Simone Marasso wrote:
> Hi All,
>
> We spent much time in order to test the SU-8 2050 to obtain the wanted
> thickness (near 120 microns). We levelled very well our hot plate and
> we tested different times, temperatures and exposure times. The major
> problem occurs after spin coating process. After spinning, there are
> no (or very few) bubbles but we observed non uniform layer . When we
> perform the soft bake SU-8 film tends to "spontaneously" form a number
> of divots or craters that are not initially present (after
> spin-coating). These problems are observed with or without the use of
> OMNICOAT both on silicon surface and Cu seed-layer also at different
> spin velocities.
> Has anyone experienced this problem?
>

I have seen such divots during the softbake. I suspected contamination
of the substrate during my cleaning process. I normally use conc. H2SO4
for cleaning (although the datasheets do recommend piranha, this needs
to be made fresh every time and is quite wasteful). The problem was
resolved after changing my H2SO4.