Study of fluorocarbon plasma in 60 and 100MHz capacitively coupled discharges using mass spectrometry

Abstract

The signals of positive ions and radicals formed in the fluorocarbon plasma of the capacitively coupled plasma reactor were measured using a quadrupole mass spectrometry and optical emission actinometry. The plasma was produced at 60 and 100MHz frequencies for the same reactor configuration and gas mixtures. Experiments were performed at 25mTorr with a SiO2 wafer on the grounded electrode. Mass spectra of ions were measured in C4F8∕O2∕Ar and C4F6∕O2∕Ar gas mixtures at 500–1500W generator powers. For 60 and 100MHz discharges production of fluorocarbon ions and radicals is discussed. It was found that the production of heavy species increases with frequency. The high mass signals such as C3F3+, C2F4+, C2F5+, C3F5+, C4F7+ decrease when CHF3 is added to the gas mixture. However, the signals of CFx+ (x=1,2,3) do not change significantly. These results are compared to the results of polymer film deposition on the wafer. It was suggested to control the polymerization film formation by adding small amount of CHF3 to the process mixture.