Papers by Author: Seung Joon Ahn

Abstract: As the number of delicate semiconductor devices in the electric equipment increases, it is also getting more important to prohibit the surge wave from intruding the equipment. The better surge-wave protection can be achieved when we reduce the earth resistance further in the earthing system. It is practically best, however, to set an appropriate value of earth resistance if we consider the cost and effort required to install the earthing system. In this work, we demonstrated an example of extracting an optimized earth resistance by using a simulator that theoretically predicts the evolution of discharge current of the earthing system. The measure discharge currents of the real earthing system with the optimum earth resistance has confirmed that our method was efficient and useful.

Abstract: The electron beam lithography has been paid great attention as a future lithography technology for the patterning of extremely fine structures. Generally the e-beam lithography means high-energy e-beam lithography where the kinetic energies of electrons are rather high(10~100 keV). Although the high-energy e-beam technology is mature and being used in semiconductor industry, the low-energy microcolumn lithography(LEML) has many great advantages as a next-generation technology, which explains the active research on the subject these days. In this work, we developed a new method to recognize the registration marks in LEML. With this novel method, there is no need to supply the bias to the mark electrodes, which remarkably simplifies the fabrication process of IC devices.

Abstract: As the design rule goes down sub-70 nm for the ULSI devices, the total thermal budget that the device can take during the fabrication is also reduced very much. Hence, in this work, we propose a novel low-temperature LPCVD process for formation of thin dielectric oxide film which does not need SiH2Cl2 gas. We have also evaluated the electrical reliability of the film by making the capacitors with oxide-nitride-oxide (ONO) structure. The leakage current of the new oxide was similar to that of the high-temperature wet oxide until the electric field is lower than 5 MV/cm. When the film was annealed by N2 gas, however, it has shown much better characteristics over the entire range.

Abstract: Chemical composition and uniaxial compressive stress are varied to observe their effect on the current-voltage behaviors of ZnO based ceramics. Chemical composition variation produces two kinds of ceramics showing ohmic and nonohmic current-voltage behaviors. The current at a fixed voltage is increased with the increase of the compressive stress for both ceramics. Ceramics with nonohmic behavior shows better reversible return of current-voltage curve when the applied compressive stress is removed from the ceramic than those with ohmic behavior do. We found out an appropriate chemical composition showing linear relation between current and stress at a fixed voltage as a potential application of the ceramic material to pressure sensor.

Abstract: The alignment precision of the electron lenses is one of the most critical factors that determine overall performance of the microcolumn system including the image resolution and aberration. Since the lens apertures are usually as small as 5 ~ 300 μm, the alignment is difficult to carry out, even if the expensive and complicated aligner is used. In this work, we have developed a novel alignment method using laser diffraction pattern, with which we can easily obtain high-precision alignment. The images of Cu grid (mesh# 1000) and carbon nanotubes (200-nm diameter) taken by the microcolumn fabricated by the new alignment scheme has confirmed that the new method was very simple and useful.

Abstract: Recently, the micro-column has been intensively studied as a potential candidate for next-generation lithography with high-throughput capability. The micro-column has a simple structure with an electron emitter, micro-lenses, a double octupole deflector, and an Einzel lens. The structure and performance of the micro-column are dependent on the characteristics of the electron emitter. The electron emitter should have several prerequisites such as stable emission of electrons, high brightness and long lifetime. It is also necessary for the emitted electrons to have sufficiently low kinetic energy, which can be achieved by using a very sharp emission tip. In this work, we made an extremely sharp tip by electro-chemically etching the tungsten wire in 10 % KOH solution. From the Fowler-Nordheim plot, the effective radius of the tip was found to be as small as ~12 nm, which is consistent with the value measured by SEM. We also discovered that the stability of emission can be enhanced very much through thermal treatment of the tip end by irradiating the Nd:YAG laser pulse

Abstract: We investigated the characteristics of the HfO2 layer deposited by ALD method in MOSFET devices where the HfO2 film is incorporated as the gate dielectric layer. The HfO2 film was annealed with forming gas (FG) or high-pressure D2 gas to investigate the effect of annealing on the characteristics of the MOSFET device. It was found that the drain current and transconductance of the D2-annealed MOSFET device increased remarkably by ~10% compared with those of FG-annealed MOSFET device, which is a definite improvement that may contribute to reliable operation of the ultra high-density MOSFET devices.

Abstract: The magnetic domain refinement was carried out by laser pulse scribing in order to reduce the core loss of SiFe. The laser pulses were generated by a Q-switched Nd:YAG laser, and the optical frequencies of the laser pulses were altered by using the SHG and the THG. The core losses were measured and analyzed to find optimal parameters of the laser treatment. The laser beam was focused with a spot size of 0.2 mm, and pulse energy of 10~30 mJ and the lines were scribed with a period of ~5 mm. The core loss was improved up to 19 % with the THG of Q-switched Nd:YAG laser in 3% SiFe.