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The electro-mechanical performance of Mo thin films grown by dc magnetron sputter deposition on polyimide substrates was investigated. A series of 500 nm thick Mo films was synthesized at different discharge powers to evaluate the effect of deposition conditions on the structure–stress relationship and to correlate the intrinsic properties of the Mo films with their electro-mechanical response. Different in-situ fragmentation tests were performed to assess the crack morphology, the change in electrical resistance and the film stress during straining. A direct relation between the residual stress state of the Mo thin films and the discharge power was noticed as the stress changed from tensile to compressive with increasing discharge power. All Mo films showed brittle fracture when strained in tension and the critical crack onset strain correlated with the residual stress state. In-situ synchrotron diffraction experiments enabled the characterization of the fracture strength, which was unaltered by the discharge power and found to be approximately 1700 MPa for all Mo thin films studied. [ABSTRACT FROM AUTHOR]

The suitability of refractory high entropy metal sublattice nitride (HEAN) thin films to act as diffusion barrier between Cu and Si was evaluated. For this purpose, bi-layers comprising a 150 nm thick Cu layer and a 20 nm thick layer based on (MoNbTaW)N and alloyed with either Ti, V, Cr, Mn, Zr or Hf have been deposited onto Si substrates using high power impulse magnetron sputtering. Subsequently, the bi-layers were annealed up to 950 °C in vacuum and analyzed by X-ray diffraction, confocal laser scanning microscopy and resistance measurements to check for barrier failure. Depending on the elements present in the HEAN layer, two failure modes were identified: (1) interdiffusion of Cu and Si leading to the formation of Cu 3 Si starting at 850 °C and (2) dewetting of the Cu layer starting at 900 °C. A better barrier performance could be correlated to a lower formation enthalpy of the binary nitride of metals present in the HEAN layer leading to the conclusion that more stable metal‑nitrogen bonds in the HEAN phase are beneficial for its diffusion barrier performance. • Diffusion barrier performance of refractory high entropy alloy nitride films assessed • Synthesis by high power impulse magnetron sputtering at room temperature • No barrier failure observed up to 800 °C for all films • Cu 3 Si formation at 850 °C and dewetting of Cu at 950 °C identified as failure modes [ABSTRACT FROM AUTHOR]

• Detailed parameter variation during sputter deposition of MoNbTaWZr films. • Influence of duty cycle, Ar pressure and pulse frequency analyzed and discussed. • Parameters enabling high energetic growth conditions lead to amorphous microstructure. • Films deposited with low energetic growth conditions have a crystalline bcc structure. • Impact of microstructure and morphology on electrical resistivity discussed. Within this study a series of MoNbTaWZr thin films were synthesized using high power impulse magnetron sputtering (HiPIMS) with varying the deposition parameters: duty cycle from 0.5 to 100 % (i.e. DC magnetron sputtering (DCMS)), Ar pressure from 0.5 to 3 Pa and pulse frequency from 25 to 200 Hz. The structure of the deposited films was analyzed by X-ray diffraction and scanning and transmission electron microscopy. In addition, the electrical resistivity and the residual stress of the films was determined. The influence of the deposition parameter variation on structure and properties of the MoNbTaWZr films is discussed on the established framework of film growth conditions achievable with HiPIMS and DCMS and how they can be influenced by adapting the deposition parameters. The performed work is intended to contribute to a comprehensive understanding about synthesis-structure-property relations for refractory high entropy alloy thin films while using MoNbTaWZr films as a model system. [ABSTRACT FROM AUTHOR]

