I have encountered this before, and I tried everything that was suggested,
including long bake times, and vacuum bakes. It is not the exposure to
radiation that is causing the wrinkles, or the exposure to vacuum. We tried
all that and verified that the wrinkles were not there. The wrinkles only
form when a film is being deposited under vacuum. It forms under all
deposition types: RF sputtering or e-beam or filament evap. I don't have a
conclusive answer, but I suspect this has something to do with the SU8
itself outgassing, not its solvent.



On Mon, Mar 16, 2009 at 6:17 PM, Andrea Lucibello wrote:

> 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?