> -----Ursprüngliche Nachricht-----
> Von: laetitia philippe [mailto:svetleis@yahoo.fr]
> Gesendet: Mittwoch, 8. Dezember 2004 17:02
> An: MEMS-talk@memsnet.org
> Betreff: [mems-talk] SU8 exposure time
>
> Hello All,
>
> I am trying to find the best exposure time for a SU8-2035 with a
> thickness of around 50 um
>
> This is not looking to be very easy. I am working with a UV
> i-line 365
> nm, with 20 mW/cm2
>
> For high exposure time (up to 100s ), I see that my structure
> does not
> developp at all, i.e. the exposed polymer is not removed in the
> developper although the sutructre is clearly visible with a
> color difference
> between the exposed and non exposed part
>
> For reasonnable exposure time (20 s), I have a good
> developpment but I
> have always a resulting mould that is small as my mask. i.e some
> feature of my pattern of 200 um would lead to only 100 um
> cavity in my
> developped polymer and so one.
>
> Finally, when I go down to 7 seconds, I have a good resulting mould,
> with much better dimensions, but I have enormous stress on my
> polymer and
> sometimes delamination which makes me thing I am under exposing of
> course
>
> Could someone share his own experience about that? especially
> about the over-exposure'?
>
> Many thanks
> Carson

Hi All,

I made some strange experiences. I have four Pyrex wafer with SU8-2025 with
different spin-parameters
  P1  500rpm -> ~140um
  P2 1000rpm ->  ~70um
  P3 1500rpm ->  ~50um
  P4 2000rpm ->   ~?um

We are working with a Suess MA/BA6 with an exposure dose of 8.6mW/cm2. With
all 4 wafers I performed a multi exposure with 10x3.5sec and 30sec delay.

After development I observed, that P1 and P2 were well exposed and could be
completely developped without any loss. But the layers on P3 and P4 start
peeling off due to stress AND/OR poor adhesion.

All 4 wafers received the same treatment (clean, dehydration, ramped
soft-bake, ramped hard-bake), so it looks to me that the last two wafers are
over-exposed.

Important for stress reduction are the bake procedures; the cleaning and
dehydration of the substrate have a high influence on the adhesion.

Best regards
Christoph Friese