Brad,

The problem still persists even with a two step spinning. I do use the same
recipe that you suggested. Streaks are radial in appearance as you mentioned. If
two step recipe has worked for you, can you suggest what ramp rate should i be
looking at? the recipe that i followed was:

Step 1: Spin at 500 rpm with ramp rate of 100 rpm/s (lowest) for 10 sec.
Step 2: Spin at 3000rpm /3500 rpm at ramp rate of 100 rpm/s for 30 sec.

What soft bake do you prefer for this kind of recipe?  Does it help get rid of
streaks? If you have any other suggestions do let me know.

Thanks in advance. I appreciate your help.
Forum
________________________________________

From: Brad Cantos [brad.cantos@holage.com]
Sent: Wednesday, July 22, 2009 10:58 AM
To: General MEMS discussion
Cc: Shah, Forum N
Subject: Re: [mems-talk]  SPR 220-7

Forum:
Are the streaks that you mention areas where you have no resist
coverage separated by lines of resist that appear radially from the
center?  Situations like this are not uncommon for very thick
photoresists that are applied statically (i.e., wafer is not spinning
during pr application) or experience ramp speeds that are too fast.
One solution to these situations is to do a two step spin, the first
spin at around 400-500 rpm to spread the resist uniformly to the edges
of the wafer, then follow with the 4k rpm/30 sec to get your desired
thickness.  You can visually evaluate the time required for the first
spin, and if possible, try to apply the resist dynamically (while it
is spinning).  Make sure you can hit the center of the wafer while
doing this or you will have a "hole" in the center.

If your streak problem is different than this, please give a more
detailed description.

Brad