Hey Vishwa,

I hope some of my experiences maybe helpful:

1) try to reduce the temperature when curing PDMS, I usually use 65-70
degree for 45 mins. This works fine for me.

2) you can also spray some isopropyl acohol on your su-8 mold to prevent
adhesion to PDMS. I am afraid that putting the whole mold into ice water
may cause micro cracks of the su-8 mold.

3) Before spinning your first su-8 layer, you can pre-wet the wafer with
thinner su-8, like su-8 2002. spin at 3000rpm to completely wet the wafer.
Then, bake this layer for 45mins. This can also help adhesion of su-8 mold
to wafer.

Peng Li

> Thanks a bunch for the response. I do have negative slope. When I tried to
> make just the array structure on the wafer, I exposed it by 10, 20 under
> and
> 10,20,30,40,50 percent over the recommended values. All them peeled out,
> when I cast the PDMS. Also, I observed the there is negative slope like
> Gareth mentioned.
>
> If i try to spin the second layer, I dont see any alignment markers to
> align
> the second layer. Is there any way of achieving this. Right now, when I do
> PEB, I see the alignment marker from the first layer and then align it to
> the second.

--
Peng Li
Research Assistant
Department of Mechanical Engineering & Applied Mechanics
University of Rhode Island
133D Kirk, 92 Upper College Road,
Kingston, RI  02881
Phone: (401) 874-2247