Thermally-Induced Morphology Changes in Subtractive Ru Lines and Their Mitigation

Etched Ru lines with 10 nm nominal linewidth and open interline space were annealed at 325 °C, 420 °C and 650 °C for up to 5 hours to explore thermal stability of their grain structure and morphology. The etched Ru lines showed drastic cylinderization of grains in cross-sectional and planar TEMs, which increased with anneal temperature. Atomistic and physics-based simulations showed surface diffusion to control the dynamics. In extreme cases, the morphology changes resulted in shorts between lines and a significant number of line breaks. Geometrical parameters such as line and grain aspect ratios, surface, interface and grain boundary energies and crystal orientation were found to be implicated. It is shown that suppressing surface diffusion of Ru will mitigate the instabilities.