Laser-Induced-Fluorescence Study of the SiH2 Density in RF SiH4 Plasmas with Xe, Ar, He, and H2 Dilution Gases

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Abstract
The silylene ( SiH2) density in a parallel-plate RF (13.56 MHz) discharge using monosilane ( SiH4) gas has been measured by using laser-induced fluorescence spectroscopy. The effect of Xe, Ar, He and H2 dilution gases on the SiH2 density was investigated at a total gas pressure of 40 mTorr. In all dilution cases, the SiH2 density was relatively insensitive to the SiH4 fraction (x) in the mixtures for x\gtrsim0.5; however, except in the case of H2 dilution, marked increase of the SiH2 density was observed with decreasing x for x\lesssim0.5. The production and loss mechanisms for SiH2 are discussed on the basis of the observed SiH2 density and supplementary optical emission measurements. The results indicate that, in highly diluted ( x\lesssim0.1)SiH4/Xe and SiH4/Ar mixtures, the production of SiH2 via energy transfer from excited Xe and Ar atoms to SiH4 is dominant over direct electron impact dissociation of SiH4.