Seungjoon Ahn

A digital miniature x-ray tube with a high-density triode carbon nanotube field emitter

We have fabricated a digital miniature x-ray tube (6 mm in diameter and 32 mm in length) with a high-density triode carbon nanotube (CNT) field emitter for special x-ray applications. The triode CNT emitter was densely formed within a diameter of below 4 mm with the focusing-functional gate. The brazing process enables us to obtain and maintain a desired vacuum level for the reliable electron emission from the CNT emitters after the vacuum packaging. The miniature x-ray tube exhibited a stable and reliable operation over 250 h in a pulse mode at an anode voltage of above 25 kV.

Guaranteed cost and H∞ filtering for discrete-time polytopic uncertain systems with time delay

The design methods of guaranteed cost filtering and H∞ filtering for discrete-time uncertain linear systems with time delay are investigated in this paper. The uncertain parameters are assumed to be unknown but belonging to known convex compact set of polytope type less conservative than norm bounded parameter uncertainty. The objective is to design stable guaranteed cost filter and H∞ filter guaranteeing asymptotic stability for filtering error dynamics and minimizing performance measures. The sufficient conditions for the existence of filters and filter design methods are established by linear matrix inequality (LMI) approach, which can be solved efficiently by so called interior point algorithm. The developed algorithms are illustrated by numerical simulation.

A Miniaturized Electron Beam Column Simulation by the Fast Moving Least Square Reproducing Kernel Point Collocation Method

A miniaturized electron beam column, microcolumn, operated at a low electron energy of 1–2 keV has been simulated by the fast moving least square reproducing kernel point collocation method (FCM) which is a new concept of point collocation calculations. The salient feature of the method here is the use of the dilation function instead of constant dilation parameter. The simulation results of FCM for microcolumn configuration show good agreement with previous calculation and experimental results. Typically, the electron beam column design has been simulated by the finite difference method (FDM) with the grid and finite element method (FEM) based on mesh generation. However, The FCM method dilation function can readily calculate high-aspect-ratio structures employing only nodes instead of grid or mesh generation. The accuracy of this method will be proved through careful analysis of the error between numerical and analytic solutions. The full microcolumn structure consisting of electron emitter, source lens, and Einzel lens parts can be readily calculated by FCM. We will discuss the basic concept of FCM and its applications in this paper.

High beam current microcolumns with large apertures

Advanced microcolumn results for lithography application including column designs for a high beam current, improved lens fabrication, and specimen current images are presented.

Inspection of open defects in a thin film transistor-liquid crystal display panel by using a low-energy electron microcolumn

The demand on the electron beam (e-beam) for the inspection of semiconductor devices or display panel is rapidly increasing since e-beam cannot only monitor the small structures but also has the potential of detecting electrical troubles or repairing the defects. However, the merit of e-beam is limited because of the high cost, low throughput, and the possible damage due to the high e-beam energy. A microcolumn is a strong candidate to solve these limitations as its size is extremely miniaturized (both column diameter and height can be reduced down to a few millimeters) and the output e-beam energy is as low as 100–1000 eV. In this work, the authors tried to test the inspection of defects by applying a low voltage microcolumn to liquid crystal display panel. In order to demonstrate the authors’ inspection method, they extracted a 7’’ thin film transistor-liquid crystal display (TFT-LCD) panel from the production line just after completing the pixel structures and used this panel as a test sample. On the s...

Fabrication of a miniaturized electron lens system and laser micro-machining condition for Silicon membrane

For a miniaturized electron beam system application, miniaturized electrostatic electron lenses and their assembly, called a microcolumn, have been fabricated using an active Q-switched 1.06 µm Nd:YAG pulsed laser beam. The laser micro-machining condition for 20 µm thick Si membrane has been investigated by varying the pulse width and the effect of power density will be discussed. The geometrical structures of laser micro-machined electron lenses such as diameter, the roundness of the aperture wall and the degree of the thermal distortion are thought to be dependent on the characteristics of the individual laser pulse. A successful alignment of electron lenses using a simple laser diffraction pattern will be reported, also.

Improved design of 5 nm class electron optical microcolumn for manufacturing convenience and its characteristics

The achievement of small probe beam size at a target plane with higher probe beam current is an important challenge in the development of electron beam equipment, such as an electron optical microcolumn. Though ∼10 nm class probe beam size with acceptable current was reported already, it was achieved through a series of sophisticated technologies. In this work, the authors would like to report on the improved design of a ∼5 nm class electron optical microcolumn which can be assembled through relatively convenient manufacturing processes. The advantage of the improved design is that it can mitigate the complexities in its manufacturing processes by simply enlarging the aperture diameter of an extractor electrode and inserting an additional subsidiary electrode. The design parameters and the results of analysis on the performance of the improved electron optical microcolumn will be discussed through simulation investigation.

LGP Pattern Design by Using a Pattern Density Function with Simple Exponential Function

A pattern density function using simulation analysis for controlling LGP output distribution was proposed. The pattern density function was found as   . We analyzed the LGP output distribution of a hemi-sphere pattern using the function and then found that its output distribution was clearly improved as compared with that of the equi-distance pattern. We found that the density function works well for the pyramid pattern case as well as.

Design of an ultra-miniaturized electron optical microcolumn with sub-5 nm very high resolution.

The achievement of a microminiaturized electrostatic electron optical column with very-high-resolution probe beam is an important challenge in the fields of electron beam lithography, metrology, and inspection for semiconductor and/or display devices. In this study, we propose an ultra-miniaturized, very-high-resolution electron optical microcolumn that can be assembled more easily compared to previous structures. The design mitigates the complexity of conventional manufacturing processes by eliminating the einzel lens without affecting the resolution performance. According to our numerical simulation results, the proposed ultra-miniaturized electron optical microcolumn produces superior performance with respect to probe beam size and deflection field size as compared to previously published results. A very high, sub-5-nm-resolution probe beam size and a deflection field size larger than 60 μm are achievable at the electron energy of 1 keV and a working distance of 1mm by inserting a focusing electrode and removing the einzel lens.

Output Characteristics of a LGP for TFT-LCD with Pyramid Shaped Pattern

We have analyzed the output characteristics of a LGP with pyramid shaped pattern by using a 3-D simulation tool. The influences on the LGP output of various parameters such as the pattern shape, pattern occupation ratio, pattern size, and etching angle were investigated. Comparing the pyramid shaped pattern with hemispherical patterns, little difference was observed. And, it was proved that the pattern occupation ratio and etching angle have relatively large effects on LGP output characteristics, while the pattern size has no effect. Therefore, we can improve the LGP characteristics by optimizing pattern structure and distribution.