This study presents detailed microstructural investigations on single and bilayer thin films of two medium entropy alloys (MEAs) synthesized using magnetron sputter deposition. Single layer thin films of CoCrFeNi and AlCoCrFe show single-phase face-centered cubic (fcc) and body-centered (bcc) structure, respectively. The bilayer thin film consisting of CoCrFeNi (fcc) and AlCoCrFe (bcc) has a sharp interface between them with an equiatomic composition. Nanodiffraction was used to characterize planar defects in the fcc films. This first study on bilayer film of two MEAs is transformative to other systems and will help fundamental studies on high entropy alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High entropy alloy (HEA) thin films are potential candidates to act as diffusion barrier between Cu and Si in microelectronics. To evaluate the suitability of refractory HEAs, six different HEA thin films based on the MoNbTaW system and alloyed with Ti, V, Cr, Mn, Zr or Hf have been deposited by high power impulse magnetron sputtering with a thickness of 20 nm on Si substrates. The bi-layer architecture was completed by a 150 nm thick top-layer of Cu. The microstructure of the bi-layers before and after annealing in vacuum up to 800 °C was investigated by X-ray diffraction to observe possible phase changes or formations. In addition, resistance measurements and confocal laser scanning microscopy were employed to check for potential barrier failure. The lowest onset temperature for barrier failure of 600 °C was found for MoNbTaWZr, whereas the highest of 700 °C was observed for CrMoNbTaW. The obtained results for the failure temperature are discussed in terms of microstructure, strain and cohesive energy of the HEA films as well as the enthalpy of mixing between the elements in the HEA and Cu. A direct correlation between the mixing enthalpy of the fifth alloying element with Cu and the barrier failure temperature was observed. [Display omitted] • Suitability of refractory high entropy alloys as diffusion barriers. • Synthesis by high power impulse magnetron sputtering. • Best barrier performance for CrMoNbTaW with failure temperature at 750 °C • No correlation between film microstructure and diffusion barrier performance. • Mixing enthalpy of elements in HEA with Cu plays decisive role. [ABSTRACT FROM AUTHOR]

Abstract Cyclic bending tests of magnetron sputter-deposited Al/Mo bilayer thin films on flexible substrates were performed with a custom-built bending apparatus to evaluate the reliability of possible applications for metal wiring electrodes such as signal and data bus lines in flexible electronics. Intermittent measurements of mechanical damage and electrical resistance were performed to elucidate the damage evolution of Al/Mo bilayers with increasing cycle numbers. It was found that a 3:1 thickness ratio would have an extremely long lifetime when only compressive bending is applied for strains <1.3% (2 mm radius, 50 μm substrate thickness). Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Magnetron sputter deposited Mo thin films are frequently used as part of the metallization of thin film transistors. To ensure technological applications these Mo thin films are often combined with Al thin films, but are inherently brittle compared to the electrical charge carrying ductile Al thin films. To improve the fracture behavior of bilayered stacks containing Mo layers for future flexible devices like rollable or foldable displays, an optimum ductile/brittle layer thickness ratio is necessary. Within this work the electro-mechanical behavior of bilayered Al/Mo thin films grown by dc magnetron sputter deposition on polyimide substrates under tensile strain was investigated. Various Al/Mo layer thickness ratios (1:1, 3:1, 5:1 and 10:1), all with a base Mo film of 30 nm were tested. In situ tensile tests combining electrical 4-point probe resistance and optical measurements revealed an optimum thickness ratio between 5:1 and 10:1 for the crack onset strain. Post mortem analysis on the crack morphology revealed that higher thickness ratios better compensate cracks by leaving wider subsurface pathways for electron conduction of the layer stack than lower thickness ratios. Highlights • Different bilayer Al/Mo thickness ratios were strained with in situ methods. • Adding thicker aluminum layers suppresses the influence of the brittle layer. • Pathways for electronic conduction remain in aluminum layers after straining. • Electronic failure can be avoided by tuning the aluminum layer thickness. [ABSTRACT FROM AUTHOR]

