Experimental and theoretical study of RF capacitively coupled plasma in Ar–CF₄–CF₃I mixtures

Radio frequency capacitively coupled plasma (RF CCP) sustained at RF frequencies of 27 MHz in an Ar–CF₄–CF₃I gas mixture is studied experimentally and theoretically. The RF CCP in Ar–CF₄–CF₃I is simulated by using a 1D hybrid particle-in-cell–fluid numerical model. We pay special attention to the changes in plasma structure and fluxes to the electrode, negative ion and neutral radical production with admixture of CF₃I in Ar–CF₄ plasma. With CF₃I admixture the plasma becomes strongly electronegative as a result of the high electron attachment rate to the CF₃I molecule. The atomic fluorine density becomes extremely low with addition of CF₃I molecules due to the large volume loss in the reaction CF₃I + F  →  CF₃ + IF. Optical emission spectrometry data on CF₂ emission at the wavelength of 250 nm indicate the essential sources of CF₂ in CF₃I-containing plasma in the studied conditions, although direct dissociation channels for the CF₃I molecule with CF₂ production have not been studied. Evaluation of CF₂ density in Ar–CF₄–CF₃I plasma was first carried out on the basis of the actinometry technique and numerical simulation. The possible mechanism of ultra-low-k film damage in the studied conditions is also discussed. (paper)