Hi Aimi,

First some background, we have coated, exposed and developed 500 µm films of
SU-8 on 200 mm wafers.  We achieved the 500 µm coatings via a 2x 250 µm coating
process.

As others have already mentioned, solvent control is a critical issue.  You will
need to carefully extract the solvents.  There are risks or crusting the top
surface of the resist layer or even beginning a thermal cross-linking of the
resist if you try to bake the resist too quickly or for too long.  I liked the
idea that one member suggested of simply letting the solvent evaporate.  I would
add one thought: vacuum might be the way to go -- especially given a 2000 µm
film thickness.  Hopefully you have enough time for this step!!

Returning to the issue of thickness, I am not sure that an 8x 250 µm spin or
spray coating process is going to be the most successful method.  Again, one
member suggested that you could simply pour the resist onto the wafer and
perhaps use a LEVEL hotplate to spread the resist.  I think that this might be
your best approach.  Assume that surface tension will keep the resist on the
wafer and that (pi)(r^2)(h) is a good approximation of the resist volume.

Exposure with wavelengths greater that 350 nm is a must.  SU-8 is very
transparent to >350 nm wavelengths.  It is questionable whether these
wavelengths will penetrate 2 mm of resist.

Developing is going to be difficult as well.  If your features are large you can
dunk develop the wafers but this will probably take in excess of five to ten
hours!  Megasonic assistance is probably a must for this resist thickness.

I urge you to contact MCC for assistance with your project.

Lastly, best of luck with your project and let everyone at MEMS-Talk know if you
succeed.

Best Regards,
Garrett Oakes

EV Group
invent * innovate * implement
Regional Sales Manager North America - Direct: +1 (480) 305 2443, Main: +1 (480)
305 2400 Fax: +1 (480) 305 2401
Cell: +1 (480) 516 6724
E-Mail: G.Oakes@EVGroup.com, Web: www.EVGroup.com

-----Original Message-----
From: A. AhmadShukri [mailto:aimisas@u.washington.edu]
Sent: Wednesday, November 26, 2008 12:31 PM
To: General MEMS discussion
Subject: [mems-talk] very thick layer of SU-8

Hi all--

I am wondering if anyone knows how I can deposit a 2mm (yes, 2,00um) layer
of SU-8 and pattern it.

Thanks,

Aimi Ahmad-Shukri