Ammonium Fluoride Crystals!!!

Mary Tang mtang at
Thu Feb 22 17:19:06 PST 2007

Everyone --

Warning:  THIS IS A RANT!!!  For two days running, there have been 
reports of ammonium fluoride crystals at the BOE tanks at wbdiff and 
wbnonmetal.  These crystals have appeared in large clumps, on top of the 
dump rinser, on the front of the bench and on the floor in front of 
wbdiff, around the tank and on TOP of the splash shield at wbnonmetal.  
This is an appalling example of bad acid handling.  This is dangerous, 
not only for the person doing this, but for unsuspecting people using 
the benches afterwards.

Now, for those of you who dared ask, "BOE" means "Buffered Oxide Etch", 
a premixed etchant which contains ammonium fluoride as the buffer to 
improve etch reliability and performance.  Now, BOE's contain a LOT of 
ammonium fluoride -- there is about as much fluorine content in a BOE 
etchant as there is in 49% concentrated liquid hydrofluoric acid.  And, 
it's just about as insidiously dangerous -- ammonium fluoride penetrates 
a little slower through your skin than HF, but the effect is much the 
same.  Basically, just a few crystals touching your skin here and there 
can result in a lot of pain....  probably many hours after exposure...

And for those of who feel that maybe a little pain is to be expected 
when pursuing the art of fine research, understand that these crystals 
are PARTICLES which can mess up your work.

Please, please, please, be conscientious about your handling of wafers 
and cassettes at these stations.  Please also be aware of what people 
are doing around you, especially if you are enabled on the system.  This 
is your lab too -- don't be afraid to talk to someone if you feel 
uncomfortable with their lab practices.  If you have any information, 
concerns, or complaints, contact your favorite staff member and we will 
follow up.


Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at

More information about the wbdiff mailing list