An electron impact cross section set for CHF3

Abstract

Trifluoromethane, CHF3, is used for plasma etching of silicon compounds for microelectronics fabrication, and so there is interest in developing computer models for plasmas sustained in CHF3. Recent measurements of electron swarm parameters, and electron impact dissociation and ionization cross sections, have provided a sufficient basis to develop a working electron impact cross section set for CHF3. Such a cross section set is reported here. We found that increased energy losses from dissociative electronic excitation processes were required to reproduce experimental ionization coefficients. The cross sections for attachment are small with there being some uncertainty in their magnitude at low energies. The cross sections were used in a plasma equipment model for an inductively coupled plasma reactor and compared to discharges sustained in C2F6. For otherwise identical operating conditions, plasmas sustained in CHF3 had higher electron and lower negative ion densities.