Papers by Author: Seung Joon Ahn

Abstract: The carbon nanotube (CNT) paste was fabricated by a very simple method where the paste composition could be controlled precisely. We have fabricated several types of field emitters from the CNT paste mixture consisting of the thin multi-walled CNT, the nanosized inorganic fillers, the ethyl cellulose binder and the terpineol solvent. The field emission current density was found to be more than 100 mA/cm² at a field of 2.5 V/μm for the planar-type CNT emitter and ~5 A/cm² for the tip-type emitter, respectively. We also optimized the filler material in the paste to make the emitter reliable under the high-temperature conditions. The developed CNT paste had good reproducibility and the field emitters made of the paste showed excellent characteristics as the electron sources for the various applications.

Abstract: Although the electron-beam (e-beam) inspection can find the non-visual defects in the semiconductor devices under the fabrication procedure, it has a problem of low inspection speed. To resolve this problem, in this work, we have demonstrate the low-energy e-beam inspection using a tiny microcolumn as the e-beam source. The experimental result indicates that the non-visual defects in the wafer can be easily identified by measuring the e-beam current at the backside of the wafer. Since it is not difficult to make the multiple e-beam sources by packing many microcolumns, we can enhance the inspection many times by using the microcolumn e-beam sources.

Abstract: The inspection of the TFT device for the LCD panel has been usually carried out by the large-scale electron column where the kinetic energy of the electron beam is higher than 10 kV, which has many disadvantages for the inspection. In this work, we replaced the bulky electron column with a tiny microcolumn and carried out the inspection of the TFT device. The result shows that the low-energy e-beam inspection can clearly observe the physical defects of the devices and also identify the abnormal electrical behavior caused by the defects in the device.

Abstract: The quality of electron lenses and precision of their alignment are very important factors that determine the resolution of the microcolumn. In this work, we have fabricated the quality electron lenses using the semiconductor processing technologies and checked their circular shapes by using the laser diffraction pattern. The observed diffraction pattern by naked eyes was the circular Airy disk and the measured eccentricity of the lens aperture was found to be less than 0.02. We have also made precise alignment of the electron lenses by illuminating the laser beam through the roughly aligned electron lenses and adjusting the electron lenses while monitoring the diffraction pattern formed by the diffracted laser light from the lens apertures. This new method can replace the conventional alignment method where the expensive equipment like the aligner or the STM is required. We have also found the misalignment limit by measuring the e-beam current that came out from the microcolumn.

Abstract: The characteristics of the e-beam have been investigated according to the various parameters of the wiggler in a miniaturized free electron laser (FEL) module by using 3-dimensional (3D) simulations. The e-beam emerging from the electron emitter was made parallel by applying a static bias to the middle electrode of the electron lens set. It was found that the width of the wiggler electrodes had great effect on the e-beam trajectory inside the wiggler.

Abstract: We have annealed the thin layer of the amorphous silicon (a-Si) using the Q-swtiched Nd:YAG laser pulses in order to transform the a-Si into polycrystalline silicon (poly-Si) and investigated the crystalline structures of the poly-Si. Before illuminating the light to the layer, the frequency of the laser was doubled through the second harmonic generation (SHG) process to enhance the absorption efficiency of the optical energy. When the optical energy was higher than 500 mJ/cm², we could obtain the micro-crystalline structure with grain size as large as 500 nm.

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