Zhou,
   We've found that the silver loaded vacuum grease used to attach a
wafer or die to a handle wafer can react with the photoresist (on the
face down device side) to form a particularly stubborn film.  We have
worked around this by using a thick positive resist as an overcoat on
the front  when etching from the back side.  We use SPR 220 which is at
least 10 microns thick and easy to solvate with acetone.

Good luck,
    Mike Martin
    U. of Louisville

>>> Florian Herrault  08/10/06 10:11 AM >>>
You could try Piranha cleaning too.


Quoting "D. Zhou" :

> Dear all,
>
> I used S1813 as the mask for the DRIE of the top layer from the
front-side.
> Then I put the chip upside down, attached it to an Oxide wafer and
did
> another DRIE of the substrate from the back-side . After the etch, I
found
> it difficult to remove the polymer formed during the etch. I dip my
chips
> in Aceton for 10 mins and then used Oxygen plasmer to clean it.
However,
> the top layer(device layer) of my chips were still not clean enough.
Could
> anybody give me some suggestions on how to completely clean the chips
after
> these two DRIE process? Thanks very much.