Effect of De-Twinning on Tensile Strength of Nano-Twinned Cu Films

Abstract

Tensile tests were carried on the electroplated Cu films with various densities of twin grain boundary. With TEM images and a selected area diffraction pattern, nano-twinned structure can be observed and defined in the electroplated Cu films. The density of the nano-twin grain structure can be manipulated with the concentration of gelatin in the Cu-sulfate electrolyte solution. We found that the strength of the Cu films is highly related to the twin-boundary density. The Cu film with a greater twin-boundary density has a larger fracture strength than the Cu film with a lesser twin-boundary density. After tensile tests, necking phenomenon (about 20 μm) occurred in the fractured Cu films. Moreover, by focused ion beam (FIB) cross-sectional analysis, the de-twinning can be observed in the region where necking begins. Thus, we believe that the de-twinning of the nano-twinned structure initiates the plastic deformation of the nano-twinned Cu films. Furthermore, with the analysis of the TEM images on the nano-twinned structure in the necking region of the fractured Cu films, the de-twinning mechanism attributes to two processes: (1) the ledge formation by the engagement of the dislocations with the twin boundaries and (2) the collapse of the ledges with the opposite twin-boundaries. In conclusion, the plastic deformation of nano-twinned Cu films is governed by the de-twinning of the nano-twinned structure. Moreover, the fracture strength of the nano-twinned Cu films is proportional to the twin-boundaries density.

Research Progress of Electroplated Nanotwinned Copper in Microelectronic Packaging

“…The newly established gelatin-controlled Winand (GCW) growth model is shown in Figure 10 . Similarly, it was also reported by Chia-Hung Lee and coworkers [ 63 ] that the density of nanotwins could be controlled by changing the gelatin concentration.…”

Stress Relaxation and Grain Growth Behaviors of (111)-Preferred Nanotwinned Copper during Annealing

“…However, it normally accompanies ductility loss. Incorporating nanotwins in Cu can be considered as the most effective approach to suppress EM failures [ 13 , 14 , 15 , 16 ] and to enhance its mechanical properties [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] while its electrical resistance can remained approximately unchanged. In recent years, nano-twinned copper (nt-Cu) has drawn significant attention due to its high mechanical strength and conductivity, low manufacturing cost, and oxidation [ 26 , 27 , 28 ].…”