Specific Process Knowledge/Lithography/SU-8: Difference between revisions
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==Exposure== | ==Exposure== | ||
Exposing SU-8 is done using light sources at 375 nm or lower. SU-8 is not (practically) sensitive to 405 nm light and above. | Exposing SU-8 is done using light sources at 375 nm or lower. SU-8 is not (practically) sensitive to 405 nm light and above. | ||
'''Exposure in mask aligner:'''<br> | '''Exposure in mask aligner:'''<br> | ||
Duration of the UV-exposure depends of resist thickness, and if the UV exposure becomes too long, the heating at the interface between the mask and resist can cause formation of "hard skin" at the surface of the SU-8; the so-called T-topping phenomena. The rule of thumb is, that if the exposure dose exceeds 250-300 mJ/cm<sup>2</sup>, it is recommended to do multiple exposures instead, with a waiting time of 15 - 20 s between the exposure steps, to allow the resist cool down. | Duration of the UV-exposure depends of resist thickness, and if the UV exposure becomes too long, the heating at the interface between the mask and resist can cause formation of "hard skin" at the surface of the SU-8; the so-called T-topping phenomena. The rule of thumb is, that if the exposure dose exceeds 250-300 mJ/cm<sup>2</sup>, it is recommended to do multiple exposures instead, with a waiting time of 15 - 20 s between the exposure steps, to allow the resist cool down. | ||
'''Exposure in maskless aligner:'''<br> | |||
The required dose at 365 nm (MLA1) is higher than the optimal dose for mask aligner, typically by a factor of approximately 1.4. For exposure at 375 nm (MLA2), the required dose is significantly higher than at 365 nm, by a factor of 5-10. | |||
==Developing== | ==Developing== | ||