Typically, the correct color of the plasma should be more purple, but bright
and pink, which typically of the excitation of the 13.56MHz sources
typically used for these application for an Ar plasma.  Dark color plasma
does indicate fluctations in the electrical potential of the target, so
check your grounding.  Typically, the shielding ring may be loose and arcing
might happen.  Also, your target may not be secured all the way to the gun
(possibly some issues with the conductive paste you're using to secure
it?).

Oxygen in the plasma will produce a blue color.

-Eric


On 7/11/06, [email protected] 
wrote:
>
>
>   1. Re: Plasma colour (Javier Ses?)
>
>
>
> ---------- Forwarded message ----------
> From: Javier Sesé 
> To: General MEMS discussion 
> Date: Tue, 11 Jul 2006 16:11:00 +0200
> Subject: Re: [mems-talk] Plasma colour
> Hello Huisheng,
>
>   I used for a long time a sputtering system in which the plasma turned
> from blue color to purple color depending on the shutter being floating
> or at ground potential. The gas was Ar and the pressure 7e-3mbar. The
> system had no gas leak, so may be your situation depends also on the
> electrical connections inside your chamber.