Defect-free metallization of through-glass vias with engineered geometry in additive-free electrolyte

Citation

Jayaraman, S., Sevem, M., Vaddi, R., Kanungo, M., & Mazumder, P. (2020). Defect-free metallization of through-glass vias with engineered geometry in additive-free electrolyte. Electrochemistry Communications, 120, 106823. 

Keywords

• Through glass via
• Metallization
• Kinetic limited deposition
• Additive-free electrolyte
• Engineered via

Brief

This article describes how to metallize through-glass vias (TGVs) without defects by using an additive-free electrolyte and engineering the vias to have an X-shape in the middle.

Summary

This article, published in 2020 in the journal Electrochemistry Communications, presents a method for defect-free metallization of through-glass vias (TGVs) using an additive-free electrolyte. The authors, Jayaraman et al., achieved this by combining two key factors: using engineered vias with an X-shape in the middle and electroplating in the kinetic-limited regime (where the plating rate is slower than the diffusion rate of copper ions).

Here's a breakdown of their findings:

• Conformal plating in cylindrical vias with uniform cross-sections leads to defects, even in the kinetic-limited regime. This is because the plating rate becomes infinitely fast as the diameter of the open hole approaches zero during plating. The authors confirmed this through X-ray tomography (XRT) imaging of cylindrical vias electroplated in an additive-free electrolyte.
• Engineering the via with an X-shape ensures pinching in the middle, preventing the formation of a seam. This, combined with operating in the kinetic-limited regime, allows for uniform deposition and complete filling of the vias without any voids. The authors demonstrated this by successfully filling engineered vias using an additive-free electrolyte at a specific current density that corresponds to the kinetic-limited regime.
• Interestingly, at very low current densities, the authors observed an unexpected increase in thickness in the middle of the via compared to the top. This phenomenon cannot be explained by a simple 1D model and requires further investigation.

The authors conclude that combining kinetic-limited deposition with engineered vias could lead to a cost-effective solution for TGV metallization by eliminating the need for expensive additives. However, further validation is needed to assess factors like plating speed, stress, and long-term reliability.

Origin: https://www.sciencedirect.com/science/article/pii/S1388248120301740