Basics of through silicon via (TSV) filling

The copper plating solution contains CuSO4, H2SO4 as a main component and several kinds of additives in addition to this.

Accelerator promotes plating, and polymeric substances are used.

Also, inhibitor inhibits the growth of plating, such as PEG (Polyethylene Glycol).

Leveling material is JGB (Janus Green) etc. makes the surface of plating smooth.

• Adsorption of the inhibitor precipitates more on the surface layer (outer side) of the via because it has characteristics that it is easy to adsorb on places where the current is high or where the stirring of the plating solution is strong.
• The electrodeposition reaction on the substrate surface is suppressed, and plating preferentially deposits in the recessed part.

• It adsorbs uniformly on the copper surface.
• The eutectoid density is increased in the concave portion which does not eutectoid on the plating film and the surface area decreases with the growth of the plating, and the electrodeposition reaction of the concave portion is promoted.

• A monomolecular film is formed at the cathode interface by interaction with chlorine ions, and copper precipitation is widely suppressed.

• Voltage applied by via filling plating may also affect. Conditions suitable for plating are necessary for current value, waveform, reverse pulse etc.

• The growth of copper cannot be suppressed unless the additives adjusted, the plating conditions are established. Then the upper part of the via is clogged by the growth of copper and becomes a void.

• By controlling the additives, ideal embedding can be realized by growing with smooth curves from the bottom of via.

• Plating equipment (stirring method, electricity applying method, facility structure).
• Plating liquid type (metal concentration, additive concentration, proportion)
• Hole diameter, depth, in-plane rate for each wafer.

*It is indispensable to determine the above three points.