Comparative Study on Electroless Deposition of Various Metals for Low-Temperature Cu/SiO2 Hybrid Bonding

초록

In this study, low-temperature Cu/SiO2 hybrid bonding (HB) is achieved by metal deposition using Au, Pt, and Sn. These metals were selected to prevent Cu oxidation and facilitate metal diffusion bonding. First, an electroless deposition solution was prepared by optimizing each precursor of metal, reducing agent, and complexing agent for Cu pads. The Cu/SiO2 HB chip was then immersed in the solution, followed by a chemical treatment to enhance the surface activity of the SiO2 layer. After treatment, two chips were aligned at their Cu/SiO2 surfaces and pressed at 120 °C. Finally, pre-bonded chips were annealed in an inert N2 atmosphere at 250 °C. The thickness of the metal layers was maintained at 10?20 nm, as excessively thick layers could hinder diffusion bonding between Cu pads. The bonding temperature was set to 250 °C to evaluate the bonding properties of each metal without failure. Cross-sectional SEM image confirmed the successful bonding of all metal layers without large voids. EDS analysis revealed that Au exhibited the highest diffusion interface. Consequently, Au-deposited HB chips demonstrated the most stable metal diffusion bonding at low temperatures. This study highlights the importance of chemical surface treatment and presents an optimized metal selection strategy for advanced packaging technologies. Keywords: Hybrid bonding, Low-temperature hybrid bonding, Advanced packaging, Electroless deposition, Metal diffusion *Corresponding Author: cmyoon4321@inha.ac.kr