High-resolution infrared spectroscopy of etching plasmas

Infrared absorption spectroscopy has been used to measure the absolute densities of neutral particles in various fluorocarbon RF plasmas. The densities of CF₂ radicals have been measured using a tunable diode laser. Moreover, broadband absorption spectra obtained using a Fourier transform spectrometer have been used to determine the densities of stable reaction products and to assess the degree of dissociation in the plasma. The results indicate that the rotational temperatures of all species involved are slightly above room temperature. The density of CF₂ at high gas pressures increases close to the electrodes, indicating production near or on the electrodes and loss in the gas phase. The dissociation degree in plasmas of gases with a high C/F ratio can be as high as 90%. From an analysis of the flow dependence of the degree of dissociation the total dissociation rate coefficients of CF₄, CF₂Cl₂, CF₃Cl and C₂F₄Cl₂ have been calculated.