Atomistic simulation of fluorocarbon deposition on Si by continuous bombardment with energetic CF+ and CF2+

Abstract

We have conducted molecular dynamics simulations of continuous CF+ and CF2+ ion bombardment of Si with incident energies Ei of 50, 100, and 200 eV at normal incidence. Continuous deposition of a fluorocarbon layer with a fluorine-to-carbon ratio (F/C) of about 0.5 occurs at all incident energies for CF+ ions. This layer grows on top of a mixed amorphous SixCyFz interfacial layer whose thickness increases with Ei. In the case of CF2+ bombardment, the steady-state transitions from relatively slow net fluorocarbon deposition at Ei=50 eV to relatively slow apparent net Si etching at Ei=200 eV. For CF2+, at all Ei’s, a relatively thin carbon-rich fluorocarbon overlayer with a F/C ratio of 0.5 also forms on top of a more fluorine-rich mixed interfacial layer whose thickness again increases with Ei, though not as sensitively as in the case of CF+. These findings support the important conclusion that the transition from net deposition to net etching due to fluorocarbon ion bombardment of Si is intimately related to the amount of energetic fluorine available due to ion fragmentation, which increases with both F content in the ion and ion energy.