Fabrication of Highly (111)-oriented Nanotwinned Cu in Fine-pitch Vias for Cu/SiO2 Hybrid Bonding

Nanotwinned Cu (NT-Cu) with highly (111)-oriented surface is beneficial to achieve low temperature Cu-Cu bonding. Nonetheless, it is difficult to deposit NT-Cu in Cu/SiO
2
in small damascene vias. To overcome the restrict of the sidewall effect that may reduce surface (111) ratio of the vias, an optimized electrodeposition (ECD) approach was carried out. By tuning the electroplating temperatures and waveforms, we can successfully deposit NT-Cu into fine-pitch Cu/SiO
2
vias. A bottom-up growing mode of NT-Cu can effectively reduce sidewall effect. Surface (111) ratio exceeds 80% and 55% for 8-µm and 2-µm Cu/SiO
2
vias in diameter, respectively. Moreover, a theoretical model of predicting (111) ratio in small Cu/SiO
2
vias based on the optimized ECD approach was proposed.