[labnetwork] Hazard due to x-ray production in e-beam evaporators?

[Price, Aimee]

Hi Aaron,
The State of Ohio has a schedule for testing/measuring/auditing all x-ray producing devices (dentistry x-rays, XRDs, electron microscopes, etc.).  The electron microscopes are a category in themselves and they eventually considered our ebeam evaporators in the same category (along with my 100kV electron beam lithography tool).  Even though they knew that the voltage on the evaporators was much lower than the SEMs/EBL, they maintained them in that category.

For many years our University EHS radiation safety officer would measure/audit these equipment yearly, the State every 3 years.  Never once were any of the measurements above background.  Eventually, they no longer required them to be measured/audited.  New instruments and any significant modifications to existing instruments, likely still require an initial measurement by our safety officer.  Typically, the instrument vendors require this as well as part of the tool qualification (although maybe not for ebeam evaporators).

We were required to train our users on the hazards of x-ray, the signs/symptoms of exposure, and give notice of which tools generate them.  I wrote a spec/document from which we trained and can share it with you off-line if you’d like.  It does have a lot of specifics to the State of Ohio, but it’ll give you an idea.  We required that users be “certified” in both the x-ray safety document as well as the specific tool before they could use any system that generated x-rays.  My feeling was that it is good for users to be aware of this for their education, even knowing that the risk was low.  Many of them will be tool owners themselves at some point and it is good to consider, the “you don’t know what you don’t know” mentality.

Long story short, if you have any questions your equipment vendor should have answers on this topic.  What shielding or safety measures, if any, they use and how they were determined would give most users a good understanding and comfort in their safety.

Best Regards,
Aimee Bross Price

Sr. Research Associate
The Ohio State University
Nanotech West Lab
Institute for Materials Research
1381 Kinnear Road
Suite 100
Columbus, OH 43212
614-292-2753



From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> On Behalf Of Aaron Hryciw
Sent: Friday, May 29, 2020 11:11 AM
To: Stephen Howe <info at fabsurplus.com>
Cc: labnetwork at mtl.mit.edu; Robert Vandusen <RobertVandusen at cunet.carleton.ca>
Subject: Re: [labnetwork] Hazard due to x-ray production in e-beam evaporators?

Dear colleagues,

Thank-you all for the excellent discussion and suggestions—this has been incredibly helpful.  Beyond allaying the fears of the user who raised the concern, going forward, we will be sure to incorporate an explanation of these considerations when training users on our evaporators.

Stay safe and healthy.

Cheers,

 – Aaron



Aaron Hryciw, PhD, PEng

Fabrication Group Manager

University of Alberta - nanoFAB

W1-060 ECERF Building

9107 - 116 Street

Edmonton, Alberta

Canada T6G 2V4 Ph: 780-940-7938
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On Fri, May 29, 2020 at 4:38 AM Stephen Howe <info at fabsurplus.com<mailto:info at fabsurplus.com>> wrote:
Dear Aaron,

I used to work on Mass Spectrometers for VG Analytical, which became part of Thermo Instruments eventually.
They had a low accelerating voltage of 8KV, but we had some tools with a FIB option installed (Fast Ion Bombardment), and that operated at up to 16 KV.
We had a viewport above the source area, so as to have a reality check on what was really going as one poked around inside the vacuum chamber. The viewport had leaded glass. This might be erring on the side of excessive caution, but such view port glasses are readily available for purchase in the market place, so that's what I'd suggest.



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On Thu, 2020-05-28 at 13:48 +0000, Robert Vandusen wrote:
Hi Aaron.
Back in 2015 we had similar concerns with our Balzers BA 510 thermal/ebeam evaporator.   We had reintroduced thermal capability to our system and had modified our internal SS shielding to allow us to have a direct line of sight to the thermal melt through a glass slide mounted on the shield and through one of the window viewports. Prior to this we only used ebeam evaporation and the shielding blocked the viewport.    As you have found, I was unable to find any literature on x-ray exposure concerns outside the chamber area.
I contacted our Health and Safety department who helped conduct x-ray testing during ebeam evaporations of a few different materials.   They found no measurable x-rays coming through the viewport or elsewhere on the chamber.  This satisfied our safety concerns.  However since the system was now identified as an potential x-ray producing source we had to get an Ontario ministry of labor x-ray permit and post it at the room doors and on the system.  It basically requires us to get a new assessment if we make any changes or modifications to the system that could result in increased exposure.
So we have piece of mind, but now a lot more questions when users see the x-ray signage.

Hope this helps.
Rob
   Robert Vandusen
   Microfabrication Cleanlab Facility Manager
   Electronics Department
   Carleton University
   room: 4184 Mackenzie Building
   613-520-2600 ext 5761
   Robert_vandusen at cunet.carleton.ca<mailto:Robert_vandusen at cunet.carleton.ca>



From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> <labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>> On Behalf Of Aaron Hryciw
Sent: May 27, 2020 11:21 PM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Hazard due to x-ray production in e-beam evaporators?

[External Email]
Dear colleagues,

One of the users in our open-access facility recently expressed concern about x-ray production in electron-beam evaporation systems.  Since the typical acceleration voltage in our e-beam systems is 7–10 kV, he was concerned that bremsstrahlung and characteristic x-rays would be generated during deposition, with a maximum energy of 7–10 keV (soft to hard x-rays), and that these x-rays would pose a health and safety hazard to an operator standing next to the viewport for ~30 minutes.

A literature search yielded a few reports describing radiation damage to sensitive devices from x-rays produced during an e-beam metallization step, but I did not find any mention of related health and safety considerations.  While some x-rays are undoubtedly produced, presumably there are reasons why they are not hazardous to an operator (e.g., perhaps total x-ray output is very small, majority of x-ray spectrum is low energy, x-rays do not penetrate stainless steel chamber walls or viewport windows, etc.).  I would like to answer this user with specific physical arguments as to why the hazard is insignificant, however, so any advice you could offer to this end would be greatly appreciated.  Many thanks.

Cheers,

 – Aaron



Aaron Hryciw, PhD, PEng

Fabrication Group Manager

University of Alberta - nanoFAB

W1-060 ECERF Building

9107 - 116 Street

Edmonton, Alberta

Canada T6G 2V4 Ph: 780-940-7938
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