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Subject: Re: Glow Discharge cleaning

Date: 12/27/01 at 8:17 PM
Posted by: D Van Vorous
E-mail: vanvorous@attbi.com
Message Posted:

In Reply to: Glow Discharge cleaning posted by Ken Hunter on 11/29/01 at 12:48 AM:

>Will this be enough voltage for the glow discharge?
2-2.5 kv is about right. Ive run as low as 1 though. For a constant current PS such as what you have, youll find that the voltage is more or less linear with pressure.
Leastwise between 10-40 Mtorr.

>Do I really need DC voltage?
Ive run DC, on insulating substrates one really should consider AC or RF instead.

>What is the typical glow discharge current?
For a small source surface area, not more than .5 amps and probably more like 1-200 ma max.

>Is there a preferred configuration for the probe or conductor inside the tank for the HV discharge?
Im kinda partial to a geometry equivalent to the substrate size but Ive run into configurations using a 1" diameter disc with the substrate connected to the + side of the Power supply.

>Should I put the glow discharge close to the glass or at the other end of the tank?

Shouldnt be any futher than 2" as glow cleanings relies on ion impimgement on the substrate surface most times.

>At what vacuum levels will the glow start and quench?
Around 10 mTorr is where itll go out. To ignite, youre probably looking at 20. A lot depends on the "target" and the power supply output characteristics.

>Will this loss of the discharge tell me that I have enough vacuum to begin the evaporation?

The pressure required for Glow cleaning is about 2-3 decades high for "clean" high specular reflectivity Alum. depositions.

>I do have gauges but wonder if the glow is a usable barometer of good/high vacuum?

I wouldnt. for the above reason.

Had you considered a simple heater arrangement instead of the glow approach? Might find its a whole lot simpler and just about as effective.

D.


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