Topic/Type: 1. Plasma Simulation, Invited
Center for Atomic and Molecular Technologies, Osaka University
In semiconductor manufacturing, as the dimensions of transistors diminish, nano-meter-scale damages caused by ion bombardment during a plasma process have become no longer negligible with respect to device performance. Especially in processes that employ small atoms such as hydrogen, the depth of a damaged layer near the material surface can be in the range of a few nanometers even with the use of a relatively low bias voltage in the plasma tool. The goal of research that I plan to discuss in this presentation is to understand the properties and mechanisms of physically and/or chemically incurred damages during processes by reactive plasmas such as reactive ion etching (RIE) and plasma enhanced chemical vapor deposition (PECVD).
Classical molecular dynamics (MD) simulations is one of the most effective theoretical tools to analyze nonequilibrium chemical reactions taking place on a material surface exposed to ion bombardment and reactive species extracted from a plasma. Such chemical reactions typically take place in a nano-meter-scale thin top layer of the material. Therefore the minimum number of atoms that MD simulations need to employ to produce nontrivial information on the system may be limited to a relatively small number of a few thousands, especially in the case where the ion bombardment energy is in the range of a few hundred eV or lower. However, the simulations are still time-consuming and, due to the limitted time scales that MD simulations can practically address, they are not effective in evaluating long-time scale phenomena such as thermal relaxation.
In this presentation, I will review the typical simulation schemes for surface reaction analyses by MD simulations, which I hope will clarify the effectiveness and limits of MD simulation for such analyses. The main focus will be given on damage formation processes during reactive ion etching. Comparison of numerical simulation results with experimental observations is crucial for further development of better simulation tools as well as a better understanding the phenomena, so recent experimental results on plasma-surface interaction obtained from mass-selected ion beam injection systems will be also discussed.