I am using SU8 2075 to get 180um thickness of resist. I spin at several speeds (1000 to 2000 rpms) but the maximum thickness that I reached was 130um (very far from the data sheet). Also, the edge beads are getting bigger and bigger during the soft bake process. Can anyone help?
Advice from MJG: use SU8 2125: you can reach 125um at 3000 rpm but if your reduce the speed, you could reach 180um. However, multicouche with SU8 seems to be not so easy... I hope this answer can help you, Doctor Malekabadi !
Thank you very much Francois. It is possible to reach higher thicknesses with higher Viscosity SU8s. However, in the case of SU8 2075 the data sheet claims that it is possible to get 240um at 1000 rpm. But I can only have 140 at this speed. I wonder why I am far from data sheet.
Yes, but MJG's experience says that the data sheet outside clean room and data sheet inside cleanroom is a little bit different: however, nobody has the inside one since it depends of your clean room (I speak about small cleanroom, not for industrial with high volume and repetitive production). So I understand that try error is the best method...
Please describe your coating process, equipment and environment. Also how are you measuring the thickness? With this information I may be able to help you.
Thanks
dear Malekabadi, you should also check the expire date and storing condition of your SU8 bottle, though over time it should get denser and therefor thicker at a given spin speed.
regards
Alvise
Why not doing the spin-coating in two steps at 2000rpm (around 105um) and 3000rpm (around 75um)...!!
And you do a soft bake before the second spin coating... and after of course... It will be more precise concerning the final thickness.
For the edge effect... you have to deal with it... or remove it manually... with a solvant...
Regards...
SU-8 is sensitive to temperature and time during spinning. The datasheet gives a spin curve for 30 seconds at 20oC. If the temperature in your spinning chamber is higher than 20oC, or if your spin time is more than 30 seconds, your film will be shorter.
You should remove the edge bead before your soft bake. Otherwise, when your soft bake temperature exceeds the Tg of the SU-8 (~65oC) the edge bead will begin to flow back towards the center of the wafer making it much wider.
Francois: Thank you very much for the comment.
John S Petersen: I am using 2 inch wafers, I pour SU8 on the wafer and then spin it for 5s at 300rpm (acceleration 200) and 30s at 1000rpm (acceleration 300). Afterward, 7min hot-plate @ 65C and 25min hot-plate @ 95C.
A. Bagolini: I recently bought this bottle.
Olivier Français: Yes, I think it is a very good idea. I did a few tries and seems working. Did you have 105 um at 2000rpm and 75um at 3000. If yes, those numbers are close to mines.
Ron Reiserer: Thank you very much. As I described for John Petersen I tried to stay close to the data sheet numbers.
Chanchal Goyal: For 3 um, you may be able to achieve this with SU8 2005 at high spin speeds, or with SU8 2002 at very low spin speeds. Here is the data sheet: http://www.microchem.com/pdf/SU-82000DataSheet2000_5thru2015Ver4.pdf
I am using SU-8 2025
Spin coating at 4000 rpm for 30 s acoording to data sheet. Pre bake at 65 deg C for 3 min and 5 min at 95 deg C. After UV exposure post bake at 95 deg for 5 min. However I have found during developing that the unexposed area is also remaining on the Si substrate. So the pattern is not developing.
Can any one suggest what is going on and what to be done ?
Is the light in your lab filtered? You should be processing all steps under yellow light. What type of mask? Chrome or Mylar? Exposure tool?
Thanks for your questions. Yes it is yellow light. Mask is finger grid pattern on Aluminum plate thickness 0.5 mm. Exposure tool is UV light 365 nm.
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