Why vinyl gloves are bad for your wafers

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)

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