A thermally grown SiO2 diffusion barrier enabling high-temperature investigation of Ag-Au-Pd-Pt thin films

Abstract

Combinatorial processing platforms (CPPs), integrating Si microtip arrays with combinatorial thin film synthesis and atom probe tomography (APT), enable near-atomic-scale characterization of compositionally complex solid solutions (CCSSs) under diverse processing and reaction conditions, including oxidation, thermal phase stability and electrocatalytic reactions. Their application at elevated temperatures, however, can be limited when CCSS constituents such as Pd and Pt react with the Si support to form silicides. Although thermally grown SiO2 has proven effective as a diffusion barrier between pure Pt and Si, its performance for multicomponent CCSS thin films is unclear. Here, using Ag-Au-Pd-Pt as a model system, we compare a 25 nm thermally grown SiO2 barrier with native Si oxide during annealing using APT and transmission electron microscopy. Native Si oxide prevents detectable interfacial reactions up to 300°C, but at 400°C Pd and Pt react with Si, causing silicide formation and substantial redistribution of the film constituents. At 600°C, extensive substrate reactions disrupt the CCSS film and produce a pronounced needle-shaped silicide morphology. In contrast, thermally grown SiO2 suppresses CCSS thin film-substrate reactions up to 600°C and retains the CCSS composition. The thermally grown SiO2 thus extends the applicable temperature range of Si-based CPPs to at least 600°C for near-atomic-scale characterization of CCSS thin films.