Microstructure of RuO 2 layer as diffusion barrier between Al and Si substrate

Abstract

The microstructure of samples consisting of a 40 nm thick RuO 2 film reactively sputtered on a Si 〈 111 〉 substrate and covered with 20 nm of Al (〈 Si 〉/RuO 2/ Al) is investigated by high-resolution cross-sectional electron microscopy. The depth distributions of elements are studied by Rutherford backscattering spectrometry and electron probe microanalysis. In the as-deposited sample, the RuO 2/Al interface is sharp, but a thin (3 nm) SiO 2 layer is observed at the 〈 Si 〉/RuO 2 interface. After annealing at temperatures ranging from 450 to 700°C for 1–6 h, that layer remains unchanged, but a crystalline compound layer forms at the RuO 2/Al interface. No diffusion of Si and Al into RuO 2 is detectable. The possible mechanisms for the barrier characteristics are discussed. We believe that the presence of the thin SiO 2 layer and the formation of an additional compound layer is intimately related to the good barrier performance of RuO 2.