Ar addition effect on mechanism of fluorocarbon ion formation in CF4/Ar inductively coupled plasma

Using a Langmuir probe and an energy-resolved ion mass spectrometer, gas-ph ase kinetics of fluorocarbon ions has been investigated as a function of th e Ar percentage in a mixed CF4/Ar plasma. Spatially resolved electron energ y distribution function, plasma potential, and ion density are measured in an inductively coupled plasma. As the Ar percentage increases, the average electron energy decreases while the electron density remains flat. The ion density also stays constant at low Ar percentages but increases over the Ar percentage larger than 63% mainly due to the increase of the Ar+ density. The plasma potential decreases as a result of the increase of Ar partial pr essure, and this is confirmed by measuring the ion energy distributions of argon and fluorocarbon ions using the ion mass spectrometry. With the mass spectrometry, it is found that the most prominent ions, CF3+ and CF+, are f ormed predominantly by a process of dissociative ionization or radical ioni zation while CF2+ ions are formed dominantly by a process of charge transfe r. As a practical application of this study for SiO2 etching, the densities of the fluorocarbon ions and radicals are correlated with the SiO2 etch ra te and its selectivity to photoresist. Microtrench profile is also investig ated as a function of Ar percentage and it is observed that the microtrench tends to be suppressed with the increase of the Ar percentage. This tenden cy is correlated with changes in the plasma chemistry as the Ar percentage increases. (C) 2000 American Vacuum Society. [S0734-211X(00)01702-9].