Hi,

I have tried this before and though I did not finally get it to work (found a
way to bypass this step) but I remember seeing a reference (sorry not able to
find it now) that claimed this problem was because of a thermal expansion
coefficient mismatch. They put the wafer on a thermoelectric cooler and held the
temperature constant during the deposition and it worked just fine!

I am not sure whether its worth the effort of fitting the TEC inside the vacuum
system - but for what its worth this is what I remember reading.

--
Good luck,
Aniruddh



-----Inline Message Follows-----

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