• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.2
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• pp.68-72
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• 2003

In this paper, we developed a new thick photoresist fabrication technology for 3-dimensional microstructures. In general, like as AZ photoresist was coated with thin film thickness about 1 $\mu\textrm{m}$ to 30 $\mu\textrm{m}$, but photoresist like SU-8 has thickness of several tens $\mu\textrm{m}$ or more and high aspect ratio. When we fabricate a microstructure using the thick photoresist like SU-8, cracks on the SU-8 thick photoresist are appeared by stress which was caused by sudden cooling down during bake of the thick photoresist spun on wafer. Thus, it was hard to fabricate the microstructure using the thick photoresist for electroplating. In this paper, we developed a new process to produce a 3-dimensional microstructure without the crack by stress through a suitable thick photoresist coating, time control of cool down and time control of PEB (Post Expose Bake).

• Journal of the Semiconductor & Display Technology
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• v.3 no.1
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• pp.27-30
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• 2004

In this work, the variation of the sidewall profile of a thick photoresist on the wavelength and proximity gap was investigated. PMER P-LA900PM, DNQ (DiazoNaphthoQuinone) novolac type photoresist, is used for experiments. The calculated results agreed well with the experimental results.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.1
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• pp.47-52
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• 2004

3D microstructures with different side-wall angles and different scales are fabricated by both methods of inclined exposure and rear-side exposure at each of selected areas on a same substrate. Conventional methods of inclined exposure are used to make side-walls with a same inclined angle on one substrate and to get a scale error due to front-side exposure through thick photoresist layer, But, by using the proposed method, we are able to fabricate 3D microstructures on a same substrate with various side-wall angles and accurate dimensions as the original design. In the rear-side exposure, UV exposure light reflects from the chromium mask pattern after passing through the thick photoresist layer, resulting in fabrication of well-defined, inclined 3D structures inside the thick photoresist layer.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.2008-2010
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• 2002

Process conditions of a novel negative thick photoresist, JSR THB-$430N^{(R)}$, are established in this paper. Although SU-8 obtains uniform and high-aspect-ratio structures, it is hard to remove the SU-8 mold after electroplating. The JSR THB-$430N^{(R)}$ can be more easily removed than the SU-8 and has a low internal stress. Introducing two step strip processes using acetone and the jSR THB-$S1^{(R)}$, the JSR THB-$430N^{(R)}$ electroplating mold was removed completely and a JSR THB-$430N^{(R)}$ film stress is compressive less than 2 MPa. In this paper, we obatined $200{\mu}m$ thick PR structure and $100{\mu}m$ thick electroplated nickel structure using the JSR THB-$430N^{(R)}$ photoresist.

• Journal of Sensor Science and Technology
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• v.16 no.5
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• pp.325-330
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• 2007

For the application to optic devices, wafer level package including spacer with particular thickness according to optical design could be required. In these cases, the uniformity of spacer thickness is important for bonding strength and optical performance. Packaging process has to be performed at low temperature in order to prevent damage to devices fabricated before packaging. And if photosensitive material is used as spacer layer, size and shape of pattern and thickness of spacer can be easily controlled. This paper presents polymer bonding using thick, uniform and patterned spacing layer of SU-8 2100 photoresist for wafer level package. SU-8, negative photoresist, can be coated uniformly by spin coater and it is cured at $95^{\circ}C$ and bonded well near the temperature. It can be bonded to silicon well, patterned with high aspect ratio and easy to form thick layer due to its high viscosity. It is also mechanically strong, chemically resistive and thermally stable. But adhesion of SU-8 to glass is poor, and in the case of forming thick layer, SU-8 layer leans from the perpendicular due to imbalance to gravity. To solve leaning problem, the wafer rotating system was introduced. Imbalance to gravity of thick layer was cancelled out through rotating wafer during curing time. And depositing additional layer of gold onto glass could improve adhesion strength of SU-8 to glass. Conclusively, we established the coating condition for forming patterned SU-8 layer with $400{\mu}m$ of thickness and 3.25 % of uniformity through single coating. Also we improved tensile strength from hundreds kPa to maximum 9.43 MPa through depositing gold layer onto glass substrate.

