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Mechanisms of silicon oxide etching in a highly polymerized fluorocarbon plasma

Reactive-ion-etching (RIE) induced surface modifications of SiO2 and phosphosilicate glass (PSG) were investigated using thermal desorption mass spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS), in order to study their reactivity variance in the highly polymerized fluorocarbon plasma. Ar+ induced reactions between the fluorocarbon adsorption layer and the underlying oxide substrates were also examined. At the C,F-film/substrate interface, the adsorption layer was found to be chemisorbed to the substrates. Both SiO2 and PSG were found to react in a very near surface region, chiefly with the adsorption layer, by reflecting the reactivity in SiOxFy reaction layer below the surface. The mechanisms of the reactivity variance were explained by the difference in density of active sites for unsaturated CFX chemisorption induced by ion bombardment, and the variance of Si-O bond breakability of the substrates. These effects are caused by the existence of P-O or P = 0 bonds in PSG. Fluorocarbon chemisorption layers were also observed to be thermally stimulated to react with the substrates in TDS apparatus with to activation energy of approximately 1.9eV. This observation indicates the possibility that chemical sputtering easily occurs in actual RIE through a thermally excited step, induced by ion bombardment.