Dear MEMS reseachers,

I am using S-1818 photoresist for a lift off process of Au/Cr on
borosilicate glass substrate. The thickness of S-1818 is around 2um. And the
thickness of Au and Cr is 50nm and 80 nm respectively. After a Cr/Au
evaporation, I soaked the chip in an acetone container in an ultrasonic
bath. I noticed that even after 50min of ultrasonication the photoresist
still remained (the manufacturer recommends 10min of ultrasonication) around
50% on the chip. On the other hand, it seems that I didn't have the undercut
pattern after development. I don't know if this have anything to do with the
remaining of photoresist. I would appreciate it very much if someone could
shed light on this problem. Thank you very much in advance.

Best regards,
Nam Cao Hoai Le, graduate student
Ritsumeikan University, Japan