ICMCTF2011 Session TS4-1: Characterization: Linking Synthesis, Microstructure, and Properties

Dark-field holography was first developed for mapping strains in strained-silicon MOSFET devices [1,3] but the technique is not limited to such cases. Strained layers grown epitaxially on a substrate also have the required geometry to apply the technique. Examples will be given of the measurement of strain in carbon-doped silicon and germanium layers grown on silicon substrates [4,5]. Results will be compared with modelling using the finite-element method (FEM). Indeed, we will show that local relaxation due to misfit dislocations can be studied and quantified in the course of the analysis. Finally, the limitations and experimental requirements will be discussed along with future developments.

[1] M.J. Hÿtch, F. Houdellier, F. Hüe, and E. Snoeck, Nature 453 (2008) 1086-1089.

[2] M.J. Hÿtch, E. Snoeck and R. Kilaas, Ultramicroscopy 74 (1998) 131–146.

[3] F. Hüe, M.J. Hÿtch, F. Houdellier, H. Bender, and A. Claverie, Appl. Phys. Lett. 95, 073103 (2009).

[4] N. Cherkashin, M. J. Hÿtch, F. Houdellier, F. Hüe, V. Paillard, A. Claverie, A. Gouyé, O. Kermarrec, D. Rouchon, M. Burdin, P. Holliger, Appl. Phys. Lett. 94 (2009) 141910.

[5] J. M. Hartmann, L. Sanchez, W. Van Den Daele, A. Abbadie, L. Baud, R. Truche, E. Augendre, L. Clavelier, N. Cherkashin, M. Hytch, and S. Cristoloveanu, Semiconductor Science and Technology 45 (2010) 075010.

Ultrathin TiN films were grown by reactive magnetron sputtering using both dc and high power impulse magnetron sputtering (HiPIMS) on amorphous SiO₂ substrates and single-crystalline MgO substrates at various growth temperatures. The resistance of the films was monitored in-situ during growth to determine the coalescence and continuity thicknesses. Structural characterization was carried out using X-ray diffraction and reflection methods. TiN films grown by dc magnetron sputtering on SiO₂ are polycrystalline and for a growth temperature of 600^oC the nominal coalescence and continuity thicknesses are 0.8 and 1.9 nm, respectively [1]. TiN films grow epitaxially on the MgO substrates from temperatures of 200^oC and upwards as shown by XRD measurements [2]. As the growth temperature is increased from room temperature to 600^oC the coalescence thickness drops from 1.09 nm to 0.08 nm and the minimum thickness for a continuous film drops from 5.5 nm to 0.7 nm [3]. A large drop in resistivity is seen with increasing growth temperature and the resistivity reaches 16.6 μΩcm for growth temperature of 600^oC. X-ray reflection measurements indicate a significantly higher density and lower roughness of the epitaxial TiN films.

[1] A. S. Ingason, F. Magnus, J. S. Agustsson, S. Olafsson, and J. T. Gudmundsson, In-situ electrical characterization of ultrathin TiN films grown by reactive dc magnetron sputtering on SiO₂, Thin Solid Films, 517 (24) (2009) 6731-6736

[2] A. S. Ingason, F. Magnus, S. Olafsson and J. T. Gudmundsson, Morphology of TiN thin films grown on MgO [100] by reactive dc magnetron sputtering, Journal of Vacuum Science and Technology A, 28(4) (2010) 912 - 915

[3] F. Magnus, A. S. Ingason, S. Olafsson and J. T. Gudmundsson, Growth and in-situ electrical characterization of ultrathin epitaxial TiN films on MgO, Thin Solid Films, submitted June 2010

Stresses and preferred grain orientations play an important role in thin films of many types and applications. X-ray diffraction (XRD) is one of the most important methods of their characterization. Selected examples of specific non-routine cases are presented we met recently during the study of thin films of a high technological interest (hard coatings, photocatalytic films, films with interesting electrical properties).

In TiO₂ thin films crystallized from amorphous state into anatase phase, tensile stresses are generated during the crystallization and inhibit further crystallization. This process results in strong dependence of both stresses and crystallization rate on the film thickness. The measured strains were highly anisotropic and recently calculated single crystal elastic constants of anatase were used for the stress evaluation by the conventional sin²ψ method and because of absence of texture simultaneously also by our newly developed software for total XRD powder pattern fitting.

