Influence of SU-8 removal process on mechanical properties of electrodeposited nickel

SU-8 negative photoresist has wide applications due to its excellent properties, such as good mechanical property, bio-compatibility and thermal stability. Nickel is often employed in MEMS devices due to its good mechanical property and chemical resistance. In MEMS actuator, elastic elements are generally fabricated by electrodeposited nickel. SU-8 will form a highly cross-linked network polymer after exposing to UV irradiation, which is difficult to dissolve in strong acid, alkali, and convenient organic solvent. Especially, highly cross-lined SU-8 is very hard to be removed after metal electroplating. Many SU-8 removal methods have been developed, including physical and oxidative techniques. Oxidative methods can reliably and effectively remove the SU-8. But they tend to damage or change the properties of the electrodeposited metal. In this paper, mechanical properties of electrodeposited nickel were investigated before and after SU-8 removal by using plasma downstream chemical etching (DCE) and molten salt bath oxidizing method. The results show that the Young's modulus of the electrodeposited nickel decreased 18% and 36% after DCE etching and molten salt bath oxidizing, respectively. The hardness test results showed little change by using these two SU-8 removal methods.