Transforming WLP Applications: Introducing Cutting-Edge Next-Generation Nanotwinned Copper Processes to Revolutionize Hybrid Bonding

Abstract

We discuss two electrochemical plating approaches for nanotwinned copper (ECP nt-Cu)—Gen 1 and Gen 2. These two approaches allow control over columnar width and transition layer thickness on Cu substrates, enabling the filling of nanotwinned Cu for bonding applications. Both approaches produce stable nt-Cu structures with minimal transition layers when electroplated on (111) Cu substrate. However, grain size, transition layer thickness on polycrystalline substrates, and feature-filling behavior differ. The researchers suggest that the choice between Gen 1 and Gen 2 depends on the feature size, aspect ratio, and applications. In addition, further exploration into other additives improves bottom-up filling capabilities, enabling more versatility for applications. Both approaches enable the filling of nanotwinned Cu inside bottom-seeded and complete-seeded features, with 100% nanotwin growth parallel to the substrate for bottom-seeded features. However, nanotwin growth percentage and direction depend on feature size and aspect ratio for complete-seeded features. Gen 2 tends to have less sidewall growth due to its smaller grain size and is more compatible with other additives, making it promising for high aspect ratio small features.