The etching of silicon in diluted SF6 plasmas: Correlation between the flux of incident species and the etching kinetics

Abstract

Etching experiments of silicon in low pressure SF6/Ar and SF6/Kr plasmas under low energy bombardment are conducted using microwave multipolar plasmas. Experimental results using Langmuir probe, emission spectroscopy, and etch profile analysis show the evolution of the etch rate and anisotropy as a function of the density of the reactive species, the ion flux, and ion energy. A correlation between the flux of incident species and etching kinetics has been found. Evolution of the vertical etch yield per incident fluorine atom (result of the interaction process at the plasma–surface interface) as a function of the ratio of ion flux to fluorine atom flux (representative of the ion and fluorine atom generation in the plasma) implicitly allows the influence of certain external parameters such as pressure, excitation power, carrier gas to be taken into account. These results are compared with the current etching models, i.e., damage and sputter desorption models. A transition to perfect anisotropy is observed below a threshold of fluorine atom flux. This critical flux of reactive species itself is a function of the ion flux. The ratio of ion flux to fluorine flux for which lateral etching appears, decreases when the ion energy is increased. These results are analyzed in the light of a new diffusion model developed elsewhere.