Tae Sik Oh

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...

Influence of Einzel Lens Structure on the Performance of a Microcolumn Fabricated through MEMS Technology

Microcolumn, a miniaturized electron optical system, is a powerful tool in manipulating electron beam for maskless direct e-beam lithography and miniaturized low voltage SEM for surface inspection, testing, and metrology. The basic parts of microcolumn are electron emitter, source lens, deflector, and Einzel lens. There are still several challenges in optimization of each component for better performance of microcolumn for aberration-free high quality imaging and large field of view. For the improvement of microcolumn, we developed a fabrication technique of making thin electrostatic lens using micro-electromechanical systems (MEMS) processes. Two types of microcolumns have been assembled by varying the spaces between Einzel lens-electrodes, and their performance have been evaluated for the comparison. The scan range is found to be increased with reducing the gap between the lenses and increasing working distance. The effect of the spatial gap on the scan range and image is analyzed through simulation study on the electric potential and field strength.

Development of arrayed microcolumns and field emitters

Electron beam devices have been widely used for inspection or lithography processes. The multibeam technology based on arrayed microcolumns has been developed to overcome the low throughput issue. However, the multicolumn system has some drawbacks such as complexity, electron optics, and electron source. The first drawback is the difficulty in multicolumn assembly. In particular, the alignment process of a source lens and a tip requires sophisticated techniques. The second drawback is that the e-beam characteristics of microcolumns constituting the multicolumn differ from column to column. To solve the first drawback, a sub-5-nm-resolution probe beam optic design with a simple structure and a two-dimensional carbon nanotube (2D-CNT) electron emitter instead of the widely used tungsten field emitter tip have been studied.

Inspection of the TFT Devices Using the Low-Energy Electron Beam Emitted from the Microcolumn

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.

Fast Inspection of Non-Visual Defects in the Wafer Surface Using Two Low-Energy E-Beam Sources

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.