Fabrication and Characterization of Microstructures Initiated Using Femtosecond Laser Direct Write from SU8 and Its Composites

• Main Authors: Chong Poh Yin, 張寶瑩
• Other Authors: 何正榮
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/y7kpq5

碩士 === 國立中央大學 === 光機電工程研究所 === 106 === Two-photon absorption is a nonlinear optical phenomenon which can be realized with a tightly focused beam with high peak intensity. The interaction region is limited to an extremely localized focal volume. In this study, two-photon polymerization of negative tone photoresist, SU8 is investigated. Titanium sapphire femtosecond laser at 740 nm is used as energy source to induce two-photon absorption which in turn leads to polymerization of SU8. Two-photon polymerization of SU8 is accumulative in nature, as bigger voxel is obtained with increased exposure time. Line width of SU8 structures demonstrate logarithmic dependence on scanning speed and laser power. Resolution is determined by laser power and scanning speed, which is greatly dependent on efficiency of photoinitiator. A minimum line width of 80 nm is achieved in this study. Adhesion of structures is influenced by pattern design. Without sufficient mechanical support, these structures are unable to withstand rinsing forces during development stage. Composite material is developed using SU8 and copper precursors, particularly copper (II) nitrate tyihydrate and copper (II) chloride dihydrate. Copper is selected as filler material due to excellent electrical conductivity and cost effectiveness. Blue, homogenous composite solution is synthesized, which can be spin coated on substrate to create a uniform thin film. Irradiation of femtosecond laser induces two-photon absorption that leads to polymerization of SU8, reduction of copper ions and sintering of copper particles. Surface morphology is affected by scanning speed, as low scanning speed subsequently leads to accumulation of heat energy and ablation. Line width of composite structure is determined by laser power. Electrical resistance of the composite structures decreases with scanning speed until optimum scanning speed is achieved. On the other hand, as laser power increases, line width increases while resistance decrease. Electrical conductivity of 365.50 S/m is achieved, which is a leap of advancement as compared to pure SU8 with conductivity of 10-14 S/m.