Mechanical strength assessment of Ruthenium nano-interconnects with Airgaps using wedge indentation

Abstract

In this paper, we used wedge indentation tests to characterize the mechanical strength of Ru semi-damascene nano-interconnects with airgaps as inter-metal dielectric. An energy-based approach was utilized to quantitatively interpret the mechanical strength of tested structures. The results revealed that the fracture energy (γ) for full airgap structures was 20% lower than that for partial airgap structures and 30% lower than for gap fill structures. Additionally, tests on structures with metal pitches ranging from 18 nm to 26 nm demonstrated a positive correlation between γ and metal density. We also showed that delamination occurs within metal layers and at interfaces around airgaps through FIB and SEM images.