[mems-talk] su8 cracking

[oygm]

Hi, everybody 
I tried to coat a 20um su8 mask on glass. Su8-50 is used in this process. After developing, cracks are observed everywhere on su8. These cracks are run through the entire su8 layer. It is really wired since I used the same protocol and get succeed last year. 
 
Here is the procedure I’ve followed:
Plasma cleaning―bakes 20mins @ 200c
Spin coating
Soft bake 3mins @65c, 15mins @95c, cool down to RT in 45mins
Expose 250mj/cm2 
Post expose bake 1mins @65c, 4mins @95c, cool down to RT in 45mins
Develop
 
Also I noticed that the su8 which I used was expired last July. Is the expiration the explanation for cracking? Or the incorrect exposure dose? Or something else?
 
Thanks 
 
--sonic