In my experience those pretty round balls you noticed are due to surface
charge artifacts - a local area has accumulated a net charge and acts as
an electron mirror with a roughly spherical distribution.  If the film
was discontinuous and the substrate has good insulating properties, you
could very easily be charging up an island of Au which then generates a
charge cloud of larger diameter, masking the presence of the charge
artifact.

Regards,

Jim Russell
Boeing


-----Original Message-----
From: Long Chen [mailto:[email protected]]
Sent: Thursday, November 03, 2005 9:31 AM
To: [email protected]
Subject: [mems-talk] Defects in Gold evaporation in E-Beam evaporator


Hi, I am doing some gold evaporation using e-beam evaporator, and
consistently I am getting defects in the resulted film. In the SEM the
defects look like pretty round balls with diameters about 100~300nm.
After putting in the ultrasonic bath for a few seconds, those defects
would partially move out and I could see that the holes beneath. I
didn't have the tool to check the element of the defects but found a
technique paper from Motorola which discussed about the similar defects
happened in their gold evaporation. It said that the defects are "spit"
gold where the carbon contaminants on the target surface act as the
spitting catalyst. They tried several approaches to reduce the carbon
amount in the target material and the density of the defects decreased
accordingly. I am wondering whether some guys here know about this and
have some idea to deal with this, i.e., to improve the film quality. Any

suggestion would help and would be deeply appreciated.
Thanks a lot,
Long