I would like to use silicone rubber in the lab

Yves Acremann acremann at slac.stanford.edu
Mon Jan 31 14:38:47 PST 2005

One of the tricky processing steps is KOH backside etching of wafers 
with metal structures on the frontside. The main problem is
the protection of the front side during the etch process. We currently 
use black wax for that purpose. We had some problems with
this in the past where the black wax layer failed during very long 
etches (up to 40 hours for 1.2mm thick Si wafers).

We would like to try to put two wafers front to front and use silicone 
rubber to seal the edge. In addition, we plan to have black wax on the
front side.
We did some tests with silicone rubber and its ability to withstand KOH 
in our lab at SLAC and this method looks promising.
We used the following product for our tests (copied from the home depot 
catalog :-)) ):

"GE 2.8 oz. Clear Silicone Household Glue
Model GE280 3TG

100% silicone. Permanently flexible. Adheres to tile, porcelain, glass, 
fiberglass, marble, wood, steel, aluminum, brick, mortar, concrete, and 
most plastics. Lifetime satisfaction guarantee. Won't dry out, crack, 
chip or peel. Easy to use squeeze tube. Can be used as glue, sealant, 
caulk or gasketing, and for many patch and repair applications around 
the house and shop."

For our real wafers, we would like to test this method in the cleanroom. 
As similar materials are likely used during construction of the wet 
benches, I hope it will be possible to get approval for
this material. Of corse we only deal with gold contaminated wafers and 
this is our last processing step (followed by solvent cleaning and 
sawing the wafer). We also will NOT heat the
wafer to a temperature higher than 75C (in KOH) and if necessary, we can 
do the KOH etch in our lab at SLAC.

I did not find the MSDS that corresponds directly to this product, but 
there is a link containing more information about it:

Yves Acremann

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