Ion milling will remove the gold seed layer a little faster than the copper
and slower than the chromium at a 45-degree angle of incidence.
It so happens that gold ion mills faster at 0 degrees, while most other
materials (and hopefully copper) mill more slowly.
Next time use a 10-nm Cr layer and thinner Au if the Cu plating uniformity
is OK.
    --Kirt Williams

----- Original Message -----
From: "Pradeep Dixit" 
To: "General MEMS discussion" 
Sent: Wednesday, February 15, 2006 8:29 AM
Subject: [mems-talk] Cr/gold etchant with very high selectivity with copper


> Hi all,
>
> I have fabricated copper inductors using through-photoresist
electroplating..
> 50 nm Cr with 300 nm Au layer is used as seed layer. Thickness of copper
> metal lines if about 4 microns and pitch between two metal lines is about
15
> microns.
>
> Now i want to etch seed layer without affecting the copper metal lines. i
> have used KI+I2 solution to etch gold, however i have found that some
copper
> metal lines are also etched away and copper electroplated surface has
become
> rougher. It seems that this gold etchant has not good slectivity with
> copper.
>
> Can any one suggest some etchant/methods using which, Cr/gold seed layer
can
> be etched away without affecting copper lines.