Hi, David,

Thanks for mentioning the edge beads. I did do edge bead exposure and
development trying to remove it. I guess I need to do this step more
aggressively, because at the corner of the wafer after edge bead
removal, there are still fringes indicating a different thickness of a
PR layer.

Wei

On Thu, May 19, 2011 at 8:35 AM, David Mathine
 wrote:
> Hello Wei,
>
> You probably also have problems with photoresist edge beads since you are
using small samples.  These edge beads can effect your resolution since the mask
is not really in contact with the waver.
>
> You can reduce this effect by wiping the edges of your sample with a clean
room type Q-tip before hard bake.  Also, spinning higher speeds with a possible
two levels of photoresist can help reduce these effects.  This is a common
problem associated with the development of a broken wafer technology.
>
> Regards,
> David

--
Wei Tang
Department of Materials Science and Engineering, UCLA
Cell: 310-357-0158
Website: http://tangweipku.googlepages.com