1.) Annealing cycles for fusion bonded wafers require that the wafers are kept
at the annealing temperature for a certain time.
Therefore, regular furnaces are usually used to perform the annealing. Also, the
annealing process for such wafers can typically be a batch process.
Thus, throughput  considerations are not a major driving factor to go one way or
the other.
2.) We have studied the effects of plasma activation in depth. We have used the
technique for many different material pairings, as well as for different surface
conditions. Of course SiO2 to Si is the most common one and has been used for
SOI applications for more than 5 years. Amongst the other, successfully studied
pairs are:
SiO2 - SiO2, Si to Si, GaAs to Si, SiN3 to Si, InP to Si, Pyrex to Si, Corning
Eagle2000 to Si, Quartz (=SiO2) to Si,...
The variety of these different applications and the desired properties of the
bond interface also dictate the use of different gases to create the plasma.
EVG makes a "closed" plasma chamber design, that allows to accurately control
the gas mixture and the plasma conditions used for activation. Without
understanding your application more in detail, I can say, that N2 or O2 plasma
is what is most likely to provide the best results. - In a direct discussion we
can verify this against your requirements.
In regards to the process flow: EVG makes equipment configurations that allow
both process flows that you describe. The results that can be achieved are
similar for most applications. In order to determine what method will work best
for your application, it will be required to understand more details such as
alignment requirements, requirements posed by the device design, etc. In
general, we can say, that plasma first and then align and bond will allow you to
achieve the most accurate alignment accuracy.

Best Regards,
Chad Brubaker

-----Original Message-----
From: [email protected]
Sent: Wednesday, April 06, 2005 5:38 PM
To: [email protected]
Subject: [mems-talk] wafer bonding

How are you? I do have two questions to ask.

1. First on annealing process after fusion bonding of oxidized patterned Si
wafers.
   Rapid thermal annealing vs. regular furnace use. Which gave you a better
result?
2. Second on fusion bonding of oxidized patterned Si wafers.
   Dried surface is required before bonding. Has anybody used Plasma wafer
   bonding method? If tried what are the gases that you have used? Externally
applied
   Plasma on each wafer then align & bond or Internally applied plasma & bond
after align?