if you just want to make a mold to fabricate some PDMS structure, you can make a
seed layer use SU8-5, or SU8-10.
Spin SU8-5 to form a 3-4 microns layer, bake, and expose to UV(without mask),
postbake, and develop, then bake it in oven at 175C for 2 hours. Then you can
spin and pattern other thick SU8 layer without adhesion problem.

Quoting Gareth Jenkins :

> Omnicoat is certainly a good idea but good adhesion is also possible
> with the following steps:
>
> Treat with conc. H2SO4 (I find this as good as Piranha and safer /
> more eco-friendly since you don't need to make it fresh each time).
> Thoroughly dehydrate. 200-220C for 30mins on a hotplate.
> Ensure even and complete crosslinking with a higher exposure dose than
> recommended.
> Take account of stress during the PEB. If large areas are being
> exposed, consider stress relief structures in the design. A lower
> temperature PEB for longer time can greatly reduce delamination
> effects.
>