Effect of alternating Ar and SF₆/C₄F₈ gas flow in Si nano-structure plasma etching

Si is very reactive to normal plasma etchants such as fluorine (F) based chemicals and the reactions are inherently isotropic. To fabricate small and/or high aspect ratio nanoscale structures in Si, an anisotropic etching process is necessary. SF₆ combined with C₄F₈ has been demonstrated as a good gas combination for anisotropic Si etching. In this study, Ar gas was introduced into the etching chamber to improve Si etching rate. In addition to mixing Ar with F etching gases directly, an alternating Ar and F gas flow process is proposed. It is interesting to see that not only Si etching rate but also etching selectivity are improved by alternating Ar bombardment and SF₆/C₄F₈ etching steps. The Si etching rate is determined by the Ar treatment step in this new alternating Ar and F two step process.