Re: coating thickness error tolerance
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Aurigema, Andrew N. (KSC-ESC-620)[QinetiQ North America - ESC]
Pics of ¡°baby George¡± are in the photos section under ¡°Drew in sunny Florida¡±. ? The door to my chamber swings sideways on a hinge.? I put my mirrors on the door.? The flow of metal gas in my chamber is horizontal ( towards the door ) as opposed to hanging a mirror on ceiling and flowing the metal gas vertically ( upward ).? I do not rotate my mirror.? I have 9 emitter stations in a circle with a center unit.? They are stationary.? Rotation of mirrors is a tricky way of getting an even coating.? If you only have one source, then you have rotationally induced overlap of some kind. ?That overlap may become a problem if the deposition rate is high.? ?In my system, I have 9 sources that each overlap the others to some degree.? The edges of the overlap are very much blended so I don¡¯t see a lot of coating variation.? ?? ?
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From: VacuumX@... [mailto:VacuumX@...] On Behalf Of deepak
Sent: Thursday, April 14, 2011 4:13 AM
To: VacuumX@...
Subject: [VacuumX] Re: coating thickness error tolerance? ? Thanks Vladimir, Andrew and Guy for making the technicalities clear and giving relevant usage data.
Andrew, the term "sideways flow stationary emitter array" seems contradictory to me, do you have a photograph?
Guy, Your calculations seem correct to me. One typing error in the third sentence, 0.044cm^3 should have been 0.44cc as mentioned later.
Your setup made me think, if emitter is placed at the Radius of curvature of the mirror it will coat the mirror uniformly. Just as illumination from a bulb brought close to a flat wall falls off by 1/r^2 law from the closest point on the wall, the thickness of coating will fall of at the edge.
I calculated:
If ROC of 20cm dia mirror being coated is 200 cm(F/5),
Thickness of film at center proportional to (1/50^2)
Edge of mirror raised by 0.25cm with respect to centre.
Edge should have been raised by 1.0 cm for ROC of 50cm
Difference of 0.75 cm is the distance Al atoms travel farther to reach the mirror.
So thickness at edge proportional to (1/50.75^2)
So the edge will be 2.925% thinner than the center if emitter is at a distance of 50cm instead of 200 cm. No great error.
Thanks and with regards
Deepak
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