Jeffrey,

Since KI etches gold but very little else, small amounts of contamination on
the surface will act as a mask.  Usually this results in swirl patterns
after etching.  Therefore it is very important to have a clean gold surface
before etching.  A short O2 plasma followed by a short SF6 plasma works for
me.  If you don't have access to plasma, or you get too much sputtering, you
could probably try 1% sulfuric followed by 15 secs of BOE.  Or if you want
to be wild, you could mix and do a short O2 plasma followed by 15 secs of
BOE.

Gabriel


---------- Forwarded message ----------
> From: "Yue Mun Pun, Jeffrey" 
> To: 
> Date: Thu, 1 Mar 2007 14:17:47 +0800
> Subject: [mems-talk] Wet etching Gold
> Hi,
> I am trying wet etch gold film from 60nm down to 30nm.  My lab has 2
> available chemistries, KCN and KI:I2 chemistries.  Due to the potential
> toxicity of KCN, I have chosen to use the KI/I2 chemistry in the proportion
> KI:I2:H2O = 4:1:40ml.  I have tested this chemistry on 80nm of gold
> evaporated on PDMS.  In the literature it was reported that KI/I2 chemistry
> in the proportion I used can etch gold at a rate of 1 micron per min, but in
> my trial, I have discovered that the 80nm gold film takes 6 times longer to
> remove.  The removal of the gold is not complete as there is still a thin
> layer of gold film left behind.
> Can anyone suggest a more effective and controllable way to wet etch gold?