Cu diffusion into the glass under bias temperature stress condition for through glass vias (TGV) applications
Citation
Kim, H., Cai, L., Fahey, A., Vaddi, R., Zhu, B., & Mazumder, P. (2018). Cu diffusion into the glass under bias temperature stress condition for through glass vias (TGV) applications. Integrated Microsystems.
Keywords
- Copper diffusion
- Through Glass Via (TGV)
- Bias Temperature Stress (BTS)
- SG 3.4 glass
- Diffusion barrier
- Activation energy
- Electrical field
- SIMS (Secondary Ion Mass Spectrometry)
- Arrhenius plot
- 2.5D/3D packaging
Brief
This article examines copper diffusion in Corning SG 3.4 glass under bias temperature stress to determine whether a Cu diffusion barrier is required for Through Glass Via (TGV) applications.
Summary
The article, published in 2018 by Hoon Kim et al., investigates Copper (Cu) migration in Corning SG 3.4 glass, a material used in Through Glass Via (TGV) applications for 2.5D/3D integrated packaging. The study focuses on understanding whether a Cu diffusion barrier is necessary to prevent electrical shorting in these applications.
Here are the key takeaways from the article:
- Cu Diffusion Mechanisms: The authors explain that Cu migration in glass happens due to both thermal diffusion and electrical drift under an applied voltage. They highlight that Cu diffusion is a two-step process: breaking the metallic bond with other Cu atoms and then breaking the bond with oxygen in the glass.
- Experimental Methodology: The researchers used a planar capacitance test structure with oxidized Cu as a source for Cu ions to simulate a worst-case scenario. They performed Bias Temperature Stress (BTS) tests at various temperatures and electrical fields to evaluate Cu diffusion.
- Findings: The results showed that Cu diffusivity increases with both temperature and applied electrical field, confirming the influence of both thermal and electrical factors. They found the activation energy of Cu diffusion in SG 3.4 glass to be 1.1eV, falling between the values for thermal SiO2 and low-k dielectrics reported in previous studies.
- Practical Implications: Based on their calculated diffusion lengths, the authors concluded that a Cu diffusion barrier might not be necessary for most TGV applications, including low-power devices and high-power MEMS devices.
The authors' findings offer valuable insights into the behavior of Cu in glass interposers, guiding the design and fabrication of future 2.5D/3D integrated circuits.