Stress Development and Adhesion in Hydrogenated Nano-Columnar Pd and Pd/Ti Ultra-Thin Films

Abstract

Stress development upon hydrogenation of about 100 nm thick palladium layers on thermally oxidized silicon wafers with and without an intermediate Ti layer is studied. Stress developed is investigated by in-situ XRD in H2/N2(hydrogenation) and N2(dehydrogenation) gas at RT. The method adopted to measure residual stress involved specimen omega- (ω) and psi- (ψ) tilting, on two different diffractometer geometries (focusing and parallel). For the stress analysis, the presence of intrinsic elastic anisotropy of the film is considered. Upon hydrogenation α-Pd transformation to β-PdHoccurs and because of the constrained in-plane expansion a large compressive stress develops. Scanning electron microscopy shows that films with a Ti intermediate layer adhere better to the substrate upon hydrogen cycling, whereas, pure Pd film start cracking and buckling.