People indeed use Ta inside the crucible to prevent spitting. There is also a
paper by Feinstein which addresses this problem:

"Reduction of nodules in electron-gun-evaporated Au films", L.G. Feinstein and
M.J. Bill, J. Vac. Sci. Technol., Vol 12, No. 3, May/June 1975, p 704-708.

I have a copy if you are interested.

Yves Bertic


-----Original Message-----
From: Brad Cantos [mailto:[email protected]]
Sent: Friday, November 04, 2005 12:37 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Defects in Gold evaporation in E-Beam
evaporator


Long,
What you are experiencing is a phenomenon called gold spitting.  It is
common when evaporating gold to see this.  In fact, if your evaporator has a
window that looks toward the e-gun you will see these spits ejected from the
melt.  Only the smallest ones get to the wafer,  you will probably find
"larger" ones in your chamber.  You can try a couple of things to solve it:
try a lower deposition rate; or, if you use a beam sweep, make sure that it
covers a large area on your melt.  If that fails, you can look for a paper
written in the 1970s that suggests adding a small piece of tantalum to your
gold.  The Ta will not melt but it will control the spitting.  I don't
remember the author's name, but I am pretty sure it was someone at IBM.
Brad