Hi Daniel,

    That's an interesting question I never got to explore in my plasma
bonding investigations for Si and oxidized Si.

A few questions:

1. How flat and smooth is your magnesium fluoride surface? I'm not
sure what the requirements would be since your PDMS is probably
somewhat complaint. Presumably, the compliance would make things
easier...

2. What plasma (and plasma chamber type?) are you using to activate
the MgF surface? how long are you activating the surface for? (for me,
30-60 s @ 150 W in an RIE parallel plate reactor at "low" pressures
seemed close to optimal); did you try activating both bonding
surfaces? What kind of plasma environment are you using? It has been
shown that with an oxygen plasma for Si-Si or Si-SiOx, an RCA-1 dip
after bonding would significantly enhance the bond strength. For argon
or nitrogen plasmas, this was not the case. Why is this is not clear
to me (maybe there's been some literature published in the last 6-7
years or so that I've missed), but you can probably make educated
guesses.

3. How much force are you applying to the bonded pair? what
temperature are you baking at while pushing them together?

4. I've always wondered if the activation by plasma was purely
physical, chemical or a bit of both...there's a line of thinking
speculating that water combined with a "damaged" surface from the
plasma enhances local, low temperature oxidation to fill in small
crevices and gaps - increasing the contact surface - and thereby
increasing the bond strength. With MgF, I am not sure what the model
would be? Perhaps you need a plasma with some fluorine in it?

Felix


On Jun 28, 2010, at 3:34 PM, Danny Gossett wrote:

> Dear Colleagues,
>
> I'm attempting to bond a polydimethysiloxane (PDMS) block to an
> antireflective coated window (Magnesium Fluoride, MIL-C-675). While
> plasma activation of uncoated glass and PDMS followed by contact of
> the two surfaces creates a strong covalent bond, the plasma does not
> appear to activate the AR coated window in a way that allows the same
> linkage. Does anyone have any suggestions as to how I might bond these
> surfaces? Thank you so much.
>
> Daniel Gossett

Felix Lu
felix_lu@yahoo.com