Characterization of electric-field enhancement leading to circuit-layout dependent damage of low-k films when exposed to processing plasma

摘要

We investigated the effects of Cu-line layouts on plasma-induced radiation damage (PRD) to interline low-k dielectric films. We carried out a finite-element-method-based three-dimensional (3D) electromagnetic simulation (EMS), in which a Drude free-electron model was implemented for the dielectric function of Cu lines. The 3D EMS analysis revealed that the electric field in the low-k films was enhanced for specific Cu-line layouts exposed to N-2 plasma irradiation, while no clear electric-field enhancement was observed for Ar plasma exposure. The specific optical emission lines produced in N-2 plasmas are the root cause of damage creation in the low-k dielectric films with embedded Cu lines. The 3D EMS analysis predicted that the electric field was enhanced with decreasing the line and space (L/S) widths. The prediction implies that the Cu-line-layout dependent PRD should be more prominent as device dimensions shrink. We verified the predicted results experimentally using devices with low-k films between various L/S Cu lines, in addition to a blanket wafer-without Cu lines. We found that an increasing peak in the low-k dielectric constant appeared at a specific L/S width after N-2 plasma exposure and no clear increase in the dielectric constant was observed after Ar plasma exposure. The obtained experimental results are consistent with the 3D EMS analysis. We propose a damage model, where the electric field enhancement plays an important role in the low-k dielectric films with embedded Cu lines. The proposed damage model is indispensable for minimizing PRD and designing Cu layouts in future devices. (C) 2019 Author(s).