Mechanical Strength Assessment of Ruthenium Nano-Interconnects with Airgaps Using Wedge Indentation

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 (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\gamma$</tex>) for full airgap structures was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 0 \%}$</tex> lower than that for partial airgap structures and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3 0 \%}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\gamma$</tex> and metal density. We also showed that delamination occurs within metal layers and at interfaces around airgaps through FIB and SEM images.