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Photoablation characteristics of novel polyimides synthesized for high-aspect-ratio excimer laser LIGA process
(IOP, 2004-01-09) Yang, Chii-Rong; Hsieh, Yu-Sheng; Hwang, Guang-Yeu; Lee, Yu-Der
The photoablation properties of two soluble polyimides DMDB/6FDA and OT/6FDA with thicknesses of over 300 μm, synthesized by the polycondensation of a hexafluoropropyl group contained in a dianhydride with two kinds of diamines, are investigated using a 248 nm krypton fluoride (KrF) laser. The incorporation of the hexafluoropropyl group into the chemical structure gives these two polyimides higher etching rates than Kapton (a commercial polyimide film which is difficult to dissolve). The etching rates of synthesized polyimides are about 0.1–0.5 μm/pulse over a fluence range of 0.25–2.25 J cm-2. The photothermal mechanism for DMDB/6FDA contributes about 19% of etching depth at a laser fluence of 0.82 J cm-2. Moreover, the number of laser pulses seriously affects the taper angle of microstructures, especially at low fluence. Near-vertical side-wall structures can be built at high fluence (~2 J cm-2). Fresnel patterns with a thickness of 300 μm and a linewidth of 10 μm were fabricated, with an attainable aspect ratio of around 30. After photoablation, the complementary metallic microstructures were also fabricated by a sequential electroplating procedure. Then, those two new polyimides could be dissolved easily in most common solvents (such as THF, DMSO, NMP and DMF). These results indicate that these two soluble polyimides are highly suitable for use in the KrF laser LIGA process.
Preparation of Organic Soluble Polyimides and Their Applications in KrF Excimer Laser LIGA Process
(Wiley-Blackwell, 2001-07-01) Hsieh, Yu-Sheng; Yang, Chii-Rong; Hwang, Guang-Yeu; Lee, Yu-Der
In this study two organic soluble polyimides were successfully synthesized via polycondensation of a hexafluoropropyl group contained dianhydride with two kinds of diamines. These two polyimides (DMDB/6FDA, OT/6FDA) can be dissolved in most aprotic solvents (for example, NMP, DMAc) and many other common solvents (for example, THF, DMSO). The soluble polyimides also show good thermal stability and high absorption at the KrF excimer laser wavelength (λ = 248 nm). (The absorption coefficients of DMDB/6FDA and OT/6FDA were 1.26×105 cm–1 and 1.49×105 cm–1, respectively.) The photoablation properties of the polyimides were studied in detail. Due to incorporating the hexafluoropropyl group into the chemical structure, these two polyimides have higher etching rates than Kapton (a commercial PI film). The effects of exposure parameters on linewidth and taper-angle of polyimides with different chemical structure were also investigated here. Under the proper control of exposure conditions, good precision patterns with near-vertical side wall can be produced. The 300 mm thick comb-shape and Fresnel patterns with 10 mm linewidth have been made. Moreover, the complementary metallic microstructures have also been realized in the following electroforming procedure. The results showed that these two soluble polyimides were very suitable for KrF Laser LIGA process.
Ultrathick SU-8 mold formation and removal, and its application to the fabrication of LIGA-like micromotors with embedded roots
(Elsevier, 2002-12-01) Ho, Chien-Hung; Chin, Kan-Ping; Yang, Chii-Rong; Wu, Hsien-Ming; Chen, Soon-Lin
In this study, a novel method to completely remove crosslinked SU-8 without remnants of the resist or destroying the electroplated microstructures was utilized. The LIGA-like fabrication of a side-driven electrostatic micromotor was employed as an example to describe polymerized SU-8 resist removal. Using near-UV light, nickel components of the micromotor were electroplated 160 μm in a 300 μm-thick SU-8 mold. A comparison of various approaches based on a commercial remover was performed during the mold removal process. Experimental results showed that components having 1 μm-deep substructures embedded in the substrate could provide stronger structures to withstand the internal stress due to the photoresist deformation. In addition, when the height of the electroplated structure was below two-thirds of the photoresist mold thickness, the net clamping force on the resist could be effectively reduced to make the removal of SU-8 with heated remover successfully. The rotor and the stator with embedded roots were released cleanly and thereby, assembled to form a high-aspect-ratio micromotor. The technique of SU-8 removal and LIGA-like process presented herein can be applied to the fabrication of other high-powered microactuators.
High etching rate of GaN films by KrF excimer laser
(Elsevier, 2001-05-22) Chu, Chen-Fu; Lee, C. K.; Yu, C. C.; Wang, Y. K.; Tasi, J. Y.; Yang, Chii-Rong; Wang, S. C.
