Louisiana State University LSU Digital Commons LSU Doctoral Dissertations Graduate School 2006 Ultra-violet lithography of thick photoresist for the applications in BioMEMS and micro optics Ren Yang Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_dissertations Part of the Engineering Science and Materials Commons Recommended Citation Yang, Ren, "Ultra-violet lithography of thick photoresist for the applications in BioMEMS and micro optics" (2006). LSU Doctoral Dissertations. 3468. https://digitalcommons.lsu.edu/gradschool_dissertations/3468 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. ULTRA-VIOLET LITHOGRAPHY OF THICK PHOTORESIST FOR THE APPLICATIONS IN BIOMEMS AND MICRO OPTICS A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Interdepartmental Program in Engineering Sciences by Ren Yang B.S., Tsinghua University, 1996 M.S., Tsinghua University, 1999 M.S., Louisiana State University, 2002 August 2006 ACKNOWLEGEMENTS The author would like to sincerely thank his major professor, Dr. Wanjun Wang. Without his constant encouragement, insightful suggestions, and many devoted help, the research work could not be done progressively. The author would also like to thank Dr. J. Choi, Dr. S. Soper, Dr. S. Pang, and Dr. R. Tague for their inspiring suggestions, their time and effort to serve on his examination committee. The author would also like to thank his fellow graduate students in the research group- J. Williams, S. Jeong, D. Lee, W. Dai, and R. Fan for their help, and the great time spent together. Finally, the author wants to express particular gratefulness to his parents, his wife, and his son for their firm and continuous love and support. ii TABLE OF CONTENTS ACKNOWLEGEMENTS ...................................................................................... ii ABSTRACT ...................................................................................................vi CHAPTER 1. INTRODUCTION..........................................................................1 CHAPTER 2. UV LITHOGRAPHY OF ULTRA THICK SU-8 PHOTORESIST ....................................................................................................6 2.1 Review of the State-of-the-Art for UV-Lithography of SU-8 ........................................ 6 2.2 Basic Steps for UV Lithography of SU-8 and Some Processing Tips............................ 7 2.2.1 Pre-treatment of the Substrate................................................................................. 8 2.2.2 Spin Coat of SU-8................................................................................................... 8 2.2.3 Soft Bake................................................................................................................. 9 2.2.4 Exposure ............................................................................................................... 10 2.2.5 Post Exposure Bake (PEB) ................................................................................... 11 2.2.6 Development......................................................................................................... 12 2.2.7 Treatment of Flood Exposure and Extra Hard Bake............................................. 15 2.2.8 Removing of Cured SU-8 ..................................................................................... 15 2.3 Study of Diffraction Compensation and Wavelength Selection in Lithography .......... 15 2.3.1 Diffraction Caused by Air Gap and Wavelength Dependence of UV Absorption Rate of SU-8 ......................................................................................................................... 16 2.3.2 Numerical Analysis of Diffraction and the Absorptions Spectrum on UV Lithography of Ultra Thick SU-8 Resist............................................................................... 19 2.3.3 Experimental Results Using Filtered Light Source and Air Gap Compensation for Diffraction............................................................................................................................. 24 2.4 Tapered Sidewall in i-line and h-line Lithography and Their Applications ................. 32 2.5 Tilted Lithography of SU-8 and Refraction Compensation.......................................... 37 CHAPTER 3. USING CURED SU-8 MICRO-MOLD INSERT TO REPLICATE BIODEGRADABLE (PLGA) MICROSTRUCTURES FOR DRUG DELIVERY................................................................................................41 3.1 Implantable Drug Delivery Systems and the Advantages of PLGA............................. 41 3.2 Design and Fabrication of the Prototype Drug Capsule ............................................... 43 3.3 Experimental Results and Discussions ......................................................................... 47 CHAPTER 4. APPLICATIONS OF UV LITHOGRAPHY OF SU-8 IN FABRICATION OF 3D MICRO MIXER / REACTORS WITH ARRAYS OF IMPINGING MICRO JETS ..........................................................................52 4.1 The Challenges in Micromixing and the State-of-the-Art in Design and Fabrication of Micro-mixers/Reactors ............................................................................................................. 52 4.2 Design for the Three-Dimensional Micromixers/Reactors Based on Impinging Micro-jets.................................................................................................................................. 54 iii 4.3 Fabrication of the Micro-mixer/Reactor ....................................................................... 58 4.4 Experiments and Discussions ....................................................................................... 62 CHAPTER 5. FABRICATION OF A NOVEL HYDRO-FOCUSING UNIT FOR MICRO FLOW CYTOMETRY USING UV LITHOGRAPHY OF SU-8 ..................................................................................................69 5.1 Basic Principle of Conventional Flow Cytometry and the Advantages of a Truly Three- Dimensional Hydrofocusing Unit............................................................................................. 69 5.2 Design of the Three-dimensional Hydro-focusing Microfluidic Unit .......................... 71 5.3 Experiments and Discussions ....................................................................................... 80 CHAPTER 6. OUT-OF-PLANE, FREE-SPACE, PREALIGNED REFRACTIVE MICRO-OPTIC COMPONENTS BASED ON UV LITHOGRAPHY OF SU-8 ...................................................................................86 6.1 Out-of-Plane Micro-optic Components and the Advantages in Integrated Optical Systems ..................................................................................................................................... 86 6.2 Principle of the Out-of-Plane Microlens and Microlens Array Fabricated Using Direct Lithography............................................................................................................................... 89 6.3 Simulation for the Surface Formation of the Out-of-plane Microlens ......................... 91 6.4 Microfabrication Process and Results......................................................................... 101 CHAPTER 7. MICROFABRICATION OF OPTIC FIBER BUNDLE COUPLER WITH INTEGRATED FOCUSING LENSES USING UV LITHOGRAPHY OF SU-8 .................................................................................110 7.1 Limitations of the Conventional Technologies and the Advantages of Integrated Fiber Coupler Fabricated Using Direct Lithography of SU-8.......................................................... 110 7.2 Design of the Fiber Bundle Coupler and Tilted Lithography of SU-8 ....................... 112 7.3.1 Wavelength Selection and Refraction Compensation in Tilted Lithography ..... 116 7.3.2 Microfabrication of Pre-aligned Fiber Bundle Coupler...................................... 118 7.4 Experimental Results and Discussions ....................................................................... 121 CHAPTER 8. A NEW TYPE OF NEGATIVE-TONE, UV LITHOGRAPHY PHOTORESIST BASED ON COMPOSITE OF EPON RESINS 165 AND 154 .........................................................................................128 8.1 Introduction................................................................................................................. 128 8.2 Material and Lithography Properties of 154............................................................... 130 8.3 Material and Lithography Properties of 165............................................................... 133 8.4 Use the Composite of EPON Resins 154 and 165 in UV Resist for Optimal Lithography Properties............................................................................................................ 136 8.4.1 The Optical Properties of the Resist Based on EPON Resins 154 and 165........ 137 8.4.2 Lithography Properties of Resist Based on EPON Resins 165 and 154............. 140 8.4.3 Lithography Results and Discussions ................................................................