• Electrical & Electronic Materials
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• v.9 no.1
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• pp.59-66
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• 1996

Polyimides containing cyclobutane ring in main chain is known to be thermally stable and able to be developed in organic solvents after photolysis with 254 nm UV light. This type of polyimides can be used as promising positive photoresist in VLSI fabrication process. In the current VLSI process, photoresist films are formed by spin coating. The film thickness is more than several hundred nano meters. It seems that there is room for improvement of film coating process by introducing Langmuir Blodgett technique. Thereby ultra thin film photoresist can be formed, and higher density of integration in VLSI be achieved. In the present work, depositing procedure of LB films of this polyimide was investigated. LB film thickness was measured by ellipsometry to evaluate deposited film status. Chemical imidization procedure was studied to avoid several problems in thermal imidization. The pattern of submicron dimension has successfully formed on LB film of 8nm thick, which found showing good contrast.

• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.4
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• pp.295-301
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• 2002

In this paper, solenoid-type 3-D passives (inductors and transformers) have been designed, fabricated, and characterized by using electroplating techniques, wire bonding techniques, multi-layer thick photoresist, and low temperature processes which are compatible with semiconductor circuitry fabrication. Two different fabrication approaches are performed to develop the solenoid-type 3-D passives and relationship of performance characteristics and geometry is also deeply investigated such as windings, cross-sectional area of core, spacing between windings, and turn ratio. Fully integrated inductor has a quality factor of 31 at 6 GHz, an inductance of 2.7 nH, and a self resonant frequency of 15.8 GHz. Bonded wire inductor has a quality factor of 120, an inductance of 20 nH, and a self resonant frequency of 8 GHz. Integrated transformers with turn ratios of 1:1 and n:l have the minimum insertion loss of about 0.6 dB and the wide bandwidth of a few GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.408-411
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• 2003

최근 활발하게 연구가 진행되고 있는 마이크로 인덕터는 자기 데이터 저장을 위한 헤드, 자기장 센서, 마이크로 변압기와 휴대폰의 수동 소자와 같은 다양한 분야에 이용되고 있다. 마이크로 인덕터를 제작하기 위해 UV-LIGA 공정을 개발하였다. 도금 공정을 이용하여 마이크로 인덕터의 철심과 구리선 제작하였다. 도금 공정을 위해 필요한 마이크로 몰드는 여러 종류의 thick photoresist를 이용하여 저응력 공정으로 제작하였다. 도금 공정을 이용하여 toroid형 마이크로 인덕터를 제작하였다. 도금 공정에서 발생 할 수 있는 응력을 최소화할 수 있는 공정을 개발하였다.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.268-270
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• 2004

This paper reports a novel masking method with various mask materials for wet etching of glass. Various mask materials such as Cr/Au, Ti/Au, Polyimide and thick SU-8 photoresist were investigated for borosilicate glass (Borofloat33) etching in concentrated hydrofluoric acid (48% HF). Polyimide and thick SU-8 photoresist are not suitable as masking material due to its poor adhesion to glass surfaces. Titanium has good adhesion is suitable as the first layer to make multi-protective layers. The best protection was obtained with a combination of Ti/Au, polyimide and Ti/Au as masking material with etch depth of $350{\mu}m$ achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.274.2-274.2
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• 2013

We described a simple and efficient fabrication method for generating microfluidic channels with a circular-cross sectional geometry by exploiting the reflow phenomenon of a thick positive photoresist. Initial rectangular shaped positive photoresist micropatterns on a silicon wafer, which were fabricated by a conventional photolithography process, were converted into a half-circular shape by tuning the temperature to around $105^{\circ}C$. Through optimization of the reflow conditions, we could obtain a perfect circular micropattern of the positive photoresist, and control the diameter in a range from 100 to 400 ${\mu}m$. The resultant convex half-circular photoresist was used as a template for fabricating a concave polydimethylsiloxane (PDMS) through a replica molding process, and a circular PDMS microchannel was produced by bonding two half-circular PDMS layers. A variety of channel dimensions and patterns can be easily prepared, including straight, S-curve, X-, Y-, and T-shapes to mimic an in vivo vascular network. To inform an endothelial cell layer, we cultured primary human umbilical vein endothelial cells (HUVECs) inside circular PDMS microchannels, and demonstrated successful cell adhesion, proliferation, and alignment along the channel.