Serious Contamination in the Clean-room!

Jia Feng fengj at
Thu Feb 15 18:36:39 PST 2007

Dear lab members:

I found a long piece of hair inside one of the teflon boxes of wbmetal just
now. This is a very serious contamination. There are oil, Na, K, and many
other contaminations you can imagine from such a piece of hair. This is NOT
a biology lab!

Let's do a simple math. If you have a 40-nm gate oxide (as used in EE 410),
you need only an ion density of 5.5E11 /cm^2 to change the threshold
voltage by 1 volt if the ions sit on the Si/SiO2 interface. For a 4-inch
wafer, this density means only 4E13 ions across the entire wafer. How heavy
are those ions if they are sodium? You only need about 1.5E-9 gram of sodium
to change the threshold voltage of all the devices on one 4-inch wafer by 1

It seems that more and more people do not make electronic devices any more.
But the particles from the hair can still destroy the mirrors, lenses, and
cantilevers. I have seen people unhappy with the paricles in nitride which
harm their optics on silicon. Then how about the particles from the hair or

Please keep our clean room really clean. What you can simply do is to change
gloves before you touch the teflon cassette, put the teflon cassette on the
inner side of the cover rather than on anything else, handle the wafers by
tweezers rather than by hand, and clean your wafers if you want to put them
into any chambers or furnaces. If you are unclear about something, ask. If
you see sources of contamination, let the staff members know. If you happen
to contaminate something, let the staff members know and they will not
punish you.


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