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Etching gold through micro-holes of copper [Ohio] 

October 12, 2009

Hello,

I have layer of gold (<2microns) underneith a layer of copper (>5 microns). The copper layer has micro-scale holes in it that allow chemical access to the gold. I have had success with large holes (160 microns) but I need to be able to do it with smaller holes (<30 microns). I have used both aqua regia (3x HCl, 1x HNO3) vapor and a liquid solution of potassium iodide, iodine, and water. Both techniques work well with the larger holes, however, I can't seem to get to the gold with smaller holes. Is there any recommendation you might have for helping my chemistry gain access to the gold?

Thanks and best regards,

Dave Lewis
Product Developer - Columbus, Ohio, USA

Dave

Getting solution to flow into small diameter round holes is very difficult. Some things that help are:
1. Use the thinnest photoresist that you can - less than 5 microns
2. Add a wetting agent to lower the surface tension of the etchant to less than 30 Dynes/cm
3. Use spray etching with the patterned area facing down and the solution spraying up into the holes.
4 Use spray pressures of approx 50 - 75 PSI
5. Either of the etching solutions you have used previously should work
6. If there is still problems with the etching use a plasma cleaning process to remove any resist residue and also to make the surfaces more hydrophilic.

Pat Mentone St Paul, Minnesota

FYI: The micro-holes are actually crosses, not round. For one pattern that I am struggling with, the arm-width is 10 um. The arm-span (end to end) is 75 um, and the distance between crosses is 50 um. Not sure if that makes much of a difference as far as etching through these features but I thought it might help paint a picture for anyone willing to help.

Thanks,
Dave Lewis

Dave Lewis
- Columbus, Ohio, USA