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: c.brubaker@EVGroup.com, www.EVGroup.com This message and any attachments contain confidential or privileged information, which is intended for the named addressee(s) only. If you have received it in error, please notify the sender immediately and then delete this e-mail. Please note that unauthorized review, copying, disclosing, distributing or otherwise making use of the information is strictly prohibited. -----Original Message----- From: Annalisa Cerutti [mailto:cerutti@bo.imm.cnr.it] Sent: Friday, December 16, 2005 5:38 AM To: mems-talk@memsnet.org 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 _______________________________________________ MEMS-talk@memsnet.org mailing list: to unsubscribe or change your list options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk Hosted by the MEMS Exchange, providers of MEMS processing services. Visit us at http://www.memsnet.org/