We are trying to fabricate free standing thin films (~2um) using SU86002. Since SU86000 is not extensively used in literature, we initially started off with the data sheet parameters and found them to be insufficient since they led to rather brittle SU8 sheets (we spin coat them on copper and then etch away the copper, silicon cannot be used since our final substrate would be a graphene CVD foil on copper). We then looked around and found literature on neural probes that used SU82000.5.
While the parameters used for 2000.5 worked better with 6002, crack formation wasn't completely gone. I suspect it might be due to the differences in thicknesses (500nm vs 2um) however, before proceeding, I wanted to check if there are any significant differences in the two formulations that might spring up unexpected surprises due to the longer hardbake/higher dosage (currently 135mJ/cm2 and 20 minutes at 180 degree celsius with soft/post exposure bakes at 65 and 95 for 2 and 4 minutes).
Dear friend Aayush Chadha
SU-8 6002 and SU-8 2000 are two different formulations of SU-8 photoresist, and there are some differences between them. SU-8 2000 is a series of high-resolution negative photoresists, while SU-8 6002 is a high-viscosity photoresist. The major differences between the two are in their viscosity, thickness, and sensitivity to processing conditions.
One of the primary differences between SU-8 6002 and SU-8 2000 is their viscosity. SU-8 6002 has a higher viscosity than SU-8 2000, which can make it more difficult to spin coat and may result in thicker coatings. In contrast, SU-8 2000 is known for its high resolution and ability to form thin, high aspect ratio structures.
Another difference between the two formulations is their thickness. SU-8 2000 is typically used for high-resolution applications and can produce coatings as thin as 200 nm. SU-8 6002, on the other hand, is often used for thicker coatings and can produce coatings up to 5000 nm.
In terms of processing conditions, both SU-8 6002 and SU-8 2000 require a high dose of UV light for proper curing, but the specific dosage and exposure time can vary depending on the desired thickness and resolution of the coating. Additionally, both formulations require a high-temperature hard bake to fully cure the resist, which can also impact the final properties of the coating.
While there may be some overlap in the processing conditions between SU-8 6002 and SU-8 2000, it's important to note that they are different formulations and may have different sensitivities to processing conditions. It's possible that the parameters used for SU-8 2000 may not be directly applicable to SU-8 6002, and additional optimization may be required to achieve the desired properties.
Based on your description, it sounds like you've already done some optimization using the parameters from the literature on neural probes. If you're still seeing issues with crack formation, it's possible that the differences in thickness between your samples and the samples in the literature could be contributing to the problem. It may be worth experimenting with different exposure times or dosage levels to see if that helps improve the properties of your coatings
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