HI Fellows,

I also observed similar picture when i use Su-8 2025 on Si. there are 2
suspected causes:
1. residual SU-8 not removed by the developer. so,
    a. try add more developer, and better have 2nd fresh bath to enhance
developing. (it helps)
    b. do not 2nd use developer. (developer work slowly and ineffectively)
    c. expose UV longer. (not likely the reason, but worth try)
2. when i used mechanial grade rather than prime grade Si wafer, it
tends to have residue. does not matter cleaning. i do not know the
ratioale. but try using better surface quality/composition glass.

zeta yu



[email protected] wrote:

>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.