Abnormal grain growth of (110)-oriented perpendicular nanotwinned copper into ultra-large grains at low temperatures

Abstract

Large grain sizes can be achieved by abnormal grain growth (AGG), but its application in Cu interconnect is limited due to the demand for high temperatures. In this study, we found that AGG occurred at a temperature as low as 200 °C in electrodeposited perpendicular nanotwinned Cu (pnt-Cu) films. After the AGG process, the pnt-Cu grew into ultra-large grains with an average grain size of 11.04 μm and a maximum grain size of 49.70 μm, while in fine-grained Cu (fg-Cu), the average grain size reached a limitation of about 2.60 μm after annealing. As a result, the pnt-Cu showed lower resistivity after annealing than fg-Cu. Cross-sectional observation of the AGG process indicated that abnormal grains nucleated at the bottom transition layer. Molecular dynamics (MD) simulation suggested that uneven grain growth in the transition layer is the cause of the nucleation of AGG seeds. The constrained nucleation location reduced the number of AGG seeds, leading to ultra-large grain sizes in the annealed pnt-Cu film, which is beneficial to the application in Cu interconnects.