Hi David,

Thank you very much for the response. That was of a
great help to enhance my understanding.

In fact I was trying to know how the cantilever combs
of a linear comb device could be fabricated. The
device is an accelerometer which works on the basis of
differential capacitance. The differential capacitance
is measured as an o/p voltage when the movable combs
move w. r. t the fixed ones.

Could you please let me know some tips or ideas out of
your experience  ..in the following matters?

1. If I am planning to make the cantilever out of
polysilicon, I can not use Polysilicon as the
sacrificial layer..(1 um). What can I use in place of
that? Al will do? I mean with regards to its
weldability to the Si surface...?

2. Can the same procedure be applied to the movable
set that gives an appearance of a two sided comb and
is anchored at ends to the Si surface..

These things might be simpler to you.. because I am
new to this field.Thanks for writing back

Ramzee, NY

--- David Springer  wrote:
> Hello Ramzee
>
> What materials are you using to make the comb
> device? What exactly do you mean by only 1um of
> clearance.
>
> If you are trying to create a 1um high space under
> your device (but no deeper) you can try the
> following. Our customers have had great success
> building devices with uniform spaces as little as
> 200nm underneath them as follows. There is no reason
> you can not go even smaller.
>
> 1. make a thin layer of oxide on the silicon wafer
> 2. add a thin layer of polysilicon, in your case 1um
> thick.
> 3. pattern the polysilicon and fill the spaces with
> oxide to create etch stops to define the shape of
> your cavity.
> 4. add your device material on top and pattern it.
> 5. remove the polysilicon using xenon difluoride.
>
> We have done this with very thin layers of poly and
> undercuts typically on the order of 30um to 100um
> using oxide as the etch stop material. Xenon
> difluoride has a high selectivity to most materials
> over silicon and does not attack the most common
> metals, for example it does not fog Al and has
> better than 1000:1 selectivity over oxide.
>
> If you have any questions or would like to try
> something out please get in contact with me.
>
> David Springer
> XACTIX, Inc.
> [email protected]
>
>  >>  Could you please let me know the fabrication
> procedure
>  >>  for the cantilever combs in the linear comb
> device?
>  >>  how can we fabricate them on a Si wafer with a
>  >>  clearance of just a micron with the wafer
> surface..
>  >>  Please do respond.
>
>  >>  Thank you very much.
>
>  >>  Ramzee
>
>
>  >>
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