Surface and gas-phase observations of Ar-diluted c-C4F8 plasma by using real-time infrared spectroscopy and planar laser-induced fluorescence

Using infrared spectroscopy with attenuated-total-reflection methods and planar laser-induced fluorescence, we examined the relationship between the thickness of amorphous fluorinated carbon (a-C:F) film on the surface of a substrate and the distribution of CF2 radical density in an inductively coupled plasma (ICP) generated from an argon-diluted octafluoro-cyclo-butane (c-C4F8) gas. The axial profiles of the CF2 radical density were consistently concave, maximally close to the surface, and minimally present around the bulk plasma. The CF2 density initially increased with increasing the ICP power and then decreased as the plasma density exceeded ∼0.5×1011 cm−3, while the thickness of the a-C:F films deposited on a nonbiased surface consistently increased. When bias power was applied, the thickness of the a-C:F film began to decrease constantly due to the sputtering effect while the CF2 density exhibited a stepwise increase, followed by a gradual decrease in response to the reduction in the thickness of the a-C:F film and its vanishing. The amount of the stepwise increase in the CF2 density depended only on the rate of sputtering of the a-C:F film, and it was negligible at high c-C4F8/Ar ratios. The positive and negative correlations revealed here between the thickness of the a-C:F film and the density of CF2 radicals are discussed in comparison with mechanisms proposed in other studies. Electron-impact-induced destruction of CF2 radicals is demonstrated as the dominant factor affecting the distribution of CF2 radicals.