[labnetwork] Bosch etch foreline and pump powder residue question...

[John Shott]

Ian:

While you will likely get more thorough responses from others on this 
matter, let me share some or our experiences in this area.  In 
particular, these tools generate a lot of polymer.  The same chemistry 
that you are relying on generating the polymer on your wafers during 
half of the switched etch/deposition process is also going to produce a 
low-grade polymer everywhere else.  Much of the polymer that you find in 
the foreline tends to be rather gummy and difficult to remove ... at 
least that is our experience.  Many (but not all) machines have heated 
turbo pumps and I believe that had been found to be pretty effective in 
terms of minimizing polymer build up in one of your most expensive 
components on these tools.  One of our machines has a water cooled trap 
between the heated turbo and the remainder of the foreline ... but, to 
be honest, that trap has not proven to be particularly effective in our 
case.

Because the forelines tend to get pretty well coated with a sticky, 
gummy polymer, we have found them to be pretty difficult to clean.  One 
"trick" that seems to work pretty well in the case of the forelines is 
to very carefully pour some liquid nitrogen down the foreline which will 
freeze it and cause it to fall off in chunks.  This, of course, has to 
be done VERY carefully due to the hazards of working with liquid 
nitrogen including worrying about "burns" due to the extreme cold and 
asphyxiation due to displacement of oxygen in the air.  One thing that 
we haven't tried, but may be easier than dealing with liquid nitrogen is 
to see whether packing a length of foreline in dry ice may have the same 
effect ... dry ice has it's own problems because of it's very low 
temperature and sublimation of something that can displace oxygen, but 
it is probably easier to handle than liquid nitrogen.

While the polymer itself isn't wildly toxic or flammable in the way that 
some of your pumps and forelines on other deposition tools are (things 
that pump silane and DCS, for example) we treat all forelines very 
carefully and, in particular, for anything that is the least bit 
"powdery or dusty" make sure that we have adequate protection to avoid 
inhaling or ingesting anything coming from these pump lines.

Finally, depending on the distance your foreline pump lives from the 
main tool, you may need to consider upsizing the diameter of your 
foreline a bit to help offset the constriction that will take place as 
your get polymer build up between periodic cleaning.

Good luck,

John


On 11/4/2013 3:36 PM, Ian Harvey wrote:
> Dear Labnetwork colleagues,
>
> We are installing a used STS DRIE tool acquired from the used tool 
> market and used for Bosch-Si etch.
>
> We are unsettled by the large amount of white powder collected in the 
> foreline and inside the large turbopump.  The turbo is becoming 
> unbalanced as flakes come off, and we are getting ready to trade in 
> the large maglev pump for a refurb, and clean the forelines.
>
> Does anyone have experience with what the powder is (F-C-S-O / EDS 
> analysis attached), its risks, and how to safely manage it during pump 
> removal, packing and declaration for shipping?
>
> Thanks!
>
> Ian
>
> ********************************************
> Ian R. Harvey, Ph.D.
> Associate Director, Utah Nanofab
> &
> Micron Microscopy Core
> 2511 SMBB (USTAR)
> University of Utah
>
> 801/585-6162 (voicemail)
> 801/581-5676 (lab main number)
> www.nanofab.utah.edu <http://www.nanofab.utah.edu>

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