Fundamental Insights into Copper-Epoxy Interfaces for High-Frequency Chip-to-Chip Interconnects

Area of Science:

• Materials Science
• Electrical Engineering
• Surface Chemistry

Background:

• Advanced multichip packages require chip-to-chip (C2C) data rates exceeding 50 GB/s.
• The skin effect causes significant signal transmission losses at high frequencies, posing a challenge for interconnects.

Purpose of the Study:

• To investigate methods for improving interfacial adhesion and mechanical reliability of copper interconnects in multichip packages.
• To understand the role of copper oxides and silane adhesion promoters in enhancing interconnect performance.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to analyze interfacial bonding.
• Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were employed to study failure mechanisms.
• Investigated smooth copper interconnects with varying cuprous (Cu2O) and cupric (CuO) oxide layers and amine-functional silane promoters.

Main Results:

• Thin cuprous oxide layers combined with silane promoters improved interfacial adhesion with epoxy dielectrics by nearly an order of magnitude.
• Evidence of Cu(I)-O-Si bond formation was observed at silane-treated interfaces.
• Thicker cuprous oxide or cupric oxide layers resulted in weaker interfaces compared to thin cuprous oxide with promoters.

Conclusions:

• Smooth copper interconnects with thin cuprous oxides and silane promoters offer a viable solution to reduce skin losses while maintaining mechanical integrity.
• The formation of Cu(I)-O-Si bonds is crucial for enhanced adhesion and reliability in high-frequency applications.
• Optimizing copper oxide layers and utilizing adhesion promoters are key for robust multichip package interconnects.