Why vinyl gloves are bad for your wafers

Eric Perozziello eap at gloworm.Stanford.EDU
Sat Oct 3 19:54:40 PDT 2009


These wands didn't used to have anything other than a metal tube
pressed into the quartz tip.   They used to rotate around (annoyingly)
when they would get loose.  I only noticed the "glue" when this
rainbow wafer showed up late last year.  It was only noticable because
the oxide grown was <300A, and thus, the thin film of silicones or
whatever produced the rainbow.  You couldn't see it on thicker oxides.

There should be some coral documentation on this.
It was initially reported as an "oxide uniformity problem"
as I recall.   (I think it might be 11/19/2008 on tylan2, which
fits the description perfectly: rainbow on left side of wafer, flat up).
This message's "clear" indicates that it was a recurring issue.

The "glue" is still on all of the wands (tylan1/2, tylan3, and thermco1/2)
as of last night.  The application looks as though it's done by hand, not
by machine.

This was observed on wafers coming out of the furnace, before being
picked up "hot".  Something transferred to the wafer cold, and then
redistributed during the process, from the wand contact point.


On Sat, 3 Oct 2009, maurice wrote:

> The "sealant" may have been the glue used by the manufacturer to hold
> the wand tip to the metal shaft.  If wafers are unloaded from the hot
> furnaces without letting them cool it melts the glue and can get on the
> tip.  I have not seen it on the tip but I have seen it the shaft.
>
> You probably have seen wands that spin on the metal shaft at the oxide
> furnaces.  If you look close you will see the glue is on the shaft.  The
> LPCVDs  open at a lower temperature so we don't see it as often there.
>
> We replace the wands as soon as it is reported and we stressed the
> importance of letting wafers cool during our trainings.  But I would
> guess we change 3 wands a week (some of that is from wands breaking or
> getting dropped).
>
> On the photo you attached, is that the front side or the back side of
> the wafer?
>
> I can't imagine any of our staff trying to fix a vacuum wand.  It is
> easier to get one from the stockroom than putting silicone in that
> little hole in the wand.
>
> I would expect that if anyone spots a damaged or questionable wand, they
> would report it on coral and if needed, use clean tweezers to
> load/unload their wafers.
>
> -maurice (and Alexander)
>
>
>
>
> Eric Perozziello wrote:
> > The same thing should go for use of silicones on "clean" vacuum wands.
> >
> > The attached photo shows a user's wafer that came out of a furnace that
> > was loaded with a "clean" vacuum wand.  When the user complained,
> > the staff response was "Try cleaning your wafers better".  But on further
> > testing and investigation, it was from sealant (silicone ?) applied to
> > the "clean" vacuum wand, presumably to "fix" it instead of replacing it!
> >
> >
> > On Fri, 2 Oct 2009, Mary Tang wrote:
> >
> >
> >> Dear labmembers:
> >>
> >>
> >>
> >>
> >>
> >> It has come to our attention that some labmembers are touching wafers with gloved hands
> >> instead of using tweezers or vacuum wands at "clean" stations, such as furnaces and wet
> >> benches.  Although there may be special circumstances where manual handling is warranted,
> >> this violates all known standards of good clean room practices.  This is no-gloves-on-wafers
> >> policy as was stated firmly in this labmembers' note from 2001:
> >>
> >> http://snf.stanford.edu/cgi-bin/ezmlm-cgi?mss:147:ebffjnejjanhflmfgmjp
> >>
> >>
> >>
> >>
> >>
> >> In this lab, vinyl gloves from the bag are "clean" for using wafer handling tools.  The gloves
> >> we use are certified Class 1 so don't shed particles and are metal ion-free.  So, these are good
> >> for handling cassettes, handles, wands, tweezers and other wafer handling tools for which
> >> we want to avoid cross-contact with other surfaces. Certainly, as anyone can see from the
> >> acid-etched buttons at any wet station, we are not as diligent as we should be with our glove
> >>  hygiene.  So, we encourage frequent glove changes in order to ensure that contaminants
> >> don't travel from one surface to another.
> >>
> >>
> >>
> >>
> >>
> >> However, vinyl is polyvinyl chloride, or PVC, which is a hard, brittle material.  To make it
> >> flexible, plasticizers are added -- up to 35-45% by weight in gloves.  Plasticizers are low molecular
> >> weight (<400), oily materials.  DEHP or DOP is the most common in cleanroom vinyl gloves.
> >> It is widely recognized in the cleanroom industry that vinyl gloves will leave a trace plasticizer
> >> residue on contact with surfaces (see page 270 of  Cleanroom Technology: Fundamentals of
> >> Design, Testing, and Operation, available on Google books at
> >> http://books.google.com/books?id=-ufEtmr1sBgC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=&f=false <http://books.google.com/books?id=-ufEtmr1sBgC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=&f=false>)
> >>
> >>
> >>
> >>
> >>
> >> Here is a simple demonstration.  A vinyl glove was pressed firmly down on 1/2 of a clean
> >> silicon wafer and then removed.  Then, contact angle measurements were made.  On the
> >> bare silicon half, contact angles were too low to measure (<5 degrees), indicating very
> >> good wetting with the native surface oxide.  On the other half, the average contact angle
> >> was 19 degrees (stdev=2 degrees), indicating a significant change in the surface energy.
> >> The wafer was then run three times through lampoly, using recipe #1 (60" main etch, silicon
> >> to resist selectivity ~ 3.6.) As can be seen in this photo, glove residue masks the etch.
> >> (The small, aligned dots show where the contact angle was measured.)
> >>
> >>
> >>
> >>
> >>
> >> Granted, this was a simple and crude demonstration. For a more rigorous approach, see
> >> the attached paper describing effects of DOP plasticizer on electronic device performance.
> >>
> >>
> >>
> >>
> >>
> >> Please understand that there is generally a good technical rationale behind our lab policies
> >> -- similar no-gloves-touching-wafers policies for CMOS-clean stations exist at the Berkeley,
> >> MIT, and Cornell cleanrooms.  We trust that these should be convincing reasons as to
> >> why we should not use gloved hands to touch wafers.
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> Your SNF staff
> >>
> >>
> > >
>
>




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