External Seminar: New Challenges of Plasma Processing for Advanced Semiconductor Devices

While the miniaturization of semiconductor devices is now approaching the atomic-scale limit, the demand for higher performance of computer chips is ever growing. This trend has driven new device technologies such as three dimensional structures and new materials, which also demands further innovation in plasma processing technologies. As the device sizes are now close to the atomic scale, the required accuracy of plasma etching and deposition processes is also at the atomic scale with little or no damage to the surface critical for device performance. In such processes, ion bombardment in a plasma processing tool must be minimized whereas surface chemical reactions must be enhanced to increase the efficiency of etching and deposition processes. When new materials are used, new surface chemical reactions must be invented to achieve the goals of the process. To form extreme three-dimensional structures, one needs extreme high-energy ion bombardment. For example, high-aspect-ratio deep-hole etching of NAND flash memories requires ion energy of thousands of volts. However, even in such processes, surface chemistry has become ever more important than before as the high selectivity against the masks and the control of etched hole shapes are achieved by surface chemical reactions. The author and his research group members have analyzed surface chemistries of various materials such as Si based materials, metal, and metal oxides, mostly for the purpose of reactive ion etching (RIE) and atomic layer etching (ALE), using beam experiments and molecular dynamics (MD)/first-principle quantum mechanical (QM) simulations. In this presentations, some of our latest results on etching mechanism analyses for these materials will be discussed.