Dear Andrea,

You should completely cure the SU8 after patterning & if I remember well (you
can check SU8 files) that means treatment (ramp up to 200 & after cool down) at
200 C for 10 min (depending on layer thickness). If you had a vacuum oven will
be better. The cracks appear because of vacuum and because the su8 isn't
completely cured (95 is too low no matter how long you keep it).
If you want to do lift off after metal deposition better use omnicoat before su8
deposition.

Best regards,
Dr.  Mihaela Carp


Der all,

I'm trying to evaporate chromiun onto uncrosslinked SU-8, i have read the other
message present in the forum written in the past about "wrinkles on SU-8" e i
had follow the suggestions, but at the end of story i have still problems. This
problems are deep crack onto Uncrosslinked SU-8. This Crack/Wrinkles appears
immediately after the deposition of Chrome.
I use SU-8 2002 to have a thikness of about 2,5 um and i have been performed the
thermal treatment of the SU-8 with an hot plate. The fabrication process is the
following:

1) Wafer cleaning
2) spin Su-8 2002 1000rpm 9(ramp) 30'' (about 2.5 um of thickness)
3) Soft Bake ramped until 95°C (from 20°C to 95°C with a ramp of 2°C/min and
hold at 95°C for 1hour and then a cool down ramp until 20°C in about 1 hours )
    (The long soft bake is performed in order to evaporate the solvent present
in the SU-8  )
4) Exposure 10'' with the conventional paramenters given by Microchem
5) Long Post Exposure Bake (2' @ 95°C and hold at 60°C for 20 hours and then a
cool down ramp until 20°C )
    (2' @95°C for the crosslik of the exposed SU-8 insteand the Long Post
Exposure Bake is performed in order to evaporate the remaining solvent present
in the uncrosslink SU-8 and also in order to
     avoid outgassing problems for the next metal deposition)
6) Evaporation of 30nm of Chrome by Thermal Evaporation (filament) with a
chamber's vaccum of 3,6 e -7 millibar  with deporate of 3A/s

For the deposition of chromium no metal deposition technologies that expose the
uncrosslinked SU-8 to photons is used ,i.e. sputtering or electron beam metal
deposition, in order to prevent the crosslink of uncured SU-8. And so i use
filament evaporators that utilize Joule effect to vaporize the metal. Chromium
at a pressure of 3,6 e -7 millibar sublimates at approximately 977 °C and  the
peak of the blackbody radiation is theoretically calculated to be in the
infrared range (about 4 um) with no generation of  photons which crosslink the
uncured SU-8. Before the deposition of chrome all appear to be ok, i also tried
to develop the SU-8  and the uncrosslink SU-8 is perfectly dissolved with is
developer.

Now my question is.... "where did I go  wrong??"...By chance is it something in
the deposition?  Or in the thermal treatment of the SU-8?  Or both of these
things?

Any suggestion are welcome.

Thanks in advance
Andrea Lucibello