A Multiscale Simulation Study of the Structural Integrity of Damascene Interconnects in Advanced Technology Nodes

The structural stability of tight-pitched (18 nm and below) damascene interconnects for back-end-of-line (BEOL) technologies are analyzed using force-field-based molecular dynamics simulations and finite-element modeling. At these pitches surface energy-dominated effects come into the picture, which lead to structural instability. The candidate metals analyzed are beyond copper (Cu) interconnect metals-ruthenium (Ru), cobalt (Co), and tungsten (W); and Cu is analyzed for reference. Cohesive traction and normal bonding energy are calculated using force-field-based molecular dynamics simulations and then fed as input to a finite-element analysis (FEA) tool, where their dependence on the physical dimensions of the interconnect lines is studied. The parameters studied for the BEOL structures are sidewall angle, aspect ratio, the internal stress of the metal, and modulus of elasticity of the dielectric material around the metal to understand the sensitivity of these parameters to the structural stability of the interconnects. We observe that a lower aspect ratio and higher modulus of elasticity of the dielectric results in stable structures whereas, intrinsic stress of the metal and side wall angle have a minor impact on the overall stability. The stability is analyzed at the seed-layer deposition step and based on this study, Co is the most stable alternate metal amongst Ru, Co, and W.