Daniel,
Wow, you asked a big question.
I'll start off with one assumption, and that is you are looking to directly bond
two silicon wafers, with no intermediate materials. This will narrow things
down from a nearly infinite discussion to something a bit more manageable.
For direct bonding, under standard circumstances, the substrate requirements
are:
<2nm surface roughness, <5A roughness for hermetic seal
reasonable TTV (<5µm, typically)
Minimal bow/warp
Now, in terms of a bonding process:
Under standard conditions - wet chemical clean performed is a reversed RCA
clean, with no HF dif
Reversed RCA:
RCA 2 - HCl:H2O2:H20 1:1:6, 60 C, ~15 - 20 minutes
RCA 1 - NH4OH:H2O2:H2O 1:1:5, 60C, ~15 minutes
After the chemical activation, you would want to contact these wafers under very
controlled circumstances. Vacuum is not necessary for blank substrates, but is
absolutely required for patterned wafers.
I've achieved excellent results by placing the pair into an EVG520 bonder. The
tooling will hold the substrates in separation until a moderate vacuum (10E-2
mbar) is achieved (if vacuum is necessary). Then, a probe will push the wafers
together at the center to initiate the bond front, after which the separators
are removed. This step is absolutely critical. By initiating contact at one
point, it ensures that only a single bond front will form, allowing bonding to
the edge of the substrate. If the front begins at more than one point, the
competing fronts will meet at a "tented" edge.
Once the wafers are fully in contact, the bond exists, but is still weak (and
can be separated by prying the wafers apart with a small amount of force). To
strengthen and complete the bond, an anneal step must take place, typically for
a few hours a temperatures >1000C.
EVG also offers our Low Tem Dry Activation Plasma Bonding system, which utilizes
a plasma rather than the wet chemical method to activate the surfaces. The
primary benefit from this is that full bonding strength can be achieved at
temperatures <300C.
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: [email protected] [mailto:[email protected]] On
Behalf Of Danielq k
Sent: Wednesday, October 27, 2004 12:27 PM
To: [email protected]
Subject: [mems-talk] wafer bonding
Hi all
Any one know how to bond two si wafers? what requirement in term of
heat, vacuum, chemical clean..
Thanks
Daniel
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