Profile control of SU-8 photoresist using different radiation sources
Cui Z., Jenkins DWK., Schneider A., McBride G.
Patterning of thick layer SU-8 photoresist has been investigated with different radiation sources, including electron beam, X-ray, I-line stepper, UV mercury lamp with collimator, as well as two different types of UV contact maskaligner. Feature profiles with thickness up to lmm have been compared. Among all the radiation sources, x-ray exposure from a synchrotron radiation source is found to produce the best feature dimension control and has the highest feature aspect ratio. I-line stepper can also produce features with steep side wall but is limited to less than 200μm resist thickness. The illumination parallelism is the key to control the resist profile, no matter what radiation sources are used. Other issues such as process condition become important when resist layer thickness is over 500μm. Conditions for better profile control with thicker layer SU-8 photoresist are suggested.