Try this:
1. Skip the ethyl alcohol step, use "out of the box"/virgin wafers.
2. Bake at 200-250 deg. C for 30 minutes and let cool to RT before spin coating.
3. I dispense the SU-8 the way you do, no problem.
4. Ramp to 500 RPM @ 100 RPM/s as you do, but keep it at 500 RPM until the SU-8
covers the entire wafer. You will need to experiment a little here.
5. Ramp and spin at your desired rate for 25 sec.

Jacques Jonsmann


-----Oprindelig meddelelse-----
Fra: Vishwanath Somashekar [mailto:vishwa@iastate.edu]
Sendt: ti 22-04-2003 05:32
Til: mems-talk@memsnet.org
Cc:
Emne: [mems-talk] Reg: Spin coating of Su-8 2025



        Hi,
        I am a grad student at Iowa State and have been involved very recently
with the
        fabrication of channels for experiments in microfluidics. I take a 100mm
        silicon wafer, clean it with ethyl alcohol and then rinse with water and
        prebake it for some time. Then, I put the wafer on the spin coating
machine.
        The diameter of the chuck on which this wafer rests is slightly smaller
than
        that of wafer. so I am not able to place the wafer such that the center
of the
        wafer and the center of the chuck match. As a result of this, when i run
the
        spin coating, I can see kinda wobbling movement at low speed which tends
to
        vanish at high speed. The way i dispose of the resist is take a syringe
and
        measure about 4ml of SU-8 2025 and dipense off at the center. Then I
ramp at
        100rpm/sec for like 5 sec and then will ramp to the desired rpm based on
the
        thickness of the coating required. The problems that I am faced with are
        1) after the spin coating, I see like streaks of su-8 strecthing from
the
        center and the coating is not uniform and its kinda wavy and sometimes,
the
        coating is not on the entire surface.
        2) we also use su-8 2100 which is really viscous and when we spin coat,
it
        coating is really pathetic. Can you suggest me some technique to
improve. As I
        am new to this fabrication, I might not have described my problem
technically.
        I apologize for that.

        Thanks very much in advance.

        vishwa


        Vishwanath Somashekar
        3219, Ross Rd.,
        Ames
        IA 50014
        Ph: 515-292-1766(Res)

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