressure increase. At low nitrogen content the dominating phase is the hexagonal γ-Ta2N phase and the stress is as high as -1.0 GPa. At higher nitrogen content the layer is essentially stress free with a mixture of cubic δ-TaN and hexagonal ε-TaNphases. This nitrogen dependence combined with the high time sensitivity of the measuring technique provides means to control the stress or phase composition in a given film during growth. It is also shown that the stress evolution in the individual layers in a TiN/faN superlattice with a period as small as 5 nm can be resolved.

National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-85686OAI: diva2:572589
Available from: 2012-11-28 Created: 2012-11-28 Last updated: 2016-08-31
In thesis
1. Nanostructural design of transition metal nitride thin films
Open this publication in new window or tab >>Nanostructural design of transition metal nitride thin films
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Early transition metal nitrides have found extensive use in a range of thin film applications. We are just beginning to understand their growth from vapor phase deposition and microstructure-property relationships. There are large fields to explore, not the least for the nanoand microstructural design in materials offered by a developed deposition process control and alloying by additional elements to grow, e.g., ternary nitrides or superlattices. The work in this thesis has been directed towards increasing the fondarnental understanding of the synthesis, characterization, and properties for some technologically relevant nitrides. Binary and ternary phases of transition metal nitrides, as well as artificial superlattice structures have been studied. In order to prepare materials of high purity, film deposition was performed by Ultra-High Vacuum Reactive Magnetron Sputtering.

In this thesis single-crystal Ti2A1N(0001) thin films were synthesized by epitaxial growth onto MgO(111) substrates at elevated temperature and using a 2Ti:A1 compound sputtering target. This is the first thin film deposition process reported for a nitride of the so called Ma+1AXn phase family of compounds - an inherently nanolaminated material that is characterized by metallic conductivity and ductility with retained ceramic strength, high-temperature stability, oxidation, and corrosion resistance. Th2A1N is found to have a room-temperature resistivity of 39 μΩcm, Young's modulus of 16-17 GPa, and hardness of 210 GPa. It is also found that nitrogen-depleted deposition conditions yield the growth of equilibriwn phases TiA1, Ti3A1 and Ti3A1N. For overstoichiometric deposition conditions with respect to Ti2A1N, a phase mixture with TiN was obtained. A super-structure in the TiN phase was also observed to form along the [111] direction at a repetition distance of 7.34 Å, possibly related to A1 segregation.

CrN/ScN superlattices were designed for use as soft x-ray mirrors and investigated with respect to thermal stability, hardness, and x-ray reflectivity properties. The combined performance of as-deposited superlattices films, with a compositional modulation period of 1.64 nm, both as a mirror and for thermal and mechanical stability was found to be far better than state of the art metallic Cr/Sc multilayers. In fact, the obtained reflectance of 6.95% at a wavelength of 3.1 nm is excellent, the structure is intact after annealing above 800 °C, and the hardness of 19 GPa makes the mirror effectively scratch-proof.

Stress measurements in the TiN/TaN system were performed in-situ. The obtained results showed that a technique based on curvature measurements by laser deflection on the sample during thin film deposition works when employed at the elevated temperatures typically used for sputtering of nitrides. Findings from the in-situ measurements show a correlation between the stress and the film microstructure and the phase composition of TaN layers. It is also shown how the individual layers in an TiN/TaN artificial superlattice affects the stress with a sub-nm resolution. The contribution from thermal stress is also detected and the fine increase in temperature due to exposure of energetic particles from the plasma can be calculated from that stress.

A multiphase region in nitrides was demonstrated to form in the NbxZr1-xN model system. The existence of such a multiphase or polytypic structure is predicted by first-principles density functional theory calculations that to occur in nitrides of compositional regions with valence electron concentrations that yield the same total energy for different crystal structures. Films with varying composition were grown and transmission electron microscopy studies revealed an increase in defect density for the x= 0.5 composition. Nanoindentation performed on such films showed an increase in hardness of - 20% compared to the binary nitrides. Analysis of the indents revealed that materials volumes had rotated away from the indenter, thus offering an alternative mechanism for plastic deformation compared to glide on preferred slip systems seen in the cubic binary nitrides. The materials design concept of such phase stability tuning for mechanical strengthening by a high density of phase interfaces is proposed to be expanded to other materials systems.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2005. 41 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 923
National Category
Natural Sciences
urn:nbn:se:liu:diva-28395 (URN)13531 (Local ID)91-85297-33-X (ISBN)13531 (Archive number)13531 (OAI)
Public defence
2005-02-18, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 14:00 (English)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-28Bibliographically approved

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