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Crystals during copper electroplating cause bridging and short circuits

2003

I'm attempting to electroplate copper onto a substrate with a Ti/Cu seed layer. The substrate is coated with photoresist and then patterned to create narrow openings in the photoresist - I'm trying to plate through these openings (about 1-2um thick). I'm using copper sulphate/sulfuric acid solution with a pure copper anode - a current of 18mA has yielded a uniform deposition and a shiny surface. I'm using a magnetic spinner to circulate the solution in the tank, and the substrate is held upright (parallel to the anode) during deposition. When the deposited copper reaches about 1um thick, large "crystals" form on the surface of the copper - this is not problematic in large open areas, but often the "crystals" will bridging areas with fine openings in the photoresist due to their large size (crystals appear to be ~20um across). I believe what I'm observing are crystals due to their appearance.

My question is: what causes this, and more importantly how can I avoid the formation of (Cu?) crystals on the surface during electroplating?

Thanks in advance,

J. Damiano
research - Raleigh, North Carolina

Are the crystals copper metal or blue copper sulphate?

Russell Richter
- Danbury, Connecticut, USA
2003

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They appear to be copper crystals. I've tried some follow-up experiments with higher current levels on unpatterned samples that appear to be much smoother (no crystals), but I haven't tried yet with a patterned substrate. If I see improvement, I'll report back here.

Thanks,

John Damiano
research - Raleigh, North Carolina
2003