It may be residue.
You can remove it by dipping the wafer in an acid such as PAN, HF and so
on.

Good luck

Best regards
Yong-Ho Kim


===========================================
Yong-Ho Kim
Ph.D. Candidate
Microsystems Lab. (  http://mems.yonsei.ac.kr)
Dept. Mechanical Engineering
Yonsei University
Seoul, Korea

Tel) 82-2-2123-2844
C.P) 82-16-9288-5157
Fax) 82-2-312-2159

===========================================

-----Original Message-----
From: kingwang@mail.ustc.edu.cn [mailto:kingwang@mail.ustc.edu.cn]
Sent: Tuesday, June 29, 2004 6:17 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] polyimide etching

Dear Memers:
        I am use O2 RIE plasma for my polyimide etching.
I use 200nm Nickle layer(RF sputtered) as mask layers.
and the Polyimide is about 10um thickness, and it spun on a 200nm Nickle
layers. But when I increase the etching times, there is still some gray
remainder on the bottom Nickle. The RIE plasma I have used is
100W,80SCCM
O2 gas.How can I remove the remained layers on the bottom. Some one can
give me some advice.
                                                 yours
                                                  wang hai
                                                  2004.6.16