Exceptional fracture resistance of ultrathin metallic glass films due to an intrinsic size effect.

Metallic glasses typically fail in a brittle manner through shear band propagation but can exhibit significant ductility when the sample size is reduced below a few hundreds of nanometers. To date the size effect was mainly demonstrated for free-standing samples and the role of extrinsic setup parameters on the observed behavior is still under debate. Therefore, in the present work we investigated the mechanical properties of polymer-supported sputtered amorphous Pd82Si18 thin films with various thicknesses. We show that the films exhibit brittle fracture for thicknesses far below 100 nm. A pronounced size effect resulting in extended crack-free deformation up to 6% strain was observed only in films as thin as 7 nm - a thickness which is lower than the typical shear band thickness. This size effect results in exceptional cyclic reliability of ultrathin metallic glass films which can sustain cyclic strains of 3% up to at least 30,000 cycles without any indication of fatigue damage or electrical conductivity degradation. Since the enhancement of mechanical properties is observed at ambient conditions using inexpensive substrates and an industrially scalable sputter deposition technique, a new research avenue for utilization of ultrathin metallic glasses in microelectronics, flexible electronics or nanoelectromechanical devices is opened up.

Enhanced Ti0.84Ta0.16N diffusion barriers, grown by a hybrid sputtering technique with no substrate heating, between Si(001) wafers and Cu overlayers.

We compare the performance of conventional DC magnetron sputter-deposited (DCMS) TiN diffusion barriers between Cu overlayers and Si(001) substrates with Ti0.84Ta0.16N barriers grown by hybrid DCMS/high-power impulse magnetron sputtering (HiPIMS) with substrate bias synchronized to the metal-rich portion of each pulse. DCMS power is applied to a Ti target, and HiPIMS applied to Ta. No external substrate heating is used in either the DCMS or hybrid DCMS/HiPIMS process in order to meet future industrial thermal-budget requirements. Barrier efficiency in inhibiting Cu diffusion into Si(001) while annealing for 1 hour at temperatures between 700 and 900 °C is investigated using scanning electron microscopy, X-ray diffraction, four-point-probe sheet resistance measurements, transmission electron microscopy, and energy-dispersive X-ray spectroscopy profiling. Ti0.84Ta0.16N barriers are shown to prevent large-scale Cu diffusion at temperatures up to 900 °C, while conventional TiN barriers fail at ≤700 °C. The improved performance of the Ti0.84Ta0.16N barrier is due to film densification resulting from HiPIMS pulsed irradiation of the growing film with synchronized Ta ions. The heavy ion bombardment dynamically enhances near-surface atomic mixing during barrier-layer deposition.