Hello,
I'm doing the lift-off process for the deposition of Cr3nm /Pt 200nm on a Pyrex substrate.
I'm using a LOR3B photoresist and S1818 resin and the developer is the MF319. For the lift-off i use the recommended remover PG.
I have a hard time for certain metallic geometries not been removed after lift-off.
I'd like to know how could i improve that?
I read that the undercut rate has an influence on my lift-off efficiently .
If I have a bigger undercut depth my lift-off should be better right ? for example i have already increase the development time which is supposed to lead to an increase of the undercut depth, the result was better but not perfect. Can i also modify de bake temperature of the photoresist? In my case I use a LOR3B photoresist which undercut rate is greater when decreasing the temperature.
am I in the good direction for the improvement ? Is the undercut "height" also a solution? for my LOR i have already 700µm of thickness for 200nm of metal deposition. It should be enough ?
If you have any ideas of how can i improve my lift-off process, i'll be very grateful
Thanks a million
What kind of deposition technique have you used? E-beam and evaporation are most suitable for lift-off due to high anisotropy. When using more isotropic method like sputtering it's much harder to achieve good results due to coating of the sidewalls of photoresist stack (especially when undercut is too small).
"For my LOR i have already 700µm of thickness for 200nm of metal deposition. It should be enough?" - It's thick enough, but I think that spin speeds for that thickness are too low (750RPM?) to achieve good quality coating and I'm not sure if double coating is a good idea for LOR resists, so you may want to use more viscous LOR (for example LOR5B). Anyway anything above 300-350nm should be enough to lift-off 203nm metalization.
S1818 is quite a thick resist for your application. If your sample is planar you can safely decrease photoresist (just PR, not LOR) thickness well below 500nm.
Instead of prolonging development to increase undercut depth (width) you may try to decrease LOR bake temperature (or time, but temperature is more crucial) in order to increase LOR development rate. In this way you can keep development time constant and avoid overdeveloping of S1818.
Finally you can try increasing temperature of remover bath, use ultrasound bath or gently brushing your sample with soft cleanroom wipe, cotton or cleanroom swab. Also you can try placing your sample vertically in order to minimize redeposition of metallization.
What is your current undercut width?
Hello,
Thank you for your answer . Indeed, i'm using sputtering. As you mentioned i use a lower bake temperature and it worked much better. In the future i'll try to change to a more viscous LOR.
Concerning the undercut i'm waiting to use SEM technique. is it possible to simply use optical microscopy to characterize LOR undercut? Indeed while using optical microscopy i can see the LOR and the S1818 resist but i don't know how interprate the thickness of the LOR i see . The lower the undercut increase?
Hi Rose, this is common issue in lift off.The choice of resist is important.A negative PR works well for lift off.Try to increase the thickness of PR for liftoff.
put sample for 15-20 min into acetone and also you can give some heat. don't dry up until metal is removed. It should be wet while checking in microscope
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