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Diffusion Barrier Performance of Ni-W Layer at Sn/Cu Interfacial Reaction
Jinye Yao1, Chenyu Li1, Min Shang1
1School of Materials Science and Engineering, Dalian University of Technology, Dalian 116000, China.
Materials (Basel, Switzerland)
|August 10, 2024
Summary
This study investigates Ni-W barrier layers for 3D integrated circuits, finding they initially impede tin diffusion but degrade at high temperatures due to Ni2WSn4 formation. This impacts solder joint reliability in microelectronic devices.
Area of Science:
- Materials Science
- Microelectronics Engineering
- Surface Science
Background:
- 3D integrated circuits (ICs) face reliability challenges from electromigration and thermomigration due to miniaturization.
- Intermetallic compound (IMC) growth in solder joints increases layer thickness and brittleness, compromising joint reliability.
- Controlling IMC formation and growth is crucial for enhancing the lifespan of microelectronic devices.
Purpose of the Study:
- To investigate the effectiveness of electrodeposited Ni-W layers as diffusion barriers between Sn and Cu.
- To analyze the impact of the Ni-W layer's structure and the formation of a "bright layer" (Ni2WSn4) on barrier properties during soldering.
- To understand the growth mechanisms of IMCs and the Ni-W layer at various temperatures.
Main Methods:
- Electrodeposition of Ni-W barrier layers on Cu substrates.
- Systematic investigation of barrier properties in Sn/Cu reactive couples.
- Analysis of IMC formation and growth kinetics at different temperatures (250°C, 275°C, 300°C) and durations.
Main Results:
- The Ni-W layer initially impedes Sn diffusion into the Cu substrate.
- A "bright layer" (Ni2WSn4) forms during reflow, growing linearly and eventually compromising the Ni-W barrier's effectiveness.
- At 300°C for 600s, the Ni-W barrier fails as Ni2WSn4 completely covers it, leading to rapid Sn and IMC growth.
- IMC growth (Ni3Sn4-based) and Ni2WSn4 layer growth are primarily grain boundary diffusion-controlled at 250°C, 275°C, and 300°C.
Conclusions:
- Ni-W layers serve as viable diffusion barriers but their long-term reliability is limited by the formation of Ni2WSn4.
- The "bright layer" formation significantly alters diffusion pathways and reduces activation energy for Sn diffusion.
- Understanding these growth mechanisms is essential for designing reliable solder joints and selecting appropriate Ni-W barrier layers for specific soldering processes in microelectronics.
