XPS Investigation into Diffusion-Bonded Homogeneous Cu-Cu and Heterogeneous Cu-Al Junctions

Diffusion bonding is an exciting technology expected to open new fields of application. To further develop this technology, it is necessary to investigate the inter-diffusion phenomena that occur at the atomic level at the interface of bonded junctions. A homogeneous Cu-Cu junction and heterogeneous Cu-Al junction were fabricated using the direct diffusion bonding method. Using XPS, we investigated the phenomena of recrystallization and inter-diffusion at the interface of the bonded junction. The Cu valence band spectrum observed using XPS measurements at the interface of the homogeneous Cu-Cu direct diffusion-bonded junction revealed that diffusion-induced recrystallization occurred. In a heterogeneous Cu-Al direct diffusion-bonded junction, the valence band spectrum observation using XPS measurements showed that the valence bands of Cu and Al overlapped at the interface of the bonded junction. Using a heterogeneous Cu-Al direct diffusion-bonded junction, we investigated the inter-diffusion at the interface of the bonded junction and found that the diffusion lengths of Al atoms in the Cu region and Cu atoms in the Al region were approximately 11.8 μm and 7.85 μm, respectively.