To overcome the scale-down dilemma of solder-based microbumps, copper-to-copper direct bonding has emerged to be one of the most promising approaches to replace solder joints in the high-end packaging technology. However, the bonding interface remains as bonding temperature is below 300 degrees C. We use highly orientated nanotwinned Cu films in the direct bonding due to its ability to transform into extremely large -oriented grains after annealing. The extremely anisotropic grain growth can be completed at 250 degrees C for 90 min, 300 degrees C for 20 min, and 350 degrees C for 5 min. By eliminating the bonding interface, the bonding strength can be increased from 46.1 MPa to 57.1 MPa. We calculated the activation energy of extremely anisotropic grain growth, which is 82 kJ/mol (0.85 eV/atom). We suggest that the reason for the extremely anisotropic grain growth is due to the strain energy induced by thermal stresses.
|Number of pages||9|
|Journal||Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing|
|State||Published - 15 Feb 2021|
- Grains and interfaces
- Cu-Cu direct Bonding
- Anisotropic grain growth
- Shear strength