Dissociative charge transfer in reactions of CCl 4 and SF 6 with ions having recombination energies between 6.4 eV and 24.5 eV

Abstract

Gas mixtures of CCl 4 and SF 6 with rare gases and simple diatomic gases in reactive plasmas are often used to etch insulating and semiconductor layers. However, much of the kinetic and product ion information for ion-molecule processes that occur in such plasmas is not known. To improve this situation, a selected ion flow tube (SIFT) study has been made of reactions of CCl 4 and SF 6 variously with D 3 +, H 3 +, D +, N +, D 2 +, N 2 +, Ar +, Ne +, He 2 +, and He + at 298 K. Because water is a common plasma impurity, the reactions of H 2O + and H 3O + have also been included. With this information, better models can be developed to predict plasma conditions that are optimal for etching. Reactions generally proceed by dissociative charge transfer with rate coefficients close to the collisional values. The degree of fragmentation (into Cl +, CCl +, CCl 2 +, CCl 3 + and SF 3 +, SF 4 +, SF 5 +) and the energy thresholds at which products are observed are frequently consistent with a long-range mechanism in which the available energy goes into fragmentation. Notable exceptions to this are reactions of D 3 + and H 3O + with CCl 4 and D +, H 3 +, H 2O +, and H 3O + with SF 6. Rate coefficients and product ion information are discussed in terms of photoelectron spectroscopy (PES) and photoionization (coincidence) data (e.g. threshold photoelectron-photoion coincidence (TPEPICO) and PEPICO techniques) available in the literature. From this comparison, a better fundamental understanding of the dynamics of charge transfer is obtained. In addition to the reactions of neutral CCl 4 and SF 6 gases, Cl 2 +, CCl 2 +, CCl 3 + and SF +, SF 2 +, SF 3 +, SF 4 +, SF 5 + studies with H 2 have also been conducted.