Recent developments of Cu-Cu non-thermo compression bonding for wafer-to-wafer 3D stacking

Smart Stacking™ and Smart Cut™ technologies for wafer level 3D integration

“…The achieved bonding strength has been sufficient to sustain post-processing such as silicon back thinning using coarse and fine grinding. In terms of electrical characterization, a specific contact resistance of 0.5Ω.µm² for a 10x10µm²contact area after annealing at 200°C and 400°C for 2h was achieved ( Figure 3b) [6,11]. The resistance per node extracted from a ~30K daisy chain after 400°C post-bond anneal showed negligible resistance induced by bonding [11,12].…”

“…The bonding process does not require any Paper L4 -Invited Paper ICICDT 2013, Pavia, Italy additional processing steps; standard dual-damascene processes and surface treatment techniques are optimized to ensure smooth hydrophilic surfaces for good bonding conditions [6]. The bonding can be done directly after standard backend processes and can be adapted with via middle and via last, F2F and F2B integration schemes.…”

“…The Cu-SiO 2 interface leads to the weakest adhesion even after 400°C annealing [6]. Copper interdiffusion and/or grain growth across the Cu-Cu bonded interface are the driving forces for achieving high bond strength [6,8]. The achieved bonding strength has been sufficient to sustain post-processing such as silicon back thinning using coarse and fine grinding.…”

“…The highest bonding energy is obtained for copper-copper (Cu-Cu) interfaces, followed by SiO 2 -SiO 2 . The Cu-SiO 2 interface leads to the weakest adhesion even after 400°C annealing [6]. Copper interdiffusion and/or grain growth across the Cu-Cu bonded interface are the driving forces for achieving high bond strength [6,8].…”

“…To address the thermal budget constraint imposed by stacking of backend of the line processed wafers (i.e., < 400°C), specific pre-bonding surface conditioning and a postbonding thermal treatment were developed to control and increase the bonding strength within the reduced thermal budget window. High bonding energies where achieved thereby providing compatibility with aggressive wafer grinding and thinning processes [5,6].…”