Hayo Brunken

Time- and space-resolved high-throughput characterization of stresses during sputtering and thermal processing of Al-Cr-N thin films

(Al100−xCrx)N thin-film materials libraries (x = 31–79 at%) were fabricated on micro-machined cantilever arrays, in order to simultaneously investigate the evolution of stresses during film growth as well as during thermal processing by analysing the changes in cantilever curvature. The issue of the dependence of stress in the growing films on composition, at comparable film thicknesses, was investigated. Among the various experimental parameters studied, it was found that the applied substrate bias has the strongest influence on stress evolution and microstructure formation. The compositions of the films, as well as the applied substrate bias, have a pronounced effect on the lattice parameter and the coherence length. For example, applying a substrate bias in general leads to compressive residual stress, increases the lattice parameter and decreases the coherence length. Moreover, bias can change the film texture from [1 1 1] orientation to [2 0 0]. Further detailed analysis using x-ray diffraction and transmission electron microscopy clearly revealed the presence of a [1 1 1] highly textured face centred cubic (B1 type) Al–Cr–N phase in the as-deposited state as well as the coexistence of the hexagonal [1 1 0] textured Cr2N phase, which forms in the Cr-rich region. These results show that the combinatorial approach provides insight into how stresses and compositions are related to phases and microstructures of different Al–Cr–N compositions fabricated in the form of materials libraries.

Dual frequency capacitive plasmas in Fe and Ni sputter applications: correlation of discharge properties on thin film properties

Dual frequency capacitively coupled plasmas (CCPs) are widely used in (large area) etching and plasma enhanced chemical vapor deposition processes. However, applications in physical vapor deposition (PVD) are still sparse due to the well-established dc magnetron cathode discharges. Nevertheless, there exist critical applications such as ferromagnetic or ceramic thin film deposition which are difficult to handle even for dc magnetron systems. For these materials systems dual frequency CCPs pose a good alternative, because for insulators charging can be avoided and for ferromagnetic materials the target thickness becomes independent of the magnetron configuration at comparable deposition rates.In this work we investigate two separate subjects. First, in dual frequency capacitive discharges a complex coupling of the applied excitation frequencies can be observed, which from a plasma parameter point of view limits the separability of ion flux (usually controlled by frequencies >60?MHz) and ion bombarding energy (usually controlled by frequency <15?MHz) onto the sputter target. By performing deposition experiments it was found that by following simple tuning guidelines a very good degree of separability is achievable. Additionally, the deposition homogeneity is not affected.Second, we correlate the growth conditions with crystalline and magnetic properties as well as the degree of O content for Fe and Ni films. Therefore, we applied different signals as a substrate bias to influence thin film growth. It was found that the crystalline and magnetic properties can be influenced for both Fe and Ni films but is more pronounced for Ni.

Combinatorial investigation of Fe-B thin-film nanocomposites.

Abstract Combinatorial magnetron sputter deposition from elemental targets was used to create Fe–B composition spread type thin film materials libraries on thermally oxidized 4-in. Si wafers. The materials libraries consisting of wedge-type multilayer thin films were annealed at 500 or 700 °C to transform the multilayers into multiphase alloys. The libraries were characterized by nuclear reaction analysis, Rutherford backscattering, nanoindentation, vibrating sample magnetometry, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Youngs modulus and hardness values were related to the annealing parameters, structure and composition of the films. The magnetic properties of the films were improved by annealing in a H2 atmosphere, showing a more than tenfold decrease in the coercive field values in comparison to those of the vacuum-annealed films. The hardness values increased from 8 to 18 GPa when the annealing temperature was increased from 500 to 700 °C. The appearance of Fe2B phases, as revealed by XRD and TEM, had a significant effect on the mechanical properties of the films.

Synthesis of Au microwires by selective oxidation of Au–W thin-film composition spreads

Abstract We report on the stress-induced growth of Au microwires out of a surrounding Au–W matrix by selective oxidation, in view of a possible application as ‘micro-Velcro’. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au–W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au48W52 composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au48W52 composition are suitable for micro-Velcro applications.

Epitaxially stabilized TiN/(Ti,Fe,Co)N multilayer thin films in (pseudo-)fcc crystal structure by sequential magnetron sputter deposition

Multilayer thin films were grown by non-reactive sequential magnetron sputter deposition from ceramic TiN and metallic FeCo targets addressing a combination of wear resistance and sensoric functionality. Coatings with bilayer period values ranging from 449 nm down to 2.6 nm were grown with the total amount of either material maintained constant. The multilayer thin films were post-annealed ex situ at 600 °C for 60 min in vacuum.X-ray diffraction results imply the multilayer thin films undergo significant changes in their crystalline structure when the bilayer period is decreased. Using high-resolution transmission electron microscopy as well as selected-area electron diffraction it is shown that in the case of multilayer thin films with bilayer periods of several tens of nanometres and higher, FeCo layers and TiN layers in their respective common CsCl- and NaCl-type crystal structures alternate. In contrast, in the multilayer thin films with bilayer periods of only a few nanometres, grain growth across the interfaces between the individual layers takes place and a strongly textured microstructure is formed which features columns in (pseudo-)fcc crystal structure grown in heteroepitaxial growth mode.It is suggested that the experimental findings imply the latter multilayer thin films to be alternately composed of TiN layers and (Ti,Fe,Co)N solid solution layers which have been formed by a solid-state reaction during the deposition process. As a consequence, heteroepitaxially stabilized columnar grains in strongly textured (pseudo-)fcc crystal structure are formed. This crystal structure is preserved after the annealing procedure which qualifies these coatings for use in applications where temperatures of up to 600 °C are reached.