A Study on the Interfacial Reactions between Gallium and Cu/Ni/Au(Pd) Multilayer Metallization

Area of Science:

• Materials Science
• Surface Science
• Microelectronics Engineering

Background:

• Low-temperature soldering is crucial for advanced microelectronic packaging.
• Gallium (Ga) soldering presents unique challenges due to its reactivity with common metallization.
• Nickel (Ni) is often used as a diffusion barrier, but its stability with Ga requires investigation.

Purpose of the Study:

• To investigate the interfacial reactions and stability of Ni diffusion barriers during low-temperature Ga soldering.
• To analyze the formation and evolution of intermetallic compounds (IMCs) at the Ga/Ni/Cu interface.
• To understand the kinetics and mechanisms governing Ni consumption and Ga infiltration.

Main Methods:

• Soldering experiments were conducted using Cu/Ni/Pd and Cu/Ni/Au metallization structures.
• Interfacial reactions were studied across temperatures of 160, 200, 240, and 280 °C for 30 to 270 minutes.
• Microstructural analysis was performed to examine IMC formation and Ni layer consumption.

Main Results:

• Ga-rich Ni-Ga IMCs (Ga_xNi) formed on Ga₇Ni₃ at lower temperatures.
• Increasing temperature and time led to Ni consumption and the formation of Cu-Ga IMCs (CuGa₂, γ3-Cu₉Ga₄).
• A widening gap between Ga-Ni and Ga-Cu IMCs allowed molten Ga infiltration, with Ga₇Ni₃ growth kinetics influenced by interface reactions (activation energy: 61.5 kJ/mol).

Conclusions:

• Nickel serves as a viable diffusion barrier in low-temperature Ga soldering, but its consumption is temperature-dependent.
• The formation of specific Ga-Ni and Ga-Cu IMCs dictates the soldering interface evolution.
• Understanding Ga diffusion through grain boundaries and porous microstructures is key to controlling Ga₇Ni₃ growth and ensuring solder joint reliability.