Hi Reza,

Yes you certainly can grow an oxide film on a Si membrane, however I suggest
depositing low-stress CVD oxide or nitride instead of growing a thermal
oxide.  The reason for this is that when the wafer cools from the oxide
growth temperature, the difference in thermal expansion coefficients between
the oxide and the silicon cause a tensile stress in the silicon near the
oxide-silicon interface.  This tensile stress can easily exceed the flow
stress of Si at elevated temperatures, resulting in plastic deformation of
the silicon near the interface and possibly bowing in the membrane
(depending on the specifics of the device design and oxidation process).  A
low-stress nitride would avoid this plastic deformation and probably offer
better chemical resistance than oxide.

Good luck,


Brian C. Stahl
Graduate Student Researcher
UCSB Materials Research Laboratory
brian.stahl@gmail.com / bstahl@mrl.ucsb.edu
Cell: (805) 748-5839
Office: MRL 3117A


On Fri, Sep 18, 2009 at 9:35 PM, Reza Rashidi  wrote:

> Hi everyone,
>
> I have a pressure sensor with a 60 um thick Si membrane which is going to
> expose to a basic environment (pH=13) at 170 °C and up to 300 psi. I am
> going to grow a silicon dioxide layer on the membrane and then coat a
> parylene film to protect it. I am wondering if it is possible to grow a
> silicon dioxide layer on a thin membrane (rather than a thick si wafer which
> is regular process), also, if these two layers together can protect the
> membrane for 8 hours.
>
> Any advise would be highly appreciated.
>
> Thanks,
> Reza Rashidi
>