High aspect ratio micro-hole filling employing emulsified supercritical CO2 electrolytes

• Electrodeposition processes for metal filling into micro-hole are compared.
• Super-filling can be achieved by employing a supercritical carbon dioxide bath.
• The advantages of supercritical carbon dioxide bath are addressed and discussed.
• The effects of wettability and deposition rate are discussed.

The feasibility of filling a high aspect-ratio micro-hole with electrodeposited NiP alloy by employing an emulsified supercritical CO2 (sc-CO2) bath was studied. The effects of current density and deposition time on the efficiency of micro-hole filling were also explored. The experimental results showed that void-free NiP alloy could be successfully filled into a micro-hole with a diameter of 50 μm and a depth of 400 μm under proper electrodeposition conditions, with the advantage of low surface tension characteristics of sc-CO2 in wetting the micro-hole over that of the conventional aqueous bath. The experimental results also showed that the deposition efficiency and the deposit morphology were significantly affected by the deposition time and current density applied. Material characterization indicated that the super-filled NiP exhibited a uniform chemical composition, and an average microhardness value of 730 Hv.

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