Impact of Plasma Activation on Copper Surface Layer for Low Temperature Hybrid Bonding

Copper to copper hybrid bonding requires a surface activation and processing steps to create proper dielectric bonds with high bond strength. Unfortunately, this surface activation process modifies the surface of the exposed copper. This modified surface layer has no impact on the quality of the bond when the post bond anneal is at high temperature (>300 degrees C). Once the anneal temperature is lowered to less than 250 degrees C the surface layer will remain between at the bonding interface and impact the electrical properties of the bond. To compensate for this modification, we optimized the plasma activation parameters (chamber, power, gas) to produce the thinnest oxide with the lowest resistivity to facilitate low temperature bonding. This new treatment produces oxides that are significantly thinner than those from industry standard activation processes.