Manganese Segregation Behavior in Damascene Metal Lines

Abstract

The effective diffusivity in Cu lines during electromigration (EM) mass flow is related to microstructure and dopant additions and is controlled by fast diffusion paths, such as interfaces between Cu and SiCN capping layer, and grain boundaries (GB). The dimensional evolution of on-chip Cu interconnections from microns to tens of nm-sized line widths has caused a change in Cu line microstructure, thus resulting in a significant change in diffusion path. Manganese (Mn) as dopant/seed plays a critical role in damascene Cu lines by paring with GB vacancies or interfacial oxygen to reduce the diffusivity.For a decade, Mn has been added in Cu seed layers for improving EM for Cu lines. Even though the doping level (less than fractions of a percent) is below physical detection limits by analytical transmission electron microscopy (TEM) techniques, the improvement of EM is observed by electrical test [1]. However after thermal stress or reliability tests, Mn segregates to the interfaces and GB at a higher concentration than in bulk Cu which makes it in the detectable range using an advanced analytical TEM technique on ultrathin lamella prepared with inverted dual beam focus ion beam (FIB). Figure 2 b) (taken at Cu GB) shows only Mn L2 while lacking O K and Mn L3 peaks indicating the metallic phase appears at the Cu GB. This may suggest that Mn coupling with the vacancies at Cu GB, which can slow down GB movement resulted in the improvement of EM reliability. The red spectrum in Figure 2 b) (acquired at the interface of Cu and capping layers) shows both Mn L2 and L3, which is a clear signature of Mn oxides. Furthermore the pre-edge of oxygen K and energy split between the Mn L2 and L3 edge peaks maximum suggests Mn3O4 appears at the interface, according to reference paper [2]. The existence of Mn oxides at the interface effectively isolates the Cu surface from oxygen preventing Cu oxide formation, which is deleterious to EM reliability.In conclusion, different Mn segregation behaviors are detected by high resolution STEM/EELS from high quality samples prepared with inverted FIB. Two different phases of Mn segregation are identified with EELS fine structures.

A novel 96.5Sn3Cu0.5Mn nanosolder with enhanced wettability applied to nanosoldering of WO3 nanomaterial

“…The 96.5Sn3Cu0.5Mn NWs released from PC membrane were ground into nanoparticles with a small size under 30 nm, to achieve the precise analysis of their crystalline structures and chemical valence using STEM and EELS. Figure 2 shows the Sn M 4,5 edge which is a signature of metallic Sn, and the single Mn L 3 edge which is a signature of metallic Mn (the L 2 edge, which is weak in the metal, is here also too weak to be seen above the noise) [41]. The spectrum in figure 2(f) from the green area (figure 2(a)) shows the Sn M 4,5 edge which is a signature of metallic Sn, and the Cu L 2,3 edge which is a signature of metallic Cu.…”