Measurement of Si, SiF, and SiF2 radicals and SiF4 molecule using very high frequency capacitively coupled plasma employing SiF4

Abstract

The behavior of the densities of Si, SiF, and SiF2 radicals and SiF4 molecule were investigated for variations in electron density at pressure of 40 mTorr in a very high frequency (VHF) 60 MHz capacitively coupled plasma employing SiF4 gas. The SiF4 molecule was measured by infrared diode laser absorption spectroscopy, the SiF2 and SiF radicals were measured by laser-induced fluorescence, the Si atom was measured by ultraviolet absorption spectroscopy, and the F atom was measured by actinometric optical emission spectroscopy. The SiF4 density decreased with an increase in electron density, and the dissociation ratio of SiF4 was saturated to about 63% at electron densities of above 8.7×1010 cm−3. The SiF2 density decreased due to electron impact dissociation, whereas the F, Si, and SiF densities increased with an increase in electron density above 1.2×1011 cm−3. The total Si density was estimated to be of the order of 1010–1011 cm−3. Furthermore, the spatial distributions of SiF, SiF2, and SiF4 densities were investigated. They were almost flat inside the plasma region, but the SiF and SiF2 radicals decreased gradually outside the plasma region, and the SiF4 molecule increased. The behavior of the Si, SiF, and SiF2 radicals was in good agreement with the emission intensity of rare gases injected as trace gases. The kinetics of the species in VHF 60 MHz SiF4 plasma was clarified on the basis of the densities of the species and electrons measured. These experimental results are useful in predicting the radical densities of VHF SiF4 plasma using simulation.