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Subject: Re: Glow Discharge cleaning
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Date: 11/29/01 at 3:42 PM
Posted by: Vladimir Tchoutko
In Reply to: Glow Discharge cleaning posted by Ken Hunter on 11/29/01 at 12:48 AM:
In general you are right but there are some trics to obtain really good glow discharge cleaning. The best standard solution is the following: (1) Glow discharge electrode is made from aluminum plate with surface that is approx. parallel to surface to be cleaned. The opposite electrode surfase is shielded with stainess steel shield placed on the distance about 3 mm from electrode. In this case discharge will be concentrated on the surface to be cleaned. For chambers with rotating parts electrode usually has shape close to triangle with sharp angle directed to the rtotation axe. It can provide uniform cleaning. The distance between electrode and surface to be cleaned should be about 6 - 10 inches. Your goal is to concentrate discharge on a glass surfasce.(2) Usually -800 V - - 2000 V DC is OK. You really need DC voltage with negative potential on electrode! Your feedthrogh and intervacuum wiring must be carefully insulated, otherwise you will get disharge from feedthrough and wire. (3) Typical discharge current depends on pressure, electrode shape, voltage. Usually from 0.2 to 1 A. Cleaning time - 7 - 15 min depends on part dimensions, design and so on.(4) Discharge might be started at pressure about 0.2 torr (during roughing pumping) and is kept stable up to 0.01 torr. The best vacuum for cleaning 0.05 - 0.2 torr. You do not need to use any special gases. air is OK. (5) To get a good Al film you have to evaporate Al in the vacuum close to 0.00001 torr. So after cleaning you have to pump down your chamber to the high vacuum with high vacuum pump (diffusion, turbo or cryo). (6)The glow discharge may be used for vacuum measurement but better use standard gauges.
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