Wet Atomic Layer Etching of Copper Structures for Highly Scaled Copper Hybrid Bonding and Fully Aligned Vias

Copper to copper hybrid bonding relies on nanometer level control of copper pad recess to create electrical contacts. To compensate for the loss of recess control during chemical mechanical planarization (CMP) due to feature scaling, a wet atomic layer etch (W-ALE) was proposed as a supplement. The process explored was a two-step cyclical wet etch to create recesses in copper patterns with sub-nanometer level control. This etching process achieved true ALE control with removal rates of ~0.28nm/cycle; roughly the atomic diameter of copper. Additionally, there was no significant impact on dielectric roughness, dielectric thickness, copper roughness or the shape of the copper feature (convexity) up to 30 cycles.