Influence of SU-8 removal process on mechanical properties of electrodeposited nickel
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摘要: SU-8负胶具有优异的力学性能、抗化学腐蚀性、热稳定性和生物兼容性,在MEMS工艺和器件中得到广泛应用。镍金属具有良好的力学性能和抗腐蚀性,因此常用来制作MEMS器件。在MEMS执行器中,弹性元件常采用电铸镍制作。SU-8经过经曝光显影后形成致密的交联网络结构是一种高分子聚合物,这种聚合物非常稳定,不溶于强酸强碱及常见的有机溶剂,尤其是在电铸金属结构后的SU-8胶的去除更为困难。目前的SU-8去胶技术,按去胶原理可分:机械物理去胶技术和氧化去胶技术。氧化去胶技术可以有效去除SU-8胶,但氧化去胶方法不同程度地损坏电铸金属,使其力学性能与去胶前相比发生显著的变化。因此需要研究去胶对Ni金属弹性模量的影响,从而为执行机构设计提供准确的基本数据。针对目前运用比较普遍的两种去除SU-8胶方式:微波等离子下游化学刻蚀和强碱熔盐浴,分别进行了去胶实验,对去胶前后的电铸Ni金属进行了弹性模量和硬度测试。实验结果表明,电铸镍的杨氏模量在经过微波等离子下游化学刻蚀后下降18%,而经过强碱熔盐浴后下降36%,但硬度下降不明显。Abstract: 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 Youngs 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.
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Key words:
- SU-8 /
- electrodeposited nickel /
- mechanical property /
- DCE /
- molten salt bath
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