Annalisa,
There are a few options which may improve your bonding results. Since you are
working with oxide surfaces, as you mention, increasing the hydrophilic nature
of the bond process is advantageous.
One method to do that (in a wet chemical manner) is to use a reversed RCA clean
(with no HF dip step).
The process would be:
RCA 2 - HCl:H2O2:H2O 1:1:6, ~70C for ~15 minutes
DI Rinse
RCA 1 - NH4OH:H2O2:H2O 1:1:5, ~70C for ~15 minutes
Di Rinse - Dry
Then, you should actually be able to perform your bonding at room temperature.
You need to be sure that the bonding front is initiated at only one point, so
that you do not get competing bond waves (this will result in a "tenting" effect
where the bond waves meet).
At this point, the bond is very weak. You should inspect using IR - if you see
significant voids, then separate the wafers, re-activate, and re-bond. Bear in
mind that, since this bonding relies on Van der Waals forces, it is crucial that
the surfaces are very flat and, more importantly, very smooth (<0.5nm RMA
roughness foe best results). Then, follow the annealing process you used, and
you should end up with a mostly void free bond.
Regarding plasma, my company as a whole has experience with this, but
unfortunately, I am not allowed to share the details over an open forum.
However, plasma does have the capability to greatly increase both the initial
bond strength and reduce the anneal temperature to full strength (to ~300C).
For further details, you can contact me, or check out the company website at
www.evgroup.com.
Best Regards,
Chad Brubaker
EV Group invent * innovate * implement
Technology - Tel: 480.727.9635, Fax: 480.727.9700 e-mail:
[email protected], www.EVGroup.com
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-----Original Message-----
From: Annalisa Cerutti [mailto:[email protected]]
Sent: Friday, December 16, 2005 5:38 AM
To: [email protected]
Subject: [mems-talk] Sio2 - Sio2 wafer bonding
Hi,
I want to bond two silicon wafers with thermal oxide (0.5 um) on the
surface.
I tried to bond them in vacuum, with a bonding pressure of 4000 mbar and at
a temperature of 500 °C. Then I performed an annealing at 900 °C for
15
hours. The result was that only small areas bonded.
To improve this result I cannot rise the temperature.
What can I change to improve bonding?
Is O2 plasma activation interesting to hydrophiize the surface?
Do I need a preparation of the surface to hydrophilize it?
Thank's
Annalisa Cerutti
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