Paper PS-FrM11
Molecular Dynamic Simulation for Selective Etching of Silicon Nitride and Silicon Oxide by Hydrofluorocarbon Ions

Friday, November 4, 2011, 11:40 am, Room 201

Selective etching of silicon oxide (SiO₂) over silicon nitride (SiN) has been widely used in microelectronics fabrication processes such as contact hole etching in self-aligned processes, formation of a stress liner, and dual/triple hard mask (DHM/THM) etching processes of dual-damascene structures. Opposite selective etching of SiN over SiO₂ with high selectivity would be also desirable for various processes. In general, when a fluorocarbon gas is used for etching processes, a carbon film tends to be accumulated on SiN surface, which is considered to reduce its etching rate. Therefore, there have been various attempts in plasma processing to increase the SiN etching rate by reducing carbon films over SiN with the use of hydrogen reactions with carbon. In such plasma processing, hydrofluorocarbon gases are typically used. In this study, we have performed molecular dynamics (MD) simulations of SiN and SiO₂ etching by CH_xF_y ions and compared their etching rates and surface chemistry, especially focusing on effects of hydrogen on the process. The reactive interatomic potential functions for atomic systems of Si, O, F, C, N, and H were developed in-house for the MD simulations code, based on atomic interaction data of small molecules in ground states obtained from ab-initio calculations. Details of the atomic potential functions used in the simulations will be presented elsewhere. Simulations are typically performed on a small block of a model substrate that consists of several thousand atoms and is subject to bombardment of energetic particles such as CH_xF_y. In the simulations, we evaluate sputtering yields, surface modification during the process, and characteristics of sputtered products. From the simulations, it has been found that hydrogen of CH_xF_y ions tends to reduce F accumulation on SiN surface, forming volatile HF, and sometimes promotes formation of cyanides such as HCN. Detailed simulation results, including sputtering yields and surface chemical compositions, will be given in this presentation.