Characterizing and smoothing of striated sidewall morphology on UV-exposed thick SU-8 structures for micromachining millimeter wave circuits
- 萨本栋－已发表论文 
Sidewall roughness is a critical parameter when a thick SU-8 process is employed for fabricating millimeter wave circuits, as it determines the conduction loss of the circuit. A striated sidewall morphology was detected in our UV-exposed thick SU-8 structure, and this rough morphology was clearly illustrated and quantitatively characterized by a confocal laser scanning microscope (CLSM) for the first time. The rms line roughness of the striated sidewall is up to similar to 1 mu m, several-fold higher than the skin depth of copper at 220 GHz. We also tried to discuss the possible causes of sidewall striations. A proper counter measure, i.e. higher temperature and longer baking time of post-exposure bake, was effectively employed to flatten the sidewall striations. It was found that the rms line roughness on the sidewall detected by the CLSM is reduced to similar to 72 nm, for the sample post-exposure-baked at 107 degrees C.