Since the small structures peel off the first SU-8 layer maybe you
problem is doing the PEB separately.
Crosslinking during the PEB stresses the film. Maybe you could try
spinning your second layer after exposure of the first but without PEB.
Then expose the second layer followed by a single PEB step for both layers.
Another thing to look at is the profile you get with you current
conditions. It could be you have a negative sidewall slope or T-topping
which allows the PDMS to grip the structures and peel them off.
Best regards

Gareth


Vishwa wrote:
> Hi,
> I use SU-8--2025 to make the mold master. The mold is comprised of two
> layers, first one is the base which is a rectangular channel(2.5mm x
> 50 mm x 60um). The mask that I use is a film which is stuck to the
> glass plate. Then I spin the second coating of SU-8 after the PEB of
> the first layer , but without developing the photoresist. The second
> layer is comparable to an array of small rectangular walls ( 2.5mm x
> 50um x 30um) and they are present all along the first layer. The walls
> are separated by 50um. After SEB and exposure, I do the PEB, which is
> then followed by developing.
>
> I plasma treat the silicon wafer before spinning the first layer and I
> plasma treat the SU-8 of first layer before spin coating the second
> layer. The mold looks good under the microscope. The problem is part
> of the small structures comes with the PDMS, when I peel it after
> baking the PDMS.
>
> Is there some sort of a solvent that I can coat the mold with for easy
> removal of PDMS or is there something that I can do in the mold
> fabrication process itself to avoid this problem.
>
> Thanks a bunch in advance. Any help is greatly appreciated as I am
> kind of stuck.
>
> Cheers,
> Vishwa