Michael, it is positive resist. Because novolak resin is highly absorbing
at deep UV radiation, the outer shell is hardened by the photon energy.
This is a flood exposure step. i,g,h-line exposure won't work. As other
members suggest, competing resist materials like SU-8 may do good or
better job. Of course, price is another factor to consider...

Or, how about using metal layer as hard mask?

Isaac

On Wed, 15 Mar 2006, [iso-8859-1] ZICKAR Michaël wrote:

> Hi Isaac,
>
> I guess AZ P4620 resist is a positive resist. How does the deep UV cure
> work? We are looking for a photoresist that survives well 400 µm of
> DRIE, while keeping its verticality. A hard bake of 200°C would
> certainly increase the selectivity between resist and silicon.