Claudio,
        HMDS chemical symbol NH-Si(CH3)Si(CH3).  The NH is very actively
looking for Hydrogen.  If you dehydrate correctly the only Hydrogen on
the wafer is at the end of a Hydroxyl ion that is bound to the wafer by
a very strong bond.  The NH sees 2 of these Hydrogen atoms and liberates
them and combines with them producing NH3, ammonia. This is given off
and the Si(CH3) replaces the Hydrogen atom.  This leaves an inorganic Si
atom linking on to the wafer and three organic molecules (CH3), Methyl
waving up in the air looking for an organic material to bond with.  I
like to think of this as a Methyl tree and the organic liquid settles in
the branches.
Bill Moffat, CEO
Yield Engineering Systems, Inc.
2185 Oakland Rd., San Jose, CA  95131
(408) 954-8353
cell 408 590 4577
[email protected]
www.yieldengineering.com

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of CLAUDIO T MUNOZ
Sent: Friday, February 09, 2007 12:32 PM
To: [email protected]
Subject: [mems-talk] Adhesion Mechanism between HMDS and PMMA

Dear Members,
In one of my  project I am characterizing PMMA films deposited on
silicon substrate. To enhance adhesion I was told to use HMDS
(hexamethyldisilozane). My question is: What is the chemical or physical
interaction between the PMMA film  and the HMDS layer that makes the
latter a good adhesion promoter for PMMA. Would PMMA films wet better
over hydrophilic substrates as SiOx? I say this thinking on the
possibility that PMMA could form strong hydrogen bonding with the SiOx
substrate.
I am specifically concerned about the mechanism of adhesion between PMMA
and HMDS.
I believe some of our dear members might probably share some ideas to
help me to understand my question.