A new fabrication process for ultra-thick microfluidic microstructures utilizing SU-8 photoresist

• Published in: Journal of micromechanics and microengineering 2002-09, Vol.12 (5), p.590-597, Article 312
• Main Authors: Lin, Che-Hsin, Lee, Gwo-Bin, Chang, Bao-Wen, Chang, Guan-Liang
• Format: Article
• Language: English
• Subjects: Applied fluid mechanics; Applied sciences; Cracking (chemical); Electronics; Exact sciences and technology; Fluid dynamics; Fluidics; Fundamental areas of phenomenology (including applications); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Lithography; Lithography, masks and pattern transfer; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectromechanical devices; Microelectronic fabrication (materials and surfaces technology); Micromechanical devices and systems; Microstructure; Photoresists; Physics; Precision engineering, watch making; Semiconductor device manufacture; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Temperature
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/12/5/312

We describe a new process for fabricating ultra-thick microfluidic devices utilizing SU-8 50 negative photoresist (PR) by standard UV lithography. Instead of using a conventional spin coater, a simple 'constant-volume-injection' method is used to create a thick SU-8 PR film up to 1.5 mm with a single coating. The SU-8 PR is self-planarized during the modified soft-baking process and forms a highly-uniform surface without any edge bead effect, which commonly occurs while using a spin coater. Photomasks can be in close contact with the PR and a better lithographic image can be generated. Experimental data show that the average thickness is 494.32 plus/minus 17.13 mum for a 500 mum thick film (n = 7) and the uniformity is less than 3.1% over a 10 x 10 cm exp 2 area. In this study, the temperatures for the soft-baking process and post-exposure baking are 120 deg C and 60 deg C, respectively. These proved to be capable of reducing the processing time and of obtaining a better pattern definition of the SU-8 structures. We also report on an innovative photomask design for fabricating ultra-deep trenches, which prevents the structures from cracking and distorting during developing and hard-baking processes. In this paper, two microfluidic structures have been demonstrated using the developed novel methods, including a micronozzle for thruster applications and a microfluidic device with micropost arrays for bioanalytical applications.