Before PDMS casting on a mould made out of patterned SU-8 on silicon wafer, I
always silanise the (silicon) mould to make it easier to remove the PDMS after
baking. During silanisation, the surface OH that could bond to my PDMS, react
with the silanisation agent and become inert. For this, only a vacuum dessicator
is needed. A silanising agent with low vapour pressure is placed inside the
dessicator along with the sample and I leave it for four hours. However, I do
not know what is the coverage (or lack thereof) of silanising agent after
silansing.

If you would like complete coverage, I can imagine why people would recommend
plasma treating the surface before exposing it to a silanising agent. I imagine
that an oxygen plasma will be more effective at making reactive groups than an
air plasma, but I also know that these reactive surface species are short lived
so I doubt whether or not a plasma is necessary. However, I do not have any
experience with this, so perhaps others can help you with this.

I hope this answers your question.

Kind regards,

Dirk Renckens
Delft University of Technology, DelftChemTech

P.S. The type of silanisation agent you use will determine your hydrophobicty of
your sample.

-----Original Message-----
From: 김태진 [mailto:tjnumber1@hotmail.com]
Sent: 07 October 2008 00:54
To: mems-talk@memsnet.org
Subject: [mems-talk] Questions regarding silane coating and surface cleaning

Hi!

I'm trying to treat Silicon wafers or PDMS with Silane to make it hydrophobic.
As far as I recall, all I need is a dessicator.

But someone told me that I need a plasma asher for it.
Is this true? How exactly do I coat Silane on surfaces?

Also, I'm trying to purchase a cost effective plasma system for Silicon, glass
and PDMS surface cleaning.

My second question is: is a microwave type oxygen plasma system good enough for
surface cleaning?

Thank you!