Dear Amirhossein,

it looks like an electrical crosstalk issue.

Providing your power cables with electric filters (e.g. ferrites) could help you. In addition please try to separate the powering of your gun and that of your pump from a common power line. Use different phases for them or even potential free power sources; at least for the pump.

An additional capacitor paralled to the gun's power switch also could help. Please ask the electronic stuff of your institution.

Good luck.

Thank you for your answer. So, in your opinion this shut down does not depend on the type of the material being deposited?

Also, I heard from a colleague of mine that she has had the similar experience with another ebeam evaporator, in which they found a short between voltage and current of the gun.

Yes, you are right.

To my opinion the shut down has nothing to do with neither the material to be deposited nor the change of the crucible itself (as far as during crucible change no short cut has been accidently established to the electron gun in any way).

So please check the gun (at least by visual inspection from inside the vacuum system).

Another idea: there may be an accidentally bump on the electron gun occurred during crucible change which may have damaged the interior of the gun (internal shortcut by any conducting flake/dust particle/impurity etc.?). You should replace the gun if you have got a spare one. At least you should clean the interior of the gun by a blow of dry air or something similar.

Good luck.

Thanks again for your answer. Can you please elaborate more on "during crucible change no short cut has been accidentally established to the electron gun in any way"?

I do not know your set-up.

But I can imagine that during crucible change the operator may have accidently 'touched' the gun more or less gently. If in such a case an external (or internal) shortcut can be established, I do not know; it's speculation. We are here in the phase of brain-storming for solving your inquiry.

However, your gun seems to be the cause of troubles since the crucible has been changed.

So checking the gun is inevitable; although I must admit that breaking the vacuum is always a nasty task.

Another idea; your wrote: ' I changed the crucible to tungsten and put new Ni pieces in it, but the problem happened again after a while'.

Does the geometry of the tungsten crucible has got a geometry different from the previous (graphite) one? If so, it could be that for the case of the tungsten crucible Ni particles (Ni+) may contaminate the gun, especially it's interior, leading to a temporary shortcut/arcing and thus triggering shut down of your pump....

or (during crucible change) omitting any shielding means/diaphragms for preventing gun contamination .... only speculations, I know.

What is about grounding the tungsten crucible...; really same potential as in case of the graphite one? Floating potential of crucible is not that option.

Any oxide layer of the tungsten crucible may prevent grounding...

So please check the electrical contact of your tungsten crucible with respect to ground potential.

You see, there are a lot of options.

Hi again,

I am having two questions regarding the cryopump shut down:

1- Does the chamber temperature have any effect in shutting down of the cryopump? Usually the chamber is at 66-70 F at the time of deposition. I heard from a friend of mine that baking chamber up to 80-85 F could contribute in solving the problem. Does this statement make any sense?

2- So far, I have been having cryopump shut down mostly for materials that evaporate with a very little ebeam power. For example, for Au, Al, and AuGe, I do not observe this shut down. However, for Ni and Ag (which apparently evaporate at very low power) I have been having issues. What are your thoughts?

Thanks!

Dear Amirhossein,

sorry for the late answer.

Point 1:

The temperature ranges 66-70F and 80-85F are not really different when baking is considered. Baking is done at very much higher temperatures.

Baking at 80-85F makes no sense.

Point 2: low e-beam power should not induce pump shut down.

You pointed out that for Ni and Ag the shut down occurs.

So the kind of material could be responsible for that, even in the case of low e-beam power.

My thought is that for example the Ni and Ag sample you take contain some kind of porous material with gas/air inclusions. So when melting/evaporation the material the gas/air suddenly goes off and increases (burst like) the pressure in your chamber and arcing will take place (leading to pump shut down).

What does your pressure readings say when switching on the e-gun in comparison to the other samples?

Thank you Gerhard for explaining your thoughts on this matter. After lots of thoughts!, I came to this conclusion that the issue with the cryopump shut down is probably somehow related to the grounding of the crucible (probably there are some interlock which connects grounding to cryo shutdown).

In the case of Ni, since it melts uniformly in the crucible, the beam should have large sweeps to cover all of the crucible area rather than hitting one spot. However, the opposite is recommended for Au. When Au melts and cools down, it usually balls up to a center spot. Therefore, the ebeam should only hit that spot, nowhere else (otherwise, cryo shutdown kicks in!).

As of now, I do not know whether this issue is common for all ebeam evaporators, or since our equipment is relatively aged, we encounter such issues.

Cheers,

Amir

Thanks for feedback and good luck.

Hello,

I am coming back with a new question! The concept of outgassing in the ebeam evaporation technique.

I know that outgassing means release of gaseous particles "during" deposition, mainly from the target material in the crucible or particles that were previously stuck to the electron gun. However, my issue related to getting to a steady and high vacuum "before" starting the deposition. There are no samples or any special target material inside the chamber. However, the vacuum does not reach the usual value and therefore I cant start the deposition. What can be the possible reason for not achieving the desired vacuum level in your opinion?

Can it be related to the sidewalls of the chamber? Can a clean & dry surface of metallic sidewall outgass?

Thanks,

Amir

Every wall of your vacuum system has adsorbed a lot of gas molecules, even when they are nominal 'clean' and dry. The outgasing of these surfaces takes a very long time at room temperature. Thus for getting the desired vacuum levels in UHV systems in a reasonable time it is advised to heat up the complete system (but except the parts that cannot withstand high temperatures).

Heating is done with special equipment (e.g. heating bands); in addition the whole system is covered with Alu-foil in order to 'keep' the heat.

You will see; when heating up the system (or even parts of it) the pressure will dramatically increase.

If heating does not help then you most propably have got a leak.