[labnetwork] burn box location

[John Shott]

Iulian:

Let me get the ball rolling on this topic.  We do have a multi-tool 
abatement for some of our LPCVD tubes in the chase area.  While it is 
not a gas-fired unit, we have had both an electrically heated 
CDI/Delatech unit in that location as well as a PureAire unit.  Our 
H2-fueled Guardian GS-4 units that deal with epi reactors have been in 
the sub-fab, not because of great concerns about particles, but because 
that's where the pumps for the tool was.

Note: as a disclaimer, while our clean room is rated at and performs at 
Class 100 conditions, I don't lose much sleep worrying about that and am 
a big believer in the "self cleaning" nature of clean rooms: a bit of 
time and a lot of air changes per hour resolves a number of issues.

That said, yes, cleaning the scrubber/burn box, and piping leading to it 
and from it can be a bit messy ... as is changing pump oil and any 
number of other things that happen in clean rooms and service chases.  
Moreover, pulling tubes and/or cantilevers for cleaning and/or 
replacement, that will likely happen in a critical area of your clean 
room, can be a rather disruptive, particle-generating process as well.  
Of course, the same can be said for maintenance and/or cleaning of may 
processes that deposit films.

My first concern is safety: some of the parts that you are hoping to 
clean can contain unreacted silane, DCS, hydrogen, and other nasties.  
While it is more likely to happen with "back end" parts from a 
hydrogen-fueled process like epitaxy, some of these post-pump parts are 
known to burst into flame when you take them apart.  If that happens, 
you've got a more serious particle problem ... not to mention the 
challenge of dealing with a flaming chunk of tubing. So, I believe in 
wearing proper PPE and doing everything possible to cap sections as 
quickly as possible to get them out of the area for most of the actual 
cleaning.  In fact, because of incorporation of pump oil and other 
things, the deposits in the tubing leading to the burn box and even 
beyond it seem to stick reasonably well to the walls if you are careful 
not to do too much beating on them.  I've always been surprised that the 
deposits aren't more light and flaky.

In short, I think that if you are prepared with appropriate numbers and 
sizes of KF flanges and other needed blank-off ports, you can quickly 
take apart a system and end up with a collection of capped segments 
without having caused great harm to your clean room or service chase.  
Then, you can take those to an area where they can be fully cleaned 
without any compromise to your clean room or service chases.

I expect that the good folks from Critical Systems will weigh in on this 
issue and I look forward to their comments and to those of some of our 
other colleagues, but my experience as an end user of various exhaust 
treatment systems is that they have to be handled carefully and that you 
need to anticipate potential problems, but I don't consider particle 
generation in the chase area as a make or break situation.

Good luck,

John

On 9/29/2014 2:32 PM, Iulian Codreanu wrote:
> Dear Colleagues,
>
> I am looking at the possibility of using a burn box (using natural gas 
> for fuel) to abate the exhaust from some CVD tools.  I would have to 
> locate it in the chase area.  It appears that a burn box is not that 
> clean; I can imagine "soot" spreading throughout the cleanroom during 
> maintenance.  Does anyone have burn boxes in the chase area?  How do 
> you keep the soot contained?
>
> Thank you very much.
>
> Iulian
>