Very good point.

If the Ga and P didn't react they might be evaporating and there could
be a differential rate of loss. Worse yet, since it is a vacuum system
there could be significant evaporation even below the melting point
through sublimination. However, monoatomic species should be very
reactive and they are arriving with some kinetic energy. I would be
inclined to think they would react, though there might be stoichiometric
imbalance. Also, any surplus Ga on the target I would think might have a
tendency to evaporate and so conditioning might not work.

To creat TiN, some processes sputter Ti with a Nitrogen in the
background gas. Perhaps you could have a vapor source of Ga when you
sputter GaP.

If you are smelling something I would talk to safety about toxicity.

Ed

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Andrew Sarangan
Sent: Thursday, January 29, 2009 3:28 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Gallium Phosphide Thin Film Deposition

Thanks for that response.  It is certainly possible that the P is being
sputtered more than Ga. My initial thought was that if the GaP bonds are
being dissociated by the Ar+ ions, then both Ga and P will be above
their melting temperature at the target surface. Ga = 30C, P = 45C. GaP
= 1540 C. So while GaP is being sputtered, any elemental remains of Ga
and P will be evaporating, with Ga faster than P. That would result in a
P-rich target and substrate. Let me know if that reasoning makes sense.
Also, I noticed a distinct 'metallic' smell in the chamber which I am
inclined to attribute to gallium.