Why vinyl gloves are bad for your wafers

John Shott shott at stanford.edu
Sun Oct 4 09:27:34 PDT 2009


Eric:

Yesterday afternoon I also looked at all of the wands and am aware of 
the white adhesive.  I have also, however, opened a brand new tip ... I 
had to cut a seal on the plastic box to open it ... and can confirm that 
this is the way that the vacuum wands are coming from H-Square.  This is 
definitely not a "home improvement" on our part.  I have also already 
asked Mary to contact H-Square to find out what that stuff is.  My 
guess, however, is that it is a high-temperature ceramic adhesive that 
is similar to the stuff shown here:

> http://www.cotronics.com/vo/cotr/ca_fastset.htm
Certainly this stuff looks a lot like the off-white stuff that H-Square 
is using and it is expressly advertised as being good for sealing metals 
to glass and capable of withstanding very high temperatures.  My guess 
is that it IS a hand-operation used to assemble these things at H-Square 
.... someone probably paints a ring of this stuff near the end of the 
steel tube (so they don't plug the vacuum) and then stuffs the tube into 
the end effector.  It also appears as if at some point they somehow 
shape any of the adhesive that has squished out so that it does not 
protrude beyond the broad, flat surfaces of the end effector.

We will investigate this stuff further to be able to more definitively 
say what it is ... but I'm guessing that it is not the problem.

> Something transferred to the wafer cold, and then
> redistributed during the process, from the wand contact point.

Of course, even if this adhesive gets a clean bill of health, there is 
nothing that would prevent other sources of contamination from getting 
on the tips.  Heck, I suppose that grabbing the tip of a vacuum wand 
with a "clean" vinyl glove could even transfer some plasticiser to a 
wafer that would likely result in non-uniformity .... or certainly there 
could be other ways of transferring contaminant to the end effector of 
the wand and then onto the wafers.

In any event, we'll try to learn more about the details of the off-white 
adhesive that H-Square is using and report back.

Thanks,

John







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