4 micron height will pose problem.  I have seen non-conformal PR coating with
even 1 um topology.
Sometimes, using high viscosity PR or lowering spun-on rate will do the trick.

J. Wu
Univ. of Notre Dame

Quoting Tom Fan :

>
>
>
> On the same topic, would 4-um high structures (serving as electrodes)
> standing
> on otherwise flat substrates be considered "high-aspect-ratio" structures?
> Would conventional resist spin coating process do the job? And also can the
> lithographic tool handle a height difference of 4 um (if exposures on and off
>
> the structures are desired)?
>
>
> Thanks,
> Tom
>
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