Either your softbake is too short or you are heating the SU-8 during
exposure. Try having gaps in your exposure to allow the SU-8 to cool
(e.g. 10s exposure followed by 10s gap and repeat until you have the
required time). You should also have a long pass filter to reduce
excessive exposure to deep UV.
Leaving your sample to rest on a leveled surface for several hours
after spinning (before softbake) may help reduce the edge bead. You
could also use a cleanroom wipe soaked in acetone to remove the edge
bead (though may be difficult with an irregular sample).


Steven Yang wrote:
> Hi, all
>
> I am using SU-8 2050 for my microfluidic pattern, but got the problem
> during the align process that the SU-8 coated sample keep sticking on
> the mask. The SU-8 sample preparation procedure I took was,
>
> 1) Spin coat SU-8 at 3000rpm accelated at 1000rpm for 40s (suppose to be 40um)
> 2) Pre bake at 65C for 3 mins and then 95C for 5 mins (hotplate)
>
> After this, I use MA8 to align and exposure my sample. I took Hard
> mode first, the align gap set at 100um, however, the sample get
> sticked on mask. Then I clean the mask and redo by setting the
> exposure mode at prox, and align gap at 150 um, exposure gap at 150
> um. However, the sample still get to stick on mask. During both
> processes, I noticed that the sample will always contact the mask
> first before the microscope come down for alignment. I do not know
> whether this is the reason that my sample will stick on mask. If so,
> how can I adjust the MA8 not to get the wafer and mask get contact
> throughout the entire process?
>
> I am also thinking whether my baking time is too short that making the
> SU-8 so sticky? Normally how long it cost to get the SU-8 2050 ready
> for the exposure?
>
> At the same time, there was a SU-8 bead along the edge of my irregular
> sample. Does anyone know how to remove this in a clean way. I I have
> tried using wipe to remove it shading with a glass slide, but the
> result is not that clean.
>
> Thanks a lot!
>