> I have unsuccessfully attempted to use 4620 recently.  The
> problem that
> I have had is a "bubbling" of the resist immediately after exposure.
> The "bubbles" nucleate in all open areas.  The resist sheds
> in circular
> flakes from the open areas - sometimes even before
> developing.  If there
> are features surrounded by lots of open area, these features flake off
> as well.  Has anyone else seen anything like this?

Nitrogen is given off when the resist is exposed.
Normally it is absorbed in the exposed resist and diffuses away,
with any left being removed upon developing.
With thick resists and high exposure powers (mW/cm^2), it can nucleate
bubbles.
Try the same dose but with a lower exposure power,
or do the exposure in pulses to allow time for diffusion.
Karl Suss had some success with pulsed exposures awhile back.

        --Kirt Williams Agilent Technologies