Annealing Induced Interfacial Evolution of Titanium/Gold Metallization on Unintentionally Doped β -Ga 2 O 3

Abstract

© The Author(s) 2019. Here, we study the kinetic evolution of the interface between a Ti/Au metal stack and bulk (010) β-Ga2O3 substrate under different annealing conditions using scanning / transmission electron microscopy. We observe distinct processes of interfacial reaction and interdiffusion between the metal films and at the metal-semiconductor junction. Upon rapid thermal annealing (RTA), the as-deposited Ti readily reacts at the β-Ga2O3 interface, driven by redox favorability. After a 1-min 470°C N2 RTA, the interface exhibits two segregated crystalline layers: a ∼5 nm Ti-rich (Ti-TiOx) layer lattice-matched to the β-Ga2O3 substrate and a ∼3 nm Ga-rich (TiGax) layer. A substitutional mechanism is proposed based on the similarity in ionic radii of Ti+3, Ti+4, and Ga+3. After 15-min RTA, the Ga-rich layer is diluted within the Ti-Au matrix, while the Ti-TiOx layer does not significantly change, and there is no further observable Ga out-diffusion from the substrate. Thus, we propose that the Ti-TiOx layer acts as a diffusion barrier, even when it is no longer lattice-matched with β-Ga2O3. In addition, Ti-rich nanocrystals form within the Ti-Au layer, presumably via the proceeding reactions. The observations here provide insights for contact stack evolution during operation of power electronic devices at elevated temperature.