• ETRI Journal
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• v.27 no.2
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• pp.188-194
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• 2005

We report on the improvement of critical dimension (CD) linearity on a photomask by applying the concept of process proximity correction to a laser lithographic process used for the fabrication of photomasks. Rule-based laser process proximity correction (LPC) was performed using an automated optical proximity correction tool and we obtained dramatic improvement of CD linearity on a photomask. A study on model-based LPC was executed using a two-Gaussian kernel function and we extracted model parameters for the laser lithographic process by fitting the model-predicted CD linearity data with measured ones. Model-predicted bias values of isolated space (I/S), arrayed contact (A/C) and isolated contact (I/C) were in good agreement with those obtained by the nonlinear curve-fitting method used for the rule-based LPC.

• Korean Journal of Optics and Photonics
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• v.33 no.1
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• pp.22-27
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• 2022

We fabricate a polarization-independent dielectric multilayer thin-film diffraction grating for a spectral-beam-combining (SBC) system with a simple grating structure and low aspect ratio. Due to the refractive index and thickness error of the manufactured thin films, the diffraction efficiency of the fabricated diffraction grating was lower than that of the design. The causes of the errors were analyzed, and it was confirmed through simulation that diffraction efficiency could be compensated through an additional coating on the manufactured diffraction grating. As a result of sputtering an additional Ta₂O₅ layer on a fabricated diffraction grating, the diffraction efficiency was corrected and a maximum 91.7% of polarization-independent diffraction efficiency was obtained.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1493-1498
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• 2007

Silicon Nitride ($Si_3N_4$), which is widely used in a variety of applications, is hard-to-machine due to its high hardness. At high temperature (e.g. above $1000^{\circ}C$), however, the machinability can be greatly improved. In this work, we used a $CO_2$ laser with a high absorptivity to $Si_3N_4$ of 0.9 to preheat the surface of a rothting $Si_3N_4$ rod. Preheating and turning of $Si_3N_4$ was executed at the same time. The result of machining was MRR of $8.0mm^3/s$ that is four times faster than normal grinding. Continuous chip formation was observed by a microscope.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.2
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• pp.169-174
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• 2014

As a versatile processing method for nanoscale memory integration, laser-induced epitaxial growth is proposed for the fabrication of vertical Si channel (VSC) transistor. The fabricated VSC transistor with 80 nm gate length and 130 nm pillar diameter exhibited field effect mobility of $300cm^2/Vs$, which guarantees "device quality". In addition, we have shown that this VSC transistor provides memory operations with a memory window of 700 mV, and moreover, the memory window further increases by employing charge trap dielectrics in our VSC transistor. Our proposed processing method and device structure would provide a promising route for the further scaling of state-of-the-art memory technology.

• Laser Solutions
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• v.18 no.2
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• pp.5-10
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• 2015

A tailor welded blank (TWB) is a welded blank comprised of two or more sheets with different properties - thickness, strengths or formabilities. TWBs are applied to the body panels to reduce weight and cost of the part. In this research, ultra high strength steel and high ductility steel were joined and laser tailor welded blanks were implemented. Yb:YAG laser welding tests were conducted with various welding conditions, and mechanical and geometrical characteristics of weldments were evaluated.

• Current Optics and Photonics
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• v.2 no.1
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• pp.79-84
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• 2018

We present a novel and simple method to enable spatially selective $ZnAl_2O_4$ nanocrystal formation on the surface of $B_2O_3$-$Al_2O_3$-ZnO-CaO-$K_2O$ glass by employing localized laser heating. Optimized precipitation of glass-ceramics containing nanocrystals doped with $Eu^{3+}$ and $Yb^{3+}$ ions was performed by controlling $CO_2$ laser power and scan speed. Micro-x-ray diffraction and transmission electron microscopy revealed the mean size and morphology of nanocrystals, and energy dispersive x-ray spectroscopy showed the lateral distribution of elements in the imaged area. Laser power and scan speed controled annealing temperature for crystalization in the range of 1.4-1.8 W and 0.01-0.3 mm/s, and changed the size of nanocrystals and distribution of dopant ions. We also report more than 20 times enhanced downshift visible emission under ultraviolet excitation, and 3 times increased upconversion emission from $Eu^{3+}$ ions assisted by efficient sensitizer $Yb^{3+}$ ions in nanocrystals under 980 nm excitation. The confocal microscope revealed the depth profile of $Eu^{3+}$ ions by showing their emission intensity variation.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.68-73
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• 1999

In this paper, the residual stresses for the wide-band laser heat treatment using a polygon mirror have been analyzed. The results of FE analysis are compared with the experimental results. ANSYS Version 5.3, a commercial FE-code, is used for the FE stress analysis. The structural analysis was performed on after thermal analysis. The residual stress distribution across the hardened area was measured by the X-ray diffraction technique. The laser hardening conditions, 2kW laser power and 2mm/s travel speed, were used for the experiment and the FE analysis. Analysis results, which is maximum tensile residual stress is about 143MPa and maximum compressive residual stress is about -380MPa. Under same parameters with the analysis, experimental results indicate that MTRS is about 152MPa and MCRS is about -312MPa. The experimental results is about 6% higher than the FE analysis. As a result, residual stress data from the experiment close well with that of the FE analysis.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.7-13
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• 2002

A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies" Requirements for Approval of $CO_2$ Laser Welding Procedures" Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to $-50^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.ximum hardness.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.26-31
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• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired fer car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. In the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6NO 1 alloy welds. Aluminum alloy plate of 2.Omm in thickness with filler metal bar was welded by twin beam Nd: YAG laser facility (total power: 5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 1/min was used. The defocusing distance is kept at 0 mm. At travel speeds off 3 to 9 and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.2068-2076
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• 2005

The influence of oxygen concentration and CO$_{2}$ as diluent in oxidizer side on soot characteristics was studied by Laser Induced Incandescence, Time Resolved LII and Transmission Electron Microscopy photography in non-premixed co flowing flames. Through the comparison of TEM photographs and the decay rate of LII signal, suitable two delay times of TIRE-LII method and signal sensitivity ($\Delta$S$_{TIRE-LII/) were determined. The effects of O$_{2}$ and CO$_{2}$ as diluent in oxidizer side on soot formation are investigated with these calibrated techniques. The O$_{2}$+CO$_{2}$, N$_{2}$, and [Ar+CO$_{2}$] mixture in co-flow were used to isolate CO2 effects systematically. The number concentration of primary particle and soot volume fraction abruptly decrease by the addition of CO$_{2}$ to the co-flow. This suppression is resulted from the short residence time in inception region because of the late nucleation and the decrease of surface growth distance by the low flame temperature due to the higher thermal capacity and the chemical change of CO$_{2}$ including thermal dissociation. As the oxygen concentration increases, the number concentration of soot particles at the inception region increases and thus this increase of nucleation enhances the growth of soot particle.