Sebastian,

First of all, it is important to know what feature sizes of your lines and
squares are. The differential development rate could be related to the
aspect ratios of the different patterns you try to develop. Just wanna
make sure, when you say squares, do you mean a hole (via) in the resist or
a block (pillar) of resist? The development rates are different.

About the peel-off issue, your process flow seems not to include HMDS
priming step for adhesion promotion before resist spin coating. If that's
the case, you need that.

Your softbake temperature is also too low. Was it an oven bake or hotplate
bake? For thick film, it's better to bake on hotplate. You need to add a
step to bake it at 110C for at least 5 mins. Perhaps you don't need the
50C bake step.

Regards,

Isaac Chan, Ph.D.

On Wed, 11 Oct 2006, sebastian wicklein wrote:

> Dear MEMS-Experts,
>
> When I'm developing a 28micron thick AZ9260 photoresist with the AZ400K
> developer in 1:4 dilution (Developer:H2O)on silicon, I can see a selective
> developing rate between thin lines and square areas that have a much bigger
> diameter.
> Since I have such a selectivity, my lines are flaking off when I use longer
> developing times in order to develop the squares as well!
>
> Can someone tell me what's going on here?
>
> Overview of procedures
>
> Spin 28microns on Si-sample
> Softbake 10 min at 50 degree C
> Softbake 30 min at 90-95 degree C
> Exposure 40 min at 10 mW / cm cubic
> Development in 1:4 dilution (Developer:H2O)