This is called "T-Topping." See http://memscyclopedia.org/su8.html

You can solve it by cutting out the light below 350 nm. I've used a
Kopp 7380 filter to solve this problem. The reference above suggests a
Hoya UV-34 filter, but I had trouble finding a supplier for those a
few years back when this last came up. Presumably that would work too
though.

- Kevin

On Tue, Mar 29, 2011 at 7:06 AM, 첸로  wrote:
> Dear all,
>
> I am using photolithography technique to make a su-8 pattern. The smallest
feature width is 10um.
>
> The mask shape is a square which side length is 10um.
>
> After developing the su-8 pattern sharp features are always lost. The square
turns to a circle due to the reflection and diffraction and some optical
phenomenon.
>
> Does anybody have any ideas about how to solve this problem?
>
> Please give me some suggestions... except OPC and PSM.
>
> Thanks in advance.