In the studied cubic KTAO₃ thin films on Si substrate with Pt interlayer, rather unusual multicomponent textures were detected when each of the component had narrow orientation distribution. In this case, a set of the so-called ω-scans was collected for finding of all the components followed by the standard θ-2θ scans at specific pre-calculated sample inclinations. Then the so-called crystallite group method could be applied for the stress determination.

The most difficult task was the analysis of compact highly textured hexagonal TiB₂ hard coatings on steel. The (00l) texture was very sharp but of fiber type. None of the above methods could be applied since the range of possible inclinations ψ was very narrow and the ratio of lattice parameters c/a could not be determined independently. Therefore, full maps of reciprocal space had to be measured and calculated. Finally, the stress could be evaluated only from the deformation and/or inclination of the diffraction spot in the map by the reciprocal map fitting.

In the last example, thin films of hexagonal ferrite SrFe₁₂O₁₉ on SrTiO₃(111) substrate were analyzed. After routine scans (symmetric or asymmetric θ-2θ scan, ω-scan, φ-scan) it seemed that there is just a strong fiber texture. Only more complex study on asymmetric planes discovered well developed epitaxial growth as a main feature of the partially inhomogeneous film and shape of diffraction spots was analyzed.

TOF-SIMS is a very sensitive surface analytical technique, covering a wide range of organic and inorganic applications. It provides detailed elemental and molecular information about surfaces, thin layers, interfaces, and full three-dimensional analysis of the sample. In recent years, the application of cluster primary ions has led to a major breakthrough in the analysis of molecular surfaces by TOF-SIMS. Compared to mono-atomic bombardment the accessible mass range has been considerably extended and the sensitivity has been increased by orders of magnitude. In particular the Bi LMIS cluster source combines the fundamental benefits of cluster ion bombardment with a high brightness source to give uncompromised lateral and mass resolution. Moreover, the Bi cluster source emits a large variety of singly and doubly charged clusters and is therefore well suited for fundamental studies.

The information depth is a key capability of every surface analytical technique. However, the influence of cluster bombardment on the information depth in SIMS has hardly been investigated. We determined the information depth for atomic Bi as well as for a large variety of Bi clusters (Bi₂ to Bi₇) at different primary ion energies. Additionally, we investigated the samples by LEIS (low energy ion scattering) which is known to be the most surface sensitive technique. The samples under investigation included different core shell nano-particles as well as special alloys which tend to form pure mono-layers of one metal component at the surface.

X-ray Photoelectron Spectroscopy (XPS) is commonly used technique for elemental near-surface analysis of the composition of materials and of their chemical binding. In this study we investigate the potential of XPS to gain structural information on thin films.

It has been observed by XPS studies on Ar atoms (Ar 2p), naturally trapped in Al₂O₃ films deposited by RF magnetron sputtering, that the line shape has to be described as a superposition of at least two doublets.

A doublet structure and the associated energy shift has been correlated in earlier work on pure metals with the existence of bubbles formed by coalescing noble gas atoms in the solid [1, 2].

In other works the shift of Ar 2p peaks has been used as a probe of residual stress in amorphous carbon ultrathin films [3].

In order to systematically study this effect we have implanted Ar atoms at various energies into different substrates: pure Al, Al₂O₃ deposited by RF magnetron sputtering, DLC (diamond-like carbon), Si single crystals and SiO₂. In the case of Al₂O₃ the naturally trapped Ar from the deposition process were also measured. The doublets of 2p transitions of Ar have been analyzed by XPS. The line shape shows that in many cases more than one doublet structure is needed to describe the data. The relative intensities of these doublets change as a function of implantation energy and annealing temperature.

There is evidence that a correlation of the local structure of the sample with the shape and shift of Ar 2p Peaks exists, making XPS on Ar a probe for the local structure of the dielectric thin films investigated in this study.

The work is funded by DFG within SFB-TR 87.

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[3] W. Lu, K. Komvopoulos, Appl. Phys. Lett. 76 (2000) 3206.