Development times can vary a lot depending on temperature and
agitation etc. If you have sufficient exposure dose and PEB it is
pretty much impossible to overdevelop SU-8. If you see white streaks
after the IPA wash, put it back in the developer for a few more
minutes. If you still see streaks you can repeat this as many times as
you like (replacing with fresh developer along the way).
If this doesn't work, then it is most likely partially exposed SU-8
somewhere (perhaps due to poor mask contact or incorrect exposure
dose).

On Tue, Jul 8, 2008 at 11:04, Dendukuri  wrote:
> Hello everyone,
>
> We are doing the following process to obtain 40 um tall structures using
> SU-8 2035-
>
> 1. Piranha wash
> 2. Dry 4" Si Wafer at 150C for 30 min
> 3. Coat SU-8 10s at 500 rpm, 30s at 3000 rpm
> 4. Immediately transfer to hot plate at 65C for 3 min and 95C for 5 min
> 5. Expose at 17 mW/cm2 for 11s using an Abet exposure source through a
> PL-360 filter placed directly on top of the mask such that the mask is
> sandwiched between the filter and the coated wafer
> 6. PEB for 1 min at 65C and 5 min at 95C
> 7. Develop for 10 min in SU-8 developer and wash with IPA
>
> We get good resolution of the features down to 10 um.  Our problem is that
> we are getting white spots and streaks on the SU-8 structures making the
> surfaces look distinctly rough.  Note that our development time is 10 min
> (longer than the recommended 6 min) so we don't think under development is
> our problem.  Our hot plates seem to be level and uniformly heated too.
> Does anyone have any recommendations about how we can eliminate these
> spots?  Are our soft bake times too low or could the filter being placed
> in direct contact with the wafer be causing a problem?