Quantum Chemical Study on Decomposition and Polymer Deposition in Perfluorocarbon Plasmas: Molecular Orbital Calculations of Excited States of Perfluorocarbons

Electronic excited states of various perfluorocarbons were investigated using an ab initio molecular orbital calculation. The chemical reactions via the excited states were also predicted from the antibonding characteristics of the molecular orbitals concerned and the first-order derivative of the potential surface of the excited state. In marked contrast to saturated perfluorocarbons, unsaturated perfluorocarbons can be easily excited to the lowest triplet state with a π–π * transition, generating biradicals and subsequently leading to polymerization. In addition to the conventionally used perfluorocarbons, the possibility of two-double-bonded, one-triple-bonded and aromatic perfluorocarbons for application to plasma processing was examined on the basis of quantum chemistry. The use of these novel types of fluorocarbon is predicted to be promising for chemical vapor deposition (CVD) of low dielectric constant interlayer films and etching with high selectivity of SiO 2 to Si and Si 3 N 4 because of the excellent potential shown by them to yield a high polymerization and deposition rate.