[labnetwork] Sulfur Smell from ICP F Wafers

[Emma Anquillare]

Dear wise and wonderful labnetwork,

I have noticed that we often get a fairly pungent sulfur odor when opening the load lock of our ICP-F etch chamber. I tried adding an extra purge cycle to the vent process, but it seems this smell is coming from the wafer itself in some kind of degas process, usually following etch recipes or cleans with Sulfur hexafluoride.

At first I thought it might just be remnant SF6 gas (which is non-toxic) but apparently SF6 is odorless, so a new sulfur compound may be forming. Today I also noticed that after putting in a brand-shiny-new Silicon cleaning wafer and running only a chamber clean (10 sccm SF6, 50 sccm O2) for 20 minutes, the wafer already had a smudge on it (see photo) and a clamp ring around the edge which usually forms after a much longer period of use.

I also noticed that a more heavily used, unmasked Si wafer that I had been using to sample the functioning of different recipes in the tool was covered in deposited swirly blotches by the end of the afternoon. (sorry for the lack of photo and better description)

Has anyone else ever experienced an unusual sulfur-like smell from an etch load lock or potential deposits on the wafer from inside the tool? Is it safe and normal to smell things or not so much?  I'm guessing a wet clean may be in order or polymer formation may be the culprit?

 The gasses we have in the tool are: He, N2, Ar, CF4, CHF3, O2, SF6, C4F8

The only materials we allow in this tool (if users are good) are: Silicon, SiO2, Aluminum Oxide/ Sapphire, Si3N4, fused silica, Polymer photoresists (eg- 950 PMMA A4 PR, PMMA 495 A4, MaN2403, ZEP, MMA), Quartz, Germanium, and SiGe. There were instances of ZeSe or Gold but they were very heavily buried and would not have been exposed. Also the plain silicon training wafer I use for demos is shared with the ICP-Cl, which sees many more materials in the chamber including lithium niobate.

Any help is greatly appreciated,
Thanks!
Emma


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

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