How do we decide or calculate exposure time for particular thickness of SU8 resist while doing photolithography?
Kindly share your experience as well as valuble suggestions.I will be thankful to you.
Hi Ramiz,
You need to check the dose in Joule/cm2 for the exposure in the datasheet.
The dose is equal to the power density of the uv light in your mask-aligner (in my clean room it is around 6mw/cm2) multiplied by the time of exposure in seconds.
If your photoresist needs 60mj/cm2, then I would expose for 10 sec with my mask aligner.
Of course, if I note after devellopment some issues, I may add or reduce exposure time, as well as vary baking temperature/ time.
Good luck
Vincent
Hi Ramiz,
You need to check the dose in Joule/cm2 for the exposure in the datasheet.
The dose is equal to the power density of the uv light in your mask-aligner (in my clean room it is around 6mw/cm2) multiplied by the time of exposure in seconds.
If your photoresist needs 60mj/cm2, then I would expose for 10 sec with my mask aligner.
Of course, if I note after devellopment some issues, I may add or reduce exposure time, as well as vary baking temperature/ time.
Good luck
Vincent
"michrochem" documents about SU8, which you can find online, would be a good starting point. I'd like to add that if you want to use thick SU8 (thicker than 25 um), use 360 nm LP filter, too. keep in mind that you better do it from the beginning of developing your recipe, since it will affect dosage. Also, just keep playing around with different parameters, and if you have thick photoresist, do a sort of PWM, i.e. instead of, say, 50 seconds exposure, use 5*10 sec, with 30 seconds time in between, to prevent possible heating in the film, if your light source is too bright. at the end of the day, you will need a ton of DOE, so just keep trying and don't give up :)
Exposure time = exposure energy required to cure the desired thickness/lithography lamp power
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