[labnetwork] Silane and Dichlorosilane Line Evacuation

[Hathaway, Malcolm R]

Hi Bruce,

Similar to what Rick at Draper described, here at Harvard CNS we do not pump down lines to tools between uses (even over Christmas Break).  We use double-wall ("coax") piping, and the pressure between the walls is monitored by the TGMS.  Any fault condition (coax fail, gas sense events, etc) will cause all toxics and flammables to shut off at the cabinet and at any associated VMBs (valve manifold boxes).  (VMBs are like little "sub-cabinets", housing what are essentially distribution manifolds in the gas line between cylinder cabinet and tool).

If you have a shared use facility where users have little or no access to gas piping and other infrastructure, this works pretty well.  In an individual professor's lab, where "borrowing" of live hardware can occur (!), different arrangements might be in order.

Regarding DCS, we have gotten around the condensation issue by using "sub-atmospheric" supply pressure, i.e. the special regulator we have on DCS and BCl3 allows delivery pressure of only a few hundred torr, so the pressure is never high enough in the lines to allow condensation, even at room temp.  Saves lots of trouble with heater tape and worries about cold spots...


Mac

Mac Hathaway
Senior Process and Systems Engineer
Harvard Center for Nanoscale Systems
11 Oxford St.
Cambridge, MA  02138
617-495-9012


On 2/14/2019 8:48 PM, Paul Spizzirri wrote:
Hi Guys

We also use these gases here in Australia too and use the xmas shutdown period to completely pump them out and perform a leak decay test for integrity reporting - otherwise they are left live throughout the year.  Same configuration as mentioned above with DC, restricted flow control, gas montoring and DC monitoring etc to life safety systems with central shutdown. Note that the pump down for DCS is tricky as you are likely to get liquid condensing in the lines - depending on how long they are, you could be pumping for days to get them cleared.

Cheers

Paul

On Fri, 15 Feb 2019 at 12:43, Bill Kiether <wjkiethe at ncsu.edu<mailto:wjkiethe at ncsu.edu>> wrote:
We do not evacuate between uses, but do evacuate if the lab or system is going to be down (and tagged out)  for an extended time (months).

For example, we were shutting a lab for 6 months for construction reasons, all of the toxic and flammables were evacuated and backfilled with UHP nitrogen ( or Argon).  The backfilling is important as you don't want to leave silane lines at vacuum.  Also, once in grad school, we did the same thing for a tool on which the only user was studying for 2 months for his prelims. That process saved lives as a new post doc decided to "borrow" a quarter turn valve off of the system without discussing it.

Bill Kiether



On Thu, Feb 14, 2019 at 7:47 AM Bruce Tolleson <betemc at rit.edu<mailto:betemc at rit.edu>> wrote:
Dear users of Silane and Dichlorosilane,
When your systems that use silane and dichlorosilane are not in use do you evacuate the lines going to the tool? We are looking for the best practices for gas line safety in a student environment microelectronic clean room.
The gas lines are wall mount or overhead coaxial stainless steel all welded lines with excess flow sensors.
What are you doing with you silane and dichlorosilane lines?
Thank you,

Bruce E. Tolleson
Rochester Institute of Technology
82  Lomb Memorial Drive, Bldg 17-2627
Rochester, NY 14623-5604
(585) 478-3836
[http://www.rit.edu/~962www/logos/tiger_walking_rit_color.jpg]

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--
Dr Paul Spizzirri
Operations and EHS Manager

Melbourne Centre for Nanofabrication
151 Wellington Road
Clayton VIC Australia 3168.

Australian National Fabrication Facility (Victorian Node)


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