Measurements of radical densities in radio-frequency fluorocarbon plasmas using infrared absorption spectroscopy

Abstract

Densities of CF2 radicals, rotational temperatures, and the degree of dissociation in radio-frequency fluorocarbon plasmas have been measured using Fourier transform infrared absorption spectroscopy and tunable diode laser infrared absorption spectroscopy. The CF2 densities obtained in CF4, CHF3, C2F6, and CF2Cl2 plasmas indicate that the partial pressure of CF2 is around 1%–5% of the total pressure. From the spatial dependence of the CF2 density it was established that at high pressure, CF2 is produced either on the rf electrode or close to the rf electrode. Furthermore, a comparison between measured absorption spectra and a simulation of the rotational distributions has revealed that the rotational temperatures of CF4, CF2, and HF are all close to room temperature. FTIR spectra indicate that in plasmas of gases with a low F/C ratio (due to the presence of H or Cl) the source gas is converted for a significant part into other species.