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 Cantos
brad.cantos@holage.com
http://holage.com


On Jul 21, 2009, at 2:19 PM, Shah, Forum N wrote:

> Hi everyone,
>
> I am using SPR 220-7 photoresist and am looking at 7 micron
> thickness. I am spinning at 3500 rpm for 30 seconds and also tried
> 3k rpm for 30 seconds.
>
> I see a lot of streaks on the wafer and not getting a uniform
> coating. I did take a look at Stanford nanofab website (www.snf.edu)
> but the problem is that I have manual spinners and their manual
> procedure is also not working fine for me.
>
> If anyone has worked with it before, your suggestions would be
> invaluable.
>
> Thanks in advance.
> Forum