Vibrational and rotational excitation in a capacitively coupled 13.56 MHz radio frequency CF4 plasma studied by infrared absorption spectroscopy

Abstract

Infrared absorption spectroscopy has been used to determine the vibrational and rotational excitation of CF4 in a parallel plate plasma etcher. The vibrational and rotational temperatures Tvib and Trot of the CF4 molecules were extracted from the band structure of the ν3 peak of CF4 around 1283 cm−1, using a double beam Fourier transform spectrometer. Measurements were performed with and without plasma, at 0.12 cm−1 apodized resolution. From the change of the relative (hot) Q-branch intensities the vibrational temperature was estimated. Furthermore the rotational temperature, which is in these conditions likely to be very close to the gas temperature, was estimated from the shape and intensity of the R branch of the ν3 peak. It was established that both Tvib and Trot have values around 400 and 350 K, respectively. It is therefore concluded that under the studied circumstances the influence of the plasma on Tvib is small.