Thanks for the reply. As you expected, the hotplate and exposure lamp
are always on. I did change developer after each trial and clean the
beaker by rinsing with developer. Is it possible there is still some
trace solvent (say cyclopentanone, the solvent for su 8, or water
vapor) remaining in the developer?
But I just blowed dust off the coverglass with nitrogen without
cleaning it with, for example, IPA. I guess it is related to the
adhesion between coverglass and su 8, but not sure which step in the
protocol determines this.

Best,
Liu Yu

On 12/27/05, Jesse D Fowler  wrote:
> Is it always the first few that are good, with worse progression over
> time? If so, you need to check things that may change/age. Assuming your
> hotplates and exposure lamp are constantly on, the most obvious thing is
> that your developer may be affected by the SU-8 it is developing. Have
> your tried refresh the developer for each wafer? Do you clean your
> coverglass? Do you clean the glassware the developer is in?
>
>