Modelling of radio frequency plasmas in tetrafluoromethane (CF₄): the gas phase physics and the role of negative ion detachment

A fluid model is used to study a radio frequency (RF) CF 4 discharge at various powers, pressures and electrode spacings and is found to compare successfully with experimental data. The discharge shows an electronegative behaviour with a high concentration of negative ions. The role of electron detaching radicals CF x is subsequently studied by varying their density. At high radical densities (1%), the discharge behaviour and operating point change drastically and attachment-induced ionization instabilities develop. The implications to plasma etching and experiments are discussed.