Agung,

        Coincidentally enough, I have just attempted a similar feat. Some of
my conditions were wavy and others not. My procedure isn't perfect, but
maybe it will help. The way I went about it was as follows:

        SU8-2050 on test grade silicon.

        1) Pirhana, BOE clean
        2) HMDS
        3) Spread on at 300RPM for 15 sec.
                Spin 1000RPM for 45 sec. (~110um thickness)
        4) Soft Bake 65C for 5 min. 90C for 10 min.
        5) Apply 2nd, 3rd, 4th layers the same way.
        8) Expose for 45 sec + 15-20 sec for each additional layer
                (3 layers = 75-80 sec.) at 10mJ/cm2
        9) Post bake at 65C for 1 min, 90C for 5 minutes.
        10) Develop with agitation for 8-12 minutes depending on features.
        11) Hard bake at whatever temperature 100-200C for a few hours.

        With 3 layers, I managed to get 300um. There is some thickness lost
to              solvent evaporation. Not 100% efficient, but a work in
progress.

        - cheers - Gabe Dagani, UT Austin NNIN


-----Original Message-----
From: Agung Shamsuddin [mailto:a.shamsuddin@gmail.com]
Sent: Tuesday, January 24, 2006 1:14 AM
To: General MEMS discussion
Subject: [mems-talk] Wavy Surface of 500 micron Thick SU8 layer after
Postbaked

Dear friends,

I have applied SU-8 layer with thickness around 500 micron on glass.
I have tried some kinds of softbake procedure:
1.   - 3 hours (from room temp. to around 100 celcius) on hotplate
      - turn of the hotplate to cooling down.

2    - 1 hour (from room temp. to around 65 celcius) on hotplate
      - 1 hour (from 65 degree to around 100 degree ) on hotplate
      - keep on around 100 degree for 2 hours
      - turn of the hotplate to cooling down.

3.   - 1 hour (from room temp. to around 65 celcius) on hotplate
      - 1 hour (from 65 degree to around 100 degree ) on hotplate
      - move to oven which has already set on 95 degree and keep there for 2
hours
      - turn of the oven to cooling down.

I thougth more longer softbake process will remove more solvent.
All the softbake procedure give me flat, smooth and dry (no stick on mask
when exposure) SU-8 layer

and then i exposed  by using recomended exposure dose from manufacturer
datasheet.

and then it continued with postbake.
I have tried:

1.   - 1 hour (from room temp. to around 65 celcius) on hotplate
      - 1 hour (from 65 degree to around 100 degree ) on hotplate
      - turn of the hotplate to cooling down.

2.   - 1 hour (from room temp. to around 65 celcius) on oven
      - 1 hour (from 65 degree to around 100 degree ) on oven
      - turn of the oven to cooling down.

3.  - set the oven on 65 degree, put the specimen inside and keep for 10
minutes
     - 1 hour (from 65 degree to around 100 degree ) on oven
     - turn of the oven to cooling down.

but all the procedure always give me wavy surface of SU8 layer in result.

Please, any opinion and suggestion welcomed.

Best regards,
--
Agung Shamsuddin S.
University of Indonesia