Hybrid bonding, particularly at fine pitches, is essential for 3D integration, enabling shorter electrical paths, reduced signal loss and enhanced device performance. However, traditional bonding processes often require high temperatures, typically around 400°C, which can be detrimental to certain materials and device architectures. The team's objective was to lower this thermal budget to approximately 200°C without compromising bond integrity.
Pulsed currents for small grain copper deposition
To achieve this, the researchers focused on optimizing the electroplating parameters for NC-Cu deposition on 300 mm wafers with varying pattern sizes and densities. By manipulating electroplating currents, including the use of pulsed currents, they developed a process that produces small-grain copper structures suitable for fine-pitch applications. The use of NC-Cu enables substantial grain growth and strong copper-to-copper bonds at lower temperatures, reducing the thermal budget required for bonding-crucial for sensitive materials and advanced device architectures.
"Our goal was to create small-grain copper using standard processes so that production lines could implement this method directly," explains Mathieu Loyer, a CEA-Leti researcher and co-author of this latest research publication. "We played with parameters relating to current, known as electroplating parameters, to develop a means of producing reliable small-grain copper deposition."
The team also addressed the challenge of reducing the deposition time while maintaining reliability. Through process optimization, they successfully decreased the deposition duration to 2-3 minutes, aligning with standard manufacturing timelines.
"By creating a process for 200°C bonding that can be integrated directly into standard manufacturing lines, we hope to streamline processes and facilitate the creation of these chips," Loyer noted. "Currently, tests are being carried out to measure the improvements in terms of efficiency and performance. Right now, we have validated the process."
The team's findings indicate that NC-Cu remains stable and maintains its bonding efficacy even weeks after deposition, underscoring its potential for reliable low-temperature hybrid bonding applications. This research represents a significant step toward more efficient and scalable 3D integration technologies, paving the way for advancements in various electronic applications.