Molecular Dynamics Studies of Surface Nucleation and Crystal Growth of Si on SiO 2 Substrates
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0899-N07-02.1
MOLECULAR DYNAMICS STUDIES OF SURFACE NUCLEATION AND CRYSTAL GROWTH OF SI ON SIO2 SUBSTRATES Byoung Min Lee1,2, Hong Koo Baik1, T. Kuranaga3, S. Munetoh3 and T. Motooka3 1
Department of Metallurgical Engineering, Yonsei University, 134 Shinchon-dong, Seodaemoon-ku, Seoul 120-749, Korea. 2 Korea Atomic Energy Research Institute, 150, Dukjin-dong, Yuseong-gu, Daejeon 305-353, Korea. 3 Department of Materials Science and Engineering, Kyushu University, Hakozaki, Fukuoka 8128581, Japan. ABSTRACT Molecular dynamics (MD) simulations of atomistic processes of nucleation and crystal growth of silicon (Si) on SiO2 substrate have been performed using the Tersoff potential based on a combination of Langevin and Newton equations. A new set of potential parameters was used to calculate the interatomic forces of Si and oxygen (O) atoms. It was found that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the surface of MD cell. The values of surface energy for (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J/m2, respectively. This result suggests that, the nucleation leads to a preferred (111) orientation in the poly-Si thin film at the surface, driven by the lower surface energy.
INTRODUCTION Laser-annealing offers a novel method for the preparation of poly-Si films on glass substrates. The technique opens new avenues in nucleation and crystal growth studies by allowing the heating and cooling of the surface region of thin Si films with fast rates that are not attainable by other methods. It is generally believed that the absorbed laser radiation by amorphous Si results in a transient melting that leads to an extremely rapid solidification of liquid Si (l-Si). However, the laser crystallized poly-Si thin film has an insufficient field-effect mobility due to an electrical potential barrier formed by the trap states at the grain boundaries (GBs) in the channel region [1-3]. Therefore, intensive studies have been made both experimentally and theoretically to increase the grain size of poly-Si and to reduce the GBs density. The final goal is to produce a single crystalline Si on SiO2. The overall structural properties of poly-Si prepared by excimer laser annealing (ELA) can be defined as three regimes in terms of the applied laser energy densities [4]. Although considerable information of the nucleation and crystal growth of Si in the three regions has been collected by using a variety of experimental techniques [5-7], it is still unclear how desirable grain orientations and larger grains can be obtained. Therefore, an atomic scale investigation of the nucleation and crystal growth processes is need. In this study, we have performed MD simulations for near-complete melting and complete melting conditions. We highlight a fundamental problem related to nucleation at the surface of thin Si films, which has been a controversial subject for many years in experimental studies. The difference between the near-complete melting and the complete meltin
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