Thermal oxide grown in pure O2 begins to flow - very moderately - at temperature ~ 1100 C at 1 atm. To lower the fusion temperature, you may want to try the following: - Phosphosilicate Glass (PSG) typically deposited by LPCVD; - Borophosphosilicate Glass (BPSG) typically deposited by LPCVD; These films were widely used on old CMOS processes at inter-dielectric between the polysilicon and the metal layer. One application was to reflow the glass over the polysilicon to have good step coverage of the metal lines. There are dopants other than P and B that lower the glass fusion temperature (Germanium for ex.), but these are the most common. The PSG and much more the BPSG films are hydrophilic and may react with ambient moisture to produce phosphoric acid and boric acid on the surface of the glass, especially if highly doped. But PSG at ~ 8 % P should be OK if you limit exposure to a reasonably dry ambient and it may flow at 900 C. Also, you may want to consider bonding in a wet ambient (H2O in O2). This will leach out P but is known to reflow the glass much better. However, there may be serious draw-back for your application. Regards, Pierre x286 -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of Annalisa Cerutti Sent: December 16, 2005 07:38 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/