Extending Copper Interconnects and Epoxy Dielectrics to Multi-GHz Frequencies

Area of Science:

• Materials Science and Engineering
• Electrical Engineering
• Semiconductor Device Physics

Background:

• Future multichip packages necessitate Die-to-Die (D2D) interconnects operating beyond 10 GHz.
• Copper interconnects and epoxy dielectrics face performance-reliability trade-offs at high frequencies.
• Interface roughness is a critical factor influencing signal integrity and mechanical stability.

Purpose of the Study:

• To investigate the impact of interface roughness on insertion losses and adhesion for D2D interconnects.
• To explore epoxy surface chemistry modifications and their effect on roughness.
• To analyze the trade-offs between power efficiency and reliability in high-frequency interconnects.

Main Methods:

• Modulation of epoxy surface roughness using wet etching techniques.
• Quantification of surface morphology via Atomic Force Microscopy (AFM) and 2D Fast Fourier Transform (2D FFT).
• Evaluation of adhesion using peel tests and signal integrity using Vector Network Analysis (VNA) up to 18 GHz.

Main Results:

• Insertion losses and adhesion are directly correlated with the type and level of interface roughness.
• Epoxy surface chemistry and curing time influence achievable surface morphology.
• Specific roughness characteristics were identified that optimize the balance between signal performance and mechanical reliability.

Conclusions:

• Controlling interface roughness is essential for achieving reliable high-frequency D2D interconnects.
• The study provides a framework for optimizing epoxy dielectric properties for advanced packaging.
• Findings offer insights into mitigating performance degradation and enhancing the longevity of multichip systems.