A study of laser processing of gallium nitride (GaN) material is reported. A pulsed KrF excimer laser at 248 nm with 20-nsec pulse width and 1 Hz repetition rate is used to etch the GaN film. We establish the material etching parameters under different environmental conditions. By changing the pulsed energy at constant pulse numbers, ablation of GaN surface was observed at threshold laser fluence about 0.3 J cm−2. Laser etching increase with reducing environment pressure. At 1.0 J cm−2 laser fluence, the etching rate is about 35 nm per pulse at atmosphere pressure and increases to 60 nm per pulse at low pressure. The etched depth also increases with increasing laser fluence. The surface morphology of the etched surface was also investigated.
Comparison of Planar and 3D Electrode Designs for Cell Lysis by Electroporation
(2006-01-15) Lu, Kuan-Ying; Lo, Ying-Jie; Chen, Ken-Chao; Lin, Chien-Ming; Wo, Andrew M.; Yang, Chii-Rong
Effects of various ion-typed surfactants on silicon anisotropic etching properties in KOH and TMAH solutions
(Elsevier, 2005-03-28) Yang, Chii-Rong; Chen, Po-Ying; Yang, Cheng-Hao; Chiou, Yuang-Cherng; Lee, Rong-Tsong
Three ion-typed surfactants, including anionic SDSS, cationic ASPEG and non-ionic PEG, which are powerful wetting agents in electroforming, were added to 30 wt.% KOH and 10 wt.% TMAH solutions to evaluate the silicon anisotropic etching properties of the (1 0 0) silicon plane without agitation and no IPA additive. The results indicate that the surfactant ion-types are not the main determinants of the silicon anisotropic etching properties in KOH and TMAH solutions. The wetting capacity of the etchants causes the efficacies of the etchants on the roughness to follow the order anionic SDSS, cationic ASPEG, non-ionic PEG and pure solution in KOH solutions, and the order cationic ASPEG, non-ionic PEG, pure solution and anionic SDSS in TMAH solutions, especially at higher etching temperatures. Moreover, the chemical activities of etchants differ so that the etching rates follow the order anionic SDSS, pure solution, non-ionic PEG and cationic ASPEG in KOH solutions, and the order anionic SDSS, pure solution, cationic ASPEG and non-ionic PEG in TMAH solutions at a given etching temperature. Anionic SDSS has the highest etching rate of 5.4 μm/min and the lowest surface roughness of 7.5 nm, which are about 1.69 times higher and 7.87 times lower, respectively, than those obtained in pure KOH solution. The cationic ASPEG has a reasonable etching rate of 0.7 μm/min and the lowest surface roughness of 4 nm in TMAH solutions for etching temperature of 100 °C. Furthermore, the surfactants used here were demonstrated to allow the utilization of usual mask materials and anionic SDSS can even increase the selectivity of silicon dissolution toward silicon dioxide in KOH solutions. A drastic reduction of the undercutting of the convex corners is obtained in TMAH solutions with non-ionic PEG surfactant. This finding reveals that the addition of non-ionic PEG to TMAH solutions is ideal when accurate profiles are required without extremely deep etching.
Miniaturized multilayer dielectric coatings using metal masks fabricated by electroforming and photolithography technologies
(SPIE, 2008-08-29) Jaing, Cheng-Chung; Yang, Chii-Rong; Chang, Chun-Ming; Chang, Yung-Hsin; Lee, Chao-Te; Hsiao, Chine-Nan
The Ni films replacing photoresist serve as a mask to selectively deposit optical thin films at a substrate temperature of 300蚓 by an electron-beam gun evaporation. The photolithograph is used to define the growth of Ni films by an electroforming technique. Mosaic patterns with a width of 20&mgr;m are chosen as an arrangement of red color filters. The red filters are formed of alternate SiO2 and TiO2 layers and the average transmittance of red filters is larger than 90%. The experimental results successfully illustrate that the combinative uses of photolithography, electroforming and electron-beam gun evaporation can make miniaturized multilayer dielectric coatings with high light transmittance in a hot deposition.
