Papers by Author: Young Min Choi

Abstract: In general, Electrostatic chuck (ESC) was used to fix and clamp the silicon wafer with electrostatic force in the semiconductor fabrication process. Recently, due to their excellent chemical and plasma stability and high thermal conductivity, sintered ceramics has been used as an insulator material in the configuration of ESC. However, metals of high melting point, such as Mo, W, still used for electrode materials. Because of the thermal mismatch between metal electrode and ceramic insulator, micro cracks were produced at the interface during sintering process of ceramic or its operation process with high temperature, which leads to reduce the life time of ESC. To improve the compatibility between metal and ceramic, mesh type metal electrode was used in ESC but this type of electrode results in inhomogeneous electrostatic force. Homogeneous clamping force is very important to determine the final quality of semiconductor. We have investigated a ceramic electrostatic chuck composed of conducting ceramic electrode of titanium nitride instead of metal electrode. Aluminum nitride was added to titanium nitride to control the thermal expansion coefficient. This composite electrode shows not only a good electrical conductivity but also an excellent compatibility to dielectric layer. Compatibility between the electrode and dielectric layer enable to design the electrode with continuous sheet type which leads to homogeneous electrostatic force. Electrostatic force of ceramic ESC with conducting ceramic electrode was about 1700gf/4inch wafer when the applied voltage was DC 3kV.

Abstract: The synthesis of high-quality monodispersed nanocrystal is very important. Typical synthetic method is rapid nucleation by injection of an organometallic precursor into a solvent maintaining the reaction temperature. Since these methods are discontinuous processes, they are not efficient for large-scale production of monodisperse nanocrystals. In this study, continuous microchannel reaction technique is presented for synthesis of monodisperse lead selenide nanocrystals in a diphenyl ether as high-temperature organic media. The microchannel reactor was used due to its possibility of continuous process and reproducibility of narrow size distribution in nanocrystal synthesis. The synthesis was carried out in microchannel reactor (800 μm diameter) made from PTFE. Lead oleate and TOP-Se were used as organic precursor and diphenyl ether as high-temperature organic solvents. Lead selenide particles with a size of less than 10nm could be continuously prepared by this method. The nanocrystals have been characterized by X-ray diffraction, TEM and optical absorption spectrometer.

Abstract: We investigated the method of joining silicon nitride having on its surface a thin layer of active silicon metal to carbon steel. The active silicon layer is formed through the thermal dissociation of silicon nitride (Si3N4) into silicon (Si) and nitrogen gas (N2). The active silicon layer is directly joined to carbon steel via an induced eutectic melting reaction between the silicon and iron (Fe) found in carbon steel, or via brazing of two materials using general brazing metal such as Ag-Cu alloys. This joining process does not require the use of expensive active brazing alloys such as Ag-Cu-Ti alloys or a sputtering method designed to coat the active metals on surface of silicon nitride.

Abstract: Gelcasting has been expected as a promising approach to prepare near-net-shaped ceramic products. The preparation of highly concentrated gelcasting slip is one of key point in this process. The rheological behavior of concentrated silicon nitride gelcasting slip was investigated with the structure effect of polymeric dispersant and the ratio of dispersant to acrylamide monomer in order to prepare highly concentrated gelcasting slip. The slip was prepared by ball milling of silicon nitride batch composed of acrylamide monomer and polymeric dispersant after premixing them by an attritor. The slip mixed with initiator will be deaired in vacuum and cast into molds, and then polymerized. The consolidated green body will be obtained by drying the gelated slip. The polymeric dispersants with different kinds of polyelectrolyte were poly(methylmetacrylic ammonium salt), poly(acrylic ammonium salt), and poly(acrylic amine salt). Before the polymerization of gelcasting slip, the viscosity vs. shear rate was measured to evaluate the rheological behavior of the slip. In case of using the polyacrylic amine salt (PAAm), the high solid loading of silicon nitride slip was obtained up to 47vol% with a low viscosity.