Papers by Author: Seong 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 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.