Re: sputtering Not you fathers metalworking

In article <1150297461.253825.168160@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
dcaster@xxxxxxx says...

systems. At any rate I am trying to help them. This is not high
vacuum aluminizing where you heat the aluminum using a tungsten
filament, but low vacuum between 0.1 and 1 torr where you use high
voltage to sputter. In their case they plan on pulling a fair vacuum
and then introducing some argon gas before applying the high voltage.

The idea is to put the target at negative voltage with respect to
the baseplate. Then an atmosphere of about 100 microns or so
of argon gas is introduced into the chamber, a small needle valve
is typically needed to do this. The argon atoms are ionized by
the potential and postively charged argon ions (basically argon
atoms where an electron has been ripped off) are accellerated
by the high voltage and smack into the aluminum target. Their
kinetic energy jackhammers some aluminum atoms out that float
around and land on whatever's nearby - hopefully the specimen!

The Gast pump might work if it could pump down to 100 microns or
so. The wech pump certainly would, be careful because if you let
the chamber sit with the pump running below about 10 microns
pressure for any length of time, the mean free path length for
an oil molecule from the pump becomes very long, and you backstream
pump oil into the coater chamber/belljar which then has to get
cleaned out. Obviously running the sputter source with 100
microns of argon will prevent that problem.

You don't need much metal to make the specimens stop charging
in an SEM. 100 angstroms is plenty. I had some run the other day,
and I could not see the gold on them after they had been run,
it was that thin. Gold works well because it won't oxidize when
you pull it out of the system to transfer into the SEM. A small
bit of gold wire will last a long time and won't cost more than
40 bucks or so.

Be carefull with the HV source. When I do plasma pre-clean to
prepare for depostions, I use a 1KV 40 mA power supply. This
is basically to do the same thing as the sputter you are talking
about. A supply like that can kill easily so be sure the system
has some rudimentary interlocks so nobody gets hurt.

Jim


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