Chad,

Could you provide more elaboration on the nature of unpredictability in
results when exposing at UV wavelengths below 350nm. Is this primarily a
resolution problem, or will the mechanical properties of the film also be
affected?

Thanks,

Michael



 >Carson,
> >
> >You have to remember that SU-8 is a negative tone material - basically,
> >where you expose, the material will remain.
> >
> >As such, this means that, the higher your exposure gets, the wider your
> >remaining linewidths will become. In the case of a massive overexposure
> >(such as your 100second, or 2 J/cm2), this can actually prevent narrow
> >trench features from developing out.
> >
> >An optimal dose for the thickness you are exposing is ~300 mJ/cm2 (or,
> >about 15 seconds).  Unfortunately, the nature of the SU-8 will mean that
> >some residual stress will exist in the film, but with care taken during
>the
> >baking steps, this stress can be minimized.
> >
> >One final comment (one I have made before) - be very careful that you are
> >not allowing the SU-8 to experience UV wavelengths below 350nm - this can
> >cause extremely unpredictable results during exposure.
> >
> >Best Regards,
> >Chad Brubaker