nitrogen vaporizer upgrade

Paul Rissman rissman at stanford.edu
Mon Nov 26 11:01:31 PST 2007


Dear Labmembers and CIS Lab Occupants:

For the past few years, we have been working with Air Products on an 
upgrade of our nitrogen vaporizer system.  As you may be aware, Air 
Products supplies our bulk liquid gases and, to some extent, the 
facilities for vaporizing them to gas form so that they can be used 
as process gases in our labs in SNF and CISX.

Collectively, we are now extracting anywhere between 3-4X the amount 
of gaseous nitrogen that our vaporizers are rated for.  Needless to 
say, this is not the best way to run.  Through a series of 
negotiations, Air Products has generously agreed to donate equipment 
and services to upgrade our vaporizers. In the current plan, Air 
Products will use a tanker truck to provide a temporary N2 in order 
to ensure continuous supply to the CIS and CISX buildings during this 
transition.  The temporary supply will be hooked up on Tuesday, 
December 18 and there should be no noticeable change in 
services.  From Wednesday, December 19 through Friday, December 21, 
the larger vaporizer and new N2 purifiers will be installed.  Once 
the new system is leak-checked and certified, it will go on-line and 
the temporary N2 supply will be removed.  During this time, metering 
systems will also be installed in order to allow us to get a handle 
on nitrogen usage.  As you may be aware, liquid nitrogen is the 
largest single expense in this building.  We have been looking 
forward for a long time for this upgrade; this should facilitate a 
more reliable and cleaner supply of N2 for the building.

However, one aspect of this installation has the potential to affect 
quality of gas delivered.  For staging the installation, the gas 
purifiers for bulk O2 and ultra-high purity N2 will need to be 
bypassed.  This is tentatively planned for Monday, December 10, 
although we need to confirm this date.  Air Products' testing 
indicates that the current N2 purifier system does not significantly 
improve the quality of the delivered gas so bypassing this should not 
have a noticeable effect.  However, the O2 purifier seems to be 
somewhat effective at filtering particles (1357 particles >0.1 um at 
the inlet versus undetectable amounts at the outlet.)  So, please be 
aware that between December 10, when the O2 purifier is taken 
off-line and December 21, when the new O2 filter is installed, that 
the quality of the O2 may be somewhat compromised.  This is not 
anticipated to affect most operations in SNF (namely, etches and 
depositions) but critical operations, such as very thin gate oxides, 
may be vulnerable.  Please be aware of this when planning your experiments.

We apologize for the inconvenience these changes may cause.  But 
please understand that these changes are necessary to ensure reliable 
and continuous bulk gas supplies.  If you have any further questions 
or concerns about this upgrade, please contact Ted Berg.

Paul Rissman




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