Study On The Fabrication Methods And Relevant Theories Of SU-8 Photoresist Micro-nano Fluidic Chips

The micro-nano fluidic chips,which are integrated chips combining micro and nano structures,have exhibited appealing applications in the fields such as DNA sequencing,biochemical analysis,and environment detection.At present,the fabrication of micro-nano fluidic chips is hindered by its high-cost,complicated,and time-consuming processes.As such,the development of novel fabrication methods with low cost and high efficiency is of great practical significance.The advantages of SU-8 photoresist include high machinability,mechanical strength,chemical stability,bio-compatiblity as well as low cost.In this thesis,the fabrication methods and relevant theories of SU-8 micro-nano fluidic chips are studied.The main contents are summarized as follows:(1)Research on the low-cost fabrication methods and relevant theories of large-area silicon nano moldsThe nano channels on the SU-8 photoresist are realized by thermal nano imprinting with silicon nano molds.Consequently,the nano molds are critical to the fabrication of nano channels.Two low-cost novel fabrication methods for large-area silicon molds were proposed in this thesis:(a)Concave silicon molds were achieved by inclined deposition and plasma etching.The influence of photoresist thickness,evaporation inclination,and etching duration on the trench dimensions was discussed.The silicon nano molds with different sizes were fabricated,among which the minimum width was 108 nm.(b)Convex silicon molds were achieved by proximity ultraviolet(UV)lithography and deep reactive ion etching.The pattern-size reduction effect in proximity exposure was analyzed based on diffraction theories.By optimizing the parameters in the processes of exposure,development,post-baking,and deep reactive ion etching,nanoscale silicon ridges were fabricated with high precision.The achieved minimum width of nano ridges was 263 nm.Both methods are capable of fabricating silicon nano molds covering four-inch wafer with high uniformity,which are simple,efficient and free from costly equipment.(2)Research on the filling behavior of SU-8 photoresist in thermal imprintingThe stress relaxation curves and shear stress/rate flow curves were measured to analyze the temperature dependent rheological properties of SU-8 photoresist.The filling behavior of SU-8 photoresist was discussed based on thermal imprinting results at various temperatures.High-precision nano channels were fabricated with replication error of 2.8%at optimized thermal imprinting temperature of 85? and duration of 3 min,which paves the way for high-precision fabrication of SU-8-based micro-nano fluidic chips.(3)Research on the hybrid micro-nano fabrication method based on double-casting and UV thermal nanoimprintingWith concave silicon nano molds,polydimethylsiloxane(PDMS)hybrid micro-nano molds were fabricated by a double-casting method.Consequently,SU-8 hybrid micro-nano fluidic chips were realized by UV-thermal nano imprinting with the PDMS hybrid micro-nano molds.The quality of micro-nano patterns was improved by optimizing the parameters in exposure,bonding,and plasma treatment.The bonding quality of the chips was characterized by fluorescent tests.The proposed fabrication method is simple,universal,stable,and high-yield.Therefore,it lowers the difficulty and cost for manufacturing hybrid micro-nano structure and enables its batch production.(4)Research on the step-by-step micro-nano fabrication method based on thin film deposition and double-bondingSU-8 nano channels were fabricated by thermal nanoimprinting with convex silicon nano molds,and their widths were reduced by Parylene thin film deposition.The influence of deposition pressure on the roughness of Parylene thin films was investigated.Micro-nano fluidic chips with channel widths under 100 nm were achieved by the double-bonding method.The bonding strength were enhanced by optimizing the bonding temperature and plasma treatment parameters.The bonding quality of the chips was characterized by fluorescent tests.The proposed method is suitable for low-cost batch production of micro-nano fluidic chips.In summary,by studying the fabrication methods and relevant theories of SU-8-photoresist-based micro and nano structures,the micro-nano fluidic chips are realized at low cost in this thesis.The proposed novel fabrication roadmaps could provide strong support for the extensive applications of micro-nano fluidic chips.