[mems-talk] Wet etching Gold

[Yue Mun Pun, Jeffrey]

Sebastien,
I have tried to test out the following combination of gold etchant, 10% KI: 5% I2: 85% H2O from Cyantek (I mixed the ingredients myself) as reported in 'Etch Rates for Micro-Machining Processing - Part II' by Kirt Williams et. al.  I placed the mixture in a glass beaker & heated it up to 67-70'C on a hot plate.  Then I placed a gold coated PDMS (polydimethylsiloxane) material into the mixture and shook the PDMS in the mixture while holding on to it with my tweezer.
The 80nm gold can be dissolved but it leaves a very thin, almost transparent layer of gold on the PDMS, which can be observed by the naked eye.  This layer is obtained inabout 1.5 minutes and further soaking in the KI:I2 mixture does not appear to etch the gold anymore.  Futhermore, KI:I2 mixture appears to stain the PDMS brownish.

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From: Sebastien Allard [mailto:sallard at lxsix.com]
Sent: Thu 3/1/2007 11:48 PM
To: Yue Mun Pun, Jeffrey
Subject: RE: [mems-talk] Wet etching Gold

Hello,

I don't know the details of your etching process, but my experience with KI:I2 dictates that agitation is absolutely essential for effective etching and heating will increase etch rates.

Transene company manufactures a ready-to-use solution TFA Gold Etch (I don't know the exact concentrations), but I have used it at  65 +/- 2 C and managed to remove completely 15 microns in 4 minutes.  Theoretically, this product etches at 28 angstroms per second at 25 C, but gets up at 350 angstroms per second at 65 C.