Tailoring small-scale plasticity of nanotwined-copper micropillars via microstructures

Nanotwined (nt) copper is attractive in applications such as microbumps in the microelectronics industry because nt-copper presents sound mechanical and physical properties. To date, most studies of the mechanical properties of nt-copper have been performed at macroscales. However, different stories are told at micro/nanoscales, e.g., smaller size leads to higher strength. Understanding the mechanical properties of nt-copper at micro/nanoscales is crucial for improving the reliability and endurability of microdevices. In this paper, we fabricated nt-copper film with tailored microstructures, i.e., twin boundaries (TBs) with different spacings and orientations (parallel or slanted to loading direction). Then, we applied micro-compression testing, atomistic simulation, and theoretical analysis to investigate the influence of vertical twin-boundary spacing lambda and orientation on the deformation behavior of nt-micropillars. Results show that the yield stress is increased with decreasing vertical lambda. Micropillars with slanted lambda = 15.5 nm TBs present the greatest strength, which may be attributed to a finer lambda. The phenomenon, strength increasing with decreasing lambda, was well explained by the Hall-Petch and confined layer slip models. Large-scale molecular dynamics simulations were used to uncover the atomistic and real-time deformation mechanisms. This microscale research on nt-micropillars may provide insights on designing advanced microelectronics. Published under an exclusive license by AIP Publishing.

Automated summary

This paper investigates the mechanical properties of nanotwined copper at micro/nanoscales. The influence of vertical twin-boundary spacing and orientation on the deformation behavior of micropillars is explored through experiments, simulations, and theoretical analysis. The results show that decreasing twin-boundary spacing leads to increased yield stress, and micropillars with slanted twin boundaries at a spacing of 15.5 nm exhibit the highest strength.