High density bump-less Cu-Cu bonding with enhanced quality achieved by pre-bonding temporary passivation for 3D wafer stacking

Face-to-face stacking of wafer-on-wafer is demonstrated successfully using bump-less Cu-Cu bonding. Using self-assembled monolayer passivation and in-situ desorption, Cu-Cu bond is enhanced in shear strength and bonding uniformity. Excellent specific contact resistance of 0.30 Ω.μm² is obtained. Continuous daisy chain of at least 6,000 contacts at 15μm pitch is connected successfully. This provides inter-IC connection density of 4.4 × 10⁵ cm^-2 suitable for wafer level 3D integration to augment Moore Law´s scaling.