Why is TSV via filling considered difficult? Where does the difficulty lie? Basic overview of TSV electroplating via filling:
- High aspect ratio: TSVs can reach depths of 50–150 μm, while the diameter is only 5–10 μm, resulting in an aspect ratio >10:1.
- Complex inner wall: The inner walls have steps, and due to the Bosch process, scallop-shaped structures are formed.
Challenges in TSV electroplating? The vias cannot be fully filled, leading to voids. Main causes of void formation in TSVs:
- Current density concentrates at the via opening → copper grows faster at the opening → metal at the opening contacts and seals, forming voids.
- Difficult electrolyte exchange inside the via: old electrolyte cannot be expelled in time, and new electrolyte cannot reach the deposition interface, resulting in poor electroplating quality and lower deposition rates in deep vias.
Deposition principles of electroplating additives:
Suppressor: Suppresses copper deposition on the surface, at the via opening, and along the via walls.
Accelerator: Speeds up copper deposition growth from the bottom upward.
Leveler: Ensures uniform copper thickness across the wafer, reducing surface roughness.
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