Sputter deposited Mo-based thin films play a key role in the manufacturing of modern flat panel displays and microelectronic components. They are widely used as source/drain electrodes, as gate material or as metallization layer for signal and data bus lines. Within this work, the sputter performance of a Mo 0.70 Al 0.20 Ti 0.10 rotatable target was investigated to correlate processing conditions to thin film growth and chemistry. An industrial-scale in-line magnetron sputter system was used to deposit a series of thin films on silicon wafers at Ar pressures from 0.25 to 0.70 Pa. The center of the substrate carrier was kept at a constant offset from the target middle axis. Film thickness and chemical composition were evaluated for substrates located at different lateral positions. The morphologies and cross-sections of the films were examined by scanning electron microscopy and focused ion beam milling, revealing dense fibrous structures opposite the target and fine isolated columnar grain structures at extended positions from the center of the target. Energy dispersive X-ray spectroscopy showed a depletion of Al in favor of Mo enrichment opposite the target and a reverse trend at extended distances. The plasma used for sputtering was modelled after realistic target geometries using the S 3 M computer code and served as input for subsequent SRIM scatter simulations. It is demonstrated that the combination of experiments and simulations allows to distinguish a high- and low-flux regime, leading to different film structures and chemical compositions. [ABSTRACT FROM AUTHOR]

With the envisioned use as high-temperature materials, the thermal stability of three high entropy alloy thin films, based on the system MoNbTaW with additional Cr, Ti or V, was studied. All films were deposited by high power impulse magnetron sputtering and subsequently annealed in vacuum up to a temperature of 1200 °C and analyzed by X-ray diffraction. The obtained body-centered cubic structure in the as-deposited state remained stable up to the maximum annealing temperature. Measurements of the residual stress by wafer curvature and sin2Ψ method revealed a general reduction of the stress with annealing temperature due to defect annihilation. • Body centered cubic structure of high entropy alloy films stable up to 1200 °C • Stress evolution during annealing proceeds in two stages • Fifth alloying element (Ti, V and Cr) influences stress relaxation [ABSTRACT FROM AUTHOR]

In flexible and/or wearable electronics the thin films deposited on compliant substrates are not only subjected to straining and bending but also to tribological loading conditions. A frequently used method to assess tribological properties of materials systems is the ball-on-disc test. In the current work, Mo films were deposited by high power impulse magnetron sputtering on polyimide substrates to serve as a model system. To establish different tribological contact conditions, a series of different counterpart materials was chosen for the performed ball-on-disc tests. A detailed analysis by 3D confocal laser scanning microscopy and scanning electron microscopy revealed details about the wear mechanisms active during sliding where mainly abrasion of the softer one of the material pair was noticed. The obtained results for friction and wear together with the performed simulations of the induced stresses due to the loading conditions show that ball-on-disc tests can contribute to the understanding of the tribological response of metallic films on compliant substrates which in turn may help to improve the lifetime of components in flexible and/or wearable electronic applications. [ABSTRACT FROM AUTHOR]

To explore structure and properties of refractory high entropy alloy (HEA) thin films, targets with five different equimolar compositions based on the MoNbTaW system and alloyed with Ti, V, Cr, Mn or Hf were used for the synthesis of films by high power impulse magnetron sputtering. All HEA films showed a body-centered cubic structure and a dense, columnar morphology as revealed by X-ray diffraction and transmission electron microscopy, respectively. Alloying of the additional element affects the film stress and the mechanical properties. The overall compressive stress state present in the films was distributed inhomogeneously with an expected gradient along the film growth direction. Hardness and Young's modulus values ranging from 14 to 17 GPa and 230 to 295 GPa, respectively, were measured by nanoindentation. • Synthesis of MoNbTaW-based films using high power impulse magnetron sputtering • All films show a bcc microstructure and a dense columnar morphology. • Mechanical properties influenced by fifth alloying element (Ti, V, Cr, Mn or Hf) • Novel method applied to determine Young's modulus of thin films [ABSTRACT FROM AUTHOR]

