A caveat to Edouard's comment: while SU-8 won't dissolve in KOH, my
experience has been that it tends to peel up. Adhesion promoters such
as Omnicoat won't help, since they dissolve in even weak bases.

On Wed, Aug 11, 2010 at 9:14 AM, Edouard Duriau
 wrote:
> Hello James,
>
> Have you considered using SU8 or BCB negative resists?
> Although 140°C might be above the glass transition temperature of SU8 (don't
> remember for BCB), both resists withstand KOH etching.
> Maybe you could try.
>
> Best regards,
>
> Edouard