Effect of impurities on anisotropic grain growth in (111)-oriented nanotwinned copper

The (111) oriented copper with a nanotwin structure, known as (111) nt-Cu, demonstrates exceptional physical properties and enhanced anti-corrosion, rendering it suitable for application as the interconnection material in integrated circuit (IC) technology. Nevertheless, the microstructure of (111) nt-Cu may intermittently diminish following annealing processes exceeding 200 °C due to the occurrence of anisotropic grain growth. This investigation delves into the determinants influencing the thermal stability of (111) nt-Cu films. The (111) nt-Cu films were continuously electroplated employing identical electrolyte. Despite the consistent depletion of the additives, the microstructure of (111) nt-Cu basically remained unchanged. Nevertheless, the thermal stability of (111) nt-Cu films with a similar microstructure decreased with the depletion of additives. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was employed to quantify the integration of non-metallic impurities (such as N, O, C, S and Cl) within the electrodeposited (111) nt-Cu, induced by the electrolyte additive chemistry. According to the SIMS analysis, a notable disparity in impurity intensity between two (111) nt-Cu films electroplated using the electrolyte for different durations was observed, primarily attributed to the presence of chlorine. Chlorine formed robust chemical bonds with Cu atoms, thereby immobilizing boundaries and impeding the anisotropic grain growth process. This study endeavors to introduce a novel perspective on enhancing the thermal stability of (111) nt-Cu through engineered chemical additives.