E-beam evaporation, Physical vapour deposition

[ak01]

TL;DR Summary

Focusing issue of electron beam

Hi all,
Hope we have some electron beam evaporation specialists in the house.
I'm working with an Telemark Electron Beam Source (Linear Multi-pocket and would like some help with the issues I am facing currently. I'm seeing blue light around both sides of the crucible when the e-beam is turned on. The electron beam is no longer focused, it is spread (in arc shape) in the direction perpendicular to the high voltage. I have tried adjusting the high voltage (in the range of 7 to 9kV) and changed the filament hoping it would help but it hasn't made any difference. How to fix this problem?
Thanks
AK

 

[Tom.G]

It's been a VERY long time since I've been near such a device, but the obvious thing to check first is the focus coil and its supply. If I recall correctly, for a fixed beam location, the focus coil source should be a steady DC.

You also mentioned that the beam is shaped as an arc. That sounds like the deflection coils are being fed AC, making it look like a focus problem. Put an oscilloscope on them to check.

Good Luck! and let us know what you find.
Tom

p.s. Telemark has their manuals on-line as PDF files. Download the one for your model and use your PDF reader to do searches, much easier, faster & more comprehensive then using the index in a printed manual.

 

[ak01]

Thanks Tom for the suggestion. I hope you are referring to electro-magnetic coil. I have the pdf file of the Telemark manual, but not much description is there related to the deflction coil or focusing of electron beam.

 

[Lord Jestocost]

Electron beam evaporation may lead to a significant charging of the whole crucible/evaporation material when there is no low impedance connection between the crucible and the common ground of the evaporation system, a disadvantage for the focusing of the electron beam.

 

[Tom.G]

On Friday, Oct. 13, the OP sent me a PM asking for confirmation of construction and Theory of Operation for the Telemark model 568 E-Beam Source.

Here is the response I sent him:

This should really be addressed in your main thread. You have my permission (and request) to copy this response (along with your request) to the public thread.

I can get to it probably around the middle of next week, the 17 or 18. I'm sort'a buried in several things right now.
I put a sticky note on the frame of my computer monitor to keep me reminded.

It makes sense that the default position (no sweep or deflection) and focus are done by the permanent magnets, cheaper and more reliable that way!

Meanwhile you can try investigating the following.
Since you describe the beam as being arc shaped, I can think of two possibilities for the symptoms:
1) The beam is grossly mis-centered and you are seeing only the edge of it.
2) The deflection circuits are involved in the problem, or more specifically, something common to both the X and Y deflection systems.

An even remoter possibility is that of another piece of nearby equipment that is generating a strong magnetic field.

I managed to find and download the manual. Beam quality problems are addressed on pages 26 and 27 of the manual.

How much of these instructions have you done and what were the results?

See especially page 27, "BEAM DOES NOT HAVE THE DESIRED SHAPE"

I agree that the manual is light on details, and not being at all familiar with the particular device, I do not believe I can be of much help, SORRY.

I recommend that if after following the instructions on pages 26, 27 you are no further ahead, that you either contact the manufacturer directly, or, as suggested on page 27, send the Emitter back to the factory for repair.

Cheers,
Tom

 

[ak01]

Hi Tom,
Many thanks for your all the efforts answering my questions. I really appreciate it.
All the suggested points were investigated and it was found that most of the beam was in the centre, but some part of the beam was hitting the edge of the crucible. In addition, a blue flourosence was observed. That flourosence was never obsered before when beam is centered.
Please see the picture of the beam herewith attached. The emitter is at the down-Left of the image. I have checked everything mentioned in troubleshoot section of the manual and found everything fine with the system.
Any additional comments/suggestions are welcome.
Cheers!
AK

 

[ak01]

Electron beam evaporation may lead to a significant charging of the whole crucible/evaporation material when there is no low impedance connection between the crucible and the common ground of the evaporation system, a disadvantage for the focusing of the electron beam.

Thanks for your suggestion. The grounding of the system was rechecked and found to be fine, so the existing issue is not related to that.
Cheers!
AK

 

[Tom.G]

I'm really reaching for the strange possibilities here.

Doesn't that Blue glow indicate that there is gas in the vacuum chamber?

But that does not explain why/how the beam got off target to the sides of the chamber.

A quick search lists Argon, Xenon and Mercury vapor as having a blue glow.

For instance, if Argon is used to purge the system and the vacuum system is not operating correctly, that could (partially) explain the Blue glow.

Try sending that photo to the manufacturer's support group and see what you get.

Cheers,
Tom