• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.410-415
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• 2004

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and $Nos\acute{e}$-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion force and friction force on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• 대한기계학회논문집A
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• 제29권6호
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• pp.852-859
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• 2005

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and Nose-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion and friction forces on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• Transactions on Electrical and Electronic Materials
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• 제3권3호
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• pp.1-7
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• 2002

The developed patterns by direct writing of electron beam are measured by AFM, FESEM and optical profiler of WYKO NT3300. From different measurement methods, the measured linewidths of the patterns are shown a little bit wider than designed pattern size due to electrons scattering effect during direct writing of electron beam. The optimized conditions of these experiments are suggested and explained for the forming of structures below 0.1 ㎛ dimension size. Because of electron scattering effects from the different under layers such as Si, Si$_3$N$_4$ and aluminum, the developed pattern size is also influenced by the accelerated energy of electrons, dose, resist and soft and hard bake conditions in PMMA. The distributions of electron beam and calculations of backscattering coefficient are demonstrated by Monte Carlo simulation. From the measured results, the developed linewidth of PMMA/Al /silicon is shown a little bit wider than that of PMMA/Si$_3$N$_4$/silicon structure due to the backscattering effects.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2450-2456
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• 2002

Microlenses and microlens arrays are fabricated using a novel fabrication technology based on the exposure of a resist (usually PMMA) to deep X-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep X-rays. The microlenses is produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. The geometry of the microlens is determined by parameters such as the X-ray dose applied to the PMMA, the diameter of the microlens, along with the heating temperature, heating time, and cooling rate in the thermal treatment. Microlenses are produced with diameters ranging from 30 to 1500 ${\mu}{\textrm}{m}$. The modified LIGA process is used not only to construct hemispherical microlenses but also structures that are rectangular-shaped, star-shaped, etc.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.228-232
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• 2003

Mircolens and microlens arrays are realized using a novel fabrication technology based on the exposure of a resist, usually PMMA, to deep X-rays and subsequent thermal treatment. Hot embossing process is also studied for mass production. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness of several nm. The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep X-rays. The microlenses were produced through the effects of volume change, surface tension. and reflow during thermal treatment of irradiated PMMA. A hot embossing machine is designed and manufactured with a servo motor transfer system. The hot embossing process follows the steps of heating mold to the desired temperature, embossing a mold insert on substrate. cooling mold to the de-embossing temperature. and de-embossing. Microlenses were produced with diameters ranging from 30 to 1500 ${\mu}{\textrm}{m}$. The surface X-ray mask is also fabricated to realize microlens arrays on PMMA sheet with a large area.

• 한국재료학회지
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• 제5권1호
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• pp.96-103
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• 1995

30KV 전자빔리소그래피 장치를 사용하여 PMMA 3000$\AA$/P(MMA/MAA) 6000$\AA$의 이중구조에서 foot width 0.1$\mu$m이하, head width 0.4$\mu$m의 T-gate를 형성하였다. PMMA/P(MMA/MAA)/GaAS 구조에 대한 Monte Carlo 시뮬레이션 결과, 산란반경 0.1$\mu$m에서 전방산란전자와 후방산란전자의 에너지 비는 19.5:1로 나타났다. 전자빔리소그래피 공정에 필요한 PMMA 및 P(MMA/MMA)의 열처리 조건, 설게 선폭에 대한 패턴감도를 구하였다. MIBK : IPA = 1 : 1 현상액에 대한 PMMA 및 P(MMA/MAA)의 감마값(gamma value)은 2.3이었다. 광 및 전자빔리소그래피 장치의 혼합사용(mix-and-match) 결과 층간정렬도 (alignment accuracy)는 0.1$\mu$m(3$\sigma$) 이하를 얻었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.187-190
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• 1999

We have developed fabrication processes that form a wide-head T-gate with a 0.2 ${\mu}{\textrm}{m}$ gate length using the combination of thickness of each PMMA layer, line doses and development times for applications in millimeter- and micro-waves monolithic integrated circuits. The three-layer resist structure (PMMA/P(MMA-MAA)/PMMA = 1800 $\AA$/5800 A/1900$\AA$), 4nC/cm and over development were used for fabrication of a wide-head T-gate by the conventional double E-beam exposure technology. The experimented results show that the cross sectional area of T-gate fabricated by the proposed method is easily enlarged without additional processes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.532-537
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• 2007

Nano imprint lithography(NIL) is a cost-efficient, high-throughput processing technique to transfer nano-scale patterns onto thin polymer films. Polymers used as the resist include UV cured resins as well as thermoplastics such as polymethyl-methacrylate(PMMA). In this study, an analytic investigation was performed for the NIL process of transferring nano scale patterns onto polymeric films. Process optimization calls for a thorough understanding of resist flow during the process. We carried out 2D and 3D numerical analyses of resist flow during NIL process. The simulation incorporated continuum-hypothesis and the effects of surface tension were taken into account. For a more effective prediction of free surface, fixed grid scheme with the volume of fluid (VOF) method were used. The simulation results were verified with experimental results qualitatively. And the parametric study was performed for various process conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.332-336
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• 2007

Temperature is an essential process variable in nanoimprint lithography(NIL) where the temperature varies between room temperature and above the glass transition temperature. To simulate NIL process, we employ both the Nose-Poincare method for temperature controlled molecular dynamics(MD) and force field for polymer material i.e. polymethyl methacrylate(PMMA), which is most widely selected as NIL resist. Nose-Poincare method, which convinces the conservation of Hamiltonian structure and time-reversal symmetry, overcomes the drawbacks inherent in the conventional methods such as Nose thermostat and Nose-Hoover thermostat. Thus, this method exhibits enhanced numerical stability even when the temperature fluctuation is large. To describe PMMA, we adopt the force field which account for bond stretch, bending, torsion, inversion, partial charge, and van der Waals energy.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(2)
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• pp.17-20
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• 2000

We have enhanced the yield of 0.25 ${\mu}{\textrm}{m}$ T-gate $Al_{0.25}$G $a_{0.75}$As/I $n_{0.2}$G $a_{0.8}$As P-HEMT using three-layer E-beam lithography process and selective etching process. The three-layer resist structure (PMMA/copolymer/ PMMA=2000 $\AA$/3000 $\AA$/2000 $\AA$) and three developers (Benzene：IPA=1：1,Methanol：IPA =1：1,MIBK：IPA=1：3) were used for fabrication of a wide-head T-gate by the conventional double E-beam exposure technology. Also 1 wt% citric acid： $H_2O$$_2$：N $H_{4}$OH(200m1：4ml：2.2ml) solution were used for uniform gate recess. The etching selectivity of GaAs over $Al_{0.25}$G $a_{0.75}$As is measured to be 80. So these P-HEMT processes can be used in X-band MMIC LNA fabrication.ion.ion.ion.