[mems-talk] AZ5214E in image reversal mode

[Yue Mun Pun, Jeffrey]

Hi,
I have tried to use AZ5214E in image reversal mode to pattern some alignment marks by lift-off process.  I have compared the image reversal mode versus the positive imaging mode and found that the lift-off process using image reversal is much more difficult than the positive image mode.  
 
Can anyone advise me on this matter?
 
Here is my image reversal process:
1.  Coat SiO2 wafer with AZ5214E spun at 2500rpm.  This gave me a resist of thickness 1.4-1.6um.
2.  Soft bake at 95'C for 120s on hot plate.
3.  Expose at 405nm near UV light with intensity of about 7.5mW/cm2 for 5.4s to obtain average energy of 40mJ/cm2.
4.  Reversal bake on hot plate at 115'C for 120s.
5.  Flood expose at 405nm with intensity of 7.5mW/cm2 for 160s to obtain average energy of 1200mJ/cm2.
6.  Develop in AZ400K developer diluted in DI water to a ratio of 1:4 for 45-60s.
7.  Thermal evaporation of 30nm Chromium.
8.  Lift off via both Acetone and PGMEA (SU-8 developer).
 
The wafer with the positive image was run as above except without the reversal bake aqnd flood exposure.
 
Lift-off using the image reveral mode is very difficult even after overnight soak in PGMEA.
 
Jeffrey