• Sputter deposition characteristics of an industrial-size rotatable Ni80W20 target. • Lateral differences of film properties over substrate carrier. • Microstructure and morphology of films change with lateral position on carrier. • Rough target surface affects emission angles of sputtered Ni and W. • Emission angles of Ni and W dominate the lateral differences of film properties. A series of NiW thin films was magnetron sputter deposited from a rotatable Ni80W20 target at Ar pressures ranging from 0.25 to 1.00 Pa on a matrix of (1 0 0) Si substrates. All films were synthesized in static deposition mode. The chosen setup allowed to study the influence of lateral substrate position and Ar pressure on film microstructure and elemental composition. All films deposited opposite the target were dense and Ni-rich, whereas films grown at extended positions from the target center had an open voided morphology and were W-rich. The differences in elemental composition with respect to the lateral position on the substrate carrier are attributed to the respective emission profiles of Ni and W and to scatter events of sputtered particles with Ar gas. To assess the influence of the target surface on final film properties, a planar Ni81W19 target was sputter eroded and investigated. The observed roughening of the target surface stems from the interplay between the high and low sputter yield of Ni and W, influencing the emission angles of both elements. Additional SRIM simulations of a thin Ni top-layer atop a W under-layer provided evidence for the existence of sputter yield amplification active within the studied system. [ABSTRACT FROM AUTHOR]

Magnetron sputter deposited Mo-based thin films are widely used as diffusion barriers and metallization layers for signal and data bus lines of flat panel displays or back electrodes of thin film solar cells. These films are deposited at large-scale from rectangular planar sputter targets, with the necessity of constant film thickness and properties over target usage. Within this work, a new 600 × 125 mm2 planar Mo-target was sputtered at a constant power of 3.5 kW until the erosion track reached 80% of the maximum useable target thickness. Every other 50 kWh, films were deposited onto a 9 × 5 matrix of (100) Si in different deposition modes (i.e. static and oscillation of the substrate carrier). By investigating the individual sample sets, the sputter behavior at different stages of target usage could be assessed. The sputter behavior changes with the progressing evolution of an erosion groove and affects thickness, stress and electrical resistivity of the films. In the beginning and end of target usage, films with low electrical resistivity and high tensile stresses are grown, whereas a medium target erosion leads to films with increased resistivity and lower tensile stresses. This time variance is attributed to two competing effects changing with proceeding target erosion, which affect the growth conditions of the films: (i) the increase of the reflection angle of Ar neutrals due to the evolution of an erosion groove, lowering the energy input into the growing film, and (ii) a rising number of Ar+ ions due to an increase of target current, directly affecting the overall number of reflected Ar neutrals, increasing the energy input into the growing film. • A rectangular planar molybdenum target was eroded until the end of its lifetime. • Films were deposited at different stages of target erosion. • Target erosion affects film microstructure and properties. • Film microstructure is influenced by substrate position and carrier movement. • Observed differences are explained by target cross-corner effect. [ABSTRACT FROM AUTHOR]

The mechanical and electrical limits of magnetron sputter deposited Al/Mo bilayer thin film systems were tested for their potential use in flexible displays and sensors. Al/Mo bilayers with different Al layer thicknesses (30, 75 and 150 nm) and a constant Mo layer thickness of 30 nm were subjected to 20,000 cycles of combined tensile and compressive bending at different bending strains (0.6, 1.3 and 3.1%). Intermittent optical and electrical measurements allowed the quantification of their reliability as electrode materials. The reliability strongly depends on the used bending strains and the Al layer thickness. Crack nucleation and growth lead to an increase in electrical resistance beyond 50% within the first 100 bending cycles at bending strains larger than 1.3%. Here, most of the studied bilayers fail electrically due to fracture. Increasing the bilayers' Al layer thickness does not improve fracture behavior, which is dominated by the Mo layer, but lowers the measured electrical resistance values for all experiments. Al/Mo bilayers with layer thicknesses of 75/30 nm revealed the least amount of surface damage for all tested bending strains, however do not have the best electrical conductivity. • Cyclic bending of Al/Mo multilayers at different bending strains and Al thicknesses • Evolution of surface damage and electrical resistance can help predict lifetimes • Further insights on the relation between bilayer damage and electrical conductivity [ABSTRACT FROM AUTHOR]