Microstructuring characteristics of a chemically amplified photoresist synthesized for ultra-thick UV-LIGA applications
(IOP, 2004-01-09) Yang, Chii-Rong; Hsieh, Gen-Wen; Hsieh, Yu-Sheng; Lee, Yu-Der
The thick-film photoresists are essential to fabricate high-aspect-ratio microstructures by the UV-LIGA process. However, current thick-film photoresists have some weaknesses including a thickness of only up to 100 µm, a poor line-width resolution and difficulty in being stripped. Consequently, a new type of thick-film photoresist is required. This work presents a novel positive-tone MMA/TBMA photoresist, formed by combining copolymerization and chemically amplification (CA) for use in the ultra-thick UV-LIGA process. An MMA/TBMA photoresist film with a thickness of 500 µm is easily achieved. For MMA/TBMA photoresist layers with thicknesses from 100 µm to 500 µm, an exposure dose from 80 to 100 mJ cm−2 per micron is required to remove all of the exposed photoresist, revealing that the selectivity between radiated and non-radiated zones during a long development process is sufficiently high; the sidewall verticality and aspect ratio of the microstructure are excellent; stress-induced cracks are not observed in the non-radiated zones after development. MMA/TBMA photoresist is demonstrated to fabricate open microstructures with aspect ratios of at least 10 and close microstructures with aspect ratios of not more than 10, such values of aspect ratio are still sufficient for most ultra-thick mold applications. Moreover, MMA/TBMA photoresist can undergo erosion by acidic electrolyte and easily be stripped using usual organic solvents. These findings demonstrate that MMA/TBMA photoresist has the potential to replace SU-8 resist in the ultra-thick UV-LIGA process.
Study on anisotropic silicon etching characteristics in various surfactant-added tetramethyl ammonium hydroxide water solutions
(IOP, 2005-09-20) Yang, Chii-Rong; Yang, Cheng-Hao; Chen, Po-Ying
Three ion-typed surfactants, including anionic sodium dihexyl sulfosuccinate (SDSS), cationic ammonium salt of poly(ethylene glycol) (ASPEG) and non-ionic poly(ethylene glycol) (PEG), were added to 10 wt% tetramethyl ammonium hydroxide water (TMAHW) solutions to evaluate the silicon anisotropic etching properties of the (1 0 0) silicon plane without agitation and no isopropyl alcohol (IPA) additive. The results indicate that the wetting capacity of the etchants cause the efficacies of the etchants on the roughness reduction to follow the order cationic ASPEG, non-ionic PEG, pure solution and anionic SDSS in TMAHW solutions, especially at high etching temperatures. Moreover, the chemical activities of the etchants cause the efficacies of the etchants on the etching rates to follow the order anionic SDSS, pure solution, cationic ASPEG and non-ionic PEG in TMAHW solutions at a given etching temperature. The cationic ASPEG has a reasonable etching rate of 0.7 µm min−1 and the lowest surface roughness of 4 nm in TMAHW solutions at an etching temperature of 100 °C. ASPEG and PEG in TMAHW solutions markedly affect aluminum passivation. The undercutting of the convex corners in PEG-added TMAHW solutions can be drastically reduced without using corner compensation; the undercutting ratio obtained using a PEG surfactant is about 45% lower than that obtained in pure TMAHW solution. This finding reveals that non-ionic PEG should be added to TMAHW solutions when accurate profiles are required without extremely deep etching. This study also demonstrated that non-ionic PEG is more appropriate than IPA for anisotropic silicon TMAHW etching.
Three dimensional electrode array for cell lysis via electroporation
(Elsevier, 2006-10-15) Lu, Kuan-Ying; Wo, Andrew M.; Lo, Ying-Jie; Chen, Ken-Chao; Lin, Cheng-Ming; Yang, Chii-Rong
Microfabricated devices for cell lysis have demonstrated many advantages over conventional approaches. Among various design of microdevices that employ electroporation for cytolysis, most utilize Ag/AgCl wires or 2D planar electrodes. Although, simple in fabrication the electric field generated by 2D electrodes decays exponentially, resulting in rather non-uniform forcing on the cell membrane. This paper investigates the effect of electric field generated by 3D cylindrical electrodes to perform cell lysis via electroporation in a microfluidic platform, and compared with that by 2D design. Computational results of the electric field for both 2D and 3D electrode geometries showed that the 3D configuration demonstrated a significantly higher effective volume ratio—volume which electric field is sufficient for cell lysis to that of net throughflow volume. Hence, the efficacy of performing cell lysis is substantially greater for cells passing through 3D than 2D electrodes. Experimentally, simultaneous multi-pores were observed on leukocytes lysed with 3D electrodes, which is indicative of enhanced uniformity of the electric field generated by 3D design. Additionally, a single row of 3D electrode demonstrated a substantially higher lysing percentage (30%) than that of 2D (8%) under that same flow condition. This work should aid in the design of electrodes in performing cell lysis via electroporation.

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