Theoretical Evaluation of Reliability and Via Resistance of Liner-Less Co Interconnect Using Co–Ti Binary Alloy

The structural and transport properties of CoTi binary alloys were investigated using density functional theory (DFT) calculations to evaluate the potential as a single-layer liner/barrier in liner-less Co interconnects. Cohesive energies of CoTi binary phases were calculated to identify thermodynamically stable compositions, with CoTi, Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sub>Ti, and Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>3</roman></sub>Ti exhibiting the lowest values. Interface binding energies were then evaluated for multiple Co/Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub>Ti<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>y</i></sub> configurations and compared with conventional Cu/TaN interfaces. We identified several Co/Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub>Ti<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\textit{y}}\vphantom{_{_{_{_{}}}}}$</tex-math></inline-formula> interfaces with binding energies lower than ~-5 J/mTEXPRESERVE8 such as fcc-Co(100)/CoTi(110), which exceeds that of the conventional Cu(111)/TaN(0001) interface. Finally, electron transport across the via stack was analyzed. Co/Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub>Ti<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>y</i></sub>/Co via structures showed consistently higher specific conductance compared to Cu/TaN/Ta/Cu, with the highest value of 4.40 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-<roman>4</roman></sup> S/nm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup> observed for fcc-Co(110)/Co<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sub>Ti(110)/ fcc-Co(110). These results support the use of CoTi alloys as reliable, high-performance alternatives to conventional liner/diffusion barrier stacks in future interconnect technologies.