Mechanistic Study of CO2 Plasma Damage to OSG Low k Dielectrics

A mechanistic study of CO2 plasma damage to OSG (organosilicate glass) low-k films was performed using both inductive-coupled ICP and capacitive-coupled RIE sources with varying plasma energy and density. The nature of the damage was investigated using spectroscopic ellipsometry (SE), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometer (XPS), and capacitance-voltage (C-V) measurements. The spectroscopic data were used to examine the origin of the dielectric loss based on the Kramers-Kronig dispersion relation to follow the change of the polarization components. Upon plasma treatment, the electronic dielectric constant was found to drop first and then rise to reach saturation while the ionic component increased and became saturated. Overall the dipolar contribution was found to dominate the dielectric loss. The extent of CO2 plasma damage was found to depend on the plasma density, plasma energy and the low k chemistry. Compared with the O2 plasma, the CO2 plasma induced less damage probably due to the compensation effect of the carbon in the CO2 plasma. While the RIE CO2 plasma induced mostly surface damage, the ICP plasma generated more damage in the bulk of the low k material.