1. 제목 : Multiscale Process and Device Simulation for Next Generation Devices

2. 연사: Dr. Kwang-Ryeol Lee

           Computational Science Center, Korea Institute of Science and Technology

3. 일시: 8월 11일 (목) 오후 4시~

4. 장소: 301동 1512-2호 세미나실

5. 내용요약

        This seminar will start with brief introduction to a national project to develop the molecular simulation technology for nano devices. Purpose of the project is to develop the design system that can optimize the Si based nano CMOS device in atomic scale and establish the web-based application environment. In the first stage, it will be confirmed that the Si Nano CMOS device can be designed and optimized by using the presently applicable simulation techniques. By combining with the device simulation technology, simulation results of Si nano CMOS with practical meaning will be demonstrated. In the second stage, the prototype of atomic scale process simulation system will be developed based on the simulation techniques approved in the 1st stage. Atomic scale simulation system will be used in the present semiconductor industry when optimizing the process for few tens nm scale devices. This system will also provide a robust design tool for the next generation devices such as single electron device, CNT devices, Graphene devices, or nanowire devices.

 

        Recent progress of the reactive molecular dynamics simulation of Si oxidation will be discussed. For last decades, scaling of Si CMOS device has proceeded with the reduction in the thickness of the SiOx dielectric layer to a few atomic layers. Engineering the interface structure between Si and the extremely thin SiOx has been thus a crucial factor in the device performance, leading to the requirement of an atomic scale understanding in the early stage of Si oxidation. In the present work, we applied reactive molecular dynamics simulation by using reactive force field (ReaxFF) integrated into LAMMPS simulation code. Validity of the potential was confirmed by simulating the molecular interaction of oxygen on Si (100) surface, which were investigated intensively by both experimentally and theoretically. The MD simulation with ReaxFF also revealed the spontaneous dissociation of adsorbed O2 molecules on Si (100) surface, the existence of molecular precursors and the existence of silicon suboxides in the initial stage of oxidation. By consecutive interaction of oxygen molecules on Si (100) surface, we further investigate the oxide structure evolution during initial stage of oxidation. At 300 K, continuous transformation of ion Si+ (or suboxide Si2O) to Si2+ (SiO), Si3+ (Si2O3) and finally to Si4+ (SiO2) clearly observed. On the other hand, High temperature silicon surface provide heat energy that enable oxygen atom to penetrate into deeper silicon surface. Secondly, we investigated the oxidation behavior of [311] oriented Si NWs having two different diameters, 5 nm and 10 nm at 1073K. After the systems had been fully relaxed up to 100 ps, oxygen molecules were placed randomly in the simulation box to simulate a conventional dry oxidation process. We focused on the stress evolution of Si NWs during the oxidation process. Since the surface oxidation results in the volume expansion of the outer shell, it shows a compressive stress along the oxide layer. The present MD simulation shows that the stress for the 10 nm Si NW exhibits larger compressive stress than that of 5 nm Si NW. This result could provide the atomistic scale mechanism of experimentally observed full oxidation of sub 10nm diameter Si NW.

 

6. 약력: 1980-1984 Department of Metallurgy, Seoul National University, Bs

           1984-1988 Department of Materials Science and Engineering, Korea Advanced 
Institute of Science and Technology Ph.D.

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※ 문의: 기계항공공학부 조경재 교수 (880-1709)