Aging effect on wettability of negative photoresist with fine-pitch micro-holes after O2 plasma treatment

O
₂
plasma treatment was performed on the JSR THB-430N negative UV photoresist to modify the surface wettability for micro-bumps electrodepositing. Wettability of photoresist was enhanced after O
₂
plasma treatment. The samples were placed for different time at room temperature. Micro-FTIR indicated that the hydroxyl groups were introduced on the surface of photoresist after O
₂
plasma surface treatment, meanwhile, the change of surface roughness and morphology was measured by atomic force microscopy. The results of contact angle between photoresist and test liquid showed that the wettability reduced with the increase of time after O
₂
plasma treatment. The best wettability which had the minimum contact angle existed within a short period after O
₂
plasma treatment. The combination of proper surface morphology and more hydroxyl groups are the reasons for photoresist to have better wettability. The mechanism of the aging effect on wettability was also discussed.