Browsing by Author "Lee, Yu-Der"

Now showing 1 - 4 of 4

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.
Novel positive-tone thick photoresist for high aspect ratio microsystem technology
(Springer Verlag, 2002-08-01) Hsieh, Gen-Wen; Hsieh, Yu-Sheng; Yang, Chii-Rong; Lee, Yu-Der
A methacrylate copolymer combining chemically amplified concept and casting technique was developed as a novel thick photoresist for the UV-LIGA process. Photoresist layers up to 500 μm in thickness can be fabricated easily. Microstructures fabricated by the novel thick photoresist were demonstrated. At present, the ring-shape microstructures with 150 μm tall and 15 μm wide have been realized and the calculated aspect ratio is 10.
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.