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 usi ng an ab initio molecular orbital calculation. The chemical reactions via t he excited states were also predicted from the antibonding characteristics of the molecular orbitals concerned and the first-or der derivative of the potential surface of the excited state. In marked contrast to saturated per fluorocarbons, unsaturated perfluorocarbons can be easily excited to the lo west triplet state with a pi-pi* transition, generating biradicals and subs equently leading to polymerization. in addition to the conventionally used perfluorocarbons, the possibility of two-double-bonded. one-triple-bonded a nd aromatic perfluorocarbons for application to plasma processing was exami ned on the basis of quantum chemistry. The use of these novel types of fluo rocarbon is predicted to be promising for chemical vapor deposition (CVD) o f low dielectric constant interlayer films and etching with high selectivit y of SiO2 to Si and Si3N4 because of the excellent potential shown by them to yield a high polymerization and deposition rate.