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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]

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]

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]

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]