[labnetwork] Material Limitations in Non-Load-Locked Etcher?

[Emma Anquillare]

Dear Wise and Wonderful LabNetwork,

I am curious to know what your lab's protocols are for limiting materials (with respect to safety) that can go into non-loadlocked RIE plasma etchers without scrubbed exhaust. I have heard a wide variety of ways to approach this and I am trying to find some consistency.

For example, at one institution the non-loadlocked RIE tools are only used for standard dielectrics and polymers, with no toxic materials allowed. At another, the open-load RIE is the most flexible tool that takes all types of 2D materials, polymers, and metals. Here, our RIE (lacking a coil) is also supposed to be the most-flexible etch tool we have.

I was advised to approach this problem by looking at the MSDS sheets for the materials being etched, and then do a worst-case-scenario safety assessment (eg- calculate an estimated amount of material released in a typical etch based on density and volume, and ensure even that will not exceed the exposure limit if it somehow all left the chamber.) This made a lot of sense with respect to 2D materials, which often have toxic MSDS material profiles but are actually only present at such a thin level that it would be impossible to exceed any risk levels. This also makes sense with respect to a blanket ban on As-based materials (commonly restricted) as the exposure limit for these can be multiple orders of magnitude smaller than typical other limits.

With other materials however, it gets more complicated. For example, BK7 glass would (I imagine) be considered a “standard” non-toxic material with no special hazard profile, but looking at the MSDS sheet (linked below), accidentally etching just a few hundred nm into a cm-scale chip substrate would easily exceed the 0.3mg/m3 limit in the chamber. Of course, this is all happening in an enclosed chamber under constant vacuum suction, then followed by a purge before venting, so it still seems very unlikely (almost absurd) that a user would be exposed. (There is also the question of noble gas milling vs a chemical plasma process that would change the compound all together, which opens up an entire other can of worms, and makes this almost an impossible question to evaluate).  But knowing such material-safety based restrictions do exist in other institutions with non-load-locked etchers- I am curious- where do we usually draw the line?

In the meantime, I have been adding a lengthy purge at the end of each recipe in addition to the standard tool purge to further reduce risk.

Any relevant wisdom is appreciated!
Best,
Emma

Link to BK7 MSDS: https://media.schott.com/api/public/content/9cc5c29497054e5ebf31228dfa311220?v=09c01a38




_____________________________________________
Emma Anquillare, PhD
Research Scientist
ASRC Nanofabrication Facility
City University of New York

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