Reactor-feature coupled model to extend Cu fill in BEOL using PVD

Back End Of Line (BEOL) features like trenches and dual damascenes are shrinking with every new node of semiconductor chips. PVD (physical vapor deposition) has been the workhorse for Cu fill inside BEOL features for decades [1]. However, tighter pitches, smaller Critical Dimensions (CDs) and higher aspect ratios (depth/top opening) in the newer nodes make it hard to fill copper without voids. Here, we present a combined reactor-feature model where a reactor-scale plasma model is used to calculate the fluxes and ion-energy and angular distributions (IEADFs) of the plasma species hitting the wafer, which are fed into a kinetic Monte Carlo feature model [2] to predict deposition inside the feature. We show that breaking the process into two steps, a low-bias deposition and a high-bias etch, prevents overhang buildup and redirects Cu inside the feature. Cu volume inside the feature can be increased further by increasing the etch time relative to dep time. Finally, we model copper reflow as a mechanism to redirect material from the field to inside the feature. We show that controlling the pre-reflow copper thickness and making sidewalls tapered can help prevent voids during reflow.

[1] Simon A., Straten O., Lanzillo N., Yang C., Nogami T. and Edelstein D., J. Vac. Sci. Technol. A 38, 053402 (2020)

[2] Zhang D., Stout P. and Ventzek P., J. Vac. Sci. Technol. A 21(1) 2003