TY - BOOK

T1 - Nanoscale Investigations of Performance-critical Regions in Non-homogeneous Metallic and Ceramic Thin Films

AU - Todt, Juraj

N1 - no embargo

PY - 2016

Y1 - 2016

N2 - Thin films and engineered surfaces often exhibit spatially non-homogeneous mechanical and functional properties, resulting in lateral and/or depth-dependent property gradients on a length scale in the sub-micrometre range. These inhomogeneities are at the focus of this work, as they often are critical to the performance of thin film based electronic devices and coated components used, for example, in the tooling industry. On the one hand, non-homogeneous property distributions can be a limiting factor, for instance in the form of concentrations of internal stresses, which may foster the growth of cracks and result in a reduced application lifetime. On the other hand, there is the possibility to deliberately introduce property gradients into thin films and engineered surfaces in order to improve their properties directly or to perform combinatorial studies with the objective of optimizing a specific desired property, as for instance to increase the hardness of a hard coating. As the investigated property gradients are at the sub-micrometre scale it is necessary to employ analytical techniques that offer a spatial resolution in the same range. The methods used in this work comprise nanoprobe synchrotron X-ray diffraction and nanoindentation, which are well-suited for these puroses, since they provide comprehensive information on structural and mechanical properties. Three cases for the application of these techniques for the identification and characterisation of regions critical to the performance of various thin films are presented within this work: • A through-silicon via lined with a conductive W film that features a scalloped morphology was investigated at the synchrotron nanoprobe beamline ID13 of the European Synchrotron Radiation Facility with regard to residual stresses. Potentially critical tensile stress concentrations with a magnitude of up to approx. 900 MPa were found and attributed to the rippled geometry of the film. An altered manufacturing process that diminishes the severity of scallops was proposed in order to increase the application lifetime. • Using a custom-built testing device, a nanocrystalline hard TiN coating of 9 µm thickness, consisting of two sublayers, was indented in-situ at the nanofocus beamline P03 of the synchrotron PETRA III located at DESY in Hamburg, while multi-axial internal strains and stresses were mapped in the region surrounding the indentation imprint. The extent, shape and distribution of various stress components were thus evaluated. Highly localised stress concentrations were identified during distinct loading stages, with magnitudes exceeding -16 GPa of compressive stress. Additionally, after through-thickness crack growth these stress concentrations were then correlated with the resulting crack path. The importance of inhomogeneities for the increase of crack growth energy is underlined by the results of this work. • For the optimization of a highly Al-rich AlTiN hard coating with a self-organized nanoscale microstructure a combinatorial refinement of process parameters was realized. Graded films were grown using gradually changing deposition conditions. They were subsequently analysed using nanoprobe X-ray diffraction, as well as nanoindentation, in order to identify regions with outstanding properties. The resulting coating features a slightly diminished Al content, but also a significant increase in hardness, which is due to changes in phase composition and in microstructural morphology.

AB - Thin films and engineered surfaces often exhibit spatially non-homogeneous mechanical and functional properties, resulting in lateral and/or depth-dependent property gradients on a length scale in the sub-micrometre range. These inhomogeneities are at the focus of this work, as they often are critical to the performance of thin film based electronic devices and coated components used, for example, in the tooling industry. On the one hand, non-homogeneous property distributions can be a limiting factor, for instance in the form of concentrations of internal stresses, which may foster the growth of cracks and result in a reduced application lifetime. On the other hand, there is the possibility to deliberately introduce property gradients into thin films and engineered surfaces in order to improve their properties directly or to perform combinatorial studies with the objective of optimizing a specific desired property, as for instance to increase the hardness of a hard coating. As the investigated property gradients are at the sub-micrometre scale it is necessary to employ analytical techniques that offer a spatial resolution in the same range. The methods used in this work comprise nanoprobe synchrotron X-ray diffraction and nanoindentation, which are well-suited for these puroses, since they provide comprehensive information on structural and mechanical properties. Three cases for the application of these techniques for the identification and characterisation of regions critical to the performance of various thin films are presented within this work: • A through-silicon via lined with a conductive W film that features a scalloped morphology was investigated at the synchrotron nanoprobe beamline ID13 of the European Synchrotron Radiation Facility with regard to residual stresses. Potentially critical tensile stress concentrations with a magnitude of up to approx. 900 MPa were found and attributed to the rippled geometry of the film. An altered manufacturing process that diminishes the severity of scallops was proposed in order to increase the application lifetime. • Using a custom-built testing device, a nanocrystalline hard TiN coating of 9 µm thickness, consisting of two sublayers, was indented in-situ at the nanofocus beamline P03 of the synchrotron PETRA III located at DESY in Hamburg, while multi-axial internal strains and stresses were mapped in the region surrounding the indentation imprint. The extent, shape and distribution of various stress components were thus evaluated. Highly localised stress concentrations were identified during distinct loading stages, with magnitudes exceeding -16 GPa of compressive stress. Additionally, after through-thickness crack growth these stress concentrations were then correlated with the resulting crack path. The importance of inhomogeneities for the increase of crack growth energy is underlined by the results of this work. • For the optimization of a highly Al-rich AlTiN hard coating with a self-organized nanoscale microstructure a combinatorial refinement of process parameters was realized. Graded films were grown using gradually changing deposition conditions. They were subsequently analysed using nanoprobe X-ray diffraction, as well as nanoindentation, in order to identify regions with outstanding properties. The resulting coating features a slightly diminished Al content, but also a significant increase in hardness, which is due to changes in phase composition and in microstructural morphology.

M3 - Doctoral Thesis

ER -